Formulation and optimization of involute spur gear in external gear pump

Xinran Zhao, Andrea Vacca (Purdue University)

CHALLENGE - External gear pumps (EGPs) have gained popularity among applications in many fields like fluid power transmissions and systems, automotive, aerospace thanks to their advantage of simplicity, robustness and low cost.​ Asymmetric gears represent one of the possible choices​ to achieve better performance in terms of flow smoothness power to weight ratio. The study focuses on developing a methodology of designing asymmetric involute gear, and formulate analytical expression for the instantaneous flowrate and flow non-uniformity given by asymmetric, non-standard involute gear pumps.

SOLUTION - These analytical expressions are then used within a multi-objective numerical optimization algorithm aimed at minimizing both the flow non-uniformity and the pump size to achieve a specific displacement. NSGA-II algorithm in modeFRONTIER was selected and executed for each number of teeth. For any given number of teeth, a Pareto front can be found with more than 1000 design evaluations. In the design selection process, linear Multiple Criteria Decision Maker (MCDM) is selected with equal weights flow non-uniformity (OF1) and volume (OF2).

BENEFITS - Optimization results show that the number of teeth has primary influence on the EGP performance: a higher number of teeth reduces outlet flow oscillations but increases the overall volume of the unit. The resulting optimal profiles are strongly affected by physical constraints such as the minimum contact ratio on drive and coast side, and minimum tip width.