Experimental Characterization of External Gear Machines with Profile Asymmetric Teeth

Devendran, R.S., Vacca, A. (Purdue University)

CHALLENGE - External gear machines (EGMs) are one of the most widely used positive displacement machines in numerous hydraulic applications. The goal of this paper is to describe the benefits of introducing gears with asymmetric teeth in EGMs, specifically, finding the optimal design for a 11.2 cm3 pump with asymmetric gears. 

SOLUTION - The optimal profile of the gear is explored together with the profile of the recesses in the lateral bushes using a numerical optimization procedure. The simulation tool used for the accurate evaluation of performance is HYGESim. An optimization algorithm was implemented in modeFRONTIER to determine the optimal design of the gears and of the lateral bushes simultaneously. HYGESim was used as the crux to evaluate performance based on the following objective functions: delivery flow pulsations, internal pressure overshoots, localized cavitation effects and volumetric efficiency.

BENEFITS - Optimal design significantly reduces the pressure ripple at the delivery. In most cases a noteworthy reduction of about 50% has been obtained experimentally. The tests confirmed initial expectations: compared to the EGM taken as reference, the proposed design has similar steady-state performance (in term of volumetric capacity) but offer lower outlet flow pulsations.