Patent Publication Number: US-2021188081-A1

Title: Resin filler tube and manufacturing method for the same

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority based on Japanese Patent Application No. 2019-231090 filed on Dec. 23, 2019, the entire contents of which are incorporated by reference herein. 
     1. TECHNICAL FIELD 
     The present invention relates to a resin filler tube and a manufacturing method for the resin filler tube. 
     2. BACKGROUND ART 
     WO2010015295A1 discloses that an outer circumferential edge of an opening hole of a fuel tank and a flange of a filler tube are fixed to each other by a clamp ring. An O-ring for sealing is disposed between an inner circumferential surface of the opening hole of the fuel tank and an outer circumferential surface of the filler tube. 
     JP2018-118498A discloses that an outer circumferential edge of an opening hole of a resin fuel tank and an axial end face of a flange of a resin filler tube are joined to each other by welding. The outer face of the resin filler tube has an outermost layer formed by an outermost layer material over the entire length. The outermost layer of the flange is welded to the fuel tank. Furthermore, a material having preferable weldability is used as the outermost layer material, whereby performance such as a welding strength of a weld surface is enhanced. 
     JP2007-8352A discloses that an outer circumferential edge of an opening hole of a fuel tank and a flange of a filler tube are welded to each other. An outer layer material and an inner layer material of the flange of the filler tube are exposed at a weld surface, and the outer layer material protrudes as compared with the inner layer material such that melted resin of the inner layer material does not hinder welding between the outer layer material and the fuel tank. Furthermore, a recessed groove is formed in the end face of the flange. Therefore, even if the inner layer material is melted, the melted inner layer material flows into the recessed groove, thereby inhibiting the melted inner layer material from flowing into the weld surface between the outer layer material and the fuel tank. 
     JP2018-69786A, JP2019-156011A, and JP2003-194380A also disclose that an outer circumferential edge of an opening hole of a fuel tank and an axial end face of a flange of a filler tube are joined to each other by welding. 
     SUMMARY 
     In a case where the outer circumferential edge of the opening hole of the fuel tank and the axial end face of the flange of the resin filler tube are joined to each other by welding, melt burrs are generated around the weld surface by the welding. That is, the melt burrs are generated so as to protrude from the weld surface toward the outer circumferential side and also protrude from the weld surface toward the inner circumferential side. 
     A small gap is formed in the radial direction between the inner circumferential surface of the opening hole of the fuel tank and the leading end tubular portion of the resin filler tube. If the gap in the radial direction is increased, accuracy for positioning the resin filler tube and the fuel tank is affected. Therefore, increase of the gap in the radial direction is not preferable. Accordingly, a sufficient portion into which the melt burrs on the inner circumferential side escape is not assured, so that the melt burrs are likely to affect stability of the weld surface. 
     An object of the present invention is to provide a resin filler tube that prevents melt burrs from affecting stability of a weld surface and allows stability of the weld surface to be enhanced, and a manufacturing method for manufacturing the resin filler tube. 
     (1. Resin Filler Tube) 
     A resin filler tube is directed to a resin filler tube to be welded to an outer circumferential edge of an opening hole of a fuel tank. The resin filler tube includes: a tubular body having an outermost layer formed by using an outermost layer material, and one or more inner layers each formed by using an inner layer material; a flange configured to protrude radially outward from an end of the tubular body on the fuel tank side, over an entire circumference, the flange having a plurality of layers that are of same kinds as those of the tubular body, the flange having outer faces all of which are formed of the outermost layer material, the flange having a first end face in an axial direction, the first end face forming a weld surface to be welded to the outer circumferential edge of the opening hole of the fuel tank; and a leading end tubular portion extending from a radially inner portion of the flange toward a leading end of the resin filler tube, the leading end tubular portion having an annular recessed groove formed at a portion of an outer circumferential surface on the flange side, over an entire circumference, the annular recessed groove storing a melt burr generated in welding of the first end face. 
     In the resin filler tube, the leading end tubular portion has the annular recessed groove. Therefore, a part of melt burrs on the inner circumferential side is stored in the annular recessed groove. Thus, the annular recessed groove assuredly forms a portion into which the melt burrs escape, so that stability of a weld surface is enhanced without the melt burrs influencing the stability of the weld surface. 
     (2. Manufacturing Method for Resin Filler Tube) 
     A manufacturing method for manufacturing the resin filler tube includes: extruding a tubular material having a plurality of layers by an extruder; and forming the resin filler tube by bringing the tubular material into close contact with an inner face formed by a plurality of split molds while sequentially moving the plurality of split molds in a direction in which the tubular material is extruded, such that the resin filler tube has an outer face corresponding to the inner face. 
