Prospects of Asymmetric Gears in EV Gearbox

The gear transmission system in an electric vehicle (EV) differs significantly from that of a conventional gasoline or diesel-powered vehicle. This distinction primarily stems from the unique torque and speed characteristics exhibited by electric motors, as compared to internal combustion engines. In most cases, EVs employ a single-speed, two-stage helical gearbox configuration (see Figure 1). Although relatively simple in design, the gearbox of an EV must meet several critical performance requirements. These include high load-carrying capacity while maintaining a compact and lightweight structure, as well as ensuring high operational efficiency and optimal noise, vibration, and harshness (NVH) performance. The study referenced in Ref. 2 provides an in-depth analysis of these specific requirements and the distinguishing features of EV transmission systems. This study focuses on reducing the size and weight of gears utilized in EVs. Optimizing the geometry of gear teeth is essential for enhancing the technical performance of EV gearboxes. EV gearboxes typically operate unidirectionally, experiencing high torque and prolonged operation during forward driving. In contrast, during reverse motion, deceleration, and power recuperation phases, the torque levels are significantly lower, and the duration of operation is shorter. These distinct operating conditions involve opposite flanks of the gear teeth, thereby enabling the full benefits of an optimized asymmetric gear tooth design to be realized. The primary design objective of asymmetric tooth gears is to enhance the performance of the drive flanks under heavy loading, while permitting a degree of compromise on the coast flanks, which are subjected to less frequent and lighter loads. The implementation of the Direct Gear Design method for asymmetric gears enables comprehensive optimization of tooth geometry. This approach results in a significant improvement in power transmission density, maximized load capacity, and a reduction in both the size and weight of the gearbox—advancements that exceed the performance limits of conventional symmetric tooth gears currently used in automotive applications.