Studies on Tribology Characteristics of Dynamically Loaded Sliding and Rolling Contact Surfacces under Soot-Abrasive Contamination in Lubricating Oil

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In order to improve the fuel economy and reliability of internal combustion engines it is required to apply the low viscosity multi-grade lubricating oils formulated as low friction engine oils and take measures against the oil deterioration and contamination caused by the EGR soot. There, the tribology problem becomes serious, namely, the friction and wear increase at the dynamically loaded sliding and rolling contact surfaces such as engine components of the piston system, bearing system and valve gear mechanism because the oil film thickness is extremely thin under the lubrication of low viscosity oil contaminated with the soot abrasive. Therefore, design criteria to reduce the friction and prevent the wear have been investigated by examining the influences of the soot abrasive mediating in the thin viscous shear flow area and by clarifying the mechanism and factors of friction and wear.The influences of the engine oil deterioration and contamination with the soot on the total frict … More ional power loss of an actual diesel engine, the friction and wear between a cam and a slipping follower or the friction between a cam and a flat tappet or a roller tappet have been examined. The research results were made obvious as follows. The total friction tends to decrease when the oil is a few deteriorated and contaminated with the soot. The friction and wear for the slipping follower depends on the soot amount, the soot size and the kind and combination of oil additives. When lubricated with the oil contaminated with the soot the friction for the roller tappet tends to increase under the high rotational speed. Tribology characteristics for the oil mixed with the carbon black being substitute for the exhaust gas soot.Accordingly, the following researches should be left in future studies to investigate the factors and mechanism of friction and wear. Actual contacts such as the piston and cylinder or the cam and follower are simulated in a test equipment to visualize the dynamically loaded sliding and rolling lubricated surfaces.The characteristics of a dynamically viscous shear flow for the oil mixed with the soot is clarified by observing the behavior of soot particles and the occurrence of oil starvation and by calculating the oil film thickness and pressure distributions analytically. It is examined how much the tribo-chemically reacted film is formed under the oil deterioration and contamination with the soot. It is a key to examine the influences of the soot amount and particle size distribution on the friction and wear, those of the nominal and effective oil viscosities, those of the kinds and combination of oil additives and so on. Less