Patent Publication Number: US-2021172684-A1

Title: Internal heat exchanger and refrigeration cycle apparatus having the internal heat exchanger

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is a continuation application of International Patent Application No. PCT/JP2019/046331 filed on Nov. 27, 2019, which designated the U.S. and claims the benefit of priority from Patent Application No. 2018-228035 filed in Japan on Dec. 5, 2018, and Patent Application No. 2019-210354 filed in Japan on Nov. 21, 2019, the whole contents of the applications are incorporated by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The disclosure herein relates to an internal heat exchanger usable in a refrigeration cycle and a refrigeration cycle apparatus having an internal heat exchanger. 
     BACKGROUND 
     An internal heat exchanger is used to improve a refrigeration cycle apparatus. The internal heat exchanger performs heat exchanger between a low-pressure refrigerant from an evaporator and a high-pressure refrigerant to the evaporator. The internal heat exchanger is required to improve efficiency. On the other hand, the internal heat exchanger is required to reduce cost. In the above aspects, or in other aspects not mentioned, there is a need for further improvements in an internal heat exchanger and a refrigeration cycle apparatus having an internal heat exchanger 
     SUMMARY 
     The internal heat exchanger according to the disclosure comprises an outer pipe forming an outside pipe of a double pipe and an inner pipe forming an inside pipe of the double pipe. 
     The inner pipe forms, thereinside, an inner flow path through which a refrigerant of a low-pressure side for a refrigeration cycle flows. The inner pipe and the outer pipe form, therebetween, an inner-outer flow path through which the refrigerant of a high-pressure side for the refrigeration cycle flows. The outer pipe has an outer diameter of 30 millimeters or less. A ratio of a difference between an inner diameter of the outer pipe and an outer diameter of the inner pipe to the inner diameter of the outer pipe is 25% or less. 
     The inner pipe and the outer pipe form, therebetween, a concentric structure which increases a flow path cross-sectional area of the inner-outer flow path and arranges the outer pipe and the inner pipe concentrically. The inner pipe has a distal end extending more outwardly in an axial direction than a distal end of the outer pipe. 
     Further, it comprises a connector which interposes between the outer pipe and the inner pipe and a connection target member and defines both a low-pressure communication flow path communicating the inner flow path with a refrigerant passage of the connection target member and a high-pressure communication flow path communicating the inner-outer flow path with a refrigerant flow path of the connection target member. 
     The distal end of the outer pipe is separated from an innermost portion of the outer pipe insertion portion of the connector to form a high-pressure communication space communicating with the high-pressure communication flow path. Further, it comprises an outer pipe side sealing member which is interposed between the outer pipe and the outer pipe insertion portion of the connector to prevent refrigerant leakage from the high-pressure communication space, and an inner pipe side sealing member which is interposed between the inner pipe and the inner pipe insertion portion of the connector to prevent refrigerant leakage from the high-pressure communication space. The double pipe and the connector are mechanically fixed. 
     According to this, since the high-pressure communication flow path and the low-pressure communication flow path of the connector connects the inner-outer flow path and the inner flow path with the refrigerant flow path of the connection target member, it is possible to communicate the inner-outer flow path with the refrigerant flow path of the connection target member without branching the refrigerant pipe from the double pipe (the outer pipe and the inner pipe). Therefore, it is possible to reduce the number of refrigerant pipe branched from the double pipe. 
     Here, “mechanically fixed” means that it is fixed by bolts, screws, caulking, press fitting, etc. That is, fixing by material bonding between base materials such as welding, brazing, and solid phase bonding, and chemical fixing such as adhesion do not correspond to “mechanically fixed”. 
     In the internal heat exchanger according to the disclosure, the inner flow path is used as a low-pressure refrigerant flow path, the inner-outer flow path is used as a high-pressure refrigerant flow path, and the inner diameter of the outer pipe is defined as the inner diameter of the outer pipe. Since the ratio of the difference from the outer diameter of the inner pipe is 25% or less, it is possible to increase the flow path cross-sectional area of the inner flow path and to reduce the flow path cross-sectional area of the inner-outer flow path. Since a pressure loss due to the flow of the refrigerant is larger in the inner passage through which the gas refrigerant flows than in the inner-outer flow path through which the liquid refrigerant flows, increasing a cross-sectional area of the inner flow path leads to an improvement in the efficiency of the refrigeration cycle. 
     In addition, since the ratio of the difference between the inner diameter of the outer pipe and the outer diameter of the inner pipe to the inner diameter of the outer pipe is 25% or less, it becomes easy to align the axes of the inner pipe and the outer pipe. 
     Further, it is possible to suppress the cross-sectional area of the refrigerant flow path (the inner flow path and the inner-outer flow path) as a whole by setting the outer diameter of the outer pipe to 30 millimeter or less. As a result, the amount of refrigerant circulating in the refrigeration cycle is not be unnecessarily increased. Since the amount of refrigerant increases in the inner-outer flow path through which the liquid refrigerant flows, setting a ratio of an average value of differences between an inner diameter of the outer pipe and an outer diameter of the inner pipe with respect to the inner diameter of the outer pipe to 25% or less is desirable to reduce the amount of refrigerant circulating in the cycle. 
     Further, the outer pipe and the inner pipe form, therebetween, a concentric structure which increases a cross-sectional area of the inner-outer flow path and arrange the outer pipe and the inner pipe concentrically, therefore, axes of the inner pipe and the outer pipe are more accurately aligned. Therefore, the sealing members are properly sandwiched and held between both the end portion of the inner pipe and the end portion of the outer pipe and the insertion portion of the connector while inserting and mechanically fixing both the end portion of the inner pipe and the end portion of the outer pipe into the inner pipe insertion portion and the outer pipe insertion portion. 
     According to the internal heat exchanger disclosed, the high-pressure communication space which communicates with the high-pressure communication flow path is formed between the distal end of the outer pipe and the innermost portion of the outer pipe insertion portion of the connector, and this high-pressure communication space is securely sealed by the sealing member arranged on the outer pipe and the sealing member arranged on the inner pipe. 
     The internal heat exchanger according to the disclosure is provided with attachments to which at least one of a service valve, a pressure switch and a pressure sensor is attached to the connector. As a result, the connector can be used as the attachment for a service valve or the like, and the attachment member for the service valve or the like can be eliminated, it is possible to reduce cost. 
     In the internal heat exchanger according to the disclosure, a concentric structure is formed by a structure in which a spiral groove is formed one of the inner pipe or the inner pipe, and a ridge portion of the spiral groove is formed on the other one of the inner pipe and the outer pipe. A surface area is increased by forming the spiral groove, and since the inner pipe and the outer pipe are in contact with each other, it is possible to improve the heat exchange efficiency of the internal heat exchanger. 
     In the internal heat exchanger according to the disclosure, a relationship between the distal end of the inner pipe, the inner pipe side sealing member, the distal end of the outer pipe, the outer pipe side sealing member, and the inner pipe insertion portion and the outer pipe insertion portion of the connector defines a structure in which, at inserting the inner pipe and the outer pipe into the connector, first, the distal end of the inner pipe comes into contact with the inner pipe insertion portion, next, the distal end of the outer pipe comes into contact with the outer pipe insertion portion, after that, the inner pipe side sealing member comes into contact with the inner pipe insertion portion, and finally, the outer pipe side sealing member comes into contact with the outer pipe insertion portion. 
     As a result, the axis alignment is performed between the connector and the inner pipe, after that, the axis alignment is performed between the connector and the outer pipe. Even if the axes of the inner pipe and the outer pipe are slightly deviated, are able to combine smoothly. The inner pipe side sealing member and the outer pipe side sealing member are inserted in a state of being axially aligned with each other. Since the outer pipe side sealing member is inserted after the inner pipe side sealing member is inserted, assembling process becomes smooth. 
     In the internal heat exchanger according to the disclosure, a gap is formed between the distal end of the inner pipe and the innermost portion of the inner pipe insertion portion. According to the internal heat exchanger in the disclosure, a contact portion which comes into contact with the connector is formed on the end portion of the outer pipe in an outer peripheral direction, and a distance of the distal end of the inner pipe and the innermost portion of the inner pipe insertion portion is longer than a distance of the distal end of the outer pipe and the innermost portion of the outer pipe insertion portion. As a result, it is possible to reliably bring the contact portion into contact with the connector by forming a gap between the distal end of the inner pipe and the innermost portion of the inner pipe insertion portion. 
     In the internal heat exchanger according to the disclosure, a portion inside than the distal end at the end portion of the outer pipe is press formed inward in the radial direction of the outer pipe over a predetermined length. That is, the outer pipe is press formed toward the inner pipe so that a diameter is reduced at the end portion. It is possible to align axes of the inner pipe and the outer pipe at ends by this pipe contracting, as a result, a positional alignment when the inner pipe and the outer pipe are inserted into the connector is ensured. 
     According to the internal heat exchanger disclosed, connectors are arranged on both sides of the inner pipe and the outer pipe. In this structure, the internal heat exchanger connects an entire length between the two connectors. Therefore, an amount of heat exchange in the internal heat exchanger is uniquely determined based on the lengths of the inner pipe and the outer pipe. 
     Therefore, the internal heat exchanger disclosed is configured so that the inner pipe and the outer pipe perform, therebetween, heat exchange efficiencies which are different at a part of portion between the inner pipe and the outer pipe and at another portion. As a result, the amount of heat exchange provided by a whole of the internal heat exchanger may be adjusted by adjusting the length of a part of the parts, it is possible to optimize a thermal efficiency of the entire refrigeration cycle. 
     The disclosure provides a refrigeration cycle apparatus having an internal heat exchanger. The refrigeration cycle apparatus includes a compressor, a condenser, an expansion valve for an indoor air-conditioning unit, an evaporator for the indoor air-conditioning unit, and an expansion valve for a rear cooler, an evaporator for the rear cooler, and an internal heat exchanger. 
     The internal heat exchanger comprises a connector located at the end portions of the outer pipe and the inner pipe. This connector is formed with a high-pressure communication flow path for communicating the inner-outer flow path with the refrigerant flow path of the connection target member and a low-pressure communication flow path for communicating the inner flow path with the refrigerant passage of the connection target member. In addition, the internal heat exchanger is interposed between both the condenser and the compressor, and the expansion valve of the indoor air-conditioning unit. Then, the connector connects the high-pressure communication flow path to the condenser and at least one of the expansion valve for the indoor air-conditioning unit and the expansion valve for the rear cooler. Further, the connector connects the low-pressure communication flow path to the compressor and at least one of the expansion valve for the indoor air-conditioning unit and the expansion valve for the rear cooler. 
     Since the refrigeration cycle apparatus according to the disclosure has an internal heat exchanger interposed between both the condenser and the compressor, and the expansion valve of the indoor air-conditioning unit, it is possible to increase enthalpy of both the indoor air-conditioning unit and the rear cooler. In addition, the liquid refrigerant flowing from the condenser to both the indoor air-conditioning unit and the rear cooler can be collected by the internal heat exchanger. 
     Reference numerals in parentheses in each means described in this section and the claims indicate an example of correspondence between the means and specific means described in the embodiment described later. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure is further described with reference to the accompanying drawings in which: 
         FIG. 1  is an overall configuration diagram of a refrigeration cycle apparatus in a first embodiment; 
         FIG. 2  is an overall configuration diagram of an internal heat exchanger according to the first embodiment; 
         FIG. 3  is a perspective view showing a part of an internal heat exchanger according to the first embodiment; 
         FIG. 4  is a cross-sectional view on a line IV-IV of  FIG. 3 ; 
         FIG. 5  is a cross-sectional view showing a part of an internal heat exchanger according to a second embodiment; 
         FIG. 6  is a cross-sectional view showing a part of an internal heat exchanger according to a third embodiment; 
         FIG. 7  is a perspective view showing a part of an internal heat exchanger according to a fourth embodiment; 
         FIG. 8  is a cross-sectional view on a line VIII-VIII in  FIG. 7 ; 
         FIG. 9  is a perspective view showing a part of an internal heat exchanger according to a fifth embodiment; 
         FIG. 10  is a cross-sectional view on a line X-X in  FIG. 9 ; 
         FIG. 11  is a cross-sectional view showing a part of an internal heat exchanger according to a sixth embodiment; 
         FIG. 12  is a cross-sectional view of double pipes; 
         FIG. 13  is a cross-sectional view showing a pipe contracting; 
         FIG. 14  is a perspective view showing an internal heat exchanger; 
         FIG. 15  is a cross-sectional view showing a part of an internal heat exchanger according to an eighth embodiment; 
         FIG. 16  is a cross-sectional view showing a part of the internal heat exchanger according to the eighth embodiment; 
         FIG. 17  is a cross-sectional view showing a part of the internal heat exchanger according to the eighth embodiment; 
         FIG. 18  is a cross-sectional view showing a part of an internal heat exchanger according to a ninth embodiment; 
         FIG. 19  is a cross-sectional view showing a part of the internal heat exchanger according to the ninth embodiment; 
         FIG. 20  is a cross-sectional view showing a part of an internal heat exchanger according to a tenth embodiment; 
         FIG. 21  is a cross-sectional view showing a part of an internal heat exchanger according to an eleventh embodiment; 
         FIG. 22  is a cross-sectional view showing a part of an internal heat exchanger according to a twelfth embodiment; 
         FIG. 23  is a cross-sectional view showing a part of the internal heat exchanger according to the twelfth embodiment; 
         FIG. 24  is a cross-sectional view showing a part of an internal heat exchanger according to a thirteenth embodiment; 
         FIG. 25  is a cross-sectional view showing a part of an internal heat exchanger according to a fourteenth embodiment; 
         FIG. 26  is a cross-sectional view showing a part of the internal heat exchanger according to the fourteenth embodiment; 
         FIG. 27  is a perspective view showing a part of the internal heat exchanger according to the fourteenth embodiment; 
         FIG. 28  is a perspective view showing a part of the internal heat exchanger according to the first embodiment; 
         FIG. 29  is a perspective view showing a part of an internal heat exchanger according to a fifteenth embodiment; and 
         FIG. 30  is a perspective view showing a part of an internal heat exchanger according to a sixteenth embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     A disclosed internal heat exchanger described has a double pipe including an outer pipe and an inner pipe. A high-pressure liquid refrigerant from a condenser of the refrigeration cycle flows through an inner-outer flow path formed between the outer pipe and the inner pipe. The low-pressure gas refrigerant evaporated by an evaporator of the refrigeration cycle flows through a flow path formed inside the inner pipe. As a result, the double pipe functions as an internal heat exchanger. 
