Patent Publication Number: US-2022221094-A1

Title: Tube fitting and tube fitting set

Description:
TECHNICAL FIELD 
     The present invention relates to a tube fitting and a tube fitting set. 
     BACKGROUND ART 
     In a valve built-in connector (tube fitting) disclosed in Patent Document 1 (Japanese Patent Application Laid-Open (JP-A) No. 2004-116733), a connector housing of the valve built-in connector is integrally configured of a tube connecting section on one axial direction side, a pipe insertion section on another axial direction side, and a valve housing section between the tube connecting section and the pipe insertion section. 
     The valve housing section is formed with an inner diameter of a sufficient size such that a valve body and a compression coil spring are housed inside the valve housing section. The compression coil spring biases the valve body toward the one axial direction side so as to abut a housing inner face. 
     PATENT DOCUMENTS 
     
         
         Patent Document 1: JP-A No. 2004-116733 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     Conventional tube fittings include a choke section formed with a choke hole that limits a through-flow rate of a fluid, and a valve unit that opens a flow aperture in a flow path in a case in which a flow rate exceeds the through-flow rate limited by the choke hole. Note that a flow rate limiting section is not provided at a downstream side of the choke section in a flow direction of the fluid. Such a flow rate limiting section would limit a through-flow rate of fluid that has passed through the flow aperture opened by the valve unit. 
     An object of the present invention is to obtain a configuration that limits a through-flow rate of fluid that has passed through a flow aperture opened by a valve unit. 
     Solution to Problem 
     A tube fitting according to a first aspect of the present invention includes: a body having a flow path formed inside for a fluid to flow through; an upstream-side choke section located inside the body and formed with an upstream-side choke hole configured to limit a through-flow rate of the fluid; a valve unit configured to open a closed flow aperture in the flow path in a case in which the fluid flows at a flow rate exceeding the through-flow rate limited by the upstream-side choke hole; and a downstream-side choke section disposed at a downstream side of the valve unit in a flow direction of the fluid and formed with a downstream-side choke hole configured to limit a through-flow rate of fluid that has passed through the flow aperture. 
     In the above configuration, the upstream-side choke hole formed in the upstream-side choke section limits the through-flow rate of fluid flowing into the tube fitting. In a case in which the fluid flows in the tube fitting at a flow rate exceeding the through-flow rate limited by the upstream-side choke hole, the closed flow aperture is opened by the valve unit. 
     The downstream-side choke hole in the downstream-side choke section disposed at the downstream side of the valve unit in the fluid flow direction limits the through-flow rate of fluid that has passed through the flow aperture opened by the valve unit. 
     Disposing the downstream-side choke section at the downstream side of the valve unit in the fluid flow direction in this manner enables a configuration that limits the through-flow rate of fluid that has passed through the flow aperture opened by the valve unit to be obtained. 
     A feature of the above aspect is that a hole diameter of the downstream-side choke hole is larger than a hole diameter of the upstream-side choke hole. 
     In the above configuration, the hole diameter of the downstream-side choke hole is larger than the hole diameter of the upstream-side choke hole. This enables the fluid through-flow rate to be limited by the upstream-side choke hole in an initial low flow rate region when the fluid starts to flow into the tube fitting, and the fluid through-flow rate to be limited by the downstream-side choke hole in a high flow rate region when the flow rate of fluid flowing into the tube fitting has increased. 
     A feature of the above aspect is that the downstream-side choke section is disposed at the downstream side of the valve unit in the flow direction and is disposed so as to be visible from outside the body. 
     In the above configuration, the downstream-side choke section is disposed at the downstream side of the valve unit in the flow direction and is disposed so as to be visible from outside the body. Thus, a check as to whether the correct downstream-side choke section is attached to the body can be performed by looking at the tube fitting from the fluid flow direction downstream side. 
