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Why is a dual-clutch gearbox quickest of them all?

Snapshot: So what is it about DSG that makes them a great performer and first choice among performance drivers? This articles answer that question in particular, design features and some other related questions.

A lot of technical advancements that have taken place in the last 100 years or so in case of cars, many pertain to the transmission system that a car uses these days, i.e. the way in which the power is sent to the wheels from an engine. A DCT transmission is an off shoot of the manual transmission or if we were to say that it is a result of continuous improvements that have taken place in the manual transmission and other technologies, it would not be wrong either.

It’s peculiar in the way it works, and offers certain advantages because of that. In this article, we answer some of the questions related to it.

Is the PDK / DSG / DCT the same technology?

DSG gearbox, aka PDK, aka DCT transmission. Yes, the underlying technology in case of the PDK, DCT and DSG is the same. The PDK stands for Porsche Doppelkupplung, the DCT stands for Dual-clutch transmission and the DSG stands for Direct-Shift gearbox, some of them are proprietary names but the technology that they use is the same.

Read about AMT (Automated Manual Transmission), the most inexpensive automatic

How is a DCT transmission different from a CVT / Manual or an AMT gearbox?

A DCT is much like a manual gearbox in a sense that it’s a stepped transmission and the gear ratios are not variable as in the case of the CVT. However, the main difference as the name indicates is that a DCT (Dual Clutch Transmission) has two clutches for transmission that connect two separate input shafts from the engine to the output. The arrangement is such that all odd gears are driven by one input shaft while the even ones are driven by the other. If you see the figure above, you will see that clutch 1 (in yellow) is driving all the odd gears (1, 3, 5 &7), while the concentric input & hollow shaft (in blue), connected to the clutch 2 is driving all the even gears (2, 4 & 6).

How does a DSG work in practice?

A DSG much like an AMT gearbox uses Electro-hydraulic or Electro-mechanical actuators for operation, all of this managed by a TCU (Transmission control unit). As you increase or decrease the speed, the corresponding clutch and appropriate gear is engaged to drive the wheels.   

Why is the DSG gearbox the quickest of them all?

The main benefit that DSG has to offer is in terms of responsiveness and fuel-efficiency (depending on the clutch they are using). Since the odd gears are on one shaft while the even on another, based on input at the throttle / brake, the transmission preselects the gear that it predicts that you might need next. It’s able to do so because odd set of gears are on one input shaft while the even ones are on the other. So for example, if you are in a 3rd gear and press the brake pedal, the TCU would senses this decrease in speed and would engage the 2nd gear in anticipation and if the speed keeps on decreasing further, it would just need to engage the appropriate clutch of one of the driveshaft for the gear shift since the gear selection has already taken place because it was on the other input shaft. The same thing happens when you press the accelerator pedal.   

What are the driving modes that the DSG offers?

Just like in case of other stepped transmission, you get a completely automatic mode and a semi-automatic mode. In case of semi-automatic mode, you can change gears with the use of flappy pedals or by using the gear-shift lever.

Which car companies use the DSG gearbox?

The DSG gearbox is proprietary technology name that’s used by some car companies from the VW group like SEAT, Skoda and VW itself. The Audi though, which belong to the same VW group, calls it the S-Tronic. Essentially they are all the same. The DCT is also used by Ford and other companies like Hyundai etc, however, the underlying technology is the same.   

Read - How does a manual transmission work?

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