Twisted wire, insulated wire, and cable

Abstract

This twisted wire is obtained by twisting a plurality of sub-twisted wires together. Each of the sub-twisted wires has the same structure in which a plurality of strands of which the cross-sectional shapes perpendicular to the longitudinal direction are circles of the same diameter, are twisted together. The strands include a steel core wire, and a copper or copper alloy cover layer covering the surface of the core wire. The twist pitch of the sub-twisted wires is at least 40 times the diameter of the circumscribed circle of the sub-twisted wires. The twist pitch of the twisted wires is 5-20 times the diameter of the circumscribed circle of the twisted wires.

Description

Stranded, insulated wire and cable

[0001] The present disclosure relates to stranded wire, insulated wire and cable.

[0002] This application claims priority based on Japanese Application No. 2022-85853 filed on May 26, 2022, and incorporates by reference all of the contents of the aforementioned Japanese application.

[0003] In factory automation (FA) equipment, robots, automobiles, other industrial equipment, consumer equipment, and the like, stranded wires, insulated wires, and cables used in moving parts that bend during operation require not only strength such as tensile strength, but also durability against repeated bending stress, i.e., flex resistance. In response to this, it has been proposed to use clad wires containing a steel core wire and a copper coating layer covering the drawn wire as element wires (see, for example, JP 2020-21620 A (Patent Document 1)). The steel core wire contributes to improved strength, and the copper coating layer provides high conductivity.

[0004] Japanese Patent Application Laid-Open No. 2020-21620

[0005] The stranded wire according to the present disclosure is a stranded wire in which multiple child strands are twisted together. Each child strand has the same structure in which multiple strands, each having a circular cross section perpendicular to the longitudinal direction and the same diameter, are twisted together. The strands include a steel core wire and a copper or copper alloy coating layer covering the surface of the core wire. The twist pitch of the child strands is 40 times or more the diameter of the circumscribing circle of the child strands. The twist pitch of the stranded wire is 5 to 20 times the diameter of the circumscribing circle of the stranded wire.

[0006] FIG. 1 is a schematic diagram showing the structure of a twisted wire. FIG. 2 is a schematic diagram showing the structure of a child twisted wire. FIG. 3 is a schematic cross-sectional view showing the structure of a single wire. FIG. 4 is a schematic cross-sectional view showing the structure of a twisted wire. FIG. 5 is a schematic diagram for explaining the twist pitch of a twisted wire and a child twisted wire. FIG. 6 is a flowchart showing an outline of a method for manufacturing a twisted wire. FIG. 7 is a schematic diagram showing the structure of a twisted wire in a second embodiment. FIG. 8 is a schematic diagram showing the structure of an insulated wire in a third embodiment. FIG. 9 is a schematic diagram showing the structure of a cable in a fourth embodiment. FIG. 10 is a schematic diagram showing the structure of a cable in a fifth embodiment. FIG. 11 is a schematic perspective view showing the connection state between an insulated wire and a crimp terminal. FIG. 12 is a schematic diagram for explaining a method for a tensile test. FIG. 13 is a schematic perspective view showing the structure of a testing device for a bending test. FIG. 14 is a schematic diagram for explaining a method for a bending test. FIG. 15 is a schematic diagram for explaining a method for a bending test.

[0007] [Problem to be Solved by the Present Disclosure] In the above-mentioned stranded wires, insulated wires, and cables, connection with a crimp terminal is important as a simple connection method. However, when the above-mentioned clad wire is used as an element wire, the toughness of the steel core wire is low, and therefore cracks may occur in the core wire when connected to the crimp terminal. This cracking of the core wire can cause a problem of reduced crimp strength.

[0008] Therefore, one of the objects of the present disclosure is to provide a twisted wire, an insulated wire, and a cable that not only improves bending resistance but also achieves both strength and conductivity, and can suppress cracking of the core wire when connected to a crimp terminal.

[0009] Effect of the Present Disclosure The above-described stranded wire not only improves bending resistance but also achieves both strength and conductivity, and can suppress cracking of the core wire when connected to a crimp terminal.

[0010] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. The stranded wire of the present disclosure is a stranded wire in which multiple child strands are twisted together. Each child strand has the same structure in which multiple strands, each having a circular cross section perpendicular to the longitudinal direction and the same diameter, are twisted together. The strands include a steel core wire and a copper or copper alloy coating layer that covers the surface of the core wire. The twist pitch of the child strands is 40 times or more the diameter of the circumscribing circle of the child strands. The twist pitch of the stranded wire is 5 times or more and 20 times or less the diameter of the circumscribing circle of the stranded wire.

[0011] The stranded wire of the present disclosure is constructed by twisting together multiple child strands, each of which is formed by twisting together strands of wires. This provides high flexibility and ensures a certain level of bending resistance. The strands constituting the child strand include a steel core wire and a copper or copper alloy coating covering the surface of the core wire. This allows for both strength and electrical conductivity to be achieved. Each of the strands has a circular cross section perpendicular to the longitudinal direction, with the same diameter, which reduces local stress concentration during repeated bending and contributes to improved bending resistance. Furthermore, by setting the twist pitch of the child strand to at least 40 times the diameter of the circumscribing circle of the child strand, the wires are properly rearranged when connected to a crimp terminal, preventing stress concentration in certain wires. As a result, cracking of the core wire when connected to a crimp terminal is suppressed. Furthermore, by setting the twist pitch of the strand to at least 5 times the diameter of the circumscribing circle of the strand, unevenness on the surface of the stranded wire is suppressed, improving bending resistance. Furthermore, by setting the twist pitch of the stranded wire to 20 times or less the diameter of the circumscribing circle of the stranded wire, it is possible to avoid stress concentration on some of the child strands when the wires are bent. Note that, in this application, the state in which the wires constituting the child strands have the same diameter means that the difference between the average diameter of the multiple wires constituting each child strand and the diameter of each wire is 6.0% or less.

