Pipe Joint Structure

Abstract

To provide a pipe joint structure which can secure seal performance between a pipe and a joint.SOLUTION: A pipe joint structure comprises: a pipe having an internal flow passage for making fluid circulate therein, and a protrusive end part formed with an opening end of the internal flow passage, and having a protrusive partial spherical shape at the outside; a cylindrical part attached to an external peripheral face of the pipe, formed into a cylindrical shape, and having a protrusive partial spherical shape at a side opposite to the protrusive end part in a center axial line of the pipe; a joint part having a tapered abutment part abutting on the protrusive end part, and making a device for handling fluid and the pipe communicate with each other; and a bag nut having a tapered pressing part which is contracted in a diameter toward a side opposite to the protrusive end part in the center axial line of the pipe therein, screwed to an external peripheral face of the joint part, pressing a sheet part of the cylindrical part by the pressing part, and pressing the protrusive end part of the pipe to the abutment part of the joint part. Curvature centers of the protrusive end part of the pipe and the sheet part of the cylindrical part are located on a center axis of the pipe.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] Conventionally, in the field of piping for internal combustion engines and the like, a pipe joint structure has been proposed that joins a pipe through which a fluid such as fuel flows to a device such as a pump that handles the fluid via a joint (see, for example, Patent Document 1). This pipe joint structure is generally structured such that a nipple is screwed onto the outer circumferential surface of the pipe, and the pipe is fastened to the joint by a cap nut. In this type of pipe joint structure, a seat surface of the nipple that protrudes from the outer circumferential surface of the pipe is formed on the outer circumferential surface of the pipe. The cap nut is screwed onto the joint while pressing the pipe against the joint via the seat surface of the nipple.

[0003] In addition, the joint of the pipe to the joint is formed into a generally spherical shape that is convex outward. The receiving portion of the joint that receives the joint of the pipe is formed into a generally truncated cone-shaped concave tapered shape. Therefore, even if the pipe is tilted with respect to the central axis of the joint, the joint of the pipe and the receiving portion of the joint can maintain a state of abutment with each other on a line. This makes it possible to make the abutment pressure between the joint of the pipe and the receiving portion of the joint higher than the pressure of the fluid, thereby ensuring the sealing between the pipe and the joint. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2010-242709 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the above-mentioned conventional pipe joint structure, both the seat surface of the nipple protruding from the outer peripheral surface of the pipe and the pressing surface of the cap nut pressing the seat surface are formed in a flat shape. Therefore, when the pipe is tightened by the cap nut in a state inclined with respect to the central axis of the joint, the contact with the pressing surface of the cap nut is biased on one side and the other side of the seat surface of the nipple across the central axis of the pipe. Due to this, the contact pressure between the joint of the pipe and the receiving part of the joint is biased, and even if the joint of the pipe and the receiving part of the joint are in a state of abutting each other on a line, there is a risk that a portion where the contact pressure is lower than the pressure of the fluid is generated between the joint of the pipe and the receiving part of the joint. As a result, there is a problem that the sealing property between the pipe and the joint is reduced.

[0006] The present invention has been made in consideration of the above circumstances, and has an object to provide a pipe joint structure that can ensure sealing performance between a pipe and a joint. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems and achieve the object, a pipe joint structure according to the present invention comprises: a pipe having an internal flow path for passing a fluid, and a convex end portion formed with an open end of the internal flow path and having a partially spherical convex shape convex outward; a tubular portion formed in a cylindrical shape to be attached to an outer circumferential surface of the pipe, the tubular portion having a seat portion having a partially spherical convex shape on an opposite side to the convex end portion in a central axial direction of the pipe, and a coupling portion having a tapered abutment portion that abuts the convex end portion, and communicating between the pipe and a device that handles the fluid; and a cap nut having an internal tapered pressing portion that reduces in diameter toward the opposite side to the convex end portion in the central axial direction of the pipe, the cap nut being screwed onto the outer circumferential surface of the coupling portion and pressing the seat portion of the tubular portion with the pressing portion to press the convex end portion of the pipe against the abutment portion of the coupling portion, wherein the centers of curvature of the convex end portion of the pipe and the seat portion of the tubular portion are located on the central axis of the pipe.

[0008] In addition, the pipe joint structure according to the present invention is characterized in that, in the above invention, the center of curvature of the seat portion of the tubular portion is at the same position as the center of curvature of the convex end portion of the pipe.

[0009] In addition, the pipe joint structure of the present invention is characterized in that, in the above-mentioned invention, the tubular portion further has a stopper portion that contacts a step portion formed on the outer peripheral surface of the pipe and limits the position of the tubular portion in the central axial direction of the pipe.

[0010] Moreover, in the pipe joint structure according to the present invention, in the above invention, the tapered surface of the pressing portion is a linear tapered surface.

[0011] Moreover, in the pipe joint structure according to the present invention, in the above invention, the tapered surface of the pressing portion is a curved tapered surface.