     A liquid pipe is brazed to a circumferential wall surface on both ends in a longitudinal direction of the outer pipe. The liquid pipe on one end side in the longitudinal direction of the outer pipe is a high-pressure pipe which communicates a refrigerant outlet of the condenser and the inner-outer flow path. The liquid pipe on the other end side in the longitudinal direction of the outer pipe is a high-pressure pipe which communicates the inner-outer flow path and a high-pressure refrigerant inlet of an expansion valve. 
     A suction pipe is brazed to a circumferential wall surface on both ends in the longitudinal direction of the inner pipe. The suction pipe on one end side in the longitudinal direction of the inner pipe is a low-pressure pipe which communicates an inner flow path of the inner pipe with a refrigerant suction port of a compressor of the refrigeration cycle. The suction pipe on the other end side in the longitudinal direction of the inner pipe is a low-pressure pipe which communicates a low-pressure refrigerant outlet of the expansion valve with the inner flow path of the inner pipe. 
     The inner pipe may be used as the high-pressure pipe communicating the refrigerant outlet of the condenser with the high-pressure refrigerant inlet of the expansion valve, and the inner-outer flow path is used as the low-pressure pipe through which the low-pressure refrigerant evaporated in the evaporator of the refrigerant cycle flows. 
     In this structure, the double pipe may be connected to a connector via an O-ring without brazing the double pipe with the liquid pipe and the suction pipe. 
     Since the liquid pipe and the suction pipe are branched from the double pipe, a space for arranging the liquid pipe and the suction pipe is required, and the overall physique becomes large. As a result, the space required for mounting becomes large and design restrictions become tight, and when a large number of the double pipes are transported at the same time, a packing shape becomes poor and a transportation efficiency becomes low. When transporting the double pipe, the liquid pipe and the suction pipe may be bent or damaged. 
     In addition, since it is hard to perform internal heat exchange on a terminal side than a part where the liquid pipe or suction pipe is branched, a length performing internal heat exchange is shortened, and an improving effect of a cycle efficiency is limited. 
     Further, since the liquid pipe and the suction pipe are brazed to the double pipe, if the brazing quality is insufficient, the refrigerant may leak. It is hard to ensure a stable manufacturing quality. 
     On the other hand, even if brazing is not performed, the inner pipe may be a high-pressure pipe and the inner-outer flow path is a low-pressure pipe. Therefore, it is necessary to design a flow path cross-sectional area of the inner pipe small and a flow path cross-sectional area of the inner-outer flow path large, and it is necessary to increase a distance between an inner diameter of the outer pipe and an outer diameter of the inner pipe by designing the inner pipe with a smaller diameter. Moreover, the internal heat exchanger may not have a structure such as a rib bridging both pipes between the inner pipe and the outer pipe because the inner-outer flow path is a low-pressure pipe. Therefore, it is difficult to arrange the inner pipe and the outer pipe concentrically. 
     It is an object of the disclosure to perform sure connection between the double pipe and the connector, while employing a structure in which the double pipe is directly connected to the connector by reducing the number of refrigerant pipe branching from the double pipe. 
     Hereinafter, embodiments is described with reference to the drawings. In the following embodiments, identical or equivalent elements are denoted by the same reference numerals as each other in the figures. 
     First Embodiment 
     A vehicle air-conditioner  10  shown in  FIG. 1  has a refrigeration cycle apparatus  11 . A double pipe type internal heat exchanger  18  is applied to the refrigeration cycle apparatus  11 . The refrigeration cycle apparatus  11  is a vapor-compression refrigerator including a compressor  12 , a condenser  13 , an expansion valve  14 , and an evaporator  15 . According to the refrigeration cycle apparatus  11  of the present embodiment, a fluorocarbon refrigerant is used as the refrigerant to configure a sub-critical refrigeration cycle in which a high-pressure side refrigerant pressure does not exceed a critical pressure of the refrigerant. 
     The compressor  12  and the condenser  13  are arranged in an engine room of a vehicle (not shown). The expansion valve  14  and the evaporator  15  are arranged in a passenger compartment of the vehicle. The compressor  12 , the condenser  13 , the expansion valve  14 , and the evaporator  15  are connected in series with respect to a flow of the refrigerant. 
     The compressor  12  sucks, compresses, and discharges the refrigerant of the refrigeration cycle apparatus  11 . The compressor  12  is a belt driven type compressor or an electric driven compressor. The belt-driven compressor is driven by transmitting driving force of an engine  4  via a crank pulley  5 , a drive belt  6 , and a pulley  7 . The electric driven compressor is driven by a motor powered by electric power supplied from a battery. 
     The condenser  13  is a radiator which condenses the high-pressure refrigerant by performing heat exchange between an outside air and the high-pressure gas refrigerant discharged from the compressor  12 , and radiates heat from the high-pressure gas refrigerant to the outside air. The condenser  13  is disposed on a vehicle front side inside the engine room. The liquid-phase refrigerant condensed by the condenser  13  flows into the high-pressure refrigerant inlet  14   a  of the expansion valve  14  via the high-pressure refrigerant pipe  16 . The high-pressure refrigerant pipe  16  corresponds to an inner-outer flow path  18   a  of the internal heat exchanger  18 . 
     The expansion valve  14  serves as a pressure reducer to decompress and expand the liquid-phase refrigerant flowing out of the high-pressure refrigerant pipe  16 . The expansion valve  14  includes a thermos-sensitive portion. The thermos-sensitive portion detects a super-heat degree of an outlet side refrigerant of the evaporator  15  based on a temperature and a pressure of the outlet side refrigerant of the evaporator  15 . The expansion valve  14  is a thermos-sensitive expansion valve which adjusts an orifice passage cross sectional area by a mechanical mechanism so that the super-heat degree of the outlet side refrigerant of the evaporator  15  falls within a specified range. 
     The evaporator  15  is a heat exchanger for cooling air which evaporates the low-pressure refrigerant by performing heat exchange between the low-pressure refrigerant flowing out of the expansion valve  14  and the air sent to the passenger compartment, and thereby cools the air sent to the passenger compartment. The gas phase refrigerant evaporated in the evaporator  15  flows into the temperature sensitive portion of the expansion valve  14 . The refrigerant passed through the temperature sensitive portion of the expansion valve  14  flows out from the low-pressure refrigerant outlet  14   b  of the expansion valve  14  to the low-pressure refrigerant pipe  17 , and is sucked into the compressor  12  via the low-pressure refrigerant pipe  17 , and is compressed. The low-pressure refrigerant pipe  17  corresponds to an inner flow path  18   b  of the internal heat exchanger  18 . 
     The evaporator  15  is accommodated in the casing  21  of the indoor air-conditioning unit  20 . The indoor air-conditioning unit  20  is disposed on an inside of an instrument panel (not shown) at a front portion of the passenger compartment. The casing  21  is an air-passage forming member which defines an air passage therein. In the air passage in the casing  21 , a heater core  22  is arranged on an air flow downstream side of the evaporator  15 . The heater core  22  is a heat exchanger for heating air which is configured to perform heat exchange between the engine cooling water and air supplied to the vehicle compartment thereby heating the air supplied to the vehicle compartment. 
     An inside/outside air switching case (not shown) and an indoor blower  23  are arranged in the casing  21 . The inside/outside air switching case is an inside/outside air switching unit which selectively introduces an inside air and an outside air into the air passage of the casing  21 . The indoor blower  23  draws the inside air and the outside air introduced into the air passage of the casing  21  via the inside/outside air switching case. 
     An air mix door  24  is arranged between the evaporator  15  and the heater core  22  in the air passage of the casing  21 . The air mix door  24  adjusts an air flow ratio between a cool air, which flows into the heater core  22 , and a cool air, which bypasses the heater core  22 , among a cool air passing through the evaporator  15 . The air mix door  24  is a rotary door which includes a rotary shaft supported by the casing  21  in a rotatable manner, and a door plate body coupled with the rotary shaft. It is possible to adjust a temperature of conditioned air, which is discharged from the casing  21  into the passenger compartment, by adjusting an opening position of the air mix door  24 . 
     Outlet openings  25  are formed at the most downstream end of the air flow of the casing  21 . Although not shown in  FIG. 1 , a plurality of outlet openings  25  are formed. The conditioned air of which temperature is adjusted in the casing  21  is discharged into the passenger compartment that is the air-conditioning target space through the outlet openings  25 . An outlet mode switching door (not shown) is arranged air flow upstream side to the plurality of outlet openings  25 . The outlet mode switching door is configured to switch the outlet modes. The outlet mode include a face mode, a bi-level mode, a foot mode, and a vent mode. 
     At least a part of the high-pressure refrigerant pipe  16  and at least a part of the low-pressure refrigerant pipe  17  are provided by the double pipe type internal heat exchanger  18  shown in  FIGS. 2 to 4 . The internal heat exchanger  18  has a total length of about 200 to 1200 mm. 
     The length of this internal heat exchanger  18  is determined according to the required heat exchange capacity. That is, the internal heat exchanger  18  increases an enthalpy of the refrigeration cycle apparatus  11  by performing heat exchange between the low-temperature and low-pressure gas-phase refrigerant toward the compressor  12  and the high-temperature and high-pressure liquid-phase refrigerant toward the expansion valve  14 . Therefore, the internal heat exchanger  18  is required to have a length sufficient to obtain a desired enthalpy. On the other hand, if the amount of heat exchanged by the internal heat exchanger  18  is too large, the temperature of the refrigerant sucked into the compressor rises too much, which is not desirable. Therefore, in a case that the length of the internal heat exchanger  18  is determined, it is desired to adjust the amount of heat exchange in the internal heat exchanger  18 . The adjustment of this heat exchange amount is described later. 
     There may be a case in which the internal heat exchanger  18  is covered with a heat insulating material in order to block heat transfer from the outside air to the internal heat exchanger  18 . This case is that, for example, the internal heat exchanger  18  is arranged in the engine room, and a direct heating of the internal heat exchanger  18  from the engine is prevented. 
     As shown in  FIG. 2 , the double pipe type internal heat exchanger  18  includes an outer pipe  181  and an inner pipe  182 . The inner pipe  182  is inserted into the outer pipe  181  to penetrate the outer pipe  181 . As a result, a double pipe is formed by the outer pipe  181  and the inner pipe  182 . 
     The outer pipe  181  is, for example, φ22 mm pipe made of aluminum. The φ22 mm pipe is a pipe having an outer diameter of 22 mm and an inner diameter of 19.6 mm. As one of the vehicle air-conditioners  10 , the outer pipe  181  used in the automobile air-conditioner has an outer diameter of about 22 mm in order to make the diameter as small as possible. Even in a case that the outer pipe  181  is designed large to enable a large circulating amount of refrigerant, it is desirable to design it less than 28 mm. Further, the wall thickness of the outer pipe  181  is also designed about 1.2 mm, and even if it is thickened, it is designed less than 2 mm. 
     The inner pipe  182  is, for example, a ¾ inch pipe made of aluminum. The ¾ inch pipe is a pipe having an outer diameter of 19.1 mm and an inner diameter of 16.7 mm. In this way, sizes are selected to increase a surface area of the inner pipe  182  while satisfying both ensuring of the inner-outer flow path  18   a  and setting the outer diameter of the inner pipe  182  and the inner diameter of the outer pipe  181  as close as possible. 
     Since the low-pressure gas refrigerant flows inside the inner pipe  182  (inner flow path  18   b ), it is necessary to secure a sufficient cross-sectional area of the flow path. In particular, since the gas refrigerant has a larger volume and a higher flow velocity than the liquid refrigerant, the pressure loss when flowing through the inner flow path  18   b  is much larger than that of the liquid refrigerant flowing through the inner-outer flow path  18   a . Therefore, as a design concept of the internal heat exchanger  18 , the inner diameter of the inner pipe  182  is determined so that the inner pipe  182  has a sufficient flow path cross-sectional area, and the outer diameter of the inner pipe  182  is determined based on a wall thickness of about 1 to 2 mm. The outer diameter of the inner pipe  182  is about 15.8 to 22 mm. 
     The diameter of the outer pipe  181  is designed to be the minimum within the range in which the high-pressure liquid refrigerant can flow through the inner-outer flow path  18   a  according to the outer diameter of the inner pipe  182 . This is because the high-pressure liquid refrigerant flows through the inner-outer flow path  18   a , enlarging the cross-sectional view of the inner-outer flow path  18   a  adversely requires unnecessarily large amount of refrigerant sealed in the refrigeration cycle. It is possible to reduce cost by reducing the amount of refrigerant used in the refrigeration cycle. Therefore, the ratio of the difference between the inner diameter of the outer pipe  181  and the outer diameter of the inner pipe  182  to the inner diameter of the outer pipe  181  is set 25% or less. More preferably, it is set 20% or less. 
     Drawings (a) to (o) in  FIG. 12  show the cross-sectional shape of the double pipe, and the outer diameter and wall thickness of each are as follows. Further, the ratio of the difference between the inner diameter of the outer pipe  181  and the outer diameter of the inner pipe  182  to the inner diameter of the outer pipe  181  calculated based on this dimension is also as follows, and is set 20% or less. 