     The resin filler tube described above is manufactured by the manufacturing method. A part of melt burrs on the inner circumferential side is stored in the annular recessed groove when the resin filler tube is welded to the fuel tank. Accordingly, the annular recessed groove exhibits the above-described effect. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates a fuel line; 
         FIG. 2  is an axial cross-sectional view of a filler tube shown in  FIG. 1  in a linearly extending state; 
         FIG. 3  is an enlarged cross-sectional view of a portion III in  FIG. 2 , illustrating a state where a flange of the filler tube is in contact with an outer circumferential edge of an opening hole of a fuel tank, and both of the flange and the outer circumferential edge of the opening hole of the fuel tank have not been welded yet, and indicating that a contour at a to-be-welded portion represents non-deformed shapes of the filler tube and the fuel tank which have not been welded yet; 
         FIG. 4  is an enlarged cross-sectional view of the portion III in  FIG. 2 , illustrating a state where the flange of the filler tube has been welded to the outer circumferential edge of the opening hole of the fuel tank, and indicating that a solid line at the welded portion represents shapes of the filler tube and the fuel tank which have been deformed by welding and an alternate long and two short dashes line at the welded portion represents non-deformed shapes of the filler tube and the fuel tank which have not been welded yet; 
         FIG. 5  is a flow chart showing a method for manufacturing a tank unit (fuel tank, filler tube, check valve); 
         FIG. 6  is a plan view of a manufacturing apparatus for manufacturing the filler tube; 
         FIG. 7  is a cross-sectional view taken along a line VII-VII in  FIG. 6 ; and 
         FIG. 8  illustrates a gap between a nozzle of an extruder and an outer face of a second end portion (inner circumferential surfaces of split molds). 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     (1. Structure of Fuel Line  1 ) 
     A structure of a fuel line  1  will be described with reference to  FIG. 1 . The fuel line  1  is a path extending from an oil filler port  10  through a fuel tank  20  to an internal combustion engine (not shown) in an automobile. In the present embodiment, a portion of the fuel line  1  from the oil filler port  10  to the fuel tank  20  will be described. 
     The fuel line  1  includes at least the oil filler port  10 , the fuel tank  20 , a resin filler tube  30 , and a check valve  40 . In the present embodiment, the fuel line  1  further includes a breather line  50 . 
     The oil filler port  10  is disposed near the outer face of an automobile, and allows an oil supply nozzle (not shown) to be inserted therein. The oil filler port  10  is made of resin or metal. The oil filler port  10  is either an oil filler port having an oil filler cap attached thereto, or a capless oil filler port which does not have an oil filler cap attached thereto. 
     The fuel tank  20  is molded by using thermoplastic resin, and stores liquid fuel such as gasoline. The fuel tank  20  includes, for example, a plurality of kinds of resin layers. The liquid fuel stored in the fuel tank  20  is fed to the not-illustrated internal combustion engine, and is used for driving the internal combustion engine. The fuel tank  20  has an opening hole  21  for feeding fuel. The opening hole  21  for feeding fuel is formed in, for example, the upper face or the side face of the fuel tank  20 . 
     The filler tube  30  is molded by using thermoplastic resin, and connects between the oil filler port  10  and the fuel tank  20 . The filler tube  30  has one or more bent portions for routing, in general. The filler tube  30  is formed by one member or is formed by a plurality of members joined to each other. In the present embodiment, an example in which the filler tube  30  is integrally formed by one member over the entire length, will be described. 
     A first end portion  31  of the filler tube  30  is press-fitted to a tubular portion  11  of the oil filler port  10 . A second end portion  32  of the filler tube  30  is welded to the outer circumferential edge of the opening hole  21  in the outer face of the fuel tank  20 . In the present embodiment, a part of the second end portion  32  is inserted in the opening hole  21  of the fuel tank  20 . 
     The oil supply nozzle is inserted in the oil filler port  10  and liquid fuel is fed through the oil supply nozzle, whereby the liquid fuel passes through the filler tube  30  and is stored in the fuel tank  20 . In a case where the fuel tank  20  has been filled with liquid fuel, liquid fuel is stored in the filler tube  30 , and the liquid fuel comes into contact with the tip of the oil supply nozzle to automatically stop feeding liquid fuel through the oil supply nozzle. 
     The check valve  40  is disposed near the opening hole  21  of the fuel tank  20 . The check valve  40  is fixed to the second end portion  32  of the filler tube  30 , or fixed between the filler tube  30  and the opening hole  21  of the fuel tank  20 . When liquid fuel is fed from the filler tube  30  into the fuel tank  20 , the liquid fuel passes through the check valve  40 . In this case, in a case where liquid fuel is fed from the filler tube  30  into the fuel tank  20 , backflow of the liquid fuel in the fuel tank  20  toward the filler tube  30  is prevented. 
