Abstract:
The circuit breaker disclosed in the invention comprises a first connection terminal, a second connection terminal, a heat generating part having conductivity disposed between the first connection terminal and second connection terminal, an igniting part igniting depending on a cut-off signal, an expandable elastic member capable of applying a force to the heat generating part so as to be departed from between the first connection terminal and second connection terminal, and a holding part for holding the elastic member in compressed state. Herein, as the igniting part ignites depending on the cut-off signal and the heat generating part generates heat, when the holding part releases the elastic member, the elastic member applies force to the heat generating part, and the heat generating part is departed from between the first connection terminal and second connection terminal, the conductive state between the first connection terminal and second connection terminal is cut off.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a circuit breaker, and more particularly to a circuit breaker for cutting off an electric circuit in a short time. 
     In an electric equipment system installed in a vehicle, if any abnormality should occur due to load of power window or the like, or if any abnormality should occur in the wire harness or the like composed of plural wires connecting the battery and each load, a large-current fuse interposed between the battery and the wire harness is melted to cut off between the battery and the wire harness, thereby preventing the loads and wire harness from burning down. 
     In the electric equipment system using such large-current fuse, however, if any abnormality should occur in the load such as power window, or if abnormality should occur in the wire harness of the like connecting the battery and each load, it is set so as not to melt down unless a current large than the preset allowable value flows in the large-current fuse. 
     Recently, various protective devices have been developed for cutting off between the battery and wire harness by detecting when a large current close to the allowable value is flowing continuously. 
     SUMMARY OF THE INVENTION 
     According to the investigation by the present inventors, a protective device as shown in FIG. 10 is considered. 
     FIG. 10 is a sectional view showing an example of protective device using a bimetal. 
     Such protective device comprises a housing  103  made of an insulating resin or the like, and forming a fuse compartment  102  at the upper side, a lid  113  for opening and closing the fuse compartment  102  of the housing  103 , a power source terminal  105  disposed at the lower side of the housing  103  so that its upper end portion projects into the fuse compartment  102 , and the lower end exposed outside, with the portion exposed outside connected to a positive terminal of a battery  104 , and a load terminal  109  disposed at the lower side of the housing so that its upper end portion projects into the fuse compartment  102 , and the lower end exposed outside, with the portion exposed outside connected to a load  108  through a wire  107  for composing a wire harness  106 . 
     Such protective device further comprises a fusible element  110  made of a low melting point metal disposed in the fuse compartment  102 , with one end connected to the upper end of the power source terminal  105 , and other end connected to the upper end of the load terminal  109 , an intermediate terminal  111  disposed at an intermediate position of the power source terminal  105  and load terminal  109 , with the lower end disposed at the lower side of the housing  103  so as to be exposed outside, and the portion exposed outside connected to a negative terminal of the battery  104 , and a bimetal  112  made of two long plate members of different metals glued together, with the lower end side connected to the upper end of the intermediate terminal  111  and the upper end side being bent in an L-shape and disposed oppositely to the fusible element  110 . 
     In such constitution, by manipulation of an ignition switch or the like of the vehicle, while a current is flowing in a route of positive terminal of battery  104 , power source terminal  105 , fusible element  110 , load terminal  109 , wire  107  of wire harness  106 , load  108 , and negative terminal of battery  104 , if any abnormality should occur in the load  108  or the wire harness  106  connecting the load  108  and the protective device  101 , and a current exceeding the allowable value should flow in the fusible element  110 , it is heated and melted down. 
     As a result, the circuit is cut off, and the load  108  and wire harness  106  are protected. 
     Or when a large current flows in the fusible element  110  due to some abnormality occurring in the load  108  or the wire harness  106  connecting the load  108  and protective device  101 , if it does not exceed the allowable value, the fusible element  110  is heated by the current flowing in the fusible element  110 , and the bimetal  112  begins to deform. In a specified time after a large current begins to flow in the fusible element  110 , the leading end of the bimetal  112  contacts with the fusible element  110 , and a large short-circuit current flows in the fusible element  110  in a route composed of positive terminal of battery  104 , power source terminal  105 , fusible element  110 , intermediate terminal  111  and negative terminal of battery  104 , so that it is melted down. 
     As a result, if lower than the allowable value, when a certain current flows longer than a preset time, the circuit is cut off, and the wire harness  106  and load  108  are protected. 
     Aside from such protective device  101 , a protective device  121  shown in FIG. 11 is also devised by the present inventor. 
