Contributing to the development of More Compact In-wheel Motors NSK Ltd. (NSK; Headquarters: Tokyo, Japan; President and CEO: Toshihiro Uchiyama) today announced that it has successfully demonstrated the world's first transmission-equipped wheel hub motor (Fig. 1), 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. Development Background As the awareness of environmental problems increases, the need for improved environmental performance, in addition to dynamic performance, has been increasing. This has resulted in the diversification of automobile drive systems such as hybrid electric vehicles (HEV), electric vehicles (EV), and fuel cell vehicles (FCV), as electrification has become a major trend. In-wheel motors that can work with various drive systems independent of the body structure of automobiles are attracting attention as next-generation drive devices. An in-wheel motor located near the wheel can reduce the weight of the vehicle body by reducing powertrain parts such as engines, controlling the drive force of each wheel, and expanding the size of the cabin space, thereby improving environmental performance, safety, and comfort (Fig. 2). For this reason, a great deal of research is being conducted for the practical application of this technology. However, there is a problem in terms of enlarging the size of the motor in order to achieve both the large drive torque necessary for acceleration and hill climbing and a sufficient maximum speed. For such reasons, this technology has not been put into practical use until now. The technology for a more compact in-wheel motor is one of the most important technologies for improving environmental performance, safety, and comfort. Product Features In order 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 (Fig. 3) that enables smooth gear changing even during acceleration by controlling the speed and torque of the two motors. For the first time in the world, NSK demonstrated the superior performance of this technology using an experimental vehicle (Fig. 4) equipped with a prototype wheel hub motor. Demonstration Purpose Building upon the knowledge gained with its prototype wheel hub motor, NSK aims to understand the required level of performance of components (Fig. 5) 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, and then commercialize them. Figure 1: Wheel hub motor structure Figure 2: Wheel hub motor benefits Figure 3: Shifting mechanism Figure 4: Wheel hub motor in the experimental vehicle Figure 5: Wheel hub motor components