Patent Publication Number: US-2023158753-A1

Title: Resin connector connection structure and method of manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of International Application number PCT/JP2022/010007 filed on Mar. 8, 2022, which claims the priority benefit of Japan Patent Application No. 2021-058510, filed on Mar. 30, 2021. The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a resin connector connection structure and a method of manufacturing the same. 
     BACKGROUND ART 
     In description of Patent Literature 1, a tube is inserted into a tubular band made of plastic that is transparent to a laser beam, and the band and the tube are welded to each other with a laser beam. 
     CITATION LIST 
     Patent Literature 
     
         
         [Patent Literature 1] 
       
    
     Japanese Patent No. 4503966 
     In connection between a resin connector and a resin tube (also referred to as a resin hose or a resin pipe), welding using a laser beam described in Patent Literature 1 can be considered. Here, in the resin connector, the resin tube is connected to a first opening side, and a separate connection target member is connected to a second opening side. This type of connector is formed to contain a filler such as a glass fiber filler in a base material resin in order to increase a bending elastic modulus (strength against deformation). 
     However, a transmittance of a laser beam changes depending on the presence or absence of the filler. Furthermore, the transmittance of a laser beam also changes depending on a density of the filler. Therefore, in a case where a welded portion between the resin connector and the resin tube is irradiated with a laser beam, heat energy generated at the welded portion varies due to an influence of the filler, and there is a possibility of joining strength varying depending on a position. 
     SUMMARY 
     The present disclosure has been made in view of such a background, and an objective of the present disclosure is to provide a resin connector connection structure capable of ensuring a bending elastic modulus of a resin connector while curbing a variation in joining strength between the resin connector and a resin tube and a method of manufacturing the same. 
     According to an aspect of the present disclosure, there is provided a resin connector connection structure including: a resin connector which has a tubular shape, and to both ends of the resin connector being configured to connect connection target members; and a resin tube which constitutes one of the connection target members, in the resin tube having a tubular shape, and the resin tube being fitted to a first opening side of the resin connector, wherein the resin connector includes a connector main body portion which has a tubular shape, the connector main body being formed of a main portion base material resin that contains a reinforcing filler, and a connector end portion which has a tubular shape, the connector end portion being formed of an end portion base material resin that (i) does not contain the reinforcing filler or (ii) contains the reinforcing filler at a lower proportion than the connector main body portion, and the connector end portion being directly or indirectly joined to the connector main body portion such that the connector end portion constitutes an end portion of the resin connector on the first opening side, and wherein the resin tube is formed of a material having a higher absorption rate of a laser beam than the connector end portion, and the resin tube is fitted to the connector end portion to be welded to an inner peripheral surface or an outer peripheral surface of the connector end portion and to be welded at a position other than an axial position at which the connector main body portion is positioned in the resin connector. 
     According to another aspect of the present disclosure, there is provided a method of manufacturing the resin connector connection structure described above, the method including: welding radially facing surfaces of the resin tube and the connector end portion to each other by emitting a laser beam from a side of the connector end portion in the radial direction in a state where the resin tube is fitted to the connector end portion. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is an axial cross-sectional view showing a resin connector connection structure of a first embodiment. 
         FIG.  2    is a flow chart showing a method of manufacturing the resin connector connection structure of the first embodiment. 
         FIG.  3    is an axial cross-sectional view showing a resin connector connection structure of a second embodiment. 
         FIG.  4    is an axial cross-sectional view showing a resin connector connection structure of a third embodiment. 
         FIG.  5    is an axial cross-sectional view showing a resin connector connection structure of a fourth embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     According to the resin connector connection structure and the method of manufacturing the same described above, the connector main body portion of the resin connector contains the reinforcing filler and thus has a high bending elastic modulus. The connector end portion of the resin connector forms the welded portion with the resin tube. The connector end portion does not contain the reinforcing filler, or contains the reinforcing filler at a lower content proportion than the connector main body portion. Therefore, the bending elastic modulus of the connector end portion is lower than that of the connector main body portion. 
     However, the connector end portion is required to have a high joining strength caused by the welding with the resin tube and a small variation in the joining strength rather than the bending elastic modulus. Here, the connector end portion does not contain the reinforcing filler, or contains the reinforcing filler at a lower content proportion than the connector main body portion. Therefore, the connector end portion has a higher transmittance of the laser beam than the connector main body portion. Furthermore, it is possible to curb a variation in the joining strength of the welded portion between the connector end portion and the resin tube caused by the emission of the laser beam due to the filler. 
