Improvements to valve mechanisms with hydraulically actuated secondary opening

摘要

A camshaft assembly comprises a fixed cam 1 and a moveable cam lobe 2 integral with a cylindrical stem 3 which runs in a cylindrical hole 26 in the fixed cam 1. The moveable cam lobe 2 is locked in its active position by hydraulic pressure which is directed into a chamber 10 formed by the base of the stem 3 and the base of the hole 26. and maintained by a one-way valve. When it is required to move the cam to its inactive position the pressure is released by means of a sliding piston 6 mounted in the stem 3 which uncovers a port 14 through which the oil can exit. In another embodiment of the invention the moveable cam lobe 2 is retained in its active position by a lower level of hydraulic pressure and in its retracted position by a higher level of hydraulic pressure. The movable lobe 2 can provide an extra exhaust valve opening event for internal EGR.