[0012] As described above, the stranded wire of the present disclosure not only improves bending resistance, but also achieves both strength and conductivity, and can suppress cracking of the core wire when connected to a crimp terminal.

[0013] In the above-mentioned stranded wire, the diameter of the wires may be 0.02 mm or more and 0.09 mm or less. By making the diameter of the wires 0.02 mm or more, breakage of the wires in the stranded wire manufacturing process can be suppressed, and productivity can be improved. By making the diameter of the wires 0.09 mm or less, the difference in strain between the outside and inside of the bend when the wires are bent can be suppressed, and bending resistance can be further improved.

[0014] In the above-mentioned stranded wire, the tensile strength of the core wire may be 1800 MPa or more and 4500 MPa or less. When the tensile strength of the core wire is 1800 MPa or more, it is easy to impart sufficient strength to the core wire. When the tensile strength of the core wire is 4500 MPa or less, it is easy to impart sufficient toughness to the core wire.

[0015] In the above-mentioned stranded wire, the carbon content of the steel constituting the core wire may be 0.70% by mass or more and 0.95% by mass or less. The carbon content of steel has a significant effect on the strength and toughness of the steel. By setting the carbon content of the steel constituting the core wire to 0.70% by mass or more, it becomes easy to impart sufficient strength to the core wire. By setting the carbon content of the steel constituting the core wire to 0.95% by mass or less, it becomes easy to impart sufficient toughness to the core wire.

[0016] In the above-mentioned stranded wire, the area of ​​the coating layer relative to the area of ​​the wires in a cross section perpendicular to the longitudinal direction of the wires may be 20% or more and 80% or less. By making the area of ​​the coating layer relative to the area of ​​the wires 20% or more, sufficient conductivity can be easily obtained. By making the area of ​​the coating layer relative to the area of ​​the wires 80% or less, sufficient strength and bending resistance can be easily obtained.

[0017] A stranded wire according to one aspect of the present disclosure is a stranded wire in which multiple child strands are twisted together. Each child strand has the same structure in which multiple strands, each having a circular cross section perpendicular to the longitudinal direction and the same diameter, are twisted together. The strands include a steel core wire and a copper or copper alloy coating layer covering the surface of the core wire. The twist pitch of the child strands is 40 times or more the diameter of the circumscribed circle of the child strands. The twist pitch of the stranded wire is 5 times or more and 20 times or less the diameter of the circumscribed circle of the strands. The diameter of the core wire is 0.02 mm or more and 0.09 mm or less. The tensile strength of the core wire is 1800 MPa or more and 4500 MPa or less. The carbon content of the steel constituting the core wire is 0.70 mass % or more and 0.95 mass % or less. In a cross section perpendicular to the longitudinal direction of the wire, the area of ​​the coating layer relative to the area of ​​the wire is 20% or more and 80% or less. The plurality of child strands include a central child strand disposed in the center in a cross section perpendicular to the longitudinal direction of the strand, and six first peripheral child strands disposed in contact with the central child strand so as to surround the outer periphery of the central child strand. The child strands include 2 to 20 element wires.

[0018] In another aspect of the present disclosure, the stranded wire is a stranded wire formed by twisting together multiple child strands. Each child strand has the same structure, in which multiple strands, each having a circular cross section perpendicular to the longitudinal direction and the same diameter, are twisted together. The strands include a steel core wire and a copper or copper alloy coating layer covering the surface of the core wire. The twist pitch of the child strands is 40 times or more the diameter of the circumscribed circle of the child strands. The twist pitch of the stranded wire is 5 times or more and 20 times or less the diameter of the circumscribed circle of the strands. The diameter of the core wire is 0.02 mm or more and 0.09 mm or less. The tensile strength of the core wire is 1800 MPa or more and 4500 MPa or less. The carbon content of the steel constituting the core wire is 0.70 mass % or more and 0.95 mass % or less. In a cross section perpendicular to the longitudinal direction of the wire, the area of ​​the coating layer relative to the area of ​​the wires is 20% or more and 80% or less. In a cross section perpendicular to the longitudinal direction of the stranded wire, the plurality of child strands include a centrally disposed central child strand, six first peripheral child strands disposed in contact with the central child strand so as to surround the outer periphery of the central child strand, and twelve second peripheral child strands disposed in contact with the first peripheral child strand on the outer periphery of the area where the first peripheral child strands are disposed. The child strands include 2 to 20 element wires.

