continuously variable transmission
Any of several forms of automatic transmission, without specific gears, in which the gear ratio may be changed without any noticeable steps.
CVT: infinite gears between two fixed speeds
A continuously variable transmission (CVT) is an automatic gearbox that replaces fixed gear ratios with a smooth, stepless transition between its lowest and highest speed ratios. Unlike a conventional automatic with three, six, or ten discrete gears, a CVT can settle on any ratio in between, continuously optimizing engine rpm for the driving condition without the brief power interruptions that happen when a standard transmission shifts gears.
The most common design uses two pulleys connected by a rubber or metal belt or chain. One pulley connects to the engine; the other drives the wheels. Each pulley has movable flanges that can spread apart or squeeze together, changing the effective diameter where the belt sits. As one pulley grows larger in diameter, the other shrinks, altering the ratio smoothly. Some CVTs use a different mechanism: a cone and roller system (toroidal CVT) or a series of balls that shift position within a race. All achieve the same outcome: a transmission with no fixed steps.
CVTs excel in fuel efficiency because the engine can operate near its optimal rpm for any road speed, rather than being locked to whatever gear the transmission selected. A CVT-equipped vehicle accelerating from a stop will hold the engine near peak torque rpm while the ratio continuously adjusts, then shift toward higher speeds and lower engine load once cruising. This is especially valuable in city driving with frequent speed changes and in hybrid powertrains, where the electric motor can cover gaps while the engine idles.
Wear and resistance to CVTs
The belt or chain in a CVT endures high contact pressures and shearing forces; longevity depends on design, fluid quality, and driving habits. The transmission relies on hydraulic pressure to move the pulley flanges and to grip the belt; low or degraded fluid accelerates wear and can cause slipping, overheating, or loss of power transmission. Sudden hard acceleration or towing loads outside the vehicle's rating can overstress the belt and shorten service life significantly.
CVTs have gained acceptance in mainstream vehicles, especially compact cars and crossovers where efficiency matters, but many drivers and engineers prefer the engaging feel and proven durability of stepped transmissions. The trade-off is clear: CVTs optimize efficiency and smoothness at the cost of added complexity, greater sensitivity to maintenance, and a monotonous engine note that some drivers find fatiguing on long drives.