Multi-core cable

Abstract

To provide a multicore cable that is capable of accurately detecting temperature rise inside a cable, and reduces alternating current resistance.SOLUTION: A multicore cable 1 comprises: a heat detecting wire 2 which has a twisted pair wire 22 in which a pair of heat detecting electric wires 21 having a first conductor 211 and a first insulator 212 covering around the first conductor 211 are twisted, and a jacket 24 covering around the twisted pair wire 22; a plurality of electric wires 3 which has a second conductor 31 and a second insulator 32 covering around the second conductor 31, and is spirally twisted around the heat detecting wire 2; and a sheath 4 which covers the heat detecting wire 2 and the plurality of electric wires 3 in a bundle, where the jacket 24 has a middle layer 242 that has an inner layer 241 and an outer layer 243, and is provided between the inner layer 241 and the outer layer 243, and the outer layer 243 has higher hardness than the inner layer 241.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a multi-core cable.

Background Art

[0002] Conventionally, for fire detection, fire detection wires have been used (see, for example, Patent Document 1). The fire detection wire has a pair of twisted wires formed by twisting a pair of fire detection electric wires each having a conductor made of a steel wire such as a piano wire and an insulator with a low melting point covering the periphery of the conductor, and is configured to cover the twisted wire with a jacket.

[0003] Conventionally, the fire detection wire is arranged along the cable. For example, in a multi-core cable used for non-contact power supply, a fire detection wire is provided between the multi-core cable and a housing that houses the multi-core cable.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in a system used in a clean environment such as an automatic transport system in a semiconductor factory or the like, non-contact power supply for performing non-contact power supply is generally used. In a power supply cable used for such non-contact power supply, since a large current flows, when an excessive current flows for some reason, it is desired to detect a temperature rise in the cable and suppress the occurrence of a fire.

[0006] In addition, since the above-described power supply cable is laid in a housing, for example, there is a limit on the outer diameter. Therefore, there is a demand to reduce the AC resistance with respect to an AC current having a high frequency (for example, 5 kHz or more) used for power supply without increasing the outer diameter.

[0007] Therefore, an object of the present invention is to provide a multi-core cable that can accurately detect a temperature rise in the cable and reduce the AC resistance.

Means for Solving the Problems

[0008] The present invention is a pair-twisted wire formed by twisting a pair of heat-detection wires each having a first conductor and a first insulator covering the periphery of the first conductor, and a heat-detection wire having a jacket covering the periphery of the pair-twisted wire, a plurality of wires each having a second conductor and a second insulator covering the periphery of the second conductor and being spirally twisted around the heat-detection wire, and a sheath covering the heat-detection wire and the plurality of wires together, wherein the jacket has an inner layer and an outer layer and an intermediate layer provided between the inner layer and the outer layer. The intermediate layer has a higher melting point than the inner layer and the outer layer. A multi-core cable is provided. Moreover, the present invention aims to solve the above problems, and provides a manufacturing method of a multi-core cable including: a pair of twisted wires formed by twisting a pair of heat-detecting wires each having a first conductor and a first insulator covering the periphery of the first conductor; a heat-detecting wire having a jacket covering the periphery of the pair of twisted wires; a plurality of wires each having a second conductor and a second insulator covering the periphery of the second conductor and being spirally twisted around the heat-detecting wire; and a sheath covering the heat-detecting wire and the plurality of wires together. The jacket has an inner layer and an outer layer, and an intermediate layer provided between the inner layer and the outer layer. The intermediate layer has a higher melting point than the outer layer. The method includes a step of forming the heat-detecting wire, a step of twisting the plurality of wires around the heat-detecting wire, and a step of forming the sheath. In the step of forming the heat-detecting wire, the outer layer is formed by insert extrusion or filling extrusion on the outer periphery of the intermediate layer so that the outer shape of the outer layer is circular.

Advantages of the Invention

[0009] According to the present invention, it is possible to provide a multi-core cable that can accurately detect a temperature rise in the cable and reduce the AC resistance.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0011] [Embodiment] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0012] (Overall Structure of Multi-Core Cable 1) FIG. 1 is a cross-sectional view showing a cross-section perpendicular to the longitudinal direction of the multi-core cable according to the present embodiment. FIG. 2 is a cross-sectional view when the multi-core cable of FIG. 1 is housed in the groove of the housing.

[0013] As shown in FIGS. 1 and 2, the multi-core cable 1 includes a heat detection wire 2, a plurality of electric wires 3, and a sheath 4 that collectively covers the heat detection wire 2 and the plurality of electric wires 3.

[0014] This multi-core cable 1 is used for non-contact power supply (for non-contact power feeding) and is housed and used in the groove 11 of the housing 10. In this example, the housing 10 has a pair of side walls 12 arranged in parallel and a bottom wall 13 perpendicular to the side walls 12 that connects the ends of the side walls 12, and is formed in a U-shape that is rotated 90 degrees in the clockwise direction in cross-sectional view as a whole. A rectangular space in cross-sectional view surrounded by the pair of side walls 12 and the bottom wall 13 and opening on the side opposite to the bottom wall 13 is the groove 11.

[0015] (Heat Detection Wire 2) The heat detection wire 2 has a pair-twisted wire 22 formed by twisting a pair of heat detection electric wires 21, a pressing tape 23 spirally wound around the pair-twisted wire 22, and a jacket 24 covering the periphery of the pressing tape 23.

[0016] Each of the pair of heat detection electric wires 21 constituting the pair-twisted wire 22 has a first conductor 211 and a first insulator 212 covering the periphery of the first conductor 211. As the first conductor 211, it is preferable to use one that can increase the force with which the first conductors 211 approach each other toward the center side of the pair-twisted wire 22 when twisted as the pair-twisted wire 22.

