Computer Controlled DSG Transmission

Figure 1 Demonstration model DSG transmission with programmable control.

 

 

The Volkswagen/Audi DSG Transmission

Early in 2003, Volkswagen introduced a new kind of automatic gearbox as fitted to the Golf RS32. This DCT (Dual Clutch Transmission), known as DSG (Direct Shift Gearbox), was also made available in the Audi 3.2 TT Quattro, who named the DSG "S-Tronic".Since then, the DSG has become optional equipment on most VW cars and is manufactured in the Kassal transmission plant which is capable of producing 1000 transmissions per day.

The DSG is a kind of automated manual gearbox in that it uses the Borg Warner DualTronic wet-clutch and control system technology in conjunction with a new configuration of VW standard gear and synchromesh mechanisms.It is a six-speed and reverse arrangement, effectively two gearboxes in one. It uses two clutches, one (C1) serving the odd numbered gear ratios, driving an input shaft to the 1st, 3rd, 5th and reverse synchronizers, and the other (C2) serving the even numbered gear ratios, driving the input shaft to the 2nd, 4th and 6th speed synchronizers. The odd and even geared shafts then drive a common differential gear. Figure 2 is a cut-away of the whole transmission.

Figure 2 DSG Transmission as fitted to the Audi TT 3.2 V6 Quattro, 4WD version.
Viewed from the front of car.

 

 

Drive to the rear axle is taken from the output at the left hand side, to a rear axle mounted Haldex clutch

The principle of operation is that whilst an odd numbered gear ratio is being driven by one clutch (C1), an even numbered gear ratio can be pre-selected, ready for engagement by switching to the second clutch (C2). This action repeats for even to odd gear changes and hence for all upshifts and downshifts.

The result is virtually continuous power flow during gearshifts that are quicker than a manual gearbox and smoother than a conventional automatic transmission.

 Typical shift times are 0.3 to 0.4 seconds; during upshifts engine power is interrupted for only 8 milliseconds. Shift quality is ensured by the modulated transfer of torque from clutch to clutch, since in multi-plate wet clutches, better control of friction and wear is possible, and heat energy is dissipated by the circulating cooling fluid. This is unlike dry clutches, which consume their friction material and require eventual replacement.

The DSG arrangement is also more efficient than the conventional hydrodynamic torque converter equipped automatic transmission (a torque converter has a peak efficiency of 86-90% at a pre-determined speed ratio, at all other speed ratios the efficiency falls to zero at stall and run-out).

 

Figure 3 DSG gear/clutch schematic and 1st and 2nd gear drive-paths.

 

 

 

 

 History

The beauty and simplicity of the DSG principle is not new, however. The invention of the double clutch gearbox is attributed to a French engineer, Andolphe Kegresse, around 1939 (figure 5). He intended to use it in the Citroen "Traction" vehicle, but business and war circumstances prevented further development.

Figure 4 Kegresse dual clutch gearbox proposal.

Years later, Automotive Products (AP) proposed a double clutch/gearbox of different design (figure 6). In 1985 Porsche raced a similar gearbox to Kegresse known as PDK (Porsche Dual Klutch), a 5-speed unit with dry plate clutches (figures 7 and 8), whilst Luk/Devotek proposed the PSG (Parallel Shift Gearbox) using wet or dry clutches (figure 9).

Figure 5 AP schematic for 4 and 6 speed designs

 Figure 6  Porsche-Audi PDKcaption.

Figure 7 Porche-Audi PDK schematic.

Figure 8 Luk/Devotek PSG twin dry plate clutch.

 

 

 

 

 

 

 

 

DSG - The Future Of The Gearbox.

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 we  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 performance 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.

 Reference:  http://blogcritics.org/scitech/article/dsg-the-future-of-the-gearbox/#ixzz1ouUvbLAt