©2009 Bo R Andersson Hydraulic systems for Mobile Applications Sid 1 TMMS10 Fluida system och...

©2009 Bo R Andersson

Hydraulic systems for Mobile Applications

Sid 1

TMMS10 Fluida system och transmissioner2014-05-08

Bo R Andersson

©2009 Bo R Andersson 2

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


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


Content

Low natural frequency and low damping- Oscillations of hydro-mechanical systems- Natural frequency- Damping by the hydraulic system- Simulations of different types of systems- Load Holding Valves

May 08, 2014Bo R Andersson


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

Open-Center Valves

©2009 Bo R Andersson Linköpings universitetSid 6

A mobile application

- Steady state performace very important


A mobile application

- Steady state performace very important- Dynamic performance still more important!


Car Suspension


Car suspension damping


Damping of a hydraulic operated boom?


Oscillations of hydro-mechanical systemsNatural Frequency

©2009 Bo R Andersson Sid 12

Oscillations of hydro-mechanical systemsNatural Frequency

Video


Natural Frequency of an arm with a load


Natural Frequency of an arm with a load

Higher working pressure


New machines will have even lower natural frequency!New machines will be even more lika a ”fishing pole”!New machines will have even lower damping!

Even more important to avoid oscillations!!

EgenfrekvensNatural Frequency


0

10

20

30

40

50

60

70

80

90

100

0 2 4 6 8 10 12

Cp = oo

Cp = 0

dP

dQ

Cp =dQ

dP

05

1015202530354045

0 5 10 15 20 25 30 35

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30 35

Cp

M

pQ diagramEgenfrekvens, dämpning


Mobile Valve Systems from a dynamic Point of View

19


Constant Pressure SystemThrottle Valve (Variable orifice)

Simulation


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%

pQ-diagram, Closed-Centre Valve


Constant Flow System – Open-CentreThrottle Valve (Variable orifice)

Simulation


pQ-diagram, open-centre valve


Damping by a LS valve

Simulation


Damping by a LS-valveIncreased damping by use of meter-out restriction

Simulering


Dämpning med LS-ventil

Va/Vb = 1/3 - 3/1, = 0.5

Va/Vb = 1/3 - 3/1, = 1.0

b

a

V

V21

4/3

1

e

bccbm m

VAK

Meter-out dampingDamping by a LS-valve:


Fig. 11, 12

CMX-valvePressure feedback

Danfoss PVG 32 has a special version with a pressure control spool

Parker has two types of pressure feedback


Damping by a LS-valveIncreased damping by use of pressure feedback

Simulation


Crane without pressure feedback


Crane with pressure feedback


Safety ...

Slangbrott: “s”


Over-center valves have the following functions :

- Hose rupture safety

- Load holding with 0 leakage

- Important part of over-load system

- Control of lowering speed

- Relief and chock valve


Load Holding Valvesof

Over-Centre Type

Easily start to oscillate! Why?

High power losses! Why?

35


Lorry Crane

Typical Over-Centre Valve


Load goes over-centre


Meter-in control

Load goes over-centre


P T

Hoist sustem

Avoid cavitation by ”pumping down” the load


Crane arm controlled by an open-center valveand an over-center valve


Steady state control of LHV

Areaförhållande: 1

2

A

A 0


Analyze of an over-centre valve system


Oscillating hydro-mechanical system


Pressure oscillations


Simulering


Over-centre valves in crane ssytems

Use of Over-Center Valves:-Hose Rupture Safety Protection-Low Leakage-Active part of OLP System-Speed Control-Pressure Relief function


Use of Over-Center Valves:-Hose Rupture Safety Protection-Low Leakage-Active part of OLP System-Speed Control-Pressure Relief function

Difficult to avoid oscillations!

Waste of energy!

Over-centre valves in crane ssytems


3G - New Load Holding Valve

How does it work?


3G - Load holding Valve

How does it eliminate power losses?


3G - LHV

Conclusions:

- Hose rupture safety without compromising safety or performance

- Elimination of tendency to oscillate associated with over-centre valve systems

- Elimination of power losses when lowering gravity loads

©2009 Bo R Andersson Hydraulic systems for Mobile Applications Sid 1 TMMS10 Fluida system och...

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