     The protective device  121  shown in FIG. 11 comprises a housing  122  made of insulating resin or the like, a power source terminal  124  buried at one side of the housing  122 , with the lower end portion connected to a positive terminal of a battery  123 , and a load terminal  128  buried at other side of the housing  122 , with the lower end portion connected to a load  127  through a wire  126  composing a wire harness  125 . 
     Moreover, one end of a wire  131  composed of a fusible conductor  129  made of a low melting point metal or the like formed in a U-shape and a heat resistant covering  130  formed to cover the fusible conductor  129  is connected to the upper end of the power source terminal  124 , and other end is connected to the upper end of the load terminal  128 . This wire  131  has a coil  132  made of a shape memory alloy, showing a shape being wound around the wire  131  as shown in FIG. 9 when it is in martensite phase, and returning to the mother phase in a shape of tightening the wire  131  when heated to temperature of 120° C. to 170° C. 
     Further, outside of the housing  122 , there is an external terminal  133  with the upper end connected to one end of the coil  132  and lower end connected to a negative terminal of the battery  123 . 
     In such constitution, by manipulation of an ignition switch or the like of the vehicle, while a current is flowing in a route of positive terminal of battery  123 , power source terminal  124 , fusible element  129  of wire  131 , load terminal  128 , wire  126  of wire harness  124 , load  127 , and negative terminal of battery  123 , if any abnormality should occur in the load  127  or the wire harness  125  connecting the load  127  and the protective device  121 , and a current exceeding the allowable value should flow in the fusible element  129 , it is heated and melted down. 
     As a result, the circuit is cut off, and the load  127  and wire harness  125  are protected. 
     Or when a large current flows in the fusible conductor  129  due to some abnormality occurring in the load  127  or the wire harness  125  connecting the load  127  and protective device  121 , if it does not exceed the allowable value, the fusible conductor  129  is heated by the current flowing in the fusible conductor  129 , and the temperature of the coil  132  climbs up. In a specified time after a large current begins to flow in the fusible conductor  129 , when the temperature of the coil  132  reaches 120° C. to 170° C., the coil  132  is shifted from the martensite phase to the mother phase, and bites into the heat resistant covering  130  softened by heat, an contacts with the fusible conductor  129 , and a large short-circuit current flows in the fusible conductor  129  in a route composed of positive terminal of battery  123 , power source terminal  124 , fusible conductor  129 , coil  132 , external terminal  133  and negative terminal of battery  123 , so that it is melted down. 
     As a result, if lower than the allowable value, when a certain current flows longer than a preset time, the circuit is cut off, and the wire harness  125  and load  127  are protected. 
     In these protective devices  101  and  121 , however, the following problems have been disclosed. 
     First, in the protective device shown in FIG. 10, since flow of large current in the fusible element  110  is detected by using the bimetal  112  gluing two kinds of metals differing in the coefficient of thermal expansion, if the magnitude of the current flowing in the fusible element  110  changes, the bimetal  112  is deformed, and the time until cutting off the circuit varies. 
     Accordingly, in the event of such an abnormality that a large current flows intermittently, the temperature of the fusible element  101  does not rise higher than a certain point, and the protective device  101  may not cut off the circuit appropriately. 
     On the other hand, in the protective device  121  shown in FIG. 11, since flow of large current in the fusible conductor  129  is detected by using the coil  132  made of shape memory alloy, if the magnitude of the current flowing in the fusible conductor  129  changes, the coil  132  is deformed, and the time until cutting off the circuit varies. 
     Accordingly, in the event of such an abnormality that a large current flows intermittently, the temperature of the fusible conductor  129  does not rise higher than a certain point, and the protective device  121  may not cut off the circuit appropriately. 
     Besides, in the protective devices shown in FIG.  10  and FIG. 11, it may be also supposed that the heat reaction time of the thermal deformation conductive members such as bimetal  112  and coil  132  may vary depending on the flowing current. Or, the heat reaction of the thermal deformation conductive members may fail to take place timely in case of abnormality of passing of overcurrent. 
     The invention is devised on the basis of such investigations, and it is hence an object thereof to present a circuit breaker capable of protecting electric parts by cutting off the circuit in a short time and securely in case an abnormal signal is fed into the vehicle. 
