Pipe structure

Abstract

A conventional pipe structure has the problem in that it is difficult to maintain desired strength, making it difficult to maintain product quality due to rattling and the like that occur with use.　In a pipe structure 10 according to the present invention, a first pipe 11 and a second pipe 12 are connected using a connection member 13 inserted into the first pipe via an insertion hole 21. A first pull-out prevention portion 24 of the connection member 13 is in contact with the inside of the first pipe 11, and a second pull-out prevention portion 25 of the connection member 13 is in contact with the inside of the second pipe 12. This structure improves assembling workability of the pipe structure 10, achieves desired strength as the pipe structure 10, and improves product quality.

Description

Pipe structure

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[0001] The present invention relates to a pipe structure.

[0002] As a conventional pipe structure, the structure described in Patent Document 1 is known. The pipe structure is configured by simply and cheaply assembling a plurality of metal pipes, and is used for, for example, handrails and fences.

[0003] The pipe structure has an assembled-side pipe and an assembling-side pipe. The assembled-side pipe and the assembling-side pipe are hollow metal pipes. A hole is formed on the side surface of the assembled-side pipe, and the hole is formed in a substantially circular shape when viewed from the front. The inner diameter of the hole is set slightly larger than the outer diameter of the assembling-side pipe.

[0004] On the other hand, a pair of claw portions and small holes are formed on the side surface of the tip end portion of the assembling-side pipe. The claw portions are formed, for example, by cutting a part of the assembling-side pipe into a substantially U shape by laser processing or the like, and are formed by bending so as to expand toward the rear end side of the assembling-side pipe. The small hole is formed on the base side of the claw portion and is used as a hole for inserting a jig for bending the claw portion.

[0005] With this structure, in the process of inserting the tip end portion of the assembling-side pipe into the assembled-side pipe, the claw portions are pushed against the edge portion of the hole of the assembled-side pipe and bent inward, so that the tip end side of the assembling-side pipe is inserted into the inside of the assembled-side pipe. After that, the claw portions expand outward inside the assembled-side pipe, catch on the inner peripheral surface of the assembled-side pipe, and cannot come out of the hole. As a result, the assembling-side pipe is assembled to the assembled-side pipe, and the pipe structure is completed.

[0006] Also, as a conventional pipe structure, the structure described in Patent Document 2 is known. The pipe structure includes two first square pipes and second square pipes, a fixing bracket, and fastening bolts and nuts.

[0007] The first square pipe is a hollow metal material, and a rectangular opening is formed on one side of it. On the other hand, at the tip of the second square pipe, two opposing sides out of the four sides are press-formed to create a stepped section. Then, on the remaining two sides out of the four sides, a pair of through holes are coaxially formed in the center, corresponding to the area where the stepped section is formed.

[0008] The fixing bracket is sized to be insertable into the interior of the first square pipe from its open end. The fixing bracket also has a pair of pieces that clamp and support the stepped portion of the second square pipe below the rectangular opening of the first square pipe. A pair of through holes are formed in the pair of pieces at positions corresponding to a pair of through-holes in the second square pipe.

[0009] In this structure, the stepped portion of the second square pipe is inserted into the first square pipe through the rectangular opening, and the second square pipe is then fixed to the fixing bracket inside the first square pipe using fastening bolts and nuts. As a result, the second square pipe is prevented from coming out of the rectangular opening of the first square pipe by the fixing bracket, thus completing the pipe structure.

[0010] Japanese Patent Publication No. 2009-209988, Japanese Patent Publication No. 7118491

[0011] The pipe structure described in Patent Document 1 is composed of a pipe to be assembled and an assembly pipe. A pair of claws formed on the assembly pipe catch into the inside of the pipe to be assembled, preventing the assembly pipe from coming loose from the pipe to be assembled, thus completing the pipe structure.

[0012] However, because the claw portion is formed by bending a part of the pipe being assembled, if a large tensile force is applied to the pipe structure, the claw portion may open up significantly inside the pipe being assembled. In this case, a large gap is created at the connection between the pipe being assembled and the pipe being assembled, resulting in rattle in the pipe structure and making it difficult to ensure the desired strength of the pipe structure.

[0013] Furthermore, repeated tensile force applied to the bent portion of the claw can cause metal fatigue, leading to the claw detaching from the pipe it is attached to, which poses a risk of the pipe becoming detached from the pipe it is attached to.

[0014] In the pipe structure described in Patent Document 2, a structure that is durable against tensile forces applied to the pipe structure is realized by using fixing brackets and fastening bolts and nuts.

[0015] However, the fixing bracket needs to be inserted into the first square pipe from its open end, and the second square pipe and the fixing bracket need to be bolted together. To implement this assembly process, there is a limitation on the length of the first square pipe, making it difficult to accommodate pipe structures of various sizes.

[0016] The present invention has been made in view of the above circumstances, and provides a pipe structure that connects pipes using connecting members to achieve a desired strength between pipes and improve product quality.

[0017] The pipe structure of the present invention is a pipe structure configured by inserting a second pipe into a first pipe and connecting the first pipe and the second pipe, comprising: an insertion hole formed in the first pipe; a connecting member inserted into the interior of the first pipe from the insertion hole; and a first slit formed in the insertion region of the second pipe into the first pipe, wherein the connecting member is disposed inside the second pipe through the first slit, and the connecting member has a first pull-out prevention portion that contacts the interior of the first pipe and a second pull-out prevention portion that contacts the interior of the second pipe.

[0018] In the pipe structure of the present invention, a first pipe and a second pipe are connected using a connecting member inserted into the inside of the pipes through a through hole. The first pull-out prevention portion of the connecting member is in contact with the inside of the first pipe, and the second pull-out prevention portion of the connecting member is in contact with the inside of the second pipe. This structure improves the assembly workability of the pipe structure, achieves the desired strength of the pipe structure, and improves product quality.

[0019] This is a perspective view illustrating a pipe structure according to one embodiment of the present invention. This is an exploded perspective view illustrating a pipe structure according to one embodiment of the present invention. This is a plan view illustrating a pipe structure according to one embodiment of the present invention. This is a cross-sectional view illustrating a pipe structure according to one embodiment of the present invention. This is a perspective view illustrating the assembly process of a pipe structure according to one embodiment of the present invention. This is a perspective view illustrating a pipe structure according to one embodiment of the present invention. This is an exploded perspective view illustrating a pipe structure according to one embodiment of the present invention. This is a cross-sectional view illustrating a pipe structure according to one embodiment of the present invention. This is a cross-sectional view illustrating a pipe structure according to one embodiment of the present invention. This is a perspective view illustrating the assembly process of a pipe structure according to one embodiment of the present invention. This is a perspective view illustrating a pipe structure according to one embodiment of the present invention. This is an exploded perspective view illustrating a pipe structure according to one embodiment of the present invention. This is a cross-sectional view illustrating a pipe structure according to one embodiment of the present invention. This is a cross-sectional view illustrating a pipe structure according to one embodiment of the present invention. This is a characteristic diagram illustrating the results of a tensile test performed on a pipe structure according to one embodiment of the present invention.

