A transmission-equipped wheel hub motor designed to improve the environmental performance, safety, and comfort of automobiles has been successfully demonstrated by NSK Ltd. of Tokyo, Japan.
The company seeks to commercialize wheel hub components such as the hub unit bearing with built-in speed reducer, the one-way clutch unit, the miniature cage and roller bearing, and the anti-corrosion bearing.
In-wheel motors that can work with various drive systems independent of the body structure of automobiles are attracting interest as next-generation electric drive devices. An in-wheel motor located near the wheel can reduce vehicle weight, control the drive force of each wheel, and enable the expansion of cabin size, resulting in enhanced environmental performance, safety, and comfort.
Enlarging the size of a wheel-hub motor in order to achieve both the large drive torque necessary for acceleration and hill climbing and a sufficient maximum speed is challenging. To make in-wheel motors more compact, NSK developed a transmission-equipped wheel hub motor that uses two motors and a special transmission.
The design includes two planetary gears which can achieve both high drive torque and a sufficient maximum speed with a small motor. The transmission has a feature that enables smooth gear changing even during acceleration by controlling the speed and torque of the two motors.