Communication cable, and wire harness

Abstract

Provided are: a communication cable in which the outer circumferences of a pair of conductors are collectively covered with an insulation coating and which can be firmly fixed to an external base material; and a wire harness provided with said communication cable.　A communication cable 1 comprises: a signal line 10 having a pair of conductors 11, 11 and an insulation coating 12 that integrally covers the outer circumferences of the conductors 11, 11; and a sheath 20 that covers the outer periphery of the signal line 10. The signal line 10 is formed such that: the entire assembly including the conductors 11, 11 and the insulation coating 20 are twisted; the conductors 11, 11 are in a state of spirally crossing each other with the insulation coating 20 therebetween; and regarding the smoothness of surfaces along a parallel direction in which the conductors 11, 11 are arranged in parallel with each other, the smoothness on the outer peripheral surface of the sheath 20 is higher than that on the outer peripheral surface of the signal line 10.

Description

Communication wires and wiring harnesses

[0001] The present disclosure relates to communication wires and wire harnesses.

[0002] In some cases, a wire harness is constructed by fixing electric wires to the surface of a sheet material made of a resin sheet or a nonwoven fabric in order to assemble a plurality of electric wires while maintaining a space-saving effect in the vertical direction. For example, Patent Document 1 discloses a form in which a wire harness in which electric wires are fixed to a sheet material by sewing or welding is arranged along a plate-like member included in an interior member of a vehicle. Among various electric wires, it is also considered that communication electric wires may be fixed to a sheet material and incorporated into a wire harness.

[0003] One type of communication wire that includes a pair of conductors and is used for transmitting differential signals is one in which the pair of conductors are arranged in parallel and an insulating coating is collectively provided on the outer peripheries of the conductors (two-core integrated wire). For example, Patent Documents 2 and 3 disclose such two-core integrated wires. As disclosed in these documents and Patent Document 4, there is also a form in which a helical twist is added to a two-core integrated wire in which an insulating coating is collectively provided on the outer peripheries of a pair of conductors.

[0004] Japanese Patent Application Laid-Open No. 2018-196174 Japanese Utility Model Application Laid-Open No. 60-123920 Japanese Patent Application Laid-Open No. 2003-36739 Japanese Patent Application Laid-Open No. 2015-191877

[0005] It is conceivable to construct a wire harness by fixing a communication electric wire consisting of a two-core integrated electric wire as disclosed in Patent Documents 2 to 4 to a substrate made of a nonwoven fabric or the like, as in the embodiment disclosed in Patent Document 1. However, in this case, an uneven structure may occur on the surface of the communication electric wire due to the shape of the pair of conductors, which may prevent the communication electric wire from being sufficiently firmly fixed to the substrate. In particular, when the two-core integrated electric wire is spirally twisted, the fixation to the substrate is likely to be incomplete, and this may have adverse effects. For example, FIG. 6 schematically shows a cross section of a two-core integrated electric wire 10 fixed to a substrate 30. In this case, the insulating coating 12 that collectively covers the pair of conductors 11, 11 may be firmly fixed to the substrate 30 in a region near one conductor 11 (below the conductor 11 on the left side of the figure) but may not be firmly fixed to the substrate 30 in a region near the other conductor 11. If the communication wire cannot be firmly fixed to the substrate near both of the pair of conductors in this way, not only will the wire harness be unable to stably hold the communication wire on the substrate, but the distance between the pair of conductors will vary along the axial direction of the communication wire, and the symmetry between the pair of conductors will be reduced, which may cause the communication wire to have unstable communication-related characteristics such as characteristic impedance or reduced noise resistance.

[0006] Therefore, an object of the present invention is to provide a communication electric wire in which the outer peripheries of a pair of conductors are collectively covered with an insulating coating and which can be firmly fixed to an external substrate, and a wire harness including such a communication electric wire.

[0007] The communication wire of the present disclosure comprises a signal wire having a pair of conductors and an insulating coating that integrally covers the outer periphery of the pair of conductors, and a sheath that covers the outer periphery of the signal wire, wherein the signal wire is formed by twisting the entire assembly including the pair of conductors and the insulating coating, so that the pair of conductors are spirally crossed with each other with the insulating coating sandwiched between them, and the smoothness of the surface along the parallel direction in which the pair of conductors are arranged side by side is higher at the outer surface of the sheath than at the outer surface of the signal wire.

