Transmission cable

Abstract

A transmission cable (10) according to the present invention comprises: a plurality of insulated wires (20) twisted in a first direction; and a tape-shaped first shield layer (40) that is wound around the plurality of insulated wires (20) along the first direction and covers the plurality of insulated wires (20). The twist pitch of the plurality of insulated wires (20) and the winding pitch of the first shield layer (40) are substantially the same.

Description

Transmission cable

[0001] The present invention relates to a transmission cable.

[0002] Transmission cables with twisted pair structures used for high-speed communications are often installed adjacent to many electronic devices. For example, transmission cables are used as wiring in automobiles, factories, robots, and so on, resulting in a concentration of precision machinery near the transmission cables. Furthermore, noise emitted from transmission cables is likely to have a significant impact on these precision machinery. Known types of noise include noise caused by leakage of common mode signals (common mode noise) and noise caused by leakage of differential mode signals (differential mode noise). Common mode noise has a significant impact on electronic devices that use common mode signals, while differential mode noise has a significant impact on electronic devices that use differential mode signals. Generally, such transmission cables are covered with metal tape to shield against noise (see, for example, Patent Document 1).

[0003] Patent Document 1 describes a twisted pair cable including a pair of twisted core wires and a metal-resin tape wrapped around the pair of core wires to cover the pair of core wires. The core wires include a conductor and an insulator that covers the conductor. The metal-resin tape is wrapped around the pair of core wires in the opposite direction to the twisted direction of the pair of core wires.

[0004] JP 2010-287337 A

[0005] In recent years, high-speed transmission has required ever-increasing reduction in noise leakage. However, to further reduce noise leakage using the twisted pair cable described in Patent Document 1, a coating of more than three layers must be used. However, applying a coating of more than three layers increases the diameter of the twisted pair cable, reducing workability and increasing manufacturing costs.

[0006] An object of the present invention is to provide a transmission cable that can suppress leakage of common mode signals.

[0007] In order to solve the above problem, according to one aspect of the present invention, there is provided a transmission cable comprising: a plurality of insulated electric wires twisted together in a first direction; and a tape-shaped first shielding layer that is wrapped around the plurality of insulated electric wires along the first direction and covers the plurality of insulated electric wires, wherein the twisting pitch of the plurality of insulated electric wires and the winding pitch of the first shielding layer are substantially the same.

[0008] According to the present invention, it is possible to provide a transmission cable that can suppress leakage of common mode signals.

[0009] 1A and 1B are schematic diagrams of a transmission cable, 2A and 2B are schematic diagrams for explaining the effects of the present invention, and 3A and 3B are graphs showing the results of investigating leakage of common mode signals.

[0010] A transmission cable according to one embodiment of the present invention will be described below. The transmission cable can be used, for example, for wiring in automobiles, factories, etc. In this specification, when a numerical range is indicated by "to", the lower limit and upper limit are included in the numerical range.

[0011] (Structure of Transmission Cable) FIG. 1A is a schematic diagram of a cross section of a transmission cable, and FIG. 1B is a schematic diagram of the transmission cable excluding the winding.

[0012] As shown in FIGS. 1A and 1B, the transmission cable 10 includes a plurality of insulated wires 20, a winding 40, a first shielding layer 50, a second shielding layer 60, and an outer jacket layer 70.

[0013] The insulated wires 20 transmit electrical signals. The number of insulated wires 20 is not particularly limited as long as there is more than one. The number of insulated wires 20 may be two, three, four, or more. The number of insulated wires 20 is preferably an even number. That is, the number of insulated wires 20 is preferably two, four, six, or an even number greater than two. In this embodiment, the number of insulated wires 20 is four (two pairs).