     The breather line  50  connects between the oil filler port  10  and the fuel tank  20 , and is disposed parallel to the filler tube  30 . The breather line  50  is a line for discharging fuel vapor in the fuel tank  20  to the outside of the fuel tank  20  when liquid fuel is fed through the filler tube  30  into the fuel tank  20 . 
     (2. Schematic Structure of Filler Tube  30 ) 
     The schematic structure of the filler tube  30  will be described with reference to  FIG. 2 . The filler tube  30  is structured to have a plurality of layers made of different kinds of thermoplastic resins. As shown in  FIG. 2 , the filler tube  30  includes the first end portion  31  formed at one end portion in the tube axis direction, the second end portion  32  formed at the other end portion in the tube axis direction, and an intermediate portion  33  connecting between the first end portion  31  and the second end portion  32 . 
     The first end portion  31  is formed in a cylindrical shape, and fitted to the outer face of the tubular portion  11  of the oil filler port  10 . The first end portion  31  is formed so as to be deformed more easily than the tubular portion  11  of the oil filler port  10 . Therefore, the first end portion  31  is fitted to the tubular portion  11  of the oil filler port  10  in a state where the first end portion  31  is deformed to increase the diameter. 
     The second end portion  32  is formed in a tubular shape, and is welded to the outer circumferential edge of the opening hole  21  of the fuel tank  20 . The second end portion  32  includes a flange  32   b  that protrudes radially outward from a tubular body  32   a  over the entire circumference. The flange  32   b  is welded to the fuel tank  20 . That is, the flange  32   b  of the second end portion  32  functions so as to assure a sufficient weld area for welding to the fuel tank  20 . The second end portion  32  further includes a leading end tubular portion  32   c  extending to be closer to the leading end side of the filler tube  30  than the flange  32   b . Apart of the leading end tubular portion  32   c  is inserted in the opening hole  21  of the fuel tank  20 . The check valve  40  is attached to the inner circumferential surface of the leading end tubular portion  32   c.    
     The intermediate portion  33  is designed as appropriate so as to form a path according to relative positions of the oil filler port  10  and the fuel tank  20  and a distance therebetween, a layout of peripheral devices, and the like. In the present embodiment, the intermediate portion  33  includes a first tubular portion  33   a  that does not have a bellows-like shape, a bellows portion  33   b , and a second tubular portion  33   c  that does not have a bellows-like shape. The first tubular portion  33   a  is connected to the first end portion  31 , and is previously bent in a mid-portion in the tube axis direction. The bellows portion  33   b  is connected to the first tubular portion  33   a , and formed in a bellows-like tubular shape so as to be bendable as appropriate. The second tubular portion  33   c  is connected to the bellows portion  33   b , and is also connected to the second end portion  32 . The second tubular portion  33   c  is substantially formed in a cylindrical shape. 
     In an example other than the above-described example, the intermediate portion  33  of the filler tube  30  includes, for example, a plurality of the bellows portions, the entirety of the intermediate portion  33  is formed of the bellows portion, or the intermediate portion  33  includes no bellows portions. The first tubular portion  33   a  does not have a bellows-like shape and is bent. However, in another example, the first tubular portion  33   a  linearly extends. 
     (3. Layer Structure of Filler Tube  30 ) 
     A layer structure of the filler tube  30  will be described with reference to  FIG. 3 .  FIG. 3  is an enlarged cross-sectional view of a portion III in  FIG. 2 , and is an axial cross-sectional view of the second end portion  32  of the filler tube  30 . The filler tube  30  has a uniform layer structure over the entire length. Therefore, portions other than the second end portion  32  of the filler tube  30  have the same layer structure. That is, in the filler tube  30 , all of the first end portion  31 , the second end portion  32 , and the intermediate portion  33  have the same layer structure. 
     As shown in  FIG. 3 , the filler tube  30  is structured to have a plurality of layers made of different kinds of thermoplastic resins. The filler tube  30  includes, for example, an innermost layer  61 , an inner adhesive layer  62 , an intermediate layer  63 , an outer adhesive layer  64 , and an outermost layer  65  in order, respectively, from the inner layer side. The filler tube  30  is structured to have the plurality of layers over the entire length. The structure of the filler tube  30  is not limited to the five layer structure. In another example, the number of the layers of the filler tube  30  is not greater than four or not less than six. 
     The layers  61  to  64  other than the outermost layer  65  are collectively referred to as inner layers. The inner layers  61  to  64  are formed of inner layer materials. The outermost layer  65  is formed of an outermost layer material. The number of the inner layers  61  to  64  is not less than one. In the present embodiment, the filler tube  30  includes the four inner layers  61  to  64 . Each layer will be described below. 
