Kia and Hyundai have unveiled the Universal Wheel Drive System — called ‘Uni Wheel’ —which they promise will revolutionise the design of electric vehicles by incorporating gears into the wheel hubs. 

It is said to dramatically improve the space available inside an electric vehicle by moving the main drive system components inside the wheel hub. 

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, using drive shafts.

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, reducing the length of the drive shafts.

The system frees up significantly more interior space compared with conventional drive systems.

“We are pleased to showcase innovative ideas that could become game changers in the future mobility market,” said Jongsool Park, Senior Fellow at the Institute of Advanced Technology Development of Hyundai Motor Group. “We will perfect the technology so that customers can experience mobility in a completely different and new way.”

Uni Wheel uses a special planetary gear configuration consisting of a sun gear in the centre, 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. 

The system saves space by moving the gearbox to the hub

Uni Wheel’s pinion gears are connected to each other 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 drive shaft deflection increases when travelling over bumpy, undulating surfaces. Uni Wheel can transmit power with almost no change to efficiency regardless of wheel movement, ensuring high durability and ride comfort.

When combined with electronic air suspension that can adjust ride height according to the driving situation, this can be increased to stabilise 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, Uni Wheel’s high reduction ratio delivers a significant torque output and allows for a more compact electric motor. 

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. 

Kia and Hyundai are currently testing the system to ensure it meets the durability requirements needed before it can be put into production.

The first application is expected to be in the companies' new commercial vehicle range