Abstract:
The circuit breaker disclosed in the invention comprises a first connection terminal, a second connection terminal, a rotatable conducting part disposed between the first connection terminal and second connection terminal, a heat generating part, an igniting part igniting depending on a cut-off signal, an elastic member capable of producing a rotating force, and a holding part for holding the conducting part while resisting the rotating force of the elastic member. Herein, when the holding part releases holding of the conducting part as the igniting part ignites depending on the cut-off signal and the heat generating part generates heat, the conducing part is rotated by the rotating force of the elastic member, and 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 inventor, a protective device as shown in FIG. 8 is considered. 
     FIG. 8 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-shaped 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. 9 is also devised by the present inventor. 
     The protective device  121  shown in FIG. 9 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. 8, 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. 9, 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.  8  and FIG. 9, 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 rotatable conducting part disposed between the first connection terminal and second connection terminal, a heat generating part, an igniting part igniting depending on a cut-off signal, an elastic member capable of producing a rotating force and free to expand and contract, and a holding part for holding the conducting part while resisting the rotating force of the elastic member. Herein, when the holding part is holding the conducting part, the conductive state between the first connection terminal and second connection terminal is maintained, and when the holding part releases holding of the conducting part as the igniting part ignites depending on the cut-off signal and the heat generating part generates heat, the conducing part is rotated by the rotating force of the elastic member, and 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 immediately releases holding of the conducting part. As a result, the conducting part is rotated by the rotating force of the elastic member, and the conduction 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 conducting part, heat generating part and igniting part are integrally contained in an outer container, and therefore the constitution is simple and the operation is secure. 
     Specifically, the holding part has a first rotation stopping part formed in the heating part, and a second rotation stopping part engaged with the first rotation stopping part and formed on the outer container, and at least one rotating stopping part of the first rotation stopping part and second rotation stopping part has a resin part. 
     More specifically, the elastic member is a coil spring, and one end of the coil spring is fixed to the igniting part, while the other end of the coil spring is fixed to the outer container. 
     The conducting part is a protrusion having a longitudinal part, and the longitudinal part connects between the first connection terminal and second connection terminal, so that the conductive state between the first connection terminal and second connection terminal is maintained, and when the longitudinal part is rotated by the rotating force of the elastic member and does not connect between the first connection terminal and second connection terminal, the conductive state between the first connection terminal and second connection terminal is cut off, which is also preferable for simple constitution and secure action. 
     Herein, the longitudinal part is preferred to be rotated by about 90 degrees by the rotating force of the elastic member, so that the circuit may be cut off securely. 
     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 of a circuit breaker in an embodiment of the invention. 
     FIG. 2 is a top view before cut-off of the circuit breaker. 
     FIG. 3 is a diagram showing the rotation locking part and its surrounding structure of the circuit breaker. 
     FIG. 4 is a sectional view of A—A of FIG.  1 . 
     FIG. 5 is a sectional view after cut-off of the circuit breaker in the embodiment of the invention. 
     FIG. 6 is a top view after cut-off of the circuit breaker. 
     FIG. 7 is a sectional view of B—B of FIG.  5 . 
     FIG. 8 is a sectional view showing an example of protective device using bimetal. 
     FIG. 9 is a sectional view showing other example of protective device. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, a preferred embodiment of the invention is described in detail below. 
     In the circuit breaker shown in FIG. 1, a first bus bar  11  of a long plate form is made of copper or copper alloy, and a round hole  12  to be connected to a battery or the like is formed in this first bus bar  11 . 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 made of copper or copper alloy, and a round hole  20  to be connected to a load or the like is formed in this second bus bar  19 . 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 , a thermite case  25  is disposed as a heating unit filled with a heating agent  27 , and a left side wall  26   a  of this termite case  25  is joined to the leading end  13  of the first bus bar  11  by means of a low melting point metal  23  as soldering material (melting point about 200 to 300 degrees). However of course, it is not limited to soldering material as far as the melting point is low and the connection strength is sufficient. 
     A right side wall  26   b  of the thermite case  25  is joined to the leading end  21  of the second bus bar  19  by means of 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 . 
     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 put in an outer case  15  as an outer container, and a case step  15   a  is formed in this outer case  15 , and a thermite compartment  16  for accommodating the thermite case  25  is formed in this case step  15   a . The outer case  15  is a container made of insulating material, and a thermoplastic resin may be preferably used. 
     The thermite case  25  has a thermite protrusion  25   a  as a conducting part with a protruding upper side as shown in FIG.  2  and FIG. 3, and this thermite protrusion  25   a  is a cylindrical form cut off at a specific width, and is composed of a linear longitudinal portion  28   a  and short arc portions  28   b  at its both ends. 
     The vertical position of the upper side of the thermite protrusion  25   a  is nearly same as the vertical position of the first bus bar  11  and second bus bar  19 , and the vertical length of the thermite protrusion  29   a  is longer than the bus bar leading ends  13 ,  21 , so that the upper surface  25   c  of the thermite case  25  may not contact with the bus bar leading ends  13 ,  21 . 