     The innermost layer  61  comes into contact with liquid fuel (gasoline), and a gasoline-resistant material is thus used as the innermost layer material (one of the inner layer materials) of the innermost layer  61 . The innermost layer  61  preferably has a catching force (disengagement preventing force) for catching the tubular portion  11  of the oil filler port  10  in the axial direction in a state where the first end portion  31  is press-fitted to the tubular portion  11  of the oil filler port  10 . In this case, a material having sealability is used as the innermost layer material of the innermost layer  61 . The innermost layer material of the innermost layer  61  essentially contains, for example, high density polyethylene (HDPE). However, another material is allowed to be used for the innermost layer  61  as long as the material exhibits the above-described performance. 
     The intermediate layer  63  is disposed on the outer circumference side of the innermost layer  6   l . The intermediate layer material (one of the inner layer materials) of the intermediate layer is, for example, resistant to fuel permeation. For the intermediate layer  63 , for example, a material that essentially contains either ethylene-vinyl alcohol copolymer (EVOH) or polyamide (PA) is preferably used as the intermediate layer material resistant to fuel permeation. However, another material is allowed to be used for the intermediate layer  63  as long as the material exhibits the above-described performance. 
     The outermost layer  65  is disposed on the outer circumference side of the intermediate layer  63 . The outermost layer  65  protects the intermediate layer  63 . The outermost layer  65  forms the outermost surface of the filler tube  30 . Therefore, for example, a material having impact resistance, weather resistance, and chemical resistance is preferably used as the outermost layer material of the outermost layer  65 . In this case, for the outermost layer  65 , a material that essentially contains either high density polyethylene (HDPE) or polyamide (PA) is used as the outermost layer material. 
     Furthermore, in the present embodiment, the outermost layer  65  forms a layer to be welded to the fuel tank  20 . Therefore, a material having preferable weldability with respect to a material of the outer face of the fuel tank  20  is preferably used for the outermost layer material of the outermost layer  65 . Particularly, the outermost layer material of the outermost layer  65  and the material of the outer face of the fuel tank  20  are preferably of the same kind. However, another material is allowed to be used for the outermost layer  65  as long as the material exhibits the above-described performance. 
     The inner adhesive layer  62  is a layer for adhering the outer circumferential surface of the innermost layer  61  and the inner circumferential surface of the intermediate layer  63  to each other. The outer adhesive layer  64  is a layer for adhering the outer circumferential surface of the intermediate layer  63  and the inner circumferential surface of the outermost layer  65  to each other. For example, a material that essentially contains modified polyethylene (modified PE) is preferably used as the inner adhesive layer material (one of the inner layer materials) of the inner adhesive layer  62  and the outer adhesive layer material (one of the inner layer materials) of the outer adhesive layer  64 . However, in a case where at least one of the innermost layer  61  and the intermediate layer  63  has adhesiveness to the other thereof, the inner adhesive layer  62  is unnecessary. In a case where at least one of the intermediate layer  63  and the outermost layer  65  has adhesiveness to the other thereof, the outer adhesive layer  64  is unnecessary. 
     (4. Layer Structure of Fuel Tank  20 ) 
     The layer structure of the fuel tank  20  will be described with reference to  FIG. 3 .  FIG. 3  is a cross-sectional view of a portion near the opening hole  21  of the fuel tank  20 . The fuel tank  20  is structured to have a plurality of layers made of different kinds of thermoplastic resins. The fuel tank  20  is structured to have, for example, five layers (innermost layer, inner adhesive layer, intermediate layer, outer adhesive layer, and outermost layer), similarly to the filler tube  30 . 
     In  FIG. 3 , the fuel tank  20  has a three layer structure, that is, includes an innermost layer  20   a , an intermediate layer  20   b , and an outermost layer  20   c . The innermost layer  20   a , the intermediate layer  20   b , and the outermost layer  20   c  are, for example, formed in manners similar to manners in which the innermost layer  61 , the intermediate layer  63 , and the outermost layer  65 , respectively, of the filler tube  30  are formed. The structure of the fuel tank  20  is not limited to the three layer structure. In another example, the number of the layers of the fuel tank  20  is two or not less than four. 
     (5. Specific Structure of Second End Portion  32  of Filler Tube  30 ) 
     Next, the specific structure of the second end portion  32  of the filler tube  30  will be described with reference to  FIG. 3 . The second end portion  32  includes the tubular body  32   a , the flange  32   b , and a leading end tubular portion  32   c.    