     That is, in the resin connector, the connector main body portion and the connector end portion are differentiated from each other in terms of a function. The connector main body portion functions as a portion that ensures the bending elastic modulus, and the connector end portion functions as a portion that ensures the joining strength caused by the welding with the resin tube. Therefore, the connection structure between the resin connector and the resin tube as a whole can ensure the bending elastic modulus of the resin connector while curbing the variation in joining strength between the resin connector and the resin tube. 
     Reference signs in parentheses in the claims indicate the correspondence with specific means described in embodiments which will be described later and do not limit the technical scope of the present disclosure. 
     1. First Embodiment 
     1-1. Configuration of resin connector connection structure  1   
     A configuration of a resin connector connection structure  1  will be described with reference to  FIG.  1   . As shown in  FIG.  1   , the resin connector connection structure  1  includes a resin connector  10 , a resin tube  20  (also referred to as a resin hose or a resin pipe) that constitutes one of connection target members, and a pipe  30  that constitutes the other of the connection target members. The resin connector  10  functions as a member that mediates connection between the resin tube  20  and the pipe  30 . The resin connector  10 , the resin tube  20 , and the pipe  30  are each formed in a tubular shape for circulating a fluid, and the fluid circulates between the resin tube  20  and the pipe  30  via the resin connector  10 . 
     The resin connector  10  is formed of a resin in a tubular shape. However, the resin connector  10  is not limited to a straight tubular shape and may have a curved tubular shape. The resin tube  20  and the pipe  30 , which are connection target members, are connected to both tubular ends of the resin connector  10 . In the present embodiment, the resin connector  10  and the resin tube  20  are joined to each other by welding using a laser beam B (indicated by a dashed line in  FIG.  1   ). On the other hand, the resin connector  10  and the pipe  30  are connected by locking with a claw or the like. However, the connection between the resin connector  10  and the pipe  30  is not limited to the locking and may be performed by an arbitrary method. 
     The resin tube  20  is formed in a long tubular shape. The resin tube  20  is formed longer than at least the resin connector  10 . The resin tube  20  is fitted to a first opening side (a right end side in  FIG.  1   ) of the resin connector  10 .  FIG.  1    illustrates a case where the resin tube  20  is inserted into the inside of the resin connector  10  on the first opening side, but the resin tube  20  may be mounted on the outside of the resin connector  10  on the first opening side. 
     The resin tube  20  is formed of a material having a high absorption rate of a laser beam B. That is, the resin tube  20  generates heat by being irradiated with the laser beam B. For example, in a case where gasoline is circulated, the resin tube  20  has a multi-layer structure in consideration of gasoline resistance, fuel permeation resistance, weather resistance, and the like. Moreover, the resin tube  20  may be formed in a straight tubular shape, or may be formed in a curved tubular shape. 
     The pipe  30  is formed of a metal or a resin in a tubular shape. The pipe  30  is fitted to a second opening side (a left end side in  FIG.  1   ) of the resin connector  10 . In the present embodiment, the pipe  30  is inserted into the inside of the resin connector  10  on the second opening side, but the pipe  30  may be fitted to the outside of the resin connector  10  on the second opening side. Further, the pipe  30  is provided with an annular flange  31  protruding radially outward at a position spaced apart from a tip end. The annular flange  31  of the pipe  30  is a portion that is locked to the resin connector  10  in an axial direction of a second opening portion of the resin connector  10 . 
     1-2. Detailed configuration of resin connector  10   
     A detailed configuration of a resin connector  10  will be described with reference to  FIG.  1   . The resin connector  10  includes a connector main body portion  11  and a connector end portion  12 . 
     The connector main body portion  11  is disposed at least in an intermediate portion of the resin connector  10  in an axial direction (a central axis direction of the tubular shape of the resin connector  10 ). However, in the present embodiment, the connector main body portion  11  is disposed not only in the intermediate portion of the resin connector  10  in the axial direction but also in a portion constituting a second opening end. The connector main body portion  11  corresponds to a portion having a high bending elastic modulus. In particular, the connector main body portion  11  has a high bending elastic modulus in order to exhibit sufficient locking force with the pipe  30 . Here, the resin tube  20  is not welded to the connector main body portion  11 . That is, in the resin connector  10 , the resin tube  20  is not welded to an axial position at which the connector main body portion  11  is positioned. 
     The connector main body portion  11  is formed in a tubular shape and is locked to the pipe  30 . The connector main body portion  11  includes, for example, a locking claw  11   a  that is locked to the annular flange  31  of the pipe  3 . The locking claw  11   a  is elastically deformed to allow the pipe  30  to be inserted and is locked to the annular flange  31  after the pipe  30  is inserted. That is, the locking claw  11   a  functions as a retaining member for the pipe  30 . 