[0014] The multiple insulated electric wires 20 are twisted together in a first direction (quad twisted). That is, the transmission cable 10 of this embodiment is a twisted pair cable. The first direction may be clockwise or counterclockwise when viewed along the extension direction of the insulated electric wires 20. The twist pitch of the multiple insulated electric wires 20 is not particularly limited as long as it does not impair the manufacturing and handling of the transmission cable 10. The twist pitch of the multiple insulated electric wires 20 is preferably 32.5 mm or more and 37.5 mm or less, more preferably 33.0 mm or more and 37.0 mm or less, and even more preferably 35.0 mm. Here, the twist pitch refers to the longitudinal distance of the insulated electric wires 20 required for one insulated electric wire 20 to make one turn when the multiple insulated electric wires 20 are twisted together.

[0015] The insulated wire 20 has a conductor 21 and a covering layer 22 that covers the conductor 21 .

[0016] The conductor 21 is made of a metal with high electrical conductivity. Examples of the metal include copper, aluminum, copper alloys, and aluminum alloys. In this embodiment, the conductor 21 is a tin-plated annealed copper wire. The outer diameter of the cross section of the conductor 21 is, for example, 0.45 mm or more and 0.50 mm or less.

[0017] The covering layer 22 covers the conductors 21 and insulates the conductors 21 from each other. The material of the covering layer 22 is not particularly limited as long as it has insulating properties. In the present embodiment, the covering layer 22 is made of polypropylene. The thickness of the covering layer 22 is not particularly limited and can be selected appropriately. The thickness of the covering layer 22 is, for example, in the range of 0.2 to 0.4 mm.

[0018] The winding 40 covers the multiple insulated wires 20 inside the first shielding layer 50. The winding 40 maintains a constant distance between the multiple insulated wires 20 and the first shielding layer 50. Examples of materials for the winding 40 include resin or glass. Examples of winding 40 include nonwoven fabric tapes made of one or more of polyester, polypropylene, aramid fiber, nylon, acrylic fiber, and glass fiber. In this embodiment, the winding 40 is made of polyester tape. The winding 40 is wound horizontally over the multiple insulated wires 20. Specifically, the winding 40 is spirally wound while overlapping the side edges of the tape with the previously wrapped tape. The number of windings 40 is not particularly limited as long as it does not impair the purpose and effect of this embodiment. The thickness of the winding 40 is not particularly limited as long as it can perform the above-mentioned functions and can be selected appropriately. The thickness of the winding 40 is, for example, within the range of 0.005 to 0.050 mm.

[0019] The first shielding layer 50 is tape-shaped and covers the winding 40 on the inner side of the second shielding layer 60. The first shielding layer 50 mainly protects the insulated wire 20 and blocks external electromagnetic waves. The first shielding layer 50 is preferably composed of a metal-resin tape. Examples of metal-resin tape include Al / PET tape, in which aluminum (Al) foil is laminated on a polyethylene terephthalate (PET) film. In this embodiment, the metal-resin tape of the first shielding layer 50 is Al / PET tape. The term "resin sheet" includes resin film. The thickness of the resin sheet (resin film) is not particularly limited and can be set as appropriate. The first shielding layer 50 is wound horizontally over the winding 40. The thickness of the first shielding layer 50 is not particularly limited as long as it can perform the above-mentioned functions and can be selected as appropriate. The thickness of the first shielding layer 50 is, for example, within the range of 0.010 to 0.050 mm.

[0020] The first shielding layer 50 is wound horizontally along a first direction, which is the same direction as the twisting direction of the insulated wires 20. That is, the first shielding layer 50 is wound spirally around the tension winding 40. The winding pitch of the first shielding layer 50 is approximately the same as the twisting pitch of the multiple insulated wires 20. Here, the "winding pitch" refers to the length in the extension direction of the transmission cable 10 per revolution in the first direction. Furthermore, "approximately the same" means that the winding pitch of the first shielding layer 50 is within a range of 94 to 106% of the twisting pitch of the multiple insulated wires 20. That is, the insulated wires 20 and the first shielding layer 50 are arranged approximately parallel at any position on the transmission cable 10. The winding pitch of the first shielding layer 50 is preferably 32.5 mm or more and 37.5 mm or less, more preferably 33 mm or more and 37 mm or less, and even more preferably 35 mm.