     The circuit breaker of the invention comprises a first connection terminal, a second connection terminal, a heat generating part having conductivity disposed between the first connection terminal and second connection terminal, an igniting part igniting depending on a cut-off signal, an expandable elastic member capable of applying a force to the heat generating part so as to be departed from between the first connection terminal and second connection terminal, and a holding part for holding the elastic member in compressed state. Herein, when the heat generating part is positioned between the first connection terminal and second connection terminal while the holding part is compressing the elastic member, the conductive state between the first connection terminal and second connection terminal is maintained, and as the igniting part ignites depending on the cut-off signal and the heat generating part generates heat, when the holding part releases the elastic member, the elastic member applies force to the heat generating part, and the heat generating part is departed from between the first connection terminal and second connection terminal, the conductive state between the first connection terminal and second connection terminal is cut off. 
     In this constitution, when the igniting part ignites by a failure signal from outside, the heat generating part generates heat, and by this heat the holding part is melted. As a result, the compressed elastic member is expanded to kick up the heat generating part, and the electric connection between the first connection terminal and second connection terminal is cut off. As the electric connection between the first connection terminal and second connection terminal is cut off, the circuit is securely cut off in a short time, so that the electric parts can be protected. 
     Herein, the holding part contains a resin part, preferably, and the resin part is melted as the igniting part ignites depending on the cut-off signal and the heat generating part generates heat, so that holding of the conductive part is released quickly. 
     More preferably, the heat generating part, igniting part and elastic member are contained in an outer container, and therefore the constitution is simple and the operation is secure. 
     Specifically, the holding part may be a rivet member coupled to the outer container. 
     In such a case, as the elastic member, a telescopic spring composed of plural slave springs differing diameter disposed concentrically may be preferably used. Since the telescopic spring is fixed to the rivet member in the compressed state, the height direction is lowered as compared with the usual compression spring, so that the circuit breaker may be reduced in size. 
     The holding part may be a resin member having a base part, a frame part coupled to the base part and wound with an elastic member, and a stopping part formed at the end of the frame part and stops the elastic member in a state of compressing the elastic member, so that the external force is not applied to the junction of the first connection terminal, second connection terminal and heating part. 
     In such a case, the outer container has an upper case and a lower case, the upper case covers the lower case, an opening is formed in the lower case, and the resin member wound with the elastic member may be constituted so as to be inserted into the opening. The entire structure may be assembled easily, and after cut-off the circuit, the lower case may be used again only by replacing the resin member and the heating part. 
     On the other hand, a side wall is formed at the end of the heat generating part, and the end of the first connection terminal and the side wall, and the end of the second connection terminal and the side wall may be individually joined with low melting point materials. 
     In such constitution, usually, the conduction between the first connection terminal and second connection terminal is improved by the low melting point material, and in case of abnormality, the low melting point material is melted securely by the heat generation of the heating agent, and the electric connection between the first connection terminal and second connection terminal is cut off by the rotating force of the elastic material. Usually, meanwhile, since rotating force is not applied to the low melting point material, the reliability of junction between the first connection terminal and second connection terminal is enhanced. 
     The low melting point material is preferred to be one selected from the group consisting of Sn, Pb, Zn, Al and Cu. 
     The heat generating part contains the heating agent, and the heating agent is preferred to contain a thermite compound mixing powder of metal oxide and powder of aluminum because the thermite reaction heat can be securely generated by the thermite reaction. 
     In other words, the heat generating part contains the heating agent, and the heating agent contains at least one metal powder selected from the group consisting of B, Sn, Fe, Si, Zr, Ti and Al, and at least one metal oxide selected from the group consisting of CuO, MnO 2 , Pb 3 O 4 , PbO 2 , Fe 3 O 4 , Fe 2 O 3  and Cr 2 O 3 . 
     Further, the heating agent may also contain additives having alumina, bentonite or talc. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view before cut-off along line A—A′ of FIG. 2 of a circuit breaker in an embodiment of the invention. 
     FIG. 2 is a top view of the circuit breaker. 
     FIG. 3 is a sectional view after cut-off of the circuit breaker. 
     FIG. 4 is a diagram showing an example of using a wire coil spring of the circuit breaker. 
     FIG.  5 A and FIG. 5B are diagrams showing examples of using compression spring of the circuit breaker. 
     FIG. 6 is a sectional view before cut-off of a circuit breaker in a second embodiment of the invention. 
     FIG. 7 is a perspective assembly view of the circuit breaker. 
     FIG. 8 is a state diagram of retainer before cut-off of the circuit breaker. 
     FIG. 9 is a state diagram of retainer after cut-off of the circuit breaker. 
