The new Audi A4 3.2 FSI and 3.0 TDI transmit their power to the road by way of the latest generation of the quattro permanent four-wheel drive system that has brought enhanced traction, safety and directional stability to the Audi range since 1980.
In the new Audi A4 the key element in the quattro driveline is a centre differential: this is a self-locking worm and wheel device. It is a purely mechanical unit and therefore takes effect with no delay. Its locking action only develops in response to an applied load; when braking or cornering, it permits the wheels to rotate at different speeds.
In normal driving conditions, 40 per cent of engine power reaches the front wheels and 60 per cent the rear wheels, permitting handling with a slight rear-end bias. Should the wheels on any axle start to spin, however, the differential redirects most of the torque to the axle revolving more slowly and therefore with better traction.
The centre differential can direct up to 65 per cent of the power to the front axle and up to 85 to the rear; as a result, the new A4 can often contain situations close to the handling limit without ESP having to make a brake application. If one wheel on an axle begins to spin, this is eliminated by the electronic differential lock (EDL) without any brake application being needed – though this situation seldom arises. EDL also acts as an aid when driving off.Published 9 February 2008