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 scale Global scale

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

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

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