     A feature of the above aspect is that the valve unit includes a valve body capable of moving in the flow direction, a biasing portion configured to bias the valve body toward an upstream side in the flow direction, a support portion configured to support an end portion at the flow direction downstream side of the biasing portion, and a contact portion overlooking the flow path and configured to contact the valve body biased by the biasing portion. The valve unit is restricted from detaching from the body toward the flow direction downstream side by the downstream-side choke section. 
     In the above configuration, the valve unit is restricted from detaching from the body toward the flow direction downstream side by the downstream-side choke section. This enables the valve unit to be restricted from detaching from the body toward the fluid flow direction downstream side without employing a dedicated component to restrict the valve unit from detaching from the body. 
     A tube fitting set according to a fifth aspect of the present invention includes: a tube fitting including a body having a flow path formed inside for a fluid to flow through, an upstream-side choke section located inside the body and formed with an upstream-side choke hole configured to limit a through-flow rate of the fluid, a valve unit configured to open a closed flow aperture in the flow path in a case in which the fluid flows at a flow rate exceeding the through-flow rate limited by the upstream-side choke hole, and a flow rate limiting section disposed at a downstream side of the valve unit in a flow direction of the fluid and configured to limit the through-flow rate of fluid that has passed through the flow aperture; and plural types of downstream-side choke sections each including a wall portion formed with a downstream-side choke hole configured to limit a flow rate of fluid that has passed through the flow aperture, and an outer peripheral portion joined to the wall portion and configured to engage with an inner peripheral face of the body. Each of the downstream-side choke sections has a different through-flow rate limitation performance due to the downstream-side choke hole having a different hole diameter. Each of the plural types of downstream-side choke sections is capable of functioning as the flow rate limiting section. 
     In the above configuration, each of the plural types of downstream-side choke sections that have a different through-flow rate limitation performance due to having a different hole diameter functions as the flow rate limiting section that limits the through-flow rate of fluid that has passed through the flow aperture. Thus, by assembling the plural types of downstream-side choke sections having different hole diameters to a common body, plural types of tube fittings that each have a different through-flow rate limitation performance can be obtained. 
     Advantageous Effects of Invention 
     The present invention enables a configuration that limits the through-flow rate of fluid that has passed through the flow aperture opened by the valve unit to be obtained. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-section illustrating a tube fitting according to an exemplary embodiment of the present invention. 
         FIG. 2  is a cross-section illustrating a tube fitting according to an exemplary embodiment of the present invention to which a flow of fluid has been added. 
         FIG. 3  is a cross-section illustrating a tube fitting according to an exemplary embodiment of the present invention to which a flow of fluid has been added. 
         FIG. 4  is a cross-section illustrating a tube fitting according to an exemplary embodiment of the present invention to which a flow of fluid has been added. 
         FIG. 5  is an exploded perspective view illustrating an upstream-side choke section, a downstream-side choke section, and so on included in a tube fitting according to an exemplary embodiment of the present invention. 
         FIG. 6  is an exploded perspective view illustrating a tube fitting according to an exemplary embodiment of the present invention. 
         FIG. 7  is a diagram illustrating performance of a tube fitting according to an exemplary embodiment of the present invention in the form of a graph. 
         FIG. 8  is a schematic configuration diagram illustrating a fuel supply system employing a tube fitting according to an exemplary embodiment of the present invention. 
         FIG. 9  is a cross-section illustrating a tube fitting according to an exemplary embodiment of the present invention. 
         FIG. 10  is a cross-section illustrating a tube fitting according to an exemplary embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Explanation follows regarding an example of a tube fitting and a tube fitting set according to an exemplary embodiment of the present invention, with reference to  FIG. 1  to  FIG. 10 . Note that in the respective drawings, the arrow R indicates a radial direction of the tube fitting, and the arrow W indicates a length direction of the tube fitting that is also a flow direction of a fuel gas, this being an example of a fluid. First, explanation follows regarding a fuel supply system  100  employing the tube fitting. 