[0017] As described above, the multi-core cable 1 is used for non-contact power supply and is wired over a long distance, for example, 30 m or more in a factory or the like. Therefore, it is necessary to maintain a high conductivity of the first conductor 211 to such an extent that a short circuit between the first conductors 211 can be detected even when wired over a long distance. In addition, a strength is required such that no disconnection occurs even when wired over a long distance. In the present embodiment, it is preferable that the outer diameter of the first conductor 211 is 0.5 mm or more and 1.0 mm or less. By setting the outer diameter of the first conductor 211 to 0.5 mm or more, the conductor resistance is suppressed and the conductivity is maintained high, and it becomes possible to detect a short circuit between the first conductors 211 even in long-distance wiring. Further, by setting the outer diameter of the first conductor 211 to 0.5 mm or more, it is possible to suppress a decrease in the force with which the first conductors 211 approach each other and a decrease in detection sensitivity, and to improve the detection sensitivity of the temperature inside the cable. On the other hand, by setting the outer diameter of the first conductor 211 to 1.0 mm or less, it is possible to suppress the multi-core cable 1 from becoming hard and difficult to bend, and to realize a multi-core cable 1 that is easy to wire.

[0018] Furthermore, in the present embodiment, as the first conductor 211, a non-magnetic material and a copper alloy having a tensile strength of 900 MPa or more are used. More specifically, the first conductor 211 uses phosphor bronze containing 7 mass% or more and 10 mass% or less of tin and 0.03 mass% or more and 0.35 mass% or less of phosphorus. By using a non-magnetic material as the first conductor 211, it is possible to suppress losses in non-contact power supply and suppress a decrease in the efficiency of non-contact power supply.

[0019] Furthermore, by setting the tensile strength of the first conductor 211 to 900 MPa or more (preferably 930 MPa or more, more preferably 990 MPa or more), the force with which the first conductors 211 of the twisted pair 22 approach each other toward the center of the twisted pair 22 in a state where the first conductors 211 are twisted together can be increased. As a result, when the first insulator 212 softens and melts, the first conductors 211 quickly move toward the center of the twisted pair 22, and the first conductors 211 come into contact with each other, enabling the detection sensitivity of the temperature inside the cable to be improved by this contact. Also, by setting the tensile strength of the first conductor 211 to 900 MPa or more, it is possible to ensure the strength that prevents disconnection even when wiring over a long distance. Furthermore, from the viewpoint of increasing the force with which the first conductors 211 of the twisted pair 22 approach each other toward the center of the twisted pair 22 to improve the detection sensitivity, the elongation of the first conductor 211 is desirably 10% or less (more preferably 3% or less). The tensile strength and elongation of the first conductor 211 are determined by a tensile test method (test piece: No. 9B) conforming to JIS Z2241 (2011).

[0020] In the present embodiment, a single wire first conductor 211 made of tin-plated phosphor bronze with a diameter of 0.63 mm was used. Note that the copper alloy used for the first conductor 211 is not limited to phosphor bronze, and for example, brass, beryllium copper, or the like can also be used. However, it can be said that it is more desirable to use phosphor bronze, which can increase the force with which the first conductors 211 of the twisted pair 22 approach each other toward the center of the twisted pair 22, and is less likely to cause disconnection and is inexpensive.

[0021] As the first insulator 212, an insulating resin with a relatively low melting point is used to be melted when the temperature inside the cable rises. More specifically, before the second insulator 32 (described later) of the electric wire 3 melts due to the heat when the temperature inside the cable rises due to an overcurrent or the like, the first insulator 212 melts (in other words, before the function of the electric wire 3 is lost due to the heat when the temperature rises as described above, the first conductor 211 is short-circuited so that the temperature rise inside the cable due to the occurrence of an overcurrent or the like is detected), the melting point of the first insulator 212 is made lower than the melting point of the second insulator 32 of the electric wire 3 (for example, 105°C or higher). In the present embodiment, it is aimed to not operate at 80°C or lower and to operate at 100°C within several minutes (within 5 minutes), and the melting point of the first insulator 212 is set to be higher than 80°C and lower than 100°C (more preferably about 90°C). Here, the first insulator 212 made of an ionomer resin with a melting point of about 89°C was used.

[0022] The thickness of the first insulator 212 is desirably 0.1 mm or more and 0.3 mm or less. By setting the thickness of the first insulator 212 to 0.1 mm or more, the mechanical strength of the first insulator 212 can be ensured, damage to the first insulator 212 that is not intended can be suppressed, and malfunction of the heat detection wire 2 can be suppressed. Also, by setting the thickness of the first insulator 212 to 0.3 mm or less, when the first insulator 212 softens and melts, the first conductors 211 can be quickly brought into contact with each other, and problems such as the first conductors 211 not contacting each other despite the temperature inside the cable rising can be suppressed. In the present embodiment, the thickness of the first insulator 212 is 0.14 mm, and the outer diameter of the heat detection electric wire 21 is 0.91 mm. The outer diameter of the twisted pair 22 formed by twisting two heat detection electric wires 21 together is 1.82 mm.

[0023] Note that, with respect to the first insulator 212, it is preferable that the thickness of the portion where the respective first heat-detection wires 21 that constitute the twisted pair 22 are in contact with each other (the portion where the first insulators 212 of the pair of first heat-detection wires 21 are in contact with each other) is smaller than the thickness of the portion where the respective first heat-detection wires 21 that constitute the twisted pair 22 are not in contact with each other (the portion where the first insulators 212 of the pair of first heat-detection wires 21 are not in contact with each other). Thereby, when the first insulator 212 softens and melts, the first conductors 211 are quickly brought into contact with each other, and it becomes easier to suppress problems such as the first conductors 211 not coming into contact with each other despite the temperature inside the cable rising. At this time, the portions where the respective first heat-detection wires 21 that constitute the twisted pair 22 are in contact with each other are preferably in surface contact. The thickness referred to here is the shortest distance (minimum thickness) from the inner surface of the first insulator 212 to the outer surface of the first insulator 212.