[0019] By configuring the child strands to include a central child strand and first peripheral child strands, or a central child strand, first peripheral child strands, and second peripheral child strands, the cross section perpendicular to the longitudinal direction of the stranded wire becomes closer to a circle. As a result, local stress concentrations during repeated bending are reduced, improving bending resistance. Furthermore, by configuring the child strands to include two or more element wires, the flexibility of the stranded wire can be ensured, improving bending resistance. By configuring the child strands to include 20 or fewer element wires, a practical outer diameter for the stranded wire can be obtained when used as an electric wire.

[0020] In the above-described stranded wire, the covering layer may be a plated layer. That is, the covering layer may be formed by plating. A plated layer is suitable as the covering layer of the present disclosure because its thickness can be easily adjusted and it can be formed by a simple process.

[0021] An insulated wire according to one aspect of the present disclosure includes the stranded wire of the present disclosure and an insulating layer covering the outer periphery of the stranded wire. The insulated wire according to one aspect of the present disclosure includes the stranded wire of the present disclosure, which not only improves bending resistance but also achieves both strength and conductivity, and can suppress cracking of the core wire when connected to a crimp terminal. This insulated wire can therefore not only improve bending resistance but also achieves both strength and conductivity, and can suppress cracking of the core wire when connected to a crimp terminal.

[0022] An insulated electric wire according to another aspect of the present disclosure includes a core formed by twisting together a plurality of insulated stranded wires and a protective layer made of an insulator that covers the outer periphery of the core. Each of the insulated stranded wires includes the stranded wire according to the present disclosure and an insulating layer that covers the outer periphery of the stranded wire. According to the insulated electric wire according to another aspect of the present disclosure, by including the stranded wire according to the present disclosure, it is possible to provide an insulated electric wire that not only has improved bending resistance but also achieves both strength and conductivity and is capable of suppressing cracking of the core wire when connected to a crimp terminal.

[0023] A cable according to an aspect of the present disclosure includes the insulated wire according to the aspect of the present disclosure, a conductive shield portion arranged to surround the outer periphery of the insulated wire, and an insulating outer sheath layer arranged to surround the outer periphery of the shield portion. The cable according to an aspect of the present disclosure includes the twisted wire according to the present disclosure, which not only improves bending resistance but also achieves both strength and conductivity, and can suppress cracking of the core wire when connected to a crimp terminal.

[0024] A cable according to another aspect of the present disclosure includes the insulated wire according to the above-described other aspect of the present disclosure, a conductive shield portion arranged to surround the outer periphery of the insulated wire, and an insulating outer sheath layer arranged to surround the outer periphery of the shield portion. According to the cable according to another aspect of the present disclosure, by including the twisted wire according to the present disclosure, it is possible to provide a cable that not only improves bending resistance but also achieves both strength and conductivity and is capable of suppressing cracking of the core wire when connected to a crimp terminal.

[0025] [Details of the embodiments of the present disclosure] Next, embodiments of the stranded wire, insulated wire, and cable according to the present disclosure will be described below with reference to the drawings. In the following drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0026] (Embodiment 1) Fig. 1 is a schematic diagram showing the structure of a stranded wire. Referring to Fig. 1, a stranded wire 1 in this embodiment has a structure in which multiple child strands 10 are twisted together. In this embodiment, the multiple child strands 10 include one central child strand 10A and six first peripheral child strands 10B. In a cross section perpendicular to the longitudinal direction of the stranded wire 1, the central child strand 10A is disposed in the center. The six first peripheral child strands 10B are disposed in contact with the central child strand 10A so as to surround the outer periphery of the central child strand 10A. The central child strand 10A is in contact with all six first peripheral child strands 10B on its outer periphery. Each first peripheral child strand 10B is in contact with the two first peripheral child strands 10B adjacent to it in the circumferential direction and the central child strand 10A on its outer periphery.

[0027] FIG. 2 is a schematic diagram showing the structure of a child strand. Referring to FIG. 2, each child strand 10 has the same structure, in which multiple strands 100, each of which has a circular cross-sectional shape perpendicular to the longitudinal direction and has the same diameter, are twisted together. In this embodiment, the multiple strands 100 include one central strand 100A and six first peripheral strands 100B. Each child strand 10 includes two to twenty (specifically, seven) strands 100. In a cross-section perpendicular to the longitudinal direction of the strand 1, the central strand 100A is disposed at the center. The six first peripheral strands 100B are disposed in contact with the central strand 100A so as to surround the outer periphery of the central strand 100A. The central strand 100A is in contact with all six first peripheral strands 100B on the outer periphery. Each first peripheral strand 100B is in contact with two first peripheral strands 100B adjacent to each other in the circumferential direction and with the central strand 100A on the outer circumferential surface.

[0028] FIG. 3 is a schematic cross-sectional view showing the structure of a wire. FIG. 3 shows a cross-section perpendicular to the longitudinal direction of the wire. Referring to FIG. 3, the wire 100 includes a core wire 101 and a coating layer 102. The core wire 101 is made of steel. The diameter of the wire 100 is, for example, 0.02 mm or more and 0.09 mm or less. The carbon content of the steel constituting the core wire 101 may be, for example, 0.70 mass % or more and 0.95 mass % or less. The carbon content of the steel constituting the core wire 101 may be 0.90 mass % or less. For example, the steel constituting the core wire 101 may be steel corresponding to the piano wire specified in JIS (Japanese Industrial Standards) G3502. The tensile strength of the core wire 101 may be, for example, 1800 MPa or more and 4500 MPa or less. The tensile strength of the core wire 101 may be 2500 MPa or more. The tensile strength of the core wire 101 can be set to 3800 MPa or less.

