Investigation of Control System Strategies for Hydraulic...

MEM47 Automotive Project

Investigation of Control System Strategies for

Hydraulic Valve Actuation in an IC Engine

Adil Karakayis

1st September 2014

Supervisor: Dr Steven Begg

University of Brighton School of Computing, Engineering and Mathematics, Division of

Engineering & Product Design

Word Count: 13259

MSc Automotive Engineering Page 1 of 93 Adil Karakayis

Disclaimer

“I certify that the attached dissertation is my own work except where otherwise indicated. I have

referenced my sources of information; in particular I have placed quotation marks before and after

any passages that have been quoted word-for-word, and identified their origins.

I give my consent that hard-copy and soft-copy of this dissertation can be made available in full for

subsequent students taking this module.”

____________________ ____________________

SIGN DATE


Abstract

Flexible control of valve lifting, timing and duration makes possible to do significant reduction of

fuel consumption and exhaust emission. Although it is possible to change valve lifting, timing and

duration with camshaft based variable valve actuation systems, they have restriction of camshaft

profile and no valve independency. Electro hydraulic valve actuation systems aim to optimize the

restrictive camshaft profile and give independency of each valve to render possible advance internal

combustion engine strategies. In this project, single electro hydraulic valve actuation system is used

to investigate MATLAB based feed-forward control system. MATLAB/Simulink Simscape library

components which are SimMechanics and SimHydraulics are used to simulate whole test rig because

pre-calculations are necessary for the feed-forward control system. Therefore, simulation model is

used to calculate a signal form for servovalve of hydraulic actuator according to engine speed and

valve lift profile. At the beginning camshaft profile is followed by electro hydraulic actuator system

to prove that this system has capable of existing mechanical systems. After that this camshaft profile

is optimized by using basic equations of volumetric efficiency and considering air choking conditions

according to piston speed. Experiments were repeated with the optimized valve lift profile.

Experiments were done from 800 rpm to 6000rpm at 70bar oil pressure. Even though the experiment

results are promising, if the simulation model and signal generation system is going to be improved,

results might be better for feed-forward control system.


Table of Contents

Acknowledgement ......................................................................................................................... 9

Abbreviations ................................................................................................................................ 10

Introduction ................................................................................................................................... 12

1- Valve Actuation Systems ...................................................................................................... 13

1.1- Mechanical Valve Actuation System ........................................................................... 13

1.1.1- Design of Camshaft .................................................................................................. 14

1.1.2- Cam Changing and Cam Phasing Systems ....................................................... 16

1.1.3- Continuously Variable Valve Lifting Systems ................................................... 20

1.2- Electro Hydraulic Valve Actuation Systems ............................................................. 22

1.3- Summary of Existing Systems ..................................................................................... 25

2- Structure of Test Rig .............................................................................................................. 26

2.1- Modification of Test Rig ................................................................................................. 27

2.2- Test Rig Equipment ......................................................................................................... 29

2.2.1- Oil Tank ....................................................................................................................... 31

2.2.2- Hydraulic Pump and Electrical Motor .................................................................. 31

2.2.3- Accumulator ............................................................................................................... 32

2.2.4- Oil Filter ....................................................................................................................... 32

2.2.5- Pressure Switch ........................................................................................................ 32

2.2.6- Moog Servovalve ...................................................................................................... 33

2.2.7- Hydraulic Valve Actuator Assembly .................................................................... 34

2.2.8- Pressure Transducer Flange ................................................................................. 37

2.2.9- Poppet Valve .............................................................................................................. 38

2.2.10- Control Box .............................................................................................................. 38

2.2.11- Main Electrical Box ................................................................................................ 39

2.3- Oil Properties .................................................................................................................... 39

2.4- Signal Generation System ............................................................................................. 39

2.4.1- Arduino Mega 2560 ................................................................................................... 40

2.4.2- Function Generator .................................................................................................. 43

2.4.3- Signal Amplifier ......................................................................................................... 44

2.5- Data Logging System ...................................................................................................... 44

2.5.1- Pressure Transducers and Charge Amplifiers ................................................. 44

2.5.2- Linear Variable Differential Transformer and Signal Conditioner ............... 45

2.5.3- Oscilloscope and Picoscope ................................................................................. 45

2.6- Test Rig Restrictions ....................................................................................................... 46


3- MATLAB/Simulink Simulation Model ................................................................................. 47

3.1- SimMechanics ................................................................................................................... 48

3.2- SimHydraulics ................................................................................................................... 50

3.2.1- Hydraulic Fluid .......................................................................................................... 52

3.2.2- Hydraulic Pump ......................................................................................................... 52

3.2.3- Accumulator ............................................................................................................... 52

3.2.4- 4-Way Directional Valve .......................................................................................... 52

3.2.5- Optimization Tool for 4-Way Directional Valve ................................................. 55

3.2.6- Double-Acting Hydraulic Cylinder ........................................................................ 56

3.3- Control System ................................................................................................................. 57

4- Method of Experiments .......................................................................................................... 58

4.1- V-tec Camshaft Profile .................................................................................................... 60

4.2- Desired Valve Lift Profile................................................................................................ 61

5- Experiment Results and Analysis ....................................................................................... 63

5.1- Discussion of Experiment Results .............................................................................. 71

6- Future Work .............................................................................................................................. 72

Conclusion ..................................................................................................................................... 74

References ..................................................................................................................................... 75

Appendix A .................................................................................................................................... 80

Appendix B .................................................................................................................................... 91

Appendix C .................................................................................................................................... 92


Acknowledgement

I want to express my sincere gratitude to Dr Steven Begg who gave me that opportunity to do

investigation of control system strategies for hydraulic valve actuation in an internal combustion

engine. I would like to thank Mr Peter Rayner, Mr Mario Palermo and Mr Jon Armory who are SHRL

technicians for their assistance to finish test rig as fast as possible. I am truly grateful to Dr Chris

Garrett, Dr Daniel Coren and Dr Guillaume de Sercey for their support on this project. Finally, I

thank my family for their encouragements.


Abbreviations

LVDT: Linear variable differential transformer

PWM: Pulse Width Modulation

DAHC: Double-acting hydraulic cylinder

4WDV: 4-way directional valve

IC: Internal combustion

EHVA: Electro hydraulic actuation

VVT: Variable valve timing

VVTL-i: Variable Valve Timing and Lifting with Intelligence

i-VTEC: Intelligent Variable Valve Timing and Electronic Lift Control

IVLC: Intake Valve Lift Control

VVEL: Variable Valve Event and Lift

MAEHV: Multi-Air Electro Hydraulic Valve Timing

PID: Proportional-Integral-Derivative

𝐴𝐸̅̅̅̅ : 𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑒𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒 𝑖𝑛𝑡𝑎𝑘𝑒 𝑓𝑙𝑜𝑤 𝑎𝑟𝑒𝑎

𝜃𝑖𝑐: 𝐼𝑛𝑡𝑎𝑘𝑒 𝑣𝑎𝑙𝑣𝑒 𝑐𝑙𝑜𝑠𝑖𝑛𝑔 𝑎𝑛𝑔𝑙𝑒 (𝑟𝑎𝑑)

𝜃𝑖𝑜: 𝐼𝑛𝑡𝑎𝑘𝑒 𝑣𝑎𝑙𝑣𝑒 𝑜𝑝𝑒𝑛𝑖𝑛𝑔 𝑎𝑛𝑔𝑙𝑒 (𝑟𝑎𝑑)

𝐶�̅�: 𝐷𝑖𝑠𝑐ℎ𝑎𝑟𝑔𝑒𝑟 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 𝑤ℎ𝑖𝑐ℎ 𝑖𝑠 𝑎𝑠𝑠𝑢𝑚𝑒𝑑 0.6

𝑍: 𝑀𝑒𝑎𝑛 𝑀𝑎𝑐ℎ 𝑛𝑢𝑚𝑏𝑒𝑟 𝑎𝑡 𝑖𝑛𝑙𝑒𝑡 𝑡ℎ𝑟𝑜𝑎𝑡

𝐴𝑝: 𝑃𝑖𝑠𝑡𝑜𝑛 𝑎𝑟𝑒𝑎

𝑆�̅�: 𝑃𝑖𝑠𝑡𝑜𝑛 𝑚𝑒𝑎𝑛 𝑠𝑝𝑒𝑒𝑑

𝑐𝑖: 𝑠𝑜𝑢𝑛𝑑 𝑠𝑝𝑒𝑒𝑑 𝑎𝑡 𝑖𝑛𝑙𝑒𝑡

𝑒𝑣: 𝑉𝑜𝑙𝑢𝑚𝑒𝑡𝑟𝑖𝑐 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦

𝑚𝑖: 𝑀𝑎𝑠𝑠 𝑖𝑛𝑑𝑢𝑐𝑒𝑑 𝑑𝑢𝑟𝑖𝑛𝑔 𝑣𝑎𝑙𝑣𝑒 𝑜𝑝𝑒𝑛 𝑡𝑖𝑚𝑒

𝜌𝑖: 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝑎𝑖𝑟 𝑎𝑡 𝑖𝑛𝑙𝑒𝑡 𝑚𝑎𝑛𝑖𝑓𝑜𝑙𝑑

𝑉𝑑: 𝐷𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑒𝑛𝑔𝑖𝑛𝑒

𝜔: 𝐸𝑛𝑔𝑖𝑛𝑒 𝑠𝑝𝑒𝑒𝑑 (rpm)

𝐴𝐶 : 𝑉𝑎𝑙𝑣𝑒 𝑐𝑢𝑟𝑡𝑎𝑖𝑛 𝑎𝑟𝑒𝑎

𝐷𝑣: 𝑉𝑎𝑙𝑣𝑒 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟

𝐿𝑣: 𝐿𝑖𝑓𝑡 𝑜𝑓 𝑣𝑎𝑙𝑣𝑒

ᵧ: 𝐻𝑒𝑎𝑡 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑟𝑎𝑡𝑖𝑜 𝑤ℎ𝑖𝑐ℎ 𝑖𝑠 𝑎𝑠𝑠𝑢𝑚𝑒𝑑 1.4


𝑅: 𝐼𝑑𝑒𝑎𝑙 𝑔𝑎𝑠 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 (287 𝑗

𝑘𝑔𝐾⁄ )

