Valve control mechanism

#This invention relates to a valve control mechanism for an internal combustion engine, to engines containing such mechanisms and to a method of operating the valves of an internal combustion engine.

#Our British Patent No. 2 190 140 describes and claims a valve control mechanism which comprises: a camshaft carrying a plurality of cams, the camshaft being mounted in a cam carrier and being arranged for a limited degree of axial movement and having associated with it means for effecting such movement, each of the cam surfaces having an outline, in a section plane containing the axis of the camshaft, which is not parallel to that axis, whereby in use the valve action is a function of the axial location of the camshaft within the range of permitted axial movement, the mechanism also comprising a cam follower for each cam, the cam follower comprising a one-piece body which reciprocates within a slideway and at one extremity acts upon the end of a valve stem through only a shim and has at the opposite extremity a trough of part-circular cross-section which receives a member in the form of a segment of a circular cylinder, the curved surface of which faces the interior surface of the trough, so that said member can turn with respect to said body, whilst a planar side surface of the member faces the cam surface. The present invention offers developments derived from this earlier valve control mechanism.

#Our British Patent Application No. 2 341 659A (published Mar. 22, 2000) describes and claims, in or for use in an internal combustion engine, a valve control mechanism which comprises: a camshaft carrying a plurality of cams, the camshaft being mounted in, or being adapted to be mounted in, a cylinder head or cam carrier, the valve control mechanism further including means for relatively advancing and retarding the rotation of the camshaft, said advance/retard means comprising a piston housed and axially displaceable within a cylinder, the axial position of said piston being under hydraulic control, and a mechanical coupling between said piston and the camshaft, said mechanical coupling serving to translate the axial movement of said piston into relative rotational movement of said camshaft.

#For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made to the accompanying drawings, in which:

#FIG. 1 is taken from GB 3 341 659A and shows part of an internal combustion engine including a VVLDT system;

#FIG. 2 illustrates a cam profile and how it affects the extent of valve lift; and

#Referring now to FIG. 1 of the drawings, a valve control mechanism of this invention is depicted and comprises an overhead camshaft 4 which carries a plurality of profiled cams 5. Each of the cams 5 cooperates with a half roller 16 which sits in a recess 19 formed on the upper surface of a rectangular cam follower body 6. The half roller 16 is in the form of a segment of a circular cylinder and is free to rotate about its longitudinal axis while seated in the recess 19. Valve stem 1 cooperates with cam follower body 6 and is held in place by retainers 2 (only the upper retainer is shown in the drawings) and compression springs 3.

#The cam profiles are three dimensional, i.e. valve lift varies tangentially with cam angle in end view and varies along the camshaft linearly at each cam angle in side view. If desired, the profile of each cam may be such that a line connecting the points of maximum radial extent of the cam at opposite ends (in the direction of the camshaft axis) thereof is non-parallel to the axis of the camshaft.

#The front end of camshaft 4 is connected to a piston 7 located within a cylinder 9 through the intermediary of a spline 8. The chamber of cylinder 9 is defined by a front plate 10 and by an annular flange 111 integral with plate 10; the rear face 12 of the chamber is part of a housing 13 which contains the spline 8. The inner surface 14 of housing 13 is provided with a screw thread (not shown) which cooperates with spline 8 so that axial movement of the spline relative to the housing 13 causes rotation of the spline.