Research ArticleA Novel Energy Recovery System for ParallelHybrid Hydraulic Excavator

Wei Li1 Baoyu Cao2 Zhencai Zhu1 and Guoan Chen1

1 School of Mechanical Engineering China University of Mining and Technology Xuzhou 221116 China2 Shanghai Chuangli Group Co Ltd Shanghai 201706 China

Correspondence should be addressed to Baoyu Cao caobaoyucumt126com

Received 11 March 2014 Accepted 4 August 2014 Published 22 October 2014

Academic Editor Mario L Ferrari

Copyright copy 2014 Wei Li et al This is an open access article distributed under the Creative Commons Attribution License whichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Hydraulic excavator energy saving is important to relieve source shortage and protect environment This paper mainly discussesthe energy saving for the hybrid hydraulic excavator By analyzing the excess energy of three hydraulic cylinders in the conventionalhydraulic excavator a new boom potential energy recovery system is proposedThemathematical models of the main componentsincluding boom cylinder hydraulic motor and hydraulic accumulator are built The natural frequency of the proposed energyrecovery system is calculated based on the mathematical models Meanwhile the simulation models of the proposed system and aconventional energy recovery systemare built byAMESim softwareThe results show that the proposed system ismore effective thanthe conventional energy saving systemAt last themain components of the proposed energy recovery system including accumulatorand hydraulic motor are analyzed for improving the energy recovery efficiency The measures to improve the energy recoveryefficiency of the proposed system are presented

1 Introduction

At present with the development of world economic con-struction the cost of the energy has increased rapidlyPollution and global warming have become extremely seriousproblems that the world has to face As the most typicalequipment of engineering machinery industry the hydraulicexcavator plays an important role in construction waterconservancy railway and highway However due to thecomplex working condition and frequent load changing only20 of the engine output power is utilized in a conventionaltype excavator [1] Combined controls of actuators requiredistribution of flows and interflows which increase looploss Meanwhile the potential of working device the kineticenergy of the turning body and braking bodywork areconverted into heat in themain throttle valveThiswill lead toenergy waste and temperature rising of systemThe hydrauliccomponent of system is damaged after the long timeworkingTherefore the energy recovery of working device has animportant significance for improving energy utilization ratiofor the conventional hydraulic excavator [2 3]

Several researches on the energy saving of the conven-tional hydraulic excavator have been proposed [4ndash6] Ingeneral the approaches for improving energy utilization ratiocan be categorized into two types One is improving theefficiencies of individual hydraulic components and the otheris developing efficient hydraulic systems [7] Furthermorethe most effective ways to create more efficient systems arematching the output power of pumps to the desired powerof loads and regenerating the recoverable energy of actuatorssuch as braking kinetic energy or gravitational potentialenergy

Hybrid is a new power system which is widely used inautomotive industry [8ndash10] It can be assigned to either serieshybrid parallel hybrid or their combination The hybridelectric vehicle (HEV) utilizesmore than two differentmotivepowers to propel the wheel one of which is electric energyThe hybrid system can thoroughly optimize the two energyconfiguration and take advantage of the benefits provided bythem [11] Therefore compared with the traditional vehicleHEV not only has a potential to improve the fuel efficiencybut also reduce the emission

Hindawi Publishing Corporatione Scientific World JournalVolume 2014 Article ID 184909 14 pageshttpdxdoiorg1011552014184909

2 The Scientific World Journal

Based on the successful application of the hybrid systemin automotive industry it attracts a lot of the worldrsquos largestcompanies and institutersquos interest Many researches on theapplication of the hybrid technology in hydraulic excavatorhave been done In order to enhance fuel economy of hybridexcavator system Gong et al [12] introduce a control strategybased on equivalent fuel consumption The results showthat the control strategy can effectively optimize the hybridpower distribution and improve fuel economy Liu et al [13]find a versatile method designing the parameters of maincomponents of hydraulic excavator The method has simplecalculation process and it can be used to carry out parametermatching on different hybrid system Lin et al [14] deal withthe method of how to regenerate the potential energy for ahybrid hydraulic excavator The simulation results show thatit is possible to increase the efficiency of the generator anddownsize the generator by adding the hydraulic accumulatorto the system

This paper mainly presents a new hybrid hydraulic exca-vator energy recovery system which combines the hydraulicaccumulator and the electric regeneration unit together Inthis system the accumulator and the regeneration unit areinstalled in the return oil lines In some operating conditionsthe excess energy supplied by the pump can be converted toelectricity and stored in the battery The cylinder velocitiesare governed by the displacement of hydraulic motor Theproposed system is simulated by AMESim software Theenergy recovery efficiency of the proposed system is clearlyverified through simulation results in comparison with theconventional energy recovery system At last in order toimprove the energy recovery efficiency of the proposedsystem the main components of the proposed energy recov-ery system including accumulator and hydraulic motor areanalyzed The results show that the different key parametersof components have a great influence on the energy recoveryefficiency

2 Design of the System Scheme

21 EnergyConsumptionAnalysis of the Traditional ExcavatorAs the hydraulic excavator starts to work the boom cylinderpiston can expand and contract twice during a work period aswell as the bucket cylinder and the bucket rod cylinder Dueto the high frequency of use three cylindersmentioned aboveare analyzed based on 25t hydraulic excavator (middle typehydraulic excavator) Simulation with conventional hydraulicexcavator has been carried out by using AMESim softwareThe model built in AMESim is shown in Figure 1 In order tosimplify the model there are two assumptions for the system

(1) The pumps in the hydraulic excavator system arereplaced by three constant pressure sources the inputpressure 119901in = 200 bar and they supply the flow ratewhich the actuators need

(2) There is not any energy loss in the hydraulic circuitand components but for the electrohydraulic direc-tional control valves and the pressure drop 119901drop =20 bar

Table 1 Input energy and excess energy of the three cylindersystems

Input energy119864in (J)

Excess energy119864ex (J)

Percentage119864ex119864in ()

Boom system 1263991198646 05986511198646 4736Bucket rod system 0676351198646 62118 918Bucket system 0740531198646 529446 715

Run the simulation for a whole work period of thehydraulic excavator The power of the pumps 119875in and thepower of the cylinders 119875out are calculated by the followingrespectively

119875in = 119901in sdot 119902in (1)

119875out = 119901out sdot 119902out (2)

where 119901in and 119902in are the pressure and flow rate of thepumps and 119901out and 119902out are the pressure and flow rate of thecylinders

According to the operating condition of the hydraulicexcavator when the boom cylinder piston is contracting andthe bucket cylinder and the bucket rod cylinder piston areexpanding the excess potential energy in the return oil linescan be recycled and reused The input power of the threecylinder systems and the output power in the return oil linesare shown in Figures 2 and 3 From Figure 3 it is shown thatthe part of output power which is greater than zero can berecycled and reused The input energy and the excess energywhich can be recycled of the three cylinder systems are givenin Table 1

From Table 1 it is shown that there is plenty of energyloss in the return oil lines when the boom cylinder pistonis contracting Compared with the bucket rod and bucketsystems the boom system has a high energy recovery per-centage Taking the complexity and cost of the system intoconsideration the boom potential energy recovery system inhybrid hydraulic excavator based on an accumulator and agenerator is proposed

22 Structure of the Boom Potential Energy Recovery SystemA new boom potential energy recovery system needs to bedesigned to satisfy the following requirements

(1) operation of the new boom energy recovery systemmust be similar to the conventional hydraulic excava-tor

(2) the new boom energy recovery system must achievehigher working efficiency and savemore energy whencomparing with the conventional system

Figure 4 shows the schematic of the proposed hydraulicsystem Itmainly consists of oil supply system boomcylindercontrol valves and energy regeneration unit The pumpis driven by the engine and the motor The pressure oilexporting from the pump was supplied to the boom cylindersystem When the boom cylinder piston is contracting theexcess energy is converted into electrical energy and stored in

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A BA B

P

QPP

Q

q

Q

QP

TP T

xx

x V

Bucket rod cylinderBucket cylinderConventional hydraulic excavator

Boom cylinderBody 1

Body 1

Body 2

Body 2

Body 3

Body 3

Body 4

Body 4

Body 5

Body 5

k

k

k PID

k

k

minus

+k

Runstats

PIDminus

+

k

k PIDminus

+

xy

k

Qq

A B

P

QP

qq

q

T

F

xy

xy

xy

x

y

times

times

times

timestimes

timesk

s

k

s

k

s

Figure 1 AMESim model of conventional hydraulic excavator

the battery Compared with the engine power 119875119890and the load

power 119875119897 there are three kinds of working conditions based

on the load change

(1) When 119875119890gt 119875119897 the pump is driven by the engine

and the excess power of the engine is converted intoelectrical energy by the motor and stored in thebattery The motor is working as a generator in thisworking condition

(2) When 119875119890lt 119875119897 electrical energy stored in the battery

is used to drive the motor The engine and the motordrive the pump together

(3) When the motor power 119875119890gt 119875119898gt 119875119897 the pump is

driven by the motor independently and the engine isworking in the idle state

The working flow chart of the proposed system is shownin Figure 5 Comparedwith the conventional energy recoverysystem the pressure oil is charged into the accumulatorinstead of flowing into themotor directly when the boomarmfalls in the first working cycle Meanwhile the pressure oilin the accumulator is discharged and flowing into the motorwhen the boom arm rises in the second working cycle It

makes sure that the generator can rotate continuously in ahigh speed Hence two working cycles of the conventionalhydraulic excavator are regarded as a complete workingperiod for the new energy saving system

3 Mathematical Modeling

31 Boom Cylinder As shown in Figure 4 the dynamics ofthe piston of the boom cylinder can be expressed as

119865119897+ 11987521198602minus 11987511198601minus 119887119888V119888minus 119865119891minus119872V10158401015840

119888= 0 (3)

Continuity equation of hydraulic cylinder piston can beexpressed as

1198761

1198601

=1198762

1198602

(4)

where119872 is the equivalent mass of the load V119888is the velocity

of the piston 119865119897is the external force and 119875

1and 119875

2are

the pressures in the large and small chamber of the boomcylinder respectively 119876

1and 119876

2are the corresponding flow

rate 1198601and 119860

2denote the corresponding working areas

119865119888is the coulomb friction force and 119887

119888is the combined

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0 10 20 30 40 5000

200

400

600

800

1000

1200

Inpu

t pow

er (k

W)

Time (s)

Bucket systemBoom systemBucket rod system

Figure 2 Input power of the three cylinder systems

Time (s)

Bucket systemBoom systemBucket rod system

0 10 20 30 40 50

0050

100150200250300350400450

Out

put p

ower

(kW

)

minus50

minus100minus150minus200minus250minus300

Figure 3 Output power in the return oil lines

coefficient of damping and viscous friction forces on the loadand the rod The value of V

119888is the differential of the piston

displacement 119909119888

32 Hydraulic Motor The dynamics of the rotor of theregeneration unit can be expressed as

119863119898(1198753minus 1198754) = 119869

119889120596119898

119889119905+ 119887119898120596119898+ 119879119891+ 119879119892 (5)

where 120596119898

is the rotational speed of the hydraulic motorJ is the total moment of inertia of the regeneration unit119879119892is the electromagnetic torque of the generator 119879

119891is the

coulomb friction torque 119861119898is the combined coefficient of

damping and viscous friction torques on the rotor 119863119898is the

E

M

M

G

Rectifier

BatteryRectifierinverter

8

7

1

2 4

3

6

59 12 10

13

11

14

(1) Engine(2) Transmission device(3) Motorgenerator(4) Pump(5) Relief valve(6) Tank(7) Electromagnetic valve

(8) Boom cylinder(9) Reversing valve(10 12) Globe valve(11) Accumulator(13) Variable displacement motor(14) Generator

Figure 4 Schematic of proposed boom energy-recovery hydraulicsystem

displacement of the hydraulic motor and 1198753and 119875

4are the

inlet and outlet pressures of the motorFlow continuity equation of the motor can be written as

1198763minus 1198621198901198981198753minus 119862119894119898(1198753minus 1198754) minus 119863119898120596119898= 0

119863119898120596119898+ 119862119894119898(1198753minus 1198754) minus 1198621198901198981198752minus 1198764= 0

(6)

where 119862119890119898

is the external leakage coefficients of the motorand 119862

119894119898is the internal leakage coefficient of the motor

Assuming that there is no loop loss in reversing valve theflow equation of the chamber between the cylinder and themotor can be written as

1198601V119888minus 119862119894119888(1198751minus 1198752) minus 1198621198901198881198751minus 119862119894119898(1198751minus 1198754)

minus 120596119898119863119898minus 119876119886=119881

120573119890

1198891198751

119889119905

(7)

where 119862119894119888is the internal leakage coefficients of the cylinder

119862119890119888

is the external leakage coefficient of the cylinder 119881 isthe volume of the hydraulic oil between the boom cylinderand motor 119876

119886is the flow of the hydraulic oil stored in the

accumulator and 120573119890is the volume elastic modulus

33 Hydraulic Accumulator Thebladder accumulator is cho-sen in this boom energy recovery system according to Boylelaw and the formula is given by

1199010119881119899

0= 1199011119881119899

1= 1199012119881119899

2= 119901119886119881119899

119886 (8)

where 1199010 1199011 1199012 119901119886denote the initial aeration pressure

initial pressure terminal state pressure and free state pressure

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System initialize

The boom up

Working normally

YesNo

The first working cycle start

The top cavity of valve 9 on

valve 10 on

Hydraulic oil returns totankAccumulator is charged

The second workingcycle start

The boom up

The top cavity ofvalve 9 onvalve 10 on

The top cavity ofvalve 9 offvalve 10 on

YesNo

Valve 12 on

Hydraulic oil from valve 9flow into valve 12

Hydraulic oil from accumulator flow into

valve 12

Motor drive generatorto rotate

End

The top cavity ofvalve 9 off

Work ending Yes No

valve 12 off

Figure 5 Working flow chart of the energy saving system

of accumulator respectively 1198810 1198811 1198812 119881119886are the initial

aeration volume initial volume terminal state volume andfree state volume of accumulator 119899 is the air polytropicexponent

119901119886and119881

119886are the random operating state of accumulator

the equality of 1199010119881119899

0= 119901119886119881119899

119886is expanded using Taylor

expansion the Taylor expansion is given by

119889119875119886

119889119905= minus

1198991198750

1198810

119889119881119886

119889119905 (9)

Flow and air chamber volume of accumulator are 119876119886and 119881

119886

and the inlet flow rate of accumulator is given by

119876119886= minus

119889119881119886

119889119905 (10)

Energy equation of accumulator

119864 = minusint

1198812

1198811

(1198810

119881119886

)

119899

119889119881119886=11987501198810

119899 minus 1[(119875119886

1198750

)

(119899minus1)119899

minus 1] (11)

According to the equations above the flow control systemis an obviously nonlinear system In order to verify itsstability and dynamic performance linearization and Laplacetransform are carried out The transfer function from thehydraulic motor speed to the load force can be expressed as120596119898(119904)

119865 (119904)

= (119863119898

1198601119879119892

)

6 The Scientific World Journal

times ([119869119872(119862119899119875

0+ 1198810)

119860211198991198750119879119892

+119872119881

11986021120573119890

] 1199042

+[119863119898119872+ 119869119860

2

1

11986021119879119892

+119872(119862119899119875

0+ 1198810)

119899119875011986021

] 119904 + 1)

minus1

(12)

where 119862 is the leakage coefficients of the energy recoverysystem

The natural frequency of the proposed energy recoverysystem can be calculated as

120596119867= radic

1

119869119872(1198621198991198750+ 1198810) 119860211198991198750119879119892+1198721198811198602

1120573119890

(13)

The natural frequency is the lowest frequency of the sys-tem The low natural frequency has an effect on the responsespeed of the system and energy recovery efficiency In orderto improve the natural frequency and response speed of thesystem based on the expression of the natural frequency thefollowing ways should be taken into consideration

(1) Reducing the loop oil volume 119881 to make the wholesystem structure compact and high-efficiency the oilline should be installed effectively and the length ofthe line should be shortened as soon as possible

(2) Increasing the volume elastic modulus of thehydraulic oil 120573

119890 while designing the system and

selecting the hydraulic oil the volume elasticmodulus 120573

119890of the oil should have a large value

relatively(3) Reducing the leakage coefficients of the energy recov-

ery system 119862 as it is hardly realistic to eliminate thesystem leakage the quality of the hydraulic compo-nents chosen in the system should satisfy the longtime using performance

(4) Reducing the total moment of inertia of the hydraulicmotor 119869 according to the characteristics of themotorthe total moment of inertia decreases along with thedecreasing of the displacement so the displacementof the motor should be reduced to a certain degreeHowever the flow rate of the return oil lines willreducewhen the displacement of themotor decreasesHence it has an effect on the working performance ofthe hydraulic excavator

4 Simulation of the Boom EnergyRecovery System

In order to verify the energy saving efficiency of the pro-posed system simulations with the proposed accumulator-generator system and the conventional energy recoverysystem have been carried out by using AMESim It aims tovalidate the impact of accumulator on energy recovery effi-ciency Figure 6 shows the AMESim model of the proposedsystem with accumulator while Figure 7 displays anotherkind of boom energy recovery system without accumulator

Table 2 Setting parameters for the two AMESim models

Common parts Parameters Values

Boom cylinderPiston diameter (mm) 350Rod diameter (mm) 220Length of stroke (m) 18

Generator Reference voltage (V) 50

Battery Nominal capacity (Ah) 50State of charge () 60

Table 3 Input energy and the energy stored in the battery

System Input energy119864in (J)

Energy storedin the battery

119864st (J)

Percentage119864st119864in ()

Conventional system 764601198646 05041198646 66Proposed system 689231198646 10081198646 146

To simplify the system the engines are replaced by twomotors in Figures 6 and 7

Including the load force and dimension parameters of theboom cylinder the setting parameters for the AMESimmod-els are obtained from the conventional hydraulic excavatorThe main setting parameters for the two AMESim modelsare given in Table 2 The input load force of the conventionalenergy recovery system and the proposed energy recoverysystem is shown in Figure 8

Run the simulations The displacement of the boomcylinder in the conventional energy recovery system and theproposed system are shown in Figure 9 Figure 9 shows thatthe piston displacement of the boom cylinder in the twosystems is quite similar The working performance of theboom cylinder is not affected by the energy recovery systeminstalled in the return oil lines

The difference between the SOC (State of Charge) of thebatteries in the two systems is shown in Figure 10 For theconventional energy recovery system the generator starts andstops four times during a working period According to themechanical characteristics of the generator high efficiencydepends on high speed and continuous rotation Becauseof the accumulator the generator of the proposed energyrecovery system starts and stops only once during a workingperiod Hence the generator can rotate in a high speedcontinuously Comparedwith the conventional energy savingsystem SOC of the battery in the proposed system can risesmoothly During a whole working period the value of SOCreaches 652 Finally the input energy and the energy storedin the batteries of the two energy saving systems are given inTable 3

Based on Table 3 the value of the energy recoveryefficiency in the proposed system is 146 while the valueof the conventional energy recovery system is 66 It isclear that the proposed boom potential energy recoverysystem brings higher energy recovery efficiency than theconventional boom potential energy recovery system

The Scientific World Journal 7

F

MOT

Boom potential recovery system

FluidA

SM

A

A

B

P T

P

A

P

PT

Q

M

q

Qq

QP

2

1

3

Runstats

k

k

k

k

f(X

)X

X

Y

times

timesk

k

Y lt Xk

s

ktimes k

s

properties

WT

J WTT +

+

T

minus

Figure 6 AMESim model of the proposed system

5 Analysis of the Main Componentsin the System

As designing the boom energy recovery system of the hybridhydraulic excavator all the components of the system arechosen based on the calculation results and working con-dition However some parameters of the main componentshave a great influence on the energy recovery efficiency of theproposed system Inappropriate parameters will lead to thedecreasing of the efficiency Therefore it is essential to anal-ysis the relationship between the energy recovery efficiencyand the key parameters of the main components like theaeration pressure of the accumulator and the displacement ofthe hydraulic motor In order to simplify the model there arethree assumptions for the simulation models

(1) Since this study concentrates on the effectivenessof the proposed boom energy recovery system theworking performance of the engine is not takeninto consideration The engine is replaced by anelectromotor

(2) The load force and the piston velocity of the boomcylinder in the simulation models are identical withthe conventional hydraulic excavator In other wordsthe boom cylinder system is working under the sameconditions

(3) A generator and a battery are selected as the energyconversion and energy storage units Regardless of theinternal structure of generator and battery the simu-lation models are replaced by the universal models

8 The Scientific World Journal

Conventional boom potential recovery system

F

M

Qq

ktimes

A B

P T

Fluid properties

Runstats

Qq

MOT

k

times

k

k

s

k

f(X

)X

X

YY lt X

A

P T

QP

ktimes k

s

kk

WTJ W

T

+SM

T

+

T

minus

Figure 7 AMESim model of a conventional boom energy recovery system

0 20 40 60 80 100

Boom

cylin

der l

oadi

ng fo

rce (

N)

12 times 106

10 times 106

80 times 105

60 times 105

40 times 105

20 times 105

00

Time (s)

Figure 8 Input load force of the energy saving system

51 Analysis of the Accumulator The key parameters of theaccumulator include the aeration pressure and the initialvolume The simulations of the relationship between theparameter values and the system energy recovery efficiencyare shown below

0 20 40 60 80 100

06

08

10

12

14

16

18

Boom

cylin

der p

iston

disp

lace

men

t (m

)

Time (s)

Conventional energy recovery systemProposed energy recovery system

Figure 9 Piston displacement of the boom cylinder

511 The Aeration Pressure In order to analyze the influenceof the different aeration pressure on the energy recovery

The Scientific World Journal 9

0 10 20 30 40 50 60 70 80 90 100600605610615620625630635640645650655

SOC

of th

e bat

tery

()

Conventional energy recovery systemProposed energy recovery system

Time (s)

Figure 10 SOC of the battery

0 20 40 60 80 100380

400

420

440

460

480

500

Volu

me c

hang

ing

of th

e acc

umul

ator

(L)

Time (s)

5MPa7MPa

9MPa10MPa

Figure 11 Volume changing of the accumulator

efficiency four values 5MPa 7MPa 9MPa and 10MPa areselected within the scope of the aeration pressure Run thesimulation models Figures 11 and 12 present the volume andpressure changing of the accumulator The rotational speedof the hydraulic motor is shown in Figure 13 The SOC of thebattery is shown in Figure 14

Based on the figures above it can be seen that thepressure of the accumulator is proportional to its aerationpressure When the boom cylinder piston is expanding inthe second working cycle the hydraulic motor is driven bythe oil stored in the accumulator The volume changing ofthe pressure oil in the accumulator increases along with theincreasing of the aeration pressure It leads to increasing theflow of the pressure oil in the energy recovery system Thepressure difference between the inlet and outlet of the motoris increasing as well Because of the constant displacement

0 20 40 60 80 100Time (s)

50

60

70

80

90

100

110

120

130

140

150

Pres

sure

chan

ging

of t

he ac

cum

ulat

or (b

ar)

5MPa7MPa

9MPa10MPa

Figure 12 Pressure changing of the accumulator

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

4000

4500Ro

tatio

nal s

peed

of t

he m

otor

(rm

in)

Time (s)

5MPa7MPa

9MPa10MPa

Figure 13 Rotational speed of the hydraulic motor

hydraulic motor the flow rate through the hydraulic motoris proportional to its rotational speed The output torqueof the motor is increasing gradually based on the pressuredifferenceThe generator is connected to the hydraulic motorcoaxially According to the characteristics of the generatorthe output torque of the motor is increasing as well Hencethe electric energy produced by the generator and SOC of thebattery are increasing

512 The Initial Volume In order to analyze the influence ofthe different initial volume on the energy recovery efficiencyfour values 450 L 470 L 480 L and 500 L are selected withinthe scope of the initial volume under the condition that theaeration pressure and the highest working pressure of theaccumulator are keeping in 10MPa and 18MPa

10 The Scientific World Journal

60

61

62

63

64

65

SOC

of th

e bat

tery

()

0 10 20 30 40 50 60 70 80 90 100Time (s)

5MPa7MPa

9MPa10MPa

Figure 14 SOC of the battery

0 10 20 30 40 50 60 70 80 90 100340

360

380

400

420

440

460

480

500

Volu

me c

hang

ing

of th

e acc

umul

ator

(L)

Time (s)

450L470L

480L500L

Figure 15 Volume changing of the accumulator

Figures 15 and 16 show the volume and pressure changingof the accumulator Keeping the aeration pressure unchangedthe simulation results indicate that the pressure of theaccumulator is inversely proportional to the initial volumeThe corresponding rotational speeds of the hydraulic motorare shown in Figure 17 The SOC of the battery is shown inFigure 18 It can be seen that the value of SOC is not changingwith the different initial volume In other words the value ofthe initial volume does not have an effect on the improving ofthe boom energy recovery efficiency

52 Analysis of the Hydraulic Motor The hydraulic motoris used to drive the generator in the boom energy recoverysystem The energy recovery system is determined by theperformance of the motor So it is essential to do someresearch on the hydraulicmotorThedisplacement is themost

0 10 20 30 40 50 60 70 80 90 100100

110

120

130

140

150

Pres

sure

chan

ging

of t

he ac

cum

ulat

or (b

ar)

Time (s)

450L470L

480L500L

Figure 16 Pressure changing of the accumulator

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

4000

4500Ro

tatio

nal s

peed

of t

he m

otor

(rm

in)

Time (s)

450L470L

480L500L

Figure 17 Rotational speed of the hydraulic motor

important parameter of the hydraulic motorThe simulationsof the displacement and the type of the motor are shownbelow

521 The Displacement In order to analyze the influence ofthe different displacement on the energy recovery efficiencyfour values 60mLr 80mLr 100mLr and 120mLr areselected as the displacement of the motor

Figure 19 shows the velocity of the boom cylinder pistonin the hybrid hydraulic excavator Based on the workingprocess of the hydraulic excavator the boom cylinder iscontracting during 52 sndash69 s and 90 sndash100 s The hydraulicmotor is driven by the pressure oil flowing into the returnoil line The result shows that the contracting velocity ofthe cylinder decreases along with the decreasing of the

The Scientific World Journal 11

0 10 20 30 40 50 60 70 80 90 10060

61

62

63

64

65

SOC

of th

e bat

tery

()

Time (s)

450L470L

480L500L

Figure 18 SOC of the battery

0 10 20Time (s)

30 40 50 60 70 80 90 100

000

005

010

015

Velo

city

of t

he b

oom

cylin

der p

iston

(ms

)

minus005

minus010

minus015

60mLr80mLr

100mLr120mLr

Figure 19 Velocity of the boom cylinder piston

displacement However it does not have an effect on thenormal work of the hydraulic excavator

Figures 20 and 21 show the rotational speed of thehydraulic motor and SOC of the battery with the differ-ent displacement According to the characteristics of thehydraulicmotor the rotational speed of themotor is inverselyproportional to the displacement When the displacement is60mLr the SOC of the battery reaches the maximum valueIt indicates that the SOC of the battery increases along withthe decreasing of the displacement

522 The Type of the Hydraulic Motor Because of thecomplex working condition of the hydraulic excavator thevelocity of the boom cylinder piston ranges from 0 to 01msThe flow rate of the pressure in the return oil line ranges

0 10 20 30 40 50 60 70 80 90 1000

1000

2000

3000

4000

5000

6000

7000

Rota

tiona

l spe

ed o

f the

mot

or (r

min

)

Time (s)

60mLr80mLr

100mLr120mLr

Figure 20 Rotational speed of the hydraulic motor

0 10 20 30 40 50 60 70 80 90 10060

61

62

63

64

65

66SO

C of

the b

atte

ry (

)

Time (s)

60mLr80mLr

100mLr120mLr

Figure 21 SOC of the battery

large So it is very important to select the hydraulic motor forimproving the energy recovery system

The hydraulicmotor is divided into the constant displace-ment and variable displacement motor The AMESim modelwith the variable displacement motor is shown in Figure 22

Run the simulation Compared with the models withthe constant displacement motor shown in Figure 6 therotational speed of the hydraulic motor in two simulationmodels is presented in the Figure 23 Figure 24 shows the SOCrange of the battery

It can be seen that the rotational speed of the constantdisplacement motor is ranging between 1300 rmin and3500 rmin during a working cycle while the rotational speedof the variable displacement motor remains at 3000 rminThe SOC of the battery of the constant displacement motorsystem increases from 60 to 648 while the SOC of the

12 The Scientific World Journal

Boom potential recovery system

F

M

Qq

ktimesA B

P T

Fluid

Runstats

properties

Qq

A

P

P

T

MOT

k

k

k

f(X

)X

X

Y timesY lt X

k

s

2

1

3

SM

A

A

P

QP

k

k

ktimes k

s

WT

J WT w

T +

+

T

minus

kPIDminus

+

Figure 22 AMESim model with the variable displacement motor

battery of the variable displacement motor system reaches708 Compared with the constant displacement motorsystem more boom potential energy of the energy recoverysystemwith the variable displacementmotor is recovered andstored in the battery Hence the energy recovery efficiencyof the variable displacement motor system is higher than thesystem with the constant displacement motor

6 Conclusions

(1) Based on the simulation of the working devicesin the conventional hydraulic excavator the energywhich can be recovered of the three cylinders iscalculated Taking the complexity and cost of thesystem into consideration this paper proposed anovel boom potential energy recovery system for theparallel hybrid excavator The boom energy regen-eration unit consists of an accumulator a hydraulicmotor an electric generator and a battery Compared

with the conventional energy recovery system theproposed system makes sure that the generator canrotate continuously in a high speed during a workingcycle The AMESim models of the two boom energyrecovery systems are built and the results show thatthe proposed energy recovery system brings higherenergy recovery efficiency than the conventionalenergy recovery system

