NSK Ltd. has successfully demonstrated the first transmission-equipped wheel hub motor, designed to improve the environmental performance, safety, and comfort of automobiles. Building on the knowledge it has gained from the prototype wheel hub motor it developed, NSK is aiming 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 the weight of the vehicle, control the drive force of each wheel for improved torque vectoring, and enable the expansion of the size of the cabin space, thereby improving environmental performance, safety, and comfort.
However, 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.
This wheel hub motor is equipped with two motors and a transmission composed of two planetary gears, which can achieve both high drive torque and a sufficient maximum speed with a small motor. In addition, this transmission has a feature that enables smooth gear changing even during acceleration by controlling the speed and torque of the two motors.
NSK demonstrated the superior performance of this technology using an experimental vehicle equipped with a prototype wheel hub motor.