[0024] FIG. 3 is a photograph for explaining the operation of the heat detection wire 2, where (a) is the photograph before operation and (b) is the photograph after operation. As shown in FIGS. 3(a) and 3(b), in the heat detection wire 2, when the temperature inside the cable (the temperature around the electric wire 3) rises to a temperature equal to or higher than the melting point of the first insulator 212 (89°C in this embodiment) and lower than the melting point of the second insulator 32, and when the first insulator 212 softens and melts due to the heat at this time, the twisted first conductors 211 move toward the center of the twisted pair 22 by the force that the first conductors 211 try to approach each other toward the center of the twisted pair 22, and the first conductors 211 come into contact with each other and electrically short-circuit. At this time, the first insulator 212 existing between the first conductors 211 is in a molten state, and the first insulator 212 existing between the first conductors 211 is pushed away from the vicinity of the center of the twisted pair 22 by the force that the first conductors 211 try to approach each other. Therefore, the outer shape of the first insulator 212 is not circular, but has a shape with a slightly flattened portion where the first insulators 212 contact each other. By detecting the short circuit of these two first conductors 211, it is possible to detect the temperature rise in the multi-core cable 1 due to overcurrent or the like. In the photographs of FIGS. 3(a) and 3(b), in order to easily confirm the cross-sectional state of the heat detection wire 2, the epoxy resin is filled around the heat detection wire 2, and after polishing the cut end face, the cut face is photographed. Also, in FIGS. 3(a) and 3(b), the jacket 24 is a single layer. The heat detection wire 2 operates in the same manner as the above operation even when the jacket 24 has three layers as shown in FIGS. 1 and 2.

[0025] Incidentally, in this heat detection wire 2, when the temperature around the heat detection wire 2 rises, before the two first conductors 211 short-circuit, the first insulator 212 softens and the distance between the two first conductors 211 decreases, and the resistance value and capacitance between the two first conductors 211 change. Therefore, by measuring the resistance value and capacitance between the two first conductors 211, it may be possible to detect that the temperature around the heat detection wire 2 has risen before the two first conductors 211 short-circuit.

[0026] Also, although not shown, the first insulator 212 may have a multilayer structure in which a plurality of layers made of an insulating resin composition are laminated. For example, by making the first insulator 212 have a two-layer structure and setting the melting point of the inner layer higher than that of the outer layer, the temperature rise in the multi-core cable 1 can be detected step by step.

[0027] Furthermore, when the first insulator 212 has a multilayer structure, at least one layer other than the layer closest to the first conductor 211 may contain particulate matter having a melting point higher than that of the insulating resin constituting the first insulator 212. By including particulate matter with a high melting point in the first insulator 212, when the temperature around the heat detection line 2 rises, the particulate matter is pushed in by the force causing the first conductors 211 to approach each other, suppressing the first insulator 212 from remaining thin, and making it possible to easily cause a short circuit between the first conductors 211. If the particulate matter is insulating, there is a risk that the particulate matter will be caught between the first conductors 211 and no short circuit will occur. Therefore, it is desirable to use conductive particulate matter as the particulate matter. For example, carbon particles can be used as the particulate matter.

[0028] The twist pitch of the twisted pair 22 is preferably about 20 times the outer diameter of the heat detection wire 21 (18 times or more and 22 times or less). This makes it possible to suppress the first insulator 212 from being destroyed by the force while maintaining the force that causes the first conductors 211 to approach each other. The twist pitch of the twisted pair 22 is the interval between the longitudinal positions where any heat detection wire 21 has the same circumferential position in the longitudinal direction of the twisted pair 22.

[0029] As the holding tape 23 wound around the twisted pair 22, for example, a resin tape such as a polyester tape can be used. The holding tape 23 is wound around the twisted pair 22 in a spiral shape so that a part in the width direction overlaps.

[0030] (Jacket 24) The jacket 24 serves as a protective layer for protecting the twisted pair 22, as a core material when twisting the electric wires 3, and as an outer skin for the heat detection wire 2 exposed at the cable terminal.

[0031] Here, the heat detection wire 2 exposed at the cable terminal is connected to a detection device (not shown) that detects an electrical short circuit due to contact between the first conductors 211. The outer diameter of the heat detection wire 2 connected to this detection device is defined by specifications and the like. However, the defined outer diameter of this heat detection wire 2 may be different from the outer diameter required to fill the gap between the electric wires 3 (that is, the outer diameter required to serve as a core material). In particular, when the conductor cross-sectional area of the electric wire 3 is increased to reduce the conductor resistance, accordingly, the gap (space) between the electric wires 3 formed at the center of the cable becomes larger, and the outer diameter of the heat detection wire 2 required to fill this gap also becomes larger. Note that if the outer diameter of the heat detection wire 2 is smaller than the gap (space) between the electric wires 3, the symmetry is broken when the electric wires 3 are twisted around the heat detection wire 2, the uniformity of the current distribution is impaired, and the AC resistance to AC of a high frequency (5 kHz or more, for example, a high frequency of about 10 kHz) increases.

[0032] Therefore, the inventors first considered making the jacket 24 a two-layer structure consisting of an inner layer and an outer layer made of polyvinyl chloride resin, and at the time of terminal processing, peeling off and removing the outer layer from the inner layer in the exposed heat detection wire 2 to make the outer diameter of the heat detection wire 2 a specified outer diameter. As a result of the inventors' study, by forming the outer layer by tube extrusion, the outer layer could be peeled off from the inner layer. However, when the outer layer was formed by tube extrusion, it was found that due to the influence of the twist of the stranding wire 22 and the unevenness on the surface of the inner layer, voids were generated between the inner layer and the outer layer, or the unevenness on the surface of the inner layer appeared on the surface of the outer layer. As a result, when the electric wire 3 was twisted around the heat detection wire 2, the symmetry of the arrangement of the electric wire 3 was disrupted, the uniformity of the current distribution was impaired, and it was found that the AC resistance to high-frequency (5 kHz or more, for example, about 10 kHz) alternating current increased. On the other hand, by forming the outer layer by insert extrusion or solid extrusion, the roundness of the outer layer (that is, the roundness of the outer layer surface in a cross section perpendicular to the cable longitudinal direction) could be increased, and the symmetry of the arrangement of the electric wires could be improved. However, in this case, it became difficult to peel off the outer layer from the inner layer. In order to solve such problems, the inventors conducted intensive studies, and as a result, they considered forming an intermediate layer between the inner layer and the outer layer that allows the outer layer to be peeled off, and thus arrived at the present invention.