[0012] In addition, the pipe joint structure according to the present invention is characterized in that, in the above-mentioned invention, the tapered surface of the pressing portion is a partially spherical tapered surface having the same center of curvature as the seat portion of the cylindrical portion. Effect of the Invention

[0013] Advantageous Effects of Invention According to the pipe joint structure of the present invention, it is possible to ensure the sealing performance between the pipe and the joint. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram showing an application example of a pipe joint structure according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic cross-sectional view showing one configuration example of a pipe joint structure according to an embodiment of the present invention. [Diagram 3] FIG. 3 is an enlarged schematic cross-sectional view of a main portion of the pipe joint structure shown in FIG. [Figure 4] FIG. 4 is a schematic cross-sectional view showing an example of a configuration of a conventional pipe joint structure. [Diagram 5]FIG. 5 is a schematic diagram for explaining the problems with the conventional pipe joint structure. [Figure 6] FIG. 6 is a schematic diagram for explaining the operation of the pipe joint structure according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, a preferred embodiment of the pipe joint structure according to the present invention will be described in detail with reference to the accompanying drawings. Note that the present invention is not limited to this embodiment. It should be noted that the drawings are schematic, and that the dimensional relationships and ratios of each element may differ from the actual ones. The drawings may also include parts whose dimensional relationships and ratios differ from each other. In addition, the same components are denoted by the same reference numerals in each drawing.

[0016] Fig. 1 is a schematic diagram showing an application example of a pipe joint structure according to an embodiment of the present invention. Fig. 2 is a schematic cross-sectional view showing an example of a configuration of a pipe joint structure according to an embodiment of the present invention. Fig. 3 is a schematic cross-sectional view showing an enlarged view of a main part of the pipe joint structure shown in Fig. 2. As shown in Figs. 1 to 3, a pipe joint structure 1 according to this embodiment includes a pipe 10 and a joint portion 30 to be joined, and a nipple 20 and a cap nut 40 for fastening the pipe 10 to the joint portion 30.

[0017] The pipe 10 is a pipe (circulation pipe) for circulating a fluid. In detail, as shown in FIG. 2, the pipe 10 is made of metal or the like, and has an internal flow path 11 and a convex end 12. The internal flow path 11 is a flow path for circulating a fluid such as fuel oil, and is formed inside the pipe 10 over the entire area from one end to the other end in the central axis C1 direction of the pipe 10, for example. The convex end 12 is a joint end of the pipe 10 to the joint part 30. As shown in FIGS. 2 and 3, the convex end 12 is formed in a partial spherical shape that is convex on the outside of the pipe 10. That is, the convex end 12 has an opening end 11a of the internal flow path 11 formed in a part of the spherical surface, and forms a partial spherical shape that is convex on the outside. For example, the convex end 12 is formed at both ends of the pipe 10 in the central axis C1 direction. In this embodiment, the outer surface (pipe end surface) of the convex end 12 is a partial spherical surface that forms a part of the imaginary spherical surface S1 of the center of curvature P, as shown in FIG. 3. The center of curvature P is located on the central axis C1 of the tube 10.

[0018] The central axis C1 of the pipe 10 is a central axis in a direction (longitudinal direction) perpendicular to the radial direction of the pipe 10. The pipe 10 is a pipe capable of withstanding the pressure of the fluid passing through it, and may be, for example, a high-pressure pipe capable of withstanding a pressure of more than 35 MPa, or a low-pressure pipe capable of withstanding a pressure of 35 MPa or less.

[0019] 2 and 3, the outer peripheral surface of the pipe 10 is formed with a threaded portion 13 for mounting the nipple 20. Furthermore, the outer peripheral surface of the pipe 10 is formed with a step portion 14 between the threaded portion 13 and the convex end portion 12 for determining the mounting position of the nipple 20. The threaded portion 13 of the pipe 10 is screwed into the threaded portion 23 of the nipple 20. The threaded portions 13, 23 of the pipe 10 and the nipple 20 are reverse threaded. This is because, when the threaded portion 43 of the cap nut 40 and the threaded portion 33 of the joint portion 30 are fastened together, the nipple 20 rotates (rotates together) with the rotation of the cap nut 40, which prevents the screw connection between the pipe 10 and the nipple 20 from loosening.

[0020] Nipple 20 is an example of a tubular portion attached to the outer peripheral surface of pipe 10. In detail, as shown in Figures 2 and 3, nipple 20 is formed into a tubular shape using a material such as metal, and has a seat portion 21, a stopper portion 22, and a threaded portion 23.

[0021] The seat portion 21 is formed at one end of the nipple 20 so as to have a partially spherical shape that is convex on the outside of the nipple 20. That is, as shown in Figs. 2 and 3, when the nipple 20 is attached to the outer circumferential surface of the pipe 10, the seat portion 21 has a partially spherical shape that is convex on the opposite side to the convex end portion 12 in the direction of the central axis C1 of the pipe 10. The surface (seat surface) of such a seat portion 21 is a partially spherical surface that forms a part of a virtual spherical surface S2, as shown in Fig. 3. When the nipple 20 is attached to the outer circumferential surface of the pipe 10, the seat portion 21 forms the partially spherical seat surface that protrudes from the outer circumferential surface of the pipe 10 along the circumferential direction around the central axis C1 of the pipe 10. The centers of curvature of the convex end portion 12 of the pipe 10 and the seat portion 21 of the nipple 20 are located on the central axis C1 of the pipe 10. 3, the center of curvature of the seat portion 21 is preferably at the same position as the center of curvature P of the convex end portion 12. In other words, it is preferable that the center of curvature P is the center of curvature of the partial spherical outer surface (imaginary spherical surface S1) of the convex end portion 12 and also the center of curvature of the partial spherical seat surface (imaginary spherical surface S2) of the seat portion 21.

[0022] 3, the radius of curvature of the sheet portion 21 is longer than the radius of curvature of the convex end portion 12. However, the radius of curvature of the sheet portion 21 is not limited to this, and may be the same as the radius of curvature of the convex end portion 12, or may be shorter than the radius of curvature of the convex end portion 12.

