Patent Publication Number: US-7901246-B2

Title: Cable connection structure

Description:
BACKGROUND 
     This invention relates to a structure of cable connection over an ground terminal, in which a coaxial cable and an ordinary cable are fixed to the ground terminal mounted, for example, on an on-vehicle antenna mounting portion, and also a braided wire of the coaxial cable is connected to the ground terminal as earth. 
       FIG. 3  is an exploded perspective view of a related structure of cable connection over an ground terminal used in a vehicle, and  FIG. 4  is a perspective view showing the structure of  FIG. 3  in its assembled condition. 
     The cable connection structure shown in  FIGS. 3 and 4  is disclosed in Patent Literature 1 mentioned below. The ground terminal (also called “earth plate”)  1  is a terminal formed of a metal plate or a metal sheet and including a grounding plate portion  2  to be fixedly mounted on a grounding structural member (not shown) such for example as an on-vehicle antenna-mounting portion (e.g. a vehicle frame) of a vehicle. The grounding plate portion  2  has a mounting hole  2   a  through which it is screw fastened to the grounding structural member. 
     The coaxial cable  11  and an ordinary cable (power cable)  21  which are to be used at the above on-vehicle antenna mounting portion or other portion are fixed onto the ground terminal  1 . 
     One end portion of the coaxial cable  11  to be connected to the ordinary cable  21  is beforehand subjected to an end processing operation in which a sheath  12 , a braided wire  13  and an inner insulator  14  are cut off or removed over respective predetermined lengths, so that exposed portions of the braided wire  13 , inner insulator  14  and inner conductor  15  are formed at the one end portion of the coaxial cable as shown in  FIG. 3 . 
     One end portion of the ordinary cable  21  to be connected to the coaxial cable  11  is beforehand subjected to an end processing operation in which a sheath  22  is cut off or removed over a predetermined length, so that an exposed portion of a core wire (conductor)  23  is formed at the one end portion of the ordinary cable  21  as shown in  FIG. 3 . 
     The exposed portion of the inner conductor  15  of the coaxial cable  11  and the exposed portion of the core wire  23  of the ordinary cable  21  are arranged in line with each other, and are press-clamped to be connected together by a crimp terminal  31 . 
     A heat-shrinkable tube  33  of an electrically-insulative nature is fitted on the portions of the cables connected by the crimp terminal  31  and its neighboring portions for insulating purposes. 
     As shown in  FIG. 4 , the heat-shrinkable tube  33  has such a length that one end portion thereof is fitted on a distal end portion of the exposed portion of the braided wire  13  of the coaxial cable  11 , while the other end portion thereof is fitted on a distal end portion of the sheath  22  at the one end portion of the ordinary cable  21 . 
     The exposed portion of the braided wire  13  disposed at the one end portion of the coaxial cable  11  has such a length that this exposed portion, although covered at its distal end portion by the heat-shrinkable tube  33 , has an uncovered portion of a predetermined length lying between the one end of the heat-shrinkable tube  33  and the sheath  12  of the coaxial cable  11  as shown in  FIG. 4 . 
     The purpose of fitting the heat-shrinkable tube  33  on the distal end portion of the braided wire  13  is to prevent the distal end portion of the braided wire  13  from becoming loose. 
     As shown in  FIG. 3 , the grounding plate portion  2  has a first sheath clamping portion  4 , a second sheath clamping portion  5  and a braided wire clamping portion  6  which are formed integrally at one end edge portion thereof. The first sheath clamping portion  4  is press-fastened onto the sheath  12  of the coaxial cable  11  so as to fix the coaxial cable  11 , and the second sheath clamping portion  5  is spaced from the first sheath clamping portion  4  in the direction of lengths of the cables  11  and  21 , and is press-fastened onto the heat-shrinkable tube  33  fitted on the sheath  22  of the ordinary cable  21  so as to fix the ordinary cable  21 , and the braided wire clamping portion  6  is disposed between the first and second clamping portions  4  and  5 , and is press-fastened onto the uncovered portion of the exposed braided wire  13  so as to groundedly connect the braided wire  13  to the grounding plate portion  2 . 
