Hydraulic systems for mobile applications
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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


Hydraulic systems for mobile applications

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


Hydraulic systems for mobile applications

Open-Center Valves

Control of position by control of velocity

(change of velocity, acceleration, deceleration)


Hydraulic systems for mobile applications

A mobile application

- Steady state performace very important

Linköpings universitet


Hydraulic systems for mobile applications

A mobile application

- Steady state performace very important

- Dynamic performance still more important!

Linköpings universitet


Hydraulic systems for mobile applications

Car Suspension

Linköpings universitet


Hydraulic systems for mobile applications

Car suspension damping

Linköpings universitet


Hydraulic systems for mobile applications

Damping of a hydraulic operated boom?

Linköpings universitet


Hydraulic systems for mobile applications

Oscillations of hydro-mechanical systems

Natural Frequency

Linköpings universitet


Hydraulic systems for mobile applications

Oscillations of hydro-mechanical systems

Natural Frequency

Video


Hydraulic systems for mobile applications

Natural Frequency of an arm with a load


Hydraulic systems for mobile applications

Natural Frequency of an arm with a load

Higher working pressure


Hydraulic systems for mobile applications

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!!


Hydraulic systems for mobile applications

Linköpings universitet


Hydraulic systems for mobile applications

Linköpings universitet


Hydraulic systems for mobile applications

M

Cp

pQ diagram

Egenfrekvens, dämpning

dQ

Cp =

dP

dQ

Cp = oo

dP

Cp = 0


Mobile valve systems from a dynamic point of view

Mobile Valve Systems from a dynamic Point of View


Hydraulic systems for mobile applications

Constant Pressure System

Throttle Valve (Variable orifice)

Simulation


Hydraulic systems for mobile applications

pQ-diagram, Closed-Centre Valve


Hydraulic systems for mobile applications

Constant Flow System – Open-Centre

Throttle Valve (Variable orifice)

Simulation


Hydraulic systems for mobile applications

pQ-diagram, open-centre valve


Hydraulic systems for mobile applications

Damping by a LS valve

Simulation


Hydraulic systems for mobile applications

Damping by a LS-valve

Increased damping by use of meter-out restriction

Simulering


Hydraulic systems for mobile applications

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


Hydraulic systems for mobile applications

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


Hydraulic systems for mobile applications

Damping by a LS-valve

Increased damping by use of pressure feedback

Simulation


Hydraulic systems for mobile applications

Crane without pressure feedback


Hydraulic systems for mobile applications

Crane with pressure feedback


Hydraulic systems for mobile applications

Safety ...

Slangbrott: “s”


Hydraulic systems for mobile applications

  • 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?


Hydraulic systems for mobile applications

Lorry Crane

Typical Over-Centre Valve


Hydraulic systems for mobile applications

Load goes over-centre


Hydraulic systems for mobile applications

Load goes over-centre

Meter-in control


Hydraulic systems for mobile applications

Hoist sustem

Avoid cavitation by ”pumping down” the load


Hydraulic systems for mobile applications

Crane arm controlled by an open-center valve

and an over-center valve


Hydraulic systems for mobile applications

Steady state control of LHV

Areaförhållande:


Hydraulic systems for mobile applications

Analyze of an

over-centre valve

system


Hydraulic systems for mobile applications

Analyze of an

over-centre valve

system


Hydraulic systems for mobile applications

Oscillating hydro-mechanical system


Hydraulic systems for mobile applications

Pressure oscillations


Hydraulic systems for mobile applications

Simulering


Hydraulic systems for mobile applications

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


Hydraulic systems for mobile applications

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!


Hydraulic systems for mobile applications

3G - New Load Holding Valve

How does it work?

Sid 50


Hydraulic systems for mobile applications

3G - Load holding Valve

How does it eliminate power losses?

Sid 51


Hydraulic systems for mobile applications

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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