Modeling of radial piston machines considering elastohydrodynamic effects in both cam–piston and piston–cylinder lubricating interfaces

This study illustrates a novel numerical approach for investigating the complex physics involved in radial piston pump (rotating cam type) operation. This approach is based on a fully-coupled model that combines the evaluation of the main flow through the unit, realized by the pistons’ displacement, with the simulation of the internal lubricating interfaces, given by the piston–cylinder interface and the cam–piston interface. These interfaces represent the main source of power dissipation due to leakages and shear. The comprehensive multi-domain simulation tool presented in this paper incorporates a robust fluid–structure interaction based numerical model for the piston–cylinder lubricating interface as well as a model for the lubricant flow in the cam–piston interface. Since the approach used for piston–cylinder interface was previously presented by the authors, in this work particular emphasis is given to the description of the elastohydrodynamic lubrication model for the cam–piston interface. The overall coupling between these models enables an accurate estimation of the piston micro-motion that is critical to analyzing fluid flow in the lubricating gaps during pump operation. Results are shown with reference to a pump with four pistons designed to reach pressures up to 2500 bar. For this unit, the outer race of the cam—which is in contact with multiple pistons during pump operation—is unconstrained in its rotation, and it undergoes a complex motion due to which experimental measurements of its angular velocity were performed. The results from the study confirm the utility of the numerical model as an effective tool for modeling radial piston machines.