The role of the oil filter is to filter out the metal wear debris, mechanical debris and oil oxides in the oil. If these sundries enter the lubricating system along with the engine oil, they will aggravate the damage of engine accessories, and may also block the oil pipe or oil passage.
There are two types of oil filters installed in front of and behind the oil pump. The oil strainer installed in front of the oil pump is called the oil strainer. Installed behind the oil pump, according to its layout method, there are two types: full flow type and split flow type.

1. Filter collector
The filter collector is usually filter screen type, which is installed in front of the oil pump to prevent large particles from entering the oil pump. There are two types of filter collectors: floating type and fixed type.
The floating filter collector can suck in cleaner engine oil on the oil, but the foam on the oil is easy to be sucked in, reducing the engine oil pressure and making lubrication unreliable.
As shown in the figure below, the fixed filter collector is installed below the oil level, and the cleanliness of the oil sucked in is slightly transmitted to the floating filter collector, but the foam suction can be avoided, the lubrication is reliable, and the structure is simple. At present, all automobile engines use this type of filter collector.

2. Full flow oil filter
The full flow oil filter is connected in series between the oil pump and the main oil passage, so all oil is filtered according to it. At present, the full flow oil filter is mostly used in automobile engines.
The filter element of the full flow oil filter has many means. At this stage, most automotive engines use paper filter elements. The oil filter with paper filter element has two types of structure, one is detachable type, which can be replaced by replacing the paper filter element,; The other is integral type, which shall be completely replaced.
The full flow oil filter has a corresponding service time limit and should be replaced at the expiration of the time limit. When the filter element of the oil filter is seriously blocked by impurities during the operation period, the oil pressure at the oil inlet of the oil filter will rise. When the working pressure reaches the standard value, the bypass valve in the oil filter will be opened (as shown in the figure below). At this time, the oil will not pass through the filter element but directly enter the main oil passage. Although the engine oil is sent to each lubricant without filtering at this time, it is much better than the lack of lubricant.

3. Split flow oil filter
The engine of large trucks, especially heavy trucks, usually adopts the full flow+split flow oil filter layout method, as shown in the figure below. The full flow filter is also known as the primary filter, which is used to filter impurities with particles above 0.05mm in the engine oil; The split flow filter, also known as the fine filter, is used to filter out small impurities with particles above 0.001 mm, and only filters 5%~10% of the oil supplied by the oil pump of the filter.
There are two types of split flow fine filters: filter type and centrifugal type. At present, centrifugal fine oil filters are widely used. There is also a rotor in such filters, which is supported on one shaft according to the rolling bearing, as shown in the figure below. There are two nozzles with opposite spouting directions in the rotor. It uses the working pressure energy of the lubrication system itself. When the oil enters the rotor and sprays out of the nozzle, it will cause a recoil torque and drive the rotor to rotate rapidly. Under the action of centrifugal force, the oil in the rotor separates solid impurities and accumulates on the inner wall of the rotor. The oil in the center of the rotor becomes clean and flows back to the oil pan from the nozzle.

4. Centrifugal oil filter
The centrifugal oil filter is characterized by stable performance and reliable structure. There is no filter element that needs to be replaced. Just dismantle the rotor on time, remove the stains accumulated on the rotor surface, and then it can be used again. The service life is long. Its deficiency depends on its complicated structure, high price, heavy weight, etc., and high technical requirements for maintenance personnel.