       FIG. 12( a ) : Outer pipe outer diameter 25 mm, Outer pipe wall thickness 1.2 mm, Inner pipe outer diameter 22.1 mm, Inner pipe wall thickness 1.2 mm, Ratio 2.2% 
       FIG. 12( b ) : Outer pipe outer diameter 21.1 mm, Outer pipe wall thickness 1.2 mm, Inner pipe outer diameter 19.1 mm, Inner pipe wall thickness 1.2 mm, Ratio 3.0% 
       FIG. 12( c ) : Outer pipe outer diameter 27.5 mm, Outer pipe wall thickness 1.7 mm, Inner pipe outer diameter 21.9 mm, Inner pipe wall thickness 1.5 mm, Ratio 9.1% 
       FIG. 12( d ) : Outer pipe outer diameter 25 mm, Outer pipe wall thickness 1.7 mm, Inner pipe outer diameter 19.1 mm, Inner pipe wall thickness 1.3 mm, Ratio 11.6% 
       FIG. 12( e ) : Outer pipe outer diameter 25 mm, Outer pipe wall thickness 1.6 mm, Inner pipe outer diameter 18.9 mm, Inner pipe wall thickness 1.1 mm, Ratio 13.3%  FIG. 12( f ) : Outer pipe outer diameter 24 mm, Outer pipe wall thickness 2 mm, Inner pipe outer diameter 17.8 mm, Inner pipe wall thickness 1.5 mm, Ratio 11.0% 
       FIG. 12( g ) : Outer pipe outer diameter 27 mm, Outer pipe wall thickness 1.6 mm, Inner pipe outer diameter 22 mm, Inner pipe wall thickness 1.5 mm, Ratio 7.6% 
       FIG. 12( h ) : Outer pipe outer diameter 25 mm, Outer pipe wall thickness 1.5 mm, Inner pipe outer diameter 20 mm, Inner pipe wall thickness 1.3 mm, Ratio 9.1% 
       FIG. 12( i ) : Outer pipe outer diameter 25 mm, Outer pipe wall thickness 1.2 mm, Inner pipe outer diameter 20 mm, Inner pipe wall thickness 1.2 mm, Ratio 11.5% 
       FIG. 12( j ) : Outer pipe outer diameter 25 mm, Outer pipe wall thickness 1.7 mm, Inner pipe outer diameter 18 mm, Inner pipe wall thickness 1.5 mm, Ratio 16.7% 
       FIG. 12( k ) : Outer pipe outer diameter 24.6 mm, Outer pipe wall thickness 1.8 mm, Inner pipe outer diameter 19.1 mm, Inner pipe wall thickness 1.8 mm, Ratio 9.1%  FIG. 12( l ) : Outer pipe outer diameter 24.6 mm, Outer pipe wall thickness 1.7 mm, Inner pipe outer diameter 19.1 mm, Inner pipe wall thickness 1.3 mm, Ratio 9.9% 
       FIG. 12( m ) : Outer pipe outer diameter 25 mm, Outer pipe wall thickness 1.5 mm, Inner pipe outer diameter 18 mm, Inner pipe wall thickness 1.5 mm, Ratio 18.2% 
       FIG. 12( n ) : Outer pipe outer diameter 25 mm, Outer pipe wall thickness 1.6 mm, Inner pipe outer diameter 18 mm, Inner pipe wall thickness 1.5 mm, Ratio 17.4% 
       FIG. 12( o ) : Outer pipe outer diameter 22.5 mm, Outer pipe wall thickness 1.6 mm, Inner pipe outer diameter 19.1 mm, Inner pipe wall thickness 1.6 mm, Ratio 1.0% 
       FIG. 12( p ) : Outer pipe outer diameter 22.5 mm, Outer pipe wall thickness 1.6 mm, Inner pipe outer diameter 19.1 mm, Inner pipe wall thickness 1.6 mm, Ratio 1.0% 
     The double pipes (a), (b), (f), (o) and (p) in  FIG. 12  has a spiral groove  1822  on the inner pipe  182 . The outer diameter of the inner pipe  182  on which the spiral groove  1822  is formed is indicated by the dimension before the spiral groove  1822  is formed, that is, the outer diameter dimension of the inner pipe  182  at the portion where the spiral groove  1822  is not formed. 
     The spiral groove  1822  includes recessed groove portions  1822   b  and ridge portions  1822   a , and is configured to have a structure in which the ridge portion  1822   a  abuts on the outer pipe  181  at a plurality of portions. Therefore, a concentric structure in which the inner pipe  182  and the outer pipe  181  are arranged coaxially is formed by coming into contact the outer peripheral surface of the inner pipe  182  with the inner peripheral surface of the outer pipe  181 . 
     The double pipe shown in  FIG. 12( p )  further has a recess on a ridge portion  1822   a  to widen a width of the ridge portion  1822   a . As described above, the shapes of the ridge portion  1822   a  and the groove portion  1822   b  may be changed to meet requirements. 
     Further, the double pipes (k) and (l) in  FIG. 12  has a spiral groove  1816  on the outer pipe  181 . The outer diameter of the outer pipe  181  is the dimension before the spiral groove  1816  is formed, that is, the outer diameter dimension of the outer pipe  181  at the portion where the spiral groove  1816  is not formed. 
     The spiral groove  1816  is also includes recessed groove portions  1816   b  and ridge portions  1816   a , and the ridge portion  1816   a  comes in contact with the outer peripheral surface of the inner pipe  182  at a plurality of portions. Therefore, a concentric structure in which the inner pipe  182  and the outer pipe  181  are arranged coaxially is formed by coming into contact the outer peripheral surface of the inner pipe  182  with the inner peripheral surface of the outer pipe  181 . Since the ridge portion represents a contact portion, the spiral groove  1822  of the inner pipe  182  and the spiral groove  1816  of the outer pipe  181  are opposite to each other. That is, the ridge portion  1822   a  is formed to protrude outward in the spiral groove  1822  of the inner pipe  182 , and the ridge portion  1816   a  is formed to protrude inward in the spiral groove  1816  of the outer pipe  181 . 
     By forming the spiral grooves  1822  and  1816  in the inner pipe  182  or the outer pipe  181  in this way, the inner pipe  182  and the outer pipe  181  can come into contact with each other at a plurality of places, and the inner pipe  182  and the outer pipe  181  are coaxially arranged and provides a concentric structure. 
     In addition, it is possible to enlarge the surface area of the inner pipe  182  or the outer pipe  181  by forming the spiral grooves  1822  and  1816  on the inner pipe  182  or the outer pipe  181 . In particular, in a case that the spiral groove  1822  is formed on the inner pipe  182 , it is possible to increase the heat exchange area between the inner flow path  18   b  and the inner-outer flow path  18   a.    
     Further, heat exchange between the inner flow path  18   b  and the inner-outer flow path  18   a  is promoted by contacting the inner pipe  182  and the outer pipe  181  at the ridge portion  1822   a  and  1816   a  of the spiral grooves  1822  and  1816  formed on the inner pipe  182  or the outer pipe  181 . 
     Further, the double pipes (c), (d), (e), (g), (i), (j), (m) and (n) of  FIG. 12  have ribs  1815 , which are formed at equal intervals and toward inwardly, on the outer pipe  181 , and are configured so that distal ends of the ribs  1815  come into contact with the outer peripheral surface of the inner pipe  182  at least in part after the inner pipe  182  is inserted. The contact of the ribs  1815  also forms a concentric structure in which the inner pipe  182  and the outer pipe  181  are arranged coaxially. 
     In addition, the rib  1815  increases the heat exchange efficiency by increasing the surface area of the inner-outer flow path  18   a , and the rib  1815  increases the heat exchange efficiency by contacting the rib  1815  with the inner pipe  182 . 
     In the double pipe of  FIG. 12( h ) , ribs  1815  are formed so as to protrude outward from the inner pipe  182  at equal intervals. A coaxially arranging structure of the inner pipe  182  and the outer pipe  181  is provided by contacting the distal end of the rib  1815  of the inner pipe  182  with the inner peripheral surface of the outer pipe  181  at least in part. 
     Moreover, the improvement of the heat exchange efficiency by the rib  1815  is the same as the above-mentioned example of the double pipe formed so as to project inward from the outer pipe  181 . 
     It is difficult to completely match the axial cores of the inner pipe  182  and the outer pipe  181  regardless of whether the spiral grooves  1822  and  1816  and the ribs  1815  are used. Therefore, in the description of this case, the concentric structure refers to a structure that acts in the direction of aligning the axial cores of the inner pipe  182  and the outer pipe  181 . Compared to a structure in which nothing exists between the inner pipe  182  and the outer pipe  181 , if the spiral grooves  1822  and  1816  and the rib  1815  are formed, the inner pipe  182  and the outer pipe  181  act to align axial cores. 
     As shown in  FIG. 2 , the outer pipe  181  and the inner pipe  182  are formed with a bent portion  1801  in order to avoid interference with the engine  4 , various in-vehicle devices (not shown), and a vehicle body, and the like. The bent portion  1801  is formed by simultaneously bending the outer pipe  181  and the inner pipe  182  while a straight inner pipe  182  inserted inside the straight outer pipe  181 . 
     In this bent portion  1801 , the concentric structure of the spiral grooves  1822 ,  1816  or the ribs  1815  is also useful for defining the inner-outer flow path  18   a  between the inner pipe  182  and the outer pipe  181 . This is because, if there is no concentric structure, the outer surface of the inner pipe  182  and the inner surface of the outer pipe  181  may come into direct contact with each other at the bent portion  1801 . In that case, the cross-sectional shape of the inner-outer flow path  18   a  becomes distorted, and the flow resistance increases. Contrary, if the concentric structure is provided, the outer surface of the inner pipe  182  and the inner surface of the outer pipe  181  do not come into direct contact with each other due to the concentric structure even in the bent portion  1801 . 
     An end portion  1810  of the outer pipe  181  in the longitudinal direction is combined with the inner pipe  182  and then the entire circumference thereof is pressed (pipe contracting) inward in the radial direction and joined to the circumferential surface of the inner pipe  182 . As shown in  FIG. 13 , the pipe contracting is performed by pressing a triple-claw chuck  201  from an outside of the outer pipe  181  with a core metal  200  applied to an inside of the inner pipe  182 . A distal ends  202  of the triple-claw chuck  201  define a circular cylindrical shape corresponding to the outer shape of the outer pipe  181  and presses the outer pipe  181  from three directions. 
     The triple-claw chuck  201  once presses the outer pipe  181 , then retracts, rotates 60 degrees in a circumferential direction, and presses the outer pipe  181  again. As a result, as shown in  FIG. 13 , the outer pipe  181  and the inner pipe  182  are arranged concentrically, especially at the end portions  1810  and  1820 . The terms of the end portions  1810  and  1820  do not mean distal ends, but indicate a portion from a position where the triple-claw chuck  201  is arranged to the distal ends. The distal end portions of the outer pipe  181  and the inner pipe  182  are illustrated by the distal end  1811  and the distal end  1821 , respectively ( FIG. 4 ). 
     The spiral groove  1822  of the inner pipe  182  begins from an inner side than the end portion  1820 , and the spiral groove  1822  is not formed at the distal end  1821 , which is in a circular cylindrical shape, than the end portion  1820  of the inner pipe  182 . Therefore, the core metal  200  is a cylinder shape, and its outer surface is in contact with the inner surface of the inner pipe  182  at the front surface. 
     Due to this pipe contracting, the inner pipe  182  and the outer pipe  181  are placed so that axes are more aligned at the end portions  1820  and  1810 . As a result, an inserting work into the connector described later becomes smooth. 
     As shown in  FIG. 4 , a space is defined between the outer pipe  181  and the inner pipe  182 , and this space is provided as the inner-outer flow path  18   a . The internal space of the inner pipe  182  is an inner flow path  18   b . Flow direction of the refrigerant in the inner-outer flow path  18   a  and the inner flow path  18   b  are opposite to each other. The inner-outer fluid flowing through the inner-outer flow path  18   a  is a high-pressure liquid refrigerant. The inner fluid flowing through the inner flow path  18   b  is a low-pressure gas refrigerant. 
     As shown in (a), (b), (f), (o), and (p) of  FIG. 12 , spiral grooves  1822  are provided on the outer surface of the inner pipe  182 . The spiral groove  1822  is a multi-line groove extending spirally in the longitudinal direction of the inner pipe  182 , and has three grooves in (a), (b), (o), and (p) of  FIG. 12 , and has two grooves in (f) of  FIG. 12 . 
     In the example of  FIG. 4 , the inner pipe  182  is formed in a bellows shape (e.g., a folded shape) by the spiral groove  1822 . Therefore, the inner-outer flow path  18   a  is spirally formed on the outer circumference of the inner pipe  182 , and as described above, the contact surface area between the inner pipe  182  and the outer pipe  181  increases, and it is possible to improve the heat exchange efficiency. 
       FIG. 4  shows an example in which the inner pipe  182  having the spiral groove  1822  shown in  FIGS. 12 ( a ), ( b ), ( f ), ( o ), and ( p )  is used, but the end portion  1820  is formed in a similar shape in a case that the other double pipe is used. In the case of the double pipes (c), (d), (e), (g), (i), (j), (m) and (n) of  FIG. 12 , the distal end  1821  of the inner pipe  182  is located more outwardly in the axial direction than the distal end  1811  of the outer pipe  181 , and the outer pipe  181  and the rib  1815  do not exist at the distal end  1820  of the inner pipe  182  (See later described  FIG. 17 ). 
     In the double pipe of  FIG. 12( h ) , the double pipe is formed by arranging the inner pipe  182  in the outer pipe  181  after the rib  1815  of the inner pipe  182  is cut at the distal end  1820 . Therefore, in the assembled double pipe, neither the outer pipe  181  nor the rib  1815  is present at the distal end  1820  of the inner pipe  182 . 
     As shown in  FIG. 2 , a liquid pipe  184  is brazed to the outer peripheral surface of the outer pipe  181  near one end in the longitudinal direction. The liquid pipe  184  communicates with the inner-outer flow path  18   a.    
     A joint  184   a , which is connected to a refrigerant outlet side of the condenser  13 , is provided at the distal end portion of the liquid pipe  184 . Therefore, as described above, the high-pressure liquid refrigerant from the condenser  13  flows into the inner-outer flow path  18   a . The joint  184   a  may be directly connected to the condenser  13  or may be connected to the condenser  13  via a piping member (not shown). 
     A suction pipe  185  is provided at one end of the inner pipe  182  in the longitudinal direction. The suction pipe  185  is a pipe forming the low-pressure refrigerant pipe  17 . A joint  185   a , which is connected to a refrigerant suction side of the compressor  12 , is provided at the distal end of the suction pipe  185 . The low-temperature low-pressure refrigerant flowing out of the evaporator  15  flows through the inner flow path  18   b  and is sucked into the compressor  12 . The joint  185   a  is usually connected to the compressor  12  via a hose member. 
     As shown in  FIG. 4 , a bulge processed portion  181   a  is formed in the vicinity of the end portion  1810  in the longitudinal direction of the outer pipe  181 . The bulge processed portion  181   a  is a contact portion that comes into contact with the end surface  1865  of the expansion valve side connector  186 , and is formed by bulging the outer pipe  181  toward the outer peripheral side. 
     An outer pipe side O-ring groove  181   b  having a circumferential groove-shape is formed between the distal end  1811  in the longitudinal direction of the outer pipe  181  and the bulge processed portion  181   a . An outer pipe side O-ring  191  in an annular shape is arranged in the outer pipe side O-ring groove  181   b . The outer pipe side O-ring  191  is a sealing member that prevents refrigerant leakage between the inner-outer flow path  18   a  and the expansion valve side connector  186 . 