     FIG. 10 is a sectional view showing an example of protective device using bimetal. 
     FIG. 11 is a sectional view showing other example of protective device. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, preferred embodiments of the invention are described in detail below. 
     A first embodiment of the invention is described below. 
     In the circuit breaker shown in FIG. 1, a first bus bar  11  of a long plate form is preferably made of copper or copper alloy, and is connected to a battery not shown or the like, and a leading end  13  of the first bus bar  11  is bent downward nearly at right angle. 
     A second bus bar  19  of a long plate form is also preferably made of copper or copper alloy, and is connected to a load not shown or the like, and a leading end  21  of the second bus bar  19  is also bent downward nearly at right angle. 
     Between the first bus bar  11  and second bus bar  19 , there is an outer case  15  of a square lid form having a case bottom  15   a,  and each leading end  16  of the outer case  15  is fixed and connected nearly to the leading ends of the first bus bar  11  and second bus bar  19  so that the relative position between the first bus bar  11  and second bus bar  19  is determined. 
     The outer case  15  is made of an insulating material, more specifically a container made of thermoplastic resin or the like, and near the center of the outer case  15 , a nearly cylindrical case protrusion  17  is formed, with the upper side being opened, and square holes  18  are formed at right and left ends. 
     A cavity  22  is formed in the outer case  15 , and this cavity  22  contains a thermite case  25  disposed oppositely to the case protrusion  17  of the outer case  15  so as to connect between the first bus bar  11  and second bus bar  19 , and this thermite case  25  is filled with a heating agent  27 . The thermite case  25  is preferably made of a material high in thermal conductivity and not melted by heat generation of the heating agent  27 , for example, brass, copper, copper alloy, or stainless steel. The thermite case  25  is formed in a cylindrical or rectangular parallelepiped shape by drawing process. 
     The thermite case  25  is located at a height position nearly equal to the height position of the first bus bar  11  and second bus bar  19 , and regarding the thermite case  25 , further, a left side wall  25   a  and a right side wall  25   b  are formed. 
     The left side wall  25   a  is joined to the leading end  13  of the first bus bar  11  by means of a low melting point metal  23  of which melting point is 200° C. to 300° C. As the low melting point material, solder is preferably used. The right side wall  25   b  is joined to the leading end  21  of the second bus bar  19  through the low melting point metal  23 . Accordingly, the first bus bar  11  and second bus bar  19  can be electrically connected with each other through the low melting point metal  23  and thermite case  25 . 
     As the low melting point metal  23 , at least one metal selected from the group consisting of Sn, Pb, An, Al and Cu is preferably used. 
     The heating agent  27  is a thermite compound composed of powder of metal oxide such as iron oxide (Fe 2 O 3 ) and powder of aluminum, which generates high heat by inducting thermite reaction by heat generation of a lead wire  31 . This thermite compound is sealed in the thermite case  25  which is a metal container to shut off moisture. Instead of iron oxide (Fe 2 O 3 ), chromium oxide (Cr 2 O 3 ) or manganese oxide (MnO 2 ) may be used. 
     The heating agent  27  may be also a mixture composed of at least one metal powder selected from the group consisting of B, Sn, Fe, Si, Zr, Ti and Al, at least one metal oxide selected from the group consisting of CuO, MnO 2 , Pb 3 O 4 , PbO 2 , Fe 2 O 4  and Fe 2 O 3 , and at least one additive selected from the group consisting of alumina, bentonite and talc. By using such heating agent, it is easily ignited by an igniting part  29 , and the low melting point metal  23  can be melted in a short time. 
     At a position confronting the case protrusion  17  in the cavity  22 , the igniting part  29  is disposed in contact with the surface of the thermite case  25 , and the led wire  31  passing through the case protrusion  17  is connected to this igniting part  29 . The igniting part  29  is designed to generated thermite reaction heat in the heating agent  27  by igniting the ignition agent by the heat generated by the current flowing in the lead wire  31  in case of abnormality of vehicle such as collision accident of vehicle. 
     Between the bottom surface of thermite case  25  and case bottom  15   a,  a telescopic spring  34  is disposed as an expandable flexible member. The telescopic spring  34  may be not only thus disposed near the heating agent  27  through the bottom surface of thermite case  25 , but also disposed in direct contact with the heating agent  27  if necessary. 
