Research on Using Non-circular Gears in Designing an Uninterrupted Two-Speed Gearbox for Electric Vehicles

In the powertrain system of electric vehicles (EVs), using a standalone electric motor or combining it with a single-speed gearbox does not guarantee maximum performance across different speed ranges and operating modes. The multi-speed gearboxes (MSGs) are considered a viable alternative, providing suitable operating modes for the electric motor, aiming to improve dynamic performance and energy consumption economy. However, MSGs have some limitations, including torque interruption during gear shifting, which causes energy loss, and jerking affecting passenger comfort. In addition, they have a more complex structure, increase vehicle weight and higher manufacturing costs. Therefore, a two-speed transmission is one of the solutions to balance the transmission performance and the system’s costs of EVs. To solve the problem of interrupted torque during the gear shifting of a two-speed gearbox, in this study, the authors used a non-circular gear pair combined with a suitable shifting strategy. The centrodes of non-circular gears are determined from the appropriate gear ratio function for the shifting between speed levels. Then, the design parameters of the tooth profile are also selected to avoid undercutting. Finally, a design calculation program was written on Matlab software to verify the theory. The results show that the design method is completely feasible to overcome the torque interruption issue of the two-speed gearbox for EVs, which is an important approach in studying MSGs for EVs.