     The tubular body  32   a  is formed in a tubular shape, and forms a portion of the second end portion  32  on the first end portion  31  side and the intermediate portion  33  side. That is, one end (not shown, the end portion located rightward of the region in  FIG. 3 ) of the tubular body  32   a  is connected to the intermediate portion  33  of the filler tube  30 . The tubular body  32   a  is formed in a cylindrical shape having a constant diameter over the entire length, a tubular shape having a plurality of diameters, or a tubular shape having a reverse tapered portion. 
     The tubular body  32   a  is structured to have the plurality of layers ( 61  to  65 ) described above, from the inner face toward the outer face. The tubular body  32   a  has a minimum outer diameter portion  32   a   1  that is formed in a cylindrical shape and that has a predetermined smallest outer diameter Doa 1  in the tubular body  32   a . The minimum outer diameter portion  32   a   1  of the tubular body  32   a  has a minimum inner diameter Dia 1 . 
     In the present embodiment, the tubular body  32   a  has a reverse tapered portion  32   a   2  having a diameter increased from the end of the minimum outer diameter portion  32   a   1  in the axial direction. The reverse tapered portion  32   a   2  is closer to the leading end side (left side in  FIG. 3 ) of the second end portion  32  than the minimum outer diameter portion  32   a   1  is. Both the outer face and the inner face of the reverse tapered portion  32   a   2  are formed in reverse taper. The tubular body  32   a  has a constant thickness over the entire length, or has various thicknesses. For example, the reverse tapered portion  32   a   2  has a thickness increased toward the leading end side of the second end portion  32 . 
     The flange  32   b  protrudes radially outward from the end of the tubular body  32   a  on the fuel tank  20  side (the leading end side of the second end portion  32 ), over the entire circumference. The outer face of the flange  32   b  includes a first end face  32   b   1  in the axial direction, a second end face  32   b   2  located on the back side surface of the first end face, and an outer circumferential surface  32   b   3 . 
     The first end face  32   b   1  forms a weld surface to be welded to the outer circumferential edge of the opening hole  21  of the fuel tank  20 . The first end face  32   b   1  is formed in a flat surface that is substantially orthogonal to the center axis of the second end portion  32  of the filler tube  30 . The second end face  32   b   2  is reversely tapered so as to be slightly tilted relative to the first end face  32   b   1 . The outer circumferential surface  32   b   3  is substantially formed in a cylindrical shape. 
     The flange  32   b  is also structured to have the plurality of layers ( 61  to  65 ) that are of the same kinds as those of the tubular body  32   a , from the inner face toward the outer face. Accordingly, the entirety of the outer face of the flange  32   b  is formed by the outermost layer material. That is, all of the first end face  32   b   1 , the second end face  32   b   2 , and the outer circumferential surface  32   b   3  that form the flange  32   b  are formed of the outermost layer material only. A melt portion at the first end face  32   b   1  by welding is formed of the outermost layer material only. 
     The outer circumferential surface  32   b   3  of the flange  32   b  has an outer diameter Dob. The flange  32   b  is filled over the entire range, in a radial range of the first end face  32   b   1  that is welded to the fuel tank  20 . Accordingly, the flange  32   b  has a thickness greater than the tubular body  32   a . In the present embodiment, a maximum inner diameter Dib of the flange  32   b  is less than an inner diameter Dit of the opening hole  21  of the fuel tank  20 . However, the present invention is not limited thereto as long as most of the radial range in which the to-be-welded first end face  32   b   1  of the flange  32   b  is welded to the fuel tank  20 , is filled. In this case, the maximum inner diameter Dib of the flange  32   b  is allowed to be slightly greater than the inner diameter Dit of the opening hole  21  of the fuel tank  20 . 
     The leading end tubular portion  32   c  extends from a radially inner portion of the flange  32   b  to the leading end side of the filler tube  30  (the leading end side of the second end portion  32 ). The check valve  40  is attached to the inner circumferential surface of the leading end tubular portion  32   c . The leading end tubular portion  32   c  is structured to have the plurality of layers ( 61  to  65 ) described above, from the inner face toward the outer face. 
     The leading end tubular portion  32   c  is formed so as to have an outer diameter that is less than the inner diameter Dit of the inner circumferential surface of the opening hole  21  of the fuel tank  20  over the entire length. That is, a gap is formed between the outer circumferential surface of the leading end tubular portion  32   c  and the inner circumferential surface of the opening hole  21  over the entire circumference. 
     The leading end tubular portion  32   c  has a maximum outer diameter portion  32   c   1  that is formed in a cylindrical shape, and that has a predetermined greatest outer diameter Doc 1  in the leading end tubular portion  32   c . The maximum outer diameter portion  32   c   1  of the leading end tubular portion  32   c  has a minimum inner diameter Dic 1 . The leading end tubular portion  32   c  is allowed to have another cylindrical portion or a tapered portion in a portion closer to the leading end than the maximum outer diameter portion  32   c   1  is. 
