Aside from its model range, Audi offers a very wide variety of car concepts – and quattro technology is correspondingly wide-ranging.
Modular longitudinal platform: the self-locking center differential
In Audi models with a longitudinally mounted front engine, the heart of the quattro drivetrain is a self-locking center differential. It is configured as a purely mechanical planetary gear with zero lag. During normal driving operation, the self-locking center differential distributes the power asymmetrically, with 60 percent flowing to the rear axle and 40 percent to the front axle.
Oblique splines produce axial forces immediately when torque is transferred by the differential. These forces act on friction discs to produce a locking torque that diverts the torque to the wheels with the better traction.
In its latest form, the center differential can divert 70 percent of the torque to the front, or up to 85 percent to the rear. The high locking values enable a clearly defined distribution of torque and highly precise interaction with the control systems, such as the ESC and wheel-selective torque control.
Even more dynamic: the sport differential
For even greater dynamics and driving safety, top-of-the-line Audi models based on the modular longitudinal platform can also be equipped with the sport differential. The sport differential really allows the handling to shine. It actively distributes the drive torque between the rear wheels, literally pushing the car into the curve and eliminating any tendency toward understeer. The vehicle is stabilized in the case of oversteer. The result is agile and predictable road behavior at all times.
The sport differential is a conventional differential with two superposition units mounted on the left and right, each containing a multi-plate clutch and an internal gear. The drive torque can be variably distributed between the wheels of the rear axle with the help of the superposition units. The hydraulic controller actuates the multi-plate clutches. An electric motor drives the high-performance oil pump, which generates the required hydraulic pressure. All functions are controlled and monitored by a separate control unit. The active distribution of torque provides for better driving dynamics, traction and stability.
Modular transverse platform: Electrohydraulic multi-plate clutch
For the compact models with transverse-mounted engine, Audi uses a quattro drivetrain featuring an electronically controlled multi-plate clutch with hydraulic actuator. It is mounted on the rear axle for better weight distribution.
Inside the clutch is a package of metal friction rings mounted in pairs one behind the other. One ring of each pair is permanently meshed with the clutch basket, which rotates with the propshaft. The other ring of each pair is connected to the shaft leading to the rear differential. The electronically controlled multi-plate clutch guarantees the best possible traction, driving dynamics and driving safety while providing for dynamic handling with actively controlled torque distribution.
In the Audi TT, Audi S1, RS Q3* and Audi RS 3 Sportback*, there is a strong dynamic bias to the management of the multi-plate clutch. On a road surface with a low coefficient of friction, controlled drifts are possible when in sport mode or with the ESC deactivated. In contrast, when driven sedately, the clutch of the TT can be automatically opened temporarily to save fuel. The quattro drive is immediately reactivated when the driving situation changes. In all three model series, the quattro all-wheel drive system works closely together with wheel-selective torque control, a software function of the ESC stabilization control that uses light, defined braking to precisely distribute the drive torque to further improve handling at the limit.
Audi R8: actively controlled front differential
In the Audi R8, the seven-speed S tronic with integrated rear-axle differential and locking center differential is mounted in the back behind the engine and sends the power to the front axle via a propshaft. The electrohydraulic multi-plate clutch integrated in the front differential transmits the calculated torque to the front wheels within just a few milliseconds. The combination of the high-performance transmission mechanism and the all-wheel drive software tailored to a mid-engine sports car allows for driving dynamics featuring an unprecedented balance between agility and driving safety.
The future: e‑tron quattro
Audi presented a future form of the quattro drive – the electrified quattro, aka the e-tron quattro – in the Audi e-tron quattro concept, a concept study that was the star of the IAA 2015. The sport SUV uses three powerful electric motors, one on the front axle and two on the rear axle. At low load, one motor is solely responsible for propulsion. When the driver floors the accelerator and all three electric motors are working together, however, 370 kW of output and more than 800 Nm (590.0 lb‑ft) of torque are available.
The drivetrain management system orients on the position of the accelerator, the mode chosen in Audi drive select, the driving program – S or D – and the battery charge level. The focus is on not just powerful performance, but also maximum efficiency. At the start of a trip, the Audi e-tron quattro concept can compute a strategy for using the smallest possible amount of electricity. Underway it can recover energy by means of braking recuperation.
Power is distributed to the front and rear axle as a function of a multitude of parameters. During sporty driving, the concept with the two electric motors on the rear axle enables electric torque vectoring similar to the function of the sport differential. The Torque Control Manager actively distributes the power between the rear wheels as necessary. This torque control provides for maximum dynamics and stability. Thanks to the nearly instantaneous response of the electric motors, all control actions are lightning-quick.
The equipment and data specified in this document refer to the model range offered in Germany. Subject to change without notice; errors and omissions excepted.