     Near the outer circumference of the thermite case  25 , two thermite grooves  25   b  are formed at positions different by about 180 degrees from each other as first concave rotation stopping parts, and rotation blocking parts  17  are formed in the case step  15   a  as second triangular rotation stopping parts to be respectively engaged with the thermite grooves  25   b . The rotation blocking parts  17  stop rotation of the thermite case  25  having the thermite protrusion  25   a  and an igniting part  29  in the outer case  15 . 
     Alternatively, the rotation blocking part  17  maybe formed as a groove, and the protrusion to be engaged with this groove may be formed in the thermite case  25 , so that the rotation may be stopped in the thermite case  25  and the outer case  15  of the igniting part  29  described below. This protrusion may be formed integrally with the thermite case  25 , or may be formed as a separate part made of resin. 
     In the lower part of the thermite case  25 , there is the igniting part  29  containing an igniting agent case  29   a . The igniting agent case  29   a  is coupled with the thermite case  25  by crimping with screw. They may be also coupled by crimping and welding, or by welding alone. The igniting part  29  is contained in the outer case  15 , and has the igniting agent, and the igniting agent is ignited by heat generation caused by the current flowing in a lead wire  31  in case of abnormality of vehicle such as vehicle collision accident, and a thermite reaction heat is generated in the heating agent  27 . 
     The igniting part  29  and the outer case  15  are linked with a coil spring  33  as a spiral elastic member free to expand and contract as shown in FIG.  3  and FIG.  4 . 
     In the state before circuit cut-off as shown in FIG. 4, with the coil spring  33  compressed, a winding start portion  33   a  of the coil spring  33  is fixed to a winding start fixing portion  35   a  of the igniting part  29 , and a winding end portion  33   b  of the coil spring  33  is fixed to a winding end fixing portion  35   b  of the outer case  15 . The winding end fixing portion  35   b  is a long groove formed in the outer case  15 , and the winding end portion  33   b  of the coil spring  33  is inserted in this long groove. 
     Since the coil spring  33  is in compressed state, it has a rotating force in the clockwise direction in FIG.  4 . In order to stop rotation of the igniting part  29  and thermite case  25  by the rotating force of the coil spring  33 , the rotating blocking part  17  is provided. 
     In the state after cut-off of the circuit, as shown in FIG. 7, the coil spring  33  is rewound about 90 degrees in the clockwise direction, and by rewinding of the coil spring  33 , as shown in FIGS. 5 and 6, the thermite case  25  and the igniting part  29  rotate about 90 degrees in the clockwise direction. 
     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 the led wire  31 . As the metal oxide, 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 the igniting part  29 , and the low melting point metal  23  can be melted in a short time. 
     In thus constituted circuit breaker of the embodiment, the operation is described below. 
     Usually, as shown in FIG. 4, the coil spring  33  is in compressed state, and in this compressed state, as shown in FIG. 2, the short portions  28   b  formed in the thermite protrusion  25   a  are electrically connected with the first bus bar  11  and second bus bar  19  through the low melting point metal  23 , and therefore, the 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  26   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  26   b  of the thermite case  25  are heated and melted. At the same time, the rotation blocking part  17  formed in the case step  15   a  of the outer case  15  is melted by heat. 
     Consequently, the coil spring  33  is rewound about 90 degrees in the counterclockwise direction as shown in FIG. 7, and by this rewinding, as shown in FIG.  5  and FIG. 6, the thermite case  25  and igniting part  29  rotate about 90 degrees in the counterclockwise direction. 
     That is, since the thermite protrusion  25   a  also rotates about 90 degrees in the counterclockwise direction, the short portions  28   b  no longer contact with the first bus bar  11  and second bus bar  19 . 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, 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 the rotation blocking part  17  arrests the rotating force of the coil spring  33 , spring force of the coil spring  33  is not applied to the low melting point metal  23  at the junction of the first bus bar  11  and second bus bar  19  and the thermite case  25 , so that the reliability of the junction may be enhanced. 
     Still more, using the coil spring  33 , as compared with the compression spring expanding and contracting in the height direction (vertical direction), the size in the height direction can be reduced, so that the circuit breaker can be reduced in size. 
     The invention is not limited to the illustrated embodiment alone. In this embodiment, comprising the coil spring  33 , rotation blocking part  17  and low melting point metal  23 , the circuit is cut off when the rotation blocking part  17  and low melting point metal  23  are melted, but, for example, without using the low melting point metal  23 , only the rotating blocking part  17  may be provided, and the circuit may be cut off when the rotating block part  17  is melted. 
     In the embodiment, the thermite groove  25   b  is concave, and the rotating blocking part  17  is convex, but, for example, a trapezoidal or semicircular thermite groove or rotating blocking part may be used. As far as the structure is designed to stop rotation of the thermite case  25 , the shape of the thermite groove and rotating blocking part is arbitrary. 
     Also in the embodiment, the coil spring  33  is applied on the outer case  15  and igniting part  29 , but the coil spring  33  may be applied on the outer case  15  and the thermite case  25 . 
     Or, in the embodiment, as the coil spring  33 , a spring having a rotating force when compressed is used, but a spring having a rotating force when expanded may be also used as the coil spring. In this case, when the coil spring is in expanded state, the thermite protrusion  25   a  is as shown in FIG. 1, and after rotation of the coil spring, the thermite protrusion  25   a  is as shown in FIG.  4 . Besides, the invention may be further changed and modified in various forms within the technical scope thereof.