NSK in-wheel motor charges wirelessly while in motion

NSK has developed the third generation of its in-wheel motor, the world’s first design of its type to feature a complete package comprising motor, inverter and wireless charging unit. The innovative wireless in-wheel motor (W-IWM) for the electric vehicle (EV) market is capable of charging from coils embedded in the road, while in motion. Development of the latest unit was conducted jointly by a research group comprising NSK, the Fujimoto Laboratory at the University of Tokyo’s Graduate School of Frontier Sciences, Bridgestone Corporation, ROHM Co Ltd and Toyo Electric Mfg Co Ltd.

Reducing CO2 emissions in order to achieve a low-carbon society is a global challenge that calls strongly for reductions in automobile emissions, hence the growing development and take-up of EVs. However, some concerns have been raised regarding the convenience of stationary EV charging and the amount of resources required to produce large amounts of battery cells. Efficient running with a minimal amount of battery cells is therefore required for the sustainable spread of EVs. As a result, wireless charging while in motion has been capturing the attention of OEMs keen on realising EVs with small batteries.

The third-generation W-IWM developed by the joint research group has vastly improved in-motion charging capability, motor performance and ease of mounting, bringing together the features required for practical application.

Importantly, the W-IWM has been developed so that the in-motion wireless power receiver circuit, as well as the EV's driving mechanism (motor and inverter), fit entirely inside the wheel.

In terms of motor performance, compared with the second-generation W-IWM for light vehicles announced in 2017 (12kW per wheel), the third-generation W-IWM has been created for use in larger passenger cars (25kW per wheel). Furthermore, while the second-generation W-IWM offered an in-motion charging capacity of 10kW per wheel, the third-generation unit sees this performance climb to 20kW.

The relevance of these improvements are linked to the future emergence of smart cities, where the installation of in-motion wireless charging systems in the road surface (even if only at traffic signals), will see EV drivers travel without having to worry about charging, dramatically increasing convenience. Based on this thinking, NSK is currently looking into the potential for in-motion charging infrastructure by analysing public road traffic data and conducting simulations.

In order to take advantage of open innovation and accelerate the practical implementation of the in-motion wireless charging system, the joint research group has agreed to leave open the basic patents associated with this project.

While the research group is currently in the process of testing and evaluating the third-generation W-IWM, it will eagerly push towards prototyping the subsequent generation unit, which will incorporate yet more new ideas. The group will integrate not only the expertise of current project members, but a wide range of knowledge from various fields held by other organisations and companies. The aim is to enter the verification phase for the real-world testing of an in-motion wireless charging system by 2025.

Through this joint research project, NSK ultimately hopes to contribute to the realisation of a more sustainable society, and make advancements that help create new momentum within the automotive industry.

The joint research group, which includes NSK, hopes that its efforts will help secure freedom from stationary charging systems

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