2-core twisted shielded cable and wire harness

Abstract

To provide a two-core twisted shielded cable and a wire harness, easier to be trimmed, and capable of preventing a deterioration in transmission characteristics.SOLUTION: A two-core twisted shielded cable 1 includes: two insulated wires 10 having a conductor 11 and an insulator 12 covering the conductor 11, and twisted together; a metal foil shield 20 disposed lengthwise on a circumference of the two insulated wires 10; a metal braiding 30 disposed on a circumference of the metal foil shield 20; and a sheath 40 disposed on a circumference of the metal braiding 30. The metal foil shield 20 includes a film layer 21 and a metal layer 23. The film layer 21 has a thickness of 20 μm or less and ellipticity of 0.75 to 0.90, and is arranged lengthwise to the two insulated wires 10.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a two-core twisted shielded cable and a wire harness. [Background technology]

[0002] A two-core shielded cable for high-speed digital signal transmission has been proposed to improve the leakage attenuation characteristics when a differential signal is applied. This two-core shielded cable includes two electric wires, a metal foil shield around the electric wires, a metal braid on the metal foil shield, and a sheath on the metal braid. In this type of two-core shielded cable, the frequency of the signal to be transmitted is high, and considering the skin effect and return current, it is effective to have a metal foil shield with a smooth surface.

[0003] In this regard, a multi-core (three or more cores) shielded cable has been proposed (see, for example, Patent Documents 1 to 3). The shielded cable described in Patent Document 1 has a pair of electric wires shielded by a metal foil shield, and multiple pairs of shielded electric wires are arranged in a circle.

[0004] The shielded cable described in Patent Document 2 has a quad configuration in which four insulated wires (four-core wires) are twisted together, with a metal foil shield provided around the four-core wires, a two-core shielded cable provided around the outer periphery of that, and a sheath further provided around the outer periphery of that.

[0005] The shielded cable described in Patent Document 3 is configured by twisting three insulated electric wires (three-core wires) together, with a tubular member containing magnetic powder wound transversely (spirally wound) around the three core wires, and a sheath provided around the outer periphery.

[0006] Furthermore, the following two-core or one-core shielded cables have been proposed (see Patent Documents 4 and 5). The shielded cable described in Patent Document 4 has a configuration in which a metal foil shield is wound laterally (spiral-wrapped) around two insulated electric wires (two-core wires) arranged in parallel, and a resin tape is provided on the outer periphery.

[0007] Moreover, the shielded cable described in Patent Document 5 has a configuration in which a metal foil shield is attached vertically around a single insulated electric wire arranged in parallel, a two-core shielded cable is attached around the outer periphery of the shield, and a sheath is further attached around the outer periphery of the shield. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2015-72774 A [Patent Document 2] JP 2003-132743 A [Patent Document 3] JP 2015-153497 A [Patent Document 4] JP 2015-185527 A [Patent Document 5] JP 2007-265797 A Summary of the Invention [Problem to be solved by the invention]

[0009] Here, it is preferable that the metal foil shield of the shielded cable be easy to trim when processing the terminals. For this reason, it is preferable that the metal foil shield be attached vertically to the two inner insulated electric wires rather than spirally wound. This is because in the case of spiral winding, it becomes difficult to trim the lower part of the overlapping metal foil shield in the lap part of the spirally wound metal foil shield. Therefore, when considering trimming, it can be said that the metal foil shield is preferably attached vertically.

[0010] However, when a metal foil shield is placed vertically around two insulated wires, the metal foil shield tends to be placed along the two insulated wires, i.e., not in close contact with the wires, which makes the position of the metal foil shield relative to the insulated wires unstable and can easily degrade the transmission characteristics.

[0011] Therefore, in order to improve the transmission characteristics, it is considered to wrap the metal foil shield so that it is more closely attached to the two insulated electric wires even when they are vertically attached. However, in a two-core twisted shielded cable in which the two insulated electric wires are twisted, if the metal foil shield is attached too closely to the two insulated electric wires, the metal foil shield is likely to tear even with a slight bending of the cable. That is, in a two-core parallel shielded cable without twisting, since the two insulated electric wires are arranged in parallel, some slippage between the insulated electric wires and the metal foil shield can be expected when the cable is bent. In contrast, when the two insulated electric wires are twisted, even if slippage can be expected in the twist direction (spiral direction), the outside of the bend is stretched in the cable longitudinal direction when bending, and is stretched in a direction different from the direction in which slippage is expected, so that slippage between the two insulated electric wires and the metal foil shield cannot be expected and the metal foil shield is likely to tear. For this reason, in a two-core twisted shielded cable, if the metal foil shield is attached too tightly to the two insulated wires, the metal foil shield can be torn, reducing noise resistance and ultimately resulting in a deterioration of transmission characteristics.

