Patent Publication Number: US-2023141502-A1

Title: Vehicle cable

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Japanese Patent Application No. 2021-182836 filed on Nov. 9, 2021, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field of the Invention 
     The present disclosure relates to vehicle cables. 
     2. Description of the Related Art 
     Patent Document 1 describes a Twinax cable that includes a pair of conductors arrayed in parallel; a pair of sheath layers in which each sheath layer is formed by insulating resin, is disposed on a peripheral surface of the corresponding one of the pair of conductors by extrusion molding, and includes a round-pipe-shaped sheath layer body covering the outer peripheral surface of the conductor and a helical protrusion integrally formed on an outer peripheral surface of the sheath layer body; a pair of round-pipe-shaped core outer layers in which each core outer layer is made of an insulating material and is disposed on an outer peripheral surface of a corresponding one of the pair of sheath layers; a drain wire disposed between the pair of core outer layers; and a shielding member configured to shield the pair of core outer layers and the drain wire. 
     Two-core cables that are also referred to as a Twinax cables are conventionally used for, for example, transmission of signals. For example, as described in Patent Document 1, various studies have been made to improve the performance of such cables. 
     In recent years, applications of autonomous driving and safety equipment have been investigated and put into use in automobiles, and there has been a demand for vehicle cables that can transmit high-frequency band signals in automobiles. 
     Therefore, an object of the present disclosure is to provide a vehicle cable capable of transmitting high-frequency band signals. 
     RELATED ART DOCUMENT 
     Patent Document 
     
         
         [Patent Document 1] Japanese Laid-open Patent Application Publication No. 2005-259660 
       
