Communication cable

Abstract

The present invention provides a communication cable that supports high-frequency data transmission and simplifies the internal structure of the cable. [Solution] A communication cable 1 is made by twisting together multiple insulated wires 12, each having a conductor 14 covered with an insulator 16, wherein the conductor 14 is made of a single wire or a compressed stranded wire with a circular cross-section, and the multiple insulated wires 12 are twisted together at a constant pitch.

Description

Technical Field

[0001] The present invention relates to a communication cable compatible with high-frequency data transmission and a method for manufacturing the same.

Background Art

[0002] In recent years, in automobiles, the performance of information communication devices has been enhanced, and in-vehicle multimedia has become more multifunctional. In the future, it is considered that further performance enhancements and an increase in mounted devices will progress, with keywords such as advanced driver-assistance systems (ADAS) and autonomous driving. Such progress has led to an increase in the volume of information communication, and data transmission at high frequencies is required. However, there are several problems in high-frequency data transmission, such as suppressing internal skew (the difference in internal propagation delay times) and suppressing the suck-out phenomenon (a sharp drop in the frequency characteristics of signal attenuation amounts) in the high-frequency band.

[0003] Patent Document 1 discloses a multi-core cable that attempts to solve these problems of high-frequency data transmission. In the technology of Patent Document 1, eight pairs of coaxial wire pairs (11 to 18) are accommodated in a multi-core cable (1). Each coaxial wire 10 has a center conductor (21) covered with an insulator (22), and its outer periphery is covered with an outer conductor (23) and an outer sheath (24). The outer conductor has a metal wire (M) wound horizontally (spirally) around the insulator as an inner layer part (23A), and a metal resin tape (T) wound horizontally around the inner layer part as an outer layer part (23B). In particular, in this technology, by setting the winding directions of the metal wire and the metal resin tape to be opposite and setting the difference in their winding angles (angle θ3) within a certain range, the suck-out phenomenon is suppressed (see paragraphs 0017 - 0027, FIGS. 1 - 2, the examples, FIG. 4, etc.).

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] Patent No. 6269718 [Disclosure of the Invention] [Problems that the invention aims to solve]

[0005] However, as described above, the wire pair in Patent Document 1 has an outer conductor placed inside the coaxial wire, which is made of thin metal wires and metal-resin tape, and even the winding direction and winding angle of the thin metal wires and metal-resin tape must be set. In other words, the internal structure of the cable in Patent Document 1 is very complex, and there is room for improvement in the internal structure of the cable. Therefore, the main objective of the present invention is to provide a communication cable that is compatible with high-frequency data transmission and that can simplify the internal structure of the cable. [Means for solving the problem]

[0006] The inventors conducted extensive technical studies to solve the above problems and discovered that, in particular, high-frequency signals have a high current density near the surface of the conductor due to the skin effect, which is disadvantageous for simple stranded wires made by twisting multiple strands together in terms of high-frequency transmission. However, they found that the closer the cross-sectional shape is to a circular shape, such as a single wire or compressed stranded wire with a circular cross-section, the lower the resistance in high-frequency transmission. Furthermore, they found that by controlling the twist pitch of the insulated wire to be constant, it is possible to support high-frequency data transmission, and thus completed the present invention. In other words, according to the present invention, a communication cable is made by twisting together multiple insulated wires, each in which a conductor is covered with an insulator, The conductor is composed of a single wire or compressed stranded wire with a circular cross-section, A communication cable is provided, characterized in that multiple insulated wires are twisted together at a pitch of 7.0 mm or more and at a pitch less than or equal to the value derived by (speed of light × NVP / frequency) × (1 / dielectric constant of the insulator). [Effects of the Invention]

[0007] According to the present invention, a simple configuration in which the conductor is merely composed of a single wire or compressed stranded wire with a circular cross-section is presumed to reduce resistance in high-frequency transmission. Based on this, if the twisting pitch of the insulated wire is controlled to be constant, the in-pair skew is 10 ps / m or less, the transmission state is stable, and the insertion loss (IL) does not drop (decrease) even at high frequencies exceeding, for example, 10 GHz, thus suppressing signal attenuation. [Brief explanation of the drawing]

