Filter paper requirements

Oil filters have higher requirements for filter paper than air filters, mainly because the temperature of the oil varies from 0 to 300 degrees, and under severe temperature changes, the concentration of the oil also changes accordingly, which affects the filtration flow rate of the oil. The filter paper of a high-quality oil filter can filter impurities and ensure sufficient flow under severe temperature changes.

Effect

In order to ensure smooth oil flow in the lubrication system and prevent impurities from scratching or scratching the surface of parts, the oil filter in the lubrication system must undergo strict filtration before being sent to the friction surface. To achieve satisfactory filtering effect without increasing oil resistance, the coarse filter is generally connected in series with the main oil passage, and the fine filter is connected in parallel with the main oil passage.

1. The float type oil collection filter is responsible for removing large particles and impurities from the lubricating oil before entering the oil pump in order to make the oil pump work well. It is connected to the oil inlet of the oil pump. When the oil pump is working, the oil is sucked in through the narrow slit between the cover and the float, filtered out of coarse impurities through a filter screen, and then enters the oil pump through the oil pipe welded to the float. When the filter is clogged, the suction force of the inlet pipe increases, overcoming the strong force of the filter and causing the damaged port to leave the cover. The oil then enters the suction pipe directly from the ring port without passing through the filter.

2. The coarse filter is connected in series between the oil pump and the main oil passage, hence it is also known as a full flow filter, used to remove larger impurities from the engine oil. It mainly consists of an upper cover, a shell, a paper filter element, and a bypass valve. When the engine is working, 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 oil outlet.

3. Fine filter: Its function is to filter out smaller impurities in lubricating oil, usually in parallel with the main oil passage, and there are two types: centrifugal and cardboard.

4. The structure of a centrifugal fine filter: a hollow shaft is fixed on the outer shell, and the rotor body and end sleeve are connected as a whole, sitting on a thrust bearing, and can freely rotate around the rotor shaft. Tighten the rotor cover and rotor body together with a compression nut, and use a spring to compress them to limit the axial movement of the rotor. Two nozzles are installed under the rotor in opposite directions. When the engine is running, a small portion of the oil is pumped out from the oil pump and enters the filter through the oil port. When the oil pressure is below 9s kPa, the inlet pressure limiting valve closes and the fine filter does not function. When the oil pressure exceeds 98 kPa and the pressure limiting valve gradually opens, the oil flows through the center hole of the rotor shaft and is sprayed out from the oil outlet hole. Then it enters the rotor body through the oil hole and sprays out from two nozzles, so the spraying reaction force pushes it to rotate again. When the oil pressure rises to 294 kPa, the rotor speed can reach over 5000 r/min. The proportion of impurities in the lubricating oil inside the rotor cavity is higher than that of the lubricating oil. Under the action of rotational centrifugal force, they are thrown towards the rotor wall and attached to it. The clean lubricating oil at the center enters the two nozzles from the center and continuously sprays outwards, and the sprayed lubricating oil flows back to the lower crankcase.