What is the Principle of Continuously Variable Transmission?
3 Answers
The working principle of a continuously variable transmission (CVT) is to use a drive belt and a primary and secondary pulley with variable working diameters to transmit power, enabling continuous changes in the transmission ratio. This allows for optimal matching between the transmission system and the engine's operating conditions. CVT is a type of automatic transmission system that can continuously achieve any transmission ratio within its range. The main difference between a CVT and a conventional automatic transmission is that it eliminates the complex and bulky gear combination for speed variation, instead using only two sets of pulleys for transmission. By altering the contact radius of the drive belt between the driving and driven pulleys, the CVT achieves speed variation. Since the CVT can continuously adjust the transmission ratio, it ensures optimal matching between the transmission system and the engine's conditions, improving the vehicle's fuel economy and power performance, as well as enhancing the driver's ease of operation and passenger comfort. Therefore, it is an ideal automotive transmission device.
As a mechanic who frequently repairs cars, I've seen many CVTs in operation. Its core mechanism involves a steel belt or chain connecting two conical pulleys, with engine power transmitted from the input pulley to the output pulley. When you press the accelerator to speed up, the control system increases the diameter of the input pulley while decreasing the output pulley's diameter, reducing the gear ratio and allowing the vehicle speed to rise smoothly. Releasing the throttle does the opposite. This keeps the engine RPM in the efficient range, eliminating the jerky shifts of traditional transmissions for a comfortable and fuel-efficient ride, especially noticeable in stop-and-go traffic. However, aging belts or insufficient fluid can cause slipping and noise, requiring regular inspection and replacement. Modern designs incorporate hydraulic and electronic control units for optimization, keeping maintenance costs relatively low and making CVTs ideal for daily commuting. Commonly found in Japanese cars, I advise owners to avoid frequent hard acceleration to prolong its lifespan.
I've been driving this CVT car for several years, and the driving experience is very smooth. The principle is that the engine's power output doesn't change through fixed gear ratios like a manual transmission, but continuously adjusts via two pulleys and a belt. Simply put, changing the pulley size alters the output speed ratio. For example, during acceleration, the engine RPM doesn't rise much but the car speed increases quickly, with less shifting vibration. I think this design optimizes fuel efficiency, and engine noise is lower at high speeds. However, initial acceleration might feel sluggish, requiring some adaptation to throttle control. From a driver's perspective, it's hassle-free and easy to maintain—just follow the manual for transmission fluid changes. CVTs are commonly seen in hybrid vehicles because they can work in tandem with electric motors for energy savings and environmental friendliness. Personally, I find them more practical than automatic transmissions for city driving, but during cold winter starts, it's important to warm up the car for a few minutes to avoid wear.
