Two-core twisted shield cable

Abstract

To provide a two-core twisted shield cable capable of suppressing deterioration of transmission characteristics.SOLUTION: A two-core twisted shield cable comprises: two insulated wires 10 each of which has a conductor 11 and an insulator 12 covering the conductor 11; a metal foil shield 20 which is provided around the two insulated wires 10; and a sheath 40 which is provided for the outer periphery of the metal foil shield 20. In the case where a distance between the centers of the two insulated wires 10 is D, the twisting pitch of the two insulated wires 10 is wpitch, the dielectric constant of the insulator 12 is εr, and the magnetic permeability of vacuum is μr, a suck-out frequency f obtained by Formula 1 is 5GHz or more.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] Conventionally, a two-core twisted shielded cable has been proposed in which two insulated electric wires, each having a conductor and an insulator covering the conductor, are twisted together and a metal foil shield is provided on the two twisted insulated electric wires (see, for example, Patent Documents 1 and 2). Compared to a two-core parallel shielded cable in which the two cores are parallel and not twisted, such a two-core twisted shielded cable is not difficult to bend in a specific direction and has improved flexibility. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-61766 A [Patent Document 2] JP 2021-174742 A Summary of the Invention [Problem to be solved by the invention]

[0004] It is known that two-core twisted shielded cables suffer from suck-out (a large increase in attenuation at a specific frequency). For this reason, the transmission characteristics of two-core twisted shielded cables deteriorate drastically at a specific frequency (suck-out frequency).

[0005] 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 that is capable of suppressing deterioration of transmission characteristics. [Means for solving the problem]

[0006] A two-core twisted shielded cable according to the present invention has a conductor and an insulator covering the conductor, and comprises two insulated wires twisted together, a metal foil shield provided around the two insulated wires, and a sheath provided around the outer periphery of the metal foil shield, where D is the distance between the centers of the two insulated wires, wpitch is the twist pitch of the two insulated wires, εr is the dielectric constant of the insulator, and μr is the magnetic permeability of a vacuum,

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[0007] According to the present invention, it is possible to provide a two-core twisted shielded cable capable of suppressing deterioration of transmission characteristics. [Brief description of the drawings]

[0008] [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] 1 is a first graph showing the suckout frequency when the twist pitch of a two-core twisted shielded cable is changed. [Figure 4] 11 is a second graph showing the suckout frequency when the twist pitch of a two-core twisted shielded cable is changed. [Diagram 5] 1 is a graph showing the correlation between twist pitch and return loss. [Figure 6] 1 is a graph showing the suckout frequency when the winding pitch of the metal foil shield is changed. [Figure 7] 1 is a graph showing the suckout frequency when the winding pitch of the metal foil shield is fixed and only the dielectric constant is changed. [Figure 8]1 is a graph showing a correlation between foam diameter of an insulation material constituting an insulated wire and suck-out. [Figure 9] This is a graph showing the insertion loss before and after a long-term durability test, and shows the case where the conductor has a two-layer structure with an inner metal plated. [Figure 10] 1 is a graph showing insertion loss before and after a long-term durability test, showing a case in which the conductor has a single-layer structure without plating. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] 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.

[0010] 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 other members such as another cable O.

[0011] The other cable O 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 O1 and an insulator O2 that covers the conductor O1. The two-core twisted shielded cable 1 and the other cable O may be wound with a resin tape RT (other member), or a corrugated tube (other member: not shown), a terminal (other member: not shown), a connector (other member: not shown), or the like may be attached.

[0012] Fig. 2 is a perspective view showing the two-core twisted shielded cable 1 shown in Fig. 1. As shown in Fig. 2, 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.

[0013] The two insulated wires 10 each include a conductor 11 and an insulator 12 covering the conductor 11, which are twisted together to form a spiral. The conductor 11 may be, for example, a soft copper wire, an aluminum wire, a copper alloy wire, an aluminum alloy 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 formed of a twisted wire in which two or more (e.g., seven) element wires are twisted together, but this is not particularly limited, and the conductor 11 may be formed of a single 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.

