Traction Motor Size Optimization with Two-Speed Gearbox in an Electric Vehicle

Abstract

As electric vehicles (EVs) are seen as the future of transportation, there are two significant challenges to overcome: range and cost. One effective strategy to address these issues is the optimization of powertrain components, which significantly impact both vehicle range and overall cost. In powertrain optimization, particular focus is placed on optimizing the electric motor and gearbox due to their crucial roles in vehicle performance and EV efficiency. A two-speed gearbox configuration for EVs has emerged as a solution to enhance dynamic performance and extend range. However, this approach comes with drawbacks such as increased weight and cost, leading to the prevalent use of single-speed gearboxes in the EV industry. Nonetheless, there is potential for optimizing motor size through the integration of a two-speed gearbox. The key question is whether the benefits of a smaller motor and increased vehicle range, enabled by a two-speed gearbox, outweigh its drawbacks. This study proposes a systematic method for co-optimizing the electric motor's sizing specifications and the gear ratios of a two-speed gearbox. This method achieved a 13% reduction in the required motor power for a sub-compact vehicle's specified 0-100 km/h acceleration, along with a significant motor weight reduction of up to 25%. Additionally, energy consumption was reduced by up to 3.8% for the EPA drive cycle while maintaining the same acceleration performance.