Towing end mounting structure

Abstract

A pull-end attachment structure (1) comprises: a cable (10) having an optical fiber; a tubular dam case (20) that is fixed to the cable so as to surround the cable; a tubular member (30) to which a hose (100) with a pulling part for accommodating an end of the optical fiber is attached and which is provided so as to surround the outer peripheral surface of the dam case; and a tubular fixed member (40) that surrounds the cable and that can be fixed to the tubular member. An outer diameter (R1) of the fixed member is equal to or less than an outer diameter (R2) of the tubular member. Formed on the inner peripheral surface of the fixed member is a contact surface (43a) that delivers a pulling force to the dam case by making contact with the dam case when the tubular member and the fixed member are pulled by the hose with pulling part.

Description

[Technical field]

[0001] The present invention relates to a towing end mounting structure. This application claims priority based on Japanese Patent Application No. 2021-202338, filed on December 14, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] Conventionally, a method is known in which a cable (optical cable) with a connector attached to its end is pulled and passed through a thin duct installed underground to connect multiple data centers. In this method, a so-called pulling end, which is a part to which a worker applies a pulling force, is attached to the cable. As a structure for attaching the pulling end to the cable (hereinafter referred to as a pulling end attachment structure), a structure is generally known in which a dam case fixed to the cable and the pulling end are fixed with multiple bolts arranged at intervals in the circumferential direction.

[0003] In recent years, with the expansion of optical cable networks, there is an increasing need to insert multiple cables into thin ducts. Patent Document 1 discloses a cable terminal structure that makes it possible to accommodate multiple cables at the pulling end by arranging multiple connectors with a shift in the front-to-rear direction (axial direction). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2002-333561 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when attempting to insert a new cable into a narrow duct in which multiple cables are already arranged, there are cases in which a sufficient space for inserting the pulling end is not secured, making it difficult to insert the pulling end. In order to enable the pulling end to be inserted into such a limited space, it is preferable to reduce the outer diameter of the pulling end.

[0006] However, even if the arrangement of the objects housed in the towing end is improved as in Patent Document 1, it is difficult to realize a smaller diameter of the towing end itself. Here, a method of reducing the diameter of the towing end by thinning the towing end is also considered. However, in the above-mentioned general towing end mounting structure, the bolt also becomes smaller as the towing end becomes thinner, and there is a possibility that sufficient mounting strength cannot be obtained. If the mounting strength is insufficient, there is a possibility that the towing end will fall off the cable when the towing end is pulled.

[0007] The present invention has been made in consideration of the above circumstances, and has an object to provide a towing end attachment structure which can achieve both a small diameter towing end and an assured attachment strength of the towing end to the cable. [Means for solving the problem]

[0008] In order to solve the above problems, a towing end mounting structure according to one embodiment of the present invention comprises a cable having an optical fiber, a cylindrical dam case fixed to the cable so as to surround the cable, a cylindrical member to which a hose with a towing part that houses an end of the optical fiber is attached and which is arranged to surround the outer peripheral surface of the dam case, and a cylindrical fixing member that surrounds the cable and can be fixed to the tubular member, wherein the outer diameter of the fixing member is equal to or smaller than the outer diameter of the tubular member, and an abutment surface is formed on the inner peripheral surface of the fixing member that abuts against the dam case and transfers the towing force to the dam case when the tubular member and the fixing member are towed via the hose with a towing part. Effect of the Invention

[0009] According to the above aspect of the present invention, it is possible to provide a pulling end attachment structure that can achieve both a small diameter of the pulling end and an assured attachment strength of the pulling end to the cable. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view showing a towing end mounting structure according to an embodiment of the present invention. [Diagram 2] FIG. 2 is an exploded view showing a towing end mounting structure according to an embodiment of the present invention. [Diagram 3] FIG. 2 is a cross-sectional view taken along line III-III shown in FIG. [Figure 4A] 10A to 10C are diagrams illustrating a method for attaching a fixing member to a cylindrical fitting according to an embodiment of the present invention. [Figure 4B] FIG. 4B is a diagram showing a state subsequent to FIG. 4A. [Figure 4C] FIG. 4B shows a state following FIG. 4B. [Figure 4D] 4D is a diagram showing a state subsequent to FIG. 4C, illustrating a method of removing the fixing member from the cable according to the embodiment of the present invention. FIG. [Diagram 5] FIG. 11 is a cross-sectional view showing a towing end mounting structure according to a modified example of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, a towing end mounting structure 1 according to an embodiment of the present invention will be described with reference to the drawings. 1 and 2, the towing end mounting structure 1 includes a cable (optical cable) 10, a dam case 20, a fixing member 40, and a towing end P. The towing end P according to this embodiment has a tubular metal fitting (tubular member) 30, and a hose with a towing part 100 attached to the tubular metal fitting 30 (see also FIG. 3). Each of the dam case 20, the tubular metal fitting 30, and the fixing member 40 according to this embodiment is formed in a cylindrical shape that can be considered to have a common central axis O. The fixing member 40 is fixed to one end (base end) of the tubular metal fitting 30, as will be described in detail later.

