Hyundai Motor Company and Kia Corporation say the new Universal Wheel Drive System, or Uni Wheel as its also called, is a paradigm-shifting vehicle drive system that will revolutionise the design of future mobility devices.

The Uni Wheel will allow for the EV’s main drive system components to be moved into 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 to the wheels via drive shafts 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.

Uni Wheel opens new possibilities and enables a flat-floor configuration by moving an EV’s reduction gear to inside the wheel hub, placing a compact individual motor close to each wheel, thereby reducing the length of the drive shafts.

The system frees up significantly more interior space compared to conventional drive systems, enabling future mobility products optimised for various applications, such as Purpose-Built Vehicles (PBVs).

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.

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, which 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. With independent control of up to four efficient electric drive units, Uni Wheel also allows for unprecedented levels of torque vectoring.

It is also possible to move away from conventional seating arrangements designed around the driver, creating new interior layouts and designs for the era of fully autonomous driving. Utilising this space to improve battery capacity can also improve driving range, which means users can achieve the range of a large EV without the physical size of the vehicle increasing.

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