The VAG Direct Shift Gearbox - sometimes called the S-Tronic in the Audi range - is the world's first production dual clutch semi automatic gearbox. The system was developed for Audi by BorgWarner for use in the companies Audi TT 3.2V6, and was so well received it is now used in much of the Volkswagen Audi Group range.
The DSG is often compared to F1 style automated or robotic manual gearboxes, but differs in some very important ways.
The DSG gearbox is, however, not a new invention. The system was first designed by Andolphe Kégresse just before the second world war but because of the lack of technology, not to mention the war, he never produced a working version of the Dual Clutch Gearbox (DCG). The system was used by another German car company in the 80's though: Porsche used the PDK (Porsche Doppelkupplungs) system in their 956 and 962 Le Mans race cars, and Audi used the same system in the Sport Quatro S1. Porsche and Audi have a long history of technology sharing.
Both of these uses eventually faded, primarily because the computing technology that allows the system to work so effectively did not prove to be reliable enough in the tough and demanding world of the race car.
To understand how revolutionary the DSG gearbox is, first I will explain the F1 style systems. These differ in name depending on the manufacturer; Ferrari call theirs the F1 system, and BMW call theirs the SMG system.
These gearboxes all have one thing in common: they are just manual gearboxes, with a manual clutch that is operated by pneumatics. This method has many of the benefits the DSG box does. The gearbox itself weighs less: as the gear change is accurate, and no human mistakes can be made, the materials can be less hardy. They are also far more performant than the manual equivalent, both the BMW SMG II and the Ferrari F1 systems change cogs in around 80 milliseconds. This means that, while the gear is being shifted, all the power from the engine is waisted and a feeling of on-off-on is felt in the car as the pneumatics shift from in gear, to clutched, and then back into gear. The smoothness of this in the car depends on the software controlling it: for the fastest changes it can feel quite 'bumpy', similar to a bad gear change in a manual car. The only way of releaving this issue in the past was to fit a torque converter, this is the way that a standard auto box does it, and why it feels far smoother than any of the manual gearboxes produced. A torque converter, however, is very wasteful in terms of power, and usually very heavy.
Article comments
1 - Michael Karesh
Perhaps the best explanation of the DSG I've come across. Excellent job.
2 - Tony
Very good article, but still haven't seen explanation on how DSG operates from standing start - Electronic controlled engagement of conventional clutch in first gear? Does this mean clutch is being continuously 'slipped' when in Drive but at standstill with brakes on? Does this not lead to increased clutch wear for the clutch that includes first gear?
3 - Ashleigh
That's correct, it's basically the same as when manual car drivers slip it during a hill start etc. Obviously the car can use it's brakes etc to compensate so the wear is actualy lower than conventional clutch.
The DSG is being re-invented soon as well. VW have announced a 7 speed, dry clutch system capable of handleing 450ft/lb torque that will be launched soon.
4 - Carl
Thank you for a very helpful article. However, when I read the published mpg figures (here in the UK) there seems to be an up to 10% fuel consumption penalty associated with a DSG gearbox. Granted that's better than the apparent 15-20% of a traditional automatic. But why the apparent 10% penalty?
5 - Ashleigh
It's mostly down to the extra weight of the DSG 'wet' box. The newer dry clutch boxes should get the penalty down a bit more.
However manufacturers figures are for an ideal manual driver, and the DSG is always going to perform the same, so in reality the difference is negligible at best.
6 - lawrence ogden
the dsg box is brilliant i have a glof tdi 170 dsg and can get 54 mpg on a run (19km/litre) it is the best auto box ever put in a car the gearchange is seamless dont bother using the paddles put it into drive and enjoy the ride if you use sport mode it holds on to 5th gear to 115 mph.tdi170gsg is one of vw`s best kept secrets
7 - LT
That's correct, it's basically the same as when manual car drivers slip it during a hill start etc. Obviously the car can use it's brakes etc to compensate so the wear is actualy lower than conventional clutch.
I doubt the wear is lower since either car can use the brakes. The difference is in a manual transmission the driver disengages the clutch. With a dsg when stopped at traffic lights for example the clutch is still dragging and you can feel this as the load is eliminated if you shift to neutral. It will be interesting to see just how long the clutch lasts in a dsg compared to an experienced driver with a conventional transmission.
8 - Federico Melo
I just bought a 2.0 T FSI with DSG and realized about the charge being applied though odd clutch when standing stop in drive mode and can’t believe it. Besides the obvious feeling, I checked it by watching instant fuel consumption increasing when switching from neutral to drive or first. I only can think that wear is so low that VAG group thinks is better, because it would be extremely easy to fully release clutch when detects speed zero and brake applied. Even if they assured that wear is minimal I would prefer full release and I think I’ll get use to place it into neutral while waiting for light or traffic to move.
9 - Ashleigh
Remember most of them are wet clutches, so wear isn't that high.