     Namely, the inner conductor  15  of the coaxial cable  11  and the core wire  23  of the ordinary cable  21  are electrically connected together by the crimp terminal  31 , and with respect to the coaxial cable  11  and the ordinary wire  21  placed over the ground terminal  1 , the coaxial cable  11  is fixed to the ground terminal  1  by press-fastening the first sheath clamping portion  4  onto the sheath  12  of the coaxial cable  11 , and the ordinary cable  21  is fixed to the ground terminal  1  by press-fastening the second sheath clamping portion  5  onto the sheath  22  of the ordinary cable  21  through the heat-shrinkable tube  33 , as shown in  FIG. 4 . Further, the coaxial cable  11  is groundedly connected to the ground terminal  1  by press-fastening the braided wire clamping portion  6  onto the uncovered portion of the braided wire  13  exposed adjacent to the one end of the heat-shrinkable tube  33 . 
     [Patent Literature 1] JP-A-2007-95489 
     [Patent Literature 2] JP-A-2001-223040 
     Incidentally, generally, the inner conductor  15  of the coaxial cable  11  has a smaller thickness and a lower strength than the core wire  23  of the ordinary cable  21 . 
     In the above cable connection structure, the inner conductor  15  of a low strength is exposed at a region indicated by A in  FIG. 5 , and therefore there is encountered a problem that when the inner insulator  14  and the heat-shrinkable tube  33  are expanded and contracted according to an ambient temperature change, etc., a tensile stress and a compressive stress immediately act on the inner conductor  15 , so that the inner conductor  15  is liable to be damaged. 
     Arrows σ 1  and σ 2  in  FIG. 5  indicate tensile stresses acting on the exposed portion of the inner conductor  15  when the inner insulator  14  and the heat-shrinkable tube  33  are contracted. 
     SUMMARY 
     It is therefore an object of this invention to solve the above problem, and more specifically to provide a structure of cable connection over an ground terminal, in which stresses are restrained from acting on an inner conductor of a coaxial cable exposed over the ground terminal, thereby preventing the inner conductor from being damaged by the stresses. 
     The above object has been achieved by the following constructions.
     (1) There is provided a cable connection structure comprising:   

     a coaxial cable that includes an inner conductor, an inner insulator covering the inner conductor, a braided wire covering the inner insulator, and a sheath covering the braided wire; 
     a cable that includes a core wire and a sheath covering the core wire, and is arranged in series with the coaxial cable; 
     a ground terminal that connects the braided wire to a ground, and fixes the coaxial cable and the cable; 
     a crimp terminal that press-clamps the inner conductor of the coaxial cable and the core wire of the cable to electrically connect to each other; and 
     an insulative heat-shrinkable tube that covers the coaxial cable, the cable, and the crimp terminal, 
     wherein the inner conductor, exposed from the inner insulator and arranged between the crimp terminal and an end portion of the inner insulator of the coaxial cable in the heat-shrinkable tube, has a bent portion. 
     Preferably, the ground terminal is formed of a metal plate and includes:
         a first sheath clamping portion which press-fastens to the sheath of the coaxial cable for fixing the coaxial cable;   a second sheath clamping portion which press-fastens to the sheath of the cable through the heat-shrinkable tube for fixing the cable; and   a braided wire clamping portion which press-fastens to the braided wire of the coaxial cable, and is arranged between the first sheath clamping portion and the second sheath clamping portion for grounding the coaxial cable.       

     Preferably, the heat-shrinkable tube covers from an end portion of the braided wire exposed at an end portion of the coaxial cable to the sheath of an end portion of the cable.
     (2) Preferably, the bent portion of the inner conductor of the coaxial cable is formed into a curved shape projecting in a direction of increasing of a distance between the inner conductor and the ground terminal.   

     Also, preferably, the bent portion of the inner conductor of the coaxial cable is formed into a curved shape projecting in a direction perpendicular to an arrangement direction of the coaxial cable and the cable. 
     In the construction of the above Paragraph (1), when the inner insulator and the heat-shrinkable tube are expanded and contracted according to an ambient temperature change, etc., the bent portion of the inner conductor disposed within the heat-shrinkable tube and exposed from the inner insulator over the ground terminal is expanded and contracted, thereby allowing the displacement of the inner insulator and the heat-shrinkable tube so as to restrain stresses from acting on the inner conductor. Therefore, the inner conductor is prevented from being damaged by the stresses. 
     In the construction of the above Paragraph (2), even when the bent portion of the inner conductor is expanded and contracted in accordance with the displacement of the inner insulator and the heat-shrinkable tube, the distance between the inner conductor and the ground terminal (to which the braided wire of the coaxial cable is grounded) can be maintained at a level not smaller than the reference distance, and therefore the inner conductor is prevented from being moved too close to the ground terminal, thus preventing cable characteristics from being lowered. 
