In-Wheel Motor Prototypes Developed for Electric Vehicles

The University of Waterloo and Nidec Corp. reveal wheel-hub systems that incorporate traction motors.  

By Murray Slovick, Contributing Editor

While the number of roadways is likely to stay about the same, automotive analysts say the number of vehicles on the road is expected to quadruple to three billion by 2050. Electric urban vehicles can be a potential solution to the resulting environmental problems, traffic congestion, and parking-space limitations due to their higher efficiency and lower greenhouse gas emissions.

However, most current urban vehicles are scaled-down versions of standard passenger cars. This imposes limitations on the safety, comfort, efficiency, performance, and customer acceptance of these vehicles.

To reduce the size and complexity of electric vehicles, integrated in-wheel systems (IIWS) based around the geometric boundaries of a conventional wheel are being developed at Canada’s University of Waterloo and by electric motor supplier Nidec Corp. (Kyoto, Japan).

While regular EV traction motors generally occupy the engine compartment, in-wheel systems are incorporated directly into the wheels of the automobile. Benefits of this setup include higher efficiency as a result of driving the wheels directly and bypassing the need for conventional power-transmission mechanisms. This allows for lighter and more compact designs. In addition, independent control of the wheels opens up the possibility of making further improvements to electronic stability control (ESC) and traction control systems (TCS).

Waterloo IIWC 

At the University of Waterloo, researchers developed a self-contained unit that combines a wheel and an electric motor with braking, suspension, steering and a control system in a single module designed to be bolted on to any vehicle frame (Fig. 1).

The University of Waterloo’s prototype includes a motor, suspension, brake, and steering systems squeezed into the space of a wheel hub. (Source: U of Waterloo).

The Waterloo IIWS is an integrated corner module comprised of multiple components, including an in-wheel suspension, an electrical in-wheel drive motor, a friction brake, steering system, and a new dual four-bar linkage system that provides an active camber. This approach results in a highly compact design for the corner module that can be integrated into narrow vehicles.

The design allows for torque vectoring and active steering, which increases directional stability control. Furthermore, direct rollover stability control is possible through vehicle track and wheel lateral force control. 

To improve the stability, researchers also designed and prototyped the units, which weigh about 40 kilograms and have about 25 horsepower, to enable active wheel cambering, or tilting.

The next step in the research involves scaling up the wheel unit, technically called a corner module, for large utility and commercial vehicles. “Companies will be able to produce a smaller car that is cheaper, too,” says Amir Khajepour, director of the Mechatronic Vehicle Systems Lab at Waterloo. “Right now, we are not there. You have to pay more to get a smaller car, to get less.”

 “It’s an economy-of-scale problem,” says Khajepour. “Corner modules would allow us, without enormous development costs, to make vehicles that are specific for each application, for each function, by concentrating only on the design of the body and the user interface.”

Mass-produced IIWS wheel units would significantly reduce production costs while also creating space for passengers that would otherwise be devoted to mechanical components such as steering columns.

A paper on the research, “Development of a Novel Integrated Corner Module for Narrow Urban Vehicles,” was co-authored by Khajepour, former master’s student Mohammad-Amin Rajaie, and post-doctoral fellows Alireza Pazooki and Amir Soltani.

A full-size prototype of the proposed integrated corner module has been fabricated and tested to validate the new steering mechanism and the integrated corner module.

Nidec’s In-Wheel Traction Motor

Nidec’s in-wheel motor produces over 1999 kW of power while weighing only 32 kg. (Source: Nidec Corp.)

Separately, Nidec Corp. has presented a prototype of a traction motor also designed to be fitted inside the wheel hubs (Fig. 2). The most prominent features of the motor are its power, torque density and its light weight.

The prototype consists of a motor with integrated reduction gears and an oil cooling system. The single in-wheel motor can achieve a power output of over 100 kW (135 PS)—equivalent to a 1,800 cc class gasoline engine—while weighing only 32 kg and being compact enough to fit inside a 20-in. wheel. The motor is compatible with all common car layouts: rear-wheel, front-wheel, and four-wheel drive.

The company said it aims to start mass-producing the motor around 2023.

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