In your car the transmission is the device that you use to change gears. You control what gear a car is in with a standard transmission and with an automatic transmission, it changes the gear for you. Today we have a new type of transmission to consider and it is called a continuously variable transmission (CVT). A CVT is a type of automatic transmission but it operates very differently than older automatics. CVTs provide more useable power, better fuel economy and smoother driving than traditional automatic transmissions.
Conventional automatic transmissions have sets of gears that provide different ratios or speeds. Complex control units sense speeds and shift an automatic’s gears to provide the most appropriate ratio for a given driving situation. A CVT replaces the complex automatic gears sets with simplicity: two variable-diameter pulleys, each shaped like a pair of opposing cones, with a metal belt running between them. The way it works is that one pulley is connected to the engine, the other to the drive wheels. During operation the pulleys move in and out such that a drive belt between moves higher on one pulley, lower on the other and this provides a numerical gear reduction. You can picture this roughly as the way a 10-speed bike works. The gearing effect with a CVT is essentially “continuous”, hence the nomenclature.
Engines do not develop constant power at all speeds; they have specific speeds where either torque, horsepower or fuel efficiency are at their optimum levels. Because a CVT can theoretically adjust to any gear ratio, engineers can program it to give maximum performance during all these situations. For example, when power is needed, or maximum fuel-economy is desired, a CVT can adjust to those conditions more accurately than a standard automatic transmission. In theory, a CVT is the perfect transmission.
The CVT’s biggest problem has been user acceptance. Because the CVT allows the engine to rotate at any speed, the noises coming from under the hood can sound odd to ears accustomed to conventional automatic transmissions. The gradual changes in engine note sound like something is “slipping”– signs of trouble with a conventional transmission, but perfectly normal for a CVT. Automakers have gone to great lengths to make the CVT feel more like a conventional transmission which defeats the purpose to some degree.
The future of the CVT remains to be seen. In spite of the obvious efficiencies of CVTs, customers can be fickle and may prefer and older technology. We will likely see how CVT transmissions fare over the next few years or so.