CVT - How it works
“CVT” stands for continuously variable transmission. What that means is that they are “infinitely variable” or without discrete steps – or “stepped gears” – like a traditional automatic transmission.
The continuously variable transmission available next year in the new Ford Five Hundred, Freestyle and Mercury Montego – and this fall in the Focus C-Max in Europe – offers many times more gear ratios than any automatic “step” transmission.
It does this by doing away with gears entirely. Instead, CVTs work with a heavy-duty chain belt. The reinforced belt runs between two cone-shaped pulleys. One pulley is hooked to the engine and the other is hooked to the drive train. As the engine turns the pulley hooked to it, the belt transfers power to the other pulley that is hooked to the drive shaft, which powers the wheels.
The portion of the pulleys that the metal belt runs over varies in diameter according to driver demands and other conditions. Varying the diameters of the pulleys is similar to the changing of gear ratios in a standard transmission, but it happens in a continuous flow, instead of in discrete steps.
The obvious benefit is smoothness because there's no shifting. But CVTs are more efficient, too, and thus save about 4 percent to 8 percent in fuel versus the traditional four-speed automatic. The second-generation CVT used in these vehicles relies on electronics to determine the ideal ratios based on driver intent and current operating conditions, including engine speed and load. Because changes take place smoothly, shift quality – the “feel” of the transmission changing gear ratios – is excellent.
“We did a lot of dyno testing, duplicating harsh conditions to prove out the durability of the CVT,” said Craig Renneker, executive engineer, new product programs, Automatic Transmission Engineering Operations.