Most cars come fitted with either of two basic transmission types: manuals, where the driver is required to change gears by depressing a clutch pedal and use a stick shift, and automatics, which do all the work by using clutches, a torque converter and sets of planetary gears. But there is also a third technology that uses the best of both previous mechanisms, and that’s the dual clutch transmission, or as it’s sometimes called, the semi-automatic transmission, or the automated manual transmission.
The dual clutch transmission is quite common in the world of racecars, in variants like the sequential manual gearbox. Yet in the world of production vehicles it is a new technology, defined by a very specific design known as the dual-clutch or direct-shift gearbox, which might just become the transmission of the future. In order to understand how a dual clutch transmission works, one needs to know that it offers the function of two manual gearboxes in one. With a normal manual transmission, a synchronizer matches the gears before they are engaged in order to prevent grinding and there is no continuous flow of power from the engine. With a dual clutch transmission however, the driver uses two clutches, but no clutch pedal. These clutches are controlled by sophisticated electronics and hydraulics like with an automatic transmission, only here the clutches operate independently. The first clutch controls the odd gears while the other has control over the even gears. This way, there is no power flow interruption from the engine to the transmission, making for a smoother transition from one gear to another.
In order for this to be possible, cars with dual clutch transmission have the outer shaft hollowed out to make room for an inner shaft which is embedded inside. Therefore, the outer shaft feeds the second and fourth gears, whereas the inner shaft does so for the first, third and fifth gears. This explains the technology behind the constant power delivery and the possibility to change gears faster than the blink of an eye.
Unlike regular cars, those fitted with dual clutch transmission don’t require torque converters, but use wet multi-plate clutches. A “wet” clutch is one that bathes the clutch components in a lubricating fluid that serves to reduce friction and limit the production of heat. Nevertheless, some manufacturers are presently working on a technology that uses dry clutches, like those used for manual transmissions. The dual clutch transmission may not be yet available in many cars, but it’s rapidly spreading all over, creating the possibility that soon most, if not all, cars be fitted this way soon.