     An inner pipe side O-ring groove  182   a  having a circumferential groove-shape is formed in the vicinity of the end portion  1820  in the longitudinal direction of the inner pipe  182 . An inner pipe side O-ring  192  in an annular shape is arranged in the inner pipe side O-ring groove  182   a . The outer pipe side O-ring  192  is a sealing member that prevents refrigerant leakage between the inner flow path  18   b  and the expansion valve side connector  186 . In particular, the inner pipe side O-ring  192  secures a seal between the inner flow path  18   b  and the high-pressure communication space  186   k  of the expansion valve side connector  186 . 
     Since the distal end  1821  of the inner pipe  182  is located more outwardly in the axial direction than the distal end  1811  of the outer pipe  181 , the expansion valve side connector  186  is formed to have a high-pressure communication space  186   k  among the distal end  1811  of the outer pipe  181 , an innermost part of the outer pipe insertion portion  186   e , and an outer periphery of the end portion  1820  of the inner pipe  182 . Then, the high-pressure refrigerant flow path  186   g  communicates with the high-pressure communication space  186   k . The outer pipe side sealing member (outer pipe side O-ring)  191  seals between the high-pressure communication space  186   k  and the atmosphere, and the inner pipe side sealing member (inner pipe side O-ring  192 ) seals between the high-pressure communication space  186   k  and the low-pressure refrigerant flow path  186   f.    
     As shown in  FIG. 3 , the expansion valve side connector  186  is arranged at the ends  1810  and  1820  of the outer pipe  181  and the inner pipe  182  in the longitudinal direction. The expansion valve side connector  186  is a member that forms a connecting portion between the internal heat exchanger  18  and the expansion valve  14 . The expansion valve  14  is a connection target member connected to the expansion valve side connector  186 . 
     The expansion valve side connector  186  is provided with a high-pressure side joint  186   a  and a low-pressure side joint  186   b . The high-pressure side joint  186   a  is connected to the high-pressure refrigerant inlet  14   a  of the expansion valve  14 . The low-pressure side joint  186   b  is connected to the low-pressure refrigerant outlet  14   b  of the expansion valve  14 . The low-pressure side joint  186   b  is a male-shaped portion that protrudes in a male shape on an extension line of the internal heat exchanger  18 . The high-pressure side joint  186   a  is a male-shaped portion that protrudes in a male shape in parallel with the low-pressure side joint  186   b.    
     The high-pressure refrigerant inlet  14   a  and the low-pressure refrigerant outlet  14   b  of the expansion valve  14  form a female joint portion. The male high-pressure joint  186   a  is inserted into the female high-pressure refrigerant inlet  14   a  of the expansion valve  14 . The male low-pressure joint  186   b  is inserted into the female low-pressure refrigerant outlet  14   b  of the expansion valve  14 . 
     As shown in  FIG. 4 , a high-pressure side O-ring groove  186   c  having a circumferential groove-shape is formed on an outer peripheral surface of the high-pressure side joint  186   a . A high-pressure side O-ring  193  is arranged in the high-pressure side O-ring groove  186   c . The high-pressure side O-ring  193  is a sealing member that prevents leakage of the refrigerant flowing out from the inner-outer flow path  18   a.    
     A low-pressure side O-ring groove  186   d  having a circumferential groove-shape is formed on an outer peripheral surface of the low-pressure side joint  186   b . A low-pressure side O-ring  194  is arranged in the low-pressure side O-ring groove  186   d . The low-pressure side O-ring  194  is a sealing member that prevents leakage of the refrigerant flowing out from the low-pressure refrigerant outlet  14   b  of the expansion valve  14 . 
     The expansion valve side connector  186  is formed with the outer pipe insertion portion  186   e , the inner pipe insertion portion  1860 , the low-pressure refrigerant flow path  186   f , the high-pressure refrigerant flow path  186   g , and bolt holes  186   h . The outer pipe  181  is inserted into the outer pipe insertion portion  186   e , and in the inserted state, the outer pipe side O-ring  191  is compressed and deformed to maintain the seal. Similarly, the inner pipe  182  is inserted into the inner pipe insertion portion  1860 , and in the inserted state, the inner pipe side O-ring  192  is compressed and deformed to maintain the seal. 
     When in an inserting work of the double pipe, the distal end  1821  of the inner pipe  182  first comes into contact with the inner pipe insertion portion  1860  of the expansion valve side connector  186 , and then the distal end  1811  of the outer pipe  181  comes into contact with the outer pipe insertion portion  186   e  of the expansion valve side connector  186 . Then, in order to perform the inserting process smoothly at this time, a taper is formed at the distal end  1821  of the inner pipe  182  and the distal end  1811  of the outer pipe  181 . Further, as described above, since the end portions  1820  and  1810  of the outer pipe  181  and the inner pipe  182  are contracted so that the axes are aligned, the insertion is smoothly performed. 
     Therefore, first, the inner pipe  182  is aligned axially with the inner pipe insertion portion  1860  of the expansion valve side connector  186  by the tapered shape, and in that state, the outer pipe  181  is axially aligned with the outer pipe insertion portion  186   e  by the tapered shape. Therefore, even if the axis of the inner pipe  182  and the axis of the outer pipe  181  are slightly shifted, smooth insertion is possible. 
     The low-pressure refrigerant flow path  186   f  is a low-pressure side communication flow path that communicates the low-pressure refrigerant outlet  14   b  of the expansion valve  14  with the inner flow path  18   b . The low-pressure refrigerant flowing out from the low-pressure refrigerant outlet  14   b  of the expansion valve  14  flows to the inner flow path  18   b  through the low-pressure refrigerant flow path  186   f . The low-pressure refrigerant flow path  186   f  extends from the inner pipe insertion portion  1860  toward the low-pressure side joint  186   b  and penetrates through an inside of the low-pressure side joint  186   b.    
     The high-pressure refrigerant flow path  186   g  is a high-pressure side communication flow path that communicates the inner-outer flow path  18   a  with the high-pressure refrigerant inlet  14   a  of the expansion valve  14 . Therefore, the high-pressure refrigerant flowing out from the inner-outer flow path  18   a  flows to the high-pressure refrigerant inlet  14   a  of the expansion valve  14  via the high-pressure refrigerant flow path  186   g . The high-pressure refrigerant flow path  186   g  is located: to open the high-pressure communication space  186   k  formed in the outer pipe insertion portion  186   e  at an one end thereof, to extend downwardly in  FIG. 4 , and then to bend and extend toward the high-pressure side joint  186   a , and to penetrate inside the high-pressure side joint  186   a.    
     The high-pressure refrigerant flow path  186   g  is formed by cutting process. An opening hole formed in the expansion valve side connector  186  in the cutting process is closed by a sealing plug  187 . 
     The bolt hole  186   h  is used to mechanically fix the expansion valve side connector  186  to the outer pipe  181  and the inner pipe  182 . Specifically, the expansion valve side connector  186  and a holding plate  188  sandwich the bulge processed portion  181   a  of the outer pipe  181 , and the expansion valve side connector  186  is mechanically fixed to the outer pipe  181  and the inner pipe  182  by fastening the expansion valve side connector  186  and the holding plate  188  with a bolt  189 . 
     The reason why the bolt  189  protrudes from the expansion valve side connector  186  in  FIG. 4  is that the bolt  189  also fixes the expansion valve side connector  186  and the expansion valve  14 . In a state before the expansion valve side connector  186  and the expansion valve  14  are fixed, as shown in  FIG. 28 , the holding plate  188  is fixed to the expansion valve side connector  186  by a flat head screw  1890 . 
     Next, operation of the above configuration is described. When the compressor  12  is driven, the compressor  12  sucks the low-pressure gas refrigerant from the evaporator  15  side, compresses it, and then discharges it to the condenser  13  side as the high-temperature high-pressure gas refrigerant. The high-pressure refrigerant is cooled by the condenser  13  and condensed to be the liquid-phase. The refrigerant here is substantially in the liquid-phase. The condensed liquefied refrigerant flows through the high-pressure refrigerant pipe  16  (the inner-outer flow path  18   a ), is decompressed and expanded by the expansion valve  14 , and is evaporated by the evaporator  15 . The refrigerant here is in a substantially saturated gas state with a super-heat degree of 0 to 3 degrees Celsius. In the evaporator  15 , the air is cooled as the refrigerant evaporates. Then, the saturated gas refrigerant evaporated in the evaporator  15  flows through the low-pressure refrigerant pipe  17  (the inner-outer flow path  18   b ) as a low-temperature and low-pressure refrigerant and returns to the compressor  12 . 
     At this time, since there is a temperature difference between the high-pressure refrigerant flowing through the high-pressure refrigerant pipe  16  and the low-pressure refrigerant flowing through the low-pressure refrigerant pipe  17 , the high-pressure refrigerant flowing through the high-pressure refrigerant pipe  16  and the low-pressure refrigerant flowing through the low-pressure refrigerant pipe  17  perform heat exchange at the internal heat exchanger  18 , the high-pressure refrigerant is cooled, and the low-pressure refrigerant is heated. 
     That is, the liquid phase refrigerant flowing out of the condenser  13  is sub-cooled by the internal heat exchanger  18  to promote lowering the temperature. The saturated gas refrigerant flowing out of the evaporator  15  is heated by the internal heat exchanger  18  to become a gas refrigerant having a super-heat degrees. This improves the performance of the refrigeration cycle apparatus  11 . 
     Since the low-pressure refrigerant flowing from the evaporator  15  to the compressor  12  has a low temperature, dew condensation on the surface of the low-pressure refrigerant pipe  17  may be concerned. However, in the internal heat exchanger  18  of this example, the inner pipe  182  is covered by the outer pipe  181 . Since the outer pipe  181  is heated to a high temperature by the high-pressure refrigerant flowing through the inner-outer flow path  18   a , dew condensation does not occur on the outer surface of the outer pipe  181 . 
     The high-pressure refrigerant flowing out from the inner-outer flow path  18   a  of the internal heat exchanger  18  flows into the high-pressure refrigerant inlet  14   a  of the expansion valve  14  through the high-pressure communication space  186   k  and the high-pressure refrigerant flow path  186   g  of the expansion valve side connector  186 . Refrigerant leakage from the inner-outer flow path  18   a  and the high-pressure communication space  186   k  is prevented by the outer pipe side O-ring  191 . Refrigerant leakage from between the high-pressure refrigerant flow path  186   g  and the high-pressure refrigerant inlet  14   a  of the expansion valve  14  is prevented by the high-pressure side O-ring  193 . 
     The low-pressure refrigerant flowing out from the low-pressure refrigerant outlet  14   b  of the expansion valve  14  flows into the inner flow path  18   b  of the internal heat exchanger  18  through the low-pressure refrigerant flow path  186   f  of the expansion valve side connector  186 . Refrigerant leakage from between the low-pressure refrigerant outlet  14   b  of the expansion valve  14  and the low-pressure refrigerant flow path  186   f  is prevented by the low-pressure side O-ring  194 . Refrigerant leakage between the low-pressure refrigerant flow path  186   f  and the high-pressure communication space  186   k  is prevented by the inner pipe side O-ring  192 . 
     According to this embodiment, the inner-outer flow path  18   a  and the high-pressure refrigerant inlet  14   a  of the expansion valve  14  are communicated with each other by the high-pressure communication space  186   k  and the high-pressure refrigerant flow path  186   g  of the expansion valve side connector  186 . Therefore, a refrigerant pipe for communicating the inner-outer flow path  18   a  and the high-pressure refrigerant inlet  14   a  of the expansion valve  14  is unnecessary. The refrigerant pipe for communicating the inner-outer flow path  18   a  and the high-pressure refrigerant inlet  14   a  of the expansion valve  14  is hereinafter referred to as an expansion valve side liquid pipe. 
     Since the expansion valve side liquid pipe is not required, it is possible to miniaturize the overall physique of the internal heat exchanger  18 . Since a space for arranging the liquid pipe on the expansion valve side is not required, it is possible to reduce necessary space required to mount the internal heat exchanger  18  on the vehicle side, and to reduce design restrictions. Further, when a large number of the internal heat exchangers  18  are transported at the same time, it is possible to improve a packaging shape and to improve the transport efficiency. 
     The expansion valve side liquid pipe may be bent and damaged during transportation of the internal heat exchanger  18 , but the expansion valve side connector  186  may not be bent during transportation of the internal heat exchanger  18 . Therefore, it is possible to reduce damage to the internal heat exchanger  18  during transportation. Since there is no liquid pipe on the expansion valve side, it is possible to increase a length of a heat exchange performing portion among the internal heat exchanger  18 , and to enhance an improving effect of the cycle efficiency. 
     In the present embodiment, the expansion valve side connector  186  is interposed between the end portion  1810  of the outer pipe  181  and the end portion  1820  of the inner pipe  182  and the expansion valve  14 , and forms a high-pressure communication space  186   k  and a high-pressure refrigerant flow path  186   g . The high-pressure communication space  186   k  and the high-pressure refrigerant flow path  186   g  communicate the inner-outer flow path  18   a  with the refrigerant flow path of the expansion valve  14 . 
     Since the connections of the two flow paths of the high-pressure refrigerant flow path and the low-pressure refrigerant flow path are completed by connecting one expansion valve side connector  186  to the expansion valve  14 , it is possible to ease assembling works of the internal heat exchanger  18  with the expansion valve  14 . The expansion valve side connector  186  is mechanically fixed to the internal heat exchanger  18 . Leakage of the high-pressure refrigerant between the expansion valve side connector  186  and the internal heat exchanger  18  is prevented by the outer pipe side O-ring  191 . Therefore, it becomes easier to secure stable manufacturing quality as compared with a case where the liquid pipe on the expansion valve side is brazed to prevent the refrigerant from leaking. 
     In the present embodiment, since the high-pressure communication space  186   k  is formed between the distal end  1811  of the outer pipe  181  and the innermost part of the outer pipe insertion portion  186   e , the distal end  1811  of the outer pipe  181  and the innermost portion of the outer pipe insertion portion  186   e  do not come into contact with each other. Therefore, the bulge-processed portion  181   a  can be reliably brought into contact with the end surface  1865  of the expansion valve side connector  186 . 
     In the present embodiment, the sealing member (the outer pipe side O-ring  191 ) prevents refrigerant leakage from the inner-outer flow path  18   a  and both the high-pressure communication space  186   k  and the high-pressure refrigerant flow path  186   g . Then, the outer pipe  181  and the expansion valve side connector  186  are mechanically fixed. According to this, the inner-outer flow path  18   a  and the refrigerant flow path of the expansion valve  14  can be communicated with each other without branching the refrigerant pipe from the outer pipe  181  and the inner pipe  182 . Therefore, it is possible to reduce the number of refrigerant pipes branched from the outer pipe  181  and the inner pipe  182 . 