[0020] Hereinafter, a pipe structure 10 according to the first embodiment of the present invention will be described in detail with reference to Figures 1 to 6. In this description, the same reference numeral will be used for the same components as a general rule, and repeated explanations will be omitted. The vertical direction of the paper indicates the height direction of the pipe structure 10, the horizontal direction of the paper indicates the width direction when the pipe structure 10 is viewed from the front, and the front-to-back direction of the paper indicates the depth direction when the pipe structure 10 is viewed from the front.

[0021] Figure 1 is a perspective view illustrating the pipe structure 10 of this embodiment. Figure 2 is an exploded perspective view illustrating the pipe structure 10 of this embodiment. Figure 3 is a plan view illustrating the first pipe 11 of the pipe structure 10 of this embodiment. Figure 4 is a cross-sectional view illustrating the assembled state of the pipe structure 10 of this embodiment. Note that Figure 4 is a cross-section along the central axis 11A of the first pipe 11 and shows the formation region of the first slit 22.

[0022] First, for example, pipe structures 10, which are constructed by connecting pipes, are used for the internal structures of mechanical structures such as the frames of four-wheeled vehicles, motorcycles, furniture, and office equipment, as well as for the internal structures of building structures such as handrails and fences. In the pipe structures 10, the pipes are welded together, for example, using known welding techniques, according to the desired strength, such as the tensile strength required for the mechanical structures. As a result, the necessary strength and reliability are achieved for the mechanical structures.

[0023] However, known welding techniques have several drawbacks, including the need to design with thermal distortion during welding in mind, environmental issues such as increased carbon dioxide emissions, the inability to weld dissimilar metals together, and increased manufacturing costs. Therefore, in this embodiment, the objective is to solve the above problems by constructing a pipe structure 10 by connecting pipes using connecting members 13, even without using known welding techniques. Furthermore, the pipe structure 10 is designed to achieve strength and reliability as close as possible to that of known welding techniques, depending on the tensile strength and other requirements of the mechanical structure.

[0024] As shown in Figure 1, the pipe structure 10 mainly comprises a first pipe 11, a second pipe 12, and a connecting member 13 (see Figure 2) that connects the first pipe 11 and the second pipe 12. The first pipe 11 and the second pipe 12 are, for example, cylindrical round pipes. The pipe structure 10 is constructed by inserting the end 12D side (see Figure 2) of the second pipe 12 into the interior of the first pipe 11. As will be described in detail later, the second pipe 12 is fixed to the first pipe 11 using the connecting member 13 to prevent it from being pulled out of the first pipe 11 or to suppress the occurrence of rattle.

[0025] Depending on the machine structure etc. in which the pipe structure 10 is used, the total lengths L1, L2, outer diameters Φ1, Φ2, and plate thicknesses T1, T2 of the first pipe 11 and the second pipe 12 can be arbitrarily modified. The first pipe 11 and the second pipe 12 are formed from, for example, aluminum steel, aluminum alloy steel, iron steel, stainless steel, carbon fiber composite material, etc. The pipe structure 10 allows for the connection of dissimilar metals by using connecting members 13.

[0026] In the following description, the pipe structure 10 is described as a structure in which two first pipes 11 and a second pipe 12 are connected in a substantially T-shape using connecting members 13, but it is not limited to this structure. Depending on the design of the above-mentioned mechanical structure etc. in which the pipe structure 10 is used, three or more pipes may be connected to each other using connecting members 13, and they can be connected in any shape. Furthermore, the pipe structure 10 is not limited to a structure in which pipes are connected perpendicularly to each other, such as the substantially T-shape described above. It may also be a structure in which pipes are connected diagonally using connecting members 13. In addition, the pipes used in the pipe structure 10 are not limited to round pipes, but square pipes may also be used.

[0027] As shown in Figure 2, the first pipe 11 has an insertion hole 21 for inserting the second pipe 12 and the connecting member 13. The insertion hole 21 is formed by cutting out a part of the first pipe 11, for example, by laser processing. When the first pipe 11 is viewed from the insertion direction of the second pipe 12, the insertion hole 21 is formed in a substantially circular shape relative to the first pipe 11 in its plan view. It should also be noted that, as will be described later using Figure 7, a second slit 32 may be formed on both sides of the insertion hole 21.

[0028] A first slit 22 is formed in the second pipe 12 from the end 12D on the side inserted into the first pipe 11. The width W1 of the first slit 22 is the same as or slightly narrower than the thickness T3 of the connecting plate 23, which serves as the connecting member 13. The first slit 22 is formed across the insertion region R1 of the second pipe 12.

[0029] With this structure, as shown in Figure 1, when the first pipe 11 and the second pipe 12 are assembled as a pipe structure 10, the first slit 22 is hidden inside the first pipe 11. In other words, the first slit 22 is not exposed to the outside of the pipe structure 10.

[0030] The connecting member 13 is formed, for example, by cutting a plate-shaped member such as steel or high-tensile steel into a desired shape. In the pipe structure 10, a single connecting plate 23 is used as the connecting member 13. As shown in the figure, the connecting plate 23 has a shape in which, for example, a first plate portion 23A and a second plate portion 23B, which are approximately square in plan view, are integrated with each other while being offset in the width direction (left-right direction of the paper).

[0031] The first plate portion 23A is disposed inside the first pipe 11 and has a first pull-out prevention portion 24 for catching on the inner circumferential surface 11B (see Figure 4) of the first pipe 11. As will be described in detail later, in the extending direction of the first pipe 11, the first plate portion 23A is disposed inside the first pipe 11 beyond the region where the insertion hole 21 is formed. The upper end surface of the first plate portion 23A functions as the first pull-out prevention portion 24, catching on the inner circumferential surface 11B of the first pipe 11 and increasing the tensile strength of the pipe structure 10.

[0032] On the other hand, the second plate portion 23B is disposed inside the second pipe 12 and has a second pull-out prevention portion 25 for catching on the inner circumferential surface 12B (see Figure 4) of the second pipe 12. As will be described in detail later, the second plate portion 23B is led out from the insertion hole 21 to the outside of the first pipe 11 and disposed inside the second pipe 12. The left and right end faces of the second plate portion 23B are processed into a sawtooth shape 25A, for example, and function as a second pull-out prevention portion 25 for catching on the inner circumferential surface 12B of the second pipe 12.