(2) The mathematical models of the main compo-nents including boom cylinder hydraulic motorand hydraulic accumulator are built The naturalfrequency of the proposed energy recovery systemis calculated based on the mathematical models Inorder to improve the natural frequency and responsespeed of the system some measures should be takenbased on the expression of the natural frequencysuch as reducing the loop oil volume 119881 the leakage

The Scientific World Journal 13

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

Rota

tiona

l spe

ed o

f the

hyd

raul

ic m

otor

(rm

in)

Constant displacement motor Variable displacement motor

Time (s)

Figure 23 Rotational speed of the hydraulic motor

0 10 20 30 40 50 60 70 80 90 100606162636465666768697071

SOC

of th

e bat

tery

()

Constant displacement motor Variable displacement motor

Time (s)

Figure 24 SOC of the battery

coefficients of the energy recovery system 119862 and thetotal moment of inertia of the hydraulic motor 119869

(3) The influence of the main components includinghydraulic motor and hydraulic accumulator on theenergy recovery efficiency of the proposed systemis analyzed The key parameters of the accumulatorinclude the aeration pressure and the initial volumeThe energy recovery efficiency of the proposed sys-tem can be improving to some extent by increasingthe aeration pressure while changing of the initialvolume does not have an effect on improving of theenergy recovery efficiency

The hydraulic motor is used to drive the generator inthe boom energy recovery system The displacement is themost important parameter of the hydraulicmotorThe energy

recovery efficiency can be improving on the premise ofnormal working by decreasing the displacement of themotorSince the flow rate of the pressure in the return oil line rangeslarge the generator can rotate continuously in a high speedby selecting the variable displacement motor in the return oilline In order to improve the energy efficiency according tothe characteristics of the generator the variable displacementhydraulic motor should be chosen in the return oil line

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work is supported by the Fundamental Research Fundsfor the Central Universities (China University of Mining andTechnology 2014Y05) PCSIRT (IRT1292) and the ProjectFunded by the Priority Academic Program Development ofJiangsu Higher Education Institutions (PAPD)

References

[1] M Kagoshima M Komiyama T Nanjo et al ldquoDevelopment ofnew hybrid excavatorrdquo Kobelco Technology Review no 27 2007

[2] T Nanjo E Imanishi and M Kagcahima ldquoPower simulationfor energy saving in hybrid excavatorrdquo JSAE Transactions vol47 pp 101ndash106 2004

[3] L Weidong S Kaikai L Wei and X Jun ldquoResearch onpotential energy recovery of 16T wheeled hybrid excavatorrdquoin Proceedings of the 2nd International Conference on DigitalManufacturing and Automation (ICDMA rsquo11) pp 996ndash998Zhangjiajie China August 2011

[4] I Y Jong K K Ahn and Q T Dinh ldquoA study on anenergy saving electro-hydraulic excavatorrdquo in Proceedings of theICROS-SICE International Joint Conference (ICCAS-SICE rsquo09)pp 3825ndash3830 Fukuoka Japan August 2009

[5] T H Ho and K K Ahn ldquoDesign and control of a closed-loop hydraulic energy-regenerative systemrdquo Automation inConstruction vol 22 pp 444ndash458 2012

[6] Z Jun J Sheng-jie S Gui-mao et al ldquoDesign of electroniccontrol system of hydraulic excavator with CAN bus andPID methodrdquo Proceedings of the International Conference onIntelligent System Design and Engineering Application (ISDEArsquo10) 2010

[7] T Wang and Q Wang ldquoModeling and control of a novelhydraulic system with energy regenerationrdquo in Proceedings ofthe IEEEASME International Conference on Advanced Intelli-gent Mechatronics (AIM rsquo12) pp 922ndash927 IEEE KachsiungTaiwan July 2012

[8] H SHamut I Dincer andG FNaterer ldquoExergoenvironmentalanalysis of hybrid electric vehicle thermal management sys-temsrdquo Journal of Cleaner Production vol 67 pp 187ndash196 2014

[9] A Poursamad and M Montazeri ldquoDesign of genetic-fuzzycontrol strategy for parallel hybrid electric vehiclesrdquo ControlEngineering Practice vol 16 no 7 pp 861ndash873 2008

[10] S Hui J-H Jiang and W Xin ldquoTorque control strategy fora parallel hydraulic hybrid vehiclerdquo Journal of Terramechanicsvol 46 no 6 pp 259ndash265 2009

14 The Scientific World Journal

[11] Z Cao S Wu M Li and C Du ldquoSeries and parallel hybridsystem performance comparison based on the city bus cyclerdquoin Proceedings of the Asia-Pacific Power and Energy EngineeringConference (APPEEC 09) Wuhan China March 2009

[12] J Gong Q He D Zhang et al ldquoPower system control strategyfor hybrid excavator based on equivalent fuel consumptionrdquo inProceedings of the 9th IEEE International Conference on Mecha-tronics and Automation (ICMA rsquo12) pp 1097ndash1102 ChengduChina August 2012

[13] Z Liu S Liu Z Huang and Q Hu ldquoHydraulic excavatorhybrid power system parameters designrdquo in Proceedings of the2nd International Conference on Digital Manufacturing andAutomation (ICDMA rsquo11) pp 602ndash605 Zhangjiajie ChinaAugust 2011

[14] T Lin Q Wang B Hu and W Gong ldquoResearch on theenergy regeneration systems for hybrid hydraulic excavatorsrdquoAutomation in Construction vol 19 no 8 pp 1016ndash1026 2010

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International Journal of

2 The Scientific World Journal

Based on the successful application of the hybrid systemin automotive industry it attracts a lot of the worldrsquos largestcompanies and institutersquos interest Many researches on theapplication of the hybrid technology in hydraulic excavatorhave been done In order to enhance fuel economy of hybridexcavator system Gong et al [12] introduce a control strategybased on equivalent fuel consumption The results showthat the control strategy can effectively optimize the hybridpower distribution and improve fuel economy Liu et al [13]find a versatile method designing the parameters of maincomponents of hydraulic excavator The method has simplecalculation process and it can be used to carry out parametermatching on different hybrid system Lin et al [14] deal withthe method of how to regenerate the potential energy for ahybrid hydraulic excavator The simulation results show thatit is possible to increase the efficiency of the generator anddownsize the generator by adding the hydraulic accumulatorto the system

This paper mainly presents a new hybrid hydraulic exca-vator energy recovery system which combines the hydraulicaccumulator and the electric regeneration unit together Inthis system the accumulator and the regeneration unit areinstalled in the return oil lines In some operating conditionsthe excess energy supplied by the pump can be converted toelectricity and stored in the battery The cylinder velocitiesare governed by the displacement of hydraulic motor Theproposed system is simulated by AMESim software Theenergy recovery efficiency of the proposed system is clearlyverified through simulation results in comparison with theconventional energy recovery system At last in order toimprove the energy recovery efficiency of the proposedsystem the main components of the proposed energy recov-ery system including accumulator and hydraulic motor areanalyzed The results show that the different key parametersof components have a great influence on the energy recoveryefficiency

2 Design of the System Scheme

21 EnergyConsumptionAnalysis of the Traditional ExcavatorAs the hydraulic excavator starts to work the boom cylinderpiston can expand and contract twice during a work period aswell as the bucket cylinder and the bucket rod cylinder Dueto the high frequency of use three cylindersmentioned aboveare analyzed based on 25t hydraulic excavator (middle typehydraulic excavator) Simulation with conventional hydraulicexcavator has been carried out by using AMESim softwareThe model built in AMESim is shown in Figure 1 In order tosimplify the model there are two assumptions for the system

(1) The pumps in the hydraulic excavator system arereplaced by three constant pressure sources the inputpressure 119901in = 200 bar and they supply the flow ratewhich the actuators need

(2) There is not any energy loss in the hydraulic circuitand components but for the electrohydraulic direc-tional control valves and the pressure drop 119901drop =20 bar

Table 1 Input energy and excess energy of the three cylindersystems

Input energy119864in (J)

Excess energy119864ex (J)

Percentage119864ex119864in ()

Boom system 1263991198646 05986511198646 4736Bucket rod system 0676351198646 62118 918Bucket system 0740531198646 529446 715

Run the simulation for a whole work period of thehydraulic excavator The power of the pumps 119875in and thepower of the cylinders 119875out are calculated by the followingrespectively

119875in = 119901in sdot 119902in (1)

119875out = 119901out sdot 119902out (2)

where 119901in and 119902in are the pressure and flow rate of thepumps and 119901out and 119902out are the pressure and flow rate of thecylinders

According to the operating condition of the hydraulicexcavator when the boom cylinder piston is contracting andthe bucket cylinder and the bucket rod cylinder piston areexpanding the excess potential energy in the return oil linescan be recycled and reused The input power of the threecylinder systems and the output power in the return oil linesare shown in Figures 2 and 3 From Figure 3 it is shown thatthe part of output power which is greater than zero can berecycled and reused The input energy and the excess energywhich can be recycled of the three cylinder systems are givenin Table 1

From Table 1 it is shown that there is plenty of energyloss in the return oil lines when the boom cylinder pistonis contracting Compared with the bucket rod and bucketsystems the boom system has a high energy recovery per-centage Taking the complexity and cost of the system intoconsideration the boom potential energy recovery system inhybrid hydraulic excavator based on an accumulator and agenerator is proposed

22 Structure of the Boom Potential Energy Recovery SystemA new boom potential energy recovery system needs to bedesigned to satisfy the following requirements

(1) operation of the new boom energy recovery systemmust be similar to the conventional hydraulic excava-tor

(2) the new boom energy recovery system must achievehigher working efficiency and savemore energy whencomparing with the conventional system

Figure 4 shows the schematic of the proposed hydraulicsystem Itmainly consists of oil supply system boomcylindercontrol valves and energy regeneration unit The pumpis driven by the engine and the motor The pressure oilexporting from the pump was supplied to the boom cylindersystem When the boom cylinder piston is contracting theexcess energy is converted into electrical energy and stored in

The Scientific World Journal 3

A BA B

P

QPP

Q

q

Q

QP

TP T

xx

x V

Bucket rod cylinderBucket cylinderConventional hydraulic excavator

Boom cylinderBody 1

Body 1

Body 2

Body 2

Body 3

Body 3

Body 4

Body 4

Body 5

Body 5

k

k

k PID

k

k

minus

+k

Runstats

PIDminus

+

k

k PIDminus

+

xy

k

Qq

A B

P

QP

qq

q

T

F

xy

xy

xy

x

y

times

times

times

timestimes

timesk

s

k

s

k

s

Figure 1 AMESim model of conventional hydraulic excavator

the battery Compared with the engine power 119875119890and the load

power 119875119897 there are three kinds of working conditions based

on the load change

(1) When 119875119890gt 119875119897 the pump is driven by the engine

and the excess power of the engine is converted intoelectrical energy by the motor and stored in thebattery The motor is working as a generator in thisworking condition

(2) When 119875119890lt 119875119897 electrical energy stored in the battery

is used to drive the motor The engine and the motordrive the pump together

(3) When the motor power 119875119890gt 119875119898gt 119875119897 the pump is

driven by the motor independently and the engine isworking in the idle state

The working flow chart of the proposed system is shownin Figure 5 Comparedwith the conventional energy recoverysystem the pressure oil is charged into the accumulatorinstead of flowing into themotor directly when the boomarmfalls in the first working cycle Meanwhile the pressure oilin the accumulator is discharged and flowing into the motorwhen the boom arm rises in the second working cycle It

makes sure that the generator can rotate continuously in ahigh speed Hence two working cycles of the conventionalhydraulic excavator are regarded as a complete workingperiod for the new energy saving system

3 Mathematical Modeling

31 Boom Cylinder As shown in Figure 4 the dynamics ofthe piston of the boom cylinder can be expressed as

119865119897+ 11987521198602minus 11987511198601minus 119887119888V119888minus 119865119891minus119872V10158401015840

119888= 0 (3)

Continuity equation of hydraulic cylinder piston can beexpressed as

1198761

1198601

=1198762

1198602

(4)

where119872 is the equivalent mass of the load V119888is the velocity

of the piston 119865119897is the external force and 119875

1and 119875

2are

the pressures in the large and small chamber of the boomcylinder respectively 119876

1and 119876

2are the corresponding flow

rate 1198601and 119860

2denote the corresponding working areas

119865119888is the coulomb friction force and 119887

119888is the combined

4 The Scientific World Journal

0 10 20 30 40 5000

200

400

600

800

1000

1200

Inpu

t pow

er (k

W)

Time (s)

Bucket systemBoom systemBucket rod system

Figure 2 Input power of the three cylinder systems

Time (s)

Bucket systemBoom systemBucket rod system

0 10 20 30 40 50

0050

100150200250300350400450

Out

put p

ower

(kW

)

minus50

minus100minus150minus200minus250minus300

Figure 3 Output power in the return oil lines

coefficient of damping and viscous friction forces on the loadand the rod The value of V

119888is the differential of the piston

displacement 119909119888

32 Hydraulic Motor The dynamics of the rotor of theregeneration unit can be expressed as

119863119898(1198753minus 1198754) = 119869

119889120596119898

119889119905+ 119887119898120596119898+ 119879119891+ 119879119892 (5)

where 120596119898

is the rotational speed of the hydraulic motorJ is the total moment of inertia of the regeneration unit119879119892is the electromagnetic torque of the generator 119879

119891is the

coulomb friction torque 119861119898is the combined coefficient of

damping and viscous friction torques on the rotor 119863119898is the

E

M

M

G

Rectifier

BatteryRectifierinverter

8

7

1

2 4

3

6

59 12 10

13

11

14

(1) Engine(2) Transmission device(3) Motorgenerator(4) Pump(5) Relief valve(6) Tank(7) Electromagnetic valve

(8) Boom cylinder(9) Reversing valve(10 12) Globe valve(11) Accumulator(13) Variable displacement motor(14) Generator

Figure 4 Schematic of proposed boom energy-recovery hydraulicsystem

displacement of the hydraulic motor and 1198753and 119875

4are the

inlet and outlet pressures of the motorFlow continuity equation of the motor can be written as

1198763minus 1198621198901198981198753minus 119862119894119898(1198753minus 1198754) minus 119863119898120596119898= 0

119863119898120596119898+ 119862119894119898(1198753minus 1198754) minus 1198621198901198981198752minus 1198764= 0

(6)

where 119862119890119898

is the external leakage coefficients of the motorand 119862

119894119898is the internal leakage coefficient of the motor

Assuming that there is no loop loss in reversing valve theflow equation of the chamber between the cylinder and themotor can be written as

1198601V119888minus 119862119894119888(1198751minus 1198752) minus 1198621198901198881198751minus 119862119894119898(1198751minus 1198754)

minus 120596119898119863119898minus 119876119886=119881

120573119890

1198891198751

119889119905

(7)

where 119862119894119888is the internal leakage coefficients of the cylinder

119862119890119888

is the external leakage coefficient of the cylinder 119881 isthe volume of the hydraulic oil between the boom cylinderand motor 119876

119886is the flow of the hydraulic oil stored in the

accumulator and 120573119890is the volume elastic modulus

33 Hydraulic Accumulator Thebladder accumulator is cho-sen in this boom energy recovery system according to Boylelaw and the formula is given by

1199010119881119899

0= 1199011119881119899

1= 1199012119881119899

2= 119901119886119881119899

119886 (8)

where 1199010 1199011 1199012 119901119886denote the initial aeration pressure

initial pressure terminal state pressure and free state pressure

The Scientific World Journal 5

System initialize

The boom up

Working normally

YesNo

The first working cycle start

The top cavity of valve 9 on

valve 10 on

Hydraulic oil returns totankAccumulator is charged

The second workingcycle start

The boom up

The top cavity ofvalve 9 onvalve 10 on

The top cavity ofvalve 9 offvalve 10 on

YesNo

Valve 12 on

Hydraulic oil from valve 9flow into valve 12

Hydraulic oil from accumulator flow into

valve 12

Motor drive generatorto rotate

End

The top cavity ofvalve 9 off

Work ending Yes No

valve 12 off

Figure 5 Working flow chart of the energy saving system

of accumulator respectively 1198810 1198811 1198812 119881119886are the initial

aeration volume initial volume terminal state volume andfree state volume of accumulator 119899 is the air polytropicexponent

119901119886and119881

119886are the random operating state of accumulator

the equality of 1199010119881119899

0= 119901119886119881119899

119886is expanded using Taylor

expansion the Taylor expansion is given by

119889119875119886

119889119905= minus

1198991198750

1198810

119889119881119886

119889119905 (9)

Flow and air chamber volume of accumulator are 119876119886and 119881

119886

and the inlet flow rate of accumulator is given by

119876119886= minus

119889119881119886

119889119905 (10)

Energy equation of accumulator

119864 = minusint

1198812

1198811

(1198810

119881119886

)

119899

119889119881119886=11987501198810

119899 minus 1[(119875119886

1198750

)

(119899minus1)119899

minus 1] (11)

According to the equations above the flow control systemis an obviously nonlinear system In order to verify itsstability and dynamic performance linearization and Laplacetransform are carried out The transfer function from thehydraulic motor speed to the load force can be expressed as120596119898(119904)

119865 (119904)

= (119863119898

1198601119879119892

)

6 The Scientific World Journal

times ([119869119872(119862119899119875

0+ 1198810)

119860211198991198750119879119892

+119872119881

11986021120573119890

] 1199042

+[119863119898119872+ 119869119860

2

1

11986021119879119892

+119872(119862119899119875

0+ 1198810)

119899119875011986021

] 119904 + 1)

minus1

(12)

where 119862 is the leakage coefficients of the energy recoverysystem

The natural frequency of the proposed energy recoverysystem can be calculated as

120596119867= radic

1

119869119872(1198621198991198750+ 1198810) 119860211198991198750119879119892+1198721198811198602

1120573119890

(13)

The natural frequency is the lowest frequency of the sys-tem The low natural frequency has an effect on the responsespeed of the system and energy recovery efficiency In orderto improve the natural frequency and response speed of thesystem based on the expression of the natural frequency thefollowing ways should be taken into consideration

(1) Reducing the loop oil volume 119881 to make the wholesystem structure compact and high-efficiency the oilline should be installed effectively and the length ofthe line should be shortened as soon as possible

(2) Increasing the volume elastic modulus of thehydraulic oil 120573

119890 while designing the system and

selecting the hydraulic oil the volume elasticmodulus 120573

119890of the oil should have a large value

relatively(3) Reducing the leakage coefficients of the energy recov-

ery system 119862 as it is hardly realistic to eliminate thesystem leakage the quality of the hydraulic compo-nents chosen in the system should satisfy the longtime using performance

(4) Reducing the total moment of inertia of the hydraulicmotor 119869 according to the characteristics of themotorthe total moment of inertia decreases along with thedecreasing of the displacement so the displacementof the motor should be reduced to a certain degreeHowever the flow rate of the return oil lines willreducewhen the displacement of themotor decreasesHence it has an effect on the working performance ofthe hydraulic excavator

4 Simulation of the Boom EnergyRecovery System

In order to verify the energy saving efficiency of the pro-posed system simulations with the proposed accumulator-generator system and the conventional energy recoverysystem have been carried out by using AMESim It aims tovalidate the impact of accumulator on energy recovery effi-ciency Figure 6 shows the AMESim model of the proposedsystem with accumulator while Figure 7 displays anotherkind of boom energy recovery system without accumulator

Table 2 Setting parameters for the two AMESim models

Common parts Parameters Values

Boom cylinderPiston diameter (mm) 350Rod diameter (mm) 220Length of stroke (m) 18

Generator Reference voltage (V) 50

Battery Nominal capacity (Ah) 50State of charge () 60

Table 3 Input energy and the energy stored in the battery

System Input energy119864in (J)

Energy storedin the battery

119864st (J)

Percentage119864st119864in ()

Conventional system 764601198646 05041198646 66Proposed system 689231198646 10081198646 146

To simplify the system the engines are replaced by twomotors in Figures 6 and 7

Including the load force and dimension parameters of theboom cylinder the setting parameters for the AMESimmod-els are obtained from the conventional hydraulic excavatorThe main setting parameters for the two AMESim modelsare given in Table 2 The input load force of the conventionalenergy recovery system and the proposed energy recoverysystem is shown in Figure 8

Run the simulations The displacement of the boomcylinder in the conventional energy recovery system and theproposed system are shown in Figure 9 Figure 9 shows thatthe piston displacement of the boom cylinder in the twosystems is quite similar The working performance of theboom cylinder is not affected by the energy recovery systeminstalled in the return oil lines

The difference between the SOC (State of Charge) of thebatteries in the two systems is shown in Figure 10 For theconventional energy recovery system the generator starts andstops four times during a working period According to themechanical characteristics of the generator high efficiencydepends on high speed and continuous rotation Becauseof the accumulator the generator of the proposed energyrecovery system starts and stops only once during a workingperiod Hence the generator can rotate in a high speedcontinuously Comparedwith the conventional energy savingsystem SOC of the battery in the proposed system can risesmoothly During a whole working period the value of SOCreaches 652 Finally the input energy and the energy storedin the batteries of the two energy saving systems are given inTable 3

Based on Table 3 the value of the energy recoveryefficiency in the proposed system is 146 while the valueof the conventional energy recovery system is 66 It isclear that the proposed boom potential energy recoverysystem brings higher energy recovery efficiency than theconventional boom potential energy recovery system

The Scientific World Journal 7

F

MOT

Boom potential recovery system

FluidA

SM

A

A

B

P T

P

A

P

PT

Q

M

q

Qq

QP

2

1

3

Runstats

k

k

k

k

f(X

)X

X

Y

times

timesk

k

Y lt Xk

s

ktimes k

s

properties

WT

J WTT +

+

T

minus

Figure 6 AMESim model of the proposed system

5 Analysis of the Main Componentsin the System

As designing the boom energy recovery system of the hybridhydraulic excavator all the components of the system arechosen based on the calculation results and working con-dition However some parameters of the main componentshave a great influence on the energy recovery efficiency of theproposed system Inappropriate parameters will lead to thedecreasing of the efficiency Therefore it is essential to anal-ysis the relationship between the energy recovery efficiencyand the key parameters of the main components like theaeration pressure of the accumulator and the displacement ofthe hydraulic motor In order to simplify the model there arethree assumptions for the simulation models

(1) Since this study concentrates on the effectivenessof the proposed boom energy recovery system theworking performance of the engine is not takeninto consideration The engine is replaced by anelectromotor

(2) The load force and the piston velocity of the boomcylinder in the simulation models are identical withthe conventional hydraulic excavator In other wordsthe boom cylinder system is working under the sameconditions

(3) A generator and a battery are selected as the energyconversion and energy storage units Regardless of theinternal structure of generator and battery the simu-lation models are replaced by the universal models

8 The Scientific World Journal

Conventional boom potential recovery system

F

M

Qq

ktimes

A B

P T

Fluid properties

Runstats

Qq

MOT

k

times

k

k

s

k

f(X

)X

X

YY lt X

A

P T

QP

ktimes k

s

kk

WTJ W

T

+SM

T

+

T

minus

Figure 7 AMESim model of a conventional boom energy recovery system

0 20 40 60 80 100

Boom

cylin

der l

oadi

ng fo

rce (

N)

12 times 106

10 times 106

80 times 105

60 times 105

40 times 105

20 times 105

00

Time (s)

Figure 8 Input load force of the energy saving system

51 Analysis of the Accumulator The key parameters of theaccumulator include the aeration pressure and the initialvolume The simulations of the relationship between theparameter values and the system energy recovery efficiencyare shown below

0 20 40 60 80 100

06

08

10

12

14

16

18

Boom

cylin

der p

iston

disp

lace

men

t (m

)

Time (s)

Conventional energy recovery systemProposed energy recovery system

Figure 9 Piston displacement of the boom cylinder

511 The Aeration Pressure In order to analyze the influenceof the different aeration pressure on the energy recovery

The Scientific World Journal 9

0 10 20 30 40 50 60 70 80 90 100600605610615620625630635640645650655

SOC

of th

e bat

tery

()

Conventional energy recovery systemProposed energy recovery system

Time (s)

Figure 10 SOC of the battery

0 20 40 60 80 100380

400

420

440

460

480

500

Volu

me c

hang

ing

of th

e acc

umul

ator

(L)

Time (s)

5MPa7MPa

9MPa10MPa

Figure 11 Volume changing of the accumulator

efficiency four values 5MPa 7MPa 9MPa and 10MPa areselected within the scope of the aeration pressure Run thesimulation models Figures 11 and 12 present the volume andpressure changing of the accumulator The rotational speedof the hydraulic motor is shown in Figure 13 The SOC of thebattery is shown in Figure 14

Based on the figures above it can be seen that thepressure of the accumulator is proportional to its aerationpressure When the boom cylinder piston is expanding inthe second working cycle the hydraulic motor is driven bythe oil stored in the accumulator The volume changing ofthe pressure oil in the accumulator increases along with theincreasing of the aeration pressure It leads to increasing theflow of the pressure oil in the energy recovery system Thepressure difference between the inlet and outlet of the motoris increasing as well Because of the constant displacement

0 20 40 60 80 100Time (s)

50

60

70

80

90

100

110

120

130

140

150

Pres

sure

chan

ging

of t

he ac

cum

ulat

or (b

ar)

5MPa7MPa

9MPa10MPa

Figure 12 Pressure changing of the accumulator

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

4000

4500Ro

tatio

nal s

peed

of t

he m

otor

(rm

in)

Time (s)

5MPa7MPa

9MPa10MPa

Figure 13 Rotational speed of the hydraulic motor

hydraulic motor the flow rate through the hydraulic motoris proportional to its rotational speed The output torqueof the motor is increasing gradually based on the pressuredifferenceThe generator is connected to the hydraulic motorcoaxially According to the characteristics of the generatorthe output torque of the motor is increasing as well Hencethe electric energy produced by the generator and SOC of thebattery are increasing

512 The Initial Volume In order to analyze the influence ofthe different initial volume on the energy recovery efficiencyfour values 450 L 470 L 480 L and 500 L are selected withinthe scope of the initial volume under the condition that theaeration pressure and the highest working pressure of theaccumulator are keeping in 10MPa and 18MPa

10 The Scientific World Journal

60

61

62

63

64

65

SOC

of th

e bat

tery

()

0 10 20 30 40 50 60 70 80 90 100Time (s)

5MPa7MPa

9MPa10MPa

Figure 14 SOC of the battery

0 10 20 30 40 50 60 70 80 90 100340

360

380

400

420

440

460

480

500

Volu

me c

hang

ing

of th

e acc

umul

ator

(L)

Time (s)

450L470L

480L500L

Figure 15 Volume changing of the accumulator

Figures 15 and 16 show the volume and pressure changingof the accumulator Keeping the aeration pressure unchangedthe simulation results indicate that the pressure of theaccumulator is inversely proportional to the initial volumeThe corresponding rotational speeds of the hydraulic motorare shown in Figure 17 The SOC of the battery is shown inFigure 18 It can be seen that the value of SOC is not changingwith the different initial volume In other words the value ofthe initial volume does not have an effect on the improving ofthe boom energy recovery efficiency

52 Analysis of the Hydraulic Motor The hydraulic motoris used to drive the generator in the boom energy recoverysystem The energy recovery system is determined by theperformance of the motor So it is essential to do someresearch on the hydraulicmotorThedisplacement is themost

0 10 20 30 40 50 60 70 80 90 100100

110

120

130

140

150

Pres

sure

chan

ging

of t

he ac

cum

ulat

or (b

ar)

Time (s)

450L470L

480L500L

Figure 16 Pressure changing of the accumulator

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

4000

4500Ro

tatio

nal s

peed

of t

he m

otor

(rm

in)

Time (s)

450L470L

480L500L

Figure 17 Rotational speed of the hydraulic motor

important parameter of the hydraulic motorThe simulationsof the displacement and the type of the motor are shownbelow

521 The Displacement In order to analyze the influence ofthe different displacement on the energy recovery efficiencyfour values 60mLr 80mLr 100mLr and 120mLr areselected as the displacement of the motor

Figure 19 shows the velocity of the boom cylinder pistonin the hybrid hydraulic excavator Based on the workingprocess of the hydraulic excavator the boom cylinder iscontracting during 52 sndash69 s and 90 sndash100 s The hydraulicmotor is driven by the pressure oil flowing into the returnoil line The result shows that the contracting velocity ofthe cylinder decreases along with the decreasing of the

The Scientific World Journal 11

0 10 20 30 40 50 60 70 80 90 10060

61

62

63

64

65

SOC

of th

e bat

tery

()

Time (s)

450L470L

480L500L

Figure 18 SOC of the battery

0 10 20Time (s)

30 40 50 60 70 80 90 100

000

005

010

015

Velo

city

of t

he b

oom

cylin

der p

iston

(ms

)

minus005

minus010

minus015

60mLr80mLr

100mLr120mLr

Figure 19 Velocity of the boom cylinder piston

displacement However it does not have an effect on thenormal work of the hydraulic excavator

Figures 20 and 21 show the rotational speed of thehydraulic motor and SOC of the battery with the differ-ent displacement According to the characteristics of thehydraulicmotor the rotational speed of themotor is inverselyproportional to the displacement When the displacement is60mLr the SOC of the battery reaches the maximum valueIt indicates that the SOC of the battery increases along withthe decreasing of the displacement

522 The Type of the Hydraulic Motor Because of thecomplex working condition of the hydraulic excavator thevelocity of the boom cylinder piston ranges from 0 to 01msThe flow rate of the pressure in the return oil line ranges

0 10 20 30 40 50 60 70 80 90 1000

1000

2000

3000

4000

5000

6000

7000

Rota

tiona

l spe

ed o

f the

mot

or (r

min

)

Time (s)

60mLr80mLr

100mLr120mLr

Figure 20 Rotational speed of the hydraulic motor

0 10 20 30 40 50 60 70 80 90 10060

61

62

63

64

65

66SO

C of

the b

atte

ry (

)

Time (s)

60mLr80mLr

100mLr120mLr

Figure 21 SOC of the battery

large So it is very important to select the hydraulic motor forimproving the energy recovery system

