Patent Publication Number: US-6222439-B1

Title: Circuit breaking device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a circuit breaking device incorporated into an automobile and others. 
     2. Description of the Related Art 
     Concerning this type circuit breaking device, it is common to use a fuse or a fusible link incorporated into an electric circuit so that the current flow in the circuit is interrupted when excessive current is generated in the electric circuit. On the other hand, in case of an emergency such as an automobile accident, it is necessary to forcibly shut off the electric circuit in a moment. For example, in an electric power supply circuit of an electric automobile which has come into wide use recently, there is a strong demand for forcibly shutting off the electric circuit in a moment in case of emergency. 
     As disclosed in Japanese Examined Patent Publication No. 58-47809, the conventional circuit breaker of this type is activated in such a manner that an electric conductor incorporated into an electric circuit is forcibly broken by an explosive force. As shown in FIG. 10, this circuit breaker is composed as follows: 
     In a reinforced glass case  105 , there are provided a fuse  102  connected between output terminals  101 , an explosive  103 , and a filament  104  for heating this explosive  103 . When an electric current generates in the input terminals  106 , this filament  104  is heated, so that explosive  103  is exploded. Utilizing the explosive force, the fuse  102  is broken. Due to the above structure, it is possible to forcibly shut off the electric circuit at an arbitrary time. 
     However, according to the conventional circuit breaker, the following problems may be encountered. The explosive force of explosive is dispersed in all directions, and only one portion of the explosive force acts on the fuse  102 . Therefore, a considerably high intensity of explosive force is required for breaking the fuse  102  positively. Therefore, the sealed glass case  105  must have a strong structure so that it can withstand a high intensity of explosive force. Further the sealed glass case  105  must be subjected to a special treatment for enhancing the mechanical strength. Accordingly, the manufacturing cost is inevitably increased. Additionally, the conventional circuit breaker is disadvantageous in that it is not simple to reset the circuit breaker after the fuse  102  has been broken. Thus, after an electric automobile has been involved in an accident, it is impossible to reset the circuit breaker immediately so that the electric automobile can be moved under its own power. 
     SUMMARY OF THE INVENTION 
     A circuit breaking device of the present invention has been accomplished in the above circumstances. It is an object of the present invention to provide a circuit breaking device by which the circuit can be positively shut off in case of emergency while an intensity of explosive force is being suppressed. Additionally, it is an object of the present invention to provide a circuit breaking device that can be reset easily for electric connection of the circuit if necessary after an electric conductor in the circuit has been broken. 
     As means for achieving the above object, according to a first aspect of the present invention, there is a feature that a circuit breaking device comprises a housing for accommodating an explosive exploding in response to a trigger signal, the housing having an opening for directing an explosive force in one direction, and an electric conductor to be broken by the explosive force of the explosive, the electric conductor provided on the way of a circuit, wherein the electric conductor is provided opposed to the opening, and an easy broken portion for facilitating a breaking of the electric conductor is formed on the electric conductor. 
     When the explosive is exploded in response to a trigger signal, its explosive force is directed to the opening of the housing, and the electric conductor provided at a position opposed to the opening receives the explosive force. Due to the foregoing, the easy broken portion is broken and the electric circuit is shut off. 
     The explosive force of explosive is directed to one direction, and the electric conductor is provided at a position where the explosive force can be effectively received, and further the easy broken portion is provided in the electric conductor so that the breaking of the electric conductor can be facilitated. Accordingly, even if an intensity of the explosive force is low, the electric conductor can be positively broken. 
     According to a second aspect of the present invention, there is a feature that, in the circuit breaking device according to a first aspect of the present invention, the easy broken portion is formed by cutting out the electric conductor so that a thickness can be thinned. 
     Since the electric conductor is cut out so that the thickness can be thinned in the cutout portion, it can be easily broken. 
     According to a third aspect of the present invention, there is a feature that, in the circuit breaking device according to a first aspect of the present invention, a cutout portion for facilitating a broken piece to be opened when the electric conductor is broken at the easy broken portion is provided on a side of the easy broken portion of the electric conductor. 
     The easy broken portion of the electric conductor is broken by the explosive force of explosive. At the same time, the broken pieces are opened while they are bent at the cutout portions. Therefore, the broken pieces of the broken portion are positively prevented from coming into contact with each other after the electric conductor has been broken. 
