Competitive Surface Interactions of Critical Additives with Piston Ring/Cylinder Liner Components under Lubricated Breaking-In conditions

Abstract

Using a commercial mineral based API SJ/SAE 5W-30 engine oil. a series of breaking-in friction experiments employing a reciprocating tribotester was conducted under simulated engine condition with actual gasoline engine piston rings (Cr-plated, Mo+NiCrBSi-coated and nitrided) and cast iron cylinder liner combinations. Elemental analyses by energy dispersive X-Ray spectroscopy (EDX) of the wear trucks indicate that the antiwear agent ZDTP display higher selectivity than tile Mg- and Ca-containing detergents toward the tribosurfaces of both rings and liners. In particular, the tribosurface activity of the cast iron cylinder liners reacting with ZDTP is higher than that of the mated piston ring tribosurfaces. The tribosurfaces of all the piston rings sliding against the same cast iron liners exhibit almost the same activity when they react with ZDTP. Stronger interaction occurs between the steel tribosurfaces and the non-metallic functional additive elements (S and P), whose hardness or softness as Lewis acids and Lewis bases can be tailored to produce desired interactions. It is suggested that the tribochemical activity of tribosurfaces, which relies on both the thermodynamic properties of the materials and the triboprocesses involved, plays a role in determining the characteristic surface interactions of functional additive elements. Presented at the 56th Annual Meeting in Orlando, Florida May 20–24, 2001