The hydraulicmotor is divided into the constant displace-ment and variable displacement motor The AMESim modelwith the variable displacement motor is shown in Figure 22

Run the simulation Compared with the models withthe constant displacement motor shown in Figure 6 therotational speed of the hydraulic motor in two simulationmodels is presented in the Figure 23 Figure 24 shows the SOCrange of the battery

It can be seen that the rotational speed of the constantdisplacement motor is ranging between 1300 rmin and3500 rmin during a working cycle while the rotational speedof the variable displacement motor remains at 3000 rminThe SOC of the battery of the constant displacement motorsystem increases from 60 to 648 while the SOC of the

12 The Scientific World Journal

Boom potential recovery system

F

M

Qq

ktimesA B

P T

Fluid

Runstats

properties

Qq

A

P

P

T

MOT

k

k

k

f(X

)X

X

Y timesY lt X

k

s

2

1

3

SM

A

A

P

QP

k

k

ktimes k

s

WT

J WT w

T +

+

T

minus

kPIDminus

+

Figure 22 AMESim model with the variable displacement motor

battery of the variable displacement motor system reaches708 Compared with the constant displacement motorsystem more boom potential energy of the energy recoverysystemwith the variable displacementmotor is recovered andstored in the battery Hence the energy recovery efficiencyof the variable displacement motor system is higher than thesystem with the constant displacement motor

6 Conclusions

(1) Based on the simulation of the working devicesin the conventional hydraulic excavator the energywhich can be recovered of the three cylinders iscalculated Taking the complexity and cost of thesystem into consideration this paper proposed anovel boom potential energy recovery system for theparallel hybrid excavator The boom energy regen-eration unit consists of an accumulator a hydraulicmotor an electric generator and a battery Compared

with the conventional energy recovery system theproposed system makes sure that the generator canrotate continuously in a high speed during a workingcycle The AMESim models of the two boom energyrecovery systems are built and the results show thatthe proposed energy recovery system brings higherenergy recovery efficiency than the conventionalenergy recovery system

(2) The mathematical models of the main compo-nents including boom cylinder hydraulic motorand hydraulic accumulator are built The naturalfrequency of the proposed energy recovery systemis calculated based on the mathematical models Inorder to improve the natural frequency and responsespeed of the system some measures should be takenbased on the expression of the natural frequencysuch as reducing the loop oil volume 119881 the leakage

The Scientific World Journal 13

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

Rota

tiona

l spe

ed o

f the

hyd

raul

ic m

otor

(rm

in)

Constant displacement motor Variable displacement motor

Time (s)

Figure 23 Rotational speed of the hydraulic motor

0 10 20 30 40 50 60 70 80 90 100606162636465666768697071

SOC

of th

e bat

tery

()

Constant displacement motor Variable displacement motor

Time (s)

Figure 24 SOC of the battery

coefficients of the energy recovery system 119862 and thetotal moment of inertia of the hydraulic motor 119869

(3) The influence of the main components includinghydraulic motor and hydraulic accumulator on theenergy recovery efficiency of the proposed systemis analyzed The key parameters of the accumulatorinclude the aeration pressure and the initial volumeThe energy recovery efficiency of the proposed sys-tem can be improving to some extent by increasingthe aeration pressure while changing of the initialvolume does not have an effect on improving of theenergy recovery efficiency

The hydraulic motor is used to drive the generator inthe boom energy recovery system The displacement is themost important parameter of the hydraulicmotorThe energy

recovery efficiency can be improving on the premise ofnormal working by decreasing the displacement of themotorSince the flow rate of the pressure in the return oil line rangeslarge the generator can rotate continuously in a high speedby selecting the variable displacement motor in the return oilline In order to improve the energy efficiency according tothe characteristics of the generator the variable displacementhydraulic motor should be chosen in the return oil line

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work is supported by the Fundamental Research Fundsfor the Central Universities (China University of Mining andTechnology 2014Y05) PCSIRT (IRT1292) and the ProjectFunded by the Priority Academic Program Development ofJiangsu Higher Education Institutions (PAPD)

References

[1] M Kagoshima M Komiyama T Nanjo et al ldquoDevelopment ofnew hybrid excavatorrdquo Kobelco Technology Review no 27 2007

[2] T Nanjo E Imanishi and M Kagcahima ldquoPower simulationfor energy saving in hybrid excavatorrdquo JSAE Transactions vol47 pp 101ndash106 2004

[3] L Weidong S Kaikai L Wei and X Jun ldquoResearch onpotential energy recovery of 16T wheeled hybrid excavatorrdquoin Proceedings of the 2nd International Conference on DigitalManufacturing and Automation (ICDMA rsquo11) pp 996ndash998Zhangjiajie China August 2011

[4] I Y Jong K K Ahn and Q T Dinh ldquoA study on anenergy saving electro-hydraulic excavatorrdquo in Proceedings of theICROS-SICE International Joint Conference (ICCAS-SICE rsquo09)pp 3825ndash3830 Fukuoka Japan August 2009

[5] T H Ho and K K Ahn ldquoDesign and control of a closed-loop hydraulic energy-regenerative systemrdquo Automation inConstruction vol 22 pp 444ndash458 2012

[6] Z Jun J Sheng-jie S Gui-mao et al ldquoDesign of electroniccontrol system of hydraulic excavator with CAN bus andPID methodrdquo Proceedings of the International Conference onIntelligent System Design and Engineering Application (ISDEArsquo10) 2010

[7] T Wang and Q Wang ldquoModeling and control of a novelhydraulic system with energy regenerationrdquo in Proceedings ofthe IEEEASME International Conference on Advanced Intelli-gent Mechatronics (AIM rsquo12) pp 922ndash927 IEEE KachsiungTaiwan July 2012

[8] H SHamut I Dincer andG FNaterer ldquoExergoenvironmentalanalysis of hybrid electric vehicle thermal management sys-temsrdquo Journal of Cleaner Production vol 67 pp 187ndash196 2014

[9] A Poursamad and M Montazeri ldquoDesign of genetic-fuzzycontrol strategy for parallel hybrid electric vehiclesrdquo ControlEngineering Practice vol 16 no 7 pp 861ndash873 2008

[10] S Hui J-H Jiang and W Xin ldquoTorque control strategy fora parallel hydraulic hybrid vehiclerdquo Journal of Terramechanicsvol 46 no 6 pp 259ndash265 2009

14 The Scientific World Journal

[11] Z Cao S Wu M Li and C Du ldquoSeries and parallel hybridsystem performance comparison based on the city bus cyclerdquoin Proceedings of the Asia-Pacific Power and Energy EngineeringConference (APPEEC 09) Wuhan China March 2009

[12] J Gong Q He D Zhang et al ldquoPower system control strategyfor hybrid excavator based on equivalent fuel consumptionrdquo inProceedings of the 9th IEEE International Conference on Mecha-tronics and Automation (ICMA rsquo12) pp 1097ndash1102 ChengduChina August 2012

[13] Z Liu S Liu Z Huang and Q Hu ldquoHydraulic excavatorhybrid power system parameters designrdquo in Proceedings of the2nd International Conference on Digital Manufacturing andAutomation (ICDMA rsquo11) pp 602ndash605 Zhangjiajie ChinaAugust 2011

[14] T Lin Q Wang B Hu and W Gong ldquoResearch on theenergy regeneration systems for hybrid hydraulic excavatorsrdquoAutomation in Construction vol 19 no 8 pp 1016ndash1026 2010

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RotatingMachinery

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International Journal of

The Scientific World Journal 3

A BA B

P

QPP

Q

q

Q

QP

TP T

xx

x V

Bucket rod cylinderBucket cylinderConventional hydraulic excavator

Boom cylinderBody 1

Body 1

Body 2

Body 2

Body 3

Body 3

Body 4

Body 4

Body 5

Body 5

k

k

k PID

k

k

minus

+k

Runstats

PIDminus

+

k

k PIDminus

+

xy

k

Qq

A B

P

QP

qq

q

T

F

xy

xy

xy

x

y

times

times

times

timestimes

timesk

s

k

s

k

s

Figure 1 AMESim model of conventional hydraulic excavator

the battery Compared with the engine power 119875119890and the load

power 119875119897 there are three kinds of working conditions based

on the load change

(1) When 119875119890gt 119875119897 the pump is driven by the engine

and the excess power of the engine is converted intoelectrical energy by the motor and stored in thebattery The motor is working as a generator in thisworking condition

(2) When 119875119890lt 119875119897 electrical energy stored in the battery

is used to drive the motor The engine and the motordrive the pump together

(3) When the motor power 119875119890gt 119875119898gt 119875119897 the pump is

driven by the motor independently and the engine isworking in the idle state

The working flow chart of the proposed system is shownin Figure 5 Comparedwith the conventional energy recoverysystem the pressure oil is charged into the accumulatorinstead of flowing into themotor directly when the boomarmfalls in the first working cycle Meanwhile the pressure oilin the accumulator is discharged and flowing into the motorwhen the boom arm rises in the second working cycle It

makes sure that the generator can rotate continuously in ahigh speed Hence two working cycles of the conventionalhydraulic excavator are regarded as a complete workingperiod for the new energy saving system

3 Mathematical Modeling

31 Boom Cylinder As shown in Figure 4 the dynamics ofthe piston of the boom cylinder can be expressed as

119865119897+ 11987521198602minus 11987511198601minus 119887119888V119888minus 119865119891minus119872V10158401015840

119888= 0 (3)

Continuity equation of hydraulic cylinder piston can beexpressed as

1198761

1198601

=1198762

1198602

(4)

where119872 is the equivalent mass of the load V119888is the velocity

of the piston 119865119897is the external force and 119875

1and 119875

2are

the pressures in the large and small chamber of the boomcylinder respectively 119876

1and 119876

2are the corresponding flow

rate 1198601and 119860

2denote the corresponding working areas

119865119888is the coulomb friction force and 119887

119888is the combined

4 The Scientific World Journal

0 10 20 30 40 5000

200

400

600

800

1000

1200

Inpu

t pow

er (k

W)

Time (s)

Bucket systemBoom systemBucket rod system

Figure 2 Input power of the three cylinder systems

Time (s)

Bucket systemBoom systemBucket rod system

0 10 20 30 40 50

0050

100150200250300350400450

Out

put p

ower

(kW

)

minus50

minus100minus150minus200minus250minus300

Figure 3 Output power in the return oil lines

coefficient of damping and viscous friction forces on the loadand the rod The value of V

119888is the differential of the piston

displacement 119909119888

32 Hydraulic Motor The dynamics of the rotor of theregeneration unit can be expressed as

119863119898(1198753minus 1198754) = 119869

119889120596119898

119889119905+ 119887119898120596119898+ 119879119891+ 119879119892 (5)

where 120596119898

is the rotational speed of the hydraulic motorJ is the total moment of inertia of the regeneration unit119879119892is the electromagnetic torque of the generator 119879

119891is the

coulomb friction torque 119861119898is the combined coefficient of

damping and viscous friction torques on the rotor 119863119898is the

E

M

M

G

Rectifier

BatteryRectifierinverter

8

7

1

2 4

3

6

59 12 10

13

11

14

(1) Engine(2) Transmission device(3) Motorgenerator(4) Pump(5) Relief valve(6) Tank(7) Electromagnetic valve

(8) Boom cylinder(9) Reversing valve(10 12) Globe valve(11) Accumulator(13) Variable displacement motor(14) Generator

Figure 4 Schematic of proposed boom energy-recovery hydraulicsystem

displacement of the hydraulic motor and 1198753and 119875

4are the

inlet and outlet pressures of the motorFlow continuity equation of the motor can be written as

1198763minus 1198621198901198981198753minus 119862119894119898(1198753minus 1198754) minus 119863119898120596119898= 0

119863119898120596119898+ 119862119894119898(1198753minus 1198754) minus 1198621198901198981198752minus 1198764= 0

(6)

where 119862119890119898

is the external leakage coefficients of the motorand 119862

119894119898is the internal leakage coefficient of the motor

Assuming that there is no loop loss in reversing valve theflow equation of the chamber between the cylinder and themotor can be written as

1198601V119888minus 119862119894119888(1198751minus 1198752) minus 1198621198901198881198751minus 119862119894119898(1198751minus 1198754)

minus 120596119898119863119898minus 119876119886=119881

120573119890

1198891198751

119889119905

(7)

where 119862119894119888is the internal leakage coefficients of the cylinder

119862119890119888

is the external leakage coefficient of the cylinder 119881 isthe volume of the hydraulic oil between the boom cylinderand motor 119876

119886is the flow of the hydraulic oil stored in the

accumulator and 120573119890is the volume elastic modulus

33 Hydraulic Accumulator Thebladder accumulator is cho-sen in this boom energy recovery system according to Boylelaw and the formula is given by

1199010119881119899

0= 1199011119881119899

1= 1199012119881119899

2= 119901119886119881119899

119886 (8)

where 1199010 1199011 1199012 119901119886denote the initial aeration pressure

initial pressure terminal state pressure and free state pressure

The Scientific World Journal 5

System initialize

The boom up

Working normally

YesNo

The first working cycle start

The top cavity of valve 9 on

valve 10 on

Hydraulic oil returns totankAccumulator is charged

The second workingcycle start

The boom up

The top cavity ofvalve 9 onvalve 10 on

The top cavity ofvalve 9 offvalve 10 on

YesNo

Valve 12 on

Hydraulic oil from valve 9flow into valve 12

Hydraulic oil from accumulator flow into

valve 12

Motor drive generatorto rotate

End

The top cavity ofvalve 9 off

Work ending Yes No

valve 12 off

Figure 5 Working flow chart of the energy saving system

of accumulator respectively 1198810 1198811 1198812 119881119886are the initial

aeration volume initial volume terminal state volume andfree state volume of accumulator 119899 is the air polytropicexponent

119901119886and119881

119886are the random operating state of accumulator

the equality of 1199010119881119899

0= 119901119886119881119899

119886is expanded using Taylor

expansion the Taylor expansion is given by

119889119875119886

119889119905= minus

1198991198750

1198810

119889119881119886

119889119905 (9)

Flow and air chamber volume of accumulator are 119876119886and 119881

119886

and the inlet flow rate of accumulator is given by

119876119886= minus

119889119881119886

119889119905 (10)

Energy equation of accumulator

119864 = minusint

1198812

1198811

(1198810

119881119886

)

119899

119889119881119886=11987501198810

119899 minus 1[(119875119886

1198750

)

(119899minus1)119899

minus 1] (11)

According to the equations above the flow control systemis an obviously nonlinear system In order to verify itsstability and dynamic performance linearization and Laplacetransform are carried out The transfer function from thehydraulic motor speed to the load force can be expressed as120596119898(119904)

119865 (119904)

= (119863119898

1198601119879119892

)

6 The Scientific World Journal

times ([119869119872(119862119899119875

0+ 1198810)

119860211198991198750119879119892

+119872119881

11986021120573119890

] 1199042

+[119863119898119872+ 119869119860

2

1

11986021119879119892

+119872(119862119899119875

0+ 1198810)

119899119875011986021

] 119904 + 1)

minus1

(12)

where 119862 is the leakage coefficients of the energy recoverysystem

The natural frequency of the proposed energy recoverysystem can be calculated as

120596119867= radic

1

119869119872(1198621198991198750+ 1198810) 119860211198991198750119879119892+1198721198811198602

1120573119890

(13)

The natural frequency is the lowest frequency of the sys-tem The low natural frequency has an effect on the responsespeed of the system and energy recovery efficiency In orderto improve the natural frequency and response speed of thesystem based on the expression of the natural frequency thefollowing ways should be taken into consideration

(1) Reducing the loop oil volume 119881 to make the wholesystem structure compact and high-efficiency the oilline should be installed effectively and the length ofthe line should be shortened as soon as possible

(2) Increasing the volume elastic modulus of thehydraulic oil 120573

119890 while designing the system and

selecting the hydraulic oil the volume elasticmodulus 120573

119890of the oil should have a large value

relatively(3) Reducing the leakage coefficients of the energy recov-

ery system 119862 as it is hardly realistic to eliminate thesystem leakage the quality of the hydraulic compo-nents chosen in the system should satisfy the longtime using performance

(4) Reducing the total moment of inertia of the hydraulicmotor 119869 according to the characteristics of themotorthe total moment of inertia decreases along with thedecreasing of the displacement so the displacementof the motor should be reduced to a certain degreeHowever the flow rate of the return oil lines willreducewhen the displacement of themotor decreasesHence it has an effect on the working performance ofthe hydraulic excavator

4 Simulation of the Boom EnergyRecovery System

In order to verify the energy saving efficiency of the pro-posed system simulations with the proposed accumulator-generator system and the conventional energy recoverysystem have been carried out by using AMESim It aims tovalidate the impact of accumulator on energy recovery effi-ciency Figure 6 shows the AMESim model of the proposedsystem with accumulator while Figure 7 displays anotherkind of boom energy recovery system without accumulator

Table 2 Setting parameters for the two AMESim models

Common parts Parameters Values

Boom cylinderPiston diameter (mm) 350Rod diameter (mm) 220Length of stroke (m) 18

Generator Reference voltage (V) 50

Battery Nominal capacity (Ah) 50State of charge () 60

Table 3 Input energy and the energy stored in the battery

System Input energy119864in (J)

Energy storedin the battery

119864st (J)

Percentage119864st119864in ()

Conventional system 764601198646 05041198646 66Proposed system 689231198646 10081198646 146

To simplify the system the engines are replaced by twomotors in Figures 6 and 7

Including the load force and dimension parameters of theboom cylinder the setting parameters for the AMESimmod-els are obtained from the conventional hydraulic excavatorThe main setting parameters for the two AMESim modelsare given in Table 2 The input load force of the conventionalenergy recovery system and the proposed energy recoverysystem is shown in Figure 8

Run the simulations The displacement of the boomcylinder in the conventional energy recovery system and theproposed system are shown in Figure 9 Figure 9 shows thatthe piston displacement of the boom cylinder in the twosystems is quite similar The working performance of theboom cylinder is not affected by the energy recovery systeminstalled in the return oil lines

The difference between the SOC (State of Charge) of thebatteries in the two systems is shown in Figure 10 For theconventional energy recovery system the generator starts andstops four times during a working period According to themechanical characteristics of the generator high efficiencydepends on high speed and continuous rotation Becauseof the accumulator the generator of the proposed energyrecovery system starts and stops only once during a workingperiod Hence the generator can rotate in a high speedcontinuously Comparedwith the conventional energy savingsystem SOC of the battery in the proposed system can risesmoothly During a whole working period the value of SOCreaches 652 Finally the input energy and the energy storedin the batteries of the two energy saving systems are given inTable 3

Based on Table 3 the value of the energy recoveryefficiency in the proposed system is 146 while the valueof the conventional energy recovery system is 66 It isclear that the proposed boom potential energy recoverysystem brings higher energy recovery efficiency than theconventional boom potential energy recovery system

The Scientific World Journal 7

F

MOT

Boom potential recovery system

FluidA

SM

A

A

B

P T

P

A

P

PT

Q

M

q

Qq

QP

2

1

3

Runstats

k

k

k

k

f(X

)X

X

Y

times

timesk

k

Y lt Xk

s

ktimes k

s

properties

WT

J WTT +

+

T

minus

Figure 6 AMESim model of the proposed system

5 Analysis of the Main Componentsin the System

As designing the boom energy recovery system of the hybridhydraulic excavator all the components of the system arechosen based on the calculation results and working con-dition However some parameters of the main componentshave a great influence on the energy recovery efficiency of theproposed system Inappropriate parameters will lead to thedecreasing of the efficiency Therefore it is essential to anal-ysis the relationship between the energy recovery efficiencyand the key parameters of the main components like theaeration pressure of the accumulator and the displacement ofthe hydraulic motor In order to simplify the model there arethree assumptions for the simulation models

(1) Since this study concentrates on the effectivenessof the proposed boom energy recovery system theworking performance of the engine is not takeninto consideration The engine is replaced by anelectromotor

(2) The load force and the piston velocity of the boomcylinder in the simulation models are identical withthe conventional hydraulic excavator In other wordsthe boom cylinder system is working under the sameconditions

(3) A generator and a battery are selected as the energyconversion and energy storage units Regardless of theinternal structure of generator and battery the simu-lation models are replaced by the universal models

8 The Scientific World Journal

Conventional boom potential recovery system

F

M

Qq

ktimes

A B

P T

Fluid properties

Runstats

Qq

MOT

k

times

k

k

s

k

f(X

)X

X

YY lt X

A

P T

QP

ktimes k

s

kk

WTJ W

T

+SM

T

+

T

minus

Figure 7 AMESim model of a conventional boom energy recovery system

0 20 40 60 80 100

Boom

cylin

der l

oadi

ng fo

rce (

N)

12 times 106

10 times 106

80 times 105

60 times 105

40 times 105

20 times 105

00

Time (s)

Figure 8 Input load force of the energy saving system

51 Analysis of the Accumulator The key parameters of theaccumulator include the aeration pressure and the initialvolume The simulations of the relationship between theparameter values and the system energy recovery efficiencyare shown below

0 20 40 60 80 100

06

08

10

12

14

16

18

Boom

cylin

der p

iston

disp

lace

men

t (m

)

Time (s)

Conventional energy recovery systemProposed energy recovery system

Figure 9 Piston displacement of the boom cylinder

511 The Aeration Pressure In order to analyze the influenceof the different aeration pressure on the energy recovery

The Scientific World Journal 9

0 10 20 30 40 50 60 70 80 90 100600605610615620625630635640645650655

SOC

of th

e bat

tery

()

Conventional energy recovery systemProposed energy recovery system

Time (s)

Figure 10 SOC of the battery

0 20 40 60 80 100380

400

420

440

460

480

500

Volu

me c

hang

ing

of th

e acc

umul

ator

(L)

Time (s)

5MPa7MPa

9MPa10MPa

Figure 11 Volume changing of the accumulator

efficiency four values 5MPa 7MPa 9MPa and 10MPa areselected within the scope of the aeration pressure Run thesimulation models Figures 11 and 12 present the volume andpressure changing of the accumulator The rotational speedof the hydraulic motor is shown in Figure 13 The SOC of thebattery is shown in Figure 14

Based on the figures above it can be seen that thepressure of the accumulator is proportional to its aerationpressure When the boom cylinder piston is expanding inthe second working cycle the hydraulic motor is driven bythe oil stored in the accumulator The volume changing ofthe pressure oil in the accumulator increases along with theincreasing of the aeration pressure It leads to increasing theflow of the pressure oil in the energy recovery system Thepressure difference between the inlet and outlet of the motoris increasing as well Because of the constant displacement

0 20 40 60 80 100Time (s)

50

60

70

80

90

100

110

120

130

140

150

Pres

sure

chan

ging

of t

he ac

cum

ulat

or (b

ar)

5MPa7MPa

9MPa10MPa

Figure 12 Pressure changing of the accumulator

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

4000

4500Ro

tatio

nal s

peed

of t

he m

otor

(rm

in)

Time (s)

5MPa7MPa

9MPa10MPa

Figure 13 Rotational speed of the hydraulic motor

hydraulic motor the flow rate through the hydraulic motoris proportional to its rotational speed The output torqueof the motor is increasing gradually based on the pressuredifferenceThe generator is connected to the hydraulic motorcoaxially According to the characteristics of the generatorthe output torque of the motor is increasing as well Hencethe electric energy produced by the generator and SOC of thebattery are increasing

512 The Initial Volume In order to analyze the influence ofthe different initial volume on the energy recovery efficiencyfour values 450 L 470 L 480 L and 500 L are selected withinthe scope of the initial volume under the condition that theaeration pressure and the highest working pressure of theaccumulator are keeping in 10MPa and 18MPa

10 The Scientific World Journal

60

61

62

63

64

65

SOC

of th

e bat

tery

()

0 10 20 30 40 50 60 70 80 90 100Time (s)

5MPa7MPa

9MPa10MPa

Figure 14 SOC of the battery

0 10 20 30 40 50 60 70 80 90 100340

360

380

400

420

440

460

480

500

Volu

me c

hang

ing

of th

e acc

umul

ator

(L)

Time (s)

450L470L

480L500L

Figure 15 Volume changing of the accumulator

Figures 15 and 16 show the volume and pressure changingof the accumulator Keeping the aeration pressure unchangedthe simulation results indicate that the pressure of theaccumulator is inversely proportional to the initial volumeThe corresponding rotational speeds of the hydraulic motorare shown in Figure 17 The SOC of the battery is shown inFigure 18 It can be seen that the value of SOC is not changingwith the different initial volume In other words the value ofthe initial volume does not have an effect on the improving ofthe boom energy recovery efficiency

52 Analysis of the Hydraulic Motor The hydraulic motoris used to drive the generator in the boom energy recoverysystem The energy recovery system is determined by theperformance of the motor So it is essential to do someresearch on the hydraulicmotorThedisplacement is themost

0 10 20 30 40 50 60 70 80 90 100100

110

120

130

140

150

Pres

sure

chan

ging

of t

he ac

cum

ulat

or (b

ar)

Time (s)

450L470L

480L500L

Figure 16 Pressure changing of the accumulator

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

4000

4500Ro

tatio

nal s

peed

of t

he m

otor

(rm

in)

Time (s)

450L470L

480L500L

Figure 17 Rotational speed of the hydraulic motor

important parameter of the hydraulic motorThe simulationsof the displacement and the type of the motor are shownbelow

521 The Displacement In order to analyze the influence ofthe different displacement on the energy recovery efficiencyfour values 60mLr 80mLr 100mLr and 120mLr areselected as the displacement of the motor

Figure 19 shows the velocity of the boom cylinder pistonin the hybrid hydraulic excavator Based on the workingprocess of the hydraulic excavator the boom cylinder iscontracting during 52 sndash69 s and 90 sndash100 s The hydraulicmotor is driven by the pressure oil flowing into the returnoil line The result shows that the contracting velocity ofthe cylinder decreases along with the decreasing of the

The Scientific World Journal 11

0 10 20 30 40 50 60 70 80 90 10060

61

62

63

64

65

SOC

of th

e bat

tery

()

Time (s)

450L470L

480L500L

Figure 18 SOC of the battery

0 10 20Time (s)

30 40 50 60 70 80 90 100

000

005

010

015

Velo

city

of t

he b

oom

cylin

der p

iston

(ms

)

minus005

minus010

minus015

60mLr80mLr

100mLr120mLr

Figure 19 Velocity of the boom cylinder piston

displacement However it does not have an effect on thenormal work of the hydraulic excavator

Figures 20 and 21 show the rotational speed of thehydraulic motor and SOC of the battery with the differ-ent displacement According to the characteristics of thehydraulicmotor the rotational speed of themotor is inverselyproportional to the displacement When the displacement is60mLr the SOC of the battery reaches the maximum valueIt indicates that the SOC of the battery increases along withthe decreasing of the displacement

522 The Type of the Hydraulic Motor Because of thecomplex working condition of the hydraulic excavator thevelocity of the boom cylinder piston ranges from 0 to 01msThe flow rate of the pressure in the return oil line ranges

0 10 20 30 40 50 60 70 80 90 1000

1000

2000

3000

4000

5000

6000

7000

Rota

tiona

l spe

ed o

f the

mot

or (r

min

)

Time (s)

60mLr80mLr

100mLr120mLr

Figure 20 Rotational speed of the hydraulic motor

0 10 20 30 40 50 60 70 80 90 10060

61

62

63

64

65

66SO

C of

the b

atte

ry (

)

Time (s)

60mLr80mLr

100mLr120mLr

Figure 21 SOC of the battery

large So it is very important to select the hydraulic motor forimproving the energy recovery system

The hydraulicmotor is divided into the constant displace-ment and variable displacement motor The AMESim modelwith the variable displacement motor is shown in Figure 22

Run the simulation Compared with the models withthe constant displacement motor shown in Figure 6 therotational speed of the hydraulic motor in two simulationmodels is presented in the Figure 23 Figure 24 shows the SOCrange of the battery

It can be seen that the rotational speed of the constantdisplacement motor is ranging between 1300 rmin and3500 rmin during a working cycle while the rotational speedof the variable displacement motor remains at 3000 rminThe SOC of the battery of the constant displacement motorsystem increases from 60 to 648 while the SOC of the

12 The Scientific World Journal

Boom potential recovery system

F

M

Qq

ktimesA B

P T

Fluid

Runstats

properties

Qq

A

P

P

T

MOT

k

k

k

f(X

)X

X

Y timesY lt X

k

s

2

1

3

SM

A

A

P

QP

k

k

ktimes k

s

WT

J WT w

T +

+

T

minus

kPIDminus

+

Figure 22 AMESim model with the variable displacement motor

battery of the variable displacement motor system reaches708 Compared with the constant displacement motorsystem more boom potential energy of the energy recoverysystemwith the variable displacementmotor is recovered andstored in the battery Hence the energy recovery efficiencyof the variable displacement motor system is higher than thesystem with the constant displacement motor

6 Conclusions

(1) Based on the simulation of the working devicesin the conventional hydraulic excavator the energywhich can be recovered of the three cylinders iscalculated Taking the complexity and cost of thesystem into consideration this paper proposed anovel boom potential energy recovery system for theparallel hybrid excavator The boom energy regen-eration unit consists of an accumulator a hydraulicmotor an electric generator and a battery Compared

with the conventional energy recovery system theproposed system makes sure that the generator canrotate continuously in a high speed during a workingcycle The AMESim models of the two boom energyrecovery systems are built and the results show thatthe proposed energy recovery system brings higherenergy recovery efficiency than the conventionalenergy recovery system

(2) The mathematical models of the main compo-nents including boom cylinder hydraulic motorand hydraulic accumulator are built The naturalfrequency of the proposed energy recovery systemis calculated based on the mathematical models Inorder to improve the natural frequency and responsespeed of the system some measures should be takenbased on the expression of the natural frequencysuch as reducing the loop oil volume 119881 the leakage

The Scientific World Journal 13

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

Rota

tiona

l spe

ed o

f the

hyd

raul

ic m

otor

(rm

in)

