Multicore cable and method for manufacturing multicore cable

Abstract

To provide a multicore cable which can accurately detect temperature rise in the cable, and reduces AC resistance, and a method for manufacturing a multicore cable.SOLUTION: A multicore cable 1 has a twisted pair wire 22 formed by twisting a pair of electric wires 21 for heat detection having a first conductor 211 and a first insulator 212 covering the periphery of the first conductor 211, a heat detection wire 2 having a jacket 24 covering the periphery of the twisted pair wire 22, a plurality of wires 3 which have a second conductor 31 and a second insulator 32 covering the periphery of the second conductor 31, and are spirally twisted in the periphery of the heat detection wire 2, and a sheath 4 collectively covering the heat detection wire 2 and the plurality of wires 3, wherein the jacket 24 has an inner layer 241 and an outer layer 243, and has an intermediate layer 242 provided between the inner layer 241 and the outer layer 243, the inner layer 241 and the outer layer 243 are formed of a resin composition containing a polyvinyl chloride resin as a main component, and the intermediate layer 242 is formed of a resin composition containing a fluorine resin as a main component.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a multi-core cable and a method for manufacturing a multi-core cable. [Background technology]

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

[0003] Conventionally, a fire detection wire is arranged along a cable. For example, in a multi-core cable used for contactless 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] Japanese Patent Publication No. 58-86695 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, contactless power supply, which supplies power without contact, is commonly used in systems used in clean environments, such as automatic conveyance systems in semiconductor factories, etc. A large current flows through the power supply cables used in such contactless power supply, so there is a demand for a system that can detect a temperature rise in the cable and prevent a fire from occurring if an excessive current flows for some reason.

[0006] Furthermore, since the above-mentioned power supply cable is laid inside a housing, for example, there is a limit to the outer diameter of the cable, and therefore there is a demand for reducing the AC resistance to high-frequency (e.g., 5 kHz or higher) AC current used for power supply without increasing the outer diameter.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a multi-core cable and a method for manufacturing the multi-core cable that are capable of accurately detecting a temperature rise within the cable and that aim to reduce AC resistance. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the present invention provides a multi-core cable comprising: a twisted pair of heat detection wires twisted together, each having a first conductor and a first insulator surrounding the first conductor; a heat detection wire having a jacket surrounding the twisted pair; a plurality of electric wires having a second conductor and a second insulator surrounding the second conductor, the electric wires being twisted spirally around the heat detection wire; and a sheath covering the heat detection wire and the plurality of electric wires collectively, wherein the jacket has an inner layer and an outer layer and an intermediate layer disposed between the inner layer and the outer layer, the inner layer and the outer layer being made of a resin composition mainly composed of polyvinyl chloride resin, and the intermediate layer being made of a resin composition mainly composed of fluororesin. Furthermore, in order to solve the above-mentioned problems, the present invention provides a method for manufacturing a multi-core cable including a twisted pair of heat detection wires twisted together, each having a first conductor and a first insulator surrounding the first conductor, and a heat detection wire having a jacket surrounding the twisted pair, a plurality of electric wires having a second conductor and a second insulator surrounding the second conductor and twisted spirally around the heat detection wire, and a sheath covering the heat detection wire and the plurality of electric wires collectively, wherein the jacket has an inner layer and an outer layer and an intermediate layer disposed between the inner layer and the outer layer, and 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, wherein in the step of forming the heat detection wire, the inner layer and the intermediate layer are formed by non-solid extrusion molding, and the outer layer is formed around the outer periphery of the intermediate layer by insertion extrusion or solid extrusion. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a multi-core cable and a method for manufacturing the multi-core cable that can accurately detect a temperature rise inside the cable and that reduces AC resistance. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing a cross section perpendicular to the longitudinal direction of a multi-core cable according to an embodiment of the present invention. [Figure 2] 2 is a cross-sectional view of the multi-core cable of FIG. 1 housed in a groove of a housing. [Figure 3] These are photographs explaining the operation of the heat detection wire, (a) is a photograph before operation, and (b) is a photograph after operation. [Figure 4] FIG. 10 is a diagram showing a simulation result of current distribution. [Figure 5] FIG. 1 is a diagram illustrating an abrasion resistance test. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Embodiment Mode] Hereinafter, an embodiment 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 a multi-core cable according to the present embodiment, Fig. 2 is a cross-sectional view showing the multi-core cable of Fig. 1 housed in a groove of a 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 covers the heat detection wire 2 and the plurality of electric wires 3 collectively.

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

[0015] (Thermal detection wire 2) The heat detection wire 2 has a twisted pair wire 22 formed by twisting a pair of heat detection electric wires 21 together, a pressure winding tape 23 wound spirally around the twisted pair wire 22, and a jacket 24 covering the pressure winding tape 23.

[0016] Each of the pair of heat detection wires 21 constituting the twisted pair 22 has a first conductor 211 and a first insulator 212 that covers the periphery of the first conductor 211. It is preferable to use a first conductor 211 that can increase the force that causes the first conductors 211 to move closer to the center of the twisted pair 22 when they are twisted together to form the twisted pair 22.

