Abstract:
A joint for joining a double pipe, which is provided with an outer pipe for transfer of a first fluid, and an inner pipe for transfer of a second fluid. The joint is provided with a flange including a first through bore and a second through bore, a branch portion and a connection pipe having a first end and a second end, the first end being brazed with the inner pipe of the double pipe and the second connection portion being inserted into the second through bore and defining a second portion for connection of the second circuit pipe, whereby the connection pipe transfers second fluid between the second circuit pipe and the outer pipe of the double pipe. The branch portion is provided with a first connection portion for connection of the first circuit pipe, the first connection portion being inserted into the first through bore.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a joint for connecting double pipes, each of which is provided with an outer pipe, an inner pipe supported inside of the outer pipe and connection ribs for connecting the outer pipe and the inner pipe and is integrally formed by extrusion forming or drawing forming, and a brazing method for brazing the joint with the double pipes. 
   2. Description of the Related Art 
   Conventional double pipe is provided with an outer pipe for transfer of a first fluid and an inner pipe for transfer of a second fluid. The double pipe is categorized as two types in a viewpoint of production methods thereof. According to a first type, the outer pipe and the inner pipe inserted thereto, which are individually produced, are ironing-formed so that projections formed on an inner surface of the outer pipe are press-welded to an outer surface of the inner pipe, thereby the inner and outer pipes are formed to be a double pipe. According to a second type, the outer pipe, the inner pipe and ribs for connecting the outer pipe and the inner pipe are integrally formed by extrusion forming or drawing forming. The double pipe of the second type is heavily used because of a low production cost thereof. 
   Japanese Patent No. 2595578 discloses a related art of a joint for a double hosepipe made of rubber. 
   SUMMARY OF THE INVENTION 
   The joint of the related art cannot be applied for connecting a double pipe of the second type but the first type. Therefore the double pipe of the second type has no means for easy connection. 
   The present invention is achieved in view of the above problem and is intended for providing a joint preferably applied for connecting double pipes having an outer pipe, an inner pipe supported inside of the outer pipe and connection ribs for connecting the outer pipe and the inner pipe which are integrally formed by extrusion forming or drawing forming. 
   A joint of the present invention is applied for joining a first double pipe to a second double pipe, where each of the first and second double pipes is provided with an outer pipe for transfer of a first fluid, an inner pipe for transfer of a second fluid and plural ribs for connecting the outer pipe and the inner pipe. 
   According to a first aspect of the present invention, the joint is provided with a first connection portion for connection of the outer pipe of the second double pipe, a second connection portion for connection of the inner pipe of the second double pipe and a branch portion. The branch portion is provided with an inner flow path which communicates with the first connection portion so as to transfer the first fluid, a first junction portion for joining the outer pipe of the first double pipe and a second junction portion for joining the inner pipe of the first double pipe. The outer pipe of the first double pipe is brazed with the first junction portion so as to communicate with the inner flow path and transfer the first fluid. The second junction portion is provided with a through hole and a first support portion for supporting brazing filler metal for brazing the inner pipe of the first double pipe with the second junction portion. The first junction portion is further provided with a stopper for stopping an end of the outer pipe of the first double pipe so that the first double pipe is disposed at an appropriate position for brazing and the inner pipe thereof passes through the through hole and communicates with the second connection portion. 
   Preferably, the first support portion is formed as a conical recess on an inside of the second junction portion. 
   More preferably, the first support portion is shaped so as to keep a molten pool of the brazing filler metal when the first support portion is faced upward. 
   More preferably, the second junction portion is further provided with a barrier member for preventing the molten pool from flowing out. 
   More preferably, the first connection portion and the second connection portion are formed as male or female components. 
   More preferably, the second connection portion is formed at an end portion of the inner pipe of the first double pipe. 
   More preferably, the joint is further provided with a connection pipe, wherein a first end thereof is brazed with an end portion of the inner pipe and a second end thereof is formed as the second connection portion. 
   More preferably, the first end of the connection pipe is further provided with a second support portion for supporting brazing filler metal. 
   More preferably, the second support portion is shaped so as to keep a molten pool of the brazing filler metal when the second support portion of the connection pipe is face upward. 
   More preferably, the brazing filler metal is sandwiched between an outer wall of the branch portion and the second support portion. 
   More preferably, the joint is further provided with a gap held between the inner pipe of the first double pipe and the through hole of the second junction portion so that molten brazing filler metal supported by the first support portion flows through the gap to braze the connection pipe with the inner pipe of the first double pipe. 
   The first double pipe with a partly removed outer pipe so as to expose the inner pipe thereof is disposed so as to dispose an end of the outer pipe close to the first junction portion and project the inner pipe from the through hole. Brazing filler metal is supported on the first support portion and the first support portion is faced upward. When the branch portion is heated so as to melt the brazing filler metal, the outer pipe and the inner pipe are simultaneously brazed with the first junction portion and the second junction portion. 
