Valve control mechanism

Abstract

An internal combustion engine is disclosed. The engine includes a camshaft carrying a plurality of cams, the camshaft being mounted in a cylinder head or cam carrier; and a valve control mechanism comprising: (a) first means for effecting a limited degree of axial movement of the camshaft; and (b) second means for varying the rotational phase of said camshaft, characterised in that said first and second means comprise a pair of concentric pistons housed within a cylinder and under independent hydraulic control, whereby the concentric pistons can be moved independently of one another. This arrangement enables the valve lift, duration and timing to be varied when the camshaft carries 3-D profiled cam lobes (i.e. valve lift varies tangentially with cam angle in end view and varies along the camshaft linearly at each cam angle in side view).

1 . An internal combustion engine including a camshaft carrying a plurality of cams, the camshaft being mounted in a cylinder head or cam carrier; and a valve control mechanism comprising: (a) first means for effecting a limited degree of axial movement of the camshaft; and (b) second means for varying the rotational phase of said camshaft, characterised in that said first and second means comprise a pair of concentric pistons housed within a cylinder and under independent control, whereby the concentric pistons can be moved independently of one another.  
     
     
         2 . An engine as claimed in  claim 1 , wherein the outer piston serves to control the rotational phase of the camshaft; and the inner piston controls the axial adjustment of the camshaft.  
     
     
         3 . An engine as claimed in  claim 1  or  2 , wherein the camshaft moves axially along a straight spline in a drive chain sprocket sleeve under the action of said inner piston.  
     
     
         4 . An engine as claimed in  claim 3 , wherein said sprocket sleeve has a helical spline on its outer surface, the arrangement being such that movement of said outer piston causes the chain sprocket sleeve to move axially along the camshaft, thereby imparting a rotational movement to said camshaft through the action of said helical spline.  
     
     
         5 . An engine as claimed in any preceding claim, wherein the position of said pistons is controlled hydraulically.  
     
     
         6 . An engine as claimed in  claim 5 , wherein high pressure oil is used as the hydraulic medium.  
     
     
         7 . An engine as claimed in any preceding claim, wherein the cam lobes are mounted on the camshaft in pairs.  
     
     
         8 . An engine as claimed in  claim 7 , wherein the cam bearings are positioned on either side of the cam lobe pairs.