[0008] [Figure 1] This is a cross-sectional view showing the general configuration of a communication cable. [Figure 2] This figure shows the relationship between frequency and insertion loss (IL) for Sample 1-2. [Figure 3] This figure shows the relationship between the frequency and insertion loss (IL) of sample 11. [Figure 4] This figure shows the relationship between the frequency and insertion loss (IL) of sample 12. [Figure 5] This figure shows the relationship between the frequency and insertion loss (IL) of sample 13. [Figure 6] This figure shows the relationship between the frequency and insertion loss (IL) of sample 21. [Figure 7] This figure shows the relationship between the frequency and insertion loss (IL) of sample 22. [Figure 8] This figure shows the relationship between the frequency and insertion loss (IL) of sample 23. [Modes for carrying out the invention]

[0009] A preferred embodiment of the present invention, specifically a communication cable, will be described below. In this specification, the "~" symbol indicating a numerical range means that the lower and upper limits are included within that numerical range.

[0010] Figure 1 is a cross-sectional view showing the schematic configuration of communication cable 1. As shown in Fig. 1, the communication cable 1 has a twisted pair 10, a spiral wrap 20, an inner sheath 30, a first shielding layer 40, a second shielding layer 50, and an outer sheath 60. The outer circumference of the twisted pair 10 is covered by the spiral wrap 20, the inner sheath 30, the first shielding layer 40, the second shielding layer 50, and the outer sheath 60 in this order.

[0011] The twisted pair 10 is composed of two insulated wires 12, and the first type of wire core 10A and the second type of wire core 10B are used in pairs. As the second twisted pair, the third type of wire core and the fourth type of wire core may be added and used in pairs (it may be composed of four cores), or pairs of subsequent wire cores may be added and used. When adding pairs of wire cores, the insulated wires 12 are cut and twisted.

[0012] The insulated wire 12 is composed of a conductor 14 and an insulator 16, and has a structure in which the outer circumference of the conductor 14 is covered with the insulator 16. The conductor 14 is a compressed stranded wire with a circular cross-section and a plurality of strands twisted and compressed. The conductor 14 may be a single wire as long as it has a circular cross-section. The conductor 14 (including strands) is preferably a soft copper wire and may be covered on the outer circumference by a plating layer (not shown) of any of tin, nickel, and silver. <00000-eight6>The outer diameter of the conductor 14 is preferably 0.4 to 0.6 mm. The insulator 16 is formed by extruding an insulating resin from the die of an extruder. The insulating resin is preferably composed of cross-linked polyethylene (XLPE) or polypropylene (PP). The thickness of the insulator 16 is preferably 0.2 to 0.4 mm.

[0013] The spiral wrap 20 is formed by overlapping tape-shaped polyethylene terephthalate (PET) or polypropylene (PP). The spiral wrap 20 may be composed of a tape-shaped non-woven fabric.

[0014] The inner sheath 30 is formed by extruding the resin for the inner sheath from the die of an extruder. The resin for the inner sheath is preferably composed of polyvinyl chloride (PVC) or thermoplastic elastomer (TPE). The inner sheath 30 is not essential and may be omitted.

[0015] The first shielding layer 40 is formed by winding a metal tape. The metal tape is a tape formed by laminating a metal foil and a resin tape, and is preferably formed by laminating an aluminum foil and a polyethylene terephthalate tape (PET tape). In the first shielding layer 40, the metal foil is wound so as to be exposed on the outer periphery. On the other hand, the second shielding layer 50 is formed by braiding a plurality of metal wires. The second shielding layer 50 may be formed by winding a plurality of metal wires horizontally at a pitch below a certain value. Each of the metal wires is preferably a so-called tinned annealed copper wire (TA) in which a soft copper wire is coated with a tin plating layer.

[0016] The outer sheath 60 is a so-called sheath and is formed by extruding the resin for the outer sheath from the die of an extruder. The resin for the outer sheath is preferably composed of polyvinyl chloride (PVC), polyolefin (PO) or thermoplastic elastomer (TPE).

[0017] In this embodiment, the twisted pair 10 is composed of two insulated wires 12 as described above, and has a configuration in which the two insulated wires 12 are twisted at a certain pitch.

[0018] The upper and lower limit values of the twist pitch of the insulated wires 12 are set from the viewpoints of intra-pair skew and insertion loss (IL).

[0019] The lower limit of the twist-pair pitch is determined from the perspective of whether stable manufacturing is possible and whether internal skew can be suppressed. In practice, this lower limit is 7.0 mm, preferably 7.9 mm. The shorter the twist-pair pitch of the insulated wire 12, the more excessively dense the twists become, and the balance of twists between the insulated wires 12 becomes unstable. As a result, differences in physical length occur between the insulated wires 12 (length variation), making it difficult to suppress internal skew.