   According to a second aspect of the present invention, the joint is provided with a first connection portion for connection of the outer pipe of the second double pipe, a second connection portion for connection of the inner pipe of the second double pipe, a branch portion, a connection pipe and a gap held between the through hole of the second junction portion and the inner pipe of the first double pipe. The branch portion is provided with an inner flow path which communicates with the first connection portion so as to transfer the first fluid, a first junction portion for joining the outer pipe of the first double pipe and a second junction portion for joining the inner pipe of the first double pipe. The outer pipe of the first double pipe is brazed with the first junction portion so as to communicate with the inner flow path so as to transfer the first fluid. The second junction portion is provided with a through hole and a first support portion for supporting brazing filler metal for brazing the inner pipe of the first double pipe with the second junction portion. The inner pipe of the first double pipe passes through the through hole. The connection pipe is provided with a second support portion for supporting brazing filler metal so that the brazing filler metal is sandwiched between the second support portion and the branch portion. The gap is held between the through hole of the second junction portion and the inner pipe of the first double pipe so that molten brazing filler metal supported by the second support portion is pumped through the gap to braze the inner pipe of the first double pipe with the second junction portion by a capillary phenomenon. 
   Preferably, the second junction portion is further provided with a barrier member for preventing the molten brazing filler metal from flowing out. 
   More preferably, the joint is further provided with a flange for connection of the first connection portion and the second connection portion. The first connection portion is rotatably fixed to the flange. The first connection portion or the second connection portion can be caulked so as to steadily fix the flange. 
   The first double pipe with a partly removed outer pipe so as to expose the inner pipe thereof is disposed so as to dispose an end of the outer pipe close to the first junction portion and project the inner pipe from the through hole. Brazing filler metal is supported on the first junction portion and the second support portion. When the branch portion is heated so as to melt the brazing filler metal, the outer pipe is brazed with the first junction portion. Further, the molten brazing filler metal partly flows into a gap between the second junction portion and the inner pipe, thereby the outer pipe is brazed with the first junction portion, the inner pipe is brazed with the connection pipe and the inner pipe is brazed with the second junction portion. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic drawing of an air conditioner for an automobile to which a joint of the present invention is applied; 
       FIG. 2  is a perspective view of a double pipe; 
       FIG. 3A  is a plan view of a joint for the double pipe according to a first embodiment of the present invention; 
       FIG. 3B  is a partial cross-sectional view of the joint according to the first embodiment of the present invention; 
       FIG. 4A  is a cross-sectional view of a flange of the joint for connecting a first connection portion and a second connection portion of the double pipe according to the first embodiment of the present invention; 
       FIG. 4B  is a cross-sectional view of the flange after connecting the first connection portion and the second connection portion; 
       FIG. 5A  is a cross-sectional view of a certain part of the double pipe and the joint before blazing according to the first embodiment of the present invention; 
       FIG. 5B  is a cross-sectional view of a certain part of the double pipe and the joint during blazing according to the first embodiment of the present invention; 
       FIG. 6  is a cross-sectional view of the certain part of the double pipe and the joint showing a blazing procedure according to the first embodiment of the present invention; 
       FIG. 7  is a plan view of a joint according to a second embodiment of the present invention; 
       FIG. 8  is a cross-sectional view of a joint according to a third embodiment of the present invention; 
       FIG. 9  is a cross-sectional view of a joint according to a fourth embodiment of the present invention; 
       FIG. 10  is a plan view of a joint according to a fifth embodiment of the present invention; 
       FIG. 11  is a cross-sectional view of the joint according to the fifth embodiment of the present invention; 
       FIG. 12A  is a cross-sectional view of a certain part of a joint according to the sixth embodiment of the present invention; 
       FIG. 12B  is a cross-sectional view of a certain part of the joint according to the sixth embodiment of the present invention; 
       FIG. 13  is a cross-sectional view of a joint according to a seventh embodiment of the present invention; 
       FIG. 14A  is a cross-sectional view of a certain part of the joint according to the seventh embodiment of the present invention; 
       FIG. 14B  is a cross-sectional view of the certain part of the joint according to the seventh embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   (A First Embodiment) 
   A first embodiment of the present invention will be described hereinafter with reference to  FIGS. 1–6B . 
   A dual type of an air conditioner shown in  FIG. 1  is usually employed for a so-called one-box car. The air conditioner is provided with a front-seat air conditioner  10  for mainly air-conditioning of front seats, a rear-seat air conditioner  20  for mainly air-conditioning of rear seats. The rear-seat air conditioner  20  is installed in a vicinity of a center or a rear side of a car compartment. Air is taken from intake units  11 ,  21  and is conducted to evaporators Ef, Er so as to be cooled. The cooled air is appropriately heated by heater cores Hf, Hr and is blown out of outlet ports  12 ,  22  to the car compartment. Mixing doors  13 ,  23  for mixing the air which flows through the heater cores Hf, Hr and the air which by-passes the heater cores Hf, Hr are rotatably fixed to the respective heater cores Hf, Hr. The temperature of the air from the outlet ports  12 ,  22  is controlled by angles of the mixing doors  13 ,  23  so as to be favorable. 
