First of all, what is “quattro”? It means “four” in Italian; it was the name of the once-famous Audi Rally car (now referred to as Ur-quattro augmentatively); it is the name of Audi’s all-wheel-drive system; it was once the name of the Audi high-performance car division (now renamed Audi Sport). It is, indeed, everything for Audi.
The quattro AWD system originated from Rally racing in the 1980s. Ferdinand Piëch, who later became the chairman of Volkswagen Group, initiated the program for an all-wheel-drive Rally car, and the effort resulted in the championship-winning Audi Ur-quattro. Cars were mostly 2WD except for trucks and off-road vehicles, and the street-legal version of Ur-quattro was the pioneer of 4WD high-performance cars. The subsidiary that produced quattro-equipped Audis was named after it as well: the quattro GmbH.
Audi was known for economical front-wheel-drive cars before the quattro-era. In the post-war era, Auto Union, the direct predecessor of Audi, was known for two-stroke-engined FWD cars badged as DKW. The company was controlled by Daimler-Benz at the time, but Volkswagen completed the acquisition in the 1960s. VW later acquired NSU and merged it with Auto Union, forming the Audi NSU Auto Union. The original Auto Union consisted of 4 brands, namely DKW, Audi, Horch, and Wanderer. Upon the VW acquisition, however, the Wanderer was already dormant, and the right to Horch was retained by Daimler-Benz, leaving VW with Audi and DKW only. The DKW brand was soon aborted to avoid the impression of producing two-stroke engines, and the company was later renamed “Audi AG”, which is the Audi brand we know today. The Audi brand, nevertheless, remained an entry-level manufacturer of FWD cars in the early 80s. In contrast, the more luxurious Daimler-Benz had always been known for RWD limousines.
In a traditional Audi layout, the engine sits longitudinally in front of the front axle, and the gearbox is located right after the front axle. This allows the driveshaft to reach the front axle more easily and provides a good basis for AWD. The downside of such is the weight balance as the engine puts all the weight on the front end. Such a layout cannot accommodate a straight-6 or V12, and the biggest engine that Audi made in the 80s was a straight-5. Audi has been using this over-the-front-axle longitudinal engine layout ever since. It even applies to some Porsche and Bentley models today although Porsche turns it into RWD on Panamera. This is why W12 and V6 are prevalent among VW Group, and why the VAG products tend to have a long front overhang. The only Audi street-legal car ever to have a V12 was the rare Q7 V12 TDI.
The success of the quattro AWD was the turning point for Audi as Audi gradually introduced the system to all the models. The introduction of the Audi V8 in 1988 marked Audi’s expansion into the premium sedan segment. Audi V8 was the unicorn at the time as it came with V8 and AWD only. The heavy sedan even won the DTM in 1990 and 1991. Audi later introduced the V6 engines to the new 100, which was soon renamed A6, and the new A4 lineup. All the effort in the 1990s made Audi a true premium brand just like the long-established Mercedes-Benz and BMW.
NSU has a great impact on Audi and quattro although it is not represented in the four-ring logo. The old NSU site in Neckarsulm is now expanded to be the production plant for A4 and the models above. The office of Audi Sport, formerly quattro GmbH, is located in the Neckarsulm site as well — in the old motorbike production factory of NSU. The iconic three-piece side window design came from one of the very last products of NSU before the consolidation — the rotary-engined NSU Ro80. Audi TT borrowed the name from the NSU 1000/1200 TT, a small sports car produced in the 1960s. The NSU TT in turn borrowed the name from the famous race — Isle of Man TT — to pay tribute to NSU’s history in motorbike racing. It is safe to say that NSU is “the fifth ring” of Audi.
Some prominent modern Audi design strokes are linked to the past as well. The famous “Audi Grille” has its origin in the Silver Arrow race cars made by Auto Union. Audi pays homage to Ur-quattro via the muscular wheel arches and the front intake duct. We can see similar design cues on models ranging from the entry-level A1 to the super-sport R8. This again shows how much success in the 1980s impacts the Audi brand.