[0023] As shown in Figs. 2 and 3, the stopper portion 22 is formed near the other end of the nipple 20 (the end opposite to the seat portion 21). For example, the stopper portion 22 has a convex shape that protrudes inward from the inner peripheral surface of the nipple 20 and contacts the step portion 14 formed on the outer peripheral surface of the pipe 10 to limit the position of the nipple 20 in the direction of the central axis C1 of the pipe 10. The threaded portion 23 is formed in a region between the seat portion 21 and the stopper portion 22 on the inner peripheral surface of the nipple 20. The nipple 20 is screwed onto the outer peripheral surface of the pipe 10 so that the threaded portion 23 and the threaded portion 13 of the pipe 10 mesh with each other. The mounting position (screwed position) of the nipple 20 in the direction of the central axis C1 of the pipe 10 is regulated and determined by the contact between the step portion 14 of the pipe 10 and the stopper portion 22 of the nipple 20 described above. As a result, the center of curvature of the seat portion 21 of the nipple 20 is easily set at the same position as the center of curvature P of the convex end portion 12 of the tube 10.

[0024] Furthermore, the threaded portions 13, 23 of the pipe 10 and nipple 20 are reverse threaded as described above. Therefore, when the threaded portion 43 of the cap nut 40 and the threaded portion 33 of the joint portion 30 are fastened together, the stopper portion 22 of the nipple 20 abuts against the step portion 14 of the pipe 10, thereby preventing the nipple 20 from rotating together with the rotation of the cap nut 40. As a result, it is possible to prevent the center of curvature of the seat portion 21 from shifting from the target position (the same position as the center of curvature P of the convex end portion 12 in this embodiment) as the cap nut 40 and the joint portion 30 are screwed together.

[0025] The joint part 30 communicates between a device that handles a fluid and the pipe 10 through which the fluid flows. In detail, as shown in Fig. 2, the joint part 30 is made of metal or the like, and integrally includes a first joint part 30a that is joined to the pipe 10 and a second joint part 30b that is joined to the device that handles the fluid. For example, an example of the device that handles the fluid is a fuel injection pump 5 (see Fig. 1) that supplies (pumps) fuel oil to a fuel injection valve provided in a cylinder of an internal combustion engine. As shown in Fig. 2, the joint part 30 includes a contact part 31, an internal flow path 32, a threaded part 33, a bolt head 34, and a bolt threaded part 35.

[0026] The abutment portion 31 is a tapered portion that abuts against the convex end portion 12 of the pipe 10 described above. In detail, as shown in Figs. 2 and 3, the abutment portion 31 is formed in a tapered shape at the end portion of the joint portion 30 on the first joint portion 30a side. The tapered shape of the abutment portion 31 may be, for example, a linear tapered shape that linearly reduces in diameter from one end side to the other end side in the direction of the central axis C2 of the joint portion 30. As shown in Figs. 2 and 3, such abutment portion 31 abuts against the convex end portion 12 of the pipe 10 in a line contact state. The central axis C2 of the joint portion 30 is a central axis in a direction (longitudinal direction) that passes through the end portion of the joint portion 30 on the first joint portion 30a side and the end portion of the joint portion 30 on the second joint portion 30b side.

[0027] The internal flow passage 32 is a flow passage for passing a fluid, and is formed inside the joint part 30 over the entire area from the abutment part 31 of the joint part 30 to the end part on the second joint part 30b side shown in FIG. 2. This internal flow passage 32 communicates the internal flow passage 11 of the pipe 10 in a state in which the convex end part 12 is abutted against the abutment part 31 of the joint part 30, and the fuel injection pump 5 to which the second joint part 30b of the joint part 30 is joined. The threaded part 33 is for screwing the joint part 30 and the cap nut 40 together. As shown in FIG. 2, the threaded part 33 is formed on the outer circumferential surface of the first joint part 30a of the joint part 30.

[0028] 1 and 2, the bolt head 34 is formed on the outer peripheral surface of the second joint portion 30b of the joint 30. The bolt thread portion 35 is formed in a predetermined region of the outer peripheral surface of the joint 30 from the end portion on the second joint portion 30b side toward the bolt head 34 side. The joint 30 is screwed to the fuel injection pump 5 as shown in FIG. 1 by rotating the bolt head 34 about the central axis C2 using a tool such as a wrench and screwing the bolt thread portion 35 into a thread portion (not shown) of the fuel injection pump 5.

[0029] The cap nut 40 joins the pipe 10 and the joint portion 30 so as to be able to communicate with each other. In particular, as shown in Figures 1 to 3, the cap nut 40 is formed in a cylindrical shape using a material such as metal. The cap nut 40 has openings 41a, 41b at both ends in a direction perpendicular to the radial direction of the cylinder (longitudinal direction), a pressing portion 42 and a threaded portion 43 inside, and a nut portion 44 on the outer circumferential surface.

[0030] The openings 41a and 41b allow communication between the inside and outside of the cap nut 40. In detail, as shown in FIG. 2, one opening 41a is formed at one end of the cap nut 40. The pipe 10 to be joined is inserted into this opening 41a. The other opening 41b is formed at the other end of the cap nut 40. The joint part 30 to be joined is inserted into this opening 41b. In the following, for convenience of explanation, the end of the cap nut 40 where one opening 41a is formed is referred to as the pipe side end, and the end of the cap nut 40 where the other opening 41b is formed is referred to as the joint side end.

