The function of the oil pump is to provide hydraulic oil with a certain pressure and flow for the hydraulic torque converter and hydraulic control system to ensure the lubrication needs of various friction pairs such as planetary gear mechanisms. The oil pump is installed at the rear of the torque converter and driven by the shaft sleeve at the rear end of the torque converter. In the oil supply system of automatic transmission, the commonly used oil pumps are internal gear oil pump, rotor oil pump and vane oil pump. The automatic transmission oil pump is usually installed at the rear of the torque converter and driven by the shaft sleeve at the rear end of the torque converter housing. In the oil supply system of automatic transmission, there are two kinds of oil pumps: quantitative pump and variable pump. Internal gear pump, rotor pump and vane pump are commonly used in quantitative oil pump, among which internal gear pump is the most widely used. The internal gear pump is mainly composed of external gear, internal gear, crescent baffle, pump shell and pump cover. The gear is tightly installed in the inner cavity of the pump body, the outer gear is the driving gear, the inner gear is the driven gear, and the crescent partition separates the outer gear from the inner gear. The pump body is cast, and there are many oil passages in the pump body after finishing, including oil inlet and oil outlet. The actual pumping capacity of the oil pump will be less than the theoretical pumping capacity, because there is a certain leakage in each sealing gap of the oil pump. Variable displacement pump is a variable vane pump. Its stator can swing around the pin shaft, changing the eccentricity between the stator and the rotor, thus adjusting the pumping capacity. The advantage is that it can avoid the power loss caused by excessive pumping and improve the fuel economy of the automobile. Cycloidal rotor pump is a kind of internal gear pump with special tooth profile. It has the advantages of stable operation and low noise, but the flow pulsation is large and the machining accuracy is high. The displacement of vane pump depends on rotor diameter, rotor width and eccentricity between rotor and stator. It has the advantages of stable operation, low noise, uniform oil quantity and high volumetric efficiency, but its structure is complex and it is sensitive to the pollution of hydraulic oil.