There must be an end gap in the piston ring because of the need of mounting and compensation for diameter after the wear of ring. Richardson’ and many author’ studies have showed the effects of the end gap to blowby and oil consumption, especially in the presence of ring or liner wear. This problem has influenced the effective utilization of the fuel energy for many years. Moreover the ring will rotate in the working cycle of engine. Once the end gaps of two compression rings come to the site of superposition, the shortest passage of gas flow is formed and blowby will be increased. The deflection of crankpin and rotation of piston were calculated according to the analytical model based on the torque transmission theory of crankshaft. The positive and negative deflections of crankpin result in the reciprocating rotation of piston in the IC engine working cycle. The peak values of deflection and rotation are in the vicinity of crank angle position of deflagration. Because the clingy moment of compression rings are less than rotational resistance moment in a few section of crank angle, they are unable to keep synchronism with piston and the rotations opposite to piston occur. The rotation angle of the second compression ring is more than that of the first ring. The superposition of the end gaps of two compression rings comes about when they turn to the same angle position. Based on above study, the structure of one compression ring in piston system should be widely used, which is in favor of reduction of friction and engine weight, pushing forward the lightweight process, being useful to the decrease of fuel consumption and emission. The pressure of combustion gas will not remarkably descend in this structure. The problem of ring suspension and pressure release in the first ring land can be resolved. Two types of rings with complete seal and economizing energy design are showed for the structure of one ring, which will also avoid the increase of end gap after the rings are worn.

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