[0008] The wire harness of the present disclosure includes the communication wires and a base material, and the communication wires are fixed to the base material on a surface along the parallel direction.

[0009] The communication electric wire and wire harness according to the present disclosure are communication electric wires in which the outer peripheries of a pair of conductors are collectively covered with an insulating coating, and are communication electric wires that can be firmly fixed to an external substrate, as well as wire harnesses that include such communication electric wires.

[0010] Fig. 1 is a plan view showing a communication electric wire according to an embodiment of the present disclosure. Fig. 2 is a cross-sectional view showing a cross section of the communication electric wire cut perpendicular to the axial direction. Fig. 3 is a plan view showing a two-core integrated parallel electric wire that is a raw material for manufacturing the communication electric wire. Fig. 4 is a plan view showing a wire harness according to an embodiment of the present disclosure. Fig. 5 is a cross-sectional view showing a location where the communication electric wire is fixed to a substrate in the wire harness. Fig. 6 is a cross-sectional view showing a state in which a communication electric wire without a sheath is fixed to a substrate. Figs. 7A and 7B show models for estimating the fixing strength of the communication electric wire to a substrate. Fig. 7A shows a case where no sheath is provided, and Fig. 7B shows a case where a sheath is provided.

[0011] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. A communication wire and a wire harness according to an embodiment of the present disclosure have the following configuration.

[0012] [1] A communication wire according to the present disclosure comprises a signal wire having a pair of conductors and an insulating coating that integrally covers the outer periphery of the pair of conductors, and a sheath that covers the outer periphery of the signal wire, wherein the signal wire is formed by twisting the entire assembly including the pair of conductors and the insulating coating, so that the pair of conductors are in a state of spirally crossing each other with the insulating coating sandwiched therebetween, and the smoothness of the surface along the parallel direction in which the pair of conductors are arranged side by side is higher at the outer surface of the sheath than at the outer surface of the signal wire.

[0013] In the above-mentioned communication electric wire, the signal wire is a two-core integrated electric wire in which the outer peripheries of a pair of conductors are collectively coated with an insulating coating. By twisting the two-core integrated electric wire, the communication electric wire achieves high stability of communication characteristics and high noise resistance. A sheath is provided around the outer periphery of the signal wire, and the outer surface of the sheath has a smoother surface along the parallel direction of the conductors than the outer surface of the signal wire. By providing a sheath with a highly smooth outer surface, when fixing the communication electric wire to the surface of a substrate, the communication electric wire can be easily fixed by contacting the surface of the substrate over a large area compared to when the communication electric wire does not have a sheath. This allows the communication electric wire to be fixed more firmly to the substrate compared to when the sheath is not provided. Furthermore, the communication electric wire can be easily fixed by contacting the surface of the substrate with high symmetry with respect to the pair of conductors. As a result, when the communication electric wire is fixed to the substrate, the communication electric wire is less likely to separate from the substrate, the twisted structure of the signal wire is stably maintained, and the stability and symmetry of the distance between the pair of conductors are kept high, so that the communication characteristics of the communication electric wire, such as the characteristic impedance, are stably maintained, and the noise resistance of the communication electric wire is also kept high.

[0014] [2] In the aspect [1] above, in a cross section of the communication electric cable taken perpendicular to the axial direction, the outer edge of the sheath may have a side along the parallel direction. This allows the outer surface of the sheath to contact the substrate over a large area, making it easier to secure the communication electric cable to the substrate particularly firmly. Furthermore, since the communication electric cable can be secured to the substrate with high symmetry at locations near each of the pair of conductors, this effectively maintains high symmetry between the pair of conductors even when secured to the substrate.

[0015] [3] In the above aspect [2], the sheath may have a rectangular shape or a rectangular shape with chamfered corners in a cross section of the communication electric wire taken perpendicular to the axial direction. In this case, when the communication electric wire and other electric wires are fixed side by side on the surface of the substrate, the distance between adjacent electric wires and the communication electric wire can be easily determined by the length of the sides of the rectangular cross section.

[0016] [4] A wire harness according to the present disclosure includes any one of the communication wires according to [1] to [3] above and a substrate, and the communication wires are fixed to the substrate on a surface along the parallel direction.

