Is the continuously variable transmission on the verge of a comeback? If a report conducted by Nissan is anything to go by then the answer is a cautionary yes.
CVTs have had a checkered history that, according to some, goes all the way back to Leonardo da Vinci. Various motorcycles made use of them in the 1920s, but the big breakthrough came in 1958 when the small Dutch car manufacturer, DAF, introduced the Hub Van Doorne-designed belt driven CVT on its 600 model.
Over the years the system was gradually improved to the point where it was used to great effect in European Rallycross events by Dutchman, Jan de Rooy in his Daf 55. Jump forward to 1993 and Williams developed a Formula One version which an impecunious David Coulthard tested before the authorities banned it (you can find footage of it on YouTube).
Generally speaking, though, CVTs have never found that much favor with car buyers, many citing the constant transmission whine off-putting as well as the monotonous engine note.
Why all this interest? Because in the past three weeks I have driven two CVT equipped cars: the new Audi A6 and the latest Seat Exeo, which used to be an Audi A4.
Both cars were diesel powered which makes an ideal partner for the CVT. In the A6 it was Audis three-liter 204 bhp, 295 lb. -ft. of torque diesel. In this application the multitronic offers a sport program with shorter gear ratios and a manual mode with eight fixed gears.
The central component of the multitronic is the variator. It enables a large gear-ratio spread, with a ratio of 6. 7 between the shortest and the longest gears.
And because the diesel engine delivers its peak torque from 1250 to 3000 mating it to a CVT means optimum fuel efficiency, especially at highway speeds.
There was some whine from the A6, but Audi had done an excellent job of reducing it to a minimum; if there is one criticism to be made, is a slight tip-in hesitancy when moving off from standstill.
The same can be said for the Seat (illustrated here) which uses a previous generation Audi multitronic linked to its 141 bhp, 236 lb. -ft. of torque common rail diesel. Like the A6, the Exeo driver can also opt for stepped ratios allowing the driver to hold onto a gear for optimum response and feedback.
Nissans report, based on a 2009 survey of Japanese vehicle speeds, suggested that where speed variability factor exceeded 48 percent a CVT was even more efficient than a manual box.
As with everything that is being developed these days in the quest for efficiency and reduced emissions, CVTs are not a silver bullet but, in the right driving conditions and mated to the appropriate engine then they could just be the answer.
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