[0020] The upper limit of the twisted-pair pitch is derived from the viewpoint of suppressing the suck-out phenomenon at high frequencies (for example, up to over 10 GHz). Through repeated prototyping of communication cable 1 and measurement of insertion loss, the inventors found that the upper limit of the twisted-pair pitch correlates with the material (dielectric constant) of the insulator 16 and can be derived from the following relational expression due to the dielectric constant of the insulator 16. In detail, while wavelength is generally expressed as wave speed / frequency, the inventors found that the upper limit of the twisted-pair pitch approximates the value obtained by dividing the wavelength by the dielectric constant of the insulator 16 (see Example). According to this, if the speed of light is 100, the speed of the signal propagating within the cable pair is approximately 70% as a matter of common technical knowledge (NVP: Nominal Velocity of Propagation). If the frequency is set to 10 GHz, the upper limit of the twisted-pair pitch can theoretically be derived as shown in the following equation. Upper limit of the twist pitch [mm] = (wavelength) × (dielectric constant of insulator 16) = (Speed ​​of light × NVP / frequency) × (Dielectric constant of insulator 16) = 300,000,000 [m / s] × 0.7 / 10 × 10 9 [Hz] × (dielectric constant of insulator 16) × 1,000 [mm]

[0021] When the wavelength of the signal transmitted within the cable pair and the twisted pair pitch of the insulated wire 12 resonate in sync, a suck-out phenomenon occurs. As shown in Table 1, (i) when the insulator 16 is made of cross-linked polyethylene, if the upper limit of the twisted pair pitch of the insulated wire 12 exceeds approximately 9.55 mm, a resonance point is formed at a low frequency of 10 GHz or less, and (ii) when the insulator 16 is made of polypropylene, if the upper limit of the twisted pair pitch of the insulated wire 12 exceeds approximately 10.00 mm, a resonance point is formed at a low frequency of 10 GHz or less, and in both cases, a suck-out phenomenon is likely to occur.

[0022] [Table 1]

[0023] Next, we will explain how to manufacture the communication cable 1.

[0024] First, a single wire or compressed stranded wire with a circular cross-section is prepared as the conductor 14. An insulating resin is extruded and coated onto the conductor 14, and an electron beam is irradiated onto it to crosslink it and form an insulator 16, thereby manufacturing an insulated electric wire 12. Then, the two insulated wires 12 are twisted together at a constant pitch (paired twist).

[0025] Subsequently, polyethylene terephthalate tape (PET tape) is wrapped around the twisted body 10 in a layered manner to form a pressed winding 20. Subsequently, the inner covering resin is extruded and applied to the rolled-up 20 to form the inner covering 30. Subsequently, a metal tape is wrapped around the inner sheath 30 to form a first shielding layer 40, and multiple metal wires are braided together to form a second shielding layer 50.

[0026] Finally, the outer sheath 60 is formed by extruding and coating the second shielding layer 50 with an outer sheath resin, thereby manufacturing the communication cable 1.

[0027] According to the above communication cable 1, the simple configuration in which the conductor 14 is simply composed of a single wire or compressed stranded wire with a circular cross-section is presumed to reduce resistance in high-frequency transmission. Based on this, if the twisted pair pitch of the insulated wire 12 is controlled to be constant, the in-pair skew is 10 ps / m or less, the transmission state is stable, and the insertion loss (IL) does not drop (decrease) to more than 10 GHz, thus suppressing signal attenuation (see the example below). According to this communication cable 1, with such a simple configuration of selecting the form of the conductor 14 and controlling the twisted pair pitch of the insulated wire 12, it is possible to provide a communication cable that is compatible with high-frequency data transmission and can realize a simplification of the internal structure of the cable.

[0028] Furthermore, the communication cable 1 can be used for any communication purpose, preferably for automotive applications, and more preferably for transmitting images or video signals from an in-vehicle camera. In other words, the communication cable 1 is preferably a cable that conforms to the ISO-6722 standard or the ISO-19642 standard. [Examples]

[0029] (1) Sample preparation (1.1) Sample 1 First, seven strands of 0.16 mm diameter soft copper wire were twisted together (26AWG) to form a conductor with an outer diameter of 0.48 mm. Subsequently, cross-linked polyethylene (XLPE) was extruded onto the conductor and irradiated with an electron beam to cross-link it, forming an insulator with a thickness of 0.225 mm and an insulated wire with an outer diameter of 0.93 mm. Subsequently, two insulated wires were twisted together at a pitch of 16 mm to form a twisted wire body.

