The Audi S4: Transmissions

Source: Audi AG

Audi delivers the S4 and S4 Avant with a six-speed manual transmission as standard – its short and precise lever travel and low operating force make every gear change a delight. Special selector fork mountings decouple the gear lever from the driveline so that the driver does not sense any vibration.

Internal friction in the transmission has been minimized, improving the already high level of efficiency still further. A change-up display in the driver information system helps the driver to adopt a more economical driving style. It shows which gear is in use and recommends a different gear if this would be a better choice.

The dual-mass flywheel and the hydraulically actuated single dry-plate clutch are not bolted to the crankshaft in the usual way, but supported on the transmission input shaft. On the S4 and S4 Avant, the differential is located in front of the clutch. Output to it is via a hollow shaft, which features a so-called beveloid gear on both sides, enabling it to be installed at an inclined angle of 7.2 degrees.

Interchanging the components has moved the front axle forward by 154 millimeters (6.06 in) compared with the previous model. This has many advantages – a long wheelbase, a short front overhang and good weight distribution. It results in handling characteristics that set new standards in terms of dynamism, precision and stability.

Dynamic and efficient: the seven-speed S tronic

On request the new S4 and S4 Avant leave the assembly line equipped with the seven-speed S tronic transmission, which is exceptionally dynamic and at the same time remarkably efficient. The innovative dual-clutch transmission can be used in various ways. The fully automatic mode features the D (Drive) and S (Sport) programs. The gears can also be manually switched with the shift selector lever or with the paddles on the steering wheel – an amazingly fast process. The gearshift feel is dynamic, comfortable and very precise – typically Audi.

The seven-speed S tronic consists of two separate transmissions and uses two multi-plate clutches that control the various gears. The large outer K1 clutch transmits the power through a solid shaft to the gear wheels for gears 1, 3, 5 and 7; they are located at the rear of the aluminum transmission housing. A hollow shaft rotates around the solid shaft. It is connected to the compact K2 clutch, which is integrated into the inside of its larger sibling, and which controls the gear wheels for gears 2, 4 and 6, as well as reverse gear. All gear wheels are arranged one behind the other on both output shafts, in the order 4, 6, 2, R, 1, 3, 7 and 5.

Both transmission structures are continuously active, but only one is powered at a time by the engine. For example, when the driver accelerates in third gear, the fourth gear is already engaged in the second transmission structure. The shifting process takes place as the clutch changes – K1 opens and K2 closes with lightning speed. The gear change takes only a few hundredths of a second and is completed without interrupting traction. It is so fluid and smooth that the driver hardly notices it.

Each component of the new seven-gear S tronic attests to Audi’s innovative approach and to the company’s uncompromising quality standards. Carbon-coated synchronizer rings guarantee synchronization of unsurpassed quality and stability. The gears one through three and reverse are also designed as three-cone synchronizations. Both multi-plate clutches are managed with supreme precision when driving off and shifting between gears thanks to the compact pressure cylinders, electronically controlled speed compensation and optimized coil spring packages.

Mechatronics – the command center

The command center of the transmission is a mechatronic module, a compact unit containing control units and hydraulic actuators. It can vary the speed of the gear change across an extensive range and controls the power required for the process with extreme precision. An efficient gear-driven oil pump builds up the control pressure; when the car is driven off, it helps a suction jet pump to cool the dual clutch. This almost doubles the oil delivery volume without any increase in drive power.

A further special feature of the seven-speed S tronic is the use of two separate oil supplies. While the dual clutch, mechatronic module and oil pump are supplied by their own oil circuit with seven liters (1.85 US gal) of automatic transmission fluid (ATF) oil, the wheel sets and the center and front-axle differential are lubricated with about 4.5 liters (1.19 US gal) of hypoid gear oil. This separation allowed the development engineers to position all of the components ideally, without being forced to compromise by using a single lubricant.

Audi has designed the new seven-speed S tronic to provide both exhilarating driving and maximum economy. It operates with very high efficiency and its intelligent control system maximizes fuel economy in automatic mode (sedan: only 9.4 liters/100 km or 25.02 US mpg). The transmission-ratio spread of 6.0:1 allows a sporty, close transmission ratio for the first gear as well as an rpm-sinking, wide ratio for the last gear. The seven-speed S tronic easily exploits the tremendous power and superior torque of the 3.0 TFSI to the full.

The equipment, data, and prices specified refer to the models offered in Germany. Subject to amendment; errors and omissions excepted.