A study of piston and slipper spin in swashplate type axial piston machines

A common assumption in the analysis of swashplate type axial piston machines (APMs) is to consider the relative rotation between the piston and cylinder block almost equal to the shaft speed. While this effect has been observed experimentally and confirmed by simplified models, an in-depth study and confirmation of the causes has never been undertaken. To address this, the presented work performs a simulation study of the piston and slipper spin in APMs. For this purpose, this work first develops a strongly coupled simulation model considering the displacing action of the machine coupled - with asynchronous time stepping - with the detailed simulation of its lubricating interfaces. The proposed approach accounts for the dynamics of the floating bodies in these machines, the ball-socket friction which couples the dynamic of each piston and slipper, and the impact on the fluid-structure induced cavitation and mixed lubrication in their tribological interfaces. As a consequence, the mutual interaction between the slipper-swash plate interface and the piston-cylinder interface of the APM is taken into account. After validating this model on a reference commercial unit, the impacts of the operating parameters (such as instantaneous displacement, pressure and shaft speed) and of the ball socket friction on the behavior of the machine are explored. It can be observed from the simulation results that the relative piston rotary motion in the cylinder bore varies with the operating conditions and the swashplate angle is one of the most influential parameters.