Hyundai Motor Company and Kia Corp. have developed the world’s first next-generation drive system that dramatically boosts vehicle design flexibility by placing electric vehicle drive components inside wheels. This new system can realize the utilization of the space between wheels, which was previously occupied by a lot of different components.
Hyundai and Kia took the wraps off the Universal Wheel Drive System developed by Hyundai Motor Group’s Advanced Technology Center in the Uni-Wheel Tech Day Event in Seoul on Nov. 28.
A Uni-Wheel is a system that integrates the functions of reducers, drive shafts, and constant velocity joints into a wheel. Reducers, drive shafts, and constant velocity joints hold the key to making cars move. A Uni-Wheel can implement all of these functions through a specialized gear structure. Motors usually located between the wheels of a car were miniaturized and placed closer to each wheel.
The Uni-Wheel has a planetary gear structure that consists of three types of gears (sun, pinion, and ring gears). A motor directly connected to a wheel moves a sun gear at the center, which in turn turns a ring gear at the outmost spot through four pinion gear links on each side that mesh with the sun gear. The ring gear is connected to the wheel, so when the ring gear moves, the wheel rolls.
This allows power generated by the drive motor to be transmitted directly to the wheels without having to go through a driveshaft, significantly increasing power efficiency. Even if the wheel moves up, down, left, or right, the power is transmitted evenly, which improves ride comfort.
Unlike the existing in-wheel system that integrates motors inside wheels, Uni-Wheel’s motor is mounted on the body of a vehicle, making it more durable, the company said. In-wheel systems developed by Hyundai Mobis and others incorporate not only a car’s suspension, steering, and braking components, but also its motor into the wheels.
The biggest strength of Uni-Wheel is its space utilization. “Even in e-GMP, Hyundai Motor Group’s electric vehicle platform, a motorized powertrain occupies a large space between the left and right wheels,” explained Park Jong-sul, a senior researcher at the Advanced Technology Center. He continued by saying, “By applying Uni-Wheel, we will be able to free up this space and design cars like never before. It will be possible to create a low-floor electric vehicle with batteries between the wheels instead of on the floor of a car, or to develop a stair-climbing wheelchair by controlling each wheel independently.”
Another advantage of Uni-Wheel is that it can transmit more power with the same motor. “By varying the reduction ratio according to gear combinations, we can realize torque 6 to 10 times higher than that delivered by a motor,” said Min Kyung-chul, a researcher at the Advanced Technology Center.
The commercialization of the new system is expected to take several years. “This technology was first developed about two years ago, so it is in the early development stage,” Park said. “If it is commercialized, it will go into expensive luxury cars first because it requires more components.” Hyundai and Kia will begin detailed targeted testing for vehicle development next year. Currently, they are testing a rear-wheel-based system, but depending on future results, they plan to develop a Uni-Wheel for front wheels.