     Fuel Supply System  100  Employing Tube fitting  10   
     As illustrated in  FIG. 8 , a tube fitting  10  is employed as part of the fuel supply system  100 . The fuel supply system  100  includes a fuel tank  110 , a filler pipe  114  for supplying fuel to the fuel tank  110 , and a return tube  116  that returns fuel gas, this being a vaporous form of the fuel inside the fuel tank  110 , to the filler pipe  114 . 
     The return tube  116  includes a first tube  116   a  that is connected to the fuel tank  110 , and a second tube  116   b  that is connected to the filler pipe  114 . The tube fitting  10  is employed in order to join the first tube  116   a  and the second tube  116   b  together. Note that the arrow UP illustrated in  FIG. 8  indicates upward with respect to gravitational force. 
     In this configuration, fuel cannot be supplied to the fuel tank  110  through the filler pipe  114  in a case in which the pressure of the fuel gas inside the fuel tank  110  has risen. Thus, the fuel gas inside the fuel tank  110  is returned from the fuel tank  110  to the filler pipe  114  through the return tube  116 . This enables fuel to be supplied to the fuel tank  110  through the filler pipe  114 , even in a case in which the pressure of the fuel gas inside the fuel tank  110  has risen. 
     Note that the tube fitting  10  controls a through-flow rate of fuel gas flowing through the tube fitting  10  so as to control the pressure of the fuel gas inside the fuel tank  110 . The configuration by which the tube fitting  10  controls the through-flow rate of fuel gas flowing through the tube fitting  10  is described in detail later. 
     Overall Configuration of Tube Fitting  10   
     As illustrated in  FIG. 1 , the tube fitting  10  includes a body  12 , an upstream-side choke section  30 , a valve body  40 , and a biasing spring  36 . A flow path  20  that extends along a flow direction (hereafter “gas flow direction) of the fuel gas that is an example of a fluid is formed inside the body  12 . An upstream-side choke hole  30   a  that limits the through-flow rate of flowing fuel gas (hereafter “gas”) is formed in the upstream-side choke section  30 . The valve body  40  is capable of moving along the gas flow direction. The biasing spring  36  biases the valve body  40  toward an upstream side in the gas flow direction. The tube fitting  10  also includes a housing section  46  formed with support portions  52   b  that support the biasing spring  36 . The upstream-side choke section  30 , the valve body  40 , and the biasing spring  36  are housed inside the housing section  46 . The tube fitting  10  also includes a downstream-side choke section  60  formed with a downstream-side choke hole  62  that limits the through-flow rate of gas that has passed through a flow aperture  38  (see  FIG. 4 ) that has opened due to the valve body  40  moving toward a downstream side in the gas flow direction. 
     Body  12   
     The body  12  is integrally formed of a resin material. As illustrated in  FIG. 1  and  FIG. 6 , the flow path  20  that extends along the gas flow direction is formed inside the body  12 . The body  12  includes a first insertion section  14  that is inserted into an end portion of the first tube  116   a , a second insertion section  16  that is inserted into an end portion of the second tube  116   b , and a coupling section  18  that couples the first insertion section  14  and the second insertion section  16  together. The first insertion section  14 , the coupling section  18 , and the second insertion section  16  are arrayed in this sequence from the upstream side (the left side in the drawings) to the downstream side (the right side in the drawings) in the gas flow direction. 
     First Insertion Section  14 , Second Insertion Section  16 , and Coupling Section  18   
     The first insertion section  14  is formed in a circular tube shape extending along the gas flow direction. Ridges (not allocated reference numerals) are formed extending around a circumferential direction at an outer peripheral face of the first insertion section  14  in order to prevent the first tube  116   a  from coming off. 
     The second insertion section  16  is formed in a circular tube shape extending along the gas flow direction. Ridges (not allocated reference numerals) are formed extending around a circumferential direction at an outer peripheral face of the second insertion section  16  in order to prevent the second tube  116   b  from coming off. 