[0014] Here, in this embodiment, the conductor 11 is preferably configured with a single-layer structure that is not plated. For this reason, it is preferable that the conductor 11 is configured with a soft copper wire, an aluminum wire, a copper alloy wire, or an aluminum alloy wire, rather than the silver-plated soft copper wire, the tin-plated soft copper wire, the tin-plated copper alloy wire, or the like, among the above examples.

[0015] The insulator 12 is a member that covers the conductor 11, and is made of, for example, PE (polyethylene) or PP (polypropylene), etc. The dielectric constant of the insulator 12 is optimized to satisfy the condition shown in formula (1) described later.

[0016] In this embodiment, the insulator 12 may be foamed to optimize the dielectric constant. In this case, the insulator 12 preferably has an average foaming diameter of 30 μm or less in the cross-sectional direction. If the average foaming diameter in the cross-sectional direction is 30 μm or less, the bubbles are unlikely to collapse when two insulated electric wires 10 are twisted together, and the distance between the two insulated electric wires 10, the dielectric constant, and other factors are unlikely to affect equation (1) described below.

[0017] Furthermore, it is preferable that the insulator 12 has an average foaming diameter of 60 μm or less in the longitudinal direction. When two insulated wires 10 are twisted together, the size of the bubbles in the cross-sectional direction has a large effect, but if the bubbles become too large in the longitudinal direction, the bubbles will be easily crushed in the cross-sectional direction. For this reason, it is more preferable that the insulator 12 has an average foaming diameter of 30 μm or less in the cross-sectional direction and an average foaming diameter of 60 μm or less in the longitudinal direction.

[0018] The average foam diameter was determined by cutting the insulator 12 of the insulated wire 10 (foam-foamed wire) in the cross-sectional and longitudinal directions, observing the cut surfaces with an electron microscope or an X-ray microscope, and measuring the diameters of a large number of bubbles (e.g., 300 or more).

[0019] The metal foil shield 20 is a shielding member that is provided around the two insulated wires 10 by being attached vertically or wound horizontally. The metal foil shield 20 has a three-layer structure, for example, including a PET (polyethylene terephthalate) film layer, a metal layer, and an adhesive layer located between the two layers to bond the PET film layer and the metal layer together. However, the present invention is not limited to this, and the metal foil shield 20 may simply have a one-layer structure consisting of a metal layer. When such a metal foil shield 20 is configured with multiple layers, such as the three-layer structure described above, it is provided on the two insulated wires 10 so that the metal layer is the outermost layer and comes into contact with the metal braid 30.

[0020] 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 weaving together a flat bundle of a plurality of metal wires that have been plated together. By providing the metal braid 30, the metal foil shield 20 is more closely attached to the two insulated wires 10.

[0021] The sheath 40 is an insulator provided on the outer periphery of the metal foil shield 20 and the metal braid 30. This sheath 40 is in a filled state on the outer periphery side of the metal foil shield 20 and the metal braid 30. That is, the sheath 40 is not a tube structure having a gap between it and the metal braid 30, 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 consisting of these. The sheath 40 is made of, for example, PE, PP, and PVC (polyvinyl chloride). Note that the sheath 40 is not limited to a solid state, and may be configured in a tube shape and disposed with a partial gap with respect to the inner metal braid 30, or some other intermediate material may be provided in the gap.

[0022] In the two-core twisted shielded cable 1 described above, when the distance between the centers of the two insulated electric wires 10 is D, the twist pitch of the two insulated electric wires 10 is wpitch, the dielectric constant of the insulator 12 is εr, and the magnetic permeability of a vacuum is μr,

