Patent Publication Number: US-9431726-B2

Title: Multi-core cable

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority from Japanese patent application No. 2013-009453 filed on Jan. 22, 2013 and Japanese Utility Model application No. 2013-006702 filed on Nov. 25, 2013, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a multi-core cable for integrating plural shielded electric wires. 
     BACKGROUND ART 
     For example, JP-2011-146163-A discloses that outer conductors of plural shielded electric wires are exposed at given positions and are integrated by solder. 
     As disclosed in JP-2011-146163-A, when the outer conductor of each of the shielded electric wires is grounded, the assembled portion of the outer conductors is soldered and a diameter of the portion becomes large. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view showing one example of an embodiment of a multi-core cable according to the invention. 
         FIG. 2  is an enlarged sectional view taken on line A-A of the multi-core cable shown in  FIG. 1 . 
         FIG. 3  is an enlarged sectional view taken on line B-B of the multi-core cable shown in  FIG. 1 . 
         FIG. 4  is a plan view showing a manufacturing method of the multi-core cable according to  FIG. 1 . 
         FIG. 5  is a plan view showing the manufacturing method of the multi-core cable according to  FIG. 1 . 
         FIG. 6  is a plan view showing the manufacturing method of the multi-core cable according to  FIG. 1 . 
         FIG. 7  is a sectional view showing one example of a multi-core cable according to a second embodiment of the invention. 
         FIG. 8  is a perspective view showing one example of distal end processing of the multi-core cable shown in  FIG. 7 . 
         FIG. 9  is a perspective view showing an example of distal end processing of a multi-core cable according to a third embodiment of the invention. 
         FIGS. 10A and 10B  are perspective views showing modified examples of the shielded electric wire according to the invention. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Description of Embodiment of the Present Invention 
     First, the contents of embodiments of the present invention will be described. 
     (1) The invention provides a multi-core cable including 
     plural shielded electric wires for signal transmission, 
     wherein the plural shielded electric wires are bundled so as to make contact with the adjacent shielded electric wires, 
     wherein sheaths of the plural shielded electric wires are respectively removed at the same position in a length direction, and 
     wherein outer conductors of the plural shielded electric wires at the position at which the sheaths are removed are bundled by a metal wire, and the bundled portion is soldered and fastened. 
     According to the multi-core cable according to the invention, the outer conductors of the shielded electric wires can be bundled by the metal wire to decrease a diameter of the position at which the outer conductors are assembled. 
     (2) The invention may provide the multi-core cable, 
     wherein the multi-core cable includes a ground electric wire made of an insulated electric wire or a shielded electric wire, 
     wherein a sheath of the ground electric wire is removed to expose a conductor at the same position in the length direction as the position at which the sheaths of the shielded electric wires for signal transmission are removed, and 
     wherein the metal wire winds around the outer conductors of the plural shielded electric wires and the conductor of the ground electric wire to thereby bundle the plural shielded electric wires and the ground electric wire, and the bundled portion is soldered and fastened. 
     (3) The invention may provide the multi-core cable, 
     wherein the ground electric wire is a shielded electric wire, 
     wherein the sheath of the ground electric wire is removed to expose an outer conductor at the same position in the length direction as the position at which the sheaths of the shielded electric wires for signal transmission are removed, and 
     wherein the metal wire winds around the outer conductors of the plural shielded electric wires and the outer conductor of the ground electric wire to thereby bundle the plural shielded electric wires and the ground electric wire, and the bundled portion is soldered and fastened. 
     According to the configuration of (2) or (3), a terminal for grounding the ground electric wire can be provided at any position and the grounding position can be designed freely. 
     (4) The invention may provide the multi-core cable, 
     wherein the plural shielded electric wires are covered with a cable sheath, 
     wherein each shielded electric wire has
         a central conductor having a cross-sectional area of 0.01 mm 2  or less,   an insulating layer covering the central conductor,   the outer conductor covering the insulating layer, and   the sheath covering the outer conductor,       

     wherein, in an end of the multi-core cable, the cable sheath is removed along a given length to expose the plural shielded electric wires, 
     wherein each of the sheaths of the plural shielded electric wires is removed at the same position in the length direction to expose each of the outer conductors, 
     wherein the metal wire wholly winds around the outer conductors so as to tighten and bundle the exposed outer conductors, 
     wherein the position at which the metal wire winds is fastened to each of the outer conductors by solder having a melting temperature of 130 to 150° C., and 
     wherein an outside diameter of the position at which the metal wire winds and the shielded electric wires are fastened by the solder is smaller than an outside diameter of the cable sheath. 
