A novel concept of dynamic wireless power transfer

NSK Ltd. (NSK; Headquarters: Tokyo, Japan; President and CEO: Toshihiro Uchiyama), the research group of Prof. Hiroshi Fujimoto at the Graduate School of Frontier Science of The University of Tokyo, and Toyo Electric Mfg. Co., Ltd. have successfully demonstrated dynamic wireless power transfer from a road facility to an in-wheel motor for the first time in the world (see Figure 1 and 2).

Development Background
The evolution of modern automobile technologies is quite remarkable. For instance, electrification on cars is an energy-saving technology adopted to address global warming, and autonomous driving is a safety technology that targets zero traffic accidents. NSK has focused on the in-wheel motor (IWM) as the next generation of electric powertrains. IWMs improve the environmental, safety, and comfort performance of vehicles by, respectively, reducing weight, offering independent drive torque control, and increasing cabin space (see Figure 3).

One of the engineering challenges with electric vehicles (EV) is extending the distance that can be travelled per charge to rival conventional internal combustion engines. Dynamic Wireless Power Transfer (D-WPT) technology is gaining worldwide attention, since it is one of the potential solutions to this challenge and does not involve increasing the number of battery cells. However, D-WPT in the past targeted onboard electric powertrains, not IWMs.

Product Features
The research group organized by The University of Tokyo, NSK Ltd., and Toyo Electric Mfg. Co., Ltd. has successfully demonstrated D-WPT from a coil array on the ground to in-wheel motors for the first time in the world (see Figures 1 and 2). This was accomplished by progress in the development of the technology for wireless power transfer between the IWM and the vehicle body, which was announced in May 2015.

IWMs have to deliver both enough drive torque and compactness, since they will be placed in a limited space near the wheel. To meet these requirements, NSK has developed a parallel-axis speed-reducer integrated hub bearing unit (see Figure 4). The HUB bearing unit achieves the necessary reduction ratio while also reducing bearing size and weight.

Future Prospects
Through this collaborative research, NSK aims to commercialize components such as parallel-axis speed-reducer integrated hub bearing unit, miniature cage and roller bearings, anti-corrosive bearings, and more. In addition, NSK will keep up with the latest engineering trends in automobile technologies, and will continue to move forward with original development.