Shielded electric wire

Abstract

A shielded electric wire (10) is provided with: a pair of core wires (11); a shielding metal foil (12) that surrounds the pair of core wires (11); and a cylindrical exterior body (13) that surrounds the pair of core wires (11) and the metal foil (12). In a cross section cut perpendicularly to the axis of the exterior body (13), when the maximum dimension of the core wire (11) in the alignment direction of the pair of core wires (11) is defined as a first dimension (17) and the maximum dimension of the core wire (11) in a direction orthogonal to the alignment direction is defined as a second dimension (18), the second dimension (18) is greater than the first dimension (17).

Description

Shielded wire

[0001] The present disclosure relates to shielded wire.

[0002] The two-core parallel shielded electric wire described in Patent Document 1 includes two insulated electric wires, a metal foil, a resin film, a shield braid, and an insulator. The resin film is wrapped around the outer periphery of the metal foil. The metal foil surrounds the outer periphery of the insulated electric wire. The shield braid covers the metal foil and the resin film. The insulator is arranged so as to be in contact with the outer periphery of the shield braid.

[0003] The shielded electric wire for communication described in Patent Document 2 includes a twisted pair wire and a conductive shield surrounding the outer periphery of the twisted pair wire. The twisted pair wire is formed by twisting together a pair of insulated electric wires.

[0004] JP 2022-188671 A JP 2017-183178 A

[0005] Generally, when there is an imbalance in the structure or length between the two core wires in a high-speed differential communication cable, a signal conversion from a differential signal to a common-mode signal, known as mode conversion, occurs. Excessive mode conversion can lead to communication failures, so it is necessary to minimize mode conversion. In particular, in shielded cables, in addition to the imbalance in the structure or length between the two core wires mentioned above, imbalance in the shield structure surrounding the core wires can also be a major factor in generating mode conversion.

[0006] In the case of Patent Document 1, the metal foil and the insulated wires can be tightly attached in the arranging direction of the two insulated wires. However, in the direction perpendicular to the arranging direction, a large gap is formed between the metal foil and the insulated wires, which may cause deformation of the metal foil in the gap. This makes it difficult to suppress the above-mentioned mode conversion.

[0007] In the case of Patent Document 2, it is possible to reduce the diameter of the shielded electric wire for communication while ensuring the required characteristic impedance value. However, the shielded electric wire for communication may be subjected to radially inward pressure during the braiding and winding process and the sheath extrusion process. If this radially inward pressure is excessive, as in Patent Document 1, a large gap may be formed in a direction perpendicular to the arrangement direction of the twisted pairs, and the shield (metal foil) may deform toward the gap.

[0008] Therefore, an object of the present disclosure is to provide a shielded wire that can suppress the occurrence of mode conversion.

[0009] The shielded electric wire of the present disclosure comprises a pair of core wires, a shielding metal foil surrounding the pair of core wires, and a cylindrical outer casing surrounding the pair of core wires and the metal foil, and in a cross section cut perpendicular to the axis of the outer casing, when the maximum dimension of the core wires in the arrangement direction of the pair of core wires is defined as a first dimension and the maximum dimension of the core wires in a direction perpendicular to the arrangement direction is defined as a second dimension, the second dimension is larger than the first dimension.

[0010] According to the present disclosure, it is possible to provide a shielded wire that can suppress the occurrence of mode conversion.

[0011] Fig. 1 is a side cross-sectional view of a shielded electric wire of embodiment 1. Fig. 2 is a cross-sectional view of the shielded electric wire of embodiment 1 taken along line A-A. Fig. 3 is a cross-sectional view of the shielded electric wire of embodiment 1 taken along line B-B. Fig. 4 is a cross-sectional view of a shielded electric wire of a reference example, showing a state in which the metal foil is deformed. Fig. 5 is a schematic view of the shielded electric wire of embodiment 1, showing the relationship between the core wire and the virtual core wire of embodiment 1.

