The function of the oil filter in the lubrication system

　In the lubrication system, the oil filter ensures smooth oil flow and prevents impurities from scratching or damaging the surface of parts. Before reaching the friction surfaces, the oil must undergo rigorous filtration. To achieve satisfactory filtration without increasing oil flow resistance, a coarse filter is generally connected in series with the main oil passage, and a fine filter is connected in parallel with the main oil passage.

　　The float-type oil strainer removes large particles from the lubricating oil before it enters the oil pump to ensure the oil pump functions properly. It is connected to the oil pump inlet. When the oil pump operates, oil is drawn in through the gap between the cover and the float, filtered through the filter screen to remove large impurities, and then enters the oil pump through the oil pipe welded to the float. When the filter screen is clogged, the suction force of the inlet pipe increases, overcoming the force of the filter screen and causing the bad port to leave the cover, allowing the oil to enter the suction pipe directly without passing through the filter screen.

　　The coarse filter is connected in series between the oil pump and the main oil passage, also known as a full-flow filter, used to remove larger impurities from the oil. Currently, paper filters are widely used domestically and internationally. It mainly consists of an upper cover, outer casing, paper filter element, and bypass valve. When the engine is running, pressurized lubricating oil is sent into the cavity around the filter element. Larger impurities in the oil are blocked by the paper filter element, while clean lubricating oil enters the inner cavity of the filter element and then enters the main oil passage of the cylinder block through the outlet.

　　Fine filter: Its function is to filter out smaller impurities in the lubricating oil. It is usually connected in parallel with the main oil passage and comes in centrifugal and paperboard types.

　　Structure of the centrifugal fine filter: The hollow shaft is fixed to the outer casing. The rotor body and end sleeve are connected as one and rest on the thrust bearing, allowing free rotation around the rotor shaft. The clamping nut fastens the rotor cover and rotor body together, pressed by a spring to limit axial movement of the rotor. Two nozzles facing opposite directions are installed below the rotor. When the engine is running, a small portion of the oil pumped from the oil pump enters the filter through the oil port. When the oil pressure is below 98 kPa, the inlet pressure limiting valve closes, and the fine filter is inactive. When the oil pressure exceeds 98 kPa, the pressure limiting valve gradually opens, and the oil passes through the central hole of the rotor shaft and is sprayed out from the outlet. Then, it enters the rotor body through the oil hole and is sprayed out from the two nozzles. The resulting jet reaction force drives the rotor to rotate. When the oil pressure reaches 294 kPa, the rotor speed can reach over 5000 r/min. Impurities in the lubricating oil inside the rotor cavity have a higher specific gravity than the lubricating oil and are thrown to the rotor wall under the action of centrifugal force and adhere to the wall. Clean lubricating oil from the center enters the two nozzles and is continuously sprayed outward. The sprayed lubricating oil flows back to the lower crankcase.