The structural function of the oil pump is to pressurize the oil in the oil pan and then send it to the oil filter and lubricating oil passages to lubricate the main moving parts of the engine and filter the oil.

The function of the oil pump is to ensure that the oil circulates in the lubrication system and can deliver a sufficient amount of oil at a high enough pressure to the lubricating parts at any engine speed.

The oil pump can be divided into gear type and rotor type according to the structure. Gear type oil pump is divided into external gear type and internal gear type. External gear type oil pump An external gear type oil pump housing is equipped with a driving gear and a driven gear. The clearance between the gear and the inner wall of the housing is very small, and there is an oil inlet on the housing.

Working principle of external gear oil pump
When the gears enter the mesh, the oil between the mesh teeth will generate great thrust between the gears due to the smaller volume. To this end, a pressure relief groove is milled on the pump cover so that the oil extruded between the teeth can flow to the oil outlet chamber through the pressure relief groove when the gear teeth are engaged. A pressure limiting valve is installed on the oil pump cover, which can control the oil pressure in the main oil passage within the normal range (0.15~0.9MPa). A radial ring groove is opened at the plunger end of the pressure limiting valve to store the wear debris and impurities entering the mating surface, so as to ensure the flexible movement of the plunger. Gear oil pump is widely used because of its simple structure, easy manufacturing and reliable operation.

The working principle of internal gear type oil pump is basically the same as that of external gear type oil pump. The internal gear of the internal gear pump is a driving gear, which is sleeved at the front end of the crankshaft and directly driven by the crankshaft through splines. The outer gear ring is a driven gear, which is installed in the oil pump body, and the pump body is fixed at the front end of the engine body.

Structure of internal gear type oil pump
Rotor type oil pump The inner rotor of the rotor type oil pump is fixed on the driving shaft, and the outer rotor is in the oil pump housing, which can rotate freely, with a certain eccentricity between them. When the inner rotor rotates, it drives the outer rotor to rotate. The tooth profile of the rotor is designed so that when the rotor is turned to any angle, the tooth profiles of each tooth of the inner and outer rotors can always contact each other at a point. In this way, four working cavities are formed between the inner and outer rotors. When a certain working chamber rotates from the oil inlet, its volume increases, generating vacuum, and the oil is sucked in through the oil inlet. The rotor continues to rotate. When the working chamber is connected with the oil outlet, the volume of the chamber decreases, the oil pressure increases, and the oil is pressed out through the oil outlet. The rotor type oil pump has a compact structure, high suction vacuum, large pump oil volume and even oil supply. When the oil pump is installed outside the crankcase and at a high position, it is more appropriate to use this type of oil pump.