Fuel pump assembly

Abstract

A fuel pump assembly for use in an engine comprising a pumping plunger which is reciprocable, in use, under the influence of an associated drive arrangement so as to cause pressurisation of fuel within a pumping chamber. The drive arrangement includes a shoe and a roller which is cooperable with a driven cam so as to impart reciprocal movement to the shoe as the cam is driven, in use. The roller has a first surface area region having a first surface roughness and a second surface area region having a second surface roughness higher than the first surface roughness and in that static friction between the roller and the cam is larger than static friction between the roller and the shoe.

1 . A fuel pump assembly for use in an engine, the fuel pump assembly comprising: 
 a pumping plunger ( 14 ) which is reciprocable, in use, under the influence of an associated drive arrangement ( 24 ,  26 ) so as to cause pressurisation of fuel within a pumping chamber ( 22 ),    the drive arrangement including a shoe ( 24 ) and a roller ( 26 ) which is cooperable with a driven cam ( 28 ) so as to impart reciprocal movement to the shoe ( 24 ) as the cam ( 28 ) is driven, in use,    characterised in that the roller ( 26 ) has a first surface area region ( 54 ) having a first surface roughness and a second surface area region ( 52 ) having a second surface roughness higher than the first surface roughness and in that static friction between the roller ( 26 ) and the cam ( 28 ) is larger than static friction between the roller ( 26 ) and the shoe ( 24 ).    
   
   
       2 . A fuel pump as claimed as in  claim 1 , wherein the first surface area region ( 54 ) and the second surface area region ( 52 ) are provided on an outer surface ( 50 ) of the roller ( 26 ).  
   
   
       3 . A fuel pump assembly as claimed in  claim 1 , wherein the shoe ( 24 ) has a bearing surface ( 49 ) for the roller ( 26 ), the bearing surface ( 49 ) being shaped so that, in use, the first surface area region ( 54 ) does not contact the bearing surface ( 49 ).  
   
   
       4 . A fuel pump assembly as claimed in  claim 3 , wherein the bearing surface ( 49 ) is shaped to having a recess ( 56 ) that corresponds substantially with the first surface area region ( 54 ) of the roller ( 26 ).  
   
   
       5 . A fuel pump assembly as claimed in  claim 4 , wherein the size of the recess ( 56 ) has a width substantially the same or larger than the width of the first surface area region ( 54 ).  
   
   
       6 . A fuel pump assembly as claimed in  claim 1 , wherein the first surface area region ( 54 ) is a band extending around the roller ( 26 ).  
   
   
       7 . A fuel pump assembly as claimed in  claim 1 , wherein the roller ( 26 ) has a third surface area region ( 52 ) having substantially the same surface roughness as the second surface area region ( 52 ), the second and third surface area regions ( 52 ) being positioned either side of the first surface area region ( 54 ).  
   
   
       8 . A fuel pump assembly as claimed in  claim 7 , wherein the surface roughness of both the second and third surface area regions ( 52 ) is higher than the first surface roughness.  
   
   
       9 . A fuel pump assembly as claimed in  claim 7 , wherein the first surface area region is approximately midway along the length of the roller ( 26 ).  
   
   
       10 . A fuel pump assembly for use in an engine, the fuel pump assembly comprising: 
 a pumping plunger ( 14 ) which is reciprocable, in use, under the influence of an associated drive arrangement ( 24 ,  26 ) so as to cause pressurisation of fuel within a pumping chamber ( 22 ),    the drive arrangement including a shoe ( 24 ) and a roller ( 26 ) which is cooperable with a driven cam ( 28 ) so as to impart reciprocal movement to the shoe ( 24 ) as the cam ( 28 ) is driven, in use,    characterised in that an outer surface ( 50 ) of the roller ( 26 ) has a first surface area region ( 54 ) having a first surface roughness and a second surface area region ( 52 ) having a second surface roughness higher than the first surface roughness.    
   
   
       11 . A fuel pump assembly as claimed in  claim 10 , wherein the shoe ( 24 ) is adapted so that the static friction between the roller ( 26 ) and the cam ( 28 ) is larger than the static friction between the roller ( 26 ) and the shoe ( 24 ).  
   
   
       12 . A fuel pump assembly for use in an engine, the fuel pump assembly comprising: 
 a pumping plunger ( 14 ) which is reciprocable, in use, under the influence of an associated drive arrangement ( 24 ,  26 ) so as to cause pressurisation of fuel within a pumping chamber ( 22 ),    the drive arrangement including a shoe ( 24 ) and a roller ( 26 ) which is cooperable with a driven cam ( 28 ) so as to impart reciprocal movement to the shoe ( 24 ) as the cam ( 28 ) is driven, in use,    characterised in that the roller ( 26 ) has a first surface area region ( 54 ) having a first surface roughness and a second surface area region ( 52 ) having a second surface roughness higher than the first surface roughness and in that the shoe ( 24 ) has a bearing surface ( 49 ) for the roller ( 26 ), which is shaped to correspond substantially with the first surface area region ( 54 ) of the roller ( 26 ) so that, in use, the first surface area region ( 54 ) does not contact the bearing surface ( 49 ).    
   
   
       13 . A fuel pump assembly as claimed in claim  14 , wherein the bearing surface ( 49 ) is shaped to having a recess ( 56 ) that corresponds substantially with the first surface area region ( 54 ) of the roller ( 26 ).