Patent Document

The present application is based on Japanese patent application No. 2011-177679 filed on Aug. 15, 2011, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a cable holding structure and, in particular, a cable holding structure for holding a shielded cable having a shield conductor on an outer periphery of a center conductor. 
     2. Description of the Related Art 
     Conventionally, an inverter device for supplying an electric current to a motor via a shielded cable having a shield conductor is known (see, e.g., JP-A-2006-115649). 
     This type of inverter device is configured such that three-phase alternating current (U, V, and W phases) of which frequency and current value are adjusted by PWM (Pulse Width Modulation) control is supplied through three shielded cables each shielded by a shield conductor. 
     Although a switching device such as IGBT (Insulated Gate Bipolar Transistor) is turned on and off at a high speed to generate three-phase alternating current, a harmonic component is superimposed on the three-phase alternating current due to the switching and high frequency electromagnetic noise is generated. An electric circuit of the inverter device is housed in a grounded case formed of a conductive metal in order to suppress generation of noise in a radio, etc., caused by the electromagnetic noise. 
     SUMMARY OF THE INVENTION 
       FIG. 10A  is a diagram illustrating an example of a structure for connecting shielded cables, showing an outer surface of a case of a conventional inverter device.  FIG. 10B  is a cross sectional view showing a structure of the shielded cable. 
     As shown in  FIGS. 10A and 10B , in each of three shielded cables  100 , a sheath  104  formed of an insulating resin is removed at an end portion to be connected to a case  110  of an inverter device and an insulation  102  covering a center conductor  101  is exposed. A shield conductor  103  formed of a braid between the insulation  102  and the sheath  104  is bundled into one bundled wire  103   a  and is electrically connected to the case  110  by soldering or bolting, etc. 
     Electromagnetic noise emitted from a portion of the shielded cable  100  in which the shield conductor  103  covers the outer periphery of the center conductor  101  is attenuated by the shield conductor  103 . However, since a portion in which the insulation  102  is exposed is not covered with the shield conductor  103 , an adverse effect such as generation of noise in a radio may occur due to the electromagnetic noise emitted from such a portion. 
     Accordingly, it is an object of the invention to provide a cable holding structure which can reduce electromagnetic noise emitted from a shielded cable. 
     (1) According to one embodiment of the invention, a cable holding structure comprises: 
     a shielded cable that comprises a center conductor and a shield conductor on an outer periphery of the center conductor; and 
     a holding portion being electrically conductive, provided on a flat plate portion and configured to hold the shielded cable, 
     wherein the holding portion comprises a through-hole aligned in a direction intersecting with the flat plate portion, and 
     wherein the shielded cable is held by the holding portion such that at least the center conductor is enclosed in the through-hole and the shield conductor is electrically connected to the conductive holding portion. 
     In the above embodiment (1) of the invention, the following modifications and changes can be made. 
     (i) The holding portion further comprises an opening to open the through-hole at a periphery in a radial direction thereof, wherein the shield conductor is in contact with the holding portion in the through-hole and partially exposed at the opening to an outside of the holding portion, and wherein the partially exposed shield conductor is pressed toward an inside of the through-hole in the radial direction. 
     (ii) The holding portion is formed columnar and further comprises a plurality of ones of the through-hole formed along a central axis of the holding portion, wherein a plurality of ones of the shielded cable are held by the holding portion, and wherein at least the center conductor of the shielded cable is enclosed in the through-hole. 
     (iii) In the shielded cables held by the holding portion, a plurality of ones of the shield conductor exposed at the opening are pressed together by an annular pressing member. 
     (iv) The holding portion further comprises an opening to open the through-hole at a periphery in a radial direction thereof, wherein the shield conductor of the shielded cable is crimped by a cylindrical conductive member and enclosed in the through-hole, and wherein the cylindrical conductive member exposed at the opening to an outside of the holding portion is pressed toward an inside of the through-hole. 
     (v) The holding portion is formed columnar and further comprises a plurality of ones of the through-hole formed along a central axis of the holding portion, wherein a plurality of ones of the shielded cable are held by the holding portion, wherein the shield conductor of the shielded cable is enclosed in each of the through-holes while being crimped by the cylindrical conductive member, and wherein a plurality of ones of the cylindrical conductive member exposed at the opening are pressed together by an annular pressing member. 