𝑇𝑜: 𝐴𝑖𝑟 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑎𝑡 𝑖𝑛𝑙𝑒𝑡 𝑚𝑎𝑛𝑖𝑓𝑜𝑙𝑑 300K

𝑁: 𝐸𝑛𝑔𝑖𝑛𝑒 𝑠𝑝𝑒𝑒𝑑 (𝑟𝑝𝑠)

D: Displacement of the poppet valve (mm)

M: Slope of LVDT sensor (mm/V)

X: Sensor output voltage (V)

𝑑: 𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟 𝑜𝑓 𝑡ℎ𝑒 𝑐 𝑦𝑙𝑖𝑛𝑑𝑒𝑟

l: Actuator rod piston length

δ: 𝑅𝑒𝑐𝑖𝑝𝑟𝑜𝑐𝑎𝑙

b: Viscous damping coefficient of hydraulic cylinder

𝜌: Density of hydraulic fluid

v: kinematic viscosity of hydraulic fluid

q: Flow rate through the orifice

𝐶𝑑: Flow discharge coefficient

A: Orifice area

𝐴𝑚𝑎𝑥: Maximum orifice area

h: Orifice opening

ℎ0: Initial opening of the spool

ℎ𝑚𝑎𝑥: Maximum orifice opening

x: Control member displacement (spool)

P: Pressure

𝜃𝐶: Crankshaft angle

s:Piston stroke

a: Crankshaft radius

l:Connecting rod length


Introduction

Efficiency of conventional four-stroke IC engines are getting better while researches continuous. As

new research techniques arise such as optical diagnostic techniques, it becomes possible to look at

inside the combustion chamber which allows researchers to visualize swirl ratio and tumble ratio to

create better air-fuel mixture. These researches illustrates and proves the importance of inlet valve

operations for volumetric efficiency and exhaust valve operations for exhaust scavenging of the IC

engine. As a result of increasing of emission regulations, limits of the engine efficiencies are forced.

IC engines require more complex valve operation systems for better fuel economy and lower exhaust

emission with the improvement of new fuel injection systems such as gasoline direct injection after

port injection system. As a result of mechanically certain design of cam lobe, valve is restricted to

follow that camshaft profile. Although it is possible to improve the restrictive cam profile with cam

phasing and valve lifting which are integrated onto mechanical valve actuation systems, it still has

restriction of the camshaft profile design. Moreover, it is required to have independence for each

valve to move one step further the engine efficiencies. Freedom of valves will allow researchers to

control swirl ratio better for creating homogenous mixture with highly atomized fuel. Even

volumetric efficiency of IC engines can be increased by using forced induction systems such as

turbocharger and supercharger, independence of valve is still required to control swirl ratio. With

EHVA system, inlet and exhaust valves can be controlled by engineers with wide variety of control

strategies to optimise IC engines volumetric efficiency and exhaust scavenging. It makes possible to

do any kind of profile shape in the inlet and exhaust strokes. EHVA system is removed restrictions

of mechanical actuation systems until the formed their own restrictions. Limitations of this system is

clearly explained below. In this project, all experiments are done for the inlet valve profile which is

the most important valve for IC engines. First of all, existing Vtec full lift camshaft profile for B15C7

engine is followed. Secondly, this profile is optimised for that specific engine and all experiments

are done for that optimised profile also. MATLAB/Simulink is used to create a simulation model of

complete system which generates a feed-forward signal for servovalve at each determined engine

speed. Experiments were done for 800, 1000, 1500, 2000, 2500, 3000, 4000, 5000, 6000rpm engine


speeds in the pressure range of 68 to 72bar. As a result of experiments, this system has been

successful up to 2500rpm at that pressure range.

1- Valve Actuation Systems

Conventional IC engines have mechanically actuated valves which are controlled by a camshaft since

they are designed. Even though they work very well, they have limitations for camshaft profiles

which effects volumetric efficiency. This limitation is result of cam lobe design because it actuates

valves in linear motion but camshaft is a rotational part. Therefore, cam lobe should have eccentric

shape. Although camshaft restrictions can be improved by using cam phasing for valve overlapping

and valve lifting systems, valve opening profile is still constraint by cam lobe profile. A lot of

research is continuing on electromagnetic and electrohydraulic valve actuation systems which

removes limitations of mechanically actuated valve systems. These systems eliminate dependency

of camshaft profile and gives freedom for each valve. Therefore, they enable infinitely flexible

control for valve lifting, duration and variable timing.

1.1- Mechanical Valve Actuation System

Working principle of mechanical valve actuation system on four-stroke engine is that turning

camshaft pulley by using timing belt or gear mechanism which is attached to the crankshaft pulley

or gear. As the piston moves downwards in the intake stroke, crankshaft rotates, hence camshaft

rotates which is attached to the crankshaft. Therefore, cam lobes pushes valves to open. While piton

moves downwards, it sucks the air trough intake ports and opened intake valves. When the piston

moves upwards at exhaust stroke same event happens to open exhaust valve [1]. Valves control the

air/fuel or just air flow and exhaust scavenging so timing of this process has critical importance to

fill the cylinder with fresh air without choking and remove the exhaust gasses efficiently. Basic

mechanical valve actuation system is illustrated in the figure.1.


Figure.1 Mechanical valve actuation system [3]

1.1.1- Design of Camshaft

Camshaft design should be considered early design of IC engines to get optimized engine

performance, fuel consumption and exhaust emission. Unique timing characteristics is necessary to

have maximum engine performance with high efficiency. However, it is hard to optimise both which

means while performance is at maximum, fuel consumption is high. Otherwise, when the fuel

consumption is reduced, performance also reduces. When costumers purchase an automobile, they

want both of them are optimised which is not possible with fixed design camshafts. In response to

this problem, manufacturers have been attempting to produce variable valve timing systems such as

cam phasing and valve lifting systems [2]. Typical camshaft profile is given in the figure.2. Cam

lobe opening and closing ramps are designed smoothly so the valve opening and landing becomes

gently. Relation of the cam lobe and valve opening profile can be seen in the figures 2 and 3.


Figure.2 Typical cam lobe profile [4]

Figure.3 Typical camshaft profile [5]


1.1.2- Cam Changing and Cam Phasing Systems

There are two types VVT systems which are valve lifting and cam phasing systems. They can be

categorized to discrete and continuously systems. Cam changing and some cam phasing systems are

in discrete systems. VVT systems are mostly mechanical designs. Therefore, although these systems

remove the fixed valve timing and duration limitation, they have limited range to change them.

Volumetric efficiency equations illustrates that VVT systems are necessarily to change valve lifting

and cam phasing during engine speed increases [14].

Figure.4 Poppet valve geometry [15]

�̅�𝐸 =1

𝜃𝑖𝑐−𝜃𝑖𝑜∫ 𝐴𝐸 𝑑𝜃 = 𝐶�̅�𝐴𝐶

𝜃𝑖𝑐

𝜃𝑖𝑜 …1

𝐴𝐶 = 𝜋𝐷𝑣𝐿𝑣 …2

𝐴𝑝 = 2𝜋𝑟2 …3

𝑍 =𝐴𝑝�̅�𝑝

𝐴𝐸𝑐𝑖 …4

𝑆�̅� = 2𝑠𝑁 …5

𝑐𝑖 = √ᵧ𝑅𝑇0 …6

𝑒𝑣 = 𝑚𝑖

𝜌𝑖𝑉𝑑=

1

𝜔𝜌𝑖𝑉𝑑∫ �̇�𝑑𝜃

𝜃𝑖𝑐

𝜃𝑖𝑜 …7

𝑒𝑣 =�̅�𝐸𝑐𝑖

𝜔𝑉𝑑(𝜃𝑖𝑐 − 𝜃𝑖𝑜) (

2

ᵧ+1)

(ᵧ+1)/2(ᵧ−1) …8

𝑒𝑣 = 0.58 (𝜃𝑖𝑐−𝜃𝑖𝑜

𝜋)

1

𝑧 …9


There is always a limiting case which flow chokes if valve lift and timing does not synchronised very

well with piston speed. According to that if choked flow is the top level for the flow, volumetric

efficiency can be calculated by using equation.8. These equations were used to calculate optimized

profiles according to engine speed in section 4.2 for EHVA system also. With respect to equation.8,

opening angle, duration time and valve lifting is affected by piston speed for the volumetric

efficiency. In response to this situation, each manufacturer has VVT systems with different names

and small changes. Even though they have different names, working principle is same for all of them.

VVTL-i and i-VTEC are examples for continuously variable cam phasing systems. All cam changing

systems are discrete valve lifting systems. VarioCam and next generation VarioCam Plus are

produced by Porsche Company. Volkswagen group cars are also used this system on 1.8t engines.

VarioCam system does cam phasing by changing the position of tensioners with the help of hydraulic

cylinder (figure.5) [6].

Figure.5 VarioCam cam phasing system [6]

VarioCam Plus does cam phasing by changing cam pulley and camshaft phase angle. This event

happens by forcing helical gear to move in liner motion with hydraulic pressure which changes phase

angle (figure.6). VarioCam Plus has cam changing system also which enables to change valve lifting.


In this system, camshaft has two different cam lobe profile. One of them is for low lifting profile and

the other one is for high lifting profile [7].

Figure.6 VarioCam Plus and Vanos cam phasing system [6]

In the VarioCam Plus system, by changing cam lobe, two different valve profile can be followed

according to engine speed (figure.7). Changing cam makes possible to switch two different cam lobes

discretely which have different opening duration and valve lift. Variable hydraulic tappets are used

to change these two lobes. Transition can be provided by changing the contact of lobes from inner

tappet to outer tappet which can be done by locking a hydraulically actuated pin. In addition to

VarioCam Plus, Vanos cam phasing system which has same working principle is used by BMW car

manufacturer (figure.6). Hydraulic pressure on the piston changes the phase angle in between the

cam pulley and camshaft by rotating the helical gear, when it is actuated by a solenoid valve [7].

