Direct Gear Design for Asymmetric Tooth Gears

Abstract

In many gear drives, the tooth load on one flank is significantly higher and is applied for longer periods of time than for the opposite one. An asymmetric tooth shape reflects this functional difference. Design intent of asymmetric gear teeth is to improve performance of the primary drive profiles at the expense of the performance off the opposite coast profiles. The coast profiles are unloaded or lightly loaded during a relatively short work period. Asymmetric tooth profiles also make it possible simultaneously to increase the contact ratio and operating pressure angle beyond the conventional gear limits. The main advantage of asymmetric gears is contact stress reduction on the drive flanks, resulting in higher torque density (load capacity per gear size). The paper presents an application of the Direct Gear Design® method to asymmetric tooth gears. This is an alternative approach to traditional design of involute gears, separating gear geometry definition from the generating (tooling) rack to maximize gear drive performance. The paper describes asymmetric tooth and gear mesh characteristics, limits of asymmetric tooth gearing, tooth geometry optimization, analytical and experimental comparison of symmetric and asymmetric tooth gears, and implementation of gears with asymmetric teeth.