What is the principle of continuously variable transmission?
3 Answers
The principle of continuously variable transmission is to use a hydraulic torque converter to generate different levels of torque, transmitting force to achieve stepless speed variation. Types of continuously variable transmission: 1. Mechanical type: There are various forms, with the most common being the cone-block metal V-belt drive, used in automobiles; 2. Hydraulic transmission type: Used in engineering vehicles and agricultural machinery; 3. Electric type: Used in electric vehicles. Starting devices for continuously variable transmission include: 1. Electromagnetic clutch type: Large in mass and size, with low thermal load capacity; 2. Electronically controlled wet friction plate type: Compact structure, fast response, and low energy loss; 3. Hydraulic torque converter type: High starting torque, good hill-start performance, easy driving, excellent driving performance, and capable of reducing vibrations and shocks caused by uneven engine torque.
The essence of continuously variable transmission lies in its variable gear ratio design, achieved through a pair of tapered pulleys connected by a steel belt or chain. The driving pulley links to the engine while the driven pulley connects to the wheels. By hydraulically adjusting the distance between the two tapered pulleys, the working radius of the belt changes. When the computer detects acceleration demand, it instantly adjusts oil pressure to increase the driving pulley's diameter while reducing the driven pulley's size – much like shifting gears on a bicycle. This creates seamless ratio changes without fixed gear steps, eliminating traditional transmission shift shock completely. Driving such vehicles on mountain roads keeps engine RPM consistently in the optimal range, delivering both fuel efficiency and smoothness. Even in stop-and-go traffic, there's no jerky motion. While belt wear and higher maintenance costs remain weaknesses, most new models now use reinforced chains to address this issue.
Having worked on cars for over 20 years and disassembled countless transmissions, the CVT's pulley set is truly ingenious. Both the driving pulley and driven pulley feature movable conical structures, with a high-strength push-type steel belt tensioned between them. The electronic system controls hydraulic pressure to push the conical plates together or apart, causing the steel belt's position to shift accordingly. When the driving pulley clamps, the belt moves outward, achieving a gear reduction effect akin to a small gear driving a large one. Conversely, when the driven pulley compresses, it switches to an overdrive state resembling a large gear driving a small one. This seamless adjustment keeps the engine RPM locked in its most efficient range—I've measured 15% better fuel economy than AT transmissions. However, excessive belt slippage can generate abnormal noises. Some owners experience engine revving without acceleration during hard throttle inputs, caused by delayed pulley adjustment. Newer models with electro-hydraulic valves have significantly improved this issue.