[0030] Subsequently, a 0.025 mm thick polyethylene terephthalate tape (PET tape) was wrapped around the twisted body as a pressing winding, overlapping by 1 / 4 of its width (the PET tape was wrapped while overlapping by 1 / 4 of its width). Subsequently, polyvinyl chloride (PVC) was extruded and coated onto the rolled material to form an inner cover with an outer diameter of 2.76 mm.

[0031] Subsequently, a metal tape was prepared as the first shielding layer by laminating aluminum foil and polyethylene terephthalate tape (PET tape). This metal tape was then wrapped around the inner cover with a 1 / 4 overlap to form a first shielding layer with an outer diameter of 2.92 mm. Subsequently, 85 tin-plated soft copper wires (TA) with a diameter of 0.1 mm were prepared as a second shielding layer, and these tin-plated soft copper wires were braided with the first shielding layer to form a second shielding layer with an outer diameter of 3.42 mm. Finally, polyvinyl chloride (PVC) was extruded and coated onto the second shielding layer to create a communication cable with an outer diameter of 4.12 mm.

[0032] (1.2) Sample 2 In Sample 1, the main change was to modify the twisted-pair pitch of the insulated wires to 7.9 mm.

[0033] (1.3) Sample 11 First, as a conductor, seven strands of soft copper wire with a diameter of 0.16 mm were twisted together (26AWG), and this was compressed to form a compressed stranded wire with an outer diameter of 0.45 mm. Subsequently, cross-linked polyethylene (XLPE) was extruded onto the conductor and irradiated with an electron beam to cross-link it, forming an insulator with a thickness of 0.345 mm, and an insulated wire with an outer diameter of 1.14 mm was formed. Subsequently, two insulated wires were twisted together at a pitch of 8.3 mm to form a twisted wire body.

[0034] Subsequently, a 0.05 mm thick polyethylene terephthalate tape (PET tape) was wrapped around the twisted body as a pressing winding, overlapping by half its width (the PET tape was wrapped while overlapping by half its width).

[0035] Subsequently, aluminum foil was prepared as the first shielding layer, and the aluminum foil was wound with a 1 / 2 overlap on the pressed winding to form a first shielding layer with an outer diameter of 2.64 mm. Subsequently, 85 tin-plated soft copper wires (TA) with a diameter of 0.1 mm were prepared as a second shielding layer, and these tin-plated soft copper wires were braided with the first shielding layer to form a second shielding layer with an outer diameter of 3.10 mm. Finally, flame-resistant polyolefin (PO) was extruded and coated onto the second shielding layer to produce a communication cable with an outer diameter of 4.00 mm.

[0036] (1.4) Sample 12 In Sample 11, the stranding pitch of the insulated wire was changed to 8.4 mm.

[0037] (1.5) Sample 13 In Sample 11, the stranding pitch of the insulated wire was changed to 11.6 mm.

[0038] (1.6) Sample 21 First, as a conductor, seven strands of soft copper wire with a diameter of 0.16 mm were twisted together (26AWG), and this was compressed to form a compressed stranded wire with an outer diameter of 0.45 mm. Subsequently, polypropylene (PP) was extruded and coated onto the conductor to form an insulator with a thickness of 0.345 mm, and an insulated wire with an outer diameter of 1.14 mm was formed. Subsequently, two insulated wires were twisted together at a pitch of 8.1 mm to form a twisted wire body.

[0039] Subsequently, a 0.05 mm thick polyethylene terephthalate tape (PET tape) was wrapped around the twisted body as a pressing winding, overlapping by half its width (the PET tape was wrapped while overlapping by half its width).

[0040] Subsequently, aluminum foil was prepared as the first shielding layer, and the aluminum foil was wound with a 1 / 2 overlap on the pressed winding to form a first shielding layer with an outer diameter of 2.64 mm. Subsequently, 85 tin-plated soft copper wires (TA) with a diameter of 0.1 mm were prepared as a second shielding layer, and these tin-plated soft copper wires were braided with the first shielding layer to form a second shielding layer with an outer diameter of 3.10 mm. Finally, polyolefin (PO) was extruded and coated onto the second shielding layer to produce a communication cable with an outer diameter of 4.00 mm.

