Used on Audi RS5 (2010-...)

Type: Full-time all wheel drive.

Crown-gear center differential, 40/60 torque split front to rear, automatically locking with torque transfer variable from 70/30 to 15/85 front to rear.

Open rear differential. Audi RS5 - rear "active sport differential".

Open front differential.

Electronic Torque-Vectoring system. This system applies brakes to the inner wheel when the vehicle is turning.

"Audi did take the time to also point out that the RS5 features new quattro technology: the crown-gear differential. This new differential is a self-locking center differential that Audi says is lightweight and maintains a high efficiency ratio. The front to rear power ratio can be shifted as extreme at 70 percent upfront, or 85 percent out back – depending on where the power is needed. Under normal conditions, the RS5 enjoys a 40:60 front to rear split."[1]

"Inside the new center differential are two rotating crown gears that owe their name to the crown-like design of their teeth. The rear crown gear drives the propshaft to the rear axle, and the front one the output shaft that runs to the front axle’s differential The crown gears are driven by four pivot-mounted compensating gears arranged at angles of 90 degrees to each other. They are driven by the housing of the differential, i.e. by the gearbox output shaft.

Under normal driving conditions, the two crown gears turn at the same speed as the housing. Because of their special geometry, they have specifically unequal lever effects. Normally 60 percent of the engine torque goes to the rear differential and 40 percent to the front differential.

If the torques change because one axle loses grip, different speeds and axial forces occur inside the differential and the adjacent plate packages are pressed against one another. The resulting self-locking effect now diverts the majority of the torque to the axle with the better traction; up to 85 percent can flow to the back. In the opposite scenario – if the rear axle has less grip – the same happens in reverse; now up to 70 percent of the torque is diverted to the front axle.

With this broad torque distribution range, the crown gear differential surpasses its predecessors – traction becomes even better. Forces and torques are redistributed without any time lag and absolutely consistently. The purely mechanical operating principle guarantees maximum efficiency and no-delay response. Other strong points of the crown gear differential are its compactness and low weight – at 4.8 kilograms (10.58 lb) it is roughly two kilograms (4.41 lb) lighter than the previous unit.

Audi combines the crown gear differential in the RS 5 – and in other models in which it will subsequently feature – with an intelligent software solution in braking management called torque vectoring. An evolutionary form of the ESP with electronic differential lock that is already standard on many front-wheel-drive models, however it can act on each of the four wheels. The new system makes cornering even more precise and dynamic.

Using the driver’s steering input and desired level of acceleration, the software calculates the optimal distribution of propulsive power between all four wheels. If it detects that the wheels on the inside of the curve, which are under a reduced load, will soon begin to slip, it marginally brakes these wheels – just slight application of the pads on the disks at minimal pressure is all that it takes. This assistance is provided smoothly and continuously. The car remains neutral noticeably longer, and understeer when turning and accelerating is practically neutralized. The ESP intervenes later and more gently – if necessary at all."

Source: DVD quattro® Highlights 2010[2]