27.a Bo Anderson Lectures on Mobilehydraulics_part1_tmms10_2011

©2009 Bo R Andersson

Hydraulic systems for Mobile

Applications• 1st Lecture

– Types of directional valves

– Steady State behaviour

Sid 1

• 2nd Lecture

– System Dynamics

TMMS10 Fluida system och transmissioner

2011-05-16

Bo R Andersson

©2009 Bo R Andersson 2

Content

- Introduction to mobile systems

- Hydraulic operation of a load

- Directional valves for mobile applications

- Closed centre valve

- Open centre valve

- LS

- Computer operated valve

1st Lecture

May 16, 2011

Bo R Andersson

Comparison of properties:

-Operateability

-Power effectiveness

-Complexity


Control of position by control of velocity(change of velocity, acceleration, deceleration)

Introduction to Mobile Systems

©2009 Bo R Andersson Linköpings universitetSid 4

Control of working hydraulics

Typical for mobile machines:

-Control of load or implement

-Controlled by an operator

-Load conditions change continuously

-Simultaneous operation of several functions

-One pump to several functions


Mobile Hydraulics”Continously operated by a human being”

Difficulties and challenges:• Wide operating range

• No consistency between flow and speed

• Simultanous operation of several functions

• Saturation of pump flow

• Low efficiency and heat generation

• Safety and stability

• Low natural frequency and low damping

• Cost

©2009 Bo R Andersson Sid 6

Closed Centre Open Centre Load Sensing

Types of mobile valves:


Types of pumps:

Constant Pressure

Variable Flow

Constant Flow

Variable Pressure

Variable Pressure

Variable Flow




Hydraulic operation of a Load


Closed Center Valve


Velocity Gain (Angular speed of Arm/Speed of cylinder)

0

1

2

3

4

5

6

7

8

0 20 40 60 80 100 120 140 160 180

Angle of Arm

Vel

oci

ty G

ain

No direct relation between flow and velocity!


Closed Center Valve

Qp-Diagram for Closed-Center Valve

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100

Q Load %

p L

oad % dQ

dp

20% 30% 40%

50%

60%

70%

80%

100%

Constant Pressure System


Open-Centre Valve

Öppningsareor

0

5

10

15

20

25

30

0 1 2 3 4 5 6

Slidläge [mm]

Öp

pn

ing

[m

m^

2]

P - A

B - T

Aoc

Load drop check valves

Constant Flow System


Example of Open-Centre Valve

Open-Centre valve with a Q-Inlet.


Open Centre valves

Most common valve type

Advantages:

- Simple and cost effective

- Control of both flow and pressure

- High damping, good dynamic performance

Disadvantages:

- Low efficiency with fixed depl. pump

- Difficult to limit port flow

- Flow control is load dependent

- Interaction between loads (load interference)


LS-system

Load Drop Check Valve

00

20

40

60

l/min

3 4 52 61 mm345 26 1

Valve Characteristic


LS-system

Load Drop Check ValvesPressure compensators


LS-system

Load Drop Check ValvesPressure compensators

Power Usage Dual OperationPower Usage Single Operation


Flow Control Valves

p

q

Post- and pre-pressure compensation

)(2 21 ppACQ q


Post-Pressure Compensation


Post-Pressure Compensation,

Rexroth type

German: LUDV – Lastunabhängige Durchfluss Verteiligung

Flow Sharing


Rexroth LUDV


Rexroth M6-15, LUDV


EFM -Electrohydraulic Flow Matching


Energy Efficient Systems


Utan laståtervinning

Conventional

LS-system

Average hydraulic power during a working cycle

Energy Efficient Systems


Reduction of Power Losses

Energy Effective Systems

Low Pressure

Regeneration

High Pressure

Regeneration

Energy

Recuperation


Reduction of Power Losses

Energy Effective Systems

3-port Valves 2-port Valves


Computer Controlled Valves


Eaton: Ultronics


4. High Power

Force Motor

6. Pilot slid

5. Centreringsfjäder

8. Pressure

transducers

2. Independent

spolls

1. Valve of Mono-

block type

3. Pilot ventil

9. Inbäddad ASIC signalprocessor

7. Position

transducer,

LVDT

Ultronics System Översikt: … TS16 Elektro-Hydraulisk Ventil


Ultronics


Husco: Incova


-Pressure sensitive (unbalanced pilot)

-Low bandwidth

-Long-stroke solenoid

-Poor accuracy

Design issues:


Decoupling of pressure and flow

- Use of sophisticated control theory

- Requires good knowledge of the application


Computer Operated Valves

• The beauty with computer control and with all sensors is that the control possibilities are endless

• At the same time, the computer control has the following disadvantages and difficulties:– Safety

– Reliability

– Development time and cost

– Production cost

– Must meet ISO 15998 and EN 61508

– …

27.a Bo Anderson Lectures on Mobilehydraulics_part1_tmms10_2011

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