   The evaporators Ef, Er, like the one commonly known, exchange heat between the air conducted thereto and cooling media which are expanded and cooled at expansion valves Vf, Vr so that the air is cooled. The heater cores Hf, Hr exchange heat between the air and an engine coolant which is heated by car engine so that the air is heated. 
   The front evaporator Ef, the rear evaporator Er, a compressor  31 , a condenser  32 , a liquid tank  33  and the expansion valves Vf, Vr are connected by coolant circuit pipes so that cooling cycle is constituted. A cooling medium which flows out of the liquid tank  33  and has a relatively high temperature and a relatively high pressure is branched into two by coolant circuit pipes  34 ,  35  branched in an engine room. The two flows of the cooling media are respectively conducted to the front evaporator Ef and the rear evaporator Er. The cooling media which respectively flow out of the front evaporator Ef and the rear evaporator Er and has relatively low temperatures and relatively low pressures flow through the coolant circuit pipes  36 ,  37  and interflow in the engine room so as to be drawn into the compressor  31 . 
   According to the dual type air conditioner, double pipes are applied to the coolant circuit pipes between the rear evaporator Er and the cooling cycle. The dual type air conditioner includes a first double pipe  100  connected to the coolant circuit pipes  35 ,  35  and a second double pipe  200  connected to the rear evaporator Er. The first double pipe  100  and the second double pipe  200  are connected with each other via a joint  40 . Outer pipes  101 ,  201  of the respective double pipes  100 ,  200  conduct evaporated low pressure cooling medium from the rear evaporator Er and inner pipes  102 ,  202  conduct condensed high pressure cooling medium from the liquid tank. The joint  50  communicates one end of the outer pipe  101  with the coolant circuit pipe  37  and also communicates one end of an inner pipe  102  with the coolant circuit pipe  35 . In the same way, the joint  60  communicates one end of the outer pipe  201  with an outlet pipe  24  connected with an outlet port of the rear evaporator Er and also communicates one end of the inner pipe  202  with an valve inlet pipe  25  connected with an inlet port of the expansion valve Vr. 
   The double pipe  100  is provided with the outer pipe  101 , the inner pipe  102  and connection ribs  103  which connects the outer pipe  101  with the inner pipe  102  as shown in  FIG. 2 . The double pipe  100  is made of aluminum and is integrally formed by means of extrusion forming or drawing forming. An outer diameter of the outer pipe  101  is approximately in a range from 16 to 25 mm and an outer diameter of the inner pipe  102  is approximately in a range from 6 to 12 mm. Three connection ribs  103  are provided between the outer pipe  101  and the inner pipe  102  at even intervals. Such a structure has a good balance of hardness distribution thereof against a triaxial bending deformation so that a high design freedom is assured. The structure also has a good balance concerning with extrusion forming. The double pipe  200  is formed as the same method and a detailed description thereof is omitted. 
   The double pipes  100 ,  200  in the present embodiment have merits described hereinafter in comparison with a case where coolant circuit pipes are individually and respectively applied to the low pressure cooling medium and the high pressure cooling medium. The double pipes  100 ,  200  have a high stiffness against bending stress so that limitations of production conditions such as a bending speed are reduced and productivity thereof is increased. The number of pipes is decreased because two pipes are substituted for one double pipe, thereby a production process is improved and a cost thereof is reduced. It is uneasy to happen that the double pipes are accidentally bent in course of transportation or installation to a car body. The installation comes to be easy and a cost thereof is reduced because the double pipe need not be fixed with brackets. 
   A constitution of the joints  50 ,  60  will be described hereinafter with reference  FIGS. 3A ,  3 B,  4 A and  4 B. The joint  60  is constituted substantially as same as the joint  50 , therefore a description will be given concerning with the joint  50 . 
   In the vicinity of one end of the double pipe  100 , the outer pipe  101  and the connection ribs  103  are partially removed and the inner pipe  102  is partially exposed as shown in  FIG. 3B . The joint  50  is brazed to such a processed end of the double pipe  100 . The processed end of the outer pipe  101  will be referred as an outer pipe end portion  101   a  hereinafter and the exposed end of the inner pipe  102  will be referred as an inner pipe end portion  102   a.    
   The joint  50  is provided with a first connection portion  51  for connecting a coolant circuit pipe  37  which conducts the low pressure cooling medium, a second connection portion  52  for connecting a coolant circuit pipe  35  which conducts the high pressure cooling medium and a branch portion  500 . The branch portion  500  includes an inner flow path  540  formed therein for conducting the evaporated low pressure cooling medium to the first connection portion  51 . The branch portion  500  is further provided with a first junction portion  510  for joining the outer pipe end portion  101   a  and the branch portion  500  so as to communicate the outer pipe  101  with the inner flow path  540 , a wall portion  502  which the inner pipe end portion  102   a  penetrates and a second junction portion  520  for joining the wall portion  502  and the inner pipe end portion  102   a  so as to communicate the inner pipe  102  with the second connection portion  52 . 