     (vi) The holding portion is formed cylindrical comprising the through-hole at a center thereof, wherein the shielded cable is pressed such that the shield conductor is in contact with a periphery of the cylindrical holding portion. 
     Points Of The Invention 
     According to one embodiment of the invention, a cable holding structure is constructed such that the center conductor of cables is accommodated in the through-hole of a holding portion. Thereby, electromagnetic noise emitted from the center conductor can be absorbed by the holding portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Next, the present invention will be explained in more detail in conjunction with appended drawings, wherein: 
         FIGS. 1A and 1B  show a cable holding structure in a first embodiment, wherein  FIG. 1A  is a perspective view showing a state before holding cables and  FIG. 1B  is a perspective view showing a state in which the shielded cables are held; 
         FIG. 2A  is a cross sectional view taken on line A-A of  FIG. 1A  and  FIG. 2B  is a cross sectional view taken on line B-B of  FIG. 1B ; 
         FIG. 3  is a graph showing radiation electric field intensity in the first embodiment; 
         FIGS. 4A and 4B  show a cable holding structure in a second embodiment, wherein  FIG. 4A  is an exploded perspective view and  FIG. 4B  is a cross sectional view taken on line C-C of  FIG. 4A ; 
         FIG. 5  is a perspective view showing a connection panel in a third embodiment; 
         FIG. 6A  is a cross sectional view taken on line D-D of  FIG. 5 ,  FIG. 6B  is an explanatory diagram illustrating a state in which shielded cables are accommodated in a holding portion and  FIG. 6C  is an explanatory diagram illustrating a state in which the holding portion and the shielded cables are crimped by a crimp pipe; 
         FIGS. 7A and 7B  show a cable holding structure in a fourth embodiment, wherein  FIG. 7A  is a perspective view showing a state before holding cables and  FIG. 7B  is a perspective view showing a state in which the shielded cables are held; 
         FIG. 8  is a cross sectional view taken on line E-E of  FIG. 7B ; 
         FIG. 9  is a graph showing radiation electric field intensity in the fourth embodiment; and 
         FIG. 10A  is a diagram illustrating an example of a structure for connecting cables with shield, showing an outer surface of a case of a conventional inverter device, and  FIG. 10B  is a cross sectional view showing a structure of the cables with shield. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
       FIGS. 1A and 1B  show a cable holding structure in the first embodiment of the invention, wherein  FIG. 1A  shows a state before holding three shielded cables  1 A,  1 B and  1 C by a connection panel  2  and  FIG. 1B  shows a state in which the three shielded cables  1 A,  1 B and  1 C are held by the connection panel  2 .  FIG. 2A  is a cross sectional view taken on line A-A of  FIG. 1A  and  FIG. 2B  is a cross sectional view taken on line B-B of  FIG. 1B . 
     The connection panel  2  is composed of a flat plate portion  20  and a columnar holding portion  21  provided thereon. A bolt (not shown) is inserted into an insertion hole (not shown) formed on the connection panel  2  and is screwed into a bolt hole formed on a case (not shown) of a device (e.g., an inverter device), thereby connecting and grounding the connection panel  2  to the case of the device (the same applies to the second, third and fourth embodiments). Note that, the connection panel  2  may be a portion of the case of the device (the same applies to the second, third and fourth embodiments). The plate portion  20  and the holding portion  21  are both formed of a metal having conductivity. In the first embodiment, the plate portion  20  and the holding portion  21  are separate parts and the columnar holding portion  21  is press-fitted into and fixed to a circular opening  20   a  formed on the plate portion  20 . Alternatively, the plate portion  20  and the holding portion  21  may be formed integrally. The plate portion  20  is an example of a plate-like member in the invention. 
     The shielded cables  1 A,  1 B and  1 C are held by the holding portion  21  and are crimped and fixed by an annular crimp pipe  3  formed of a metal having conductivity. Alternatively, the crimp pipe  3  may be formed of a resin. 
