The oil filter generally has three levels, namely the oil collector, the coarse oil filter and the fine oil filter. The filter collector is installed in the front oil sump of the oil pump, and generally adopts a metal filter screen type. The coarse oil filter is installed behind the oil pump and connected in series with the main oil passage. There are mainly metal scraper type, sawdust filter type, and microporous filter paper type. Now the microporous filter paper type is mainly used. The fine oil filter is installed behind the oil pump and connected in parallel with the main oil passage. There are mainly two types: microporous filter paper type and rotor type. The rotor-type oil fine filter adopts centrifugal filtration and has no filter element, which effectively solves the contradiction between oil passability and filtration efficiency.

The function of the oil filter is to filter out impurities in the oil and keep the oil clean;
1. The automobile oil filter is located in the engine lubrication system. Its upstream is the oil pump, and downstream is the parts that need to be lubricated in the engine. In order to reduce the frictional resistance between the relative moving parts in the engine and reduce the wear of the parts, the oil is continuously delivered to the friction surface of each moving part to form a lubricating oil film for lubrication;
2. The engine oil itself contains a certain amount of colloids, impurities, moisture and additives. At the same time, the introduction of metal wear debris, the entry of sundries in the air, and the production of oil oxides during the operation of the engine gradually increase the sundries in the engine oil. If the oil is not filtered and directly enters the lubricating oil circuit, it will bring the sundries contained in the oil to the friction surface of the moving pair, accelerating the wear of the parts and reducing the service life of the engine;
3. If the oil does not pass through the oil filter and directly enters the lubricating oil circuit, the debris contained in the oil will be brought to the friction surface of the moving pair, which will accelerate the wear of parts and reduce the service life of the engine.