How it Works
Although there are different variations on the CVT theme, most passenger cars use a similar setup. Essentially, a CVT transmission operates by varying the working diameters of the two main pulleys in the transmission.

The pulleys have V-shaped grooves in which the connecting belt rides. One side of the pulley is fixed; the other side is moveable, actuated by a hydraulic cylinder. When actuated, the cylinder can increase or reduce the amount of space between the two sides of the pulley. This allows the belt to ride lower or higher along the walls of the pulley, depending on driving conditions, thereby changing the gear ratio. If you think about it, the action is similar to the way a mountain bike shifts gears, by "derailing" the chain from one sprocket to the next — except that, in the case of CVT, this action is infinitely variable, with no "steps" between.

The "stepless" nature of its design is CVT's biggest draw for automotive engineers. Because of this, a CVT can work to keep the engine in its optimum power range, thereby increasing efficiency and gas mileage. A CVT can convert every point on the engine's operating curve to a corresponding point on its own operating curve.

With these advantages, it's easy to understand why manufacturers of high-mileage vehicles often incorporate CVT technology into their drivetrains.

Look for more CVTs in the coming years as the battle for improved gas mileage accelerates and technological advances further widen their functionality. In fact, Audi recently announced that it will offer a Multitronic CVT in the 2002 A4. Although this will be available only in front-wheel-drive mode and not quattro, it indicates CVT's continuing move toward the mainstream. According to Audi, it can be used in Tiptronic six-speed manual mode, or as a standard CVT automatic.