Constant displacement motor Variable displacement motor

Time (s)

Figure 23 Rotational speed of the hydraulic motor

0 10 20 30 40 50 60 70 80 90 100606162636465666768697071

SOC

of th

e bat

tery

()

Constant displacement motor Variable displacement motor

Time (s)

Figure 24 SOC of the battery

coefficients of the energy recovery system 119862 and thetotal moment of inertia of the hydraulic motor 119869

(3) The influence of the main components includinghydraulic motor and hydraulic accumulator on theenergy recovery efficiency of the proposed systemis analyzed The key parameters of the accumulatorinclude the aeration pressure and the initial volumeThe energy recovery efficiency of the proposed sys-tem can be improving to some extent by increasingthe aeration pressure while changing of the initialvolume does not have an effect on improving of theenergy recovery efficiency

The hydraulic motor is used to drive the generator inthe boom energy recovery system The displacement is themost important parameter of the hydraulicmotorThe energy

recovery efficiency can be improving on the premise ofnormal working by decreasing the displacement of themotorSince the flow rate of the pressure in the return oil line rangeslarge the generator can rotate continuously in a high speedby selecting the variable displacement motor in the return oilline In order to improve the energy efficiency according tothe characteristics of the generator the variable displacementhydraulic motor should be chosen in the return oil line

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work is supported by the Fundamental Research Fundsfor the Central Universities (China University of Mining andTechnology 2014Y05) PCSIRT (IRT1292) and the ProjectFunded by the Priority Academic Program Development ofJiangsu Higher Education Institutions (PAPD)

References

[1] M Kagoshima M Komiyama T Nanjo et al ldquoDevelopment ofnew hybrid excavatorrdquo Kobelco Technology Review no 27 2007

[2] T Nanjo E Imanishi and M Kagcahima ldquoPower simulationfor energy saving in hybrid excavatorrdquo JSAE Transactions vol47 pp 101ndash106 2004

[3] L Weidong S Kaikai L Wei and X Jun ldquoResearch onpotential energy recovery of 16T wheeled hybrid excavatorrdquoin Proceedings of the 2nd International Conference on DigitalManufacturing and Automation (ICDMA rsquo11) pp 996ndash998Zhangjiajie China August 2011

[4] I Y Jong K K Ahn and Q T Dinh ldquoA study on anenergy saving electro-hydraulic excavatorrdquo in Proceedings of theICROS-SICE International Joint Conference (ICCAS-SICE rsquo09)pp 3825ndash3830 Fukuoka Japan August 2009

[5] T H Ho and K K Ahn ldquoDesign and control of a closed-loop hydraulic energy-regenerative systemrdquo Automation inConstruction vol 22 pp 444ndash458 2012

[6] Z Jun J Sheng-jie S Gui-mao et al ldquoDesign of electroniccontrol system of hydraulic excavator with CAN bus andPID methodrdquo Proceedings of the International Conference onIntelligent System Design and Engineering Application (ISDEArsquo10) 2010

[7] T Wang and Q Wang ldquoModeling and control of a novelhydraulic system with energy regenerationrdquo in Proceedings ofthe IEEEASME International Conference on Advanced Intelli-gent Mechatronics (AIM rsquo12) pp 922ndash927 IEEE KachsiungTaiwan July 2012

[8] H SHamut I Dincer andG FNaterer ldquoExergoenvironmentalanalysis of hybrid electric vehicle thermal management sys-temsrdquo Journal of Cleaner Production vol 67 pp 187ndash196 2014

[9] A Poursamad and M Montazeri ldquoDesign of genetic-fuzzycontrol strategy for parallel hybrid electric vehiclesrdquo ControlEngineering Practice vol 16 no 7 pp 861ndash873 2008

[10] S Hui J-H Jiang and W Xin ldquoTorque control strategy fora parallel hydraulic hybrid vehiclerdquo Journal of Terramechanicsvol 46 no 6 pp 259ndash265 2009

14 The Scientific World Journal

[11] Z Cao S Wu M Li and C Du ldquoSeries and parallel hybridsystem performance comparison based on the city bus cyclerdquoin Proceedings of the Asia-Pacific Power and Energy EngineeringConference (APPEEC 09) Wuhan China March 2009

[12] J Gong Q He D Zhang et al ldquoPower system control strategyfor hybrid excavator based on equivalent fuel consumptionrdquo inProceedings of the 9th IEEE International Conference on Mecha-tronics and Automation (ICMA rsquo12) pp 1097ndash1102 ChengduChina August 2012

[13] Z Liu S Liu Z Huang and Q Hu ldquoHydraulic excavatorhybrid power system parameters designrdquo in Proceedings of the2nd International Conference on Digital Manufacturing andAutomation (ICDMA rsquo11) pp 602ndash605 Zhangjiajie ChinaAugust 2011

[14] T Lin Q Wang B Hu and W Gong ldquoResearch on theenergy regeneration systems for hybrid hydraulic excavatorsrdquoAutomation in Construction vol 19 no 8 pp 1016ndash1026 2010

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Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

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Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

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Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

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Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

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Chemical EngineeringInternational Journal of Antennas and

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International Journal of

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International Journal of

4 The Scientific World Journal

0 10 20 30 40 5000

200

400

600

800

1000

1200

Inpu

t pow

er (k

W)

Time (s)

Bucket systemBoom systemBucket rod system

Figure 2 Input power of the three cylinder systems

Time (s)

Bucket systemBoom systemBucket rod system

0 10 20 30 40 50

0050

100150200250300350400450

Out

put p

ower

(kW

)

minus50

minus100minus150minus200minus250minus300

Figure 3 Output power in the return oil lines

coefficient of damping and viscous friction forces on the loadand the rod The value of V

119888is the differential of the piston

displacement 119909119888

32 Hydraulic Motor The dynamics of the rotor of theregeneration unit can be expressed as

119863119898(1198753minus 1198754) = 119869

119889120596119898

119889119905+ 119887119898120596119898+ 119879119891+ 119879119892 (5)

where 120596119898

is the rotational speed of the hydraulic motorJ is the total moment of inertia of the regeneration unit119879119892is the electromagnetic torque of the generator 119879

119891is the

coulomb friction torque 119861119898is the combined coefficient of

damping and viscous friction torques on the rotor 119863119898is the

E

M

M

G

Rectifier

BatteryRectifierinverter

8

7

1

2 4

3

6

59 12 10

13

11

14

(1) Engine(2) Transmission device(3) Motorgenerator(4) Pump(5) Relief valve(6) Tank(7) Electromagnetic valve

(8) Boom cylinder(9) Reversing valve(10 12) Globe valve(11) Accumulator(13) Variable displacement motor(14) Generator

Figure 4 Schematic of proposed boom energy-recovery hydraulicsystem

displacement of the hydraulic motor and 1198753and 119875

4are the

inlet and outlet pressures of the motorFlow continuity equation of the motor can be written as

1198763minus 1198621198901198981198753minus 119862119894119898(1198753minus 1198754) minus 119863119898120596119898= 0

119863119898120596119898+ 119862119894119898(1198753minus 1198754) minus 1198621198901198981198752minus 1198764= 0

(6)

where 119862119890119898

is the external leakage coefficients of the motorand 119862

119894119898is the internal leakage coefficient of the motor

Assuming that there is no loop loss in reversing valve theflow equation of the chamber between the cylinder and themotor can be written as

1198601V119888minus 119862119894119888(1198751minus 1198752) minus 1198621198901198881198751minus 119862119894119898(1198751minus 1198754)

minus 120596119898119863119898minus 119876119886=119881

120573119890

1198891198751

119889119905

(7)

where 119862119894119888is the internal leakage coefficients of the cylinder

119862119890119888

is the external leakage coefficient of the cylinder 119881 isthe volume of the hydraulic oil between the boom cylinderand motor 119876

119886is the flow of the hydraulic oil stored in the

accumulator and 120573119890is the volume elastic modulus

33 Hydraulic Accumulator Thebladder accumulator is cho-sen in this boom energy recovery system according to Boylelaw and the formula is given by

1199010119881119899

0= 1199011119881119899

1= 1199012119881119899

2= 119901119886119881119899

119886 (8)

where 1199010 1199011 1199012 119901119886denote the initial aeration pressure

initial pressure terminal state pressure and free state pressure

The Scientific World Journal 5

System initialize

The boom up

Working normally

YesNo

The first working cycle start

The top cavity of valve 9 on

valve 10 on

Hydraulic oil returns totankAccumulator is charged

The second workingcycle start

The boom up

The top cavity ofvalve 9 onvalve 10 on

The top cavity ofvalve 9 offvalve 10 on

YesNo

Valve 12 on

Hydraulic oil from valve 9flow into valve 12

Hydraulic oil from accumulator flow into

valve 12

Motor drive generatorto rotate

End

The top cavity ofvalve 9 off

Work ending Yes No

valve 12 off

Figure 5 Working flow chart of the energy saving system

of accumulator respectively 1198810 1198811 1198812 119881119886are the initial

aeration volume initial volume terminal state volume andfree state volume of accumulator 119899 is the air polytropicexponent

119901119886and119881

119886are the random operating state of accumulator

the equality of 1199010119881119899

0= 119901119886119881119899

119886is expanded using Taylor

expansion the Taylor expansion is given by

119889119875119886

119889119905= minus

1198991198750

1198810

119889119881119886

119889119905 (9)

Flow and air chamber volume of accumulator are 119876119886and 119881

119886

and the inlet flow rate of accumulator is given by

119876119886= minus

119889119881119886

119889119905 (10)

Energy equation of accumulator

119864 = minusint

1198812

1198811

(1198810

119881119886

)

119899

119889119881119886=11987501198810

119899 minus 1[(119875119886

1198750

)

(119899minus1)119899

minus 1] (11)

According to the equations above the flow control systemis an obviously nonlinear system In order to verify itsstability and dynamic performance linearization and Laplacetransform are carried out The transfer function from thehydraulic motor speed to the load force can be expressed as120596119898(119904)

119865 (119904)

= (119863119898

1198601119879119892

)

6 The Scientific World Journal

times ([119869119872(119862119899119875

0+ 1198810)

119860211198991198750119879119892

+119872119881

11986021120573119890

] 1199042

+[119863119898119872+ 119869119860

2

1

11986021119879119892

+119872(119862119899119875

0+ 1198810)

119899119875011986021

] 119904 + 1)

minus1

(12)

where 119862 is the leakage coefficients of the energy recoverysystem

The natural frequency of the proposed energy recoverysystem can be calculated as

120596119867= radic

1

119869119872(1198621198991198750+ 1198810) 119860211198991198750119879119892+1198721198811198602

1120573119890

(13)

The natural frequency is the lowest frequency of the sys-tem The low natural frequency has an effect on the responsespeed of the system and energy recovery efficiency In orderto improve the natural frequency and response speed of thesystem based on the expression of the natural frequency thefollowing ways should be taken into consideration

(1) Reducing the loop oil volume 119881 to make the wholesystem structure compact and high-efficiency the oilline should be installed effectively and the length ofthe line should be shortened as soon as possible

(2) Increasing the volume elastic modulus of thehydraulic oil 120573

119890 while designing the system and

selecting the hydraulic oil the volume elasticmodulus 120573

119890of the oil should have a large value

relatively(3) Reducing the leakage coefficients of the energy recov-

ery system 119862 as it is hardly realistic to eliminate thesystem leakage the quality of the hydraulic compo-nents chosen in the system should satisfy the longtime using performance

(4) Reducing the total moment of inertia of the hydraulicmotor 119869 according to the characteristics of themotorthe total moment of inertia decreases along with thedecreasing of the displacement so the displacementof the motor should be reduced to a certain degreeHowever the flow rate of the return oil lines willreducewhen the displacement of themotor decreasesHence it has an effect on the working performance ofthe hydraulic excavator

4 Simulation of the Boom EnergyRecovery System

In order to verify the energy saving efficiency of the pro-posed system simulations with the proposed accumulator-generator system and the conventional energy recoverysystem have been carried out by using AMESim It aims tovalidate the impact of accumulator on energy recovery effi-ciency Figure 6 shows the AMESim model of the proposedsystem with accumulator while Figure 7 displays anotherkind of boom energy recovery system without accumulator

Table 2 Setting parameters for the two AMESim models

Common parts Parameters Values

Boom cylinderPiston diameter (mm) 350Rod diameter (mm) 220Length of stroke (m) 18

Generator Reference voltage (V) 50

Battery Nominal capacity (Ah) 50State of charge () 60

Table 3 Input energy and the energy stored in the battery

System Input energy119864in (J)

Energy storedin the battery

119864st (J)

Percentage119864st119864in ()

Conventional system 764601198646 05041198646 66Proposed system 689231198646 10081198646 146

To simplify the system the engines are replaced by twomotors in Figures 6 and 7

Including the load force and dimension parameters of theboom cylinder the setting parameters for the AMESimmod-els are obtained from the conventional hydraulic excavatorThe main setting parameters for the two AMESim modelsare given in Table 2 The input load force of the conventionalenergy recovery system and the proposed energy recoverysystem is shown in Figure 8

Run the simulations The displacement of the boomcylinder in the conventional energy recovery system and theproposed system are shown in Figure 9 Figure 9 shows thatthe piston displacement of the boom cylinder in the twosystems is quite similar The working performance of theboom cylinder is not affected by the energy recovery systeminstalled in the return oil lines

The difference between the SOC (State of Charge) of thebatteries in the two systems is shown in Figure 10 For theconventional energy recovery system the generator starts andstops four times during a working period According to themechanical characteristics of the generator high efficiencydepends on high speed and continuous rotation Becauseof the accumulator the generator of the proposed energyrecovery system starts and stops only once during a workingperiod Hence the generator can rotate in a high speedcontinuously Comparedwith the conventional energy savingsystem SOC of the battery in the proposed system can risesmoothly During a whole working period the value of SOCreaches 652 Finally the input energy and the energy storedin the batteries of the two energy saving systems are given inTable 3

Based on Table 3 the value of the energy recoveryefficiency in the proposed system is 146 while the valueof the conventional energy recovery system is 66 It isclear that the proposed boom potential energy recoverysystem brings higher energy recovery efficiency than theconventional boom potential energy recovery system

The Scientific World Journal 7

F

MOT

Boom potential recovery system

FluidA

SM

A

A

B

P T

P

A

P

PT

Q

M

q

Qq

QP

2

1

3

Runstats

k

k

k

k

f(X

)X

X

Y

times

timesk

k

Y lt Xk

s

ktimes k

s

properties

WT

J WTT +

+

T

minus

Figure 6 AMESim model of the proposed system

5 Analysis of the Main Componentsin the System

As designing the boom energy recovery system of the hybridhydraulic excavator all the components of the system arechosen based on the calculation results and working con-dition However some parameters of the main componentshave a great influence on the energy recovery efficiency of theproposed system Inappropriate parameters will lead to thedecreasing of the efficiency Therefore it is essential to anal-ysis the relationship between the energy recovery efficiencyand the key parameters of the main components like theaeration pressure of the accumulator and the displacement ofthe hydraulic motor In order to simplify the model there arethree assumptions for the simulation models

(1) Since this study concentrates on the effectivenessof the proposed boom energy recovery system theworking performance of the engine is not takeninto consideration The engine is replaced by anelectromotor

(2) The load force and the piston velocity of the boomcylinder in the simulation models are identical withthe conventional hydraulic excavator In other wordsthe boom cylinder system is working under the sameconditions

(3) A generator and a battery are selected as the energyconversion and energy storage units Regardless of theinternal structure of generator and battery the simu-lation models are replaced by the universal models

8 The Scientific World Journal

Conventional boom potential recovery system

F

M

Qq

ktimes

A B

P T

Fluid properties

Runstats

Qq

MOT

k

times

k

k

s

k

f(X

)X

X

YY lt X

A

P T

QP

ktimes k

s

kk

WTJ W

T

+SM

T

+

T

minus

Figure 7 AMESim model of a conventional boom energy recovery system

0 20 40 60 80 100

Boom

cylin

der l

oadi

ng fo

rce (

N)

12 times 106

10 times 106

80 times 105

60 times 105

40 times 105

20 times 105

00

Time (s)

Figure 8 Input load force of the energy saving system

51 Analysis of the Accumulator The key parameters of theaccumulator include the aeration pressure and the initialvolume The simulations of the relationship between theparameter values and the system energy recovery efficiencyare shown below

0 20 40 60 80 100

06

08

10

12

14

16

18

Boom

cylin

der p

iston

disp

lace

men

t (m

)

Time (s)

Conventional energy recovery systemProposed energy recovery system

Figure 9 Piston displacement of the boom cylinder

511 The Aeration Pressure In order to analyze the influenceof the different aeration pressure on the energy recovery

The Scientific World Journal 9

0 10 20 30 40 50 60 70 80 90 100600605610615620625630635640645650655

SOC

of th

e bat

tery

()

Conventional energy recovery systemProposed energy recovery system

Time (s)

Figure 10 SOC of the battery

0 20 40 60 80 100380

400

420

440

460

480

500

Volu

me c

hang

ing

of th

e acc

umul

ator

(L)

Time (s)

5MPa7MPa

9MPa10MPa

Figure 11 Volume changing of the accumulator

efficiency four values 5MPa 7MPa 9MPa and 10MPa areselected within the scope of the aeration pressure Run thesimulation models Figures 11 and 12 present the volume andpressure changing of the accumulator The rotational speedof the hydraulic motor is shown in Figure 13 The SOC of thebattery is shown in Figure 14

Based on the figures above it can be seen that thepressure of the accumulator is proportional to its aerationpressure When the boom cylinder piston is expanding inthe second working cycle the hydraulic motor is driven bythe oil stored in the accumulator The volume changing ofthe pressure oil in the accumulator increases along with theincreasing of the aeration pressure It leads to increasing theflow of the pressure oil in the energy recovery system Thepressure difference between the inlet and outlet of the motoris increasing as well Because of the constant displacement

0 20 40 60 80 100Time (s)

50

60

70

80

90

100

110

120

130

140

150

Pres

sure

chan

ging

of t

he ac

cum

ulat

or (b

ar)

5MPa7MPa

9MPa10MPa

Figure 12 Pressure changing of the accumulator

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

4000

4500Ro

tatio

nal s

peed

of t

he m

otor

(rm

in)

Time (s)

5MPa7MPa

9MPa10MPa

Figure 13 Rotational speed of the hydraulic motor

hydraulic motor the flow rate through the hydraulic motoris proportional to its rotational speed The output torqueof the motor is increasing gradually based on the pressuredifferenceThe generator is connected to the hydraulic motorcoaxially According to the characteristics of the generatorthe output torque of the motor is increasing as well Hencethe electric energy produced by the generator and SOC of thebattery are increasing

512 The Initial Volume In order to analyze the influence ofthe different initial volume on the energy recovery efficiencyfour values 450 L 470 L 480 L and 500 L are selected withinthe scope of the initial volume under the condition that theaeration pressure and the highest working pressure of theaccumulator are keeping in 10MPa and 18MPa

10 The Scientific World Journal

60

61

62

63

64

65

SOC

of th

e bat

tery

()

0 10 20 30 40 50 60 70 80 90 100Time (s)

5MPa7MPa

9MPa10MPa

Figure 14 SOC of the battery

0 10 20 30 40 50 60 70 80 90 100340

360

380

400

420

440

460

480

500

Volu

me c

hang

ing

of th

e acc

umul

ator

(L)

Time (s)

450L470L

480L500L

Figure 15 Volume changing of the accumulator

Figures 15 and 16 show the volume and pressure changingof the accumulator Keeping the aeration pressure unchangedthe simulation results indicate that the pressure of theaccumulator is inversely proportional to the initial volumeThe corresponding rotational speeds of the hydraulic motorare shown in Figure 17 The SOC of the battery is shown inFigure 18 It can be seen that the value of SOC is not changingwith the different initial volume In other words the value ofthe initial volume does not have an effect on the improving ofthe boom energy recovery efficiency

52 Analysis of the Hydraulic Motor The hydraulic motoris used to drive the generator in the boom energy recoverysystem The energy recovery system is determined by theperformance of the motor So it is essential to do someresearch on the hydraulicmotorThedisplacement is themost

0 10 20 30 40 50 60 70 80 90 100100

110

120

130

140

150

Pres

sure

chan

ging

of t

he ac

cum

ulat

or (b

ar)

Time (s)

450L470L

480L500L

Figure 16 Pressure changing of the accumulator

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

4000

4500Ro

tatio

nal s

peed

of t

he m

otor

(rm

in)

Time (s)

450L470L

480L500L

Figure 17 Rotational speed of the hydraulic motor

important parameter of the hydraulic motorThe simulationsof the displacement and the type of the motor are shownbelow

521 The Displacement In order to analyze the influence ofthe different displacement on the energy recovery efficiencyfour values 60mLr 80mLr 100mLr and 120mLr areselected as the displacement of the motor

Figure 19 shows the velocity of the boom cylinder pistonin the hybrid hydraulic excavator Based on the workingprocess of the hydraulic excavator the boom cylinder iscontracting during 52 sndash69 s and 90 sndash100 s The hydraulicmotor is driven by the pressure oil flowing into the returnoil line The result shows that the contracting velocity ofthe cylinder decreases along with the decreasing of the

The Scientific World Journal 11

0 10 20 30 40 50 60 70 80 90 10060

61

62

63

64

65

SOC

of th

e bat

tery

()

Time (s)

450L470L

480L500L

Figure 18 SOC of the battery

0 10 20Time (s)

30 40 50 60 70 80 90 100

000

005

010

015

Velo

city

of t

he b

oom

cylin

der p

iston

(ms

)

minus005

minus010

minus015

60mLr80mLr

100mLr120mLr

Figure 19 Velocity of the boom cylinder piston

displacement However it does not have an effect on thenormal work of the hydraulic excavator

Figures 20 and 21 show the rotational speed of thehydraulic motor and SOC of the battery with the differ-ent displacement According to the characteristics of thehydraulicmotor the rotational speed of themotor is inverselyproportional to the displacement When the displacement is60mLr the SOC of the battery reaches the maximum valueIt indicates that the SOC of the battery increases along withthe decreasing of the displacement

522 The Type of the Hydraulic Motor Because of thecomplex working condition of the hydraulic excavator thevelocity of the boom cylinder piston ranges from 0 to 01msThe flow rate of the pressure in the return oil line ranges

0 10 20 30 40 50 60 70 80 90 1000

1000

2000

3000

4000

5000

6000

7000

Rota

tiona

l spe

ed o

f the

mot

or (r

min

)

Time (s)

60mLr80mLr

100mLr120mLr

Figure 20 Rotational speed of the hydraulic motor

0 10 20 30 40 50 60 70 80 90 10060

61

62

63

64

65

66SO

C of

the b

atte

ry (

)

Time (s)

60mLr80mLr

100mLr120mLr

Figure 21 SOC of the battery

large So it is very important to select the hydraulic motor forimproving the energy recovery system

The hydraulicmotor is divided into the constant displace-ment and variable displacement motor The AMESim modelwith the variable displacement motor is shown in Figure 22

Run the simulation Compared with the models withthe constant displacement motor shown in Figure 6 therotational speed of the hydraulic motor in two simulationmodels is presented in the Figure 23 Figure 24 shows the SOCrange of the battery

It can be seen that the rotational speed of the constantdisplacement motor is ranging between 1300 rmin and3500 rmin during a working cycle while the rotational speedof the variable displacement motor remains at 3000 rminThe SOC of the battery of the constant displacement motorsystem increases from 60 to 648 while the SOC of the

12 The Scientific World Journal

Boom potential recovery system

F

M

Qq

ktimesA B

P T

Fluid

Runstats

properties

Qq

A

P

P

T

MOT

k

k

k

f(X

)X

X

Y timesY lt X

k

s

2

1

3

SM

A

A

P

QP

k

k

ktimes k

s

WT

J WT w

T +

+

T

minus

kPIDminus

+

Figure 22 AMESim model with the variable displacement motor

battery of the variable displacement motor system reaches708 Compared with the constant displacement motorsystem more boom potential energy of the energy recoverysystemwith the variable displacementmotor is recovered andstored in the battery Hence the energy recovery efficiencyof the variable displacement motor system is higher than thesystem with the constant displacement motor

6 Conclusions

(1) Based on the simulation of the working devicesin the conventional hydraulic excavator the energywhich can be recovered of the three cylinders iscalculated Taking the complexity and cost of thesystem into consideration this paper proposed anovel boom potential energy recovery system for theparallel hybrid excavator The boom energy regen-eration unit consists of an accumulator a hydraulicmotor an electric generator and a battery Compared

with the conventional energy recovery system theproposed system makes sure that the generator canrotate continuously in a high speed during a workingcycle The AMESim models of the two boom energyrecovery systems are built and the results show thatthe proposed energy recovery system brings higherenergy recovery efficiency than the conventionalenergy recovery system

(2) The mathematical models of the main compo-nents including boom cylinder hydraulic motorand hydraulic accumulator are built The naturalfrequency of the proposed energy recovery systemis calculated based on the mathematical models Inorder to improve the natural frequency and responsespeed of the system some measures should be takenbased on the expression of the natural frequencysuch as reducing the loop oil volume 119881 the leakage

The Scientific World Journal 13

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

Rota

tiona

l spe

ed o

f the

hyd

raul

ic m

otor

(rm

in)

Constant displacement motor Variable displacement motor

Time (s)

Figure 23 Rotational speed of the hydraulic motor

0 10 20 30 40 50 60 70 80 90 100606162636465666768697071

SOC

of th

e bat

tery

()

Constant displacement motor Variable displacement motor

Time (s)

Figure 24 SOC of the battery

coefficients of the energy recovery system 119862 and thetotal moment of inertia of the hydraulic motor 119869

(3) The influence of the main components includinghydraulic motor and hydraulic accumulator on theenergy recovery efficiency of the proposed systemis analyzed The key parameters of the accumulatorinclude the aeration pressure and the initial volumeThe energy recovery efficiency of the proposed sys-tem can be improving to some extent by increasingthe aeration pressure while changing of the initialvolume does not have an effect on improving of theenergy recovery efficiency

The hydraulic motor is used to drive the generator inthe boom energy recovery system The displacement is themost important parameter of the hydraulicmotorThe energy

recovery efficiency can be improving on the premise ofnormal working by decreasing the displacement of themotorSince the flow rate of the pressure in the return oil line rangeslarge the generator can rotate continuously in a high speedby selecting the variable displacement motor in the return oilline In order to improve the energy efficiency according tothe characteristics of the generator the variable displacementhydraulic motor should be chosen in the return oil line

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work is supported by the Fundamental Research Fundsfor the Central Universities (China University of Mining andTechnology 2014Y05) PCSIRT (IRT1292) and the ProjectFunded by the Priority Academic Program Development ofJiangsu Higher Education Institutions (PAPD)

References

[1] M Kagoshima M Komiyama T Nanjo et al ldquoDevelopment ofnew hybrid excavatorrdquo Kobelco Technology Review no 27 2007

[2] T Nanjo E Imanishi and M Kagcahima ldquoPower simulationfor energy saving in hybrid excavatorrdquo JSAE Transactions vol47 pp 101ndash106 2004

[3] L Weidong S Kaikai L Wei and X Jun ldquoResearch onpotential energy recovery of 16T wheeled hybrid excavatorrdquoin Proceedings of the 2nd International Conference on DigitalManufacturing and Automation (ICDMA rsquo11) pp 996ndash998Zhangjiajie China August 2011

[4] I Y Jong K K Ahn and Q T Dinh ldquoA study on anenergy saving electro-hydraulic excavatorrdquo in Proceedings of theICROS-SICE International Joint Conference (ICCAS-SICE rsquo09)pp 3825ndash3830 Fukuoka Japan August 2009

[5] T H Ho and K K Ahn ldquoDesign and control of a closed-loop hydraulic energy-regenerative systemrdquo Automation inConstruction vol 22 pp 444ndash458 2012

[6] Z Jun J Sheng-jie S Gui-mao et al ldquoDesign of electroniccontrol system of hydraulic excavator with CAN bus andPID methodrdquo Proceedings of the International Conference onIntelligent System Design and Engineering Application (ISDEArsquo10) 2010

[7] T Wang and Q Wang ldquoModeling and control of a novelhydraulic system with energy regenerationrdquo in Proceedings ofthe IEEEASME International Conference on Advanced Intelli-gent Mechatronics (AIM rsquo12) pp 922ndash927 IEEE KachsiungTaiwan July 2012

[8] H SHamut I Dincer andG FNaterer ldquoExergoenvironmentalanalysis of hybrid electric vehicle thermal management sys-temsrdquo Journal of Cleaner Production vol 67 pp 187ndash196 2014

[9] A Poursamad and M Montazeri ldquoDesign of genetic-fuzzycontrol strategy for parallel hybrid electric vehiclesrdquo ControlEngineering Practice vol 16 no 7 pp 861ndash873 2008

[10] S Hui J-H Jiang and W Xin ldquoTorque control strategy fora parallel hydraulic hybrid vehiclerdquo Journal of Terramechanicsvol 46 no 6 pp 259ndash265 2009

14 The Scientific World Journal

[11] Z Cao S Wu M Li and C Du ldquoSeries and parallel hybridsystem performance comparison based on the city bus cyclerdquoin Proceedings of the Asia-Pacific Power and Energy EngineeringConference (APPEEC 09) Wuhan China March 2009

[12] J Gong Q He D Zhang et al ldquoPower system control strategyfor hybrid excavator based on equivalent fuel consumptionrdquo inProceedings of the 9th IEEE International Conference on Mecha-tronics and Automation (ICMA rsquo12) pp 1097ndash1102 ChengduChina August 2012

[13] Z Liu S Liu Z Huang and Q Hu ldquoHydraulic excavatorhybrid power system parameters designrdquo in Proceedings of the2nd International Conference on Digital Manufacturing andAutomation (ICDMA rsquo11) pp 602ndash605 Zhangjiajie ChinaAugust 2011