     In this embodiment, the outer pipe  181  and the expansion valve side connector  186  are mechanically fixed by the bolt  189 . As a result, the outer pipe  181  and the expansion valve side connector  186  can be mechanically fixed with a simple configuration. 
     In the present embodiment, the expansion valve side connector  186  has a male high-pressure side joint  186   a  and a low-pressure side joint  186   b . The male high-pressure side joint  186   a  and the low-pressure side joint  186   b  are inserted into the female joint portion (not shown) of the expansion valve  14 . As a result, it is possible to connect the expansion valve side connector  186  to the female expansion valve  14 . 
     In the present embodiment, the expansion valve side connector  186  is formed so that end portions of the high-pressure refrigerant flow path  186   g  on a side to the expansion valve  14  open in a direction parallel to an extension direction of the outer pipe  181  and the inner pipe  182 . Thereby, in a case that the expansion valve  14  is arranged on the extension direction side of the outer pipe  181  and the inner pipe  182 , the expansion valve side connector  186  can be satisfactorily connected to the expansion valve  14 . 
     Second Embodiment 
     In the first embodiment, the expansion valve side connector  186  is fixed to the outer pipe  181  and the inner pipe  182  by using the bolt  189 , but in the present embodiment, as shown in  FIG. 5 , the expansion valve side connector  186  is caulked and fixed to the outer pipe  181  and the inner pipe  182 . A caulking fixing portion  186   i  is formed around the bulge processed portion  181   a  of the outer pipe  181  among the expansion valve side connector  186 . The caulking fixing portion  186   i  is caulked so as to involve the bulge processed portion  181   a  of the outer pipe  181 . 
     Also in this embodiment, since the expansion valve side connector  186  is mechanically fixed to the outer pipe  181  and the inner pipe  182 , the same effect as that of the first embodiment can be obtained. In the present embodiment, the outer pipe  181  and the expansion valve side connector  186  are mechanically caulked and fixed. As a result, the outer pipe  181  and the expansion valve side connector  186  can be reliably and mechanically fixed. 
     Although the caulking fixing portion  186   i  is formed on the expansion valve side connector  186  in  FIG. 5 , in a case that the holding plate  188  is used as shown in  FIG. 4 , the caulking fixing portion may be formed on the holding plate  188 . 
     Third Embodiment 
     In the first embodiment, the expansion valve side connector  186  is fixed to the outer pipe  181  and the inner pipe  182  by using the bolt  189 , and in the second embodiment, the expansion valve side connector  186  is caulked and fixed to the outer pipe  181  and the inner pipe  182 . However, in the present embodiment, as shown in  FIG. 6 , the expansion valve side connector  186  is fixed to the outer pipe  181  and the inner pipe  182  by utilizing an elastic force of a resin member  30 . 
     The resin member  30  is formed of an elastic resin in a circular cylindrical shape. The outer pipe side claw portion  30   a  and the connector side claw portion  30   b  are formed on the resin member  30 . The outer pipe side claw portion  30   a  is formed in a circumferential shape on the inner cylinder surface of the resin member  30 . The connector side claw portion  30   b  is formed in a circumferential shape on the outer cylinder surface of the resin member  30 . 
     An outer pipe side engaging portion  181   c  is formed on the outer peripheral surface of the outer pipe  181 . The outer pipe side engaging portion  181   c  has a concave shape so that the outer pipe side claw portion  30   a  engages with the outer pipe  181  and the inner pipe  182  in the axial direction (a left-right direction in  FIG. 6 ). A connector-side engaging portion  186   l  is formed on the inner peripheral surface of the outer pipe insertion portion  186   e  of the expansion valve side connector  186 . The connector side engaging portion  186   l  has a concave shape so that the connector side claw portion  30   b  engages with the outer pipe  181  and the inner pipe  182  in the axial direction (the left-right direction in  FIG. 6 ). 
     An outer diameter of the connector side claw portion  30   b  is slightly larger than an inner diameter of the connector side engaging portion  186   l . Therefore, when the connector side claw portion  30   b  engages with the connector side engaging portion  186   l , the resin member  30  elastically deforms so as to reduce the diameter, and an urging force is generated to press the connector side engaging portion  186   l . Therefore, since the expansion valve side connector  186  is fixed to the outer pipe  181  and the inner pipe  182  by using the elastic force of the resin member  30 , the expansion valve side connector  186  is mechanically fixed to the outer pipe  181  and the inner pipe  182 . 
     In the present embodiment, first, the outer pipe side claw portion  30   a  of the resin member  30  is engaged with the outer pipe side engaging portion  181   c , and the resin member  30  is attached to the end portion  1810  of the outer pipe  181 . In that state, the double pipe is inserted into the expansion valve side connector  186 . At that time, first, the distal end  1821  of the inner pipe  182  comes into contact with the inner pipe insertion portion  1860  of the expansion valve side connector  186 , and the axis alignment is performed. Next, the distal end  1811  of the outer pipe  181  comes into contact with the outer pipe insertion portion  186   e , and the outer pipe  181  is axially aligned. After that, the connector side claw portion  30   b  of the resin member  30  engages with the connector side engaging portion  186   l  of the expansion valve side connector  186 . 
     In the present embodiment, the mechanical assembly can be completed only by pressing the double pipe axially against the expansion valve side connector  186  with the resin member  30  attached to the double pipe. It is not necessary to tighten the bolt  189  as in the first embodiment or to crimp the caulking fixing portion  186   i  as in the second embodiment. Therefore, it is particularly effective for mechanical assembly in a narrow space. 
     Fourth Embodiment 
     In the above embodiment, the high-pressure side joint  186   a  and the low-pressure side joint  186   b  project in a direction parallel to the extension direction of the outer pipe  181  and the inner pipe  182 . However, in the present embodiment, as shown in  FIGS. 7 and 8 , the high-pressure side joint  186   a  and the low-pressure side joint  186   b  project in a direction orthogonal to the extension direction of the outer pipe  181  and the inner pipe  182 . As a result, even if the expansion valve  14  cannot be arranged on the extension direction side of the outer pipe  181  and the inner pipe  182  due to layout restrictions, the internal heat exchanger  18  and the expansion valve  14  can be connected by the expansion valve side connector  186 . 
     In the present embodiment, the expansion valve side connector  186  opens in a direction in which the end of the high-pressure refrigerant flow path  186   g  and the low-pressure refrigerant flow path  186   f  on the expansion valve  14  side is orthogonal to the extension direction of the outer pipe  181  and the inner pipe  182 . It is formed to do. Therefore, a connection is improved in a case that the expansion valve  14  is arranged on a side in an orthogonal direction to the extension direction of the outer pipe  181  and the inner pipe  182 . 
     In this embodiment, the high-pressure communication space  186   k  is formed between the distal end  1811  of the outer pipe  181  and the innermost portion of the outer pipe insertion portion  186   e , and the low-pressure refrigerant flow path  186   f  is formed between the distal end  1821  of the inner pipe  182  and the innermost portion of the inner pipe insertion portion  1860 . Therefore, the distal end  1811  of the outer pipe  181  and the distal end  1821  of the inner pipe  182  are both free and do not interfere with the member of the expansion valve side connector  186 . As a result, the bulge processed portion  181   a  of the outer pipe  181  can be reliably brought into contact with the end surface  1865 . 
     In particular, as a result of forming the bent portion  1801  on the double pipe, the distal end  1821  of the inner pipe  182  and the distal end  1811  of the outer pipe  181  are capable of being adversely shifted in the axial direction. Even in such a case, in the present embodiment, since the distal end  1811  of the outer pipe  181  and the distal end  1821  of the inner pipe  182  are both free, it is possible to absorb this shift in the axial direction. 
     Fifth Embodiment 
     In the above embodiment, the end portions of the outer pipe  181  and the inner pipe  182  opposite to the expansion valve  14  are connected to the condenser  13  and the compressor  12  by the liquid pipe  184 , the suction pipe  185  and the joints  184   a  and  185   a . Contrary, as shown in  FIGS. 9 and 10 , the present embodiment employs a structure in which the end portions of the outer pipe  181  and the inner pipe  182  opposite to the expansion valve  14  are connect to the condenser  13  and the compressor  12  by a counter-expansion valve side connector  31 . 
     The present embodiment provides a structure in which both ends of the outer pipe  181  and the inner pipe  182  are connected by the expansion valve side connector  186  and the counter-expansion valve side connector  31 . 
     The basic structure of the counter-expansion valve side connector  31  is the same as that of the expansion valve side connector  186 . Therefore, in the following, detailed description of the basic structure of the counter-expansion valve side connector  31  is omitted. As shown in  FIG. 9 , a high-pressure side service valve  32 , a low-pressure side service valve  33 , and a pressure switch  34  are attached to the counter-expansion valve side connector  31 . Therefore, an attachment tool for attaching the high-pressure side service valve  32  or the like to the refrigerant pipe becomes unnecessary, it is possible to reduce the cost by reducing the number of parts. As is described later, a pressure sensor may be used instead of the pressure switch. The pressure sensor is a sensor that detects a refrigerant pressure. 
     However, the high-pressure side service valve  32 , the low-pressure side service valve  33 , and the pressure switch  34  do not necessarily have to be all attached to the counter-expansion valve side connector  31 , and some of them may be provided around the counter-expansion valve side connector  31 . Depending on restrictions such as an attaching position, all of the high-pressure side service valve  32  and the like may be provided around the counter-expansion valve side connector  31 . 
     For example, in the illustrated embodiment, the high-pressure side service valve  32  is arranged upward and the low-pressure side service valve  33  is arranged sideways, but there may be a needs to place both the high-pressure side service valve  32  and the low-pressure side service valve  33  being arranged upwards. In such a case, it is desirable to dispose the low-pressure side service valve  33  upward at a position away from the counter-expansion valve side connector  31 . 
     The high-pressure side service valve  32  and the low-pressure side service valve  33  are valves which are used for supplementary filling of the refrigerant. The pressure switch  34  is a switch that switches on and off depending on whether a refrigerant pressure is higher or lower than a predetermined value. A high-pressure side piping member  35  made of a hard material is fixed to the counter-expansion valve side connector  31  by using a high-pressure side joint plate  36  and a bolt (not shown). The high-pressure side piping member  35  made of a hard material is, for example, a pipe shaped member made of a hard material such as a metal such as aluminum or a hard resin. A metal made low-pressure side piping member  37  at an end portion of a soft hose member is fixed to the counter-expansion valve-side connector  31  by using a low-pressure side joint plate  38  and a bolt (not shown). The soft hose member is, for example, a tubular member made of a soft material such as rubber or a soft resin. 
     As shown in  FIG. 10 , the counter-expansion valve side connector  31  is formed with a high-pressure side service valve mounting portion  31   a , a low-pressure side service valve mounting portion  31   b , and a pressure switch mounting portion  31   c . The high-pressure side service valve  32  is attached to the high-pressure side service valve mounting portion  31   a . The high-pressure side service valve mounting portion  31   a  communicates with the high-pressure refrigerant flow path  311  of the counter-expansion valve side connector  31 . The low-pressure side service valve  33  is attached to the low-pressure side service valve mounting portion  31   b . The low-pressure side service valve mounting portion  31   b  communicates with the low-pressure refrigerant flow path  312  of the counter-expansion valve side connector  31 . The pressure switch  34  is attached to the pressure switch attachment portion  31   c . The pressure switch mounting portion  31   c  communicates with the high-pressure refrigerant flow path  311  of the counter-expansion valve side connector  31 . 
     In a case that the pressure sensor is attached, the size and shape of the pressure sensor are almost the same as those of the pressure switch  34 , so that the shape of the pressure sensor mounting portion is almost the same as that of the pressure switch mounting portion  31   c.    
     The pressure sensor mounting portion communicates with the high-pressure refrigerant flow path  311  of the counter-expansion valve side connector  31 . As described above, it is possible to provide mounting portions of the pressure switch  34  and the pressure sensor on other than the counter-expansion valve side connector  31 . For example, the pressure sensor may be provided in the condenser  13 . 
     The high-pressure side service valve  32  is air-tightly and liquid-tightly attached to the counter-expansion valve side connector  31  via an elastic sealing material  39  (for example, an O-ring). Similarly, the low-pressure side service valve  33 , the pressure switch  34 , and the pressure sensor are air-tightly and liquid-tightly attached to the counter-expansion valve side connector  31  via an elastic sealing material (not shown). 
     The counter-expansion valve side connector  31  also has the outer pipe insertion portion  3111  into which the end portion  1810  of the outer pipe  181  is inserted, and the end surface  3112  with which the bulge processed portion  181   a  of the outer pipe  181  comes in contact. A high-pressure communication space  3110  that communicates with the high-pressure refrigerant flow path  311  is formed between the distal end  1811  of the outer pipe  181  and the innermost portion of the outer pipe insertion portion  3111 . 
     Further, an inner pipe insertion portion  3113  is also formed in the counter-expansion valve side connector  31 , and the end portion  1820  of the inner pipe  182  is inserted into the inner pipe insertion portion  3113 . Then, the inner pipe side O-ring  192  is held by the inner pipe insertion portion  3113 . Further, the innermost portion of the inner pipe insertion portion  3113  and the distal end  1821  of the inner pipe  182  form a gap  1821   a  therebetween. 
     The counter-expansion valve side connector  31  is formed with a high-pressure side joint portion  313  and a low-pressure side joint portion  314 . The high-pressure side joint portion  313  is a female joint into which a high-pressure side piping member  35  made of a hard material is inserted. The low-pressure side joint portion  314  is a female type joint into which the low-pressure side piping member  37  is inserted. The high-pressure side joint portion  313  and the low-pressure side joint portion  314  are female-shaped portions. 
     In  FIG. 10 , a holding plate  390  is placed to press against the bulge processed portion  181   a  of the outer pipe  181  and the internal heat exchanger  18  is fixed by using a bolt (not shown). 
     In the present embodiment, the counter-expansion valve side connector  31  has the high-pressure side service valve mounting portion  31   a , the low-pressure side service valve mounting portion  31   b , and the pressure switch mounting portion  31   c . As a result, the number of members can be reduced and the configuration can be simplified as compared with the case where the dedicated member for attaching the high-pressure side service valve  32 , the low-pressure side service valve  33 , and the pressure switch  34  is separately provided. 
     In the present embodiment, the counter-expansion valve side connector  31  has a female high-pressure side joint portion  313  into which the male high-pressure side piping member  35  is inserted. The counter-expansion valve side connector  31  has a female low-pressure side joint portion  314  into which a male low-pressure side piping member  37  is inserted. As a result, the male high-pressure side piping member  35  and the low-pressure side piping member  37  can be connected to the counter-expansion valve side connector  31 . 