[0031] The pressing portion 42 is a tapered portion for pressing the pipe 10, to which the nipple 20 is attached on the outer peripheral surface, against the joint portion 30. In detail, as shown in Figs. 2 and 3, the pressing portion 42 is formed inside the cap nut 40 so as to have a tapered shape that reduces in diameter in the direction from the joint side end of the cap nut 40 to the pipe side end (hereinafter referred to as the central axis direction of the cap nut 40). That is, in a state in which the pipe 10 is inserted into the opening 41a of the cap nut 40, the pressing portion 42 has a tapered shape that reduces in diameter in the opposite direction to the convex end 12 in the central axis C1 direction of the pipe 10. Such a pressing portion 42 presses the seat portion 21 of the nipple 20 attached to the outer peripheral surface of the pipe 10 as the cap nut 40 is screwed into the joint portion 30, and presses the convex end 12 of the pipe 10 against the abutment portion 31 of the joint portion 30 via the seat portion 21.

[0032] In this embodiment, the tapered surface of the pressing portion 42 is a linear tapered surface that linearly reduces in diameter toward the central axis direction of the cap nut 40, as shown in, for example, FIGS. 2 and 3. From the viewpoint of increasing the contact area with the seat portion 21 of the nipple 20 attached to the outer circumferential surface of the pipe 10 and reducing the surface pressure of the seat portion 21, the tapered surface of the pressing portion 42 is preferably a curved tapered surface. Examples of the curved tapered surface include an exponential tapered surface that exponentially reduces in diameter toward the central axis direction of the cap nut 40, a parabolic tapered surface that quadratically reduces in diameter toward the central axis direction, and a spherical tapered surface that spherically reduces in diameter toward the central axis direction. Among them, it is particularly preferable that the tapered surface of the pressing portion 42 is a partially spherical tapered surface having the same center of curvature as the seat portion 21 of the nipple 20 (the center of curvature P shown in FIG. 3 in this embodiment).

[0033] As shown in Fig. 2, the threaded portion 43 is formed in a predetermined region (e.g., a region corresponding to the inside of the nut portion 44) on the inner peripheral surface of the cap nut 40 from the joint side end to the pipe side end. The cap nut 40 is screwed onto the outer peripheral surface of the joint portion 30 so that the threaded portion 43 and the threaded portion 33 of the joint portion 30 mesh with each other. The nut portion 44 is a portion that is held by the operator's hand or a tool when screwing the cap nut 40 onto the outer peripheral surface of the joint portion 30. As shown in Figs. 1 and 2, the nut portion 44 is formed into a polygonal shape on the outer peripheral surface of the portion of the cap nut 40 that is screwed onto the joint portion 30.

[0034] The cap nut 40 having the above-mentioned configuration is screwed onto the outer circumferential surface of the joint part 30, and presses the seat part 21 of the nipple 20 with the pressing part 42 to press the convex end part 12 of the pipe 10 against the abutment part 31 of the joint part 30. In this way, the cap nut 40 tightens and joins the pipe 10 to the joint part 30.

[0035] The pipe joint structure 1 according to the present embodiment is applied to both ends of a pipe 10 to be joined (specifically, both ends in the direction of a central axis C1 of the pipe 10). For example, the above-described pipe joint structure 1 is applied to one end of the pipe 10, whereby, as shown in Figs. 1 to 3, one end of the pipe 10 and a fuel injection pump 5 are joined so as to be able to communicate with each other via a joint portion 30. In addition, although not shown in particular, a pipe joint structure 1 similar to that of the one end of the pipe 10 is applied to the other end of the pipe 10. As a result, the other end of the pipe 10 and a fuel injection valve are joined so as to be able to communicate with each other. The fuel injection valve is an example of a device that handles a fluid circulated by the pipe 10, and is provided in a cylinder of an internal combustion engine such as a marine diesel engine, for example. When both ends of the pipe 10 are joined to the fuel injection pump 5 and the fuel injection valve by the pipe joint structure 1 as described above, fuel oil can be pressure-fed from the fuel injection pump 5 through the pipe 10 to the fuel injection valve, and the fuel oil can be injected from the fuel injection valve into the cylinder (combustion chamber) of the internal combustion engine.

[0036] In this embodiment, the device that handles the fluid is not limited to the fuel injection pump or fuel injection valve described above. For example, the device that handles the fluid may be a fuel injection pump, a fuel injection valve, a water injection pump, a water injection valve, a hydraulic oil pump, a supercharger, an air intake system, an exhaust system, or other devices that are connected to a pipe in an internal combustion engine or an engine other than an internal combustion engine. In addition, the fluid that flows through the pipe 10 may be, for example, a liquid or gas such as fuel oil, water, hydraulic oil, lubricating oil, combustion gas, or exhaust gas.

[0037] Next, problems with conventional pipe joint structures will be described. Fig. 4 is a schematic cross-sectional view showing one configuration example of a conventional pipe joint structure. Fig. 4 shows a cross-section of a main part of a conventional pipe joint structure 101. As shown in Fig. 4, the conventional pipe joint structure 101 includes a pipe 110 and a joint portion 130 to be joined, and a nipple 120 and a cap nut 140 for fastening the pipe 110 to the joint portion 130.

[0038] The pipe 110 is configured similarly to the pipe 10 of the pipe joint structure 1 according to the present invention, except that the above-mentioned step portion 14 (see Figs. 2 and 3) is not formed on the outer circumferential surface. For example, as shown in Fig. 4, the pipe 110 has an internal flow path 11, an open end 11a, and a threaded portion 13, similar to the pipe 10 of the present invention. In addition, the convex end 112 of the pipe 110 is given a different reference number to distinguish it from the convex end 12 of the pipe 10 of the present invention for convenience of explanation, but is formed in a partially spherical shape convex outwardly, similar to the pipe 10 of the present invention. The central axis C11 of the pipe 110 is a central axis perpendicular to the radial direction of the pipe 110, similar to the central axis C1 of the pipe 10 of the present invention.