    
     SUMMARY 
     A vehicle cable of the present disclosure is a vehicle cable capable of transmitting a signal of 4 GHz or higher including a two-core cable, a general shield layer that has a braided structure and is disposed on an outer periphery of the two-core cable, and an outer sheath disposed on an outer periphery of the general shield layer. The two-core cable includes two conductors that are a pair of stranded wires arranged in parallel to each other, an insulation layer configured to bundle and cover the two conductors, and a first shield layer including a first metal foil that is disposed on an outer periphery of the insulation layer. 
     According to the present disclosure, a vehicle cable capable of transmitting a high-frequency band signal can be provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a cross-sectional view taken along a plane perpendicular to a longitudinal direction of a vehicle cable according to an embodiment of the present disclosure; 
         FIG.  2    is a cross-sectional view taken along a plane perpendicular to the longitudinal direction of a vehicle cable according to another embodiment of the present disclosure; 
         FIG.  3    is a cross-sectional view taken along a plane perpendicular to the longitudinal direction of an insulating tape that can be applied to an insulating tape layer; 
         FIG.  4 A  is a cross-sectional view taken along a plane perpendicular to the longitudinal direction of a metal tape that can be applied to a first shield layer; 
         FIG.  4 B  is a cross-sectional view taken along a plane perpendicular to the longitudinal direction of a metal tape that can be applied to the first shield layer and a second shield layer; 
         FIG.  5    is a cross-sectional view taken along a plane perpendicular to the longitudinal direction of a cable according to configuration 2 manufactured in EXPERIMENT EXAMPLES 1 and 3; 
         FIG.  6    is a cross-sectional view taken along a plane perpendicular to the longitudinal direction of a cable according to configuration 3 manufactured in EXPERIMENT EXAMPLE 3; 
         FIG.  7    is a graph illustrating the frequency characteristics of insertion loss evaluated in EXPERIMENT EXAMPLE 1; 
         FIG.  8    is a view explaining a flexibility test; and 
         FIG.  9    is a view explaining a bending test. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments will be described below. 
     DESCRIPTION OF EMBODIMENTS OF PRESENT DISCLOSURE 
     Embodiments of the present disclosure will be listed and described. In the following description, the same reference symbols denote the same or corresponding elements, and a description thereof will be omitted. 
     (1) A vehicle cable according to an embodiment of the present disclosure is a vehicle cable capable of transmitting a signal of 4 GHz or higher. The vehicle cable according to the embodiment includes a two-core cable, a general shield layer that has a braided structure and is disposed on an outer periphery of the two-core cable, and an outer sheath disposed on an outer periphery of the general shield layer. The two-core cable includes two conductors that are a pair of stranded wires arranged in parallel to each other, an insulation layer configured to bundle and cover the two conductors, and a first shield layer including a first metal foil that is disposed on an outer periphery of the insulation layer. 
     Using a stranded wire as a conductor increases the flexibility, in which the vehicle cable can be easily bent, and the bendability, in which the vehicle cable is not easily broken when bent repeatedly, compared to a case where the conductor is a solid wire instead of a stranded wire. 
     Also, in the vehicle cable according to the embodiment, since the two conductors are bundled and covered, the material environment between the two conductors can be made uniform easily. Hence, it is possible to sufficiently suppress the insertion loss in high-frequency band signals of 4 GHz or higher, and thus implement a vehicle cable capable of transmitting a high-frequency band signal of 4 GHz or higher. 
     (2) The first metal foil included in the first shield layer may be in contact with the general shield layer. 
     Since the first metal foil included in the first shield layer is in contact with the general shield layer, the first shield layer can be easily coupled to an external terminal through, for example, the general shield layer. 
     (3) A plurality of two-core cables may be included. The plurality of two-core cables may be twisted, and a second shield layer including a second metal foil may be disposed on the outer periphery of the twisted plurality of two-core cables. The general shield layer and the outer sheath may be disposed so as to cover the outer periphery of the second shield layer. 
     Including the plurality of two-core cables can increase the variety of devices that can be supported. 
     Furthermore, by disposing the second shield layer on the outer periphery of the two-core cables, an electrical coupling can be formed between the first shield layer and the general shield layer. 
     (4) The second shield layer includes a double-sided metal tape that is wound helically along the longitudinal direction of the plurality of two-core cables and includes the second metal foil on an upper surface and a lower surface of a substrate. The second metal foil disposed on the upper surface of the substrate may be in contact with the general shield layer. 
     By helically winding the double-sided metal tape, which includes the metal foil on the upper and lower surface of the substrate, along the longitudinal direction of the plurality of two-core cables, the metal foils disposed on the upper and lower surfaces of the substrate come into contact with each other at an overlapping portion, thus allowing the two members to be electrically coupled. The metal foil disposed on the upper surface of the substrate contacting the general shield layer can form an electrical coupling between the first shield layer of the two-core cable and the general shield layer through the second shield layer. Electrically coupling the first shield layer, the second shield layer and the general shield layer to each other allows the first shield layer and the second shield layer to be easily coupled to an external terminal through the general shield layer. Furthermore, the first shield layer, the second shield layer and the general shield layer can suppress the leakage of signals to the outside of the cable and the introduction of electromagnetic waves from the outside of the cable. 
     (5) The second metal foil may be made of copper or aluminum. 
     By using copper or aluminum to form the second metal foil included by the second shield layer, the metal foil can have a uniform and sufficient conductivity. This can suppress the leakage of signals to the outside of the cable and the introduction of electromagnetic waves from the outside of the cable. 
     (6) The insulation layer may contain one or more types of insulating resins selected from polypropylene and cross-linked polyethylene. 
     Since polypropylene and cross-linked polyethylene have excellent heat resistance, containing one or more types of insulating resins selected from polypropylene and cross-linked polyethylene increases heat resistance of the insulation layer and the vehicle cable that includes the insulation layer. 
     (7) The first metal foil may be made of copper or aluminum. 
     By using copper or aluminum to form the first metal foil included in the first shield, the metal foil can have a uniform and sufficient conductivity. This can suppress the leakage of signals to the outside of the cable and the introduction of electromagnetic waves from the outside of the cable. 
     (8) The two-core cable includes an insulating tape layer between the insulation layer and the first shield layer. The insulating tape layer may include an insulating tape that is wound helically along the longitudinal direction of the insulation layer and includes an insulating substrate layer containing polyethylene terephthalate. 
     Polyethylene terephthalate has a higher permittivity than polypropylene, polyethylene, or the like. Hence, when the characteristic impedance of the vehicle cable is to be set to a desired value, providing the insulating tape layer containing polyethylene terephthalate can reduce the size of the insulation layer more than in a case where the insulating tape layer is not provided. Therefore, the size of the vehicle cable can be reduced, and thus the handling of the vehicle cable can be improved. 
     (9) The thickness of the outer sheath may be 0.3 mm or more to 1.0 mm or less. 
     Setting the thickness of the outer sheath to 0.3 mm or more to 1.0 mm or less can improve the abrasion resistance, the flame retardancy, and the flexibility of the vehicle cable. 
     (10) The thickness of the outer sheath may be 0.4 mm or more to 0.8 mm or less. 
     Setting the thickness of the outer sheath to 0.4 mm or more to 0.8 mm or less can improve the abrasion resistance, the flame retardancy, and the flexibility of the vehicle cable. 
     Details of Embodiments of Present Disclosure 
     Specific examples of the vehicle cable according to each embodiment (to be referred to as “the embodiment” hereinafter) of the present disclosure will be described below with reference to the accompanying drawings. Note that the present invention is not limited to these examples. The present invention is intended to be indicated by the appended claims and to include all changes and modifications within the scope of the appended claims and within the meaning and scope of the equivalents of the appended claims. 
     Vehicle Cable 
     (1) First Embodiment 
       FIG.  1    illustrates a cross-sectional view taken along a plane perpendicular to the longitudinal direction of a vehicle cable  10  according to the embodiment. In  FIG.  1   , the X-axis direction indicates the height direction of the vehicle cable  10 , the Y-axis direction indicates the width direction of the vehicle cable  10 , and the Z-axis direction perpendicular to the page indicates the longitudinal direction of the vehicle cable  10 . 
     The inventor of the present invention has investigated a vehicle cable capable of transmitting a signal of 4 GHz or higher, that is, a vehicle cable in which insertion loss with respect to a high-frequency band signal of 4 GHz or higher is suppressed. The inventor has found that a two-core cable including an insulation layer that bundles and covers two conductors for signal transmission can be used to implement a vehicle cable in which insertion loss with respect to a high-frequency band signal of 4 GHz or higher is suppressed. The inventor has completed the invention based on this finding. 
     Therefore, the vehicle cable according to the embodiment relates to a vehicle cable capable of transmitting a signal of 4 GHz or higher. 
     The components included by the vehicle cable according to the embodiment will be described hereinafter. 
     (1-1) Two-Core Cable 
     As illustrated in  FIG.  1   , the vehicle cable  10  according to the embodiment includes a two-core cable  101  including two conductors  11  that are a pair of stranded wires arranged in parallel to each other, an insulation layer  12  bundling and covering the two conductors  11 , and a first shield layer  14  including a first metal foil disposed on the outer periphery of the insulation layer  12 . The components included in the two-core cable  101  will be described below. 
     (1-1-1) Conductors 
     The vehicle cable according to the embodiment can include two conductors that are a pair of stranded wires arranged in parallel to each other. 
     In the interest of enhancing the workability when wiring is performed to attach the vehicle cable to a vehicle, the vehicle cable is required to have flexibility that allows it to be bent easily in accordance with the shape of the attachment position. Also, the vehicle cable may bend repeatedly due to a force being applied in accordance with the movement of a connected component. Thus, the vehicle cable is required to have bendability that curtails breaking when it is bent repeatedly. 
     Hence, as illustrated in  FIG.  1   , the vehicle cable  10  according to the embodiment can use a stranded wire as each conductor  11  for signal transmission. Using a stranded wire as the conductor  11  increases the flexibility, in which the vehicle cable can be easily bent, and the bendability, in which the vehicle cable is not easily broken when bent repeatedly, compared to a case where the conductor  11  is a solid wire instead of a stranded wire. 
     A wire diameter D 111  of each wire  111  and the number of the wires  111  forming the stranded wire of each conductor  11  are not particularly limited, and can be selected based on the type of signals to be transmitted by the vehicle cable  10  or the degree of the flexibility or the like required for the vehicle cable  10 . 
     (Wire Diameter D 111 ) 
     The wire diameter D 111  of each wire forming the stranded wire serving as each conductor  11  is preferably, for example, 0.100 mm or more to 0.500 mm or less. More preferably, the wire diameter D 111  may be 0.110 mm or more to 0.220 mm or less. By setting the wire diameter D 111  to 0.100 mm or more, the productivity of the stranded wire serving as the conductor  11  can be enhanced while reducing the number of wires used to form the stranded wire serving as the conductor  11 . In addition, setting the wire diameter D 111  of each wire forming the stranded wire serving as the conductor  11  to 0.500 mm or less can increase the flexibility and the bendability of each conductor  11  and the flexibility and the bendability of the vehicle cable  10  including the conductors  11 . 
     The wire diameter of each wire can be measured and calculated based on the following procedure. 
     First, in any cross section perpendicular to the longitudinal direction of a wire, the wire diameter of the wire is measured by a micrometer along the two orthogonal diameters of the wire that is being evaluated. An average of the values measured at the aforementioned two locations can be set as the wire diameter of the wire. In this specification, the wire diameter of each wire can be measured and calculated in the same manner. 
     (Number of Wires) 