[0017] As described above, the multi-core cable 1 is used for contactless power supply and is wired over long distances, for example, 30 m or more, in factories and the like. Therefore, the conductivity of the first conductors 211 must be maintained high enough to enable detection of short circuits between the first conductors 211 even when wired over long distances. Furthermore, the first conductors 211 must be strong enough to prevent breakage even when wired over long distances. In this embodiment, the outer diameter of the first conductors 211 is preferably set to 0.5 mm or more and 1.0 mm or less. Setting the outer diameter of the first conductors 211 to 0.5 mm or more suppresses conductor resistance and maintains high conductivity, making it possible to detect short circuits between the first conductors 211 even when wired over long distances. Furthermore, setting the outer diameter of the first conductors 211 to 0.5 mm or more suppresses a decrease in the force that causes the first conductors 211 to approach each other, thereby preventing a decrease in detection sensitivity, thereby improving the temperature detection sensitivity within the cable. On the other hand, by setting the outer diameter of the first conductors 211 to 1.0 mm or less, it is possible to prevent the multi-core cable 1 from becoming stiff and difficult to bend, and it is possible to realize a multi-core cable 1 that is easy to wire.

[0018] Furthermore, in this embodiment, a non-magnetic copper alloy having a tensile strength of 900 MPa or more is used as first conductor 211. More specifically, phosphor bronze containing 7 mass% to 10 mass% tin and 0.03 mass% to 0.35 mass% phosphorus is used as first conductor 211. Using a non-magnetic material as first conductor 211 can reduce loss in contactless power transfer and prevent a decrease in the efficiency of contactless power transfer.

[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 wire 22 move toward the center of the twisted pair wire 22 when twisted together can be increased. As a result, when the first insulator 212 softens or melts, the first conductors 211 quickly move toward the center of the twisted pair wire 22 and come into contact with each other, which improves the temperature detection sensitivity within the cable. Furthermore, by setting the tensile strength of the first conductor 211 to 900 MPa or more, strength that prevents breakage even when the cable is wired over a long distance can be ensured. Furthermore, from the viewpoint of increasing the force with which the first conductors 211 of the twisted pair wire 22 move toward the center of the twisted pair wire 22 and improving detection sensitivity, it is desirable that the elongation of the first conductor 211 be 10% or less (more preferably 3% or less). The tensile strength and elongation of the first conductors 211 are determined by a tensile test method (test piece: No. 9B) in accordance with JIS Z2241 (2011).

[0020] In this embodiment, a single wire of tin-plated phosphor bronze with a diameter of 0.63 mm is used as the first conductor 211. The copper alloy used for the first conductor 211 is not limited to phosphor bronze, and other alloys such as brass and beryllium copper can also be used. However, it is more desirable to use phosphor bronze, which can increase the force that moves the first conductors 211 of the twisted pair 22 toward the center of the twisted pair 22, is less likely to break, and is inexpensive.

[0021] The first insulator 212 is made of an insulating resin with a relatively low melting point so that it melts when the temperature inside the cable rises. More specifically, the melting point of the first insulator 212 is set lower than the melting point of the second insulator 32 of the wire 3 (e.g., 105°C or higher) so that the first insulator 212 melts before the second insulator 32 (described later) of the wire 3 melts due to heat generated when the temperature inside the cable rises due to an overcurrent or the like (in other words, so that a temperature rise inside the cable due to an overcurrent or the like is detected by a short circuit of the first conductor 211 before the function of the wire 3 is lost due to the heat generated when the temperature rises). In this embodiment, the melting point of the first insulator 212 is set to be higher than 80°C but lower than 100°C (more preferably, approximately 90°C) with the goal of not operating at temperatures below 80°C but operating at 100°C within a few minutes (within 5 minutes). Here, the first insulator 212 made of an ionomer resin with a melting point of approximately 89°C is used.

[0022] The thickness of the first insulator 212 is preferably 0.1 mm or more and 0.3 mm or less. By making the thickness of the first insulator 212 0.1 mm or more, the mechanical strength of the first insulator 212 is ensured, and unintended damage to the first insulator 212 and malfunction of the heat detection wire 2 can be suppressed. Furthermore, by making the thickness of the first insulator 212 0.3 mm or less, the first conductors 211 can be quickly brought into contact with each other when the first insulator 212 softens or melts, thereby suppressing problems such as the first conductors 211 not coming into contact with each other despite a rise in temperature within the cable. In this embodiment, the thickness of the first insulator 212 is 0.14 mm, and the outer diameter of the heat detection wire 21 is 0.91 mm. The outer diameter of the twisted pair 22 formed by twisting two heat detection wires 21 together is 1.82 mm.

[0023] It is preferable that the thickness of the first insulator 212 be smaller at a portion where the pair of heat detecting wires 21 constituting the twisted pair 22 come into contact with each other (a portion where the first insulators 212 of the pair of heat detecting wires 21 come into contact with each other) than at a portion where the pair of heat detecting wires 21 do not come into contact with each other (a portion where the first insulators 212 of the pair of heat detecting wires 21 do not come into contact with each other). This allows the first conductors 211 to quickly come into contact with each other when the first insulator 212 softens or melts, making it easier to prevent problems such as the first conductors 211 not coming into contact with each other despite an increase in temperature within the cable. In this case, it is preferable that the portion where the pair of heat detecting wires 21 constituting the twisted pair 22 come into contact with each other be in surface contact. The thickness here refers to the shortest distance (minimum thickness) from the inner surface of the first insulator 212 to the outer surface of the first insulator 212.

