Many cars today are being made today with continuously variable transmissions (CVTs). A CVT is a type of automatic transmission but it operates differently than older automatics. Conventional automatic transmissions use sets of gears inside that provide different gear ratios or speeds. Control units sense speeds and shift the transmission’s gears automatically: lowest gears for low speeds, middle gears for acceleration and higher gears for efficient cruising. This is visually indicated with a selector display (P-R-N-D-L).
A CVT replaces the complex gear sets common in standard transmissions with two variable-diameter pulleys. One pulley is connected to the engine, the other to the drive wheels. The way it works is that during operation the pulleys move in and out such that a drive belt between moves higher on one pulley, lower on the other. You can picture this roughly as the way a 10-speed bike works, by routing the chain over smaller or larger gears to change the gear ratios. The controls for a CVT-based car are the same as an automatic-based car: Two pedals (gas and brake) and a P-R-N-D-L-style shift pattern.
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When driving a car with a CVT, you won’t hear or feel the transmission shift, though. It simply changes the engine speed as needed, calling up higher engine speeds (or RPMs) for better acceleration and lower RPMs for better fuel economy while cruising.
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.
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.
Because early automotive CVTs were limited as to how much horsepower they could handle, there has been some concern about the long-term reliability of the CVT. This has not proven to be a problem, though. Advanced technology has made the CVT quite robust and reliable.
Source: Central Avenue Chrysler