CN202205509U - Multi-core cable - Google Patents

Abstract

The utility model provides a multi-core cable, which can carry out end treatment without damaging the insulator, and can ensure stable transmission characteristics. In a multi-core cable (1) formed by bundling and sheathing a plurality of coaxial cables (11), the coaxial cable has: a center conductor (12); an insulator (13) surrounding the center conductor Formed by extruding and coating fluorine resin; the outer conductor (15) around the insulator; and the coating layer (16) around the outer conductor, the insulator has 6 to 9 cross-sections formed in a circular or elliptical shape and along the length The gaps (14) with continuous directions, 6 to 9 gaps are evenly arranged in the circumferential direction of the insulator. The total porosity of all voids is greater than or equal to 43%. At the end of the multi-core cable, a plurality of coaxial cables are divided into multiple groups and arranged in parallel, and soldered to the terminals of the connector (6) or PWB (20) respectively to connect each group as a unit. .

Description

multi-core cable

technical field

The utility model relates to a multi-core cable used for signal transmission and the like in electrical equipment and medical equipment.

Background technique

A multi-core cable is used for signal transmission of electronic equipment and medical equipment, and a multi-core cable in which a plurality of coaxial cables are bundled is known (for example, refer to Patent Document 1).

A coaxial cable constituting a multi-core cable has, as an example, an inner conductor formed by twisting a plurality of conductive wires; an insulator formed on the outer periphery of the inner conductor; an outer conductor arranged on the outer periphery of the insulator. a periphery; and a sheath formed on the periphery of the outer conductor.

It is known that a coaxial cable has a low-permittivity foam insulator formed of a porous tape body as an insulator formed on the outer periphery of an inner conductor (for example, refer to Patent Document 2).

Patent Document 1: Japanese Patent Laid-Open No. 2007-188738

Patent Document 2: Japanese Patent Laid-Open No. 2003-234026

Utility model content

In order to connect the coaxial cable constituting the multi-core cable to the connector, the end of the coaxial cable is terminated. In terminal processing, the outer sheath, outer conductor, and insulator are sequentially cut, and the outer conductor, insulator, and central conductor are exposed from the outer sheath in a stepwise manner.

In the case of using a porous tape to form the insulator, since it is porous, it may be damaged and the center conductor and the outer conductor may be brought close to reduce the withstand voltage. Resin belt made of ethylene glycol ester (PET) resin to ensure voltage resistance. However, the PET resin tape is also cut when the outer conductor is cut by the YAG laser in the stepwise peeling process. In addition, the heat generated when soldering the outer conductor and the ground portion may damage the resin tape.

Since the PET resin tape is cut or damaged, the voltage resistance between the central conductor and the outer conductor cannot be sufficiently ensured, the mechanical strength is reduced, and sufficient bending resistance may not be ensured.

An object of the present invention is to provide a multi-core cable capable of end-processing without damaging an insulator and ensuring stable transmission characteristics.

The multi-core cable of the present invention that can solve the above-mentioned problems is formed by bundling a plurality of coaxial cables and covering them with a sheath,

in,

The coaxial cable has: a central conductor; an insulator formed by extrusion-coating a fluorine-based resin around the central conductor; an outer conductor composed of a metal wire provided around the insulator; a coating formed by extrusion-coating a fluorine-based resin around the outer conductor,

The insulator has a plurality of voids formed in a circular or elliptical cross-section and continuous along the length direction, and the plurality of voids are equally arranged in the circumferential direction of the insulator,

There are 6 to 9 voids, and in a section perpendicular to the longitudinal direction of the coaxial cable, when the ratio of the voids to the sum of the areas of all voids and the area of the insulator is defined as the porosity, all The total porosity of the voids is greater than or equal to 43%,

At the end of the multi-core cable, a plurality of coaxial cables are divided into a plurality of groups in a state exposed from the outer sheath, and the coaxial cables are arranged in parallel in units of each group,

The ground rods are soldered to the outer conductors in units of the groups, the center conductors are soldered to the terminals of the connecting members, and connected to the connecting members in units of the groups.

