Our solution for front wheel drive vehicles is double clutch

Interview: Dr. Thomas Weber, board member of Daimler AG, responsible for Group Research and Mercedes-Benz Cars development

You have said that Mercedes-Benz will meet the really stringent European regulations for passenger-car CO₂ emissions in the next five years. How important is transmission design in the improvements you need to achieve?

On the transmission side it's possible to achieve between 5 and 10 percent better fuel efficiency. We're working on this at full speed. Our solution for front wheel drive vehicles is double clutch - it's more expensive than CVT, but also superior to CVT. I can announce that we will have such a (DCT) system in our upcoming front wheel driven compact cars - that's the A-Class and B-Class as well as further new models.

If your front-drive cars will have DCT, what is your preferred transmission solution for your RWD models?

For rear wheel drive applications it is clear that we have already today the lightest and the most efficient - and also the most cost-effective - transmission in the market: our seven-speed. We will advance this technology and will soon come with further improvements.

Will you incorporate stop-start and more speeds?

For the customer, seven speeds are better than six - so we could come to a situation where some people believe eight is better than seven. But speeds are not what really matters: the most important driver is the spread of ratios. If you have an eight-speed with the same ratio range as a seven-speed, you have no real benefit. What we are working on is a transmission with a really wide range - and of course the number of gears could be different.

Will the range be wider than the Porsche Panamera, where the DCT has a spread of more than 10?

That's quite wide, but from our point of view not the limit. If we go in a downsizing direction for smaller vehicles, then the number of speeds and the ratio range will be important to further improve the fuel economy. Short-term, we will improve economy of our transmission by at least 2 to 3 percent; in the next step we will also incorporate start-stop in the automatic transmission with additional benefits for fuel efficiency.

Why have automakers been so slow to bring in stop-start?

The only reason why everyone is currently focusing start-stop on the manual transmission is that on an automatic it is necessary to electrify the transmission on the pump side to maintain the oil pressure. In the long run all Mercedes vehicles in Europe will be equipped with start-stop - without exception.

You get better performance and lower fuel consumption with a dual clutch transmission - so will manual transmissions eventually disappear?

No - cost-wise, manuals are good. And with younger drivers the emotional feeling of shifting gears is still there. We thought at one point in time that we could completely switch over to automatic transmissions, but we concluded that it wouldn't be possible for specific models.

But is it a declining market (for manual transmissions)?

We thought the trend was approaching zero, but this is changing. There's now a revival, driven first of all by fuel consumption and now costs – especially as the alternatives are becoming more expensive.

Are you developing your dual clutch transmission yourselves, or are you buying the system from a supplier?

We're doing it in house.

So there will be no DCT for your rear-drive models?

We won't use DCT on rear-drive cars because everything we need in terms of comfort, shifting speed, sportiness can be addressed by our planetary automatic transmission.

The recently announced SLS super-sports car has rear drive and a double clutch transmission. Is that an exception?

Yes, the SLS is a completely different story. It is an extreme sports car, hence different solutions had to be considered.

So will other less extreme sports versions, such as your AMG models, use the wet-clutch planetary automatic that is already fitted to the SL?

Yes, that's right. These are really expensive technologies we are talking about. This is the important message about transmissions: the technology has to be perfected for hybrids. Hybrids are more influenced by the transmission and the combinations within the transmission.

Dr Thomas Weber has been a member of the board of management of Daimler AG (formerly DaimlerChrysler) since 2003 and is responsible for group-wide research as well as the development of Mercedes-Benz cars.

Born in 1954, he graduated in mechanical engineering from Stuttgart university in 1980 and joined Daimler-Benz AG in 1987. After a series of roles in engine development and production he took charge of the Rastatt plant in 1999 and oversaw the launch of the A-Class in 2002.

Story Filed: 11/24/2009
By Tony Lewin, managing editor DCTfacts.com