Hyundai Motor Company and Kia Corporation unveiled a universal wheel drive system — called Uni Wheel — at “Uni Wheel Tech Day” in Seoul, Korea. The companies said Uni Wheel is a functionally integrated wheel drive system that improves available space inside an electric vehicle (EV) by moving the main drive system components to the vacant space within the wheel hub. In doing so, Hyundai Motor and Kia have designed a completely new structure for the drive system.

In internal combustion engine (ICE) vehicles, power is transmitted from the engine through the transmission and to the wheels via driveshafts and constant velocity (CV) joints. In EVs, the engine and transmission are replaced by a motor and reduction gear, but the final method of transmission to the wheels is the same.

Hyundai and Kia said Uni Wheel opens new possibilities and 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 and 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. Uni Wheel’s pinion gears are connected to form two linkages, and this multi-link mechanism enables Uni Wheel’s multi-axis movement to allow a wide range of suspension articulation.

A conventional drive system using a regular CV joint suffers from a decrease in efficiency and durability as the angle of driveshaft deflection increases when traveling over bumpy, undulating surfaces. However, the companies said Uni Wheel can transmit power with almost no change to efficiency regardless of wheel movement. When combined with electronic air suspension that can adjust ride height according to the driving situation, this can be increased to stabilize the vehicle on rough roads or decreased for high-speed driving to improve power and stability.

By moving the reduction gear to the wheel hub, Hyundai and Kia said Uni Wheel’s high-reduction ratio delivers a significant torque output and allows for a more compact electric motor. With independent control of up to four electric drive units, the Uni Wheel also allows for torque vectoring to boost dynamic ability and deliver high levels of steering and driving stability.

Hyundai and Kia said Uni Wheel is highly flexible and easily adaptable to all types of EVs, including regular passenger and high-performance EVs, as the system can implement the same powertrain and reduction gear functions required for conventional EVs. In addition to vehicles of various sizes, Uni Wheel can also be applied to other types of mobility devices, such as wheelchairs, bicycles and delivery robots. Depending on the requirements of these different forms of mobility, Uni Wheel can be scaled to work with wheel sizes as small as four inches and as large as 25 inches or more. In addition, Uni Wheel’s ability to move the rotation axis of the wheel makes it possible to create forms of personal mobility that can climb stairs smoothly.

Hyundai Motor and Kia said they are continuously verifying the stability, efficiency and durability of Uni Wheel through various tests and said it will continue efforts to improve its efficiency by adjusting the reduction gear ratio and upgrading the lubrication and cooling system.