Numerical analysis of the dynamic behaviour of axial piston pumps and motors slipper bearings

This paper reports an analysis of the lubrication mechanism and the dynamic behaviour of axial piston pumps and motors slipper bearings. A numerical procedure is used to solve the Reynolds equation, written here with respect to the slipper-swash plate gap, whose height is considered variable in a two dimensional field and with time. The contributions of forces and moments acting on the slipper are illustrated and discussed, then the numerical method is presented to solve the Reynolds equation. Taking into consideration the slipper surface that is facing the swash plate, different geometry profiles are considered and the subsequent dynamic behaviour of the slipper is investigated; in particular, it is shown that a flat profile cannot always guarantee the bearing capability of the slipper and the lubrication in the gap is compromised for some critical operating conditions. Successively, different non-flat profiles of the surface are considered and their impact on the slipper bearing dynamic behaviour is investigated in terms of tilt of the slipper α and central clearance height h0. Then, focusing on one of these non-flat profiles, the results are discussed highlighting the influence of machine operating conditions. These include rotational speed and a high pressure level and involve introducing a friction coefficient in order to evaluate the magnitude of friction losses determined by the slipper behaviour. Finally, some considerations are expressed about differences between mode of operation of the pump and the motor related to slipper behaviour. Copyright © 2009 SAE International.