Valve actuating mechanism

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. In the invention, an element of the valve actuating mechanism transmitting force from one of the cams to the valve stem is formed in two parts, one part movable by the associated cam and the other transmitting force to the valve stem, and a latching mechanism is provided for selectively locking the two parts of the element for movement in unison with one another and disconnecting the two parts of the element from one another to inhibit transmission of force from the associated cam to the valve stem. The latching mechanism is such that a change of state from locked to disconnected and vice versa can only take place when at least one of the two rockers is at or near the base circle of the associated cam and the change of state is initiated by the movement of the rocker system whilst the poppet valve is closed.

1 . An internal combustion engine comprising a poppet valve and a valve actuating mechanism for acting on a stem of the poppet valve to open and close the valve, the valve actuating mechanism including
 two rotatable cams,   a first rocker mounted on a pivot shaft and acting between a first of the two cams and the valve stem, 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, wherein   an element of the valve actuating mechanism transmitting force from one of the cams to the valve stem is formed in two parts, one part movable by the associated cam and the other transmitting force to the valve stem,   a latching mechanism is provided for selectively locking the two parts of the element for movement in unison with one another and disconnecting the two parts of the element from one another to inhibit transmission of force from the associated cam to the valve stem, and   the latching mechanism is such that a change of state from locked to disconnected and vice versa can only take place when at least one of the two rockers is at or near the base circle of the associated cam and the change of state is initiated by the movement of the rocker system whilst the poppet valve is closed.   
   
   
       2 . An internal combustion engine as claimed in  claim 1 , wherein the rocker system actuates a pair of valves, and both valves are adapted to be deactivated simultaneously. 
   
   
       3 . An internal combustion engine as claimed in  claim 1 , wherein the rocker system actuates a pair of valves, and only one valve of the pair is capable of being deactivated. 
   
   
       4 . An internal combustion engine as claimed in  claim 1 , wherein the rocker system actuates a pair of valves, and each valve of the pair may be selectively deactivated. 
   
   
       5 . An internal combustion engine as claimed in  claim 3 , wherein the rocker system actuates a pair of valves, and deactivation one valve of the pair alters the lift characteristic of the second valve. 
   
   
       6 . An internal combustion engine as claimed in  claim 1 , wherein a plunger is mounted in a rocker in such a manner as to permit the plunger to be retracted into the rocker in order to deactivate the associated valve and the latching mechanism serves to inhibit retraction of the lash adjuster so as to cause the valve to be actuated by movement of the rocker. 
   
   
       7 . An internal combustion engine as claimed in  claim 6 , wherein the latching mechanism is hydraulically operated. 
   
   
       8 . An internal combustion engine as claimed in  claim 6 , wherein the latching mechanism is mechanically operated. 
   
   
       9 . An internal combustion engine as claimed in  claim 6 , wherein the latching mechanism exhibits a bistable characteristic such that the operating forces will always drive the latch into a fully locked or fully unlocked position. 
   
   
       10 . An internal combustion engine as claimed in  claim 6 , wherein the latching mechanism is forced into its fully engaged position if the locking system becomes loaded before it has fully disengaged. 
   
   
       11 . An internal combustion engine as claimed in  claim 1 , wherein one of the rockers is formed of two sections that are pivotable relative to one another, one section being cam actuated and the other serving directly or indirectly to actuate a valve, pivoting of the two sections relative to one another serving to deactivate the valve and the latching mechanism being operative to lock the two sections for movement in unison with one another in order to activate the valve. 
   
   
       12 . An internal combustion engine as claimed in  claim 11 , wherein a control spring acts between the two sections of the rocker to ensure that the respective sections maintain a contact force on the cam lobe and the valve tip throughout the operating cycle of the rocker system. 
   
   
       13 . An internal combustion engine as claimed in  claim 11 , wherein the latching mechanism is hydraulically operated. 
   
   
       14 . An internal combustion engine as claimed in  claim 11 , wherein the latching mechanism is mechanically operated. 
   
   
       15 . An internal combustion engine as claimed in  claim 11 , wherein the latching mechanism exhibits a bistable characteristic such that the operating forces will always drive the latch into a fully locked or fully unlocked position. 
   
   
       16 . An internal combustion engine as claimed in  claim 11 , wherein the latching mechanism is forced into its fully engaged position if the locking system becomes loaded before it has fully disengaged. 
   
   
       17 . An internal combustion engine as claimed in  claim 1 , wherein a cam follower is formed in two sections that are slidable relative to one another, one section being cam actuated and the other serving to actuate one of the rockers, sliding of the two sections relative to one another serving to deactivate the valve and the latching mechanism being operative to lock the two sections for movement in unison with one another in order to activate the valve. 
   
   
       18 . An internal combustion engine as claimed in  claim 17 , wherein a control spring acts between the two sections of the cam follower to ensure that the respective sections maintain a contact force on the cam lobe and the corresponding rocker throughout the operating cycle of the rocker system. 
   
   
       19 . An internal combustion engine as claimed in  claim 17 , wherein the latching mechanism is hydraulically operated. 
   
   
       20 . An internal combustion engine as claimed in  claim 17 , wherein the latching mechanism is mechanically operated. 
   
   
       21 . An internal combustion engine as claimed in  claim 17 , wherein the latching mechanism exhibits a bistable characteristic such that the operating forces will always drive the latch into a fully locked or fully unlocked position. 
   
   
       22 . An internal combustion engine as claimed in  claim 17 , wherein the latching mechanism is forced into its fully engaged position if the locking system becomes loaded before it has fully disengaged.