Oil-starved valve assembly
Reference Number: N 01-02
Inventors: Rao, V. Durga N.; Crosbie, Gary M.
The present invention is an oil-starved valve assembly which is used in an internal combustion engine. The assembly comprises a valve stem guide mounted within the engine. The valve stem guide is provided with an internal bore having a solid film lubricant impregnated therewithin. The solid film lubricant comprises intermixed phases of a dry lubricant which are impregnated into pores, or anchoring sites, in the valve guide which remain after a metal phase is removed by etching.
Within the valve stem guide, a valve is reciprocatingly received. The valve includes an axially extending valve stem which cooperates with the solid film lubricant within the internal bore, thereby reducing friction and oil leakage therebetween.
Conventionally, a valve seat insert is provided within a cylinder head of the engine which may cooperate with the valve head to provide a sealing relationship therebetween. In an alternate embodiment of the invention, the valve seat insert is provided with a solid film lubricant impregnated therewithin.
The invention also comprises a process for preparing the oil-starved valve assembly. The process includes the step of providing a resin suspension of a lubricant selected from the group consisting essentially of boron nitride, molybdenum disulfide, graphite, and mixtures thereof. A metal phase is removed from an intermixed phase composite of the metal, a metal oxide, and silicon carbide, of which the valve component is made. This step creates pores or anchoring sites for retaining the lubricant. The valve component is exposed to the resin suspension of lubricants so that they may infiltrate or permeate the anchoring sites formed within the intermixed phase composite.
The lubricant-impregnated valve component is then exposed to a vacuum environment to expel air from the anchoring sites. After ambient pressure is restored, the lubricant becomes driven or impregnated into the anchoring sites. The valve component and lubricant are then desiccated to create an intermixed composite of solid dry lubricant which is impregnated into the valve component.
By a similar process, the solid dry lubricant may be impregnated into the valve seat insert, thus providing an acceptable combination of lubricity under conditions of minimal, or zero clearance.