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[0023] Here, the present inventors have found through various experiments and simulations that the suckout frequency f is determined by formula (1). It is generally known that suckout occurs in a two-core twisted shielded cable. However, the mechanism by which suckout occurs is only roughly understood, and the details have not been elucidated. For this reason, the present inventors have collected a large amount of data through various experiments and simulations, and have found formula (1) based on the large amount of data. As a result of verifying a large amount of data, the present inventors have found that the suckout frequency changes with the distance D between the centers of the two insulated electric wires 10, the twist pitch wpitch of the two insulated electric wires 10, and the dielectric constant εr of the insulator 12 as variables. In addition, when the two-core twisted shielded cable 1 is used as a communication line, if the suckout frequency f is set to 5 GHz or more, communication up to approximately 12 Gbps can be performed in the communication method NRZ (Non-Return-to-Zero) (extreme deterioration of transmission characteristics due to suckout can be suppressed). Therefore, by configuring the two-core twisted shielded cable 1 according to this embodiment so that the suckout frequency f obtained by formula (1) is 5 GHz or higher, it is possible to easily suppress deterioration of the transmission characteristics.

[0024] Furthermore, the twist pitch wpitch of the two insulated wires 10 is preferably 15 mm or more, because this makes it difficult for localized reductions in reflection loss to occur, making it easier to suppress deterioration of transmission characteristics.

[0025] In addition, in the two-core twisted shielded cable 1, the metal foil shield 20 may be either vertically attached or horizontally wound. If it is horizontally wound, it is preferable that the suckout frequency f calculated by the following formula (2) be 5 GHz or higher.

[0026]

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[0027] Next, the operation of the two-core twisted shielded cable 1 according to the present embodiment will be described. FIG. 3 is a graph showing the suckout frequency f when the twist pitch wpitch of the two-core twisted shielded cable 1 is changed. In FIG. 3, the solid line shows an example in which the twist pitch wpitch is 17 mm and the dielectric constant εr is 2.05, the dashed line shows an example in which the twist pitch wpitch is 20 mm and the dielectric constant εr is 1.55, and the dashed line shows an example in which the twist pitch wpitch is 22 mm and the dielectric constant εr is 1.87. In the example shown in FIG. 3, the distance D between the centers of the two insulated wires 10 is 1.22, and the magnetic permeability μr in vacuum is 0.000001256. The metal foil shield 20 is wound horizontally with a winding pitch mpitch of 13 mm.

[0028] As shown by the solid line, when the twist pitch wpitch was 17 mm and the dielectric constant εr was 2.05, the suckout frequency f was around 7.8 GHz. Also, as shown by the dashed line, when the twist pitch wpitch was 20 mm and the dielectric constant εr was 1.55, the suckout frequency f was around 6.4 GHz. On the other hand, as shown by the dashed line, when the twist pitch wpitch was 22 mm and the dielectric constant εr was 1.87, the suckout frequency f was around 4.6 GHz.

[0029] In this way, it can be said that the suckout frequency f changes depending on the factors shown in formula (1) (particularly, since the distance D is a fixed value in FIG. 3, it can be said that the suckout frequency f changes depending on the twist pitch wpitch and the dielectric constant εr). Therefore, by setting the suckout frequency f to 5 GHz or higher based on formula (1) (i.e., by using a 2-core twisted shielded cable 1 shown by the solid line and the dashed line in the example shown in FIG. 3), it is possible to easily suppress deterioration of the transmission characteristics.

[0030] Fig. 4 is a graph showing the suckout frequency f when the distance D of the two-core twisted shielded cable 1 is 1.54. In Fig. 4, the solid line shows an example where the twist pitch wpitch is 15 mm and the dielectric constant εr is 1.80, and the dashed line shows an example where the twist pitch wpitch is 14 mm and the dielectric constant εr is 1.70. Note that the vacuum permeability μr is also set to 0.000001256 in the example shown in Fig. 4. The metal foil shield 20 is wound horizontally and the winding pitch mpitch is 13 mm.

[0031] As shown by the solid line, when the twist pitch wpitch is 15 mm and the dielectric constant εr is 1.80, the suckout frequency f is around 7.38 GHz. Also, as shown by the dashed line, when the twist pitch wpitch is 14 mm and the dielectric constant εr is 1.70, the suckout frequency f is around 8.01 GHz.

