Modelling and simulation of hydraulic motor tribology
description
Transcript of Modelling and simulation of hydraulic motor tribology
Modelling and simulation of hydraulic motor tribology
Patrik Isaksson
Agenda
• Introduction
• Mixed lubrication model
• Test rig-validation
• Micro EHL
• Tribology modeling - Project leakage reduction
Introduction-tribological interfaces
• Piston assembly
• Distributor plate
• Seals• Rolling
element bearings
• …
Tribology of hydraulic motor
– Wide speed and load range
– High loads-EHL– All lubrication
regimes has to be considered
Modelling tribology of hydraulic motors
• Fluid dynamics– Thin film approximation of Reynolds
equation is used• Structural deformation
– High loads• Fluid property model
– Viscosity dependence• Surface roughness
-when film thickness is small
Mixed lubrication-modelling strategy
• Separate the problem into two different scales– Local scale representing surface roughness– Global scale representing the piston bearing structure– Deformation is calculated on both scales
Local scaleGlobal scale
Mixed lubrication model
• Modified Reynolds equation
– Incorporating the effects of the local scale fluid flow through flow factors
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12)(
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hh shdp
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)()()(
h
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sy
sxs
pyypyx
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Mixed lubrication model-friction calculation
– Friction is calculated as the sum of friction from asperity contact and hydrodynamic friction
,HCtot FLF
Simulation software
• Commercial software package-COMSOL– Based on finite element method– Facilitates flexibility as a design
tool– Fluid dynamics and other
needed equations can easily be implemented
– Full system solution approach
Test rig-validation
• Friction, leakage and oil film pressure is measured in the roller-piston interface
Validation-modeling test rig setup
• Mixed lubrication model applied in roller/piston interface
Validation-Oil film pressure
Validation-Leakage
Validation-mixed lubrication
Movie clip
Lift off zone
Not always very good correlation, some effect and/or input is missing
Micro EHL
Deterministic EHL model of high pressure zone with transverse ”roughness”
Micro EHL
Micro EHL will influence transition between full film and mixed/boundary
Tribology modeling - Project leakage reduction
Task:
• Reduce leakage in piston to 50%
• Keep low friction
Project leakage reduction-result
• New piston design in production