Continuously variable transmissions (CVT) change steplessly through an infinite number of effective gear ratios, unlike other mechanical transmissions that only allow a few different distinct gear ratios to be selected.
There are no gears to create gear ratios in a CVT. Instead the design typically involves two pairs of cones mounted on shafts.
Each pair of cones act like a pulley system. When the cones move together they create a larger diameter pulley, and a smaller diameter pulley when moving apart. Because the pulleys can be any diameter in relation to each other, the number of ratios is effectively infinite.
This flexibility within the CVT design can provide better transmission response and fuel economy than other transmissions by enabling the engine to consistently run at its most efficient revolutions per minute (RPM) for a range of vehicle speeds.
The challenge for the additive in a CVT is different to that for a step-type automatic transmission (AT). Step AT’s employ friction plates with paper (cellulose) friction material. Whereas CVTs have a steel to steel interface requiring different friction properties, strong wear protection and high film strength.