Tribological characterization of composite powder metallurgy valve train components for heavy duty diesel engines under starved or unlubricated conditions

Abstract

A valve train system which could work in the absence of lubricants could reduce engine oil consumption. Routes to produce such a valve system have been explored, and composites, mostly powder metallurgy (PM) containing solid lubricants, have been tried. The expectation from utilizing these materials, keeping, at least, unchanged the life of engine components, is a reduction in oil consumption and oil fog in the cylinder head and a big environmental benefit. Various sintered materials for three different engine components ‐ valve cap, valve seat and valve guide ‐ have been developed and tested by disk‐on‐disk and fretting tests, in cold and hot conditions, respectively. Prototype components were produced, and the successful ones were then evaluated by an engine endurance test. The sintered valve cap and guide gave very interesting results in terms of friction coefficient and reduction of environmental pollution. Discusses the tribological characterization and the evaluation of these sintered materials.