     According to a fourth aspect of the present invention, there is a feature that, in the circuit breaking device according to a first aspect of the present invention, a restricting wall for restricting a movement of the housing is provided on one side of the opening is formed and opposite side of the opening is formed. 
     When the explosive has exploded, the housing is prevented from retracting by the restricting wall. Therefore, the explosive force is intensely collected in the opening. 
     According to a fifth aspect of the present invention, there is a feature that, in the circuit breaking device according to a first aspect of the present invention, the device further comprises a resetting electric conductor by which both sides of a broken portion of the electric conductor can be reconnected to each other after the electric conductor has been broken. 
     After the electric conductor has been broken and the flow of current in the circuit has been interrupted, the resetting electric conductor is connected to both sides of the broken portion of the electric conductor. Thus, the circuit can be electrically connected again. 
     According to a sixth aspect of the present invention, there is a feature that, in the circuit breaking device according to a fifth aspect of the present invention, a lid is attached to a case, the resetting electric conductor is provided on the lid, the resetting electric conductor is not contacted with the electric conductor in the case when the lid is normally attached to the case, and the resetting electric conductor is contacted with both sides of the broken portion of the electric conductor when the lid is shifted from a normal position. 
     In the normal operating condition, the resetting electric conductor is not contacted with the electric conductor. Therefore, when the electric conductor is broken by an explosive force, the circuit is shut off. After that, when the lid-is shifted and the resetting electric conductor is connected to both sides of the broken portion of the electric conductor, the circuit is electrically connected again. Since the resetting electric conductor is provided on the lid, it is easy to handle it. 
     According to a seventh aspect of the present invention, there is a feature that, in the circuit breaking device according to a sixth aspect of the present invention, the case is provided with a display section for displaying a resetting state of the device for electrical connection at a position capable of being visually checked from the outside when the lid is moved for resetting the device for electrical connection. 
     When the lid is moved to reset the circuit breaking device for electric connection, the display provided on the case is exposed so that it can be visually checked. Accordingly, it is possible to make sure that the circuit breaking device has been reset for electric connection. 
     The present disclosure relates to the subject matter contained in Japanese patent application Nos. Hei. 10-35117 (filed on Feb. 17, 1998) and Hei. 10-35107 (filed on Feb. 17, 1998) which are expressly incorporated herein by reference in its entirely. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of the first embodiment of the present invention; 
     FIG. 2 is a partially cutout perspective view of the first embodiment; 
     FIG. 3 is a partially cutout plan view of the first embodiment; 
     FIG. 4 is a partially cutout exploded perspective view of the second embodiment of the present invention; 
     FIG. 5 is a partially cutout plan view of the second embodiment of the present invention; 
     FIG. 6 is a partially cutout plan view in a state in which the circuit is reset so that the circuit can be electrically connected; 
     FIG. 7 is a perspective view of a spare bus bar; 
     FIG. 8 is a front view of the third embodiment; 
     FIG. 9 is a plan view of the third embodiment; and 
     FIG. 10 is a cross-sectional view of a conventional example. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments in which the present invention is applied to an electric power supply circuit of an electric automobile will be described with reference to the accompanying drawings. 
     &lt;First Embodiment&gt; 
     A first embodiment of the present invention will be described with reference to FIG. 1 to FIG.  3 . 
     In the drawings, reference numeral  1  represents a lower case which is made of synthetic resin and has such a plane outer shape of which is a rectangular base plate  2  having a protruding portion  8  provided to a left end of an upper edge portion of the rectangular base plate  2  as shown in FIG.  3 . On the base plate  2  in the right region of the rectangular lower case  1 , there is formed an insertion hole  4  into which a battery post  3  (shown by a chain line in FIG. 3) of a battery (not shown) mounted on an electric automobile is inserted. At an edge inside the insertion hole  4 , there is provided a substantially semicircular wall  5  which is vertically attached to the lower case  1 . It is possible to connect a fastening ring  6  made of an electric conductor on the insertion hole  4 . 
     In the left region of the rectangular lower case  1 , there is provided a peripheral wall  7  which is formed in the periphery of the left region. At the center of the left region, there is provided an accommodation chamber  12  for accommodating a casing  13  described later. In the protruding portion  8 , there is provided a side wall  9  which is vertically attached to the right edge of the protruding portion  8 . In the protruding portion  8 , there is provided a stud bolt  10  for connecting an electric power supply wire not shown in the drawing. 
