An engine is a machine that converts other forms of energy into mechanical energy, including internal combustion engines (such as gasoline engines), external combustion engines (such as Stirling engines and steam engines), electric motors, and so on. For example, internal combustion engines typically convert chemical energy into mechanical energy. Engines can be used as power generation devices or refer to entire machines including power units (such as gasoline engines and aero engines). Pulleys belong to the category of disc-hub components, generally with relatively large dimensions, and are mainly manufactured through casting and forging processes. The function of engine pulleys is to transmit power. Accessory belts transfer the power output by the crankshaft to components such as the air conditioning compressor, power steering pump, water pump, and generator; timing belts transmit the power output by the crankshaft to the camshaft to drive the timing system; some engines with balance shafts also use belts to drive the balance shafts.