A Study on the Effects of Gear Specifications in Electric Vehicle Motor Gearboxes on Shaft Rotational Orbit Behavior and Gear Noise

This study investigates the correlation between the rotational orbit of a gear shaft and gear whine noise based on gear specifications in electric vehicles. Four different gear specifications with nearly identical center distances and gear ratios were designed and manufactured using the Run Many Cases (RMC) program. Under controlled test cell conditions, shaft rotational orbits were measured and compared. Gear whine noise measurements were conducted in the same electric vehicle. Each gear specification exhibited unique rotational orbit characteristics. In particular, the gear set with a near-circular square shaft orbit exhibited superior noise performance, resulting in approximately 15 dBA reduction in gear whine noise compared to that of a gear set with a triangular orbit. The observed improvement in gear noise is possibly a consequence of reduced gear slippage during power transmission. This reduction is attributed to the combined effects of a smaller module and an increased number of teeth, which, in turn, affect the tooth contact angle. Developing an analytical method to predict the rotational behavior patterns of shafts based on gear specifications would enable forecasting the noise stability associated with gear specifications during the development of high-speed motor reducers.