It is rare that a single technology can appease the demands of markets in Europe, Japan and North America. But a clutchless manual transmission may come close.
In Europe and Japan, traffic-weary motorists might prefer them to traditional manual transmissions. A clutchless manual would offer the convenience of an automatic without hurting fuel economy. In the United States, only 10 percent of cars and trucks are sold with manual transmissions.
But U.S. automakers want to improve the fuel economy of pickups, minivans and sport-utilities. And that has created an opportunity for suppliers of clutchless manual transmissions. Siemens Automotive, Magneti Marelli, Sachs Automotive, Aisin Seiki Co. Ltd. and ZF Friedrichshafen AG each has developed a version of this technology.
In a clutchless manual transmission, the work of engaging and disengaging the clutch - normally performed by the driver - is handled by an electric or hydraulic activator. The driver changes gears by moving a lever or by pressing buttons on the steering wheel. The gear changes are sequential, which means the transmission runs through the gears in order - the driver cannot skip a gear. If the driver does not want to shift manually, a computer chooses the best shift points. So far, that is no different than an automatic transmission with a gear-change option, such as the Porsche Tiptronic.
The big difference is the torque converter - a clutchless manual gearbox does not have one. The torque converter is the main reason automatic transmissions get poor fuel economy. A clutchless manual transmission gives the motorist the convenience of an automatic gearbox without weakening fuel economy. Moreover, it eases the task of powertrain design. Because the system uses a manual gearbox, it also can handle the high torque loads of powerful engines.
Sound like a gimmick? Ferrari offers a Selespeed clutchless manual from Magneti Marelli as an option on the 360 Modena. The system traces its past to the Italian automaker's Formula One race cars. Last year, most Modena buyers chose that option. Selespeed also is used on the Aston Martin DB7 Vantage and the Alfa Romeo 156.
At the other end of the performance scale, DaimlerChrysler's Smart city car offers a Sachs system, while the Volkswagen Lupo uses a Siemens system. This spring, Ford will add the Siemens system to its Transit van. BMW's high-performance M division uses clutchless manual componentry from Siemens and Sachs in the new M3.
'In Europe and Japan, the primary reason for using clutchless manuals is convenience,' says Glen Barton, technical marketing manager for powertrain hydraulics at Siemens Automotive in Detroit. 'In the U.S. market we see potential for it to improve fuel economy of trucks.'
To popularize this technology, automakers must design a clutchless manual to shift nearly as smoothly as an automatic. This issue is known as shift shock. Shift shock is not a great problem for sports cars, because those drivers expect a bit of a jolt, or in small cars, where driver expectations are lower. But in larger and luxury vehicles, smoothness counts.
'No one complains about a clutchless manual versus a conventional manual,' says Barton. 'But when you compare it to an automatic, everyone's got a different opinion.'
That is why Mercedes-Benz will not bring its Sequentronic six-speed clutchless manual transmission to the United States, says Fred Heiler, spokesman for Mercedes-Benz USA Inc. The Sequentronic is offered as an option on the C class in Europe. It is more expensive than a traditional manual transmission but costs less than an automatic.
The secret to a smooth shift is allowing enough time for the engine and transmission speeds to synchronize. A longer interval ensures a smoother shift. A smooth shift can take several hundred milliseconds to complete. Today's automatics shift in about 150 to 200 milliseconds. But automakers aim to complete shifts in less than 100 milliseconds, their threshold for a noticeable delay in shifting.
Engineers at Siemens and other suppliers believe that with a new generation of transmission control software, they can reach the 100-millisecond goal with a smooth shift. The advent of integrated starter generators, which could quickly synchronize the engine and transmission speeds, could enable shift changes in 50 milliseconds, Barton says.
Despite the advantages of clutchless manual transmissions, not many are produced. Says Barton: 'If you can give people a manual they can drive, will they want it? Nobody knows.'
E-mail writer Dale Jewett at [email protected]