PHOTO CAPTION: University of Tokyo-developed wireless in-wheel motor.

University of Tokyo Develops Wireless In-Wheel Motor

New in-wheel motor uses magnetic coils to transmit energy across a 10 cm gap, eliminating the need for electric cables.

Published: 02-Jun-2015

According to researchers with the University of Tokyo, if you can eliminate the need for heavy electric cables and drive shafts, you can deduce the weight and complexity of an electric vehicles. In turn you can reduce the amount of energy needed to propel it and that translates into smaller motors and battery packs.

Up until now, wireless charging has been focused on recharging electric vehicle battery packs so that they don't have to be physically plugged in. The driver simply parks over a magnetic coil and a corresponding coil on the car wireless charge the battery. Embedded in the roadway, the same system can be used to power the vehicle while it's in motion. A system like this is currently in on a shuttle bus route in South Korea.

Taking the concept one step further, Hiroshi Fujimoto, an associate professor, and other researchers at the Tokyo Unversity, have built a prototype in-wheel electric motor that can be powered wirelessly, or what is called inductive charging, across a 10 cm gap between the charging coil and coil on the wheel. This approach eliminates the need for cables to power the typical in-wheel motor and the drive shaft used to mechanically transmit electric motor torque to the wheels. Control data is sent to the motor by Bluebooth wireless connection, similar to how the BIKE+ motor by ZeHus is controlled on the Quikbyke K15.

The prototype motor reportedly can produce a maximum of 3kW (4hp) and is said to be capable of propelling a vehicle up to 85 km/h (46mph).

One of the issues that will need addressing is the outboard mass of the wheel, which can affect vehicle handling, a phenomenon known as 'unsprung mass."

However, a study conducted by Martyn Anderson with Lotus Engineering and Damian Harty of Dunamos Ltd concluded, "While perceptible differences emerge with increased unsprung mass, on the whole they are small and unlikely to be apparent to an average driver. The nature and magnitude of the changes appears to be nothing that cannot be overcome by the application of normal engineering processes within a product development cycle. Conversely, the promise of individual wheel motor control shows good potential for substantial improvements in vehicle behaviour."

At 4 hp per wheel, the vehicle won't be a Model S, but for in-city, urban runabouts like the Renault Twizy or Toyota iRoad, such a set up would plenty adequate.

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