Abstract:
Rotation of a bolt is prevented when a nut is screwed onto a threaded shaft portion of the bolt while a head portion of the bolt is fitted to a receiving portion formed on a fixed member. The head portion of the bolt has a shape of a polygon, an ellipse or an oblong. At least one of an end surface and a periphery surface of the head portion of the bolt has an anti-rotation protruding portion formed thereon. A positioning recess is formed on an inner surface of the receiving portion for receiving the anti-rotation protruding portion. The head portion of the bolt is fitted to the receiving portion to prevent the bolt from rotating when the nut is screwed onto the threaded shaft portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority under 35 U.S.C. §119 of Japanese Application No. 2008-210094, filed on Aug. 18, 2008, the disclosure of which is expressly incorporated by reference herein in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a bolt rotation prevention structure, and more specifically, relates to a bolt rotation prevention structure for preventing rotation of a bolt when a nut is screwed onto a threaded shaft portion of the bolt while a head portion of the bolt is fixed to a fixed member. 
         [0004]    2. Description of Related Art 
         [0005]      FIG. 10  shows an electrical junction box having a conventional bolt rotation prevention structure (see Related Art 1). In the electrical junction box  1 , a head portion  4   a  of a bolt  4  is fixedly press-fitted to a bolt receiving portion  3  formed as a concave region on an upper surface of a plastic case  2 . An LA terminal  5  and a bus bar  6  become connected in between the bolt  4  and a nut (not shown in the figure). 
         [0006]    In the electrical junction box  1 , the head portion  4   a  of the bolt  4  has a shape of a quadrangle, and the bolt receiving portion  3  also has a shape of a quadrangle, corresponding to the shape of the head portion  4   a , thereby preventing rotation of the bolt  4  when the nut is screwed thereonto. 
         [0007]    However, as in the electrical junction box  1 , when the case  2  that fixedly retains the head portion  4   a  of the bolt  4  is plastic while the bolt  4  is metallic, the inner surface of the bolt receiving portion  3  of the case  2  may be scraped by a rotational force applied to the head portion  4   a  when the nut is screwed onto the bolt  4 . As a result, it is possible that the bolt receiving portion  3  becomes bigger and unable to prevent rotation of the bolt  4 . In particular, when a bolt fastening jig is used to screw the nut, it is easy to apply an excessive rotational force to the bolt  4  when the nut is screwed thereonto, and it is possible that the bolt receiving portion  3  is scraped. 
         [0008]    [Related Art 1] Japanese Utility Model Publication H3-62474 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention is provided to resolve the above-described problems. An object of the present invention is to provide a bolt rotation prevention structure capable of surely preventing rotation of a bolt when a nut is screwed onto a threaded shaft portion of the bolt while a head portion of the bolt is fixedly retained to a fixed member. 
         [0010]    To achieve the above objective, the present invention provides a bolt rotation prevention structure that includes a head portion of a bolt and a receiving portion for receiving the head portion of the bolt. The head portion of the bolt has a shape of a polygon, an ellipse or an oblong, and at least one of an end surface and a periphery surface of the head portion has an anti-rotation protruding portion formed on a region thereof. The receiving portion is formed on a fixed member and has a positioning recess formed on an inner surface thereof for receiving the anti-rotation protruding portion. The head portion of the bolt is fitted to the receiving portion to prevent the bolt from rotating when a nut is screwed onto a threaded shaft portion of the bolt. 
         [0011]    The fixed member is a case of an electrical junction box, and is made of plastic. The head portion of the bolt is fixedly retained to the case, making the threaded shaft portion protruding. Parts installed on the case are fixedly retained in between the head portion of the bolt and the nut. The head portion has a shape of a quadrangle. The anti-rotation protruding portion formed on the head portion is a linear protruding portion that is formed on the end surface of the head portion and extends from one side to an opposite side of the head portion or a protruding portion that is formed on at least opposing sides of the periphery surface of the head portion. 
         [0012]    When there is not enough space for forming the positioning recess on a periphery of an opening of the receiving portion, it is preferred that the anti-rotation protruding portion be formed on the end surface of the head portion of the bolt. When there is not enough space for forming the positioning recess on a bottom of the receiving portion, it is preferred that the anti-rotation protruding portion be formed on the periphery surface of the head portion of the bolt. 
         [0013]    Examples of the electrical junction box include an electrical junction box that connects to a wire harness installed in a car. Examples of the parts that are fixedly retained in between the head portion of the bolt and the nut include a bus bar that connects to an internal circuit of an electrical junction box and a terminal of a power wire. The receiving portion may be formed on a horizontal wall or a vertical wall of a case of an electrical junction box. 
