Abstract: A schedule which is logged in terms of engine speed and which is divided into a number of engine operational zones, is used to determine the amount of axial displacement should be induced in a cam shaft on which a specially shaped cam is mounted. The cam has a first section which configured to simultaneously induce a change in valve lift and the valve closure timing, and a second section which maintains the valve closure timing at essentially a fixed value and induces a further increase in valve lift.

Abstract: In a valve train for an I.C. engine, a cam shaft has cams formed with compound curvatures which allow the valve timing to be altered while the engine is operating, to suit the engine driving conditions by shifting the cam shaft along its axis. To reduce the force necessary to shift the cam shaft along its axis the valve closure springs are replaced by closure cams. In some embodiments pivoting arrangements comprising a pair of ball and socket joints are provided to eliminate lateral sway of the rocker arms allowing precise adjustment of the valve timing when the cam shaft is shifted along its axis. In other embodiments the rocker arms are journalled on a rocker shaft provided with stops for preventing lateral sway. In some embodiments the closure rocker arms have cupped ends in which either the valve stem retainer or the valve stem seal is received.