[0024] 3A and 3B are photographs illustrating the operation of the heat detection wire 2, with (a) being a photograph before operation and (b) being a photograph after operation. As shown in FIGS. 3A and 3B, in the heat detection wire 2, the temperature inside the cable (the temperature around the electric wire 3) rises to a temperature above the melting point of the first insulator 212 (89°C in this embodiment) but below the melting point of the second insulator 32. When the first insulator 212 softens and melts due to the heat, the twisted first conductors 211 move toward the center of the twisted pair 22 due to a force that tries to move them toward each other, causing the first conductors 211 to come into contact with each other and become electrically short-circuited. At this time, the first insulators 212 present between the first conductors 211 are in a molten state, and the force that tries to move the first conductors 211 toward each other pushes the first insulators 212 present between the first conductors 211 away from the center of the twisted pair 22. Therefore, the outer shape of the first insulators 212 is not circular, but is slightly flattened at the contact points between the first insulators 212. By detecting a short circuit between these two first conductors 211, it is possible to detect a temperature rise in the multi-core cable 1 due to an overcurrent or the like. In the photographs of Figures 3(a) and 3(b), the heat detection wire 2 is filled with epoxy resin to make it easier to see the cross-section of the heat detection wire 2, and the cut end surface was polished before photographing the cut surface. Also, in Figures 3(a) and 3(b), the jacket 24 has one layer. The heat detection wire 2 operates in the same way as described above even when the jacket 24 has three layers, as shown in Figures 1 and 2.

[0025] Incidentally, in this heat detection wire 2, when the temperature around the heat detection wire 2 rises, the first insulator 212 softens and the distance between the two first conductors 211 decreases before the two first conductors 211 are short-circuited, causing a change in the resistance value and capacitance between the two first conductors 211. Therefore, by measuring the resistance value and capacitance between the two first conductors 211, it is possible to detect a rise in the temperature around the heat detection wire 2 before the two first conductors 211 are short-circuited.

[0026] Although not shown, first insulator 212 may have a multi-layer structure in which multiple layers made of an insulating resin composition are stacked. For example, by making first insulator 212 have a two-layer structure and making the melting point of the inner layer higher than the melting point of the outer layer, it is possible to detect temperature increases in multi-core cable 1 in stages.

[0027] Furthermore, when the first insulator 212 has a multi-layer structure, at least one layer other than the layer closest to the first conductor 211 may contain a particulate material with a higher melting point than the insulating resin that constitutes the first insulator 212. By including a particulate material with a high melting point in the first insulator 212, when the temperature around the heat detection wire 2 rises, the particulate material is prevented from being pushed in by the force that causes the first conductors 211 to approach each other, resulting in a thin layer of the first insulator 212 remaining. This makes it easier for a short circuit to occur between the first conductors 211. If the particulate material is insulating, there is a risk that the particulate material will become trapped between the first conductors 211, preventing a short circuit from occurring. Therefore, it is desirable to use a conductive particulate material. For example, carbon particles can be used as the particulate material.

[0028] The twist pitch of the twisted pair wires 22 is preferably about 20 times (18 to 22 times) the outer diameter of the heat detection electric wires 21. This makes it possible to maintain the force that draws the first conductors 211 closer to each other, while preventing the first insulators 212 from being destroyed by this force. Note that the twist pitch of the twisted pair wires 22 is the interval between longitudinal positions at which any two heat detection electric wires 21 are at the same circumferential position in the longitudinal direction of the twisted pair wires 22.

[0029] A resin tape such as a polyester tape can be used as the pressure winding tape 23 that is wound around the twisted pair wires 22. The pressure winding tape 23 is wound spirally around the twisted pair wires 22 so that portions of the pressure winding tape 23 overlap each other in the width direction.

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

[0031] Here, the heat detection wire 2 exposed at the cable end is connected to a detection device (not shown) that detects electrical short circuits caused by contact between the first conductors 211. The outer diameter of the heat detection wire 2 connected to this detection device is specified by standards, etc. However, this specified outer diameter of the heat detection wire 2 may differ from the outer diameter required to fill the gaps between the electric wires 3 (i.e., the outer diameter required to function as a core material). In particular, if the conductor cross-sectional area of ​​the electric wire 3 is increased to reduce the conductor resistance, the gap (space) formed between the electric wires 3 at the center of the cable will increase accordingly, and the outer diameter of the heat detection wire 2 required to fill this gap will also increase. Note that if the outer diameter of the heat detection wire 2 is made smaller than the gap (space) between the electric wires 3, symmetry will be lost when the electric wires 3 are twisted around the heat detection wire 2, resulting in a loss of uniformity in current distribution and an increase in AC resistance to high-frequency AC (5 kHz or higher, for example, a high frequency of about 10 kHz).

