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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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Hydraulic systems for mobile applications

TMMS10 Fluida system och transmissioner

2014-05-08

Bo R Andersson

Hydraulic systems for Mobile Applications


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


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


Open-Center Valves

Control of position by control of velocity

(change of velocity, acceleration, deceleration)


A mobile application

- Steady state performace very important

Linköpings universitet


A mobile application

- Steady state performace very important

- Dynamic performance still more important!

Linköpings universitet


Car Suspension

Linköpings universitet


Car suspension damping

Linköpings universitet



Oscillations of hydro-mechanical systems

Natural Frequency

Linköpings universitet





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!!




M

Cp

pQ diagram

Egenfrekvens, dämpning

dQ

Cp =

dP

dQ

Cp = oo

dP

Cp = 0



Constant Pressure System

Throttle Valve (Variable orifice)

Simulation



Constant Flow System – Open-Centre

Throttle Valve (Variable orifice)

Simulation




Damping by a LS-valve

Increased damping by use of meter-out restriction

Simulering


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


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


Damping by a LS-valve

Increased damping by use of pressure feedback

Simulation


Crane without pressure feedback


Crane with pressure feedback


Safety ...

Slangbrott: “s”



Load holding valves of over centre type

Load Holding ValvesofOver-Centre Type

Easily start to oscillate! Why?

High power losses! Why?


Lorry Crane

Typical Over-Centre Valve



Load goes over-centre

Meter-in control


Hoist sustem

Avoid cavitation by ”pumping down” the load



Steady state control of LHV

Areaförhållande:


Analyze of an

over-centre valve

system


Analyze of an

over-centre valve

system





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


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!


3G - New Load Holding Valve

How does it work?

Sid 50


3G - Load holding Valve

How does it eliminate power losses?

Sid 51


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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