Hyundai’s Uni Wheel Creates Space for EV Powertrains

By rethinking how a wheel works, Hyundai can eliminate the CV joints and reduce the lengths of the drive shafts to pack more batteries in an EV, for example.

The Uni Wheel’s multi-axis movement allows for a wide range of suspension articulation. (Hyundai)

Hyundai Motor Group’s visual design team has been on a roll in creating unusual and attractive passenger vehicles. Now, the automaker’s engineering team has come up with its own unique creation: the Universal Wheel Drive System.

Hyundai’s Uni Wheel has four pinion gears on each side of a sun gear, with multi-link connections between each. (Hyundai)

The Uni Wheel is a significant development for both Hyundai Motor Company and the Kia Corporation, which jointly unveiled the device at a “Uni Wheel Tech Day” in Seoul, South Korea, in November. The Uni Wheel is not a hub motor, but it does move some of the main drive system components to the available room inside the wheel hub.

The gears that make up the Uni Wheel fit inside traditionally unused space, which then creates more room in the vehicle. (Hyundai)

Hyundai calls the Uni Wheel a “functionally integrated wheel drive system.” The Uni Wheel has a newly designed planetary gear configuration made up of a central sun gear and four surrounding pinion gears. These all sit inside a ring gear that makes up the outside of the Uni Wheel and then rotates the tire. The pinion gears are arranged so that, with their multi-link connections, they enable “Uni Wheel’s multi-axis movement to allow a wide range of suspension articulation,” the company said.

An example of an EV with Uni Wheels (bottom) reveals how more batteries could be packaged there than in a traditional EV layout (top). (Hyundai)

The Uni Wheel also does away with traditional CV joints to transfer power from the motor to the wheel at a constant speed. CVs themselves found a home in EVs because they have long been used with ICE powertrains, but Hyundai wanted to use some of the space near the wheels for other components. To do this, engineers put small, individual motors near each wheel and moved the reduction gear to inside the wheel hub. They also reduced the length of the drive shafts.

Finding room

One of the reasons Hyundai wanted to invent the Uni Wheel was to create more room in an EV’s interior, either for powertrain components, more cargo space or a larger flat-floor configuration. The space benefits are real, but many questions remain about the Uni Wheel’s durability, effects on unsprung weight, issues with heat dissipation and potential repair costs.

A Hyundai spokesperson told SAE Media that it’s too early to discuss these aspects in detail but said that price competitiveness is not one of the ways the Uni Wheel will distinguish itself. “If the Uni Wheel is applied to replace the CV joint and the reducer that make up the existing system, there will be no significant difference in cost,” the spokesperson said.

Hyundai Motor and Kia have applied for or registered eight patents related to Uni Wheel globally, including in South Korea, the U.S. and Europe.