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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

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Modelling and simulation of hydraulic motor tribology

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  1. Modelling and simulation of hydraulic motor tribology Patrik Isaksson

  2. Agenda • Introduction • Mixed lubrication model • Test rig-validation • Micro EHL • Tribology modeling - Project leakage reduction

  3. Introduction-tribological interfaces • Piston assembly • Distributor plate • Seals • Rolling element bearings • …

  4. Tribology of hydraulic motor • Wide speed and load range • High loads-EHL • All lubrication regimes has to be considered

  5. Modellingtribology 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

  6. 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 scale Global scale

  7. Mixed lubrication model • Modified Reynolds equation • Incorporating the effects of the local scale fluid flow through flow factors

  8. Mixed lubrication model-friction calculation • Friction is calculated as the sum of friction from asperity contact and hydrodynamic friction

  9. 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

  10. Test rig-validation • Friction, leakage and oil film pressure is measured in the roller-piston interface

  11. Validation-modeling test rig setup • Mixed lubrication model applied in roller/piston interface

  12. Validation-Oil film pressure

  13. Validation-Leakage

  14. Validation-mixed lubrication Movie clip

  15. Lift off zone Not always very good correlation, some effect and/or input is missing

  16. Micro EHL Deterministic EHL model of high pressure zone with transverse ”roughness”

  17. Micro EHL Micro EHL will influence transition between full film and mixed/boundary

  18. Tribology modeling - Project leakage reduction Task: • Reduce leakage in piston to 50% • Keep low friction

  19. Project leakage reduction-result • New piston design in production

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