     In addition, the connector main body portion  11  includes a joining surface  11   b  for directly joining with the connector end portion  12  and a positioning end surface  11   c  for positioning the resin tube  20  by coming into contact with a tip end surface of the resin tube  20  at an end on a side opposite to a side into which the pipe  30  is inserted (a right end in  FIG.  1   ). In the present embodiment, the positioning end surface  11   c  is positioned radially inside the joining surface  11   b . Further, in the present embodiment, the joining surface  11   b  and the positioning end surface  11   c  are formed on the same plane, but they may be formed at different positions in the axial direction. 
     The connector main body portion  11  is required to have strength against deformation in order to lock with the pipe  30 . Therefore, the connector main body portion  11  is formed to contain a reinforcing filler in a main portion base material resin. 
     Examples of the main portion base material resin include polypropylene, polyamide, polyphenylene sulfide, polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polybutylene naphthalate, polymethylpentene, polyethylene, polyacetal, a fluorine resin, and the like. As the polypropylene, for example, one having a refractive index of 1.47 to 1.51 is used. As the polyamide, for example, one having a refractive index of 1.51 to 1.55 is used. 
     As the reinforcing filler, glass fiber, carbon fiber, potassium titanate, glass beads, milled fiber, talc, and the like are used. Here, since the connector main body portion  11  is not a portion irradiated with the laser beam B for welding, it is not necessary to consider a transmittance of the laser beam B for the reinforcing filler used in the connector main body portion  11 . Therefore, the reinforcing filler may be applied without considering the refractive index. 
     The resin connector connection structure  1  preferably includes an annular sealing member  40  such as an O-ring between an inner peripheral surface of the connector main body portion  11  and an outer peripheral surface of the pipe  30 . The sealing member  40  can ensure sealing performance between the connector main body portion  11  and the pipe  30 . 
     The connector end portion  12  constitutes a portion of the resin connector  10  on the first opening side, that is, an end portion on a side into which the resin tube  20  is inserted. The connector end portion  12  corresponds to a welded portion with the resin tube  20 . The connector end portion  12  is formed in a tubular shape. 
     Further, in the present embodiment, the connector end portion  12  has a joining surface  12   a  that is directly joined to the joining surface  11   b  of the connector main body portion  11  at an axial end portion. The connector end portion  12  is directly joined to the connector main body portion  11  by, for example, two-color molding, friction welding, or the like. That is, the joining surface  12   a  of the connector end portion  12  is directly joined to the joining surface  11   b  of the connector main body portion  11 . However, the connector end portion  12  may be indirectly joined to the connector main body portion  11  via a separate member. Further, the joining surface  12   a  of the connector end portion  12  may be provided at an outer peripheral surface or an inner peripheral surface without being limited to the axial end portion. 
     Furthermore, in the connector end portion  12 , the outer peripheral surface and the inner peripheral surface are exposed over the entire circumference at least in part in the axial direction. In particular, the outer peripheral surface and the inner peripheral surface of the connector end portion  12  are exposed at a portion of the resin connector  10  on the first opening side. That is, it means that the connector main body portion  11  does not present in the exposed portion of the connector end portion  12 . 
     The connector end portion  12  includes a guide portion  12   b  formed in a tapered shape on the inner peripheral surface of an opening end of the connector end portion  12 . The maximum inner diameter of the tapered shape of the guide portion  12   b  is approximately the same as an outer diameter of a tip end portion of the resin tube  20  or slightly larger than the outer diameter of the tip end portion of the resin tube  20 . Further, the minimum inner diameter of the tapered shape of the guide portion  12   b  is smaller than the outer diameter of the tip end portion of the resin tube  20 . Therefore, when the resin tube  20  is inserted into the inside of the connector end portion  12 , the guide portion  12   b  comes into contact with an outer peripheral surface of the resin tube  20 . The guide portion  12   b  guides contraction of the resin tube  20 . 
     Further, the connector end portion  12  includes a cylindrical inner peripheral surface portion  12   c  which is formed adjacent to the guide portion  12   b  on the inner peripheral surface of the connector end portion  12  and is formed in a cylindrical inner peripheral surface shape. The cylindrical inner peripheral surface portion  12   c  is formed over the entire axial range between the tapered guide portion  12   b  and the joining surface  12   a  that is directly joined to the connector main body portion  11 . 