     This telescopic spring  34  is composed of plural slave springs  34   a  to  34   n  differing in diameter disposed concentrically. In the state before circuit cut-off shown in FIG. 1, the telescopic spring  34  is compressed and fixed to the case bottom  15   a  by a resin-made rivet  35  having heads  35   a,    35   c,  and a body  35   b.    
     In the state after circuit cut-off shown in FIG. 3, when the low melting point metal  23  and rivet  35  are heated and melted by the thermite reaction heat of the heating agent  27 , the plural slave springs  34   a  to  34   n  differing in diameter disposed concentrically are elongated in steps, and the thermite case  25  and igniting part  29  are kicked up. 
     In thus constituted circuit breaker of the embodiment, the operation is described below. 
     Usually, the first bus bar  11  and second bus bar  19  are electrically connected with each other through the low melting point metal  23  and the thermite case  25 , and a current is supplied from the battery to the load (neither shown). 
     If the vehicle collides against an obstacle or tumbles off a cliff or the like, the abnormality of the vehicle is detected by a collision sensor or the like. By detection of such abnormality of vehicle, a current flows into the igniting part  29  through the lead wire  31 . 
     As a result, by heat generation by the current, the igniting part  29  ignites, and the heating agent  27  which is the thermite compound generates thermite reaction heat in the following reaction formula. 
     
       
         Fe 2 O 3 +2Al→Al 2 O 3 +2Fe+386.2 (kcal) 
       
     
     By this thermite reaction heat, the thermite case  25  is heated, and by the heat generation of the heating agent  27  and the heat of the thermite case  25 , the low melting point metal  23  joining the bus bar leading end  13  and the left side wall  25   a  of the thermite case  25 , and the low melting point metal  23  joining the bus bar leading end  21  and the right side wall  25   b  of the thermite case  25  are heated and melted. At the same time, the resin-made rivet  35  compressing and fixing the telescopic spring  34  to the case bottom  15   a  is melted by the same heat. 
     Consequently, as shown in FIG. 3, the plural slave springs  34   a  to  34   n  differing in diameter disposed concentrically are elongated in steps, and the thermite case  25  and igniting part  29  are kicked up. 
     As a result, the electric connection between the thermite case  25  and the first bus bar  11  and second bus bar  19  is cut off. That is, the first bus bar  11  and second bus bar  19  are electrically cut off, and the electric circuit of the vehicle is cut off. 
     Thus, according to the circuit breaker of the embodiment, receiving an input of failure signal from the vehicle, the igniting part  29  ignites, the heating agent  27  induces thermite reaction, and the low melting point metal  23  and rivet  35  are melted by this thermite reaction heat, so that the telescopic spring  34  springs up instantly. 
     Accordingly, the electric circuit of the vehicle can be cut off securely in a short time, and the electric parts can be protected. Moreover, by using the thermite reaction heat of the heating agent  27 , the circuit breaker in a simple structure can be presented. 
     Moreover, since spring force is not applied to the low melting point metal  23  at the junction of the first bus bar  11 , second bus bar  19  and thermite case  25 , the reliability of the junction can be enhanced. 
     Further, using the telescopic spring  34  as the spring member, since the resin-made rivet  35  is fixed in the compressed state of the telescopic spring  34 , the height direction can be lowered as compared with the constitution of using the ordinary compression spring, so that the circuit breaker can be reduced in size. 
     In the first embodiment, using the telescopic spring  34  and low melting point metal  23 , the circuit is cut off when the rivet  35  and low melting point metal  23  are melted, but without using low melting point metal  23 , only the telescopic spring  34  may be provided, and the circuit may be cut off when the rivet  35  is melted. 
     As the elastic member, the telescopic spring  34  winding leaf springs is used, but instead of the telescopic spring  34 , a coil spring  37  winding a wire spirally as shown in FIG. 4 may be also used. 
     Or, by using a spiral compression spring  39  as shown in FIG. 5A instead of the telescopic spring  34 , this compression spring  39  may be put in the outer case  15  as shown in FIG. 5B, and compressed by a disk  41  made of resin member. In such a case, too, when the rivet  35  is melted, the thermite case  25  is kicked up by the spring force of the compression spring  39 . 
     The resin-made rivet  35  for fixing the telescopic spring  34  may be formed integrally with the case bottom  15   a.    
     A circuit breaker in a second embodiment of the invention is described below. 