         [0014]    It is preferred that a protruding height of the anti-rotation protruding portion from the end surface of the head portion of the bolt is 0.1 mm or more and 10 mm or less. This is because a protruding height less than 0.1 mm is too low for the anti-rotation protruding portion to exhibit sufficient anti-rotation capability, and when the protruding height is more than 10 mm, bolt material strength decreases. Further, it is desirable that the protruding height is 0.3 mm or more and 8 mm or less, and in particular, 0.5 mm or more and 5 mm or less. 
         [0015]    When the shape of the head portion of the bolt is an ellipse or an oblong, it is desirable that the protruding portion is formed on the end surface of the head portion extending along a major axis direction or on opposing sides of the periphery surface of the head portion along the major axis direction. This allows applying an anti-rotation force to the two ends of the major axis that are most distant from the threaded shaft portion of the bolt, thereby allowing effective bolt rotation prevention. 
         [0016]    As described above, according to the bolt rotation prevention structure of the present invention, in addition to making a head portion of a bolt a polygon, an ellipse or an oblong, an anti-rotation protruding portion protruding from the head portion of the bolt is fitted to a positioning recess formed on an inner surface of a receiving portion of a fixed member, thereby allowing double bolt rotation prevention. Consequently, the bolt is surely prevented from rotating even when a rotational force is applied when a nut is screwed onto the bolt. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The present invention is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present invention, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein: 
           [0018]      FIG. 1  is a plain view of a case of an electrical junction box according to a first embodiment; 
           [0019]      FIG. 2  is a perspective view of a bolt according to the first embodiment; 
           [0020]      FIG. 3(   a ) is a perspective exploded view of a power wire connection portion illustrated in  FIG. 1 ; 
           [0021]      FIG. 3(   b ) is an explanatory cross-sectional exploded view of the power wire connection portion illustrated in  FIG. 1 ; 
           [0022]      FIG. 4  is an explanatory cross-sectional view of the power wire connection portion illustrated in  FIG. 1 ; 
           [0023]      FIG. 5  is a perspective view of a bolt and a receiving portion of a case according to a second embodiment; 
           [0024]      FIG. 6  is a plain view illustrating a state that a head portion of the bolt shown in  FIG. 5  is fixedly retained in the receiving portion of the case; 
           [0025]      FIG. 7  illustrates a first different shape of a bolt according to the present invention; 
           [0026]      FIG. 8  illustrates a second different shape of a bolt according to the present invention; 
           [0027]      FIG. 9(   a ) is a perspective view illustrating a third different shape of a bolt according to the present invention; 
           [0028]      FIG. 9(   b ) is a front view illustrating the third different shape of a bolt according to the present invention; and 
           [0029]      FIG. 10  illustrates a prior art. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]    The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description is taken with the drawings making apparent to those skilled in the art how the forms of the present invention may be embodied in practice. 
         [0031]    The embodiments of the present invention are explained in the following with reference to the drawings. In all of the embodiments, the present invention is directed to a structure for fixedly retaining a bolt  21  to a case  11  of an electrical junction box  10  installed in a car. 
         [0032]      FIGS. 1-4  illustrate a bolt rotation prevention structure according to the first embodiment of the present invention. The case  11  of the electrical junction box  10  is plastic. As shown in  FIG. 1 , on an upper surface of a horizontal wall  12 , a fuse housing  13  and a relay housing  14  are formed, along with a power wire connection portion A, which is formed at a corner. As shown in  FIGS. 3(   a ) and  3 ( b ), a circuit bus bar  15  contained inside the case  11  and a power wire W are fixedly retained by the bolt  21  and a nut  28 . The upper surface and a lower surface of the case  11  are respectively covered by an upper cover and a lower cover (not shown in the figures), which are lock-coupled. 
         [0033]    As shown in  FIG. 2 , the bolt  21  has a head portion  22 , which has a shape of a quadrangle in a planar view, and a threaded shaft portion  23  protruding from the head portion  22 . A linear anti-rotation protruding portion  26  is formed on an end surface  24  of the head portion  22 , extending across the center of the quadrangle and connecting a pair of opposing sides. Protruding height h of the anti-rotation protruding portion  26 , measured from the end surface  24  of the head portion  22 , is 0.3 mm or more and 8 mm or less, and is 5 mm in the present embodiment. 
         [0034]    An LA terminal  30 , bent into an L-shape, is crimped onto an end of the power wire W. The LA terminal  30  has a wire crimp portion  31  and an electrical connection portion  32 . The wire crimp portion  31  is formed in a vertical direction and the electrical connection portion  32  is formed on top of the wire crimp portion  31  and bends toward a horizontal direction. A bolt hole  33  is formed on the electrical connection portion  32 . 