     An inner diameter of the cylindrical inner peripheral surface portion  12   c  of the connector end portion  12  matches the minimum inner diameter of the guide portion  12   b . That is, the inner diameter of the cylindrical inner peripheral surface portion  12   c  is smaller than the outer diameter of the tip end portion of the resin tube  20 . Therefore, the tip end portion of the resin tube  20  is inserted into the inside of the cylindrical inner peripheral surface portion  12   c  in the radial direction in a contracted state. That is, the cylindrical inner peripheral surface portion  12   c  is brought into a state in which the outer peripheral surface of the resin tube  20  having a reduced diameter is in close contact with the cylindrical inner peripheral surface portion  12   c.    
     The connector end portion  12  is required to have joining strength with the resin tube  20 . As described above, the connector end portion  12  and the resin tube  20  are joined to each other by being welded together by being irradiated with the laser beam B. Here, the resin tube  20  is formed of a material having a higher absorption rate of the laser beam B than the connector end portion  12 . 
     The higher the transmittance of the laser beam B, the better the connector end portion  12 , and the smaller the variation in the transmittance of the laser beam B, the better the connector end portion  12 . The higher the transmittance of the laser beam B, the more the laser beam B can be emitted to the welded portion. The smaller the variation in the transmittance of the laser beam B, the smaller the variation in the joining strength caused by the welding. In particular, it is known that the filler affects the variation in the transmittance of the laser beam B. Therefore, the connector end portion  12  is formed without containing the reinforcing filler in the end portion base material resin, or is formed to contain the reinforcing filler in the base resin for an end portion at a lower proportion than the connector main body portion  11 . 
     In a case where the reinforcing filler is not contained, the end portion base material resin only has to be any resin material that transmits the laser beam B. In a case where the reinforcing filler is not contained, of course, there is no effect of the reinforcing filler, and thus there is no variation in the transmittance of the laser beam B due to the reinforcing filler. In this case, examples of the end portion base material resin include polypropylene, polyamide, polyphenylene sulfide, polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polybutylene naphthalate, polymethylpentene, polyethylene, polyacetal, a fluorine resin, and the like. 
     Here, from the viewpoint of a joining force between the connector main body portion  11  and the connector end portion  12 , the main portion base material resin of the connector main body portion  11  and the end portion base material resin of the connector end portion  12  are preferably polymers of the same type. However, even polymers of different types can be mechanically or chemically connected to each other as long as they have close melting points or have functional groups (for example, maleic anhydride and the like). 
     In a case where the connector end portion  12  contains the reinforcing filler, it is required not to interfere with the transmission of the laser beam B and not to greatly affect the variation in the transmittance of the laser beam B. Therefore, firstly, it is effective to make a content proportion of the reinforcing filler extremely low. Secondly, it is possible to make the refractive index of the end portion base material resin and the refractive index of the reinforcing filler close to each other. For example, it is preferable that a difference in refractive index be within 0.02. However, even if a reinforcing filler having a refractive index close to that of the end portion base material resin is used, it is preferable that the content proportion of the reinforcing filler be low. 
     When the reinforcing filler is contained, polypropylene, polyamide, or the like is used as the end portion base material resin. As the polypropylene, for example, one having a refractive index of 1.47 to 1.51 is used. As the polyamide, for example, one having a refractive index of 1.51 to 1.55 is used. 
     A glass fiber filler is used as the reinforcing filler having a refractive index close to that of the end portion base material resin. The refractive index of the glass fiber filler is, for example, 1.4 to 1.7. Examples of the glass fiber which is a material of the glass filler include D glass (low dielectric constant glass), NE glass (acid-resistant alkali glass), A glass (alkali glass), S glass (high strength and high elastic modulus glass), alkali-resistant glass, and the like. 
     The connector end portion  12  and the resin tube  20  are welded to each other by the laser beam B. In the present embodiment, the cylindrical inner peripheral surface portion  12   c  of the connector end portion  12  and the outer peripheral surface of the tip end portion of the resin tube  20  are welded to each other. Specifically, the welded portion between the connector end portion  12  and the resin tube  20  is formed in a ring shape that is closed over the entire circumference. For example, the welded portions may be formed at a plurality of locations in the axial direction, or the welded portion may be formed at one location in the axial direction. In order to ensure the joining strength caused by the welding, it is preferable to ensure a width of the welded portion to be equal to or larger than a specified width. The welded portions formed at a plurality of locations are a plurality of discontinuous welded portions each having a ring shape. 