   The branch portion  500  includes a base portion  500   a  at a lower side thereof according to  FIG. 3B , which is formed in a substantially cubic shape, and a tubular portion  500   b  formed integrally with the base portion  500   a . The tubular portion  500   b  also forms the first connection portion  51 . The wall portion  502  is provided with a through hole  541  through which the inner pipe  102  passes. An opening  542  penetrating the wall  503  is formed on a wall  503  opposite to the wall portion  502 . An inner diameter of the opening  542  is in accordance with the outer diameter of the outer pipe  101 . The opening  542  forms the first junction portion  510  and the through hole  541  forms the second junction portion  520 . The through hole  541  and the opening  542  are coaxially aligned. Thereby the inner pipe  102  projected from the outer pipe end portion  101   a  passes through the inner flow path  540  and is straightly extended so as to penetrate the wall portion  502 . 
   The branch portion  500  can be made of various appropriate metals, for example, aluminum. A forming method thereof is not particularly limited but is exemplified as a cutting method. A butt joint method, where press-formed plural bodies are joined together, can be applied. 
   An inner surface of the opening  542  is stepped and projected inward so as to be a stopper  511  which abuts a tip of the outer pipe end portion  101   a . The outer pipe end portion  101   a  is appropriately positioned by abutting the stopper  511 . 
   The second junction portion  520  is provided with a support portion  523  for supporting a brazing filler metal  522  to be applied for brazing the inner pipe  102  there with. The support portion  523  is positioned inside the second junction portion  520  and is formed to be a conical recess on the inside of the second junction portion  520 . When the inner pipe  102  is brazed to the second junction portion  520 , a periphery  523   a  of the support portion  523  is faced upward so as to temporarily support the brazing filler metal  522  and keep the molten brazing filler metal  522  therein. The conical recess shape of the support portion  523  effectively conducts the molten brazing filler metal  522  to a small gap between the through hole  541  and the outer surface of the inner pipe  102 . 
   The double pipe  100  is inserted through the opening  542  into the branch portion  500 . The outer pipe end portion  101   a  abuts the stopper  511  so as to be brazed to the first junction portion  510 . The exposed inner pipe  102  is brazed to the second junction portion  520 . 
   According to the first embodiment, the inner pipe end portion  102   a is further provided with a connection pipe  550  brazed therewith. A second end  550   b  of the connection pipe  550  forms the second connection portion  52 . A brazed portion where the inner pipe end portion  102   a  is brazed to an end  550   a  of the connection pipe  550  will be referred as a third junction portion  530  hereinafter. 
   An end of the third junction portion  530  is formed tapered so as to be a support portion  533  for supporting a brazing filler metal  532 . When the connection pipe  550  is brazed to the inner pipe end portion  102   a , an aperture  533   a  of the support portion  533  is faced upward so as to temporarily support the brazing filler metal  532  and keep the molten brazing filler metal  532  therein. The tapered shape of the support portion  533  effectively conducts the molten brazing filler metal  532  to a small gap between the outer surface of the inner pipe  102  and the inner surface of the connection pipe  550 . 
   A size in which the inner pipe  102  is projected from the wall portion  502  and a dimension of the end  550   a  of the connection pipe  550  are determined so that the end  550   a  comes close to the wall portion  502 . The brazing filler metal  532  is sandwiched between the wall portion  502  and the end  550   a  so as to be supported in the support portion  533 . (as shown in  FIG. 5A ) Thereby the brazing filler metal  532  is prevented from displacing. 
   The first connection portion  51  is connected with the second connection portion  52  via a flange  560  shaped like a sheet. The flange  560  is provided with a through hole  561  to which the first connection portion  51  is inserted, a through hole  562  to which the second connection portion  52  and a bolt hole  563  to which fastening means such as a bolt  169  is inserted. 
   Before fixing the first connection portion  51  and the second connection portion  52  to the flange  560 , both the first connection portion  51  and the second connection portion  52  have straight tubular shapes. First, the first connection portion  51  is rotatably fixed to the through hole  561  of the flange  560  so that an angular position of the flange  560  to the first connection portion  51  can be regulated. Next, the end portion of the first connection portion  51  is caulked outward so that the angular position of the flange  560  is fixed. The end portion of the second connection portion  52  is caulked outward and fixed to the through hole  562  in the same way. The end  550   a  of the connection pipe  550  is brazed to the inner pipe end portion  102   a  so that the flange  560  is further fixed to the first connection portion. 
   According to the first embodiment, both the first connection portion  51  and the second connection portion  52  are female components and both the coolant circuit pipes  35  and  37  which are respectively connected with the connection portions  51  and  52  are male components. The coolant circuit pipes  35 ,  37  need to be projected from the opposite flange  166  as drawn in double-dotted lines in  FIG. 3B . O-rings  167 ,  168  are installed to the respective coolant circuit pipes  35 ,  37  at distal ends thereof. 