Figure.7 VarioCam Plus cam phasing system and valve lifting mechanism [7]


Moreover, Toyota uses VVTL-i which is sophisticate variable valve timing system. This system is

the combination of VVT-i and V-TEC. The difference of VVTL-i is just lifting mechanism. Shifting

the whole camshaft phase angle is possible with VVT-i system. In this system, cam phasing

mechanism is placed into the camshaft pulley which changes cam pulley and stator phase angle by

just controlling hydraulic pressure. Engine oil fills into the stator oil channels and changes the phase

angle with cam pulley. Honda uses i-VTEC which is similar to VVTL-i system (figure.8). These two

systems enable continuously cam phasing which gives flexibility to control cam phasing from low

to high engine speeds [7].

Figure.8 i-VTEC cam phasing system [9]

Figure.9 VVTL-i valve lifting mechanism [7]


VVTL-i uses single rocker system similar to V-TEC mechanism with some design differences

(figure.9). There are two different cam lobes as VarioCam Plus system. Difference of this system is

that rocker follows lower profile at low engine speed and other lobe rotates freely. While engine

speed increases hydraulically actuated pin locks the rocker arm to follow higher cam lobe. Rocker

arm activation/de-activation is used by many other manufacturer also. For instance, V-TEC and GM

IVLC. Although i-VTEC has similar system, it has three stages cam lobes which are low, medium

and high lift cam lobe profiles. Audi valve lifting system is another design for valve lifting which

has two stages with three different cam lobes. Transition occurs by sliding camshaft with actuator

rod and grove on the camshaft (figure.10). Mercedes Camtronic system is similar to the Audi valve

lifting system [7].

Figure.10 Audi valvelift mechanism [11]

1.1.3- Continuously Variable Valve Lifting Systems

With the improvement of the VVT technology, continuously valve lifting systems have been

developed such as BMW Valvetronic, Toyota Valvematic and Nissan VVEL systems. Valvetronic

system is the first continuous variable valve lifting system in the world. Working principle of this

system is that additional electric motor rotates eccentric shaft to push the secondary rocker arm which


opens valve more variably (figure.11). Therefore, valve lift displacement can be controlled

continuously by just rotating eccentric shaft [7].

Figure.11 BMW Valvetronic system [7]

In Toyota Valvematic system, although the design is different from BMW Valvetronic system,

working principle is same. While intermediate shaft rotates to have wide angle, valve lift becomes

high lift (figure.12) [7].

Figure.12 Toyota Valvematic system [7]


VVEL system is another design by Nissan which does same job with other continuous valve lifting

systems. When control shaft rotates by electric motor because of it has eccentric shape, it pushes

output cam to change the lift of valve (figure.13) [7].

Figure.13 Toyota Valvematic system [7]

1.2- Electro Hydraulic Valve Actuation Systems

There are camless engines and hybrid systems which combines both systems. In the nutshell, camless

engines have electrohydraulic or electromagnetic systems which have capable of all camshaft

systems and more to do valve lifting and cam phasing. Although hybrid systems have semi-

independence for the valves, they still have restrictions of the camshaft profile. Thus, fully EHVA

systems are developed for full independency of each valve. It enables to control each valve with

different profiles if it is necessary. Even though there are lots of researches on the fully EHVA

systems, they are not on the production line yet. However, hybrid system such as MAEHV system

which is developed by Fiat is on production cars. As it can be seen in the figure.14, this system can

achieve five different strategies which are full lift, late intake valve opening, early valve closing,

partial load and even multi lift. Firstly, full lift is conventional cam control which follows rigid cam

profile. It is suitable for high engine speed. In second strategy, late intake valve opening is obtained


by electronic hydraulic solenoid valve which respects to the cam profile. This strategy is suitable for

low load conditions. Early valve closing allows to anticipate the intake valve closing time which is

suitable for part load operations. Fourth strategy gives possibility of closing intake valve earlier to

prevent air escape to intake manifold. This strategy is done to improve acceleration at low engine

speed. Final mode enables the possibility of multi valve lift in the intake stroke. This strategy is the

combination of second and third strategies to regulate consumption while increase the performance

at low engine speed [7].

Figure.14 Fiat Multi-Air system [7]

Cam-Camless Eaton design is also hybrid system which allows to do different valve profile strategies

for camless system. Possible strategies of this system are given in the figure.16 where can be seen

wide variety of strategies are possible to be generated with camless system in addition to mechanical

system benefits [11].


Figure.15 Eaton cam-camless hybrid system [11]

Figure.16 Eaton cam-camless hybrid system strategies [11]

Furthermore, Ricardo Company has been developed camless HYDRA single cylinder research

engine with electro-hydraulic valvetrain system which enables flexibility of continuously variable

valve timing and lifting, variable opening and closing rate, multiple events, port deactivation and


variable valve profile [12]. Additionaly, in 2009, with the cooperation of Lotus and Eaton, active

valve train system is produced which is fully VVT system with AVT actuator. Similarly, Ricardo

uses this type actuator with servovalve. This system is controlled by a closed loop system. Currently,

the system makes possible advance engine strategies such as homogenous charge compression

ignition, without throttle operations to eliminate throttling losses, variable firing order, possible fast

start, ultimately air hybridisation and differential cylinder loading [13].

Figure.17 Valve Block of Research AVT Actuator [13]

1.3- Summary of Existing Systems

All mechanical systems can be applied on both inlet and exhaust camshaft. However, as it can be

seen in the figure.3, although Valvetronic, Valvematic and VVEL have ability to alter valve lift

infinitely according to the requirements of engine in addition to continuously variable cam phasing,

valves are still restricted to follow the cam lobe profile. Unlimited flexibility is not possible for

different valve strategies in mechanical systems. However, EHVA systems offer infinite variations

of continuously variable and independent valve control. Which enables different strategies of valve

openings, timings and profiles. With the improvement of all these variations, as it explained above,

it allows engineers to develop advanced engine strategies. In next chapters, EHVA system

MATLAB/Simulink based feed-forward control strategy is tested to enable all these advance engine

strategies.


2- Structure of Test Rig

Figure.18 Diagram of the complete setup


Electro hydraulic valve actuation test rig was designed to do all determined experiments for

generating desired valve profile. In this test rig, hydraulic pump is controlled by a control box for oil

pressure supply. This oil pressure is kept constant by an on/off closed loop control system which is

controlled by a pressure switch. Moreover, all data are saved by a picoscope. Furthermore, complete

test rig is simulated into a MATLAB/Simulink model to create signal form for a servovalve.

This simulated signal form for the servovalve is generated by a function generator when it

is triggered by a triggering button to control the poppet valve. In brief, the simulation model

enables feed-forward control system for the EHVA system. Because of the simulation is used,

all specifications about the test rig equipment should be known to enter all necessarily

parameters for simulation model. Required equipment and their specifications are explained

below.

2.1- Modification of Test Rig

EHVA test rig was already existing but it was modified according to needs for new experiments.

First of all, test rig was designed to be more rigid. EHVA assembly and oil filter bracket was designed

to be more robust. This bracket allows to change oil filter easily, if it is necessary. Protective clear

polycarbonate sheet and its frame was designed to protect the operator from any leakage or frangible

parts. All leakages were fixed and sink was designed to catch oil leakage of the hydraulic actuator

which is completely normal. This leakage keeps away dust particle from the actuator. Test rig was

designed to become all connections with solid pipes. However, although pipes are ordered, they did

not arrive at the expected time. Therefore, flexible pipes are used which were already available.

Detailed Solidworks drawings for new designed parts are given in the appendix A. Desired designed

test rig appearance is like that;


Figure.19 Back view of the test rig design [24]

Figure.20 Front view of the test rig design [24]


Figure.21 Front view of the test rig design [24]

2.2- Test Rig Equipment

These equipment which are listed below are all required for actuation of a poppet valve and data

logging system. All necessarily specifications are given for the simulation model.

Figure.22 Equipment of test rig control system


Figure.23 Back view of test rig equipment

Figure.24 Top view of test rig equipment


Item Description Quantity

1 Oil tank x1

2 Hydra micro pack hydraulic pump x1

3 Electrical motor x1

4 Parker Olaer accumulator x1

5 Fox pressure switch x1

6 Parker high pressure oil filter x1

7 Moog servovalve x1

8 Kistler pressure transducer x1

9 Pressure transducer flange x1

10 Helipebs hydraulic valve actuator x1

11 Poppet valve x1

12 Control box x1

13 Main electrical box x1

14 Fuse box x1

15 TTi TG1010A function generator x1

16 Custom signal amplifier x1

17 Linear variable differential transformer x1

18 Microstrain signal conditioner x1

19 Kistler pressure charge amplifier x2

20 Tektronix TDS 220 oscilloscope x1

21 National instrument picoscope x1

22 Computer x1

23 Protective clear polycarbonate and frame x1

24 Oil filter & EHVA assembly bracket x1

25 High pressure flexible hydraulic pipes x1

26 Ball valve x1

27 Pressure gauge x1

Table.1 List of test rig equipment

2.2.1- Oil Tank

4.5 litre aluminium oil tank is used such as a secondary tank. When oil decreases in actual oil

reservoir of the hydraulic pump because of the leakage at hydraulic actuator, ball valve is opened to

fill it.

2.2.2- Hydraulic Pump and Electrical Motor

Hydraulic oil pressure source of the test rig is Hydra Products micro pack hydraulic pump. This

micro pack includes XV-0P/0.25 group fixed displacement gear pump. Mounting of the hydraulic

pump assembly should be horizontal because gear pump type is in tank and the filler position is at

the side of the pimp. Moreover, air breather position is at top. Additionally, it has pressure relief


valve. When this valve is activated, it relieves all pressure in the system. Assembly includes 0.5 litre

plastic oil tank which can be filled by secondary oil tank. After it is filled ball valve should be closed.

Otherwise, all oil in the secondary tank comes out from the air breather. This pump which has

0.24𝑐𝑚3/𝑟𝑒𝑣 size has the capable of 260bar maximum pressure in the speed range of 700 to

9000rpm. According to the selection of the electric motor which is AC motor – 250 Watt 240V 50Hz

S2 duty in this project, moto-pump performance is given in the graph.17 in appendix A. The pressure

range is in between 10 to maximum 120 bar. Volumetric efficiency is in the range of 0.91 to 0.96,

mechanical efficiency is 0.85 to 0.90, recommended oil is mineral oil and working temperature range

is in between -15 to 70 𝐶° [16] [17].