[0012] The present invention has been made to solve these conventional problems, and an object of the invention is to provide a two-core twisted shielded cable and wire harness that is easier to trim and capable of suppressing deterioration of transmission characteristics. [Means for solving the problem]

[0013] The two-core twisted shielded cable according to the present invention comprises two insulated wires having a conductor and an insulator covering the conductor, the two insulated wires being twisted together, a metal foil shield provided longitudinally around the two insulated wires, a metal braid provided on the outer periphery of the metal foil shield, and a sheath provided on the outer periphery of the metal braid, the metal foil shield having a PET film layer and a metal layer, the sum of the thickness of the PET film layer and the thickness of the metal layer being 16 μm or more and 30 μm or less, and the thickness of the PET film layer being 12 The insulating layer 14 has an ellipticity of 0.75 to 0.90 and is attached longitudinally to the two insulated wires.

[0014] Moreover, a wire harness according to the present invention includes any one of the two-core twisted shielded cables described above, and another member adjacent to the two-core twisted shielded cable. Effect of the Invention

[0015] According to the present invention, it is possible to provide a two-core twisted shielded cable and a wire harness that are easier to trim and capable of suppressing deterioration of transmission characteristics. [Brief description of the drawings]

[0016] [Figure 1] 1 is a perspective view of a wire harness including a two-core twisted shielded cable according to an embodiment of the present invention. [Diagram 2] 2 is a perspective view showing the two-core twisted shielded cable shown in FIG. 1. [Diagram 3] 2 is a cross-sectional view showing the two-core twisted shielded cable shown in FIG. 1. [Figure 4] 1 is a table showing two-core twisted shielded cables according to Examples 1 to 3 and Comparative Example 1. [Diagram 5] 1 is a graph showing the transmission characteristics of two-core twisted shielded cables according to Examples 1 to 3 and Comparative Example 1. [Figure 6]1 is a graph showing the correlation between the thickness and ellipticity of a film layer of two-core twisted shielded cables according to Examples 1 to 3 and Comparative Example 1. [Figure 7] 10 is a graph showing the transmission characteristics of the two-core twisted shielded cable according to Example 2, illustrating the characteristic impedance. [Figure 8] 10 is a graph showing the transmission characteristics of the two-core twisted shielded cable according to Example 2, illustrating the insertion loss. [Figure 9] 10 is a graph showing the transmission characteristics of the two-core twisted shielded cable according to Example 2, illustrating the return loss. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The present invention will be described below along with preferred embodiments. Note that the present invention is not limited to the embodiments shown below, and can be modified as appropriate within the scope of the present invention. In addition, in the embodiments shown below, some configurations are omitted from illustration and description, but it goes without saying that publicly known or well-known technologies are appropriately applied to the details of the omitted technologies within the scope of the contents described below.

[0018] Fig. 1 is a perspective view of a wire harness including a two-core twisted shielded cable according to an embodiment of the present invention. As shown in Fig. 1, the wire harness WH includes a two-core twisted shielded cable 1 and another cable (other member) 100.

[0019] The other cable 100 is, for example, a thick electric wire such as a power line or a thin electric wire such as another signal line, and includes a conductor 101 and an insulator 102 that covers the conductor 101. The two-core twisted shielded cable 1 and the other cable 100 may be wound with a resin tape RT, or a corrugated tube (not shown), a terminal (not shown), a connector, etc. may be attached.

[0020] Fig. 2 is a perspective view showing the two-core twisted shielded cable 1 shown in Fig. 1, and Fig. 3 is a cross-sectional view showing the two-core twisted shielded cable 1 shown in Fig. 1. As shown in Figs. 2 and 3, the two-core twisted shielded cable 1 includes two insulated wires 10, a metal foil shield 20, a metal braid 30, and a sheath 40.

