Numerical and experimental investigation of internal micromotions in Gerotor units considering contact mechanics and lubricating interfaces

Abstract

This paper presents a numerical approach for evaluating the performance and the micromotions of the rotors in a Gerotor unit, accompanied by an extensive experimental activity aimed at validating this approach. The simulation model begins with a geometrical module that preprocesses the CAD drawings of a given unit. The model then performs a fluid dynamic analysis using a lumped-parameter formulation to solve for the pressures inside properly defined control volumes within the unit. The fluid dynamics is solved simultaneously with the planar motion of the inner and outer rotors using Newton’s law of motion. The body motion solution is coupled with the solution of the lubricating interfaces surrounding the rotors, which is based on the Reynolds equation. Contact dynamics formulations and elastohydrodynamic relations are applied at the contact locations, considering the possibility of multiple contact locations between the two rotors. An experimental test setup was purposely built within this research to quantify the micromotions of the outer rotor, along with basic measurements of torque and outlet flow. The comparison between simulation results and experimental data shows a good match in volumetric, hydromechanical, and radial motion prediction with an accuracy of 0.9%, 2%, and 2.5% respectively. The proposed methodology gives detailed insight and understanding of the behavior of the rotors and can be used to improve the current design and evaluate new concepts.