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March 2003 - DSG Transmission Technology at Audi

Audi has a long tradition in the development of innovative transmission technologies and their use in production vehicles. The tiptronic, for example, which enables very sporty gear changes and manual intervention at any time, was first introduced on the A8 in 1994. Since 1999, the innovative continuously variable multitronic transmission has been setting new standards in terms of acceleration comfort and economy. Thanks to its ingenious design and control logic, it is a sporty alternative to the conventional geared automatic transmission. In the world of automatic transmissions, the Direct-Shift Gearbox is now following the tiptronic and multitronic as a further milestone in transmission technology at Audi.

This transmission principle, however, is not unknown territory for Audi. The technology of the twin-clutch transmission has its roots in motor racing. Audi used it in the legendary Audi Sport quattro back in 1985, with Walter Röhrl behind the wheel. He completed successful test drives in the Audi Sport quattro S1, a rally vehicle whose victories included the legendary Pikes Peak Hill Climb.

The revolutionary Direct-Shift Gearbox combines the advantages of a conventional 6-speed manual gearbox with the qualities of a modern automatic transmission. The driver thus benefits from enormous agility and driving enjoyment with acceleration that is as harmonious as it is dynamic, without any interruption in the power flow. This is combined with good economy thanks to low fuel consumption, and convenient operation.

The basis for this new development is a three-shaft 6-speed manual gearbox which offers considerable variability in the selection of the transmission ratio. Thanks to the use of a twin multi-plate clutch with ingenious electro-hydraulic control, two gears can be engaged at the same time.

During dynamic operation of the car, one gear is engaged. When the next gearshift point is approached, the appropriate gear is preselected, but its clutch kept disengaged. The gearshift process opens the clutch of the activated gear and closes the other clutch at the same time with a certain overlap. The gear change takes place under load, with the result that a permanent flow of power is maintained. The control logic integrated into the transmission casing maintains optimum gearshift strategies that perform lightning-fast gearshifts that are nevertheless smooth and almost jolt-free. The driver can directly influence the gear selected and the gearshift timing at will, by means of the gear lever in the manual gate or, in the style of a racing driver, using the standard-fit shift paddles on the steering wheel.

In the automatic mode, the driver can shift to the ultra-sporty S program in which upshifts are significantly retarded, downshifts advanced and the shifting process accelerated. A remote one-touch function accessed via the shift paddles on the steering wheel in addition temporarily calls up the manual mode, even in automatic modes D and S. The design of the transmission gate with a high-quality aluminium surface is reminiscent of typical Audi tiptronic or multitronic counterparts. High overall efficiency is thus combined with superlative road performance and ease of operation to produce an exceptional drive concept.

As on conventional manual gearboxes, the transmission ratios are present on input and auxiliary shafts in the form of pairs of toothed wheels. In contrast to manual gearboxes, the input shaft is divided into two sections. It comprises an outer hollow shaft and an inner shaft. The 1st, 3rd, 5th and reverse gears are located on the inner shaft. The hollow shaft handles the 2nd, 4th and 6th gears. Each of these shafts is selected by means of a separate multi-plate clutch running in oil. The two electronically controlled, hydraulically actuated multi-plate packages are packed inside each other for maximum space economy.

As well as their high efficiency and ability to transmit high torques, clutches of this type permit a wide range of starting characteristics. In other words, the multi-plate clutch can be controlled in such a way that every conceivable form of pulling away is possible, from an ultra-gentle edging along on a slippery surface to sports-style acceleration at full throttle.

The gearshifts it produces feel spontaneous and decisive, as if executed at the push of a button. The electronically controlled throttle blip in the manual and S modes reinforces the impression of ultra-dynamic gearshifts. A shift-by-wire control concept has been implemented. This means that there is an electronic connection between the selector lever and the transmission, like on modern engine management systems with drive-by-wire technology. The parking lock is mechanically activated.

The control module and electro-hydraulic control unit are located in the top part of the transmission casing. The signals from twelve individual sensors are processed centrally there, and the actuation values calculated using the relevant information on the momentary driving situation from the drive CAN bus. The application pressure of the two clutches is regulated by special solenoid-operated valves depending on the situation, and the gear positioners operated. The electronics also calculate which additional gear is to be preselected by the corresponding positioning cylinder and selector forks, and manages all actuators and the oil cooling circuit via six pressure regulation valves and five on/off valves.

The DSG has been developed at group level and is built at the Kassel transmission plant. It goes without saying that the new design satisfies the exacting requirements of convenient gear-shifting and maximum operating life for everyday use in production vehicles. Despite its compact dimensions, the DSG transmits a torque of up to 350 Nm.

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