     The plate portion  20  is attached and electrically grounded to a case of, e.g., an inverter device which supplies three-phase alternating current to a motor as a drive source of a vehicle. Then, the shielded cables  1 A,  1 B and  1 C are connected to, e.g., a terminal block in the inverter device to supply three-phase alternating current generated by PWM control to the motor. 
     Three through-holes  211 ,  212  and  213  are formed on the holding portion  21  along a central axis C thereof. In the first embodiment, the holding portion  21  is fixed so that the central axis C orthogonally crosses a front surface  20   b  of the plate portion  20 . Accordingly, the through-holes  211 ,  212  and  213  are formed to extend in a direction orthogonally crossing the front surface  20   b  of the plate portion  20 . 
     The three through-holes  211 ,  212  and  213  are formed at equal intervals in a circumferential direction about the central axis C of the holding portion  21 . The three through-holes  211 ,  212  and  213  are open to the front surface  20   b  side of the plate portion  20  at one end in an extending direction thereof and are open to a back surface  20   c  side of the plate portion  20  at another end. 
     In addition, an outer peripheral opening  211   a  for opening the through-hole  211  to the outside in a radial direction thereof, an outer peripheral opening  212   a  for opening the through-hole  212  to the outside in a radial direction thereof and an outer peripheral opening  213   a  for opening the through-hole  213  to the outside in a radial direction thereof are formed on the holding portion  21 . The outer peripheral openings  211   a ,  212   a  and  213   a  are formed along the through-holes  211 ,  212  and  213  over the entire length thereof. In other words, on the holding portion  21 , three grooves (corresponding to the through-holes  211 ,  212  and  213 ) having a depth in a radial direction from the outer peripheral openings  211   a ,  212   a  and  213   a  formed on an outer peripheral surface  21   a  toward the central axis C are formed parallel to the central axis C. 
     The shielded cables  1 A,  1 B and  1 C each have a center conductor  11 , an insulation  12  covering the center conductor  11 , a shield conductor  13  formed of a braid and arranged on the outer peripheral side of the center conductor  11  and the insulation  12 , and a sheath  14  covering the outer peripheral side of the shield conductor  13 . The center conductor  11  and the shield conductor  13  are formed of a conductive metal such as copper or aluminum. The insulation  12  and the sheath  14  are formed of an insulating resin. 
     Each sheath  14  of the shielded cables  1 A,  1 B and  1 C is peeled off at one end over the length of the holding portion  21  or longer in the direction of the central axis C, and the portions without the sheath  14  are respectively accommodated in the through-holes  211 ,  212  and  213  of the holding portion  21 . 
     In more detail, as shown in  FIG. 2B , the center conductor  11 , the insulation  12  and the shield conductor  13  of the shielded cable  1 A are accommodated in the through-hole  211  of the holding portion  21 , and the shield conductor  13  of the shielded cable  1 A is in contact with an inner surface  211   b  of the through-hole  211 . Then, the center conductor  11 , the insulation  12  and the shield conductor  13  of the shielded cable  1 B are accommodated in the through-hole  212  of the holding portion  21 , and the shield conductor  13  of the shielded cable  1 B is in contact with an inner surface  212   b  of the through-hole  212 . In addition, the center conductor  11 , the insulation  12  and the shield conductor  13  of the shielded cable  1 C are accommodated in the through-hole  213  of the holding portion  21 , and the shield conductor  13  of the shielded cable  1 C is in contact with an inner surface  213   b  of the through-hole  213 . 
     Due to the contact with the inner surfaces  211   b ,  212   b  and  213   b  of the through-holes  211 ,  212  and  213 , the shield conductors  13  of the shielded cables  1 A,  1 B and  1 C are electrically connected and grounded to the holding portion  21 . 
     As shown in  FIGS. 1B and 2B , in the region in which the shielded cables  1 A,  1 B and  1 C are held by the holding portion  21 , the shield conductor  13  is partially exposed from the outer peripheral openings  211   a ,  212   a  and  213   a  to the outside of the holding portion  21  and the exposed portions of the shield conductors  13  are pressed by the crimp pipe  3  toward the inside of the through-holes  211 ,  212  and  213  (i.e., toward the central axis C). 
