The track record
“quattro” means “Audi,” and “Audi” often means “quattro.” Now, 40 years after the original quattro first appeared, the brand with the four rings has notched up some impressive figures. Through 2020, Audi had produced 11,199,144 cars with all-wheel drive. Some 45.31 percent had all-wheel drive in 2020.
The quattro drive system has been one of the biggest cornerstones of the Audi brand for 40 years. It is represented in every model series except the compact A1. All larger models – the A8, the Q7, the Q8, the e-tron*, and the e-tron Sportback*, the R8 and all S and RS models transfer their horsepower to the road through four wheels as standard. Audi currently has 16 quattro models in its portfolio on the German market.
The mechanical quattro systems
Throughout its model range, Audi offers a very wide variety of car concepts – and quattro technology is equally multifaceted. One thing that all versions share is a supplementary solution: Wheel-selective torque control is a software function of Electronic Stabilization Control (ESC). During dynamic cornering, it applies the brakes very gently to the unloaded wheels on the inside of the curve before they have the chance to slip. Due to the difference in propulsion forces, the car turns slightly into the corner. This input makes the handling even more neutral, dynamic, and stable.
Two systems: quattro drive for longitudinal engines
The Audi models with longitudinal front-mounted engines and tiptronic automatic transmissions employ the classic quattro drive system with a self-locking center differential, which operates by purely mechanical means and therefore without any delay whatsoever. It is configured as a planetary gear. This involves an internal gear encompassing a sun gear, with cylindrical planet gears, joined to the rotating housing, turning between them.
In regular driving operation, 60% of the drive torque flows to the rear axle via the internal gear, which has a larger diameter, and its associated output shaft. The remaining 40% goes to the front axle via the smaller sun gear. This asymmetric, dynamic torque distribution results in sporty, rear-biased basic handling. If the wheels on one axis lose traction, the geometry of the gearwheels and helical gearing in the differential produce axial forces. These forces act on friction discs to produce a locking effect that diverts the bulk of the drive torque to the wheels with the better traction. Up to 70% can be directed to the front wheels and up to 85% to the rear.
The quattro with ultra technology optimized for efficiency is designed for Audi models featuring a longitudinal front-mounted engine working with a manual transmission or the S tronic dual-clutch transmission. During moderate driving, quattro with ultra technology enjoys all the advantages of front-wheel drive. All-wheel drive remains continuously available however, and is there immediately when needed.
The control system for the quattro powertrain is comprehensively networked. It acquires and evaluates data – in ten millisecond cycles – such as the steering angle, transverse and longitudinal acceleration and engine torque. As a result, all-wheel drive is generally activated predictively, i.e. in anticipation of the need for it. When cornering at speed, the control unit detects roughly half a second in advance when the wheel on the inside of the curve will reach the traction limit and quickly sends drive torque to the rear wheels. There are no differences in terms of traction and handling compared with conventional permanent quattro drive systems.
The concept with two clutches in the drivetrain gives quattro with ultra technology a significant efficiency advantage of on average roughly 0.3 liters of fuel per 100 kilometers (62.1 mi) over the competition. When the system changes to front-wheel drive, the front clutch – a multi-plate clutch at the transmission output – disconnects the propshaft. A decoupling clutch also opens in the rear differential. It shuts down the rotating components that cause the most drag losses here, such as the large crown wheel running in the oil bath.
Mechanical torque vectoring at the rear axle: sport differential
The sport differential is available for the particularly powerful and sporty Audi models with tiptronic. It further improves handling, traction, and stability by distributing drive torque ideally between the rear left and right wheels in all operating states. During turning or acceleration, mechanical torque vectoring literally presses the car into the curve without producing any understeer.
In addition to the functions covered by a conventional differential, the sport differential has a transmission stage and hydraulic multi-plate clutch fed by an oil pump. During fast cornering, the clutch engages for the wheel on the outside of the curve, which has better grip due to the dynamic wheel load distribution. The clutch variably imposes a higher speed on the transmission stage for the relevant wheel. The extra torque required is taken from the opposite wheel via the differential, which means that almost all the torque goes to the wheel on the outside of the curve. Up to 1,200 Nm (885.1 lb-ft) of drive torque can be transferred to one wheel in this way.