Assembled Camshaft for I.C. Engines with Forged Powder Metal Cams

A key element in the Automotive Industry's efforts to improve fuel economy and engine performance is the introduction of roller tappets to reduce friction in valve trains. As a result, contact stresses in excess of 200,000 psi may be experienced at the roller and cam (shaft) interface. Conventional cast iron camshafts cannot effectively carry this stress level. After studying several alternatives, the authors have developed a camshaft which promises to be a viable solution to the problem, both technically and economically. The purpose of this work was to demonstrate the acceptable wear performance of an assembled camshaft containing forged powder metal lobes in a series of motored engine tests with roller hydraulic valve train. In this study, a camshaft consisting of a carbon steel tube and forged powder metal lobes (4660 composition) joined by brazing was tested at low speed and at high speed in a motored engine at approximately 250,000 psi maximum contact stress. Changes in cam lobe surface finish and wear at various locations in the load zone have been monitored. For the purpose of reference, a similar series of tests was performed on a commercially available steel camshaft believed to be machined from bar stock. It was concluded that the powder metal camshaft matched the wear performance of the commercial steel camshaft.