Dual-clutch gearboxes are spreading quickly across the automotive world thanks their fast changes and superior fuel efficiency. Porsche and Audi both used the technology in racecars of the 1980s, but it took until 2003 for Volkswagen to introduce the technology in a road car – the Golf R32. Now dual clutch gearboxes are in a wide range of models including everything from the Porsche 911 Turbo to the Ford Focus. Mitsubishi Fuso has even used a dual clutch shifter for its Canter light truck range.
Some brands such as Porsche prefer dual clutch transmissions for the super fast pace of the shifts, while brands such as Volkswagen are more interested in improved fuel economy. A dual clutch transmission is not a regular automatic; there is no torque convertor to slur the gear changes. It is instead a special kind of manual with two automated clutches. The basic premise is that the dual clutch system can select the next gear before releasing the current gear. This means there is almost no interruption in power delivery. The lack of a torque convertor also means the system uses far less fuel than a traditional automatic.
Instead of all the gears being located on one shaft, they are spread across two in a dual clutch gearbox. This way, two gears can be selected at the same time. One shaft houses gears 1, 3, 5 and sometimes 7, while the other houses 2, 4, 6 and reverse. The two clutches sit at the front of the gearbox, with one nestled in behind the other. One clutch spins freely while the other is engaged.
The transmission takes information from the engine computer to determine which gear should be selected next. For example, if revs are rising it will select a higher gear. It doesn’t always predict the correct gear and this can cause some ponderous changes in stop-start conditions. Unlike a traditional manual, there is no clutch pedal in the cabin. The clutches are instead controlled by electro-hydraulic actuators.
How It Works is part of a technology focus series that features first in the CarAdvice iPad magazine app that can be downloaded free every month.