The active sport differential distributes torque from the engine in continuously variable proportions between the rear wheels. This greatly enhances agility, driving pleasure and active driving safety. Targeted control of the power flow enables the car to steer even more spontaneously and directly into bends, and produces a far more robust directional stability.
With the active sport differential driving the rear wheels, the car quite literally takes every corner as if on rails. Depending on the steering angle, lateral acceleration, yaw angle, road speed and other signals, the control unit calculates the most suitable distribution of torque to the wheels for every driving situation. When the steering wheel is turned or the car is accelerated in a bend, power is redirected in a controlled manner to the outer rear wheel. This has the effect of “forcing” the car into the corner so that it accurately follows the angle of the front wheels. The difference in tractive force between the left and right wheels exerts an additional steering effect, so that the usual corrections by the driver at the steering wheel are no longer needed. Understeer, that is to say the tendency for the car to run wide at the front, is completely eliminated.
Active torque distribution is based on an entirely new design principle for the rear-axle differential. So that the new high-tech unit can also divert torque to the outer wheel of the axle, which revolves faster than the inner wheel when cornering, the classic rear-axle differential has been equipped with superposition stages on the left and right, each with a multi-plate clutch running in an oil bath. The clutches are activated by an electro-hydraulic actuator.
The superposition stage rotates ten percent faster than the half-shaft that normally drives the wheel; the two components can be coupled by the multi-plate clutch. If the clutch is engaged, the wheel is accelerated by the superposition stage, which is running at a higher speed, and thus receives an additional torque input. The differential reduces the tractive force reaching the opposite wheel accordingly. In most driving situations, almost the complete input torque can be diverted to one rear wheel in this way. The maximum difference in torque between the wheels is 1,800 newton metres.
The quattro® drive with active sport differential is part of the innovative Audi drive select driving dynamics system. As part of an optimal combination with Audi dynamic steering and electronic damping control, the quattro permanent four-wheel drive and the sport differential demonstrate their immense capabilities with regard to driving dynamics.