An engine is a machine that can convert other forms of energy into mechanical energy, including internal combustion engines (gasoline engines, etc.), external combustion engines (Stirling engines, steam engines, etc.), electric motors, etc. Internal combustion engines typically convert chemical energy into mechanical energy. The engine is applicable to both the power generation device and the entire machine including the power device (such as gasoline engines, aircraft engines). The engine was first born in the UK, so the concept of the engine also originated from English. Its original meaning refers to the "mechanical device that generates power".

Engine lubrication system: During engine operation, many transmission components undergo high-speed relative motion with very small clearances, such as the crankshaft main journal and main bearing, crankshaft pin and connecting rod bearing, camshaft journal and camshaft bearing, piston, piston ring and cylinder wall, various motion pairs of the valve train, and transmission gear pairs. Although the working surfaces of these parts have been finely processed, upon magnification, these surfaces appear uneven and rough