[0012] (direction definition) In this embodiment, the direction parallel to the central axis O of the tubular metal fitting 30 etc. is referred to as the longitudinal direction Z, Z direction, or axial direction Z. The direction from the fixing member 40 toward the tubular metal fitting 30 along the axial direction Z is referred to as the +Z direction, forward, or tip side. The direction opposite to the +Z direction is referred to as the -Z direction, rear, or base end side. The direction perpendicular to the central axis O of the tubular metal fitting 30 etc. is referred to as the radial direction. The direction approaching the central axis O along the radial direction is referred to as the radial inner side, and the direction moving away from the central axis O is referred to as the radial outer side. The direction going around the central axis O as viewed from the axial direction Z is referred to as the circumferential direction.

[0013] 1 and 2, the hose with a towing part 100 includes a hose 110 extending in an axial direction Z, and a towing part 120 attached to the tip of the hose 110. A handle 121 is provided at the tip of the towing part 120 according to this embodiment. The handle 121 is a part to which an operator actually applies a traction force when towing the cable 10.

[0014] 3, the hose 110 according to this embodiment has a flexible structure 111 and is flexible. For example, the flexible structure 111 may have a structure in which a plurality of wires (element plate) 111a having an S-shape in cross section are spirally wound and the wound plurality of wires 111a are connected in the axial direction Z. For example, a stainless steel (SUS) plate may be used as the wires 111a. However, the structure of the flexible structure 111 is not limited to the above example and may be modified as appropriate as long as it is flexible.

[0015] As shown in Figs. 2 and 3, the cable 10 according to this embodiment has a plurality of optical fibers 11 extending in the axial direction Z, a sheath 12, and a plurality of tension members 13. Each optical fiber 11 has a core (not shown) and a cladding (not shown). For example, the optical fiber 11 may have only a core and a cladding. Alternatively, an optical fiber wire having a cladding coated with a resin or the like may be used as the optical fiber 11. Furthermore, two or more optical fibers 11 may constitute a so-called optical fiber ribbon. In other words, two or more optical fibers 11 may be collectively coated with a resin or the like and have a ribbon-like shape.

[0016] The sheath 12 covers and coats the optical fibers 11 from the radial outside. The sheath 12 may be made of a polyolefin (PO) resin such as polyethylene (PE), polypropylene (PP), ethylene ethyl acrylate copolymer (EEA), ethylene vinyl acetate copolymer (EVA), ethylene propylene copolymer (EP), polyvinyl chloride (PVC), or the like. The sheath 12 may also be made of a mixture (alloy, mixture) of the above resins. The front end of the sheath 12 according to this embodiment is located in the dam case 20.

[0017] 2, a connector C may be attached to the tip of the optical fiber 11. The connector C may be attached to each optical fiber 11 in a one-to-one correspondence, or one connector C may be attached to two or more optical fibers 11. The tip (connector C) of each optical fiber 11 is housed in a hose 100 with a towing section.

[0018] The tension members 13 according to this embodiment are embedded in the sheath 12. Each tension member 13 extends in the axial direction Z along the optical fiber 11. The tension members 13 are members having a spring constant or tensile strength in the axial direction Z higher than that of the sheath 12. The tension members 13 may be made of a material such as a metal wire (steel wire, etc.) or fiber reinforced plastic (FRP). When a traction force (tension) is applied to the cable 10 along the axial direction Z, the tension members 13 have a role of receiving the traction force and protecting the optical fiber 11. In this embodiment, four tension members 13 are arranged so as to sandwich the optical fibers 11 in the radial direction. The number and positions of the tension members 13 are not limited to the illustrated example and can be changed as appropriate.