     According to the configuration of (4), the metal wire tightens and bundles the plural shielded electric wires. As a result, the outside diameter of the position at which the metal wire winds and the shielded electric wires are fastened by the solder can be made smaller than the outside diameter of the multi-core cable, and handleability of the multi-core cable is improved. 
     Since the outer conductors and the metal wire winding therearound are fastened by the low-melting-point solder having the melting temperature of 130 to 150° C., deterioration of the insulating layer due to heat transferred in the case of soldering can be prevented. 
     (5) The invention may provide the multi-core cable, 
     wherein the multi-core cable further includes plural insulated electric wires for signal transmission, 
     wherein each insulated electric wire has
         a central conductor having an area of 0.01 mm 2  or less, and   a covering covering the central conductor, and       

     wherein the plural insulated electric wires are bundled together with all the outer conductors of the plural shielded electric wires by the metal wire. 
     According to the configuration of (5), in the multi-core cable including the plural insulated electric wires, the insulated electric wires are bundled together with the shielded electric wires by the metal wire. As a result, handleability of the multi-core cable is improved. 
     (6) The invention may provide the multi-core cable, 
     wherein the metal wire has an insulating part of an insulating material covering a part of the metal wire, 
     wherein each of the outer conductors is wholly bundled by the metal wire exposed from the insulating part, and 
     wherein the insulating part is arranged in parallel with each of the sheaths. 
     According to the configuration of (6), the insulating part can mechanically protect the metal wire. The insulating part can also prevent the metal wire from being short-circuited by unnecessarily making contact with the shielded electric wires arranged in parallel. 
     (7) The invention may provide the multi-core cable, 
     wherein the plural shielded electric wires are covered with a cable sheath, 
     wherein each shielded electric wire has
         plural central conductors having cross-sectional area of 0.01 mm 2  or less, respectively,   plural insulating layers covering the plural central conductors, respectively,   an outer conductor wholly covering the insulating layers, and   a sheath covering the outer conductor,       

     wherein, in an end of the multi-core cable, the cable sheath is removed along a given length to expose the plural shielded electric wires, 
     wherein each of the sheaths of the plural shielded electric wires is removed at the same position in the length direction to expose each of the outer conductors, 
     wherein the metal wire wholly winds around the outer conductors so as to tighten and bundle the exposed outer conductors, 
     wherein the position at which the metal wire winds is fastened to each of the outer conductors by solder having a melting temperature of 130 to 150° C., and 
     wherein an outside diameter of the position at which the metal wire winds and the shielded electric wires are fastened by the solder is smaller than an outside diameter of the cable sheath. 
     According to the configuration of (7), the metal wire tightens and bundles the plural shielded electric wires. As a result, the outside diameter of the position at which the metal wire winds and the shielded electric wires are fastened by the solder can be made smaller than the outside diameter of the multi-core cable, and handleability of the multi-core cable is improved. 
     Since the outer conductors and the metal wire winding therearound are fastened by the low-melting-point solder having the melting temperature of 130 to 150° C., deterioration of the insulating layer due to heat transferred in the case of soldering can be prevented. 
     (8) The invention may provide the multi-core cable, 
     wherein the multi-core cable further includes plural insulated electric wires for signal transmission, 
     wherein each insulated electric wire has
         a central conductor having a cross-sectional area of 0.01 mm 2  or less, and   a covering covering the central conductor, and       

     wherein the plural insulated electric wires are bundled together with all the outer conductors of the plural shielded electric wires by the metal wire. 
     According to the configuration of (8), even for the multi-core cable including the plural insulated electric wires, the insulated electric wires are bundled together with the shielded electric wires by the metal wire. As a result, handleability of the multi-core cable is improved. 
     Details of Embodiment of the Present Invention 
     Examples of embodiments of a multi-core cable according to the invention will hereinafter be described with reference to the drawings. 
