Hyundai and Kia have revealed an all-new Universal Wheel Drive System for EVs, called Uni Wheel, at a dedicated Uni Wheel Tech Day event held in Seoul, Korea. Through the new system, the OEMs will look to enable, facilitate, and support the design of future mobility devices.
Uni Wheel is a functionally integrated wheel-drive system that moves the components found in a typical main drive system to the vacant space within the wheel hub, resulting in both a new structure for the EV drive system and enhanced interior space. This represents a shift in the design approach seen across ICE and electric vehicles – where in an ICE vehicle power is transmitted from the engine through the transmission and wheels through the drive shafts and constant velocity (CV) joints, while in EVs the engine and transmission are replaced by a motor and reduction gear with the final method of transmission remaining the same.
By comparison, Uni Wheel moves the EV reduction gear inside the wheel hub – facilitating new possibilities while enabling a flat-floor configuration. A compact, individual, motor is positioned close to each wheel that, in turn, reduces the length of the drive shafts. The configuration ultimately provides drivers with more interior space when compared to conventional drive systems, while enabling OEMs to develop future mobility products optimized for various applications such as purpose-built vehicles (PBVs), which themselves are positioned to play a key role in the Hyundai Group’s future EV and mobility activities.
The new drive system works through a dedicated ‘planetary’ gear configuration that consists of a central ‘sun’ gear, four pinion gears at either side of this central gear, and a ring gear that surrounds this arrangement. The power generated by the motor is transmitted first to the sun gear, which engages the eight pinion gears to rotate the ring gear connected to the wheel, turning the wheels and enabling drive.
The pinion gears are connected to one another to form two linkages, with this multi-link mechanism enabling a multi-axis movement to allow a wide range of suspension articulation. At the same time, Uni Wheel is able to transmit power in this manner without a reduction in efficiency, ensuring high durability and comfort. When paired with electronic air suspension that can adjust the ride height according to the driving situation, this can be increased to stabilize the vehicle when driving on rough roads or decreased for high-speed driving scenarios to improve power and stability.
Uni Wheel offers similar enhancements to EV performance by moving the reduction gear to the wheel hub, allowing for enhanced torque output based on the new system’s high reduction ratio. Here, independent control of up to four EDUs also enables enhanced torque vectoring capabilities, boosting the vehicle’s dynamic ability and offering high levels of stability when steering and driving.
By relocating many drive system components to the wheel hub and downsizing the electric motor with no impact on performance, Uni Wheel frees up interior space that Hyundai and Kia claim was previously unavailable and can provide additional space for cargo in the trunk or ‘frunk’ areas, for example. The OEMs also envision this space being used to create non-conventional seating arrangements tailored to various use cases, including those related to autonomous driving, while improving battery capacity and, therefore, increasing the driving range. An optimized battery packaging design sees EV battery cells spread to the space previously taken by the drive system components also provides Uni Wheel with a low, flat-floor, design. This design will work to support future PBVs by maximizing interior space and facilitating various options for flexibility and scalability.
Flexibility is another key feature of Uni Wheel, which can be adapted to all EV types, including passenger and high-performance EVs, since it can implement the same powertrain and reduction gear functions required for conventional EV drivetrains. Hyundai and Kia confirmed that the system can be scaled to work with wheel sizes ranging from 4 inches up to more than 25 inches, enabling compatibility with further mobility devices such as wheelchairs, bicycles, and autonomous delivery robots.
While Hyundai and Kia have not yet indicated which vehicle will receive Uni Wheel first, the OEMs did confirm that they have applied and registered eight patents for the drive system in South Korea, the U.S., and Europe.