The new system combines current drive elements to provide superior efficiency, power, and durability while maintaining ride comfort. This enhanced packaging possibility paves the way for increased driving range, more passenger space, and advancements in Purpose-Built Vehicle (PBV) development.
Hyundai Motor Company and Kia Corporation recently showcased their Universal Wheel Drive System, named ‘Uni Wheel’, at the ‘Uni Wheel Tech Day’ in Seoul, Korea. This innovative drive system marks a significant shift in vehicle design for future mobility. Uni Wheel, a functionally integrated wheel drive system, significantly enhances the space inside an electric vehicle (EV) by relocating major drive system components into the empty space within the wheel hub. This reconfiguration by Hyundai and Kia has resulted in a novel drive system structure.
In traditional internal combustion engine (ICE) vehicles, power flows from the engine through the transmission to the wheels via drive shafts and constant velocity (CV) joints. EVs replace the engine and transmission with a motor and reduction gear, yet the power transmission method to the wheels remains unchanged.
Uni Wheel introduces new design possibilities, allowing for a flat-floor configuration in EVs by incorporating the reduction gear into the wheel hub and situating a compact motor near each wheel, thereby shortening the drive shafts. This change frees up considerably more interior space compared to traditional drive systems, making it ideal for a variety of future mobility solutions, including purpose-built vehicles (PBVs).
Uni Wheel employs a unique planetary gear setup with a central sun gear, four pinion gears on either side, and a surrounding ring gear. The motor’s power is transmitted to the sun gear, which drives the pinion gears to rotate the ring gear attached to the wheel, propelling the vehicle. The system’s pinion gears are linked to create a multi-link mechanism that enables multi-axis movement, allowing for a wide range of suspension movement.
Traditional drive systems using regular CV joints lose efficiency and durability when drive shaft angles increase over uneven terrain. Uni Wheel, however, maintains efficiency and durability regardless of wheel movement, ensuring a comfortable ride.
When paired with electronic air suspension capable of adjusting ride height based on driving conditions, Uni Wheel enhances vehicle stability on rough roads and improves power and stability at high speeds. With its high reduction ratio, Uni Wheel provides substantial torque output and enables the use of a more compact electric motor. Its ability to independently control up to four electric drive units allows for advanced torque vectoring, enhancing steering and driving stability.
The Uni Wheel design creates new vehicle interior possibilities by relocating drive components to the wheel hub and reducing motor size without sacrificing performance. This newly available space can be used for additional cargo, innovative seating layouts, or increased battery capacity to extend driving range.
This design also improves passenger space. Traditional EVs, with batteries positioned low in the body, often compromise passenger space. Uni Wheel minimizes this space loss, which is beneficial for PBVs that prioritize a low, flat-floor design for maximum interior flexibility. Uni Wheel is versatile, fitting various types of EVs, including standard passenger and high-performance models. It can also be adapted to other mobility devices like wheelchairs, bicycles, and delivery robots.
Hyundai and Kia are rigorously testing Uni Wheel to ensure its stability, efficiency, and durability, focusing on refining the reduction gear ratio and enhancing the lubrication and cooling systems. They have filed and registered eight patents related to Uni Wheel in South Korea, the United States, and Europe, demonstrating their commitment to its development and future applications.