     As shown in  FIGS. 1 to 3 , a multi-core cable  1  is constructed by assembling plural (eight herein) shielded electric wires  10  for signal transmission and one ground electric wire  20 . The eight shielded electric wires  10  are bundled so as to make contact with the adjacent shielded electric wires  10 . The shielded electric wires  10  transmit electrical signals or electric power. 
     As shown in  FIG. 2 , in the case of the eight shielded electric wires  10 , the shielded electric wires  10  are bundled so as to round the outer periphery of the bundled shielded electric wires  10  when viewed in a cross section perpendicular to a length direction of the shielded electric wires  10 . 
     Although the number of shielded electric wires  10  is eight in the present example, the number of shielded electric wires  10  is not limited to eight as long as the number is two or more. In the case of the four shielded electric wires  10 , the shielded electric wires  10  are bundled so as to form the outer periphery of the bundled shielded electric wires  10  in a quadrilateral when viewed in the cross section perpendicular to the length direction of the shielded electric wires  10 . 
     As shown in  FIG. 2 , the shielded electric wire  10  has a central conductor  11 , an inner insulator  12 , an outer conductor  13  and a sheath  14  from the center toward the outside in a cross section along a radial direction orthogonal to the central axis of the shielded electric wire  10 . As the shielded electric wire  10 , for example, a shielded electric wire thinner than AWG  40  in conformity with standards of AWG (American Wire Gauge) is desirably used. For example, a shielded electric wire of AWG  46  having an outside diameter of 0.2 mm can be used. 
     By way of example, the shielded electric wire  10  includes, for example, the central conductor  11  made of a twisted wire formed by twisting plural tin-plated annealed copper wires, the inner insulator  12  made of a fluorine resin such as PFA (tetra fluoroethylene perfluoroalkyl vinyl ether copolymer), the outer conductor  13  made of a copper evaporated polyester tape or copper foil or winding of plural tin-plated annealed copper wires, and the sheath  14  made of polyester, PTFE, etc. 
     An insulated electric wire can be used as the ground electric wire  20 . The ground electric wire  20  of the insulated electric wire has a conductor  21  and a sheath  22  from the center toward the outside. The thickness of the ground electric wire  20  is, for example, AWG  46  (an outside diameter of the conductor portion is 0.05 mm). A shielded electric wire can also be used as the ground electric wire. The ground shielded electric wire may be an electric wire having a configuration different from that of the shielded electric wire. 
     As shown in  FIG. 3 , each of the sheaths  14  and the sheath  22  are removed at the same position in a length direction of the multi-core cable  1 . 
     A metal wire  30  winds around the outer conductors  13  of the eight shielded electric wires  10  at the position at which the sheaths  14  are removed and the conductor  21  of the ground electric wire  20  at the position at which the sheath  22  is removed. Accordingly, the eight shielded electric wires  10  and the ground electric wire  20  are bundled. 
     As the metal wire  30 , for example, a tin-plated annealed copper wire gavubg an outside diameter of about 0.08 mm can be used. 
     The portion in which the outer conductors  13  and the conductor  21  are bundled by the metal wire  30  is fastened by solder S to integrate the outer conductors  13  of the eight shielded electric wires  10  with the conductor  21  of the ground electric wire  20 . That is, electrical connection between the outer conductors  13  of the eight shielded electric wires  10  and the conductor  21  of the ground electric wire  20  is provided through the metal wire  30 . The shielded electric wires  10  can be grounded to a substrate, a connector, etc. through the metal wire  30 . 
     When a shielded electric wire is used as the ground electric wire, a sheath of the shielded electric wire of the ground electric wire is removed and an outer conductor of the ground electric wire is exposed and is brought into contact with the outer conductors  13  of the shielded electric wires  10 , whereby the shielding electric wires  10  and the outer conductors  13  are integrated. 
     Next, a step of manufacturing the multi-core cable  1  configured as described above will be described with reference to  FIGS. 4 to 6 . 
     First, the eight shielded electric wires  10  and the ground electric wire  20  are juxtaposed in line and are fixed by a tape (not shown) etc. Next, in one end side of a group of the shielded electric wires  10  juxtaposed, the sheaths  14  are cut by a CO 2  laser etc. Then, the cut sheaths  14  are moved to one end side by, for example, about 1 to 2 mm, and the outer conductors  13  are exposed. Similarly, the sheath  22  of the ground electric wire  20  is cut by a CO 2  laser etc., and the sheath  22  of one end side is removed to expose the conductor  21 . 
