The Dual-Clutch transmission or DCT which some motorheads might refer to as Twin-clutch transmission or DSG as the very vocal VAG boys would insist, is among one of the several types of other multi-clutch transmissions. By multi-clutch, I mean transmissions with more than one clutch pack. As you keep pondering about several clutches, let me derail a bit and tell you about the Koenigsegg Jesko which has a clutch for each of its seven gears, this means that this car has seven gears and seven clutches as well, I can only imagine how fast (and decisive) those shifts are!
A little history: Before I befriended Google and furnished my mind with information, I used to think DCTs were a very recent development only to be met by the shock that these transmissions were actually here before what I would term as modernity. The first ever DCT transmission to feature in a vehicle did so in the 1961 Hillman Minx mid-size car, after this, the transmission showed up in several tractors, only the transmissions in them used a single clutch pedal to down and upshift.
Fast forward to 1985, Porsche incorporated a DCT into their 962 C which was a racing-oriented car – this tells you that they must have thought the DCT was a fast gearbox, and boy were they right! After the Porsche DCT escapade, The Volkswagen Group then made the first ever modern-day DCT use in their 2003 Volkswagen Golf R32 manufactured by BorgWarner and marketed by VAG as the DSG Gearbox (Direct-Shift Gearbox), if you are a German car fanatic, this car needs no introduction, if you are not, maybe you should do some reading, you can start with this article by Car & driver.
The Dual-Clutch Transmission Design & Functionality
The design of the DCT is much more alike to that of the manual transmission, where we have an actual set of plenary gears only, there is a minor (or major) twist. First, DCTs have two separate transmissions, yes, each with its own housing and clutch kit. However, in its use, it functions as a fully automatic system that requires zero input from the driver unless otherwise preferred by them (in racing track scenarios where it makes more sense to shift gears yourself by paddles).
I will try to make this as simple as it’s not; With the two clutches, one drives the even gears while the other drives the odd gears. So if it’s a 7-speed, we have one clutch for gears 1,3,5, and 7 and another clutch for 2,4, and 6. This enables the transmission to pre-select a gear in readiness to upshift or downshift. For instance, if the car is on gear 2, the transmission is able to pre-select 3, and by timing the operation of the two clutches, one clutch is able to engage at the exact moment (well, almost) the other is disengaging therefore shifting from 2 to 3 without interrupting the torque supply to the wheels. Genius, isn’t it?
Also, it is worth mentioning that instead of a torque converter as you would usually have in a conventional hydraulic gearbox, DCT utilizes either a dry or wet clutch depending on the use case, with the latter being bathed in oil for cooling purposes and is also predominantly utilized in high power and torque setups like the 7-speed dual-clutch transmission manufactured by Ricardo for Bugatti (used in the Bugatti Veyron which makes just 50nm shy of 1300nm of torque).
Fun fact: The first commercial use of a DCT on a truck was done on the Mitsubishi Fuso 6-speed Duonic transmission.
In conclusion, this piece by no means does justice to what a marvel of engineering DCTs are but it just gives you an idea of what it actually is. There are so many articles, and Youtube videos explaining this much more elaborately and with vivid examples. However, it is worth mentioning that ever since the first use of DCTs in the R32 Volkswagen Golf the VAG group, as well as other manufacturers like Honda, Porsche, and Bugatti, have gone mainstream in fitting these gearboxes on their cars.
With the evolution of technology, these transmissions have been used in so many application areas: In bikes – Honda VFR1200F, Mitsubishi Evo X, Nissan GT-R, and in almost any modern Audi you can see on the road. The most recent and most intriguing is the use of DCT by Honda in their Hybrid cars like the 1.5 Litre Honda Vezel Hybrid (marketing strategy? I don’t know, some even claim this will save us from the nasty CVTs). Enough with the DCT, until the next episode of The Gearbox Edition, Adios!