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Hyundai and Kia unveil new wheel drive system for EVs

[All images courtesy: Hyundai Motor Group]

 

 

What if you took the CV joint, drive shaft, and reducer and moved them all into the wheel for electric vehicles (EVs)? Then, you split the motor into smaller components and move those into each wheel too? That's what a development partnership between Hyundai and Kia has done, creating a new, functionally integrated wheel called "Uni Wheel."

Hyundai and Kia unveiled the Uni Wheel at a special event in Seoul, Korea, on Nov. 29. Both companies think they are on to something -- a "paradigm-shifting vehicle drive system" that will have real influence on the design of future mobility devices.

The Uni Wheel concept has many benefits. Among them is a dramatic improvement in available space inside an EV due to moving the main drive system components to the vacant space within the wheel hub. In doing so, Hyundai Motor and Kia have designed a completely new structure for the drive system beyond a simple in-wheel motor design.

In internal combustion engine (ICE) vehicles, power is transmitted from the engine through the transmission and to the wheels via drive shafts and constant velocity (CV) joints. In most EVs, the engine and transmission are replaced by a motor (or motors) and reduction gear(s), but the final method of power transmission to the wheels is the same.

Uni Wheel opens new possibilities and enables a completely 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, enabling future mobility products optimized for various applications, such as Purpose Built Vehicles (PBVs).

New tech may advance future mobility
Recent advances in electrification, autonomous driving, and connectivity technologies are transforming mobility products into enclosed areas that are closer to living spaces. Hyundai Motor and Kia's focus on space utilization in future vehicle architectures aims to boost customer value further and provide owners with richer user experiences as a result.

Uni Wheel uses a special planetary gear configuration consisting of a sun gear in the center, 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 for 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 traveling 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 deflection can be increased to stabilize 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 also 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.

More efficiency, more interior space
The Uni Wheel concept frees up space within a vehicle that was previously unavailable to users. By relocating many components of the drive system to the wheel hub and downsizing the electric motor with no impact on performance, the extra space made available within the vehicle body can be utilized as additional cargo room, such as a larger trunk (or "frunk").

It's 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. Utilizing this space to improve battery capacity can also improve driving range, meaning users can achieve the range of a large EV without the physical size of the vehicle increasing.

The developments Uni Wheel allows will also significantly increase passenger space. EV batteries are conventionally located low down in a vehicle's body, which requires a raised ride height, often reducing passenger space by the volume of the battery. However, Uni Wheel optimizes battery packaging, with the loss of passenger space minimized.

This will be a valuable feature for PBVs, which need to maximize interior space by offering a low, flat-floor design. The flat-floor platform enabled by Uni Wheel allows for strong flexibility and scalability when it comes to PBVs, enabling the design of various body types depending on the intended use case.

Hyundai says Uni Wheel is highly flexible and easily adaptable to all types of EVs, including regular passenger and high-performance EVs, as the system can implement the same powertrain and reduction gear functions required for conventional EVs.

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 4 in. and as large as 25 in. or more. In addition, Uni Wheel's ability to move the rotation axis of the wheel makes it possible to create forms of personal mobility that can climb stairs as smoothly as an escalator.

For now, Hyundai and Kia have a system that is pretty much ready to go, although they continue to test and verify the stability, efficiency, and durability of Uni Wheel through myriad tests to perfect its development. Efforts are also being made to improve the design's efficiency by adjusting the reduction gear ratio and upgrading the lubrication and cooling system.

Hyundai Motor and Kia have applied for and registered eight patents related to Uni Wheel in South Korea, the United States, and Europe.

Source: Hyundai Motor Group

Published December 2023

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