Common rail for diesel engines

Abstract

A common rail for a diesel engine has a main pipe rail with an axial flow passage. Branch holes are made in the main pipe rail and communicate with the axial flow passage. The main pipe rail is worked to decrease stress concentration near the branch holes. The whole inner peripheral surface of the main pipe rail and the branch holes then is subjected to autofrettage processing to generate a compressive residual stress on the entire inner peripheral surface of the main pipe rail and the branch holes for increasing fatigue strength.

1 . A method for manufacturing a common rail for diesel engines, comprising: providing a main pipe rail having therein a flow passage extending in an axial direction, branch holes extending angularly to the axial direction and communicating with the flow passage; decreasing stress concentration in the vicinity of inner peripheral edges of openings of the branch holes; and subjecting a whole inner peripheral surface of the main pipe rail and the branch holes to autofrettage processing for generating a compressive residual stress on the entire inner peripheral surface of the main pipe rail and the branch holes, thereby increasing fatigue strength for pressure within the common rail.  
   
   
       2 . The method of  claim 1 , wherein the main pipe rail comprises a forging made of a material S45C and having a thick-walled tubular portion.  
   
   
       3 . The method of  claim 1 , further comprising forming flattened surfaces at least at the inner peripheral edges of openings of the branch.  
   
   
       4 . The method of  claim 1 , wherein the step of providing a main pipe rail comprises providing a main pipe rail with boss portions integral with the main pipe rail, the branch holes being in the boss portions and having a predetermined diameter.  
   
   
       5 . A method for manufacturing a common rail for diesel engines comprising: providing a main pipe rail having therein a flow passage extending in an axial direction, branch holes extending angularly to the axial direction and communicating with the flow passage; flattening at least areas of the flow passage adjacent the branch holes to decrease stress concentration; and subjecting a whole inner peripheral surface of the main pipe rail and the branch holes to autofrettage processing for generating a compressive residual stress on the entire inner peripheral surface of the main pipe rail and the branch holes, thereby increasing fatigue strength for pressure within the common rail.  
   
   
       6 . The method of  claim 5 , wherein the main pipe rail comprises a forging made of a material S45C and having a thick-walled tubular portion.  
   
   
       7 . The method of  claim 5 , further comprising forming flattened surfaces at least at the inner peripheral edges of openings of the branch.  
   
   
       8 . The method of  claim 5 , wherein the step of providing a main pipe rail comprises providing a main pipe rail with boss portions integral with the main pipe rail, the branch holes being in the boss portions and having a predetermined diameter.  
   
   
       9 . A method for manufacturing a common rail for diesel engines, comprising: providing a main pipe rail having therein a flow passage extending in an axial direction, branch holes extending angularly to the axial direction and communicating with the flow passage; applying pressing forces to areas of the main pipe rail substantially adjacent the branch holes to decrease stress concentration; and subjecting a whole inner peripheral surface of the main pipe rail and the branch holes to autofrettage processing for generating a compressive residual stress on the entire inner peripheral surface of the main pipe rail and the branch holes, thereby increasing fatigue strength for pressure within the common rail.  
   
   
       10 . The method of  claim 9 , wherein the main pipe rail comprises a forging made of a material S45C and having a thick-walled tubular portion.  
   
   
       11 . The method of  claim 9 , further comprising forming flattened surfaces at least at the inner peripheral edges of openings of the branch.  
   
   
       12 . The method of  claim 9 , wherein the step of providing a main pipe rail comprises providing a main pipe rail with boss portions integral with the main pipe rail, the branch holes being in the boss portions and having a predetermined diameter.  
   
   
       13 . A method for manufacturing a common rail for diesel engines, comprising: providing a main pipe rail having therein a flow passage in an axial direction and branch holes extending through the main pipe rail and communicating with the flow passage; inserting tip ends of branch pipes deeply into the branch holes and beyond an inner peripheral surface of the main pipe rail up to an interior of the flow passage for relaxing stress concentration in the vicinity of the branch holes; firmly connecting the branch pipes to the main pipe rail; and subjecting a whole inner peripheral surface of the main pipe rail and interiors of connections of the branch holes to autofrettage processing.  
   
   
       14 . The method of  claim 13 , wherein the main pipe rail comprises a forging made of a material S45C and having a thick-walled tubular portion.  
   
   
       15 . The method of  claim 13 , further comprising forming flattened surfaces at least at the inner peripheral edges of openings of the branch.  
   
   
       16 . The method of  claim 13 , wherein the step of providing a main pipe rail comprises providing a main pipe rail with boss portions integral with the main pipe rail, the branch holes being in the boss portions and having a predetermined diameter.