Circuit breaker

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a circuit breaker for breaking an electric circuit for a short time.

2. Description of the Related Art

In an electrical equipment system provided in a vehicle, when a certain abnormality is generated in a load such as a power window or the like or a certain abnormality is generated in a wire harness or the like constituted by a plurality of electric wires for connecting a battery to respective loads, a great current fuse interposed between the battery and the wire harness is melted and broken so as to break a communication between the battery and the wire harness, thereby preventing the respective loads, the wire harness or the like from being burned out.

However, in the electric equipment system using the great current fuse mentioned above, since the great current fuse is melted out and broken only when a current equal to or more than a predetermined allowable value flows through the great current fuse, even in the case that a certain abnormality is generated in the load such as the power window or the like or a certain abnormality is generated in the wire harness or the like for connecting the battery to the respective loads, there is a case that the circuit can not be broken and the various loads, the wire harness or the like can not be protected.

SUMMARY OF THE INVENTION

The present invention has been made by taking the matters mentioned above into consideration. Accordingly, an object of the present invention is to provide a circuit breaker which can protect electric parts by securely breaking a circuit for a short time.

Another object of the present invention is to provide a circuit breaker which can securely break a circuit for a short time even in the case that an abnormality signal is not sent due to a trouble of a control portion or the like.

In order to achieve the objects mentioned above, according to a first aspect of the present invention, there is provided a circuit breaker comprising: a heating portion charged with heating agent and having a conductivity, the heating portion being arranged between a first connecting terminal connected to a power source side and a second connecting terminal connected to a load side, and the heating portion being brought into contact with each of the first connecting terminal and the second connecting terminal; an ignition portion for causing the heating agent charged in the heating portion to generate heat by igniting an ignition agent; an expandable/contractable elastic member arranged near the heating portion or in contact with the heating portion and pressing the heating portion; an outer container receiving the elastic member, the ignition portion and the heating portion; a pressing operation restricting member preventing the elastic member from being pressed to the heating portion, the pressing operation restricting member being melted due to heat of the heating agent; and a heat conduction member bringing any one of the first connecting terminal and the second connecting terminal into contact with the ignition portion, wherein the circuit breaker normally supplies a current from the power source to the load, and the circuit breaker breaks a circuit from the power source to the load when the vehicle is abnormal.

In accordance with the invention mentioned above, when an excessive current flows through the first connecting terminal and the second connecting terminal, a temperature of the connecting terminals is increased due to the excessive current, a heat in one connecting terminal is conducted to the ignition portion via the heat conduction member and the ignition portion is ignited due to the heat. Then, the heating agent charged in the heating portion generates heat, the pressing operation restricting member is melted due to the heat and the elastic member is expanded so as to jump up the heating portion, whereby the electric connection between the heating portion, and the first connecting terminal and the second connecting terminal is broken, so that it is possible to securely break the circuit for a short time.

In accordance with a second aspect of the present invention, as it depends from the first aspect, the ignition portion ignites the ignition agent on the basis of an abnormality signal input from a control portion provided in an outer portion at a time of the abnormality of the vehicle so that the heating agent generates heat.

In accordance with the invention mentioned above, since the ignition portion ignites the ignition agent on the basis of the abnormality signal input from the control portion provided in the outer portion at a time of the abnormality of the vehicle such that the heating agent generates heat, it is possible to securely break the circuit for a short time also by an input of the abnormality signal. Further, even in the case that the circuit can not be broken since the abnormality signal is not input to the ignition portion due to the trouble in the control portion or the like, it is possible to securely break the circuit for a short time due to the temperature of one connecting terminal and it is possible to protect the electric parts.

In accordance with a third aspect of the present invention, as it depends from the first or the second aspect, the ignition portion has a pair of ignition portion terminals, a resistance provided between the pair of ignition portion terminals and the ignition agent arranged near or in contact with the resistance; one of the pair of ignition portion terminals is brought into contact with one end of the heat conduction member; another ignition portion terminal is connected to the control portion; and another end of the heat conduction member is brought into contact with the one connecting terminal.

