The Direct-Shift Gearbox (German: DirektSchaltGetriebe), or DSG, is an electronically controlled, twin-shaft dual-clutch manual gearbox, without a conventional clutch pedal, with full automatic, or semi-manual control. In simple terms, it is two separate manual gearboxes, contained within one housing, and working as one unit. It was designed by BorgWarner and initially licensed to Volkswagen Group (which owns the Volkswagen, Audi, SEAT, Bentley, Bugatti, Lamborghini, and Škoda brands), with support by IAV GmbH. By using two clutches, fast shifts can be achieved, and the torque converter of a conventional epicyclic automatic transmission is eliminated.
At the present time, the DSG transmission is only available in transaxle-mounted front engine, front-wheel drive or four-wheel drive. The Bugatti Veyron is a notable exception, due to its Ricardo-developed transmission.
The First DSG gearbox that went into production had 6 speeds and wet/submerged clutch packs. The new 7 speed DSG Gearbox uses dry clutches, is used in cars such as the new Skoda Superb and the new Seat Ibiza
Once the vehicle has shifted up to second gear, the first gear is immediately de-selected, and third gear (being on the same shaft as 1st and 5th) is pre-selected, and is pending. Once the time comes to shift, the second clutch disengages and the first clutch re-engages. This method of operation continues in the same manner up to 6th gear.
Downshifting is similar to upshifting but in reverse order. The car's computer senses the car slowing down or more power required, and thus lines up a lower gear on one of the shafts not in use, and then completes the downshift. The actual shift timings are determined by the DSG's Electronic Control Unit, or ECU, which commands a hydro-mechanical unit, and the two units combined are called a "mechatronics" unit. Because the DSG ECU uses "fuzzy logic", the operation of the DSG is said to be "adaptive"; that is, the DSG will "learn" how the user drives the car, and will tailor the shift points accordingly.
In the vehicle instrument display, between the speedometer and tachometer, the available shift positions are shown, the current position of the shift lever is highlighted, and the current gear ratio is also displayed as a number.
Under "normal", progressive acceleration and deceleration, the DSG shifts in a "sequential" mode, i.e. under acceleration: 1 > 2 > 3 > 4 > 5 > 6, and the same sequence reversed for deceleration. However, if the car is being driven at sedate speeds, with a light throttle opening, and the accelerator pedal is then pressed fully to the floor, this activates the "kick-down" function. During kick-down, the DSG can skip gears, going from 6th gear straight down to 3rd gear.
When the floor-mounted gear selector lever is in position D, the DSG works in fully automatic mode, with emphasis placed on gear shifts programmed to deliver maximum fuel economy. That means that shifts will change up and down very early in the rev-range. As an example, on the Golf Mk5 GTI, sixth gear will be engaged around 33mph, when initially using the DSG 'box with the 'default' ECU adaptation, although with an "aggressive" or "sporty" driving style, the adaptive shift pattern will increase the speed at which 6th gear engages.
S is also highlighted in the instrument display, and like D mode, the currently used gear ratio is also displayed as a number.
The readout in the instrument display changes to 6 5 4 3 2 1, and just like the automatic modes, the currently used gear ratio is highlighted. To change up a gear, the lever is pushed forwards (against a spring pressure) towards the "+", and to change down, the lever is pulled rearwards towards the "−". The DSG box can now be operated with the gear changes being (primarily) determined by the driver. This method of operation is commonly called "tiptronic". In the interests of engine preservation, when accelerating in Manual/tiptronic mode, the DSG will still automatically change up just before the redline, and when decelerating, it will change down automatically at very low revs, just before the engine idle speed (tickover). Furthermore, if the driver calls for a gear when it is not appropriate (i.e., engine speed near the redline, and a down change is requested) the DSG will delay the change until the engine revs are at an appropriate level to cope with the requested gear.
The paddle shifters have two distinct advantages: the driver can safely keep both hands on the steering wheel when using the Manual/tiptronic mode; and the driver can immediately manually override either of the automatic programmes (D or S) on a temporary basis, and gain instant manual control of the DSG box. If the manual override of one of the automatic programmes (D or S) is utilised intermittently, the gearbox will "default" back to the previously selected automatic mode after a predetermined duration of inactivity of the paddles, or when the car becomes stationary. Alternatively, should the driver wish to revert immediately to automatic control, this can be done by holding the "+" paddle for at least two seconds.
Other vehicles with DSG gearboxes: