“More power, Less fuel consumption”

Dr. Gerhard Wagner, Group Executive ZF car driveline division, explains why there has been no focus on the number of gears but in further improvements in performance and fuel consumption.

But ZF is nevertheless bringing an 8-speed automatic transmission to market in 2009?

Wagner: For the development the objective at ZF was not to increase the number of speeds; instead, a more efficient transmission concept with respect to fuel consumption, driving performance, mechanical design, and costs. For the foregoing study various control levers and also the number of gears were examined. At the end it emerged that this concept with eight speeds offers the best prerequisites..

Will eight gears be the maximum or will we soon see automatic nine or even ten-speed transmissions?

Wagner: I am not ruling out anything. However, a major step towards the reduction of fuel consumption such as the one we have seen from the automatic six to the eight-speed transmission will not be possible with more gear steps. If there was an ideal transmission, with our current solution we are only about 11 percent away from it.

Is the 6-speed automatic transmission thus outdated?

Wagner: Certainly not. The 6-speed automatic transmission will continue to provide the benchmark with the reaction and shifting times of a dual clutch transmission. We also lead the competition when it comes to shifting comfort and consumption. Therefore, the 6-speed will surely remain in our program until 2015.

In what regard the new 8-speed automatic transmission will it be better than the automatic six-speed transmission?

Wagner: The new transmission reduces consumption by 6% and makes shifting more comfortable with smaller jumps between gears. It is no larger or heavier and it re-quires no more components than the 6-speed automatic transmission. It can thus be manufactured at a comparable cost. It has also been developed from the very beginning such that it can be integrated easily for all hybrid concepts from micro to mild to full hybrid as a parallel hybrid without requiring more space in the existing drive train. This applies to the same extent for all current all-wheel drive systems.

Both the 8-speed automatic and the 7-speed dual clutch transmission are ready for start-stop operation -- until recently an innovation for automatic transmissions.

Wagner: That is true. In both cases we have found a solution that is cost-effective and efficient. With the 8-speed automatic transmission in the form of a hydraulic im-pulse accumulator (HIS). Normally if you switch off the engine and restart it, it takes nearly a second until it achieves idle speed and the necessary pressure is built up in the transmission's hydraulic system - only then can it shift into the first drive position and drive away. With an additional electric pump, you could keep the system under pressure permanently. However, the pump requires installation space and is noisy. Instead of this, we put a constantly-filled hydraulic accumulator in the transmission housing, whose content is injected into the system by using spring force on restart. The vehicle can thus move within 350 milliseconds, an acceptable time span.

ZF is one of the largest independent transmission manufacturers active worldwide, and yet the lion's share of production is still devoted to automatic torque converter transmissions. Will the new technologies - the key words being dual clutch transmissions and electric car - change the production volume at ZF?

Wagner: In 2008, we produced approximately 1.3 million automobile transmissions a year; approximately one million of these came from the automatic transmission plant in Saarbrücken. In Brandenburg, we are producing manual 6-speed transmissions and the new 7-speed dual clutch transmission. And in the next few years, automatic torque converter transmissions will be our most important business segment. Electric cars, including fuel-cell-powered cars will not achieve the volume of conventional cars in foreseeable time. And today we are already quite successful on the market with the dual clutch transmissions.

What is the situation like in the segment of automatic transmissions?

Wagner: In Germany automatic transmissions share about 28 percent and we expect an annual growth of at least one percent. In Europe, the rate equals approx. 19 percent with similar growth. In Asia and the USA, automatic transmissions with torque converters outweigh manual transmissions anyway. Now, dual clutch transmissions are being used gradually, but this applies particularly to Europe. With our product portfolio we are in a good position and due to development expenditure of EUR 700 million on the right track for new, future products.

What about the future of automated manual transmissions and CVTs?

Wagner: The future of CVT transmissions is tied particularly with front-transverse solutions, but because of the unsatisfactory efficiency, there would probably be problems in terms of CO2 emissions at some stage. And, automated manual transmissions will only carve out a niche existence because of the lacking comfort; most automotive manufacturers have already discarded this solution by now.