[0032] Therefore, the inventors first considered forming the jacket 24 into a two-layer structure consisting of an inner layer and an outer layer made of polyvinyl chloride resin, and then peeling and removing the outer layer from the exposed heat detection wire 2 during terminal processing, thereby achieving the specified outer diameter of the heat detection wire 2. As a result of their investigations, the inventors found that forming the outer layer by tube extrusion enabled the outer layer to be peeled from the inner layer. However, when the outer layer was formed by tube extrusion, it was found that unevenness on the surface of the inner layer due to the twisting of the twisted pair wires 22 could cause gaps to form between the inner and outer layers, or that the unevenness on the surface of the inner layer could be exposed on the surface of the outer layer. As a result, it was found that when the electric wires 3 were twisted around the heat detection wire 2, the symmetry of the arrangement of the electric wires 3 was lost, the uniformity of the current distribution was impaired, and the AC resistance to high-frequency AC (5 kHz or higher, for example, about 10 kHz) increased. In response to this problem, by forming the outer layer by insertion extrusion or solid extrusion, it becomes possible to increase the circularity of the outer layer (i.e., the circularity of the outer layer surface in a cross section perpendicular to the cable longitudinal direction) and improve the symmetry of the arrangement of the electric wires. However, in this case, it becomes difficult to peel the outer layer from the inner layer. To solve this problem, the inventors conducted extensive research and as a result, they came up with the idea of ​​forming an intermediate layer between the inner layer and the outer layer that allows the outer layer to be peeled off, and arrived at the present invention.

[0033] That is, in the multi-core cable 1 according to this embodiment, the jacket 24 of the heat detection wire 2 includes an inner layer 241 and an outer layer 243, as well as an intermediate layer 242 disposed 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 is configured so that the outer layer 243 can be peeled away from the intermediate layer 242. This allows the outer layer 243 to be formed by insertion extrusion or solid extrusion, thereby increasing the roundness of the outer layer 243, improving the symmetry of the arrangement of the electric wire 3, improving the uniformity of the current distribution, and reducing AC resistance to high-frequency AC. Furthermore, by peeling the outer layer 243 from the intermediate layer 242, the outer diameter of the heat detection wire 2 exposed at the cable terminal can be set to a specified diameter. Each layer of the jacket 24 is described in detail below.

[0034] The inner layer 241 is made of an insulating resin composition with 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 too thick, there is a risk that the first insulator 212 will melt due to the heat generated when molding the inner layer 241. Therefore, the thickness of the inner layer 241 must be determined in consideration of the melting point (molding temperature) of the inner layer 241 so as not to melt the first insulator 212 during extrusion molding. In this embodiment, a resin composition containing a lead-free heat-resistant vinyl (polyvinyl chloride) resin as a main component is used for the inner layer 241. In this case, the thickness of the inner layer 241 is preferably no more than five times the thickness of the first insulator 212 (here, 0.14 mm), and is preferably no more than 0.7 mm. 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 formed, it is preferable to quickly perform a cooling process using cooling water or the like to prevent the first insulator 212 from melting.

[0035] Like the inner layer 241, the intermediate layer 242 is made of an insulating resin composition with a higher melting point than the first insulator 212 so as not to melt before the first insulator 212 melts. In this embodiment, the intermediate layer 242 serves to improve the peelability of the outer layer 243, and is the outermost layer of the heat detection line 2 exposed at the cable terminal. Therefore, the intermediate layer 242 has a higher melting point than the outer layer 243 and is made of an insulating resin composition that is easily peeled from the outer layer 243. Note that in this embodiment, the melting point of the intermediate layer 242 is higher than both the melting points of the inner layer 241 and the outer layer 243.

[0036] Although details will be described later, in this embodiment, a resin composition mainly composed of polyvinyl chloride resin is used for outer layer 243, and therefore intermediate layer 242 is made of a resin composition mainly composed of fluororesin, which has high peelability from polyvinyl chloride resin. This makes it possible to easily peel and remove outer layer 243 from intermediate layer 242, even if outer layer 243 is molded by insertion extrusion or solid extrusion, which have high adhesion.

[0037] Examples of fluororesin that can be used to form the intermediate layer 242 include ETFE (tetrafluoroethylene-ethylene copolymer), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), and PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer). Among these, ETFE and FEP, which have a melting point of 250°C or higher but lower than 300°C, are more preferably used for the intermediate layer 242. This is to prevent the first insulator 212 from melting during molding of the intermediate layer 242. In this embodiment, ETFE is used as the fluororesin that forms the intermediate layer 242. ETFE has a relatively high hardness compared to other fluororesins. This improves the roundness of the outer layer 243 formed around the intermediate layer 242 by insertion extrusion or solid extrusion. Furthermore, it also makes it easier to maintain the desired outer diameter of the heat detection wire 2 when multiple electric wires 3 are arranged around it. This improves the symmetry of the arrangement of the multiple electric wires 3, and also makes it easier to maintain the specified outer diameter of the heat detection wire 2 exposed at the cable end.

[0038] If the intermediate layer 242 is too thick, the first insulator 212 may melt due to the heat generated during molding, and the entire multi-core cable 1 may become stiff and difficult to bend. Therefore, it is desirable to make the thickness of the intermediate layer 242 as thin as possible. Specifically, it is desirable that the thickness of the intermediate layer 242 be at least 50% or less of the thickness of the inner layer 241, and more preferably about 1 / 3 of the thickness of the inner layer 241. In this 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 a detection device. The intermediate layer 242 is formed by non-solid extrusion molding (so-called tube extrusion molding).

