Direct Shift Gearbox DSG
Text and pictures courtesy of Audi of America
INGOLSTADT, Germany - 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.
Following the tiptronic and multitronic, Audi is now introducing the Direct Shift Gearbox - also with an automatic function - as a further landmark in its transmission technology.
This transmission principle is not new to 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. It also proved its worth in the Audi Sport quattro S1, a rally car that was victorious in many events, including the legendary Pikes Peak hillclimb.
The new Direct Shift Gearbox DSG
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 and 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 ratios. Thanks to the use of a double multi-plate clutch with an ingenious electro-hydraulic control system, two gears can remain engaged at the same time.
Apart from its high efficiency and the ability to transmit high torque, the big advantage of this special kind of clutch is the various options it offers the driver when setting off. The driver is able to control the multi-plate clutch as he desires, varying from a particularly gentle acceleration process on slippery ground all the way to sporting, full-power acceleration, and with countless variants in between.
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.
When the car is on the move, one gear is engaged. When the next gearshift point is approached, the appropriate gear is pre-selected 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 provides optimum gearshift strategies, with 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, at the shift paddles on the steering wheel, which are standard equipment.
In the automatic mode, the driver can shift to the ultra-sporty S program in which upshifts are significantly delayed, downshifts occur more readily and the shift process is accelerated. An additional one-touch function accessed via the shift paddles on the steering wheel calls up the manual mode temporarily even in automatic modes D and S.
High overall efficiency is thus combined with superlative road performance and ease of operation to produce an exceptional drive concept.
High tech in very confined conditions
As in conventional manual gearboxes, the transmission ratios are present on input and auxiliary shafts in the form of pairs of toothed wheels. However, the input shaft is divided into two sections, comprising an outer hollow shaft and an inner shaft. 1st, 3rd, 5th and reverse gears are located on the inner shaft, 2nd, 4th and 6th gears on the hollow shaft.
Each shaft is selected by a separate multi-plate clutch running in oil. The two electronically controlled, hydraulically actuated multi-plate packages are housed one inside the other for maximum space economy.
A `shift-by-wire' concept is used: 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 actuated mechanically.
The control module and electro-hydraulic control unit are located in the upper part of the transmission casing. The signals from twelve individual sensors are processed centrally there, and the actuation values calculated using information on the momentary driving situation from the drive CAN bus. The contact pressure of the two clutches is regulated by special solenoid-operated valves and the gear selectors operated according to the actual operating situation.
The electronics also calculate which additional gear is to be pre-selected by the corresponding positioning cylinder and selector forks, and manage all actuators and the oil cooling circuit via six pressure regulation valves and five on/off valves.