1. Force
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, the friction force between the ring and the cylinder and the ring groove, as shown in the figure. Due to these forces, the ring will produce basic movements such as axial movement, radial movement, and rotational movement. In addition, due to its movement characteristics, along with irregular movement, the piston ring inevitably appears floating and axial vibration, radial irregular movement and vibration, twisting movement caused by axial irregular movement. These irregular movements often prevent the piston ring from functioning. When designing a piston ring, it is necessary to give full play to the favorable movement and control the unfavorable side.

2. Thermal conductivity
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 30-40% of the heat absorbed by the top of the piston.

3. Air tightness
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 gas ring, that is, the leakage of compressed air and gas of the engine should be controlled to a minimum under any operating conditions to improve thermal efficiency; prevent the cylinder and the piston or the cylinder and the ring from being caused by air leakage Seizure; to prevent malfunctions caused by deterioration of lubricating oil.

4. Oil control
The second function of the piston ring is to properly scrape off the lubricating oil attached to the cylinder wall and maintain normal oil consumption. When the supply of lubricating oil is too much, it will be sucked into the combustion chamber, which will increase the fuel consumption, and the carbon deposit produced by combustion will have a very bad impact on the engine performance.

5. Supporting
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 cannot move freely. At the same time, the ring should prevent the piston from directly contacting the cylinder, and play a supporting role. Therefore, the piston ring moves up and down in the cylinder, and its sliding surface is fully borne by the ring.