In accordance with the invention mentioned above, since the temperature of the first connecting terminal is increased due to the excessive current and the heat due to the temperature increase is conducted to the first connecting terminal, the heat conduction member, one ignition portion terminal, the resistance and the ignition agent, it is possible to ignite the ignition agent due to the heat. Further, since another ignition portion terminal is connected to the control portion, the abnormality signal from the control portion is sent to the resistance via another ignition portion terminal and the ignition agent can be ignited due to the heat generation of the resistance.

In accordance with a fourth aspect of the present invention, as it depends from one aspect among the first aspect to the third aspect, the control portion has an electromagnetic coil through which an exciting current flows on the basis of the abnormality signal; and the control portion further has a switch having one end connected to the another ignition portion terminal and another end which is grounded, thereby the switch is turned on due to the exciting current.

In accordance with the invention mentioned above, in the control portion, when the exciting current flows through the electromagnetic coil on the basis of the abnormality signal, the switch is turned on due to the exciting current. Accordingly, the current flows from the power source along a path of the first connecting terminal, the heat conduction member, one ignition portion terminal, the resistance, another ignition portion terminal, the switch and the earth, so that it is possible to ignite the ignition agent due to the heat generation of the resistance and it is possible to break the circuit by using the power source provided in the connecting terminal side.

In accordance with a fifth aspect of the present invention, as it depends from one aspect among the first aspect to the fourth aspect, the pressing operation restricting member mounts the elastic member in a compression state and is freely attached to and detached from the outer container; the pressing operation restricting member is arranged near or in contact with the heating portion when being mounted to the outer container; and the pressing operation restricting member is an attaching and detaching member which is melted due to heat of the heating agent.

In accordance with the invention mentioned above, the attaching and detaching member mounting the expandable/contractable elastic member in a compression state is arranged near or in contact with the heating portion when being mounted to the outer container. When the ignition portion is ignited, the heating agent charged in the heating portion generates heat, and the attaching and detaching member is melted due to the heat. Since the elastic member is expanded so as to jump up the heating portion, it is possible to securely break the circuit for a short time so as to protect the electric parts. Further, since the attaching and detaching member is structured such as to be freely attached to and detached from the outer container, it becomes easy to attach and detach the attaching and detaching member. Further, since the elastic member is held by the attaching and detaching member, no external force is applied to the connection portion between the first connecting terminal and the second connecting terminal, and the heating portion.

In accordance with a sixth aspect of the present invention, as it depends from one aspect among the first aspect to the fifth aspect, a side wall portion is formed in an end portion of the heating portion; and respective front end portions of the first connecting terminal and the second connecting terminal are bonded to the side wall portion by a material having a low melting point.

In accordance with the invention mentioned above, since the respective front end portions of the first connecting terminal and the second connecting terminal are bonded to the side wall portion by the material having a low melting point, the heating portion is jumped up when the pressing operation restricting member and the member having a low melting point are melted due to the heat generation of the heating agent, whereby an electric connection between the first connecting terminal and the second connecting terminal is broken. Accordingly, it is possible to securely break the circuit for a short time so as to protect the electric parts. Further, since no spring force is applied to the material having a low melting point corresponding to the connecting portion between the first connecting terminal and the second connecting terminal, and the heating portion, it is possible to improve a reliability of the connecting portion.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

FIG. 1

is a cross-sectional view showing an embodiment of a protecting apparatus employing a bimetal in accordance a first embodiment;

FIG. 2

is a cross-sectional view showing another embodiment of a protecting apparatus according to a second embodiment;

FIG. 3

is a perspective view of a fusible conductor for a fusible link;

FIG. 4

is a cross-sectional view of a circuit breaker according to a third embodiment before being broken;

FIG. 5

is a perspective view of an assembly of the circuit breaker;

FIG. 6

is a detailed view of a heat conduction terminal provided in the circuit breaker and a peripheral portion thereof;

FIG. 7

is a circuit diagram of a control portion connected to the circuit breaker;

FIG. 8

is a state view of a retainer of the circuit breaker before being broken; and

FIG. 9

is a state view of the retainer of the circuit breaker after being broken.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will be given below of a first embodiment according to the present invention with reference to FIG.

