Abstract: A mechanism for actuating an engine poppet valve includes two rotatable cams, a first rocker mounted on a pivot shaft and acting between a first of the two cams and the stem of the valve, and a second rocker mounted for rotation about a fixed axis and acting between the second of the two cams and the pivot shaft of the first rocker to raise and lower the pivot axis of the first rocker cyclically in synchronism with the rotation of the second cam, whereby the valve is operated in dependence upon the instantaneous sum of the lifts of the two cams.

Abstract: A valve operating mechanism is described for an internal combustion engine in which at least one valve (14) of an engine cylinder is operated by two cams (10,12). The cams (10,12) have respective cam followers (38,36) which are resiliently biased to remain in contact with the cams (10,12) at all times and which act on the valve (14) by way of a summation linkage (20,24) in such a manner that the displacement of the valve (14) at any instant is determined by a combination of the displacements of the two cam followers (38,36). In the invention, movement of each of the two cam followers (38,36) is transmitted to the summation linkage (20,24) by way of a respective one of two pushrods (28,30).