[0021] The second shielding layer 60 is made of a metallic braided wire and covers the first shielding layer 50. The second shielding layer 60 blocks electromagnetic waves from the outside and also blocks leakage from the inside. The second shielding layer 60 may be a single layer or multiple layers. In this embodiment, the second shielding layer 60 has a single-layer structure. The material of the second shielding layer 60 is not particularly limited as long as it is a metal and can exhibit the above-mentioned functions. Examples of materials for the second shielding layer 60 include tin-plated annealed copper wire braid. The wire diameter of the second shielding layer 60 is, for example, in the range of 0.05 to 0.10 mm.

[0022] The outer jacket layer 70 is made of resin and covers the second shielding layer 60. The outer jacket layer 70 protects the second shielding layer 60 from external factors. Examples of materials for the outer jacket layer 70 include polyolefin and polyvinyl chloride. In this embodiment, the material for the outer jacket layer 70 is polyolefin. The thickness of the outer jacket layer 70 is not particularly limited. The thickness of the outer jacket layer 70 is, for example, in the range of 0.3 mm to 1.0 mm.

[0023] Here, the mechanism by which the above-described transmission cable 10 can suppress leakage of common-mode signals will be described. Fig. 2A is a schematic diagram of the positional relationship between the insulated wire 20 and the first shielding layer 50 in this embodiment, and Fig. 2B is a schematic diagram of the positional relationship between the insulated wire 20 and the first shielding layer 50 in a comparative example. The dotted lines in Figs. 2A and 2B schematically indicate magnetic fields M1, M2, M3, and M4. The thick arrows in Figs. 2A and 2B indicate the direction of magnetic force, and the thin arrows indicate the signal transmission direction.

[0024] 2A , in transmission cable 10 of this embodiment, insulated wires 20 and first shielding layer 50 are arranged substantially parallel to each other. Therefore, the direction of current flowing through insulated wires 20 and the direction of current flowing through first shielding layer 50 are substantially parallel to each other. At this time, magnetic field M1 generated around insulated wires 20 and magnetic field M2 generated around first shielding layer 50 cancel each other out. Therefore, in this embodiment, no source of common mode signals is generated, and leakage of common mode signals can be suppressed.

[0025] As shown in FIG. 2B , in the transmission cable 10 of the comparative example, the twist pitch of the insulated wires 20 is not substantially the same as the winding pitch of the first shielding layer 50. Specifically, the twist pitch of the insulated wires 20 is smaller than the winding pitch of the first shielding layer 50. That is, the insulated wires 20 and the first shielding layer 50 are arranged so as to intersect. Therefore, the direction of the current flowing through the insulated wires 20 and the direction of the current flowing through the first shielding layer 50 are not parallel. Here, when the magnetic field M2 generated around the first shielding layer 50 is decomposed into two vectors in directions perpendicular to each other, it becomes magnetic fields M3 and M4. In this case, the magnetic field M1 generated around the insulated wires 20 and the magnetic field M3 generated around the first shielding layer 50 partially cancel each other out, but the remaining part of the magnetic field M4 becomes a source of a common-mode signal. Therefore, the transmission cable 10 of the comparative example cannot sufficiently suppress leakage of common-mode signals.

[0026] (Method of Manufacturing Transmission Cable) There is no particular limitation on the method of manufacturing the transmission cable 10. The transmission cable 10 can be manufactured, for example, by the following method.