In the multi-core cable of the present invention, preferably, the plurality of groups are bundled in units of the groups, and a shielding layer is formed around these wire bundles,

A sheath is formed around the shielding layer.

The effect of utility model

According to the multi-core cable of the present invention, by arranging the insulator having a plurality of gaps formed in a circular or elliptical cross-section and continuous in the longitudinal direction around the center conductor, it is possible to ensure that each coaxial cable The ratio of the void to the insulator has a low dielectric constant, and is less likely to be damaged by external pressure or bending, ensuring stable transmission characteristics.

In addition, since the insulator is formed by extrusion-coating a fluororesin, damage to the insulator due to laser or soldering heat when the coaxial cable is terminated and connected to a connecting member can be suppressed. This can eliminate the problem that, like a coaxial cable reinforced by winding a resin tape made of PET resin around a porous insulator, the resin tape is damaged by the heat of laser or soldering and cannot be fixed. Sufficient voltage resistance between the center conductor and the outer conductor is ensured, but mechanical strength is reduced, and sufficient bending resistance cannot be ensured.

As shown above, it is possible to eliminate problems when soldering the individual coaxial cables to the connecting parts, and to ensure stable transmission characteristics. signal transmission.

Description of drawings

FIG. 1 is a perspective view showing a multi-core cable according to an embodiment of the present invention.

Fig. 2 is a cross-sectional view of the multi-core cable of Fig. 1 .

Fig. 3 is a cross-sectional view showing a coaxial cable provided in the multi-core cable of Fig. 1 .

Fig. 4 is a schematic perspective view of an extruder used for manufacturing the coaxial cable of Fig. 1 .

Fig. 5 is a perspective view of a coaxial cable after terminal processing.

Fig. 6 is a partial perspective view showing a connection structure to a PWB at an end portion of a multi-core cable.

Fig. 7 is a partial plan view showing a connection structure with a connector at an end portion of a multi-core cable.

Detailed ways

Next, an example of embodiment of the multi-core cable according to the present invention will be described with reference to the drawings.

As shown in FIGS. 1 and 2 , the multi-core cable 1 has a plurality (for example, 192) of coaxial cables 11 , and the intermediate portions of the coaxial cables 11 are bundled by being covered with a sheath 2 .

As shown in FIG. 2 , inside the multi-core cable 1 , 12 cable bundles 11 a in which, for example, 16 coaxial cables 11 are bundled are arranged. Alternatively, all the coaxial cables 11 may be bundled into one bundle. Around these, two press-wound layers 4 and 5, a shielding layer 3, and a sheath 2 are sequentially formed. Each cable bundle 11a may be pressed and wound with a resin tape or the like on a bundle-by-bundle basis.

The two press-wound layers 4 and 5 are, for example, PET (polyethylene terephthalate) tapes that are longitudinally attached and wound around the 12 cable bundles 11a. An adhesive is provided on the inner peripheral surface of the outer push-wound layer 5, and the two push-wound layers 4 and 5 are bonded and integrated by this adhesive. The push-wrap layers 4 and 5 may not be provided.

The shielding layer 3 is formed, for example, by horizontally winding or braiding a plurality of bare copper wires around the press-wound layer 5 . The shielding layer 3 can also be formed by horizontal winding or braiding in two layers.

The sheath 2 is, for example, PVC (polyvinyl chloride).

The coaxial cables 11 exposed from the outer sheath 2 of the multi-core cable 1 are arranged in parallel in a group of multiple (for example, 32 cables consisting of two cable bundles 11a), and are respectively connected to a plurality (for example, 6) Device 6 is connected. At the portion connected to the connector 6, the coaxial cables 11 are arranged in parallel. Instead of the connector 6, each coaxial cable 11 may be connected to a PWB (Printed Wiring Board). Connectors, PWBs, etc. are connected to coaxial cables and connected to other boards, etc., called connection parts.

