Electric vehicles are rapidly increasing in the global market. Most electric vehicles have adopted a reducer, which is a double reduction gear set. Although the traction motor of an electric vehicle has a wide rotational speed range, the reducer has the disadvantages of lowering the efficiency of the motor operating region and limiting the maximum vehicle speed.

To overcome the shortcomings of the reducer, it is necessary to apply a two-speed transmission to electric vehicles. Based on the patent of system configuration, a unique two-speed transmission with a planetary gear set and two synchronizers set has been developed and applied to an electric vehicle.

The advantage of this two-speed transmission is that traction force increases by more than 40% at first gear and top speed increases by more than 30% at second gear.

The system configuration was designed with the idea of making a compact, efficient and cost-effective product. The gearbox, shift mechanism, shift logic and TCU were developed. The TCU controls the two shift motors to engage and disengage the two synchronizers during gear shifting and connects to the MCU to synchronize the traction motor speed and vehicle speed immediately before gear shifting is complete.

Transmission for electric vehicle is required to be matched with traction motor and have the characteristics such as shift time, efficiency, compact size, reliability, cost-effectiveness. A two-speed transmission for an electric vehicle could optimize capacity of motor and inverter smaller than that of electric vehicle with reducer because an electric vehicle with reducer needs high rpm, torque, power motor and inverter to cover overall speed and torque range of electric vehicle.

Even though two-speed transmission has disadvantages such as complex system and torque interrupt, two-speed transmissions are becoming more utilized like multi-step transmissions in vehicles with combustion engine in the near future.