Two clutches, one gearbox: how a dual-clutch transmission shifts without a pause
A dual-clutch gearbox splits its gears into two teams. One clutch looks after the odd gears, the other the even ones, so while you accelerate in third, fourth is already waiting. The handover happens as one clutch lets go and the other bites, and power to the wheels never drops.
Think of it as two manual gearboxes sharing a single housing, run by a computer so the driver never touches a pedal. Because the next gear is preselected, changes happen several times faster than any human can manage with a stick. The clutches can be dry, or wet and bathed in oil for cooling; wet ones handle heavier loads, such as the 1,250 newton-metres from the Bugatti Veyron's 16-cylinder engine. Most car versions nest one clutch inside the other on the flywheel's axis, while Volkswagen's DQ200 places two equal clutches side by side.
The idea belongs to French engineer Adolphe Kégresse, who conceived it in 1939 for the Citroën Traction Avant but ran out of money before building one. The first production version, the Easidrive from Smiths Industries and Rootes, appeared on the 1961 Hillman Minx using electromagnetic clutches and solenoids. It proved unreliable, and many owners swapped it for a conventional manual.
Racing revived the concept. Porsche began work in the late 1970s because a turbocharged engine loses boost during a normal shift. Its PDK gearbox was tried in a 956 in 1983, raced in the 962 C in 1985, and helped that car win the 1986 World Sportscar Championship. Eastern European tractors of the 1970s also used manually operated versions.
The modern era began with BorgWarner's unit in the 2003 Volkswagen Golf R32. Volkswagen later claimed its seven-speed DQ200 used 6 percent less fuel than a six-speed manual and 20 percent less than a conventional automatic. Honda put one in a motorcycle first, the 2009 VFR1200F, and in 2010 a Mitsubishi Fuso truck became the first lorry to use one. The Koenigsegg Jesko takes the principle further, with a separate clutch for each of its seven gears.
Source: Dual-clutch transmission