     In the structure of cable connection over the ground terminal provided according to the invention, the bent portion is formed at the portion of the inner conductor exposed from the inner insulator over the ground terminal, and therefore when the inner insulator and the heat-shrinkable tube are expanded and contracted according to an ambient temperature change, etc., the bent portion of the inner conductor is expanded and contracted, thereby allowing the displacement of the inner insulator and the heat-shrinkable tube. 
     Therefore, stresses are restrained from acting on the inner conductor, and the inner conductor is prevented from being damaged by the stresses. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein: 
         FIG. 1  is a view showing an important portion of a structure of cable connection over an ground terminal provided in accordance with one preferred embodiment of the present invention; 
         FIGS. 2A and 2B  are views showing the process of forming a bent portion at an inner conductor of a coaxial cable shown in  FIG. 1 ; 
         FIG. 3  is an exploded perspective view of a conventional structure of cable connection over an ground terminal; 
         FIG. 4  is a perspective view of the conventional cable connection structure in its assembled condition; and 
         FIG. 5  is an enlarged view of an important portion of the conventional cable connection structure. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     A structure of cable connection over an ground terminal provided in accordance with a preferred embodiment of the present invention will now be described in detail with reference to the drawings. 
       FIG. 1  is a view showing an important portion of the cable connection structure of the invention, and  FIGS. 2A and 2B  are views showing the process of forming a bent portion at an inner conductor of a coaxial cable shown in  FIG. 1 . 
     In the cable connection structure of this embodiment, the inner conductor  15  of the coaxial cable  11  and a core wire  23  of an ordinary cable  21  arranged in line with each other are press-clamped to be electrically connected together by a crimp terminal  31 , and the coaxial cable  11  and the ordinary cable  21  are fixed onto the ground terminal  1  formed of a metal plate or sheet, and also a braided wire  13  of the coaxial cable  11  is groundedly connected to the ground terminal  1 . 
     The ground terminal  1  used in this embodiment has the same structure as the ground terminal shown in  FIG. 3 , and includes a grounding plate portion  2  for being fixedly mounted on a grounding structural member such for example as an on-vehicle antenna-mounting portion (e.g. a vehicle frame) of a vehicle. The grounding plate portion  2  has a first sheath clamping portion  4 , a second sheath clamping portion  5  and a braided wire clamping portion  6  which are formed integrally at one end edge portion thereof. The first sheath clamping portion  4  is press-fastened onto a sheath  12  of the coaxial cable  11  so as to fix the coaxial cable  11 , and the second sheath clamping portion  5  is spaced from the first sheath clamping portion  4  in the direction of lengths of the cables  11  and  21 , and is press-fastened onto a heat-shrinkable tube  33  fitted on a sheath  22  of the ordinary cable  21  so as to fix the ordinary cable  21 , and the braided wire clamping portion  6  is disposed between the first and second clamping portions  4  and  5 , and is press-fastened onto an uncovered (exposed) portion of a braided wire  13  so as to groundedly connect the braided wire  13  to the grounding plate portion  2 . 
     One end portion of the coaxial cable  11  to be connected to the ordinary cable  21  is beforehand subjected to an end processing operation in which the sheath  12 , the braided wire  13  and an inner insulator  14  are cut off or removed over respective predetermined lengths, so that exposed portions of the braided wire  13 , inner insulator  14  and inner conductor  15  are formed at the one end portion of the coaxial cable  11  as shown in  FIG. 2A . Further, a curved portion  41  for forming the bent portion  41 A (described later) is formed at that portion of the exposed inner conductor  15  exposed from the inner insulator  14  and disposed near to the inner insulator  14 . 
     One end portion of the ordinary cable  21  to be connected to the coaxial cable  11  is beforehand subjected to an end processing operation in which the sheath  22  is cut off or removed over a predetermined length, so that the core wire  23  is exposed over a predetermined length as shown in  FIG. 3 . 
     A distal end portion of the exposed portion of the inner conductor  15  at the one end portion of the coaxial cable  11  and a distal end portion of the exposed portion of the core wire  23  at the one end portion of the ordinary cable are butted together or arranged in line with each other, and are press-clamped to be connected together by a crimp terminal  31 . 