[0032] In this way, even when the distance D is 1.54, it can be said that the suckout frequency f changes due to the factor shown in formula (1) (since the distance D is also a fixed value in FIG. 4, it can be said that the suckout frequency f changes due to the twist pitch wpitch and the dielectric constant εr).

[0033] In addition, when the distance D, twist pitch wpitch, and dielectric constant εr, which are the conditions of each of the 2-core twisted shielded cables described with reference to Figs. 3 and 4, are substituted into formula (1), the suckout frequencies approximately coincide with those shown in Figs. 3 and 4, respectively. Therefore, it can be said that the suckout frequency f changes depending on the factors (three factors) corresponding to the variables shown in formula (1).

[0034] Fig. 5 is a graph showing the correlation between the twist pitch wpitch and the return loss. In Fig. 5, the solid line shows the case where the twist pitch wpitch is 17 mm, the dashed line shows the case where the twist pitch wpitch is 15 mm, and the dashed line shows the case where the twist pitch wpitch is 14 mm.

[0035] As shown by the dashed line in FIG. 5, when the twist pitch wpitch is 14 mm, the return loss is locally decreased at a frequency of 2 GHz. On the other hand, when the twist pitch wpitch is 17 mm and when the twist pitch wpitch is 15 mm, such a localized decrease in return loss does not occur. Therefore, if the twist pitch wpitch is 15 mm or more, it is possible to avoid a localized decrease in return loss. This is because, if the twist pitch wpitch is too small, the insulator 12 of the insulated wire 10 is crushed. Therefore, in the two-core twisted shielded cable 1 according to this embodiment, in addition to satisfying formula (1), by setting the twist pitch wpitch to 15 mm or more, it is possible to further easily suppress the deterioration of the transmission characteristics.

[0036] Fig. 6 is a graph showing the suck-out frequency f when the winding pitch mpitch of the metal foil shield 20 is changed. In Fig. 6, the solid line shows the case where the winding pitch mpitch is 11 mm, the dashed line shows the case where the winding pitch mpitch is 13 mm, and the broken line shows the case where the winding pitch mpitch is 15 mm.

[0037] The two-core twisted shielded cables 1 shown by the solid line, the dashed line, and the broken line in FIG. 6 have the same conditions as those shown in formula (1) (for example, the twist pitch wpitch is 13 mm), and all of them have a suckout at a frequency f near 9 GHz. Furthermore, the two-core twisted shielded cable 1 shown by the solid line has a winding pitch mpitch of the metal foil shield 20 of 11 mm, and in addition to 9 GHz, a suckout based on formula (2) occurs, and this suckout frequency f is near 13.6 GHz. The two-core twisted shielded cable 1 shown by the dashed line has a winding pitch mpitch of the metal foil shield 20 of 13 mm, and in addition to 9 GHz, a suckout occurs near 12.1 GHz. Similarly, the two-core twisted shielded cable 1 shown by the broken line has a winding pitch mpitch of the metal foil shield 20 of 15 mm, and in addition to 9 GHz, a suckout occurs near 11.7 GHz.

[0038] Fig. 7 is a graph showing the suckout frequency f when the winding pitch mpitch of the metal foil shield 20 is fixed and only the dielectric constant εr is changed. In Fig. 7, the solid line shows the case where the dielectric constant εr is 1.88, and the dashed line shows the case where the dielectric constant εr is 1.78. The winding pitch mpitch condition is fixed at 13 mm. Furthermore, the two-core twisted shielded cables 1 shown by the solid and dashed lines in Fig. 7 are also uniform in terms of the twist pitch wpitch and distance D, which are the conditions shown in formula (1).

[0039] In the 2-core twisted shielded cable 1 shown by the solid line, in addition to the suckout based on formula (1) (the suckout frequency is not shown in the figure), there is also a suckout based on formula (2), with the suckout frequency f being around 11.9 GHz. Similarly, in the 2-core twisted shielded cable 1 shown by the dashed line, in addition to the suckout based on formula (1) (the suckout frequency is also not shown in the figure), there is also a suckout based on formula (2), with the suckout frequency f being around 12.1 GHz.