[0012] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be described. A shielded electric wire of the present disclosure is: (1) a shielded electric wire including a pair of core wires, a shielding metal foil surrounding the pair of core wires, and a cylindrical outer casing surrounding the pair of core wires and the metal foil, wherein, in a cross section cut perpendicular to the axis of the outer casing, a first dimension is defined as a maximum dimension of the pair of core wires in an arrangement direction of the core wires, and a second dimension is defined as a maximum dimension of the core wires in a direction perpendicular to the arrangement direction, and the second dimension is larger than the first dimension.

[0013] The above-mentioned configuration (1) can reduce the space formed between the core wires and the outer casing in a direction perpendicular to the arrangement direction of the core wires, thereby reducing the space in which the metal foil can deform, thereby suppressing the occurrence of mode conversion.

[0014] (2) In the shielded electric wire described in (1) above, the direction originating from the center of the outer casing in the cross section is defined as the radial direction, and the points on the outer circumferential surfaces of the core wires at which the circumscribing lines circumscribing the pair of core wires come into contact are defined as outer contact points. A pair of imaginary core wires with circular cross sections each having a diameter that is half the inner diameter of the outer casing are virtually arranged in the same direction as the arranging direction within the outer casing, and the points on the outer circumferential surfaces of the imaginary core wires at which the circumscribing lines circumscribing the pair of virtual core wires come into contact are defined as imaginary outer contact points. In this case, it is preferable that the opposing distance between the outer contact points and the outer casing in the radial direction is narrower than the opposing distance between the imaginary outer contact points and the outer casing in the radial direction.

[0015] According to (2) above, the space formed between the core wire and the outer conductor in a direction perpendicular to the arrangement direction of the core wire can be made narrower than the space formed between the virtual core wire and the outer conductor in a direction perpendicular to the arrangement direction of the virtual core wire, thereby suppressing the occurrence of mode conversion.

[0016] (3) In the shielded electric wire described in (1) or (2) above, it is preferable that the pair of core wires constitute a twisted pair wire, the core wires are in line contact with each other in the cross section, and have a surface contact area in the longitudinal direction of the core wires.

[0017] According to the above (3), the planar contact areas of the core wires contact the twisted pair wires in the longitudinal direction, which prevents the core wires from shifting in a direction perpendicular to the arrangement direction. This makes it difficult for imbalance to occur in the structure between the core wires, and further reduces the occurrence of mode conversion.

[0018] (4) In the shielded electric wire described in (3) above, it is preferable that the pair of core wires are in contact with each other while being twisted in opposite directions around the axis of each of the core wires.

[0019] According to the above feature (4), the core wire can be brought into close contact with the mating core wire in a pressed state by the restoring force in the twisting back direction of the core wire itself, thereby further preventing the core wire from shifting out of position.

[0020] (5) In the shielded electric wire described in either (3) or (4) above, it is preferable that the maximum curvature of the outer surface of the core wire between the contact area with the metal foil and the outer tangent point is smaller than the minimum curvature of the outer surface of the core wire between the outer tangent point and the surface contact area.

[0021] According to the above (5), the space formed between the outer circumferential surface of the core wire and the outer casing can be narrowed from the curved portion from the contact area with the metal foil to the outer contact point, thereby making it possible to further reduce the space in which the metal foil can deform. [Details of the Embodiments of the Present Disclosure] Specific examples of the embodiments of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples, but is defined by the claims, and all modifications within the meaning and scope of the claims are intended to be included.

[0022] <Embodiment 1> A shielded electric wire 10 of embodiment 1 is exemplified as an STP electric wire (Shielded Twisted Pair Cable). As shown in Fig. 1 , the shielded electric wire 10 includes a pair of core wires 11, a metal foil 12, and an outer casing 13. The shielded electric wire 10 has a shape extending with its axis facing in the longitudinal direction.

[0023] The pair of core wires 11 are twisted pair wires 14, twisted together in a spiral shape. As shown in Fig. 2, each core wire 11 has a plurality of core wires 15 and an insulating coating 16. Each core wire 15 is a stranded wire made by twisting together wires made of conductive metal such as copper or aluminum. The insulating coating 16 covers the outer periphery of each core wire 15. The insulating coating 16 is made of synthetic resin and has insulating properties.