     The leading end tubular portion  32   c  has an annular recessed groove  32   c   2  formed on the flange  32   b  side of the outer circumferential surface over the entire circumference. The cross-section of the annular recessed groove  32   c   2  in the axial direction is shaped in a curved recess. The annular recessed groove  32   c   2  has a surface continuous with the first end face  32   b   1  without having a stepped portion between the annular recessed groove  32   c   2  and the first end face  32   b   1  of the flange  32   b . The annular recessed groove  32   c   2  is formed so as to have a groove width Wc 2  that is less than a thickness Wt of the inner circumferential surface of the opening hole  21  of the fuel tank  20 . That is, the annular recessed groove  32   c   2  is located outward of the inner circumferential surface of the opening hole  21  of the fuel tank  20 . 
     The maximum outer diameter Doc 1  of the leading end tubular portion  32   c  is greater than the outer diameter Doa 1  of the minimum outer diameter portion  32   a   1  of the tubular body  32   a . A minimum outer diameter Doc 2  of the annular recessed groove  32   c   2  of the leading end tubular portion  32   c  is less than the maximum outer diameter Doc 1  of the leading end tubular portion  32   c , and equal to or greater than the outer diameter Doa 1  of the minimum outer diameter portion  32   a   1  of the tubular body  32   a . In the present embodiment, the minimum outer diameter Doc 2  of the annular recessed groove  32   c   2  of the leading end tubular portion  32   c  is greater than the outer diameter Doa 1  of the minimum outer diameter portion  32   a   1  of the tubular body  32   a.    
     (6. Welded State in which Flange  32   b  and Fuel Tank  20  are Welded to Each Other) 
     Next, a welded state in which the first end face  32   b   1  of the flange  32   b  and the outer circumferential edge of the opening hole  21  of the fuel tank  20  are welded to each other, will be described with reference to  FIG. 4 . As shown in  FIG. 4 , the first end face  32   b   1  and the outer circumferential edge of the opening hole  21  are melted and adhered to each other. At this time, melt burrs are generated in welding between the first end face  32   b   1  and the outer circumferential edge of the opening hole  21 . The melt burrs protrude toward both the outer circumferential side of the weld surface and the inner circumferential side of the weld surface. 
     An outer region outside the outer circumferential surface  32   b   3  of the flange  32   b  is on the outer circumferential side of the weld surface, and thus has a sufficient space. Meanwhile, a radial gap region between the inner circumferential surface of the opening hole  21  of the fuel tank  20  and the outer circumferential surface of the leading end tubular portion  32   c  is on the inner circumferential side of the weld surface. The leading end tubular portion  32   c  has the annular recessed groove  32   c   2  formed therein. Accordingly, the annular recessed groove  32   c   2  stores the melt burrs generated in welding of the first end face  32   b   1  of the flange  32   b.    
     Thus, since the leading end tubular portion  32   c  has the annular recessed groove  32   c   2 , a part of the melt burrs on the inner circumferential side is stored in the annular recessed groove  32   c   2 . Thus, the annular recessed groove  32   c   2  assuredly forms a portion into which the melt burrs escape. Therefore, stability of the weld surface is enhanced without the melt burrs influencing the stability of the weld surface. 
     (7. Method for Manufacturing Tank Unit ( 20 ,  30 ,  40 )) 
     Next, a method for manufacturing the tank unit ( 20 ,  30 ,  40 ) that includes the fuel tank  20 , the filler tube  30 , and the check valve  40  will be described with reference to  FIG. 5 . 
     Firstly, the filler tube  30  is manufactured (S 1 : □filler tube manufacturing step□). The filler tube  30  is formed by extrusion molding. Accordingly, in the filler tube manufacturing step S 1 , a primary material  30   a  (shown in  FIG. 6 ) is formed by extrusion molding (S 11 ), and a secondary material  30   b  (shown in  FIG. 6 ) is formed by corrugation forming (S 12 ), and the secondary material  30   b  is finally cut, thereby forming the filler tube  30  (S 13 ). The method for manufacturing the filler tube  30  will be described below in more detail. 
     The fuel tank  20  is prepared (manufactured) (S 2 : □fuel tank preparing step□). The check valve  40  is prepared (S 3 : □check valve preparing step□). Subsequently, the check valve  40  is attached to the second end portion  32  of the filler tube  30  (S 4 : □check valve attaching step□). Subsequently, the second end portion  32  of the filler tube  30  is disposed at the position (welding initial position) of the opening hole  21  of the fuel tank  20  (S 5 : □initial position disposition step□). Subsequently, the flange  32   b  of the second end portion  32  of the filler tube  30  and the outer circumferential edge of the opening hole  21  of the fuel tank  20  are welded to each other (S 6 : □welding step□). In a case where the check valve  40  is attached after the welding, step S 4  is performed after step S 6 . 
