3-Speed Transmission Using Dual Motors and One-Way Clutches

The use of electric vehicles has begun to increase, and the ratio of electric vehicles will continually increase due to environmental regulations. The speed-torque characteristic of an electric motor is better than that of a combustion engine for vehicle driving due to the high torque in a low-speed range. However, the efficiency of the motor declines in the low-speed range; therefore, when an electric vehicle climbs a steep slope slowly, severe heat may be generated due to the high current in the low-efficiency range. In this regard, for driving at a high efficiency, electric vehicles also require mechanical multispeed transmissions, but a conventional mechanical multispeed transmission is bulky, heavy, and energy consuming. This paper suggests a 3-speed transmission using dual-electric motors and one-way clutches. The transmission has a structure simple enough to be used in an in-wheel drive unit, and it does not have actively moved clutches, resulting in high reliability and eliminating the need for energy to move the clutches during speed changes. The operational principle is explained, and a prototype and its experimental results are presented.