[0041] (1.7) Sample 22 In Sample 21, the twist-pair pitch of the insulated wires was changed to 8.4 mm.

[0042] (1.8) Sample 23 In Sample 21, the twist-pair pitch of the insulated wires was changed to 12.4 mm.

[0043] (2) Evaluation of the sample Each sample was cut to a length of 5m, and the in-body skew and insertion loss in the high-frequency band were measured for each sample. The measurement results are shown in Tables 2-3 and Figures 2-8. In Tables 2 and 3, the insertion loss values ​​represent the frequencies at which the suck-out phenomenon was observed. In Figures 3-8, the thick solid line represents the automotive Ethernet standard, specifically the IEEE 802.3ch Multi-Gig Automotive Ethernet PHY 10GBASE-T1 (hereinafter simply referred to as the "Multi-Gig Automotive Ethernet standard"). The Multi-Gig Automotive Ethernet standard only defines specifications up to a high-frequency bandwidth of 4 GHz.

[0044] [Table 2]

[0045] [Table 3]

[0046] (3) Summary As shown in Tables 2-3, a comparison between Sample 1-2 and Samples 11-13 and 21-23 reveals that when the conductor configuration is stranded wire, the in-pair skew is 10 ps / m or more, while in the case of compressed stranded wire, it decreases sharply. This is presumed to be because, in the case of compressed stranded wire, the variation in the distance between the conductor surface and the shielding layer is small in the length direction of the cable, and the effect of reflection due to electromagnetic coupling (reverse phase current) is reduced. In general, the in-pair skew is 10 ps / m or less, and practically, it is preferably 5 ps / m or less. As shown in Table 2 and Figure 2, in samples 1-2, the conductor was stranded wire, and in addition to a large in-pair skew, a suck-out phenomenon was observed before the frequency reached 10 GHz. As shown in Table 3, Figure 5, and Figure 8, in samples 13 and 23, although the conductor was compressed stranded wire with a circular cross-section, the pair-twist pitch of the insulated wire exceeded the permissible upper limit, and a suck-out phenomenon was observed before the frequency reached 10 GHz. In contrast, as shown in Figures 3-4 and 6-7, in samples 11-12 and 21-22, the conductor was compressed stranded wire with a circular cross-section, and the pair-twist pitch of the insulated wire was below the permissible upper limit, resulting in small in-pair skew, and no suck-out phenomenon was observed until the frequency exceeded 10 GHz. From the above, it was found that in providing a communication cable compatible with high-frequency data transmission, it is useful to use a single wire or compressed stranded wire with a circular cross-section as the conductor and to control the twisting pitch of the insulated wire to be constant.

[0047] This application claims priority under Japanese Patent Application No. 2021-188499, filed on November 19, 2021. All contents described in the specification and drawings of said application are incorporated herein by reference. [Industrial applicability]

[0048] The present invention relates to a communication cable and a method for manufacturing the same, and is particularly useful in providing a communication cable that is compatible with high-frequency data transmission and can simplify the internal structure of the cable. [Explanation of Symbols]

[0049] 1. Communication cable 10 pairs of twisted bodies 10A~10B 1st~2nd type wire core 12 Insulated wires 14 Conductors 16 Insulator 20 Pressed Roll 30 Inner coat 40 First shielding layer 50 Second shielding layer 60 Outer cover

Claims

1. A communication cable made by twisting together multiple insulated wires, each having a conductor covered with an insulator, The conductor is composed of a single wire or compressed stranded wire with a circular cross-section, A communication cable characterized in that multiple insulated wires are twisted together at a pitch of 7.0 mm or more and at a pitch less than or equal to the value derived by (speed of light × NVP / frequency) × (1 / dielectric constant of the insulator).

2. In the communication cable described in claim 1, The aforementioned insulator is a cross-linked polyethylene, A communication cable characterized in that multiple insulated wires are twisted together at a pitch of 7.0 mm or more and 9.55 mm or less.

3. In the communication cable described in claim 1, The aforementioned insulator is polypropylene, A communication cable characterized in that multiple insulated wires are twisted together at a pitch of 7.0 mm or more and 10.00 mm or less.

4. In a communication cable according to any one of claims 1 to 3, A communication cable characterized by its use in automotive applications.

Images