The greatest share of hydromechanic and volumetric losses in axial piston machines are produced within the tribological interfaces piston / cylinder, cylinder block / valve plate and slipper / swash plate. Hydrostatic and hydrodynamic effects are used to minimise the sum of solid friction, viscous friction and throttle losses. Other tribological interfaces have minor influence on efficiency losses in most operating points in machines of this type.

This paper focuses on experimental investigations with the objective to acquire further knowledge on the cylinder block / valve plate contact. The investigations are part of a project funded by the German Research Foundation in which experimental and simulative investigations are combined to identify the effects influencing this tribological interface.

The experiments focus on the multi-directional movement of the cylinder block and the friction torque within the contact. Therefore a test rig was built, capable of measuring the cylinder block movement in all degrees of freedom and the friction torque between both parts. A sensor system is built around a standard rotary group of an axial piston pump with a spherical cylinder block / valve plate contact. The pump functionality is maintained and measurements under standard operating conditions up to 30 MPa are possible.

Procedures of the design process and descriptions of the measuring system are presented, followed by results of the cylinder block movement measurement, comparing the behavior under different pressure levels and speeds.

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