The function of piston rings includes sealing, regulating oil (oil control), heat conduction (heat transfer), guidance (support) four roles. Sealing: refers to sealing gas, do not let the combustion chamber gas leakage to the crankcase, the gas leakage is controlled at a minimum, improve thermal efficiency. Gas leakage will not only make the power of the engine drop, but also make the oil deteriorate, which is the main task of the gas ring; Regulating oil (oil control): Scrape off the excess lubricating oil on the cylinder wall, and at the same time make a thin oil film on the cylinder wall to ensure the normal lubrication of the cylinder, piston and ring. In modern high-speed engines, special attention is paid to the role of the piston ring in controlling the oil film; Heat conduction: The heat of the piston is transferred to the cylinder liner through the piston ring, which plays a cooling role. According to reliable data, 70-80% of the heat received by the piston top is dissipated through the piston ring to the cylinder wall; Support: The piston ring keeps the piston in the cylinder, prevents the direct contact between the piston and the cylinder wall, ensures smooth movement of the piston, reduces frictional resistance, and prevents the piston from knocking the cylinder.