[0017] In the above-mentioned wire harness, the communication wire constituting the wire harness has a sheath with a smooth outer surface around the signal wire formed by twisting a two-core integrated wire, and the wire harness is fixed to the substrate at the outer surface of the sheath, resulting in a wire harness in which the communication wire is more firmly fixed to the substrate than in a wire harness without a sheath. Furthermore, since the communication wire is fixed to the substrate with high symmetry with respect to a pair of conductors, changes in the inter-conductor distance due to loosening of the twisted structure of the signal wire and decreases in symmetry between the pair of conductors are less likely to occur. As a result, the communication characteristics of the communication wire can be stably maintained over a long period of time, and the communication wire results in a wire harness with high noise resistance.

[0018] [5] In the aspect of [4] above, the substrate may be made of a nonwoven fabric, and the communication wires may be fixed to the substrate by fusion bonding. This allows the wire harness to maintain high flexibility even when the communication wires are firmly fixed to the substrate, improving the ease of handling of the wire harness. Furthermore, the communication wires can be easily and firmly fixed to the substrate.

[0019] [6] In the above-mentioned aspects [4] or [5], the substrate and the sheath may contain the same type of organic polymer and be fused to each other. By containing the same type of organic polymer in the substrate and the sheath, high fixing strength can be obtained at the fusion point between the substrate and the communication cable. Furthermore, in many cases, the additives added to the same type of organic polymer are the same or similar, so that migration of additives, such as plasticizers, through the fusion point between the sheath and the substrate is less likely to occur.

[0020] [Details of Embodiments of the Present Disclosure] The communication wires and wire harnesses according to the embodiments of the present disclosure will be described in detail below with reference to the drawings. The wire harnesses according to the embodiments of the present disclosure are configured to include the communication wires according to the embodiments of the present disclosure. In this specification, terms indicating the shape or arrangement of components, such as "parallel," "straight," and "rectangle," are intended to include not only strict geometrical concepts but also tolerances within a generally acceptable range for communication wires and wire harnesses, such as approximately ±15% in length and approximately ±15° in angle.

[0021] <Configuration of communication wire> First, a communication wire according to an embodiment of the present disclosure will be described. Fig. 1 shows a plan view of a communication wire 1 according to one embodiment of the present disclosure. Fig. 2 shows a cross section of the communication wire 1 taken perpendicular to the axial direction (longitudinal direction).

[0022] The communication electric wire 1 includes a signal wire 10 and a sheath 20. The sheath 20 covers the outer periphery of the signal wire 10. In FIG. 1 , the sheath 20 is removed at one end to allow the signal wire 10 to be seen. The communication electric wire 1 may include components other than the signal wire 10 and the sheath 20. However, from the viewpoint of enhancing the effect of the sheath 20 (described later), it is preferable that no other components be provided between the signal wire 10 and the sheath 20 or on the outer periphery of the sheath 20. Hereinafter, in this specification, the term "cross section" refers to a cross section perpendicular to the axial direction of the communication electric wire 1. Furthermore, relative directions such as the horizontal direction and the vertical direction correspond to the directions shown in the cross-sectional view of FIG. 2. In other words, the horizontal direction refers to the parallel direction in which a pair of conductors 11, 11 (described below) are arranged in parallel with each other, and the vertical direction refers to the direction perpendicular to the horizontal direction in the cross section.

[0023] The signal line 10 is an electric wire for transmitting differential signals and includes a pair of conductors 11 and an insulating coating 12. The insulating coating 12 integrally covers the outer peripheries of the pair of conductors 11, so that the signal line 10 is configured as a two-core integrated electric wire. In other words, the insulating coating 12 covers the outer peripheries of each of the pair of conductors 11, and the portions covering the outer peripheries of the conductors 11 are integrally continuous with each other. The insulating coating 12 serves to insulate the pair of conductors 11 from each other and from the outside.

[0024] In the signal wire 10, the entire assembly including the pair of conductors 11 and the insulating coating 12 that collectively coats the conductors 11 is twisted, so that the pair of conductors 11 cross each other in a spiral shape with the insulating coating 12 sandwiched between them. That is, the signal wire 10 is configured such that an assembly of the conductors 11 and the insulating coating 12 is formed as a two-core integrated parallel electric wire in which the insulating coating 12 is formed around the outer peripheries of the conductors 11 arranged in parallel (shown in a plan view in FIG. 3 ), and then the entire assembly is twisted. As described above, the parallel direction (horizontal direction) refers to the direction in which the pair of conductors 11 are arranged in parallel with each other. However, strictly speaking, due to the twisted structure of the two-core integrated electric wire, the direction connecting the centers of gravity of the two conductors 11 changes along the axial direction. In a state where the two conductors 11 are not twisted (untwisted), the parallel direction corresponds to the direction connecting the centers of gravity of the two conductors 11. In a state where the two conductors 11 are twisted, the parallel direction corresponds to the direction connecting the centers of gravity of the two conductors 11 at the midpoint between two adjacent intersections of the two conductors 11.