     The heat-shrinkable tube  33  of an electrically-insulative nature is fitted on the portions of the cables connected by the crimp terminal  31  and its neighboring portions for insulating purposes. 
     As shown in  FIG. 1 , the heat-shrinkable tube  33  has such a length that one end portion thereof is fitted on a distal end portion of the exposed portion of the braided wire  13  of the coaxial cable  11 , while the other end portion thereof is fitted on a distal end portion of the sheath  22  at the one end portion of the ordinary cable  21 . 
     The exposed portion of the braided wire  13  disposed at the one end portion of the coaxial cable  11  has such a length that this exposed portion, although covered at its distal end portion by the heat-shrinkable tube  33 , has the uncovered portion of a predetermined length lying between the one end of the heat-shrinkable tube  33  and the sheath  12  of the coaxial cable  11  as shown in  FIG. 1 . 
     The purpose of fitting the heat-shrinkable tube  33  on the distal end portion of the braided wire  13  is to prevent the distal end portion of the braided wire  13  from becoming loose. 
     In this embodiment, also, the coaxial cable  11  is fixed to the ground terminal  1  by press-fastening the first sheath clamping portion  4  of the ground terminal  1  onto the sheath  12  of the coaxial cable. The ordinary cable  21  is fixed to the ground terminal  1  by press-fastening the second sheath clamping portion  5  of the ground terminal  1  onto the sheath  22  of the ordinary cable  21  through the heat-shrinkable tube  33 . Further, the coaxial cable  11  is groundedly connected to the ground terminal  1  by press-fastening the braided wire clamping portion  6  of the ground terminal  1  onto the uncovered portion of the exposed portion of the braided wire  13  disposed adjacent to the one end of the heat-shrinkable tube  33 . 
     In this embodiment, utilizing the curved portion  41  of  FIG. 2B , the bent portion (or slack portion)  41 A is formed at that portion of the inner conductor  15  disposed within the heat-shrinkable tube  33  and exposed between the crimp terminal  31  and the distal end of the inner insulator  14  of the coaxial cable  11 , as shown at a portion B of  FIG. 1 . 
     In  FIG. 1 , a dimension L represents the distance from the center (axis) of the inner conductor  15  of the coaxial cable  11  (fixed to the ground terminal  1  by press-fastening the braid wire clamping portion  6  onto the braided wire  13 ) from a surface  1   a  of the ground terminal  1 . The bent portion  41 A is held in a curved shape over the ground terminal  1 , and projects in a direction of increasing of the distance between the inner conductor  15  and the ground terminal  1  (that is, projects in a direction C ( FIG. 1 ) away from the surface  1   a  of the ground terminal  1 ). 
     In the above cable connection structure of this embodiment, when the inner insulator  14  and the heat-shrinkable tube  33  are expanded and contracted according to an ambient temperature change, etc., the bent portion  41 A of the inner conductor  15  exposed from the inner insulator  14  over the ground terminal  1  is expanded and contracted, thereby allowing the displacement of the inner insulator  14  and the heat-shrinkable tube  33  so as to restrain stresses from acting on the inner conductor  15 . Therefore, the inner conductor  15  is prevented from being damaged by the stresses. 
     In  FIG. 1 , arrows D indicate the directions of expansion of the bent portion  41 A upon contraction of the inner conductor  14  and the heat-shrinkable tube  33 . 
     In the above embodiment, the bent portion  41 A formed at the inner conductor  15  is formed into the curved shape projecting in the direction of increasing of the distance between the inner conductor  15  and the ground terminal  1 , and therefore even when the bent portion  41 A of the inner conductor  15  is expanded and contracted in accordance with the displacement of the inner insulator  14  and the heat-shrinkable tube  33 , the distance between the inner conductor  15  and the ground terminal  1  (to which the braided wire  13  of the coaxial cable  11  is grounded) is maintained at a level not smaller than the reference distance L (see  FIG. 1 ), and therefore the inner conductor  15  is prevented from being moved too close to the ground terminal  1 , thus preventing cable characteristics from being lowered. 
     The present invention is not limited to the above embodiment, and suitable modifications, improvements, etc., can be made. Furthermore, the material, shape, dimensions, numerical values, form, number, disposition, etc., of each of the constituent elements of the above embodiment are arbitrary and are not limited in so far as the invention can be achieved. 
     The present application is based on Japanese Patent Application No. 2008-279315 filed on Oct. 30, 2008, the contents of which are incorporated herein for reference.