[0019] 2 and 3, the dam case 20 is disposed so as to surround the cable 10 from the radial outside. Although not shown, the dam case 20 according to this embodiment is fixed to the cable 10 by an adhesive injected into the internal space S of the dam case 20. More specifically, the inner circumferential surface 21 of the dam case 20 is bonded to each of the optical fiber 11, the sheath 12, and the tensile body 13 of the cable 10 by the adhesive. However, as long as the dam case 20 can be fixed to the cable 10, the fixing method is not limited to adhesive fixing and can be changed as appropriate.

[0020] 3, the tubular metal fitting (tubular member) 30 is provided so as to surround the outer circumferential surface 22 of the dam case 20 from the radially outer side. In this embodiment, an inner circumferential surface 31 of the tubular metal fitting 30 is formed with a recess 33 that is recessed radially outward and opens forward. In addition, the recess 33 of the tubular metal fitting 30 is formed with a spiral projection 33a that projects radially inward.

[0021] As described above, the hose with a towing part 100 is attached to the tubular metal fitting 30. As shown in Fig. 3, the hose with a towing part 100 according to this embodiment is attached so as to be housed in the recess 33 of the tubular metal fitting 30. More specifically, the protrusion 33a formed in the recess 33 of the tubular metal fitting 30 is inserted into the flexible structure 111 (between two wires 111a adjacent in the axial direction Z) of the hose 110, thereby fixing the hose 110 to the tubular metal fitting 30. However, the structure for attaching the hose with a towing part 100 to the tubular metal fitting 30 is not limited to the above example and can be changed as appropriate.

[0022] Here, the outer peripheral surface 22 of the dam case 20 according to this embodiment has a small diameter portion 23. The outer diameter of the small diameter portion 23 is smaller than the outer diameter of the outer peripheral surface 22 in other portions. The small diameter portion 23 is formed at the tip portion of the dam case 20. By forming the small diameter portion 23 in the dam case 20, the hose 110 and the dam case 20 are less likely to interfere with each other, and the deformation of the hose 110 is less likely to be hindered by the dam case 20.

[0023] 3, the towing end mounting structure 1 according to this embodiment includes an O-ring 50. The O-ring 50 is housed in a groove formed in the outer circumferential surface 22 of the dam case 20, and abuts against the inner circumferential surface 31 of the tubular metal fitting 30. The O-ring 50 serves to improve the waterproofing of the towing end mounting structure 1. The O-ring 50 is made of an elastic material (e.g., rubber, etc.).

[0024] As shown in Fig. 3, the fixing member 40 is provided so as to surround the cable 10 from the radial outside. The outer diameter R1 of the fixing member 40 according to this embodiment is substantially equal to the outer diameter R2 of the tubular metal fitting 30. Note that the term "substantially equal" also includes the case where the outer diameters R1 and R2 are equal when manufacturing errors are removed. However, the outer diameter R1 may be equal to or smaller than the outer diameter R2. In other words, the outer peripheral surface 42 of the fixing member 40 is located at the same position in the radial direction as the outer peripheral surface 32 of the tubular metal fitting 30, or is located radially inward of the outer peripheral surface 32 of the tubular metal fitting 30.

[0025] In the present embodiment, an inner peripheral surface 41 of the fixed member 40 is formed with an accommodating recess 43 that is recessed radially outward and opens forward. The rear end of the dam case 20 is accommodated in the accommodating recess 43 of the fixed member 40. The accommodating recess 43 of the fixed member 40 also includes an abutment surface 43a facing forward. The abutment surface 43a faces the rear end surface 20a of the dam case 20 in the axial direction Z. Although details will be described later, the abutment surface 43a abuts against the dam case 20 and plays a role in transferring the towing force to the dam case 20 when the cylindrical metal fitting 30 and the fixed member 40 are towed via the towing-equipped hose 100.

[0026] The front end of the fixing member 40 according to this embodiment is provided with a first screw portion 42a. In the example shown in FIG. 3, the first screw portion 42a is a so-called male screw, and has a structure in which a helical protrusion is formed on the outer circumferential surface 42. On the other hand, the rear end of the tubular metal fitting 30 according to this embodiment is provided with a second screw portion 31a. In the example shown in FIG. 3, the second screw portion 31a is a so-called female screw, and has a structure in which a helical groove is formed on the inner circumferential surface 31. The fixing member 40 is fixed to the tubular metal fitting 30 by screwing the first screw portion 42a into the second screw portion 31a. However, the second screw portion 31a may be a male screw, and the first screw portion 42a may be a female screw. In other words, the second screw portion 31a may be formed on the outer circumferential surface 32 of the tubular metal fitting 30, and the first screw portion 42a may be formed on the inner circumferential surface 41 (the accommodation recess 43) of the fixing member 40.