     The above accommodation chamber  12  is formed in such a manner that the width of the forward end portion (the left in FIG. 3) is more narrow than the width of the rear end portion (the right in FIG.  5 ); and the casing  13  is accommodated in this-accommodation chamber  12 . The casing  13  is made of stainless steel or the like and formed into a box shape so that it can be tightly accommodated in the accommodation chamber  12  while a predetermined clearance is provided on the forward end side. In the casing  13 , there is provided an insulating case  14  in such a manner that the insulating case  14  covers the forward end side, upper side, lower side, right and left of the inside of the casing  13 . In the casing  13 , there is provided a housing  16  in which an explosive sealing portion  15  is accommodated, and also there is provided one portion of a bus bar  17  which corresponds to an electric conductor of the present invention. 
     The explosive sealing portion  15  is composed in such a manner that the explosive is filled around a filament and enclosed in the sealing portion. On the base end side of the explosive sealing portion  15 , there is provided a connecting body  18  for connecting the filament with a trigger wire  19  connected with the battery. The housing  16  is made of synthetic resin and formed into a block shape. Inside the housing  16  on the base end side, the explosive sealing portion  15  and the connecting body  18  are accommodated. On the forward end surface of the housing  16 , there is formed an opening  20  which reaches the explosive sealing portion  15 . 
     The bus bar  17  is made of, for example, copper alloy or the like and formed into a U-shaped portion  21  which covers the forward end surface and both sides of the housing  16  as shown in FIG.  1 . One end side (the viewer&#39;s side in FIG. 1) of the U-shaped portion  21  is bent outside at a right angle and an L-shaped portion is extended from the lower edge. A first connecting portion  22  is raised at the forward end of the extended L-shaped portion. This first connecting portion  22  can be fastened with a connecting plate  26  of the fasten ring  6  by a bolt  24  and a nut  25 . The other end side of the U-shaped portion  21  is bent outside by a right angle in the same manner and bent twice to the forward end side and outside. At the lower edge of U-shaped portion directed outside, there is horizontally provided a second connecting portion  23  in which an attaching hole  29  is formed. While the stud bolt  10  is inserted into this second connecting section  23 , this second connecting section  23  can be disposed on the protruding portion  8 . 
     In the forward end portion, which will be referred to as a broken portion  27  hereinafter, of the U-shaped portion  21  of the bus bar  17 , a recess portion  28  is formed all over the width on the outside at the center in the longitudinal direction. On the outside of both corner portions (both ends of the broken portion  27 ) of the U-shaped portion  21 , cutout portions  30  are formed all over the width in the same manner. 
     An example of the assembling procedure will be described as follows: 
     While the explosive sealing portion  15  and the connecting body  18  are combined with each other, they are accommodated on the base end side of the housing  16 . This housing  16  is engaged with the inside of the U-shaped portion  21  of the bus bar  17 . Due to the foregoing, a portion of the bus bar  17  in which the recess portion  28  of the broken portion  27  is provided, which corresponds to the easy broken portion of the present invention, is located just before the opening  20  of the housing  16 . After that, the casing  13  is engaged with the outside of the U-shaped portion  21  of the bus bar  17 . When a rear plate  32  is set and caulked, these parts are fixed. This casing  13  is engaged in the accommodation chamber  12  of the lower case  1  together with the bus bar  17 . In this assemblage, the rear surface of the housing  16  comes into contact with a restricting wall  31  raised from the lower case  1 . On the forward end surface of the casing  13  and on the forward end surface of the insulating case  14 , there is formed a vent hole  33  from which a blast of explosion is released, and also on the outer surface of the accommodation chamber  12 , there is formed a vent hole  34  from which a blast of explosion is released. 
     The first connecting portion  22  of the bus bar  17  is located close to the insertion hole  4  of the battery post  3  and provisionally assembled to the connecting plate  26  of the fasten ring  6  by the bolt  24  and the nut  25 . Concerning the second connecting section  23 , while the stud bolt  10  is inserted into the attaching hole  29  of the second connecting section  23 , the second connecting section  23  is disposed on the protruding portion  8 . A trigger wire  19  drawn out from the housing  16  is engaged in a guide groove  36  which is formed around the insertion hole  4  and along the peripheral wall  7 . Then the trigger wire  19  is drawn outside. 
