To put it simply, the development of the dual clutch aims to bring together in a single gearbox the efficiency of a manual gearbox and the comfort of an automatic gearbox.
An automatic transmission is less efficient than a manual transmission, especially when changing gear; the break in torque at the time of the change slows down the acceleration.
This is what led Porsche, in the early 1980s, to study the PDK box (DoppelKupplung). It is a seven-speed automated gearbox which has the advantage of ultra-fast gear changes without any break in torque.
Ideal for sports
This ultra-fast gearbox, which could be ordered manually or automatically, ended up on the prototype sports Porsche 956 and 962C. A modified version was entrusted to Audi, which equipped the Audi 200 Turbo Sport Quattro with it.
It allowed spectacular acceleration compared to competitors. The dual-clutch system began to interest mainstream manufacturers in the early 1990s.
It took Volkswagen and Borg Warner six years of development to be able to install it in series. The Golf R32 unveiled it in 2003.
The Principe of fonctionment
The DSG gearbox actually consists of two traditional half-boxes placed in parallel. Their structure is similar to a manual gearbox. The first half-box consists of odd gears (1-3-5) and reverse, while the second uses even gears (2-4-6).
The DSG therefore requires two specific clutches (first in an oil bath then in a dry sump) to which the torque is transmitted. When a gear is engaged, the second half-box already has the next gear pre-engaged so that there is no break in acceleration while limiting fuel consumption.
Work since 1935
In fact, the first works were carried out by Adolphe Kégresse after he left Citroën. This engineer, to whom we owe the Citroën-Kégresse tankettes (black cruisers, then yellow), filed the patent for the first double-clutch automatic gearbox in 1935.
A prototype of this box called « AutoServe » was installed in a Citroën « Traction avant » in 1939 but the project was never followed up.
After the Second World War, the Société des Brevets Kégresse (he died in 1943) filed a patent for a two-clutch seven-speed gearbox.
In 1947, a dual-clutch four-speed gearbox developed by Kégresse was presented at the Paris Motor Show (mounted on Citroën 11CV).