Circuit breaker

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.

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.degree. C. to 170.degree. 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.degree. C. to 170.degree. 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.sub.2, Pb.sub.3
 O.sub.4, PbO.sub.2, Fe.sub.3 O.sub.4, Fe.sub.2 O.sub.3 and Cr.sub.2
 O.sub.3.
 Further, the heating agent may also contain additives having alumina,
 bentonite or talc.

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 26a 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 26b 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
 15a is formed in this outer case 15, and a thermite compartment 16 for
 accommodating the thermite case 25 is formed in this case step 15a. 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 25a as a conducting part
 with a protruding upper side as shown in FIG. 2 and FIG. 3, and this
 thermite protrusion 25a is a cylindrical form cut off at a specific width,
 and is composed of a linear longitudinal portion 28a and short arc
 portions 28b at its both ends.
 The vertical position of the upper side of the thermite protrusion 25a 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 29a is
 longer than the bus bar leading ends 13, 21, so that the upper surface 25c
 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
 25b 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 15a as second triangular rotation stopping
 parts to be respectively engaged with the thermite grooves 25b. The
 rotation blocking parts 17 stop rotation of the thermite case 25 having
 the thermite protrusion 25a 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 29a. The igniting agent case 29a 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 33a of the coil spring 33 is
 fixed to a winding start fixing portion 35a of the igniting part 29, and a
 winding end portion 33b of the coil spring 33 is fixed to a winding end
 fixing portion 35b of the outer case 15. The winding end fixing portion
 35b is a long groove formed in the outer case 15, and the winding end
 portion 33b 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.sub.2 O.sub.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.sub.2
 O.sub.3), chromium oxide (Cr.sub.2 O.sub.3) or manganese oxide (MnO.sub.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.sub.2, Pb.sub.3 O.sub.4, PbO.sub.2, Fe.sub.2 O.sub.4 and Fe.sub.2
 O.sub.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 28b
 formed in the thermite protrusion 25a 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.
EQU Fe.sub.2 O.sub.3 +2Al.fwdarw.Al.sub.2 O.sub.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 26a of the thermite case 25, and the low melting point
 metal 23 joining the bus bar leading end 21 and the right side wall 26b of
 the thermite case 25 are heated and melted. At the same time, the rotation
 blocking part 17 formed in the case step 15a 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 25a also rotates about 90 degrees in
 the counterclockwise direction, the short portions 28b 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 25b 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 25a is as shown in
 FIG. 1, and after rotation of the coil spring, the thermite protrusion 25a
 is as shown in FIG. 4. Besides, the invention may be further changed and
 modified in various forms within the technical scope thereof.