As shown in FIG. 3 , the coaxial cable 11 has: a center conductor 12; an insulator 13 formed by extruding and coating a fluorine-based resin around the center conductor 12; surrounding metal wires; and a cladding layer 16 formed by extrusion-coating a fluororesin around the outer conductor 15, and the insulator 13 has a plurality of voids 14 continuous in the longitudinal direction.

The center conductor 12 is formed of a single core wire or a twisted wire made of silver-plated or tin-plated annealed copper wire, or a copper alloy wire. In the case of stranded wire, for example, use a stranded wire with an outer diameter of 0.075 mm (equivalent to AWG (American Wire Gauge) #42) formed by twisting seven bare wires with a conductor diameter of 0.025 mm. Or a stranded wire with an outer diameter of 0.38 mm (equivalent to AWG#28) formed by twisting 7 bare wires with a bare wire conductor diameter of 0.127 mm.

In addition, the outer conductor 15 is formed by using a bare copper wire (annealed copper wire or copper alloy wire) with the same thickness as the bare wire conductor used in the central conductor 12, or an annealed silver-plated or tin-plated copper wire, or a copper alloy wire, The outer periphery of the insulator 13 is wound laterally or arranged in a braided structure. In addition, in order to improve the shielding function, a metal foil tape may also be provided as shown in the immediately outer layer of the outer conductor 15 . The cover layer 16 is formed by extrusion molding of a resin material such as a fluororesin, or by winding a resin tape such as a polyester tape.

The insulator 13 is formed by extrusion molding using a fluorine-based resin as a thermoplastic resin. As the fluororesin material, for example, PFA (tetrafluoroethylene-perfluoroalkylvinyl ether copolymer), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), ETFE (tetrafluoroethylene-ethylene copolymer) and the like are used.

Preferably, when the conductor diameter of the center conductor 12 is D2, the outer diameter D1 of the insulator 13 is approximately D2×(2.2 to 3.0). For example, when the conductor diameter of the said central conductor 12 is 0.38 mm (AWG#28), the outer diameter of the insulator 13 is 0.84 mm - 1.1 mm. For electric wires whose central conductor 12 has a conductor diameter smaller than AWG#42, it may be necessary to make the capacitance of the insulator 13 low (for example, 60 pF/m or less) depending on the application. In this case, the outer diameter D1 of the insulator 13 is preferably D2 ×(2.2～3.6). For example, when the conductor diameter of the central conductor 12 is 0.075 mm, the outer diameter of the insulator 13 is 0.17 mm to 0.27 mm.

The multi-core cable 1 having the coaxial cable 11 of this size is often used as a cable for connecting the detector and the main body of the equipment in medical equipment such as ultrasonic diagnostic equipment for signal transmission. Due to the miniaturization of equipment, the coaxial cable 11 is required to be thin Diameter reduction and multi-core cable 1 reduction. The coaxial cable 11 needs to have a predetermined impedance (50Ω, 75Ω, or 80Ω to 90Ω), and the diameter should be reduced as much as possible while achieving this impedance. Therefore, it is necessary to reduce the dielectric constant of the insulating layer between the center conductor 12 and the outer conductor 15 . In the present embodiment, by providing the cavities 14 in the insulator 13 so that the total porosity of all the cavities 14 is 43% or more, diameter reduction is achieved within the above-mentioned range. It is difficult to make the impedance of the coaxial cable a predetermined value if the overall porosity is to be less than 43% and the diameter reduction is satisfied.

In the case where the outer diameter D1 of the insulator 13 of the coaxial cable 11 of this embodiment is D2×(2.4 to 2.7), since the diameter is small and the thickness of the insulator 13 is thin, if the gap 14 is too large, it may not be possible to Withstands external pressure or bending applied to the coaxial cable 11 . Therefore, in the thinner coaxial cable 11 which is the object of the present invention, the size of each void portion 14 provided in the insulator 13 becomes a problem. This is a problem that does not exist in the coaxial cable 11 thicker than this coaxial cable. In the present embodiment, by setting the porosity of each void portion 14 to 6.8% or less, sufficient durability is achieved in the coaxial cable 11 of this size.