[0039] As shown in FIG. 4, the nipple 120 has a planar seat portion 121 and does not have the above-mentioned outwardly convex partially spherical seat portion 21 (see FIG. 3). That is, the seat surface of the nipple 120 is a plane facing the middle part side of the pipe 110 (opposite side to the convex end portion 112) unlike the seat surface (partial spherical surface) of the nipple 20 of the pipe joint structure 1 according to the present invention. In addition, the nipple 120 does not have the stopper portion 22 (see FIG. 3) of the nipple 20 according to the present invention. The nipple 120 has the same configuration as the nipple 20 according to the present invention except for the configuration of the partially spherical seat portion 21 and the stopper portion 22. For example, as shown in FIG. 4, the nipple 120 has a threaded portion 23 on its inner peripheral surface and is screwed to the outer peripheral surface of the pipe 110. As a result, the nipple 120 forms the planar seat surface protruding from the outer peripheral surface of the pipe 110 along the circumferential direction around the central axis C11 of the pipe 110.

[0040] The joint part 130 is configured in the same manner as the joint part 30 of the pipe joint structure 1 according to the present invention. For example, as shown in Fig. 4, the joint part 130 has a tapered abutment part 131, similar to the joint part 30 in the present invention. The convex end part 112 of the pipe 110 abuts against this abutment part 131.

[0041] As shown in FIG. 4, the cap nut 140 has a flat pressing portion 142 and does not have the above-mentioned tapered pressing portion 42 (see FIG. 3). That is, the pressing surface of the cap nut 140 is a flat surface facing the joint portion 130 (the lower side of the paper surface in FIG. 4), unlike the pressing surface (tapered surface) of the cap nut 40 of the pipe joint structure 1 according to the present invention. The cap nut 140 has a configuration similar to that of the cap nut 40 in the present invention, except for the configuration of the tapered pressing portion 42. For example, as shown in FIG. 4, the cap nut 140 is screwed onto the outer peripheral surface of the joint portion 130, and presses the flat seat portion 121 of the nipple 120 with the flat pressing portion 142 to press the convex end portion 112 of the pipe 110 against the abutment portion 131 of the joint portion 130.

[0042] FIG. 5 is a schematic diagram for explaining the problems of a conventional pipe joint structure. In a conventional pipe joint structure 101 (see FIG. 4), a nipple 120 is screwed onto an outer peripheral surface of a pipe 110, and a convex end 112 of the pipe 110 is butted against an abutment portion 131 of a joint portion 130 by manual work or the like of an operator. Next, a torque (skin torque) is applied to the cap nut 140 by the operator's manual force. As a result, the cap nut 140 is temporarily attached to the outer peripheral surface of the joint portion 130, and the flat pressing portion 142 presses the flat sheet portion 121 of the nipple 120, and the convex end 112 of the pipe 110 is pressed against the abutment portion 131 of the joint portion 130 via the sheet portion 121. Then, a tightening torque is further applied to the cap nut 140 by a tool such as a spanner or a torque wrench. As a result, the cap nut 140 is completely screwed onto the outer circumferential surface of the joint part 130, and the convex end part 112 of the pipe 110 is pressed against the abutment part 131 of the joint part 130 by the pressing part 142 via the seat part 121. As a result, the pipe 110 is finally tightened to the joint part 130 by the cap nut 140.

[0043] Here, as shown in Figure 5, when the central axis C11 of the pipe 110 is tilted relative to the central axis C12 of the joint part 130 and the convex end 112 of the pipe 110 abuts against the abutment part 131 of the joint part 130, the nipple 120 screwed onto the outer peripheral surface of the pipe 110 becomes tilted together with the pipe 110 (state A1).

[0044] In this state A1, the convex end 112 of the pipe 110 maintains a state of linear contact with the abutment portion 131 of the joint portion 130. On the other hand, since the seat portion 121 of the nipple 120 has a planar seat surface, as shown in FIG. 5, the height position H2 of the seat portion 121 changes to a position higher than the height position H1 of the seat portion 121 when the central axis C11 of the pipe 110 is not inclined with respect to the central axis C12 of the joint portion 130. That is, a height difference occurs between one side (the right side of the paper in FIG. 5) and the other side (the left side of the paper in FIG. 5) of the seat portion 121 across the central axis C11 of the pipe 110. The height positions H1 and H2 are positions in the height direction based on a predetermined position.

[0045] When the cap nut 140 is screwed onto the joint part 130 in a state in which a height difference occurs in the seat part 121 of the nipple 120 as described above, the contact between the pressing part 142 of the cap nut 140 and the seat part 121 of the nipple 120 becomes uneven. For example, as shown in Fig. 5, among the seat part 121, the seat part 121b at the height position H2 can come into contact with the pressing part 142. However, the seat part 121a on the opposite side to the seat part 121b across the central axis C11 of the pipe 110 is not in contact with the pressing part 142 (state A2).

