How Does Audi Quattro AWD Work?

Beverly Braga | Apr 14, 2020

The term quattro is Italian for “four,” which is appropriate given its association with Audi’s all-wheel drive system. But this wasn’t always the case. The Audi Quattro (yes, with a capital Q) was actually a standalone model introduced in 1980.

Quattro was, indeed, the first Audi vehicle to have AWD but also was the first to enter competitive rally racing after a rule change made the drive system eligible. The vehicle won four world championships for the brand in the early 80s. Fast forward 40 years and Quattro (officially trademarked as quattro in lowercase, but capitalized here) refers specifically to the automaker’s AWD system, which is available on much of its lineup.

So, how does a champion rally car translate to a drive system the average consumer should care about or even want? For the same reasons the Audi Quattro was a motorsport success, of course.

How Audi Quattro AWD Works

A differential is a set of gears that powers wheels at the axle. The original Quattro system featured three differentials (front, rear, and center), which allowed for better torque distribution to each wheel. Because wheels can spin at different speeds, the differentials are left open. This way, when the car is turning, the outside wheels can rotate faster than the inside ones.

How Does Audi Quattro AWD Work

Normally, the front differential doesn’t have a lock because those wheels need to turn. But adding the ability to lock a differential, like in the rear, means the wheels will spin at the same time to find grip—even if one is off the ground. In turn, that means better traction in slippery situations. Additionally, Audi’s early system had a driver-operated switch that allowed the center differential to lock both the front and rear differentials.

Within a decade, the center differential was replaced with a torque-sensing (Torsen) one. This system automatically split power delivery evenly between the front and rear axles. When wheel slip occurred, the design of the gears within the system reallocated torque to the axle that needed it most. The Torsen differential channels up to two-thirds of the vehicle’s torque to either the front or the rear axle. The rear locking differential switch remained available, but some larger vehicles also received a rear Torsen differential for additional control.

The Evolution of Audi Quattro AWD

As Quattro evolved, redesigns occurred as much to the engineering as to the exterior styling. When the Audi TT sports coupe entered the market in 2000, for example, its small size required a sideways (transverse) mounting of its engine. More commonplace vehicles, like sedans, have engines, transmissions, and differentials laid out neatly running lengthwise. With the TT, the transmission was placed underneath the engine and so its differential had to change as well.

A Haldex coupling solved this problem. A propeller shaft (propshaft) that connects to the Haldex coupling runs from the transmission to the rear differential. The input shaft is where the propshaft connects to the Haldex coupling. The output shaft is where the Haldex coupling connects to the differential.

When traction is lost, the speeds of the input and output shafts will change. The Haldex system senses the differences and adjusts rotational distribution to the front and rear axles. Voilà, now you have an AWD system with a non-traditional engine layout. In addition to the Haldex system, other systems and sensors inform power distribution based on engine speed, torque output, and gas pedal position.

Modern Audi Quattro AWD Systems

Today, the Audi Quattro AWD system includes mechanical and electronic activation as well as intelligent software and sensors monitoring steering angle, traction, stability control, movement of the wheels, and yaw angle. There are also five versions of Audi quattro technologies, including an efficient version that disconnects from the rear axle unless power transfer is required (Quattro Ultra).

Audi offers multiple versions of Quattro AWD because overall system packaging is based on a specific vehicle’s architecture and transmission, and that frequently calls for unique tweaks. So, an electric vehicle with battery packs placed along its floor base will require a different setup from a transverse-engine coupe, which will also be unlike the system in a large SUV.

The modern Quattro AWD system itself operates in much the same way as the previous three-differential versions, but with advanced technology to adapt the system to each vehicle’s intended driving nature. This gives consumers not only added driving confidence but also the responsive performance and handling expected of the Audi brand.

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