Preferably, the cavities 14 of the insulator 13 are formed to have a circular cross section (perfect circle, ellipse), and are provided so that 6 to 9 cavities 14 are evenly arranged around the center conductor 12 . If the void portion 14 is formed in, for example, a substantially perfect circle with an inner diameter of D3, it is preferable that the ratio of a single void portion 14 to the insulator 13 falls within

In the range of "0.068≥({D3/2} ² ×π)/({D1/2} ² ×π-{D2/2} ² ×π)".

In addition, the consideration method of the above-mentioned formula can be similarly applied to the elliptical cavity portion 14 . That is, it is preferable to make the porosity of a single void portion 14 less than or equal to 6.8% in order to satisfy the strength of the void portion 14 itself. Also, if the porosity of a single cavity portion 14 is too small, a predetermined porosity cannot be obtained, and a low dielectric constant cannot be ensured. The void portion 14 as a whole has a porosity of 43% or more. In the case of seven voids 14, the porosity of each is greater than or equal to 6.1%, and in the case of eight voids 14, the porosity of each is greater than or equal to 5.4%. In the case of each, the porosity of each is greater than or equal to 4.8%. In addition, the ellipse referred to here is not limited to an ellipse in a mathematical sense, and includes shapes obtained by deforming a circle.

When the number of voids 14 provided in the insulator 13 is seven, the overall porosity is 43% to 47.6%, in the case of eight, in the range of 43% to 54.4%, in the case of nine , becoming 43% to 61.2%. Thereby, a low dielectric constant for obtaining a predetermined impedance can be ensured. In addition, since a single porosity is less than or equal to 6.8%, the mechanical strength of the insulator 13 as a whole can be improved, it is not easily damaged against external pressure or bending, and the stability of transmission characteristics can be ensured.

When the number of voids 14 is eight, if the conductor diameter D2 of the central conductor 12 is set to 0.38 mm, the outer diameter D1 of the insulator 13 is set to 0.96 mm, and the inner diameter D3 of the voids 14 is set to 0.225 mm , the porosity of the insulator 13 becomes 52%. In addition, if the outer diameter of the insulator 13 is wound with a plated annealed copper wire of 0.127 mm as the outer conductor 15, and as the coating layer 16, a fluororesin (such as PFA) with a coating thickness of about 0.04 mm is extruded. A coaxial cable with an outer diameter of 1.3 mm was obtained.

In addition, when the number of voids 14 provided in the insulator 13 is preferably six, D1/D2 is 3.2 to 4.0, and the capacitance of the insulator 13 is set to be less than or equal to 60 pF/m, the total of all voids The porosity is greater than or equal to 54%. When the central conductor 12 is a stranded wire (corresponding to AWG#42) formed by twisting seven silver-plated silver-copper alloy wires with an outer diameter of 0.025 mm, the total porosity of all the voids 14 is 54. %, the capacitance of the coaxial cable 11 can be set to 60 pF/m. In order to realize this porosity, it is only necessary to provide six voids 14 . When D1/D2 is 3.2 to 4.0, the insulator 13 is slightly thicker than the diameter of the central conductor 12, so the total porosity of all the voids 14 must be increased in order to achieve a capacitance of 60 pF/m. In this case, if the number of voids 14 is more than seven, the insulator 13 between the voids 14 becomes thinner, and when a force from the outside is applied, the gaps 14 may be broken and the insulator 13 may be broken. damage. If the number of cavities 14 is six, it is possible to form a porosity capable of realizing a capacitance of 60 pF/m or less while securing the thickness of the insulator 13 between the cavities 14 . Thereby, even if force is applied to the coaxial cable 11 when winding the coaxial cable 11, etc., the insulator 13 will not be damaged.

The coaxial cable 11 of this embodiment can be manufactured using the extruder 30 which combined the die 31 and the gate 41 shown in FIG.

