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 that enters the main oil passage. The split-flow filter is connected in parallel with the main oil passage to filter only part of the lubricating oil sent by the oil pump. During the working process of the engine, metal wear debris, dust, carbon deposits and colloidal deposits oxidized at high temperature, water, etc. are constantly mixed into the lubricating oil. The function of the oil filter is to filter out these mechanical impurities and colloids, keep the lubricating oil clean, and extend its service life.
The oil filter should have strong filtering capacity, low flow resistance, and long service life. Generally, several filters with different filter capabilities are installed in the lubrication system—collecting filter, coarse filter and fine filter, which are respectively connected in parallel or in series in the main oil passage. (The one connected in series with the main oil passage is called a full-flow filter. When the engine is working, all lubricating oil is filtered through the filter; the one connected in parallel is called a split-flow filter). The coarse filter is connected in series in the main oil passage, which is a full-flow type; the fine filter is connected in parallel in the main oil passage, which is a split-flow type. Modern car engines generally only have a filter and a full-flow oil filter. The coarse filter filters out impurities with a particle size of 0.05mm or more in the oil, and the fine filter is used to filter out fine impurities with a particle size of 0.001mm or more.
Technical characteristics of oil filter:
• Filter paper: Oil filters have higher requirements for filter paper than air filters, mainly because the temperature of the oil varies from 0 to 300 degrees. Under severe temperature changes, the concentration of the oil also changes accordingly. It will affect the filtering flow of the oil. The filter paper of a high-quality oil filter should be able to filter impurities under severe temperature changes while ensuring sufficient flow.
• Rubber sealing ring: The filter sealing ring of high-quality engine oil is made of special rubber to ensure 100% oil-free leakage.
• Backflow suppression valve: only available in high-quality oil filters. When the engine is turned off, it can prevent the oil filter from drying out; when the engine is re-ignited, it immediately generates pressure to supply oil to lubricate the engine. (Also called check valve)
• Relief valve: only available in high-quality oil filters. When the external temperature drops to a certain value or when the oil filter exceeds the normal service life, the overflow valve will open under special pressure, allowing unfiltered oil to flow directly into the engine. Even so, the impurities in the oil will enter the engine together, but the damage is much smaller than the damage caused by the absence of oil in the engine. Therefore, the overflow valve is the key to protect the engine in an emergency. (Also known as bypass valve)