     The number of wires forming the stranded wire serving as the conductor  11  is not particularly limited. For example, the number of wires is preferably 7 or more to 37 or less, and is more preferably 7 or more to 19 or less. Setting the number of wires that form the stranded wire serving as the conductor  11  to  7  can increase the flexibility and the bendability of each conductor  11  as well as the flexibility and the bendability of the vehicle cable  10  including the conductors  11 . Furthermore, setting the number of wires foaming the stranded wire serving as the conductor  11  to 37 or less can enhance the productivity of the stranded wire serving as the conductor  11 . The number of wires forming the stranded wire serving as the conductor  11  represents the number of wires included in each conductor  11 , that is, the number of wires included in each of a conductor  11 A and a conductor  11 B. 
     Each of the conductor  11 A and the conductor  11 B can include, for example, the above-described number of wires that have the above-described wire diameter D 111 , and can be formed by helically twisting the wires along the longitudinal direction. It is preferable for the conductor  11 A and the conductor  11 B to be formed by the same wires and the same number of wires. A stranded wire formed by twisting seven strands of wire with a wire diameter of 0.2 mm can be a specific configurational example of each of the conductor  11 A and the conductor  11 B. 
     (Distance L 11 ) 
     A distance L 11  between the conductor  11 A and the conductor  11 B is not particularly limited. However, it is preferable for the distance L 11  to be 0.5 mm or more to 3.0 mm or less, and more preferably be 0.8 mm or more to 2.0 mm or less. Setting the distance L 11  between the conductor  11 A and the conductor  11 B to 0.5 mm or more can ensure a sufficient distance between the conductor  11 A and the conductor  11 B and can reliably prevent electrical contact between the conductors  11 A and  11 B, that is, reliably prevent the generation of short circuits. Also, setting the distance L 11  between the conductor  11 A and the conductor  11 B to 3.0 mm or less can restrain the size of the vehicle cable  10  while increasing the flexibility of the vehicle cable  10 . 
     The distance L 11  between the conductor  11 A and the conductor  11 B represents the distance between the center of the conductor  11 A and the center of the conductor  11 B in a cross section perpendicular to the longitudinal direction of the vehicle cable  10 . The center of the conductor  11 A and the center of the conductor  11 B each represents the center of a circumscribed circle of the conductor in a cross section perpendicular to the longitudinal direction of the vehicle cable  10 . 
     The distance L 11  between the conductors can be, for example, a value measured on any cross section perpendicular to the longitudinal direction of the vehicle cable  10 . However, since the distance L 11  between the conductors may include a certain amount of variation, it is preferable for the distance L 11  to be the average of values measured on multiple cross sections perpendicular to the longitudinal direction of the vehicle cable  10 . For example, it is preferable for the distance L 11  between the conductors to be the average of the values obtained by measuring the distance between the conductors on 3 or more to 10 or less cross sections, which are perpendicular to the longitudinal direction of the vehicle cable  10 . Particularly, in the interest of efficiency, it is preferable for the distance L 11  of the conductors to be the average of the values obtained by measuring the distance between the conductors on three cross sections. When the distance L 11  between the conductors is to be measured on multiple cross sections perpendicular to the longitudinal direction of the vehicle cable  10 , the distance between two adjacent measurement surfaces in the longitudinal direction of the vehicle cable  10  is preferably 10 mm or more to 50 mm or less. For example, the distance between two adjacent measurement surfaces in the longitudinal direction of the vehicle cable  10  can be 20 mm. 
     A specific configurational example of the distance L 11  between the conductor  11 A and the conductor  11 B is 1.8 mm. 
     The conductors  11 A and  11 B can be arranged in parallel to each other in the above-described manner. It is preferable for the distance L 11  between the conductor  11 A and the conductor  11 B to be constant. However, even in such a case, the distance L 11  between the conductor  11 A and the conductor  11 B can be within a range that can be considered constant, including manufacturing tolerances. 
     (Material of Conductors) 
     The material of each conductor  11  is not particularly limited, but one or more conductive materials selected from, for example, annealed copper, silver, nickel-plated annealed copper, tin-plated annealed copper, and the like can be used. 
     (1-1-2) Insulation Layer 
     The vehicle cable  10  according to the embodiment can use the insulation layer  12  that bundles and covers the two conductors  11 . 
     Conventionally, in the two-core cable referred to as the Twinax cable, each conductor is covered with an insulation layer, and the two coated wires are subsequently covered by a shield layer or an outer sheath. However, covering each conductor with an insulation layer may generate variation in the thickness of the insulation layers due to manufacturing or may cause the shield layer to fall in a recessed portion between the two coated wires, and thus it is difficult to maintain a uniform environment for, for example, the materials between the two conductors. Hence, it is difficult to implement a cable that is capable of transmitting a high-frequency band signal of, for example, 4 GHz or higher while suppressing insertion loss in a high-frequency band signal of 4 GHz or higher. 
     In contrast, since the two conductors  11  are bundled and covered in the vehicle cable according to the embodiment, the the environment for the material between the two conductors  11  can be made uniform easily. Hence, it is possible to implement a cable that is capable of transmitting a high-frequency band signal of 4 GHz or higher while suppressing insertion loss in the high-frequency band signal of 4 GHz or higher. 
     Note that the vehicle cable  10  according to the embodiment suffices to be capable of transmitting a high-frequency band signal of 4 GHz or higher. Although there is no particular upper limit to the frequency band of the signal to be transmitted, it is preferable for the vehicle cable  10  to be capable of transmitting a signal in a high-frequency band that ranges from, for example, 4 GHz or higher to 30 GHz or lower. 
     (Size of Insulation Layer) 
     The size of the insulation layer  12  is not particularly limited. However, it is preferable for a width W 121  corresponding to the length of the long axis of the insulation layer  12 , in a cross section perpendicular to the longitudinal direction of the vehicle cable  10 , to be 1.5 mm or more to 9.0 mm or less and more preferably to be 1.5 mm or more to 4.0 mm or less. 
     By setting the width W 121  to 1.5 mm or more, the surfaces of the conductors  11  can be covered with the insulation layer  12  of a sufficient thickness to protect the conductors  11  while ensuring a sufficient distance between the conductors  11 . Also, by setting the width W 121  to 9.0 mm or less, it is possible to restrain the size of the vehicle cable  10  and improve the handling of the vehicle cable  10 . 
     In addition, the height H 12  corresponding to the length of the short axis of the insulation layer  12  is preferably 0.75 mm or more to 4.5 mm or less, and is more preferably 0.8 mm or more to 3.5 mm or less. 
     By setting the height H 12  of the insulation layer  12  to 0.75 mm or more, the surfaces of the conductors  11  can be covered with the insulation layer  12  of a sufficient thickness to protect the conductors  11 . Also, by setting the height H 12  of the insulation layer  12  to 4.5 mm or less, it is possible to restrain the size of the vehicle cable  10  and to particularly increase the flexibility of the vehicle cable  10 . 
     The insulation layer  12  can also include a flat part  122  along the width direction, that is, the Y-axis direction in a cross section perpendicular to the longitudinal direction of the vehicle cable  10 . Although a width W 122  of the flat part  122  is not particularly limited, it is preferable for the width W 122  to be, for example, 0.5 mm or more to 3.0 mm or less and more preferably to be 0.8 mm or more to 2.5 mm or less. 
     The vehicle cable  10  can be easily bent along, for example, the X-axis direction. However, by setting the width W 122  of the flat part  122  to be 0.5 mm or more, the vehicle cable  10  can particularly be bent more easily. That is, the flexibility of the vehicle cable  10  can be increased. 
     In addition, by setting the width W 122  of the flat part  122  to be 3.0 mm or less, it is possible to restrain the size of the vehicle cable  10 , and thus improve the handling of the vehicle cable  10 . 
     The length of each part of the insulation layer  12  is not particularly limited, and the length of each part can be selected in the above described manner from, for example, the above-described ranges. For example, as representative values, the width W 121  can be 3.7 mm, the height H 12  can be 1.8 mm, and the width W 122  of the flat part  122  can be 1.8 mm. 
     The respective dimensions of the parts of the insulation layer  12 , that is, the width W 121 , the width W 122  of the flat part, and the height H 12  can be values obtained by measuring, for example, any cross section perpendicular to the longitudinal direction of the vehicle cable  10 . However, since the length of each part of the insulation layer  12  of the vehicle cable  10  may include a certain amount of variation, it is preferable for the length of each part to be the average of values measured on multiple cross sections perpendicular to the longitudinal direction of the vehicle cable  10 . For example, it is preferable for each of the width W 121 , the width W 122  of the flat part, and the height H 12  described above to be the average of the values obtained by measuring the length of the part on 3 or more to 10 or less cross sections, which are perpendicular to the longitudinal direction of the vehicle cable  10 . Particularly, in the interest of efficiency, it is preferable for the length of each part to be the average of the values obtained by measuring the length of each part on three cross sections. When the length of each part is to be measured on multiple cross sections perpendicular to the longitudinal direction of the vehicle cable  10 , the distance between two adjacent measurement surfaces in the longitudinal direction of the vehicle cable  10  is preferably 10 mm or more to 50 mm or less. For example, the distance between two adjacent measurement surfaces in the longitudinal direction of the vehicle cable  10  can be 20 mm. 
     (Material of Insulation Layer) 
     The material of the insulation layer  12  is not particularly limited, and can be selected in accordance with the properties required for the vehicle cable  10 . 
     The insulation layer  12  can contain, for example, an insulating resin. The insulating resin is not particularly limited, but is preferable to be one or more types of insulating resins selected from, for example, polypropylene and cross-linked polyethylene. That is, the insulation layer  12  preferably contains one or more types of insulating resins selected from polypropylene and cross-linked polyethylene. 
     Since polypropylene and cross-linked polyethylene have excellent heat resistance, containing one or more types of insulating resins selected from polypropylene and cross-linked polyethylene in the insulation layer  12  increases heat resistance of the insulation layer  12  and the vehicle cable  10  that includes the insulation layer  12 . 
     Note that since it is typically difficult for polypropylene to be cross-linked, a non-crosslinked polypropylene, which has not been cross-linked, can be suitably used. 
     The insulation layer  12  can also contain various types of additives other than the insulating resin described above. The insulation layer  12  can contain, as an additive, one or more types of additives selected from, for example, a flame retardant, an antioxidant, a cross-linking agent, a cross-linking coagent, a lubricant, and the like. 
     The flame retardant, the antioxidant, cross-linking agent, and the like are not particularly limited, and known materials can be used as the flame retardant, the antioxidant, cross-linking agent, and the like. 
     For example, halogenated flame retardants and non-halogenated flame retardants can be used as the flame retardants. Brominated flame retardants or the like can be used as the halogenated flame retardants. Metal hydroxides such as magnesium hydroxide, nitrogen-based flame retardants, antimony trioxide, and phosphate-based flame retardants such as red phosphorus and organophosphates can be used as the non-halogenated flame retardants. 
     Although the formation method of the insulation layer  12  is not particularly limited, the material contained in the insulation layer can be formed on the outer periphery of the conductors  11  by full extrusion molding. 
     Although a drain wire or the like can be provided other than the above-described conductors  11  in the insulation layer  12 , it is preferable not to include a drain wire or the like in the insulation layer  12  of the vehicle cable according to the embodiment. Since a drain wire is electrically coupled to a shield layer or the like, it is usually used without coating. Hence, if a drain wire is disposed in the insulation layer  12 , the drain wire may come into contact with the conductors  11  and cause a short circuit. In contrast, by not disposing a drain wire in the insulation layer  12 , it is possible to prevent electrical coupling between the conductors  11  and the drain wire, that is, it is possible to prevent the generation of a short circuit. 
     In particular, in the vehicle cable  10  according to the embodiment, it is preferable for the conductors  11  to be the only electric wires present in the insulation layer  12 . 
     (1-1-3) First Shield Layer 
     The vehicle cable  10  can include the first shield layer  14  including a first metal foil disposed on the outer periphery of the insulation layer  12 . 
