What is a Direct Shift Gearbox (DSG) and how does it work?

Despite that DSG changes gears in a similar manner as a traditional automatic transsmision, it is in the same time a little bit different.

What is actually a DSG?

A Direct Shift Gearbox is an electronically controlled dual-clutch multiple-shaft automatic gearbox with fully automatic or semi-manual gear selection. It is actually two gearboxes in one, connected to the engine by two drive shafts. Its main difference from a automatic transmission is that DSG eliminates the torque converter by using two independent clutches.

DSG uses usually two wet multi-plate clutches where the smaller clutch is packed inside the bigger one.

How does DSG work?

DSG has two clutches, as well as two separate input shafts. One input shaft provides odd-numbered speeds, such as first, third and fifth gear, the other input shaft provides even-numbered speeds like second, fourth and sixth gear. Because of this technical decision the gearbox that is not in use is able to work out which gear to prepare next for immediate use. In order to change gears as quick as possible, an electronic control unit for the transmission manages information such as engine rpm, road speed, throttle position, brake application and driving mode to select the optimum gear.

When you start the car the first gear is engaged by the odd-numbered gearbox which transfers the torque to the wheels via its input shaft. Simultaneously with the engaging of the first gear, electronics predicts the subsequent engaging of the second gear and makes it ready. This way you have already the next gear always pre-selected. When the time comes to change gears, DSG simply uses the clutches to switch from the "odd" gearbox to the "even" gearbox. In the same time he "odd" gearbox immediately pre-selects the third gear and vice versa when downshifting.