Double-Wall Pipe, Method Of Manufacturing The Same And Refrigerant Cycle Device Provided With The Same

Abstract

A double-wall pipe includes an outer pipe, and an inner pipe disposed inside the outer pipe. An outer wall of the inner pipe has thereon a ridge portion, which defines a groove portion extending in a longitudinal direction of the inner pipe. The outer pipe and the inner pipe are bent to have a straight portion extending straightly, and a bend portion bent from the straight portion. In the straight portion, the outer pipe has an inside diameter that is larger than an outside diameter of an imaginary cylinder defined by an outer surface of the ridge portion of the inner pipe. Furthermore, the ridge portion of the inner pipe contacts an inside surface of the outer pipe to be radially squeezed and held by the outer pipe, in the bend portion. The double-wall pipe can be suitably used for a refrigerant cycle device.

What is claimed is: 
     
         1 . A method of manufacturing a double-wall pipe including an outer pipe and an inner pipe, the method comprising the steps of:
 forming a groove portion extending in a longitudinal direction on an outer wall of the inner pipe, so as to form thereon a ridge portion defining the groove portion;   inserting the inner pipe into the outer pipe having an inside diameter greater than an outside diameter of an imaginary cylinder defined by an outer surface of the ridge portion of the inner pipe, after the groove portion is formed; and   bending a part of both the inner pipe and the outer pipe after the inserting step, to form a bend portion in such a manner that the ridge portion contacts an inside surface of the outer pipe by radially squeezing and deforming the outer pipe in the bend portion, thereby the outer pipe squeezes the inner pipe radially to hold and fix the inner pipe therein in the bend portion.   
     
     
         2 . The method according to  claim 1 , wherein:
 in the forming step of the groove portion, a helical groove of the groove portion extending helically in the longitudinal direction is formed by deforming radially inside the outer wall of the inner pipe.   
     
     
         3 . The method according to  claim 1 , wherein:
 in the forming step of the groove portion, the groove portion is formed to have a groove depth in a range of 5% to 15% of an outside diameter of the inner pipe.   
     
     
         4 . The method according to  claim 1 , wherein:
 in the forming step of the groove portion, the groove portion is formed to have a longitudinal length in a range of 300 mm to 800 mm.   
     
     
         5 . The method according to  claim 1 , wherein the inner pipe is formed in such a manner that an outside diameter of the outer pipe is in a range of 1.1 to 1.3 times of an outside diameter of the inner pipe. 
     
     
         6 . The method according to  claim 5 , wherein the bending step is performed in such a manner that a minimum outside diameter of the outer pipe in the bend portion is equal to or larger than 0.85 times of an outside diameter of the outer pipe in the straight portion. 
     
     
         7 . The method according to  claim 1 , wherein the forming step of the groove portion is performed such that the outside diameter of an imaginary cylinder defined by an outer surface of the ridge portion is in a range of 0.7 to 0.95 times of an inside diameter of the outer pipe. 
     
     
         8 . The method according to  claim 1  further comprising:
 forming a branch pipe branching out from an end part of the outer pipe. 
 
     
     
         9 . The method according to  claim 8 , further comprising:
 connecting a connection pipe to an end of the inner pipe.   
     
     
         10 . The method according to  claim 9 , further comprising:
 forming a holding member for fixedly holding the branch pipe and the connecting pipe in a predetermined positional relation.   
     
     
         11 . The method according to  claim 10 , wherein the holding member is fixed to the branch pipe and the connecting pipe by blazing or fastening. 
     
     
         12 . The method according to  claim 10 , wherein the holding member is fixedly put on the branch pipe and the connecting pipe. 
     
     
         13 . The method according to  claim 8 , further comprising
 adjusting an end position of the branch pipe.   
     
     
         14 . The method according to  claim 13 , wherein a bend portion is formed in the branch pipe before the end portion of the branch pipe is adjusted. 
     
     
         15 . The method according to  claim 1 , wherein at least one of the bend portions is formed in a longitudinal length of 700 mm of the outer pipe and the inner pipe.