Numerical Analysis of the Dynamic Behaviour of Axial Piston Pumps and Motors Slipper Bearings

This paper reports an analysis of the lubricationmechanism and the dynamic behaviour of axial pistonpumps and motors slipper bearings. A numericalprocedure is used to solve the Reynolds equation,written here with respect to the slipper-swash plate gap,whose height is considered variable in a twodimensional field and with time.The contributions of forces and moments acting on theslipper are illustrated and discussed, then the numericalmethod is presented to solve the Reynolds equation.Taking into consideration the slipper surface that isfacing the swash plate, different geometry profiles areconsidered and the subsequent dynamic behaviour ofthe slipper is investigated; in particular, it is shown that aflat profile cannot always guarantee the bearingcapability of the slipper and the lubrication in the gap iscompromised for some critical operating conditions.Successively, different non-flat profiles of the surface areconsidered and their impact on the slipper bearingdynamic behaviour is investigated in terms of tilt of theslipper α and central clearance height h0. Then, focusingon one of these non-flat profiles, the results arediscussed highlighting the influence of machineoperating conditions. These include rotational speed anda high pressure level and involve introducing a frictioncoefficient in order to evaluate the magnitude of frictionlosses determined by the slipper behaviour. Finally,some considerations are expressed about differencesbetween mode of operation of the pump and the motorrelated to slipper behaviour.