What is a dual clutch transmission

Car: automatic and dual clutch transmissions in comparison

Automatic transmissions are sluggish, increase fuel consumption and cause the driver to nod his head involuntarily when changing gears. These prejudices are no longer true: the gears are now smoothly merging, and the driving performance and consumption data are also correct.

However, the machines are expensive compared to manual switches. By and large, their triumphant advance is limited to upper-middle-class cars. The case is different with the cheaper double clutch that helped Volkswagen achieve its breakthrough.

But first to the conventional multi-step automatic: In 2006 the automotive supplier ZF Friedrichshafen saw a trend reversal. "With the 6-speed automatic transmission, better applications were achieved in normal operation than with the manual transmission," says ZF spokesman Holger Kirsch. For the first time, the supplier had built an automatic transmission with which cars used less fuel than the manual switch. Kirsch claims of the current 8-speed automatic machine: "As a driver, you will not be able to change gear better by hand." From 2013, ZF plans to produce a new automatic transmission with 9 gears.

Engineers in vehicle construction were concerned with automating gear changes from an early stage. In 1939 General Motors put the first automatic transmission into series production. From 1952, VW and Audi supplier BorgWarner offered a machine with a 3-speed planetary gear set. In 1961, ZF presented its 3-speed automatic transmission with a hydraulically controlled 3-stage planetary gear set. These were all solutions for drivers who were lazy to change gear - there was still no talk of efficiency.

"In the past, the converter in particular swallowed a lot of energy, there were high frictional losses, and the gear ratio spread was lower," explains Kirsch. To curb the thirst for fuel, the highest possible spread, i.e. the ratio of the lowest and highest gear, is the top development goal. "The higher it is, the better the engine can be operated with optimum efficiency," explains Kirsch.

Modern computer technology later made it possible to simulate the complicated interplay of the gear sets and to build competitive machines accordingly. And they are quite expensive: "You have to reckon with 3,000 to 4,000 euros surcharge compared to the manual switch," says Helmut Klein from the ADAC Technik Zentrum. However, the modern automatic torque converters are still one step ahead of other concepts when it comes to comfort with soft gear changes. "There is a trend towards automation, especially in the premium segment," says Kirsch.

Volkswagen made a significant contribution to the image enhancement of automatic transmissions in lower vehicle classes. At the end of 2002, the Lower Saxony company presented its direct shift gearbox, also known as DSG (Direct Shift Gearbox), for the series production. Initially installed in the Golf R32, the DSG is now available for many VW models, including the Golf, Passat and Touran. But also BMW, Audi, Seat, Skoda, Renault, Alfa Romeo, Porsche, Ford or Mitsubishi offer the corresponding technology.

In principle, these transmissions with two clutches work like this: While one is driving in one gear, the next is already preset, but is still idle. As soon as the ideal shift point is reached, the corresponding clutch opens and the next gear is activated at lightning speed.

Volkswagen's advantages include better acceleration values, smooth gear changes in the millisecond range without interruption of tractive power and lower consumption compared to conventional automatic systems. Compared to manual switches, dual clutch transmissions usually achieve similar values. The current Golf 1.2 TSI with 77 kW / 105 PS with manual gearshift needs 5.7 liters in the standard cycle and 5.8 liters in the 7-speed DSG variant. According to the spokesman Peter Weisheit, 1825 euros are due as a surcharge - and thus less than with a step automatic.

ADAC technician Klein confirms the slight price advantage of the dual clutch transmission. Compared to the modern automatic stepped automatic, however, you have to accept a loss of comfort: "You shift a little bit more roughly, and you notice a difference even when you roll." On the other hand, dual clutch transmissions are easier to fit in compact vehicles than classic automatic transmissions because of their smaller design, which is likely to contribute significantly to their widespread use. (dpa)