     The outer conductors  13  and the conductor  21  are exposed at the same position in the length direction of the eight shielded electric wires  10  and the ground electric wire  20 . 
     Subsequently, the metal wire  30  winds around the position at which the outer conductors  13  of the eight shielded electric wires  10  and the conductor  21  of the ground electric wire  20  are exposed. This results in a state shown in  FIG. 4 . 
     As shown in  FIG. 5 , the outer conductors  13  and the conductor  21  are tightly bound by strongly pulling the metal wire  30  from side to side (in the direction cross to the length direction). Accordingly, the eight shielded electric wires  10  and the ground electric wire  20  are arranged in a roundly bundled state when viewed in a cross section perpendicular to the length direction. 
     The portion in which the outer conductors  13  and the conductor  21  are bound by the metal wire  30  is immersed in a solder bath of, for example, 260° C. to thereby apply solder S as shown in  FIG. 6 . In this manner, the eight outer conductors  13  and the conductor  21  are joined and integrated by soldering. The portion in which the outer conductors  13  and the conductor  21  are bound by the metal wire  30  may be immersed in the solder bath of 130 to 150° C. to thereby apply the low-melting-point solder S having a melting temperature of 130 to 150° C. 
     The multi-core cable  1  shown in  FIG. 1  is manufactured by cutting and removing the portion in which the metal wire  30  and the conductor  21  protrude from the solder S. 
     The multi-core cable  1  according to the embodiment described above has the plural shielded electric wires  10  for signal transmission. The plural shielded electric wires  10  are bundled so as to make contact with the adjacent shielded electric wires  10 . The sheaths  14  of the plural shielded electric wires  10  are respectively removed at the same position in the length direction. The outer conductors  13  of the plural shielded electric wires  10  at the position at which the sheaths  14  are removed are bundled by the metal wire  30  and the bundled portion is soldered and fastened. 
     This enables a decrease in diameter of the position at which the outer conductors  13  of the shielded electric wires  10  are bundled. 
     The multi-core cable  1  according to the embodiment includes the ground electric wire  20  made of an insulated electric wire or a shielded electric wire. The grounding position of the ground electric wire can be designed freely. 
     Second Embodiment 
     Next, a multi-core cable  101  according to a second embodiment will be described. 
     As shown in  FIG. 7 , the multi-core cable  101  according to the second embodiment has plural shielded electric wires for signal transmission. The shielded electric wires have plural large-diameter shielded electric wires  110  and plural small-diameter shielded electric wires  120 . The multi-core cable  101  has plural insulated electric wires for signal transmission. The insulated electric wires have plural large-diameter insulated electric wires  130  and at least one small-diameter insulated electric wire  140 . The multi-core cable  101  further includes a wrapping  102  for bundling these electric wires, an overall shielding layer  103  covering the wrapping  102 , and a cable sheath  104  covering the overall shielding layer  103 . 
     Each large-diameter shielded electric wire  110  has a central conductor  111 , an inner insulator (insulating layer)  112 , an outer conductor  113  and a sheath  114  from the center toward the outside in a cross section along the radial direction orthogonal to the central axis. 
     As the large-diameter shielded electric wire  110 , for example, a shielded electric wire of AWG  38  in conformity with standards of AWG (American Wire Gauge), in which a cross-sectional area of the central conductor  111  is, for example, 0.01 mm 2  or less, is desirably used. 
     As the central conductor  111  of the large-diameter shielded electric wire  110 , a twisted wire having an outside diameter of, for example, 0.12 mm formed by twisting seven tin-plated annealed copper alloy wires having a diameter of, for example, 0.04 mm is used. 
     As a material of the inner insulator  112  of the large-diameter shielded electric wire  110 , a fluorine resin such as perfluoroalkoxy resin (PFA) excellent in heat resistance, chemical resistance, non-viscosity, self-lubricating properties, etc. is preferably used. The inner insulator  112  is formed by extruding this fluorine resin. The inner insulator  112  can be formed in, for example, a thickness of 0.08 mm and an outside diameter of 0.27 mm. 