     The welded portion is positioned at a position spaced apart from a boundary portion between the connector main body portion  11  and the connector end portion  12 . That is, the welded portion does not include the connector main body portion  11 . In other words, the resin tube  20  is welded to a position of the resin connector  10  other than the axial position at which the connector main body portion  11  is positioned. In further other words, the resin tube  20  is welded to a portion of the connector end portion  12  which is exposed to the outer peripheral surface and the inner peripheral surface. Furthermore, the resin tube  20  is welded to the cylindrical inner peripheral surface portion  12   c  of the connector end portion  12 , but is not welded to the guide portion  12   b.    
     1-3. Method of manufacturing resin connector connection structure  1   
     Next, a method of manufacturing the resin connector connection structure  1  will be described with reference to  FIGS.  1  and  2   . First, as shown in  FIG.  2   , the resin connector  10  is manufactured (S 1 ). In the present embodiment, the connector main body portion  11  and the connector end portion  12  are integrally formed with each other by two-color molding. In this manner, the connector main body portion  11  and the connector end portion  12  are directly joined to each other. 
     Subsequently, the tip end portion of the resin tube  20  is inserted into the opening (the first opening) of the resin connector  10  on a side of the connector end portion  12  (S 2 ). Due to a relationship between the maximum inner diameter and the minimum inner diameter of the guide portion  12   b  of the connector end portion  12  and the outer diameter of the tip end portion of the resin tube  20 , an outer peripheral edge of the tip end portion of the resin tube  20  comes into contact with the guide portion  12   b.    
     When the resin tube  20  is inserted into the connector end portion  12 , the tip end portion of the resin tube  20  is contracted while the outer peripheral edge of the tip end portion of the resin tube  20  comes into contact with the guide portion  12   b . The tip end portion of the resin tube  20  comes into close contact with the cylindrical inner peripheral surface portion  12   c  of the connector end portion  12  in a contracted state. The resin tube  20  is inserted to a position at which the tip end of the resin tube  20  comes into contact with the positioning end surface  11   c  of the connector main body portion  11 . 
     Subsequently, in a range where the resin tube  20  is fitted (inserted in the present embodiment) to the connector end portion  12 , the laser beam B is emitted from a side of the connector end portion  12  in the radial direction, that is, from an outside in the radial direction, to weld radially facing surfaces of the connector end portion  12  and the resin tube  20  to each other (S 3 ). 
     The connector end portion  12  is formed of a material that transmits the laser beam B, and the resin tube  20  is formed of a material that absorbs the laser beam B. Further, in S 2 , the cylindrical inner peripheral surface portion  12   c  of the connector end portion  12  and the outer peripheral surface of the tip end portion of the resin tube  20  are in close contact with each other. Further, the axial portion of the connector end portion  12  that is in close contact with the resin tube  20  corresponds to a portion of the connector end portion  12  which is exposed to the outer peripheral surface and the inner peripheral surface. 
     In this state, the connector end portion  12  is irradiated with the laser beam B from the outside in the radial direction. That is, the laser beam B is emitted to a portion of the connector end portion  12  of the resin connector  10  which is exposed to the outer peripheral surface and the inner peripheral surface. In other words, the portion irradiated with the laser beam B is a portion formed only by the connector end portion  12  in the entire radial width of the resin connector  10 . As a result, most of the laser beam B is transmitted through the connector end portion  12 , heat is generated on the facing surface (the close contact surface) between the connector end portion  12  and the resin tube  20 , and the connector end portion  12  and the resin tube  20  are welded to each other. In particular, the laser beam B is emitted such that the welded portions between the connector end portion  12  and the resin tube  20  are formed at a plurality of locations in the axial direction and are formed in a closed ring shape over the entire circumference. 
     For example, when the plurality of locations in the axial direction is irradiated with the laser beam B, the welded portions in a ring shape which each have an irradiation width of the laser beam B may be formed at the plurality of locations in the axial direction. In addition, when the laser beam B is spirally emitted such that some of irradiation ranges of the laser beam B overlap each other, the welded portion in a ring shape which has a longer axial length than the irradiation width of the laser beam B may be formed at one location. Further, in a case where the irradiation width of the laser beam B is equal to or larger than a specified width for ensuring the joining strength, when only one location in the axial direction is irradiated with the laser beam B, the welded portion in a ring shape which has an irradiation width of the laser beam B may be formed at the one location in the axial direction. 
     Subsequently, the pipe  30  is inserted into the connector main body portion  11  (S 4 ). In this manner, the resin connector connection structure  1  is manufactured. 
