They are hydraulic automatic transmission (AT), mechanically continuously variable automatic transmission (CVT), and electronically controlled mechanical automatic transmission (AMT). At present, AT is commonly used in cars, and AT has almost become synonymous with automatic transmission. AT is composed of a hydraulic torque converter, planetary gears and a hydraulic control system. It achieves variable speed and torque conversion by means of hydraulic transmission and gear combination. Among them, the hydraulic torque converter is the most important part of the lamp. It is composed of pump wheels, turbines, guide wheels and other components, and has the functions of transmitting torque and clutching.