Numerical simulation of Gerotor pumps considering rotor micro-motions

Gerotor units are widely used in low-pressure (up to 30 bar) fluid power applications, injection as well as lubrication systems, due to their compact package and low cost. Their performance in terms of volumetric efficiency, flow pulsations, internal pressure peaks or localized cavitation depends on many parameters, such as the rotors' profiles and the manufacturing tolerances. This paper proposes a multi-domain simulation approach for the numerical analysis of the performance of Gerotor units. Characterized by simulation swiftness, the model can be used for virtual prototyping of units considering the actual geometry of the rotors, their geometrical tolerances and the properties of the working fluid. The approach is based on the coupling of different models: a numerical geometric model evaluates the instantaneous volumes and flow areas inside the unit; a lumped parameter fluid dynamic model describes the displacing process of the tooth space volumes; finally, a mechanical model evaluates the internal micro-motions of the rotors axes according to their tolerances. In this way, the model determines the actual loading of the rotors, considering also the actual location of the points of contact. After presenting the approach, the paper describes the potentials of the proposed method with reference to a particular Gerotor pump design. Specific experiments were performed within this research to permit a detailed model validation, and comparisons in terms of significant steady-state as well as transient pressure and flow features are presented. The approach used in the current paper can be considered valuable when studying the impact of real-life technological clearances on the fluid-dynamic performance of the pump.