Patent Publication Number: US-7592892-B2

Title: Fusible link unit accommodated in in-vehicle electrical connection box

Description:
The present invention claims priority from Japanese Patent Application No. 2006-114078 filed on Apr. 18, 2006, the entire content of which is incorporated herein by reference. 
     BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The present invention relates to a fusible link unit adapted to be accommodated in an in-vehicle electrical connection box. More specifically, the present invention relates to a fusible link unit including a bus bar, the bus bar forming a raw power supply circuit to be connected to a battery. The present invention provides a safety measure for such a bus bar. 
     2. Description of the Related Art 
     Bus bars are generally accommodated inside a case of an in-vehicle electrical connection box. Each of the bus bars is formed into a required shape by blanking a conductive metal sheet, thereby, serving as an internal circuit. 
     Among the bus bars, there is a bus bar which is connected to a battery without interposing a fuse therebetween. In other words, such a bus bar is connected to a raw power supply circuit. Since a high current of 100 amperes or more flows through such a bus bar, in the event that a tool or the like erroneously falls when installing the electrical connection box to the vehicle and a cover or an upper wall of a housing accommodating the bus bar therein is damaged, the bus bar may become exposed, whereby a short circuit may occur. 
     For example, as shown in  FIGS. 6A and 6B , a bus bar  5  to be connected to a raw power supply circuit includes a fusible link and is accommodated in a fuse box  1  arranged on a side surface of a battery, and an upper cover  6  is placed thereover (see, e.g., JP-A-2001-256878). 
     The bas bar  5  is formed such that a primary bus bar portion  2 , a secondary bus bar portion  3  and a fuse element  4  are formed in a one-piece structure, and battery attaching portions  2   a  of the bas bar  5  are directly attached to the battery. The battery attaching portions  2   a  are accommodated in the fuse box  1  without being molded. 
     With the fuse box  1  that is configured as described above, in the event that a tool or the like falls on the cover  6  and breaks the same when installing the fuse box  1  on a vehicle, the battery attaching portions  2   a  of the bus bar  5  may become exposed, whereby a short circuit or an electric leak may occur. 
     SUMMARY OF INVENTION 
     The present invention has been made in view of the above described problems, and it is an object thereof to provide a safe and secure fusible link unit in which an electric leak or a short circuit can be prevented even when the bus bar including a fusible link becomes exposed. 
     According to an aspect of the invention, a fusible link unit includes a bus bar adapted to be connected to a battery without interposing a fuse between the bus bar and the battery, and a heat resistant insulating sheet which covers at least an upper edge portion of the bus bar. The fusible link unit is adapted to be accommodated inside an in-vehicle electrical connection box. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing a case and a fusible link unit according to an exemplary embodiment of the invention; 
         FIG. 2  is an exploded perspective view showing the fusible link unit shown  FIG. 1 ; 
         FIG. 3  is a front view of a bus bar according to the exemplary embodiment; 
         FIG. 4  is a plan view of a heat resistant insulating sheet. 
         FIG. 5A  is a front view of the bus bar covered by the heat resistant insulating sheet; 
         FIG. 5B  is a sectional view taken along the line V-V in  FIG. 5A . 
         FIGS. 6A and 6B  show an example of a related art. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an exemplary embodiment of the invention will be described with reference to the drawings. The following exemplary embodiment does not limit the scope of the invention. 
       FIG. 1  shows a case  10  of a fuse box which is installed close to a battery (not shown) on a vehicle. 
     The case  10  has an accommodating portion  11  in which a fusible link unit  20  shown in  FIG. 2  is accommodated. In the fusible link unit  20 , a bus bar  22  including a fusible link is accommodated in a housing  23 . 
     The fusible link unit  20  is positioned on a side of an upper end  10   a  of the case  10 , and is accommodated in the accommodating portion  11  in such a manner that an upper portion of the housing  23  projects from the upper end  10   a  of the case  10 . 
     As shown in  FIG. 2 , the fusible link unit  20  includes a bus bar  22  covered by a heat resistant insulating sheet  21 , the housing  23  which is made of a resin and accommodates the bus bar  22 , and a cover  24  which is slidably attached to the housing  23 . The bus bar  22  includes vertical bus bars which are vertically disposed inside the housing  23 , and the vertical bus bars form a raw power supply circuit which is directly connected to the battery without interposing a fuse therebetween. 
     As shown in  FIG. 3 , the bus bar  22  is formed by blanking a conductive metal sheet, and includes a plurality of fusible portions  22   c , each formed as an S-shaped narrow portion. 
