The forces acting on the piston ring include gas pressure, the elastic force of the ring itself, the inertial force of the ring's reciprocating motion, and the friction between the ring and the cylinder and the ring groove, as shown in the figure. Due to these forces, the ring will produce basic motions such as axial motion, radial motion, and rotary motion. In addition, due to its motion characteristics, piston rings inevitably appear suspended and axial vibrations caused by axial irregular motions, radial irregular motions and vibrations, twisted motions, etc., along with irregular motions. These irregular movements often prevent the piston ring from functioning. When designing the piston ring, it is necessary to give full play to the favorable movement and control the disadvantage.
The high heat generated by combustion is transmitted to the cylinder wall through the piston ring, so it can cool the piston. The heat dissipated to the cylinder wall through the piston ring can generally reach 30 to 40% of the heat on the top of the piston
The first function of the piston ring is to maintain the seal between the piston and the cylinder wall, and to control air leakage to a minimum. This role is mainly borne by the air ring, that is, under any operating conditions of the engine, the leakage of compressed air and gas should be minimized to improve thermal efficiency; prevent the leakage between the cylinder and the piston or between the cylinder and the ring Seizure; prevent malfunction caused by deterioration of lubricant.
The second role of the piston ring is to properly scrape off the oil attached to the cylinder wall and maintain normal fuel consumption. When too much lubricating oil is supplied, it will be sucked into the combustion chamber, which will increase the fuel consumption, and because of the coke produced by the combustion, the engine performance will be extremely bad.
Because the piston is slightly smaller than the inner diameter of the cylinder, if there is no piston ring, the piston is unstable in the cylinder and it is impossible to move freely. At the same time, the ring also needs to prevent the piston from directly contacting the cylinder to play a supporting role. Therefore, the piston ring moves up and down in the cylinder, and its sliding surface is all borne by the ring.