     The coupling section  18  is formed in a circular tube shape extending along the gas flow direction. A large diameter abutting portion  18   a  that is abutted by an end of the first tube  116   a  is formed at a first insertion section  14 -side portion of the coupling section  18 . A large diameter abutting portion  18   b  that is abutted by an end of the second tube  116   b  is formed at a second insertion section  16 -side portion of the coupling section  18 . 
     Flow Path  20   
     The flow path  20  formed in the body  12  includes a funnel shaped inflow area  22 , a first placement area  24  where the housing section  46  is disposed, a second placement area  26  where the downstream-side choke section  60  is disposed, and a circular column shaped outflow area  28 , these areas being formed in this sequence from the upstream side to the downstream side in the gas flow direction. 
     The inflow area  22  is formed in a funnel shape in the first insertion section  14  and part of the coupling section  18 , such that a gas flow direction upstream side area has a larger diameter than a gas flow direction downstream side area thereof. Note that a circular tube shaped inflow area with a uniform inner diameter along the gas flow direction may be provided instead of the funnel shaped inflow area  22 . 
     As mentioned previously, the housing section  46  is disposed in the first placement area  24 . The first placement area  24  is formed in part of the coupling section  18  and part of the second insertion section  16 . The first placement area  24  is formed in a circular column shape having a larger diameter than a small diameter area of the inflow area  22 . A stepped face  18   c  that faces toward the gas flow direction downstream side is formed between the inflow area  22  and the first placement area  24 . The stepped face  18   c  is formed with a step. 
     As mentioned previously, the downstream-side choke section  60  is disposed in the second placement area  26 . The second placement area  26  is formed in part of the second insertion section  16 . Ridges (not allocated reference numerals) are formed extending around a circumferential direction at an inner peripheral face  12   a  of the body  12  where the second placement area  26  is formed in order to prevent the downstream-side choke section  60  from coming off toward the gas flow direction downstream side. 
     The outflow area  28  is formed in part of the second insertion section  16  in a circular column shape that has a larger diameter than the flow path  20 , the first placement area  24 , and the second placement area  26 . 
     In this configuration, when assembling the respective components disposed in the flow path  20  to the body  12 , these respective components are assembled inside the body  12  from the outflow area  28  side. 
     Housing Section  46   
     As mentioned previously, the housing section  46  is disposed in the first placement area  24  of the flow path  20 . As illustrated in  FIG. 1  and  FIG. 6 , the housing section  46  is divided into an upstream housing section  48  at the gas flow direction upstream side, and a downstream housing section  50  at the gas flow direction downstream side. 
     Upstream Housing Section  48   
     The upstream housing section  48  is integrally formed of a resin material. As illustrated in  FIG. 5 , the upstream housing section  48  includes a circular tube shaped circular tube portion  48   a , and a flange portion  48   b  formed at the gas flow direction upstream side of the circular tube portion  48   a . An outer peripheral face of the circular tube portion  48   a  contacts the inner peripheral face  12   a  of the body  12  where the first placement area  24  is formed in a radial direction (hereafter “tube radial direction”) of the tube fitting  10 . The flange portion  48   b  is provided in order to narrow an opening in a gas flow direction upstream side portion of the circular tube portion  48   a , and contacts the stepped face  18   c  of the coupling section  18  in the gas flow direction. The flange portion  48   b  is formed with a corner portion  42  (see  FIG. 2 ) that overlooks the flow path  20  and contacts a conical face  40   a , described later, formed to the valve body  40 . The corner portion  42  is an example of a contact portion. 
     Downstream Housing Section  50   
     The downstream housing section  50  is integrally formed of a resin material. As illustrated in  FIG. 5 , the downstream housing section  50  includes a circular tube shaped circular tube portion  50   a , and four ribs  50   b  that are coupled to an inner peripheral face of the circular tube portion  50   a  and are arranged at uniform intervals around the circumferential direction of the circular tube portion  50   a.    
