Friday, November 23, 2001

Automatic transmissions are favored by the overwhelming majority of drivers. But driving enthusiasts prefer manual transmissions because stick shifts enable them to match gear ratio to driving conditions with more precision, and give a greater feel of controlling a vehicle. However, now a new breed of automatic, a Continuously Variable Transmission, may make automatics more acceptable to driving aficionados.
Audi is the first luxury car company to offer a CVT in its A4 and A6 front-drive models. Audi’s engineers hope CVTs will make automatic transmissions not only palatable, but also able to enhance the driving experience. The German engineers claim the CVT offers the advantages of automatics without their penalties.
My own experience confirms that opinion. The Audi multitronic transmission is among the smoothest transmissions I’ve ever used. Its shifting is imperceptible. The CVT is also quiet and free of any clunks or thuds I’ve experienced with conventional automatic transmissions.
Audi’s multitronic offers an infinite range of gear ratios between its highest and lowest points. Most importantly, it does so seamlessly, without hesitation or lurching. That’s possible because a conventional automatic transmission has fixed gear sets to achieve a limited number of ratios with the aid of a torque converter. Engineers claim that the multitronic improves acceleration and boosts mpg.
Although CVTs have been available on other vehicles, they have not been a hit with U.S. drivers. Audi plans to change that with technology changes it has devised for the CVT. These contributions include a new type of variator, or pulley, and an all-new link-plate chain that’s designed to handle the torque generated by powerful six-cylinder engines.
The multitronic is a stepless transmission, comprised of a pair of pulleys and a steel drive belt that rides on the pulleys. There is no torque converter. Gear changes are effected by the belt riding between the pulleys. Audi claims that its multitronic eliminates the slipping clutch syndrome that has plagued previous CVTs.
Using new electronic controls and a clever dual-piston system on the pulleys, Audi engineers improve the efficiency of its CVT. In addition, the CVT electronics monitor the way a driver uses the accelerator to determine if performance or fuel economy is preferred. If fuel efficiency is desired, the CVT uses a low gear ratio (overdrive) to channel engine speed into propulsion even at speeds as low as 38 mph.
If a driver stomps on the accelerator, the CVT adjusts to sports driving mode and changes the ratio to underdrive. Thus, high engine speeds are available even at low speeds. For normal driving, the multitronic selects the optimum ratio between the two extremes. All of these gear changes occur smoothly and seamlessly, without the driver being aware that the changes are occurring.
The multitronic also offers a “manual mode” with six fixed transmission points that a driver controls by using a rocker switch on the steering wheel. But even in manual mode, the multitronic changes its gear ratios imperceptibly.
Performance is terrific. Acceleration from 0 to 60 mph is 1.3 seconds faster than with a conventional automatic transmission. It’s also actually one-tenth of a second faster than with a 5-speed stick shift.
What’s most impressive is that the multitronic delivers better fuel economy than a conventional automatic transmission and even has better fuel efficiency than a manual gear shift model.
Marc Trahan, Audi’s product management leader, says the company will deliver 7,000-10,000 multitronics in the first year.
The CVT will be the only automatic available in front-drive cars, which account for a mere 15 percent of Audi’s output. For the 85 percent of Audi A4 and A6 models that come with the all-wheel drive system, a conventional automatic transmission will be used until the multitronic is available 2004.

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