     When the battery post  3  is inserted into the insertion hole  4  and the fastening ring  6 , the lower case  1  assembled in the above manner is disposed on an upper surface of the battery. Then, the bolt  24  and the nut  25  are fastened. Due to the foregoing, the fastening ring  6  is diminished in diameter, so that the fasten ring  6  can be fixed to the battery post  3 . At the same time, the battery post  3  and the first connecting section  22  of the bus bar  17  are connected with each other by the fastening ring  6 . A connecting terminal of an electric power supply wire (not shown) is connected to the stud bolt  10  and pressed and fixed to the second connecting section  23  by a nut (not shown). Due to the foregoing, an electric power supply circuit can be formed from the battery to the electric power supply wire through the bus bar  17 . A trigger wire  19  is also connected to the battery side. Finally, an upper case (not shown), the shape of which is like a lid, is set and fixed onto an upper surface of the lower case  1 . 
     The structure of the first embodiment of the invention is described above. Successively, operation of the first embodiment is described as follows: 
     When an emergency signal is sent out due to the occurrence of an automobile accident, electric current generates in the trigger wire  19 . Therefore, the filament in the is explosive sealing portion  15  is heated, and explosive is exploded. Since the rear surface of the housing  16  is received by the restricting wall  31  so that the housing  16  can not be retracted, explosive force is mainly directed to the opening  20  of the housing  16 . Therefore, the broken portion  27  of the bus bar  17  opposed to the opening  20  receives the explosive force. Accordingly, as shown by the chain line in FIG. 3, the recess portion  28  of the bus bar  17  is broken. In this case, both broken pieces  38  are bent at the cutout portions  30  and opened so that they are separated from each other. Due to the foregoing, the electric power supply circuit is shutoff. In this connection, blast of explosion is released outside from the vent holes  33 ,  34 . 
     In this first embodiment, the explosive force is directed from the opening  20  of the housing  16  in one direction, the broken portion  27  of the bus bar  17  is provided at a position where the explosive force can be effectively received, and further the recess portion  28  for facilitating the break is provided in the broken portion  27 . Accordingly, even if an intensity of the explosive force is relatively low, the broken portion  27  can be positively broken. Additionally, the structure of the housing  16  or the like can be relatively simplified. 
     Simultaneously when the broken portion  27  is broken, the broken pieces are opened while they are bent at the cutout portions  30  by the explosive force. Accordingly, the broken pieces of the broken portion  27  are positively prevented from coming into contact with each other again. When both broken pieces  38  are opened, there is a possibility that forward end portions of the broken pieces  38  come into contact with the inside of the casing  13 . However, since the inside of the casing  13  in the contacting portion is provided with the insulating case  14 . Consequently, there is no possibility that the bus bar  17  is electrically connected. 
     Since the bus bar  17  provided with the broken portion  27  is directly connected to the battery post  3 , the structure can be simplified and the space can be saved as compared with a case in which a broken conductor is provided on the way of the electric power supply wire drawn out from the battery post  3 . 
     &lt;Second Embodiment&gt; 
     A second embodiment of the present invention will be described with reference to FIG. 4 to FIG.  7 . 
     In FIGS. 4 and 5, reference numeral  1  is the lower case which is made of synthetic resin and has such a plane outer shape of which is the rectangular base plate  2  having the protruding portion  8  provided to a left end of an upper edge portion of the rectangular base plate  2  as shown in FIG.  5 . On the base plate  2  in the right region of the rectangular lower case  1 , there is formed an insertion hole into which the battery post  3  of a battery (not shown) mounted on an electric automobile is inserted. The fastening ring  6  made of an electric conductor can be set above the insertion hole. In the protruding portion  8 , there is provided the side wall  9  which is vertically attached to the right edge of the protruding portion  8 . In the protruding portion  8 , there is provided the stud bolt  10  for connecting an electric power supply wire not shown in the drawing. 
     In the left region of the rectangular lower case  1 , there is provided the peripheral wall  7  which is formed in the periphery of the left region. The right end of the peripheral wall  7  extends to a position close to the center of the fastening ring  6 . At the center on the left of the peripheral wall  7  in the longitudinal direction, there is formed the accommodation chamber  12  partitioned by the partition walls  45 ,  45 . Right ends of both partition walls  45  are respectively bent outside at a right angle, so that auxiliary walls  46  are formed at the right ends. The above accommodation chamber  12  is formed in such a manner that the width of the forward end portion (the left in FIG. 5) is more narrow than the width of the rear end portion (the right in FIG.  5 ); and the casing  13  is accommodated in this accommodation chamber  12 . On both sides of the portion in which a narrow width portion  47  is formed, there is provided an accommodating space  48  for accommodating a spare bus bar  60  described later which corresponds to a resetting electric conductor of the present invention. 