[0029] The coating layer 102 is made of copper (Cu) or a copper alloy. The coating layer 102 covers the surface 101A (outer circumferential surface) of the core wire 101. The thickness of the coating layer 102 is constant in the circumferential direction. The coating layer 102 may be a plated layer. The coating layer 102 may be a layer formed by plating. In a cross section perpendicular to the longitudinal direction of the wire 100 (the cross section shown in FIG. 3 ), the area of ​​the coating layer 102 relative to the area of ​​the wire 100 may be 20% or more and 80% or less. Note that a state in which the thickness of the coating layer 102 is constant in the circumferential direction refers to a state in which the difference between the maximum and minimum thickness values ​​of the coating layer 102 in each wire 100 is 7.0% or less of the average thickness.

[0030] Fig. 4 is a schematic cross-sectional view showing the structure of a stranded wire. Fig. 5 is a schematic view for explaining the twist pitch of a stranded wire and a child strand. Fig. 4 shows a cross section perpendicular to the longitudinal direction of the stranded wire 1. Referring to Figs. 4 and 5, in this embodiment, the twist pitch P of the child stranded wire 10 is determined by the ratio of the diameter d of the circumscribed circle of the child stranded wire 10 to the diameter d of the circumscribed circle of the child stranded wire 10. ２ 5, the twist pitch P of the child strand 10 is defined as the length of one turn of one wire 100 constituting the child strand 10 around the child strand 10, measured parallel to the longitudinal direction of the child strand 10. In this embodiment, the twist pitch P of the strand 1 is defined as the diameter d of the circumscribing circle of the strand 1. １ 5 (except for those in parentheses), the twist pitch P of the stranded wire 1 is defined as the length of one child strand 10 constituting the stranded wire 1 that makes one turn around the stranded wire 1, measured parallel to the longitudinal direction of the stranded wire 1.

[0031] The stranded wire 1 of this embodiment is constructed by twisting together a plurality of child strands 10, each of which is constructed by twisting together strands 100. This provides high flexibility and ensures a certain level of bending resistance. The strands 100 that make up the child strand 10 include a steel core 101 and a copper or copper alloy coating layer 102 that covers the surface 101A of the core 101. This allows for both strength and electrical conductivity to be achieved. The cross-sectional shape of each strand 100 perpendicular to the longitudinal direction is a circle of the same diameter, which reduces local stress concentration during repeated bending and contributes to improved bending resistance. Furthermore, the twist pitch P of the child strands 10 is set to a value equal to the diameter d of the circumscribed circle of the child strands 10. ２ By setting the twist pitch P of the stranded wire 1 to 40 times or more, the strands 100 are properly rearranged when connected to the crimp terminal, and stress concentration on some of the strands 100 is avoided. As a result, cracking of the core wire 101 when connected to the crimp terminal is suppressed. Furthermore, by setting the twist pitch P of the stranded wire 1 to 40 times or more, the diameter d of the circumscribed circle of the stranded wire 1 is prevented. １ By making the twist pitch P of the stranded wire 1 five times or more, it is possible to suppress irregularities on the surface of the stranded wire 1 and improve bending resistance. １ By setting the thickness to 20 times or less, it is possible to avoid stress concentration on some of the child strands 10 when bent. In this way, the stranded wire 1 of this embodiment is a stranded wire that not only improves bending resistance but also achieves both strength and conductivity, and is capable of suppressing cracking of the core wire when connected to a crimp terminal.

[0032] In this embodiment, each of the multiple child strands 10 constituting the stranded wire 1 includes, in a cross section perpendicular to the longitudinal direction of the stranded wire 1, a centrally located center child strand 10A and six first peripheral child strands 10B that are arranged in contact with the central child strand 10A and surround the outer periphery of the central child strand 10A. The child strand 10 includes two to twenty strands 100. This results in a cross section perpendicular to the longitudinal direction of the stranded wire 1 that is closer to a circle. As a result, local stress concentrations during repeated bending are reduced, improving bending resistance. Furthermore, by including two or more strands 100 in the child strand 10, the flexibility of the stranded wire 1 can be ensured, improving bending resistance. By including 20 or fewer strands 100 in the child strand 10, the outer diameter of the stranded wire 1 can be made practical for use as an electric wire.

[0033] Next, a method for manufacturing the stranded wire 1 according to this embodiment will be described. FIG. 6 is a flowchart showing an outline of the method for manufacturing the stranded wire. Referring to FIG. 6, the method for manufacturing the stranded wire 1 according to this embodiment first performs a raw steel wire preparation step as step S10. In step S10, a raw steel wire is prepared. Specifically, a steel wire having a carbon content of 0.70% by mass or more and 0.95% by mass or less is prepared. The steel constituting the raw steel wire may contain 0.4% by mass or more and 2.5% by mass or less of silicon (Si), 0.6% by mass or more and 0.9% by mass or less of manganese (Mn), and 0.1% by mass or more and 1.8% by mass or less of chromium (Cr). A piano wire rod specified in G3502 (e.g., SWRS82A) can be used as the steel constituting the raw steel wire.