[0039] Like the inner layer 241 and the intermediate layer 242, the outer layer 243 is made of an insulating resin composition with a higher melting point than the first insulator 212 so as not to melt before the first insulator 212 melts. In this embodiment, the outer layer 243 fills the gap between the intermediate layer 242 and the surrounding electric wire 3, thereby improving the roundness of the outer shape of the thermal detection wire 2. Because the inner layer 241 and the intermediate layer 242 are formed by tube extrusion molding, the twisting of the heat detection electric wire 21 causes unevenness on the surface of the intermediate layer 242 in accordance with the twisting. In order to prevent gaps from being generated between the intermediate layer 242 and the outer layer 243 due to the influence of this unevenness, and to finish the surface of the outer layer 243 in a shape that is free of unevenness in accordance with the twisting of the heat detection electric wire 21, the outer layer 243 is molded by insertion extrusion or solid extrusion, which increases the degree of adhesion to the intermediate layer 242.

[0040] By increasing the circularity of the outer layer 243 (i.e., by maintaining the outer shape of the heat detection wire 2 as close to a circle as possible), the pressing force generated between the electric wires 3 and the heat detection wire 2 by the sheath 4 (described later) becomes uniform across each electric wire 3, resulting in uniform deformation of all electric wires 3. As a result, as shown in FIG. 1, the cross-sectional structure of the entire multi-core cable 1 becomes highly symmetrical. Note that, for example, if the outer shape of the heat detection wire 2 arranged at the center of the cable is elliptical or has irregularities due to the twisting of the heat detection wires 21, the outer shapes of the electric wires 3 arranged around the heat detection wire 2 will vary accordingly, resulting in different current losses (difficulty in flowing) for each electric wire 3. In other words, when a high-frequency AC current (5 kHz or higher, e.g., about 10 kHz) is passed through the heat detection wire 2, the current distribution will become non-uniform. Non-uniform current distribution increases AC resistance and reduces the efficiency of contactless power transfer.

[0041] In other words, by keeping the outer shape of the heat detection wire 2 as close to a circle as possible when the multiple electric wires 3 are twisted around the heat detection wire 2, it is possible to make the cross-sectional shapes of the multiple electric wires 3 twisted around the heat detection wire 2 uniform (reducing variations in the outer shapes of the multiple electric wires 3), as shown in Fig. 1 . Note that when the electric wires 3 are twisted around the heat detection wire 2 arranged in the center of the cable and the sheath 4 is provided, the heat detection wire 2 is pressed toward the center of the cable by the electric wires 3. Therefore, due to the influence of the pressing forces generated between the heat detection wire 2 and each of the multiple electric wires 3, the outer shape of the heat detection wire 2 actually becomes non-circular as shown in Fig. 1 (the outer surface of the part of the outer layer 243 that comes into contact with the electric wires 3 is pressed toward the center of the cable). In this embodiment, the heat detection wire 2 is pressed down by six electric wires 3, so that the outer shape of the heat detection wire 2 becomes approximately hexagonal.

[0042] Figures 4(a) and (b) show the simulation results of current distribution when six conductors with the same cross-sectional shape and cross-sectional area are uniformly arranged around the center of the cable (heat detection wire 2) and a total AC current of 1 ampere (1 / 6 ampere per conductor) with a frequency of approximately 10 kHz is passed through each conductor. Figure 4(a) is a grayscale representation of the original color diagram, while Figure 4(b) is a representation of the original color diagram with different colors replaced by different hatching. The simulation results shown in Figures 4(a) and (b) show that by arranging six conductors (i.e., electric wires 3) with uniform cross-sectional shapes and cross-sectional areas around the heat detection wire 2, a large amount of current flows outside the conductors (toward the outer sheath) and the current distribution for each conductor is uniform. This uniform current distribution suppresses the increase in AC resistance caused by non-uniform current distribution, thereby reducing AC resistance.

[0043] 1 and 2 , the electric wire 3 is pressed against the outer layer 243 when the electric wire 3 is twisted around it. Therefore, it is desirable to use a resin composition with a relatively high hardness, and a resin composition with a hardness at least higher than that of the inner layer 241, in order to minimize deformation of the outer layer 243 when the electric wire 3 is pressed against it and maintain the outer shape of the heat detection wire 2 as close to a circular shape as possible. More specifically, it is desirable to use a resin composition with a hardness higher than that of the inner layer 241, as measured in accordance with JIS K7215 Type D. The hardness of the inner layer 241 is lower than that of the outer layer 243, for example, 30 to 35 in Shore D hardness. The hardness of the intermediate layer 242 is harder than that of the inner layer 241 and the outer layer 243, for example, 60 to 70 in Shore D hardness. The heat detection wire 2 has a jacket 24 consisting of three layers (an inner layer 241, a middle layer 242, and an outer layer 243) with the above-mentioned hardness, which improves the symmetry of the arrangement of the multiple electric wires 3 (as shown in FIG. 1, the cross-sectional shapes of the multiple electric wires 3 twisted around the heat detection wire 2 can be made uniform). As a result, when a high-frequency (e.g., 5 kHz or higher) AC current is passed through the multi-core cable 1, the current distribution in the multiple electric wires 3 becomes uniform, and AC resistance can be reduced.