[0033] That is, in the multi-core cable 1 according to the present embodiment, the jacket 24 of the heat detection wire 2 has an inner layer 241 and an outer layer 243, and also has an intermediate layer 242 provided between the inner layer 241 and the outer layer 243. The intermediate layer 242 has a higher melting point than the inner layer 241 and the outer layer 243, and the outer layer 243 is configured to be peelable from the intermediate layer 242. Thereby, the outer layer 243 can be formed by insert extrusion or solid extrusion to increase the roundness of the outer layer 243, improve the symmetry of the arrangement of the electric wires 3, improve the uniformity of the current distribution, and reduce the AC resistance to high-frequency alternating current. It is also possible to peel off the outer layer 243 from the intermediate layer 242 and make the outer diameter of the heat detection wire 2 exposed at the cable terminal a specified outer diameter. Hereinafter, each layer of the jacket 24 will be described in detail.

[0034] The inner layer 241 is made of an insulating resin composition having a melting point higher than that of the first insulator 212 so as not to melt before the first insulator 212 melts. However, if the inner layer 241 is made too thick, there is a risk that the first insulator 212 will melt due to the heat during the molding of the inner layer 241. Therefore, the thickness of the inner layer 241 needs to be set to a thickness such that the first insulator 212 does not melt during the extrusion molding, taking into account the melting point (molding temperature) of the inner layer 241. In the present embodiment, a resin composition mainly composed of a non-lead heat-resistant vinyl (polyvinyl chloride) resin is used as the inner layer 241. In this case, it is desirable that the thickness of the inner layer 241 be 5 times or less the thickness of the first insulator 212 (here, 0.14 mm), and it is desirable that the thickness be 0.7 mm or less. Here, the thickness of the inner layer 241 is set to 0.45 mm, and the outer diameter of the inner layer 241 is set to 2.82 mm. The inner layer 241 is formed by non-solid extrusion molding (so-called tube extrusion molding). After the inner layer 241 is molded, it is advisable to perform a cooling treatment promptly with cooling water or the like to suppress the melting of the first insulator 212.

[0035] Similar to the inner layer 241, the intermediate layer 242 is made of an insulating resin composition having a melting point higher than that of the first insulator 212 so as not to melt before the first insulator 212 melts. In the present embodiment, the intermediate layer 242 serves to enhance the peelability of the outer layer 243 and is the outermost layer of the heat detection wire 2 exposed at the cable terminal. Therefore, the intermediate layer 242 is made of an insulating resin composition having a melting point higher than that of the outer layer 243 and being easily peelable from the outer layer 243. In the present embodiment, the melting point of the intermediate layer 242 is higher than both the melting point of the inner layer 241 and the melting point of the outer layer 243.

[0036] Although details will be described later, in the present embodiment, since a resin composition mainly composed of a polyvinyl chloride resin is used as the outer layer 243, the intermediate layer 242 is constituted by a resin composition mainly composed of a fluororesin having high peelability with respect to this polyvinyl chloride resin. As a result, even if the outer layer 243 is molded by insertion extrusion or solid extrusion with a high adhesion degree, the outer layer 243 can be easily peeled off and removed from the intermediate layer 242.

[0037] As the fluororesin constituting the intermediate layer 242, for example, ETFE (tetrafluoroethylene-ethylene copolymer), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PFA (ethylene tetrafluoride-perfluoroalkoxyethylene copolymer), etc. can be used. Among them, it is more preferable to use ETFE or FEP whose melting point is 250 °C or higher and less than 300 °C as the intermediate layer 242. This is to prevent the first insulator 212 from melting during the molding of the intermediate layer 242. In the present embodiment, ETFE is used as the fluororesin constituting the intermediate layer 242. Since ETFE has relatively high hardness among fluororesins, when the outer layer 243 is formed by insert extrusion or solid extrusion on the outer periphery of the intermediate layer 242, the roundness of the outer layer 243 can be increased, and when a plurality of electric wires 3 are arranged around, the thermal detection wire 2 can be easily maintained at a desired outer diameter. Therefore, it is possible to improve the symmetry of the arrangement of the plurality of electric wires 3, and it is easy to maintain the outer diameter of the thermal detection wire 2 exposed at the cable terminal at the specified outer diameter.

[0038] Note that if the intermediate layer 242 is made too thick, the first insulator 212 may melt due to heat during molding, and the entire multi-core cable 1 becomes hard and difficult to bend. Therefore, it is desirable to make the thickness of the intermediate layer 242 as thin as possible. Specifically, the thickness of the intermediate layer 242 is desirably at least 50% or less of the thickness of the inner layer 241, more preferably about 1 / 3 of the thickness of the inner layer 241. In the present embodiment, the thickness of the intermediate layer 242 is 0.14 mm, and the outer diameter of the intermediate layer 242 is 3.1 mm, which is the outer diameter specified for connection to the detection device. The intermediate layer 242 is formed by non-solid extrusion molding (so-called tube extrusion molding).

[0039] The outer layer 243, like the inner layer 241 and the intermediate layer 242, is composed of an insulating resin composition having a melting point higher than that of the first insulator 212 so as not to melt before the first insulator 212 melts. In the present embodiment, the outer layer 243 fills the gap between the intermediate layer 242 and the surrounding electric wire 3 and serves to increase the roundness of the outer shape of the heat detection wire 2. Since the inner layer 241 and the intermediate layer 242 are formed by tube extrusion molding, due to the influence of the twist of the heat detection electric wire 21, irregularities corresponding to the twist appear on the surface of the intermediate layer 242. In order to prevent a gap from occurring between the intermediate layer 242 and the outer layer 243 due to the influence of this irregularity and to finish the surface of the outer layer 243 into a shape without irregularities corresponding to the twist of the heat detection electric wire 21, the outer layer 243 is formed by insert extrusion or full extrusion that increases the adhesion to the intermediate layer 242.

[0040] By increasing the roundness of the outer shape of the outer layer 243 (that is, keeping the outer shape of the heat detection wire 2 as close to a circular shape as possible), the pressing force generated between the electric wire 3 and the heat detection wire 2 due to the pressing of the sheath 4 described later becomes substantially uniform for each electric wire 3, and all the electric wires 3 are deformed evenly. As a result, as shown in FIG. 1, the symmetry of the structure in a cross-sectional view of the entire multi-core cable 1 is increased. For example, if the outer shape of the heat detection wire 2 arranged at the center of the cable is elliptical or has irregularities corresponding to the twist of the heat detection electric wire 21, the variation in the outer shape of the electric wires 3 arranged around the heat detection wire 2 will increase accordingly, and the current loss (difficulty of flowing) will be different for each electric wire 3. That is, the current distribution when an alternating current of high frequency (5 kHz or more, for example, about 10 kHz) flows becomes non-uniform. When the current distribution becomes non-uniform, the AC resistance increases and the efficiency of non-contact power feeding decreases.

