Hyundai Motor and Kia presented a new transmission system called the Universal Wheel Drive System, or Uni Wheel for short. This system aims to move the reduction gear placed after the electric motor into the wheel (the reduction gear is what acts as the gearbox in an electric car, which only has one gear). The Uni Wheel, which Hyundai presents as an epicyclic gear train but which is not one, is an articulated gear train that fits into a cylindrical shroud. The numerous joints allow the mechanism to move both vertically and horizontally, therefore following the movements of the wheel. Hyundai claims that its system guarantees better power transmission because it allows the electric motor to be placed much closer to the wheel and therefore to opt for a much shorter transmission shaft than usual, reducing some losses.
The main advantage of the system is that it concentrates a large part of the machinery in the wheel, therefore freeing up a lot of space for something else: more space in the passenger compartment, larger batteries, and larger trunks at the front. like at the rear… By moving the reduction gear in the wheel and thanks to the better power transmission (i.e., a higher torque to the wheel since there is less loss between the motor and the wheel), the Korean group believes that we can therefore use a smaller electric motor for the same result and thus add them up more easily. It is practical for torque vectoring to use one motor per wheel, thus independently controlling the speed of each wheel.
However, there is a real problem that Hyundai does not address in its presentation: weight. If the space gain in the center of the chassis is convincing, it is also done by moving a mass that becomes unsprung since it is attached to the wheel. However, the heavier a wheel is, the more it generates jolts, even percussions, and other harsh movements in the passenger compartment, which greatly harms comfort.
It remains to be seen, therefore, how this Uni Wheel will be useful for everyday vehicles. In any case, Hyundai announced that it can adapt its technology for very different wheel sizes ranging from 4 inches to more than 25 inches in diameter, which could make it viable for applications not only in automobiles but in mobility in general.
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