Audi has built its five millionth vehicle equipped with quattro all-wheel drive. The milestone car was an Audi A6 Allroad built at the company's Neckarsulm plant in Germany. Audi first launched all-wheel drive in 1980 on the original quattro coupé.
Today, Audi says it offers 140 different vehicles -- when factoring in different engine choices and bodystyles -- with quattro. Last year, more than 43 percent of all Audis were equipped with all-wheel-drive. The technology is standard globally on the Q7, R8, A4 Allroad, A6 Allroad, and all RS and S performance models, but optional on other Audis. In the U.S. market, quattro is also standard on the A5, A7, A8, and Q5.
On Audi models with a transversely mounted engine, like the TT, the quattro driveline uses a multi-plate clutch that is electronically controlled, and can send up to 100 percent engine torque to the rear wheels. Models with a longitudinally mounted engine, for instance the A8, have a self-locking center differential in the middle of the vehicle. These quattro systems normally produce a 40/60 front/rear torque split.
Some sporty models, including the Audi RS5, use a variation of that system with a "crown" center differential that can more quickly vary the car's torque split -- to as much as 85 percent front or 70 percent rear. The Audi R8, meanwhile, has a unique quattro system due to its mid-engine construction. A driveshaft runs through the engine's crankcase to a viscous coupling on the front axle, sending 15 to 30 percent of engine torque to the front wheels.