     1-4. Effects 
     According to the resin connector connection structure  1 , the connector main body portion  11  of the resin connector  10  contains the reinforcing filler and thus has a high bending elastic modulus. The connector end portion  12  of the resin connector  10  forms the welded portion with the resin tube  20 . The connector end portion  12  does not contain the reinforcing filler, or contains the reinforcing filler at a lower content proportion than the connector main body portion  11 . Therefore, the bending elastic modulus of the connector end portion  12  is lower than that of the connector main body portion  11 . 
     However, the connector end portion  12  is required to have a high joining strength caused by the welding with the resin tube  20  and a small variation in the joining strength rather than the bending elastic modulus. Here, the connector end portion  12  does not contain the reinforcing filler, or contains the reinforcing filler at a lower content proportion than the connector main body portion  11 . Therefore, the connector end portion  12  has a higher transmittance of the laser beam B than the connector main body portion  11 . Furthermore, it is possible to curb a variation in the joining strength of the welded portion between the connector end portion  12  and the resin tube  20  caused by the emission of the laser beam B due to the reinforcing filler. 
     That is, in the resin connector  10  the connector main body portion  11  and the connector end portion  12  are differentiated from each other in terms of a function. The connector main body portion  11  functions as a portion that ensures the bending elastic modulus, and the connector end portion  12  functions as a portion that ensures the joining strength caused by the welding with the resin tube  20 . Therefore, the connection structure between the resin connector  10  and the resin tube  20  as a whole can ensure the bending elastic modulus of the resin connector  10  while curbing the variation in joining strength between the resin connector  10  and the resin tube  20 . 
     In particular, by making the connector end portion  12  not contain the reinforcing filler, it is possible to further curb the variation in joining strength at the welded portion. If the connector end portion contains the reinforcing filler, it is preferable that the content proportion of the reinforcing filler be low and the end portion base material resin and the reinforcing filler have the refractive indexes close to each other. 
     Further, the resin tube  20  is inserted into the inside of the connector end portion  12  in the radial direction, and the outer peripheral surface of the resin tube  20  is welded to the inner peripheral surface of the connector end portion  12 . With this configuration, the laser beam B can be emitted from the outside in the radial direction, and thus the equipment and the emission of the laser beam B are facilitated. In particular, it is preferable that the resin tube  20  be inserted the inside of the connector end portion  12  in the radial direction in a contracted state. As a result, the adhesion between the resin tube  20  and the connector end portion  12  is enhanced, and the welding caused by the laser beam B can be easily performed, and the variation in joining strength can be curbed. 
     Further, the welded portion is the cylindrical inner peripheral surface portion  12   c  of the connector end portion  12 , not the tapered guide portion  12   b . If the tapered guide portion  12   b  is used as the welded portion, the heat energy generated by the emission of the laser beam B may vary depending on a position because the radial thickness of the connector end portion  12  varies in the axial direction. However, when the cylindrical inner peripheral surface portion  12   c  is used as the welded portion, it is possible to curb the variation in the joining strength. 
     Further, the welded portion is positioned at a position spaced apart from a boundary portion between the connector main body portion  11  and the connector end portion  12 . As a result, it is possible to prevent the laser beam B from being affected by the reinforcing filler contained in the connector main body portion. Therefore, the variations in joining strength can be curbed. 
     Further, the welded portion is formed in a ring shape that is closed over the entire circumference. As a result, the welded portion exhibits a sealing function between the connector end portion  12  and the resin tube  20 . Furthermore, it is preferable that the welded portions be formed at a plurality of locations in the axial direction. As a result, a high sealing function can be exhibited while ensuring a high joining strength. 
     2. Second Embodiment 
     A resin connector connection structure  2  of a second embodiment will be described with reference to  FIG.  3   . The resin connector connection structure  2  of the present embodiment differs from the resin connector connection structure  1  of the first embodiment in a connector main body portion  51  and a connector end portion  52 . 
     However, in the resin connector connection structure  2 , the same components as those of the resin connector connection structure  1  of the first embodiment are denoted by the same reference signs, and the description thereof is omitted. 
     The connector main body portion  51  has a tubular main body jaw portion  51   b  which extends toward the connector end portion  52 . The main body jaw portion  51   b  axially protrudes from an outer portion of an axial end surface in the radial direction. The axial end surface of the main body jaw portion  51   b , an inner peripheral surface of the main body jaw portion  51   b , and a surface  51   c  which is normal to the axial direction at a base of the main body jaw portion  51   b  constitute a joining surface for directly joining with the connector end portion  52 . That is, the joining surface is formed stepwise. The connector main body portion  51  has a positioning end surface  51   d  having a normal line in the axial direction in the inside of the main body jaw portion  51   b  in the radial direction. In the present embodiment, the surface  51   c  and the positioning end surface  51   d  are positioned on the same plane. 