[0033] Here, the sawtooth shape 25A has multiple sharp teeth, and these sharp teeth are inclined toward the first pipe 11 in the direction of extension of the second pipe 12. When a tensile force is applied to the second pipe 12 in the pulling direction, the tips of the sharp teeth of the sawtooth shape 25A bite into the inner circumferential surface 12B of the second pipe 12 and catch, thereby maintaining the connection between the second pipe 12 and the connecting plate 23.

[0034] Furthermore, the structure is not limited to the formation of the sawtooth shape 25A on both end faces of the second plate portion 23B. Any structure that maintains the connection between the second pipe 12 and the connecting plate 23 is acceptable, and it is also acceptable for burrs or the like to be left on both end faces during the manufacturing process of the second plate portion 23B, resulting in the end faces being formed as rough surfaces. In addition, depending on the strength of the pipe structure 10, the end faces may be flat surfaces, and frictional resistance may be utilized. In other words, any design changes are possible depending on the required strength of the pipe structure 10.

[0035] As shown in Figure 3, in the plan view, the inner diameter Φ3 of the circular insertion hole 21 is the same as or shorter than the outer diameter Φ2 (see Figure 1) of the second pipe 12. In this embodiment, the lower limit of the inner diameter Φ3 of the insertion hole 21 is such that the second pipe 12 does not bend when the second pipe 12 is pressed into the first pipe 11, and the second pipe 12 can be designed to bend within the range of elastic deformation, thereby maintaining the desired product quality as a pipe structure 10.

[0036] As shown in Figure 4, the shape of the first plate portion 23A of the connecting plate 23 is a plate-like body with a roughly square shape in plan view. Specifically, the width W2 of the first plate portion 23A is the same as or slightly narrower than the inner diameter Φ3 of the insertion hole 21, its vertical width W3 is the same as or slightly wider than the inner diameter Φ4 of the first pipe 11, and its plate thickness T3 (see Figure 2) is the same as or slightly wider than the width W1 of the first slit 22.

[0037] As shown in the diagram, the connecting plate 23 is positioned in the extending direction of the first pipe 11, aligned with the central axis 11A of the first pipe 11 (see Figure 1), and the first plate portion 23A is positioned to fit inside the first pipe 11. In other words, the first plate portion 23A is press-fitted into the first pipe 11. The first pull-out prevention portion 24 of the first plate portion 23A is then in contact with the inner circumferential surface 11B of the first pipe 11.

[0038] Furthermore, the shape of the second plate portion 23B of the connecting plate 23 is a plate-like body with a roughly square shape in plan view, and is integrally formed on the upper side of the first plate portion 23A. The second plate portion 23B is then led out to the outside of the first pipe 11 through the insertion hole 21.

[0039] The insertion region R1 (see Figure 2) of the second pipe 12 is press-fitted into the interior of the first pipe 11, and the end portion 12D of the second pipe 12 is in contact with the inner circumferential surface 11B of the first pipe 11. At this time, the first plate portion 23A is inserted into the first slit 22 of the second pipe 12. In other words, when the second pipe 12 is press-fitted into the first pipe 11, the first plate portion 23A is fitted into the first slit 22 due to the relationship between the width W1 and the plate thickness T3.

[0040] On the other hand, the second plate portion 23B is positioned inside the second pipe 12 in alignment with the central axis 12A (see Figure 1) of the second pipe 12, so that the second plate portion 23B is fitted inside the second pipe 12 via the sawtooth shape 25A which serves as the second pull-out prevention portion 25.

[0041] With this structure, the first pipe 11 and the second pipe 12 are connected by press-fitting the second pipe 12 into the insertion hole 21. Furthermore, the second pipe 12 is firmly connected to the connecting plate 23, so the first pipe 11 and the second pipe 12 are also connected via the connecting plate 23. In other words, in the pipe structure 10, as shown by arrow 15 (see Figure 1), if the second pipe 12 is subjected to a tensile force in the direction of being pulled out of the first pipe 11, the first pull-out prevention portion 24 of the connecting plate 23 catches on the inner circumferential surface 11B of the first pipe 11.

[0042] At this time, the second pipe 12 is press-fitted into the first pipe 11, and the second pipe 12 is fixed to the first pipe 11 through the insertion hole 21. This prevents the first plate portion 23A from sliding toward the insertion hole 21, and maintains the engagement between the first pipe 11 and the first pull-out prevention portion 24.

[0043] Furthermore, as described above, the sawtooth shape 25A, which is the second pulling prevention portion 25, is formed on both end faces in the left-right direction of the drawing plane of the second plate portion 23B. After the second pipe 12 and the connecting plate 23 are connected, the tip of the acute-angled tooth of the sawtooth shape 25A catches on the inner peripheral surface 12B of the second pipe 12. As a result, the second pipe 12 becomes difficult to be pulled out from the connecting plate 23, and the connected state of the pipe structure 10 is maintained.

[0044] Next, the assembling process of the pipe structure 10 will be described with reference to FIGS. 5 to 6. FIGS. 5 and 6 are perspective views for explaining the assembling process of the pipe structure 10 of the present embodiment. Note that, for the shapes and materials of the first pipe 11, the second pipe 12, and the connecting member 13, refer to the descriptions of FIGS. 1 to 4 above.

[0045] As shown in FIG. 5, first, the first pipe 11, the second pipe 12 (see FIG. 6), and the connecting member 13 are prepared. Then, an insertion hole 21 is formed, for example, by laser processing or the like, at a position in the first pipe 11 where the second pipe 12 is to be inserted. Further, a first slit 22 (see FIG. 6) is formed in the second pipe 12, for example, by laser processing or the like. Further, as the connecting member 13, for example, a connecting plate 23 is formed by laser processing or the like, and the sawtooth shape 25A, which is the second pulling prevention portion 25, is formed on the connecting plate 23.

[0046] Next, the connecting plate 23 is assembled to the first pipe 11. The first plate portion 23A of the connecting plate 23 is inserted into the first pipe 11 from the insertion hole 21. Then, as shown in FIG. 4, the connecting plate 23 is slid until the alignment portion 23C between the first plate portion 23A and the second plate portion 23B contacts the first pipe 11 at the edge of the insertion hole 21. As a result, the first plate portion 23A is disposed inside the first pipe 11 so as to be hidden from the insertion hole 21. Then, due to the relationship between the width W3 and the inner diameter Φ4, the first plate portion 23A is press-fitted inside the first pipe 11, so that the first plate portion 23A is fitted inside the first pipe 11. By this assembling method, the first pull-out prevention portion 24 of the first plate portion 23A comes into contact with the inner peripheral surface 11B (see FIG. 4) of the first pipe 11.