[0034] Next, a patenting step is carried out as step S20. In this step S20, patenting is carried out on the raw steel wire prepared in step S10. Specifically, the raw steel wire is heated to a temperature range equal to or higher than the austenitizing temperature (point A1), and then rapidly cooled to a temperature range higher than the martensite transformation start temperature (point MS), and a heat treatment is carried out in which the raw steel wire is maintained in that temperature range. As a result, the metal structure of the raw steel wire becomes a fine pearlite structure with narrow lamellar spacing. Here, in the patenting treatment, the treatment of heating the raw steel wire to a temperature range equal to or higher than point A1 is preferably carried out in an inert gas atmosphere in order to suppress the occurrence of decarburization.

[0035] Next, a surface roughening step is carried out as step S30. In this step S30, the raw steel wire that has been patented in step S20 is subjected to a surface roughening treatment. Specifically, the surface of the raw steel wire is brought into contact with an acid such as hydrochloric acid or sulfuric acid to increase the surface roughness. The concentration of hydrochloric acid can be, for example, 35 mass %, and the concentration of sulfuric acid can be, for example, 65 mass %.

[0036] Next, a coating layer forming step is carried out as step S40. In this step S40, a coating layer is formed on the first intermediate steel wire obtained by carrying out steps up to S30. Specifically, for example, a coating layer made of copper (pure copper) is formed on the first intermediate steel wire by plating. Furthermore, in addition to copper, a metal layer such as tin (Sn) or zinc (Zn) may be formed by plating, and these may be alloyed to form a coating layer made of a copper alloy.

[0037] Next, a wire drawing step is carried out as step S50. In this step S50, the second intermediate steel wire obtained by carrying out steps up to S40 is subjected to wire drawing (drawing). The true strain in the wire drawing step S50 can be, for example, 2.3 to 4.9, and preferably 3.0 to 4.0. In this way, the wire 100 of the present embodiment is obtained.

[0038] Next, a first stranding step is carried out as step S60. In step S60, the wires 100 obtained through steps S10 to S50 are stranded together to produce the child stranded wire 10. Specifically, referring to FIG. 2, seven wires 100 produced in steps S10 to S50 are prepared, and one is twisted as the central wire 100A and six are twisted as the first peripheral wires 100B. In this way, the child stranded wire 10 is obtained. At this time, referring to FIGS. 4 and 5, the twist pitch P of the child stranded wire 10 is determined by the diameter d of the circumscribing circle of the child stranded wire 10. ２ It is said to be more than 40 times that.

[0039] Next, a second stranding step is carried out as step S70. In step S70, the child strands 10 obtained in step S60 are twisted together to produce the stranded wire 1. Specifically, referring to FIG. 1, seven child strands 10 produced in step S60 are prepared, and one is twisted as the central child strand 10A and six are twisted as the first peripheral child strands 10B. In this way, the stranded wire 1 is obtained. At this time, referring to FIGS. 4 and 5, the twist pitch P of the stranded wire 1 is determined by twisting the diameter d of the circumscribed circle of the stranded wire 1. １ The thickness is set to be 5 to 20 times greater than the thickness of the wire. By the above-described procedure, the stranded wire 1 of the present embodiment can be easily manufactured.

[0040] Second Embodiment Next, a second embodiment of the present disclosure will be described. Fig. 7 is a schematic diagram showing the structure of a stranded wire according to the second embodiment. Referring to Fig. 7 and Fig. 1, the stranded wire 1 according to the second embodiment basically has the same structure as the stranded wire 1 according to the first embodiment and achieves the same effects. However, the stranded wire 1 according to the second embodiment differs from the first embodiment in the number of child strands 10 that make up the stranded wire 1.

[0041] 7 , the plurality of child strands 10 constituting the stranded wire 1 of this embodiment include, in a cross section perpendicular to the longitudinal direction of the stranded wire 1, a centrally located central child strand 10A, six first peripheral child strands 10B arranged in contact with the central child strand 10A and surrounding the outer periphery of the central child strand 10A, and twelve second peripheral child strands 10C arranged in contact with the first peripheral child strands 10B on the outer periphery of the area where the first peripheral child strands 10B are arranged. In this embodiment, the stranded wire 1 includes 19 child strands 10.

[0042] The central strand 10A is in contact with all six of the first peripheral strands 10B on its outer periphery. Each first peripheral strand 10B is in contact with two circumferentially adjacent first peripheral strands 10B and the central strand 10A on its outer periphery. Each second peripheral strand 10C is in contact with two circumferentially adjacent second peripheral strands 10C and the first peripheral strand 10B located radially inward on its outer periphery. Like the strand 1 of the first embodiment, the strand 1 of this embodiment, in which the number and arrangement of the child strands 10 included in the strand 1 are modified in this manner, not only improves bending resistance but also achieves both strength and conductivity and is capable of suppressing cracking of the core wires when connected to a crimp terminal.

[0043] Third Embodiment Next, an example of an insulated wire according to the third embodiment of the present disclosure will be described. FIG. 8 is a schematic diagram illustrating the structure of an insulated wire according to the third embodiment. Referring to FIG. 8, an insulated wire 3 according to the present embodiment includes a core 9 and an insulating layer 12. The core 9 has a structure in which a plurality of (here, two) insulated stranded wires 2 are twisted together. The insulating layer 12 is made of an insulator such as resin. The insulating layer 12 is a protective layer disposed so as to cover the outer periphery of the core 9. The insulated stranded wire 2 includes the stranded wire 1 according to the first or second embodiment and an insulating layer 11 that covers the outer periphery of the stranded wire 1. The insulating layer 11 is made of an insulator such as resin.

