The Future Belongs to DCT
Continuously variable transmissions and automated manuals are destined to lose popularity and the market will swing toward automatics and dual clutch transmissions. These were the collective predictions of 700 auto industry executives gathered in Berlin in December for the CTI International Symposium on Innovative Automotive Transmissions.
In an electronic vote in the conference hall after an on-stage discussion between experts, 38 percent of delegates felt DCT technology was just as good as AT technology; 37 percent believed it to be superior. When asked which transmission technology would be the first to disappear, almost half of all delegates singled out AMTs; 30 percent felt CVTs would be the first to dwindle, while only 10 percent thought manual transmissions would disappear.
Andy Yu, vice president of engineering at BorgWarner Drivetrain Systems, was emphatic that dual clutch was the superior technology. “It’s only because of history, and the manufacturing infrastructure that has been built up, that we still adhere to planetary automatics,” he commented. “The question isn’t just that of the torque converter versus the clutch – in the U.S., a lot of the investment is in planetary, so it is hard to move away from this manufacturing base.”
Citing the example of China, where there is no established automatic infrastructure, he said that with the advantage of a free choice, automakers would always go for the dual clutch solution.
“Our joint venture is proceeding; the first products will launch in 2011,” Yu told delegates. “There is a lot of activity beyond this [China] too, such as in Japan and with European automakers for a smaller DCT that will give a very high efficiency transmission for the A and B segments.”
The expected decline of CVTs could be attributed to their still-poor efficiency levels, explained Prof. Leopold Mikulic, vice president of powertrain technologies at Daimler AG. Replacing the CVT transmission of the front-drive A- and B-Class models with a DCT would result in fuel savings of five percent, he said. “The A-Class has a high proportion of automatics [in its sales] but we need to improve the efficiency and economy, which is where the CVT has certain disadvantages. We also have to look at market trends, and we expect DCT to take a significant proportion of front transverse applications.”
“It is true that both are not cheap technologies,” continued Mikulic, “but DCT uses some elements from standard transmissions, so there will be synergies and lower costs there.”
Asked if the lubricants had a significant impact on fuel efficiency, Mikulic said that work on the ATF would be essential for further developments. “We are busy working on this,” he said. “We’re looking at a gain of 1 to 1.5 percent.”
The solutions eventually chosen would be dependent on the vehicle platforms, observed Ralf Najork, group vice president of R&D at Getrag. For premium vehicles with between 300 and 500 horsepower the most important factor will become a wide spread of ratios, rather than the number of gears. “Front wheel drive systems are different,” he noted. “Here we are fighting for every gram of CO2. The EU color labeling system will be decisive in [influencing] how we choose the ratios. For instance, we might adjust them to get under the under-120 g/km color.”
DCT will be very big in front wheel drive, concluded Najork. AMT failed because of comfort, but it will be seen again. With electric fill-in torque its shift quality might be brought up to an acceptable standard, and it could be used as a three or four speed unit in conjunction with a range extender motor.
AMTs would continue to be important in commercial vehicle applications, observed Georg Weinberg, head of truck product engineering and vice president of Daimler Trucks, the world leader. “AMTs are efficient in heavy goods vehicles, especially in direct drive. Powershift is well accepted, but DCT is also possible.”
“DCT means no interruption of torque when shifting, so you could run the engine at a lower speed,” said Weinberg. “Up to 2 to 3 percent fuel savings could be possible, depending on the class of vehicle and the terrain.”
For a medium sized car, an AMT can offer a fuel economy benefit over the equivalent model of around 4 percent, said Mark Findlay of industry analysts Drive Systems Design. He stated that its relatively low extra cost could prove attractive to automakers; an automated transmission capable of handling 400 Nm would cost between ?750 and ?950, some ?250 more than its manually-shifted equivalent.
Findlay presented a matrix of transmission types, weights and costs, as follows:
Transmission type Unit weight
(based on 400 Nm capacity), kg Unit cost, ?
Manual transmission 55 500-750
AMT 65 750-950
AT 85 1000-1200
DCT 90 1100-1300
CVT 95 1300-1500