[0021] The insulated wire 10 includes a conductor 11 and an insulator 12 on the conductor 11, which are twisted together to form a spiral. The conductor 11 may be, for example, a soft copper wire, a silver-plated soft copper wire, a tin-plated soft copper wire, or a tin-plated copper alloy wire. In this embodiment, the conductor 11 is a stranded wire in which two or more (specifically, seven) element wires are twisted together, but this is not particularly limited, and the conductor 11 may be a single solid wire. Furthermore, the cross-sectional area of ​​the conductor 11 is assumed to be 0.22 sq. or less, but is not particularly limited thereto.

[0022] The insulator 12 is a member that covers the conductor 11, and is made of, for example, PE (polyethylene) or PP (polypropylene). The insulator 12 has, for example, a dielectric constant of 3.0 or less. The insulator 12 preferably has a thickness of 0.52 mm or less based on the following formula (1). TIFF0007649275000001.tif19118 Here, Z0 is the characteristic impedance, and for example, 100Ω is substituted. εe is the dielectric constant, and for example, the above-mentioned value of 3.0 or less is substituted. dw is the wire diameter constituting the conductor 11, and is assumed to be, for example, 0.16 mm. d is the outer diameter of the conductor 11, and is 0.48 mm when seven wires with a wire diameter of 0.16 mm are twisted. k1 is the conductor outer diameter coefficient, and is 0.939 in the above example. B is the center-to-center distance of the conductors 11 of the two insulated electric wires 10. For the insulator 12, the thickness is preferably 0.52 mm or less, as calculated by substituting the above values ​​into formula (1).

[0023] The metal foil shield 20 has a three-layer structure consisting of a film layer (PET film layer) 21, an adhesive layer 22 that bonds the film layer 21 and the metal layer 23 together, and the metal layer 23. The film layer 21 is a non-conductive resin film made of PET (polyethylene terephthalate) resin. Moreover, the film layer 21 is preferably a biaxially stretched film made by stretching in two directions, lengthwise and widthwise, at high temperatures. This is because it is possible to make the film layer 21 strong in both the lengthwise and widthwise directions and less likely to tear. Furthermore, in this embodiment, the film layer 21 has a thickness of 20 μm or less.

[0024] The metal layer 23 is a layer of conductive metal, and is made of a metal such as copper or aluminum. In this embodiment, the metal layer 23 preferably has a thickness of 20 μm or less. From the viewpoint of ensuring shielding performance, the metal layer 23 preferably has a thickness of 8 μm or more when made of copper, and preferably has a thickness of 10 μm or more when made of aluminum. For most metals, the metal layer 23 can exhibit sufficient shielding performance if it has a thickness of 10 μm or more. The metal foil shield 20 is vertically attached on the two insulated wires 10 so that the metal layer 23 is on the outside.

[0025] The metal braid 30 is formed by bundling a plurality of metal wires, such as soft copper wire, silver-plated soft copper wire, tin-plated soft copper wire, and tin-plated copper alloy wire, and weaving the bundles together. The metal wires may be plated fibers in which metal plating is applied to fibers. Furthermore, the metal braid 30 may be formed by collectively plating a plurality of metal wires to form a flat bundle, which is then woven together.

[0026] The sheath 40 is an insulator that covers the outer periphery of the metal braid 30. This sheath 40 is filled on the outer periphery of the metal foil shield 20 and the metal braid 30. That is, the sheath 40 is not a tube having a void inside, but is provided in a so-called solid state. Such a sheath 40 is provided around the insulated electric wire 10, the metal foil shield 20, and the metal braid 30 by solid extrusion of the composition. The sheath 40 is made of, for example, PE, PP, and PVC (polyvinyl chloride). Note that the sheath 40 is not limited to being solid, and may be configured in a tubular shape and disposed with a partial void with respect to the inner metal braid 30, or some other intermediate material may be provided in the void.

[0027] Here, in the two-core twisted shielded cable 1 according to this embodiment, the thickness of the film layer 21 is 20 μm or less, and the rigidity is suppressed to a certain degree. Therefore, when the metal foil shield 20 is placed vertically around the two insulated electric wires 10, the metal foil shield 20 can be wrapped around the two insulated electric wires 10 so as to conform to the shape of the two twisted insulated electric wires 10. This contributes to stabilizing the position of the metal foil shield 20 with respect to the two insulated electric wires 10. In particular, if the thickness of the film layer 21 is 20 μm or less, the metal layer 23 can be wrapped around the two insulated electric wires 10 so that the ellipticity (the ellipticity in a cross section perpendicular to the longitudinal direction, the same applies below) is 0.90 or less, as long as the metal layer 23 is not excessively thick.