     More specifically, the bus bar  22  includes an input terminal portion  22   a  which is disposed at one end thereof for a connection to the battery, a common circuit portion  22   d  which is continuously connected to the input terminal portion  22   a , and a plurality of branch circuit portions  22   e  which is disposed in such a manner as to be branched from the common circuit portion  22   d . Each of the branch circuit portions  22   e  includes the narrow fusible portion  22   c  and an output terminal portion  22   b  disposed at a distal end portion of the branch circuit portion  22   e  on a downstream side of the fusible portion  22   c.    
     As shown in  FIGS. 1 and 3 , a bolt hole  22   f  is formed on the input terminal portion  22   a , so that the input terminal portion  22   a  is connected to a terminal W 1  of an electric wire by tightening a bolt through the hole  22   f . The terminal W 1  is connected to the battery. The output terminal portions  22   b  includes a large current output terminal portions  22   g  and a small current output terminal portions  22   h . A bolt hole  22   i  is formed on each of the large current output terminal portions  22   g , so that the large current output terminal portions  22   g  are connected to respective terminal W 2  of electric wires by tightening a bolt through each of the bolt hole  22   i . The terminals W 2  are connected to an electric component such as an alternator or a generator which requires a large current. The small current output terminals  22   h  are connected to a terminal W 3  of electric wires which are connected to other electric components. Boss holes  22   j  are formed on the bus bar  22  at predetermined positions, whereby the bus bar  22  is positioned when being accommodated in the housing  23 . 
     The bus bar is accommodated in a vertical direction inside the housing  23 , and a thin upper edge portion  22   k  of the common circuit portion  22   d  is positioned in such a manner as to face an inner surface of an upper end wall  23   d  of the housing  23 . The upper edge portion  22   k  of the common circuit portion  22  is covered by the heat resistant insulating sheet  21  such that the heat resistant insulating sheet  21  straddles the upper edge portion  22   k.    
     When the bus bar  22  is covered by the heat resistant insulating sheet  21  in this way, the heat resistant insulating sheet  21  does not fall off from the surface of the bus bar  22  even when an impact is applied thereto from outside (e.g., a vibration of the vehicle or a collision of a tool), whereby the bus bar  22  can be reliably protected. Moreover, the portion that is to be covered by the heat resistant insulating sheet  21  can be minimum, thereby keeping heat releasing property of the bus bar  22 . 
     The heat resistant insulating sheet  21  may be formed from a fluorine plastic sheet having a heat-resisting property and an electrically insulating property. In such a case, an adhesive agent is coated on an inner surface of the fluorine plastic sheet, whereby the fluorine plastic sheet is adhered to a surface of the bus bar  22  via the adhesive agent. 
     The fluorine plastic sheet has superior heat resistance so that it neither deforms nor melts even when the temperature inside the case  10  increases. In addition, the fluorine plastic sheet is excellent in an electrical insulation. Therefore, the an electric leak and a short circuit of a current flowing through the bus bar  22  can be reliably prevented from occurring. 
     As shown in  FIG. 4 , the heat resistant insulating sheet  21  is formed substantially into a tape shape which is vertically symmetrical across a center line  21   a . A length of the heat resistant insulating sheet  21  along a longer side thereof is slightly shorter than a length of the common circuit portion  22   d  of the bus bar  22  along a longer side thereof. A length of the heat resistant insulating sheet  21  along a shorter side thereof is such that respective side edges  21   b  on the longer side reach the boss holes  22   j  when the heat resistant insulating sheet  21  straddles the upper edge portion  22   k  of the bus bar  22  and is folded along the center line  21   a  into two halves. 
     A plurality of concave portions  21   c  is formed along the respective side edges  21   b  by cutting out the portions which faces the boss hole  22   j  of the common circuit portion  22   d.    
     As shown in  FIGS. 5A and 5B , the heat resistant insulating sheet  21  is folded along the center line  21   a  thereof into two halves, and the concave portions  21   c  of the heat resistant insulating sheet  21  are aligned at the positions where the boss holes  22   j  are in the bus bar  22 , and then the heat resistant insulating sheet  21  is brought to straddle the upper edge portion  22   k  of the bus bar  22 , thereby covering both side surfaces of the upper edge portion  22   k.    
     The housing  23  for accommodating the bus bar  22  is made of a glass containing material in order to enhance heat resistance and strength thereof. 