         [0035]    As shown in  FIGS. 3(   a ) and  3 ( b ), a concave receiving portion  16  is formed in the power wire connection portion A on the upper surface of the horizontal wall  12  for fixedly inserting thereto the head portion  22  of the bolt  21 . As shown in  FIG. 4 , the head portion  22  of the bolt  21  is fixedly fitted into the receiving portion  16 , making the threaded shaft portion  23  of the bolt  21  protruding upwardly. Specifically, the receiving portion  16  has a shape of a quadrangle in a planar view corresponding to the shape of the head portion  22  of the bolt  21 , and a positioning recess  19  is formed on a bottom surface  18  of the receiving portion  16 . An inner surface  17  of the receiving portion  16  is put in tight contact with a periphery surface  25  of the head portion  22  of the bolt  21 , while the anti-rotation protruding portion  26  protruding from the head portion  22  is fitted in the positioning recess  19 . 
         [0036]    First, the threaded shaft portion  23  protruding from the bolt  21  is put through a bolt hole  15   a  that is formed on the circuit bus bar  15 , the bolt  21  being fixedly fitted in the receiving portion  16  of the case  11 . Next, the threaded shaft portion  23  is put through the bolt hole  33  of the LA terminal  30  so that the electrical connection portion  32  of the LA terminal  30  is placed on top of the circuit bus bar  15 . Under this setting, the nut  28  is screwed onto the threaded shaft portion  23  from above, thereby fixedly retaining the LA terminal  30  and the circuit bus bar  15  onto the case  11 , as shown in  FIG. 4 . 
         [0037]    According to the above-described structure, in addition to bolt rotation prevention by fixedly fitting the quadrangle-shaped bolt head portion  22  to the quadrangle-shaped receiving portion  16 , fitting the anti-rotation protruding portion  26  protruding from the bolt head portion  22  to the positioning recess  19  formed in the receiving portion  16  also allows bolt rotation prevention. This double bolt rotation prevention structure allows sure prevention of rotation of the bolt  21  when the nut  28  is screwed thereonto. Further, since the protruding height h from the end surface  24  of the head portion  22  is 0.3 mm or more and 8 mm or less, rotation prevention capability can be sufficiently realized. 
         [0038]      FIGS. 5 and 6  illustrate the second embodiment of the present invention. In the second embodiment, anti-rotation protruding portions  27  are formed on a pair of opposing periphery surfaces  25   a  and  25   b  of the quadrangle-shaped head portion  22  of the bolt  21 . Each anti-rotation protruding portion  27  is formed as a strip-shaped protrusion extending along a direction parallel to the shaft line of the bolt  21 . Positioning recesses  20  for receiving the anti-rotation protruding portions  27  are formed in a longitudinal direction on a pair of inner surfaces  17   a  and  17   b  on the inner surface  17  of the quadrangle-shaped receiving portion  16  of the case  11 . 
         [0039]    As shown in  FIG. 6 , the present embodiment also provides a double rotation prevention structure including bolt rotation prevention by making the bolt head portion  22  quadrangle-shaped and rotation prevention by fitting the anti-rotation protruding portions  27  to the positioning recesses  20 , thereby allowing surer prevention of rotation of the bolt  21  when a nut is screwed thereonto. 
         [0040]    It is also possible to make the shape of the head portion  22  of the bolt  21  an ellipse as shown in  FIG. 7  or an oblong as shown in  FIG. 8 . In either case, as shown in the figures, it is desirable that, when the anti-rotation protruding portion  26  is formed on the end surface  24  of the head portion  22 , the anti-rotation protruding portion  26  is formed extending along a major axis direction, and when the anti-rotation protruding portions  27  are formed on the external periphery surface  25  of the head portion  22 , the anti-rotation protruding portions  27  are formed at both ends of the major axis. 
         [0041]    Further, as shown in  FIGS. 9(   a ) and  9 ( b ), even when a bolt  21 -A is used that has a threaded shaft portion  23 A and a threaded shaft portion  23 B protruding respectively from upper and lower surfaces of a head portion  22  of the bolt  21 -A, it is also possible to form anti-rotation protruding portions  27  on a pair of opposing periphery surfaces of the head portion  22 . 
         [0042]    It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to exemplary embodiments, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular structures, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims. 
         [0043]    The present invention is not limited to the above described embodiments, and various variations and modifications may be possible without departing from the scope of the present invention.