     In other words, the crimp pipe  3  presses the shield conductors  13  protruding from the outer peripheral openings  211   a ,  212   a  and  213   a  to the outside of the through-holes  211 ,  212  and  213  all together so as to pushes the shield conductors  13  into the through-holes  211 ,  212  and  213 . Accordingly, the shield conductors  13  of the shielded cables  1 A,  1 B and  1 C are in pressure contact with the holding portion  21  and the crimp pipe  3 . In addition, the crimp pipe  3  is electrically grounded due to the contact with the shield conductors  13  and the outer peripheral surface  21   a  of the holding portion. 
     Functions and Effects of the First Embodiment 
     The following functions and effects are obtained in the first embodiment. 
     (1) Since the center conductors  11  are accommodated in the through-holes  211 ,  212  and  213  of the holding portion  21  on the front surface  20   b  side of the plate portion  20 , electromagnetic noise emitted from the center conductors  11  is absorbed by the holding portion  21 . Especially, in the first embodiment, since the radially outside area of the center conductor  11  is entirely surrounded by the grounded conductive members (the shield conductor  13 , the holding portion  21  and the crimp pipe  3 ), electromagnetic noise emitted from the region in which the shielded cables  1 A,  1 B and  1 C are held by the holding portion  21  is greatly reduced. 
     (2) Since the three shielded cables  1 A,  1 B and  1 C are held by the columnar holding portion  21  at equal intervals in a circumferential direction, the three shielded cables  1 A,  1 B and  1 C are arranged closer to each other than the case of, e.g., linearly arranging the shielded cables  1 A,  1 B and  1 C. Accordingly, electromagnetic noises emitted from the respective shielded cables  1 A,  1 B and  1 C cancel out each other and electromagnetic noise is thus further reduced. In addition, it is possible to contribute to downsizing and weight reduction of the holding portion  21 . 
     (3) Since the shield conductors  13  of the three shielded cables  1 A,  1 B and  1 C are pressed all together by the crimp pipe  3 , an increase in the number of parts is suppressed. 
       FIG. 3  is a graph showing radiation electric field intensity at a position 1 meter away from end portions of the shielded cables  1 A,  1 B and  1 C (the holding portion  21 ) based on comparison with that of a conventional example ( FIG. 10 ). In the graph, the horizontal axis indicates frequency of current flowing through the shielded cables  1 A,  1 B and  1 C and the vertical axis is a decibel value indicating a difference between radiation electric field intensity in the first embodiment and that of the conventional example. 
     As shown in  FIG. 3 , not less than 30 dB of attenuation is observed in a frequency region of not less than 300 kHz, not less than 40 dB of attenuation in a frequency region of not less than 1 MHz and not less than 60 dB of attenuation in a frequency region of not less than 10 MHz. 
     Second Embodiment 
       FIGS. 4A and 4B  show a cable holding structure in a second embodiment, wherein  FIG. 4A  is an exploded perspective view and  FIG. 4B  is a cross sectional view taken on line C-C of  FIG. 4A . Members having the same functions as those described in the first embodiment are denoted by the same reference numerals in  FIGS. 4A and 4B , and the overlapped explanation will be omitted. 
     In the first embodiment, the shield conductors  13  of the shielded cables  1 A,  1 B and  1 C are directly in contact with the inner surfaces  211   b ,  212   b  and  213   b  of the through-holes  211 ,  212  and  213 . On the other hand, in the second embodiment, the shield conductors  13  of the shielded cables  1 A,  1 B and  1 C are respectively crimped by cylindrical small diameter crimp pipes  31  to  33  each formed to have a smaller diameter than the crimp pipe  3  and are then held in the through-holes  211 ,  212  and  213 . The small diameter crimp pipes  31  to  33  are formed of a metal having conductivity such as copper, etc. The small diameter crimp pipes  31  to  33  are an example of a cylindrical conductive member in the invention. 
     In more detail, the shield conductor  13  of the shielded cable  1 A is crimped by the small diameter crimp pipe  31  and is held in the through-hole  211  of the holding portion  21 . In addition, the shield conductor  13  of the shielded cable  1 B is crimped by the small diameter crimp pipe  32  and is held in the through-hole  212  of the holding portion  21 . Likewise, the shield conductor  13  of the shielded cable  1 C is crimped by the small diameter crimp pipe  33  and is held in the through-hole  213  of the holding portion  21 . 