     By including the first shield layer  14  in the vehicle cable  10 , it is possible to prevent the leakage of signals to the outside of the cable and to prevent the introduction of electromagnetic waves from the outside of the cable. That is, a shielding effect can be exerted. 
     Further, it is preferable for the first metal foil included in the first shield layer to be in contact with a general shield layer  15  (to be described later). The first metal foil included in the first shield layer  14  being in contact with the general shield layer  15  allows the first shield layer  14  to be easily coupled to an external terminal or the like via, for example, the general shield layer  15 . 
     Although the configuration of the first shield layer  14  is not particularly limited, it can include, for example, a metal tape including metal foil helically wound on the outer periphery of the insulation layer  12  or an insulating tape layer  13  (to be described later) along the longitudinal direction of the insulation layer  12 . The first shield layer  14  can be formed by this aforementioned metal tape. In such a case, the metal foil included by the metal tape is the first metal foil. 
     As described above, in a case where the first shield layer  14  includes the metal tape, the configuration of the metal tape is not particularly limited. However, it is preferable for the metal tape to include the metal foil on, for example, at least one of the surfaces of its substrate. 
     The metal tape used to form the first shield layer  14  can have, for example, the configuration of a metal tape  141  whose cross section perpendicular to the longitudinal direction is illustrated in  FIG.  4 A . 
     The metal tape  141  illustrated in  FIG.  4 A  has a structure in which a substrate  1411  and a metal foil  1412  are stacked. Hence, the first shield layer  14  including the first metal foil can be formed by helically winding the metal tape  141  on the outer periphery of the insulation layer  12  or the like along the longitudinal direction of the insulation layer  12 . Note that to form the first shield layer  14  on the entire outer periphery of the insulation layer  12 , it is preferable to wind the metal tape  141  on the outer periphery of the insulation layer  12  so that the parts of the metal tape  141  overlap each other. 
     The metal tape  141  can also include an adhesive layer  1413  on a surface of the substrate  1411  on which the metal foil  1412  is not disposed. Including the adhesive layer  1413  in the metal tape  141  allows the parts of the metal tape  141  to be adhered together, via the adhesive layer  1413 , at the overlapping parts of the metal tape  141  when the metal tape  141  is helically wound on the outer periphery of the insulation layer  12  or the like in the longitudinal direction of the insulation layer  12 . Hence, the shape of the first shield layer  14  can be stabilized. 
     In a case where the first shield layer  14  is to be famed by the metal tape  141 , it is preferable to wind the metal tape  141  on the outer periphery of the insulation layer  12  by positioning a surface  141 B, which is on the side of the metal foil  1412 , on the side of the general shield layer  15  so that the metal foil  1412  can contact and be electrically coupled to the general shield layer  15  or the like. In this case, a surface  141 A, which is on the side of the substrate  1411 , is positioned on the side of the insulation layer  12 . 
     The metal tape used to form the first shield layer  14  is not limited to the metal tape  141 . The metal tape used to foam the first shield layer  14  may be a double-sided metal tape that includes a metal foil on both sides, that is, the upper and lower surfaces, of a substrate as in a double-sided metal tape  142  illustrated in  FIG.  4 B . The double-sided metal tape  142  includes an upper metal foil  1422  on the upper surface of a substrate  1421  and a lower metal foil  1423  on the lower surface of the substrate  1421 . 
     Even in a case of the double-sided metal tape  142  illustrated in  FIG.  4 B , an adhesive layer can be provided on either a surface  142 A of the lower metal foil  1423  or a surface  142 B of the upper metal foil  1422 . Alternatively, an adhesive layer may be provided on both of the surfaces  142 A and  142 B. 
     The size of the metal tape used to form the first shield layer  14  is not particularly limited. For example, if the metal tape  141  illustrated in  FIG.  4 A  is used, it is preferable the total of the thicknesses of the metal foil and the substrate, that is, a thickness T 141  in  FIG.  4 A  is preferably, for example, 5 μm or more to 30 μm or less and is more preferably 10 μm or more to 30 μm or less. By setting the total of the thicknesses of the metal foil and the substrate in the metal tape  141  illustrated in  FIG.  4 A  to 5 μm or more, the metal foil can be ensured to have a sufficient thickness, and thus enhance a shielding effect. Also, by setting the total of the thicknesses of the metal foil and the substrate to 30 μm or less, it becomes easier to make the metal tape follow the outer shape of the insulation layer  12  or the like when the metal tape is wound on the outer periphery of the insulation layer  12  or the like. Hence, the shape of the first shield layer  14  can be made uniform regardless of its position on the longitudinal direction of the vehicle cable, and the signal transmission performance of the vehicle cable can be stabilized. 
     If the double-sided metal tape  142  illustrated in  FIG.  4 B  is used to foam the first shield layer  14 , it is preferable the total of the thicknesses of the metal foil and the substrate, that is, a thickness T 142  is preferably, for example, 10 μm or more to 100 μm or less and is more preferably 15 μm or more to 80 μm or less. By setting the total of the thicknesses of the metal foil and the substrate to 10 μm or more, each metal foil can be ensured to have a sufficient thickness, and thus enhance the shielding effect. Also, by setting the total of the thicknesses of the metal foil and the substrate to 100 μm or less, it becomes easier to make the metal tape follow the outer shape of the insulation layer  12  or the like when the metal tape is wound on the outer periphery of the insulation layer  12  or the like. Hence, the shape of the first shield layer  14  can be made uniform regardless of its position on the longitudinal direction of the vehicle cable, and the signal transmission performance of the vehicle cable can be stabilized. 
     The thicknesses T 141  and T 142  are not particularly limited, and can be selected in the above describe manner from, for example, the above-described ranges. For example, as representative values, the thickness T 141  can be 15 μm, and the thickness T 142  can be 20 μm. 
     A thickness T 1413  of the adhesive layer  1413  is also not particularly limited. However, it is preferable for the thickness T 1413  to be, for example, 0.1 μm or more to 10 μm or less, and more preferably to be 0.1 μm or more to 5 μm or less. By setting the thickness T 1413  of the adhesive layer  1413  to 0.1 μm or more, a sufficient amount of adhesive can be contained, and the shape of the first shield layer  14  can be particularly stabilized. Since there is no difference in the stabilizing effect even if the adhesive layer  1413  is made excessively thick, it is preferable for the thickness T 1413  to be 10 μm or less as described above in terms of cost. The thickness T 1413  of the adhesive layer  1413  is not particularly limited, and can be selected in the above described manner from, for example, the above-described ranges. For example, as a representative value, the thickness T 1413  can be 2 μm. 
     In the interest of the shielding effect, the material of the first metal foil included in the first shield layer  14  suffices to be a conductive material and is not particularly limited. However, it is preferable for the material of the first metal foil to be, for example, copper or aluminum. By using copper or aluminum as the first metal foil included in the first shield layer  14 , the metal foil can be ensured to have a uniform and sufficient conductivity. This can particularly suppress the leakage of signals to the outside of the cable and the introduction of electromagnetic waves from the outside of the cable. 
     Note that the material of the substrate  1411  of the metal tape  141  or the material of the substrate  1421  of the double-sided metal tape  142  is not particularly limited. However, for example, it is possible to use polyethylene terephthalate (PET) as the material of each substrate. 
     (1-1-4) Insulating Tape Layer 
     The two-core cable  101  can also include the insulating tape layer  13  between the insulation layer  12  and the first shield layer  14  described above. 
     The insulating tape layer  13  can include an insulating tape  130 , which is illustrated in  FIG.  3   , that is helically wound on the outer periphery of the insulation layer  12  along the longitudinal direction of the insulation layer  12 . Note that the insulating tape layer  13  can also be formed by the insulating tape  130 . 
       FIG.  3    illustrates a cross section of the insulating tape  130  in the thickness direction. The insulating tape  130  can include an insulating substrate layer  131  containing polyethylene terephthalate (PET). The insulating substrate layer  131  can also be made of polyethylene terephthalate. 
     The permittivity of polyethylene terephthalate is higher than those of polypropylene, polyethylene, and the like. Hence, when the characteristic impedance of the vehicle cable  10  is to be set to a desired value, providing the insulating tape layer  13  containing polyethylene terephthalate can reduce the size of the insulation layer  12  more than in a case where the insulating tape layer  13  is not provided. Therefore, the size of the vehicle cable  10  can be reduced, and thus the handling of the vehicle cable  10  can be improved. 
     The insulating tape  130  can also include an adhesive layer  132  on either the upper surface or the lower surface of the insulating substrate layer  131 . Providing the adhesive layer  132  allows the parts of the insulating tape  130  to be adhered together, via the adhesive layer  132 , at the overlapping portions of the insulating tape  130  when the insulating tape  130  is helically wound on the outer periphery of the insulation layer  12  along the longitudinal direction of the insulation layer  12 . Hence, the shape of the insulating tape layer  13  can be stabilized. 
     Note that when winding the insulating tape  130  including the adhesive layer  132  on the outer periphery of the insulation layer  12 , it is preferable to wind the insulating tape  130  so that a surface  13 B on which the adhesive layer  132  is disposed is positioned on the side of the aforementioned first shield layer  14 . That is, in this case, it is preferable to arrange the insulating tape  130  so that a surface  13 A on which the adhesive layer  132  is not disposed is positioned on the side of the insulation layer  12 . 
     By arranging the surface  13 A on which the adhesive layer  132  is not disposed on the side of the insulation layer  12 , it is possible to prevent the insulation layer  12  from being adhered to the insulating tape layer  13  by the adhesive layer  132 . As a result, the process of removing an outer sheath  16  or the like and taking out the conductors  11  at the end of the vehicle cable  10  in the longitudinal direction can be performed more easily when the vehicle cable  10  is to be coupled to a device or the like. 
     Although a thickness T 131  of the insulating substrate layer  131  included in the insulating tape  130  is not particularly limited, it is preferable for the thickness T 131  to be, for example, 5 μm or more to 80 μm or less, and more preferably to be 5 μm or more to 20 μm or less. 
     By setting the thickness of the insulating substrate layer  131  to 5 μm or more, the insulating tape layer, which is the layer containing polyethylene terephthalate that has high permittivity, can be made sufficiently thick, thereby reducing the core formed by the insulation layer  12 . As a result, the size of the vehicle cable  10  can be restrained and the flexibility of the vehicle cable  10  can be increased. 
     Setting the thickness of the insulating substrate layer  131  to 80 μm or less can restrain the size of the vehicle cable  10  and increase the flexibility of the vehicle cable  10 . 
     In a case where the insulating tape  130  includes the adhesive layer  132 , a thickness T 132  of the adhesive layer  132  is not particularly limited. However, it is preferable for the thickness T 132  to be, for example, 0.1 μm or more to 10 μm or less, and more preferably to be 0.1 μm or more to 5 μm or less. 
     By setting thickness T 132  of the adhesive layer  132  to 0.1 μm or more, a sufficient amount of adhesive can be contained, and the shape of the insulating tape layer  13  can be particularly stabilized. Since there is no difference in the stabilizing effect even if the adhesive layer  132  is made excessively thick, it is preferable for the thickness T 132  to be 10 μm or less as described above in terms of cost. 
     The thickness T 131  of the insulating substrate layer  131  and the thickness T 132  of the adhesive layer  132  are not particularly limited, and each thickness can be selected from, for example, the above-described ranges. However, for example, thickness T 131  of the insulating substrate layer  131  can be 12 μm, and the thickness T 132  of the adhesive layer  132  can be 2 μm. 
     (1-2) General Shield Layer 
     The vehicle cable  10  according to the embodiment can include the general shield layer  15  that has a braided structure and is disposed on the outer periphery of the two-core cable  101 . 
     The general shield layer  15  can be formed by disposing metal wires so as to form the braided structure as described above. The material of the metal wires included in the general shield layer  15  is not particularly limited, but a material such as copper, aluminum, a copper alloy, or the like can be used. The surfaces of the metal wires of the general shield layer  15  may be plated with nickel or tin. Hence, for example, a silver-plated copper alloy, a tin-plated cooper alloy, or the like can also be used as the metal wires of the general shield layer  15 . 