     As shown in FIG.  6  and FIG. 7, in the circuit breaker of the embodiment, an extension  50  having a square groove  51  is formed inn a cap  14   a,  and a wedge-shaped stopping part  55  is formed in a resin case  14   b,  and as the stopping part  55  fits into the groove  51 , the cap  14   a  covers the resin case  14   b.  The cap  15   a  and resin case  14   b  are containers of insulating material, preferably made of thermoplastic resin. 
     In an opening  53  formed in the resin case  14   b,  a cylindrical thermite case  26  is placed, and this thermite case  26  contains a heating agent  27  and an igniting part  29  having a lead wire  31 , and an upper lid  24  is put on the heating agent. 
     A first bus bar  11   a  having a round hole  12  and a second bus bar  19   a  having a round hole  20  are bent upward nearly at right angle, and the bend portions pass through the resin case  14   b,  and bus bar leading ends  13   a,    16   a  contact with right and left side walls of the thermite case  26  through the low melting point metal  23 . 
     The right and left side walls of the thermite case  26  are joined to the bus bar leading ends  13   a,    16   a  through the low melting point metal  23 , and the first bus bar  11   a  and second bus bar  19   a  are connected with each other electrically through the low melting point metal  23  and thermite case  26 . 
     In the lower part of the thermite case  26  within the opening  53  of the resin case  14   b,  there is a retainer  45  made of a resin member which is melted by heat generation of the heating agent  27 . This retainer  45  is composed of, as shown in FIG. 8, a base part  61 , a notch  54  formed in this base part  61 , a retainer frame  65  planted on the notch  63  and base part  61 , and a retainer stopper  67  formed at the leading end of the retainer frame  65 . 
     Outside of the retainer frame  65 , a compression spring  39   a  winding the retainer frame  65  spirally is disposed, and the leading end of this compression spring  39   a  is stopped by the retainer stopper  67 . That is, the compression spring  39   a  is fitted into the retainer  45  in the compressed state. 
     A part of the retainer frame  65  is disposed in contact with the thermite case  26 , and the hook of the retainer stopper  67  is engaged with the resin case  14   b.    
     In the circuit breaker of this embodiment, the same parts as in the circuit breaker of the first embodiment are identified with same reference numerals, and their detailed description is omitted. 
     In thus constituted circuit breaker of the second embodiment, the operation is explained below by referring to the accompanying drawings. 
     Usually, the first bus bar  11   a  and second bus bar  19   a  are electrically connected with each other through the low melting point metal  23  and the thermite case  26 , and a current is supplied from the battery to the load (neither shown). 
     If the vehicle collides against an obstacle or tumbles off a cliff or the like, the abnormality of the vehicle is detected by a collision sensor or the like. By detection of such abnormality of vehicle, a current flows into the igniting part  29  through the lead wire  31 . 
     As a result, by heat generation by the current, the igniting part  29  ignites, and the heating agent  27  generates thermite reaction heat. By this thermite reaction heat, the thermite case  26  is heated, and by the heat generation of the heating agent  27  and the heat of the thermite case  26 , the low melting point metal  23  is heated and melted. 
     At the same time, the resin-made retainer stopper  67  having the compression spring  39   a  compressed and fixed to the retainer  45  is melted by the same heat. Consequently, as shown in FIG. 9, the compression spring  39   a  is elongated, and the thermite case  26  is kicked up. 
     Accordingly, the electric connection between the thermite case  26  and the first bus bar  11   a  and second bus bar  19   a  is cut off. That is, the electric circuit of the vehicle is cut off. 
     Thus, according to the circuit breaker of this embodiment, too, the same effects as in the circuit breaker of the first embodiment are obtained. 
     Moreover, since the compression spring  39   a  is held by the retainer  45 , external force is not applied to the junction of the first bus bar  11   a,  second bus bar  19   a  and thermite case  26 . 
     Still more, since the sub-assembly of the compression spring  39   a  and retainer  45  are inserted from the lower side, that is, from the lower side of the opening  53  of the resin case  14   b,  the circuit breaker can be assembled easily. 
     After the circuit is cut off, only by replacing the retainer  45  and thermite case  26 , the resin case  14   b  can be recycled and used as fuse. 
     In the second embodiment, using the compression spring  39   a  and low melting point metal  23 , the circuit is cut off when the retainer  45  and low melting point metal  23  are melted, but without using the low melting point metal  23 , only the retainer  45  may be provided, and the circuit may be cut off when the retainer  45  is melted. 
     Besides, these embodiments may be further changed and modified in various forms without departing from the technical scope of the invention.