How Continuously Variable Transmissions Work

Basic CVT
The basic CVT system that has found the most favor over the years is a simple layout with two pulleys connected by a flexible belt. One pulley is connected to the engine, while the other is connected to the rest of the driveline and ultimately the wheels. Each pulley is split in the middle, and looks something like two saucers positioned bottom-to-bottom. When the saucers are pulled apart, the belt rides close to the center. When the saucers are pushed together, the belt moves out. So by changing the spacing of the saucers, the pulley's effective diameter changes too. To create a "neutral" that allows the engine to idle without moving the vehicle, one or both pulleys open up and the belt goes slack and slips harmlessly.


A number of low-powered cars have used CVT transmission over the years, but now strength and durability advancements mean that CVT transmission is headed into the realm of mid-powered vehicles. Flexible metal belt designs and advancing material technologies have made CVT transmissions tougher than ever. Audi now offers it on the 220-horsepower A6, and Saturn uses it on the 143-horsepower version of the Vue. Other applications are just around the corner.


Even the slightly odd driving feel of CVT transmissions is being dealt with. To drivers who've spent their lives hearing and feeling the distinct ratios of conventional transmissions, the "disconnected" feel of a CVT can be at first disconcerting. Audi addresses that subjective issue with a manual shift mode that makes the CVT mimic the operation of a six-speed transmission by creating six distinct ratios to choose from. True, a small amount of efficiency and smoothness is lost, but a bit of comforting familiarity is gained for old-school drivers who aren't quite ready to leave the feel of old conventional transmission behind. Inevitably they will, as Constantly Variable Transmissions move fully into the mainstream.