In-Wheel Motor System

Under the current circumstances in which more attention is being paid to environmental performance and problems concerning energy, the automobile industry, academic research institutes and a number of similar organizations are engaged in the technological development of electric vehicles (EV) as a next-generation automobile candidate. Two different drive systems are available for EVs. The first is the one-motor system in which a motor is installed in the body and the power is transmitted to both the left and right wheels via a differential device and a drive shaft. The other is the in-wheel motor (IWM) system in which motors are installed in the wheels. Since the motors and reducers are installed directly in the wheels, an IWM system does not need a differential, drive shaft or other parts1–8) when compared to a one-motor system. Free of the layout restrictions caused by these drive system components, the degree of freedom in vehicle design is increased greatly by an IWM system. In addition, with the removal of the differential and the drive shaft, energy loss is reduced and this allows for a reduction in electricity consumption required when running, thereby allowing the driving range per charge to be increased. Furthermore, this system is capable of not only controlling the driving force of individual wheels independently but also of directly transmitting the driving force to the tire without the intervention of a drive shaft. This makes it possible to achieve highlyresponsive control of the driving force. Making the most of this drive characteristic allows the vehicle driving performance to be improved significantly. Noting that IWM systems provide driving systems suitable for next-generation EVs in this way, we have developed the NTN-IWM System that incorporates an IWM, which is composed of a reducer and a motor, and a control system linked with sensor-based information. This paper reports the results of evaluation tests of the IWM reducer and motor sections, and of a road evaluation test done on an IWM-equipped vehicle.