Fuel Economy Emergency: Six-Speed Transmissions to the RescueBy Michelle Krebs May 29, 2008
By Bill Visnic
Automakers scrambling for quick fixes to polish up vehicle economy numbers in the eyes of fuel-price-fatigued U.S. customers are reaping real results from their -- and the supplier community's -- investments in the new generation of six-speed automatic transmissions.
The powertrain sector's shift to six-speed automatics has been coming since as early as 2001, but $4-per-gallon gasoline and $5 diesel fuel has turned up the heat on vehicle engineers to deliver more or less immediate efficiency enhancements for existing vehicles.
The migration to six-speed automatics was initiated by large transmission suppliers and a few major ventures by automakers' own transmission-making operations when gasoline was still considered cheap. Now, the industry is geared up to crank out the more efficient six-speed automatics in volume -- and with the high-tech transmissions promising as much as a 6 or 7 percent boost in fuel economy, the timing couldn't be better.
Since the introduction of its first six-speed automatic for the BMW 7 Series in 2001, Germany's transmission mega-supplier ZF Friedrichshafen AG has ramped up production exponentially to the point where it manufactured 1.3 million six-speed automatics last year -- and that number was a 30 percent jump from the 994,000 six-speed automatics ZF made just the year before.
Many European premium-car manufacturers -- not to mention volume producer Volkswagen AG -- were early adopters of the six-speed automatic, which has become common across their model ranges.
Meanwhile, data from Edmunds.com indicates a corresponding explosion of six-speed adoption in vehicles for the U.S. market. In 2001, there were just 15 models equipped with a six-speed automatic. For 2008, the number has increased by a factor of 12: there are 181 vehicles now offering the efficiency-enhancing six-speed.
ZF says its current-generation six-speed automatic increases fuel economy by 7 percent when compared to the four-speed automatic that for years was the industry standard -- and still is a staple in many vehicle segments. And the six-speed transmissions still deliver a significant 5 percent boost compared with five-speed automatics.
Maybe 7 percent doesn't sound like much. But a vehicle with a combined fuel economy rating of 25 mpg goes to 27 mpg. Or a city fuel economy figure of 17 mpg perhaps goes to 18 mpg. Small differences may be large when measured in consumer-perception terms. And with significant production volumes, these improvements mean a lot of fuel saved -- not to mention a genuine boost for automakers' CAFE calculations.
General Motors Corp., for example, made haste to make its new 6T40 six-speed automatic available with the 2.4-liter four-cylinder in its successful new Chevrolet Malibu midsize sedan; four-cylinder versions of the car launched only with four-speed automatic. The payoff from the move to the 6T40 for the '08 Malibu LTZ: a 2-mpg improvement in highway fuel economy, from 30 mpg to 32 mpg.
A spokesman for the company's Powertrain division says GM currently offers nine six-speed transmissions in 40 global vehicle models and by the close of 2009 plans to use the transmission in another 10 models, when it will be producing 3 million six-speed (manual and automatic) transmissions annually.
Rival Ford Motor Co., with whom GM in 2002 created a precedent-setting joint-venture to design and develop six-speed automatics, also is ready to use its version of the transmission as a springboard for near-term fuel-economy gains.
Ford recently said by the end of 2009 it will have doubled its production of six-speed automatics for North American cars and trucks -- to 1.4 million units annually. It also claims that by the end of 2012, 98 percent of its transmissions in North America will have six speeds.
Ford's new applications reinforce improvements claimed industrywide. For the '09 Escape compact crossover, for example, the gains for the 6F35 are 1 mpg in both city and highway driving - despite the fact the Escape's revised four-cylinder and V6 engines are markedly more powerful. Ford already uses a higher-capacity version of the 6F35 for its larger, six-cylinder vehicles, including the Edge crossover and Taurus midsize sedan and wagon.
Japanese automakers have been slower to join the six-speed automatic party -- partly due to distraction from competing technologies such as the continuously variable transmission -- but now are converting. In the late 1990s, Japan transmission supplier Aisin AW -- which supplies its six-speed automatics to automakers in Japan, Europe and the U.S. -- was the first licensee of the now-famous Lepelletier design that is the basis for almost all contemporary six-speed automatics.
Aisin, in fact, has jacked up the stakes. It makes an eight-speed automatic for Toyota Motor Corp.'s Lexus, and Nissan Motor Co. Ltd. recently launched an Aisin-made seven-speed automatic for its Infiniti premium division.
Engineers at ZF said just as six-speeds have replaced four- and five-speeds as the industry standard, there's a chance seven- and eight-speed planetary-gear automatics could lead to the same type of transition, "simply because of the fuel savings and performance benefits provided."
Photo from GM
Chevrolet Malibu LTZ, first GM North American front-driver to match four-cylinder power with a six-speed automatic, nets a 2-mpg improvement in highway fuel economy.