The continuously variable transmission (CVT) was first used in auto-mobiles in the late 1880s. The most common type is a friction-drive device using a belt and two pulleys with a deep V-shaped gap. The distance between the pulley halves is adjusted to make the belt ride higher or lower in the gap, effectively changing the diameter of the pulleys, and therefore, the drive ratio. Springs and flyweights can be used to change pulley gap, but for automotive applications, something a little more sophisticated is required.
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