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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”. Difficulties and challenges: Wide operating range No consistency between flow and speed

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Hydraulic systems for Mobile Applications

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  1. TMMS10 Fluida system och transmissioner 2014-05-08 Bo R Andersson Hydraulic systems for Mobile Applications

  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

  3. 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

  4. 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

  5. Open-Center Valves Control of position by control of velocity (change of velocity, acceleration, deceleration)

  6. A mobile application - Steady state performace very important Linköpings universitet

  7. A mobile application - Steady state performace very important - Dynamic performance still more important! Linköpings universitet

  8. Car Suspension Linköpings universitet

  9. Car suspension damping Linköpings universitet

  10. Damping of a hydraulic operated boom? Linköpings universitet

  11. Oscillations of hydro-mechanical systems Natural Frequency Linköpings universitet

  12. Oscillations of hydro-mechanical systems Natural Frequency Video

  13. Natural Frequency of an arm with a load

  14. Natural Frequency of an arm with a load Higher working pressure

  15. 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!!

  16. Linköpings universitet

  17. Linköpings universitet

  18. M Cp pQ diagram Egenfrekvens, dämpning dQ Cp = dP dQ Cp = oo dP Cp = 0

  19. Mobile Valve Systems from a dynamic Point of View

  20. Constant Pressure System Throttle Valve (Variable orifice) Simulation

  21. pQ-diagram, Closed-Centre Valve

  22. Constant Flow System – Open-Centre Throttle Valve (Variable orifice) Simulation

  23. pQ-diagram, open-centre valve

  24. Damping by a LS valve Simulation

  25. Damping by a LS-valve Increased damping by use of meter-out restriction Simulering

  26. 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

  27. 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

  28. Damping by a LS-valve Increased damping by use of pressure feedback Simulation

  29. Crane without pressure feedback

  30. Crane with pressure feedback

  31. Safety ... Slangbrott: “s”

  32. 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

  33. Load Holding ValvesofOver-Centre Type Easily start to oscillate! Why? High power losses! Why?

  34. Lorry Crane Typical Over-Centre Valve

  35. Load goes over-centre

  36. Load goes over-centre Meter-in control

  37. Hoist sustem Avoid cavitation by ”pumping down” the load

  38. Crane arm controlled by an open-center valve and an over-center valve

  39. Steady state control of LHV Areaförhållande:

  40. Analyze of an over-centre valve system

  41. Analyze of an over-centre valve system

  42. Oscillating hydro-mechanical system

  43. Pressure oscillations

  44. Simulering

  45. 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

  46. 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!

  47. 3G - New Load Holding Valve How does it work? Sid 50

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