     As described above, it is preferable for the general shield layer  15  to contact and be electrically coupled to the first metal foil of the above-described first shield layer  14 . In such a case, the first shield layer  14  can be, for example, easily connected to an external terminal or the like via the general shield layer  15 . 
     By providing the general shield layer  15  together with the above-described first shield layer  14 , it is possible to reduce the introduction of noise from the outside of the cable and to reduce signal leakage to the outside of the cable. In addition, by electrically coupling the general shield layer  15  to the above-described first shield layer  14 , the first shield layer  14  can be easily connected to an external terminal via the general shield layer  15 . 
     Although a thickness T 15  of the general shield layer  15  is not particularly limited, it is preferable for the thickness T 15  to be 0.1 mm or more to 0.5 mm or less and more preferably be 0.1 mm or more to 0.3 mm or less. 
     By setting the thickness T 15  of the general shield layer  15  to 0.1 mm or more, it is particularly possible to reduce the introduction of noise from the outside of the cable and to reduce signal leakage to the outside of the cable. Also, by setting the thickness T 15  of the general shield layer  15  to 0.5 mm or less, the flexibility of the vehicle cable  10  can be increased. 
     The thickness T 15  of the general shield layer  15  can be freely selected from, for example, the above-described ranges. However, as a representative value, the thickness T 15  of the general shield layer  15  can be, for example, 0.2 mm. 
     The thickness T 15  of the general shield layer  15  can be measured and calculated by, for example, the following procedure. 
     The thickness of the general shield layer  15  is measured by measuring, by a micrometer, a total of two locations in any cross section perpendicular to the longitudinal direction of the vehicle cable  10 . The two locations to be measured by the micrometer are a location along the width direction of the vehicle cable  10  and a location along the height direction of the vehicle cable  10 . Note that the width direction is the Y-axis direction in  FIG.  1    and can also be called the long hand direction. The thickness direction is the X-axis direction in  FIG.  1    and can also be called the short hand direction. 
     Subsequently, the average of the measure values obtained by measuring the two locations can be set as the thickness T 15  of the general shield layer  15 . 
     The thickness T 15  of the general shield layer  15  can be a value obtained by measuring any cross section perpendicular to the longitudinal direction of the vehicle cable  10 . However, as the thickness T 15  of the general shield layer  15  may include a certain amount of variation, it is preferable for the thickness T 15  to be the average of values measured on multiple cross sections perpendicular to the longitudinal direction of the vehicle cable  10 . For example, it is preferable for the thickness T 15  of the general shield layer  15  to be the average of the values obtained by measuring the thickness T 15  on 3 or more to 10 or less cross sections, which are perpendicular to the longitudinal direction of the vehicle cable  10 , in the above-described manner. Particularly, in the interest of efficiency, it is preferable for the length of each part to be the average of the values obtained by measuring the thickness T 15  on three cross sections. When the length of each part is to be measured on multiple cross sections perpendicular to the longitudinal direction of the vehicle cable  10 , the distance between two adjacent measurement surfaces in the longitudinal direction of the vehicle cable  10  is preferably 10 mm or more to 50 mm or less. For example, the distance between two adjacent measurement surfaces in the longitudinal direction of the vehicle cable  10  can be 20 mm. 
     A thickness T 16  of the outer sheath  16  can also be measured in the same manner. 
     (1-3) Outer Sheath 
     The vehicle cable according to the embodiment includes the outer sheath  16  that is disposed on the outer periphery of the general shield layer  15 . By providing the outer sheath  16 , the two-core cable  101  and the general shield layer  15  that are disposed inside of the cable can be protected. 
     Although the material of the outer sheath  16  is not particularly limited, it can contain one or more types of resin selected from, for example, polyolefin resins such as polyethylene and polypropylene, and polyvinyl chloride and the like. The resin of the outer sheath  16  may be cross-linked or may not be cross-linked. 
     In addition to the above-described resins, the outer sheath  16  can contain additives such as flame retardants, flame retardant coagents, antioxidants, lubricants, colorants, reflective additives, concealers, processing stabilizers and plasticizers. 
     Although the formation method of the outer sheath  16  is not particularly limited, the outer sheath  16  can be formed by performing filled extrusion molding or drawdown extrusion molding by using, for example, the above-described materials contained in the outer sheath  16 . 
     The thickness T 16  of the outer sheath  16  is not particularly limited. However, for example, it is preferable for the thickness T 16  to be 0.2 mm or more to 1.2 mm or less, more preferably be 0.3 mm or more to 1.0 mm or less, and even more preferably be 0.4 mm or more to 0.8 mm or less. 
     By setting the thickness T 16  of the outer sheath  16  to 0.2 mm or more, the two-core cable  101  and the general shield layer  15  inside the cable can be sufficiently protected. Also, by setting the thickness T 16  of the outer sheath  16  to 1.2 mm or less, the size of the vehicle cable  10  can be restrained, and the flexibility of the vehicle cable  10  can be increased. 
     Also, setting the thickness T 16  of the outer sheath  16  to 0.3 mm or more to 1.0 mm or less, or more particularly to 0.4 mm or more to 0.8 mm or less can particularly improve the abrasion resistance, the flame retardancy, and the flexibility of the vehicle cable. 
     The thickness T 16  of the outer sheath  16  can be freely selected from, for example, the above-described ranges. However, as a representative value, the thickness T 16  of the outer sheath  16  can be, for example, 0.5 mm. 
     Since the thickness T 16  of the outer sheath  16  can be measured in a similar manner to the thickness T 15  of the general shield layer  15  describe above, a description thereof will be omitted. 
     (2) Second Embodiment 
     The vehicle cable according to the embodiment can also include a plurality of two-core cables in accordance with the device to be coupled. 
     As illustrated in  FIG.  2   , a vehicle cable  20  according to the embodiment can include the plurality of two-core cables  101 . In this case, the plurality of two-core cables  101  are twisted together, and a second shield layer  24  including a second metal foil on the outer periphery of the twisted plurality of two-core cables  101  can be arranged in the vehicle cable  20 . 
     The general shield layer  15  and the outer sheath  16  described above can be disposed to cover the outer periphery of the second shield layer  24 . 
     Including the plurality of two-core cables  101  in the vehicle cable  20  according to the embodiment in the above described manner can increase the types of devices that can be supported by the vehicle cable  20 . 
     Note that a description of some of the matters already described in the first embodiment with respect to the two-core cable  101  and the like will be omitted. The components included in the vehicle cable  10  according to the embodiment will be described hereinafter. 
     (2-1) Two-Core Cables 
     The vehicle cable  20  illustrated in  FIG.  2    includes two two-core cables  101 . However, the vehicle cable according to the embodiment can also include three or more two-core cables. 
     The plurality of two-core cables  101  can be helically twisted with each other along the longitudinal direction. At this time, the twist rate is not particularly limited and can be selected in accordance with the size of the twisted units. However, for example, it is preferable for the twist rate to be 100 mm or more to 300 mm or less. Note that each two-core cable  101  includes, as described above, two conductor  11  that are two stranded wires arranged in parallel to each other, the insulation layer  12  configured to bundle and cover the two conductors  11 , and the first shield layer  14  disposed on the outer periphery of the insulation layer  12 . The insulating tape layer  13  can also be provided between the first shield layer  14  and the insulation layer  12 . 
     Since the two-core cable  101  has already been described, a description thereof will be omitted here. 
     (2-2) Second Shield Layer 
     The second shield layer  24  can be disposed on the outer periphery of the twisted plurality of two-core cables  101 , and can be disposed so as to be in contact with the respective outer peripheries (outer surfaces) of the two-core cables  101 . Disposing the second shield layer on the outer periphery of the two-core cable allows an electrical coupling to be formed between the first shield layer  14  and the general shield layer  15 . 
     The second shield layer  24  preferably includes a metal tape that can include the second metal foil and be helically wound along the longitudinal direction of, for example, the plurality of two-core cables  101 . To form the second shield layer  24  so as to cover the entirety of the plurality of two-core cables  101 , it is preferable to wind the metal tape around the outer periphery of the plurality of two-core cables  101  so that parts of the metal tape will overlap each other. 
     It is preferable for the metal tape included in the second shield layer  24  to be a double-sided metal tape that includes a metal foil on both surfaces of the substrate. That is, it is preferable for the metal tape included in the second shield layer  24  to include the upper metal foil  1422  on the upper surface of the substrate  1421  and the lower metal foil  1423  on the lower surface of the substrate  1421  as in the double-sided metal tape  142  illustrated in  FIG.  4 B . It is also preferable for the upper metal foil  1422 , which is the metal foil disposed on the upper surface of the substrate  1421 , to be in contact with the general shield layer  15 . It is also preferable for the lower metal foil  1423 , which is the metal foil disposed on the lower surface of the substrate  1421 , to be in contact with the first metal foil of the first shield layer  14 . In this case, the upper metal foil  1422  and the lower metal foil  1423  form the second metal foil included in the second shield layer  24 . 
     By helically winding a double-sided metal tape, which includes the metal foil on the upper and lower surface of the substrate  1421 , along the longitudinal direction of the plurality of two-core cables  101 , the upper metal foil  1422  and the lower metal foil  1423  can come into contact at overlapping portions and be electrically coupled. The upper metal foil  1422  disposed on the upper surface of the substrate  1421  contacting the general shield layer  15  allows, for example, the first shield layer  14  of each two-core cable  101  to be electrically coupled to the general shield layer  15  via the second shield layer  24 . By electrically coupling the first shield layer  14 , the second shield layer  24 , and the general shield layer  15  as described above, the first shield layer  14  and the second shield layer  24  can be easily connected to an external terminal via the general shield layer  15 . Further, the first shield layer  14 , the second shield layer  24 , and the general shield layer  15  can be used to suppress signal leakage to the outside of the cable and to suppress the introduction of electromagnetic waves from the outside of the cable. 
     In the interest of the shielding effect, the material of the second metal foil included in the second shield layer  24  suffices to be a conductive material and is not particularly limited. However, it is preferable for the material of the second metal foil to be, for example, copper or aluminum. By using copper or aluminum as the second metal foil of the second shield layer  24 , the metal foil can be ensured to have a uniform and sufficient conductivity. This can particularly suppress the leakage of signals to the outside of the cable and the introduction of electromagnetic waves from the outside of the cable. 
     As the preferable thicknesses of the respective portions of the double-sided tape illustrated in  FIG.  4 B  have already been described, a description thereof will be omitted here. 
     (2-3) General Shield Layer and Outer Sheath 
     The general shield layer  15  and the outer sheath  16  can be formed in the same manner as in the first embodiment. Hence, a description thereof will be omitted. 
     EXAMPLES 
     Although specific examples of the embodiment will be described hereinafter, the present invention is not limited to these examples. 
     Experiment Example 1 
     The vehicle cable  10  (to be also referred to as “the cable of configuration 1” hereinafter) that has the cross-sectional structure illustrated in  FIG.  1    and a cable  50  (to be also referred to as “the cable of configuration 2” hereinafter) that has the cross-sectional structure illustrated in  FIG.  5    were prepared, and the skew and the insertion loss of each cable were evaluated. 
     The cable of configuration 1 is the example of the embodiment, and the cable of configuration 2 is the comparative example. 
     (1) Configuration of Cables 
     (Cable of Configuration 1) 
     The vehicle cable  10  having the cross-sectional structure illustrated in  FIG.  1    is famed according to CONFIGURATION 1 indicated in TABLE 1. More specifically, the vehicle cable  10  included two conductors  11 . Each conductor  11  was formed by twisting  7  wires  111  that were tin-plated copper wires. The wire diameter D 111  of each wire  111  was 0.16 mm. The diameter of each conductor  11  was 0.48 mm. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 CONFIGURATION 1 
                 CONFIGURATION 2 
                 CONFIGURATION 3 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 REFERENCE 
                 LENGTH 
                 REFERENCE 
                 LENGTH 
                 REFERENCE 
                 LENGTH 
               
