Elasto-hydrodynamic simulation of complex geometries in hydraulic motors

As many other machines, the radial piston hydraulic motor contains a lot of tribological interfaces. One important area is the piston assembly and the journal bearing contact between the piston and cam roller. There exist good models to describe the performance of simpler geometries such as journal bearings, but when put into a system or when having a more complex geometry, the models do not apply very well. To be able to predict the tribological performance of such components, it is important to have a model that is able to include the real geometry and the properties of the system. A simulation model of the piston assembly in Hägglunds Compact hydraulic motor was built using FE software which made it easy to include the complex geometries. The model includes the deformation of the piston. The hydrodynamics is solved by using Reynolds equation. Density/pressure and viscosity/pressure dependency for the oil are included. Simulation results such as friction, hydrodynamic pressure and oil leakage were compared with test results. Good agreement between simulation and tests shows that this kind of model can be a useful tool in the development and optimization of tribological systems.