     The outer conductor  113  of the large-diameter shielded electric wire  110  is formed by spirally winding plural tin-plated annealed copper alloy wires having a diameter of, for example, 0.03 mm around the inner insulator  112 . 
     As the sheath  114  of the large-diameter shielded electric wire  110 , a general resin tape of polyester, PTFE, etc. is used, and an outside diameter of the sheath  114  is, for example, 0.37 mm. 
     Each small-diameter shielded electric wire  120  has a central conductor  121 , an inner insulator (insulating layer)  122 , an outer conductor  123  and a sheath  124  from the center toward the outside in a cross section along the radial direction orthogonal to the central axis. 
     As the small-diameter shielded electric wire  120 , for example, a shielded electric wire of AWG  44  in conformity with standards of AWG (American Wire Gauge), in which a cross-sectional area of the central conductor  121  is, for example, 0.01 mm 2  or less, is desirably used. 
     As the central conductor  121  of the small-diameter shielded electric wire  120 , a twisted wire having an outside diameter of, for example, 0.063 mm formed by twisting seven silver-plated copper alloy wires having a diameter of, for example, 0.021 mm is used. 
     The inner insulator  122  of the small-diameter shielded electric wire  120  is formed by extruding a fluorine resin such as perfluoroalkoxy resin (PFA). A thickness of this inner insulator  122  is, for example, 0.05 mm, and an outside diameter of the inner insulator  122  is, for example, 0.16 mm. 
     The outer conductor  123  of the small-diameter shielded electric wire  120  is formed by spirally winding plural tin-plated annealed copper alloy wires having a diameter of, for example, 0.03 mm around the inner insulator  122 . 
     As the sheath  124  of the small-diameter shielded electric wire  120 , a general resin tape of polyester, PTFE, etc. is used, and an outside diameter of the sheath  124  is, for example, 0.25 mm. 
     Each large-diameter insulated electric wire  130  has a central conductor  131  covered with a covering  132  made of an insulating material. In the embodiment, as the large-diameter insulated electric wire  130 , for example, an electric wire of AWG  32 , in which a cross-sectional area of the central conductor  131  is 0.039 mm 2  or less, is used. 
     As the central conductor  131  of the large-diameter insulated electric wire  130 , a twisted wire having an outside diameter of 0.26 mm formed by twisting twenty tin-plated annealed copper wires having a diameter of, for example, 0.05 mm is used. 
     The covering  132  of the large-diameter insulated electric wire  130  is formed by extruding a fluorine resin such as PFA. A thickness of this covering  132  is, for example, 0.06 mm, and an outside diameter of the covering  132  is, for example, 0.38 mm. 
     Each small-diameter insulated electric wires  140  has a central conductor  141  covered with a covering  142  made of an insulating material. In the embodiment, as the small-diameter insulated electric wire  140 , for example, an electric wire of AWG  36  is used. 
     As the central conductor  141  of the small-diameter insulated electric wire  140 , a twisted wire having an outside diameter of 0.15 mm formed by twisting seven tin-plated annealed copper wires having a diameter of, for example, 0.05 mm is used. 
     The covering  142  of the small-diameter insulated electric wire  140  is formed by extruding a fluorine resin such as PFA. A thickness of the covering  142  is, for example, 0.07 mm, and an outside diameter of the covering  142  is, for example, 0.28 mm. 
     As shown in  FIG. 7 , in the multi-core cable  101  of the embodiment, the plural (for example, two herein) small-diameter shielded electric wires  120  and at least one (for example, one herein) small-diameter insulated electric wire  140  are arranged in an inner layer and the plural (for example, five herein) large-diameter shielded electric wires  110  and the plural (for example, two herein) large-diameter insulated electric wires  130  are coaxially arranged in the periphery of the three electric wires of this inner layer in a cross section perpendicular to a length direction of the multi-core cable  101 . Gaps between these electric wires may be provided with a filler such as aramid fibers or staple yarns. 
     The wrapping  102  is wrapped around the plural large-diameter shielded electric wires  110  and the plural large-diameter insulated electric wires  130  arranged in this manner and therefore, the electric wires are bundled without disturbing arrangement of each of the electric wires. The wrapping  102  is formed of, for example, a resin tape made of polyester. 