[0047] Next, as shown in FIG. 6, using the insertion hole 21, the insertion region R1 (see FIG. 2) of the second pipe 12 is press-fitted into the first pipe 11. First, the first slit 22 of the second pipe 12 is aligned with the first plate portion 23A inside the first pipe 11. Then, the second pipe 12 is press-fitted into the first pipe 11 so that the first plate portion 23A is fitted into the first slit 22.

[0048] At this time, due to the relationship between the inner diameter Φ3 of the insertion hole 21 and the outer diameter Φ2 of the second pipe 12, the second pipe 12 is press-fitted into the first pipe 11. Then, while the width of the first slit 22 narrows, the second pipe 12 is inserted into the first pipe 11. As a result, the first plate portion 23A is fitted into the first slit 22 of the second pipe 12, so that the second pipe 12 and the connecting plate 23 are in a connected state.

[0049] On the other hand, in the second plate portion 23B, the sawtooth shape 25A is inclined toward the first pipe 11, so that when the second pipe 12 is press-fitted into the first pipe 11, the second pipe 12 is inserted into the first pipe 11 relatively easily. Then, as a result of the press-fitting operation, the second pipe 12 bends inward within the range of elastic deformation that maintains its shape, causing the sharp tips of the teeth of the sawtooth shape 25A to bite into the inner circumferential surface 12B of the second pipe 12.

[0050] As described above, this assembly process ensures that the first pipe 11, the second pipe 12, and the connecting member 13 are connected within an appropriate clearance range at the point of contact, making it difficult for the second pipe 12 to be pulled out of the first pipe 11. Furthermore, looseness between the three components—the first pipe 11, the second pipe 12, and the connecting member 13—is reduced, thereby improving the product quality of the pipe structure 10.

[0051] Next, a pipe structure 30 according to the second embodiment of the present invention will be described in detail with reference to the drawings, using Figures 7 to 12. In principle, the same reference numerals will be used for the same components as those in the pipe structure 10 when describing the pipe structure 30, and repeated explanations will be omitted.

[0052] Figure 7 is a perspective view illustrating the pipe structure 30 of this embodiment. Figure 8 is an exploded perspective view illustrating the pipe structure 30 of this embodiment. Figures 9 and 10 are cross-sectional views illustrating the assembled state of the pipe structure 30 of this embodiment. Figure 9 is a cross-section along the central axis 11A of the first pipe 11 and shows the formation region of the first slit 22. Figure 10 is a cross-section along the center of the insertion hole 21 of the first pipe 11 and shows a cross-section perpendicular to the central axis 11A.

[0053] As shown in Figure 7, the pipe structure 30 mainly comprises a first pipe 11, a second pipe 12, and a connecting member 31 (see Figure 8) that connects the first pipe 11 and the second pipe 12. In the pipe structure 30, the structure of the connecting member 31 mainly differs from the structure of the connecting member 13 of the pipe structure 10. Therefore, in the following description, the structure of the connecting member 31 and its surrounding structure will be described, and other structures will be omitted here, as they are described in the description of the pipe structure 10 above.

[0054] As shown in Figure 8, the first pipe 11 has an insertion hole 21 for inserting the second pipe 12 and the connecting member 31. The first pipe 11 also has a second slit 32 that is continuous with the insertion hole 21. The second slit 32 is formed along the central axis 11A (see Figure 7) of the first pipe 11, extending in the direction of the first pipe 11. As will be described in detail later, the second slit 32 only needs to be formed along the central axis 11A on at least one side of the insertion hole 21. Alternatively, if the widths W5 and W7 (see Figure 8) of the first plate portions 33A and 34A are narrower than the inner diameter Φ3 of the insertion hole 21, the structure may not have a second slit 32.

[0055] Two first slits 22 are formed in the second pipe 12 from the end 12D on the side inserted into the first pipe 11. The two first slits 22 are formed symmetrically with respect to the central axis 12A of the second pipe 12 (see Figure 7).

[0056] The connecting member 31 is formed, for example, by cutting a plate-shaped member such as steel or high-tensile steel into a desired shape. In the pipe structure 30, a first connecting plate 33, a second connecting plate 34, and a third connecting plate 35 are used as the connecting member 31.

[0057] As shown in the diagram, the first connecting plate 33 has a shape in which, for example, a first plate portion 33A and a second plate portion 33B, which are approximately square in plan view, are integrated and offset in the width direction (left-right direction of the paper). The second plate portion 33B has a locking slit 36 ​​for inserting and locking the third connecting plate 35. The first plate portion 33A is disposed inside the first pipe 11 and has a first pull-out prevention portion 24 for catching on the inner circumferential surface 11B of the first pipe 11 (see Figure 9).

[0058] The second connecting plate 34 has a shape in which, for example, the first plate portion 34A and the second plate portion 34B, which are approximately square in plan view, are offset in the width direction (left-right direction of the paper) and integrated together. In the second connecting plate 34, a locking slit 36 ​​is formed in the second plate portion 34B, similar to the first connecting plate 33. The first plate portion 34A also has a first pull-out prevention portion 24 for hooking onto the inner circumferential surface 11B of the first pipe 11.

[0059] The third connecting plate 35 has, for example, a first plate portion 35A which is roughly square in plan view, and a second enlarged diameter portion 37 which is roughly semicircular in plan view and serves as a second pull-out prevention portion 25, formed on the tip side of the first plate portion 35A. A pair of enlarged diameter portions 37 are formed on both sides of the locking slit 38. The width W4 of the enlarged diameter portion 37 is the same as, or slightly narrower than, the inner diameter Φ3 of the insertion hole 21 of the first pipe 11, in order to allow passage through the insertion hole 21. As will be described in detail later, the purpose of the enlarged diameter portion 37 is to contact the inner circumferential surface 12B of the second pipe 12 and enlarge the outer diameter Φ2 of the insertion area R1 of the second pipe 12. For this reason, the shape of the enlarged diameter portion 37 is not limited to the semicircular shape described above, and may be triangular or polygonal in plan view.

[0060] Furthermore, the first plate portion 35A of the third connecting plate 35 has a locking slit 38 formed therein for inserting and locking the first connecting plate 33 and the second connecting plate 34. The third connecting plate 35 then locks the first connecting plate 33 and the second connecting plate 34 using the locking slit 38. In other words, the third connecting plate 35 is sandwiched between the locking slits 36 of the first connecting plate 33 and the second connecting plate 34 and is locked by the first connecting plate 33 and the second connecting plate 34.