     The casing  13  is made of stainless steel or the like and formed into a box shape so that it can be tightly accommodated in the accommodation chamber  12  while a predetermined clearance is provided on the forward end side. In the casing  13 , there is provided an insulating case  14  in such a manner that the insulating case  14  covers the forward end side, upper side, lower side, right and left of the inside of the casing  13 . In the casing  13 , there is provided a housing  16  in which an explosive sealing portion  15  is accommodated, and also there is provided one portion of the bus bar  17  which corresponds to an electric conductor of the present invention. 
     The explosive sealing portion  15  is composed in such a manner that explosive is filled around a filament and enclosed in the sealing portion. The housing  16  is made of synthetic resin and formed into a block shape. On the forward end surface of the housing  16 , there is formed an opening  20  which reaches the explosive sealing portion  15 . 
     The bus bar  17  is made of, for example, copper alloy or the like and formed into the U-shaped portion  21  which covers the forward end surface and both sides of the housing  16 . On one end side (lower side in FIG. 2) of the U-shaped portion  21 , there is provided a resetting portion  49  which is bent outside at a right angle. This resetting portion  49  is provided along the auxiliary wall  46  in such a manner that a predetermined clearance is provided between the resetting portion  49  and the auxiliary wall  46 . An L-shaped portion extending from the lower edge of the resetting portion  49  is provided on the base plate  2 . At the forward end of the L-shaped portion, the first connecting portion  22  is formed being raised. This first connecting portion  22  can be connected with a connecting plate  26  of the fasten ring  6  by the bolt  24  and the nut  25 . 
     The other end side of the U-shaped portion  21  is bent outside by a right angle in the same manner, so that the resetting portion  49  is formed. In the same manner, this resetting portion  49  is provided along the auxiliary wall  46  in such a manner that a predetermined clearance is provided between the resetting portion  49  and the auxiliary wall  46 . The other end side of the U-shaped portion  21  is bent twice to the forward end side and outside. At the lower edge of U-shaped portion  21  directed outside, there is horizontally provided the second connecting portion  23  in which the attaching hole  29  is formed. While the stud bolt  10  is inserted into this second connecting section  23 , this second connecting section  23  can be disposed on the protruding portion  8 . 
     In the forward end piece portion, which will be referred to as the broken portion  27  hereinafter, of the U-shaped portion  21  of the bus bar  17 , the recess portion  28  is formed all over the width on the outside at the center in the longitudinal direction. On the outside of both corner portions (both ends of the broken portion  27 ) of the U-shaped portion  21 , cutout portions  30  are formed all over the width in the same manner. 
     As shown in FIG. 4, there is provided a lid  51  for covering an upper surface of the lower case  1 . This lid  51  is made of synthetic resin and formed into a plane which covers all the upper surf ace of the lower case  1 . In portions where the peripheral wall  7  of the lower case  1  or the side wall  9  are not provided, a peripheral wall  52  is formed on the lid  51 . 
     On a lower surface of the lid  51 , there are provided four engaging pieces  53 , which extend downward, capable of entering the inside of the peripheral wall  7  of the lower case  1 . Each engaging piece  53  can be bent to the inside respectively, and a protrusion  54  is formed outward at a lower end portion of each engaging piece  53 . On the other hand, on the peripheral wall  7  of the lower case  1 , there are formed engaging holes  55  capable of engaging with the protrusions  54  of the engaging pieces  53 . Accordingly, when the lid  51  is provisionally assembled, each engaging piece  53  is pushed inside the peripheral wall  7  being bent inward. Next, when the lid  51  is assembled at a predetermined position, the engaging piece  53  returns to its original shape, so that the protrusion  54  can be engaged with the corresponding engaging hole  55 , and the lid  51  is fixed. 
     As shown the left in FIG. 4, on an upper surface of the forward end portion of the peripheral wall  7  of the lower case  1 , there is provided a display section  50  on which a pattern of stripes are formed. 
