Variable event timing mechanism

A mechanism for enabling the duration of a valve event in an internal combustion engine to be varied, comprising a drive shaft (10) rotatable in synchronism with the engine crankshaft, a cam sleeve (12) rotatably mounted on the drive shaft for opening and closing an engine valve and a drive member (14) coupled to the drive shaft and the cam sleeve. The drive member (14) is mounted for rotation about an axis parallel to that of the drive shaft and its axis is variably offset from the drive shaft axis. The extent of the offset of the axis of the drive member (14) serves to vary the phase of the cam sleeve relative to the drive shaft cyclically thereby superimposing a variable amplitude oscillation on the steady rotation of the cam sleeve by the drive shaft to vary the valve event duration.In the invention, the means for coupling the drive member (14) for rotation with the drive shaft (10) includes a pin (20) fixedly received in a radial bore (22) in the drive shaft (10). The end of the pin (20) projecting from the drive shaft is pivotably connected to the drive member (14) by means of a link (27) that is pivoted at its respective ends to the pin (20) and drive member (14) about axes that extend parallel to the axis of the drive shaft (10).As an alternative to the provision of an intermediate drive member that can be moved to an eccentric position, the drive shaft may itself be moved to an eccentric position in relation to the axis of rotation of the cams.