What is the difference between AT and CVT
3 Answers
AT and CVT differ in the following aspects: 1. Principle: AT works by using a torque converter whose automatic shifting and torque variation range is insufficient, so several rows of planetary gears are connected in series behind the turbine to improve efficiency. The hydraulic control system automatically operates the planetary gears according to the engine's working changes, achieving automatic shifting and torque variation. CVT's transmission pulley structure is quite unique, divided into movable left and right halves that can move closer or apart. The conical discs can tighten or expand under hydraulic thrust, squeezing the steel belt chain to adjust the width of the V-shaped groove. When the conical discs move inward to tighten, the steel belt chain is pushed outward from the center, and vice versa. This changes the diameter of the disc driven by the steel belt chain, altering the transmission ratio. 2. Usage: AT does not require clutch shifting, has fewer gears but significant changes, and connects smoothly, making it easy to operate. It provides convenience for the driver and comfort for passengers. CVT, lacking the transmission gears of a typical automatic transmission, eliminates the shifting process and the associated jerky sensation. Therefore, CVT transmissions deliver linear power output, offering a very smooth driving experience.
I've driven manual transmission cars for over a decade, and recently studied transmissions when changing cars. AT uses gear sets for shifting, with multiple planetary gear sets inside - it's like several gears of different sizes working together. CVT is completely different, relying on two cone pulleys clamping a steel belt to transmit power, with the belt sliding along the cones to change ratios. With AT you can feel the gear shift jerk, especially during hard acceleration like being lightly kicked. But CVT doesn't have this sensation, accelerating as smoothly as a cable car going uphill. CVT does save fuel in city traffic jams, though the steel belt tends to overheat and slip on long steep slopes. My friend's AT car has run 200,000 km with just two oil changes - simpler structure makes it more durable.
Back in the day when modifying cars, I've disassembled many transmissions. The AT transmission structure resembles Russian nesting dolls—torque converters, planetary gear sets, and multi-plate clutches nested layer by layer, with shifts controlled precisely by solenoid valves regulating oil pressure. The CVT essentially turns the transmission into a continuously variable unit, where the engine drives the primary pulley via a chain, and the pulley squeezes a metal push belt to rotate the secondary pulley. The belt functions like a bicycle chain but with far greater precision, its sides interlocked by thousands of thrust steel segments. However, CVTs operate at sustained temperatures exceeding 120°C, making the belt prone to fatigue fractures—especially during summer hill climbs at full load, so it's wise to take it easy. Although maintenance manuals recommend fluid changes at 80,000 km, replacing it at 60,000 km is more prudent.