     (8. Structure of Manufacturing Apparatus  100  for Filler Tube  30 ) 
     Next, the structure of a manufacturing apparatus  100  for manufacturing the filler tube  30  will be described with reference to  FIG. 6  and  FIG. 7 . The filler tube  30  is manufactured by the manufacturing apparatus  100  shown in  FIG. 6 . The manufacturing apparatus  100  includes an extruder  110 , a corrugation molding machine  120  arranged continuously with the extruder  110 , and a cutting machine  130  arranged continuously with the corrugation molding machine  120 . 
     That is, the tubular primary material  30   a  (tubular material) is formed by the extruder  110  (S 11  in  FIG. 5 ), the tubular secondary material  30   b  is formed by the corrugation molding machine  120  (S 12  in  FIG. 5 ), and the filler tube  30  is formed by the cutting machine  130  (S 13  in  FIG. 5 ). 
     The extruder  110  performs extrusion molding to form the tubular primary material  30   a . The primary material  30   a  is structured to have a plurality of layers ( 61  to  65 ) as shown in  FIG. 3 , and is formed in a cylindrical shape having a constant inner diameter and a constant outer diameter in the axial direction. That is, the primary material  30   a  is formed so as to have a constant thickness in the radial direction as a whole, and each layer is also formed so as to have a constant thickness in the radial direction. An extruding speed of the extruder  110  is adjustable to any speed. 
     While sequentially moving each of a plurality of split molds  123 ,  124  in the direction in which the primary material  30   a  is extruded, the corrugation molding machine  120  brings the primary material  30   a  into close contact with an inner face formed by the plurality of split molds  123 ,  124  to form the secondary material  30   b  that corresponds to the filler tube  30  having an outer face corresponding to the inner face. 
     The corrugation molding machine  120  is used for a portion at which the shape of the primary material  30   a  formed through extrusion molding by the extruder  110  is changed. In the present embodiment, the corrugation molding machine  120  is mainly used for forming the bellows portion  33   b  and forming the second end portion  32 . The corrugation molding machine  120  is used for changing the outer diameter of the primary material  30   a  also in a portion having a cylindrical shape. 
     The corrugation molding machine  120  includes a guide table  121 , a suctioning device  122 , a plurality of the split molds  123 ,  124 , and a drive gear  125 . An ellipsoidal first guide groove  121   a  and a second guide groove  121   b  which has the same shape as the first guide groove  121   a  and which is disposed adjacent to the first guide groove  121   a  are formed in the upper face of the guide table  121 . Furthermore, communication holes  121   c  that communicate with the first guide groove  121   a  and the second guide groove  121   b  are formed in the guide table  121 , as shown in  FIG. 7 . As shown in  FIG. 7 , the suctioning device  122  is connected to the communication holes  121   c  in the guide table  121 , and suctions air in a space communicating with the communication holes  121   c.    
     A plurality of first split molds  123  are molds for shaping one of two portions into which the filler tube  30  is divided along the axial direction. The plurality of first split molds  123  are sequentially moved on and along the first guide groove  121   a  of the guide table  121 . That is, each of the plurality of first split molds  123  is sequentially moved to form a half part of the filler tube  30 . Each of the plurality of first split molds  123  has a rack gear on the upper face. 
     A plurality of second split molds  124  are molds for shaping the other of the two portions into which the filler tube  30  is divided along the axial direction. The plurality of second split molds  124  are sequentially moved on and along the second guide groove  121   b  of the guide table  121 . That is, each of the plurality of second split molds  124  is sequentially moved to form a remaining half part of the filler tube  30 . Each of the plurality of second split molds  124  has a rack gear on the upper face. 
     A portion of the first split molds  123  and a portion of the second split molds  124  each have a shaping surface corresponding to the bellows portion  33   b . Another portion of the first split molds  123  and another portion of the second split molds  124  each have a shaping surface corresponding to the second end portion  32 . 
     A discharge opening of a nozzle  111  of the extruder  110  is disposed at a position, on the extruder  110  side, of a pair of molds formed by combining the plurality of first split molds  123  and the plurality of second split molds  124  with each other. That is, the primary material  30   a  is suctioned onto the inner circumferential surfaces of the pair of molds  123 ,  124  located at the position and thus shaped. 
     The drive gear  125  is a pinion gear for moving the plurality of first split molds  123  and the plurality of second split molds  124 . The drive gear  125  is disposed on the extruder  110  side of the pair of molds formed by combining the plurality of first split molds  123  and the plurality of second split molds  124  with each other. The drive gear  125  meshes with the first split molds  123  and the second split molds  124 , and is driven to rotate, whereby the plurality of first split molds  123  and the plurality of second split molds  124  are sequentially moved. 