[0027] First, the prepared conductor 21 is coated with the coating layer 22 to obtain the insulated wire 20. Next, a plurality of the insulated wires 20 are twisted together in a first direction. Next, the plurality of insulated wires 20 are coated by horizontally winding the coil winding 40. Next, the coil winding 40 is coated by horizontally winding the coil winding 40 in the first direction. Here, the twist pitch of the plurality of insulated wires 20 and the winding pitch of the first shielding layer 50 are approximately the same. Next, the first shielding layer 50 is coated with the second shielding layer 60. Finally, the second shielding layer 60 is coated with the outer jacket layer 70. In this manner, the transmission cable 10 is obtained.

[0028] (Experiment) Next, the leakage of common mode signals (shielding attenuation) was investigated for the transmission cable 10 of the present embodiment and the transmission cable 10 of the comparative example. The shielding attenuation was measured in accordance with IEC 62153-4-7. The transmission cables used in the present embodiment and the comparative example included two pairs (four) of insulated wires 20, a winding 40, an Al / PET tape as the first shielding layer 50, and a tin-plated annealed copper wire braid as the second shielding layer 60. In the transmission cable 10 of the present embodiment, the twist direction of the insulated wires 20 was a first direction, and the twist pitch was 35 mm. In addition, in the transmission cable 10 of the present embodiment, the winding direction of the first shielding layer 50 was a first direction, and the winding pitch was 35 mm. In the transmission cable 10 of the comparative example, the twist direction of the insulated wires 20 was a first direction, and the twist pitch was 35 mm. In the comparative example, the first shielding layer 50 is wound in the first direction at a winding pitch of 12.5 mm. The operating frequency of the transmission cable 10 in this embodiment is 700 to 2400 MHz.

[0029] Fig. 3A shows the results of measuring the leakage of common mode signals in a transmission cable of a comparative example, and Fig. 3B shows the results of measuring the leakage of common mode signals in a transmission cable of this embodiment. The horizontal axis of Fig. 3A and Fig. 3B shows the frequency (MHz), and the vertical axis shows the leakage of common mode signals (dB).

[0030] As shown in FIG. 3A, in the transmission cable of the comparative example, the average value of the shielding attenuation in the range of 700 to 2400 MHz was about −70 dB, and the maximum value was about −50 dB.

[0031] 3B, in the transmission cable of this embodiment, the average shielding attenuation in the range of 700 to 2400 MHz was about −90 dB, which was about 20 dB lower than that of the comparative transmission cable 10. In addition, the maximum shielding attenuation in the range of 700 to 2400 MHz was −75 dB or less, which was about 25 dB lower than that of the comparative transmission cable 10.

[0032] (Effect) As described above, according to the transmission cable 10 of the present invention, the twisting direction of the multiple insulated wires 20 and the winding direction of the first shielding layer 50 are the same, and the twisting pitch of the insulated wires 20 and the winding pitch of the first shielding layer 50 are approximately the same, so leakage of common mode signals can be suppressed.

[0033] The transmission cable according to the present invention is useful for wiring in automobiles, wiring in factories, wiring in robots, and the like.

[0034] REFERENCE SIGNS LIST 10 Transmission cable 20 Insulated wire 21 Conductor 22 Covering layer 40 Winding 50 First shielding layer 60 Second shielding layer 70 Outer covering layer

Claims

1. A transmission cable comprising: a plurality of insulated electric wires twisted together in a first direction; and a tape-shaped first shielding layer wrapped around the plurality of insulated electric wires along the first direction and covering the plurality of insulated electric wires, wherein the twist pitch of the plurality of insulated electric wires and the winding pitch of the first shielding layer are substantially the same.

2. A transmission cable according to claim 1, characterized in that the winding pitch of the first shielding layer is within the range of 94 to 106% of the twist pitch of the plurality of insulated wires.

3. A transmission cable as claimed in claim 1, further comprising: a winding disposed between the plurality of insulated wires and the first shielding layer and covering the plurality of insulated wires; a second shielding layer covering the first shielding layer; and an outer sheath layer covering the second shielding layer, wherein the first shielding layer is made of a metal resin tape, the second shielding layer is made of a metal braided wire, and the outer sheath layer is made of resin.

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