In 2021, Audi revives the “Horch” marque as a luxury sub-brand, debuting with A8L Horch in China. It is said that VW Group bought back the right to the Horch marque from Daimler after the Auto Union acquisition in exchange for disclaiming the name “Silver Arrow”. Both Mercedes and Auto Union race cars were nicknamed “Silver Arrow” in the 1930s, but only the Mercedes race cars can have this title now. The Horch marque had stayed dormant for half a century ever since and surprisingly resurrects recently thanks to the growing demand for extreme luxury. The Silver Arrow returned to the Gran Prix racing in 2010 when Daimler bought the Brawn GP F1 team. The Mercedes-AMG is still a dominating force even after decades of absence.
Various quattro AWD systems have been deployed to different Audi models throughout the years, but they can be roughly divided into four types: longitudinal-engined permanent AWD, longitudinal-engined part-time AWD, transverse-engined AWD, and the mid-engined AWD seen on R8. If electric-powered vehicles are included, the fifth type of quattro would be the “electric quattro”.
The first and the most classic quattro type is the longitudinal-engined permanent AWD that brought success on the Rally course. This system features a mechanical self-locking center differential that cannot be disengaged, making it “permanent” from the engine start. The basic idea for the mechanical permanent AWD stays the same, but Audi has implemented different types of center differentials throughout time, ranging from bevel gear, Torsen types A to C, planetary gear, and crown gear differentials. The mechanical center differential is tuned to be rear-wheel-drive biased, so it offers high performance with good traction to S and RS models. The advantage of this system is greatly revealed in drag races as the Audis often beat the rivals off the line. Currently, self-locking mechanical differentials can be seen on all variants of A8, Q7, Q8, and the selective high-performance variants of A4, A5, A6, and A7.
The second type is the “quattro ultra” introduced a few years ago, an electrically-controlled AWD substitution for the classic quattro. It is indeed a part-time AWD system although Audi describes it as “permanently available”. The mechanical center differential is replaced with a multi-plate clutch that is controlled by the computer. The center clutch is engaged when necessary and only offers up to a 50:50 front-rear power split. The quattro ultra offers lower fuel consumption because it drives front wheels only most of the time, but it loses the RWD-biased driving experience on the other hand. The clutch is inherently more prone to overheating compared to the mechanical differential, making the quattro ultra more suitable for city uses with occasional slight off-roading. The quattro ultra is optional on selective A4, A5, A6, A7, and Q5 models with up to 500Nm torque and comes together with the 7-speed dual-clutch S-Tronic transmission.
The third one is the system for transverse-engined models like A1, A3, Q2, Q3, and TT. It debuted with the very first generation of A3 and has become more popular ever since as Audi keeps expanding its entry-level lineup. Unlike the longitudinal-engined models with the center differential or center clutch, the transverse-engined models have the multi-plate clutch right in front of the rear axle for better weight balance. The principle of this system is similar to that of the quattro ultra, engaging the rear-axle clutch according to the computer calculation. This type of quattro system is sourced from the Swedish company Haldex Traction which is often referred to as the Haldex system.
The fourth one is the mid-engined quattro exclusively made for R8. The latest Audi R8 has a mechanical differential on the rear axle, and a multi-plate clutch sitting behind the front axle transmits the power to the front wheels. Unlike the front-axle viscous coupling from the previous generation of R8, the clutch solution allows a greater adjustment of the power delivered to the front. R8 is tuned to be RWD-biased to match the characteristics of a supercar.
With the rise of electric power, quattro makes its way into electric models like e-tron quattro, e-tron GT, and Q4. The fifth type of quattro is revolutionary just as the shift to electric cars the world is experiencing now. In an electric quattro layout, each of the front and the rear axle has at least one electric motor, and the output of the motors is adjusted by the computer according to the sensors around the car. If the industry is to abandon internal combustion engines, the electric quattro will be the one to stay around.
(For more details on different types of quattro, see Audi Technology Portal
https://www.audi-technology-portal.de/en/)