[0027] As shown in Fig. 2 and Fig. 4A, the fixing member 40 according to this embodiment has a first member 40A and a second member 40B arranged so as to sandwich the cable 10 in the radial direction. The fixing member 40 is separable into the first member 40A and the second member 40B. In other words, the fixing member 40 has a divided structure. However, the fixing member 40 does not necessarily have to have a divided structure. The divided structure will be described below.

[0028] As shown in FIG. 4A, the first member 40A has a first opposing surface S1 that faces the second member 40B (second opposing surface S2) in the radial direction. The second member 40B has a second opposing surface S2 that faces the first member 40A (first opposing surface S1) in the radial direction. A pair of pins 44 that protrude toward the second member 40B (second opposing surface S2) are formed on the first opposing surface S1. The pair of pins 44 are arranged so as to sandwich the cable 10 in the radial direction. In addition, a pair of pin holes 45 into which the pair of pins 44 are inserted are formed on the second opposing surface S2.

[0029] By inserting the pin 44 into the pin hole 45, the first opposing surface S1 and the second opposing surface S2 come into contact with each other, and the first member 40A and the second member 40B are fitted together. In addition, by inserting the pin 44 into the pin hole 45, the first member 40A and the second member 40B are prevented from being displaced in the axial direction Z. Conversely, by removing the pin 44 from the pin hole 45, the fixing member 40 is divided into the first member 40A and the second member 40B. Note that the number and arrangement of the pins 44 and the pin holes 45 are not limited to the example in FIG. 4A and can be changed as appropriate.

[0030] Next, the operation of the towing end mounting structure 1 configured as above will be described.

[0031] When the pulling end P according to this embodiment is used to insert the cable 10 into a duct or the like, an attachment process of attaching the pulling end P to the cable 10 and a process of pulling the cable 10 via the pulling end P are performed.

[0032] In the attachment process, first, the cable 10 is inserted from the rear end of the pulling end P so that the dam case 20 and the cylindrical metal fitting 30 face each other in the radial direction (see Fig. 2 and Fig. 4A). Next, as shown in Fig. 4A and Fig. 4B, the first member 40A and the second member 40B are fitted together so as to sandwich the cable 10. Next, as shown in Fig. 4B and Fig. 4C, the fixing member 40 is rotated relative to the cylindrical metal fitting 30, and the first screwing portion 42a is screwed into the second screwing portion 31a. This fixes the fixing member 40 to the cylindrical metal fitting 30. In addition, the above screwing prevents the first member 40A and the second member 40B from being unexpectedly separated from each other. By carrying out the above process, the pulling end P and the fixing member 40 are fixed, and the dam case 20 fixed to the cable 10 is accommodated in the accommodation recess 43 of the fixing member 40 (see also Fig. 3).

[0033] After the above-mentioned attachment process is performed, the towing process is performed. In the towing process, for example, the handle 121 of the towing part 120 is pulled forward. Here, since the towing part 120, the hose 110, the tubular metal fitting 30, and the fixing member 40 are fixed to each other, they are pulled forward as a unit. In other words, the tubular metal fitting 30 and the fixing member 40 are pulled via the towing part-equipped hose 100. At this time, the abutment surface 43a of the fixing member 40 and the rear end surface 20a of the dam case 20 come into contact with each other (see also FIG. 3). Therefore, the forward pulling force is transferred to the dam case 20 via the abutment surface 43a. As a result, the dam case 20 and the cable 10 fixed to the dam case 20 are pulled forward.

[0034] After the cable 10 has been pulled by the above method, the fixing member 40 may be rotated in the reverse direction relative to the cylindrical metal fitting 30 to release the screw engagement between the first screw engagement portion 42a and the second screw engagement portion 31a (see FIG. 4D). This allows the pulling end P to be removed from the cable 10. By removing the pulling end P from the cable 10, the connector C (optical fiber 11) can be connected to an adapter provided in a data center or the like.

[0035] 4D, the fixing member 40 may be divided into a first member 40A and a second member 40B after the pulling end P is removed from the cable 10. This allows the fixing member 40 to be removed from the cable 10. Since the fixing member 40 has a divided structure in this way, it is possible to prevent the fixing member 40 from remaining attached to the cable 10 after wiring in a data center or the like.