   Procedures of connecting the coolant circuit pipes  35 ,  37  to the double pipe  100  are as follows. First, the coolant circuit pipe  37  is engaged with the first connection portion  51  and the coolant circuit pipe  35  is engaged with the second connection portion  52 . Next, the opposite flange  166  and the flange  560  are fastened with the bolt  169 . Then the outer pipe  101  is communicated with the coolant circuit pipe  37  via the inner flow path  540  and the inner pipe  102  is communicated with the coolant circuit pipe  35  via the connection pipe  550  so that a connection of the double pipe  100  is finished. The O-rings  167 ,  168  prevent leakage of the cooling medium. The coolant circuit pipes  35 ,  37  can be fixed to the flange  560  with respective screws, then the opposite flange  166  are not necessary. 
   As can be seen in  FIG. 3B , where the opening  542  is directed to the left and the connection portions  51 ,  52  are directed upward, the coolant circuit pipes  35 ,  37  run at right angle to the double pipe  100 . 
   According to the first embodiment of the present invention, the outer pipe end portion  101   a  and the inner pipe end portion  102   a  are directly inserted to the branch portion  500  and respectively brazed to the first connection portion  510  and the second connection portion  520 , thereby the joint  40  can be preferably applied to the double pipe  100  which are integrally formed. 
   In the meanwhile, the branch portion might be formed in a block-like shape and be provided with another through hole bored therein, then the inner pipe end portion  102   a  and the coolant circuit pipe  35  might be communicated via the through hole. But the block-like shaped branch portion causes an increase of weight of the joint. In comparison with that case, the first embodiment of the present invention improves a weight saving of the joint because the inner pipe end portion  102   a  and the coolant circuit pipe  35  are communicated with a light-weight piping so that the weight of the branch portion  500  is relatively small. 
   Next, a method of brazing the joint  50  with the double pipe  100  where the outer pipe end portion  101   a  is brazed to the first junction portion  510  which is formed on the branch portion  500  and opposed outward, the inner pipe  102  is brazed to the second junction portion  520  and the connection pipe  550  is brazed to the inner pipe end portion  102   a , will be described hereinafter with reference to  FIGS. 5A ,  5 B and  6 . 
   First, the brazing filler metal  532  is put between the wall portion  502  and the end  550   a  of the connection pipe  550  so as to be held in the support portion  533  as shown in  FIG. 5A . The brazing filler metal  532  is formed in a ring shape and includes the metal and flux. 
   Next, the brazing filler metal  512  is put and supported around the outer pipe end portion  101   a  and the brazing filler metal  522  is put and supported around the inner pipe end portion  102   a . Subsequently, the double pipe  100  is inserted into the opening  542 . The brazing filler metals  512 ,  522  are also formed in a ring shape and include the metal and flux. 
   Next, the double pipe  100  is further inserted so that an end tip of the outer pipe end portion  101   a  abuts the stopper  511 . Thereby the outer pipe end portion  101   a  is steadily positioned in the first junction portion  510  and the outer pipe end portion  102   a  passes through the wall portion  502  so as to be engaged with the connection pipe  550 . The brazing filler metal  522  is supported in the support portion  523  and the brazing filler metal  532  is supported in the support portion  533 . 
   Next, the branch portion  500  is positioned so that the periphery  523   a  of the support portion  523  and the aperture  533   a  of the support portion  533  are directed upward. In that state, the branch portion  500 , the first junction portion  510  and the second junction portion  530  are heated so that the brazing filler metals  522 ,  530  and  532  melt and brazing is processed. 
   Thereby brazing of the outer pipe end portion  101   a  with the first junction portion  510 , the inner pipe  102  with the second junction portion  520  and the connection portion  550  with the third junction portion  530  is simultaneously processed. Therefore joining process of the joint  50  and the double pipe  100  is easily and quickly achieved. 
   The first junction portion  510  and the third junction portion  530  are directed outward so that maintenance thereof is easy to be done. On the other hand, the second junction portion  520  is housed in the branch portion  500 . Therefore, if brazing thereof is not completed, the joint  50  and the double pipe  100  in their entirety come to be an inferior product. 
   At this point, the brazing filler metal  522  is supported on the periphery  523   a  of the support portion  523  directed upward so that a molten pool of the brazing filler metal  522  is assuredly supported and the molten metal effectively flows into a small gap between the inner pipe  102  and the through hole  541  by a capillary phenomenon. Therefore the joining of the inner pipe  102  and the second junction portion  520  is assured and has enough strength so that a leakage of the cooling medium from the second junction portion  520  is effectively prevented. Thereby there are few concerns about the inferior product. Supposing that a brazing defect is formed, necessary maintenance thereof is achieved from an outside of the branch portion  500 . 
   Furthermore, the brazing filler metal  532  is supported on the aperture  533   a  of the support portion  533  directed upward so that a molten pool of the brazing filler metal  532  is assuredly supported and the molten metal effectively flows into a small gap between the inner pipe end portion  102   a  and the connection pipe  550  by a capillary phenomenon. Therefore the joining of the connection pipe  550  and the third junction portion  530  is assured and has enough strength so that a leakage of the cooling medium from the third junction portion  530  is effectively prevented. Thereby there are few concerns about the inferior product. Supposing that a brazing defect is formed, necessary maintenance thereof is achieved from an outside of the branch portion  500  because the third junction portion  530  is directed outward. 
