This year, Audi is celebrating forty years of the iconic Ur Quattro, the rally racing legend that put Audi on the performance-car map. However, it’s not only the car itself that the brand is celebrating. It’s also celebrating the all-wheel drive system the Ur Quattro was named after, which has been the entire Audi brand’s calling card ever since.
As part of Audi’s ‘Tech Talk’ series, we’re taking a look at the famous Quattro all-wheel drive system, how it works and its history.
Back in the late ’70s, four-wheel drive on a road car was essentially unheard of, for good reason. Having a full-time four-wheel drive system in a car — not a truck — was heavy, complicated, difficult to package and expensive. But when Audi saw what its parent company Volkswagen was doing with an off-road military vehicle, the Iltis, it took notice.
Rather than using the bulky all-wheel drive systems of the past, VW and Audi pioneered a system that used a center-locking differential that could lock the torque-split between the axles. That was improved on in the early ’80s, a couple of years after the Ur Quattro debuted, with a new Torsen (Torque-Sensing) center differential. The Torsen diff was, and is, a viscous-coupling differential that allows for real-time, mechanical torque vectoring between the axles. The Torsen diff changed the game for Audi.
The only issue with Torsen center diffs is that they require a longitudinal engine layout. That’s fine for most Audis, as they’re almost all longitudinal. However, some VW-based products, like the original Audi TT, used a transverse-engine (sideways) setup, which couldn’t fit a Torsen diff. So Audi adopted a Haldex all-wheel drive system for cars like the TT and A3, yet it was still named Quattro.
Haldex has a rear driveshaft off of the transmission that connects to a clutch pack on the rear differential. When necessary, the clutch pack will engage the rear driveshaft and make it all-wheel drive. However, for the most part, Haldex-equipped cars are otherwise front-wheel drive.
Fast forward to today and there are five different variations of the Quattro all-wheel drive system on sale. Aside from the standard Quattro, which is now electronically-controlled, the most important new system is Quattro Ultra. The ‘Ultra’ version combines the best aspects of traditional Quattro with Haldex, by allowing the rear driveshaft to be temporarily disconnected. During that time, the car is essentially front-wheel drive, which reduces drivetrain loss and improves fuel efficiency. But when it’s needed, that driveshaft is reconnected and it becomes a proper all-wheel drive Audi.
Haldex is still used in transverse-engine, MQB-based Audis, such as the A3, Q3 and TT. It’s essentially the same as always, just with more sensors and a more advanced electronically-controlled clutch.
There’s also the system in the Audi R8. Being mid-engine, the engine and transmission are mounted behind the driver and the transmission is actually a transaxle, as it’s one with the rear differential. There’s also another differential hooked up to the transmission with spins a driveshaft connected to the front axle, making it all-wheel drive.
Lastly, there’s the new electric Quattro system, which is used by Audi’s new e-tron products. This uses an electric motor at each axle, with nothing connecting them except some wires and software. The e-tron’s brain then cleverly blends the use of both motors to create a more seamless, even more instantaneous all-wheel drive system than any other Quattro setup.
Over the four decades since Audi has been using all-wheel drive, its Quattro system has changed quite a bit. However, four-wheel grip is still very much the heart and soul of Audi’s products and it has the original rally-racer from forty years ago to thank for that.