     In the present embodiment, a high-pressure communication space  3110  is formed between the innermost portion of the outer pipe insertion portion  3111  of the counter-expansion valve side connector  31  and the distal end  1811  of the outer pipe  181 . In addition, the innermost portion of the inner pipe insertion portion  3113  of the counter-expansion valve side connector  31  and the distal end  1821  of the inner pipe  182  form a gap  1821   a  therebetween. Therefore, the bulge processed portion  181   a  of the outer pipe  181  can be reliably brought into contact with the end surface  3112 . That is, the distal end  1811  of the outer pipe  181  and the distal end  1821  of the inner pipe  182  do not interfere with the portion of the counter-expansion valve side connector  31  at the time of insertion. 
     Sixth Embodiment 
     In the above embodiment, the expansion valve  14  is connected to the expansion valve side connector  186 , but in the present embodiment, the expansion valve  14  is integrated with the expansion valve side connector  186  as shown in  FIG. 11 . Specifically, the valve body portion  141  and the element portion  142  are arranged in the expansion valve side connector  186 , and a low-pressure refrigerant passage  143 , an orifice passage  144 , and a valve chamber  145  are formed in an inside of the expansion valve side connector  186 . 
       FIG. 11  shows a portion where the outer pipe  181  and the inner pipe  182  are in contact with each other. Similar to the above-described embodiment, the inner-outer flow path  18   a  is formed between the outer pipe  181  and the inner pipe  182 . Then, the inner-outer flow path  18   a  communicates with the high-pressure communication space  186   k , and the high-pressure liquid refrigerant flows into the valve chamber  145  from the high-pressure refrigerant flow path  186   g.    
     The low-pressure refrigerant passage  143  is used as a refrigerant passage where a temperature and a pressure of the low-pressure refrigerant is detected, and allows the low-pressure refrigerant flowing out of the evaporator  15  to flow. The orifice passage  144  is a refrigerant passage that functions as an orifice that reduces the pressure of the high-pressure refrigerant flowing out of the condenser  13  until it becomes a low-pressure refrigerant by reducing the passage cross-sectional area of the refrigerant passage. The valve chamber  145  is a space arranged on an upstream side of the refrigerant flow of the orifice passage  144  and accommodating the valve body portion  141 . The valve chamber  145  communicates with the high-pressure refrigerant flow path  186   g.    
     The valve body portion  141  is a spherical valve. Passage cross-sectional area of the orifice passage  144  is changed by displacing the valve body portion  141 . A coil spring  146  is housed inside the valve chamber  145 . The coil spring  146  is an elastic member that applies a load to the valve body portion  141  on a side that reduces the passage cross-sectional area of the orifice passage  144 . 
     The evaporator side outlet  14   c  and the low-pressure side inlet  14   d  are open on the outer surface of the expansion valve side connector  186 . The evaporator side outlet  14   c  discharges the low-pressure refrigerant decompressed in the orifice  144 . The low-pressure side inlet  14   d  causes the low-pressure refrigerant flowing out of the evaporator  15  to flow into the low-pressure refrigerant passage  143 . 
     The evaporator side outlet  14   c  and the low-pressure side inlet  14   d  are female joints. A connection target member (not shown) on the evaporator  15  side, such as a refrigerant pipe, is inserted into the evaporator side outlet  14   c  and the low-pressure side inlet  14   d . The evaporator side outlet  14   c  and the low-pressure side inlet  14   d  are open on the same surface (the surface on the right side in  FIG. 11 ) of the expansion valve side connector  186 . 
     The element portion  142  outputs a driving force for displacing the valve body portion  141 . The element portion  142  has a diaphragm  147 . The diaphragm  147  is made of a thin plate-shaped metal, and is deformed according to the temperature and the pressure of the low-pressure refrigerant flowing through the low-pressure refrigerant passage  143 . An operating rod  148  is connected to the diaphragm. The operating rod  148  transmits the displacement due to the deformation of the diaphragm to the valve body portion  141  to displace the valve body portion  141 . 
     Next, operation of the above configuration is described. The high-pressure refrigerant flowing out of the inner-outer flow path  18   a  of the internal heat exchanger  18  flows into the valve chamber  145  through the high-pressure refrigerant flow path  186   g  of the expansion valve side connector  186 . The refrigerant entered the valve chamber  145  is decompressed in the orifice passage  144 , and then flows out from the evaporator side outlet  14   c  to the evaporator  15 . 
     The refrigerant evaporated by the evaporator  15  flows into the low-pressure refrigerant passage  143  through the low-pressure side inlet  14   d . The diaphragm  147  is deformed according to the temperature and pressure of the low-pressure refrigerant flowing through the low-pressure refrigerant passage  143 , and the operating rod  148  transmits the displacement due to the deformation of the diaphragm  147  to the valve body portion  141  to displace the valve body portion  141 . As a result, the amount of refrigerant flowing into the evaporator  15  is adjusted, and the super-heat degree of the refrigerant flowing out of the evaporator  15  is maintained constant. The refrigerant flowing through the low-pressure refrigerant passage  143  flows into the inner passage  18   b  of the internal heat exchanger  18 . 
     According to this embodiment, since the expansion valve is integrated with the expansion valve side connector  186 , the number of parts can be reduced and the man-hours for assembling the refrigeration cycle apparatus  11  to the vehicle body can be reduced. 
     In the present embodiment, the low-pressure refrigerant passage  143  and the orifice passage  144  are formed in an inside of the expansion valve side connector  186 . The low-pressure refrigerant passage  143  communicates with the inner flow path  18   b . The throttle passage  144  communicates with the inner-outer flow path  18   a  to decompress and reduce the refrigerant on the high-pressure side. The valve body portion  141  and the element portion  142  are arranged on the expansion valve side connector  186 . The valve body portion  141  changes the passage cross-sectional area of the orifice passage  144 . The element portion  142  outputs a driving force for displacing the valve body portion  141 . As a result, since the expansion valve  14  can be integrated with the expansion valve side connector  186 , it is possible to reduce the number of parts of the refrigeration cycle apparatus  11 . 
     In this embodiment as well, similar to the fourth and fifth embodiments described above, the high-pressure communication space  186   k  is formed among the innermost portion of the outer pipe insertion portion  186   e  of the expansion valve side connector  186 , the distal end  1811  of the outer pipe  181 , and the outer circumference of the end portion  1820  of the inner pipe  182 . In addition, the innermost portion of the inner pipe insertion portion  1860  of the expansion valve side connector  186  and the distal end  1821  of the inner pipe  182  form a gap  1821   a  therebetween. 
     Therefore, the distal end  1811  of the outer pipe  181  and the distal end  1821  of the inner pipe  182  do not interfere with the expansion valve side connector  186  at the inserting process, and the bulge processed portion  181   a  of the outer pipe  181  can be reliably brought into contact with the end surface  1865 . In particular, even when the distal end  1821  of the inner pipe  182  and the distal end  1811  of the outer pipe  181  are displaced in the axial direction, reliable assembly is possible. 
     In  FIG. 11 , the holding plate  188  is placed to press against the bulge processed portion  181   a , and the bulge processed portion  181   a  is sandwiched and held between the holding plate  188  and an end surface  1865  of the expansion valve side connector  186 . Then, in that state, the internal heat exchanger  18  and the expansion valve side connector  186  are assembled using the bolt  189 . However, as in the third embodiment shown in  FIG. 6 , the assembling process may be performed by using the resin member  30 . In particular, as shown in  FIG. 1 , the expansion valve  14  is attached to the casing  21  together with the evaporator  15 . 
     As described above, the internal heat exchanger  18  is arranged in the engine room of an automobile, and the casing  21  is arranged in the passenger compartment. The expansion valve  14  is exposed more to a side of the engine room than the firewall that separates the engine room and the passenger compartment. Therefore, the exposed portion of the expansion valve  14   a  provide a limited work space. 
     As described above, in a case that the resin member  30  is used, the internal heat exchanger  18  can be attached to the expansion valve side connector  186  by pressing the internal heat exchanger  18  in the axial direction. Therefore, in the example of integrating the expansion valve  14  with the expansion valve side connector  186 , it is desirable to use the resin member  30 . 
     Seventh Embodiment 
     In the above-described embodiment, the spiral groove  1822  is formed over almost the entire length of the inner pipe  182  except for the end portion  1820 . The spiral groove  1822  allows the inner-outer flow path  18   a  to be formed in a spiral shape, and the heat exchange efficiency can be improved. 
     On the other hand, in a case that the expansion valve side connector  186  is arranged at one end of the internal heat exchanger  18  and the counter-expansion valve side connector  31  is also arranged on the opposite side, a space between the expansion valve side connector  186  and the counter-expansion valve side connector  31  is entirely provided by the internal heat exchanger  18 . Therefore, the heat exchange amount of the internal heat exchanger  18  is uniquely defined by a distance between the expansion valve side connector  186  and the counter-expansion valve side connector  31 . 
     However, it is necessary to optimize the amount of heat exchange as a system. As the amount of heat exchange in the internal heat exchanger  18  increases, the temperature of the refrigerant flowing into the compressor  12  tends to rise. As a result, the system may not be optimized. 
     For example, in a case that cooling other equipment by using a low-temperature intake refrigerant from the evaporator  15  to the compressor  12 , it is not desirable that the temperature of the intake refrigerant rises too high. Other devices may include, for example, inverters of electric compressors of electric vehicles or hybrid vehicles. 
     Therefore, in order to ensure consistency between the amount of heat exchange required for the internal heat exchanger  18  and the length of the internal heat exchanger  18 , the spiral groove  1822  may be formed on a part of the internal heat exchanger  18 , i.e., the spiral groove  1822  may not be formed in other parts, as shown in  FIG. 14 . In particular, in a case that it is necessary to reduce the amount of heat exchange of the internal heat exchanger  18 , the portion where the spiral groove  1822  is formed is shortened. In  FIG. 14 , the spiral groove  1822  is formed in the portion indicated by  1802 , and the spiral groove  1822  is not formed in the remaining portion. 
     Further, as described above, the spiral groove  1822  also has a function as a concentric structure of the inner pipe  182  and the outer pipe  181 . As a portion where this concentric structure is required, in addition to the end portions  1820  and  1810  to be assembled with the expansion valve side connector  186  and the counter-expansion valve side connector  31 , there is also a bending portion  1801 . Therefore, in the example of  FIG. 14 , the spiral grooves  1822  are formed at the end portions  1820  and  1810  and the bent portion  1801 . 
     In addition, it is possible to adjust the heat exchange efficiency by partially cutting the rib  1815  in the example in which the rib  1815  toward inwardly is formed on the outer pipe  181  in a protruding manner similar to the double pipes (c), (d), (e), (g), (i), (j), (m) and (n) in  FIG. 12 , and the rib  1815  toward outwardly from the inner pipe  182  is formed in a protruding manner similar to (h). 
     Further, adjusting heat exchange efficiency is possible to form a partial coating of a heat insulating material, instead of forming or not forming the spiral groove  1822  or the rib  1815 , or in addition to the spiral groove  1822  and the like. 
     Eighth Embodiment 
     In the above-described embodiment, the inner pipe  182  and the outer pipe  181  are provided with the inner pipe side O-ring groove  182   a  and the outer pipe side O-ring groove  181   b  for holding the O-ring, respectively, but the end portions  1820  and  1810  of the inner pipe  182  and the outer pipe  181  may have straight cylindrical shapes. As shown in  FIG. 15 , the outer pipe side O-ring  191  is sandwiched and held between the bulge processed portion  181   a  and the outer pipe insertion portion  186   e  of the expansion valve side connector  186 . A flange portion (a bulge processed portion)  1825  is formed on the inner pipe  182  similarly, and the inner pipe side O-ring  192  is sandwiched and held between the bulge processed portion  1825  and the inner pipe O-ring holding portion  186   l  of the expansion valve side connector  186 . 
     Also in this embodiment, a distance from the end surface  1865  of the expansion valve side connector  186  to a beginning point (a left end in  FIG. 15 ) of the outer pipe insertion portion  186   e  and a distance from the end surface  1865  to a beginning point (the left end in  FIG. 15 ) of the inner pipe insertion portion  1860 , and a distance from the distal end  1811  of the outer pipe  181  to the distal end  1821  of the inner pipe  182  are set in order to prevent the outer pipe side O-ring  191  and the inner pipe side O-ring  192  from an abnormally biting. 
     As shown in  FIG. 15 , at inserting the internal heat exchanger  18  into the expansion valve side connector  186 , first, the distal end  1821  of the inner pipe  182  comes into contact with the inner pipe insertion portion  1860  of the expansion valve side connector  186 . Since the distal end  1821  of the inner pipe  182  and the inner pipe insertion portion  1860  of the expansion valve side connector  186  are both formed with the tapers, the inner pipe  182  is guided by this taper and is smoothly inserted into the inner pipe insertion portion  1860 . 
     Next, the distal end  1811  of the outer pipe  181  comes into contact with the outer pipe insertion portion  186   e  of the expansion valve side connector  186 . Since the distal end  1821  of the outer pipe  181  and the outer pipe insertion portion  186   e  of the expansion valve side connector  186  are also both formed with the tapers, the outer pipe  181  is guided by this taper and is smoothly inserted into the outer pipe insertion portion  186   e.    
     When the insertion is further advanced from that state, the inner pipe side O-ring  192  comes into contact with the inner pipe O-ring holding portion  186   l  of the expansion valve side connector  186 . The inner pipe O-ring holding portion  186   l  is a part of the inner pipe insertion portion  1860  of the expansion valve side connector  186 , and is formed on a side to the outer pipe insertion portion  186   e  (a right side in  FIG. 15 ). The inner diameter of the inner pipe O-ring holding portion  186   l  is formed to be larger than the outer diameter of the bulge processed portion  1825  of the inner pipe  182 . Since the inner pipe O-ring holding portion  186   l  is also formed with the taper, the inner pipe side O-ring  192  is inserted into the inner pipe O-ring holding portion  186   l  along the taper while being compressed and deformed. 
     When the insertion is further advanced, the outer pipe side O-ring  191  comes into contact with the outer pipe O-ring holding portion  1862  of the expansion valve side connector  186 . The outer pipe O-ring holding portion  1862  is also a part of the outer pipe insertion portion  186   e . It is formed among the outer pipe insertion portion  186   e  on a side of the end surface  1865  of the expansion valve side connector  186 . 
