The force acting on the piston ring has the gas pressure, the ring self elasticity, the inertia force of the ring reciprocating movement, the ring and the friction of the cylinder and the ring groove, etc., as shown in the figure. Because of the effect of these forces, the ring will produce the basic motions of axial motion, radial motion and rotational motion. In addition, because of its motion characteristics, the piston ring is accompanied by irregular motion, which inevitably leads to floating suspension and axial vibration, irregular movement, vibration and twisting motion caused by irregular motion. These irregular movements often hinder the piston ring from functioning. When designing piston rings, we should give full play to the favorable movement and control the unfavorable side.
The high heat produced by the combustion will be passed to the cylinder wall by the piston ring, so that it can play the role of cooling piston. The heat from the piston ring to the cylinder wall can generally reach 30 ~ 40 of the top of the piston.
The first function of the piston ring is to keep the seal between the piston and the cylinder wall, and to control the leakage to a minimum. This role is mainly borne by the gas ring, that is, the engine under any operating conditions, its compressed air and gas leakage should be controlled to a minimum to improve the thermal efficiency, to prevent leakage caused by the cylinder and the piston or cylinder and the ring between the dead, to prevent the deterioration of lubricating oil caused by the failure.
The second action of the piston ring is to properly scrape the lubricating oil attached to the cylinder wall and maintain a normal fuel consumption. When the supply of lubricating oil too much will be sucked into the combustion chamber, so that the fuel consumption increased, and due to the combustion of carbon deposition, the engine performance is very bad.
Because the piston is slightly smaller than the diameter of the cylinder, if there is no piston ring, the piston in the cylinder instability, it is impossible to exercise freely. At the same time, the ring also to prevent the piston direct contact with the cylinder, play a supporting role. Therefore, the piston ring moves up and down in the cylinder, its sliding surface depends on the ring to bear.