[0040] As described above, when the metal foil shield 20 is wound laterally, suckout occurs depending on the winding pitch mpitch and the dielectric constant εr of the metal foil shield 20. For this reason, it can be said that the two-core twisted shielded cable 1 according to this embodiment can further easily suppress deterioration of the transmission characteristics by setting the suckout frequency f calculated by formula (2) to 5 GHz or more.

[0041] Fig. 8 is a graph showing the correlation between the foam diameter and suck-out of the insulator 12 constituting the insulated wire 10. In Fig. 8, the solid line indicates the case where the average foam diameter in the cross-sectional direction is 30 µm or less and the average foam diameter in the longitudinal direction is 60 µm or less, and the dashed line indicates the case where the average foam diameter in the cross-sectional direction is 30 µm or less and the average foam diameter in the longitudinal direction is 70 µm.

[0042] As shown in Fig. 8, both two-core twisted shielded cables 1 have a twist pitch wpitch of 15 mm and a dielectric constant εr of the insulator 12 of 1.78. Other conditions are the same as those described with reference to Fig. 3. Therefore, for both two-core twisted shielded cables 1 shown in Fig. 8, the suckout frequency f calculated by formulas (1) and (2) exceeds 8 GHz. Therefore, as shown by the solid line in Fig. 8, the two-core twisted shielded cables 1 do not exhibit suckout in the region below 8 GHz.

[0043] In contrast, as shown by the dashed line in FIG. 8, when the average foaming diameter is 30 μm or less and the average foaming diameter in the longitudinal direction is 70 μm, the air bubbles are crushed depending on how the two insulated wires 10 are twisted, causing a change in the suckout frequency f, and the suckout frequency f becomes approximately 7.4 GHz.

[0044] Therefore, from the viewpoint of controlling the suckout frequency f and easily suppressing deterioration of the transmission characteristics, it was found that it is preferable that the average foam diameter in the cross-sectional direction is 30 μm or less and the average foam diameter in the longitudinal direction is 60 μm or less.

[0045] Although not shown in FIG. 8, when the average bubble diameter in the cross-sectional direction exceeds 30 μm or when the average bubble diameter in the longitudinal direction is larger, the same characteristics as those shown by the dashed line were obtained.

[0046] Fig. 9 is a graph showing the insertion loss before and after the long-term heat resistance test, showing the case where the conductor 11 has a two-layer structure with plating on the inner metal. Fig. 10 is a graph showing the insertion loss before and after the long-term heat resistance test, showing the case where the conductor 11 has a single-layer structure with no plating. In Figs. 9 and 10, the solid line shows the results before the long-term heat resistance test, and the dashed line shows the results after the long-term heat resistance test.

[0047] First, as shown in Figs. 9 and 10, the insertion loss before the long-term heat resistance test shows a predetermined characteristic. A long-term heat resistance test (85°C x 3000 hours) was performed on the two-core twisted shielded cable 1 showing such a predetermined characteristic. In the case of the two-core twisted shielded cable 1 using the two-layered conductor 11 shown in Fig. 9, the insertion loss after the long-term heat resistance test tended to increase as the signal frequency increased. In contrast, in the case of the two-core twisted shielded cable 1 using the single-layered conductor 11 shown in Fig. 10, the insertion loss after the long-term heat resistance test was approximately the same as that before the test. This is considered to be because, in the case of the two-layered conductor 11, metal atoms of either the plating or the inner metal of the plating diffuse and alloy into the metal layer of the other side, and the resistance value of the conductor surface decreases due to the influence of the alloying, and the insertion loss worsens. Therefore, it was found that when the two-core twisted shielded cable 1 is used in an environment (such as a wire harness WH) where it may be exposed to a high-heat environment for a long period of time, the conductor 11 is preferably a single-layered structure without plating.

[0048] Next, a description will be given of an example of a method for manufacturing the two-core twisted shielded cable 1 according to this embodiment. First, in order to manufacture the two-core twisted shielded cable 1, it is necessary to manufacture the insulated wire 10.