     Similar to the inner pipe O-ring holding portion  186   l  described above, since the outer pipe O-ring holding portion  1862  is also formed with the taper, the outer pipe side O-ring  191  is also inserted while being compressed and deformed along the taper. The inner diameter of the outer pipe O-ring holding portion  1862  is smaller than the outer diameter of the bulge processed portion  181   a  of the outer pipe  181 . When the inserting process is further advanced, the bulge processed portion  181   a  of the outer pipe  181  finally comes into contact with the end surface  1865  of the expansion valve side connector  186 . Then, in order to perform the above insertion smoothly, the pipe contracting described with reference to  FIG. 13  are performed at the end portions  1820  and  1810  of the inner pipe  182  and the outer pipe  181 . The pipe contracting is molded so that the axes of the inner pipe  182  and the outer pipe  181  are aligned. 
     A state in which the inserting process is completed is a state shown in  FIG. 16 , and the inner pipe side O-ring  192  is held by the outer peripheral surface of the end portion  1820  of the inner pipe  182 , the bulge processed portion  1825 , and the inner peripheral surface of the inner pipe O-ring holding portion  186   l . The outer pipe side O-ring  191  is held by the outer peripheral surface of the end portion  1810 , the bulge processed portion  181   a , and the inner peripheral surface of the outer pipe O-ring holding portion  1862 . 
     In the present embodiment, a positional relationship of the distal end  1821  of the inner pipe, the inner pipe side O-ring  192 , the distal end  1811  of the outer pipe, and the outer pipe side O-ring  191 , and the inner pipe insertion portion  1860  and the outer pipe insertion portion  186   e  of the expansion valve side connector  186  defines a following configuration. At inserting the inner pipe  182  and the outer pipe  181  into the expansion valve side connector  186 , first the distal end  1821  of inner pipe comes into contact with the inner pipe insertion portion  1860 , and next the distal end  1811  of the outer pipe  181  comes into contact with the outer pipe insertion portion  186   e . After that, the inner pipe side O-ring  192  comes into contact with the inner pipe insertion portion  1860 , and then the outer pipe side O-ring  191  comes into contact with the outer pipe insertion portion  186   e . In the structure, finally the bulge processed portion  181   a  abuts on the end surface  1865  of the expansion valve side connector  186 . 
     As a result, an axis alignment is first performed between the expansion valve side connector  186  and the inner pipe  182 . In that state, an axis alignment is performed between the expansion valve side connector  186  and the outer pipe  181 . Therefore, even if the axes of the inner pipe and the outer pipe are slightly deviated from each other, smooth coupling is possible. 
     Moreover, since the inner pipe side O-ring  192  and the outer pipe side O-ring  191  are already inserted in a state where the inner pipe  182  and the outer pipe  181  are axially aligned with each other, the risk of biting is greatly reduced. In particular, since the outer pipe side O-ring  191  is inserted after the inner pipe side O-ring  192  is inserted, the two O-rings do not start to be deformed at the same time, and the assembly becomes smooth. 
     The positional relationship between the inner pipe  182 , the inner pipe side O-ring  192 , the outer pipe  181  and the outer pipe side O-ring  191  and the expansion valve side connector  186 , in an assembled state, is described as follows. 
     A beginning point of a portion, which comes into contact with the inner pipe  182 , among the inner pipe insertion portion  1860 , i.e., a boundary portion with the inner pipe O-ring holding portion  186   l  among the inner pipe insertion portion  1860  is indicated by reference numeral  1860   a . The beginning point of a portion, which comes into contact with the outer pipe  181 , among the outer pipe insertion portion  186   e , i.e., a boundary portion with the outer pipe O-ring holding portion  1862  among the outer pipe insertion portion  186   e  is indicated by reference numeral  186   ea . Then, Y indicates a distance between the beginning point  1860   a  of the inner pipe insertion portion  1860  and the beginning point  186   ea  of the outer pipe insertion portion  186   e.    
     The distance X of the distal end  1821  of the inner pipe  182  and the distal end  1811  of the outer pipe  181  is longer than the distance Y. As a result, as described above, the distal end  1821  of the inner pipe  182  is inserted into the inner pipe insertion portion  1860  prior to the distal end  1821  of the outer pipe  181 . 
     Further, X 1  indicates a distance of the inner pipe O-ring holding part  186   l  among the inner pipe insertion part  1860 . Then, Y 1  indicates a distance of the outer pipe O-ring holding portion  1862  among the outer pipe insertion portion  186   e.    
     An assembled state provides a structure in which the distance X 1  is longer than the distance Y 1 . That is, the inner pipe O-ring holding portion  186   l  is longer than the outer pipe O-ring holding portion  1862 . As a result, as described above, a structure is that the inner pipe side O-ring  192  comes into contact with the inner pipe O-ring holding portion  186   l  prior to the outer pipe side O-ring  191  in a prior manner. 
     Further, in an assembled state, X 2  indicates a distance between the distal end  1821  of the inner pipe  182  and a surface  1825   a  (a surface on the right side in  FIG. 15 ) on a side of the inner pipe side O-ring  192  of the bulge processed portion  1825 . This distance X 2  is longer than a sum of the distance X 1  to the beginning point  1860   a  of a portion, which comes into contact with the inner pipe  182 , among the inner pipe insertion portion  1860  and a diameter of the inner pipe side O-ring  192 . The distance X 1  to the beginning point  1860   a  of the portion which comes into contact with the inner pipe  182  among the inner pipe insertion portion  1860  is also the length X 1  of the inner pipe O-ring holding portion  186   l  among the inner pipe insertion portion  1860 . 
     As a result, the inner pipe side O-ring  192  is inserted into the inner pipe O-ring holding portion  186   l  after the distal end  1821  of the inner pipe  182  is inserted into the inner pipe insertion portion  1860 . 
     The outer pipe  181  also has a distance Y 2  of the distal end  1811  thereof and a surface  181   aa  (a surface on the right side in  FIG. 15 ) on a side of the outer pipe side O-ring  191  of the bulge processed portion  181   a  longer than a sum of a distance Y 1  to the beginning point  186   ea  of the portion, which comes into contact with the outer pipe  181 , among the outer pipe insertion portion  186   e  and the diameter of the outer pipe side O-ring  191 . The distance Y 1  to the beginning point  186   ea  of the portion, which comes into contact with the outer pipe  181 , among the outer pipe insertion portion  186   e  is also the distance Y 1  of the outer pipe O-ring holding portion  1862  among the outer pipe insertion portion  186   e.    
     The distal end  1811  of the outer pipe  181  is also inserted into the outer pipe insertion portion  186   e  prior to the outer pipe side O-ring  191 . Therefore, biting of the outer pipe side O-ring  191  can be satisfactorily prevented. 
     In this embodiment, similar to the fourth embodiment described above, the high-pressure communication space  186   k  is formed between the distal end  1811  of the outer pipe  181  and the innermost portion of the outer pipe insertion portion  186   e , and the low-pressure refrigerant flow path  186   f  is formed between the distal end  1821  of the inner pipe  182  and the innermost portion of the inner pipe insertion portion  1860 . Therefore, the distal end  1811  of the outer pipe  181  and the distal end  1821  of the inner pipe  182  are both free and do not interfere with other portions of the expansion valve side connector  186 , and the bulge processed portion  181   a  of the outer pipe  181  ca be surely abut to the end surface  1865 . Even if a positional shift between the distal end  1821  of the inner pipe  182  and the distal end  1811  of the outer pipe  181  occurs, it is possible to perform fine assembly. 
     In the embodiment of  FIGS. 15 and 16 , as in the example of  FIG. 8 , the outlet direction of the high-pressure refrigerant flow path  186   g  of the expansion valve side connector  186  and the inlet of the low-pressure refrigerant flow path  186   f  are placed so that the axes thereof are orthogonal with respect to the internal heat exchanger  18 . However, as in the embodiment of  FIG. 4 , the axes of the high-pressure refrigerant flow path  186   g  of the expansion valve side connector  186  and the inlet of the low-pressure refrigerant flow path  186   f  may be in the same direction as the axis of the internal heat exchanger  18 . Similar to the above examples, it is possible to have a degree of freedom in positional arrangements by changing the shape of the expansion valve side connector  186 .  FIG. 17  shows an example in which the axes of the outlet of the high-pressure refrigerant flow path  186   g  and the inlet of the low-pressure refrigerant flow path  186   f  and the axis of the internal heat exchanger  18  are in the same direction. 
     Also in the embodiment of  FIG. 17 , since the gap  1821   a  is formed between the distal end  1821  of the inner pipe  182  and the innermost portion (right side of  FIG. 17 ) of the inner pipe insertion portion  1860 , it is possible to bring into contact the bulge processed portion  181   a  of the outer pipe  181  with the end surface  1865 . 
     In the embodiment of  FIG. 17 , the rib  1815  is used instead of the spiral groove  1822  of  FIGS. 15 and 16 . The rib  1815  is formed integrally and toward inwardly from the outer pipe  181  similar to the double pipe of (c), (d), (e), (g), (i), (j), (m) and (n) of  FIG. 12 . Therefore, the rib  1815  is cut and removed at the end portion  1810  of the outer pipe  181 , and then the bulge processed portion  181   a  is formed in that state. 
     Ninth Embodiment 
     In the above-described embodiment, the high-pressure refrigerant flow path  186   g  is formed inside the expansion valve side connector  186  to communicate the high-pressure side joint  186   a  and the inner-outer flow path  18   a . However, as shown in  FIG. 18 , the high-pressure side joint  186   a  may be directly opposed to the high-pressure communication space  186   k  sealed by the inner pipe side O-ring  192  and the outer pipe side O-ring  191 . 
     In this case, the inside of the high-pressure side joint  186   a  becomes the high-pressure refrigerant flow path  186   g . Therefore, since the sealing plug  187  ( FIG. 4 ) of the expansion valve side connector  186  is also unnecessary, this facilitates a molding process. 
     In the embodiment of  FIG. 18 , the high-pressure side joint  186   a  and the low-pressure side joint  186   b  are formed in male shapes, but as shown in  FIG. 19 , the high-pressure side joint  186   a  and the low-pressure side joint  186   b  may be formed in female shapes. 
     Even in this embodiment, the distal end  1811  of the outer pipe  181  and the distal end  1821  of the inner pipe  182  are free, and the bulge processed portion  181   a  can be reliably brought into contact with the end surface  1865  similar to the above described embodiment. 
     In the embodiments shown in  FIGS. 18 and 19 , the inner pipe side O-ring groove  182   a  is formed in the inner pipe  182  to hold the inner pipe side O-ring  192 , as in the first embodiment. Similar to the eighth embodiment, the outer pipe  181  is formed in a straight at the end portion  1810  and holds the outer pipe side O-ring  191  on the outer circumference. 
     Here, compared to the straight shape, the inner pipe side O-ring groove O-ring groove  182   a  requires more steps to form, but on the other hand, if the straight shape is used, it is required to process the bulge processed portion  1825  for holding the inner pipe side O-ring  192 . Choice of a holding method may be determined to meet requirements by considering a sealing performance of the O-ring, an axial tolerance of the inner pipe  182  and/or the outer pipe  181  and the like. 
     This also applies to an example in which the outer pipe side O-ring groove  181   b  is formed in the outer pipe  181 . Therefore, whether the O-ring grooves  181   b  and  182   a  are formed or the straight shape is determined in consideration of the sealing performance, cost, and the like. 
     Further, in the embodiment of  FIGS. 18 and 19 , the bulge processed portion  181   a  of the outer pipe  181  is fixed by the caulking fixing portion  186   i  of the expansion valve side connector  186  as in the second embodiment shown in  FIG. 5 . In this way, combinations of embodiments may be selected to meet requirements. 
     Tenth Embodiment 
     In the above embodiment, the high-pressure side joint  186   a  and the low-pressure side joint  186   b  of the expansion valve side connector  186  are formed only on one side of the connector, but may be formed on both sides as shown in  FIG. 20 . The high-pressure side joint  186   a  and the low-pressure side joint  186   b  projecting to the right in  FIG. 20  are connected to the high-pressure refrigerant inlet  14   a  and the low-pressure refrigerant outlet  14   b  of the expansion valve  14 . The high-pressure side joint  186   a  and the low-pressure side joint  186   b  are also formed on the left side, and are connected to the high-pressure liquid refrigerant pipe  205  and the low-pressure gas refrigerant pipe  206 , respectively. The high-pressure liquid refrigerant pipe  205  has an outer diameter of 8 mm and a wall thickness of 1.0 mm. The low-pressure gas refrigerant pipe  206  has an outer diameter of 12.7 mm and a wall thickness of 1.2 mm. 
     The high-pressure liquid refrigerant pipe  205  and the low-pressure gas refrigerant pipe  206  in  FIG. 20  are connected to a rear cooler expansion valve  140  located at a rear of an automobile passenger compartment. The rear cooler expansion valve  140  is attached to the rear cooler evaporator  150  and decompresses and expands the refrigerant flowing into the rear cooler evaporator  150 . An operation of the expansion valve  140  for the rear cooler and the evaporator  150  for the rear cooler is the same as that of the expansion valve  14  and the evaporator  15  of the indoor air conditioning unit  20  described above. 
     Eleventh Embodiment 
     In the embodiment of  FIG. 20 , two pipes including the high-pressure liquid refrigerant pipe  205  and the low-pressure gas refrigerant pipe  206  are shown, but the pipes  205  and  206  both may be double pipes.  FIG. 21  shows an example in which a rear pipe connecting the rear cooler and the expansion valve side connector  186  is a rear side internal heat exchanger  208  made of the double pipe. The low-pressure refrigerant from the low-pressure refrigerant outlet  14   b  of the expansion valve  14  and the low-pressure refrigerant from the inner pipe  182  of the rear internal heat exchanger  208  flow into the low-pressure refrigerant flow path  186   f , and two low-pressure refrigerants are merged in the low-pressure refrigerant flow path  186   f , and are sucked into the compressor  12  through the inner flow path  18   b  of the inner pipe  182 . 
     The high-pressure refrigerant flow path  186   g  of the expansion valve side connector  186  branches at the branch portion  1867 , and one of the high-pressure refrigerant flow paths  186   g  flows from the high-pressure side joint  186   a  into the high-pressure refrigerant inlet  14   a  of the expansion valve  14 . The other branched portion flows from the rear side high-pressure refrigerant flow path  1868  and into the inner-outer flow path  18   a  of the rear side internal heat exchanger  208 . The connection between the outer pipe  181  and the inner pipe  182  of the rear side internal heat exchanger  208  and the expansion valve side connector  186  is the same as that of the above-described embodiment. An outer diameter of the inner pipe  182  of the rear side internal heat exchanger  208  is 12.7 mm, and an outer diameter of the outer pipe  181  is 15.9 mm. Each wall thickness is 1.2 mm. 
