Manual transmission fans speak derisively of automatic transmissions as "slushboxes." But you don't find many vocal proponents of automatic transmissions, as most people use them out of convenience and regard their cars as more functional than fun. This split in how people regard their cars goes much deeper than just transmissions, but it may be a transmission that bridges the gap. The double-clutch transmission, Audi's Direct Shift Gearbox (DSG) being the most successful incarnation, combines the performance of a manual with the convenience of an automatic.
Audi's DSG uses two computer-controlled clutches, delivering the convenience of an automatic and the performance of a manual.
As the name implies, double-clutch transmissions work by using two clutches assigned to different sets of gears. For example, in a six-speed gearbox, one clutch engages gears one, three, and five while the other handles two, four, and six. The gearbox has to anticipate which gear you will want next, so it can position the off-gear clutch correctly. For example, if you are in second gear and accelerating, the gearbox will probably anticipate third as being your next gear, and position one of the clutches to shift into that gear.
Automatic, manual, double-clutch, or CVT?
None of this would work very well without computer control, as the clutches are controlled by a processor that looks at various inputs from the car and the driver to figure out what it should be doing. There were double-clutch transmissions before silicon, starting in 1939, but mere mechanical control wasn't enough to make them work very well. The newest generation of these transmissions was proven in race cars, then Audi got the jump on putting them in production cars.
Having used the DSG in the Audi A3 and the Volkswagen Eos, and the F1 gearbox in a pair of Ferraris, the F430 and the 612 Scaglietti, I'm sold. The more mundane DSG is set up to let drivers shift themselves or put it into automatic mode, where the car uses rpms and other information to decide when to make the shifts. Even with the car in automatic mode, it doesn't feel anything like a conventional automatic. As each gear engages, you get a more direct feeling of power from the engine, as if it's tied right to the wheels, as with a standard manual transmission. And the shifts are much quicker than you could manage while manually working a clutch.
The DSG makes the Audi A3 a very fun and practical car to drive.
I've heard manual-transmission enthusiasts discount double-clutch transmissions, saying they prefer using a clutch. Well, I've heard writers say they prefer using a pen, but most of the world has moved on to word processors. One argument for a manual clutch is that you can use it to control your speed by varying how fast you engage it. But that's how you burn out a clutch. The double-clutch transmission forces you to use the throttle to control speed, which is what you should be doing anyway. But it also permits some leeway, letting you creep along at 2 mph in traffic and easily get moving on a hill start.
Of course, you don't have many choices right now if you want a double-clutch gearbox. But that is changing. Mitsubishi is bringing out its Sports Shift Transmission (SST) for the next Evo, while Daimler-Chrysler is working with Getrag to produce one for its 2010 models. The sell-off of Chrysler from Daimler-Chrysler puts a potential snag in plans for using a double-clutch transmission in Chrysler models, but as work has already started on a plant to build these transmissions for Chrysler, the company's new owners will probably go forward with it.
Are double-clutch transmissions an answer to road rage? Not necessarily, but think of the extra little bit of camaraderie you will feel with the driver of that SUV going 55 in the passing lane, knowing that your quick little sports car shares the same type of gearbox.