[0049] The insulated wire 10 is manufactured by extruding the insulator 12 onto the conductor 11. In this case, it is preferable that the conductor 11 has a single-layer structure without plating. Furthermore, the insulator 12 may be foamed.

[0050] Here, there are two methods for foaming the insulator 12: a chemical foaming method and a physical foaming method. The chemical foaming method is a method in which a foamed coating layer is formed on a base resin using a thermally decomposable chemical foaming agent. The thermally decomposable chemical foaming agent is mixed in during extrusion, and decomposes and foams due to the heat during extrusion. On the other hand, the physical foaming method is a method in which an inert gas is injected into an extrusion cylinder and then a foamed coating layer is formed. The inert gas is mixed into the base resin to form bubbles.

[0051] In addition, when foaming the insulator 12, it is preferable to use a physical foaming method. Examples of thermal decomposition type chemical foaming agents include azodicarbonamide (ADCA) and oxybisbenzenesulfonylhydrazide (OBSH). This is because these foaming agents have a high dielectric constant and cause a deterioration in insertion loss in the GHz band. In particular, ADCA is a substance of high concern under the REACH regulation, and is problematic in terms of environmental impact. Furthermore, in the case of the chemical foaming method, since the thermal decomposition type chemical foaming agent is mixed in the extrusion process, the dispersion of the thermal decomposition type chemical foaming agent during melting is poor, making it difficult to achieve a uniform foam diameter. In addition, if a thermal decomposition type chemical foaming agent is used to achieve a uniform foam diameter, it is necessary to melt the agent sufficiently in the cylinder, which causes problems such as a slow production speed and poor production efficiency.

[0052] When foaming is performed by a physical foaming step, the base resin is preferably a resin composition containing a polypropylene resin, and more preferably the resin composition containing a polypropylene resin has physical properties of a melt tension of 15 mN to 45 mN and a melt viscosity of 120 Pa s to 200 Pa s measured by a capillary rheometer at 200°C.

[0053] In this manner, the insulated wire 10 is obtained. For the insulated wire 10 obtained here, the distance D between the centers of the two insulated wires 10 and the dielectric constant εr of the insulator 12 in formula (1) are taken into consideration.

[0054] After the insulated wire 10 is obtained, two insulated wires 10 are twisted together at a predetermined twist pitch wpitch of at least 15 mm. At this time, the two insulated wires 10 are twisted together at a twist pitch wpitch such that the suckout frequency f obtained by formula (1) is 5 GHz or higher.

[0055] Then, the metal foil shield 20 is provided on the two insulated wires 10. When the metal foil shield 20 is wound transversely around the two insulated wires 10, the metal foil shield 20 is wound transversely at a winding pitch mpitch such that the suckout frequency f in formula (2) is 5 GHz or higher.

[0056] Then, a metal braid 30 is provided on the metal foil shield 20, and a sheath 40 is formed, for example by extrusion.

[0057] In this way, according to the two-core twisted shielded cable 1 of this embodiment, when the distance between the centers of the two insulated wires 10 is D, the twist pitch of the two insulated wires 10 is wpitch, the dielectric constant of the insulator 12 is εr, and the magnetic permeability in a vacuum is μr, the suckout frequency f obtained by formula (1) is 5 GHz or more. Therefore, it is possible to avoid the influence of suckout during communication by setting the suckout frequency f to 5 GHz or more. Therefore, it is possible to provide a two-core twisted shielded cable that can suppress deterioration of the transmission characteristics.

[0058] In addition, since the twist pitch wpitch is set to 15 mm or more, it is possible to suppress an unexpected decrease in insertion loss at a frequency that occurs when the twist pitch wpitch is too small and the insulator 12 of the insulated wire 10 is crushed.

[0059] Furthermore, when the speed of light is c, the suckout frequency f obtained from formula (2) is set to 5 GHz or higher. Therefore, the suckout frequency f when suckout occurs due to the horizontally wound metal foil shield 20 is also set to 5 GHz or higher. This makes it possible to set both suckout frequencies f to 5 GHz or higher. Therefore, it is possible to provide a two-core twisted shielded cable that can further suppress deterioration of transmission characteristics.