[0044] The insulated wire 3 of the present embodiment includes the stranded wire 1 of the first or second embodiment, which not only improves bending resistance but also achieves both strength and conductivity, and is capable of suppressing cracking of the core wire 101 when connected to a crimp terminal. This allows the insulated wire 3 to achieve not only improved bending resistance but also achieves both strength and conductivity, and is capable of suppressing cracking of the core wire 101 when connected to a crimp terminal. The insulated stranded wire 2 constituting the core 9 can also be used as the insulated wire. That is, the insulated stranded wire 2 as an insulated wire in another embodiment includes the stranded wire 1 of the first or second embodiment and an insulating layer 11 covering the outer periphery of the stranded wire 1. The insulated stranded wire 2 includes the stranded wire 1 of the first or second embodiment, which not only improves bending resistance but also achieves both strength and conductivity, and is capable of suppressing cracking of the core wire 101 when connected to a crimp terminal. This allows the insulated wire 3 to achieve not only improved bending resistance but also achieves both strength and conductivity, and is capable of suppressing cracking of the core wire 101 when connected to a crimp terminal.

[0045] Fourth Embodiment Next, an example of a cable according to the fourth embodiment of the present disclosure will be described. FIG. 9 is a schematic diagram illustrating the structure of a cable according to the fourth embodiment. Referring to FIG. 9, a cable 300 includes the stranded wire 1 according to the first or second embodiment, an insulating layer 4 arranged to cover the outer periphery 1A of the stranded wire 1, a shield portion 5 arranged to surround the outer periphery 4A of the insulating layer 4, and an outer sheath layer 6 arranged to cover the outer periphery 5A of the shield portion 5. From another perspective, the cable 300 includes the insulated stranded wire 2 as the insulated electric wire described in the third embodiment above, a shield portion 5 made of a conductor arranged to surround the outer periphery of the insulated stranded wire 2, and an outer sheath layer 6 made of an insulator arranged to surround the outer periphery of the shield portion 5. The shield portion 5 may have a structure in which metal wires are braided. The wires 100 according to the above embodiment may be used as the metal wires constituting the shield portion 5.

[0046] The cable 300 of this embodiment not only has improved bending resistance, but also achieves both strength and conductivity, and is capable of suppressing cracking of the core wire 101 when connected to a crimp terminal.By including the twisted wire 1 of this embodiment 1 or 2, the cable is capable of not only improving bending resistance, but also achieving both strength and conductivity, and suppressing cracking of the core wire 101 when connected to a crimp terminal.

[0047] Fifth Embodiment Next, another example of the cable of the present disclosure will be described as a fifth embodiment of the present disclosure. FIG. 10 is a schematic diagram showing the structure of a cable according to the fifth embodiment. Referring to FIG. 10 , a cable 400 according to the present embodiment includes the insulated wire 3 (see FIG. 8 ) described in the third embodiment above, a shield portion 5 made of a conductor and arranged to surround the outer periphery of the insulated wire 3, and an outer sheath layer 6 made of an insulator and arranged to surround the outer periphery 5A of the shield portion 5. The shield portion 5 may have a structure in which metal wires are braided. The wires 100 according to the above embodiment may be used as the metal wires constituting the shield portion 5.

[0048] The cable 400 of this embodiment not only has improved bending resistance, but also achieves both strength and conductivity, and is capable of suppressing cracking of the core wire 101 when connected to a crimp terminal.By including the twisted wire 1 of this embodiment 1 or 2, the cable is capable of not only improving bending resistance, but also achieving both strength and conductivity, and suppressing cracking of the core wire 101 when connected to a crimp terminal.

[0049] Experiments were conducted to confirm the bending resistance of the stranded wire, insulated wire, and cable of the present disclosure, and the suppression of cracking of the core wire when connected to a crimp terminal. The experimental procedure was as follows.

[0050] A stranded wire 1 was prepared according to the manufacturing method described in the first embodiment. The outer periphery of this stranded wire 1 was coated with an insulating layer 11 to produce an insulated electric wire (insulated stranded wire 2). SWRS82A, a piano wire material specified in JIS G3502, was used as the raw steel wire prepared in step S10. In step S40, a pure copper coating layer 102 was formed by plating. The thickness of the coating layer 102 was adjusted to change the area ratio of the coating layer 102 in a cross section perpendicular to the longitudinal direction of the stranded wire 100. In step S50, wire drawing was performed so that the outer diameter (diameter) of the stranded wire 100 was 0.05 mm. Furthermore, in step S60, the twist pitch of the child stranded wire 10 was changed to 60, and the number of stranded wires 100 included in the child stranded wire 10 was changed within a range of 7 to 16. In step S70, the twist pitch of the stranded wire 1 was also changed. Samples A to S were obtained in this manner. Furthermore, raw steel wires with different outer diameters and carbon contents were prepared in step S10, and samples T to W were produced by varying the outer diameter of the wire 100 by wire drawing in step S50.