     The connector end portion  52  has a tubular end jaw portion  52   a  which extends toward the connector main body portion  51 . The end jaw portion  52   a  axially protrudes from an inner portion of an axial end surface in the radial direction. The axial end surface of the end jaw portion  52   a , an outer peripheral surface of the end jaw portion  52   a , and a surface  52   b  which is normal to the axial direction at a base of the end jaw portion  52   a  constitute a joining surface for directly joining with the connector main body portion  51 . That is, the joining surface is formed stepwise. 
     According to the present embodiment, an area of the joining surface between the connector main body portion  51  and the connector end portion  52  can be enlarged. Therefore, the joining strength between the connector main body portion  51  and the connector end portion  52  can be increased. 
     Here, the welded portion is a portion of the connector end portion  52  on an opening end side of the connector end portion  52  (the first opening side of the resin connector  10 ) rather than the end jaw portion  52   a . That is, the portion irradiated with the laser beam B is a portion formed only by the connector end portion  52  in the entire radial width of the resin connector  10 . 
     3. Third Embodiment 
     A resin connector connection structure  3  of a third embodiment will be described with reference to  FIG.  4   . The resin connector connection structure  3  includes a resin connector  60 , a first resin tube  70 , and a second resin tube  80 . The resin connector  60  includes a connector main body portion  61 , a first connector end portion  62  positioned on a first opening side (a right side in  FIG.  4   ) of the resin connector  60 , and a second connector end portion  63  positioned on a second opening side (a left side in  FIG.  4   ) of the resin connector  60 . 
     The connector main body portion  61  requires, for example, a bending elastic modulus for fixing it to a mating member. The first connector end portion  62  is directly joined to one axial end (a right end in  FIG.  4   ) of the connector main body portion  61 . The second connector end portion  63  is directly joined to the other axial end (a left end in  FIG.  4   ) of the connector main body portion  61 . In this manner, the connector main body portion  61 , the first connector end portion  62 , and the second connector end portion  63  are integrally formed with each other. The first connector end portion  62  is joined to the first resin tube  70  by welding using the laser beam B. The second connector end portion  63  is joined to the second resin tube  80  by welding using the laser beam B. 
     Here, a relationship between the first connector end portion  62  and the first resin tube  70  and a relationship between the second connector end portion  63  and the second resin tube  80  are substantially the same as a relationship between the connector end portion  12  and the resin tube  20  in the first embodiment. In  FIG.  4   , the reference signs of the parts in the first embodiment are given. 
     4. Fourth Embodiment 
     A resin connector connection structure  4  of a fourth embodiment will be described with reference to  FIG.  5   . In the following description, in the resin connector connection structure  4 , the same components as those of the resin connector connection structure  3  of the third embodiment are denoted by the same reference signs, and the description thereof is omitted. 
     The resin connector connection structure  4  includes a resin connector  90 , a first resin tube  70 , and a second resin tube  80 . The resin connector  90  includes a connector main body portion  91 , a low-strength intermediate portion  92 , a first connector end portion  93  positioned on a first opening side (a right side in  FIG.  5   ) of the resin connector  90 , and a second connector end portion  94  positioned on a second opening side (a left side in  FIG.  5   ) of the resin connector  90 . 
     The connector main body portion  91  is formed in a tubular shape and constitutes an outer layer of an intermediate part of the resin connector  90  in the axial direction. The connector main body portion  91  requires, for example, a bending elastic modulus for fixing it to a mating member. Therefore, the connector main body portion  91  is formed to contain a reinforcing filler in a main portion base material resin. 
     The low-strength intermediate portion  92  is formed in a tubular shape and constitutes an inner layer of the intermediate part of the resin connector  90  in the axial direction. The low-strength intermediate portion  92  is directly joined to an inner peripheral surface of the connector main body portion  91 . The low-strength intermediate portion  92  includes a positioning end surface  92   a  which is normal to the first opening side (the right side in  FIG.  5   ) and a positioning end surface  92   b  which is normal to the second opening side (the left side in  FIG.  5   ). The positioning end surface  92   a  positions the first resin tube  70  by coming into contact with a tip end surface of the first resin tube  70 . The positioning end surface  92   b  positions the second resin tube  80  by coming into contact with a tip end surface of the second resin tube  80 . 