     The through-holes  211 ,  212  and  213  of the holding portion  21  have the outer peripheral openings  211   a ,  212   a  and  213   a , and the small diameter crimp pipes  31  to  33  exposed from the outer peripheral openings  211   a ,  212   a  and  213   a  to the outside of the holding portion  21  are pressed by the crimp pipe  3  toward the inside of the through-holes  211 ,  212  and  213 . 
     Functions and Effects of the Second Embodiment 
     In the second embodiment, since the shield conductors  13  of the shielded cables  1 A,  1 B and  1 C are individually crimped and pressure-contact by the small diameter crimp pipes  31  to  33  and the small diameter crimp pipes  31  to  33  are in pressure contact with the holding portion  21  by the crimp pipe  3 , mechanical strength at a connecting portion between the shielded cables  1 A,  1 B,  1 C and the holding portion  21  is improved and electrical contact resistance between the shield conductor  13  and the holding portion  21  is reduced, in addition to the functions and effects (1) and (2) described in the first embodiment. 
     Note that, when the through-holes  211 ,  212  and  213  are formed into a shape corresponding to the shape after crimping by the small diameter crimp pipes  31  to  33 , it is possible to further improve mechanical strength and to reduce electrical contact resistance. 
     Third Embodiment 
     Next, the third embodiment of the invention will be described in reference to  FIGS. 5 to 6C . Members having the same functions as those described in the first embodiment are denoted by the same reference numerals in  FIGS. 5 to 6C , and the overlapped explanation will be omitted. 
       FIG. 5  is a perspective view showing a connection panel  4  in the third embodiment. 
     In the connection panel  4  in the third embodiment, a holding portion  41  is press-fitted into and fixed to a rounded-rectangle-shaped opening  40   a  formed on a flat plate portion  40 . 
     Three through-holes  411 ,  412  and  413  extending in a direction crossing the plate portion  40  are formed on the holding portion  41  so as to be aligned in one direction. In the third embodiment, the through-holes  411 ,  412  and  413  are formed along a direction orthogonal to the plate portion  40  so as to be parallel to each other. 
     In addition, an outer peripheral opening  411   a  for opening the through-hole  411  to the outside in a radial direction thereof, an outer peripheral opening  412   a  for opening the through-hole  412  to the outside in a radial direction thereof and an outer peripheral opening  413   a  for opening the through-hole  413  to the outside in a radial direction thereof are formed on the holding portion  41 . The outer peripheral openings  411   a ,  412   a  and  413   a  are formed along the through-holes  411 ,  412  and  413  over the entire length thereof. 
       FIGS. 6A to 6C  show the holding portion  41  and the shielded cables  1 A,  1 B and  1 C, wherein  FIG. 6A  is a cross sectional view taken on line D-D of  FIG. 5 ,  FIG. 6B  is an explanatory diagram illustrating a state in which the shielded cables  1 A,  1 B and  1 C are accommodated in the holding portion  41  and  FIG. 6C  is an explanatory diagram illustrating a state in which the holding portion  41  and the shielded cables  1 A,  1 B and  1 C are crimped by a crimp pipe  42 . 
     As shown in  FIG. 6B , in the state that the shielded cables  1 A,  1 B and  1 C are accommodated in the through-holes  411 ,  412  and  413  of the holding portion  41 , portions of the shield conductors  13  of the shielded cables  1 A,  1 B and  1 C are in contact with inner surfaces  411   b ,  412   b  and  413   b  of the through-holes  411 ,  412  and  413  and other portions of the shield conductors  13  are protruding from the outer peripheral openings  411   a ,  412   a  and  413   a  to the outside of the through-holes  411 ,  412  and  413 . 
     As shown in  FIG. 6C , the shielded cables  1 A,  1 B and  1 C are crimped by the crimp pipe  42  and are fixed to the holding portion  41 . That is, the crimp pipe  42  presses the shield conductors  13  protruding from the outer peripheral openings  411   a ,  412   a  and  413   a  to the outside of the through-holes  411 ,  412  and  413  all together so as to pushes the shield conductors  13  into the through-holes  411 ,  412  and  413 . Accordingly, the shield conductors  13  of the shielded cables  1 A,  1 B and  1 C are in pressure contact with the holding portion  41  and the crimp pipe  42 . 