[0025] The signal wire 10 employs a two-core integrated structure in which a pair of conductors 11, 11 are collectively coated with a common insulating coating 12, thereby simplifying the structure of the signal wire 10 and maintaining a stable inter-wire distance between the pair of conductors 11, 11, thereby improving the stability of communication-related characteristics such as characteristic impedance. Furthermore, twisting the two-core integrated electric wire increases the symmetry of the pair of conductors 11, 11, suppressing common-mode noise and thereby improving the noise resistance of the signal wire 10. Furthermore, the signal wire 10 has high bending resistance, making it less likely that communication-related characteristics such as characteristic impedance will change when bent.

[0026] Each conductor 11 included in the signal wire 10 may be made of any conductive material, with suitable examples including metal materials such as copper, copper alloy, aluminum, and aluminum alloy. Each conductor 11 may be made of a single wire, but from the viewpoints of ease of twisting the two-core integrated electric wire and the bending flexibility of the signal wire 10, it is preferable that the conductor 11 be made of a twisted wire in which multiple wires 11a are twisted together. In this case, after twisting the multiple wires 11a, compression molding may be performed to form a compressed twisted wire as shown in FIG. 2. The multiple wires 11a constituting the conductor 11 may all be the same wire, or may be made of two or more types of wire. The size of the conductor 11 is not particularly limited, but from the viewpoints of suitability as a communication electric wire, it is preferable that the size of the conductor 11 be 0.01 mm or less. ２ That's it, and 0.22mm ２ The following ranges can be exemplified:

[0027] The constituent material of the insulating coating 12 is not particularly limited, and the insulating coating 12 can be formed using various organic polymers. Examples of organic polymers that can form the insulating coating 12 include polyolefins such as polyethylene and polypropylene, halogen-based polymers such as polyvinyl chloride, engineering plastics such as polystyrene, polytetrafluoroethylene, and polyphenylene sulfide, various elastomers, rubber, etc. The organic polymers can be used alone or in combination of two or more types by mixing, laminating, etc. The organic polymers can be crosslinked or foamed. In addition to the organic polymer, the insulating coating 12 can also contain additives such as flame retardants as appropriate.

[0028] In the signal wire 10, the thickness of the insulating coating 12 is not particularly limited, but an example is one in which the thickness is 0.1 mm or more and 0.3 mm or less at locations other than between the conductors 11. In the signal wire 10, the insulating coating 12 has a portion covering the outer periphery of one conductor 11 and a portion covering the outer periphery of the other conductor 11, and as long as these two portions are integrally continuous, the insulating coating 12 may have any specific shape and be formed by any specific method. For example, a two-core integrated electric wire may be formed by arranging two insulated electric wires each provided with an insulating coating that covers the entire periphery of one conductor 11 side by side, contacting the two insulated electric wires, and fusing the contact points of the two insulated electric wires. However, from the viewpoint of structural stability of the signal wire 10, it is preferable to form the insulating coating 12 by integrally extruding a coating material that occupies the space between and around the outer periphery of a pair of parallel conductors 11.

[0029] The overall external shape of the signal wire 10 is not particularly limited. However, as shown in the cross-sectional view of FIG. 2 , it is preferable that the outer surface of the insulating coating 12 has a substantially arc-shaped region that reflects the shape of the conductors 11, 11, which have a substantially circular cross section. In other words, it is preferable that, in the cross section, the outer edge of the insulating coating 12 has a substantially arc-shaped region except for the portion between the pair of conductors 11, 11, and that the upper and lower outer edges of the insulating coating 12 have an inwardly constricted shape (represented by 10a in the figure) between the pair of conductors 11, 11. Providing this constricted portion 10a facilitates twisting the signal wire 10 configured as a two-core integrated electric wire. The twist pitch of the signal wire 10 is not particularly limited. However, from the viewpoint of suitability as a communication electric wire, a range of 5 mm or more and 50 mm or less can be exemplified.

[0030] The sheath 20 is provided on the communication cable 1 as a covering member that covers the outer periphery of the signal wire 10. The sheath 20 integrally covers the entire periphery of the signal wire 10. It is preferable that the sheath 20 be in close contact with the entire outer periphery of the signal wire 10, except for areas where an unavoidable gap occurs between the signal wire 10 and the sheath 20.

