As is the case with their gas-burning counterparts, electric cars are limited in spaciousness and design by the layout of their drivetrain. The Hyundai Motor Company and Kia Corporation have set about addressing that issue, with their radical new Universal Wheel Drive System.
In internal combustion engine cars, the engine takes up a lot of space, as do the transmission and drive shafts which transfer power from the engine to the wheels. In an electric car, the engine is replaced by a motor, but the vehicle's design still has to allow for a means of linking that one motor to at least two of the wheels.
That's where the Universal Wheel Drive System – aka Uni Wheel – comes in.
Unveiled Nov. 29th at a media event in Seoul, the setup swaps one big motor for four smaller ones. Each of those motors is located right beside one of the vehicle's wheels, and is connected to it via a short drive shaft.
Occupying what would otherwise be empty space inside each wheel hub is a reduction gear. It consists of a central "sun gear" that is turned by the drive shaft, and which is connected via articulated linkages to four outlying pinion gears. Those pinions are in turn meshed with a single large "ring gear" that runs around the circumference of the hub.
So, on each Uni Wheel unit … the motor turns the driveshaft, which turns the sun gear, which turns the pinion gears, which turn the ring gear, which turns the wheel. If that sounds confusing, watching the explanation in the video at the end of this article will help.
Additionally, thanks to the pivot points in the linkages (which allow them to flex as the gears are turning), power transmission from each motor to each wheel stays efficient and consistent even as the wheel moves up and down while going over bumps in the road. By contrast, when the wheels on a traditional drivetrain move vertically, power transmission efficiency decreases as the angle of drive shaft deflection increases.
Other claimed advantages of the Uni Wheel system include increased durability and torque, along with the ability to independently control torque at each wheel for better handling. And as mentioned earlier, there's also the fact that by moving most of the drivetrain into the wheels, additional space becomes available inside the vehicle.
That space could be used for more seating, more cargo capacity, or for reconfigurable interiors – the fact that the floor could be completely flat would certainly help in that regard. The extra space could also be used for more batteries, thus expanding the range of EVs without making them physically larger.
Hyundai and Kia now plan on improving Uni Wheel's reduction gear ratio, and upgrading its lubrication and cooling systems. There's currently no word on when it might actually enter production.
"We are pleased to showcase innovative ideas that could become game changers in the future mobility market," said Jongsool Park, Senior Fellow at the Institute of Advanced Technology Development of Hyundai Motor Group. "We will perfect the technology so that customers can experience mobility in a completely different and new way."
And as an interesting side note, Hyundai previously developed an e-Control Module system in which four separate all-in-one wheel units are able to independently pivot, allowing for 90-degree turning. A team at Canada's University of Waterloo is working on a similar system.
Source: Hyundai
In my country we have a yearly car test, and there are several points of regular failure removed from the setup with this. However will the test center want to look inside these wheels periodically to see if they are fit for the road? I dunno, maybe?
Controlled vertical movement is important in order not to change the track width under brisk cornering. That's what the unequal radius arms go along way to achieve.
Also...I dont think these guys fully understand what such an increase in unsprung weight will do to the wheel assembly. Hub motor/gears are fine for fork lifts .
on the subject of interesting sus' check out the DeDion sliding tube with watts linkage for the rear geometry first seen on the Rover P6..also includes inboard disc brakes. For lower un sprung weight? you cannot change the laws of physics, but you can go a long way to lessen the effect.