[0061] Furthermore, a sawtooth shape 25A may be formed on the inner circumferential surface of the locking slit 38. In this case, as described above, the tips of the sharp teeth of the sawtooth shape 25A bite into the sides of the first connecting plate 33 and the second connecting plate 34, thereby further strengthening the connection between the connecting members 31.

[0062] As shown in Figure 9, the first connecting plate 33 and the second connecting plate 34 are inserted into the first pipe 11 through the insertion hole 21 and are positioned to align with the central axis 11A of the first pipe 11 (see Figure 7). The first plate portion 33A of the first connecting plate 33 is inserted into the left side of the insertion hole 21 and is positioned to fit inside the first pipe 11. On the other hand, the first plate portion 34A of the second connecting plate 34 is inserted into the right side of the insertion hole 21 and is positioned to fit inside the first pipe 11.

[0063] Here, in the first connecting plate 33, the width W5 of the first plate portion 33A (see Figure 8) is wider than the width W6 of the second plate portion 33B (see Figure 8), and is also wider than the inner diameter Φ3 of the insertion hole 21 (see Figure 3). Similarly, in the second connecting plate 34, the width W7 of the first plate portion 34A (see Figure 8) is wider than the width W8 of the second plate portion 34B (see Figure 8), and is also wider than the inner diameter Φ3 of the insertion hole 21 (see Figure 3). Furthermore, the area in which the first pull-out prevention portion 24 of the first connecting plate 33 contacts the inner circumferential surface 11B of the first pipe 11 is also widened. Similarly, the area in which the first pull-out prevention portion 24 of the second connecting plate 34 contacts the inner circumferential surface 11B of the first pipe 11 is also widened.

[0064] With this structure, in the pipe structure 30, as shown by arrow 15 (see Figure 7), when the second pipe 12 is subjected to a tensile force in the direction of being pulled out from the first pipe 11, the first pull-out prevention portion 24 of the first connecting plate 33 and the first pull-out prevention portion 24 of the second connecting plate 34 catch on the inner circumferential surface 11B of the first pipe 11. In the pipe structure 30, the tensile strength is improved by increasing the contact area between the first pull-out prevention portion 24 and the first pipe 11.

[0065] As shown in the figure, the second plate portion 33B of the first connecting plate 33 and the second plate portion 34B of the second connecting plate 34 are led out to the outside of the first pipe 11 through the insertion hole 21, and the locking slits 36 are aligned and arranged to overlap each other. The third connecting plate 35 is connected to the first connecting plate 33 and the second connecting plate 34 via the locking slits 36 and 38, and locks the first connecting plate 33 and the second connecting plate 34.

[0066] On the other hand, as described above, a second slit 32 is formed in the first pipe 11, continuous with the insertion hole 21. As described above, because the width W5 is wider than the inner diameter Φ3, the first plate portion 33A of the first connecting plate 33 is inserted into the first pipe 11 using the second slit 32. The alignment portion 33C of the first connecting plate 33 is inserted into the second slit 32 and comes into contact with the end of the second slit 32, so that the first connecting plate 33 is fixed in position relative to the first pipe 11.

[0067] Similarly, as described above, because the width W7 is wider than the inner diameter Φ3, the first plate portion 34A of the second connecting plate 34 is inserted into the first pipe 11 using the second slit 32. The alignment portion 34C of the second connecting plate 34 is inserted into the second slit 32 and comes into contact with the end of the second slit 32, so that the second connecting plate 34 is fixed in position relative to the first pipe 11.

[0068] As a result, the first connecting plate 33 and the second connecting plate 34 are positioned in line with the central axis 11A of the first pipe 11. The locking slits 36 of the first connecting plate 33 and the second connecting plate 34 are aligned with the center of the insertion hole 21. The third connecting plate 35 is then inserted into the locking slit 36, aligning and fixing it to the center of the insertion hole 21.

[0069] As shown in Figure 10, the insertion region R1 (see Figure 8) of the second pipe 12 is press-fitted into the first pipe 11. When the second pipe 12 overcomes the enlarged diameter portion 37 of the third connecting plate 35, it is enlarged using the first slit 22 (see Figure 8). Here, the shape of the enlarged diameter portion 37 is designed so that the second pipe 12 bends within the range of elastic deformation.

[0070] In other words, in the insertion region R1 of the second pipe 12, the enlarged diameter portion 37 and the inner circumferential surface 12B of the second pipe 12 maintain contact, and the outer diameter Φ2 of the second pipe 12 becomes wider than the inner diameter Φ3 of the insertion hole 21, starting from the insertion hole 21. The second pipe 12 is enlarged by the enlarged diameter portion 37, and as a reaction force, the enlarged diameter portion 37 is pushed toward its center. As a result, the third connecting plate 35 firmly grips the first connecting plate 34 and the second connecting plate 35 through the locking slit 38, and the entire connecting member 31 becomes firmly connected to each other.

[0071] This structure allows the second pipe 12 to be fitted into the first pipe 11 through the insertion hole 21, and the second pipe 12 to be firmly connected to the connecting member 31. Furthermore, the first pull-out prevention part 24 firmly catches on the inner circumferential surface 11B of the first pipe 11, making it difficult for the second pipe 12 to be pulled out of the first pipe 11, and thus maintaining the assembled state of the pipe structure 30.

[0072] Next, the assembly process of the pipe structure 30 will be explained using Figures 11 and 12. Figures 11 and 12 are perspective views illustrating the assembly process of the pipe structure 30 in this embodiment. The shapes and materials of the first pipe 11, the second pipe 12, and the connecting member 31 will be described in the explanation of Figures 7 to 10 above.

[0073] As shown in Figure 11, first, the first pipe 11, the second pipe 12, and the connecting member 31 are prepared. Then, in the first pipe 11, an insertion hole 21 and a second slit 32 are formed at the position where the second pipe 12 will be inserted, for example by laser processing. Also, in the second pipe 12, a pair of first slits 22 (see Figure 8) are formed, for example by laser processing. Furthermore, as the connecting member 31, a first connecting plate 33, a second connecting plate 34, and a third connecting plate 35 are formed, for example by laser processing.

[0074] Next, the first connecting plate 33, the second connecting plate 34, and the third connecting plate 35 are assembled to the first pipe 11. The first connecting plate 33 and the second connecting plate 34 are inserted into the first pipe 11 through the insertion hole 21. As described above, the widths W5 and W7 (see Figure 8) of the first plate portions 33A and 34A are wider than the inner diameter Φ3 of the insertion hole 21, so the second slit 32 is also used to insert the first plate portions 33A and 34A into the first pipe 11.

