This article introduces the process of polish grinding of gears. Improved surface quality increases the overall efficiency of gearboxes, resulting in reduced friction and torque loss, higher power density, and noise-optimized gears (lower NVH); all these factors are highly relevant, especially for electric drives. When Reishauer developed polish grinding in 2012, the process aimed to improve the efficiency of ICE engine transmissions, and the set goals were easy to achieve. Today, in 2023, the situation is dramatically different. While an ICE engine operates at around 3,000 rpm and supplies acoustic masking of the gear noise, EV drivetrains feature up to 20,000 rpm and offer no such masking.
A deep dive into the world of gear dynamics and gear noise has led many a mechanical engineer to Columbus, OH in search of the methods by which gear noise is measured and predicted as well as the techniques employed in gear noise and vibration reduction. Over the past 40+ years, about 2,550 engineers and technicians from 385+ companies have attended the Gear Dynamics and Gear Noise Short Course at The Ohio State University.
In modern automotive vehicles, gear noise becomes more and more of an issue. The main reason is the reduced masking noise of the engine, which vanishes completely in the case of an electric driveline. Improved gear quality unfortunately does not correlate with a better noise performance in any case. High gear quality makes sure that the gear flanks are inside tight tolerances and that all teeth are nearly identical. Even if the running behavior of such gear sets shows a very low sound pressure level, the noise perception for human ears may be annoying.