[0041] That is, when a plurality of electric wires 3 are twisted around the heat detection wire 2, by keeping the outer shape of the heat detection wire 2 as close to a circular shape as possible, as shown in FIG. 1, the cross-sectional shape of the plurality of electric wires 3 twisted around the heat detection wire 2 can be made uniform (the variation in the outer shapes of the plurality of electric wires 3 can be reduced). In the state where the electric wire 3 is twisted around the heat detection wire 2 arranged at the center of the cable and the sheath 4 is provided, since the heat detection wire 2 is pressed toward the cable center side by the electric wire 3, actually, due to the influence of the pressing force generated between the heat detection wire 2 and each of the plurality of electric wires 3, the outer shape of the heat detection wire 2 becomes a non-circular shape as shown in FIG. 1 (the outer surface of the portion in contact with the electric wire 3 in the outer layer 243 is pushed into the cable center side). In the present embodiment, since the heat detection wire 2 is pressed by the six electric wires 3, the outer shape of the heat detection wire 2 becomes a substantially hexagonal shape.

[0042] FIGS. 4(a) and (b) are diagrams showing the simulation results of the current distribution when six conductors having the same cross-sectional shape and cross-sectional area are uniformly arranged around the cable center (heat detection wire 2), and an alternating current of 1 ampere in total for six conductors (1 / 6 ampere for each conductor) and a frequency of about 10 kHz is passed through each conductor. FIG. 4(a) shows the color original drawing in grayscale, and FIG. 4(b) shows the color original drawing with the difference in color replaced by the difference in hatching. From the simulation results shown in FIGS. 4(a) and (b), it can be seen that by arranging the six conductors (that is, the electric wires 3) around the heat detection wire 2 with a uniform cross-sectional shape and cross-sectional area, a large amount of current flows outside the conductors (on the outer sheath side), and the current distribution for each conductor becomes uniform. By making the current distribution uniform, an increase in the AC resistance due to the non-uniform current distribution can be suppressed, and the AC resistance can be reduced.

[0043] Returning to FIGS. 1 and 2, when the electric wires 3 are twisted around the outer layer 243, the electric wires 3 will be pressed against it. Therefore, in order to suppress the deformation of the outer layer 243 when the electric wires 3 are pressed as much as possible and keep the outer shape of the heat detection wire 2 as close to a circular shape as possible, it is desirable to use a resin composition with relatively high hardness, and it is desirable to use a resin composition with a hardness at least higher than that of the inner layer 241. More specifically, the hardness of the outer layer 243 may be such that the Shore D hardness measured in accordance with JIS K7215 Type D is 55 or more and less than 60. The hardness of the inner layer 241 is smaller than that of the outer layer 243. For example, the Shore D hardness is 30 or more and 35 or less. The hardness of the intermediate layer 242 is harder than those of the inner layer 241 and the outer layer 243. For example, the Shore D hardness is 60 or more and 70 or less. By having the heat detection wire 2 have a jacket 24 composed of three layers (inner layer 241, intermediate layer 242, and outer layer 243) having the above-described hardness, the symmetry of the arrangement of the plurality of electric wires 3 can be improved (as shown in FIG. 1, the cross-sectional shapes of the plurality of electric wires 3 twisted around the heat detection wire 2 can be made uniform). As a result, in the multi-core cable 1, when an alternating current with a high frequency (for example, 5 kHz or more) flows, the current distribution in the plurality of electric wires 3 becomes uniform, and the alternating current resistance can be reduced.

[0044] In this embodiment, an outer layer 243 made of a resin composition mainly composed of a semi-rigid non-lead vinyl (polyvinyl chloride) resin is used. The thickness of the outer layer 243 is appropriately adjusted in consideration of the outer diameter and the number of the electric wires 3 to be used so as to have an appropriate outer diameter suitable for the space at the center of the cable. In this embodiment, the thickness of the outer layer 243 is set to 0.35 mm, and the outer diameter of the outer layer 243, that is, the outer diameter of the entire heat detection wire 2 is set to 3.8 mm.

[0045] (Electric wire 3) The wire 3 has a second conductor 31 made of a stranded conductor formed by collectively stranding a plurality of fine wires, and a second insulator 32 covering the second conductor 31. As the six wires 3, those having the same structure are used. In the present embodiment, tinned soft copper wires are used as the fine wires used for the second conductor 31. The outer diameter of the fine wire used for the second conductor 31 is preferably 0.15 mm or more and 0.32 mm or less. This is because when the outer diameter of the fine wire is less than 0.15 mm, disconnection is likely to occur, and when it exceeds 0.32 mm, there is a risk that the second insulator 32 will penetrate through and protrude when the second insulator 32 is made thinner.

[0046] As a method of twisting fine wires, a method called concentric twisting is known. However, when the second conductor 31 is formed by this method, the fine wires are twisted in a stable state, and it becomes difficult for the shape of the second conductor 31 to change due to an external force when the multi-core cable 1 is accommodated in the groove 11. Therefore, as the second conductor 31, one formed by collective stranding is used so that the shape of the second conductor 31 is likely to change due to an external force when the multi-core cable 1 is accommodated in the groove 11. In the present embodiment, by collectively stranding 136 fine wires of 0.26 mm, the conductor cross-sectional area is 7 mm 2 or more and 8 mm 2 or less of the second conductor 31 is formed. The outer diameter of the second conductor 31 is about 3.47 mm.