   Though heat capacity of the branch portion  500  is relatively larger than one of the outer pipe end portion  101   a , the inner pipe end portion  102   a  or the connection pipe  550 , respective heating rates need to be approximately uniform so as to get a good brazed product. Positions, temperature and heat amount of heating means such as burners and torches are approximately selected so as to uniformly heat the respective members. 
   More preferably, the heating process may include a preliminary heating process of heating the branch portion  500  having large heat capacity and a main heating process of heating the branch portion  500 , the first junction portion  510  and the third junction portion  530  in their entirety. The branch portion  500  is heated up to a predetermined temperature at the preliminary heating process before starting the main heating process. 
   (Modifications of the First Embodiment) 
   According to the first embodiment set forth, the brazing filler metal  522  is put around the inner pipe  102  in advance. The brazing metal  522  may be disposed in the support portion  523  before the inner pipe  102  is inserted thereto. 
   Though three parts are simultaneously brazed according to the first embodiment set forth, simultaneous brazing is not necessary. Brazing concerning with the first junction portion  510  and the second junction portion  520  maybe achieved in advance. The third junction portion  530  may be brazed after that. 
   The aspects and the shapes of the brazing filler metals  512 ,  522  and  532  may be preferably modified. For example, flux may be coated after the brazing filler metals are disposed, instead of applying the brazing filler metal including flux. For example, brazing filler metal is wound around the outer pipe end portion  101   a  and flux is coated thereon after that. 
   More preferably, the first junction portion  510  may also be provided with a support portion like as the support portion  523 ,  533 . 
   More preferably, though the embodiment wherein the first connection portion  51  and the second connection portion  52  are formed as a female type are set forth, they may be formed as union type having union nuts. 
   (A Second Embodiment) 
   A second embodiment of the present invention will be described hereinafter with reference to  FIG. 7 . 
   A joint  50   a  for double pipes of the second embodiment is characterized in a flange  560  which is inclined from a central axis of the double pipe  100  in comparison with the first embodiment set forth. 
   Depending on a piping layout of the air conditioner, a necessity that the coolant circuit pipe  35  must be disposed apart from the axis line of the double pipe  100  may arise. Even in that case, modifications of shapes of the branch portion  500  and the flange  560  and machining of the double pipe  100  should be avoided because such modifications cause an increase of the number of parts and a cost increase. 
   The flange  560  according to the second embodiment is rotatably fixed to the first connection portion  51  as set forth, thereby a direction thereof can be regulated around the first connection portion  51 . According to the second embodiment, a modification in response to a change of the piping layout is limited to curvature of the connection pipe  551 . The branch portion  500 , the flange  560  and the double pipe  100  with no changes from the first embodiment can be applied to the second embodiment. Therefore the second embodiment prevents an increase of the number of parts, an increase of the brazing steps and a change of an inspection so as to contribute a reduction of a production cost of the air conditioner. 
   (A Third Embodiment) 
   A third embodiment of the present invention will be described hereinafter with reference to  FIG. 8 . 
   A joint  50   b  for double pipes of the third embodiment is characterized in a structure of the second junction portion  520  in comparison with the first embodiment set forth. 
   The second junction portion  520  of the third embodiment is provided with a support portion  523  for supporting the brazing filler metal  522  like as the first embodiment. The second junction portion  520  of the third embodiment is further provided with a barrier member  525  for preventing flow-out of the molten brazing metal  522 . The barrier member  525  can be easily formed by means of drilling the branch portion  500  from an upside thereof and from the opening  542 . 
   The barrier member  525  prevents the molten brazing filler metal  522  from flowing out from the support portion  523  in course of a brazing process. Thereby an enough amount of the molten brazing filler metal  522  can be kept in the support portion  523  even if a depth thereof is relatively small. 
   (A Fourth Embodiment) 
   A fourth embodiment of the present invention will be described hereinafter with reference to  FIG. 9 . 
   A joint  50   c  for double pipes of the fourth embodiment is characterized in omitting the connection pipe  550  in comparison with the first embodiment set forth. 
   Though the connection pipe  550  includes the second connection portion  52  according to the first embodiment set forth, the end tip of the inner pipe end portion  102   a  is machined so that the second connection connection portion  52  can be formed integral with the inner pipe  102  according to the fourth embodiment. 
   A portion of the inner pipe  102  projected from the outer pipe  101  is extended so as to supersede the connection pipe  550  of the first embodiment and the inner pipe end portion  102   a  is outspread like a flare to form a second connection portion  52 . The portion outspread like a flare can be formed by means of punching the inner pipe end portion  102   a . If the second connection portion  52  should be formed in a smaller diameter than the inner pipe  102 , the inner pipe end portion  102   a  might be reduced in diameter. 
   According to the fourth embodiment of the present invention, one brazing step is omitted because the third junction portion  530  is omitted. Thereby the fourth embodiment contributes a reduction of a production cost of the air conditioner. 