A cylindrical member 45 corresponding to the number of voids 14 is provided on the gate 41, and is combined with a mold 31 having a circular outlet 33 to squeeze out between the gate 41 and the mold 31 (flow paths 51, 52). out the resin. The center conductor 12 is pulled out from the center hole 44 of the cylindrical portion 43 of the gate 41 . The extruded resin is coated on the central conductor 12 . The resin coating may also be performed by a drawing method in which the resin extruded from the outlet of the die 31 is stretched to reduce the diameter for coating. No resin flows through the columnar member 45 , and this portion forms the void 14 . If the vent hole 46 is provided in the member 45, the resin extruded from the die 31 can ensure the void part 14 through which the resin does not flow, and its cross section is circular or elliptical.

In the multi-core cable 1 having the above-mentioned coaxial cable 11, in order to connect to connecting parts such as the connector 6 or PWB, a laser processing machine such as a YAG laser or a CO ₂ laser is used to form the coating layer 16, the outer conductor 15 and The insulator 13 is sequentially cut, and as shown in FIG. 5 , the outer conductor 15 , the insulator 13 , and the central conductor 12 are exposed from the cladding layer 16 in a stepwise manner.

Specifically, first, as many coaxial cables 11 as are connected to connecting members such as connectors 6 and PWBs are arranged in parallel, and are fixed with an adhesive tape or the like to maintain this state. The intervals between the coaxial cables 11 are set at predetermined intervals. They may also be arranged in parallel so that the covering layers 16 are in contact with each other.

On the parallel coaxial cables 11, a CO ₂ laser is scanned and irradiated in the parallel direction. The wavelength and intensity of the CO ₂ laser were adjusted, and the cladding layer 16 was cut at a predetermined distance from the end, and pulled out to remove the end side. Then, the exposed outer conductor 15 is irradiated by scanning the YAG laser in the same manner. The wavelength and intensity of the YAG laser are adjusted, the outer conductor 15 is cut at a position closer to the end by a predetermined length than the cutting position of the coating layer 16 , and the outer conductor 15 on the end side is removed by pulling out. Then, the exposed insulator 13 is irradiated by scanning the CO ₂ laser in the same manner. The wavelength and intensity of the CO ₂ laser were adjusted, the insulator 13 was cut at a position closer to the end, and the insulator 13 on the end side was removed by pulling out.

After the end treatment is performed as described above, the outer conductor 15 is soldered to the ground rod 17 by pulse heat or the like. The central conductor 12 is connected by soldering to the terminals 7 and 22 (refer to FIGS. 6 and 7 ) of connecting parts such as the connector 6 or the PWB 20, and the ground rod 17 is connected to the connector 6 by soldering or crimping. or ground pad 21 of PWB 20. Since the insulator 13 is formed by extruding and coating a fluorine-based resin, as described above, it is possible to suppress laser or soldering when the coaxial cable 11 is terminated and connected to a connecting member such as the connector 6 or PWB 20. The heat of the soldering can cause damage.

According to the multi-core cable 1 according to the above-mentioned embodiment, by providing the insulator 13 having the plurality of voids 14 having a circular or elliptical cross-section and continuous in the longitudinal direction around the central conductor 12, it is possible to use the multi-core cable 1 in each The ratio of the void portion 14 to the insulator 13 is ensured in the coaxial cable 11 to obtain a low dielectric constant. In addition, even if there is no protective layer such as PET tape, the insulator is not easily damaged by external pressure or bending, and it is stable in voltage resistance and capacitance.

In addition, it is possible to suppress damage to the insulator due to the heat of laser or soldering when the coaxial cable 11 is terminated and connected to a connecting member such as the connector 6 or PWB. This can solve the problem that, like a coaxial cable reinforced by winding a PET resin tape around a porous insulator, the central conductor cannot be sufficiently secured due to damage to the resin tape by the heat of laser or soldering. The withstand voltage between the external conductor and the external conductor reduces the mechanical strength and cannot ensure sufficient bending resistance.

