The analysis on the mixed lubrication of piston rings in a 4-stroke cycle diesel engine is made. The analysis uses the average Reynolds equation developed by Patir and Cheng, which governs the mean hydrodynamic pressure generated between two partially lubricated surfaces. The asperity contact pressure and the real contact area are estimated by the formulas of Lee and Ren, which are functions of the statistical surface roughness parameters, material hardness and load.
Effects of statistical surface roughness parameters, which include the surface pattern parameter, combined rms roughness and auto-correlation length, on the film thickness and friction characteristics between piston rings and a liner are investigated. The cyclic variations of the minimum film thickness and friction force are significantly affected by the surface pattern parameter. The film thickness and friction characteristics of barrel-faced ring are also examined.