Surface Deformations Enable High Pressure Operation of Axial Piston Pumps

In this paper, a fully coupled fluid-structure interaction and thermal numerical model developed by the authors is used to demonstrate the impact of surface elastic deformations on the piston/cylinder fluid film thickness and on the overall axial piston pump rotating kit performance. The piston/cylinder interface is one of the most critical lubricating interfaces of axial piston machines. This interface fulfills simultaneously a bearing and sealing function under oscillating load conditions in a purely hydrodynamic regime. It represents one of the main sources of energy dissipation and it is therefore a key design element, determining axial piston machine efficiency. In the past years, the research group of the authors studied the impact of advanced micro surface design and fluid film thickness micro alteration in the piston/cylinder interface through extensive simulations and experiments. However, the numerical models used did not include the influence of surface elastic deformations, heat transfer and therefore material properties on the piston/cylinder interface behavior. Hence, the aim of this paper is to show the alterations on fluid film thickness and on the consequent coupled physical parameters due to the solid boundaries pressure and thermal surface elastic deformations. A simulation study considering two different material properties for the cylinder bores is performed, where a steel cylinder block and a steel cylinder block with brass bushings are separately studied. Piston/cylinder gap pressure field and coupled gap surface elastic deformations due to pressure and thermal loading are shown for the different materials. The impact of the different materials behavior on lubricating interface performance is discussed.