[0044] In this embodiment, the outer layer 243 is made of a resin composition whose main component is semi-rigid lead-free vinyl (polyvinyl chloride) resin. The thickness of the outer layer 243 is adjusted appropriately to obtain an appropriate outer diameter that fits into the space at the center of the cable, taking into account the outer diameter and number of the electric wires 3 used. In this embodiment, the thickness of the outer layer 243 is 0.35 mm, and the outer diameter of the outer layer 243, i.e., the outer diameter of the entire heat detection wire 2, is 3.8 mm.

[0045] (Electric wire 3) Each electric wire 3 has a second conductor 31 made of a stranded conductor formed by bunching a plurality of wires together, and a second insulator 32 covering the second conductor 31. The six electric wires 3 have the same structure. In this embodiment, tin-plated annealed copper wire is used as the wire used for the second conductor 31. The outer diameter of the wire used for the second conductor 31 should be 0.15 mm or more and 0.32 mm or less. This is because if the outer diameter of the wire is less than 0.15 mm, it is likely to break, and if it exceeds 0.32 mm, it may break through the second insulator 32 when the second insulator 32 is made thin.

[0046] A method called concentric twisting is known as a method for twisting wires together. However, if the second conductor 31 is formed using this method, the wires will be twisted in a stable state, making it difficult for the shape of the second conductor 31 to change due to the external force applied when the multi-core cable 1 is accommodated in the groove 11. For this reason, the second conductor 31 is formed by bunch twisting so that the shape of the second conductor 31 can be easily changed due to the external force applied when the multi-core cable 1 is accommodated in the groove 11. In this embodiment, the second conductor 31 has a conductor cross-sectional area of ​​7 mm2 or more and 8 mm2 or less, formed by bunch twisting 136 0.26 mm wires. The outer diameter of the second conductor 31 is approximately 3.47 mm.

[0047] 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 be as thin as possible. More specifically, the thickness of the second insulator 32 should be between 1 / 2 and 1 time the outer diameter of the wires used in the second conductor 31. If the thickness of the second insulator 32 is less than 1 / 2 of the outer diameter of the wires, the wires may break through the second insulator 32 due to the external force applied when inserting the multi-core cable 1 into the groove 11. If the thickness of the second insulator 32 exceeds 1 time the outer diameter of the wires, the diameter of the electric wires 3 becomes large, leading to an increase in the diameter of the entire multi-core cable 1. In this embodiment, the thickness of the second insulator 32 is set to approximately 0.2 mm (approximately 0.77 times the outer diameter of the wires). To minimize the thickness, the second insulator 32 of each electric wire 3 is preferably made of the same material and is a single layer. Furthermore, in order to enable contactless supply of large amounts of power, it is preferable that the same amount of current is supplied to each of the second conductors 31 of the plurality of electric wires 3.

[0048] The second insulator 32 is preferably made of a material that can be molded into a thin wall, 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 (is less likely to deform due to external forces when the multi-core cable 1 is placed in the groove 11). For example, fluororesins such as ETFE (tetrafluoroethylene-ethylene copolymer), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PTFE (polytetrafluoroethylene), and PVDF (vinylidene polyfluoride), as well as polyimide and PEEK (polyether ether ketone) can be used. More preferably, the second insulator 32 is made of a fluororesin with a smooth surface, which allows the wire 3 to move more easily within the sheath 4 when an external force is applied, making it easier to insert the multi-core cable 1 into the groove 11. Here, the second insulator 32 made of ETFE was used.

[0049] The second insulator 32 is formed by non-solid extrusion (so-called tube extrusion). This means that the second insulator 32 is not in close contact with the wires, allowing the wires to move relative to each other within the second insulator 32, making it easier for the cross-sectional shape of the electric wire 3 to deform when an external force is applied. This makes it easier to insert the multi-core cable 1 into the groove 11.

[0050] In the multi-core cable 1, the second conductor 31 is formed so that its cross-sectional shape perpendicular to the longitudinal direction of the cable is non-circular. More specifically, the second conductor 31 is formed so that its circumferential width gradually increases from the radially inner side to the radially outer side, forming a generally fan-shaped configuration. This allows the cross-sectional area of ​​the second conductor 31 to be maximized within the limited space within the sheath 4. Furthermore, the current flowing through the second conductor 31 mainly flows through the outer portion (outer periphery) of the second conductor 31 in the cable radial direction. However, by forming the second conductor 31 so that its circumferential width gradually increases from the radially inner side to the radially outer side, the cross-sectional area and surface area of ​​the second conductor 31 in the outer periphery where the current is concentrated can be increased (see FIGS. 4( a) and 4(b)). This reduces current loss in the second conductor 31 in the multi-core cable 1, contributing to improved efficiency of contactless power transfer.

[0051] The electric wires 3 are pressed by the sheath 4, which will be described later, so that the overall cross-sectional shape of the electric wires 3, including the second conductor 31, is non-circular. More specifically, parts of the outer surfaces of the electric wires 3 are in surface contact with the outer surface of the heat detection wire 2. In the multi-core cable 1, the electric wires 3 adjacent in the circumferential direction are also in surface contact with each other, and this surface contact portion forms a substantially flat surface that is substantially aligned in the cable radial direction. Furthermore, parts of the outer surfaces of the electric wires 3 are shaped to fit along the inner surface of the sheath 4 and are in direct contact with the inner surface of the sheath 4.

