Cams and cam followers

Abstract

A cam ( 24 ) for use in a fuel pump, the fuel pump having a pump filling phase and a pump delivery phase, wherein the cam ( 24 ) comprises a cam surface ( 18 ) provided with a portion corresponding to the pump filling phase and a portion corresponding to the pump delivery phase. The cam surface ( 18 ) further comprises a channel ( 18, 26, 28 ) suitable for guiding a cam follower ( 30 ) in contact with the cam surface ( 18 ). The width (W, WT, WB) of the channel ( 18, 26, 28 ) is adapted to permit guidance of the cam follower ( 30 ) only for the portion of the cam surface ( 18 ) corresponding to the pump filling phase.

1 . A cam ( 24 ) for use in a fuel pump, the fuel pump having a pump filling phase and a pump delivery phase, wherein the cam ( 24 ) comprises a cam surface ( 18 ) provided with a portion corresponding to the pump filling phase and a portion corresponding to the pump delivery phase, the cam surface ( 18 ) further comprising a channel ( 18 ,  26 ,  28 ) suitable for guiding a cam follower ( 30 ) in contact with the cam surface ( 18 ) characterised in that the width (W, W T , W B ) of the channel ( 18 ,  26 ,  28 ) is adapted to permit guidance of the cam follower ( 30 ) only for the portion of the cam surface ( 18 ) corresponding to the pump filling phase.  
   
   
       2 . A cam ( 24 ) according to  claim 1  wherein the channel ( 18 ,  26 ,  28 ) is substantially narrower than the width of the cam.  
   
   
       3 . A cam ( 24 ) according to  claim 1  or  claim 2  for use in a common-rail fuel pump.  
   
   
       4 . A cam ( 24 ) according to any preceding claim wherein the width (W, W T , W B ) of the channel ( 18 ,  26 ,  28 ) varies around the circumference of the cam ( 24 ).  
   
   
       5 . A common-rail fuel pump suitable for use with an internal combustion engine incorporating a cam ( 24 ) according to any one of the preceding claims.  
   
   
       6 . A common-rail fuel pump according to  claim 5  wherein the common-rail fuel pump is a radial fuel pump.  
   
   
       7 . A method of guiding a cam follower ( 30 ) along the surface ( 18 ) of a cam ( 24 ) for use in a fuel pump, the cam surface ( 18 ) comprising a portion corresponding to a pump filling phase and a portion corresponding to a pump delivery phase, characterised in that guidance is provided by the cam ( 24 ) to the cam follower ( 30 ) only during the pump filling phase.  
   
   
       8 . The method of  claim 7  wherein the channel ( 28 ) presented to the cam follower ( 30 ) varies in width around the circumference of the cam ( 24 ).