[14] T Lin Q Wang B Hu and W Gong ldquoResearch on theenergy regeneration systems for hybrid hydraulic excavatorsrdquoAutomation in Construction vol 19 no 8 pp 1016ndash1026 2010

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The Scientific World Journal 5

System initialize

The boom up

Working normally

YesNo

The first working cycle start

The top cavity of valve 9 on

valve 10 on

Hydraulic oil returns totankAccumulator is charged

The second workingcycle start

The boom up

The top cavity ofvalve 9 onvalve 10 on

The top cavity ofvalve 9 offvalve 10 on

YesNo

Valve 12 on

Hydraulic oil from valve 9flow into valve 12

Hydraulic oil from accumulator flow into

valve 12

Motor drive generatorto rotate

End

The top cavity ofvalve 9 off

Work ending Yes No

valve 12 off

Figure 5 Working flow chart of the energy saving system

of accumulator respectively 1198810 1198811 1198812 119881119886are the initial

aeration volume initial volume terminal state volume andfree state volume of accumulator 119899 is the air polytropicexponent

119901119886and119881

119886are the random operating state of accumulator

the equality of 1199010119881119899

0= 119901119886119881119899

119886is expanded using Taylor

expansion the Taylor expansion is given by

119889119875119886

119889119905= minus

1198991198750

1198810

119889119881119886

119889119905 (9)

Flow and air chamber volume of accumulator are 119876119886and 119881

119886

and the inlet flow rate of accumulator is given by

119876119886= minus

119889119881119886

119889119905 (10)

Energy equation of accumulator

119864 = minusint

1198812

1198811

(1198810

119881119886

)

119899

119889119881119886=11987501198810

119899 minus 1[(119875119886

1198750

)

(119899minus1)119899

minus 1] (11)

According to the equations above the flow control systemis an obviously nonlinear system In order to verify itsstability and dynamic performance linearization and Laplacetransform are carried out The transfer function from thehydraulic motor speed to the load force can be expressed as120596119898(119904)

119865 (119904)

= (119863119898

1198601119879119892

)

6 The Scientific World Journal

times ([119869119872(119862119899119875

0+ 1198810)

119860211198991198750119879119892

+119872119881

11986021120573119890

] 1199042

+[119863119898119872+ 119869119860

2

1

11986021119879119892

+119872(119862119899119875

0+ 1198810)

119899119875011986021

] 119904 + 1)

minus1

(12)

where 119862 is the leakage coefficients of the energy recoverysystem

The natural frequency of the proposed energy recoverysystem can be calculated as

120596119867= radic

1

119869119872(1198621198991198750+ 1198810) 119860211198991198750119879119892+1198721198811198602

1120573119890

(13)

The natural frequency is the lowest frequency of the sys-tem The low natural frequency has an effect on the responsespeed of the system and energy recovery efficiency In orderto improve the natural frequency and response speed of thesystem based on the expression of the natural frequency thefollowing ways should be taken into consideration

(1) Reducing the loop oil volume 119881 to make the wholesystem structure compact and high-efficiency the oilline should be installed effectively and the length ofthe line should be shortened as soon as possible

(2) Increasing the volume elastic modulus of thehydraulic oil 120573

119890 while designing the system and

selecting the hydraulic oil the volume elasticmodulus 120573

119890of the oil should have a large value

relatively(3) Reducing the leakage coefficients of the energy recov-

ery system 119862 as it is hardly realistic to eliminate thesystem leakage the quality of the hydraulic compo-nents chosen in the system should satisfy the longtime using performance

(4) Reducing the total moment of inertia of the hydraulicmotor 119869 according to the characteristics of themotorthe total moment of inertia decreases along with thedecreasing of the displacement so the displacementof the motor should be reduced to a certain degreeHowever the flow rate of the return oil lines willreducewhen the displacement of themotor decreasesHence it has an effect on the working performance ofthe hydraulic excavator

4 Simulation of the Boom EnergyRecovery System

In order to verify the energy saving efficiency of the pro-posed system simulations with the proposed accumulator-generator system and the conventional energy recoverysystem have been carried out by using AMESim It aims tovalidate the impact of accumulator on energy recovery effi-ciency Figure 6 shows the AMESim model of the proposedsystem with accumulator while Figure 7 displays anotherkind of boom energy recovery system without accumulator

Table 2 Setting parameters for the two AMESim models

Common parts Parameters Values

Boom cylinderPiston diameter (mm) 350Rod diameter (mm) 220Length of stroke (m) 18

Generator Reference voltage (V) 50

Battery Nominal capacity (Ah) 50State of charge () 60

Table 3 Input energy and the energy stored in the battery

System Input energy119864in (J)

Energy storedin the battery

119864st (J)

Percentage119864st119864in ()

Conventional system 764601198646 05041198646 66Proposed system 689231198646 10081198646 146

To simplify the system the engines are replaced by twomotors in Figures 6 and 7

Including the load force and dimension parameters of theboom cylinder the setting parameters for the AMESimmod-els are obtained from the conventional hydraulic excavatorThe main setting parameters for the two AMESim modelsare given in Table 2 The input load force of the conventionalenergy recovery system and the proposed energy recoverysystem is shown in Figure 8

Run the simulations The displacement of the boomcylinder in the conventional energy recovery system and theproposed system are shown in Figure 9 Figure 9 shows thatthe piston displacement of the boom cylinder in the twosystems is quite similar The working performance of theboom cylinder is not affected by the energy recovery systeminstalled in the return oil lines

The difference between the SOC (State of Charge) of thebatteries in the two systems is shown in Figure 10 For theconventional energy recovery system the generator starts andstops four times during a working period According to themechanical characteristics of the generator high efficiencydepends on high speed and continuous rotation Becauseof the accumulator the generator of the proposed energyrecovery system starts and stops only once during a workingperiod Hence the generator can rotate in a high speedcontinuously Comparedwith the conventional energy savingsystem SOC of the battery in the proposed system can risesmoothly During a whole working period the value of SOCreaches 652 Finally the input energy and the energy storedin the batteries of the two energy saving systems are given inTable 3

Based on Table 3 the value of the energy recoveryefficiency in the proposed system is 146 while the valueof the conventional energy recovery system is 66 It isclear that the proposed boom potential energy recoverysystem brings higher energy recovery efficiency than theconventional boom potential energy recovery system

The Scientific World Journal 7

F

MOT

Boom potential recovery system

FluidA

SM

A

A

B

P T

P

A

P

PT

Q

M

q

Qq

QP

2

1

3

Runstats

k

k

k

k

f(X

)X

X

Y

times

timesk

k

Y lt Xk

s

ktimes k

s

properties

WT

J WTT +

+

T

minus

Figure 6 AMESim model of the proposed system

5 Analysis of the Main Componentsin the System

As designing the boom energy recovery system of the hybridhydraulic excavator all the components of the system arechosen based on the calculation results and working con-dition However some parameters of the main componentshave a great influence on the energy recovery efficiency of theproposed system Inappropriate parameters will lead to thedecreasing of the efficiency Therefore it is essential to anal-ysis the relationship between the energy recovery efficiencyand the key parameters of the main components like theaeration pressure of the accumulator and the displacement ofthe hydraulic motor In order to simplify the model there arethree assumptions for the simulation models

(1) Since this study concentrates on the effectivenessof the proposed boom energy recovery system theworking performance of the engine is not takeninto consideration The engine is replaced by anelectromotor

(2) The load force and the piston velocity of the boomcylinder in the simulation models are identical withthe conventional hydraulic excavator In other wordsthe boom cylinder system is working under the sameconditions

(3) A generator and a battery are selected as the energyconversion and energy storage units Regardless of theinternal structure of generator and battery the simu-lation models are replaced by the universal models

8 The Scientific World Journal

Conventional boom potential recovery system

F

M

Qq

ktimes

A B

P T

Fluid properties

Runstats

Qq

MOT

k

times

k

k

s

k

f(X

)X

X

YY lt X

A

P T

QP

ktimes k

s

kk

WTJ W

T

+SM

T

+

T

minus

Figure 7 AMESim model of a conventional boom energy recovery system

0 20 40 60 80 100

Boom

cylin

der l

oadi

ng fo

rce (

N)

12 times 106

10 times 106

80 times 105

60 times 105

40 times 105

20 times 105

00

Time (s)

Figure 8 Input load force of the energy saving system

51 Analysis of the Accumulator The key parameters of theaccumulator include the aeration pressure and the initialvolume The simulations of the relationship between theparameter values and the system energy recovery efficiencyare shown below

0 20 40 60 80 100

06

08

10

12

14

16

18

Boom

cylin

der p

iston

disp

lace

men

t (m

)

Time (s)

Conventional energy recovery systemProposed energy recovery system

Figure 9 Piston displacement of the boom cylinder

511 The Aeration Pressure In order to analyze the influenceof the different aeration pressure on the energy recovery

The Scientific World Journal 9

0 10 20 30 40 50 60 70 80 90 100600605610615620625630635640645650655

SOC

of th

e bat

tery

()

Conventional energy recovery systemProposed energy recovery system

Time (s)

Figure 10 SOC of the battery

0 20 40 60 80 100380

400

420

440

460

480

500

Volu

me c

hang

ing

of th

e acc

umul

ator

(L)

Time (s)

5MPa7MPa

9MPa10MPa

Figure 11 Volume changing of the accumulator

efficiency four values 5MPa 7MPa 9MPa and 10MPa areselected within the scope of the aeration pressure Run thesimulation models Figures 11 and 12 present the volume andpressure changing of the accumulator The rotational speedof the hydraulic motor is shown in Figure 13 The SOC of thebattery is shown in Figure 14

Based on the figures above it can be seen that thepressure of the accumulator is proportional to its aerationpressure When the boom cylinder piston is expanding inthe second working cycle the hydraulic motor is driven bythe oil stored in the accumulator The volume changing ofthe pressure oil in the accumulator increases along with theincreasing of the aeration pressure It leads to increasing theflow of the pressure oil in the energy recovery system Thepressure difference between the inlet and outlet of the motoris increasing as well Because of the constant displacement

0 20 40 60 80 100Time (s)

50

60

70

80

90

100

110

120

130

140

150

Pres

sure

chan

ging

of t

he ac

cum

ulat

or (b

ar)

5MPa7MPa

9MPa10MPa

Figure 12 Pressure changing of the accumulator

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

4000

4500Ro

tatio

nal s

peed

of t

he m

otor

(rm

in)

Time (s)

5MPa7MPa

9MPa10MPa

Figure 13 Rotational speed of the hydraulic motor

hydraulic motor the flow rate through the hydraulic motoris proportional to its rotational speed The output torqueof the motor is increasing gradually based on the pressuredifferenceThe generator is connected to the hydraulic motorcoaxially According to the characteristics of the generatorthe output torque of the motor is increasing as well Hencethe electric energy produced by the generator and SOC of thebattery are increasing

512 The Initial Volume In order to analyze the influence ofthe different initial volume on the energy recovery efficiencyfour values 450 L 470 L 480 L and 500 L are selected withinthe scope of the initial volume under the condition that theaeration pressure and the highest working pressure of theaccumulator are keeping in 10MPa and 18MPa

10 The Scientific World Journal

60

61

62

63

64

65

SOC

of th

e bat

tery

()

0 10 20 30 40 50 60 70 80 90 100Time (s)

5MPa7MPa

9MPa10MPa

Figure 14 SOC of the battery

0 10 20 30 40 50 60 70 80 90 100340

360

380

400

420

440

460

480

500

Volu

me c

hang

ing

of th

e acc

umul

ator

(L)

Time (s)

450L470L

480L500L

Figure 15 Volume changing of the accumulator

Figures 15 and 16 show the volume and pressure changingof the accumulator Keeping the aeration pressure unchangedthe simulation results indicate that the pressure of theaccumulator is inversely proportional to the initial volumeThe corresponding rotational speeds of the hydraulic motorare shown in Figure 17 The SOC of the battery is shown inFigure 18 It can be seen that the value of SOC is not changingwith the different initial volume In other words the value ofthe initial volume does not have an effect on the improving ofthe boom energy recovery efficiency

52 Analysis of the Hydraulic Motor The hydraulic motoris used to drive the generator in the boom energy recoverysystem The energy recovery system is determined by theperformance of the motor So it is essential to do someresearch on the hydraulicmotorThedisplacement is themost

0 10 20 30 40 50 60 70 80 90 100100

110

120

130

140

150

Pres

sure

chan

ging

of t

he ac

cum

ulat

or (b

ar)

Time (s)

450L470L

480L500L

Figure 16 Pressure changing of the accumulator

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

4000

4500Ro

tatio

nal s

peed

of t

he m

otor

(rm

in)

Time (s)

450L470L

480L500L

Figure 17 Rotational speed of the hydraulic motor

important parameter of the hydraulic motorThe simulationsof the displacement and the type of the motor are shownbelow

521 The Displacement In order to analyze the influence ofthe different displacement on the energy recovery efficiencyfour values 60mLr 80mLr 100mLr and 120mLr areselected as the displacement of the motor

Figure 19 shows the velocity of the boom cylinder pistonin the hybrid hydraulic excavator Based on the workingprocess of the hydraulic excavator the boom cylinder iscontracting during 52 sndash69 s and 90 sndash100 s The hydraulicmotor is driven by the pressure oil flowing into the returnoil line The result shows that the contracting velocity ofthe cylinder decreases along with the decreasing of the

The Scientific World Journal 11

0 10 20 30 40 50 60 70 80 90 10060

61

62

63

64

65

SOC

of th

e bat

tery

()

Time (s)

450L470L

480L500L

Figure 18 SOC of the battery

0 10 20Time (s)

30 40 50 60 70 80 90 100

000

005

010

015

Velo

city

of t

he b

oom

cylin

der p

iston

(ms

)

minus005

minus010

minus015

60mLr80mLr

100mLr120mLr

Figure 19 Velocity of the boom cylinder piston

displacement However it does not have an effect on thenormal work of the hydraulic excavator

Figures 20 and 21 show the rotational speed of thehydraulic motor and SOC of the battery with the differ-ent displacement According to the characteristics of thehydraulicmotor the rotational speed of themotor is inverselyproportional to the displacement When the displacement is60mLr the SOC of the battery reaches the maximum valueIt indicates that the SOC of the battery increases along withthe decreasing of the displacement

522 The Type of the Hydraulic Motor Because of thecomplex working condition of the hydraulic excavator thevelocity of the boom cylinder piston ranges from 0 to 01msThe flow rate of the pressure in the return oil line ranges

0 10 20 30 40 50 60 70 80 90 1000

1000

2000

3000

4000

5000

6000

7000

Rota

tiona

l spe

ed o

f the

mot

or (r

min

)

Time (s)

60mLr80mLr

100mLr120mLr

Figure 20 Rotational speed of the hydraulic motor

0 10 20 30 40 50 60 70 80 90 10060

61

62

63

64

65

66SO

C of

the b

atte

ry (

)

Time (s)

60mLr80mLr

100mLr120mLr

Figure 21 SOC of the battery

large So it is very important to select the hydraulic motor forimproving the energy recovery system

The hydraulicmotor is divided into the constant displace-ment and variable displacement motor The AMESim modelwith the variable displacement motor is shown in Figure 22

Run the simulation Compared with the models withthe constant displacement motor shown in Figure 6 therotational speed of the hydraulic motor in two simulationmodels is presented in the Figure 23 Figure 24 shows the SOCrange of the battery

It can be seen that the rotational speed of the constantdisplacement motor is ranging between 1300 rmin and3500 rmin during a working cycle while the rotational speedof the variable displacement motor remains at 3000 rminThe SOC of the battery of the constant displacement motorsystem increases from 60 to 648 while the SOC of the

12 The Scientific World Journal

Boom potential recovery system

F

M

Qq

ktimesA B

P T

Fluid

Runstats

properties

Qq

A

P

P

T

MOT

k

k

k

f(X

)X

X

Y timesY lt X

k

s

2

1

3

SM

A

A

P

QP

k

k

ktimes k

s

WT

J WT w

T +

+

T

minus

kPIDminus

+

Figure 22 AMESim model with the variable displacement motor

battery of the variable displacement motor system reaches708 Compared with the constant displacement motorsystem more boom potential energy of the energy recoverysystemwith the variable displacementmotor is recovered andstored in the battery Hence the energy recovery efficiencyof the variable displacement motor system is higher than thesystem with the constant displacement motor

6 Conclusions

(1) Based on the simulation of the working devicesin the conventional hydraulic excavator the energywhich can be recovered of the three cylinders iscalculated Taking the complexity and cost of thesystem into consideration this paper proposed anovel boom potential energy recovery system for theparallel hybrid excavator The boom energy regen-eration unit consists of an accumulator a hydraulicmotor an electric generator and a battery Compared

with the conventional energy recovery system theproposed system makes sure that the generator canrotate continuously in a high speed during a workingcycle The AMESim models of the two boom energyrecovery systems are built and the results show thatthe proposed energy recovery system brings higherenergy recovery efficiency than the conventionalenergy recovery system

(2) The mathematical models of the main compo-nents including boom cylinder hydraulic motorand hydraulic accumulator are built The naturalfrequency of the proposed energy recovery systemis calculated based on the mathematical models Inorder to improve the natural frequency and responsespeed of the system some measures should be takenbased on the expression of the natural frequencysuch as reducing the loop oil volume 119881 the leakage

The Scientific World Journal 13

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

Rota

tiona

l spe

ed o

f the

hyd

raul

ic m

otor

(rm

in)

Constant displacement motor Variable displacement motor

Time (s)

Figure 23 Rotational speed of the hydraulic motor

0 10 20 30 40 50 60 70 80 90 100606162636465666768697071

SOC

of th

e bat

tery

()

Constant displacement motor Variable displacement motor

Time (s)

Figure 24 SOC of the battery

coefficients of the energy recovery system 119862 and thetotal moment of inertia of the hydraulic motor 119869

(3) The influence of the main components includinghydraulic motor and hydraulic accumulator on theenergy recovery efficiency of the proposed systemis analyzed The key parameters of the accumulatorinclude the aeration pressure and the initial volumeThe energy recovery efficiency of the proposed sys-tem can be improving to some extent by increasingthe aeration pressure while changing of the initialvolume does not have an effect on improving of theenergy recovery efficiency

The hydraulic motor is used to drive the generator inthe boom energy recovery system The displacement is themost important parameter of the hydraulicmotorThe energy

recovery efficiency can be improving on the premise ofnormal working by decreasing the displacement of themotorSince the flow rate of the pressure in the return oil line rangeslarge the generator can rotate continuously in a high speedby selecting the variable displacement motor in the return oilline In order to improve the energy efficiency according tothe characteristics of the generator the variable displacementhydraulic motor should be chosen in the return oil line

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work is supported by the Fundamental Research Fundsfor the Central Universities (China University of Mining andTechnology 2014Y05) PCSIRT (IRT1292) and the ProjectFunded by the Priority Academic Program Development ofJiangsu Higher Education Institutions (PAPD)

References

[1] M Kagoshima M Komiyama T Nanjo et al ldquoDevelopment ofnew hybrid excavatorrdquo Kobelco Technology Review no 27 2007

[2] T Nanjo E Imanishi and M Kagcahima ldquoPower simulationfor energy saving in hybrid excavatorrdquo JSAE Transactions vol47 pp 101ndash106 2004

[3] L Weidong S Kaikai L Wei and X Jun ldquoResearch onpotential energy recovery of 16T wheeled hybrid excavatorrdquoin Proceedings of the 2nd International Conference on DigitalManufacturing and Automation (ICDMA rsquo11) pp 996ndash998Zhangjiajie China August 2011

[4] I Y Jong K K Ahn and Q T Dinh ldquoA study on anenergy saving electro-hydraulic excavatorrdquo in Proceedings of theICROS-SICE International Joint Conference (ICCAS-SICE rsquo09)pp 3825ndash3830 Fukuoka Japan August 2009

[5] T H Ho and K K Ahn ldquoDesign and control of a closed-loop hydraulic energy-regenerative systemrdquo Automation inConstruction vol 22 pp 444ndash458 2012

[6] Z Jun J Sheng-jie S Gui-mao et al ldquoDesign of electroniccontrol system of hydraulic excavator with CAN bus andPID methodrdquo Proceedings of the International Conference onIntelligent System Design and Engineering Application (ISDEArsquo10) 2010

[7] T Wang and Q Wang ldquoModeling and control of a novelhydraulic system with energy regenerationrdquo in Proceedings ofthe IEEEASME International Conference on Advanced Intelli-gent Mechatronics (AIM rsquo12) pp 922ndash927 IEEE KachsiungTaiwan July 2012

[8] H SHamut I Dincer andG FNaterer ldquoExergoenvironmentalanalysis of hybrid electric vehicle thermal management sys-temsrdquo Journal of Cleaner Production vol 67 pp 187ndash196 2014

[9] A Poursamad and M Montazeri ldquoDesign of genetic-fuzzycontrol strategy for parallel hybrid electric vehiclesrdquo ControlEngineering Practice vol 16 no 7 pp 861ndash873 2008

[10] S Hui J-H Jiang and W Xin ldquoTorque control strategy fora parallel hydraulic hybrid vehiclerdquo Journal of Terramechanicsvol 46 no 6 pp 259ndash265 2009

14 The Scientific World Journal

[11] Z Cao S Wu M Li and C Du ldquoSeries and parallel hybridsystem performance comparison based on the city bus cyclerdquoin Proceedings of the Asia-Pacific Power and Energy EngineeringConference (APPEEC 09) Wuhan China March 2009

[12] J Gong Q He D Zhang et al ldquoPower system control strategyfor hybrid excavator based on equivalent fuel consumptionrdquo inProceedings of the 9th IEEE International Conference on Mecha-tronics and Automation (ICMA rsquo12) pp 1097ndash1102 ChengduChina August 2012

[13] Z Liu S Liu Z Huang and Q Hu ldquoHydraulic excavatorhybrid power system parameters designrdquo in Proceedings of the2nd International Conference on Digital Manufacturing andAutomation (ICDMA rsquo11) pp 602ndash605 Zhangjiajie ChinaAugust 2011

[14] T Lin Q Wang B Hu and W Gong ldquoResearch on theenergy regeneration systems for hybrid hydraulic excavatorsrdquoAutomation in Construction vol 19 no 8 pp 1016ndash1026 2010

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Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

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DistributedSensor Networks

International Journal of

6 The Scientific World Journal

times ([119869119872(119862119899119875

0+ 1198810)

119860211198991198750119879119892

+119872119881

11986021120573119890

] 1199042

+[119863119898119872+ 119869119860

2

1

11986021119879119892

+119872(119862119899119875

0+ 1198810)

119899119875011986021

] 119904 + 1)

minus1

(12)

where 119862 is the leakage coefficients of the energy recoverysystem

The natural frequency of the proposed energy recoverysystem can be calculated as

120596119867= radic

1

119869119872(1198621198991198750+ 1198810) 119860211198991198750119879119892+1198721198811198602

1120573119890

(13)

The natural frequency is the lowest frequency of the sys-tem The low natural frequency has an effect on the responsespeed of the system and energy recovery efficiency In orderto improve the natural frequency and response speed of thesystem based on the expression of the natural frequency thefollowing ways should be taken into consideration

(1) Reducing the loop oil volume 119881 to make the wholesystem structure compact and high-efficiency the oilline should be installed effectively and the length ofthe line should be shortened as soon as possible

(2) Increasing the volume elastic modulus of thehydraulic oil 120573

119890 while designing the system and

selecting the hydraulic oil the volume elasticmodulus 120573

119890of the oil should have a large value

relatively(3) Reducing the leakage coefficients of the energy recov-

ery system 119862 as it is hardly realistic to eliminate thesystem leakage the quality of the hydraulic compo-nents chosen in the system should satisfy the longtime using performance

(4) Reducing the total moment of inertia of the hydraulicmotor 119869 according to the characteristics of themotorthe total moment of inertia decreases along with thedecreasing of the displacement so the displacementof the motor should be reduced to a certain degreeHowever the flow rate of the return oil lines willreducewhen the displacement of themotor decreasesHence it has an effect on the working performance ofthe hydraulic excavator

4 Simulation of the Boom EnergyRecovery System

In order to verify the energy saving efficiency of the pro-posed system simulations with the proposed accumulator-generator system and the conventional energy recoverysystem have been carried out by using AMESim It aims tovalidate the impact of accumulator on energy recovery effi-ciency Figure 6 shows the AMESim model of the proposedsystem with accumulator while Figure 7 displays anotherkind of boom energy recovery system without accumulator

Table 2 Setting parameters for the two AMESim models

Common parts Parameters Values

Boom cylinderPiston diameter (mm) 350Rod diameter (mm) 220Length of stroke (m) 18

Generator Reference voltage (V) 50

Battery Nominal capacity (Ah) 50State of charge () 60

Table 3 Input energy and the energy stored in the battery

System Input energy119864in (J)

Energy storedin the battery

119864st (J)

Percentage119864st119864in ()

Conventional system 764601198646 05041198646 66Proposed system 689231198646 10081198646 146

To simplify the system the engines are replaced by twomotors in Figures 6 and 7

Including the load force and dimension parameters of theboom cylinder the setting parameters for the AMESimmod-els are obtained from the conventional hydraulic excavatorThe main setting parameters for the two AMESim modelsare given in Table 2 The input load force of the conventionalenergy recovery system and the proposed energy recoverysystem is shown in Figure 8

Run the simulations The displacement of the boomcylinder in the conventional energy recovery system and theproposed system are shown in Figure 9 Figure 9 shows thatthe piston displacement of the boom cylinder in the twosystems is quite similar The working performance of theboom cylinder is not affected by the energy recovery systeminstalled in the return oil lines

The difference between the SOC (State of Charge) of thebatteries in the two systems is shown in Figure 10 For theconventional energy recovery system the generator starts andstops four times during a working period According to themechanical characteristics of the generator high efficiencydepends on high speed and continuous rotation Becauseof the accumulator the generator of the proposed energyrecovery system starts and stops only once during a workingperiod Hence the generator can rotate in a high speedcontinuously Comparedwith the conventional energy savingsystem SOC of the battery in the proposed system can risesmoothly During a whole working period the value of SOCreaches 652 Finally the input energy and the energy storedin the batteries of the two energy saving systems are given inTable 3

Based on Table 3 the value of the energy recoveryefficiency in the proposed system is 146 while the valueof the conventional energy recovery system is 66 It isclear that the proposed boom potential energy recoverysystem brings higher energy recovery efficiency than theconventional boom potential energy recovery system

The Scientific World Journal 7

F

MOT

Boom potential recovery system

FluidA

SM

A

A

B

P T

P

A

P

PT

Q

M

q

Qq

QP

2

1

3

Runstats

k

k

k

k

f(X

)X

X

Y

times

timesk

k

Y lt Xk

s

ktimes k

s

properties

WT

J WTT +

+

T

minus

Figure 6 AMESim model of the proposed system

5 Analysis of the Main Componentsin the System

As designing the boom energy recovery system of the hybridhydraulic excavator all the components of the system arechosen based on the calculation results and working con-dition However some parameters of the main componentshave a great influence on the energy recovery efficiency of theproposed system Inappropriate parameters will lead to thedecreasing of the efficiency Therefore it is essential to anal-ysis the relationship between the energy recovery efficiencyand the key parameters of the main components like theaeration pressure of the accumulator and the displacement ofthe hydraulic motor In order to simplify the model there arethree assumptions for the simulation models

(1) Since this study concentrates on the effectivenessof the proposed boom energy recovery system theworking performance of the engine is not takeninto consideration The engine is replaced by anelectromotor

(2) The load force and the piston velocity of the boomcylinder in the simulation models are identical withthe conventional hydraulic excavator In other wordsthe boom cylinder system is working under the sameconditions

(3) A generator and a battery are selected as the energyconversion and energy storage units Regardless of theinternal structure of generator and battery the simu-lation models are replaced by the universal models

8 The Scientific World Journal

Conventional boom potential recovery system

F

M

Qq

ktimes

A B

P T

Fluid properties

Runstats

Qq

MOT

k

times

k

k

s

k

f(X

)X

X

YY lt X

A

P T

QP

ktimes k

s

kk

WTJ W

T

+SM

T

+

T

minus

Figure 7 AMESim model of a conventional boom energy recovery system

0 20 40 60 80 100

Boom

cylin

der l

oadi

ng fo

rce (

N)

12 times 106

10 times 106

80 times 105

60 times 105

40 times 105

20 times 105

00

Time (s)

Figure 8 Input load force of the energy saving system

51 Analysis of the Accumulator The key parameters of theaccumulator include the aeration pressure and the initialvolume The simulations of the relationship between theparameter values and the system energy recovery efficiencyare shown below

0 20 40 60 80 100

06

08

10

12

14

16

18

Boom

cylin

der p

iston

disp

lace

men

t (m

)

Time (s)

Conventional energy recovery systemProposed energy recovery system

Figure 9 Piston displacement of the boom cylinder

511 The Aeration Pressure In order to analyze the influenceof the different aeration pressure on the energy recovery

The Scientific World Journal 9

0 10 20 30 40 50 60 70 80 90 100600605610615620625630635640645650655

SOC

of th

e bat

tery

()

Conventional energy recovery systemProposed energy recovery system

Time (s)

Figure 10 SOC of the battery

0 20 40 60 80 100380

400

420

440

460

480

500

Volu

me c

hang

ing

of th

e acc

umul

ator

(L)

Time (s)

5MPa7MPa

9MPa10MPa

Figure 11 Volume changing of the accumulator

efficiency four values 5MPa 7MPa 9MPa and 10MPa areselected within the scope of the aeration pressure Run thesimulation models Figures 11 and 12 present the volume andpressure changing of the accumulator The rotational speedof the hydraulic motor is shown in Figure 13 The SOC of thebattery is shown in Figure 14

