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To meet diesel emission regulations, high injection pressure is demanded for the supply pump of electronically controlled common-rail type injection system. DENSO has produced common-rail type injection system in 1999. Cam and roller to generate high pressure in the supply pump at the system are composed of steel and silicon nitride ceramics, and are rolling contact under light oil lubrication. Therefore, rolling contact fatigue failure had been concerned. In order to assure the components, we estimated the influence on the materials and the lubrication on the rolling fatigue strength of silicon nitride ceramics, the contact fatigue life was tested under oil lubrication.

This paper describes the development of the ceramic cam roller follower manufactured from silicon nitride. The impact strength of the ceramic roller was investigated and proven to have sufficient strength and reliability for use in automotive engine applications. Motor simulation tests were conducted in order to study the best design for the ceramic cam roller. Results from testing show that super finishing of the roller surface is necessary in order to prevent severe wear of the metal shaft and cam. Optimum bearing clearance range was also studied. Performance tests were conducted in order to study the wear properties of the ceramic cam roller. Wear of the tested cam shaft when using the ceramic roller, was less than the conventional steel roller, even though the calculated contact stress was higher. The total amount of wear of the valve train components was significantly reduced when using the ceramic cam roller, when compared to the conventional steel roller.