ROHM, in collaboration with a research group headed by Associate Professor Hiroshi Fujimoto of the Graduate School of Frontier Sciences at the University of Tokyo (hereafter the " University of Tokyo group") as well as Bridgestone Corporation, NSK Ltd., and Toyo Electric MFG. Co., Ltd. (all collectively referred to as "this research group"), has developed a "third generation in-wheel motor with power transfer during travel" (Figure 1) that enables direct supply of power from the road to the in-wheel motor (IWM) during travel, and announced success in travel experiments in an actual vehicle in a news release (Japanese only) dated October 10, 2019. These achievements were also described in the ROHM booth at CEATEC 2019, held in October and November of 2019, at the NSK booth and Bridgestone booth of the Tokyo Motor Show 2019, and elsewhere.
This "third-generation in-wheel motor with wireless power transfer during travel" is a further extension of a "second-generation wireless IWM" announced by the Tokyo University group in March 2017, and greatly improves power transfer performance during travel, motor performance, and vehicle mountability in moving toward practical application.
IWMs capable of wireless power transfer during travel have been studied as one solution to problems surrounding charging of EVs, which are a powerful means of reducing automotive CO2 emissions. If EVs can be charged during travel, it is argued, the following advantages can be expected.
- ・The capacity of the onboard battery can be reduced, so that the EV becomes lighter and can travel using less energy.
- ・For similar reasons, EV prices will fall.
- ・EVs can be used without worries about the remaining battery charge or charging times.
In relation to the third-generation status of the IWM, the following improvements and anticipated advances have been reported.
- ・Whereas motor performance had been adequate for kei cars (12 kW per wheel), an IWM with standard passenger car-class performance (25 kW per wheel) was achieved.
- ・The IWM unit had previously protruded from the wheel, but miniaturization greatly improved mountability on the vehicle (Figure 2).
- ・Power feed capacity was improved from about 10 kW per wheel to 20 kW.
- ・When this power feeding system is installed where appropriate, it will become possible to travel in EVs without worries about charging.
Optimization of the motor design, and incorporation of an ultra-compact SiC power module resulting from ROHM R&D in a construction suitable for IWMs, contributed to realization of a unit that is compact in the shaft direction, to improve mountability in the vehicle.
Hereafter there are plans to advance to a demonstration experiment phase in 2025, moving toward realization of IWMs capable of wireless power transfer during travel.
This article is an excerpt from a news release, and the text of the news release should be referenced for further details.