     Functions and Effects of the Third Embodiment 
     The third embodiment achieves the same functions and effects as (1) described in the first embodiment. In addition, it is possible to reduce the size of the holding portion  41  in a thickness direction (a vertical direction in  FIGS. 5 to 6C ). 
     Fourth Embodiment 
     Next, the fourth embodiment of the invention will be described in reference to  FIGS. 7A to 8 . Members having the same functions as those described in the first embodiment are denoted by the same reference numerals in  FIGS. 7A to 8 , and the overlapped explanation will be omitted. 
       FIGS. 7A and 7B  show a cable holding structure in a fourth embodiment of the invention, wherein  FIG. 7A  shows a state before holding the shielded cables  1 A,  1 B and  1 C by a connection panel  5  and  FIG. 7B  shows a state in which the shielded cables  1 A,  1 B and  1 C are held by the connection panel  5 .  FIG. 8  is a cross sectional view taken on line E-E of  FIG. 7B . 
     The connection panel  5  is composed of a flat plate portion  50  and circular cylinders  51  to  53  provided thereon. The plate portion  50  and the cylinders  51  to  53  are formed of a metal having conductivity. The cylinders  51  to  53  function as a holding portion for holding the shielded cables  1 A,  1 B and  1 C. 
     Through-holes  511 ,  512  and  513  extending in a direction orthogonally crossing the plate portion  50  are formed at respective center portions of the cylinders  51  to  53 . 
     As shown in  FIG. 8 , the center conductor  11  and the insulation  12  of the shielded cable  1 A are accommodated in the through-hole  511  of the cylinder  51 . The shield conductor  13  of the shielded cable  1 A is stretched so as to enlarge an inner diameter thereof and is arranged so as to be in contact with an outer peripheral surface  51   a  of the cylinder  51 . The shield conductor  13  is pressed against the outer peripheral surface  51   a  of the cylinder  51  by an annular crimp pipe  6  formed of a metal having conductivity. Alternatively, the crimp pipe  6  may be formed of a resin. 
     Likewise, the center conductor  11  and the insulation  12  of the shielded cable  1 B are accommodated in the through-hole  512  of the cylinder  52  and the shielded cable  1 B is pressed by the crimp pipe  6  so that the shield conductor  13  is in contact with an outer peripheral surface  52   a  of the cylinder  52 . 
     Also, in the same manner, the center conductor  11  and the insulation  12  of the shielded cable  1 C are accommodated in the through-hole  513  of the cylinder  53  and the shielded cable  1 C is pressed by the crimp pipe  6  so that the shield conductor  13  is in contact with an outer peripheral surface  53   a  of the cylinder  53 . 
     Functions and Effects of the Fourth Embodiment 
     The fourth embodiment achieves the same functions and effects as (1) described in the first embodiment. In addition, since the shield conductor  13  is crimped while being sandwiched between the cylinder  51  and the crimp pipe  6 , electrical contact resistance between the shield conductors  13  and the cylinders  51  to  53  is reduced. 
       FIG. 9  is a graph showing radiation electric field intensity at a position 1 meter away from end portions of the shielded cables  1 A,  1 B and  1 C based on comparison with that of the conventional example ( FIG. 10 ). In the graph, the horizontal axis indicates frequency of current flowing through the shielded cables  1 A,  1 B and  1 C and the vertical axis is a decibel value indicating a difference between radiation electric field intensity of the fourth embodiment and that of the conventional example. 
     As shown in  FIG. 9 , not less than 28 dB of attenuation is observed in a frequency region of not less than 300 kHz, not less than 30 dB of attenuation in a frequency region of not less than 1 MHz and not less than 50 dB of attenuation in a frequency region of not less than 10 MHz. 
     Although the embodiments of the invention have been described, the invention according to claims is not to be limited to the above-mentioned embodiments. Further, it should be noted that all of the combinations of features as described in the embodiment and Examples are not always needed to solve the problem of the invention.

Technology Category: h