Multi-Objective Optimization of Gerotor Port Design by Genetic Algorithm with Considerations on Kinematic vs. Actual Flow Ripple 2019-01-0827
Gerotor pumps are common in low pressure automotive applications such as fuel delivery, lubrication, and automatic transmissions. Recent automotive trends, such as electrification, demand these units to perform in more demanding conditions, so modern design methodologies must be developed to meet these challenges. Previous work in gerotor gear geometry design used the kinematic flow ripple as an objective function during extensive profile optimization. Although more sophisticated methods exist for predicting the flow ripple, the kinematic flow ripple was used to reduce the computation time of optimizations. However, compressibility, internal leakages, and throttling effects have an impact on the performance of the pump and cause the flow ripple to deviate from the kinematic flow ripple. As a way to counter this phenomenon, the ports can be designed to account for fluid effects to reduce the outlet flow ripple, internal pressure peaks, and localized cavitation due to throttling while simultaneously improving the volumetric efficiency. The design of the ports is typically heuristic, but a more advanced approach can be to use a numerical fluid model for virtual prototyping. In this work, a multi-objective optimization by genetic algorithm using an experimentally validated, lumped parameter, fluid-dynamic model is used to design the port geometry. This optimization is repeated for five pumps with varying kinematic flow ripples at pressures of 5 and 50 bar, and the simulated performance of the pumps with optimized port geometries is compared to the kinematic flow in each case. The kinematic flow ripples deviate from their simulated counterparts, however they do predict the trend of the magnitude of the simulated flow ripples very well. In addition to demonstrating a multi-objective optimization strategy for port geometry, this work also demonstrates that the kinematic flow ripple is a suitable objective function for gerotor gear design for low pressure applications.