Based on the figures above it can be seen that thepressure of the accumulator is proportional to its aerationpressure When the boom cylinder piston is expanding inthe second working cycle the hydraulic motor is driven bythe oil stored in the accumulator The volume changing ofthe pressure oil in the accumulator increases along with theincreasing of the aeration pressure It leads to increasing theflow of the pressure oil in the energy recovery system Thepressure difference between the inlet and outlet of the motoris increasing as well Because of the constant displacement

0 20 40 60 80 100Time (s)

50

60

70

80

90

100

110

120

130

140

150

Pres

sure

chan

ging

of t

he ac

cum

ulat

or (b

ar)

5MPa7MPa

9MPa10MPa

Figure 12 Pressure changing of the accumulator

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

4000

4500Ro

tatio

nal s

peed

of t

he m

otor

(rm

in)

Time (s)

5MPa7MPa

9MPa10MPa

Figure 13 Rotational speed of the hydraulic motor

hydraulic motor the flow rate through the hydraulic motoris proportional to its rotational speed The output torqueof the motor is increasing gradually based on the pressuredifferenceThe generator is connected to the hydraulic motorcoaxially According to the characteristics of the generatorthe output torque of the motor is increasing as well Hencethe electric energy produced by the generator and SOC of thebattery are increasing

512 The Initial Volume In order to analyze the influence ofthe different initial volume on the energy recovery efficiencyfour values 450 L 470 L 480 L and 500 L are selected withinthe scope of the initial volume under the condition that theaeration pressure and the highest working pressure of theaccumulator are keeping in 10MPa and 18MPa

10 The Scientific World Journal

60

61

62

63

64

65

SOC

of th

e bat

tery

()

0 10 20 30 40 50 60 70 80 90 100Time (s)

5MPa7MPa

9MPa10MPa

Figure 14 SOC of the battery

0 10 20 30 40 50 60 70 80 90 100340

360

380

400

420

440

460

480

500

Volu

me c

hang

ing

of th

e acc

umul

ator

(L)

Time (s)

450L470L

480L500L

Figure 15 Volume changing of the accumulator

Figures 15 and 16 show the volume and pressure changingof the accumulator Keeping the aeration pressure unchangedthe simulation results indicate that the pressure of theaccumulator is inversely proportional to the initial volumeThe corresponding rotational speeds of the hydraulic motorare shown in Figure 17 The SOC of the battery is shown inFigure 18 It can be seen that the value of SOC is not changingwith the different initial volume In other words the value ofthe initial volume does not have an effect on the improving ofthe boom energy recovery efficiency

52 Analysis of the Hydraulic Motor The hydraulic motoris used to drive the generator in the boom energy recoverysystem The energy recovery system is determined by theperformance of the motor So it is essential to do someresearch on the hydraulicmotorThedisplacement is themost

0 10 20 30 40 50 60 70 80 90 100100

110

120

130

140

150

Pres

sure

chan

ging

of t

he ac

cum

ulat

or (b

ar)

Time (s)

450L470L

480L500L

Figure 16 Pressure changing of the accumulator

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

4000

4500Ro

tatio

nal s

peed

of t

he m

otor

(rm

in)

Time (s)

450L470L

480L500L

Figure 17 Rotational speed of the hydraulic motor

important parameter of the hydraulic motorThe simulationsof the displacement and the type of the motor are shownbelow

521 The Displacement In order to analyze the influence ofthe different displacement on the energy recovery efficiencyfour values 60mLr 80mLr 100mLr and 120mLr areselected as the displacement of the motor

Figure 19 shows the velocity of the boom cylinder pistonin the hybrid hydraulic excavator Based on the workingprocess of the hydraulic excavator the boom cylinder iscontracting during 52 sndash69 s and 90 sndash100 s The hydraulicmotor is driven by the pressure oil flowing into the returnoil line The result shows that the contracting velocity ofthe cylinder decreases along with the decreasing of the

The Scientific World Journal 11

0 10 20 30 40 50 60 70 80 90 10060

61

62

63

64

65

SOC

of th

e bat

tery

()

Time (s)

450L470L

480L500L

Figure 18 SOC of the battery

0 10 20Time (s)

30 40 50 60 70 80 90 100

000

005

010

015

Velo

city

of t

he b

oom

cylin

der p

iston

(ms

)

minus005

minus010

minus015

60mLr80mLr

100mLr120mLr

Figure 19 Velocity of the boom cylinder piston

displacement However it does not have an effect on thenormal work of the hydraulic excavator

Figures 20 and 21 show the rotational speed of thehydraulic motor and SOC of the battery with the differ-ent displacement According to the characteristics of thehydraulicmotor the rotational speed of themotor is inverselyproportional to the displacement When the displacement is60mLr the SOC of the battery reaches the maximum valueIt indicates that the SOC of the battery increases along withthe decreasing of the displacement

522 The Type of the Hydraulic Motor Because of thecomplex working condition of the hydraulic excavator thevelocity of the boom cylinder piston ranges from 0 to 01msThe flow rate of the pressure in the return oil line ranges

0 10 20 30 40 50 60 70 80 90 1000

1000

2000

3000

4000

5000

6000

7000

Rota

tiona

l spe

ed o

f the

mot

or (r

min

)

Time (s)

60mLr80mLr

100mLr120mLr

Figure 20 Rotational speed of the hydraulic motor

0 10 20 30 40 50 60 70 80 90 10060

61

62

63

64

65

66SO

C of

the b

atte

ry (

)

Time (s)

60mLr80mLr

100mLr120mLr

Figure 21 SOC of the battery

large So it is very important to select the hydraulic motor forimproving the energy recovery system

The hydraulicmotor is divided into the constant displace-ment and variable displacement motor The AMESim modelwith the variable displacement motor is shown in Figure 22

Run the simulation Compared with the models withthe constant displacement motor shown in Figure 6 therotational speed of the hydraulic motor in two simulationmodels is presented in the Figure 23 Figure 24 shows the SOCrange of the battery

It can be seen that the rotational speed of the constantdisplacement motor is ranging between 1300 rmin and3500 rmin during a working cycle while the rotational speedof the variable displacement motor remains at 3000 rminThe SOC of the battery of the constant displacement motorsystem increases from 60 to 648 while the SOC of the

12 The Scientific World Journal

Boom potential recovery system

F

M

Qq

ktimesA B

P T

Fluid

Runstats

properties

Qq

A

P

P

T

MOT

k

k

k

f(X

)X

X

Y timesY lt X

k

s

2

1

3

SM

A

A

P

QP

k

k

ktimes k

s

WT

J WT w

T +

+

T

minus

kPIDminus

+

Figure 22 AMESim model with the variable displacement motor

battery of the variable displacement motor system reaches708 Compared with the constant displacement motorsystem more boom potential energy of the energy recoverysystemwith the variable displacementmotor is recovered andstored in the battery Hence the energy recovery efficiencyof the variable displacement motor system is higher than thesystem with the constant displacement motor

6 Conclusions

(1) Based on the simulation of the working devicesin the conventional hydraulic excavator the energywhich can be recovered of the three cylinders iscalculated Taking the complexity and cost of thesystem into consideration this paper proposed anovel boom potential energy recovery system for theparallel hybrid excavator The boom energy regen-eration unit consists of an accumulator a hydraulicmotor an electric generator and a battery Compared

with the conventional energy recovery system theproposed system makes sure that the generator canrotate continuously in a high speed during a workingcycle The AMESim models of the two boom energyrecovery systems are built and the results show thatthe proposed energy recovery system brings higherenergy recovery efficiency than the conventionalenergy recovery system

(2) The mathematical models of the main compo-nents including boom cylinder hydraulic motorand hydraulic accumulator are built The naturalfrequency of the proposed energy recovery systemis calculated based on the mathematical models Inorder to improve the natural frequency and responsespeed of the system some measures should be takenbased on the expression of the natural frequencysuch as reducing the loop oil volume 119881 the leakage

The Scientific World Journal 13

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

Rota

tiona

l spe

ed o

f the

hyd

raul

ic m

otor

(rm

in)

Constant displacement motor Variable displacement motor

Time (s)

Figure 23 Rotational speed of the hydraulic motor

0 10 20 30 40 50 60 70 80 90 100606162636465666768697071

SOC

of th

e bat

tery

()

Constant displacement motor Variable displacement motor

Time (s)

Figure 24 SOC of the battery

coefficients of the energy recovery system 119862 and thetotal moment of inertia of the hydraulic motor 119869

(3) The influence of the main components includinghydraulic motor and hydraulic accumulator on theenergy recovery efficiency of the proposed systemis analyzed The key parameters of the accumulatorinclude the aeration pressure and the initial volumeThe energy recovery efficiency of the proposed sys-tem can be improving to some extent by increasingthe aeration pressure while changing of the initialvolume does not have an effect on improving of theenergy recovery efficiency

The hydraulic motor is used to drive the generator inthe boom energy recovery system The displacement is themost important parameter of the hydraulicmotorThe energy

recovery efficiency can be improving on the premise ofnormal working by decreasing the displacement of themotorSince the flow rate of the pressure in the return oil line rangeslarge the generator can rotate continuously in a high speedby selecting the variable displacement motor in the return oilline In order to improve the energy efficiency according tothe characteristics of the generator the variable displacementhydraulic motor should be chosen in the return oil line

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work is supported by the Fundamental Research Fundsfor the Central Universities (China University of Mining andTechnology 2014Y05) PCSIRT (IRT1292) and the ProjectFunded by the Priority Academic Program Development ofJiangsu Higher Education Institutions (PAPD)

References

[1] M Kagoshima M Komiyama T Nanjo et al ldquoDevelopment ofnew hybrid excavatorrdquo Kobelco Technology Review no 27 2007

[2] T Nanjo E Imanishi and M Kagcahima ldquoPower simulationfor energy saving in hybrid excavatorrdquo JSAE Transactions vol47 pp 101ndash106 2004

[3] L Weidong S Kaikai L Wei and X Jun ldquoResearch onpotential energy recovery of 16T wheeled hybrid excavatorrdquoin Proceedings of the 2nd International Conference on DigitalManufacturing and Automation (ICDMA rsquo11) pp 996ndash998Zhangjiajie China August 2011

[4] I Y Jong K K Ahn and Q T Dinh ldquoA study on anenergy saving electro-hydraulic excavatorrdquo in Proceedings of theICROS-SICE International Joint Conference (ICCAS-SICE rsquo09)pp 3825ndash3830 Fukuoka Japan August 2009

[5] T H Ho and K K Ahn ldquoDesign and control of a closed-loop hydraulic energy-regenerative systemrdquo Automation inConstruction vol 22 pp 444ndash458 2012

[6] Z Jun J Sheng-jie S Gui-mao et al ldquoDesign of electroniccontrol system of hydraulic excavator with CAN bus andPID methodrdquo Proceedings of the International Conference onIntelligent System Design and Engineering Application (ISDEArsquo10) 2010

[7] T Wang and Q Wang ldquoModeling and control of a novelhydraulic system with energy regenerationrdquo in Proceedings ofthe IEEEASME International Conference on Advanced Intelli-gent Mechatronics (AIM rsquo12) pp 922ndash927 IEEE KachsiungTaiwan July 2012

[8] H SHamut I Dincer andG FNaterer ldquoExergoenvironmentalanalysis of hybrid electric vehicle thermal management sys-temsrdquo Journal of Cleaner Production vol 67 pp 187ndash196 2014

[9] A Poursamad and M Montazeri ldquoDesign of genetic-fuzzycontrol strategy for parallel hybrid electric vehiclesrdquo ControlEngineering Practice vol 16 no 7 pp 861ndash873 2008

[10] S Hui J-H Jiang and W Xin ldquoTorque control strategy fora parallel hydraulic hybrid vehiclerdquo Journal of Terramechanicsvol 46 no 6 pp 259ndash265 2009

14 The Scientific World Journal

[11] Z Cao S Wu M Li and C Du ldquoSeries and parallel hybridsystem performance comparison based on the city bus cyclerdquoin Proceedings of the Asia-Pacific Power and Energy EngineeringConference (APPEEC 09) Wuhan China March 2009

[12] J Gong Q He D Zhang et al ldquoPower system control strategyfor hybrid excavator based on equivalent fuel consumptionrdquo inProceedings of the 9th IEEE International Conference on Mecha-tronics and Automation (ICMA rsquo12) pp 1097ndash1102 ChengduChina August 2012

[13] Z Liu S Liu Z Huang and Q Hu ldquoHydraulic excavatorhybrid power system parameters designrdquo in Proceedings of the2nd International Conference on Digital Manufacturing andAutomation (ICDMA rsquo11) pp 602ndash605 Zhangjiajie ChinaAugust 2011

[14] T Lin Q Wang B Hu and W Gong ldquoResearch on theenergy regeneration systems for hybrid hydraulic excavatorsrdquoAutomation in Construction vol 19 no 8 pp 1016ndash1026 2010

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

The Scientific World Journal 7

F

MOT

Boom potential recovery system

FluidA

SM

A

A

B

P T

P

A

P

PT

Q

M

q

Qq

QP

2

1

3

Runstats

k

k

k

k

f(X

)X

X

Y

times

timesk

k

Y lt Xk

s

ktimes k

s

properties

WT

J WTT +

+

T

minus

Figure 6 AMESim model of the proposed system

5 Analysis of the Main Componentsin the System

As designing the boom energy recovery system of the hybridhydraulic excavator all the components of the system arechosen based on the calculation results and working con-dition However some parameters of the main componentshave a great influence on the energy recovery efficiency of theproposed system Inappropriate parameters will lead to thedecreasing of the efficiency Therefore it is essential to anal-ysis the relationship between the energy recovery efficiencyand the key parameters of the main components like theaeration pressure of the accumulator and the displacement ofthe hydraulic motor In order to simplify the model there arethree assumptions for the simulation models

(1) Since this study concentrates on the effectivenessof the proposed boom energy recovery system theworking performance of the engine is not takeninto consideration The engine is replaced by anelectromotor

(2) The load force and the piston velocity of the boomcylinder in the simulation models are identical withthe conventional hydraulic excavator In other wordsthe boom cylinder system is working under the sameconditions

(3) A generator and a battery are selected as the energyconversion and energy storage units Regardless of theinternal structure of generator and battery the simu-lation models are replaced by the universal models

8 The Scientific World Journal

Conventional boom potential recovery system

F

M

Qq

ktimes

A B

P T

Fluid properties

Runstats

Qq

MOT

k

times

k

k

s

k

f(X

)X

X

YY lt X

A

P T

QP

ktimes k

s

kk

WTJ W

T

+SM

T

+

T

minus

Figure 7 AMESim model of a conventional boom energy recovery system

0 20 40 60 80 100

Boom

cylin

der l

oadi

ng fo

rce (

N)

12 times 106

10 times 106

80 times 105

60 times 105

40 times 105

20 times 105

00

Time (s)

Figure 8 Input load force of the energy saving system

51 Analysis of the Accumulator The key parameters of theaccumulator include the aeration pressure and the initialvolume The simulations of the relationship between theparameter values and the system energy recovery efficiencyare shown below

0 20 40 60 80 100

06

08

10

12

14

16

18

Boom

cylin

der p

iston

disp

lace

men

t (m

)

Time (s)

Conventional energy recovery systemProposed energy recovery system

Figure 9 Piston displacement of the boom cylinder

511 The Aeration Pressure In order to analyze the influenceof the different aeration pressure on the energy recovery

The Scientific World Journal 9

0 10 20 30 40 50 60 70 80 90 100600605610615620625630635640645650655

SOC

of th

e bat

tery

()

Conventional energy recovery systemProposed energy recovery system

Time (s)

Figure 10 SOC of the battery

0 20 40 60 80 100380

400

420

440

460

480

500

Volu

me c

hang

ing

of th

e acc

umul

ator

(L)

Time (s)

5MPa7MPa

9MPa10MPa

Figure 11 Volume changing of the accumulator

efficiency four values 5MPa 7MPa 9MPa and 10MPa areselected within the scope of the aeration pressure Run thesimulation models Figures 11 and 12 present the volume andpressure changing of the accumulator The rotational speedof the hydraulic motor is shown in Figure 13 The SOC of thebattery is shown in Figure 14

Based on the figures above it can be seen that thepressure of the accumulator is proportional to its aerationpressure When the boom cylinder piston is expanding inthe second working cycle the hydraulic motor is driven bythe oil stored in the accumulator The volume changing ofthe pressure oil in the accumulator increases along with theincreasing of the aeration pressure It leads to increasing theflow of the pressure oil in the energy recovery system Thepressure difference between the inlet and outlet of the motoris increasing as well Because of the constant displacement

0 20 40 60 80 100Time (s)

50

60

70

80

90

100

110

120

130

140

150

Pres

sure

chan

ging

of t

he ac

cum

ulat

or (b

ar)

5MPa7MPa

9MPa10MPa

Figure 12 Pressure changing of the accumulator

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

4000

4500Ro

tatio

nal s

peed

of t

he m

otor

(rm

in)

Time (s)

5MPa7MPa

9MPa10MPa

Figure 13 Rotational speed of the hydraulic motor

hydraulic motor the flow rate through the hydraulic motoris proportional to its rotational speed The output torqueof the motor is increasing gradually based on the pressuredifferenceThe generator is connected to the hydraulic motorcoaxially According to the characteristics of the generatorthe output torque of the motor is increasing as well Hencethe electric energy produced by the generator and SOC of thebattery are increasing

512 The Initial Volume In order to analyze the influence ofthe different initial volume on the energy recovery efficiencyfour values 450 L 470 L 480 L and 500 L are selected withinthe scope of the initial volume under the condition that theaeration pressure and the highest working pressure of theaccumulator are keeping in 10MPa and 18MPa

10 The Scientific World Journal

60

61

62

63

64

65

SOC

of th

e bat

tery

()

0 10 20 30 40 50 60 70 80 90 100Time (s)

5MPa7MPa

9MPa10MPa

Figure 14 SOC of the battery

0 10 20 30 40 50 60 70 80 90 100340

360

380

400

420

440

460

480

500

Volu

me c

hang

ing

of th

e acc

umul

ator

(L)

Time (s)

450L470L

480L500L

Figure 15 Volume changing of the accumulator

Figures 15 and 16 show the volume and pressure changingof the accumulator Keeping the aeration pressure unchangedthe simulation results indicate that the pressure of theaccumulator is inversely proportional to the initial volumeThe corresponding rotational speeds of the hydraulic motorare shown in Figure 17 The SOC of the battery is shown inFigure 18 It can be seen that the value of SOC is not changingwith the different initial volume In other words the value ofthe initial volume does not have an effect on the improving ofthe boom energy recovery efficiency

52 Analysis of the Hydraulic Motor The hydraulic motoris used to drive the generator in the boom energy recoverysystem The energy recovery system is determined by theperformance of the motor So it is essential to do someresearch on the hydraulicmotorThedisplacement is themost

0 10 20 30 40 50 60 70 80 90 100100

110

120

130

140

150

Pres

sure

chan

ging

of t

he ac

cum

ulat

or (b

ar)

Time (s)

450L470L

480L500L

Figure 16 Pressure changing of the accumulator

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

4000

4500Ro

tatio

nal s

peed

of t

he m

otor

(rm

in)

Time (s)

450L470L

480L500L

Figure 17 Rotational speed of the hydraulic motor

important parameter of the hydraulic motorThe simulationsof the displacement and the type of the motor are shownbelow

521 The Displacement In order to analyze the influence ofthe different displacement on the energy recovery efficiencyfour values 60mLr 80mLr 100mLr and 120mLr areselected as the displacement of the motor

Figure 19 shows the velocity of the boom cylinder pistonin the hybrid hydraulic excavator Based on the workingprocess of the hydraulic excavator the boom cylinder iscontracting during 52 sndash69 s and 90 sndash100 s The hydraulicmotor is driven by the pressure oil flowing into the returnoil line The result shows that the contracting velocity ofthe cylinder decreases along with the decreasing of the

The Scientific World Journal 11

0 10 20 30 40 50 60 70 80 90 10060

61

62

63

64

65

SOC

of th

e bat

tery

()

Time (s)

450L470L

480L500L

Figure 18 SOC of the battery

0 10 20Time (s)

30 40 50 60 70 80 90 100

000

005

010

015

Velo

city

of t

he b

oom

cylin

der p

iston

(ms

)

minus005

minus010

minus015

60mLr80mLr

100mLr120mLr

Figure 19 Velocity of the boom cylinder piston

displacement However it does not have an effect on thenormal work of the hydraulic excavator

Figures 20 and 21 show the rotational speed of thehydraulic motor and SOC of the battery with the differ-ent displacement According to the characteristics of thehydraulicmotor the rotational speed of themotor is inverselyproportional to the displacement When the displacement is60mLr the SOC of the battery reaches the maximum valueIt indicates that the SOC of the battery increases along withthe decreasing of the displacement

522 The Type of the Hydraulic Motor Because of thecomplex working condition of the hydraulic excavator thevelocity of the boom cylinder piston ranges from 0 to 01msThe flow rate of the pressure in the return oil line ranges

0 10 20 30 40 50 60 70 80 90 1000

1000

2000

3000

4000

5000

6000

7000

Rota

tiona

l spe

ed o

f the

mot

or (r

min

)

Time (s)

60mLr80mLr

100mLr120mLr

Figure 20 Rotational speed of the hydraulic motor

0 10 20 30 40 50 60 70 80 90 10060

61

62

63

64

65

66SO

C of

the b

atte

ry (

)

Time (s)

60mLr80mLr

100mLr120mLr

Figure 21 SOC of the battery

large So it is very important to select the hydraulic motor forimproving the energy recovery system

The hydraulicmotor is divided into the constant displace-ment and variable displacement motor The AMESim modelwith the variable displacement motor is shown in Figure 22

Run the simulation Compared with the models withthe constant displacement motor shown in Figure 6 therotational speed of the hydraulic motor in two simulationmodels is presented in the Figure 23 Figure 24 shows the SOCrange of the battery

It can be seen that the rotational speed of the constantdisplacement motor is ranging between 1300 rmin and3500 rmin during a working cycle while the rotational speedof the variable displacement motor remains at 3000 rminThe SOC of the battery of the constant displacement motorsystem increases from 60 to 648 while the SOC of the

12 The Scientific World Journal

Boom potential recovery system

F

M

Qq

ktimesA B

P T

Fluid

Runstats

properties

Qq

A

P

P

T

MOT

k

k

k

f(X

)X

X

Y timesY lt X

k

s

2

1

3

SM

A

A

P

QP

k

k

ktimes k

s

WT

J WT w

T +

+

T

minus

kPIDminus

+

Figure 22 AMESim model with the variable displacement motor

battery of the variable displacement motor system reaches708 Compared with the constant displacement motorsystem more boom potential energy of the energy recoverysystemwith the variable displacementmotor is recovered andstored in the battery Hence the energy recovery efficiencyof the variable displacement motor system is higher than thesystem with the constant displacement motor

6 Conclusions

(1) Based on the simulation of the working devicesin the conventional hydraulic excavator the energywhich can be recovered of the three cylinders iscalculated Taking the complexity and cost of thesystem into consideration this paper proposed anovel boom potential energy recovery system for theparallel hybrid excavator The boom energy regen-eration unit consists of an accumulator a hydraulicmotor an electric generator and a battery Compared

with the conventional energy recovery system theproposed system makes sure that the generator canrotate continuously in a high speed during a workingcycle The AMESim models of the two boom energyrecovery systems are built and the results show thatthe proposed energy recovery system brings higherenergy recovery efficiency than the conventionalenergy recovery system

(2) The mathematical models of the main compo-nents including boom cylinder hydraulic motorand hydraulic accumulator are built The naturalfrequency of the proposed energy recovery systemis calculated based on the mathematical models Inorder to improve the natural frequency and responsespeed of the system some measures should be takenbased on the expression of the natural frequencysuch as reducing the loop oil volume 119881 the leakage

The Scientific World Journal 13

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

Rota

tiona

l spe

ed o

f the

hyd

raul

ic m

otor

(rm

in)

Constant displacement motor Variable displacement motor

Time (s)

Figure 23 Rotational speed of the hydraulic motor

0 10 20 30 40 50 60 70 80 90 100606162636465666768697071

SOC

of th

e bat

tery

()

Constant displacement motor Variable displacement motor

Time (s)

Figure 24 SOC of the battery

coefficients of the energy recovery system 119862 and thetotal moment of inertia of the hydraulic motor 119869

(3) The influence of the main components includinghydraulic motor and hydraulic accumulator on theenergy recovery efficiency of the proposed systemis analyzed The key parameters of the accumulatorinclude the aeration pressure and the initial volumeThe energy recovery efficiency of the proposed sys-tem can be improving to some extent by increasingthe aeration pressure while changing of the initialvolume does not have an effect on improving of theenergy recovery efficiency

The hydraulic motor is used to drive the generator inthe boom energy recovery system The displacement is themost important parameter of the hydraulicmotorThe energy

recovery efficiency can be improving on the premise ofnormal working by decreasing the displacement of themotorSince the flow rate of the pressure in the return oil line rangeslarge the generator can rotate continuously in a high speedby selecting the variable displacement motor in the return oilline In order to improve the energy efficiency according tothe characteristics of the generator the variable displacementhydraulic motor should be chosen in the return oil line

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work is supported by the Fundamental Research Fundsfor the Central Universities (China University of Mining andTechnology 2014Y05) PCSIRT (IRT1292) and the ProjectFunded by the Priority Academic Program Development ofJiangsu Higher Education Institutions (PAPD)

References

[1] M Kagoshima M Komiyama T Nanjo et al ldquoDevelopment ofnew hybrid excavatorrdquo Kobelco Technology Review no 27 2007

[2] T Nanjo E Imanishi and M Kagcahima ldquoPower simulationfor energy saving in hybrid excavatorrdquo JSAE Transactions vol47 pp 101ndash106 2004

[3] L Weidong S Kaikai L Wei and X Jun ldquoResearch onpotential energy recovery of 16T wheeled hybrid excavatorrdquoin Proceedings of the 2nd International Conference on DigitalManufacturing and Automation (ICDMA rsquo11) pp 996ndash998Zhangjiajie China August 2011

[4] I Y Jong K K Ahn and Q T Dinh ldquoA study on anenergy saving electro-hydraulic excavatorrdquo in Proceedings of theICROS-SICE International Joint Conference (ICCAS-SICE rsquo09)pp 3825ndash3830 Fukuoka Japan August 2009

[5] T H Ho and K K Ahn ldquoDesign and control of a closed-loop hydraulic energy-regenerative systemrdquo Automation inConstruction vol 22 pp 444ndash458 2012

[6] Z Jun J Sheng-jie S Gui-mao et al ldquoDesign of electroniccontrol system of hydraulic excavator with CAN bus andPID methodrdquo Proceedings of the International Conference onIntelligent System Design and Engineering Application (ISDEArsquo10) 2010

[7] T Wang and Q Wang ldquoModeling and control of a novelhydraulic system with energy regenerationrdquo in Proceedings ofthe IEEEASME International Conference on Advanced Intelli-gent Mechatronics (AIM rsquo12) pp 922ndash927 IEEE KachsiungTaiwan July 2012

[8] H SHamut I Dincer andG FNaterer ldquoExergoenvironmentalanalysis of hybrid electric vehicle thermal management sys-temsrdquo Journal of Cleaner Production vol 67 pp 187ndash196 2014

[9] A Poursamad and M Montazeri ldquoDesign of genetic-fuzzycontrol strategy for parallel hybrid electric vehiclesrdquo ControlEngineering Practice vol 16 no 7 pp 861ndash873 2008

[10] S Hui J-H Jiang and W Xin ldquoTorque control strategy fora parallel hydraulic hybrid vehiclerdquo Journal of Terramechanicsvol 46 no 6 pp 259ndash265 2009

14 The Scientific World Journal

[11] Z Cao S Wu M Li and C Du ldquoSeries and parallel hybridsystem performance comparison based on the city bus cyclerdquoin Proceedings of the Asia-Pacific Power and Energy EngineeringConference (APPEEC 09) Wuhan China March 2009

[12] J Gong Q He D Zhang et al ldquoPower system control strategyfor hybrid excavator based on equivalent fuel consumptionrdquo inProceedings of the 9th IEEE International Conference on Mecha-tronics and Automation (ICMA rsquo12) pp 1097ndash1102 ChengduChina August 2012

[13] Z Liu S Liu Z Huang and Q Hu ldquoHydraulic excavatorhybrid power system parameters designrdquo in Proceedings of the2nd International Conference on Digital Manufacturing andAutomation (ICDMA rsquo11) pp 602ndash605 Zhangjiajie ChinaAugust 2011

[14] T Lin Q Wang B Hu and W Gong ldquoResearch on theenergy regeneration systems for hybrid hydraulic excavatorsrdquoAutomation in Construction vol 19 no 8 pp 1016ndash1026 2010

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

8 The Scientific World Journal

Conventional boom potential recovery system

F

M

Qq

ktimes

A B

P T

Fluid properties

Runstats

Qq

MOT

k

times

k

k

s

k

f(X

)X

X

YY lt X

A

P T

QP

ktimes k

s

kk

WTJ W

T

+SM

T

+

T

minus

Figure 7 AMESim model of a conventional boom energy recovery system

0 20 40 60 80 100

Boom

cylin

der l

oadi

ng fo

rce (

N)

12 times 106

10 times 106

80 times 105

60 times 105

40 times 105

20 times 105

00

Time (s)

Figure 8 Input load force of the energy saving system

51 Analysis of the Accumulator The key parameters of theaccumulator include the aeration pressure and the initialvolume The simulations of the relationship between theparameter values and the system energy recovery efficiencyare shown below

0 20 40 60 80 100

06

08

10

12

14

16

18

Boom

cylin

der p

iston

disp

lace

men

t (m

)

Time (s)

Conventional energy recovery systemProposed energy recovery system

Figure 9 Piston displacement of the boom cylinder

511 The Aeration Pressure In order to analyze the influenceof the different aeration pressure on the energy recovery

The Scientific World Journal 9

0 10 20 30 40 50 60 70 80 90 100600605610615620625630635640645650655

SOC

of th

e bat

tery

()

