Internal combustion engine and cam drive mechanism therefor

Claim 1

A cam drive mechanism for driving the camshaft of a four-stroke internal combustion engine having one or more sets of n number of cylinders where n is a positive integer, a piston connected to a crankshaft and reciprocable in each cylinder and being either in phase or out of phase with any other piston in the set to which it belongs by a phase angle A°, or an integral multiple thereof, and a camshaft carrying a plurality of rotatable cams for actuating inlet and/or exhaust valves for each cylinder in the set, characterized in the cam drive mechanism comprising means for rotating the camshaft with a rotational movement which is a combination of a circular motion about its axis of rotation which has a predetermined phase relationship with the circular movement of the crankshaft and an oscillatory motion about its axis of rotation to advance and retard the angular position of the cams relative to the valves with which they are associated, the oscillatory motion having a predetermined phase relationship with the crankshaft, and means for varying the amplitude of the oscillatory motion whereby the timing of the opening and closing of the valves may be varied, characterized in that the speed of the circular movement of the camshaft is half the speed of the crankshaft and the frequency of oscillations of the camshaft is f times the frequency of rotation of the crankshaft, wherein: f=2n when the number of engine cylinders n=1; f=n or n/2 when n=2; f=n when n/2= 3 or more; the cam drive mechanism means comprising a rotatable drive member drivable by the crankshaft, and a connection between the drive member and camshaft for transmitting the rotary motion of the drive member thereto, said connection including a sleeve element rotatable by said drive element and axially slidable relative thereto and having a helically splined connection with the camshaft whereby axial movement of the sleeve element effects a rotation of the camshaft relative to the drive member, and means effecting a continuous reciprocation of the sleeve element first in one axial direction and then in the return opposite direction, to provide a continuous oscillatory movement of the camshaft relative to the drive member and crankshaft.