[0024] The core wires 11 are arranged side by side in a first direction (the X direction in FIGS. 2 and 3 ) inside the outer casing 13. Here, in a cross section (hereinafter simply referred to as a "cross section" unless otherwise specified) obtained by cutting each core wire 11 at an arbitrary position in the longitudinal direction of the shielded electric wire 10 (the outer casing 13), the maximum dimension of the core wire 11 in the first direction is defined as a first dimension 17. The maximum dimension of the core wire 11 in a second direction (the Y direction in FIGS. 2 and 3 ), which is a direction perpendicular to the first direction in the cross section, is defined as a second dimension 18. In this regard, in the first embodiment, the second dimension 18 is configured to be larger than the first dimension 17. In particular, the second dimension 18 is configured to be 1.1 times or more the first dimension 17.

[0025] The cross section of the core wire 11 may be an irregular cross section other than a perfect circle in which the second dimension 18 is greater than the first dimension 17, and the shape is not particularly limited. In the first embodiment, the cross section of the core wire 11 has an oval outer peripheral shape in which the second dimension 18 is longer than the first dimension 17. Specifically, in a cross section when the core wire 11 is disposed inside the outer casing 13, the core wire 11 has a straight portion 19 located radially toward the center of the outer casing 13 and extending linearly in the second direction, and a curved portion 20 extending radially outward from the outer casing 13 in an arc-like (major arc-like) shape. Both ends of the curved portion 20 and the straight portion 19 are connected to each other. The straight portions 19 of a pair of core wires 11 are in contact with each other along the second direction. The radially outer region of the curved portion 20 is in contact with the metal foil 12, as described below. However, the cross section of the core wire 11 is not limited to the above-mentioned oval shape, and may have an outer peripheral shape such as an ellipse, a semicircle, a track shape, a flat shape, a polygonal shape such as a rectangle, etc. Among these, the ellipse shape is not necessarily limited to an ellipse defined mathematically, and may be any shape that can be normally recognized as an ellipse.

[0026] As described above, each core wire 11 is twisted together in a spiral shape to form a twisted pair wire 14. Therefore, when each core wire 11 is viewed in the longitudinal direction, the first and second directions in the cross section of each core wire 11 change circumferentially as needed. For example, in the cross section of each core wire 11 in FIG. 2, which is a cross section taken along line A-A in FIG. 1, the first direction is the left-right direction and the second direction is the up-down direction. On the other hand, in the cross section of each core wire 11 in FIG. 3, which is a cross section taken along line B-B in FIG. 1, the first direction is the up-down direction and the second direction is the left-right direction. This is because each core wire 11 is wound 90 degrees (1 / 4 cycle) from the cross section of line A-A to the cross section of line B-B in FIG. 1.

[0027] As shown in FIG. 2 , the metal foil 12 is disposed so as to surround the outer periphery of the twisted pair wire 14. The metal foil 12 is disposed inside the exterior body 13. The metal foil 12 is made of a conductive metal such as copper or aluminum, and is configured as a thin paper-like or film-like member that may lose its shape over time. In the case of the first embodiment, the metal foil 12 is configured as a metal tape that is spirally wrapped around the twisted pair wire 14. However, the metal foil 12 may also be attached longitudinally to the twisted pair wire 14. As shown in FIGS. 2 and 3 , each core wire 11 has a contact portion 29 that contacts the metal foil 12 along the second direction. The contact portion 29 is the portion of the curved portion 20 that contacts the metal foil 12.

[0028] In the first embodiment, the exterior body 13 is composed of a braided wire 21 and a sheath 22. The braided wire 21 is formed by weaving together a plurality of conductive metal wires. The braided wire 21 has a hollow cylindrical shape. The metal foil 12 is disposed along the inner circumferential surface of the braided wire 21 as a whole.