[0028] In addition, in the two-core twisted shielded cable 1, the metal foil shield 20 is wound around the two insulated wires 10 with an ellipticity of 0.75 or more. This prevents the metal foil shield 20 from being wound around the two insulated wires 10 in an excessively tight contact state.

[0029] Next, examples and comparative examples of the two-core twisted shielded cable 1 according to this embodiment will be described. Fig. 4 is a table showing the two-core twisted shielded cables according to Examples 1 to 3 and Comparative Example 1. In the two-core twisted shielded cables according to Examples 1 to 3 and Comparative Example 1, the conductor was a stranded wire made by twisting together seven soft copper wires, and had a cross-sectional area of ​​0.13 sq. The outer diameter was 0.48 mm. The insulator was made of cross-linked polyolefin, and when coated on the conductor, the outer diameter was 1.22 mm.

[0030] The outer shield 1 was made of a metal foil shield with a metal layer thickness of 10 μm, and was attached vertically to the two insulated wires. The outer shield 2 was made of a braided shield made of metal wires. The sheath was made of flame-retardant polyolefin. With the above configuration, the two-core twisted shielded cables according to Examples 1 to 3 and Comparative Example 1 had a finished outer diameter of 3.8 mm.

[0031] In addition, the metal foil shield serving as the external shield 1 had a PET layer (film layer) thickness of 6 μm in Example 1, 12 μm in Example 2, 20 μm in Example 3, and 25 μm in Comparative Example 1.

[0032] Fig. 5 is a graph showing the transmission characteristics of the two-core twisted shielded cables according to Examples 1 to 3 and Comparative Example 1. As shown in Fig. 5, the results of Examples 1 to 3 satisfied the standard values ​​over the entire frequency range of 0.01 GHz or more and 1 GHz or less. In contrast, the results of Comparative Example 1 did not satisfy the standard values ​​in the range of more than 0.04 GHz to approximately 0.2 GHz. This is because the ellipticity in Comparative Example 1 did not reach 0.90 or less.

[0033] Fig. 6 is a graph showing the correlation between the thickness and ellipticity of the film layer of the two-core twisted shielded cables according to Examples 1 to 3 and Comparative Example 1. As shown in Fig. 6, in Examples 1 to 3, when the thickness of the film layer is 6 μm, 12 μm, and 20 μm, the ellipticity is 0.75, 0.83, and 0.90, respectively. Therefore, the ellipticity is 0.90 or less in all cases, and it can be said that the metal foil shield is wrapped to fit the shapes of the two insulated electric wires to some extent. Therefore, the transmission characteristics meet the standard values, as shown in Fig. 5.

[0034] On the other hand, the two-core twisted shielded cable of Comparative Example 1 had a film layer thickness of 25 μm and an ellipticity of more than 0.90. Therefore, the metal foil shield was not wrapped to fit the shapes of the two insulated wires, and the transmission characteristics did not satisfy the standard values, as shown in Figure 5.

[0035] In the example shown in Fig. 6, the thickness of the metal layer is 10 µm. However, although not shown, it was found that when the thickness of the film layer is 20 µm, even if the thickness of the metal layer is 40 µm, there is no problem in achieving an ellipticity of 0.90 or less depending on the winding method during vertical attachment. It was also found that, from the standpoint of ease in achieving an ellipticity of 0.90 or less, the thickness of the metal layer is preferably 20 µm or less.

[0036] In addition, a 180° bending test was performed on the two-core twisted shielded cables according to Examples 1 to 3 and Comparative Example 2 (wherein the thickness of the film layer of Comparative Example 1 was changed to 4 μm). In the 180° bending test, a weight W of 200 g was hung from one end (lower end) of the two-core twisted shielded cable, and the upper part of the two-core twisted shielded cable (slightly lower than the upper end) was sandwiched between a pair of mandrels M of φ30 mm. Next, the other end (upper end) of the two-core twisted shielded cable was repeatedly bent along the mandrels M so that the bending angle was 180°. The number of bendings at which the resistance value of the metal foil shield increased by 10% due to repeated bending was measured.