     Furthermore, moving speeds of the plurality of split molds  123 ,  124  are changed by changing a rotation speed of the drive gear  125 . Increase of the moving speeds of the plurality of split molds  123 ,  124  causes the filler tube  30  to have a thickness reduced in the radial direction at portions corresponding to the split molds  123 ,  124  located near the nozzle  111  of the extruder  110 . Meanwhile, reduction of the moving speeds of the plurality of split molds  123 ,  124  causes the filler tube  30  to have a thickness increased in the radial direction at portions corresponding to the split molds  123 ,  124  located near the nozzle  111  of the extruder  110 . 
     For example, moving speeds of the split molds  123 ,  124  corresponding to the flange  32   b  are lower than moving speeds of the split molds  123 ,  124  corresponding to the tubular body  32   a . Accordingly, the thickness of the flange  32   b  in the radial direction is made greater than the thickness of the tubular body  32   a  in the radial direction. 
     The secondary material  30   b  discharged from the corrugation molding machine  120  has a shape continuous in the axial direction. That is, the continuous secondary material  30   b  has such a shape that a plurality of the filler tubes  30  connect to each other. Therefore, the continuous secondary material  30   b  shaped by the corrugation molding machine  120  is cut, by the cutting machine  130 , so as to have a predetermined length, thereby forming each filler tube  30 . 
     (9. Action of Molding Second End Portion  32 ) 
     Next, the action of molding the second end portion  32  of the filler tube  30  (secondary material  30   b ) will be described with reference to  FIG. 8 .  FIG. 8  shows a contour of the outer face of the second end portion  32  in the secondary material  30   b . That is, the contour of the outer face of the second end portion  32  represents the inner circumferential surfaces of the plurality of the split molds  123 ,  124 . The leading end of the nozzle  111  of the extruder  110  is also shown. 
     As indicated by an arrow in  FIG. 8 , the molded secondary material  30   b  (split molds  123 ,  124 ) moves rightward with respect to the nozzle  111  in  FIG. 8 . That is, the order in which the portions of the secondary material  30   b  are molded is the order of the first end portion  31  (shown in  FIG. 2 ), the intermediate portion  33  (shown in  FIG. 2 ), and the second end portion  32 . The order in which the portions of the second end portion  32  are molded is the order of the tubular body  32   a , the flange  32   b , and the leading end tubular portion  32   c.    
     Gaps between the radially outer end of the nozzle  111  and the outer face of the second end portion  32  in the secondary material  30   b  are as follows. A gap between the minimum outer diameter portion  32   a   1  of the tubular body  32   a  and the nozzle  111  is Ga 1 . A gap between the outer circumferential surface  32   b   3  of the flange  32   b  and the nozzle  111  is Gb. A minimum gap between the annular recessed groove  32   c   2  of the leading end tubular portion  32   c  and the nozzle  111  is Gc 2 . A gap between the maximum outer diameter portion  32   c   1  of the leading end tubular portion  32   c  and the nozzle  111  is Gc 1 . 
     In general, in a case where the gap between the portion and the nozzle  111  is continuously great, air is likely to enter, and a degree of vacuum tends to be reduced. In this case, the accuracy of the shape of the molded product is likely to be degraded. 
     The gap between the nozzle  111  and the outer circumferential surface  32   b   3  of the flange  32   b  is the largest of these gaps. That is, a gap is increased from the tubular body  32   a  toward the flange  32   b . Therefore, the degree of vacuum is gradually reduced. The leading end tubular portion  32   c  is molded in a state where the degree of vacuum has been reduced at the flange  32   b . Therefore, whether or not the accuracy of the shape of the leading end tubular portion  32   c  is made high needs to be considered. 
     However, the annular recessed groove  32   c   2  is located immediately following the flange  32   b . The gap Gc 2  for the annular recessed groove  32   c   2  is less than the gap Gc 1  for the maximum outer diameter portion  32   c   1  of the leading end tubular portion  32   c . Accordingly, after the degree of vacuum is reduced at the flange  32   b  portion, the gap Gc 2  for the annular recessed groove  32   c   2  is reduced. Therefore, the degree of vacuum is inhibited from being continuously low. 
     The degree of vacuum is made sufficiently high at the annular recessed groove  32   c   2 . Thus, the degree of vacuum is not made continuously low in the subsequent molding of the maximum outer diameter portion  32   c   1  of the leading end tubular portion  32   c . Accordingly, the accuracy of molding the leading end tubular portion  32   c  is made high.