     A cross-section profile of the circular tube portion  50   a  is similar to a cross-section profile of the circular tube portion  48   a . A gas flow direction length of the circular tube portion  50   a  is longer than a gas flow direction length of the circular tube portion  48   a . An outer peripheral face of the circular tube portion  50   a  makes tube radial direction contact with the inner peripheral face  12   a  of the body  12  where the first placement area  24  is formed. 
     Plate faces of the ribs  50   b  face the circumferential direction of the circular tube portion  50   a , and each of the ribs  50   b  has an L shape as viewed along the circumferential direction of the circular tube portion  50   a . Each of the ribs  50   b  includes a base portion  52   a  extending along the gas flow direction, and the support portion  52   b  projecting in the tube radial direction from a gas flow direction downstream side portion of the base portion  52   a . The support portions  52   b  support a flow direction downstream side end portion of the biasing spring  36 . 
     In this configuration, a space where the upstream-side choke section  30  and so on are disposed is formed inside the housing section  46  in a state in which the upstream housing section  48  and the downstream housing section  50  have been combined. 
     Upstream-Side Choke Section  30 , Valve Body  40   
     The upstream-side choke section  30  and the valve body  40  are integrally formed of a resin material, and are housed inside the housing section  46  as illustrated in  FIG. 1  and  FIG. 5 . 
     Upstream-Side Choke Section  30   
     The upstream-side choke section  30  is formed in a circular tube shape extending along the gas flow direction. The upstream-side choke hole  30   a  that has a circular cross-section profile is formed inside the upstream-side choke section  30 . Note that “choke hole” refers here to a through-hole that has a smaller flow path area than the directly preceding flow path area. For example, the choke hole may be a through-hole having a flow path area that is no greater than 50% of the directly preceding flow path area, such that the through-hole limits the gas through-flow rate. 
     Valve Body  40   
     The valve body  40  is formed in a collar shape at a gas flow direction upstream side portion of the upstream-side choke section  30 . The valve body  40  has a circular outer profile as viewed along the gas flow direction. The cone shaped conical face  40   a  that faces toward the gas flow direction upstream side is formed to the valve body  40 . 
     The valve body  40  further includes guide portions  34  extending toward the gas flow direction upstream side with their respective base end portions coupled to the conical face  40   a . The guide portions  34  are arranged at uniform intervals around the circumferential direction of the upstream-side choke section  30 . The guide portions  34  make tube radial direction contact with the inner peripheral face  12   a  of the body  12  where the inflow area  22  is formed so as to guide the upstream-side choke section  30  and the valve body  40  along the gas flow direction. In other words, the upstream-side choke section  30  and the valve body  40  are capable of moving along the gas flow direction as a result of the guide portions  34 . 
     Biasing Spring  36   
     The biasing spring  36  is a compression coil spring that is housed inside the housing section  46  and extends along the gas flow direction as illustrated in  FIG. 1  and  FIG. 5 . The circular tube shaped upstream-side choke section  30  is inserted inside the biasing spring  36 . The biasing spring  36  is then sandwiched between the support portions  52   b  and the valve body  40  in the gas flow direction. The biasing spring  36  is an example of a biasing portion. 
     In this configuration, the biasing spring  36  biases the valve body  40  toward the gas flow direction upstream side, such that the conical face  40   a  of the valve body  40  is pressed against the corner portion  42  of the upstream housing section  48  and the conical face  40   a  contacts the corner portion  42  as illustrated in  FIG. 2 . The flow aperture  38  (see  FIG. 4 ) formed between the corner portion  42  and the conical face  40   a  is closed in this state. 
     However, in a case in which the gas flow rate exceeds the through-flow rate limited by the upstream-side choke hole  30   a , the biasing spring  36  compresses under gas pressure transmitted to the biasing spring  36  through the valve body  40 . As illustrated in  FIG. 4 , when the biasing spring  36  compresses, the valve body  40  that is being pressed by the flowing gas moves toward the gas flow direction downstream side, and stops on contacting gas flow direction upstream ends of the base portions  52   a  of the ribs  50   b . The conical face  40   a  of the valve body  40  moves apart from the corner portion  42  as a result, thereby opening the flow aperture  38  such that gas flows through. 
