-First in the World, all components from receiving power to driving are set in the wheel-


 A press conference about the development of a 3rd generation wireless in-wheel motor was held in the media hall of the University of Tokyo, Kashiwa Campus, and a vehicle driving demonstration was performed at the adjacent test site on October 10, 2019 (Thu).



Hiroshi Fujimoto (Ph.D.)

Associate Professor, The University of Tokyo,

Department of Advanced Energy, Graduate School of Frontier Sciences,

Department of Electrical Engineering, Graduate School of Engineering Osamu Shimizu

Osamu Shimizu (Ph.D.)

Project Assistant Professor, The University of Tokyo,

Department of Advanced Energy, Graduate School of Frontier Sciences,

Isao Kuwayama (Ph.D.)

Next Generation Technology Development Dept I, Chief Researcher, Bridgestone Corporation.

Mitsuru Araki

Intellectual Property Division, Director, Bridgestone Corporation.

Daisuke Gunji (Ph.D.)

 Assistant manager, NSK Ltd.

 Powertrain Technology Development Department,

 Automotive Technology Development Center

Ken Nakahara (Ph.D.)

General Manager of ROHM Research & Development Center, ROHM Co., Ltd.


  The research group led by Associate Professor Hiroshi Fujimoto of the Graduate School of Frontier Sciences at the University of Tokyo developed a 3rd generation wireless in-wheel motor (WIWM-3) powered by electric energy from the road to WIWM and succeeded in a vehicle driving test with in-motion wireless charging(Fig.1). The research group members are the University of Tokyo, Bridgestone Corporation (Bridgestone), NSK Ltd. (NSK), ROHM Co., Ltd. (ROHM), and TOYO ELECTRIC MFG. Co., Ltd. (Toyo Electric MFG).

  The WIWM-3 is an evolution of the 2nd generation wireless in-wheel motor (WIWM-2) announced in March 2017 and has greatly improved the wireless power transfer (WPT) performance, motor performance, and vehicle mountability for practical application. In order to further develop the technology, the group has also started research and development on tires and wheels that do not affect WPT performance.



(a)Test Vehicle with IWM-3

(b) Structure of IWM-3

Fig.1  Overview of IWM-3


(a)Smart City Use    (b)High-way Use

Fig.2   Future Image of WPT in-motion


3 keywords of WIWM-3

1) All Components in Wheel

  The research group has developed WIWM-3 that has the motor/inverter, which is the drive system for electric vehicles, and the power receiving circuit for WPT during driving, in the interior of the wheel. WIWM-3 designed for private vehicles output 25 kW/unit, which is double or greater the output of the WIWM-2(Fig.3).

2) Infinity Driving Range

   WIWM-3 receives 20 kW/unit WPT from the road, which is double the WPT of WIWM-2. If a smart city installed a WPT system with this performance in a limited area at intersections, drivers of electric vehicles (EV) will have no need to charge their vehicles themselves. As a result, the convenience of EVs will greatly increase (Fig.2).

3) Industry-academia Collaboration Open Innovation

   This project is being implemented through industry-academia collaboration between many companies, centered on the University of Tokyo. In order to accelerate the practical application of the WPT in-motion system proposed by this research group through open innovation, the University of Tokyo and four other companies have agreed to open a basic patent related to this project.




Contents of Presentation in Press Conference

■Background and Motivation

  The realization of a “low-carbon society” that reduces greenhouse gas emissions in order to prevent global climate change is an international issue. Private vehicles are the cause of 17.9% of Japan's carbon dioxide (CO2) emissions (announced by the Ministry of the Environment in FY2017), which are a leading cause of climate change. Therefore, the regulation for CO2 emissions from vehicles is becoming stricter every year worldwide.


  Electric vehicles have no internal combustion engines, therefore produce no CO2 emissions and are more efficient, making them the best method for reducing vehicle emissions. On the contrary, EVs require inconvenient charging, and have concerns regarding the amount of resources required to produce large quantities of batteries. For the sustainable spread of EVs, the EVs that can run efficiently using a small battery are required. There is much research being carried out globally to realize WPT in-motion with the intent of reducing the necessary battery size for EVs. There are many advantages to providing the power supply while driving:

Ⅰ.Battery capacity can be small, The EV becomes lighter and can drive with less energy

Ⅱ.Battery capacity can be small, EV becomes more reasonable price

Ⅲ.Drivers can drive EVs without worrying about the remaining charge or charging time


  In addition, WPT in-motion is characterized by a positive relationship with renewable energy. Since power generated by solar or wind fluctuates greatly depending on weather conditions, a system that absorbs the fluctuations is necessary for a reliable power grid. The idea of using an EV battery as a power storage facility to absorb the fluctuations has long been considered, but only an EV that is parked and connected to the power grid via the charger would be functional in this role. If electric power can be freely supplied to a driving EV by the WPT system, an EV battery can be connected to the grid at all times. Therefore, WPT in-motion is an important technology not only for reducing CO2 emissions in the transportation sector but also for supporting the flaws in renewable energy systems.



■History of R&D

  The University of Tokyo has been focusing on the superior characteristics of EVs and researching control methods for vehicle dynamics and the improvement of cruising distance. In particular, IWM, which has a motor inside the wheel, has the potential to improve the safety, environmental friendliness, and comfort of EVs, and has demonstrated many attributes unique to IWM. There is also a significant amount of research on the industrial applications of wireless power transfer.