[0046] In such a state A2, the pressing portion 142 of the cap nut 140 presses the seat portion 121b of the seat portion 121 of the nipple 120 on one side with respect to the central axis C11 of the pipe 110 in a biased manner. As a result, a rotational force is generated in the pipe 110 due to the pressing force of the pressing portion 142 against the seat portion 121b on one side, as shown in FIG. 5. In this case, the convex end portion 112 of the pipe 110 and the abutment portion 131 of the joint portion 130 maintain a state of apparent line contact. However, the abutment pressure between the convex end portion 112 and the abutment portion 131 is biased due to the rotational force. Specifically, among the contact pressures between the convex end 112 and the contact portion 131, the contact pressure on the opposite side of the central axis C11 of the tube 110 to the sheet portion 121b pressed by the pressing portion 142, i.e., the contact pressure between the convex end 112a and the contact portion 131a shown in Fig. 5, increases. Accordingly, the contact pressure on the same side of the central axis C11 of the tube 110 to the sheet portion 121b pressed by the pressing portion 142, i.e., the contact pressure between the convex end 112b and the contact portion 131b shown in Fig. 5, decreases.

[0047] As a result, a portion where the contact pressure between the convex end 112 of the pipe 110 and the abutment portion 131 of the joint portion 130 is lower than the pressure of the fluid flowing through the pipe 110 occurs, causing a problem of reduced sealing performance between the convex end 112 and the abutment portion 131. With such a conventional pipe joint structure 101, it is difficult to prevent fluid from leaking between the pipe 110 and the joint portion 130.

[0048] In addition, in the conventional pipe joint structure 101, as illustrated in state A2 of FIG. 5, the pressing portion 142 of the cap nut 140 is in contact with one side of the seat portion 121 of the nipple 120. Therefore, even if the cap nut 140 is temporarily attached to the joint portion 130 by the skin torque, it is difficult to eliminate the uneven contact between the pressing portion 142 and the seat portion 121. Due to this, a problem occurs in that the tightening angle of the cap nut 140 varies from the state in which the cap nut 140 is temporarily attached to the joint portion 130 by the skin torque to the state in which the cap nut 140 is finally tightened to the joint portion 130 by the tightening torque. In this case, it becomes difficult to manage the final tightening of the cap nut 140 to the joint portion 130 by the tightening angle of the cap nut 140, and it is necessary to manage it by the tightening torque of the cap nut 140. In other words, a torque wrench larger than a tool such as a spanner must be used to finally tighten the cap nut 140. As a result, in the conventional pipe fitting structure 101, a large working space in which a torque wrench can be used is required for the final tightening of the cap nut 140, making it difficult to connect pipes in places with limited working space, such as on the cylinder cover of an internal combustion engine, and reducing the workability of connecting pipes.

[0049] The tightening torque is the torque required to fully tighten (screw) the cap nut to the joint. The tightening angle is the angle by which the cap nut rotates around the central axis of the joint (see Figure 1, for example) from the state in which the cap nut is temporarily attached to the joint to the state in which it is fully tightened.

[0050] Next, the operation of the pipe joint structure 1 according to the embodiment of the present invention will be described. FIG. 6 is a schematic diagram for explaining the operation of the pipe joint structure according to the embodiment of the present invention. In the pipe joint structure 1 according to this embodiment (see FIGS. 1 to 3), the nipple 20 is screwed onto the outer peripheral surface of the pipe 10, and the convex end 12 of the pipe 10 is butted against the abutment portion 31 of the joint portion 30 by manual work by an operator or the like. Next, a skin-fitting torque is applied to the cap nut 40, whereby the cap nut 40 is temporarily attached to the outer peripheral surface of the joint portion 30, and the tapered seat portion 21 of the nipple 20 is pressed by the partially spherical pressing portion 42. The cap nut 40 presses the convex end 12 of the pipe 10 against the abutment portion 31 of the joint portion 30 via the seat portion 21. Then, a tightening torque is further applied to the cap nut 40, whereby the cap nut 40 is completely screwed onto the outer peripheral surface of the joint portion 30. At the same time, the cap nut 40 presses the convex end 112 of the pipe 10 against the abutment portion 31 of the joint portion 30 with the pressing portion 42 via the seat portion 21. As a result, the pipe 10 is finally fastened to the joint portion 30 by the cap nut 40.

[0051] Here, as shown in Figure 6, when the central axis C1 of the pipe 10 is tilted relative to the central axis C2 of the joint part 30 and the convex end 12 of the pipe 10 abuts against the abutment part 31 of the joint part 30, the nipple 20 screwed onto the outer peripheral surface of the pipe 10 becomes tilted together with the pipe 10 (state A11).

[0052] In this state A11, the convex end 12 of the pipe 10 maintains a state of linear contact with the abutment portion 31 of the joint portion 30. Also, the seat portion 21 of the nipple 20 forms a partially spherical seat surface as described above. Therefore, the seat surface of the seat portion 21 maintains a state of being included in an imaginary spherical surface S2 whose center of curvature (for example, the center of curvature P shown in FIG. 3) is located on the central axis C1 of the pipe 10, as shown in FIG. 6. In other words, the seat surface of the seat portion 21 is always located within the imaginary spherical surface S2, regardless of the degree of inclination of the pipe 10.

[0053] When the cap nut 40 is screwed onto the joint part 30 in a state in which the pipe 10 is butted against the joint part 30 at an angle as described above, the pressing part 42 of the cap nut 40 comes into uniform contact with the seat part 21 of the nipple 20. That is, as shown in Fig. 6, since the pressing part 42 forms the tapered pressing surface described above and the seat part 21 forms the partially curved seat surface described above, the pressing part 42 and the seat part 21 can come into contact with each other over the entire area in the circumferential direction (outer circumferential direction) around the central axis C1 of the pipe 10 (state A12).

