Oil filters can be divided into the following types: 
·Classified by lubrication circuit:
A. Quantitative filtration type: filter all the oil, a large amount of filtration, coarse filtration, a certain flow pressure rise, filtration efficiency is small, and the flow rate is large;
B. Constant pressure filter type: filter a part of the total flow, with a small amount of filtration, fine filtration, a certain pressure flow reduction, high filtration efficiency, low flow, and high filtration efficiency;
C. Combined type;
D. Joint type; 
·Classification by shape:
A. Bullet type;
B. Tin can type
C. Paper core type (upper and lower connection type).

The role of oil filter:
1. The oil filter, also known as the oil grid, is used to remove impurities such as dust, metal particles, carbon deposits and soot particles in the oil to protect the engine;
2. The oil filter is divided into full-flow type and split-flow type. The full-flow filter is connected in series between the oil pump and the main oil passage, so it can filter all the lubricating oil entering the main oil passage. The split-flow cleaner is connected in parallel with the main oil passage to filter only part of the lubricating oil sent by the oil pump;
3. During the working process of the engine, metal wear debris, dust, carbon deposits oxidized at high temperature and colloidal deposits, water, etc. are constantly mixed into the lubricating oil. The function of the oil filter is to filter out these mechanical impurities and gums, to keep the lubricating oil clean, and to extend its service life.