[0031] The material of the sheath 20 is not particularly limited, and the same materials as those listed for the insulating coating 12 of the signal wire 10 can be used. That is, the sheath 20 can be made of organic polymers such as polyolefins (e.g., polyethylene, polypropylene, etc.), halogen-based polymers (e.g., polyvinyl chloride, etc.), engineering plastics (e.g., polystyrene, polytetrafluoroethylene, polyphenylene sulfide, etc.), various elastomers, and rubber. The organic polymers may be used alone or in combination of two or more types by mixing, laminating, etc. The organic polymers may be crosslinked or foamed. In addition to the organic polymer, the sheath 20 may also contain additives such as flame retardants, as appropriate. As described above, it is preferable not to place other components between the signal wire 10 and the sheath 20. However, it is also preferable to form the sheath 20 after disposing a release agent containing an inorganic powder material (e.g., talc) around the outer periphery of the signal wire 10.

[0032] The sheath 20 has a highly smooth outer surface. Specifically, the smoothness of the surface along the parallel direction (lateral direction) of the pair of conductors 11, 11 is higher on the outer surface of the sheath 20 than on the outer surface of the signal wire 10. That is, in cross section, the smoothness of the upper and lower outer edges of the sheath 20 is higher than the smoothness of the upper and lower outer edges of the signal wire 10 located inside the sheath 20. In other words, the difference in height at the outer edges is smaller on the upper and lower outer edges of the sheath 20 than on the upper and lower outer edges of the signal wire 10. As described above, the outer surface of the signal wire 10 has a constricted portion 10a between the pair of conductors 11, 11. However, the outer surface of the sheath 20 does not have such an inwardly constricted structure of the upper and lower outer edges, or has only a shallower unevenness structure than the constricted portion 10a of the signal wire 10. The specific degree of smoothness of the outer peripheral surface of the sheath 20 is not particularly limited, but it is preferable that the difference in height between the upper and lower outer edges of the sheath 20 in cross section (the distance in the vertical direction between the outermost and innermost points of each outer edge) be 30% or less of the difference in height between the upper and lower outer edges of the signal wire 10. It is also preferable that the difference in height between the upper and lower outer edges of the sheath 20 in cross section be 10% or less of the height (dimension in the vertical direction) of the signal wire 10. The smoother the outer peripheral surface of the sheath 20, the better, and there is no particular lower limit to these numerical values.

[0033] The high smoothness of the outer peripheral surface of the sheath 20 on both the top and bottom surfaces facilitates ensuring a larger contact area of ​​the communication wire 1 with the surface of an external member, such as the substrate 30, compared to when the sheath 20 is not provided around the signal wire 10 or when the outer peripheral surface of the sheath 20 has low smoothness, as will be described in detail later with respect to the wire harness 3. This increases the strength and stability of the fixation when the communication wire 1 is fixed to the external member at the contact points. Furthermore, the communication wire 1 can be fixed with high uniformity near each of the pair of conductors 11, 11, making it easier to maintain symmetry between the pair of conductors 11, 11. The strength, stability, and uniformity of the fixation result in less loosening of the twisted structure of the signal wire 10, even when the communication wire 1 is fixed to the external member. As a result, the communication wire 1 can stably maintain communication-related characteristics, such as characteristic impedance, and achieve high noise resistance. In the first place, the effect of providing the sheath 20 around the outer periphery of the signal wire 10 is to suppress loosening of the twisted structure of the signal wire 10, and because the sheath 20 has a smooth outer surface, it is highly effective in suppressing loosening of the signal wire 10 even when the communication wire 1 is fixed to an external member.