[0054] In such a state A12, the pressing portion 42 of the cap nut 40 presses the seat portion 21 of the nipple 20 uniformly over the entire circumferential area around the central axis C1 of the pipe 10. As a result, the pressing force from the pressing portion 42 is uniformly transmitted to the convex end portion 12 of the pipe 10 via the seat portion 21, as shown in FIG. 6. As a result, the contact pressure between the convex end portion 12 of the pipe 10 and the abutment portion 31 of the joint portion 30 is maintained at a high pressure equal to or higher than the pressure of the fluid flowing through the pipe 10 over the entire contact area between the convex end portion 12 and the abutment portion 31. In such a pipe joint structure 1, the sealing property between the convex end portion 12 and the abutment portion 31 can be maintained at a high level, so that it is possible to prevent the fluid from leaking between the pipe 10 and the joint portion 30. In particular, the pipe joint structure 1 of this embodiment is effective for joining a pipe 10 and a joint portion 30 through which a high-pressure fluid (e.g., a pressure greater than 35 MPa) flows, in which it is difficult to maintain sealing properties using sealing members such as O-rings.

[0055] In addition, in the pipe joint structure 1 according to this embodiment, as illustrated in state A12 in FIG. 6, the pressing portion 42 of the cap nut 40 contacts the seat portion 21 of the nipple 20 over the entire circumferential area around the central axis C1 of the pipe 10. Therefore, when the cap nut 40 is temporarily attached to the joint portion 30 by the skin attachment torque, the pressing portion 42 and the seat portion 21 can be closely attached over the entire circumferential area around the central axis C1 of the pipe 10. This makes it possible to suppress the variation in the tightening angle of the cap nut 40 from the state in which the cap nut 40 is temporarily attached to the joint portion 30 to the state in which the cap nut 40 is fully tightened. In this case, it becomes possible to manage the final tightening of the cap nut 40 to the joint portion 30 by the tightening angle of the cap nut 40. As a result, there is no need to use a torque wrench, and the cap nut 40 can be properly tightened using a smaller tool such as a wrench, making it easier to connect pipes in places with limited working space, such as on the cylinder cover of an internal combustion engine, and improving the workability of connecting pipes.

[0056] As described above, in the pipe joint structure 1 according to the embodiment of the present invention, the nipple 20 having the partially spherical seat portion 21 is attached to the outer circumferential surface of the pipe 10 having the internal flow path 11 for passing a fluid and the convex end portion 12 having a partially spherical shape convex on the outside, the convex end portion 12 of the pipe 10 abuts against the tapered abutment portion 31 of the joint portion 30, the device that handles the fluid (e.g., the fuel injection pump 5) and the pipe 10 communicate with each other via the joint portion 30, and the cap nut 40 having the tapered pressing portion 42 therein is screwed onto the outer circumferential surface of the joint portion 30, and the pressing portion 42 presses the seat portion 21 of the nipple 20 to press the convex end portion 12 of the pipe 10 against the abutment portion 31 of the joint portion 30. In this pipe joint structure 1, the pressing portion 42 of the cap nut 40 is tapered so as to decrease in diameter toward the opposite side to the convex end portion 12 in the direction of the central axis C1 of the pipe 10. The seat portion 21 of the nipple 20 has a partially spherical shape that is convex on the opposite side to the convex end portion 12 in the direction of the central axis C1 of the pipe 10. The centers of curvature of the convex end portion 12 of the pipe 10 and the seat portion 21 of the nipple 20 are located on the central axis C1 of the pipe 10.

[0057] With the above configuration, regardless of the inclination of the pipe 10 relative to the joint part 30, the convex end 12 of the pipe 10 and the abutment part 31 of the joint part 30 can maintain a state of abutting each other linearly, while the pressing part 42 of the cap nut 40 can uniformly contact the seat part 21 of the nipple 20 without uneven contact over the entire area in the outer circumferential direction of the pipe 10. Therefore, while the cap nut 40 is screwed onto the joint part 30, it can uniformly press the seat part 21 of the nipple 20 over the entire area in the outer circumferential direction of the pipe 10 with the pressing part 42, and press the convex end 12 of the pipe 10 against the abutment part 31 of the joint part 30 via this seat part 21. This allows the pipe 10 and the joint part 30 to be joined with the cap nut 40, with the convex end 12 of the pipe 10 abutting the abutment part 31 of the joint part 30 evenly over the entire circumferential area around the central axis C2 of the joint part 30. As a result, the abutment pressure between the convex end 12 of the pipe 10 and the abutment part 31 of the joint part 30 can be maintained at a high pressure equal to or higher than the fluid pressure over the entire contact area between the convex end 12 and the abutment part 31, so that high sealing performance between the joined pipe 10 and joint part 30 can be ensured.

[0058] In addition, in the pipe joint structure 1 according to the embodiment of the present invention, the pressing portion 42 of the cap nut 40 contacts the seat portion 21 of the nipple 20 over the entire circumferential direction of the pipe 10. Therefore, the cap nut 40 can be temporarily attached to the joint portion 30 by a skin-fitting torque, and the pressing portion 42 and the seat portion 21 can be tightly attached over the entire circumferential direction of the pipe 10 without uneven contact. This makes it possible to suppress variation in the tightening angle of the cap nut 40, and to manage the final tightening of the cap nut 40 to the joint portion 30 by the tightening angle of the cap nut 40. As a result, there is no need to use a torque wrench, and the cap nut 40 can be easily tightened in a narrow working space, improving the workability of pipe connection.