     The low-strength intermediate portion  92  does not require a high bending elastic modulus unlike the connector main body portion  91  and only has to ensure the shape of the positioning end surfaces  92   a  and  92   b . Therefore, the low-strength intermediate portion  92  is formed without containing the reinforcing filler in the base material resin, or is formed to contain the reinforcing filler in the base resin at a lower proportion than the connector main body portion  91 . 
     The first connector end portion  93  is formed in a tubular shape and is formed integrally with one axial end (the right end in  FIG.  5   ) of the low-strength intermediate portion  92 . Further, in the present embodiment, for example, the first connector end portion  93  may be integrally formed with the low-strength intermediate portion  92  by injection molding or the like. However, the first connector end portion  93  may be formed of a material different from that of the low-strength intermediate portion  92  and joined to the low-strength intermediate portion  92 . 
     Here, the first connector end portion  93  is formed similarly to the first connector end portion  62  in the third embodiment. Therefore, the first connector end portion  93  is joined to the first resin tube  70  by welding using the laser beam B. 
     The second connector end portion  94  is formed in a tubular shape and is formed integrally with the other axial end (the left end in  FIG.  5   ) of the low-strength intermediate portion  92 . Further, in the present embodiment, for example, the second connector end portion  94  may be integrally formed with the low-strength intermediate portion  92  by injection molding or the like. However, the second connector end portion  94  may be formed of a material different from that of the low-strength intermediate portion  92  and joined to the low-strength intermediate portion  92 . 
     Here, the second connector end portion  94  is formed similarly to the second connector end portion  63  in the third embodiment. Therefore, the second connector end portion  94  is joined to the second resin tube  80  by welding using the laser beam B. 
     In the present embodiment, the first connector end portion  93  is disposed continuously with the low-strength intermediate portion  92  and is connected to the connector main body portion  91  via the low-strength intermediate portion  92 . That is, the first connector end portion  93  is directly joined only to the low-strength intermediate portion  92  and not directly joined to the connector main body portion  91 . Therefore, the first connector end portion  93  is indirectly joined to the connector main body portion  91  via the low-strength intermediate portion  92 . The first connector end portion  93  may be directly joined to both the connector main body portion  91  and the low-strength intermediate portion  92 , or may be directly joined to only the connector main body portion  91 . 
     Similarly, in the present embodiment, the second connector end portion  94  is disposed continuously with the low-strength intermediate portion  92  and is connected to the connector main body portion  91  via the low-strength intermediate portion  92 . That is, the second connector end portion  94  is directly joined only to the low-strength intermediate portion  92  and not directly joined to the connector main body portion  91 . Therefore, the second connector end portion  94  is indirectly joined to the connector main body portion  91  via the low-strength intermediate portion  92 . The second connector end portion  94  may be directly joined to both the connector main body portion  91  and the low-strength intermediate portion  92 , or may be directly joined to only the connector main body portion  91 . 
     The present embodiment also has the same effect as the third embodiment. Moreover, since a volume of the connector main body portion  91  can be reduced, the cost can be reduced. Furthermore, in a case where the low-strength intermediate portion  92 , the first connector end portion  93 , and the second connector end portion  94  are integrally molded with each other by injection molding or the like, an area of the joining surface between the integrally molded body and the connector main body portion  91  can be enlarged. Therefore, the joining strength between the connector main body portion  91  and the integrally molded body, that is, the joining strength between the connector main body portion  91  and the connector end portions  93  and  94 , can be increased. 
     5. Others 
     In the first embodiment, the connector end portion  12  and the resin tube  20  are welded to each other by emitting the laser beam B from the outside in the radial direction in a state where the resin tube  20  is inserted into the inside of the connector end portion  12 . In addition, the connector end portion  12  and the resin tube  20  may be welded to each other by emitting the laser beam B from the inner side in the radial direction, that is, a side of the connector end portion  12  in the radial direction in a state where the resin tube  20  is fitted to the outside of the connector end portion  12 . 
     Further, in the first embodiment, the connector main body portion  11  is formed to include a claw that is locked to the pipe  30 . Alternatively, the following is also possible. A plurality of annular protrusions protruding in the radial direction is formed on the outer peripheral surface of the connector main body portion  11  in the axial direction. The pipe  30  may be expanded and fitted to the outer peripheral surface of the connector main body portion  11  to be axially locked to the plurality of annular protrusions. 
     Further, in the fourth embodiment, the resin connector  90  is formed to include the low-strength intermediate portion  92 . Also in the first embodiment and the second embodiment, a member corresponding to the low-strength intermediate portion  92  may be provided.