     In this manner, a valve unit  44  that opens and closes the flow aperture  38  is configured including the valve body  40  that is capable of moving in the gas flow direction, the biasing spring  36  that biases the valve body  40  toward the gas flow direction upstream side, the support portions  52   b  that support an end portion of the biasing spring  36 , and the corner portion  42  that contacts the conical face  40   a  of the valve body  40  biased by the biasing spring  36 . 
     Downstream-Side Choke Section  60   
     The downstream-side choke section  60  is integrally formed of a resin material, and is disposed at the downstream side of the valve unit  44  and is disposed so as to be visible from outside the body  12 , as illustrated in  FIG. 1  and  FIG. 5 . 
     The downstream-side choke section  60  includes a circular tube shaped outer peripheral portion  60   a  that engages with the inner peripheral face  12   a  of the body  12 , and a wall portion  60   b  formed with the downstream-side choke hole  62 . A gas flow direction upstream side portion of the outer peripheral portion  60   a  of the downstream-side choke section  60  contacts the housing section  46  in the gas flow direction. 
     Ridges (not allocated reference numerals) that engage with the inner peripheral face  12   a  of the body  12  are formed extending around the circumferential direction of the outer peripheral portion  60   a . The wall portion  60   b  extends outward in a radial direction so as to be joined to the outer peripheral portion  60   a . The wall portion  60   b  is formed with the downstream-side choke hole  62  that has a circular profile as viewed along the gas flow direction. A hole diameter of the downstream-side choke hole  62  is larger than a hole diameter of the upstream-side choke hole  30   a  formed in the upstream-side choke section  30 . 
     In this configuration, the downstream-side choke hole  62  limits the through-flow rate of gas that has passed through the flow aperture  38  opened by the valve unit  44 . The downstream-side choke section  60  thereby functions as a flow rate limiting section that limits the through-flow rate of gas that has passed through the flow aperture  38  opened by the valve unit  44 . The valve unit  44  is also restricted from detaching from the body  12  toward the gas flow direction downstream side by the downstream-side choke section  60 . 
     By configuring the downstream-side choke section  60  as a separate body to the body  12 , a downstream-side choke section  260  having a different through-flow rate limitation performance than the downstream-side choke section  60  simply due to having a larger hole diameter can be attached to the body  12  (see  FIG. 9 ). Namely, the downstream-side choke section  260  is formed with a downstream-side choke hole  262  that has a larger hole diameter d 2  than a hole diameter d 1  of the downstream-side choke hole  62  in the downstream-side choke section  60 . In such a case, a tube fitting  210  configured by attaching the downstream-side choke section  260  illustrated in  FIG. 9  has a different through-flow rate limitation performance than the tube fitting  10 . 
     Furthermore, a downstream-side choke section  360  having a different through-flow rate limitation performance than the downstream-side choke sections  60 ,  260  simply due to having a larger hole diameter can be attached to the body  12  (see  FIG. 10 ). Namely, the downstream-side choke section  360  is formed with a downstream-side choke hole  362  that has a larger hole diameter d 3  than the hole diameter d 2  of the downstream-side choke hole  262  in the downstream-side choke section  260 . In such a case, a tube fitting  310  configured by attaching the downstream-side choke section  360  illustrated in  FIG. 10  has a different through-flow rate limitation performance than the tube fittings  10 ,  210 . 
     Configuring the downstream-side choke sections  60 ,  260 ,  360  as separate bodies to the body  12  in this manner enables a tube fitting set  200  to be realized including plural types of tube fittings  10 ,  210 ,  310  that each have a different through-flow rate limitation performance due to the respective downstream-side choke holes  62 ,  262 ,  362  having different hole diameters. 