[0034] As described above, the sheath 20 is not particularly limited in terms of its specific thickness or shape, as long as the upper and lower surfaces of the outer periphery have an outer periphery that is smoother than the upper and lower surfaces of the signal wire 10. However, from the viewpoint of effectively fulfilling the role of the sheath 20, such as smoothing the outer periphery of the entire communication cable 1, the average thickness is preferably 0.1 mm or more. On the other hand, from the viewpoint of ensuring space-saving of the communication cable 1, the average thickness is preferably 0.5 mm or less. Regarding the shape of the sheath 20, it is preferable that the outer edge of the sheath 20 has sides along the parallel direction in cross section, i.e., the upper and lower outer edges of the sheath 20, particularly the lower outer edge, extend linearly along the horizontal direction. Furthermore, it is preferable that the upper and lower outer edges are parallel to each other. In this way, the upper and lower outer edges of the sheath 20 extending linearly along the horizontal direction in cross section means that the outer periphery of the sheath 20 has a surface that can approximate a plane along the parallel direction of the conductors 11, 11, and this can enhance the effects of the smoothness of the sheath 20, such as improved fixation to external members. In particular, it is preferable that the cross-sectional shape of the sheath 20 has an outer shape that is rectangular or rectangular with chamfered (rounded) corners, as shown in Fig. 2. In this case, when the communication electric wire 1 is arranged next to other electric wires (including communication electric wires 1 of the same type) in a wire harness 3 or the like described below, the distance between adjacent electric wires can be clearly defined by the length of the sides of the rectangle.

[0035] <Configuration of Wire Harness> Next, a wire harness according to an embodiment of the present disclosure will be described. Fig. 4 shows a plan view of a wire harness 3 according to an embodiment of the present disclosure. Fig. 5 shows a cross section of the wire harness 3, taken perpendicular to the axial direction of the communication wire 1, in a region near where the communication wire 1 is disposed. In Fig. 4, as in Fig. 1, the sheath 20 of the communication wire 1 is omitted from the end portion.

[0036] The wire harness 3 according to the present embodiment includes the communication electric wire 1 according to the embodiment of the present disclosure described above and a substrate 30. The communication electric wire 1 is fixed to the substrate 30 on a surface along the parallel direction (lateral direction) of the conductors 11, 11, specifically on the lower surface. The wire harness 3 may include only one or more communication electric wires 1 according to the embodiment of the present disclosure. In the embodiment shown in FIG. 4 , the wire harness 3 includes two communication electric wires 1. Furthermore, the wire harness 3 may include other types of electric wires 5 in addition to the communication electric wire 1 according to the embodiment of the present disclosure. When the wire harness 3 includes multiple electric wires 1, 5 including the communication electric wire 1 of the present disclosure, the multiple electric wires 1, 5 are preferably arranged with their axial directions parallel to each other and fixed to a common substrate 30.

[0037] The base material 30 is not particularly limited in type as long as it has a surface on which the communication electric wire 1 and, if necessary, other types of electric wires 5 can be aligned and fixed. However, from the viewpoint of ensuring the routing of the wire harness 3, it is preferable that the base material 30 be composed of a sheet body, i.e., a flexible planar member. Examples of the sheet body that can be used include fabrics such as woven fabrics, nonwoven fabrics, and knitted fabrics, and resin sheets. The method of fixing the electric wires 1 and 5, including the communication electric wire 1, to the base material 30 is not particularly limited, and examples include fusion bonding, sewing, bonding using an adhesive or pressure-sensitive adhesive, and fixing using a fixing member such as a fastener. Among these, fixing the communication electric wire 1 by fusion bonding is preferable from the viewpoints of secure fixation, space-saving, and the number of fixing members required. Using a nonwoven fabric as the base material 30 makes it easy to fix the communication electric wire 1 firmly and easily using fusion bonding. When the communication cable 1 is fixed to the nonwoven fabric by fusion bonding, the communication cable 1 may sink deeply into the surface of the nonwoven fabric as a result of the fusion. However, from the viewpoint of not impairing the properties of the substrate 30 and from the viewpoint of obtaining a significant effect of increasing the fixing strength by the sheath 20, it is preferable to keep the contact depth, i.e., the length by which the position of the contact point between the communication cable 1 and the substrate 30 sinks downward relative to the surrounding surface of the substrate 30, to 10% or less of the thickness of the sheath 20 and 0.02 mm or less.

[0038] The constituent material of the substrate 30 is not particularly limited. However, when fusion bonding is used to secure the communication cable 1, it is preferable that the substrate 30 and the sheath 20 of the communication cable 1 contain the same type of organic polymer. Here, "containing the same type of organic polymer" refers to the organic polymers contained in each material containing the same type of monomer unit. Preferably, the organic polymer constituting the substrate 30 and the organic polymer constituting the sheath 20 of the communication cable 1 are the same. In this case, the strength of the fusion bond between the communication cable 1 and the substrate 30 is easily increased. Furthermore, since the same or similar additives are often added to the same type of organic polymer, migration of additives such as plasticizers and the resulting material denaturation between the substrate 30 and the sheath 20 of the communication cable 1 through the fusion joint is less likely to occur. For example, a preferred example is one in which both the organic polymer constituting the substrate 30 and the organic polymer constituting the sheath 20 of the communication cable 1 are polyvinyl chloride (PVC). In many cases, a plasticizer is added to PVC, and if both the substrate 30 and the sheath 20 are made of PVC containing a plasticizer, migration of the plasticizer through the fused portion is unlikely to occur.

