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. 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

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