   (A Fifth Embodiment) 
   A fifth embodiment of the present invention will be described hereinafter with reference to  FIGS. 10 and 11 . 
   A joint  50   d  for double pipes of the fifth embodiment is characterized in a junction structure thereof with the coolant circuit pipes  35 ,  37  in comparison with the first embodiment set forth. 
   The support portion  523  of the fifth embodiment is formed like a bell-mouthed funnel and a bell mouth portion of the funnel is a barrier portion  525 . 
   The first connection portion  51  and the second connection portion  52  is fixed to a flange  660 . The flange  660  is provided with a clip tongue piece  661  fixing around the first connection portion  51 , a through hole  662  to which the second connection portion  52  is inserted and a bolt hole  663  to which fastening means such as a bolt  169  is inserted. 
   The flange  660  is rotatably fixed to the second connection portion  51  with the clip tongue piece  661  so that an angular position of the flange  660  to the first connection portion  51  can be regulated. When a midsection of the second connection portion  52  is fitted to the through hole  662  so, as to be caulked, the angular position of the flange  660  is fixed. The first connection portion  51  is not caulked. A second end  650   b  of the connection pipe  650  forms a second connection portion  52 . A first end  650   a  of the connection pipe  650  is brazed to the inner pipe end portion  102   a  so that the flange  660  is finally fixed. 
   Both the first connection portion  51  and the second connection portion  52  are male components according to the fifth embodiment, though they are female components according to the first embodiment. Both the first connection portion  51  and the second connection portion  52  are further provided with looped grooves and o-rings  667 ,  668  are respectively fitted to the looped grooves. Ends of the coolant circuit pipes  35 ,  37  are formed as female components. The coolant circuit pipes  35 ,  37  are respectively connected to openings  164 ,  165  of the opposite flange  166  as drawn in double-dotted lines in  FIG. 11 . 
   When the coolant circuit pipes  35 ,  35  are connected with the double pipe  100 , first, the connection portion  51  is fitted to the opening  165  and the second connection portion  52  is fitted to the opening  164 . Next, the flange  660  is fixed to the opposite flange  166  with a bolt  169  so that the outer pipe  101  communicates with the coolant circuit pipe  37  via the inner flow path  640  and the inner pipe  102  communicates with the coolant circuit pipe  35  via the connection pipe  650 . 
   Dimension and design of the joint  50   d  can be easily modified depending on modifications about the first connection portion  51  and the second connection portion  52 . Thereby the fifth embodiment assures a design freedom and contributes a reduction of a production cost of the air conditioner. 
   More preferably, though the embodiment wherein the first connection portion  51  and the second connection portion  52  are formed as a male type are set forth, they may be formed as union type having union nuts. 
   (A Sixth Embodiment) 
   A sixth embodiment of the present invention will be described hereinafter with reference to  FIGS. 12A and 12B . 
   A joint  50   e  for double pipes of the sixth embodiment is characterized in a structure of the third junction portion  530  in comparison with the first embodiment set forth. 
   An end  750   a  of a connection pipe  750  is formed tapered so as to be a support portion  733 . When the connection pipe  750  is brazed to the inner pipe end portion  102   a , an aperture  733   a  of the support portion  733  is faced upward. The brazing filler metal is not supported on the support portion  733  but have a function of keeping the molten brazing filler metal therein. 
   An inner peripheral surface of the wall portion  502  and an outer peripheral surface of the inner pipe  102  have a gap S therebetween and a size of the gap S is slightly wider than one of the first embodiment. When the brazing filler metal  522  is melted, the molten brazing filler metal  522  flows through the gap S to the support portion  733 . The molten brazing filler metal  522  supported on the support portion  733  further flows into a small gap between the outer peripheral surface of the inner pipe end portion  102   a  and the inner peripheral surface of the connection portion  750 . The brazing filler metal  522  finally fixes the end  750   a  of the connection pipe  750  to the inner pipe end portion  102   a.    
   According to the sixth embodiment, it is necessary to put an enough amount of the brazing filler metal  522  on the support portion  523 . Therefore preferably, the second connection portion  520  is provided with a barrier member  525  so as to prevent the molten brazing filler metal  522  from flowing out. 
   According to the sixth embodiment, the brazing filler metal  522  can be attached to the inner pipe end portion  102   a  in advance and another brazing metal needs not to be attached in course of brazing process. Therefore brazing can be achieved easier. 
   (A Seventh Embodiment) 
   A seventh embodiment of the present invention will be described hereinafter with reference to  FIGS. 13 ,  14 A and  14 B. 
   A joint  50   f  for double pipes of the seventh embodiment is characterized in a structure of the second junction portion  520  in comparison with the first embodiment set forth. 
   A branch portion  500  of the joint  50   f  is provided with a first junction portion  510  for joining the outer pipe end portion  101   a  and the branch portion  500  so as to communicate the outer pipe  101  with the inner flow path  540 , a wall portion  502  which the inner pipe end portion  102   a  penetrates and a second junction portion  520  for joining the wall portion  502  and the inner pipe end portion  102   a  so as to communicate the inner pipe  102  with the second connection portion  52 . The second junction portion  520  of the sixth embodiment does not include a support portion and a brazing filler metal is not supported on the support portion unlike with the first embodiment. 