               
                   
                 SYMBOL 
                 (THICKNESS) 
                 SYMBOL 
                 (THICKNESS) 
                 SYMBOL 
                 (THICKNESS) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 WIRE DIAMETER 
                 D111 
                 0.16 
                 D511 
                 0.16 
                 D61 
                 0.41 
               
               
                 (CONDUCTOR 
               
               
                 DIAMETER) 
               
               
                 (mm) 
               
               
                 DISTANCE 
                 L11 
                 1.48 
                 L51 
                 1.23 
                 L61 
                 1.40 
               
               
                 BETWEEN 
               
               
                 CONDUCTORS 
               
               
                 (mm) 
               
               
                 SIZE OF 
                 W121 
                 2.96 
                 D52 
                 1.23 
                 W621 
                 2.80 
               
               
                 INSULATION 
                 H12 
                 1.48 
                   
                   
                 H62 
                 1.40 
               
               
                 LAYER 
               
               
                 (mm) 
               
            
           
           
               
               
               
               
               
            
               
                 TWIST RATE 
                 — 
                 52A, 52B 
                 12 
                 — 
               
               
                 (mm) 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 INSULATING 
                 T131 
                 12 
                 T131 
                 12 
                 T131 
                 12 
               
               
                 TAPE LAYER 
               
               
                 (μm) 
               
               
                 FIRST 
                 T141 
                 15 
                 T141 
                 15 
                 T141 
                 15 
               
               
                 SHIELD LAYER 
               
               
                 (μm) 
               
               
                 GENERAL 
                 T15 
                 0.4 
                 T55 
                 0.4 
                 — 
                 — 
               
               
                 SHIELD LAYER 
               
               
                 (mm) 
               
               
                 OUTER SHEATH 
                 T16 
                 0.5 
                 T56 
                 0.5 
                 — 
                 — 
               
               
                 (mm) 
               
               
                   
               
            
           
         
       
     