[0052] It is possible to spirally wrap a pressure winding tape around the electric wires 3, for example. However, since the outer diameter of the cable is limited for insertion into the groove 11, providing a pressure winding tape would require reducing the conductor cross-sectional area of ​​the second conductor 31 accordingly, which would contribute to an increase in conductor resistance. Therefore, it is preferable to use a structure in which the electric wires 3 and the sheath 4 are in direct contact with each other without using a pressure winding tape. If it is necessary to hold the electric wires 3 in a twisted state for manufacturing reasons, thread (such as resin thread or cotton thread) may be spirally wound around the twisted electric wires 3.

[0053] (Aggregation 6) A plurality of electric wires 3 are twisted in a spiral shape around the heat detection wire 2. Hereinafter, the plurality of electric wires 3 twisted around the heat detection wire 2 will be referred to as an assembly 6.

[0054] When the number of electric wires 3 used in the assembly 6 is one to three, the multi-core cable 1 is less likely to be deformed by an external force. Therefore, the number of electric wires 3 used in the assembly 6 of the multi-core cable 1 is set to four or more. In this embodiment, the number of electric wires 3 used in the assembly 6 is set to six, which allows the outer diameter to be the smallest and the total conductor resistance of all the electric wires 3 to be the lowest. 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. Furthermore, the electric wires 3 are in surface contact with the heat detection wire 2 and the sheath 4.

[0055] The twisting direction of the assembly 6 is preferably opposite to the twisting direction of the twisted pairs 22 in the heat detection wire 2. By twisting the assembly 6 in the opposite direction to the twisting direction of the twisted pairs 22, the twisting of the electric wires 3 is less likely to loosen, and it becomes possible to maintain the heat detection wire 2 in a fastened state by the electric wires 3. As a result, when the temperature inside the cable rises, the first conductors 211 are more likely to come into contact with each other due to the fastening of the electric wires 3, making it possible to improve the detection sensitivity. Note that the twisting direction of the assembly 6 is the direction in which the electric wires 3 rotate from one end to the other end of the assembly 6 when viewed from the other end. Furthermore, the twisting direction of the twisted pairs 22 is the direction in which the heat detection electric wires 21 rotate from the other end to the one end when viewed from the one end of the twisted pairs 22.

[0056] Thread-like fillers may be arranged between the heat detection wire 2 and the multiple electric wires 3, and between the electric wires 3 and the sheath 4. To prevent the fillers from burning due to a rise in temperature inside the cable, it is recommended to use materials with high heat resistance (a heat-resistant temperature of at least 100°C or higher). The presence of fillers makes the overall outer shape of the multi-core cable 1 closer to a circular shape, improving handleability. In this embodiment, no thread-like fillers are arranged between the heat detection wire 2 and the multiple electric wires 3, or between the electric wires 3 and the sheath 4. This is to prevent the fillers from burning due to a rise in temperature and to ensure space for the electric wires 3 to move circumferentially and radially outwardly 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, the sheath 4 is thinned to increase the conductor cross-sectional area of ​​the electric wires 3 while maintaining the cable outer diameter, thereby reducing the conductor resistance. For this reason, it is necessary to use a resin composition for the sheath 4 that is resistant to breakage due to abrasion even when thinned.

[0058] In this embodiment, the sheath 4 is made of a resin composition consisting of a polymer alloy (PUV: Polymer alloy with thermoplastic polyurethane and soft polyvinyl chloride) whose base polymer contains polyvinyl chloride resin and a thermoplastic urethane elastomer. The base polymer constituting the resin composition preferably contains 20 to 230 parts by mass of the thermoplastic urethane elastomer per 100 parts by mass of polyvinyl chloride resin. In the multi-core cable 1, the sheath 4 is made of the above-described resin composition, which improves the abrasion resistance of the sheath 4 (making it less likely to break due to abrasion), allowing the sheath 4 to be made thinner. 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, i.e., the outer diameter of the multi-core cable 1, is set to approximately 12.6 mm (maximum outer diameter 13.0 mm). This allows the conductor cross-sectional area of ​​the electric wire 3 to be increased and the conductor resistance of the electric wire 3 to be reduced while maintaining an outer cable diameter that can be inserted into the groove 11.

[0059] The sheath 4 is formed by non-solid extrusion molding (so-called tube extrusion molding). The sheath 4 is formed in the shape of a hollow cylinder having a hollow portion along the longitudinal direction, and the heat detection wire 2 and the electric wire 3 (i.e., the assembly 6) are arranged inside this hollow portion. In this embodiment, the sheath 4 presses the electric wire 3 radially inward, thereby pressing 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 reducing the thickness of the sheath 4 to 0.7 mm or less, it is possible to create irregularities on the outer surface of the sheath 4 so that the sheath 4 becomes convex at the position of the electric wire 3. This makes it easier to insert the multi-core cable 1 into the groove 11 of the housing 10.