     The plural large-diameter shielded electric wires  110  and the plural large-diameter insulated electric wires  130  are covered with the overall shielding layer  103  through the wrapping  102 . The overall shielding layer  103  is formed by singly braiding plural tin-plated annealed copper alloy wires having a diameter of, for example, 0.03 mm on the wrapping  102 . 
     The outer periphery of this overall shielding layer  103  is covered with the cable sheath  104 . The cable sheath  104  is formed by extruding a fluorine resin made of, for example, black PFA. An outside diameter of this cable sheath  104  is, for example, 1.7 mm. 
     As the cable sheath  104 , a resin tape of polyester etc. may be wrapped around the overall shielding layer  103  instead of the fluorine resin. 
     As shown in  FIG. 8 , in the end of the multi-core cable  101  of the embodiment, the cable sheath  104  is removed by laser processing etc. The sheaths  114  of the large-diameter shielded electric wires  110  and the sheaths  124  of the small-diameter shielded electric wires  120  are further removed at the same position in the axial direction (length direction) along, for example, a length of about 1 to 5 mm, respectively. At its removed position, conductors of the shielded electric wires (that is, the outer conductors  113  of the large-diameter shielded electric wires  110  and the outer conductors  123  of the small-diameter shielded electric wires  120 ) are in once an exposed state. 
     The plural large-diameter shielded electric wires  110  and the plural small-diameter shielded electric wires  120  with the outer conductors  113  and the outer conductors  123  respectively exposed to a part of the axial direction are bundled cylindrically. Specifically, a metal wire  150  having a diameter of, for example, 0.03 to 0.1 mm winds around a position at which the outer conductors  113  and the outer conductors  123  are exposed. The plural large-diameter shielded electric wires  110  and the plural small-diameter shielded electric wires  120  are wholly tightened and bundled by the metal wire  150  in the outer conductors  113  and the outer conductors  123  exposed. It may be configured to wind the metal wire  150  and then wrap a metal tape etc. around the metal wire  150 . In an example shown in  FIG. 8 , the large-diameter insulated electric wires  130  and the small-diameter insulated electric wire  140  are not bundled by the metal wire  150 . 
     The metal wire  150  winding around the outer conductors  113  and the outer conductors  123  is fastened to the outer conductors  113  and the outer conductors  123  by low-melting-point solder S having a melting temperature of 130 to 150° C. As this solder S, lead-free solder is preferably used from the standpoint of handling. The melting temperature of this solder S is obtained from the maximum endothermic point in a DSC curve of a differential scanning calorimetry. 
     Instead of this low-melting-point solder, a conductive adhesive made of, for example, a material in which metal particles are mixed with an epoxy resin can be used. 
     As shown in  FIG. 8 , even when the small-diameter shielded electric wires  120  get in the large-diameter shielded electric wires  110 , the outer conductors  113  of the large-diameter shielded electric wires  110  are tightened by the metal wire  150  and thereby, the outer conductors  113  of the large-diameter shielded electric wires  110  make contact with the outer conductors  123  of the small-diameter shielded electric wires  120  to obtain electrical connection between the outer conductors  113  and the outer conductors  123 . The large-diameter shielded electric wires  110  and the small-diameter shielded electric wires  120  which are the shielded electric wires for signal transmission can be grounded to a substrate or a connector at any position through the metal wire  150 . 
     According to such a configuration, an outside diameter of the portion in which the outer conductors  113  of the large-diameter shielded electric wires  110  and the outer conductors  123  of the small-diameter shielded electric wires  120  are exposed and are bundled by the metal wire  150  and are fastened by the solder S is, for example, 1.3 mm, and becomes smaller than an outside diameter (1.7 mm) of the multi-core cable  101 . 
     In the multi-core cable  101 , respective conductor resistances, insulation resistances, dielectric strengths, characteristic impedances and allowable currents of the large-diameter shielded electric wire  110 , the small-diameter shielded electric wire  120 , the large-diameter insulated electric wire  130  and the small-diameter insulated electric wire  140  were measured. 
     As a result, in the large-diameter shielded electric wire  110 , for example, the conductor resistance was a maximum of 3300 Ω/Km, and the insulation resistance was 1524 MΩ/Km or more, and the dielectric strength was 500 ACV/min, and the characteristic impedance was 50 Ω±5. 