     The measurement of the wire diameter was performed in accordance with the following procedure. First, in any cross section perpendicular to the longitudinal direction of the wire, the diameter of the wire was measured by a micrometer along the two orthogonal diameters of the wire. The average of the measured values obtained in the aforementioned two locations was obtained as the wire diameter. The conductor diameter was also measured and calculated in a similar manner. 
     The two conductors  11  are arranged in parallel to each other, and the insulation layer  12  bundles and covers the two conductors  11 . Polypropylene was used for the material of the insulation layer  12 , and no cross-linking was performed. The distance L 11  between the conductors  11  and the width W 121  and the height H 12  of the insulation layer  12  were as indicated in TABLE 1. Note that the distance between the conductors  11  correspond to the distance between the respective centers of the circumscribed circles of the conductors  11 . 
     The distance L 11  between the conductors  11  and the width W 121  and the height H 12  of the insulation layer  12  were measured and calculated according to the following procedure. The procedure will be described by using the distance L 11  between the conductors  11  as an example. 
     The distance L 11  between the conductors  11  was measured on each of the acquired three cross sections perpendicular to the longitudinal direction of the vehicle cable. The average of the measured values thereof was set as the distance L 11  between the conductors  11  of the vehicle cable. The three measured cross sections were set so that the distance between adjacent cross sections was 20 mm in the longitudinal direction of the cable. The width W 121  and the height H 12  of the insulation layer  12  were measured in the same manner. 
     The insulating tape layer  13 , the first shield layer  14 , the general shield layer  15 , and the outer sheath  16  are disposed on the outer periphery of the insulation layer  12 . The thickness of each layer is as indicated in TABLE 1. 
     The insulating tape layer  13  was formed using the insulating tape  130  illustrated in  FIG.  3   . Hence, the thickness T 131  of the insulating substrate layer  131  is indicated as the thickness of the insulating tape layer in TABLE 1. The insulating substrate layer  131  was made of polyethylene terephthalate. 
     The first shield layer  14  was formed by using the metal tape  141  illustrated in  FIG.  4 A . Hence, the thickness T 141  as the total of the thicknesses of the substrate  1411  and the metal foil  1412  in the metal tape  141  is indicated in TABLE 1. The substrate  1411  is made of polyethylene terephthalate, and the metal foil  1412  is made of aluminum foil. 
     When the insulating tape layer  13  and the first shield layer  14  were formed, the insulating tape  130  and the metal tape  141  were helically wound along the longitudinal direction of the insulation layer  12  so that the adhesive layer  132  of the insulating tape  130  and the adhesive layer  1413  of the metal tape  141  would adhere. That is, the insulating tape  130  was wound so that the surface  13 A was positioned on the side of the insulation layer  12 , and the metal tape  141  was wound so that the surface  141 A was positioned on the side of the insulation layer  12 . 
     Tin-plated copper wires were used as the wires forming the general shield layer  15 . Polyethylene was used as the resin material of the outer sheath  16 , and cross-linking was performed. 
     The thickness T 15  of the general shield layer  15  and the thickness T 16  of the outer sheath  16  were measured and calculated according to the following procedure. The procedure will be described using the case of the general shield layer  15  as an example. 
     First, in each of the acquired three cross sections perpendicular to the longitudinal direction of the vehicle cable  10 , the thickness T 15  was measured by a micrometer at a total of two locations, that is, one location along the width direction and the one location along the height direction of the vehicle cable  10 . The average of the measured values of the two locations was set as the thickness T 15  of the general shield layer  15  at each cross section. 
     Next, the average of all of the thicknesses T 15  of the general shield layer  15  that were individually calculated for the three cross sections was obtained and set as the thickness T 15  of the general shield layer  15  of the vehicle cable. The three measured cross sections were set so that the distance between adjacent cross sections was 20 mm in the longitudinal direction of the cable. 
     The thickness T 16  of the outer sheath  16  was also measured and calculated in a similar manner to the thickness T 15  of the general shield layer  15 . 
     (Cable of Configuration 2) 
     The cable  50  that has the cross-sectional structure illustrated in  FIG.  5    has the configuration of CONFIGURATION 2 indicated in TABLE 1. More specifically, the cable  50  included two conductors  51 . Each conductor  51  was formed by twisting  7  wires  511  that were tin-plated copper wires. A wire diameter D 511  of each wire  511  were 0.16 mm. The outer diameter of each conductor  51  was 0.48 mm. 
     The wire diameter of each wire and the outer diameter of each conductor were measured and evaluated in a similar manner to the cable of configuration 1. 
     The conductors  51  were formed as coated wires  52 A and  52 B, each of which with an insulation layer  521  disposed on the outer periphery. The two coated wires  52 A and  52 B were twisted at a twist rate of 12 mm. Cross-linked polyethylene was used for the insulation layer of each of the coated wires  52 A and  52 B. 
     The outer diameter D 52  of each coated wire was 1.23 mm, and a distance L 51  between the conductors  51  was 1.23 mm. Note that the distance L 51  between the conductors  51  correspond to the distance between the respective centers of the circumscribed circles of the conductors  51 . 
     The outer diameter D 52  of each coated wire was evaluated in the same manner as the wire diameter. The distance L 51  between the conductors  51  was evaluated in the same manner as the cable of configuration 1. 
     A insulating tape layer  53 , a first shield layer  54 , a general shield layer  55 , and an outer sheath  56  are disposed on the outer periphery of the two coated wires  52 A and  52 B. The respective thicknesses of the layers are as indicated in TABLE 1. 
     The insulating tape layer  53  to the outer sheath  56  were famed in the same manner as the vehicle cable  10  of configuration 1 described above. 
     Since the length of each of the insulating tape layer  53  to the outer sheath  56  was measured and calculated in the same manner as the cable of configuration 1, a description thereof will be omitted. 
     (2) Evaluation 
     (Skew) 
     A digital serial analyzer was used to send electric pulses to the two conductors of the cable of the configuration 1 described above and to the two conductors of the cable of configuration 2, and the skew was obtained by measuring the delay time per meter.  20  cables of the same configuration were measured for each of the cable of configuration 1 and the cable of configuration 2. 
     In the case of the vehicle cable  10  of configuration 1, it was confirmed that skew was distributed in the range of 0 psec/m or more to 4 psec/m or less. 
     In contrast, in the case of the cable  50  of configuration 2, it was confirmed that skew was distributed in the range of 0 psec/m or more to 15 psec/m or less. 
     That is, it was confirmed that the delay time was suppressed more in the vehicle cable  10  of configuration 1 than in the cable  50  of configuration 2. 
     (Insertion Loss) 
     Differential signals were input to each of the cable of configuration 1 and the cable of configuration 2 to evaluate the frequency characteristics of insertion loss. The evaluation was carried out in air at room temperature. The results are indicated in  FIG.  7   . In  FIG.  7   , line  71  indicates the evaluation result of the cable of configuration 1, and line  72  indicates the evaluation result of the cable of configuration 2. 
     As is obvious from  FIG.  7   , it was confirmed that the cable of configuration 1 according to the example is able to transmit signals of 4 GHz or higher, particularly, signals of 5 GHz or higher. Note that although it is indicated in  FIG.  7    that signals can be transmitted without a large insertion loss in frequency bands of 10 GHz or less, it was confirmed that signals are also able to be transmitted without a large insertion loss in higher frequency bands, for example, in frequency bands higher than 10 GHz. 
     In contrast, with respect to the cable of configuration 2 according to the comparative example, a large insertion loss was confirmed when the frequency band exceeded 4 GHz, and it was confirmed that the cable of configuration 2 is not applicable for transmitting signals of 4 GHz or higher. 
     Experiment Example 2 
     The abrasion resistance, the flame retardancy, and the flexibility of the vehicle cable  10 , which has the cross-sectional shape indicated in  FIG.  1   , were evaluated. EXPERIMENT EXAMPLES 2-1 to 2-6 all are examples of the embodiment. 
     In each experiment example, the vehicle cable  10  were manufactured in the same manner as configuration 1 of EXPERIMENT EXAMPLE 1 except that the thickness of the outer sheath  16  was adjusted to be the value indicated in TABLE 2. 
     The abrasion resistance was evaluated by performing a tape test in compliance with JASO D 618 . The coated wire of each sample was cut to a length of 1000 mm, and #150 G abrasion tape was pressed on to the coated wire with a pressing load of 1.9 kg. Subsequently, the tape was sent out at a tape moving speed of 1500 ram/min, and the amount of the tape that was sent out was measured until the conductors were exposed. 
     Flame retardancy was evaluated by performing a horizontal burning test in compliance with JASO-D618. In the horizontal burning test, the underside of the center of the electric wire, held horizontally, was brought into contact with the flame of a tirrill burner at an angle of 20° for 30 seconds, and the time until the flame was extinguished was measured. 
     Flexibility was evaluated by placing an evaluation cable  80  with a length of 50 cm on a table  81  as illustrated in  FIG.  8   , thus setting a state where the cable  80  protrudes 25 cm from the table  81 . That is, a length L 801  and a length L 802  in  FIG.  8    each were 25 cm. 
     In this case, an evaluation was performed by measuring a distance L 80  between a ground  82  and an end  80 A of the cable  80 . The bend of the vehicle cable increases as shorter the distance L 80  is, thus indicating better flexibility. 
     With respect to abrasion resistance, a case that was 250 cm or more was evaluated as A, a case that was 200 cm or more but less than 250 cm was evaluated as B, and a case that was 200 cm or less was evaluated as C. An evaluation of A represents a case with the best abrasion resistance, that is, a case that can withstand abrasion. The abrasion resistance decreases in the order of evaluations B and C. 
     With respect to flame retardancy, a case that was 30 seconds or less was evaluated as A, a case that was 30 seconds or longer to 40 seconds or less was evaluated as B, and a case that was longer than 40 seconds was evaluated as C. An evaluation of A represents a case with the best flame retardancy, that is, a case that can withstand burning. The flame retardancy decreases in the order of evaluations B and C. 
     With respect to flexibility, a case that was 130 mm or less was evaluated as A, a case that was 130 mm or longer to 135 mm or less was evaluated as B, and a case that was longer than 135 mm was evaluated as C. An evaluation of A represents a case with the best flexibility, that is, a case that can be bent easily. The flexibility decreases in the order of evaluations B and C. 
     As the overall evaluation, for the three types of evaluations described above, an evaluation of C was given when at least one C was contained, an evaluation of B was given when no C was contained but at least one B was contained, and an evaluation of A was given when all the three types of evaluations were A. 
     TABLE 2 indicates the thickness of the outer sheath of the vehicle cable subjected to the evaluation and the evaluation results. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                   
                 ABRASION 
                   