[0039] As described above, in the wire harness 3 according to the present embodiment, the communication electric wire 1 includes a sheath 20 having a lower surface with a smoothness greater than that of the signal wire 10, and the communication electric wire 1 is fixed by contacting the lower surface of the sheath 20 with the substrate 30. Since the lower surface of the sheath 20 has high smoothness, the communication electric wire 1 contacts the substrate 30 over a large area and is fixed thereto, compared to when the signal wire 10, which is not covered by the sheath 20, is fixed directly to the substrate 30 or when the lower surface of the sheath 20 has low smoothness. In particular, if the lower surface of the sheath 20 is configured as a flat surface, the entire lower surface can contact the surface of the substrate 30 in a flat manner and be fixed thereto. This results in a wire harness 3 in which the signal wire 10 is firmly fixed to the substrate 30 over a large area. As a result, the signal wire 10 can be stably maintained fixed to the substrate 30 even when the wire harness 3 is bent during use or used for a long period of time.

[0040] If the signal wire 10 were directly fixed to the substrate 30 without being covered with the sheath 20, as described above, the conductors 11, 11 would have a generally circular cross-sectional shape, and therefore the outer peripheral surface of the signal wire 10, including the constricted portion 10a, would be exposed and have a low smoothness, making it difficult to ensure a large contact area with the substrate 30. As a result, the twisted structure of the signal wire 10 may gradually loosen when the wire harness is bent or used for a long period of time. In addition, as shown in FIG. 6 , the signal wire 10 is fixed to the substrate 30 only below one of the pair of conductors 11 (the left conductor 11 in the figure), and the signal wire 10 is not fixed to the substrate 30 or the fixing strength is low below the other conductor 11. This means that the fixing locations and / or fixing strengths of the pair of conductors 11, 11 are likely to be uneven at least in part of the axial direction of the communication electric cable. When this occurs, the twisted structure of the signal line 10 becomes more likely to loosen. Also, the symmetry between the pair of conductors 11, 11 becomes more likely to decrease. When the twisted structure of the signal line 10 loosens, the distance between the pair of conductors 11, 11 changes, destabilizing the communication characteristics of the signal line 10, such as the characteristic impedance. Furthermore, when the symmetry between the pair of conductors 11, 11 decreases, common-mode noise increases, and noise resistance decreases.

[0041] In contrast, in the wire harness 3 according to the present embodiment, the communication wire 1 is formed by covering the outer periphery of the signal wire 10 with the sheath 20. Furthermore, the communication wire 1 is firmly fixed to the substrate 30 by the smooth outer periphery of the sheath 20. Therefore, even when the wire harness 3 is bent or used for a long period of time, the twisted structure of the signal wire 10 is less likely to loosen. This stably maintains the inter-wire distance between the pair of conductors 11, 11, and also maintains high symmetry between the pair of conductors 11, 11. The signal wire 10 has a structure in which the twisting is added to a two-core integrated wire, which allows the signal wire 10 itself to be excellent in maintaining the inter-wire distance and symmetry between the pair of conductors 11, 11. However, by forming the sheath 20 and fixing the sheath 20 to the substrate 30 using the smooth surface of the sheath 20, these inherent properties of the signal wire 10 can be effectively utilized as properties of the wire harness 3. By stably maintaining the distance between the pair of conductors 11, 11, it is possible to stably maintain communication characteristics such as characteristic impedance in the communication electric cable 1. Furthermore, by maintaining a high degree of symmetry between the pair of conductors 11, 11, common mode noise is less likely to occur, and high noise resistance is achieved.