     Operation 
     In a case in which the flow rate of gas flowing into the tube fitting  10  from the first tube  116   a  is no greater than the through-flow rate limited by the upstream-side choke hole  30   a , the valve body  40  that is being biased by the biasing force of the biasing spring  36  does not move under the pressure of gas flowing into the tube fitting  10 , as illustrated in  FIG. 2 . Contact between the conical face  40   a  of the valve body  40  and the corner portion  42  of the upstream housing section  48  is thereby maintained, such that the flow aperture  38  remains closed (see  FIG. 4 ). The inflowing gas thereby flows through the inflow area  22 , the upstream-side choke hole  30   a , the downstream-side choke hole  62 , and the outflow area  28  in this sequence (see the arrows in  FIG. 2 ). 
     Explanation follows regarding a relationship between the pressure of gas flowing into the tube fitting  10  and the flow rate of gas passing through the tube fitting  10 . In the graph illustrated in  FIG. 7 , the horizontal axis represents the pressure of gas flowing into the tube fitting  10 , and the vertical axis represents the flow rate of gas passing through the tube fitting  10 . When the pressure is no greater than P 1 , contact between the conical face  40   a  of the valve body  40  and the corner portion  42  of the upstream housing section  48  is maintained, and the gas through-flow rate is limited by the upstream-side choke hole  30   a . As is evident from this graph, the gas through-flow rate is limited by the upstream-side choke hole  30   a  while the flow rate of gas passing through the tube fitting  10  is no greater than L 1 . 
     However, when the gas flow rate of gas flowing into the tube fitting  10  from the first tube  116   a  exceeds the through-flow rate limited by the upstream-side choke hole  30   a , the biasing spring  36  compresses under gas pressure transmitted to the biasing spring  36  through the valve body  40 , as illustrated in  FIG. 3  and  FIG. 4 . When the biasing spring  36  compresses, the valve body  40  that is being pressed by the flowing gas moves toward the gas flow direction downstream side, and stops on contacting the gas flow direction upstream ends of the base portions  52   a  of the ribs  50   b . The conical face  40   a  of the valve body  40  moves apart from the corner portion  42  as a result, thereby opening the flow aperture  38  such that gas flows through. 
     In this manner, gas having a flow rate that has exceeded the through-flow rate limited by the upstream-side choke hole  30   a  flows along the inflow area  22 , the upstream-side choke hole  30   a  and flow aperture  38 , the downstream-side choke hole  62 , and the outflow area  28  in this sequence (see the arrows in  FIG. 3  and  FIG. 4 ). 
     The gas through-flow rate is limited to no greater than a flow rate L 2  illustrated in the graph in  FIG. 7  by the downstream-side choke hole  62  that has a larger hole diameter than the hole diameter of the upstream-side choke hole  30   a . As is evident from this graph, the gas through-flow rate is limited by the downstream-side choke hole  62  in a range in which the flow rate of gas passing through the tube fitting  10  exceeds L 1  but is no greater than L 2 . 
     By making the hole diameter of the downstream-side choke hole  62  larger than the hole diameter of the upstream-side choke hole  30   a  in this manner, the through-flow rate is limited by the upstream-side choke hole  30   a  in a low flow rate region, and the through-flow rate is limited by the downstream-side choke hole  62  in a high flow rate region. 
     SUMMARY 
     As described above, by providing the downstream-side choke hole  62  at the gas flow direction downstream side of the upstream-side choke hole  30   a , the through-flow rate of gas that has passed through the flow aperture  38  opened by the valve unit  44  can be limited. 
     Moreover, configuring the downstream-side choke section  60  formed with the downstream-side choke hole  62  as a separate body to the body  12  enables plural types of tube fittings that each have a different performance with respect to limiting the gas through-flow rate in the high flow rate region to be prepared by preparing plural types of downstream-side choke sections which only differ in the hole diameter of their respective downstream-side choke holes. 
