SEOUL—Engineers at Hyundai Motor Co. and Kia Corp. have developed a paradigm-shifting drive system called the Uni Wheel. The Universal Wheel Drive System dramatically improves available space inside an electric vehicle. It enables a flat-floor configuration by moving an EV’s reduction gear inside the wheel hub, locating a compact individual motor close to each wheel, reducing the length of the drive shafts.
Uni Wheel uses a special planetary gear configuration consisting of a sun gear in the center, four pinion gears on each side and a ring gear surrounding this arrangement. Power generated by the motor is transmitted to the sun gear, which in turn engages the pinion gears to rotate the ring gear. This is connected to the wheel to drive the vehicle.