     In the small-diameter shielded electric wire  120 , for example, the conductor resistance was a maximum of 10000 Ω/Km, and the insulation resistance was 1524 MΩ/Km or more, and the dielectric strength was 500 ACV/min, and the characteristic impedance was 50Ω±5. 
     In the large-diameter insulated electric wire  130 , for example, the conductor resistance was a maximum of 600 Ω/Km, and the insulation resistance was 1524 MΩ/Km or more, and the dielectric strength was 500 ACV/min, and the allowable current was a maximum of 1.2 A. 
     In the small-diameter insulated electric wire  140 , for example, the conductor resistance was a maximum of 1540 Ω/Km, and the insulation resistance was 1524 MΩ/Km or more, and the dielectric strength was 500 ACV/min, and the allowable current was a maximum of 0.7 A. 
     This could check that the multi-core cable  101  according to the embodiment has sufficiently practicable electrical characteristics. 
     wherein the position at which the metal wire winds is fastened to each of the outer conductors by solder having a melting temperature of 130 to 150° C., and wherein an outside diameter of the position at which the metal wire winds and the shielded electric wires are fastened by the solder is smaller than an outside diameter of the cable sheath. 
     The multi-core cable  101  according to the embodiment can make an outside diameter of the position at which the metal wire  150  is fastened by the solder S smaller than an outside diameter of the multi-core cable  101 . The outside diameter of the multi-core cable becomes locally large through the whole length thereof. As a result, when the multi-core cable  101  is used as a wiring member of a medical device such as an endoscope or a catheter inserted into the body of a patient, an invasiveness to the patient can be reduced in the case of inserting the medical device into the body of the patient. 
     Since the metal wire  150  winding around the outer conductors  113  and the outer conductors  123  is fastened to the outer conductors  113  and the outer conductors  123  by low-melting-point solder having a melting temperature of 130 to 150° C., deterioration of the insulating layers  112 ,  122  can be prevented. 
     Also when both of the shielded electric wires for signal transition and the insulated electric wires for signal transmission are bundled by the metal wire  150 , handling is simple and it is easy to manufacture the multi-core cable  101 . 
     Third Embodiment 
     Next, a multi-core cable  101   a  according to a third embodiment of the invention will be described. Since the multi-core cable  101   a  of the third embodiment shown in  FIG. 9  is a modified example of the second embodiment described above, the description is omitted by assigning the same numerals to the same members. 
     As shown in  FIG. 9 , in the end of the multi-core cable  101   a  of the third embodiment, a cable sheath  104  is removed by laser processing etc. Sheaths  114  of large-diameter shielded electric wires  110  and sheaths  124  of small-diameter shielded electric wires  120  are removed at the same position in the axial direction along, for example, a length of about 1 to 5 mm, respectively, and at its position, outer conductors  113  of the large-diameter shielded electric wires  110  and outer conductors  123  of the small-diameter shielded electric wires  120  are in an exposed state. 
     The outer conductors  113 ,  123  exposed in this manner are wholly bundled by a metal wire  151  together with coverings  132  of large-diameter insulated electric wires  130  and a covering  142  of a small-diameter insulated electric wire  140 . 
     As the metal wire  151  of the embodiment, for example, a metal wire having a diameter of 0.03 to 0.1 mm can be adopted. This metal wire  151  is provided with an insulating part  156  made of an insulating material covering a part of the metal wire  151  in the length direction. 
     Both ends of this metal wire  151  are exposed from the insulating part  156 . The metal wire  151  of one end exposed from the insulating part  156  winds so as to wholly bundle the outer conductors  113 ,  123  and the coverings  132 ,  142 . The metal wire  151  exposed to the other end can be used in connection to a ground terminal of a connector or a substrate (not shown). 
     The insulating part  156  arranged in the center in the length direction of the metal wire  151  is arranged in parallel with the sheaths  114  of the plural large-diameter shielded electric wires  110  or the coverings  132  of the plural large-diameter insulated electric wires  130 . 
     The metal wire  151  winding around the outer conductors  113 ,  123  and the coverings  132 ,  142  is fastened by low-melting-point solder having a melting temperature of 130 to 150° C. 
