DSG or Direct shift Gearbox is a groundbreaking dual-clutch concept that takes automatic transmission Technology even further.
Why have one clutch when you can have two? To understand the advantages of a twin-clutch system, let’s rewind to how a conventional manual gearbox works. When you want to change gears in a manual ‘box, you press down on the clutch pedal to operate a single clutch which disconnects the engine from the gearbox. Releasing the clutch reconnect the engine to the gearbox and transmits power back to the wheels.
In a manual transmission, power from the engine to the wheels is interrupted during gearshifts. I you have ever sat with someone just learning to drive, you can feel this interruption most acutely.
The DSG on the other hand is a dual-clutch gearbox. Sophisticated electronics and mechanicals control the clutch, just as they do in a standard automatic transmission. However, in a DSG, one clutch controls the odd gears (first, third, fifth, seventh and reverse), while the other controls the even gears (second, fourth and sixth). Thus, gears can be changed without interrupting the power flow from the engine to the transmission. That’s the trick that allows lightning-fast gear changes and keeps power delivery constant.
A conventional automatic gearbox uses a viscous or liquid coupling known as a torque converter, instead of a clutch. But torque converters sap a lot of power from the engine, so performance and efficiency both suffer. This makes the DSG more efficient than a conventional automatic transmission.
Skoda was the first company to offer this advanced automatic transmission in India on the Laura way back in 2005. It had six gears and came mated to a strong diesel engine. Now, you can also get a seven-speed DSG transmission in the new Skoda Superb and most other companies have their own twin-clutch autos.
How does it work while driving? When you select Drive mode, one shaft selects first gear on ‘standby’. As the gearbox change to second, the second shaft is engaged and the original shaft reaches third. As you shift upwards, the sequence continues in a series of seamless moves. Because power is simply switched from one shaft to another, gear shifts, are not only silky smooth but also very fast. Each change takes around eight milliseconds.
The DSG gearbox, apart from being seamless and quick, is also smart. For example, if you are braking heavily, if you are braking heavily into a tight corner with the intent of downshifting two or even three gears, the computer will respond to your braking and steering input and change down either more quickly or skip past gears altogether. This allows you to keep the revs in the best range for drivability. Likewise, if driving in snow or mud, the computer will control wheelspin at low speeds, by shifting up into a higher gear.
And if you want to take over, you can control the DSG manually. Nudge the Tiptronic gearlever forwards or backwards to change gear, or use the puddle shifts mounted on the steering wheel to go up or down. Seamless, lightning-fast gear changes along with the control of a manual ‘box, now that’s something only a DSG ‘box can give you.
Thanks to the dual-clutch design, the DSG is more efficient than conventional automatic transmissions. This efficiency, together with its low weight and intelligent control, means the DSG can achieve the same, and in some instances better, fuel consumption than a manual gearbox or even lower, depending on the style of driving.
So the next time you drive a Skoda with a DSG gearbox, and slot the drive into D, you will not be wrong to think that D stands for Delight.
Source: Autocar September 2011