Conventional energy recovery systemProposed energy recovery system

Time (s)

Figure 10 SOC of the battery

0 20 40 60 80 100380

400

420

440

460

480

500

Volu

me c

hang

ing

of th

e acc

umul

ator

(L)

Time (s)

5MPa7MPa

9MPa10MPa

Figure 11 Volume changing of the accumulator

efficiency four values 5MPa 7MPa 9MPa and 10MPa areselected within the scope of the aeration pressure Run thesimulation models Figures 11 and 12 present the volume andpressure changing of the accumulator The rotational speedof the hydraulic motor is shown in Figure 13 The SOC of thebattery is shown in Figure 14

Based on the figures above it can be seen that thepressure of the accumulator is proportional to its aerationpressure When the boom cylinder piston is expanding inthe second working cycle the hydraulic motor is driven bythe oil stored in the accumulator The volume changing ofthe pressure oil in the accumulator increases along with theincreasing of the aeration pressure It leads to increasing theflow of the pressure oil in the energy recovery system Thepressure difference between the inlet and outlet of the motoris increasing as well Because of the constant displacement

0 20 40 60 80 100Time (s)

50

60

70

80

90

100

110

120

130

140

150

Pres

sure

chan

ging

of t

he ac

cum

ulat

or (b

ar)

5MPa7MPa

9MPa10MPa

Figure 12 Pressure changing of the accumulator

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

4000

4500Ro

tatio

nal s

peed

of t

he m

otor

(rm

in)

Time (s)

5MPa7MPa

9MPa10MPa

Figure 13 Rotational speed of the hydraulic motor

hydraulic motor the flow rate through the hydraulic motoris proportional to its rotational speed The output torqueof the motor is increasing gradually based on the pressuredifferenceThe generator is connected to the hydraulic motorcoaxially According to the characteristics of the generatorthe output torque of the motor is increasing as well Hencethe electric energy produced by the generator and SOC of thebattery are increasing

512 The Initial Volume In order to analyze the influence ofthe different initial volume on the energy recovery efficiencyfour values 450 L 470 L 480 L and 500 L are selected withinthe scope of the initial volume under the condition that theaeration pressure and the highest working pressure of theaccumulator are keeping in 10MPa and 18MPa

10 The Scientific World Journal

60

61

62

63

64

65

SOC

of th

e bat

tery

()

0 10 20 30 40 50 60 70 80 90 100Time (s)

5MPa7MPa

9MPa10MPa

Figure 14 SOC of the battery

0 10 20 30 40 50 60 70 80 90 100340

360

380

400

420

440

460

480

500

Volu

me c

hang

ing

of th

e acc

umul

ator

(L)

Time (s)

450L470L

480L500L

Figure 15 Volume changing of the accumulator

Figures 15 and 16 show the volume and pressure changingof the accumulator Keeping the aeration pressure unchangedthe simulation results indicate that the pressure of theaccumulator is inversely proportional to the initial volumeThe corresponding rotational speeds of the hydraulic motorare shown in Figure 17 The SOC of the battery is shown inFigure 18 It can be seen that the value of SOC is not changingwith the different initial volume In other words the value ofthe initial volume does not have an effect on the improving ofthe boom energy recovery efficiency

52 Analysis of the Hydraulic Motor The hydraulic motoris used to drive the generator in the boom energy recoverysystem The energy recovery system is determined by theperformance of the motor So it is essential to do someresearch on the hydraulicmotorThedisplacement is themost

0 10 20 30 40 50 60 70 80 90 100100

110

120

130

140

150

Pres

sure

chan

ging

of t

he ac

cum

ulat

or (b

ar)

Time (s)

450L470L

480L500L

Figure 16 Pressure changing of the accumulator

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

4000

4500Ro

tatio

nal s

peed

of t

he m

otor

(rm

in)

Time (s)

450L470L

480L500L

Figure 17 Rotational speed of the hydraulic motor

important parameter of the hydraulic motorThe simulationsof the displacement and the type of the motor are shownbelow

521 The Displacement In order to analyze the influence ofthe different displacement on the energy recovery efficiencyfour values 60mLr 80mLr 100mLr and 120mLr areselected as the displacement of the motor

Figure 19 shows the velocity of the boom cylinder pistonin the hybrid hydraulic excavator Based on the workingprocess of the hydraulic excavator the boom cylinder iscontracting during 52 sndash69 s and 90 sndash100 s The hydraulicmotor is driven by the pressure oil flowing into the returnoil line The result shows that the contracting velocity ofthe cylinder decreases along with the decreasing of the

The Scientific World Journal 11

0 10 20 30 40 50 60 70 80 90 10060

61

62

63

64

65

SOC

of th

e bat

tery

()

Time (s)

450L470L

480L500L

Figure 18 SOC of the battery

0 10 20Time (s)

30 40 50 60 70 80 90 100

000

005

010

015

Velo

city

of t

he b

oom

cylin

der p

iston

(ms

)

minus005

minus010

minus015

60mLr80mLr

100mLr120mLr

Figure 19 Velocity of the boom cylinder piston

displacement However it does not have an effect on thenormal work of the hydraulic excavator

Figures 20 and 21 show the rotational speed of thehydraulic motor and SOC of the battery with the differ-ent displacement According to the characteristics of thehydraulicmotor the rotational speed of themotor is inverselyproportional to the displacement When the displacement is60mLr the SOC of the battery reaches the maximum valueIt indicates that the SOC of the battery increases along withthe decreasing of the displacement

522 The Type of the Hydraulic Motor Because of thecomplex working condition of the hydraulic excavator thevelocity of the boom cylinder piston ranges from 0 to 01msThe flow rate of the pressure in the return oil line ranges

0 10 20 30 40 50 60 70 80 90 1000

1000

2000

3000

4000

5000

6000

7000

Rota

tiona

l spe

ed o

f the

mot

or (r

min

)

Time (s)

60mLr80mLr

100mLr120mLr

Figure 20 Rotational speed of the hydraulic motor

0 10 20 30 40 50 60 70 80 90 10060

61

62

63

64

65

66SO

C of

the b

atte

ry (

)

Time (s)

60mLr80mLr

100mLr120mLr

Figure 21 SOC of the battery

large So it is very important to select the hydraulic motor forimproving the energy recovery system

The hydraulicmotor is divided into the constant displace-ment and variable displacement motor The AMESim modelwith the variable displacement motor is shown in Figure 22

Run the simulation Compared with the models withthe constant displacement motor shown in Figure 6 therotational speed of the hydraulic motor in two simulationmodels is presented in the Figure 23 Figure 24 shows the SOCrange of the battery

It can be seen that the rotational speed of the constantdisplacement motor is ranging between 1300 rmin and3500 rmin during a working cycle while the rotational speedof the variable displacement motor remains at 3000 rminThe SOC of the battery of the constant displacement motorsystem increases from 60 to 648 while the SOC of the

12 The Scientific World Journal

Boom potential recovery system

F

M

Qq

ktimesA B

P T

Fluid

Runstats

properties

Qq

A

P

P

T

MOT

k

k

k

f(X

)X

X

Y timesY lt X

k

s

2

1

3

SM

A

A

P

QP

k

k

ktimes k

s

WT

J WT w

T +

+

T

minus

kPIDminus

+

Figure 22 AMESim model with the variable displacement motor

battery of the variable displacement motor system reaches708 Compared with the constant displacement motorsystem more boom potential energy of the energy recoverysystemwith the variable displacementmotor is recovered andstored in the battery Hence the energy recovery efficiencyof the variable displacement motor system is higher than thesystem with the constant displacement motor

6 Conclusions

(1) Based on the simulation of the working devicesin the conventional hydraulic excavator the energywhich can be recovered of the three cylinders iscalculated Taking the complexity and cost of thesystem into consideration this paper proposed anovel boom potential energy recovery system for theparallel hybrid excavator The boom energy regen-eration unit consists of an accumulator a hydraulicmotor an electric generator and a battery Compared

with the conventional energy recovery system theproposed system makes sure that the generator canrotate continuously in a high speed during a workingcycle The AMESim models of the two boom energyrecovery systems are built and the results show thatthe proposed energy recovery system brings higherenergy recovery efficiency than the conventionalenergy recovery system

(2) The mathematical models of the main compo-nents including boom cylinder hydraulic motorand hydraulic accumulator are built The naturalfrequency of the proposed energy recovery systemis calculated based on the mathematical models Inorder to improve the natural frequency and responsespeed of the system some measures should be takenbased on the expression of the natural frequencysuch as reducing the loop oil volume 119881 the leakage

The Scientific World Journal 13

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

Rota

tiona

l spe

ed o

f the

hyd

raul

ic m

otor

(rm

in)

Constant displacement motor Variable displacement motor

Time (s)

Figure 23 Rotational speed of the hydraulic motor

0 10 20 30 40 50 60 70 80 90 100606162636465666768697071

SOC

of th

e bat

tery

()

Constant displacement motor Variable displacement motor

Time (s)

Figure 24 SOC of the battery

coefficients of the energy recovery system 119862 and thetotal moment of inertia of the hydraulic motor 119869

(3) The influence of the main components includinghydraulic motor and hydraulic accumulator on theenergy recovery efficiency of the proposed systemis analyzed The key parameters of the accumulatorinclude the aeration pressure and the initial volumeThe energy recovery efficiency of the proposed sys-tem can be improving to some extent by increasingthe aeration pressure while changing of the initialvolume does not have an effect on improving of theenergy recovery efficiency

The hydraulic motor is used to drive the generator inthe boom energy recovery system The displacement is themost important parameter of the hydraulicmotorThe energy

recovery efficiency can be improving on the premise ofnormal working by decreasing the displacement of themotorSince the flow rate of the pressure in the return oil line rangeslarge the generator can rotate continuously in a high speedby selecting the variable displacement motor in the return oilline In order to improve the energy efficiency according tothe characteristics of the generator the variable displacementhydraulic motor should be chosen in the return oil line

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work is supported by the Fundamental Research Fundsfor the Central Universities (China University of Mining andTechnology 2014Y05) PCSIRT (IRT1292) and the ProjectFunded by the Priority Academic Program Development ofJiangsu Higher Education Institutions (PAPD)

References

[1] M Kagoshima M Komiyama T Nanjo et al ldquoDevelopment ofnew hybrid excavatorrdquo Kobelco Technology Review no 27 2007

[2] T Nanjo E Imanishi and M Kagcahima ldquoPower simulationfor energy saving in hybrid excavatorrdquo JSAE Transactions vol47 pp 101ndash106 2004

[3] L Weidong S Kaikai L Wei and X Jun ldquoResearch onpotential energy recovery of 16T wheeled hybrid excavatorrdquoin Proceedings of the 2nd International Conference on DigitalManufacturing and Automation (ICDMA rsquo11) pp 996ndash998Zhangjiajie China August 2011

[4] I Y Jong K K Ahn and Q T Dinh ldquoA study on anenergy saving electro-hydraulic excavatorrdquo in Proceedings of theICROS-SICE International Joint Conference (ICCAS-SICE rsquo09)pp 3825ndash3830 Fukuoka Japan August 2009

[5] T H Ho and K K Ahn ldquoDesign and control of a closed-loop hydraulic energy-regenerative systemrdquo Automation inConstruction vol 22 pp 444ndash458 2012

[6] Z Jun J Sheng-jie S Gui-mao et al ldquoDesign of electroniccontrol system of hydraulic excavator with CAN bus andPID methodrdquo Proceedings of the International Conference onIntelligent System Design and Engineering Application (ISDEArsquo10) 2010

[7] T Wang and Q Wang ldquoModeling and control of a novelhydraulic system with energy regenerationrdquo in Proceedings ofthe IEEEASME International Conference on Advanced Intelli-gent Mechatronics (AIM rsquo12) pp 922ndash927 IEEE KachsiungTaiwan July 2012

[8] H SHamut I Dincer andG FNaterer ldquoExergoenvironmentalanalysis of hybrid electric vehicle thermal management sys-temsrdquo Journal of Cleaner Production vol 67 pp 187ndash196 2014

[9] A Poursamad and M Montazeri ldquoDesign of genetic-fuzzycontrol strategy for parallel hybrid electric vehiclesrdquo ControlEngineering Practice vol 16 no 7 pp 861ndash873 2008

[10] S Hui J-H Jiang and W Xin ldquoTorque control strategy fora parallel hydraulic hybrid vehiclerdquo Journal of Terramechanicsvol 46 no 6 pp 259ndash265 2009

14 The Scientific World Journal

[11] Z Cao S Wu M Li and C Du ldquoSeries and parallel hybridsystem performance comparison based on the city bus cyclerdquoin Proceedings of the Asia-Pacific Power and Energy EngineeringConference (APPEEC 09) Wuhan China March 2009

[12] J Gong Q He D Zhang et al ldquoPower system control strategyfor hybrid excavator based on equivalent fuel consumptionrdquo inProceedings of the 9th IEEE International Conference on Mecha-tronics and Automation (ICMA rsquo12) pp 1097ndash1102 ChengduChina August 2012

[13] Z Liu S Liu Z Huang and Q Hu ldquoHydraulic excavatorhybrid power system parameters designrdquo in Proceedings of the2nd International Conference on Digital Manufacturing andAutomation (ICDMA rsquo11) pp 602ndash605 Zhangjiajie ChinaAugust 2011

[14] T Lin Q Wang B Hu and W Gong ldquoResearch on theenergy regeneration systems for hybrid hydraulic excavatorsrdquoAutomation in Construction vol 19 no 8 pp 1016ndash1026 2010

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

The Scientific World Journal 9

0 10 20 30 40 50 60 70 80 90 100600605610615620625630635640645650655

SOC

of th

e bat

tery

()

Conventional energy recovery systemProposed energy recovery system

Time (s)

Figure 10 SOC of the battery

0 20 40 60 80 100380

400

420

440

460

480

500

Volu

me c

hang

ing

of th

e acc

umul

ator

(L)

Time (s)

5MPa7MPa

9MPa10MPa

Figure 11 Volume changing of the accumulator

efficiency four values 5MPa 7MPa 9MPa and 10MPa areselected within the scope of the aeration pressure Run thesimulation models Figures 11 and 12 present the volume andpressure changing of the accumulator The rotational speedof the hydraulic motor is shown in Figure 13 The SOC of thebattery is shown in Figure 14

Based on the figures above it can be seen that thepressure of the accumulator is proportional to its aerationpressure When the boom cylinder piston is expanding inthe second working cycle the hydraulic motor is driven bythe oil stored in the accumulator The volume changing ofthe pressure oil in the accumulator increases along with theincreasing of the aeration pressure It leads to increasing theflow of the pressure oil in the energy recovery system Thepressure difference between the inlet and outlet of the motoris increasing as well Because of the constant displacement

0 20 40 60 80 100Time (s)

50

60

70

80

90

100

110

120

130

140

150

Pres

sure

chan

ging

of t

he ac

cum

ulat

or (b

ar)

5MPa7MPa

9MPa10MPa

Figure 12 Pressure changing of the accumulator

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

4000

4500Ro

tatio

nal s

peed

of t

he m

otor

(rm

in)

Time (s)

5MPa7MPa

9MPa10MPa

Figure 13 Rotational speed of the hydraulic motor

hydraulic motor the flow rate through the hydraulic motoris proportional to its rotational speed The output torqueof the motor is increasing gradually based on the pressuredifferenceThe generator is connected to the hydraulic motorcoaxially According to the characteristics of the generatorthe output torque of the motor is increasing as well Hencethe electric energy produced by the generator and SOC of thebattery are increasing

512 The Initial Volume In order to analyze the influence ofthe different initial volume on the energy recovery efficiencyfour values 450 L 470 L 480 L and 500 L are selected withinthe scope of the initial volume under the condition that theaeration pressure and the highest working pressure of theaccumulator are keeping in 10MPa and 18MPa

10 The Scientific World Journal

60

61

62

63

64

65

SOC

of th

e bat

tery

()

0 10 20 30 40 50 60 70 80 90 100Time (s)

5MPa7MPa

9MPa10MPa

Figure 14 SOC of the battery

0 10 20 30 40 50 60 70 80 90 100340

360

380

400

420

440

460

480

500

Volu

me c

hang

ing

of th

e acc

umul

ator

(L)

Time (s)

450L470L

480L500L

Figure 15 Volume changing of the accumulator

Figures 15 and 16 show the volume and pressure changingof the accumulator Keeping the aeration pressure unchangedthe simulation results indicate that the pressure of theaccumulator is inversely proportional to the initial volumeThe corresponding rotational speeds of the hydraulic motorare shown in Figure 17 The SOC of the battery is shown inFigure 18 It can be seen that the value of SOC is not changingwith the different initial volume In other words the value ofthe initial volume does not have an effect on the improving ofthe boom energy recovery efficiency

52 Analysis of the Hydraulic Motor The hydraulic motoris used to drive the generator in the boom energy recoverysystem The energy recovery system is determined by theperformance of the motor So it is essential to do someresearch on the hydraulicmotorThedisplacement is themost

0 10 20 30 40 50 60 70 80 90 100100

110

120

130

140

150

Pres

sure

chan

ging

of t

he ac

cum

ulat

or (b

ar)

Time (s)

450L470L

480L500L

Figure 16 Pressure changing of the accumulator

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

4000

4500Ro

tatio

nal s

peed

of t

he m

otor

(rm

in)

Time (s)

450L470L

480L500L

Figure 17 Rotational speed of the hydraulic motor

important parameter of the hydraulic motorThe simulationsof the displacement and the type of the motor are shownbelow

521 The Displacement In order to analyze the influence ofthe different displacement on the energy recovery efficiencyfour values 60mLr 80mLr 100mLr and 120mLr areselected as the displacement of the motor

Figure 19 shows the velocity of the boom cylinder pistonin the hybrid hydraulic excavator Based on the workingprocess of the hydraulic excavator the boom cylinder iscontracting during 52 sndash69 s and 90 sndash100 s The hydraulicmotor is driven by the pressure oil flowing into the returnoil line The result shows that the contracting velocity ofthe cylinder decreases along with the decreasing of the

The Scientific World Journal 11

0 10 20 30 40 50 60 70 80 90 10060

61

62

63

64

65

SOC

of th

e bat

tery

()

Time (s)

450L470L

480L500L

Figure 18 SOC of the battery

0 10 20Time (s)

30 40 50 60 70 80 90 100

000

005

010

015

Velo

city

of t

he b

oom

cylin

der p

iston

(ms

)

minus005

minus010

minus015

60mLr80mLr

100mLr120mLr

Figure 19 Velocity of the boom cylinder piston

displacement However it does not have an effect on thenormal work of the hydraulic excavator

Figures 20 and 21 show the rotational speed of thehydraulic motor and SOC of the battery with the differ-ent displacement According to the characteristics of thehydraulicmotor the rotational speed of themotor is inverselyproportional to the displacement When the displacement is60mLr the SOC of the battery reaches the maximum valueIt indicates that the SOC of the battery increases along withthe decreasing of the displacement

522 The Type of the Hydraulic Motor Because of thecomplex working condition of the hydraulic excavator thevelocity of the boom cylinder piston ranges from 0 to 01msThe flow rate of the pressure in the return oil line ranges

0 10 20 30 40 50 60 70 80 90 1000

1000

2000

3000

4000

5000

6000

7000

Rota

tiona

l spe

ed o

f the

mot

or (r

min

)

Time (s)

60mLr80mLr

100mLr120mLr

Figure 20 Rotational speed of the hydraulic motor

0 10 20 30 40 50 60 70 80 90 10060

61

62

63

64

65

66SO

C of

the b

atte

ry (

)

Time (s)

60mLr80mLr

100mLr120mLr

Figure 21 SOC of the battery

large So it is very important to select the hydraulic motor forimproving the energy recovery system

The hydraulicmotor is divided into the constant displace-ment and variable displacement motor The AMESim modelwith the variable displacement motor is shown in Figure 22

Run the simulation Compared with the models withthe constant displacement motor shown in Figure 6 therotational speed of the hydraulic motor in two simulationmodels is presented in the Figure 23 Figure 24 shows the SOCrange of the battery

It can be seen that the rotational speed of the constantdisplacement motor is ranging between 1300 rmin and3500 rmin during a working cycle while the rotational speedof the variable displacement motor remains at 3000 rminThe SOC of the battery of the constant displacement motorsystem increases from 60 to 648 while the SOC of the

12 The Scientific World Journal

Boom potential recovery system

F

M

Qq

ktimesA B

P T

Fluid

Runstats

properties

Qq

A

P

P

T

MOT

k

k

k

f(X

)X

X

Y timesY lt X

k

s

2

1

3

SM

A

A

P

QP

k

k

ktimes k

s

WT

J WT w

T +

+

T

minus

kPIDminus

+

Figure 22 AMESim model with the variable displacement motor

battery of the variable displacement motor system reaches708 Compared with the constant displacement motorsystem more boom potential energy of the energy recoverysystemwith the variable displacementmotor is recovered andstored in the battery Hence the energy recovery efficiencyof the variable displacement motor system is higher than thesystem with the constant displacement motor

6 Conclusions

(1) Based on the simulation of the working devicesin the conventional hydraulic excavator the energywhich can be recovered of the three cylinders iscalculated Taking the complexity and cost of thesystem into consideration this paper proposed anovel boom potential energy recovery system for theparallel hybrid excavator The boom energy regen-eration unit consists of an accumulator a hydraulicmotor an electric generator and a battery Compared

with the conventional energy recovery system theproposed system makes sure that the generator canrotate continuously in a high speed during a workingcycle The AMESim models of the two boom energyrecovery systems are built and the results show thatthe proposed energy recovery system brings higherenergy recovery efficiency than the conventionalenergy recovery system

(2) The mathematical models of the main compo-nents including boom cylinder hydraulic motorand hydraulic accumulator are built The naturalfrequency of the proposed energy recovery systemis calculated based on the mathematical models Inorder to improve the natural frequency and responsespeed of the system some measures should be takenbased on the expression of the natural frequencysuch as reducing the loop oil volume 119881 the leakage

The Scientific World Journal 13

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

Rota

tiona

l spe

ed o

f the

hyd

raul

ic m

otor

(rm

in)

Constant displacement motor Variable displacement motor

Time (s)

Figure 23 Rotational speed of the hydraulic motor

0 10 20 30 40 50 60 70 80 90 100606162636465666768697071

SOC

of th

e bat

tery

()

Constant displacement motor Variable displacement motor

Time (s)

Figure 24 SOC of the battery

coefficients of the energy recovery system 119862 and thetotal moment of inertia of the hydraulic motor 119869

(3) The influence of the main components includinghydraulic motor and hydraulic accumulator on theenergy recovery efficiency of the proposed systemis analyzed The key parameters of the accumulatorinclude the aeration pressure and the initial volumeThe energy recovery efficiency of the proposed sys-tem can be improving to some extent by increasingthe aeration pressure while changing of the initialvolume does not have an effect on improving of theenergy recovery efficiency

The hydraulic motor is used to drive the generator inthe boom energy recovery system The displacement is themost important parameter of the hydraulicmotorThe energy

recovery efficiency can be improving on the premise ofnormal working by decreasing the displacement of themotorSince the flow rate of the pressure in the return oil line rangeslarge the generator can rotate continuously in a high speedby selecting the variable displacement motor in the return oilline In order to improve the energy efficiency according tothe characteristics of the generator the variable displacementhydraulic motor should be chosen in the return oil line

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work is supported by the Fundamental Research Fundsfor the Central Universities (China University of Mining andTechnology 2014Y05) PCSIRT (IRT1292) and the ProjectFunded by the Priority Academic Program Development ofJiangsu Higher Education Institutions (PAPD)

References

[1] M Kagoshima M Komiyama T Nanjo et al ldquoDevelopment ofnew hybrid excavatorrdquo Kobelco Technology Review no 27 2007

[2] T Nanjo E Imanishi and M Kagcahima ldquoPower simulationfor energy saving in hybrid excavatorrdquo JSAE Transactions vol47 pp 101ndash106 2004

[3] L Weidong S Kaikai L Wei and X Jun ldquoResearch onpotential energy recovery of 16T wheeled hybrid excavatorrdquoin Proceedings of the 2nd International Conference on DigitalManufacturing and Automation (ICDMA rsquo11) pp 996ndash998Zhangjiajie China August 2011

[4] I Y Jong K K Ahn and Q T Dinh ldquoA study on anenergy saving electro-hydraulic excavatorrdquo in Proceedings of theICROS-SICE International Joint Conference (ICCAS-SICE rsquo09)pp 3825ndash3830 Fukuoka Japan August 2009

[5] T H Ho and K K Ahn ldquoDesign and control of a closed-loop hydraulic energy-regenerative systemrdquo Automation inConstruction vol 22 pp 444ndash458 2012

[6] Z Jun J Sheng-jie S Gui-mao et al ldquoDesign of electroniccontrol system of hydraulic excavator with CAN bus andPID methodrdquo Proceedings of the International Conference onIntelligent System Design and Engineering Application (ISDEArsquo10) 2010

[7] T Wang and Q Wang ldquoModeling and control of a novelhydraulic system with energy regenerationrdquo in Proceedings ofthe IEEEASME International Conference on Advanced Intelli-gent Mechatronics (AIM rsquo12) pp 922ndash927 IEEE KachsiungTaiwan July 2012

[8] H SHamut I Dincer andG FNaterer ldquoExergoenvironmentalanalysis of hybrid electric vehicle thermal management sys-temsrdquo Journal of Cleaner Production vol 67 pp 187ndash196 2014

[9] A Poursamad and M Montazeri ldquoDesign of genetic-fuzzycontrol strategy for parallel hybrid electric vehiclesrdquo ControlEngineering Practice vol 16 no 7 pp 861ndash873 2008

[10] S Hui J-H Jiang and W Xin ldquoTorque control strategy fora parallel hydraulic hybrid vehiclerdquo Journal of Terramechanicsvol 46 no 6 pp 259ndash265 2009

14 The Scientific World Journal

[11] Z Cao S Wu M Li and C Du ldquoSeries and parallel hybridsystem performance comparison based on the city bus cyclerdquoin Proceedings of the Asia-Pacific Power and Energy EngineeringConference (APPEEC 09) Wuhan China March 2009

[12] J Gong Q He D Zhang et al ldquoPower system control strategyfor hybrid excavator based on equivalent fuel consumptionrdquo inProceedings of the 9th IEEE International Conference on Mecha-tronics and Automation (ICMA rsquo12) pp 1097ndash1102 ChengduChina August 2012

[13] Z Liu S Liu Z Huang and Q Hu ldquoHydraulic excavatorhybrid power system parameters designrdquo in Proceedings of the2nd International Conference on Digital Manufacturing andAutomation (ICDMA rsquo11) pp 602ndash605 Zhangjiajie ChinaAugust 2011

[14] T Lin Q Wang B Hu and W Gong ldquoResearch on theenergy regeneration systems for hybrid hydraulic excavatorsrdquoAutomation in Construction vol 19 no 8 pp 1016ndash1026 2010

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

10 The Scientific World Journal

60

61

62

63

64

65

SOC

of th

e bat

tery

()

0 10 20 30 40 50 60 70 80 90 100Time (s)

5MPa7MPa

9MPa10MPa

Figure 14 SOC of the battery

0 10 20 30 40 50 60 70 80 90 100340

360

380

400

420

440

460

480

500

Volu

me c

hang

ing

of th

e acc

umul

ator

(L)

Time (s)

450L470L

480L500L

Figure 15 Volume changing of the accumulator

Figures 15 and 16 show the volume and pressure changingof the accumulator Keeping the aeration pressure unchangedthe simulation results indicate that the pressure of theaccumulator is inversely proportional to the initial volumeThe corresponding rotational speeds of the hydraulic motorare shown in Figure 17 The SOC of the battery is shown inFigure 18 It can be seen that the value of SOC is not changingwith the different initial volume In other words the value ofthe initial volume does not have an effect on the improving ofthe boom energy recovery efficiency

52 Analysis of the Hydraulic Motor The hydraulic motoris used to drive the generator in the boom energy recoverysystem The energy recovery system is determined by theperformance of the motor So it is essential to do someresearch on the hydraulicmotorThedisplacement is themost

0 10 20 30 40 50 60 70 80 90 100100

110

120

130

140

150

Pres

sure

chan

ging

of t

he ac

cum

ulat

or (b

ar)

Time (s)

450L470L

480L500L

Figure 16 Pressure changing of the accumulator

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

4000

4500Ro

tatio

nal s

peed

of t

he m

otor

(rm

in)

Time (s)

450L470L

480L500L

Figure 17 Rotational speed of the hydraulic motor

important parameter of the hydraulic motorThe simulationsof the displacement and the type of the motor are shownbelow

521 The Displacement In order to analyze the influence ofthe different displacement on the energy recovery efficiencyfour values 60mLr 80mLr 100mLr and 120mLr areselected as the displacement of the motor

Figure 19 shows the velocity of the boom cylinder pistonin the hybrid hydraulic excavator Based on the workingprocess of the hydraulic excavator the boom cylinder iscontracting during 52 sndash69 s and 90 sndash100 s The hydraulicmotor is driven by the pressure oil flowing into the returnoil line The result shows that the contracting velocity ofthe cylinder decreases along with the decreasing of the

The Scientific World Journal 11

0 10 20 30 40 50 60 70 80 90 10060

61

62

63

64

65

SOC

of th

e bat

tery

()

Time (s)

450L470L

480L500L

Figure 18 SOC of the battery

0 10 20Time (s)

30 40 50 60 70 80 90 100

000

005

010

015

Velo

city

of t

he b

oom

cylin

der p

iston

(ms

)

minus005

minus010

minus015

60mLr80mLr

100mLr120mLr

Figure 19 Velocity of the boom cylinder piston

displacement However it does not have an effect on thenormal work of the hydraulic excavator

Figures 20 and 21 show the rotational speed of thehydraulic motor and SOC of the battery with the differ-ent displacement According to the characteristics of thehydraulicmotor the rotational speed of themotor is inverselyproportional to the displacement When the displacement is60mLr the SOC of the battery reaches the maximum valueIt indicates that the SOC of the battery increases along withthe decreasing of the displacement

