Two-step rocker arm having roller element cam followers

Abstract

The invention provides a two-step rocker arm assembly for use in an internal combustion engine in which a plurality of two-step rocker arm assemblies enable the engine poppet valves to switch between two lift profiles. The two-step rocker arm assembly of the present invention has an inner rocker arm assembly and an outer rocker arm assembly. The outer rocker arm assembly is characterized as having two rail portions spaced from each other forming an open space within which at least a portion of the inner rocker arm is disposed. Each of the rail portions and the inner rocker arm assembly has a generally cylindrical roller cam follower rotatably affixed thereto. Preferably, each of the roller element cam followers will be shaft mounted, the shafts being welded to the respective inner rocker arm and outer rocker arm for increased structural rigidity.

1 . A two-step rocker arm assembly comprising: 
 a movable outer rocker arm characterized by two rail portions spaced a distance apart from one another and defining an open space therebetween, each of said rail portions having a generally cylindrical roller element cam follower rotatably attached thereto for engagement with a high-lift cam;    wherein each of said roller element cam followers is disposed at least partially within said outer rocker arm and is rotatable attached to a respective one of said rail portions via an axle, said axle being welded to said respective rail portion;    an inner rocker arm movably connected to said outer rocker arm such that at least a portion of said inner rocker arm is in said open space, said inner rocker arm having another generally cylindrical roller element cam follower rotatably attached thereto for engagement with a low-lift cam; and    wherein said outer rocker arm and said inner rocker arm are selectively lockable for unitary movement.    
   
   
       2 . (cancelled)  
   
   
       3 . The two-step rocker arm assembly of  claim 1 , wherein said roller element cam follower disposed at least partially within said inner rocker arm is rotatably attached to said inner rocker arm via an axle, said axle being welded to said inner rocker arm.  
   
   
       4 . The two-step rocker arm assembly of  claim 1 , further comprising: 
 a torsion spring operatively connected to said inner rocker arm and said outer rocker arm; and    wherein said torsion spring biases said outer rocker arm in a direction to maintain contact between each of said roller element cam follower and its respective high-lift cam or low lift cam.    
   
   
       5 . The two-step rocker arm assembly of  claim 1 , wherein said generally cylindrical roller element cam followers have substantially equal diameters.  
   
   
       6 . The two-step rocker arm assembly of  claim 1 , wherein said inner rocker arm is characterized by a pivot interface for contacting a portion of a hydraulic lash adjustor upon which said inner rocker arm is pivotable.  
   
   
       7 . The two-step rocker arm assembly of  claim 1 , further comprising: 
 a generally cylindrical pivot shaft about which said inner rocker arm and said outer rocker arm are pivotably movable with respect to one another;    a contact pad operable to engage a poppet valve, wherein said poppet valve has rotational symmetry about an axis; and    wherein said pivot shaft is positioned with respect to said contact pad such that when said contact pad engages said valve, said pivot shaft substantially intersects said axis of said poppet valve.    
   
   
       8 . The two-step rocker arm assembly of  claim 1 , wherein said inner rocker arm and said outer rocker arm are investment cast.  
   
   
       9 . A valvetrain comprising: 
 a camshaft having a low-lift cam and two high-lift cams, said two high-lift cams being on opposite sides of said low-lift cam;    a movable outer rocker arm characterized by two rail portions spaced a distance apart from one another and defining an open space therebetween, each of said rail portions having a generally cylindrical roller element cam follower rotatably attached thereto for engagement with a respective one of said high-lift cams;    wherein each of said roller element cam followers is disposed at least partially within said outer rocker arm and is rotatable attached to a respective one of said rail portions via an axle, said axle being welded to said respective rail portion;    an inner rocker arm movably connected to said outer rocker arm such that at least a portion of said inner rocker arm is in said open space, said inner rocker arm having a generally cylindrical roller element cam follower rotatably attached thereto for engagement with said low-lift cam; and    wherein said outer rocker arm and said inner rocker arm are selectively lockable for unitary movement.    
   
   
       10 . (cancelled)  
   
   
       11 . The valvetrain of  claim 9 , wherein said roller element cam follower disposed at least partially within said inner rocker arm is rotatably attached to said inner rocker arm via an axle, said axle being welded to said inner rocker arm.  
   
   
       12 . The valvetrain of  claim 9 , further comprising: 
 a torsion spring operatively connected to said inner rocker arm and said outer rocker arm; and    wherein said torsion spring biases said outer rocker arm in a direction to maintain contact between each of said roller element cam follower and a high-lift cam.    
   
   
       13 . The valvetrain of  claim 9 , wherein said generally cylindrical roller element cam followers have substantially equal diameters.  
   
   
       14 . The valvetrain of  claim 9 , wherein said inner rocker arm is characterized by a pivot interface for contacting a portion of a hydraulic lash adjustor upon which said inner rocker arm is pivotable.  
   
   
       15 . The valvetrain of  claim 9 , further comprising: 
 a generally cylindrical pivot shaft about which said inner rocker arm and said outer rocker arm are pivotably movable with respect to one another;    a contact pad operable to engage a poppet valve, wherein said poppet valve has rotational symmetry about an axis; and    wherein said pivot shaft is positioned with respect to said contact pad such that when said contact pad engages said valve, said pivot shaft substantially intersects said axis of said valve.    
   
   
       16 . A two-step rocker arm assembly comprising: 
 a movable outer rocker arm characterized by two rail portions spaced a distance apart from one another and defining an open space therebetween, each of said rail portions having a generally cylindrical roller element cam follower rotatably attached thereto for engagement with a high-lift cam;    an inner rocker arm movably connected to said outer rocker arm such that at least a portion of said inner rocker arm is in said open space, said inner rocker arm having a generally cylindrical roller element cam follower rotatably attached thereto for engagement with a low-lift cam;    wherein said outer rocker arm and said inner rocker arm are selectively lockable for unitary movement;    wherein each of said roller element cam followers, disposed at least partially within said rail portions, is rotatably attached to its respective rail portion via an axle, said axle being welded to said rail portion; and    wherein said roller element cam follower disposed at least partially within said inner rocker arm is rotatably attached to said inner rocker arm via an axle, said axle being welded to said inner rocker arm.    
   
   
       17 . The two-step rocker arm assembly of  claim 16 , wherein said generally cylindrical roller element cam followers have substantially equal diameters.