2.2.3- Accumulator

Parker Olaer diaphragm accumulator which has the capacity of 0.16litre is used on the test rig to

stabilize the oil pressure in the system. It is pre-charged with nitrogen which gives maximum 130bar

pressure load [18].

2.2.4- Oil Filter

Any tiny dust particles can block servovalve or may affect the performance. Therefore, Parker

hydraulic filter is used on the test rig to filter out these particles. Although the size of the filter

elements are 10µm, pressure is not affected a lot. Pressure differential is 0.2 bar at 17.05 l/min flow

rate which is maximum flow rate of the servovalve. Therefore, it is not considered into the simulation

model. It can be seen in the graph.18 in appendix A. [20]

2.2.5- Pressure Switch

Fox F4 adjustable pressure switch is used on the test rig to control pressure in the system. Switch is

set to remain the system at determined pressure. It can be adjusted by rotating the screw with 2 mm

hexagonal key manually. This pressure switch is used for closed loop on/off control system. Working

principle is that when the oil pressure force is more than spring force which is adjusted by the screw,

needle opens the electric circuit. For this reason, main electric box cannot send any electric signal to


the electric motor until pressure drop. While pressure drops, pressure switch closes electric circuit

and send electric signal back to the electric motor to increase the oil pressure [19].

Figure.25 Diagram of Pressure switch [19]

2.2.6- Moog Servovalve

Servovalve controls the flow rate for the hydraulic actuator according to electrical current signal. It

can be divided to three main parts which are torque motor, hydraulic amplifier and valve spool.

Operation procedure is such that electrical current signal creates magnetic forces on the armature

which creates torque according to the current value in the range of +/- 50 mA. This torque rotates the

flapper to close or reduce the opening area of the one end of the nozzle while opens or increases the

opening area of the other end. It changes the flow balance in the hydraulic amplifier. Changed flow

goes to return line through drain orifice which creates imbalance hydraulic force on the spool.

Because of that, the spool moves to one direction. When the spool moves one direction, it opens

pressure port on that direction which allows main oil flow to the hydraulic actuator. On the other

hand, it opens return port for the other end of the hydraulic actuator at the same time. Additionally,


spool movement generates some force on the feedback spring which helps torque armature and

flapper to return its original position immediately after current signal becomes 0 value [23]. Moog

series 31 servovalve specifications are given in the table.2 Flow datasheet characteristics are given

in the graph.19 in appendix A.

Figure.26 Diagram of the servovalve [23]

System Pressure 280 bar (4000 Psi)

Rated Flow 15.0 l/min +/- 10% at 70 bar

Maximum Leakage 1.95 l/min

Rated Signal +/- 50.0 mA

Response Type High

Fluid Mineral oil

Seals N90D

Body Type 31 Series

Connector Type Bendix

Screws Std

Additional Comments 10% P-C2

Table.2 Moog servovalve specifications [22]

2.2.7- Hydraulic Valve Actuator Assembly

Helipebs hydraulic valve actuator is the main part of the test rig which provides movement of the

poppet valve according to the controlled oil flow. Working principle is very basic which oil fills the


piston area in order to provide linear movement of the poppet valve. Poppet valve is attached on the

one end of actuator rod. Other end is used for LVDT sensor. There is no piston ring for sealing but

piston has four groves which are for lubrication of the piston to reduce the friction of the rod.

However, it creates small damping force. Therefore, viscous damping coefficient should be

calculated for the simulation by these equations;

𝑘δ =𝑑

δ …10

𝑘l = 𝑙

𝑑 …11

𝑏 = 𝜋 . 𝜌 . 𝑣 . 𝑘δ . 𝑘l . 𝑑 …12

Figure.27 Sectional view of the actuator rod piston and cylinder [35]

According to the equations, damping coefficient is equal to 1.6N.s/m.

Where;

𝜌: 843.64𝑘𝑔/𝑚3at 27𝐶°

𝑣: 125.427cst (0.000125427𝑚2/𝑠) at 27𝐶°

𝑑: 11.00mm

δ: 0.50mm

𝑙: 22.00mm


Because of there is no sealing on the piston and heads, leakage occurs. In order to prevent leakage at

ports of servovalve and flange, O-rings are used in between pressure transducer flange and

servovalve. Ports should be exactly matched to avoid any dislocation of ports, when parts are

assembled. Therefore, dowels are used for each parts. Exploded view of the hydraulic actuator

assembly is illustrated in the figure.28

Figure.28 Exploded view of hydraulic valve assembly [24]

# Description

1 LVDT sensor

2 Top head of actuator

3 Pressure inlet for actuator

4 Return

5 Pressure line for servovalve

6 Return line

7 Kistler pressure transducers

8 Bolt for transducer

9 Pressure transducer flange

10 Moog type31 servovalve

11 Hydraulic actuator rod

12 Bottom head

13 Poppet valve

Table.3 Hydraulic valve assembly parts

Hydraulic actuator has complex geometry at two ends which improves end damping of actuator rod.

It is showed in the figure.29.


Figure.29 Sectional view of hydraulic valve assembly [24]

Heads have some tolerance in between the cylinder. Head diameter is 10.62 mm and cylinder

diameter is 11.0 mm. In theory, oil passes through this tolerance to reach cavity for improving end

damping. Moreover, heads have groove to allow oil flow when the rod is at very end. For end

damping, 𝑉1 and 𝑉2 should be considered into the SimHydraulics double-acting hydraulic cylinder

block so they were calculated by using Solidworks drawings. 𝑉1 is 20.25𝑚𝑚3and 𝑉2 is 434.405𝑚𝑚3

2.2.8- Pressure Transducer Flange

Pressure transducer flange is assembled in between servovalve and actuator for measuring the

pressure differential of two pressure lines. This location is selected for pressure transducers because

of technical issues such as hardness of actuator body material. Although it is possible to drill with

carbide drill bit, it is too hard for tapping. Therefore, flange is made which is the easiest way to attach

pressure transducers on the pressure lines. By this method, dynamic of the fluid is affected as little

as possible.


Figure.30 Hydraulic valve actuator and pressure transducer flange body [24]

# Description

1 Top pressure line

2 Bottom pressure line

3 Kistler bottom pressure transducer

4 Pressure transducer bolt

5 Pressure inlet for actuator

6 Pressure line for servovalve

7 Top pressure line

8 Bottom pressure line

Table.4 Pressure lines and measurement equipment

2.2.9- Poppet Valve

Conventional poppet valve is used for this project which has 36 mm diameter and 45 mm length.

2.2.10- Control Box

Control box has three functions which are data logging, communication to main electrical box and

signal triggering. Control box has high quality 0.1 microfarad capacitor for triggering cable ground

connection to avoid triggering the function generator without trigger signal because of electric motor

high current jump. Additionally, it has emergency button if anything goes wrong which activates the

pressure relief valve of hydraulic pump to relieve pressure in the system. Schematic drawing of the

control box is given in the figure.52 in appendix. A.


2.2.11- Main Electrical Box

Main electrical box controls hydraulic pump according to signal of control box. Feedback control

system with on/off controller is used to control oil pressure into the system. Pressure switch is used

as an on/off switch. The main electrical box schematic drawing is given in figure.53 in appendix. A.

Figure.31 Block diagram of pressure control system

2.3- Oil Properties

Mobil Super 2000 10W 40 fully synthetic engine oil is used in this project because IC engines already

use this oil. Although this system can work with hydraulic oil which will give better performance. It

is important to know the performance of the EHVA system with standard engine oil to reduce the

cost of complete system on IC engines. Less components mean low cost. Typical properties of 10W

40 Mobil Super 2000 oil is given in the table.5

SAE Grade 10W 40

Viscosity ASTM D44S

CSt at 40 𝑪° 70

CSt at 100 𝑪° 10.8

Sulfated Ash, ASTM D874 (wt%) 0.96

Pour Point, ASTM D97 (𝑪°) -30

Flash Point, ASTM D92 (𝑪°) 226

Density at 15.6 𝑪°, ASTM D4052 (g/ml) 0.87

Table.5 Mobil Super 2000 4T oil properties [28]

2.4- Signal Generation System

Although the signal is calculated by the MATLAB/Simulink model, computer requires an interface

to generate analog signal for the servovalve. Firstly, Arduino Mega 2560 electronic board is used to

generate that signal. Even though it generates the signal successfully, modulation frequency which


is 488 Hz is not enough to generate same signal form in valve opening time interval above 500 rpm.

Therefore, TTi TG1010A function generator is used which has higher frequency.

2.4.1- Arduino Mega 2560

As it is explained, MATLAB/Simulink model is used in this project to generate feed-forward signal

so interface should be able to communicate with MATLAB software. Arduino has able to do this

communication but it can generate just digital or PWM signal output. However, analog output is

required for signal amplifier to convert it current signal. Therefore, PWM signal is converted to the

analog signal by using low-pass filter which increases clock timing. Specifications of Arduino Mega

2560 is given in the table.6 [29].

Operation Voltage 5V

Input Voltage 7-12V

Input Voltage Limits 6-20V

Digital I/O Pins 54 (14 of them PWM)

Analog Input Pins 16

DC Current per I/O Pin 40mA

DC Current for 3.3V Pin 50mA

SRAM 8KB

EEPROM 4KB

Flash Memory 256KB (8KB used for Bootloader)

Clock Speed 16MHz

Table.6 Mobil Super 2000 4T oil properties [29]

PWM signal can be explained such as a duty cycle in the figure.32. The Arduino can generate 0-5v

which is equal to 0-255 in PWM. Therefore, Arduino generates 0 voltage when the signal is 0 and

constant 5 volt when the signal value is 255. However, any value in between these two values creates

duty cycle percentages in the PWM signal form. Therefore, by using low-pass filter, average of this

duty cycle can be converted to analog voltage output. Low-pass filter schematic drawing is given in

the figure.33. By changing the resistor or capacitor value response time which means frequency of

each period for the PWM signal can be changed. Response time is equal to multiplication of resistor

and capacitor value. Firstly, 10kohm resistor is tried. After that 4.7kohm and then 1kohm resistors

with 1microfarad capacitor. Which gives us respectively 0.01s, 0.0047s and 0.0001s for the period

time interval [30]. Additionally, sample rate of simulated signal into the MATLAB/Simulink model


should be above this period time interval to be able to download it into the Arduino. These signals

which are just example are given in the graph.1

Figure.32 Pulse Width Modulation [30]

Figure.33 Schematic drawing of the low-pass filter [30]

First of all, signal into the MATLAB/Simulink model should have offset value because PWM cannot

generate negative values. Therefore, signal which is calculated into the model should be multiplied

by 127.5 and summed with 127.5 offset value to generate the signal in the range of 0-255. The plan

was generating the signal in the range of 0-5v. When the signal became below the offset value which

is 2.75v, negative value would be generated by custom designed signal amplifier. In other case, signal

would be positive.