[0060] The insulator 12 is made of a foam, and has an average foam diameter of 30 μm or less in the cross-sectional direction and 60 μm or less in the longitudinal direction. Therefore, for example, when the insulator 12 is foamed to adjust the dielectric constant of the insulator 12, it is possible to reduce the possibility that the bubbles will be crushed when the two insulated wires 10 are twisted together, resulting in an unexpected suckout frequency f.

[0061] In addition, the conductor 11 has a single-layer structure that is not plated. Therefore, when exposed to a high-temperature environment for a long time, such as a wire harness WH used in a vehicle, it is possible to prevent either the plating or the metal inside the plating from diffusing metal atoms into the mating metal layer and forming an alloy. If alloying occurs, the resistance value of the conductor surface may decrease, and the insertion loss may worsen. However, by forming the conductor 11 into a single layer structure, it is possible to provide a wire harness WH that does not have such concerns.

[0062] 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.

[0063] 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 faces outward, but this is not limiting and the metal layer may face inward.

[0064] Furthermore, the two-core twisted shielded cable 1 according to this embodiment includes the metal braid 30, but is not limited thereto, and may not include the metal braid 30. Furthermore, the two-core twisted shielded cable 1 may include, in addition to the two insulated wires 10, a drain wire that is a bare wire.

[0065] In addition, in the two-core twisted shielded cable 1 according to the present embodiment, the suckout frequency f in formulas (1) and (2) is set to 5 GHz or more, but it is not limited to 5 GHz, and may be any of 1 GHz or more, 4 GHz or more, 6 GHz or more, 15 GHz or more, 20 GHz or more, 30 GHz or more, and 40 GHz or more, depending on the use other than the wire harness WH, the progress of technology, and the like. That is, in the two-core twisted shielded cable 1 according to the present embodiment, the suckout frequency f in formulas (1) and (2) may be set so as not to affect communication. Therefore, in the above, only the lower limit is set to, for example, 5 GHz. However, this is not limited to this, and if there is a reason for not wanting to set the suckout frequency too high, the suckout frequency f obtained by formulas (1) and (2) may be limited by an upper limit, such as less than 1 GHz, less than 4 GHz, less than 5 GHz, less than 6 GHz, less than 15 GHz, less than 20 GHz, less than 30 GHz, and less than 40 GHz. Furthermore, lower and upper limits may be set, such as 1 GHz or more and less than 4 GHz, 4 GHz or more and less than 5 GHz, 1 GHz or more and less than 15 GHz, 20 GHz or more and less than 40 GHz, and the like.

[0066] Further, in the above description, an example has been described in which the dielectric constant of the insulator 12 is adjusted by foaming. However, the dielectric constant of the insulator 12 is not limited to being foamed, and the dielectric constant may be adjusted to an appropriate value simply by selecting the material. [Explanation of symbols]

[0067] 1: 2-core twisted shielded cable 10: Insulated wire 11: Conductor 12: Insulator 20: Metal foil shield 30: Metal braid 40: Sheath O: Other cables

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 provided around the two insulated wires; a sheath provided around the outer periphery of the metal foil shield; When the distance between the centers of the two insulated wires is D, the twist pitch of the two insulated wires is wpitch, the dielectric constant of the insulator is εr, and the magnetic permeability of a vacuum is μr, [0010] The suck-out frequency f obtained by the above is set to 5 GHz or more. A two-core twisted shielded cable.

2. The twist pitch wpitch of the two insulated wires is set to 15 mm or more.

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

3. The metal foil shield is wound transversely around the two insulated wires, If the speed of light is c and the winding pitch of the metal foil shield is mpitch, [0025] The suck-out frequency f obtained by the above is set to 5 GHz or more.

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

4. The insulation of the two insulated wires is made of foam, and the average foam diameter is 30 μm or less in the cross-sectional direction and 60 μm or less in the longitudinal direction.

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

5. The conductors of the two insulated wires are formed in a single layer structure that is not plated.

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

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