Composite Camshafts

Abstract

Composite camshafts have been developed using a variety of techniques to lock the cam profiles on to the camshaft. These include mechanically locking, in situ sintering, brazing, and more recently injection moulding. The work described here is concerned with in situ sintering. A series of sintering trials was undertaken to determine the optimum composition and sintering conditions required to produce suitable cams. Cams were pressed from alloy powders mixed with 2·25%graphite and 0·7% zinc stearate, presintered, positioned on the camshaft and sintered for ∼30 min at 1120°C. Properties such as push off strength and dimensional accuracy were found to be satisfactory. Cam wear results showing the performance of sintered cams running against chilled cast iron and case hardened steel tappets indicated the effect of different tappet materials on the tendency to produce scuffing at greater and lesser levels of load. The lubricant used for the tests was a CEC reference oil, designated RL–85, which was an API ‘SE’ quality oil with the viscosity characteristics of an SAE 15W/50 lubricant. Comparison with similar recent work using the same test oil and tappet material (chilled cast iron) indicated that the sintered iron cams were slightly superior in performance to chilled cast iron cams. Tests with case hardened steel tappets produced slightly poorer results than in earlier work. PM/0555