     Twelfth Embodiment 
     In the above-described embodiment, the axis of the double pipe is aligned with or orthogonal to the extension direction of the high-pressure side joint  186   a  and the low-pressure side joint  186   b . However, an angle between the axis of the double pipe and the extension direction of the high-pressure side joint  186   a  and the low-pressure side joint  186   b  can be freely set. 
       FIGS. 22 and 23  are examples in which the angle between the extension direction of the high-pressure side joint  186   a  and the low-pressure side joint  186   b  and the axis of the double pipe is an obtuse angle. This angle may be designed according to an assembling direction of the double pipe to meet requirements, and of course, it may be an acute angle. 
     Thirteenth Embodiment 
     As described above, the pressure switch  34  and the like may be eliminated from the fifth embodiment of  FIGS. 9 and 10 .  FIG. 24  shows the counter-expansion valve side connector  31  in which the pressure switch  34  and the like are eliminated. The high-pressure side piping member  35  through which the high-pressure liquid refrigerant flows from the condenser  13  is inserted into the high-pressure side joint portion  313  of the counter-expansion valve side connector  31  and fixed by using the high-pressure side joint plate  36  and a bolt (not shown). 
     The low-pressure side piping member  37  through which the low-pressure gas refrigerant flowing toward the suction port of the compressor  12  flows is inserted into the low-pressure side joint portion  314  of the counter-expansion valve side connector  31  and fixed by the low-pressure side joint plate  38  and the bolt  381 . In this embodiment, the high-pressure side joint portion  313  and the low-pressure side joint portion  314  are female members. 
     In the counter-expansion valve side connector  31 , the distal end  1821  of the inner pipe  182  is inserted into the inner pipe insertion portion  3113  and the distal end  1811  of the outer pipe  181  is inserted into the outer pipe insertion portion  3111 . In an inserted state, the bulge processed portion  181   a  comes into contact with the end surface  3112  and is fixed by a holding plate  390  and the bolt  391 . 
     The distal end  1811  of the outer pipe  181  is open to the high-pressure communication space  3110  and does not interfere at the inserting process. Further, the distal end  1821  of the inner pipe  182  enters into an inside of the low-pressure side piping member  37 , and the distal end  1821  is not interfered. 
     The high-pressure communication space  3110  is sealed by the outer pipe side O-ring  191  and the inner pipe side O-ring  192 . Then, the high-pressure communication space  3110  communicates with the inner-outer flow path  18   a . Therefore, in the present embodiment, the high-pressure communication space  3110  forms a high-pressure refrigerant flow path. 
     The inner pipe  182  enters into an inside of the low-pressure side piping member  37 , and the inner flow path  18   b  is sealed by the inner pipe side O-ring  192  and an O-ring  370  of the low-pressure side piping member  37 . Therefore, in the present embodiment, the low-pressure side refrigerant flow path corresponds to the end portion  1820  of the inner pipe  182 . At the portion of the counter-expansion valve side connector  31 , the inner pipe insertion portion  3113  holding the end portion  1820  corresponds to the low-pressure side refrigerant flow path. 
     Fourteenth Embodiment 
     In the eleventh embodiment in  FIG. 20  and the twelfth embodiment in  FIG. 21 , both the high-pressure liquid refrigerant pipe  205  and the low-pressure gas refrigerant pipe  206  for the rear cooler are branched by the expansion valve side connector  186 . 
     The present embodiment is the same as the eleventh embodiment and the twelfth embodiment in that the high-pressure liquid refrigerant pipe  205  for the rear cooler is branched by the expansion valve side connector  186 . However, as shown in  FIGS. 25 to 27 , the low-pressure gas refrigerant pipe  206  for the rear cooler is fixed to the counter-expansion valve side connector  31  by a holding plate  380  and a bolt (not shown). 
     In this embodiment, the high-pressure communication space  3110  of the counter-expansion valve side connector  31  communicates with the inner-outer flow path  18   a  of the internal heat exchanger  18  ( FIG. 26 ). Therefore, all the high-pressure liquid refrigerant from the condenser  13  flows into the inner-outer flow path  18   a . Then, the expansion valve side connector  186  branches into a flow flowing to the expansion valve  14  of the indoor air conditioning unit  20  for a front side and a flow flowing to the expansion valve of the rear cooler. 
     On the other hand, the flow of the low-pressure gas refrigerant merges in the low-pressure communication space  3120  of the counter-expansion valve side connector  31  ( FIG. 25 ). That is, the inner flow path  18   b  and the low-pressure gas refrigerant pipe  206  of the rear cooler are open to the low-pressure communication space  3120 . The low-pressure side piping member  37  is also connected to the low-pressure communication space  3120 , and the gas refrigerant merged is sucked into the compressor  12  via the low-pressure side piping member  37 . 
     As shown in  FIG. 27 , an arrangement position of the high-pressure side piping member  35  and an arrangement position of the low-pressure gas refrigerant pipe  206  of the rear cooler are orthogonal to each other.  FIG. 25  shows a cross-sectional view at a position where the low-pressure gas refrigerant pipe  206  of the rear cooler is shown, and  FIG. 26  shows a cross-sectional view at a position where the high-pressure side piping member  35  is shown. 
     The internal heat exchanger  18  and the counter-expansion valve side connector  31  are sealed by the outer pipe side O-ring  191  and the inner pipe side O-ring  192  as in the above embodiment. Further, the counter-expansion valve side connector  31  and the low-pressure side piping member  37  are sealed by the O-ring  370 , and the rear cooler low-pressure gas refrigerant piping  206  is also sealed by an O-ring  3800 . The high-pressure side piping member  35  is also sealed by an O-ring  350 . Performing a connection of the double pipe or the piping member by mechanical assembling using the O-ring and the bolt is the same as the above-described embodiment. 
     As shown in  FIG. 27 , the low-pressure side service valve  33  is attached to the low-pressure side piping member  37 . Although not shown, a high-pressure side service valve  32  is attached to the high-pressure side piping member  35 . The pressure sensor or pressure switch  34  is attached to an outlet side tank of the high-pressure side piping member  35  or the condenser  13 . However, the pressure switch  34  or the like may be attached to the counter-expansion valve side connector  31  as in the fifth embodiment shown in  FIG. 10 . 
     In the present embodiment, it is possible to obtain a predetermined sub-cool to the high-temperature and high-pressure liquid refrigerant flowing through the inner-outer flow path  18   a  by performing heat exchange with the low-temperature and low-pressure gas refrigerant from the evaporator  15  of the indoor air-conditioning unit  20  on the front side. In that state, it flows into both expansion valves  14  and  140  for the indoor air-conditioning unit  20  on the front side and the rear cooler, and is evaporated by the evaporators  15  and  150 , respectively, therefore, it is possible to perform efficient operation of the refrigeration cycle. 
     On the other hand, among the refrigerant sucked into the compressor  12 , the refrigerant from the evaporator  15  of the indoor air-conditioning unit  20  on the front side is overheated by performing heat exchange at the internal heat exchanger  18 , but the refrigerant from the rear cooler evaporator  150  does not perform heat exchange. Therefore, it is possible to prevent a situation in which the temperature of the refrigerant sucked into the compressor  12  becomes higher than necessary. In addition, a degree of freedom in handling the low-pressure gas refrigerant pipe  206  of the rear cooler is increased. 
     Fifteenth Embodiment 
     In the thirteenth embodiment shown in  FIG. 24 , the inner pipe  182  is fitted into the counter-expansion valve side connector  31 , but the expansion valve side connector  186  may be similarly configured. As shown in  FIG. 29 , the inner pipe  182  may penetrate the expansion valve side connector  186  to configure a low-pressure joint. In this example, a low-pressure side O-ring groove  186   d  is formed in the inner pipe  182  to hold the low-pressure side O-ring  194 . 
     Also in this embodiment, the low-pressure side refrigerant flow path corresponds to the end portion  1820  of the inner pipe  182 . At the counter-expansion valve side connector  186 , the inner pipe insertion portion  1860  holding the end portion  1820  corresponds to the low-pressure side refrigerant flow path. 
     In the present embodiment, the low-pressure side O-ring groove  186   d  having a circumferential groove-shape is formed on the inner pipe  182  during condition in which the double pipe is inserted into the expansion valve side connector  186  and fixed by the holding plate  188  with a bolt (not shown). Since the inner pipe  182  is deformed and comes into contact with the expansion valve side connector  186  when the low-pressure side O-ring groove  186   d  is formed, a joint between the double pipe and the expansion valve side connector  186  becomes stronger. 
     Sixteenth Embodiment 
     In the eleventh embodiment in  FIG. 21 , the double pipe is used from the rear cooler to the expansion valve side connector  186 , and further, the double pipe is also used from the expansion valve side connector  186  to a side of the compressor  12  and the condenser  13 . Therefore, as compared with the example in  FIG. 20 , the liquid refrigerant flowing toward the rear cooler is more sub-cooled. In other words, an amount of super-heat of the gas refrigerant flowing from the rear cooler to the compressor  12  becomes large. Therefore, an adoption of the double pipe connected to the rear cooler requires to determine whether the internal heat exchanger  18  is adopted, and an amount of heat exchange thereof based on evaluating an efficiency of the entire refrigeration cycle. 
     Therefore, as in the embodiment shown in  FIG. 30 , a connector connecting two double pipes may be adopted for the counter-expansion valve side connector  31 . In this case, the internal heat exchanger  18  communicates with the front-side indoor air-conditioning unit  20  arranged in the casing  21 , and the rear-side internal heat exchanger  208  communicates with the rear cooler. 
     The low-pressure gas refrigerant from the indoor air-conditioning unit  20  on the front side and the rear cooler flows into the counter-expansion valve side connector  31  from the respective inner flow paths  18   b  and merges in the low-pressure communication space  3120 . Next, it is sucked into the compressor  12  from the low-pressure side piping member  37 . The high-pressure liquid refrigerant condensed by the condenser  13  is separated in the high-pressure communication space  3110  of the counter-expansion valve side connector  31 , and flows out to the indoor air conditioning unit  20  on the front side and the rear cooler through the respective inner-outer flow paths  18   a.    
     That is, the high-pressure liquid refrigerant that has flowed into the high-pressure communication space  3110  from the high-pressure side joint portion  313  of the counter-expansion valve side connector  31  flows into the inner-outer flow path  18   a  of the internal heat exchanger  18 . The flow of this high-pressure refrigerant is the same as in  FIG. 26 . 
     In the present embodiment, the counter-expansion valve side connector  31  is formed with a rear side high-pressure refrigerant flow path  311   a  toward the rear side internal heat exchanger  208 . Then, the high-pressure refrigerant branches in the high-pressure communication space  3110  and also flows into the rear-side high-pressure refrigerant flow path  311   a . The liquid refrigerant entering into the rear side high-pressure refrigerant flow path  311   a  flows into the inner-outer flow path  18   a  of the rear side internal heat exchanger  208 . 
     The low-pressure gas refrigerant entering into from the inner flow path  18   b  of the internal heat exchanger  18  and the low-pressure gas refrigerant entering into from the inner flow path  18   b  of the rear side internal heat exchanger  208  are merged in the low-pressure communication space  3120  of the counter-expansion valve side connector  31 . Then, the low-pressure gas refrigerant merged flows from the low-pressure side joint portion  314  to the suction port of the compressor  12  via the low-pressure side piping member  37 . 
     OTHER EMBODIMENTS 
     The above-described embodiments may be combined with each other to meet requirements. The above-described embodiments may be variously modified as follows, for example. 
     (1) The spiral groove on the outer surface of the inner pipe  182  is not limited to the one having three threads, but may be a groove portion having one, two, four, etc., and may be a plurality of spiral grooves are provided in a crossing manner. Alternative to the spiral groove, a straight groove extending linearly parallel to the axial direction of the inner pipe  182  may be formed. This is similar to the spiral groove  1816  formed on the outer pipe  181 . 
     (2) In the above embodiment, the outer pipe  181  and the inner pipe  182  are made of aluminum, but is not limited to this, and may be made of iron or copper etc. Other materials may be used as long as they have a good heat transfer coefficient. 
     (3) In the above embodiment, the internal heat exchanger  18  arranged in the refrigeration cycle apparatus  11  is applied to the vehicle air conditioner  10 , but is not limited to this, and may be applied to a stationary air conditioner such as an air conditioner for homes and buildings etc. 
     (4) In the above-described embodiment, a fluorocarbon refrigerant is used as the refrigerant for the refrigeration cycle apparatus  11  and configures a sub-critical refrigeration cycle in which a high-pressure side refrigerant pressure does not exceed a critical pressure of the refrigerant. However, carbon dioxide may be used as the refrigerant to configure a super-critical refrigeration cycle in which a high-pressure side refrigerant pressure is equal to or higher than the critical pressure of the refrigerant. 
     (5) In the fifth embodiment, both ends of the outer pipe  181  and the inner pipe  182  are connected by the expansion valve side connector  186  and the counter-expansion valve side connector  31 . However, only one end on the condenser  13  side and the compressor  12  side among the outer pipe  181  and the inner pipe  182  may be connected by the counter-expansion valve side connector  31 . 
     That is, it may be possible to employ a structure in which the end of the outer pipe  181  and the inner pipe  182  opposite side to the expansion valve  14  is connected to the condenser  13  and the compressor  12  by the counter-expansion valve side connector  31 , and the end of the outer pipe  181  and the inner pipe  182  side to the expansion valve  14  is connected to the expansion valve  14  by a liquid pipe, a suction pipe and a joint. 
     (6) Similarly, in the fifth embodiment, the pressure sensor is used instead of the pressure switch  34 , but if necessary, both the pressure switch  34  and the pressure sensor may be used. 
     (7) In the above-described embodiment, although a positional relation is designed so that the inner pipe side O-ring  192  comes into contact with the expansion valve side connector  186  prior to the outer pipe side O-ring  191  when the double pipe is inserted into the expansion valve side connector  186 , if necessary, a reverse relation may be employed. That is, the outer pipe side O-ring  191  may come into contact with the expansion valve side connector  186  in a prior manner. 
     When the inner pipe side O-ring  192  and the outer pipe side O-ring  191  are in contact with the expansion valve side connector  186 , the inner pipe  182  and the outer pipe  181  are inserted into the expansion valve side connector  186  and the axes are aligned, therefore, biting of the inner pipe side O-ring  192  and the outer pipe side O-ring  191  can be satisfactorily prevented.