[0075] Next, the first connecting plate 33 slides its first plate portion 33A to the left in the direction of extension of the first pipe 11. Meanwhile, the second connecting plate 34 slides its first plate portion 34A to the right in the direction of extension of the first pipe 11. When the first plate portions 33A and 34A are pressed into the first pipe 11, they become fitted into the first pipe 11.

[0076] At this time, the alignment portion 33C of the first connecting plate 33 comes into contact with the end of the second slit 32, and the first connecting plate 33 is fixed in position relative to the first pipe 11. Similarly, the alignment portion 34C of the second connecting plate 34 comes into contact with the end of the second slit 32, and the second connecting plate 34 is fixed in position relative to the first pipe 11. Above the insertion hole 21, the second plate portion 33B of the first connecting plate 33 and the second plate portion 34B of the second connecting plate 34 are superimposed, and their respective locking slits 36 are aligned.

[0077] Next, as shown in Figure 12, the third connecting plate 35 is positioned inside the first pipe 11 through the insertion hole 21 so that the first connecting plate 33 and the second connecting plate 34 are inserted into the locking slit 38 (see Figure 8) of the third connecting plate 35. Then, inside the first pipe 11 below the insertion hole 21, the third connecting plate 35 is fixed in a position perpendicular to the first connecting plate 33 and the second connecting plate 34.

[0078] Next, the first slit 22 of the second pipe 12 is aligned with the first plate portions 33A and 34A, and the second pipe 12 is press-fitted into the first pipe 11 so that the first plate portions 33A and 34A are inserted into the first slit 22.

[0079] At this time, as the second pipe 12 is pressed into the first pipe 11, the width of the first slit 22 narrows, and the second pipe 12 is inserted into the first pipe 11. Subsequently, the tip of the second pipe 12 reaches the enlarged diameter portion 37 (see Figure 8) and overcomes the enlarged diameter portion 37, causing the outer diameter Φ2 of the insertion area R1 of the second pipe 12 to expand to be wider than the inner diameter Φ3 of the insertion hole 21, starting from the point of contact with the insertion hole 21.

[0080] As described above, this assembly process ensures that the first pipe 11, the second pipe 12, and the connecting member 31 are connected within an appropriate clearance range at the contact points, making it difficult for the second pipe 12 to be pulled out of the first pipe 11. Furthermore, looseness between the first pipe 11, the second pipe 12, and the connecting member 13 is reduced, thereby improving the product quality of the pipe structure 30.

[0081] Next, a pipe structure 40 according to the third embodiment of the present invention will be described in detail with reference to the drawings, using Figures 13 to 16. In the description of the pipe structure 40, the same reference numerals will be used in principle for members identical to those of the pipe structures 10 and 30, and repeated explanations will be omitted.

[0082] Figure 13 is a perspective view illustrating the pipe structure 40 of this embodiment. Figure 14 is an exploded perspective view illustrating the pipe structure 40 of this embodiment. Figures 15 and 16 are cross-sectional views illustrating the assembled state of the pipe structure 40 of this embodiment. Figure 15 is a cross-section along the central axis 11A of the first pipe 11, showing the formation region of the first slit 22. Figure 16 is a cross-section along the center of the insertion hole 21 of the first pipe 11, showing a cross-section perpendicular to the central axis 11A.

[0083] As shown in Figure 13, the pipe structure 40 mainly comprises a first pipe 11, a second pipe 12, and a connecting member 41 (see Figure 14) that connects the first pipe 11 and the second pipe 12. In the pipe structure 40, the structure of the connecting member 41 mainly differs from the structure of the connecting member 31 of the pipe structure 30. Therefore, in the following description, the structure of the connecting member 41 and its surrounding structure will be described, and other structures will be omitted here, as they are described in the descriptions of the pipe structures 10 and 30 above.

[0084] As shown in Figure 14, the first pipe 11 has an insertion hole 21 for inserting the second pipe 12 and the connecting member 41. The first pipe 11 also has a third slit 42 that is continuous with the insertion hole 21. The third slit 42 is formed on both sides of the insertion hole 21 along the central axis 11A of the first pipe 11.

[0085] Two first slits 22 are formed in the second pipe 12 from the end 12D on the side inserted into the first pipe 11. The two first slits 22 are formed symmetrically with respect to the central axis 12A of the second pipe 12.

[0086] The connecting member 41 is formed, for example, by cutting a plate-shaped member such as steel or high-tensile steel into a desired shape. In the pipe structure 40, a fourth connecting plate 43, a fifth connecting plate 44, and a third connecting plate 35 are used as the connecting member 41.

[0087] As shown in the diagram, the fourth connecting plate 43 has a shape in which, for example, a first plate portion 43A and a second plate portion 43B, which are roughly square in plan view, and a reinforcing plate portion 43C, which is roughly triangular in plan view, are integrated. The second plate portion 43B has a locking slit 36 ​​for inserting and locking the third connecting plate 35. A locking slit 45 for inserting the second pipe 12 is formed between the second plate portion 43B and the reinforcing plate portion 43C. A locking slit 46 for inserting the first pipe 11 is formed between the reinforcing plate portion 43C and the first plate portion 43A. The first plate portion 43A is disposed inside the first pipe 11 and has a first pull-out prevention portion 24 for catching on the inner circumferential surface 11B (see Figure 14) of the first pipe 11.

[0088] The fifth connecting plate 44 has a shape in which, for example, a first plate portion 44A and a second plate portion 44B, which are approximately square in plan view, and a reinforcing plate portion 44C, which is approximately triangular in plan view, are integrated. The second plate portion 44B has a locking slit 36 ​​for inserting and locking the third connecting plate 35. A locking slit 45 for inserting the second pipe 12 is formed between the second plate portion 44B and the reinforcing plate portion 44C. A locking slit 46 for inserting the first pipe 11 is formed between the reinforcing plate portion 44C and the first plate portion 44A. The first plate portion 44A is disposed inside the first pipe 11 and has a first pull-out prevention portion 24 for catching on the inner circumferential surface 11B (see Figure 14) of the first pipe 11.

[0089] As shown in Figure 15, the fourth connecting plate 43 and the fifth connecting plate 44 are press-fitted into the first pipe 11 through the insertion hole 21 and positioned to align with the central axis 11A of the first pipe 11 (see Figure 13). The first plate portion 43A of the fourth connecting plate 43 is inserted into the left side of the insertion hole 21 and positioned to fit inside the first pipe 11. On the other hand, the first plate portion 44A of the fifth connecting plate 44 is inserted into the right side of the insertion hole 21 and positioned to fit inside the first pipe 11.