[0029] The sheath 22 is made of synthetic resin and has insulating properties. The cross section (transverse cross section) of the sheath 22 has a circular, more specifically, perfect circular, outer peripheral shape. The sheath 22 surrounds the outer periphery of the braided wire 21. The braided wire 21 is arranged along the inner peripheral surface of the sheath 22 as a whole. The metal foil 12 is arranged between the twisted pair wire 14 and the braided wire 21. A space 23 is formed in the second direction between the braided wire 21 of the exterior body 13 and the twisted pair wire 14. Note that the exterior body 13 may not have the braided wire 21 and may be composed only of the sheath 22. In that case, the space is formed between the sheath 22 and the twisted pair wire 14.

[0030] (Manufacturing Method of Shielded Electric Wire 10) An example of a manufacturing method of the shielded electric wire 10 will be described. When manufacturing the core wire 11, first, a core wire 15 that will become a stranded wire is manufactured by twisting together a plurality of wires. Next, molten synthetic resin is extruded so as to cover the outer periphery of the core wire 15 in a tubular shape. After that, the synthetic resin is cooled and solidified. In this manner, the core wire 11 in which the outer periphery of the core wire 15 is covered with the insulating coating 16 is manufactured. In the case of the first embodiment, at this point, the cross section of the core wire 11 has an outer periphery that is a perfect circle.

[0031] Next, a description will be given of the manufacturing process of the twisted pair wire 14. Of the pair of core wires 11, one core wire 11 is twisted in one direction around its own axis, and the other core wire 11 is twisted in the other direction around its own axis. In other words, each core wire 11 is twisted in the opposite directions around its respective axis.

[0032] Next, the core wires 11 are twisted together in a spiral shape while maintaining their twisted state. When twisting the core wires 11, pressure is applied to each core wire 11 toward the center between the core wires 11. As a result, the core wires 11 are twisted together while being deformed into the oval cross-sectional outer circumferential shape shown in FIG. 2. In the case of the first embodiment, the distance between the centers of the core wires 11 is set to be equal to or close to the second dimension 18. As a result, each core wire 11 is formed with an oval cross-sectional outer circumferential shape in which the second dimension 18 is larger than the first dimension 17 over the entire length of the core wire 11.

[0033] By twisting the core wires 11 together, the core wires 11 form straight sections 19 in line contact with each other in cross section, and form surface contact regions 24 in surface contact in the longitudinal direction. The surface contact regions 24 are regions that extend continuously in a spiral shape in the longitudinal direction of the shielded electric wire 10. This makes it difficult for the core wires 11 to become misaligned with each other, thereby suppressing the occurrence of mode conversion resulting from the structure between the core wires 11. Furthermore, since the distance between the core wires 15 of each core wire 11 can be maintained constant in the longitudinal direction, it is also possible to suppress disturbances in the characteristic impedance.

[0034] Furthermore, since the core wires 11 are twisted in opposite directions, the restoring force of one core wire 11 in the untwisting direction of the other core wire 11 can press and tightly contact the surface contact region 24 of the other core wire 11. This further prevents the core wires 11 from shifting position.

[0035] After the twisted pair wire 14 is manufactured as described above, the metal foil 12 is wound spirally around the outer periphery of the twisted pair wire 14. At this time, as shown in Fig. 2, a space 23 is formed in the second direction between the twisted pair wire 14 and the braided wire 21. The space 23 corresponds to the spiral direction of the twisted pair wire 14 and is formed in the length direction of the twisted pair wire 14 while changing as needed in the circumferential direction.

[0036] Next, a plurality of metal wires are braided so as to surround the outer periphery of the twisted pair wires 14 wrapped with the metal foil 12. This forms a hollow, cylindrical braided wire 21. The twisted pair wires 14 and the metal foil 12 are housed inside the braided wire 21. Molten synthetic resin is then poured into a heated mold. The braided wire 21 on the twisted pair wires 14 is then inserted into the mold, and the molten synthetic resin is extruded so as to cover the outer periphery of the braided wire 21 in a tubular shape. The synthetic resin is then cooled with water or the like to solidify. This produces a shielded electric wire 10 in which the outer periphery of the braided wire 21 is covered with the sheath 22.