[0036] In the meantime, as a conventional pulling end mounting structure, a structure is generally known in which a dam case fixed to a cable and the pulling end are fixed by a plurality of bolts arranged at intervals in the circumferential direction. In such a pulling end mounting structure, when a new cable is to be inserted into a thin duct in which a plurality of cables are already arranged, there are cases in which it is difficult to insert the pulling end because a sufficient space for inserting the pulling end is not secured. In order to be able to insert the pulling end into a limited space, it is preferable to reduce the outer diameter of the pulling end.

[0037] Here, a method of thinning the towing end is conceivable in order to reduce the outer diameter of the towing end. However, in the above-mentioned general towing end mounting structure, the bolts are also made smaller as the towing end is thinned, and there is a possibility that sufficient mounting strength cannot be obtained. If the mounting strength is insufficient, the towing end may fall off the cable when towing the towing end. Another conceivable method is to increase the number of bolts, but this method also has the possibility of making the mounting strength unstable. This is because, if the load on the multiple bolts becomes uneven, the load may be locally concentrated on a specific bolt, causing damage to that bolt.

[0038] In contrast, in the towing end mounting structure 1 according to the present embodiment, the towing end P is attached to the cable 10 by a cylindrical fixing member 40 arranged so as to surround the cable 10. Here, in the conventional towing end mounting structure, a plurality of bolts are provided intermittently in the circumferential direction, whereas the fixing member 40 according to the present embodiment is a member that is continuous in the circumferential direction. Therefore, the contact area between the fixing member 40 and the towing end P can be made larger than the contact area between the bolt and the towing end in the conventional structure. Therefore, according to the towing end mounting structure 1 according to the present embodiment, the mounting strength can be ensured even if the towing end P is made thin and has a small diameter. In other words, it is possible to achieve both a small diameter of the towing end P and ensuring the mounting strength of the towing end P to the cable 10.

[0039] Furthermore, the outer diameter R1 of the fixing member 40 according to this embodiment is equal to or smaller than the outer diameter R2 of the tubular metal fitting 30. This makes it less likely that the fixing member 40 will interfere with other cables, etc., in the duct when the cable 10 is pulled through the duct. This makes it easier to pull the cable 10.

[0040] In addition, in the towing end mounting structure 1 according to this embodiment, it is not necessary to screw in a plurality of bolts. Therefore, the time required to attach the towing end P to the cable 10 or detach it from the cable 10 can be reduced compared to the conventional structure.

[0041] As described above, the towing end mounting structure 1 of this embodiment comprises a cable 10 having an optical fiber 11, a cylindrical dam case 20 fixed to the cable 10 so as to surround the cable 10, a tubular metal fitting 30 to which a towing section-equipped hose 100 that houses an end of the optical fiber 11 is attached and which is arranged to surround the outer peripheral surface 22 of the dam case 20, and a cylindrical fixing member 40 that surrounds the cable 10 and can be fixed to the tubular metal fitting 30, the outer diameter R1 of the fixing member 40 being equal to or smaller than the outer diameter R2 of the tubular metal fitting 30, and an abutment surface 43a is formed on the inner peripheral surface 41 of the fixing member 40 which abuts against the dam case 20 and transfers the towing force to the dam case 20 when the tubular metal fitting 30 and the fixing member 40 are towed via the towing section-equipped hose 100.

[0042] According to this configuration, the contact area between the fixing member 40 and the towing end P can be made larger than the contact area between the bolt and the towing end in the conventional structure. Therefore, it is possible to achieve both a smaller diameter of the towing end P and an improved attachment strength of the towing end P to the cable 10.

[0043] Furthermore, the fixing member 40 has a first screw-threaded portion 42a, and the tubular metal fitting 30 has a second screw-threaded portion 31a, and the fixing member 40 is fixed to the tubular metal fitting 30 by screwing the first screw-threaded portion 42a into the second screw-threaded portion 31a. According to this configuration, the fixing member 40 can be reliably fixed to the tubular metal fitting 30 by screwing the first screw-threaded portion 42a into the second screw-threaded portion 31a.

[0044] In addition, the first screw-type portion 42a is a male screw, and the second screw-type portion 31a is a female screw. With this configuration, the fixing member 40 can be fixed to the tubular metal fitting 30 more reliably by screwing the first screw-type portion 42a, which is a male screw, into the second screw-type portion 31a, which is a female screw.