[0042] <Estimation of Fixing Strength of Communication Cable> Here, the change in the fixing strength of the communication cable to the substrate 30 depending on whether or not the sheath 20 is present is estimated by calculation. For the estimation, a model shown in cross section in FIGS. 7A and 7B was used. Here, ２ or 0.13 mm ２Two circular conductors 11 with a conductor cross-sectional area of ​​0.1 mm were arranged side by side, and an insulating coating 12 was integrally formed around the outer periphery of each conductor to form a signal wire 10. The distance between the conductors 11 was 0.35 mm, and the thickness of the insulating coating 12 was 0.2 mm in the region other than between the conductors. In the sheathless model shown in FIG. 7A , the signal wire 10 was used as a communication wire. On the other hand, in the sheathed model shown in FIG. 7B , sheaths 20 were provided above and below the signal wire 10 to form a communication wire. In reality, the sheath 20 surrounds the entire outer periphery of the signal wire 10, but here, to simplify the model, the sheath 20 was provided only above and below the signal wire 10. Specifically, the sheath 20 was configured to fill the upper and lower constrictions of the signal wire 10 so that the outer edge of the sheath 20 formed a tangent to the signal wire 10.

[0043] A model was created in which the two types of communication wires described above were fixed to a substrate 30 at their undersides. Specifically, a substrate 30, which simulates a nonwoven fabric, was placed below each communication wire, and contact was established at a contact depth of 0.01 mm. The length of the contact point where the substrate 30 and the surface of the communication wire are in contact was geometrically calculated as the contact distance, as indicated by the bold line in the figure. The contact depth of 0.01 mm is close to the contact depth actually observed when a conventional insulated wire with a generally circular cross section is fused to a nonwoven fabric. To calculate the contact distance, each contact point indicated by the bold line in the figure was decomposed into a straight portion and a curved portion, and the curved portion was approximated to an elliptical arc to calculate its length.

[0044] Furthermore, for each model, the fixing strength between the communication cable and the substrate 30 was estimated. ２ The fixing strength for each configuration was estimated as being proportional to the contact distance, with the fixing strength in this case being set to 1. The fact that a proportional relationship exists between the contact distance and the fixing strength was confirmed through a preliminary test in which the conductor cross-sectional area was changed and the fusion strength was measured for a configuration in which a conventional, generally circular insulated electric wire was fused to a nonwoven fabric.

[0045] Table 1 below summarizes the calculated values ​​of the conductor cross-sectional area, contact distance, and fixing strength for the case where the communication electric wire is not provided with the sheath 20 and for the case where the sheath 20 is provided.

[0046]

[0047] According to Table 1, it is confirmed that for any conductor cross-sectional area, the provision of the sheath 20 increases the contact area between the communication electric wire and the substrate 30 and also increases the fixing strength compared to when the sheath 20 is not provided. With the case where the sheath 20 is not provided as the reference, the fixing strength when the sheath 20 is provided is ２ In the case of 1.7 times, the conductor cross section is 0.13 mm ２ When the conductor cross-sectional area is large, the rate of increase in the fixing strength due to the installation of the sheath 20 is greater.

[0048] The present invention is not limited to the above-described embodiment, and various modifications are possible within the scope of the present invention.

[0049] REFERENCE SIGNS LIST 1 Communication wire 10 Signal wire (two-core integrated wire) 10a Necked portion 11 Conductor 11a Wire 12 Insulating coating 20 Sheath 3 Wire harness 30 Base material 5 Other types of wire

Claims

1. A communication electric wire comprising: a signal wire having a pair of conductors and an insulating coating integrally covering the outer circumference of the pair of conductors; and a sheath covering the outer circumference of the signal wire, wherein the signal wire is formed by twisting the entire assembly including the pair of conductors and the insulating coating, so that the pair of conductors are crossed in a spiral shape with the insulating coating sandwiched between them, and the smoothness of the surface along the parallel direction in which the pair of conductors are arranged in parallel is higher on the outer surface of the sheath than on the outer surface of the signal wire.

2. The communication electric wire according to claim 1, wherein, in a cross section of said communication electric wire cut perpendicular to the axial direction, the outer edge of said sheath has a side along said parallel direction.

3. The communication electric wire according to claim 2, wherein, in a cross section of the communication electric wire cut perpendicular to the axial direction, the sheath has an outer shape that is rectangular or has a rectangular shape with chamfered corners.

4. A wire harness comprising: a communication electric wire according to any one of claims 1 to 3; and a substrate, wherein the communication electric wire is fixed to the substrate on a surface along the parallel direction.

5. The wire harness according to claim 4, wherein the base material is made of a nonwoven fabric, and the communication electric wires are fixed to the base material by fusion bonding.

6. The wire harness according to claim 4, wherein the substrate and the sheath contain the same kind of organic polymer and are fused to each other.

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