Figure.34 PWM form of MATLAB/Simulink servovalve signal [31]

Because of the limited memory of Arduino (256 KB) all model cannot be downloaded into the

Arduino so signal is saved to workspace of MATLAB for exporting it excel file. After that, it is

imported to signal builder into another model which is created for Arduino to download it into the

Arduino.

Figure.35 PWM conversion of MATLAB/Simulink servovalve signal for Arduino [31]

Graph.1 Comparison of response times a:1, b:4.7 and c:10kohm [32]


Although, the signal form could be catch with 1kohm resistor and 1 microfarad capacitor low-pass

filter, it cannot be used to be connected to signal amplifier because there is too much noise. As a

solution of this problem function generator is used.

2.4.2- Function Generator

TTi TG1010A function generator is used to generate analog voltage for the simulated signal.

Simulated signal is saved in comma separated value form to be able to download it into the function

generator. RS-232 to USB adaptor is required for the connection of the function generator and

computer. Schematic drawing is given in the figure.36. Although the function generator can generate

downloaded signal form with high resolution (1023x1023), every time, frequency of function

generator should be adjusted very carefully to get same time interval of the signal with simulated

signal into the model. Signal can be controlled by an oscilloscope while frequency is adjusted.

Because of that, problem occurs. It is not easy to generate exactly same signal with the model. Thus,

some error occurs for the duration of valve opening.

Figure.36 Diagram of the RS-232 to USB adaptor [33]


Repetition for signal form can be set to repeat signal as much as wanted. However, according to the

setup of test rig, triggering signal which comes from picoscope is required to activate triggering mode

of the function generator to do desired repetition. That triggering signal controls beginning of data

saving for picoscope also. Therefore, signal for servovalve and data saving is triggered at the same

time.

2.4.3- Signal Amplifier

Generated signal by the function generator is sent to signal amplifier to convert the voltage signal to

current signal form for the servovalve. There is a scale factor for current monitoring because signal

amplifier has10k ohm resistance in between the current monitoring and actual current signal which

goes to servovalve. Moreover, 1V is equal to 1A for current monitoring of signal amplifier for saved

data. Therefore, when measurements are illustrated in voltage such as 500 mV means 50 mA for

current monitoring in data analysis section. Schematic drawings of the custom designed signal

amplifier is given in the appendix. A.

2.5- Data Logging System

National instruments NI USB-6008 picoscope is used to save data in numerical form and Tektronix

TDS220 oscilloscope is used to illustrate real-time data for data logging of the test rig. Pressure

transducer’s signals are saved by the picoscope to determine the pressure differential of both inlet of

hydraulic actuator. For determining the displacement of the poppet valve, LVDT sensor signal is

saved. Finally, both function generator voltage and signal amplifier current signal monitoring are

saved by the picoscope to determine signal amplifier performance and signal which goes to

servovalve.

2.5.1- Pressure Transducers and Charge Amplifiers

Kistler piezoelectric sensors and charge amplifiers are used to measure pressure as it explained in

the section of 2.2.8. These pressure sensors are generally used to measure brake mean effective

pressure of IC engines but it works onto this system very well. Scale factor is 20 bar/v for both charge

amplifiers [34].


2.5.2- Linear Variable Differential Transformer and Signal Conditioner

Graph.2 Calibration of the LVDT sensor

Microstrain LVDT sensor is used to measure the poppet valve displacement. LVDT sensor is

connected to the microstrain signal conditioner. Additionally, the signal conditioner is connected to

the picoscope to save the movement of the valve. This sensor is frictionless which means that it does

not affect the movement of the poppet valve. It is required to do calibration to know the values in

each mm movement. However, these values are reliable if the LVDT sensor does not remove or

replace. Slope is 2.972292 mm/V. Therefore, according to voltage output of the LVDT sensor,

displacement can be calculated by equation.13.

𝐷 = 𝑀 𝑥 𝑋 …13

2.5.3- Oscilloscope and Picoscope

Tektronix TDS220 oscilloscope is used to demonstrate real-time data for adjusting function generator

signal frequency. Additionally, LabVIEW Signal Express software is used to save data in numerical

form with picoscope. Configuration of the software is set to save data when it is triggered. Trigger

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

20.3 22.3 24.3 26.3 28.3 30.3

LVD

T Se

nso

re (

V)

Valve Displacement (mm)

LVDT Sensor Calibration


source is on the picoscope channels where triggering switch is connected to PFIO to +5v channel

with an on/off switch. In the configuration, digital rising edge is selected to begin data saving.

Moreover, this triggering signal triggers the function generator also. All data is saved in voltage form

and scale factors are used to convert them in pressure, displacement and current form during

analysing. 5 analog channels are used on the 8 channel (10kHz) picoscope which are signal input

voltage after function generator, signal current monitoring after signal amplifier, two pressure

transducers and LVDT sensor output. Therefore, sampling rate for 5 channels becomes 2 kHz

(0.0005s). The voltage range of measurements is +/- 10v [26].

2.6- Test Rig Restrictions

Test rig has some restrictions because of high pressure oil so pressure endurances of each equipment

are given in the table.7.

Equipment Maximum Pressure (bar)

Parker oil Filter 414

Parker Olaer accumulator 210

Fox F4 Pressure switch 70

Hydra Products Hydraulic Pump 120

Moog servovalve 280

Flexible hydraulic hoses ≌220

Table.7 Test rig pressure restrictions [17] [18] [19] [20] [21]


3- MATLAB/Simulink Simulation Model

Figure.37 MATLAB/Simulink model [31]


Whole test rig is simulated by created MATLAB/Simulink model according to the real parameters

of the hydraulic components. Some realistic assumptions were done which are explained below.

Physical modelling components of Simscape such as SimMechanics and SimHydaulics were used to

create the simulation model of EHVA system. SimMechanics and SimHydraulics uses physical

connections so actual EHVA system matches with the simulation model as much as possible.

Subsystems for SimHydraulics and SimMechanics were used to make the model more tidy [36] [37].

Figure.38 Simulation model [45]

3.1- SimMechanics

SimMechanics are used to simulate physical properties of the poppet valve and hydraulic actuator

such as mass of the poppet valve and actuator rod. In addition to mass, viscous damping coefficient

of hydraulic piston which is calculated in the hydraulic valve actuator section is considered in the

model also. It can be entered by using the function of internal mechanics. Blocks are representing

bodies, joints, constraints and force elements. For example, Hydraulic_Valve_Assembly_1_RIGID

represents the constraints. Poppet_valve_with_hydraulic_rod_1_RIGID represents the moving part

in linear motion and cylindrical block represents cylindrical joint [38]. Figure.39 illustrates the

SimMechanics components of hydraulic actuator.


Figure.39 SimMechanics simulation model [31]

Cylindrical joint is the most important part in the SimMechanics because it determines displacement,

velocity and acceleration of the poppet valve. In addition to them, physical connection of the poppet

valve actuation is provided by this block. As it can be seen in the figure.39 ideal force sensor is

connected to that physical line to calculate the force which acts on the poppet valve by hydraulic

cylinder. Moreover, ideal transitional velocity source is used to do the connection in between

SimMechanics and SimHydraulics. The reason of using this sensor is that sensing the movement of

the double acting hydraulic cylinder and converting it to force. After that, this force is applied to the

cylindrical joint to calculate the poppet valve velocity according to its weight and internal mechanics.

Finally, determined velocity is connected to the ideal transitional velocity source again for relative

velocity [41]. These sensors do not affect the connected physical line such as inertia, friction, delays

and energy consumption so they are called ideal sensors [39]. PS-Simulink Converters are used to

convert Simulink input signal to physical signal. Units of the output can be changed by using these

blocks [40]. These blocks were attached to scopes for illustrating solutions. The easiest way to

implement hydraulic valve actuator, actuator rod and poppet valve into the SimMechanics which was

drawn into the Solidworks is SimMechanics Link into the Solidworks. There are two generations for


SimMechanics but second generation SimMechanics is used into this modelling which has less

blocks and more functions [38]. Additionally, SimMechanics can illustrate the movement of these

parts in 3D environment.

Figure.40 SimMechanics [31] [38]

3.2- SimHydraulics

SimHydraulics are used to simulate electric motor, hydraulic pump, accumulator, servovalve and

hydraulic actuator. Ideal angular velocity source, fixed-displacement hydraulic pump, gas-charged

accumulator, 4-way directional valve and double acting hydraulic cylinder components of

SimHydraulics are used to represent them respectively. PS-Simulink Converters are used for same

purpose. Hydraulic flow rate sensors were connected in between the DAHC and 4WDV to calculate

the flow rate according to opening signal of 4WDV [43] [46].


Figure.41 SimHydraulics simulation model flow control [31]

Figure.42 SimHydraulics simulation model of power unit [31]

In the actual test rig, pump is rotated by the electric motor but in the simulation, pump is controlled

by an ideal angular velocity source. Therefore, pressure can be easily controlled by increasing or

decreasing the angular velocity of the pump [42]. There is a difference between actual test rig and

simulation model in this situation but it does not affect the signal which is simulated for the


servovalve. The difference is that pump is not rotated continuously in the actual test rig because it

has control system to stop electric motor when it reaches the expected pressure. However, pump

rotates incessantly in the simulation to keep the pressure constant. Finally, hydraulic pressure sensor

is used to calculate the pressure in the simulation.