[0037] (Function of Shielded Electric Wire 10) Next, the function of the shielded electric wire 10 will be described in more detail. FIG. 4 shows a reference example different from the first embodiment. In the case of FIG. 4, the core wire is configured as a circular core wire 25 having a perfectly circular cross-sectional outer peripheral shape. Between each circular core wire 25 and the braided wire 26, a space 27 larger than the space 23 is formed in the second direction. The space 27 makes the area in which the metal foil 28 can deform larger than the space 23, so deformation of the metal foil 28 is likely to cause imbalance in the structure of the metal foil 28. Because deformation of the metal foil 28 cannot be controlled, manufacturing variations may cause mode conversion beyond the allowable limit. In contrast, in the first embodiment, the space 23 is smaller than the space 27, reducing the area in which the metal foil 12 can deform. This makes it difficult for the metal foil 12 to deform toward the space 23, thereby suppressing mode conversion.

[0038] FIG. 5 is a schematic diagram illustrating the shielded electric wire 10 of the first embodiment. In FIG. 5, a pair of imaginary core wires 30 (not components of the presently disclosed invention) with a diameter half the inner diameter of the outer casing 13 are virtually aligned in the first direction. Each imaginary core wire 30 has a perfectly circular cross section and an imaginary contact portion 31 that contacts the metal foil 12 along the second direction. As described above, each core wire 11 has an oval cross-sectional outer peripheral shape in which the second dimension 18 is greater than the first dimension 17. Therefore, the contact portion 29 is larger than the imaginary contact portion 31, and the metal foil 12 is tightly tensioned radially outward. This prevents the metal foil 12 from deforming toward the space 23 even when a large pressure is applied to the shielded electric wire 10 during the braided wire 21 winding process or the sheath 22 extrusion process. This stabilizes the structure of the metal foil 12.

[0039] Here, the point where the circumscribing line 32 contacts the outer peripheral surface of the core wire 11 is defined as an outer tangent point 33, and the point where the imaginary circumscribing line 34 contacts the outer peripheral surface of the imaginary core wire 30 is defined as an imaginary outer tangent point 35. In this case, the facing distance 36 between the outer tangent point 33 and the outer circumscribing body 13 in the radial direction of the outer circumscribing body 13 is smaller than the imaginary facing distance 37 between the imaginary outer tangent point 35 and the outer circumscribing body 13 in the radial direction. This also reduces the deformable space 23 of the metal foil 12, making it possible to suppress the occurrence of mode conversion.

[0040] Furthermore, in the case of the first embodiment, the maximum curvature of the curved portion 20 from the contact point 29 to the outer tangent point 33 in the cross section is smaller than the minimum curvature of the curved portion 20 from the outer tangent point 33 to the straight portion 19. This allows the proximity space 38 formed between the curved portion of the curved portion 20 from the outer tangent point 33 to the contact point 29 and the exterior body 13 to be smaller than the imaginary proximity space 39 formed between the curved portion of the imaginary core wire 30 from the imaginary outer tangent point 35 to the imaginary contact point 31 and the exterior body 13. In particular, in the case of the first embodiment, since the contact point 29 is larger than the imaginary contact point 31 as described above, each core wire 11 can be in close contact with the inner circumferential surface of the metal foil 12 for a long period, thereby strengthening the tension of the metal foil 12 radially outward. This stabilizes the structure of the metal foil 12 and further suppresses the occurrence of mode conversion.

[0041] [Other Embodiments of the Present Disclosure] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. In the above-described first embodiment, each core wire has a straight portion that is in line contact in cross section. In contrast, according to other embodiments, each core wire may be in point contact rather than line contact in cross section. Furthermore, according to other embodiments, each core wire may not be in contact with each other, and, for example, inclusions may be formed between each core wire.