     On a lower surface of the lid  51  on the left edge side of FIG. 4, the aforementioned spare bus bar  60  is fixed. This spare bus bar  60  is made of the same copper metal or the like as that of the bus bar. As shown in FIG. 7, this spare bus bar  60  has inserting portions  62  which branches into two. These inserting portions  62  are formed on the lower side surface of both ends of a straight connecting portion  61 . An interval between both inserting portions  62  is determined in such a manner that the narrow width portion  47  of the partition wall  45  composing the accommodating chamber  12  and the base end side of the U-shaped portion  21  of the bus bar  17  can be interposed between both inserting portions  62 . The resetting portion  49  of the bus bar  17  can be inserted into the inserting portion  62 . On the inner surfaces of the inserting portion  62  which are opposed to each other, there is provided a louver  63  made of conductive material of low resistance, and this louver  63  elastically bulges inward. Further, lower ends of the inner surfaces of the inserting portion  62 , which are opposed to each other, are chamfered for the purpose of guiding, therefore the chamfered portion  64  are formed. The connecting portion  61  is made to attach onto the lower surface of the lid  51  and fixed. 
     An example of the assembling procedure will be described as follows: 
     The explosive sealing portion  15  is accommodated on the base end side of the housing  16 . This housing  16  is engaged with the inside of the U-shaped portion  21  of the bus bar  17 . Due to the foregoing, a portion of the bus bar  17  in which the recess  28  of the broken portion  27  is provided is located just before the opening  20  of the housing  16 . After that, the casing  13  is engaged with the outside of the U-shaped portion  21  of the bus bar  17 . This casing  13  is engaged in the accommodation chamber  12  of the lower case  1  together with the bus bar  17 . On the forward end surface of the casing  13 , there is formed the vent hole  33  from which a blast of explosion is released, and also on the outer surface of the accommodation chamber  12 , there is formed the vent hole  34  from which a blast of explosion is released. 
     The first connecting portion  22  of the bus bar  17  is located close to the battery post  3  and provisionally assembled to the connecting plate  26  of the fasten ring  6  by the bolt  24  and the nut  25 . Concerning the second connecting section  23 , while the stud bolt  10  is inserted into the attaching hole  29  of the second connecting section  23 , the second connecting section  23  is dispose on the protruding portion  8 . A trigger wire  19 , which is connected with the explosive sealing portion  15  and drawn out from the housing  16 , is engaged in the guide groove  36  which is formed around the fastening ring  6  and along the peripheral wall  7 . Then the trigger wire  19  is drawn outside. 
     When the battery post  3  is inserted into the insertion hole and the fastening ring  6 , the lower case  1  assembled in the above manner is dispose on an upper surface of the battery. Then, the bolt  24  and the nut  25  are fastened. Due to the foregoing, the fastening ring  6  is diminished in diameter, so that the fasten ring  6  can be fixed to the battery post  3 . At the same time, the battery post  3  and the first connecting section  22  of the bus bar  17  are connected with each other by the fastening ring  6 . A connecting terminal of an electric power supply wire (not shown) is connected to the stud bolt  10  and pressed and fixed to the second connecting section  23  by a nut (not shown). Due to the foregoing, an electric power supply circuit can be formed from the battery to the electric power supply wire through the bus bar  17 . The trigger wire  19  is also connected to the battery side. 
     Finally, the lid  51  is disposed and fixed onto an upper surface of the lower case  1 . At this time, the spare bus bar  60  provided on the lower surface of the lid  51  is accommodated in the accommodating space  48  as shown in FIG. 5 while the narrow width portion  47  of the accommodating chamber  12  is interposed between the spare bus bar  60 . In this case, the spare bus bar  60  is not contacted with the bus bar  17 , therefore the spare bus bar  60  is non-conductive state with the bus bar  17 , and the display section  50  is hidden by the lid  51 . 
     Successively, operation of this second embodiment will be described as follows: 
     When an emergency signal is sent out due to the occurrence of an automobile accident, electric current generates in the trigger wire  19 . Therefore, the filament in the explosive sealing portion  15  is heated, and the explosive is exploded. Explosive force is mainly directed to the opening of the housing  16 . Therefore, the broken portion  27  of the bus bar  17  opposed to the opening  20  receives the explosive force. Accordingly, as shown in FIG. 6, the recess portion  28  of the bus bar  17  is broken. In this case, both broken pieces  38  are bent at the cutout portions  30  and opened so that they are separated from each other. Due to the foregoing, the electric power supply circuit is shut off. In this connection, a blast of explosion is released outside from the vent holes  33 ,  34 . 