3.2.1- Hydraulic Fluid

Hydraulic fluid block was used to set oil properties which are explained in the chapter.2. Because

10W 40 oil is used hydraulic fluid was selected 10W in the block parameters. Relative amount of

trapped air was entered 0.0001 which is an assumption. System temperature was selected 27𝐶° which

is the room temperature because there is no heat source to heat the oil except pressurized oil itself

and electric motor. Therefore, experiments were repeated while the electric motor and oil cool down

to room temperature. Viscosity derating factor was entered 0.7028. As a result of these values,

hydraulic fluid block calculated the density, viscosity and bult modulus respectively 843.64𝑘𝑔/𝑚3,

125.427cst and 1.83784𝑒9. These calculations are matched with real parameters.

3.2.2- Hydraulic Pump

All hydraulic pump parameters which are explained in the chapter.2 are required for the fixed-

displacement hydraulic pump block. Pump displacement was entered 24𝑒−7𝑚3/𝑟𝑒𝑣. Volumetric

and mechanical efficiencies were entered 0.92 and 0.87. Finally, nominal pressure, angular velocity

and kinematic viscosity were entered respectively 120bar, 314rad/s and 0.001567𝑚2/𝑠.

3.2.3- Accumulator

Accumulator parameters are such that capacity is 0.16litre, pre-load pressure is 130bar, initial volume

0𝑚3, specific heat ratio is 1.4 and structural compliance is 1𝑒−13𝑚3/𝑃𝑎. Last two parameters are

assumptions.

3.2.4- 4-Way Directional Valve

This component simulates the most important part of whole system which is Moog servovalve.

Normally, the servovalve system is more complex than a 4WDV but all required parameters have

not been known so it is simplified by using 4WDV. Although it is simplified, it does its job as good


as possible. The principle of 4WDV is that the signal is connected to the signal port which controls

the spool movement. Movement of the spool is scaled in the range of 0-100% for one direction which

means for fully opening, it will be 100% and for fully closing, it will be 0%. Spool can move both

direction so the range becomes -100 to 100%. According to rated input signal, spool opens port A or

B as determined area [47]. Opening areas are given in the table.8

Figure.43 4-way directional valve block [44]

The spool opening areas which is given in the table.8 are calculated by optimization tool for 4-way

directional valve according to Moog series 31 servovalve flow datasheet characteristics. Flow data

sheet is given in the appendix A. In the MATLAB/Simulink model, 4WDV has 100% efficiency for

spool movement so it can open instantaneously. However, actual servovalve cannot do this because

it has torque motor delay, hydraulic amplifier delay and spool inertia. Therefore, if rapid opening is

required which is showed in the figure.44, transfer function should be applied into the model just

before 4WDV signal to simulate phase lag. Generally, it is required for exact square valve profile.

For other cases, simulation model is good enough. Signal change can be seen in the figure.44 by

using transfer function.


Figure.44 Moog servovalve transfer function effect [31]

Moog servovalve transfer function is given by the manufacturer such that;

Figure.45 Moog servovalve transfer function [49]


During the calculation of Moog series 31 servovalve phase lag, sine wave was used so frequency is

from peak to peak [49]. Therefore, period interval should be calculated in between opening and

closing signals. First order transfer function is good enough up to 1500rpm. Above that engine speed,

second order transfer function should be used up to 300Hz. However, transfer function was not use

in the simulation model because of the factors which are explained with more details in the optimized

valve lift profile section. For valve lifting profile, there is not any square shape.

3.2.5- Optimization Tool for 4-Way Directional Valve

This optimization tool is created by Mathwork engineers to tune the 4WDV opening areas according

to Moog series 31 servovalve flow datasheet characteristics by using optimization algorithms.

Figure.46 Optimization Tool for 4-Way Directional Valve [48]

This MATLAB optimization tool uses these equations with iteration system to calculate valve

opening areas for required flow rate.

𝑞 = 𝐶𝑑 . 𝐴√2 |𝑃|

𝑃𝑠𝑖𝑔𝑛(𝑃) …14

𝐴 =𝐴𝑚𝑎𝑥

ℎ𝑚𝑎𝑥 ℎ …15

ℎ𝑃𝐴 = ℎ𝑃𝐴,0 + 𝑥 …16


ℎ𝑃𝐵 = ℎ𝑃𝐵,0 + 𝑥 …17

ℎ𝐴𝑇 = ℎ𝐴𝑇,0 + 𝑥 …18

ℎ𝐵𝑇 = ℎ𝐵𝑇,0 + 𝑥 …19

There is an assumption which is ℎ𝑃𝐴 = ℎ𝑃𝐵 = ℎ𝐴𝑇 = ℎ𝐵𝑇 = 0 because it is not known if the

servovalve spool has initial opening. There are another assumptions which are 1x10−9𝑚𝑚2 leakage

area and 0.2𝑚𝑚2 maximum spool opening area for the optimization tool. By entering flow rate

parameters of Moog servovalve and pressure drop in bar, opening areas can be calculated. In table.8

flow rates are given according to rated movement of the spool.

Breakpoints Actual Servovalve

current (mA)

Vector Output

Values (mm)

Flow Rate

(lpm)

Opening Areas

(𝒎𝒎𝟐)

0 0 0 0 0

1 5 0.1 2.25 0.000795

2 10 0.2 3.79 0.001327

3 15 0.3 5.68 0.001987

4 20 0.4 7.57 0.002647

5 25 0.5 9.46 0.003308

6 30 0.6 11.36 0.003972

7 35 0.7 13.25 0.004632

8 40 0.8 14.57 0.005093

9 45 0.9 15.9 0.005558

10 50 1 17.03 0.005942

Table.8 Flow datasheet characteristics of series 31 Moog servovalve [23]

3.2.6- Double-Acting Hydraulic Cylinder

Double-acting hydraulic cylinder component is used for simulating the hydraulic actuator. As it

mentioned in chapter.2 and as it can be seen in the figure.27, viscous damping coefficient parameters

were entered via SimMechanics cylindrical joint internal mechanics so the model does not have

additional dumping component. The block parameters are given in table.9.

Piston Area A (𝒎𝟐) 0.0000114

Piston Area B (𝒎𝟐) 0.0000114

Piston Stroke (m) 0.0118

Dead Volume A (𝒎𝟑) 0.000000454655

Dead Volume B (𝒎𝟑) 0.000000454655

Specific Heat ratio 1.4

Contact Stiffness (N/m) 100

Contact Damping (N.s/m) 1.5


Chamber A Initial Pressure (bar) 70

Chamber B Initial Pressure (bar) 70

Table.9 Double-acting hydraulic cylinder block parameters

3.3- Control System

Feed-forward control system is used for the test rig which has some benefits such as LVDT sensor

does not required which means less cost. For this project, LVDT sensor was assembled to illustrate

actual movement of the poppet valve. Although feed-forward control systems is used for actual

servovalve signal (figure.18), feedback control system is used to simulate the signal in the simulation

model for the feed-forward control system. As it explained in chapter.2, simulation is used to

simulate the movement of the poppet valve according to desired profile. Accordingly, required flow

rate is calculated for the movement to open valve (spool) of 4WDV. In summary, Feedback control

system is used to calculate the signal for opening of the spool according to required flow rate. After

that, simulated signal is used such as feed-forward signal for actual servovalve.

Figure.47 Block diagram of the simulation feedback control system

Figure.48 Block diagram of feed-forward control system of the test rig


Error occurs in between desired position and actual position of the poppet valve in the simulation.

Therefore, all parameters were entered as real as possible to simulate the actual EHVA system error

for generating realistic feed-forward signal. PID controller is used to fix that error. Even though just

proportional part was used for experiments, integral and derivative parts also can be used to improve

correction of the error. Working principle is such that desired profile is sent to 4WDV by using signal

builder, this signal is subtracted from actual position of the poppet valve which is 0 at the beginning.

Therefore, error becomes highest value at that point which is multiplied by determined proportional

value. This value becomes 4WDV opening signal. According to that signal, it sends calculated

amount of oil flow to DAHC. Poppet valve moves up to the amount of DAHC movement and this

position is sent back to be subtracted from desired profile signal. While error reduces, opening signal

of the 4WDV changes. This signal is saved to download into the function generator to become feed-

forward signal for the desired profile. However, signal should be inverted while it is downloaded

into the function generator because of the signal amplifier terminal connections.

4- Method of Experiments

Experiments were done for 800, 1000, 1500, 2000, 2500, 3000, 4000, 5000 and 6000rpm engine

speeds for both valve lift profiles. First of all, V-tec camshaft profile which is for B15C2 Honda

engine was tried to be followed. After that, this profile was improved for that specific engine by

using the flexibility of EHVA system. These profiles were imported into the simulation model by

using signal builder block of MATLAB/Simulink. Afterwards, 4WDV input signals which are saved

by Simout block were downloaded into the function generator after they were inverted. Frequencies

of these signals were adjusted to have same time interval with the simulated signals. Offset values

were adjusted to close the valve fully and balance the hydraulic amplifier of the servovalve.

Downloaded signals were sent to the signal amplifier by triggering to allow the signal amplifier

changes them from voltage to current form. Subsequently, current signal was sent to the Moog

servovalve in order to provide movement of the actual poppet valve. The movement was saved by

picoscope via LVDT sensor. During these processes, pressure on both inlets of hydraulic actuator

were saved by picoscope via pressure transducers to analyse dynamics of hydraulic actuator


behaviour. All these processes are explained with more details in chapter.2. Operation procedure is

given in the table.10

# Description

1 Run simulation in MATLAB/Simulink model

2 Save signal data in Sigdata.csv file format

3 Download it into TTi TG1010A function generator

4 Check all sensors and actuator connections

5 Check all pipe connections

6 Turn on main switch on main electrical switch

7 Press “on” button to run hydraulic pump which is on control box

8 Adjust pressure switch to 70bar

9 Adjust offset value for servovalve

10 Run picoscope software

11 Press “triggering” button which is on control box

12 Collect data and save them

13 Press “off” button to stop hydraulic pump which is on control box. It will release

all pressure in the system

14 Press “emergency” button to relief all pressure into the system if anything goes

wrong

Table.10 Operation procedure of the test rig

Experiment Engine Speed

(rpm)

Proportional

Gain

Frequency

(Hz)

DC Offset

(mV)

Amplitude (Vpp)

(Peak-Peak)

1 800 0.2 25 -100 0.85

2 1000 0.3 24 -100 0.9

3 1500 0.3 36 -100 1.3

4 2000 0.4 46 -90 1.8

5 2500 0.5 52 -80 1.95

6 3000 0.6 62.2 -50 2.4

7 4000 0.8 100 -40 3

8 5000 0.8 105 -30 3.05

9 6000 0.9 125 -20 3.8

Table.11 Function generator and Simulink model parameters for V-tec camshaft profile

Experiment Engine Speed

(rpm)

Proportional

Gain

Frequency

(Hz)

DC Offset

(mV)

Amplitude (Vpp)

(Peak-Peak)

1 800 0.3 20 -100 0.92

2 1000 0.3 27 -95 1.22

3 1500 0.5 37.5 -75 1.8

4 2000 0.7 55 -69 2.7

5 2500 0.8 56 -55 3

6 3000 0.9 68 -55 3.2

7 4000 1 68 -50 3.3

8 5000 1.1 70 -35 4.3

9 6000 1.2 84 -35 4.87

Table.12 Function generator and Simulink model parameters for optimized profile


4.1- V-tec Camshaft Profile

V-tec full lift camshaft profile was used to be followed to prove that the EHVA system have ability

to produce existing profiles. Camshaft profile is given in the graph.3.