[0047] In order to increase the cross-sectional area of the conductor portion in the multi-core cable 1, it is desirable that the second insulator 32 of each electric wire 3 is as thin as possible. More specifically, the thickness of the second insulator 32 is preferably not less than 1 / 2 times and not more than 1 time the outer diameter of the strand used for the second conductor 31. If the thickness of the second insulator 32 is less than 1 / 2 of the outer diameter of the strand, the strand may break through the second insulator 32 due to an external force when the multi-core cable 1 is housed in the groove 11. If it exceeds 1 time the outer diameter of the strand, the electric wire 3 will have a large diameter, leading to an increase in the overall diameter of the multi-core cable 1. In this embodiment, the thickness of the second insulator 32 is set to about 0.2 mm (about 0.77 times the outer diameter of the strand). Note that, from the viewpoint of making the thickness as thin as possible, the second insulators 32 of each electric wire 3 are preferably made of the same material and are single-layer. Also, in order to enable non-contact and large-capacity power supply, in the plurality of electric wires 3, currents of the same magnitude may be supplied to each second conductor 31.

[0048] As the second insulator 32, a material that can be formed thinly, is harder than the jacket 24 of the heat detection wire 2 to facilitate elastic deformation of the jacket 24, and is resistant to external pressure (not easily deformed by an external force when the multi-core cable 1 is housed in the groove 11) is preferably used. For example, fluororesins such as ETFE (tetrafluoroethylene-ethylene copolymer), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PTFE (polytetrafluoroethylene), PVDF (polyvinylidene fluoride), polyimide, and PEEK (polyetheretherketone) can be used. More preferably, as the second insulator 32, a fluororesin with good surface slipperiness is used. Thereby, when an external force is applied, the electric wire 3 moves more easily within the sheath 4, and the insertion of the multi-core cable 1 into the groove 11 becomes easier. Here, the second insulator 32 made of ETFE is used.

[0049] The second insulator 32 is formed by non-full extrusion molding (so-called tube extrusion molding). As a result, the second insulator 32 is not in close contact with the strands, and the strands can move relative to each other within the second insulator 32. When an external force is applied, the cross-sectional shape of the electric wire 3 is easily deformed. Therefore, the insertion of the multi-core cable 1 into the groove 11 becomes easier.

[0050] In addition, in the multi-core cable 1, the second conductor 31 is formed such that the cross-sectional shape perpendicular to the cable longitudinal direction is non-circular. More specifically, the second conductor 31 has a shape in which the width along the circumferential direction gradually increases from the inner side to the outer side in the radial direction, and is formed in a substantially fan shape. Thereby, the cross-sectional area of the second conductor 31 can be made as large as possible within the limited space in the sheath 4. Further, the current flowing through the second conductor 31 mainly flows through the outer portion (outer peripheral portion) of the second conductor 31 in the cable radial direction. By forming the second conductor 31 in a shape in which the width along the circumferential direction gradually increases from the inner side to the outer side in the radial direction, the second conductor 31 (cross-sectional area and surface area) in the outer peripheral portion where the current concentrates can be increased (see FIGS. 4(a) and 4(b)). Thereby, in the multi-core cable 1, the current loss in the second conductor 31 can be suppressed, contributing to the improvement of the efficiency of non-contact power feeding.

[0051] Due to the pressing by the sheath 4 described later, the entire cross-sectional shape of the electric wire 3 including the second conductor 31 is non-circular. More specifically, a part of the outer surface of the electric wire 3 is in surface contact with the outer surface of the heat detection wire 2. In the multi-core cable 1, the electric wires 3 adjacent to each other in the circumferential direction are also in surface contact, and the surface contact portion is a substantially flat surface along the substantially cable radial direction. Further, a part of the outer surface of the electric wire 3 has a shape along the inner surface of the sheath 4 and is in direct contact with the inner surface of the sheath 4.

[0052] For example, it is conceivable to wind a holding tape spirally around the electric wire 3. However, since there is a limit to the outer diameter of the cable for insertion into the groove 11, if a holding tape is provided, it is necessary to reduce the conductor cross-sectional area of the second conductor 31 accordingly, which contributes to an increase in conductor resistance. Therefore, it is desirable to adopt a structure in which the electric wire 3 and the sheath 4 are in direct contact without using a holding tape. If it is necessary to hold the electric wire 3 in a twisted state for manufacturing convenience, a thread (such as a resin thread or a cotton thread) may be wound spirally around the twisted electric wire 3.

[0053] (Assembly 6) A plurality of electric wires 3 are spirally twisted around the outer periphery of the heat detection wire 2. Hereinafter, an assembly in which a plurality of electric wires 3 are twisted around the heat detection wire 2 is referred to as an assembly 6.

[0054] When the number of electric wires 3 used in the assembly 6 is 1 to 3, the multi-core cable 1 is less likely to be deformed by an external force. Therefore, in the multi-core cable 1, the number of electric wires 3 used in the assembly 6 is set to 4 or more. In the present embodiment, the number of electric wires 3 used in the assembly 6 is set to 6, which results in the smallest outer diameter and the lowest total conductor resistance of all the electric wires 3. In the assembly 6, the electric wires 3 adjacent to each other in the circumferential direction of the cable are in surface contact with each other. Further, the electric wire 3 is in surface contact with the heat detection wire 2 and the sheath 4.

[0055] It is desirable that the twisting direction of the assembly 6 be opposite to the twisting direction of the twisted pair wire 22 in the heat detection wire 2. By making the twisting direction of the assembly 6 opposite to that of the twisted pair wire 22, the twist of the electric wire 3 becomes difficult to loosen, and it becomes possible to maintain the state in which the heat detection wire 2 is tightened by the electric wire 3. As a result, when the temperature inside the cable rises, the first conductors 211 are likely to come into contact with each other due to the tightening of the electric wire 3, and the detection sensitivity can be improved. Note that the twisting direction of the assembly 6 is the direction in which the electric wire 3 rotates from the other end side to the one end side when the assembly 6 is viewed from one end side. Also, the twisting direction of the twisted pair wire 22 is the direction in which the heat detection electric wire 21 rotates from the other end side to the one end side when the twisted pair wire 22 is viewed from one end side.

[0056] Between the heat detection wire 2 and the plurality of electric wires 3, and between the electric wire 3 and the sheath 4, a filamentous interposition may be arranged. In order to suppress the burning of the interposition due to the temperature rise inside the cable, it is preferable to use one having high heat resistance (at least a heat resistance temperature of 100 ° C or higher). By having the interposition, the outer shape of the entire multi-core cable 1 can be made closer to a circular shape, and the handleability can be improved. Note that in the present embodiment, no filamentous interposition is arranged between the heat detection wire 2 and the plurality of electric wires 3, and between the electric wire 3 and the sheath 4. This is to suppress the burning of the interposition due to the temperature rise and to secure a space in which the electric wire 3 can move in the circumferential direction and the outer diameter direction of the heat detection wire 2 when an external force is applied to the multi-core cable 1.

