Multi-objective optimization of circular-toothed gerotors for kinematics and wear by genetic algorithm

Andrea Vacca (Purdue University, Maha Fluid Power Research Center)

CHALLENGE -  Gerotor pumps are common components for low-pressure applications such as charge pumps, engine lubrication pumps, automatic transmission pumps, and fuel injection pumps. New trends in applications of fluid power technology demand gerotors in operating conditions not experienced before in terms of speed, pressure, and working fluid. Electrification of hydraulic pumps would be one example. A new design methodology is required to meet these challenges that makes use of modern pump simulation tools and optimization strategies.

SOLUTION - The main goal of the present work is to develop a gear design methodology that identifies the Pareto front for four objective functions. It serves as an expansion on previous work that determined a Pareto front considering just two objective functions: minimize pump size and minimize kinematic flow ripple. A gear generation algorithm is presented that defines a circular-toothed gear geometry and evaluates each of the objective functions (OF) and constraints (C). The algorithm was implemented in modeFRONTIER and the NSGA-II genetic algorithm was used to identify a Pareto front. The commercial application modeFRONTIER links multi-disciplinary engineering software to optimization and statistical methodologies. Three pump geometries used in industry were also compared to the Pareto front, and an additional design was selected as a good compromise between each of the objective functions. Although only the circular-toothed gerotor profile type design space is explored in this work, the optimization methodology presented can be applied to other profile types, so this work serves as a benchmark in defining novel gear profiles.

BENEFITS - A clear Pareto front was found against which 3 pumps used in automotive applications were compared. The industry reference pumps lie very near to or on the Pareto front, which demonstrates that some pump designers in industry have been able to find optimal pump geometries. This fact was not known in literature before this work. Another design is also selected that uses information gained from the Pareto front that offers a good compromise between each of the objective functions.