[0090] Here, in the fourth connecting plate 43, the width W9 of the first plate portion 43A (see Figure 14) is wider than the width W10 of the second plate portion 43B (see Figure 14), and is also wider than the inner diameter Φ3 of the insertion hole 21. Similarly, in the fifth connecting plate 44, the width W11 of the first plate portion 44A (see Figure 14) is wider than the width W12 of the second plate portion 44B (see Figure 14), and is also wider than the inner diameter Φ3 of the insertion hole 21. Furthermore, the area in which the first pull-out prevention portion 24 of the fourth connecting plate 43 contacts the inner circumferential surface 11B of the first pipe 11 is also widened. Similarly, the area in which the first pull-out prevention portion 24 of the fifth connecting plate 44 contacts the inner circumferential surface 11B of the first pipe 11 is also widened. As described above, in the insertion region R1 of the second pipe 12, the second pipe 12 expands in diameter, and the connecting members 41 become firmly connected to each other.

[0091] With this structure, in the pipe structure 40, as indicated by arrow 15 (see Figure 13), when the second pipe 12 is subjected to a tensile force in the direction of being pulled out from the first pipe 11, the first pull-out prevention portion 24 of the fourth connecting plate 43 and the first pull-out prevention portion 24 of the fifth connecting plate 44 catch on the inner circumferential surface 11B of the first pipe 11. In the pipe structure 40, the contact area between the first pull-out prevention portion 24 and the first pipe 11 is increased, thereby improving the tensile strength.

[0092] Furthermore, as shown in the figure, in the fourth connecting plate 43 and the fifth connecting plate 44, the first pipe 11 is inserted into the locking slit 46, and the reinforcing plate portions 43C and 44C are in contact with the outer circumferential surface 11C of the first pipe 11. Similarly, the second pipe 12 is inserted into the locking slit 45, and the reinforcing plate portions 43C and 44C are in contact with the outer circumferential surface 12C of the second pipe 12. In other words, the reinforcing plate portion 43C is positioned at the orthogonal connection point between the first pipe 11 and the second pipe 12 and functions as a rib member. This ensures that the pipe structure 40 has the necessary strength and reliability to withstand torsional forces and tilting forces applied to it.

[0093] Furthermore, the fourth connecting plate 43 and the fifth connecting plate 44 are positioned and fixed along the central axis 11A of the first pipe 11 by being arranged within the third slit 42. The ends of the locking slits 46 of the fourth connecting plate 43 and the fifth connecting plate 44 are positioned relative to the first pipe 11 by contacting the ends of the third slit 42. As a result, the second plate portions 43B and 44B are arranged overlapping above the insertion hole 21 so that the locking slits 36 coincide at the center of the insertion hole 21.

[0094] As shown in Figure 16, the insertion region R1 (see Figure 14) of the second pipe 12 is press-fitted into the first pipe 11. However, as the second pipe 12 overcomes the enlarged diameter portion 37 of the third connecting plate 35, it is enlarged using the first slit 22. In the insertion region R1 of the second pipe 12, the enlarged diameter portion 37 and the inner circumferential surface 12B of the second pipe 12 maintain contact, and starting from the point of contact with the insertion hole 21, the outer diameter Φ2 of the second pipe 12 becomes wider than the inner diameter Φ3 of the insertion hole 21.

[0095] This structure allows the second pipe 12 to be fitted into the first pipe 11 through the insertion hole 21, and the second pipe 12 to be firmly connected to the connecting member 41. Furthermore, the first pull-out prevention part 24 firmly catches on the inner circumferential surface 11B of the first pipe 11, making it difficult for the second pipe 12 to be pulled out of the first pipe 11, and thus maintaining the assembled state of the pipe structure 40.

[0096] Furthermore, in the pipe structure 40, similar to the pipe structure 30, the first pipe 11, the second pipe 12, and the connecting member 41 are connected within an appropriate clearance range at the point of contact, making it difficult for the second pipe 12 to be pulled out of the first pipe 11. Moreover, rattling is less likely to occur among the three components of the pipe structure 40, thereby improving the product quality of the pipe structure 40.

[0097] Finally, regarding the assembly process of the pipe structure 40, please refer to the explanation of the assembly process of the pipe structure 30 described using Figures 11 to 12, and the explanation will be omitted here. The assembly process of the pipe structure 40 is the same as that of the pipe structure 30, except that when assembling the fourth connecting plate 43 and the fifth connecting plate 44 to the first pipe 11, the first pipe 11 is inserted into the locking slit 46, and when press-fitting the second pipe 12 into the first pipe 11, the second pipe 12 is inserted into the locking slit 45.

[0098] Next, using Figure 17, we will explain the results of the tensile tests conducted on the pipe structures 30 and 40.

[0099] Here, the solid line shows the tensile test results for pipe structure 30, and the dotted line shows the tensile test results for pipe structure 40. On the other hand, the dashed line shows the tensile test results for a structure in which pipe structure 30 is used as the base structure and a sawtooth shape 25A (see Figure 4) is provided in the area indicated by the circle 26 in Figure 8. The dashed line shows the tensile test results for a structure in which pipe structure 40 is used as the base structure and a sawtooth shape 25A (see Figure 4) is provided in the area indicated by the circle 26 in Figure 14.

[0100] The test conditions are as follows: the first pipe 11, the second pipe 12, and the first to fifth connecting plates 33, 34, 35, 43, and 44 are made of steel. The outer diameter Φ1 of the first pipe 11 is 31.8 mm, the outer diameter Φ2 of the second pipe 12 is 25.4 mm, and the plate thickness T3 of the first to fifth connecting plates 33, 34, 35, 43, and 44 is 2.0 mm. The first pipe 11 is fixed to the test stand, and a tensile test is performed by pulling the second pipe 12 vertically. In Figure 17, the vertical axis represents the tensile force N, and the horizontal axis represents the displacement mm.

[0101] As shown by the solid line, in the pipe structure 30 without the sawtooth shape 25A, a maximum tensile force of approximately 9800 N was measured when the displacement was approximately 38 mm. On the other hand, as shown by the dashed line, in the pipe structure 30 with the sawtooth shape 25A, a maximum tensile force of approximately 11800 N was measured when the displacement was approximately 15 mm.

[0102] As shown by the dotted line, in the pipe structure 40 without the sawtooth shape 25A, a maximum tensile force of approximately 12,200 N was measured when the displacement was approximately 21 mm. On the other hand, as shown by the dashed line, in the pipe structure 40 with the sawtooth shape 25A, a maximum tensile force of approximately 12,000 N was measured when the displacement was approximately 13 mm.

