Faster gearshifts, sportier driving: the S tronic combines the sporty characteristics of a manual gearbox with the advantages of an automatic. Gear-changes with the dual-clutch gearbox are performed easily and with no appreciable delay. Depending on the driver’s preference, the gears may be shifted in fully automatic mode or in manual mode using the gearshift paddles on the steering wheel.
This new S tronic transmission can also handle up to 550 Nm of torque, meaning it can be coupled to engines such as the 3.0 V6 TDI or the 4.2 V8 engine of the S5. Or the 4.2 V8 of the RS4, for that matter, since it can handle engines revving up to 9,000 rpm!
Double act: the dual clutch forms the technical basis of the S tronic. One of the two clutches engages the odd-numbered gears and reverse, the other engages the even-numbered gears. The benefit: a gearbox that shifts from one gear to the next in less than 0.2 seconds and with no interruption in power flow.
When in operation, one gear is always engaged and another is pre-selected: while the first clutch is transmitting power in one gear, the second clutch has the next gear selected and ready to engage as shown in the following figures.
Operating principle, acceleration in 1st gear
IMG Ref: www.audi.com (Click on the picture for a larger image)
Operating principle, acceleration in 2nd gear
IMG Ref: www.audi.com (Click on the picture for a larger image)
Highly precise management of both multidisk clutches was one of the most important development goals. This was achieved in part with a compact pressure cylinder, electronically controlled rotation speed compensation and the use of an optimized coil spring package. This package of technology provides maximum precision and comfort at startup and shifting.
The transmission is managed by the so-called mechatronic module. This module involves a compact group of control units and hydraulic control valves that is integrated on the left of the transmission when facing the direction of travel. Its control concept allows the speed of the gear shifting process to vary and extremely precise control of the power necessary for the process.
The required control pressure is provided by an efficiently operating oil pump that is located next to the mechatronic module and is driven by a gear section. The oil pump is supported by a vacuum booster for cooling the twin clutch during starting. This allows the amount of oil pumped to be roughly doubled as needed without increasing power.
A unique feature of the seven-speed S tronic is its two separate oil systems. While the twin clutch, mechatronic module and oil pump are supplied by their own oil circuit with seven liters of automatic transmission fluid (ATF) oil, the wheel sets and the central and front-axle differential are lubricated with about 4.5 liters 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.
The consistently efficient power transmission ideally supports a sporty driving style – both in automatic mode and with manual shifting:
- The flexible automatic mode allows the driver to vary the gearshift behaviour between the sporty character of the shift programme S (Sport) and the comfort-oriented shift programme D (Drive).
- If the driver prefers manual gearshift, the gears can be changed in sporty style with the gearshift paddles on the steering wheel or with the selector lever.
Reference:
http://www.audiusa.com/us/brand/en/tools/advice/glossary/s_tronic.browser.html
http://www.eurocarblog.com/post/677/the-new-audi-s-tronic-7-speed-gearbox
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