Design of a Lead-Free Slipper Bearing for Low Speed Axial Piston Pump Applications

New application areas for hydrostatic machines result in novel challenges for the fluid film performance of the lubrication interfaces. In the past hydrostatic machines were designed with a combustion engine or a constant speed electric motor in mind. Therefore, they typically have a minimal speed requirement and are optimized for a low variation in their operating speed range. Electrification and flow by demand change this requirement drastically, forcing the pumps often in both very high and very low operating speeds. Typically, lubricating gaps in positive displacement machines consist of a hard/soft material pairing, where the soft pairing usually is a yellow brass with variable lead content. The lead is added to allow for mix friction contact at low speeds and other critical conditions. New developments in surface structuring allow for precise manufacturing of the surface shaping in the sub micro-meter range. This paper combined this technology with state of the art numerical simulations to design a surface structure that is capable withstanding pump operations without significant wear and therefore allows for lead free materials – even steel/steel pairings. The different materials were tested in simulation, on a novel hydrostatic-tribometer test rig as well as on the pump test rig. The design process as well as the simulation and measurement results will be presented in this paper.