Mechanochemical Surface Finishing for High-Speed Gears for EV Transmissions

Powertrain electrification has been a growing trend in the automotive industry. Electric motors used in battery electric vehicles (BEVs) operate at high speeds ranging from 3,000 to 16,000 rpm, with high-performance motors reaching over 20,000 rpm. For instance, Tesla’s carbon-sleeved motor used in Tesla Model S Plaid may reach 24,000 rpm at the top speed of 330 km/h. There are experimental designs of interior permanent magnet synchronous motors (IPMSM) reaching 100,000 rpm. The combined inverter/motor efficiency of a typical BEV equipped with a single-speed reduction gearbox reaches a maximum close to the maximum motor speed. Small high-revving motors achieve higher power density and are also lighter and cheaper to manufacture. However, a single-speed gearbox cannot ensure optimum efficiency and driving comfort at different speeds and loads. Hence, quite a few multi-speed gearboxes have hit the market over recent years. Even though the use of a multi-speed gearbox tends to increase the engineering complexity and manufacturing cost of an EV, it is well justified for premium passenger cars, off-road vehicles, and commercial vehicles due to improvements in the driving range, dynamic performance, and gradability (Ref. 1).