[0045] Moreover, the fixing member 40 has a first member 40A and a second member 40B arranged so as to sandwich the cable 10 in the radial direction, and can be separated into the first member 40A and the second member 40B. This configuration can prevent the fixing member 40 from remaining attached to the cable 10 after the optical fiber 11 is laid out in a data center or the like.

[0046] The first member 40A has a first opposing surface S1 facing the second member 40B and a pin 44 protruding from the first opposing surface S1 towards the second member 40B, and the second member 40B has a second opposing surface S2 facing the first member 40A and a pin hole 45 formed in the second opposing surface S2, and the first member 40A and the second member 40B are fitted together by inserting the pin 44 into the pin hole 45. With this configuration, misalignment between the first member 40A and the second member 40B is suppressed, and the fixing member 40 can be fixed to the tubular metal fitting 30 more reliably.

[0047] The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0048] For example, in the above embodiment, the fixing member 40 is fixed to the tubular metal fitting 30 by screwing, but the method of fixing the fixing member 40 to the tubular metal fitting 30 is not limited to screwing. As an example, as in a towing end mounting structure 1A shown in FIG. 5, a claw portion 46 may be provided instead of the first screwing portion 42a, and a hook portion 34 may be provided instead of the second screwing portion 31a. The claw portion 46 protrudes radially inward from the inner circumferential surface 41 (accommodating recess 43) of the fixing member 40. The hook portion 34 protrudes radially outward from the outer circumferential surface 32 of the tubular metal fitting 30. In this towing end mounting structure 1A, when fixing the fixing member 40 to the tubular metal fitting 30, for example, the claw portion 46 can be elastically deformed to hook onto the hook portion 34. Alternatively, in the case where the fixing member 40 has a divided structure as in the above embodiment, the first member 40A and the second member 40B may be fitted together so that the claw portions 46 and the hook portions 34 mesh with each other.

[0049] Furthermore, in the above embodiment, the cable 10 has a plurality of optical fibers 11, but the cable 10 may have only one optical fiber 11.

[0050] Furthermore, the cylindrical member 30 does not have to be made of a metal.

[0051] In addition, within the scope of the spirit of the present invention, it is possible to replace the components in the above-described embodiments with well-known components as appropriate, and the above-described embodiments and variations may be combined as appropriate. [Explanation of symbols]

[0052] 1, 1A... traction end mounting structure 10... cable 11... optical fiber 20... dam case 22... outer circumferential surface 30... cylindrical metal fitting (cylindrical member) 31a... second screw-fitting portion 40... fixing member 40A... first member 40B... second member 41... inner circumferential surface 42a... first screw-fitting portion 43a... abutment surface 44... pin 45... pin hole S1... first opposing surface S2... second opposing surface

Claims

1. a cable having an optical fiber; a cylindrical dam case that is fixed to the cable so as to surround the cable, the dam case being fixed to the cable by an adhesive that is filled into an internal space of the dam case; a cylindrical member, which is a cylindrical metal fitting to which a hose with a traction part for accommodating an end of the optical fiber is attached and which is provided so as to surround an outer circumferential surface of the dam case; a cylindrical fixing member that surrounds the cable and is fixable to the cylindrical member; an O-ring that is received in a groove formed in the outer peripheral surface of the dam case and abuts against an inner peripheral surface of the cylindrical member; an outer diameter of the fixing member is equal to or smaller than an outer diameter of the tubular member; an abutment surface is formed on an inner circumferential surface of the fixing member, the abutment surface abutting against the dam case and transferring a towing force to the dam case when the tubular member and the fixing member are towed via the towing hose, the fixing member has a first member and a second member arranged to sandwich the cable in a radial direction, The fixing member is separable into the first member and the second member, The fixing member has a first screw portion, The cylindrical member has a second screw portion, The first threaded portion is threadedly engaged with the second threaded portion, thereby fixing the fixing member to the tubular member.

2. The first screw-type engagement portion is a male screw, The towing end attachment structure of claim 1 , wherein the second threaded portion is an internal thread.

3. The first member has a first opposing surface that faces the second member, and a pin that protrudes from the first opposing surface toward the second member, The second member has a second opposing surface facing the first member and a pin hole formed in the second opposing surface, 2. The towing end attachment structure according to claim 1, wherein the first member and the second member are fitted together by inserting the pin into the pin hole.

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