Forty years on, Audi quattro has become synonymous with all-wheel drive, earning its mettle through motorsports and harsh road conditions to propel the Audi brand forward to what it has become today. Audi quattro all-wheel-drive technology is known for providing the maximum grip available on any road surface during dry or inclement weather.
The quattro all-wheel-drive system defines Audi in many ways and remains its unfair advantage on the road and racetrack. In motorsports, quattro propelled Audi to numerous World Rally Championships in the 1980s. It catapulted Audi’s success in IMSA and Trans-Am racing in the ‘80s and 1990s. And, it was a driving force behind the R18 e-tron quattro’s success at the 24 Hours of Le Mans.
The idea of quattro stemmed from the desire to mass-produce cars with traction to all four wheels, with Audi engineers first developing a lightweight all-wheel-drive system based on the fundamental traits demonstrated by the Volkswagen Iltis off-roader in the 1970s. The technology was then brought under the Audi banner in 1980 with the first production quattro all-wheel-drive systems. Today’s quattro all-wheel drive builds on the 40 years of learnings since entering production, with several different types available in various applications. Before getting to today’s drivetrains, it’s important to understand how earlier quattro systems worked.
Early quattro systems
The first quattro all-wheel-drive system used three mechanical differentials to distribute torque between the front and rear wheels. Via a vacuum-operated switch, the driver could select to lock the center differential to lock the front and rear differentials together, causing them to turn at the same speed without slip.
Ordinarily, the differential—a set of gears driving the wheels at each axle—are fully open to help compensate for the difference in speed each wheel travels. Think of taking a corner, for instance: the inside wheel will rotate far less than the outside wheel. Locking the rear differential helps ensure power gets to both wheels equally, which is needed when driving on slick surfaces or traction-limited situations but also to maximize grip in any condition. The front does not have a locking differential because of the need to turn.
In the first major update of quattro in the late-1980s, a Torsen (short for torque-sensing) differential that automatically split power 50:50 from front to rear replaced the original manually operated center differential. A rear differential lock switch remained; some larger vehicles were available with a rear Torsen differential as well.
The Torsen center differential housed a pair of helical planetary gears. The gears were held in tight-fitting pockets inside the housing and splined together through spur gears at their ends. These spur gears did not allow the planetary gears to rotate in the same direction. However, when an axle would lose traction, the spur gears would help channel torque to the wheels with traction. This could allow up to two-thirds of the vehicle’s torque to be sent to either the front or rear axle.
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