Studies on the Characteristics of Piston Ring Friction

The present paper refers to the studies on the frictional characteristics between piston rings and cylinder liners in reciprocating internal combustion engines. An improved floating liner method by means of hydrostatic bearings has been developed to measure accurately the frictional force as a function of crank angle under the firing operation. The major results are that: (i) the measured frictional force shows the boundary or mixed lubrication near the dead centers, but shows mainly the fluid lubrication during mid-strokes; (ii) the total frictional loss is reduced, but the peak friction just after the dead centers increases with the decrease in engine speed or oil viscosity; and (iii) the peak friction at the beginning of the expansion stroke increases remarkably due to the gas pressure in cylinder, and this increasing tendency is promoted according to the reduction in the number of piston rings.