[0061] As shown in Figure 5, an abrasion resistance test was conducted on a multi-core cable 1 having a 0.5 mm thick sheath 4 made of PUV. In the abrasion resistance test, both ends of the sample multi-core cable 1 were fixed and held horizontally. A weight 103 with a load W of 300 g was placed at the center of the top of the cable, and abrasion tape 101 (tape type: 150 G) was placed in contact with the center of the bottom of the multi-core cable 1. A roller 102 supporting the abrasion tape 101 was placed opposite the weight 103 across the multi-core cable 1. The angle between the abrasion tape 101 and the multi-core cable 1 (sheath 4) was set to 30°, and the abrasion tape 101 was moved in one direction (from left to right in Figure 5) at a speed of 1500 mm / min. Although not shown, conductive members approximately 10 mm wide are provided at 150 mm intervals along the longitudinal direction of the wear tape 101. The wear tape 101 is moved continuously until continuity is achieved in the conductive members (i.e., until the sheath 4 is torn), and the count at which continuity is achieved is measured. As a result, continuity is achieved at 60 counts in the multi-core cable 1 according to the present embodiment. For comparison, a similar test was conducted on a conventional example in which a 1.0 mm-thick sheath made of a resin composition with polyvinyl chloride resin as the base polymer was formed, and continuity is achieved at 35 counts. In other words, the present embodiment achieves 1.7 times the abrasion resistance of the conventional example with half the thickness.

[0062] (Compared to conventional examples) Table 1 shows the results of a comparison between the multi-core cable 1 of the example according to this embodiment and a conventional multi-core cable in which a polyethylene string insert is placed in the center of the cable instead of the heat detection wire 2, and six electric wires are arranged around the string insert to form an assembly, with a 1.0 mm thick sheath made of a resin composition with polyvinyl chloride resin as the base polymer formed around the assembly.

[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 than that of the conventional example, which allows the conductor cross-sectional area of ​​the second conductor 31 to be made larger than that of the conventional example, thereby reducing the conductor resistance. Furthermore, in the multi-core cable 1 of the embodiment, the jacket 24 has a three-layer structure, which increases the roundness of the outer shape of the heat detection wire 2, thereby making it possible to uniformly distribute the current in each electric wire 3 and reducing the AC resistance. In the example of Table 1, the multi-core cable 1 of the embodiment has an AC resistance of 0.574 mΩ / m at a high frequency of approximately 10 kHz, which is a 13% reduction compared to the AC resistance of the conventional multi-core cable, which is 0.662 mΩ / m.

[0065] (Actions and Effects of the Embodiments) As described above, the multi-core cable 1 according to this embodiment includes a heat detection wire 2, a plurality of electric wires 3 twisted spirally around the heat detection wire 2, and a sheath 4 collectively covering the heat detection wire 2 and the plurality of electric wires 3. The jacket 24 of the heat detection wire 2 has an inner layer 241 and an outer layer 243, as well as an intermediate layer 242 provided between the inner layer 241 and the outer layer 243, and the outer layer 243 has a higher hardness than the inner layer 241. The intermediate layer 242 has a higher melting point than the outer layer 243, and is configured so that the outer layer 243 can be peeled off from the intermediate layer 242.

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

[0067] (Summary of the embodiment) Next, the technical ideas grasped from the above-described embodiments will be described by using the reference numerals and the like in the embodiments. However, the reference numerals and the like in the following description do not limit the components in the claims to the members and the like specifically shown in the embodiments.

[0068] [1] A heat detection wire (2) having a pair of heat detection wires (21) twisted together to form a twisted pair (22), each having a first conductor (211) and a first insulator (212) surrounding the first conductor (211), and a jacket (24) surrounding the twisted pair (22), and a second conductor (31) and a second insulator (32) surrounding the second conductor (31), spirally twisted around the heat detection wire (2). a sheath (4) that collectively covers the heat detection wire (2) and the plurality of electric wires (3), wherein the jacket (24) 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), and the outer layer (243) has a higher hardness than the inner layer (241).

[0069] [2] The multi-core cable (1) described in [1], wherein 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).

[0070] [3] The multi-core cable (1) according to [1] or [2], wherein 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.

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

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

[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 [1] to [6], wherein the jacket (24) has the intermediate layer (242) having a higher hardness than the outer layer (243).

[0075] (Addendum) Although the embodiments of the present invention have been described above, the invention according to the claims is not limited to the embodiments described above. It should be noted that not all of the combinations of features described in the embodiments are necessarily essential to the means for solving the problems of the invention.

[0076] The present invention can be implemented by appropriately modifying it within the scope of the spirit thereof. For example, in the above embodiment, the multi-core cable 1 is described as a cable for contactless power supply, but the present invention can also be applied to applications other than contactless power supply. [Explanation of symbols]

[0077] 1...Multi-core cable 2...Heat detection wire 3...Electric wire 4...Sheath 21...Heat detection wire 211...First conductor 212...First insulator 22...Twisted pair wire 24...Jacket 241...Inner layer 242...Middle class 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 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. Multi-core cable.

2. the intermediate layer has a higher melting point than the outer layer; 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 thickness of the intermediate layer is 50% or less of the thickness of the inner layer.

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. A multi-core cable according to claim 1.

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 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 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 thermal detection line, the inner layer and the intermediate layer are formed by non-solid extrusion molding, and the outer layer is formed around the outer periphery of the intermediate layer by insertion extrusion or solid extrusion. A method for manufacturing multi-core cables.

9. The intermediate layer has a higher melting point than the outer layer. The method for manufacturing the multi-core cable according to claim 8.

10. the outer layer is formed from a resin composition containing polyvinyl chloride resin as a main component; The intermediate layer is formed from a resin composition containing a fluororesin as a main component. A method for manufacturing a multi-core cable according to claim 8 or 9.

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