     In some cases, after the electric power supply circuit has been shut off, it becomes necessary for the vehicle to be moved. In this case, operation is conducted as follows: 
     First, the protrusions  54  engaged in the engaging holes  55  are pushed inward so as to release the engagement, and then the lid  51  is lifted upward and released from the peripheral walls. Next, the lid  51  is shifted from the normal setting position to the right as shown by a chain line in FIG.  6 . Then, the lid  51  is assembled while both the inserting portions  62  of the spare bus bar  60  are being inserted into both the resetting portions  49  of the bus bar  17  which was broken. Then both the resetting portions  49  of the broken bus bar  17  are connected with each other by the spare bus bar  60  by the louver  63  of low resistance. Due to the foregoing, the electric power supply circuit can be electrically connected again. 
     At this time, the display section  50  provided on the peripheral wall  7  of the lower case  1  is exposed. Therefore, when this display section  50  is visually checked, it is possible to make sure that the electric power supply circuit has been electrically connected again. 
     As described above, according to this second embodiment, after the electric power supply circuit has been shut off by the break of the bus bar  17 , the lid  51  is disassembled once and the spare bus bar  60  fixed on the lid  51  is inserted into both the resetting portions  49  of the broken bus bar  17 . Due to the above simple operation, it is possible to quickly reset the electric power supply circuit for electric connection. 
     Since the spare bus bar  60  is fixed onto the lid  51 , it is unnecessary for an operator to search the spare bus bar  60  in case of emergency. Therefore, this circuit breaking device is handy. Usually, the spare bus bar  60  is accommodated in a surplus space (accommodating space  48 ) in the lower case  1 . Therefore, the size of the entire case is not increased. 
     &lt;Third Embodiment&gt; 
     A third embodiment of the present invention will be described with reference to FIG.  8  and FIG.  9 . 
     In the first embodiment described above, the circuit breaking device is provided onto a surface on which the battery post  3  of the battery is erected while a portion of the circuit breaking device is protruded outside. 
     On the other hand, in this third embodiment, the circuit breaking device is provided on both the surface on which the battery post  3  of the battery is erected and a surface adjacent to the above surface. Accordingly, it is easy to provide the circuit breaking device in accordance with a empty space around the battery. 
     In accordance with the above change in the structure, outer shapes of the housing and the bus bar are also changed. However, the essential function and arrangement are the same as those of the first embodiment described before. Therefore, like reference numerals are used to indicate like parts in the first and the third embodiment, and explanations are omitted here. 
     Therefore, the circuit breaking device of this third embodiment is described as follows: 
     A portion  41 , in which the insertion hole  4  of the battery  3  is provided, and a portion  42 , in which the casing  13  accommodating the explosive sealing portion  15  and the stud bolt  10  are provided, make a right angle with each other. Accordingly, the circuit breaking device of the third embodiment can be provided in such a manner that the circuit breaking device comes into contact with the surface on which the battery post  3  is erected and also with the surface adjacent to the above-mentioned surface. 
     It should be noted that the present invention is not limited to the above specific embodiments described above referring to the accompanying drawings. For example, the following embodiments are included in the technical scope of the present invention, and variations may be made by one skilled in the art without departing from the scope of the present invention. 
     The means for composing the easy broken portion of the electric conductor is not limited to the above embodiments, but it is possible to adopt a means in which perforations are made in the electric conductor. 
     As a feature of the display section, the display section may be colored differently from the surroundings. A position at which the display section is disposed may be any position as long as the display section can be visually checked from the outside when the lid is moved to the electric connection resetting position. 
     The spare bus bar is not necessarily fixed onto the lid beforehand. It is possible to store the spare bus bar at a different place. 
     In the above embodiment, the louver of low resistance is provided in the inserting portion of the spare bus bar, however, it is possible to provide the louver in the resetting portion of the bus bar. 
     It is possible to adopt an arrangement in which the spare bus bar is provided with a fuse, which is fused so as to shut off the circuit when an overcurrent generates in the case of a short circuit caused after the circuit has been connected again. 
     The present invention is applied to not only the electric power supply circuit of an electric automobile shown in the above embodiment but also a circuit which must be shut off in case of emergency and can be reset so that the circuit can be connected again.