[0057] (Sheath 4) A sheath 4 is provided around the assembly 6. In the multi-core cable 1 according to the present embodiment, by making the sheath 4 thin, the cross-sectional area of the conductor of the electric wire 3 is increased while maintaining the cable outer diameter, and the conductor resistance is reduced. Therefore, as the sheath 4, it is necessary to use a resin composition that is not easily broken due to wear even when it is made thin.

[0058] In this embodiment, as the sheath 4, a resin composition made of a polymer alloy (PUV: Polymer alloy with thermoplastic polyurethane and soft polyvinyl chloride) in which the base polymer contains a polyvinyl chloride resin and a urethane thermoplastic elastomer is used. Note that the base polymer constituting the resin composition preferably contains 20 parts by mass or more and 230 parts by mass or less of the urethane thermoplastic elastomer with respect to 100 parts by mass of the polyvinyl chloride resin. In the multi-core cable 1, since the sheath 4 is made of the above-described resin composition, the wear resistance of the sheath 4 can be improved (making it less likely to break due to wear), so the thickness of the sheath 4 can be reduced. The thickness of the sheath 4 is preferably 0.7 mm or less. Here, the thickness of the sheath 4 is set to 0.5 mm, and the outer shape of the sheath 4, that is, the outer diameter of the multi-core cable 1 is set to about 12.6 mm (maximum outer diameter 13.0 mm). Thereby, while making the cable outer diameter insertable into the groove 11, the conductor cross-sectional area of the electric wire 3 can be increased and the conductor resistance of the electric wire 3 can be reduced.

[0059] The sheath 4 is formed by non-solid extrusion molding (so-called tube extrusion molding). The sheath 4 is formed in a hollow cylindrical shape having a hollow portion along the longitudinal direction, and the heat detection wire 2 and the electric wire 3 (that is, the aggregate 6) are disposed in this hollow portion. Further, in this embodiment, the sheath 4 serves to press the electric wire 3 inward in the radial direction and press the electric wire 3 against the heat detection wire 2. The contact area between the electric wire 3 and the sheath 4 is larger than the contact area between the electric wire 3 and the heat detection wire 2.

[0060] Furthermore, by forming the sheath 4 by tube extrusion molding and making the thickness of the sheath 4 as thin as 0.7 mm or less, unevenness can be generated on the outer surface of the sheath 4 so that the sheath 4 bulges at the position of the electric wire 3. Thereby, the insertion of the multi-core cable 1 into the groove 11 of the housing 10 becomes easy.

[0061] As shown in Fig. 5, a sheath abrasion test was conducted on a multi-core cable 1 with a 0.5-mm-thick sheath 4 made of PUV. In the abrasion test, both ends of the multi-core cable 1 serving as a sample were fixed and held horizontally, a weight 103 with a load W of 300 g was placed at the center of the upper part thereof, and an abrasion tape 101 (tape type: 150G) was brought into contact with the center of the lower part of the multi-core cable 1. A roller 102 for supporting the abrasion tape 101 was placed at a position facing the weight 103 with the multi-core cable 1 interposed therebetween, the angle formed by the abrasion tape 101 and the multi-core cable 1 (sheath 4) was set to 30°, the speed of the abrasion tape 101 was set to 1500 mm / min, and the abrasion tape 101 was moved in one direction (from the left side to the right side in Fig. 5). Although not shown, conductive members with a width of approximately 10 mm are provided at intervals of 150 mm along the longitudinal direction of the abrasion tape 101, and the movement of the abrasion tape 101 was continued until conduction occurred in the conductive members (i.e., until the sheath 4 was broken), and the count when conduction occurred in the conductive members was measured. As a result, in the multi-core cable 1 according to the present embodiment, conduction occurred at 60 counts. For comparison, the same test was conducted on a conventional example in which a 1.0-mm-thick sheath made of a resin composition based on polyvinyl chloride resin was formed, and conduction occurred at 35 counts. That is, in the present embodiment, abrasion resistance 1.7 times that of the conventional example was obtained with a thickness half that of the conventional example.

[0062] (Comparison with the conventional example) When the multi-core cable 1 of the example according to the present embodiment is compared with an aggregate having a structure in which a string interposition made of polyethylene is arranged at the center of the cable instead of the heat detection line 2, and six electric wires are arranged around the string interposition, and a sheath made of a resin composition based on polyvinyl chloride resin is formed with a thickness of 1.0 mm around the aggregate, the result is as shown in Table 1.

[0063]

Table 1

[0064] In the multi-core cable 1 of the embodiment, while the outer diameter is the same as that of the conventional example, the sheath 4 can be made thinner compared to the conventional example. Therefore, the conductor cross-sectional area of the second conductor 31 can be made larger than that of the conventional example, and the conductor resistance can be reduced. Further, in the multi-core cable 1 of the embodiment, by making the jacket 24 have a three-layer structure and increasing the roundness of the outer shape of the heat detection wire 2, the current distribution of each electric wire 3 can be made uniform, and the AC resistance can be reduced. In the example of Table 1, the multi-core cable 1 of the embodiment can have an AC resistance of 0.574 mΩ / m at a high frequency of about 10 kHz, which can be reduced by 13% compared to the AC resistance of 0.662 mΩ / m of the multi-core cable of the conventional example.

[0065] (Functions and Effects of the Embodiment) As described above, in the multi-core cable 1 according to the present embodiment, the heat detection wire 2, a plurality of electric wires 3 spirally twisted around the heat detection wire 2, and a sheath 4 that collectively covers the heat detection wire 2 and the plurality of electric wires 3 are provided. The jacket 24 of the heat detection wire 2 has an inner layer 241 and an outer layer 243, and also has an intermediate layer 242 provided between the inner layer 241 and the outer layer 243. The outer layer 243 has a higher hardness than the inner layer 241. Further, the intermediate layer 242 has a higher melting point than the outer layer 24, and the outer layer 243 is configured to be peelable from the intermediate layer 242.