522 The Type of the Hydraulic Motor Because of thecomplex working condition of the hydraulic excavator thevelocity of the boom cylinder piston ranges from 0 to 01msThe flow rate of the pressure in the return oil line ranges

0 10 20 30 40 50 60 70 80 90 1000

1000

2000

3000

4000

5000

6000

7000

Rota

tiona

l spe

ed o

f the

mot

or (r

min

)

Time (s)

60mLr80mLr

100mLr120mLr

Figure 20 Rotational speed of the hydraulic motor

0 10 20 30 40 50 60 70 80 90 10060

61

62

63

64

65

66SO

C of

the b

atte

ry (

)

Time (s)

60mLr80mLr

100mLr120mLr

Figure 21 SOC of the battery

large So it is very important to select the hydraulic motor forimproving the energy recovery system

The hydraulicmotor is divided into the constant displace-ment and variable displacement motor The AMESim modelwith the variable displacement motor is shown in Figure 22

Run the simulation Compared with the models withthe constant displacement motor shown in Figure 6 therotational speed of the hydraulic motor in two simulationmodels is presented in the Figure 23 Figure 24 shows the SOCrange of the battery

It can be seen that the rotational speed of the constantdisplacement motor is ranging between 1300 rmin and3500 rmin during a working cycle while the rotational speedof the variable displacement motor remains at 3000 rminThe SOC of the battery of the constant displacement motorsystem increases from 60 to 648 while the SOC of the

12 The Scientific World Journal

Boom potential recovery system

F

M

Qq

ktimesA B

P T

Fluid

Runstats

properties

Qq

A

P

P

T

MOT

k

k

k

f(X

)X

X

Y timesY lt X

k

s

2

1

3

SM

A

A

P

QP

k

k

ktimes k

s

WT

J WT w

T +

+

T

minus

kPIDminus

+

Figure 22 AMESim model with the variable displacement motor

battery of the variable displacement motor system reaches708 Compared with the constant displacement motorsystem more boom potential energy of the energy recoverysystemwith the variable displacementmotor is recovered andstored in the battery Hence the energy recovery efficiencyof the variable displacement motor system is higher than thesystem with the constant displacement motor

6 Conclusions

(1) Based on the simulation of the working devicesin the conventional hydraulic excavator the energywhich can be recovered of the three cylinders iscalculated Taking the complexity and cost of thesystem into consideration this paper proposed anovel boom potential energy recovery system for theparallel hybrid excavator The boom energy regen-eration unit consists of an accumulator a hydraulicmotor an electric generator and a battery Compared

with the conventional energy recovery system theproposed system makes sure that the generator canrotate continuously in a high speed during a workingcycle The AMESim models of the two boom energyrecovery systems are built and the results show thatthe proposed energy recovery system brings higherenergy recovery efficiency than the conventionalenergy recovery system

(2) The mathematical models of the main compo-nents including boom cylinder hydraulic motorand hydraulic accumulator are built The naturalfrequency of the proposed energy recovery systemis calculated based on the mathematical models Inorder to improve the natural frequency and responsespeed of the system some measures should be takenbased on the expression of the natural frequencysuch as reducing the loop oil volume 119881 the leakage

The Scientific World Journal 13

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

Rota

tiona

l spe

ed o

f the

hyd

raul

ic m

otor

(rm

in)

Constant displacement motor Variable displacement motor

Time (s)

Figure 23 Rotational speed of the hydraulic motor

0 10 20 30 40 50 60 70 80 90 100606162636465666768697071

SOC

of th

e bat

tery

()

Constant displacement motor Variable displacement motor

Time (s)

Figure 24 SOC of the battery

coefficients of the energy recovery system 119862 and thetotal moment of inertia of the hydraulic motor 119869

(3) The influence of the main components includinghydraulic motor and hydraulic accumulator on theenergy recovery efficiency of the proposed systemis analyzed The key parameters of the accumulatorinclude the aeration pressure and the initial volumeThe energy recovery efficiency of the proposed sys-tem can be improving to some extent by increasingthe aeration pressure while changing of the initialvolume does not have an effect on improving of theenergy recovery efficiency

The hydraulic motor is used to drive the generator inthe boom energy recovery system The displacement is themost important parameter of the hydraulicmotorThe energy

recovery efficiency can be improving on the premise ofnormal working by decreasing the displacement of themotorSince the flow rate of the pressure in the return oil line rangeslarge the generator can rotate continuously in a high speedby selecting the variable displacement motor in the return oilline In order to improve the energy efficiency according tothe characteristics of the generator the variable displacementhydraulic motor should be chosen in the return oil line

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work is supported by the Fundamental Research Fundsfor the Central Universities (China University of Mining andTechnology 2014Y05) PCSIRT (IRT1292) and the ProjectFunded by the Priority Academic Program Development ofJiangsu Higher Education Institutions (PAPD)

References

[1] M Kagoshima M Komiyama T Nanjo et al ldquoDevelopment ofnew hybrid excavatorrdquo Kobelco Technology Review no 27 2007

[2] T Nanjo E Imanishi and M Kagcahima ldquoPower simulationfor energy saving in hybrid excavatorrdquo JSAE Transactions vol47 pp 101ndash106 2004

[3] L Weidong S Kaikai L Wei and X Jun ldquoResearch onpotential energy recovery of 16T wheeled hybrid excavatorrdquoin Proceedings of the 2nd International Conference on DigitalManufacturing and Automation (ICDMA rsquo11) pp 996ndash998Zhangjiajie China August 2011

[4] I Y Jong K K Ahn and Q T Dinh ldquoA study on anenergy saving electro-hydraulic excavatorrdquo in Proceedings of theICROS-SICE International Joint Conference (ICCAS-SICE rsquo09)pp 3825ndash3830 Fukuoka Japan August 2009

[5] T H Ho and K K Ahn ldquoDesign and control of a closed-loop hydraulic energy-regenerative systemrdquo Automation inConstruction vol 22 pp 444ndash458 2012

[6] Z Jun J Sheng-jie S Gui-mao et al ldquoDesign of electroniccontrol system of hydraulic excavator with CAN bus andPID methodrdquo Proceedings of the International Conference onIntelligent System Design and Engineering Application (ISDEArsquo10) 2010

[7] T Wang and Q Wang ldquoModeling and control of a novelhydraulic system with energy regenerationrdquo in Proceedings ofthe IEEEASME International Conference on Advanced Intelli-gent Mechatronics (AIM rsquo12) pp 922ndash927 IEEE KachsiungTaiwan July 2012

[8] H SHamut I Dincer andG FNaterer ldquoExergoenvironmentalanalysis of hybrid electric vehicle thermal management sys-temsrdquo Journal of Cleaner Production vol 67 pp 187ndash196 2014

[9] A Poursamad and M Montazeri ldquoDesign of genetic-fuzzycontrol strategy for parallel hybrid electric vehiclesrdquo ControlEngineering Practice vol 16 no 7 pp 861ndash873 2008

[10] S Hui J-H Jiang and W Xin ldquoTorque control strategy fora parallel hydraulic hybrid vehiclerdquo Journal of Terramechanicsvol 46 no 6 pp 259ndash265 2009

14 The Scientific World Journal

[11] Z Cao S Wu M Li and C Du ldquoSeries and parallel hybridsystem performance comparison based on the city bus cyclerdquoin Proceedings of the Asia-Pacific Power and Energy EngineeringConference (APPEEC 09) Wuhan China March 2009

[12] J Gong Q He D Zhang et al ldquoPower system control strategyfor hybrid excavator based on equivalent fuel consumptionrdquo inProceedings of the 9th IEEE International Conference on Mecha-tronics and Automation (ICMA rsquo12) pp 1097ndash1102 ChengduChina August 2012

[13] Z Liu S Liu Z Huang and Q Hu ldquoHydraulic excavatorhybrid power system parameters designrdquo in Proceedings of the2nd International Conference on Digital Manufacturing andAutomation (ICDMA rsquo11) pp 602ndash605 Zhangjiajie ChinaAugust 2011

[14] T Lin Q Wang B Hu and W Gong ldquoResearch on theenergy regeneration systems for hybrid hydraulic excavatorsrdquoAutomation in Construction vol 19 no 8 pp 1016ndash1026 2010

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

The Scientific World Journal 11

0 10 20 30 40 50 60 70 80 90 10060

61

62

63

64

65

SOC

of th

e bat

tery

()

Time (s)

450L470L

480L500L

Figure 18 SOC of the battery

0 10 20Time (s)

30 40 50 60 70 80 90 100

000

005

010

015

Velo

city

of t

he b

oom

cylin

der p

iston

(ms

)

minus005

minus010

minus015

60mLr80mLr

100mLr120mLr

Figure 19 Velocity of the boom cylinder piston

displacement However it does not have an effect on thenormal work of the hydraulic excavator

Figures 20 and 21 show the rotational speed of thehydraulic motor and SOC of the battery with the differ-ent displacement According to the characteristics of thehydraulicmotor the rotational speed of themotor is inverselyproportional to the displacement When the displacement is60mLr the SOC of the battery reaches the maximum valueIt indicates that the SOC of the battery increases along withthe decreasing of the displacement

522 The Type of the Hydraulic Motor Because of thecomplex working condition of the hydraulic excavator thevelocity of the boom cylinder piston ranges from 0 to 01msThe flow rate of the pressure in the return oil line ranges

0 10 20 30 40 50 60 70 80 90 1000

1000

2000

3000

4000

5000

6000

7000

Rota

tiona

l spe

ed o

f the

mot

or (r

min

)

Time (s)

60mLr80mLr

100mLr120mLr

Figure 20 Rotational speed of the hydraulic motor

0 10 20 30 40 50 60 70 80 90 10060

61

62

63

64

65

66SO

C of

the b

atte

ry (

)

Time (s)

60mLr80mLr

100mLr120mLr

Figure 21 SOC of the battery

large So it is very important to select the hydraulic motor forimproving the energy recovery system

The hydraulicmotor is divided into the constant displace-ment and variable displacement motor The AMESim modelwith the variable displacement motor is shown in Figure 22

Run the simulation Compared with the models withthe constant displacement motor shown in Figure 6 therotational speed of the hydraulic motor in two simulationmodels is presented in the Figure 23 Figure 24 shows the SOCrange of the battery

It can be seen that the rotational speed of the constantdisplacement motor is ranging between 1300 rmin and3500 rmin during a working cycle while the rotational speedof the variable displacement motor remains at 3000 rminThe SOC of the battery of the constant displacement motorsystem increases from 60 to 648 while the SOC of the

12 The Scientific World Journal

Boom potential recovery system

F

M

Qq

ktimesA B

P T

Fluid

Runstats

properties

Qq

A

P

P

T

MOT

k

k

k

f(X

)X

X

Y timesY lt X

k

s

2

1

3

SM

A

A

P

QP

k

k

ktimes k

s

WT

J WT w

T +

+

T

minus

kPIDminus

+

Figure 22 AMESim model with the variable displacement motor

battery of the variable displacement motor system reaches708 Compared with the constant displacement motorsystem more boom potential energy of the energy recoverysystemwith the variable displacementmotor is recovered andstored in the battery Hence the energy recovery efficiencyof the variable displacement motor system is higher than thesystem with the constant displacement motor

6 Conclusions

(1) Based on the simulation of the working devicesin the conventional hydraulic excavator the energywhich can be recovered of the three cylinders iscalculated Taking the complexity and cost of thesystem into consideration this paper proposed anovel boom potential energy recovery system for theparallel hybrid excavator The boom energy regen-eration unit consists of an accumulator a hydraulicmotor an electric generator and a battery Compared

with the conventional energy recovery system theproposed system makes sure that the generator canrotate continuously in a high speed during a workingcycle The AMESim models of the two boom energyrecovery systems are built and the results show thatthe proposed energy recovery system brings higherenergy recovery efficiency than the conventionalenergy recovery system

(2) The mathematical models of the main compo-nents including boom cylinder hydraulic motorand hydraulic accumulator are built The naturalfrequency of the proposed energy recovery systemis calculated based on the mathematical models Inorder to improve the natural frequency and responsespeed of the system some measures should be takenbased on the expression of the natural frequencysuch as reducing the loop oil volume 119881 the leakage

The Scientific World Journal 13

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

Rota

tiona

l spe

ed o

f the

hyd

raul

ic m

otor

(rm

in)

Constant displacement motor Variable displacement motor

Time (s)

Figure 23 Rotational speed of the hydraulic motor

0 10 20 30 40 50 60 70 80 90 100606162636465666768697071

SOC

of th

e bat

tery

()

Constant displacement motor Variable displacement motor

Time (s)

Figure 24 SOC of the battery

coefficients of the energy recovery system 119862 and thetotal moment of inertia of the hydraulic motor 119869

(3) The influence of the main components includinghydraulic motor and hydraulic accumulator on theenergy recovery efficiency of the proposed systemis analyzed The key parameters of the accumulatorinclude the aeration pressure and the initial volumeThe energy recovery efficiency of the proposed sys-tem can be improving to some extent by increasingthe aeration pressure while changing of the initialvolume does not have an effect on improving of theenergy recovery efficiency

The hydraulic motor is used to drive the generator inthe boom energy recovery system The displacement is themost important parameter of the hydraulicmotorThe energy

recovery efficiency can be improving on the premise ofnormal working by decreasing the displacement of themotorSince the flow rate of the pressure in the return oil line rangeslarge the generator can rotate continuously in a high speedby selecting the variable displacement motor in the return oilline In order to improve the energy efficiency according tothe characteristics of the generator the variable displacementhydraulic motor should be chosen in the return oil line

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work is supported by the Fundamental Research Fundsfor the Central Universities (China University of Mining andTechnology 2014Y05) PCSIRT (IRT1292) and the ProjectFunded by the Priority Academic Program Development ofJiangsu Higher Education Institutions (PAPD)

References

[1] M Kagoshima M Komiyama T Nanjo et al ldquoDevelopment ofnew hybrid excavatorrdquo Kobelco Technology Review no 27 2007

[2] T Nanjo E Imanishi and M Kagcahima ldquoPower simulationfor energy saving in hybrid excavatorrdquo JSAE Transactions vol47 pp 101ndash106 2004

[3] L Weidong S Kaikai L Wei and X Jun ldquoResearch onpotential energy recovery of 16T wheeled hybrid excavatorrdquoin Proceedings of the 2nd International Conference on DigitalManufacturing and Automation (ICDMA rsquo11) pp 996ndash998Zhangjiajie China August 2011

[4] I Y Jong K K Ahn and Q T Dinh ldquoA study on anenergy saving electro-hydraulic excavatorrdquo in Proceedings of theICROS-SICE International Joint Conference (ICCAS-SICE rsquo09)pp 3825ndash3830 Fukuoka Japan August 2009

[5] T H Ho and K K Ahn ldquoDesign and control of a closed-loop hydraulic energy-regenerative systemrdquo Automation inConstruction vol 22 pp 444ndash458 2012

[6] Z Jun J Sheng-jie S Gui-mao et al ldquoDesign of electroniccontrol system of hydraulic excavator with CAN bus andPID methodrdquo Proceedings of the International Conference onIntelligent System Design and Engineering Application (ISDEArsquo10) 2010

[7] T Wang and Q Wang ldquoModeling and control of a novelhydraulic system with energy regenerationrdquo in Proceedings ofthe IEEEASME International Conference on Advanced Intelli-gent Mechatronics (AIM rsquo12) pp 922ndash927 IEEE KachsiungTaiwan July 2012

[8] H SHamut I Dincer andG FNaterer ldquoExergoenvironmentalanalysis of hybrid electric vehicle thermal management sys-temsrdquo Journal of Cleaner Production vol 67 pp 187ndash196 2014

[9] A Poursamad and M Montazeri ldquoDesign of genetic-fuzzycontrol strategy for parallel hybrid electric vehiclesrdquo ControlEngineering Practice vol 16 no 7 pp 861ndash873 2008

[10] S Hui J-H Jiang and W Xin ldquoTorque control strategy fora parallel hydraulic hybrid vehiclerdquo Journal of Terramechanicsvol 46 no 6 pp 259ndash265 2009

14 The Scientific World Journal

[11] Z Cao S Wu M Li and C Du ldquoSeries and parallel hybridsystem performance comparison based on the city bus cyclerdquoin Proceedings of the Asia-Pacific Power and Energy EngineeringConference (APPEEC 09) Wuhan China March 2009

[12] J Gong Q He D Zhang et al ldquoPower system control strategyfor hybrid excavator based on equivalent fuel consumptionrdquo inProceedings of the 9th IEEE International Conference on Mecha-tronics and Automation (ICMA rsquo12) pp 1097ndash1102 ChengduChina August 2012

[13] Z Liu S Liu Z Huang and Q Hu ldquoHydraulic excavatorhybrid power system parameters designrdquo in Proceedings of the2nd International Conference on Digital Manufacturing andAutomation (ICDMA rsquo11) pp 602ndash605 Zhangjiajie ChinaAugust 2011

[14] T Lin Q Wang B Hu and W Gong ldquoResearch on theenergy regeneration systems for hybrid hydraulic excavatorsrdquoAutomation in Construction vol 19 no 8 pp 1016ndash1026 2010

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

12 The Scientific World Journal

Boom potential recovery system

F

M

Qq

ktimesA B

P T

Fluid

Runstats

properties

Qq

A

P

P

T

MOT

k

k

k

f(X

)X

X

Y timesY lt X

k

s

2

1

3

SM

A

A

P

QP

k

k

ktimes k

s

WT

J WT w

T +

+

T

minus

kPIDminus

+

Figure 22 AMESim model with the variable displacement motor

battery of the variable displacement motor system reaches708 Compared with the constant displacement motorsystem more boom potential energy of the energy recoverysystemwith the variable displacementmotor is recovered andstored in the battery Hence the energy recovery efficiencyof the variable displacement motor system is higher than thesystem with the constant displacement motor

6 Conclusions

(1) Based on the simulation of the working devicesin the conventional hydraulic excavator the energywhich can be recovered of the three cylinders iscalculated Taking the complexity and cost of thesystem into consideration this paper proposed anovel boom potential energy recovery system for theparallel hybrid excavator The boom energy regen-eration unit consists of an accumulator a hydraulicmotor an electric generator and a battery Compared

with the conventional energy recovery system theproposed system makes sure that the generator canrotate continuously in a high speed during a workingcycle The AMESim models of the two boom energyrecovery systems are built and the results show thatthe proposed energy recovery system brings higherenergy recovery efficiency than the conventionalenergy recovery system

(2) The mathematical models of the main compo-nents including boom cylinder hydraulic motorand hydraulic accumulator are built The naturalfrequency of the proposed energy recovery systemis calculated based on the mathematical models Inorder to improve the natural frequency and responsespeed of the system some measures should be takenbased on the expression of the natural frequencysuch as reducing the loop oil volume 119881 the leakage

The Scientific World Journal 13

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

Rota

tiona

l spe

ed o

f the

hyd

raul

ic m

otor

(rm

in)

Constant displacement motor Variable displacement motor

Time (s)

Figure 23 Rotational speed of the hydraulic motor

0 10 20 30 40 50 60 70 80 90 100606162636465666768697071

SOC

of th

e bat

tery

()

Constant displacement motor Variable displacement motor

Time (s)

Figure 24 SOC of the battery

coefficients of the energy recovery system 119862 and thetotal moment of inertia of the hydraulic motor 119869

(3) The influence of the main components includinghydraulic motor and hydraulic accumulator on theenergy recovery efficiency of the proposed systemis analyzed The key parameters of the accumulatorinclude the aeration pressure and the initial volumeThe energy recovery efficiency of the proposed sys-tem can be improving to some extent by increasingthe aeration pressure while changing of the initialvolume does not have an effect on improving of theenergy recovery efficiency

The hydraulic motor is used to drive the generator inthe boom energy recovery system The displacement is themost important parameter of the hydraulicmotorThe energy

recovery efficiency can be improving on the premise ofnormal working by decreasing the displacement of themotorSince the flow rate of the pressure in the return oil line rangeslarge the generator can rotate continuously in a high speedby selecting the variable displacement motor in the return oilline In order to improve the energy efficiency according tothe characteristics of the generator the variable displacementhydraulic motor should be chosen in the return oil line

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work is supported by the Fundamental Research Fundsfor the Central Universities (China University of Mining andTechnology 2014Y05) PCSIRT (IRT1292) and the ProjectFunded by the Priority Academic Program Development ofJiangsu Higher Education Institutions (PAPD)

References

[1] M Kagoshima M Komiyama T Nanjo et al ldquoDevelopment ofnew hybrid excavatorrdquo Kobelco Technology Review no 27 2007

[2] T Nanjo E Imanishi and M Kagcahima ldquoPower simulationfor energy saving in hybrid excavatorrdquo JSAE Transactions vol47 pp 101ndash106 2004

[3] L Weidong S Kaikai L Wei and X Jun ldquoResearch onpotential energy recovery of 16T wheeled hybrid excavatorrdquoin Proceedings of the 2nd International Conference on DigitalManufacturing and Automation (ICDMA rsquo11) pp 996ndash998Zhangjiajie China August 2011

[4] I Y Jong K K Ahn and Q T Dinh ldquoA study on anenergy saving electro-hydraulic excavatorrdquo in Proceedings of theICROS-SICE International Joint Conference (ICCAS-SICE rsquo09)pp 3825ndash3830 Fukuoka Japan August 2009

[5] T H Ho and K K Ahn ldquoDesign and control of a closed-loop hydraulic energy-regenerative systemrdquo Automation inConstruction vol 22 pp 444ndash458 2012

[6] Z Jun J Sheng-jie S Gui-mao et al ldquoDesign of electroniccontrol system of hydraulic excavator with CAN bus andPID methodrdquo Proceedings of the International Conference onIntelligent System Design and Engineering Application (ISDEArsquo10) 2010

[7] T Wang and Q Wang ldquoModeling and control of a novelhydraulic system with energy regenerationrdquo in Proceedings ofthe IEEEASME International Conference on Advanced Intelli-gent Mechatronics (AIM rsquo12) pp 922ndash927 IEEE KachsiungTaiwan July 2012

[8] H SHamut I Dincer andG FNaterer ldquoExergoenvironmentalanalysis of hybrid electric vehicle thermal management sys-temsrdquo Journal of Cleaner Production vol 67 pp 187ndash196 2014

[9] A Poursamad and M Montazeri ldquoDesign of genetic-fuzzycontrol strategy for parallel hybrid electric vehiclesrdquo ControlEngineering Practice vol 16 no 7 pp 861ndash873 2008

[10] S Hui J-H Jiang and W Xin ldquoTorque control strategy fora parallel hydraulic hybrid vehiclerdquo Journal of Terramechanicsvol 46 no 6 pp 259ndash265 2009

14 The Scientific World Journal

[11] Z Cao S Wu M Li and C Du ldquoSeries and parallel hybridsystem performance comparison based on the city bus cyclerdquoin Proceedings of the Asia-Pacific Power and Energy EngineeringConference (APPEEC 09) Wuhan China March 2009

[12] J Gong Q He D Zhang et al ldquoPower system control strategyfor hybrid excavator based on equivalent fuel consumptionrdquo inProceedings of the 9th IEEE International Conference on Mecha-tronics and Automation (ICMA rsquo12) pp 1097ndash1102 ChengduChina August 2012

[13] Z Liu S Liu Z Huang and Q Hu ldquoHydraulic excavatorhybrid power system parameters designrdquo in Proceedings of the2nd International Conference on Digital Manufacturing andAutomation (ICDMA rsquo11) pp 602ndash605 Zhangjiajie ChinaAugust 2011

[14] T Lin Q Wang B Hu and W Gong ldquoResearch on theenergy regeneration systems for hybrid hydraulic excavatorsrdquoAutomation in Construction vol 19 no 8 pp 1016ndash1026 2010

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

The Scientific World Journal 13

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

Rota

tiona

l spe

ed o

f the

hyd

raul

ic m

otor

(rm

in)

Constant displacement motor Variable displacement motor

Time (s)

Figure 23 Rotational speed of the hydraulic motor

0 10 20 30 40 50 60 70 80 90 100606162636465666768697071

SOC

of th

e bat

tery

()

Constant displacement motor Variable displacement motor

Time (s)

Figure 24 SOC of the battery

coefficients of the energy recovery system 119862 and thetotal moment of inertia of the hydraulic motor 119869

(3) The influence of the main components includinghydraulic motor and hydraulic accumulator on theenergy recovery efficiency of the proposed systemis analyzed The key parameters of the accumulatorinclude the aeration pressure and the initial volumeThe energy recovery efficiency of the proposed sys-tem can be improving to some extent by increasingthe aeration pressure while changing of the initialvolume does not have an effect on improving of theenergy recovery efficiency

The hydraulic motor is used to drive the generator inthe boom energy recovery system The displacement is themost important parameter of the hydraulicmotorThe energy

recovery efficiency can be improving on the premise ofnormal working by decreasing the displacement of themotorSince the flow rate of the pressure in the return oil line rangeslarge the generator can rotate continuously in a high speedby selecting the variable displacement motor in the return oilline In order to improve the energy efficiency according tothe characteristics of the generator the variable displacementhydraulic motor should be chosen in the return oil line

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work is supported by the Fundamental Research Fundsfor the Central Universities (China University of Mining andTechnology 2014Y05) PCSIRT (IRT1292) and the ProjectFunded by the Priority Academic Program Development ofJiangsu Higher Education Institutions (PAPD)

References

[1] M Kagoshima M Komiyama T Nanjo et al ldquoDevelopment ofnew hybrid excavatorrdquo Kobelco Technology Review no 27 2007

[2] T Nanjo E Imanishi and M Kagcahima ldquoPower simulationfor energy saving in hybrid excavatorrdquo JSAE Transactions vol47 pp 101ndash106 2004

[3] L Weidong S Kaikai L Wei and X Jun ldquoResearch onpotential energy recovery of 16T wheeled hybrid excavatorrdquoin Proceedings of the 2nd International Conference on DigitalManufacturing and Automation (ICDMA rsquo11) pp 996ndash998Zhangjiajie China August 2011

[4] I Y Jong K K Ahn and Q T Dinh ldquoA study on anenergy saving electro-hydraulic excavatorrdquo in Proceedings of theICROS-SICE International Joint Conference (ICCAS-SICE rsquo09)pp 3825ndash3830 Fukuoka Japan August 2009

[5] T H Ho and K K Ahn ldquoDesign and control of a closed-loop hydraulic energy-regenerative systemrdquo Automation inConstruction vol 22 pp 444ndash458 2012

[6] Z Jun J Sheng-jie S Gui-mao et al ldquoDesign of electroniccontrol system of hydraulic excavator with CAN bus andPID methodrdquo Proceedings of the International Conference onIntelligent System Design and Engineering Application (ISDEArsquo10) 2010

[7] T Wang and Q Wang ldquoModeling and control of a novelhydraulic system with energy regenerationrdquo in Proceedings ofthe IEEEASME International Conference on Advanced Intelli-gent Mechatronics (AIM rsquo12) pp 922ndash927 IEEE KachsiungTaiwan July 2012

[8] H SHamut I Dincer andG FNaterer ldquoExergoenvironmentalanalysis of hybrid electric vehicle thermal management sys-temsrdquo Journal of Cleaner Production vol 67 pp 187ndash196 2014

[9] A Poursamad and M Montazeri ldquoDesign of genetic-fuzzycontrol strategy for parallel hybrid electric vehiclesrdquo ControlEngineering Practice vol 16 no 7 pp 861ndash873 2008

[10] S Hui J-H Jiang and W Xin ldquoTorque control strategy fora parallel hydraulic hybrid vehiclerdquo Journal of Terramechanicsvol 46 no 6 pp 259ndash265 2009

14 The Scientific World Journal

[11] Z Cao S Wu M Li and C Du ldquoSeries and parallel hybridsystem performance comparison based on the city bus cyclerdquoin Proceedings of the Asia-Pacific Power and Energy EngineeringConference (APPEEC 09) Wuhan China March 2009

[12] J Gong Q He D Zhang et al ldquoPower system control strategyfor hybrid excavator based on equivalent fuel consumptionrdquo inProceedings of the 9th IEEE International Conference on Mecha-tronics and Automation (ICMA rsquo12) pp 1097ndash1102 ChengduChina August 2012

[13] Z Liu S Liu Z Huang and Q Hu ldquoHydraulic excavatorhybrid power system parameters designrdquo in Proceedings of the2nd International Conference on Digital Manufacturing andAutomation (ICDMA rsquo11) pp 602ndash605 Zhangjiajie ChinaAugust 2011

[14] T Lin Q Wang B Hu and W Gong ldquoResearch on theenergy regeneration systems for hybrid hydraulic excavatorsrdquoAutomation in Construction vol 19 no 8 pp 1016ndash1026 2010

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

14 The Scientific World Journal

[11] Z Cao S Wu M Li and C Du ldquoSeries and parallel hybridsystem performance comparison based on the city bus cyclerdquoin Proceedings of the Asia-Pacific Power and Energy EngineeringConference (APPEEC 09) Wuhan China March 2009

[12] J Gong Q He D Zhang et al ldquoPower system control strategyfor hybrid excavator based on equivalent fuel consumptionrdquo inProceedings of the 9th IEEE International Conference on Mecha-tronics and Automation (ICMA rsquo12) pp 1097ndash1102 ChengduChina August 2012

[13] Z Liu S Liu Z Huang and Q Hu ldquoHydraulic excavatorhybrid power system parameters designrdquo in Proceedings of the2nd International Conference on Digital Manufacturing andAutomation (ICDMA rsquo11) pp 602ndash605 Zhangjiajie ChinaAugust 2011

[14] T Lin Q Wang B Hu and W Gong ldquoResearch on theenergy regeneration systems for hybrid hydraulic excavatorsrdquoAutomation in Construction vol 19 no 8 pp 1016ndash1026 2010

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of