     As shown in  FIG. 2 , the housing  23  includes a primary housing portion  23 A and a secondary housing portion  23 B. The primary housing portion  23 A and the secondary housing portion  23 B are formed with window openings  23   a  at positions facing the fusible portions  22   c  of the bus bar  22 , so that a fusing state of the fusible portions  22   c  can be visually checked from an exterior through the window openings  23   a.    
     In addition, a sliding cover attaching portion  23   b  is formed along a center portion of an external surface of each of the primary housing portion  23 A and the secondary housing portion  23 B, while a engaging hole  23   c  is provided on one end of an internal surface of each of the primary housing portion  23 A and the secondary housing portion  23 B. The upper end wall  23   d  having a shape like a pentroof is formed at an upper end portion of the primary housing portion  23 A. 
     A plurality of locking grooves  23   e  is formed on a side edge of the primary housing portion  23 A, while locking pieces  23   f  are formed on the secondary housing portion  23 B at positions facing the locking grooves  23   e  of the primary housing portion  23 A. The locking grooves  23   e  of the primary housing portion  23 A and the locking pieces  23   f  of the secondary housing portion  23 B joins together and locks, interposing the bus bar  22  therebetween. 
     The cover  24  which is attached to the housing  23  is made of a transparent resin and is formed into a shape having a substantially U-shaped cross section by bending a resin plate. A pair of engaging pieces  24   b  is provided on respective end portions  24   a  of the cover  24  on a side to be inserted in the housing  23 , and the pair of engaging pieces  24   b  engage with the respective engaging holes  23   c  of the housing  23 . 
     The bus bar  22  covered by the heat resistant insulating sheet  21  is held between the primary housing portion  23 A and the secondary housing portion  23 B in such a state that the bus bar  22  is positioned at the boss holes  22   j , and the locking grooves  23   e  of the primary housing portion  23 A and the locking pieces  23   f  of the secondary housing portion  23 B are joined together in a locked fashion, whereby the bus bar  22  is accommodated in the housing  23 . When the bus bar  22  is accommodated in the housing  23 , the upper edge portion  22   k  of the common circuit portion  22   d  of the bus bar  22  is disposed to face the inner surface of the upper end wall  23   d  of the primary housing portion  23 A. 
     The cover  24  is slid along the longer side direction of the housing  23  from a side of the input terminal portion  22   a  of the bus bar  22  so as to be inserted into the cover attaching portions  23   b  of the housing  23  inside which the bus bar  22  is accommodated, and the engaging pieces  24   b  provided on the cover  24  then engages with the engaging holes  23   c  provided on an inner side of the housing  23 . 
     According to the above configuration, the bus bar  22  that is directly connected to the battery from which a high current flows is accommodated inside the housing  23  which is made of a material containing glass. Therefore, the housing  23  likely to be broken when receiving an impact from a tool or other members. Further, it is the upper end wall  23   d  of the housing  23  where it is more likely to be broken when the tool falls thereon while installing an electrical connection box on a vehicle. 
     However, according to the above exemplary embodiment, the bus bar  22  is covered by the heat resistant insulating sheet  21  on a portion where it faces the upper end wall  23   d  of the housing  23 . Therefore, the safety can be secured even when an unexpected event occurs. 
     More specifically, even when the upper cover of the fuse box as well as the upper end wall  23   d  of the primary housing portion  23 A are broken by a tool falling thereon and the bus bar  22  becomes exposed, since the heat resistant insulating sheet  21  covers the upper edge portion  22   k  of the bus bar  22  facing the upper end wall  23   d  of the primary housing portion  23 A, a metallic portion of the bas bur  22  forming a raw power supply circuit does not becomes exposed, whereby a short circuit and an electric leak can be prevented from occurring so that the safety of the bus bar  22  is enhanced. 
     If the whole surface of the bus bar  22  is covered by the heat resistant insulating sheet  21 , the heat releasing property of the bus bar  22  decreases. Therefore, at least the upper edge portion  22   k  of the bus bar  22  where it is likely to be exposed is covered by the heat resistant insulating sheet  21 , thereby satisfying both the heat releasing property and the safety of the bus bar  22 . 
     The heat resistant insulating sheet  21  that covers the bus bar  22  is inexpensive. Therefore, the production cost can be suppressed. Furthermore, since the heat resistant insulating sheet  21  only has to be affixed to the bus bar  22 , little working time is required, thereby resulting in good workability. 
     While description has been made in connection with an exemplary embodiment of the present invention, it will be obvious to those skilled in the art that various changes and modification may be made therein without departing from the present invention. It is aimed, therefore, to cover in the appended claims all such changes and modifications falling within the true spirit and scope of the present invention.