[0042] In the first embodiment, the core wires are deformed into an oval shape when they are twisted together. In contrast, in other embodiments, the core wires are not necessarily deformed into an oval shape when they are twisted together. For example, the core wires may be twisted together after the cross-sectional outer peripheral shape of each core wire is deformed into an oval shape, or the core wires may be twisted together and then the cross-sectional outer peripheral shape of each core wire may be deformed into an oval shape.

[0043] In the first embodiment, each core wire has a contact portion that contacts the metal foil. In contrast, in other embodiments, each core wire does not need to be in contact with the metal foil. For example, an inclusion may be formed between each core wire and the metal foil.

[0044] Furthermore, in the present disclosure, when a pair of core wires constitute a twisted pair wire, the core wires are in line contact with each other in cross section, and have a surface contact area in the longitudinal direction of the core wires, the shielded wire may be configured as follows: The shielded wire is configured by a tubular braided wire in which the outer casing is braided to surround the twisted pair wire, and a tubular sheath surrounding the braided wire, and in cross section, the continuous contact area of ​​the outer surface of the core wire that is in continuous contact with the metal foil in the circumferential direction is shorter than the surface contact area.

[0045] A short continuous contact area between the core wire and the metal foil means that the force tightening the metal foil from the outer periphery during the braided wire weaving process is weak, thereby suppressing deformation of the metal foil caused by weaving the braided wire.

[0046] DESCRIPTION OF SYMBOLS 10...Shielded wire 11...Core wire 12...Metal foil 13...Outer body 14...Twisted pair wire 15...Core wire 16...Insulating coating 17...First dimension 18...Second dimension 19...Straight portion 20...Curved portion 21...Braided wire 22...Sheath 23...Space 24...Area contact area 25...Circular core wire 26...Braided wire 27...Space (reference example of Figure 4) 28...Metal foil 29...Contact portion 30...Imaginary core wire 31...Imaginary contact portion 32...Circumscribed line 33...Outer contact point 34...Imaginary circumscribed line 35...Imaginary outer contact point 36...Face-to-face distance 37...Imaginary face-to-face distance 38...Proximity space 39...Imaginary proximity space

Claims

1. A shielded electric wire comprising: a pair of core wires; a metal foil for shielding surrounding the pair of core wires; and a cylindrical exterior body surrounding the pair of core wires and the metal foil, wherein, in a cross section cut perpendicular to the axis of the exterior body, when the maximum dimension of the core wires in the direction in which the pair of core wires are aligned is defined as a first dimension and the maximum dimension of the core wires in a direction perpendicular to the direction in which the pair of core wires are aligned is defined as a second dimension, the second dimension is greater than the first dimension.

2. The shielded electric wire according to claim 1, wherein the direction originating from the center of the outer casing in the cross section is defined as the radial direction, and the points on the outer circumferential surface of the core wire in the cross section where a circumscribing line circumscribing the pair of core wires contact are defined as outer contact points, and a pair of imaginary core wires with circular cross sections whose diameter is half the inner diameter of the outer casing are imaginarily arranged in the same direction as the arranging direction within the outer casing, and the points on the outer circumferential surface of the imaginary core wires where a virtual circumscribing line circumscribing the pair of imaginary core wires contact are defined as imaginary outer contact points, and the opposing distance between the outer contact points and the outer casing in the radial direction is narrower than the opposing distance between the imaginary outer contact points and the outer casing in the radial direction.

3. The shielded electric wire according to claim 2, wherein the pair of core wires constitute a twisted pair wire, the core wires are in line contact with each other in the cross section, and have a surface contact area in the longitudinal direction of the core wires.

4. The shielded electric wire according to claim 3, wherein the pair of core wires are in contact with each other while twisted in opposite directions around the axis of each of the core wires.

5. A shielded electric wire as described in claim 3 or 4, wherein the maximum curvature of the outer surface of the core wire between the contact area with the metal foil and the outer contact point is smaller than the minimum curvature of the outer surface of the core wire between the outer contact point and the surface contact area.

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