     Moreover, the hole diameter of the downstream-side choke hole  62  is larger than the hole diameter of the upstream-side choke hole  30   a . This enables the gas through-flow rate to be limited by the upstream-side choke hole  30   a  in the initial low flow rate region when gas starts to flow into the tube fitting  10 , and the gas through-flow rate to be limited by the downstream-side choke hole  62  in the high flow rate region when the flow rate of gas flowing into the tube fitting  10  has increased. 
     Moreover, the downstream-side choke section  60  is disposed at the downstream side of the valve unit  44  in the gas flow direction, and is disposed so as to be visible from outside the body  12 . Thus, for example, in a case in which plural types of downstream-side choke sections each differing only in the hole diameter of their respective downstream-side choke holes are available, a check for mistaken assembly of a downstream-side choke section can be performed by looking at the tube fitting  10  from the gas flow direction downstream side. In other words, a check as to whether the correct downstream-side choke section is attached can be performed by looking at the tube fitting  10  from the gas flow direction downstream side. 
     Moreover, the valve unit  44  is restricted from detaching from the body  12  toward the gas flow direction downstream side by the downstream-side choke section  60 . This enables the valve unit  44  to be restricted from detaching from the body  12  toward the gas flow direction downstream side by the downstream-side choke section  60  without employing a dedicated component to restrict the valve unit  44  from detaching from the body  12 . 
     Moreover, configuring the downstream-side choke sections  60 ,  260 ,  360  as separate bodies to the body  12  enables the tube fitting set  200  to be obtained including the plural types of tube fittings  10 ,  210 ,  310  that each have a different through-flow rate limitation performance due to the respective downstream-side choke holes  62 ,  262 ,  362  having different hole diameters. In other words, assembling the plural types of downstream-side choke sections  60 ,  260 ,  360  each having a different hole diameter to a common body  12  enables the tube fitting set  200  to be obtained including the plural types of tube fittings  10 ,  210 ,  310  that each have a different through-flow rate limitation performance. In other words, configuring the downstream-side choke sections  60 ,  260 ,  360  as separate bodies to the body  12  enables one tube fitting to be selected from out of the plural types of tube fittings  10 ,  210 ,  310  based on the required through-flow rate limitation performance. 
     Note that although a specific exemplary embodiment of the present invention has been described in detail, the present invention is not limited to this exemplary embodiment, and it would be clear to a person skilled in the art that various other exemplary embodiments may be implemented within the range of the present invention. For example, although the upstream-side choke section  30  and the valve body  40  are integrally formed in the above exemplary embodiment, they may be configured as separate bodies. 
     Moreover, although one upstream-side choke hole  30   a  is formed in the upstream-side choke section  30  in the above exemplary embodiment, plural holes may be formed therein. Similarly, although one downstream-side choke hole  62  is formed in the downstream-side choke section  60 , plural holes may be formed therein. 
     Moreover, although gas is employed as an example of a fluid in the above exemplary embodiment, either a liquid or a gas may be employed, as long as it is a fluid. 
     Moreover, although not described in the above exemplary embodiment, the plural types of downstream-side choke sections  60 ,  260 ,  360  may each have a different color. This enables the downstream-side choke section that is attached to the body  12  to be easily identified from the outside. 
     Moreover, although the tube fitting set  200  includes the three types of tube fittings  10 ,  210 ,  310  in the above exemplary embodiment, two types, or four or more types, of tube fittings may be included. 
     EXPLANATION OF REFERENCE NUMERALS 
     
         
         
           
               10  tube fitting 
               12  body 
               20  flow path 
               30  upstream-side choke section 
               30   a  upstream-side choke hole 
               36  biasing spring (example of biasing portion) 
               38  flow aperture 
               40  valve body 
               42  corner portion (example of contact portion) 
               44  valve unit 
               52   b  support portion 
               60  downstream-side choke section 
               60   a  outer peripheral portion 
               60   b  wall portion 
               200  downstream-side choke hole 
               200  tube fitting set 
               210  tube fitting 
               260  downstream-side choke section 
               262  downstream-side choke hole 
               310  tube fitting 
               360  downstream-side choke section 
               362  downstream-side choke hole