Graph.3 V-tec camshaft profile [51]

As it can be seen in the graph.3, camshaft profile is given in crankshaft angles but signal builder into

the simulation model cannot accept degrees so these equations are used to calculate time interval per

one crankshaft angle.

𝜃𝐶 . (1

𝑟𝑝𝑚/60) /360 …20

Opening durations of valve profiles for 210CA V-tec camshaft and desired valve lift according to

engine speeds are given in the table.13.

Engine Speed

(rpm)

V-tec Profile Opening

Duration (ms)

Optimized Profile Opening

Duration (ms)

800 43.75 37.5

1000 35.00 30.0

1500 23.33 20.0

2000 17.50 15.0

2500 14.00 12.0

3000 16.60 10.0

4000 8.750 7.50

5000 7.000 6.00

6000 5.830 5.00

Table.13 Opening duration of 210CA camshaft and 180CA desired profiles

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0

1

2

3

4

5

6

7

8

9

10

0 50 100 150 200 250 300

Val

ve V

elo

city

[m

m/d

egr

ee

]

Val

ve L

ift

[mm

]

Cam Angle [degrees]Exhaust Valve Lift Primary Valve LiftSecondary Valve Lift VTEC Valve LiftExhaust Valve Velocity Primary Valve Velocity


4.2- Desired Valve Lift Profile

EHVA systems which eliminate dependency of the restrictive camshaft profile and give freedom for

each valves allow infinitely controls for valve lifting, duration and variable timing. Therefore, V-tec

camshaft profile was optimized with the flexibility of EHVA system. Although this system has ability

to provide almost square valve profile. There are some limitations for IC engine volumetric efficiency

in addition to mechanical limitations such as valve failure under high speed opening and closing

conditions [14] [52] [53]. For this reason, during the optimization of valve opening profile for B15C2

engine volumetric efficiency and valve opening and closing velocities are considered too. B15C2

engine required parameters are given in the table.14 to calculate valve opening profile without air

choking condition. Moreover, valve full lifting should be at maximum piston speed. Accordingly,

volumetric efficiency was calculated as high as possible by considering piston speed and air choking

during the calculation of valve lifting profiles. Although it is required to do more complex

calculations and experiments to determine the best profile for an engine, equation.1, 2, 3, 4, 5, 6, 7

and 8 are used for calculation of valve lifting profiles for opening. Unlike opening profiles, just valve

speed was considered for closing profiles because opening duration time should be as much as

possible for letting air breathing more. However, it cannot have square profile because of the speed

factor so it is calculated to limit speed of the valve as little as possible without losing area. Finally,

the equation for 180CA opening profile becomes such that;

𝑠 = 𝑎. sin(𝜃𝐶) + (𝑙2 − 𝑎2𝑠𝑖𝑛2(𝜃𝐶))1/2 …21

𝑆𝑝 =𝑑𝑠

𝑑𝑡 …22

𝐿𝑣 = 𝐴𝑝.𝑆𝑝

(0.676.𝐶𝑖.𝜋.𝐶𝐷𝐷𝑣)𝑥1000 …23

Where;

𝐴𝑝: 0.010306𝑚2

𝑆𝑝: Changes with the engine speed

𝐶𝑖: 364.1346m/s


𝐶𝐷: It is assumed 0.6

𝐷𝑣: 0.036m

Figure.49 IC engine geometry for piston speed calculation [54]

Bore “B”

(mm)

Connecting Rod Length “l”

(mm)

Crankshaft Radius “a”

(mm)

81 137.9 77.4

Table.14 Honda B15C2 engine specifications [55]

Although all profiles are given in the experiment result section, an opening profile is given in the

graph.4 to illustrate one of the desired profile shape. The difference in between opening profile and

closing profile can be seen in the graph.4. Moreover, while engine speed increases, opening profile

changes because of the relation of piston speed and valve lifting profile. After 2500rpm, due to speed


factor, same opening profile with 2500rpm was used for above engine speeds. On the other hand,

closing profile is fixed for every engine speeds.

Graph.4 Desired valve profile for 1000rpm

5- Experiment Results and Analysis

18 experiments were done for each engine speed and both profiles. Therefore, it is not possible to

illustrate every experiment results in this report. Thus, major points are explained in this section.

Other experiment results and analysis are given in the attached CD at the back of the dissertation.

Although experiment’s target pressure is 70bar, all experiments were done in the pressure range of

68 to 72bar for both V-tec and optimized valve profiles. Because of the pressure switch low response,

control system is unable to maintain the constant pressure. Minimum error was caught at 800 and

1000rpm so every explanations of analysis will be at these engine speeds. Moreover, explanation of

reasons for increasing error of the other engine speeds are given in this section also. Additionally,

time interval in each 5 crank angle becomes approximately 0.0002 but picoscope can record with dt:

0.0005 (2kHz). Therefore, some points are missed in data logging after 2000rpm. For example, it can

-4

-3

-2

-1

0

1

2

0

2

4

6

8

10

12

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035

Vel

oci

ty (

m/s

)

Lift

(m

m)

Time (s)

Desired Profile (1000rpm)

Desired Lift (mm) Desired Velocity (m/s)


be seen clearly for optimized profile input signal at 5000 and 6000rpm. First of all, V-tec camshaft

profile comparison is given to illustrate the error of the actual valve lift according to varying engine

speed from 800 to 6000rpm. Although EHVA system has the capable of lifting profile repetitions,

each experiment is done separately because just one signal form can be downloaded into the function

generator. However, they are combined to show them together in a graph. Repetition experiments

analysis are given in the CD.

Graph.5 Comparison of desired, simulation and actual valve lift for V-tec lift profile

Duration of the signal is adjusted by adjusting function generator frequency. It is explained in

chapter.2 with more details. Therefore, one of the reason of these errors for valve opening durations

are because of human error in addition to simulation error. Errors are acceptable up to 2000rpm but

after that engine speed valve lifting begins to lose which is directly related about pressure. By

increasing the pressure, it can be solved but leakage of the actuator will also increase so without

doing experiment with higher pressure it is hard to predict that. Valve speed comparisons are given

in the graph.6.

0

2

4

6

8

10

12

0 0.05 0.1 0.15 0.2 0.25 0.3

Lift

(m

m)

-En

gin

e sp

eed

x1

00

0(r

pm

)

Time (s)

Valve Lift

Desired Lift (mm) Engine Speed x1000 (rpm) LVDT(mm) Simulation Lift (mm)


Graph.6 Comparison of desired and actual valve speeds for V-tec lift profile

Even though speed of the valve is almost matched with desired speed up to 1000rpm after that engine

speed, valve could not move fast enough to catch desired profile so speed of the actual valve

movement is less than desired valve speed. Signal of function generator and after signal amplifier

which is called current monitoring is given in the graph.7.

Graph.7 Input signals for V-tec lift profile (500mV=50mA)

-20

-15

-10

-5

0

5

10

15

0

1

2

3

4

5

6

7

0 0.05 0.1 0.15 0.2 0.25 0.3

Vel

oci

ty (

m/s

)

Engi

ne

Spee

d (

x10

00

rpm

)

Time (s)

Valve Speed

Engine Speed x1000 (rpm) Desired Velocity (m/s) Actual Velocity (m/s)

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

0

1

2

3

4

5

6

7

0 0.05 0.1 0.15 0.2 0.25 0.3

Am

plit

ud

e (V

)

Engi

ne

Spee

d (

x10

00

rpm

)

Time (s)

Input Signal

Engine Speed x1000 (rpm) Current Monitoring (A) Input Signal (v)


As it can be seen in the signal analysing, oil flow rate is related by time and servovalve spool opening.

Therefore, the spool should be opened more to get same oil flow rate in shorter time interval to supply

more oil into the hydraulic cylinder. Furthermore, there is an offset value for the moog servovalve.

While amplitude increases offset value changes also in the function generator but output voltage is

almost same. DC offset value of the function generator is very important because servovalve spool

does not close ports at the beginning. In theory, it might happen because servovalve spool has initial

openings with ports or internal leakages of the spool. The other reason might be that the spool does

not stop, it always moves one direction excessive slowly while DC offset is given. Therefore, DC

offset should be adjusted very carefully to close ports. Otherwise, offset value may affect by ignoring

or reducing opening or closing signal. It depends which way is selected. As it explained above, it is

assumed to move very slowly to one direction. Therefore, in these experiments, DC offset value is

selected to close valve fully which means spool direction is selected to move one direction excessive

slowly to open one port to allow oil flow for pushing valve to be fully close. After that, signal is sent

to servovalve. Value of DC offset is selected very low to do not affect the signal and can be different

a little bit for function generator when same experiment is repeated. However, it is same for output

of function generator according to the graph.7. For example, DC offset value may change + and - 5

mV. Table of function generator parameters are given in chapter.4.