[0037] As a result, the number of times was about 400 in Example 1, about 500 in Example 2, and about 600 in Example 3, all of which exceeded 300. In contrast, the number of times was about 200 in Comparative Example 2, in which the film layer of the metal foil shield was 4 μm, which was less than 300. Therefore, it was confirmed that when the ellipticity was less than 0.75, the metal foil shield broke, causing a deterioration in noise resistance performance (deterioration in transmission characteristics).

[0038] Fig. 7 to Fig. 9 are graphs showing the transmission characteristics of the two-core twisted shielded cable according to Example 2, with Fig. 7 showing the characteristic impedance, Fig. 8 showing the insertion loss, and Fig. 9 showing the return loss. In Fig. 7 to Fig. 9, the dashed lines show standard values.

[0039] As shown in FIG. 7, the two-core twisted shielded cable in accordance with Example 2 maintained a characteristic impedance of approximately 100Ω, satisfying the standard value of 95Ω or more and 105Ω or less.

[0040] Moreover, as shown in FIG. 8, the two-core twisted shielded cable according to Example 2 exhibited small insertion loss over the entire frequency range from 1 MHz to 1000 MHz, satisfying the standard value.

[0041] Furthermore, as shown in FIG. 9, the two-core twisted shielded cable according to Example 2 exhibited small return loss over the entire frequency range from 1 MHz to 1000 MHz, satisfying the standard value.

[0042] In this way, according to the two-core twisted shielded cable 1 of the present embodiment, the metal foil shield 20 is provided by being vertically attached, which makes it easier to trim. In addition, since the thickness of the film layer 21 of the metal foil shield 20 is 20 μm or less and the ellipticity is 0.90 or less, the metal foil shield 20 adheres to the two insulated electric wires 10 to a certain extent, and the position is unlikely to become unstable, and deterioration of the transmission characteristics can be suppressed. Furthermore, since the metal foil shield 20 has an ellipticity of 0.75 or more, it does not adhere too closely to the two insulated electric wires 10, which leads to preventing the metal foil shield 20 from being easily torn when bending, and thus makes it possible to suppress deterioration of the transmission characteristics due to the breakage of the metal foil shield 20. Therefore, it is possible to provide a two-core twisted shielded cable 1 that is easier to trim and can suppress deterioration of the transmission characteristics.

[0043] Moreover, since the thickness of the metal layer 23 is 20 μm or less, it is possible to prevent a situation in which it becomes difficult to achieve an ellipticity of 0.90 or less due to the metal layer 23 being too thick.

[0044] Moreover, according to the wire harness WH according to the present embodiment, it is possible to provide a wire harness WH that is easier to trim and capable of suppressing deterioration of transmission characteristics.

[0045] The present invention has been described above based on an embodiment, but the present invention is not limited to the above embodiment, and modifications may be made or well-known and publicly known technologies may be combined without departing from the spirit of the present invention.

[0046] For example, in the above embodiment, the metal foil shield 20 in the two-core twisted shielded cable 1 is arranged so that the metal layer 23 faces outward, but this is not limiting and the metal layer 23 may face inward.

[0047] Furthermore, in the two-core twisted shielded cable 1 according to the present embodiment, it is assumed that the metal braid 30 is attached to a shielded connector, but the attachment target does not have to be a shielded connector. [Explanation of symbols]

[0048] 1: 2-core twisted shielded cable 10: Insulated wire 11: Conductor 12: Insulator 20: Metal foil shield 21: Film layer (PET film layer) 22: Adhesive layer 23: Metal layer 30: Metal braid 40: Sheath 100: Other cables (other parts) WH: Wire harness

Claims

1. Two insulated wires each having a conductor and an insulator covering the conductor, the two insulated wires being twisted together; A metal foil shield is provided vertically around the two insulated wires; a metal braid provided on an outer periphery of the metal foil shield; A sheath is provided around the outer periphery of the metal braid, The metal foil shield has a PET film layer and a metal layer, the sum of the thickness of the PET film layer and the thickness of the metal layer is 16 μm or more and 30 μm or less, the thickness of the PET film layer is 12 μm or less, and the ellipticity is 0.75 to 0.90, and the metal foil shield is attached longitudinally to the two insulated wires. A two-core twisted shielded cable.

2. The metal foil shield has a metal layer having a thickness of 20 μm or less.

2. The two-core twisted shielded cable according to claim 1.

3. A two-core twisted shielded cable according to claim 1 or 2, Another member adjacent to the two-core twisted shield cable; A wire harness comprising:

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