[0051] The obtained samples were then measured for (1) the strength of the crimped portion when connected to the crimp terminal and (2) the bending resistance as follows.

[0052] (1) Strength of Connection When Connected to a Crimp Terminal FIG. 11 is a schematic perspective view showing the connection between an insulated electric wire and a crimp terminal. FIG. 12 is a schematic view illustrating a tensile test method. Referring to FIG. 11 , a crimp terminal 80 includes a main body 83, a conductor barrel 81 connected to the main body 83, and an insulation barrel 82 connected to the side of the conductor barrel 81 opposite the side connected to the main body 83. When connecting an insulated stranded wire 2, which is an insulated electric wire, to the crimp terminal 80, the insulating layer 11 at the end of the insulated stranded wire 2 is first removed to expose the stranded wire 1. The conductor barrel 81 is then crimped to hold the exposed stranded wire 1, and the insulating layer 11 is held by the insulation barrel 82. If a crack occurs in the core wire 101 of the wires 100 constituting the stranded wire 1 held by the conductor barrel 81, the strength of the connection between the conductor barrel 81 and the stranded wire 1 decreases.

[0053] In this experiment, for each sample, the insulated stranded wire 2 was connected to the crimp terminal 80 while the stranded wire 1 was held by the conductor barrel 81 as described above, but the insulating layer 11 was not held by the insulation barrel 82. Then, as shown in Fig. 12, a tensile test was performed with the main body 83 of the crimp terminal 80 held by the first chuck 91 of the tensile tester and the insulated stranded wire 2 held by the second chuck 92 of the tensile tester, and the strength of the connection was evaluated based on the load at break.

[0054] (2) Bending Resistance FIG. 13 is a schematic perspective view showing the structure of a testing device for a bending test. FIGS. 14 and 15 are schematic views for explaining a bending test method. Referring to FIG. 13 , a bending test device 70 includes mandrels 71 and 72, a pair of jigs 73a and 73b, and a weight 74. The weight 74 is attached to one longitudinal end of the insulated stranded wire 2. In this test, the mass of the weight 74 was set to 100 g. The pair of jigs 73a and 73b sandwich the insulated stranded wire 2. The mandrels 71 and 72, each having a cylindrical shape, are disposed between the weight 74 and the jigs 73a and 73b. An outer circumferential surface 711 of the mandrel 71 and an outer circumferential surface 721 of the mandrel 72 contact the outer circumferential surface of the insulated stranded wire 2. The longitudinal direction of the mandrels 71 and 72 is perpendicular to the longitudinal direction of the insulated stranded wire 2. The diameter Q of the mandrels 71 and 72 is 20 mm (see FIGS. 14 and 15). The state shown in FIG. 13 is the initial state. Then, the test is carried out as follows.

[0055] 13 to 15, first, the insulated stranded wire 2 is １ At this time, the insulated stranded wires 2 are bent along the outer peripheral surface 711 of the mandrel 71 as shown in FIG. １ Next, after returning to the initial state shown in FIG. 13, the insulated stranded wire 2 is rotated in the direction indicated by the arrow R in FIG. ２ At this time, the insulated stranded wires 2 are bent along the outer peripheral surface 721 of the mandrel 72 as shown in FIG. ２ The angle of bending was 90°. The above operation was repeated, and the number of times that each sample could be bent until the stranded wire 1 in the insulated stranded wire 2 broke was investigated.

[0056] Table 1 shows the results of the above experiments (1) and (2).

[0057]

[0058] Twist pitch / d of the child strands in Table 1 ２ The state where the value in the column is ∞ (infinity) means that the wires that make up the child strand are not twisted, that is, the wires are arranged parallel to the longitudinal direction of the child strand. Also, the notation "No break" in the column for the number of flexes until break in Table 1 means that no break occurred after 10 million flexes, and the test was discontinued.

[0059] Referring to Table 1, the twist pitch / d of the child strand ２ The strength of the joints of Samples A to C, in which the value of (the diameter of the circumscribed circle of the child stranded wire) is 40 or less, which is within the range of the present disclosure, is ２ The value of d clearly exceeds the strength of the connection of samples D, E, H, K, N and Q, which are outside the scope of the present disclosure. This is thought to be because cracking of the core wire 101 when connected to the crimp terminal 80 is suppressed. １ Samples F and G, which have a diameter of the circumscribed circle of the stranded wire outside the range of 5 to 20 inclusive of the present disclosure, fractured early, whereas the other samples did not fracture even after 10 million repeated flexes. Furthermore, sample G had significant unevenness on the surface of the stranded wire 1, which resulted in poor insulation. The above experimental results confirm that the stranded wire, insulated wire, and cable of the present disclosure not only improve flex resistance but also suppress cracking of the core wire when connected to a crimp terminal.

[0060] It should be understood that the embodiments and examples disclosed herein are illustrative in all respects and are not limiting in any respect. The scope of the present invention is defined not by the above description but by the scope of the claims, and it is intended to include all modifications within the meaning and scope of the claims.