[0103] The above test results show that the maximum tensile force of pipe structures 30 and 40 increases when the sawtooth shape 25A is provided. On the other hand, when pipe structures 30 and 40 do not have the sawtooth shape 25A, the maximum tensile force decreases, but the time to failure of pipe structures 30 and 40 increases. Figure 17 does not show the test results for pipe structure 10, but various designs can be used with individual pipe structures 10, 30, and 40 or combinations thereof, depending on the tensile strength required for the above-mentioned mechanical structures.

[0104] In the description of the pipe structures 10, 30, and 40 of this embodiment, the case in which the pipes are connected to each other using connecting members 13, 31, and 41 without using known welding techniques has been described, but the description is not limited to this case. For example, in a state in which the pipes are connected to each other using connecting members 13, 31, and 41, full welding or partial welding using known welding techniques may be performed on the boundary between the pipes, and the tensile strength of the pipe structures 10, 30, and 40 may be increased by combining the two connection techniques.

[0105] Furthermore, in the description of the pipe structure 10, the case in which one connecting plate 23 is used as the connecting member 13 to connect the first pipe 11 and the second pipe 12 was described, but the description is not limited to this case. For example, another connecting plate 23 of the same shape is prepared, with the first plate portion 23A positioned to the right of the extending direction of the first pipe 11, and the tensile strength of the pipe structure 10 can be further improved by using two connecting plates 23.

[0106] Furthermore, in the description of the pipe structure 10, the case in which the sawtooth shape 25A as the second pull-out prevention part 25 is formed on the second plate portion 23B of a single connecting plate 23 as the connecting member 13 was described, but it is not limited to this case. For example, both end faces of the second plate portion 23B in the left-right direction of the paper may be flat surfaces, as in the pipe structures 30 and 40. And, as described above, if the pipe structure 10 is a structure that combines the connecting member 13 with known welding techniques, it is sufficient to maintain the connected state between the first pipe 11 and the second pipe 12 during welding.

[0107] Furthermore, in the description of the pipe structures 30 and 40, the case in which the contact surfaces with the inner circumferential surface 12B of the second pipe 12 are formed as flat surfaces was described for the second plate portion 33B of the first connecting plate 33, the second plate portion 34B of the second connecting plate 34, the second plate portion 43B of the fourth connecting plate 43, and the second plate portion 44B of the fifth connecting plate 44, but the invention is not limited to this case. For example, similar to the pipe structure 10, the sawtooth shape 25A as the second pull-out prevention portion 25 may be formed on the contact surfaces of the second plate portions 33B, 34B, 43B, 44B. In addition, various modifications are possible without departing from the spirit of the present invention.

[0108] Finally, the embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included. Furthermore, configurations obtained by combining the configurations of the different embodiments described herein are also included in the scope of the invention.

[0109] 10 Pipe structure 11 First pipe 11A Central axis 11B Inner surface 11C Outer surface 12 Second pipe 12A Central axis 12B Inner surface 12C Outer surface 12D End 13 Connecting member 21 Through hole 22 First slit 23 Connecting plate 23A First plate portion 23B Second plate portion 23C Alignment portion 24 First anti-pull-out portion 25 Second anti-pull-out portion 25A Sawtooth shape 30 Pipe structure 31 Connecting member 32 Second slit 33 First connecting plate 33A First plate portion 33B Second plate portion 33C Alignment portion 34 Second connecting plate 34A First plate portion 34B Second plate portion 34C Alignment portion 35 Third connecting plate 35A First plate section 36 Locking slit 37 Enlarged diameter section 38 Locking slit 40 Pipe structure 41 Connecting member 42 Third slit 43 Fourth connecting plate 43A First plate section 43B Second plate section 43C Reinforcement plate section 44 Fifth connecting plate 44A First plate section 44B Second plate section 44C Reinforcement plate section 45 Locking slit 46 Locking slit

Claims

1. A pipe structure comprising inserting a second pipe into a first pipe and connecting the first pipe and the second pipe, the pipe structure comprising: an insertion hole formed in the first pipe; a connecting member inserted into the interior of the first pipe from the insertion hole; and a first slit formed in the insertion region of the second pipe into the first pipe, wherein the connecting member is disposed inside the second pipe through the first slit, and the connecting member has a first pull-out prevention portion that contacts the interior of the first pipe and a second pull-out prevention portion that contacts the interior of the second pipe.

2. The pipe structure according to claim 1, characterized in that the first pipe and the second pipe are round pipes, the through hole is circular in shape when viewed from the insertion direction of the second pipe, and the inner diameter of the through hole is the same as or shorter than the outer diameter of the second pipe.

3. The pipe structure according to claim 1 or 2, characterized in that the second pull-out prevention portion has a sawtooth shape inclined toward the first pipe side.

4. The connecting member comprises a first connecting plate on which the first pull-out prevention portion is formed, a second connecting plate on which the first pull-out prevention portion is formed, and a third connecting plate on which an enlarged diameter portion serving as the second pull-out prevention portion is formed, wherein the third connecting plate is locked to the first connecting plate and the second connecting plate, and the outer diameter of the insertion area of ​​the second pipe is longer than the inner diameter of the insertion hole by contact with the enlarged diameter portion, as described in claim 1 or 2.

5. The pipe structure according to claim 4, characterized in that the second connecting plate has a sawtooth shape inclined toward the first pipe side as a second pull-out prevention part.

6. The pipe structure according to claim 4, wherein the first pipe has a second slit formed in the direction of extension of the first pipe, which is continuous with the insertion hole, and the width of the first plate portion of the first connecting plate and the width of the first plate portion of the second connecting plate are each wider than the inner diameter of the insertion hole.

7. The pipe structure according to claim 1 or 2, wherein the first pipe has a third slit formed in the direction of extension of the first pipe, continuous with the insertion hole, the connecting member has a fourth connecting plate having a first pull-out prevention portion and a first reinforcing plate portion exposed to the outside of the first pipe through the third slit, a fifth connecting plate having a first pull-out prevention portion and a second reinforcing plate portion exposed to the outside of the first pipe through the third slit, and a third connecting plate having an enlarged diameter portion as the second pull-out prevention portion, the third connecting plate is locked to the fourth connecting plate and the fifth connecting plate, and the outer diameter of the insertion area of ​​the second pipe is longer than the inner diameter of the insertion hole by contact with the enlarged diameter portion.

8. The pipe structure according to claim 7, characterized in that the third connecting plate has a sawtooth shape inclined toward the first pipe side as the second pull-out prevention part.

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