In addition, the coaxial cable 11 of the multi-core cable 1 may be connected to a connecting member such as a connector 6 or a PWB at both ends, or may be connected to a connecting member only at one end, and the other end may be connected to a substrate by soldering. Wait for the connection.

[Example]

(Example 1)

As shown in FIG. 6, the coaxial cable 11 of the multi-core cable is connected to the PWB 20.

The multi-core cable is a cable for an ultrasonic probe formed by bundling 160 coaxial cables 11, and the center conductor 12 of each coaxial cable 11 corresponds to AWG 42. The coaxial cable 11 has: a central conductor 12; an insulator 13 formed by extrusion-coating PFA around the central conductor 12; an outer conductor 15 composed of a copper alloy wire wound laterally around the insulator 13; The coating layer 16 is formed by extruding coating PFA around the outer conductor 15, and the insulator 13 has six voids 14 continuous in the longitudinal direction. In each coaxial cable 11 , the outer diameter of the insulator 13 was 0.29 mm, the porosity of each void 14 was 9.0%, and the total porosity of all the voids was 54%. The 16 above-mentioned coaxial cables 11 are collectively bundled to form one unit (cable bundle 11a in FIG. 2 ), 10 units are collected and bundled, and the shielding layer 3 is integrally provided around the periphery, and then formed around the shielding layer 3 Sheath 2 (refer to Figure 2) to obtain a multi-core cable.

Remove the sheath 2 at the end of the multi-core cable, and connect the shielding layer 3 to the overall shielding grounding terminal of the PWB 20.

At the end of each unit, as shown in FIG. 6 , the coaxial cables 11 are arranged in parallel in a planar shape, and terminal processing is performed (see FIG. 5 ). Then, for each unit, the outer conductor 15 is sandwiched by the ground rod 17 from the upper and lower sides of the parallel surface, and fixed by the solder 23 . Then, the central conductor 12 of each coaxial cable 11 is soldered to each terminal (signal pad) 22 of the PWB 20. The ground rod 17 on one side is then soldered to the ground pad 21 of the PWB 20.

(Example 2)

As shown in FIG. 7 , the coaxial cable 11 of the multi-core cable is connected to the connector 6 .

The multi-core cable is a cable for an ultrasonic probe formed by bundling 120 coaxial cables 11, and the central conductor 12 of each coaxial cable 11 corresponds to AWG 42. The configuration of the coaxial cable 11 is the same as that of the above-mentioned embodiment. 20 coaxial cables 11 are collectively bundled to form one unit (cable bundle 11a in FIG. 2 ), six units are collected and bundled, and a shielding layer 3 is integrally provided around the periphery, and then a sheath is formed around the shielding layer 3 2 (see Figure 2) to obtain a multi-core cable.

At the end of the above-mentioned multi-core cable, the sheath 2 is removed, and the shielding layer 3 is concentrated. At the end of each unit, as shown in FIG. 7 , the coaxial cables 11 are arranged in parallel in a planar shape, and terminal processing is performed (see FIG. 5 ). Then, for each unit, the outer conductor 15 is sandwiched by the ground rods 17 from the upper and lower sides of the parallel surface, and fixed with flux. Then, the central conductor 12 of each coaxial cable 11 is soldered to each terminal (signal pad) 7 of the connector 6 . Then, the housing (not shown) of the connector 6 is stacked on the ground rod 17, and the ground rod 17 and the housing are soldered.

In the first and second embodiments described above, when the outer conductor 15 was cut by the YAG laser at the end of the coaxial cable 11, the insulator 13 was not damaged. In addition, even if the ground rod 17 is soldered by pulse heating, the insulator 13 will not be damaged.