     The metal wire  151  winding around the outer conductors  113 ,  123  and the coverings  132 ,  142  in one end side preferably has a length about 1.5 to 5 times the circumference of the portion in which the outer conductors  113 ,  123  and the coverings  132 ,  142  are bundled. The insulating part  156  preferably has, for example, a length of about 1 to 5 mm. 
     According to such a configuration, an outside diameter of the portion bundled by the metal wire  151  and fastened by solder S is, for example, 1.5 mm, and can be made smaller than an outside diameter (1.7 mm) of the multi-core cable  101   a.    
     In the multi-core cable  101   a  according to the embodiment, the metal wire  151  has the insulating part  156  of the insulating material covering a part of the metal wire  151 . Each of the outer conductors  113 ,  123  is wholly bundled by the metal wire  151  exposed from the insulating part  156 , and the insulating part  156  is arranged in parallel with each of the sheaths  114 ,  124 . 
     This insulating part  156  can mechanically protect the metal wire  151 , and can also prevent the metal wire  151  from being short-circuited by making contact with the shielded electric wires  110 ,  120  for signal transmission or the insulated electric wires  130 ,  140  for signal transmission arranged in parallel. 
     The examples of the embodiments of the invention have been described above, but the invention is not limited to the embodiments described above, and can adopt other configurations as necessary. 
     The multi-core cable  101   a  shown in  FIG. 9  is configured to bundle the large-diameter insulated electric wires  130  and the small-diameter insulated electric wire  140  together with the large-diameter shielded electric wires  110  and the small-diameter shielded electric wires  120  by the metal wire  151 , but it may be configured to bundle and tighten only the large-diameter shielded electric wires  110  and the small-diameter shielded electric wires  120  by the metal wire  151  depending on use of the multi-core cable  101   a.    
     The number of shielded electric wires and ground electric wires is not limited to the embodiments described above. That is, the multi-core cable can include a necessary number of shielded electric wires and ground electric wires according to usage environment etc. It is unnecessary for the multi-core cable to include the ground electric wire. 
     In order to improve electrical characteristics, processing of metal plating or wrapping by a metal tape may be performed on surfaces of the sheaths  114 ,  124  and the coverings  132 ,  142 . 
     In the second and third embodiments described above, the large-diameter shielded electric wires  110  are not limited to the example shown in  FIG. 7 . 
     For example, as shown in  FIGS. 10A and 10B , large-diameter shielded electric wires  110   a ,  110   b  may be configured as a two-core parallel wire ( FIG. 10A ) and a twisted pair wire ( FIG. 10B ) in which two central conductors  111  covered with inner insulators  112  are arranged adjacently and the outer periphery of the inner insulators  112  is wholly covered with an outer conductor  113 . The same applies to the small-diameter shielded electric wires  120 . Also in this case, work and effect similar to those of the embodiments described above can be obtained. 
     Multi-core cables using the large-diameter shielded electric wires  110   a ,  110   b  shown in  FIGS. 10A and 10B  have the following configuration. 
     Plural shielded electric wires for signal transmission are covered with a cable sheath. Each shielded electric wire has plural central conductors having cross-sectional area of 0.01 mm 2  or less, respectively, insulating layers covering the plural central conductors, respectively, an outer conductor wholly covering the insulating layers, and a sheath covering the outer conductor. In the end of the multi-core cable, the cable sheath is removed along a given length to expose the plural shielded electric wires. Each of the sheaths of the plural shielded electric wires is removed at the same position in the length direction to expose each of the outer conductors. A metal wire wholly winds around each of the outer conductors so as to tighten and bundle each of the exposed outer conductors. The winding portion of the metal wire is fastened to the outer conductors by solder S having a melting temperature of 130 to 150° C. An outside diameter of the winding portion of the metal wire fastened by the solder is smaller than an outside diameter of the cable sheath. 
     In the multi-core cables using the large-diameter shielded electric wires  110   a ,  110   b  shown in  FIGS. 10A and 10B , the metal wire  151  provided with the insulating part  156  may be wholly wind around each of the outer conductors so as to tighten and bundle each of the exposed outer conductors by the metal wire  151  provided with the insulating part  156  as shown in  FIG. 9 . 
     The invention has been described in detail with reference to the specific embodiments, but it is apparent to those skilled in the art that various changes or modifications can be made without departing from the spirit and scope of the invention.