This paper presents main results of an investigation of the tribological system formed by the piston/cylinder assembly of swash plate axial piston machines. Main focus has been given to the influence of a piston macro and micro geometry variation on energy dissipation generated by piston/cylinder assembly. Using the simulation tool CASPAR, which has been developed at the institute for Aircraft Systems Engineering, an optimization of the piston shape has been realized to achieve minimum energy dissipation in a wide range of operating parameters of the axial piston machine. Micro geometry stands for surface roughness here. Its influence has been investigated within a second task especially in the area of low speed, where full lubrication is not achievable and therefore mixed friction occurs. For the investigation a special friction force measurement test rig has been developed, which has also been used for verification of the simulation tool CASPAR.

Keywords: axial piston machine, piston cylinder assembly, pressure field, friction force, gap flow, surface roughness, friction force measurement