In addition, regarding the coaxial cable 11 used in Examples 1 and 2, changes in the outer diameter of the insulator and changes in capacitance were investigated. On the other hand, as a comparative example relative to the examples, a coaxial cable in which a porous tape body was used as the insulator of the coaxial cable was prepared (the foamed insulating tape was wound: the capacitance was the same as that of the examples), and the change in the outer diameter of the insulator was also investigated. and capacitance changes. In addition, the YAG laser damaged the insulator at the time of terminal processing of the multi-core cable constructed using the coaxial cable of the comparative example.

In Examples 1 and 2 in which the insulator 13 of the coaxial cable 11 is formed by extrusion-coating PFA, the variation of the outer diameter of the insulator 13 falls within ±1.5% from the design value. In Comparative Examples 1 and 2 in which a porous tape was used as an insulator, the change in the outer diameter of the insulator was ±5.2% from the design value. In addition, the change in capacitance of Examples 1 and 2 fell within ±1.7% from the design value, whereas in Comparative Examples 1 and 2, the change in capacitance was ±3.3% from the design value. As described above, by changing the insulator around the central conductor from a foamed insulating tape winding layer (Comparative Examples 1, 2) to a layer formed by extrusion coating a fluorine-based resin (Examples 1, 2), it is possible to Stabilizes the capacitance of the coaxial cable and suppresses fluctuations in the diameter of the insulator and breakage of the insulator. In addition, since the fluctuations in the capacitance of the coaxial cables are small, when these are bundled to form a multi-core cable, the fluctuations in the capacitance between the coaxial cables are small. When this multi-core cable is used for an ultrasonic diagnostic device, the image becomes clearer.

Regarding bending resistance, a wire harness formed by winding 40 coaxial cables used in Examples 1 and 2 with a PTFE tape was bent, and the number of times of bending until any one of them was broken was investigated. The bending condition is to install a weight of 500g at the end of the above wire harness and hang the wire harness, use two mandrels (mandrel) with a diameter of 4mm to clamp the wire harness, and apply ±90° angle at a frequency of 30 times/min. bent.

As an average value of three samples, the harness of the coaxial cable of the example was subjected to 26,000 times of bending, and the harness of the coaxial cable of the comparative example was subjected to 23,000 times of bending, and the bending resistance of the coaxial cable of the example was confirmed. Excellent foldability.

Perform a torsion test on the same harness. The test conditions were to hold two parts of the wire harness at intervals of 10 mm, and to apply a twist of ±180° around the axial direction of the wire harness at a frequency of 60 times/min.

In the wire harness using the coaxial cable of the embodiment, even if it was twisted 150,000 times, the coaxial cable did not break. For the wire harness using the coaxial cables of the comparative example, after twisting 80,000 times, the initial disconnection occurred (1 disconnection in 40 coaxial cables). It was confirmed that the coaxial cables of Examples are excellent in torsion resistance.

Claims (2)

1. A multi-core cable formed by bundling a plurality of coaxial cables and covering them with a sheath, It is characterized by, The coaxial cable has: a central conductor; an insulator formed by extrusion-coating a fluorine-based resin around the central conductor; an outer conductor composed of a metal wire provided around the insulator; a coating formed by extrusion-coating a fluorine-based resin around the outer conductor, The insulator has a plurality of voids formed in a circular or elliptical cross-section and continuous along the length direction, and the plurality of voids are equally arranged in the circumferential direction of the insulator, There are 6 to 9 voids, and in a section perpendicular to the longitudinal direction of the coaxial cable, when the ratio of the voids to the sum of the areas of all voids and the area of the insulator is defined as the porosity, all The total porosity of the voids is greater than or equal to 43%, At the end of the multi-core cable, a plurality of coaxial cables are divided into a plurality of groups in a state exposed from the outer sheath, and the coaxial cables are arranged in parallel in units of each group, The ground rods are soldered to the outer conductors in units of the groups, the center conductors are soldered to the terminals of the connecting members, and connected to the connecting members in units of the groups. 2. The multi-core cable according to claim 1, characterized in that, The plurality of groups are bundled in units of the groups, and a shielding layer is formed around these wire bundles, A sheath is formed around the shielding layer. the

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