Decreasing of movable masses in valve timing using roller tappet

The method for reduction of valve timing movable masses, by the use of composite cams for camshaft, which mate with roller tappet, is presented. It has been carried out an analysis of stresses under the surface of the cam using the methodology and computer programs allowing the synthesis and analysis of the cam mechanism, and to estimate the fatigue life, as well as using the finite element method. Mating roller tappets with a light camshaft, forged from TiAl alloy, can be done if the camshaft has steel caps set under the pressure on the surfaces their cams. The problem, however, is the formation of high stress in the Bielaiev point, when a roller tappet mates with segment cam. Because of the certainty for the cap fixing, it is assumed that the depth for the Bielaiev point should not exceed half the thickness of the cap. The stress analysis shows, that exceeding of the material yield strength is controlled by the interference value between the cam and its cap and by the apex radius of the cam. Effect of contact stress is at least an order of magnitude smaller. The maximum depth of the Bielaiev point does not exceed 0.09 mm, which is about half the thickness of the proposed cap. There is a need not for too small radii between the cam and the apical cap. Optimal selection of proper geometry of the cam will be easier after a proper modification of the program used for the synthesis and analysis of the cam mechanism, such that it is possible to ask any operational surface of the cam profile.