[0066] By incorporating the heat detection wire 2, it becomes possible to accurately detect the temperature rise in the multi-core cable 1 laid in the housing 10. Further, by making the jacket 24 have a three-layer structure, the outer layer 243 can be formed by insert extrusion or solid extrusion to increase the roundness of the outer layer 243. Furthermore, by making the outer layer 243 harder than the inner layer 241, the electric wires 3 can be arranged uniformly. As a result, the current distribution of each electric wire 3 can be made uniform, and the AC resistance to high-frequency alternating current can be reduced. As a result, for example, it can contribute to improving the efficiency of non-contact power supply. And it is also possible to peel the outer layer 243 from the intermediate layer 242 and make the outer diameter of the heat detection wire 2 exposed at the cable terminal the desired outer diameter.

[0067] (Summary of the Embodiment) Next, the technical idea grasped from the embodiments described above will be described by referring to the reference numerals and the like in the embodiments. However, each reference numeral and the like in the following description are not limited to the members and the like specifically shown in the embodiments for the components in the claims.

[0068] [1] A stranded wire (22) formed by twisting a pair of heat detection wires (21) each having a first conductor (211) and a first insulator (212) covering the periphery of the first conductor (211), and a heat detection wire (2) having a jacket (24) covering the periphery of the stranded wire (22); a plurality of wires (3) having a second conductor (31) and a second insulator (32) covering the periphery of the second conductor (31), the plurality of wires (3) being spirally twisted around the heat detection wire (2); and a sheath (4) covering the heat detection wire (2) and the plurality of wires (3) together. The jacket (24) has an inner layer (241) and an outer layer (243), and an intermediate layer (242) provided between the inner layer (241) and the outer layer (243). The outer layer (243) is harder than the inner layer (241). Multi-core cable (1).

[0069] [2] The intermediate layer (242) has a higher melting point than the outer layer (243), and the outer layer (243) is configured to be peelable from the intermediate layer (242). The multi-core cable (1) according to [1].

[0070] [3] The inner layer (241) and the outer layer (243) are made of a resin composition mainly composed of polyvinyl chloride resin, and the intermediate layer (242) is made of a resin composition mainly composed of fluororesin. The multi-core cable (1) according to [1] or [2].

[0071] [4] The fluororesin constituting the intermediate layer (242) is a tetrafluoroethylene-ethylene copolymer. The multi-core cable (1) according to [3].

[0072] [5] The sheath (4) is made of a resin composition composed of a polymer alloy in which the base polymer contains a polyvinyl chloride resin and a urethane thermoplastic elastomer, and the multi-core cable (1) according to any one of [1] to [4].

[0073] [6] The multi-core cable (1) according to [5], wherein the thickness of the sheath (4) is 0.7 mm or less.

[0074] [7] The multi-core cable (1) according to any one of [i] to [6], wherein the jacket (24) has a higher hardness in the intermediate layer (242) than in the outer layer (243).

[0075] (Supplementary Note) Although the embodiments of the present invention have been described above, the embodiments described above do not limit the invention according to the claims. Also, it should be noted that not all combinations of the features described in the embodiments are essential means for solving the problems of the invention.

[0076] The present invention can be appropriately modified and implemented without departing from its gist. For example, in the above embodiment, the case where the multi-core cable 1 is a cable for non-contact power supply has been described, but the present invention is also applicable to uses other than non-contact power supply.

Explanation of Reference Numerals

[0077] 1... Multi-core cable 2... Heat detection wire 3... Electric wire 4... Sheath 21... Heat detection electric wire 211... First conductor 212... First insulator 22... Twisted pair 24... Jacket 241... Inner layer 242... Intermediate layer 243... Outer layer 31... Second conductor 32... Second insulator

Claims

1. a heat detection wire having a twisted pair formed by twisting together a pair of heat detection wires, each having a first conductor and a first insulator covering the first conductor, and a jacket covering the twisted pair; a plurality of electric wires including a second conductor and a second insulator covering the second conductor, the electric wires being twisted spirally around the heat detection wire; a sheath that collectively covers the heat detection wire and the plurality of electric wires, the jacket has an inner layer and an outer layer, and an intermediate layer provided between the inner layer and the outer layer; The intermediate layer has a melting point higher than that of the inner layer and the outer layer. Multi-core cable.

2. The outer layer has a higher hardness than the inner layer, The outer layer is configured to be peelable from the intermediate layer.

2. The multi-conductor cable according to claim 1.

3. the inner layer and the outer layer are made of a resin composition containing a polyvinyl chloride resin as a main component, The intermediate layer is made of a resin composition containing a fluororesin as a main component.

3. The multi-core cable according to claim 1 or 2.

4. the fluororesin constituting the intermediate layer is made of a tetrafluoroethylene-ethylene copolymer; 4. The multi-core cable according to claim 3.

5. The sheath is made of a resin composition in which a base polymer is a polymer alloy containing a polyvinyl chloride resin and a urethane thermoplastic elastomer.

5. A multi-core cable according to claim 1.

6. The thickness of the sheath is 0.7 mm or less.

6. The multi-core cable according to claim 5.

7. The jacket has a hardness of the intermediate layer higher than that of the outer layer.

7. A multi-core cable according to any one of claims 1 to 6.

8. A twisted pair wire formed by twisting together a pair of heat detection wires having a first conductor and a first insulator covering the first conductor, and a heat detection wire having a jacket covering the twisted pair wire; a plurality of electric wires including a second conductor and a second insulator covering the second conductor, the electric wires being twisted spirally around the heat detection wire; a sheath that collectively covers the heat detection wire and the plurality of electric wires, the jacket has an inner layer and an outer layer, and an intermediate layer provided between the inner layer and the outer layer; the intermediate layer has a higher melting point than the outer layer; The method includes the steps of: forming the heat detection wire; twisting the plurality of electric wires around the heat detection wire; and forming the sheath; In the step of forming the heat detection wire, the outer layer is formed on the outer periphery of the intermediate layer by insert extrusion or solid extrusion so that the outer shape of the outer layer becomes circular. Method for manufacturing a multi-core cable.

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