Improved range for Electric Vehicles using direct-drive outer-rotor in-wheel motors

In response to the dual challenges of global warming and dwindling world oil reserves, interest in Electric Vehicles (EVs) has increased dramatically over the past few years. We have developed an in-wheel outer-rotor Interior Permanent Magnet (IPM) synchronous motor for EVs with high power density and sufficient torque output to drive the wheels directly rather than via a gear reduction, offering significant improvement in efficiency and mileage. A 300mm diameter motor with a novel electromagnetic structure able to fit in a standard passenger vehicle's 16-inch wheel with a maximum power of 65kW, maximum torque exceeding 700Nm and rated power 20kW was developed, built and tested at our lab. An automated winding process providing a 60% space factor winding was also developed, and only standard materials and manufacturing methods were used. Motor dynamometer tests showed the motor not only met the required specifications, but also had a 10-20% efficiency improvement over inner-rotor gear-reduction motors over a wide area of operation, while chassis dynamometer tests on a converted EV indicated 16-30% improvement in one-charge vehicle range using this motor due to its high efficiency. The significant extension of EV range possible will have a positive impact on market acceptance of EVs.