Fast gear changes, no interruption of tractive power and maximum feed.
When dual clutch transmissions were first used in racing cars around 40 years ago, the technology ensured faster lap times.
The first applications and patents for this already existed in the 1930s.
The double clutch transmission (DKG) has many product names depending on the manufacturer, such as Powershift, PDK or DCT.
But it always means the same thing: It can be operated like an automatic without a clutch pedal and works more efficiently than a manual switch.
The name DSG, which is also used colloquially today, means direct shift transmission - a product name from VW.
But who chooses such an automatic transmission, and how does it differ from a normal one, the automatic converter?
The automatic makes life as a driver more comfortable
"Which transmission drivers choose is decided by their wallet, but it is also a question of philosophy," says Marcel Mühlich from the Auto Club Europa (ACE).
Manual transmissions are cheap, simply constructed and well-engineered.
"Sporty drivers often appreciate the shift work, although DSG change gears faster," he says.
But an automatic gives drivers more comfort.
Both the double clutch and the classic automatic converter shift automatically - the driver no longer has a clutch pedal.
Often, however, gear changes can be brought about using shift paddles or the selector lever, for example.
A DSG works with two automatically actuated clutches - one for starting up and shifting the uneven gears, the second for the even gears.
Thus, the transmission shifts into the next higher or lower gear, depending on whether the vehicle is accelerating or decelerating.
"So before it is needed," says Mühlich.
The two couplings alternate with one another in a flash.
This means that changing gears is quick and easy without any interruption in tractive power.
He sees disadvantages with the DSG in the possible additional weight and, in the case of a repair, in the higher costs.
“One weak point is the electronically controlled mechanism for changing gears,” he says.
It also usually costs up to 2500 euros surcharge to the switching truck.
In the past, some models also caused problems and hit the headlines, such as the 7-speed DSG DQ200 with dry clutch from VW.
However, ACE expert Mühlich does not see any consumption advantages compared to modern automatic transmissions with automatic converter.
Automatic transmissions with eight or nine gears work just as efficiently.
"It is currently the most robust technology for changing gears, but it costs more," he says.
Lots of power and torque from the lower speed range
With a classic automatic converter, there is no continuous mechanical connection between engine and transmission when starting, shifting and stopping, explains Mühlich.
The power transmission takes over here an oil.
An additional clutch only provides a mechanical connection if the vehicle is driven smoothly.
This prevents the so-called slip.
This means that no energy is lost through the oil.
This torque converter also provides more torque at low speeds, thus also when starting off.
If you often pull heavy trailers, Mühlich advises you to use an automatic vehicle with a converter transmission.
According to the ACE man, a DSG would have a high level of wear and tear due to the clutch that slips when starting.
From motorsport to mass production
Andreas Felske is responsible for transmission development within the technical development department in Wolfsburg at Volkswagen.
VW has been using the DSG in its vehicles since 2003, for the first time in the Golf R32.
“The idea for the DSG had long been known from motorsport at Porsche and was slumbering in development for mass-produced vehicles,” says Felske.
"Up until the beginning of 2000, the problem was the high computer expenditure for the control." Only when the computer processors became faster and cheaper, VW was able to develop the transmissions for the broad market.
The DSG-typical quick gear changes, the direct connection of the engine and the starting via a friction clutch are well received by customers in Europe and China.
North American drivers, who have been used to torque converters with different gear changing and starting characteristics for decades, are still more likely to use the converter.
In North America, the DSG is more likely to be found in sporty vehicles.
More gears and less friction
Michael Drabek from the transmission manufacturer ZF also sees the advantage of dual clutch transmissions in quick gear changes, comfortable behavior and efficiency-oriented innovations.
ZF has been developing dual clutch transmissions since 2003, which they call DT.
“Dual clutch transmissions show their advantages in sporty vehicles.
Combined with outstanding efficiency, maximum convenience and hybridization, they have an advantage over the manual switch, ”explains Michael Drabek.
In the past few years, manufacturers have continued to develop gearboxes.
VW increased the number of gears from six to seven today, reduced the friction within the transmission, optimized the electronic control and further reduced consumption.
In addition to classic manual switches, many manufacturers also offer automatic transmissions for their models
The increased computing power of today's chips also benefits the switching quality in particular.
“Today, modern DSG gearshifts are very comfortable and, if desired, sporty.
They can also be easily expanded into hybrid drives, ”says VW developer Felske.
Professor Karsten Stahl was thrilled 17 years ago during a test drive with the first production car with DSG.
“In the VW Golf R32 with DSG, the switching times were in the millisecond range.
Those were sensational values for a series transmission at the time, ”says the head of the Research Center for Gears and Gear Construction (FZG) at the Technical University of Munich (TUM).
Because of its design, a DSG is particularly suitable for cars with transversely installed front-wheel drive engines.
When the double clutch treats itself to a “moment of thought”
To date, that has not changed significantly, as have the disadvantages of a double clutch.
"With the DSG, the shift times are so short that the next expected gear is already preset and only has to be activated," says Professor Stahl.
"This is different with hectic driving maneuvers: Here the shift times can be relatively high if the DSG has to preselect a different gear." This is noticeable for the driver in driving maneuvers that cannot be foreseen for the transmission control by a "second of thought".
The drag and friction losses with the DSG would be as low as with a manual transmission.
However, since the shift strategy stored in the control of the transmission ensures that the optimum gear is always engaged, a car with DSG usually uses less fuel than one with a manual transmission.
Theoretically, an automatic transmission with a converter shifts a little slower than a DSG, but with appropriate parameterization it can be achieved that it feels exactly like a DSG.
When it comes to the number of gears, Professor Stahl considers seven to eight gears to be technically sensible: “With more than seven gears, the additional benefit is very limited.
More gears make for even more sportiness, but also cause higher energy losses due to the more frequent shifting. ”That didn't matter with racing cars around 40 years ago - today, however, efficiency is one of the most important development goals.