The global mobility market is slowly but surely transitioning into a bright, all-electric future. This shift has brought about changes in design techniques and mechanical components, with many of them being minimized. However, one component that has remained relatively unchanged in the move from internal combustion engine (ICE) vehicles to electric vehicles (EVs) is the drivetrain.
In internal combustion engine cars, power is transmitted from the engine through the transmission and 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.
To address this issue, the Hyundai Motor Company and Kia Corporation unveiled a new Universal Wheel Drive System called ‘Uni Wheel’ that can create even more platform space while maintaining the efficiency necessary for an effective EV range.
Unveiled at ‘Uni Wheel Tech Day’ in Seoul, Uni Wheel is a functionally integrated wheel drive system that dramatically improves available space inside an electric vehicle by moving the main drive system components to the vacant space within the wheel hub. In doing so, Kia and Hyundai Motor have designed a completely new structure for the drive system.
Uni Wheel’s innovative design allows for a flat-floor configuration by placing the EV’s reduction gear inside the wheel hub. This means that the compact individual motor can be located close to each wheel, thereby reducing the length of the drive shafts. As a result, Uni Wheel creates more interior space compared to conventional drive systems, providing greater flexibility for future mobility products that are optimized for different applications, including purpose-built vehicles (PBVs).
Uni Wheel has a unique planetary gear system that includes a central sun gear, four pinion gears on each side, and a surrounding ring gear. The motor produces power that is sent to the sun gear, which then engages with the pinion gears. Those pinions, in turn, rotate the ring gear connected to the wheel, which propels the vehicle forward. Uni Wheel’s pinion gears are linked together, forming two linkages, and this multi-link mechanism allows for Uni Wheel’s multi-axis movement, which enables a wide range of suspension articulation.
Additionally, Uni Wheel can transmit power with almost no change to efficiency regardless of wheel movement, ensuring high durability and ride comfort even when traveling over bumpy, undulating surfaces. By contrast, 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.
By moving most of the drivetrain into the wheels, 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 to boost dynamic ability and deliver high levels of steering and driving stability.
The Uni Wheel concept frees up space within a vehicle that can be utilized as additional cargo room, such as a larger trunk or a ‘frunk.’ The extra space could also be used for more battery, thereby improving the driving range of the EVs without making them physically larger.
Uni Wheel is a highly flexible and easily adaptable system that can be easily integrated into various types of electric vehicles. It offers the same powertrain and reduction gear functions as traditional EVs, making it compatible with both regular passenger and high-performance EVs. Uni Wheel can also be applied to other mobility devices, such as wheelchairs, bicycles, and delivery robots, and can be scaled to work with wheel sizes ranging from 4 to 25 inches or more.
Hyundai Motor and Kia are committed to ensuring the stability, efficiency, and durability of the Uni Wheel through a series of tests to perfect its development. The companies are continuously working to improve their efficiency by adjusting the reduction gear ratio and upgrading the lubrication and cooling system.