Graph.8 Comparison of the valve lifting for V-tec lift profile at 1000rpm

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0

2

4

6

8

10

12

0 0.005 0.01 0.015 0.02 0.025 0.03

Sign

al (

x0.1

A)

Lift

(m

m)

Time (s)

V-tec Camshaft Profile vs Signal (at 1000rpm)

LVDT(mm) Desired Lift (mm) LVDT(mm) Simulation (mm) Current Monitoring (A)


Graph.9 Valve speed for V-tec lift profile at 1000rpm

Graph.10 Pressure of the hydraulic actuator inlets according to V-tec lift profile at 1000rpm

Although actual valve lifting error is low at 1000rpm which is the lowest error for V-tec profile,

valve closes too fast. It should be improved to avoid valve failure. Hydraulic actuator both sides

pressure are given in the graph.10. Dynamic behaviour can be understood from these pressure

measurements. They are used to improve simulation model by comparing them with the calculated

pressure into the simulation model. For instance, because of the Moog servovalve spool internal

geometry is not known, opening areas of the 4WDV were assumed according to optimized tool of

-4

-3

-2

-1

0

1

2

3

0

2

4

6

8

10

12

0 0.005 0.01 0.015 0.02 0.025 0.03

Vel

oci

ty (

m/s

)

Lift

(m

m)

Time (s)

Valve Speed (at 1000rpm)

LVDT(mm) Desired Lift (mm) Actual Velocity (m/s) Desired Velocity (m/s)

-20

-10

0

10

20

30

40

50

0

1

2

3

4

5

6

7

8

9

10

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04

Pre

ssu

re (

Bar

)

Lift

(m

m)

Time (s)

Pressure (at 1000rpm)

LVDT(mm) Bottom Pressure (bar) Top Pressure (bar)


MATLAB. However, these areas are modified to get similar pressure graph into the simulation

model. Pressure measurements demonstrate pressure differential of both inlets. Pressure drop can be

seen for both inlets at valve opening and closing times. Pressure graphs are very similar because the

profile is same for valve opening and closing. However, they are not same for optimized profile

which is illustrated in the graph.16. Secondly, Optimized valve lifting profile comparison is given to

show actual valve lifting error for varying engine speed from 800 to 6000rpm. Lowest error is at

800rpm for optimized profile experiments. Although displacement of the hydraulic actuation is

11.8mm, desired poppet valve lift is maximum 10mm to prove that valve does not fluctuate at full

lift opening duration. Similar to camshaft profile experiments, valve lifting begins to lose after

1000rpm.

Graph.11 Comparison of desired, simulation and actual valve lift for optimized lift profile

Valve speed is given in the graph.12 which demonstrates error increases as engine speed increase

because valve lift profile does not follow desired lift profile as expected.

0

2

4

6

8

10

12

0 0.05 0.1 0.15 0.2 0.25 0.3

Lift

(m

m)

-En

gin

e Sp

eed

(x1

00

0rp

m)

Time (s)

Valve Lift

Desired Lift (mm) Simulation Lift (mm) LVDT(mm) Engine Speed x1000 (rpm)


Graph.12 Comparison of desired and actual valve speeds for optimized lift profile

Graph.13 Input signals for optimized lift profile (500mV=50mA)

Valve opening and closing profiles have differences as it mentioned before. Therefore, signals for

opening and closing are different also as demonstrated in graph.13. When engine speed increases,

both profiles becomes similar so signal also becomes similar. However, after 2000rpm data logging

-22

-17

-12

-7

-2

3

8

13

18

23

0

1

2

3

4

5

6

7

0 0.05 0.1 0.15 0.2 0.25 0.3

Vel

oci

ty (

m/s

)

Engi

ne

Spee

d (

x10

0rp

m)

Time (s)

Valve Speed

Engine Speed x1000 (rpm) Desired Velocity (m/s) Actual Velocity (m/s)

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

0

1

2

3

4

5

6

7

0 0.05 0.1 0.15 0.2 0.25 0.3

Am

plit

ud

e (V

)

Engi

ne

Spee

d (

x10

00

rpm

)

Time (s)

Input Signal

Engine Speed x1000 (rpm) Current Monitoring (A) Input Signal (v)


system sample rate does not enough to save each 5CA. It can be seen easily on 5000 and 6000rpm

input signals.

Graph.14 Comparison of the valve lifting for optimized lift profile at 800rpm

Graph.15 Valve speed for V-tec lift profile at 1000rpm

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0

1

2

3

4

5

6

7

8

9

10

0 0.01 0.02 0.03 0.04

Sign

al (

x0.1

A)

Lift

(m

m)

Time (s)

Optimized Profile vs Signal ( at 800rpm)

Simulation (mm) LVDT(mm) Desired Lift (mm) Current Monitoring (A)

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

0

1

2

3

4

5

6

7

8

9

10

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04

Vel

oci

ty (

m/s

)

Lift

(m

m)

Time (s)

Valve Speed (at 800rpm)

Desired Lift (mm) LVDT(mm) Desired Velocity (m/s) Actual Velocity (m/s)


Graph.16 Pressure of the hydraulic actuator inlets according to optimized lift profile at 800rpm

Same problem with V-tec lift profile occurs in this profile also. Valve closes very quickly which

might cause valve failure. Pressure graph of the optimized valve lift profile is used to modify

MATLAB/Simulink model to adopt it actual test rig.

5.1- Discussion of Experiment Results

Although simulation model is used to create signal form of the desired valve lift profile, signal form

is distorted partially while it is downloaded into the function generator. Moreover, signal is changed

partly by signal amplifier also. Furthermore, it changes a little when the frequency is adjusted because

of human error. For these reasons, error becomes more than it should be. Thus, besides simulation

model, signal generation system is also required to improve. As it expected, valve lifting profile error

increased while engine speed increased. The pressure should be increased to fix that error because

flow rate does not enough to fill hydraulic actuator instantaneously in 2500rpm and above engine

speed's time intervals. If pressure switch is replaced, test rig pressure endurance changes which

means EHVA system pressure can be increased up to 120bar. This increment may reduce that error.

-40

-30

-20

-10

0

10

20

30

40

50

0

1

2

3

4

5

6

7

8

9

10

0 0.01 0.02 0.03 0.04 0.05

Pre

ssu

re (

Bar

)

Lift

(m

m)

Time (s)

Pressure (at 800rpm)

LVDT(mm) Bottom Pressure (bar) Top Pressure (bar)


6- Future Work

This setup which was created to do experiments works quite well but transitions of signals for

different engine speeds takes time. Therefore, although this system can be applied for real engine, it

is not possible to do experiments for different engine speeds at once. Which means that if the setup

is configured for 1000rpm, engine speed should be exactly 1000rpm. It can be done by making a one

tooth trigger wheel which is connected to the cranks shaft. This system will enables to know piston

position to triggering the function generator for the signal and picoscope at the same time instead of

manually triggering. This experiment can be repeated for different engine speeds. However, there is

a solution for that problem which is XPC target or similar interfaces. By using XPC target, it is

possible to change the setup to do experiments with real-time controls. This is called hardware in the

loop system [56]. Additionally, this system enables to measure the pressure into the EHVA system

to change the parameters into the simulation model. Because of the simulation model is sensitive to

pressure changes, it will change the 4WDV control signal. Possible pressure sensing model is

demonstrated in the figure.50

Figure.50 SimHydraulics actual pressure measurement for power unit [31]

Moreover, it will enable to change the controller parameters in real-time. Besides all these

improvements, it is required to change the 100% 4WDV block by advanced servovalve model which


is provided by MATLAB/Simulink [8]. This replacement will be improved the simulation model to

generate more realistic signal to become more compatible with the real test rig. However, it is

necessary to know all internal dimensions and specifications to enter them into the advanced

servovalve model. This model has simulations blocks of flapper/armature for torque motor,

flapper/nozzle for hydraulic amplifier and main valve for the spool.

Figure.51 SimHydraulics advance servovalve model [31]

Finally, in addition to these improvements feedback control system might be added to feed-forward

control system to reduce the error. It might work better than just feedback or feed-forward control

system because feed-forward will reduce the huge error for feed-back control system. Therefore,

possible collision of the poppet valve and piston wil be avoided.


Conclusion

This project is about the investigation of control system strategies for hydraulic valve actuation in an

IC engine. This investigation makes possible to increase flexibility of control of valve lifting profile,

timing, and duration. Which might reduce significant amount of fuel consumption and exhaust

emission by using advanced engine strategies. In this project, feed-forward control system is used to

control EHVA system which is required pre-calculation to determine the signal form of servovalve

to manage hydraulic actuator. Therefore, MATLAB/Simulink Simscape physical modelling

components are used such as SimMechanics and SimHydaulics to simulate required signal form for

EHVA system. First of all, existing camshaft profile was followed to prove that the EHVA systems

have capable of existing technologies. Secondly, this profile is optimized to illustrate that this

systems can remove the restrictions of camshaft profiles and VVA systems. Although experiments

were done from 800 to 6000rpm, utilizable profile forms are just up to 2000. However, in my opinion,

this engine speed is good enough to do experiments of advance engine strategies on research engines.

Even though 18 experiments were done, it does not possible to insert each experiment analysis in

this report. Therefore, major points are explained in this report and other analysis of experiment are

insert into the CD which is attached at the back of the report. MATLAB/Simulink model files,

solidworks drawings, valve lift profiles, function generator signals, test rig equipment specifications

and interim report are inserted into the CD also.


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Appendix A

Graph.17 Motor-pump performance [17]

Graph.18 Parker 10µm oil filter pressure-flow characteristics [20]


Graph.19 Moog series 31 servovalve flow datasheet characteristics [23]


Figure.52 Schematic of Control box [25] [27]


Figure.53 Schematic of main electrical box [25] [27]


Figure.54 Schematic of signal amplifier [25] [27]


All drawings are in mm.

Figure.55 Solidworks drawing of pipes t-connection bracket [24]


Figure.56 Solidworks drawing of HVA and oil filter bracket.a [24]


Figure.57 Solidworks drawing of HVA and oil filter bracket.b [24]


Figure.58 Solidworks drawing of Pprotective glass frame [24]


Figure.59 Solidworks drawing of sink [24]


Figure.60 Solidworks drawing of pressure transducer flange [24]


Appendix B


Appendix C

Figure.61 Plan of the project

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