The Function of Oil Filter

What is the function of oil filter? When the engine is working, metal wear debris, dust in the atmosphere and carbon particles produced by incomplete combustion of fuel will penetrate into the oil, and the oil itself will also produce colloidal deposits due to thermal oxidation. If such dirty oil is sent directly to the surface of the moving parts, the mechanical impurities in the oil will become abrasives, which will accelerate the wear of the parts, and cause blockage of the oil passages and cementation of parts such as piston rings and valves. Therefore, an oil filter must be installed in the lubrication system, so that the circulating oil can be purified before being sent to the surface of the moving parts, so as to ensure good lubrication of the friction surface and prolong its service life.

Generally, several filters with different filtering capacities are installed in the lubrication system, namely the collector filter, the coarse filter and the fine filter, which are respectively connected in series and in parallel in the main oil passage. The filter connected in series with the main oil passage is called a full-flow filter, which is generally a coarse filter: the filter connected in parallel with the main oil passage is called a split-flow filter, which is generally a fine filter, and the oil flow is 10%~30%.

Collector filter

The filter is equipped with a wire mesh, which is installed on the oil inlet pipe of the oil pump. Its function is to prevent the large machine from being impurity into the oil dish. There are two common types of floating filter and fixed filter.

The internal floating filter floats on the oil surface to absorb oil, which can absorb the cleaner oil on the oil surface, but the foam on the oil surface is easy to break and absorb, which reduces the oil pressure and the lubrication is not reliable. It is not widely used at present. The fixed filter is submerged under the oil surface, and the cleanliness of the sucking oil is poor, but it can prevent the foam from sucking, the lubrication is reliable, the structure is simple, and the floating filter is gradually replaced.

Strainer

The coarse filter is used to filter out the impurities with larger particle size in the oil. The primary filter has small oil flow resistance, and is usually connected in series between the oil pump and the main oil passage, and belongs to a full-flow filter. The working principle of the coarse filter is to use the oil to pass through the small holes or gaps, leaving impurities larger than the holes or gaps on the outside of the filter element. Therefore, the coarse filter is a filter filter. Depending on the filter element, there are various structural forms. The traditional coarse filter mostly adopts metal sheet slot type and winding type, and now mostly adopts paper type and sawdust type.

1.Paper filter

element type coarse filter is made of microporous filter paper. In order to increase the filtration area, the microporous filter paper is generally folded into a fan shape or a corrugated shape. Corrosion ability and resistance to water and moisture, as well as small quality, small volume, simple structure, good filtration effect, low filtration resistance, low cost and convenient maintenance, so it has been widely used.

2. Sawdust filter

its filter element is a sawdust filter element bonded with phenolic resin, which has low resistance, good filtering effect and long service life

3. Fine filter

The oil fine filter is used to remove small impurities. This filter has a large positive force on the flow of the oil, so it is mostly used as a component flow, which is connected in parallel with the main oil passage. Only a small amount of oil passes through it and returns to the oil after being filtered. bottom element. There are two types of humidifiers: filter type and centrifugal type. There is a contradiction between the filtering capacity and the passing capacity of the filtering oil fine filter, so most engines use a centrifugal fine filter. The centrifugal fine filter uses the principle of centrifugal force to separate the mechanical impurities in the oil.

The structure and working principle of the centrifugal fine filter. After the oil from the main oil channel enters the fine filter, it enters the inner cavity of the rotor assembly through the base and the central hole of the rotor, and then sprays out from the two nozzles. The rotor is driven by the reaction force. rotate. The higher the oil pressure is, the faster the rotor body rotates. When the oil pressure reaches about 0.3MPa, the rotating speed of the rotor reaches more than 500/min. The dirt in the oil is thrown to the rotor wall by centrifugal force and deposited on the rotor wall to achieve the purpose of filtering the oil. After the clean oil is sprayed out, it flows back to the oil pan of the engine. When the pressure of the main oil passage is lower than 0.098MPa, the oil inlet pressure limiting valve is closed. At this time, the oil does not pass through the fine filter, and all enters the main oil passage to ensure the lubrication of the engine.

The centrifugal fine filter has strong filtration capacity, good passing capacity, and is not affected by sediment. It does not need to replace the filter element, but only needs to be cleaned regularly. However, the effect of colloid filtration is poor, and generally only a shunt fine filter is used.

4. Composite filter

It connects the fine filter element and the coarse filter element in series and is installed in the same casing. Its structure and working principle are under normal circumstances. The oil pumped from the oil pump enters the composite oil filter through the oil inlet. For sealing effect, the lubricating oil is first filtered by the coarse filter element, then filtered by the fine filter element and enters the central cavity, and then flows up the central cavity, passes through the oil outlet, and flows to the main oil passage.

If the fine filter element is blocked, when the pressure difference between the front and rear of the filter element exceeds 0.09~0.1MPa, the bypass valve will be opened, and the lubricating oil after coarse filtering will enter the main oil passage through the cavity hole of the filter element cover, as shown in Figure 2-109(b); if When the coarse filter element is blocked, and the pressure difference between the oil inlet and the oil outlet exceeds 0.196~0.245MPa, the safety valve is opened, and the lubricating oil directly enters the main oil passage without the filter element.This composite filter is compact in structure and reliable in operation. The paper filter element can be replaced regularly and the cost is low, so it is widely used.

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