   The joint  50   f  is further provided with a connection pipe  850 . A first end  850   a  of the connection pipe  850  is brazed to the inner pipe end portion  102   a  penetrating the through hole  541  and a second end  850   b  forms the second connection portion  52 . The first end  850   a  is formed tapered so as to be a support portion  833  for supporting the brazing filler metal  532 . When the connection pipe  850  is brazed to the inner pipe end portion  102   a , an aperture  833   a  of the support portion  833  is faced upward so as to temporarily support the brazing filler metal  532  and keep the molten brazing filler metal  532  therein. The tapered shape of the support portion  833  effectively conducts the molten brazing filler metal  532  to a small gap between the outer surface of the inner pipe  102  and the inner surface of the connection pipe  850 . 
   An inner peripheral surface of the wall portion  502  and an outer peripheral surface of the inner pipe  102  have a gap S therebetween and a size of the gap S is set so as to pump the molten brazing filler metal  532  there to by a capillary phenomenon. The molten brazing filler metal  532  is supplied to the gap S so that the inner pipe  102  is brazed to the second junction portion  520 . 
   The molten brazing filler metal  532  is prevented from flowing out of the support portion  833  and successfully flows into the gap S by the capillary phenomenon so that the first end  850   a  of the connection pipe  850  is brazed to the inner pipe end portion  102   a.    
   Brazing method of joint  50   f  to the double pipe  100  is described hereinafter. 
   First, the outer pipe end portion  101   a  is disposed in the the first junction portion  510  and the brazing filler metal  512  is disposed therearound. 
   Next, the brazing filler metal  532  is put between the wall portion  502  and the end  850   a  of the connection pipe  850  so as to be held in the support portion  833  as shown in  FIG. 14A . 
   Next, the branch portion  500  and the connection pipe  850  are heated so that the brazing filler metal  532  melts. The connection pipe  850  is brazed to the inner pipe end portion  102   a  and, at the same time, the molten brazing filler metal  532  is partly supplied to the gap between the wall portion  502  and the inner pipe  102  by the capillary phenomenon. The inner pipe  102  is brazed to the second junction portion  520  with the partly supplied metal  532 . 
   According to the seventh embodiment of the present invention, the outer pipe end portion  101   a  and the inner pipe end portion  102   a  are directly inserted to the branch portion  500  and respectively brazed to the first connection portion  510  and the second connection portion  520 , thereby the joint  50   f  can be preferably applied to the double pipe  100  which are integrally formed. Furthermore, brazing filler metal needs not to be disposed in an inside of the branch portion  500  in advance, therefore brazing can be achieved easier. 
   The brazing process of the outer pipe end portion  101   a  and the brazing process of the connection pipe  850  to the inner pipe  102  may be achieved either independently or simultaneously. 
   Preferably, the second junction portion  520  may be further provided with barrier means  526 , as drawn in double-dotted lines in  FIG. 14B , so as to prevent the molten brazing filler metal  532  from flowing out. The barrier means  526  is constituted of a ring-like wall projected from an inside of the wall portion  502  so as to encircle the inner pipe  102 . The barrier means  526  can be a recession or a tapered recession formed on an inside surface of the wall portion  502 . The barrier means  526  may be formed in various shapes so as to prevent the molten brazing filler metal  532  from flowing out. By means of the barrier means  526 , an enough amount of the molten brazing filler metal  532  can be kept so that the inner pipe  102  is more solidly brazed. 
   (A Machining Method of the Double Pipe  100 ) 
   A machining method of the double pipe  100  will be described hereinafter. 
   A slit  104  is circumferentially cut from the outer surface of the outer pipe  101  so as to reach the outer surface  102   a  of the inner pipe  102 . A distance from the end of the double pipe  100  to the slit  104  is in accordance to an exposed length of the inner pipe  102 . Next, distal ends of the connection ribs  103  are cut along an axial direction from the end of the double pipe  100  by a cutting tool which is guided by an inner surface  102   b  of the inner pipe  102  so as to rotate and move along the axial direction. Therefore if the inner pipe  102  is misaligned from a central axis of the double pipe  100 , the cutting tool cuts the connection ribs  103  to keep a thickness of the inner pipe  102 . When the cutting tool reaches the slit  104 , the outer pipe  101  is partly cut off and a predetermined length of the inner pipe  102  is exposed. 
   According to a conventional method, the outer pipe  101  and the connection ribs  103  are grinded off from the outer surface of the outer pipe  101 , thereby burrs are formed on the outer pipe end portion  101   a . A finishing process is necessary to remove the burrs. On the contrary, according to the embodiment of the method, the slit  104  is formed in advance so that the burrs are uneasy to be formed. The finishing process can be omitted. 
   The contents of Japanese Patent Application No. 2002-89786 (filed on Mar. 27, 2002) are incorporated herein by reference in its entirety. 
   Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art, in light of the above teachings.