When the engine is running, if some friction parts are not properly lubricated, dry friction will occur. Practice has proved that the heat generated by dry friction in a short period of time is enough to melt the metal, causing damage to the parts and even getting stuck (many water leaking or oil leaking cars have problems such as pulling cylinders and axles). Therefore, it is necessary to give good lubrication to the friction parts in the engine. When the lubricating oil flows to the friction part, it will adhere to the friction surface to form an oil film, reducing the resistance between the friction parts, and the strength and toughness of the oil film is the key to exert its lubrication effect.
(2) Cooling effect
Only a small part of the heat generated by the combustion of fuel in the engine is used for power output and friction resistance consumption and the driving of auxiliary mechanisms; most of the remaining heat will be carried by the engine's cooling medium in addition to the exhaust gas discharged to the atmosphere. Take part. The excess heat in the engine must be removed from the body, otherwise the engine will burn out due to excessive temperature. This is accomplished on the one hand by the engine cooling system, on the other hand, the lubricating oil takes heat from the surface of the cylinder, piston, crankshaft, etc. and distributes it to the oil pan.
(3) Washing effect
During the operation of the engine, a lot of dirt is generated. Such as sand and dust brought in the air, coal deposits formed after the combustion of the mixed gas, gums formed after the oxidation of the lubricating oil, metal scraps caused by friction between parts, and so on. These dirt will adhere to the friction surface of the machine, if not cleaned, it will increase the wear of the machine. In addition, a large amount of glue will cause the piston ring to stick and cause the engine to malfunction. Therefore, these pollutants must be cleaned in time. This cleaning process is completed by circulating the lubricating oil in the body.
(4) Sealing effect
There is a certain gap between the cylinder and the piston of the engine, the piston ring and the ring groove, and the valve and the valve seat, so as to ensure that the moving pairs will not get stuck. However, these gaps can cause poor sealing of the cylinder, and the leakage of the combustion chamber results in a decrease in cylinder pressure and engine output. The oil film formed by the lubricating oil in these gaps ensures the tightness of the cylinder, maintains the cylinder pressure and engine output, and prevents exhaust gas from flowing down into the crankcase.
(5) Anti-rust effect
When the engine is running or stored, moisture in the atmosphere, lubricating oil, fuel oil, and acid gases generated by combustion will cause corrosion and rust on the parts, thereby increasing the damage to the friction surface. The oil film formed by the lubricant on the surface of the machine can prevent the machine from directly contacting water and acid gases, and prevent corrosion and rust.
(6) Elimination of impact
At the end of the compression stroke, the mixture starts to burn and the cylinder pressure rises sharply. At this time, the lubricating oil in the bearing clearance will alleviate the impact load on the piston, piston pin, connecting rod, crankshaft and other components, make the engine work smoothly, prevent direct metal contact, and reduce wear.