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TMMS10 Fluida system och transmissioner 2014-05-08 Bo R Andersson. Hydraulic systems for Mobile Applications. Mobile Hydraulics ” Continously operated by a human being”. Difficulties and challenges: Wide operating range No consistency between flow and speed

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mobile hydraulics continously operated by a human being
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 being1
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
slide4
May 08, 2014

Bo R Andersson

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
slide5
Open-Center Valves

Control of position by control of velocity

(change of velocity, acceleration, deceleration)

slide6
A mobile application

- Steady state performace very important

Linköpings universitet

slide7
A mobile application

- Steady state performace very important

- Dynamic performance still more important!

Linköpings universitet

slide8
Car Suspension

Linköpings universitet

slide9
Car suspension damping

Linköpings universitet

slide11
Oscillations of hydro-mechanical systems

Natural Frequency

Linköpings universitet

slide15
Egenfrekvens

Natural Frequency

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!!

slide18
M

Cp

pQ diagram

Egenfrekvens, dämpning

dQ

Cp =

dP

dQ

Cp = oo

dP

Cp = 0

slide20
Constant Pressure System

Throttle Valve (Variable orifice)

Simulation

slide22
Constant Flow System – Open-Centre

Throttle Valve (Variable orifice)

Simulation

slide25
Damping by a LS-valve

Increased damping by use of meter-out restriction

Simulering

slide26
Dämpning med LS-ventil

Va/Vb = 1/3 - 3/1, k2 = 0.5

Va/Vb = 1/3 - 3/1, k2 = 1.0

Damping by a LS-valve:

Meter-out damping

slide27
CMX-valve

Pressure feedback

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

Parker has two types of pressure feedback

Fig. 11, 12

slide28
Damping by a LS-valve

Increased damping by use of pressure feedback

Simulation

slide32
Safety ...

Slangbrott: “s”

slide33
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 valves of over centre type

Load Holding ValvesofOver-Centre Type

Easily start to oscillate! Why?

High power losses! Why?

slide36
Lorry Crane

Typical Over-Centre Valve

slide38
Load goes over-centre

Meter-in control

slide39
Hoist sustem

Avoid cavitation by ”pumping down” the load

slide42
Steady state control of LHV

Areaförhållande:

slide43
Analyze of an

over-centre valve

system

slide44
Analyze of an

over-centre valve

system

slide48
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
slide49
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

Difficult to avoid oscillations!

Waste of energy!

slide50
3G - New Load Holding Valve

How does it work?

Sid 50

slide51
3G - Load holding Valve

How does it eliminate power losses?

Sid 51

slide52
3G - Load holding Valve

How does it eliminate power losses?

Sid 52

3g lhv
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

Sid 53

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