[0059] In addition, in the pipe joint structure 1 according to the embodiment of the present invention, the center of curvature of the seat portion 21 of the nipple 20 is located at the same position as the center of curvature P of the convex end portion 12 of the pipe 10. Therefore, the imaginary spherical surface S2 including the partially spherical seat surface formed by the seat portion 21 of the nipple 20 can be made a spherical surface concentric with the imaginary spherical surface S1 including the partially spherical pipe end surface formed by the convex end portion 12 of the pipe 10. This can reduce the positional deviation between the seat surface of the seat portion 21 and the imaginary spherical surface S2 when the pipe 10 is tilted relative to the joint portion 30. As a result, a structure that can uniformly contact the seat portion 21 of the nipple 20 and the pressing portion 42 of the cap nut 40 can be easily realized.

[0060] Furthermore, in the pipe fitting structure 1 according to the embodiment of the present invention, a step portion 14 is formed on the outer peripheral surface of the pipe 10, and a stopper portion 22 is provided on the nipple 20 which comes into contact with the step portion 14 to limit the position of the nipple 20 in the direction of the central axis C1 of the pipe 10. For this reason, the attachment position of the nipple 20 on the outer peripheral surface of the pipe 10 can be easily determined so that the center of curvature of the seat portion 21 of the nipple 20 and the center of curvature of the convex end portion 12 of the pipe 10 are in the same position.

[0061] In the above-described embodiment, a pipe having convex ends 12 at one end and the other end in the direction of the central axis C1 is exemplified as the pipe 10 to be joined, but the present invention is not limited to this. For example, the pipe 10 may be a pipe having a convex end 12 at only one end of both ends in the direction of the central axis C1, or may be a pipe having a multiple branched form. In addition, the pipe 10 may be a straight pipe or a pipe having a curved or bent portion, and the shape of the pipe 10 is not important in the present invention.

[0062] In the above embodiment, the center of curvature of the partially spherical convex end 12 of the tube 10 and the center of curvature of the partially spherical seat portion 21 of the nipple 20 are set at the same position on the central axis C1 of the tube 10, but the present invention is not limited to this. In the present invention, the centers of curvature of the convex end 12 and the seat portion 21 may be at the same position or at different positions as long as they are located on the central axis C1 of the tube 10.

[0063] In the above embodiment, the nipple 20 is screwed onto the outer circumferential surface of the pipe 10, but the present invention is not limited to this. For example, the nipple 20 may be attached to the outer circumferential surface of the pipe 10 by fitting, or may be attached by adhesion, welding, or the like.

[0064] In the above embodiment, a linearly tapered abutment portion is exemplified as the abutment portion 31 of the joint portion 30, but the present invention is not limited to this. For example, the tapered surface of the abutment portion 31 may be a linearly tapered surface or a curved tapered surface.

[0065] Furthermore, the present invention is not limited to the above-described embodiment. The present invention also includes configurations in which the above-described components are appropriately combined. In addition, other embodiments, examples, operation techniques, etc. made by those skilled in the art based on the above-described embodiment are all included in the scope of the present invention. [Explanation of symbols]

[0066] 1 Pipe joint structure 5. Fuel injection pump 10 tubes 11 Internal flow path 11a Open end 12 Convex end 13 Threaded part 14 Step 20 Nipples 21 Seat section 22 Stopper part 23 Threaded section 30 Joint 30a 1st joint 30b 2nd joint 31 Contact part 32 Internal flow path 33 Threaded part 34 Bolt head 35 Bolt thread 40 Cap nut 41a, 41b opening 42 Pressing part 43 Threaded part 44 Nut part 101 Conventional pipe joint structure 110 tube 112, 112a, 112b convex end 120 nipple 121, 121a, 121b seat part 130 Joint 131, 131a, 131b Contact part 140 Cap nut 142 Pressing part C1, C2, C11, C12 center axis S1, S2 Virtual sphere P center of curvature

Claims

1. a tube having an internal flow path through which a fluid flows and an open end of the internal flow path formed therein and having a convex end portion that is convex outwardly and partially spherical; a cylindrical portion that is screwed onto an outer peripheral surface of the pipe and has a seat portion that is convex in a partially spherical shape on an opposite side to the convex end portion in a central axis direction of the pipe; a coupling portion having a tapered abutment portion that abuts against the convex end portion and that connects the fluid handling device and the pipe; a cap nut having a tapered pressing portion therein, the diameter of which decreases toward the opposite side to the convex end in the central axis direction of the pipe, the cap nut being screwed onto the outer circumferential surface of the joint portion and pressing the seat portion of the tubular portion with the pressing portion to press the convex end of the pipe against the abutment portion of the joint portion; Equipped with The cylindrical portion further includes a stopper portion that limits a screwing position of the cylindrical portion in a central axis direction of the pipe, the stopper portion has a convex shape that protrudes inward from an inner circumferential surface of the cylindrical portion and contacts a step portion formed on an outer circumferential surface of the tube to limit a screwing position of the cylindrical portion; The centers of curvature of the convex end of the tube and the seat portion of the tubular portion are located on the central axis of the tube. A pipe joint structure comprising:

2. the center of curvature of the seat portion of the tubular portion is at the same position as the center of curvature of the convex end of the tube; 2. The pipe joint structure according to claim 1 .

3. The tapered surface of the pressing portion is a linear tapered surface.

3. The pipe joint structure according to claim 1 or 2.

4. The tapered surface of the pressing portion is a curved tapered surface.

3. The pipe joint structure according to claim 1 or 2.

5. The tapered surface of the pressing portion is a partially spherical tapered surface having the same center of curvature as the seat portion of the cylindrical portion.

5. The pipe joint structure according to claim 4.

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