  The research of the applications of WPT to EVs at the University of Tokyo began with the wireless connection between IWM and the vehicle body. In order to supply power, the conventional IWM had to connect the vehicle body and IWM with wires, a method which risked the breaking of wires. Therefore, under the concept of “No Wire for IWM,” the University of Tokyo developed “First Generation Wireless IWM (WIWM-1)” in collaboration with NSK and Toyo Electric MFG, May 2015. The WIWM-1 successfully drove for the first time, proving the value of the concept (


  The next step was to realize WPT in-motion to WIWM. As a result, WIWM-2 was developed in March 2017 and succeeded in WPT from the coil installed in the road to the WIWM-2 during motion (


  To further promote R&D for the WIWM, the University of Tokyo has joined with Bridgestone and NSK as joint research institutes from FY2018, and Toyo Denki MFG as joint research institutes from FY2019. The research project “Future society pioneered by direct power supply while driving to electric vehicles” is adopted and supported by JST-Mirai Program. As a result, WIWM-3 was developed and successfully powered by WPT from the coil installed on the road.


■ 3 keywords of WIWM-3

1) All Components in Wheel

  This research group have developed the WIWM-3 that has all its components, the motor/inverter which is the drive system for electric vehicles, and the power receiving circuit for WPT during driving, inside the wheel. The WIWM-2 is too large to fit the inside of a wheel, forcing some components to be mounted outside the wheel(Fig.3). The WIWM-3 is not only compact but has a higher output than WIWM-2. Designed for private vehicles, the WIWM-3 can output 25 kW/unit. This amount is twice that or greater of the WIWM-2, designed for small cars. One of the biggest reasons why both compact packaging and high power can be achieved is due to the ultra-small SiC power module produced by ROHM.



(a)WIWM-2                                  (b)WIWM-3

Fig.3 Comparison of Vehicle Mountability


  One of the major features of the WIWM system is the receiving coil position. The receiving coil is set as unsprung coil. When the receiving coil is “onboard” like the bottom of the car body panel, the distance between the road coil and the receiving coil varies greatly depending on the evenness of the road surface and the weight of passengers in the car(Fig.4). The performance of WPT varies greatly depending on the distance between the road coil and the receiving coil, then a large change in the distance between the coils makes it difficult to optimize the design of the WPT system.

  In the case of the “unsprung coil” arrangement proposed by the research group, the change in distance between the road surface and the receiving coil is extremely small, facilitating the optimization of the WPT system design and improving the power supply capacity and efficiency.

(a)Onboard coil                              (b) Unsprung coil

Fig.4 Comparison of Coil Position


  In addition, the receiving coil position “unsprung coil” has another advantage. In the WPT system that transmits power using a magnetic field, if there is a metal foreign object between the transmitting coil and the receiving coil, the foreign object will be heated by the energy transfer. For this reason, it is desirable to have a structure that prevents foreign matter objects from entering between the coils.


  The newer structural concept of the WIWM is proposed to prevent foreign matter objects from entering between the coils(Fig.5). Coil position of the newer structure is “inside of wheel”. It can reduce possibility to enter foreign matter much more. However, it is necessary to change the tire and the wheel not to interfere WPT. Therefore, this research group is also doing R & D of materials and structures for tires and wheels with Bridgestone.



(a)Outside of Wheel                     (b)Inside of Wheel

Fig.5 2 Variation of Receiving Coil Position for WIWM


2) Infinity Driving Range

  This research group studies the feasibility of infinity driving range with small battery. This group acquired vehicle driving data on urban roads in Kanagawa Prefecture, and quantified the percentage of time a car stays in front of intersection in 2018. As a result of the simulation using that data, if it is possible to supply power during driving in the section of 30 m from the stop line of all intersections, the change in the state of charge of battery will be almost zero before and after driving. This result shows 3 points.

1. It is not necessary to install power supply on all the roads, and only during a limited section before the intersection,

2. Amount of vehicle battery can be significantly reduced,

3. Charging at home is not required.


  WIWM-2 achieved 12 kW WPT output. However, it is not enough for this simulation with passenger car. Then this research group proposed the new optimization methodology of coil design and it realizes high performance coil design. As the result, 20 kW WPT output with 92.5% efficiency was realized on test bench. WPT efficiency will be more improved by control optimization.

  If a smart city with a WPT system with this performance installed only in a limited area in front of the intersection is realized, the user of the EV can drive without charging by himself. Convenience of EV will greatly increase.


3) Industry-academia Collaboration Open Innovation

  This project consists of main five members: University of Tokyo, Bridgestone, NSK, ROHM and Toyo Denki MFG. WIWM-3 is a collection of diverse technologies such as power electronics, control methods, mechanical parts, tire and wheel structures, electronic components, semiconductor power devices, and materials. It can be said that this is the result of maximizing the framework of joint research by industry-academia collaboration. For social implementation of WPT in-motion, it is necessary to build a large system that includes not only vehicles but also infrastructure, and collaboration beyond the industrial field is indispensable. Therefore, University of Tokyo, Bridgestone, NSK, and Toyo Denki MFG have agreed to open a basic patent related to this project, and the intellectual property mechanism that allows companies and organizations approved by the project's steering committee to use the rights-free technology for free. This framework can promote research and development through open innovation.


Future prospects

  This research group continue to experiment and evaluate WIWM-3 and will enthusiastically proceed with the proposal and prototyping of next-generation WIWM incorporating new ideas and technologies. WIWM proposed by this project, this research group will enter the demonstration experiment phase in 2025, incorporating the knowledge of a wide range of organizations and companies, not just the current participating members.


Event Information

1/1 Scale Model Exhibition

Oct. 24 - Nov. 4, 2019

Tokyo Motor Show (NSK Booth and Bridgestone Booth)