[0061] REFERENCE SIGNS LIST 1 Stranded wire, 1A Outer periphery, 2 Insulated stranded wire, 3 Insulated wire, 4 Insulating layer, 4A Outer periphery, 5 Shield portion, 5A Outer periphery, 6 Outer sheath layer, 9 Core, 10 Child stranded wire, 10A Central child stranded wire, 10B First peripheral child stranded wire, 10C Second peripheral child stranded wire, 11 Insulating layer, 12 Insulating layer, 70 Bending test device, 71 Mandrel, 72 Mandrel, 73a Jig, 73b Jig, 80 Crimp terminal, 81 Conductor barrel, 82 Insulation barrel, 83 Main body, 91 First chuck, 92 Second chuck, 100 Wire, 100A Central wire, 100B First peripheral wire, 101 Core wire, 101A Surface, 102 Coating layer, 300 Cable, 400 Cable, 711 Outer surface, 721 Outer surface, P Twist pitch, R １ Arrow, R ２ Arrow, θ １ Maximum bending angle, θ ２ Maximum bending angle.

Claims

1. A stranded wire in which a plurality of child strands are twisted together, Each of the child strands has the same structure in which a plurality of wires, each of which has a circular cross-sectional shape perpendicular to the longitudinal direction and has the same diameter, are twisted together, The wire is A steel core wire, A coating layer made of copper or a copper alloy that covers a surface of the core wire, The twist pitch of the child strands is 40 times or more the diameter of a circumscribing circle of the child strands, A twist pitch of the twisted wire is 5 to 20 times the diameter of a circumscribing circle of the twisted wire.

2. 2. The stranded wire according to claim 1, wherein the diameter of the strands is not less than 0.02 mm and not more than 0.09 mm.

3. The stranded wire according to claim 1 , wherein the tensile strength of the core wire is 1800 MPa or more and 4500 MPa or less.

4. 2. The stranded wire according to claim 1, wherein the carbon content of the steel constituting the core wire is 0.70 mass % or more and 0.95 mass % or less.

5. 2. The stranded wire according to claim 1, wherein an area of ​​the coating layer relative to an area of ​​the wires in a cross section perpendicular to a longitudinal direction of the wires is 20% or more and 80% or less.

6. A stranded wire in which a plurality of child strands are twisted together, Each of the child strands has the same structure in which a plurality of wires, each of which has a circular cross-sectional shape perpendicular to the longitudinal direction and has the same diameter, are twisted together, The wire is A steel core wire, A coating layer made of copper or a copper alloy that covers a surface of the core wire, The twist pitch of the child strands is 40 times or more the diameter of a circumscribing circle of the child strands, The twist pitch of the twisted wire is 5 to 20 times the diameter of the circumscribing circle of the twisted wire, The diameter of the core wire is 0.02 mm or more and 0.09 mm or less, The tensile strength of the core wire is 1800 MPa or more and 4500 MPa or less, The carbon content of the steel constituting the core wire is 0.70% by mass or more and 0.95% by mass or less, In a cross section perpendicular to the longitudinal direction of the wire, the area of ​​the coating layer is 20% or more and 80% or less of the area of ​​the wire, The plurality of child strands have, in a cross section perpendicular to the longitudinal direction of the strand, a central strand disposed at the center; six first peripheral strands arranged in contact with the central strand so as to surround the outer circumferential side of the central strand; Each of the child strands is a strand including 2 to 20 of the wires.

7. A stranded wire in which a plurality of child strands are twisted together, Each of the child strands has the same structure in which a plurality of wires, each of which has a circular cross-sectional shape perpendicular to the longitudinal direction and has the same diameter, are twisted together, The wire is A steel core wire, A coating layer made of copper or a copper alloy that covers a surface of the core wire, The twist pitch of the child strands is 40 times or more the diameter of a circumscribing circle of the child strands, The twist pitch of the twisted wire is 5 to 20 times the diameter of the circumscribing circle of the twisted wire, The diameter of the core wire is 0.02 mm or more and 0.09 mm or less, The tensile strength of the core wire is 1800 MPa or more and 4500 MPa or less, The carbon content of the steel constituting the core wire is 0.70% by mass or more and 0.95% by mass or less, In a cross section perpendicular to the longitudinal direction of the wire, the area of ​​the coating layer is 20% or more and 80% or less of the area of ​​the wire, The plurality of child strands have, in a cross section perpendicular to the longitudinal direction of the strand, a central strand disposed at the center; six first peripheral strands arranged in contact with the central strand so as to surround an outer circumferential side of the central strand; twelve second peripheral strands arranged in contact with the first peripheral strands on the outer circumferential side of the region in which the first peripheral strands are arranged, Each of the child strands is a strand including 2 to 20 of the wires.

8. The stranded wire according to claim 1 , wherein the coating layer is a plating layer.

9. A stranded wire according to any one of claims 1 to 8; and an insulating layer covering an outer periphery of the stranded wire.

10. A core having a plurality of insulated stranded wires twisted together; a protective layer made of an insulating material covering the outer periphery of the core; Each of the insulated stranded wires comprises: A stranded wire according to any one of claims 1 to 8; and an insulating layer covering an outer periphery of the stranded wire.

11. The insulated wire according to claim 9 , a shield portion made of a conductive material and arranged to surround an outer periphery of the insulated wire; and an outer sheath layer made of an insulating material arranged to surround the outer periphery of the shield portion.

12. The insulated wire according to claim 10; a shield portion made of a conductive material and arranged to surround an outer periphery of the insulated wire; and an outer sheath layer made of an insulating material arranged to surround the outer periphery of the shield portion.