                   
                   
               
               
                   
                 THICKNESS 
                 RESISTANCE 
                 FLAME RETARDANCY 
                 FLEXIBILITY 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 OF OUTER 
                 MEASURED 
                   
                 MEASURED 
                   
                 MEASURED 
                   
                 OVERALL 
               
               
                   
                 SHEATH 
                 VALUE 
                 EVALUA- 
                 VALUE 
                 EVALUA- 
                 VALUE 
                 EVALUA- 
                 EVALUA- 
               
               
                   
                 (mm) 
                 (cm) 
                 TION 
                 (sec) 
                 TION 
                 (mm) 
                 TION 
                 TION 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 EXPERIMENT 
                 1.2 
                 882 
                 A 
                 10 
                 A 
                 140 
                 C 
                 C 
               
               
                 EXAMPLE 2-1 
               
               
                 EXPERIMENT 
                 1.0 
                 735 
                 A 
                 14 
                 A 
                 133 
                 B 
                 B 
               
               
                 EXAMPLE 2-2 
               
               
                 EXPERIMENT 
                 0.8 
                 588 
                 A 
                 20 
                 A 
                 127 
                 A 
                 A 
               
               
                 EXAMPLE 2-3 
               
               
                 EXPERIMENT 
                 0.4 
                 294 
                 A 
                 26 
                 A 
                 121 
                 A 
                 A 
               
               
                 EXAMPLE 2-4 
               
               
                 EXPERIMENT 
                 0.3 
                 220 
                 B 
                 36 
                 B 
                 115 
                 A 
                 B 
               
               
                 EXAMPLE 2-5 
               
               
                 EXPERIMENT 
                 0.2 
                 147 
                 C 
                 57 
                 C 
                 109 
                 A 
                 C 
               
               
                 EXAMPLE 2-6 
               
               
                   
               
            
           
         
       
     
     According to the results indicated in TABLE 2, the overall evaluation result was A or B in cases where the thickness T 16  of outer sheath  16  was 0.3 mm or more to 1.0 mm or less, confirming excellence in abrasive resistance, flame retardancy, and flexibility. 
     Furthermore, the overall evaluation result was A in cases where the thickness T 16  of outer sheath  16  was 0.4 mm or more to 0.8 mm or less, confirming particular excellence in abrasive resistance, flame retardancy, and flexibility. 
     Experiment Example 3 
     In addition to evaluations performed on the cable of configuration 1 and the cable of configuration 2 in EXPERIMENT EXAMPLE 1, a cable of configuration 3 was prepared and evaluated for bendability. 
     EXPERIMENT EXAMPLE 3-1 indicates the evaluation result of the vehicle cable of configuration 1 and is an example of the embodiment. 
     EXPERIMENT EXAMPLE 3-2 indicates the evaluation result of the vehicle cable of configuration 2 and is a comparative example. 
     EXPERIMENT EXAMPLE 3-3 indicates the evaluation result of the vehicle cable of configuration 3 and is a comparative example. 
     (1) Cable of Configuration 3 The cable of configuration 3 has a cross-sectional structure illustrated in  FIG.  6   , and includes two conductors  61  that are solid wires instead of stranded wires. The conductor diameter D 61  of the conductor  61  was 0.41 mm as indicated in TABLE 1, and a distance L 61  between the conductors was 1.4 mm. A tin-plated copper wire was used as each conductor  61 . 
     The two conductors  61  are bundled and covered by an insulation layer  62 . Polypropylene was used for the material of the insulation layer  62 , and no cross-linking was performed. A width W 621  of the insulation layer  62  was 2.80 mm, and a height H 62  of the insulation layer  62  was 1.40 mm. 
     A drain wire  612  was also disposed in the insulation layer  62 . 
     An insulating tape layer  63  and a first shield layer  64  were disposed on the outer periphery of the insulation layer  62 . The insulating tape layer  63  and the first shield layer  64  were formed in the same manner as the cable of configuration 1 in EXPERIMENT EXAMPLE 1. 
     Since the insulating tape layer  63  was formed by using the insulating tape  130  illustrated in  FIG.  3   , the thickness T 131  of the insulating substrate layer  131  is indicated as the thickness of the insulating tape layer  63  in TABLE 1. Also, since the first shield layer  64  was formed by using the metal tape  141  illustrated in  FIG.  4 A , the thickness T 141 , which is the total of the thicknesses of the substrate  1411  and the metal foil  1412  in the metal tape  141 , is indicated in TABLE 1 as the thickness of the first shield layer  64 . 
     The general shield layer and the outer sheath were not provided. 
     As the cable of configuration 1 and the cable of configuration 2 have the same configurations as those in the case of EXPERIMENT EXAMPLE 1, a description thereof will be omitted here. 
     (2) Evaluation 
     The bendability evaluation was performed by placing, as illustrated in  FIG.  9   , a cable  90  to be evaluated between two mandrels  911  and  912 , which were arranged horizontally and parallel to each other and had a diameter of 4 mm, and applying a load of 200 g vertically downward on the cable  90 . In this state, an operation in which the upper end of the cable  90  is bent 90° in the horizontal direction to be abutted against the upper side of one mandrel  911 , and is subsequently bent 90° in the horizontal direction to be abutted against the upper side of the other mandrel  912  was repeatedly performed. 
     The repeated operation described above was pertained by measuring the resistance values of all of the conductors in the cable  90 . The number of bending operations performed until the resistance increased to 10 times or more of the initial resistance value was counted with respect to one of the conductors. Note that one bending operation comprises an operation in which the cable is first bent to the left side, then bent to the right side, and subsequently returned to the left side. The superiority of the bendability increases as the number of bending operations, as a result of the bending test, increases. 
     Three cables were prepared for the same configuration, and three evaluations were performed. The average value of the three evaluation is also indicated. 
     Each evaluation result is indicated by a converted value obtained by converting the number of bending operations of the first test of EXPERIMENT EXAMPLE 3-2 as 100. The superiority of the bendability increases as this numerical value increases. For example, the number of bending operations of the first test of EXPERIMENT EXAMPLE 3-1 is 2.7 times higher than the number of bending operations of the first test of EXPERIMENT EXAMPLE 3-2. The evaluation results are indicated in TABLE 3. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 EXPERIMENT 
                 EXPERIMENT 
                 EXPERIMENT 
               
               
                   
                 EXAMPLE 
                 EXAMPLE 
                 EXAMPLE 
               
               
                   
                 3-1 
                 3-2 
                 3-3 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 FIRST 
                 270 
                 100 
                 25 
               
               
                 EVALUATION 
               
               
                 SECOND 
                 330 
                 130 
                 30 
               
               
                 EVALUATION 
               
               
                 THIRD 
                 290 
                 110 
                 45 
               
               
                 EVALUATION 
               
               
                 AVERAGE 
                 297 
                 113 
                 33 
               
               
                   
               
            
           
         
       
     
     According to the results indicated in TABLE 3, it was confirmed that the cable of EXPERIMENT EXAMPLE 3-1 which is the example of the embodiment has superior bendability. 
     In contrast, it was confirmed that the cable of EXPERIMENT EXAMPLE 3-3 has a particularly inferior bendability because the conductor was not a stranded wire.