1

.

FIG. 1

is a cross-sectional view showing an embodiment of a protecting apparatus employing a bimetal among protecting apparatuses. The protecting apparatus shown in

FIG. 1

is provided with a housing

103

constituted by insulating resin or the like and having a fuse receiving portion

102

formed in an upper portion side, a lid

113

closing the fuse receiving portion

102

of the housing

103

so as to freely open and close, a power source terminal

105

arranged in a lower side of the housing

103

such that an upper end portion is protruded into the fuse receiving portion

102

and a lower end is exposed externally, the portion exposed externally being connected to a plus terminal of a battery

104

, a load terminal

109

arranged in the lower side of the housing

103

such that an upper end portion is protruded into the fuse receiving portion

102

and a lower end is exposed externally, the portion exposed externally being connected to a load

108

via an electric wire

107

constituting a wire harness

106

, a fusible body

110

constituted by metal having a low melting point or the like arranged within the fuse receiving portion

102

, having one end connected to an upper end of the power source terminal

105

and another end connected to an upper end of the load terminal

109

, an intermediate terminal

111

arranged in the lower side of the housing

103

so as to be disposed at an intermediate position between the power source terminal

105

and the load terminal

109

and to be exposed externally at a lower end, the portion exposed externally being connected to a minus terminal of the battery

104

, and a bimetal

112

constituted by an elongated sheet member obtained by sticking two kinds of metals with each other, and arranged such that a lower end side is connected to an upper end of the intermediate terminal

111

and an upper end side is bent in an L shape so as to oppose to the fusible body

110

.

Then, in the case that an ignition switch or the like of a vehicle is operated, and current flows along a path comprising the plus terminal of the battery

104

, the power source terminal

105

, the fusible body

110

, the load terminal

109

, the electric wire

107

of the wire harness

106

, the load

108

and the minus terminal of the battery

104

, when a certain abnormality is generated in the load

108

or the wire harness

106

connecting the load

108

to the protecting apparatus

101

and the current equal to or more than an allowable value flows through the fusible body

110

, the fusible body is melted and broken due to the heat generation, thereby protecting the load

108

, the wire harness

106

and the like.

Further, even in the case that a certain abnormality is generated in the load

108

or the wire harness

106

connecting the load

108

to the protecting apparatus

101

and a great current flows through the fusible body

110

, when the current is not over the allowable value, the fusible body

110

generates heat due to the current flowing through the fusible body

110

and the bimetal

112

starts deforming. Then, at a time when a predetermined time has elapsed after the great current starts flowing through the fusible body

110

, the front end of the bimetal

112

is brought into contact with the fusible body

110

, a great short circuiting current flows through the fusible body

110

along the path comprising the plus terminal of the battery

104

, the power source terminal

105

, the fusible body

110

, the intermediate terminal

111

and the minus terminal of the battery

104

, so that the fusible body

110

is melted and broken.

Accordingly, even when the current equal to or less than the allowable value flows for a time equal to or more than the predetermined time, the circuit is broken and the wire harness

106

and the load

108

are protected.

Next, a description will be given of a second embodiment with reference to FIG.

2

.

A protecting apparatus

121

shown in

FIG. 2

is provided with a housing

122

constituted by insulating resin or the like, a power source terminal

124

installed in one side surface side of the housing

122

and connected to a plus terminal of a battery

123

in a lower end portion, a load terminal

128

installed in another side surface side of the housing

122

and having a lower end portion connected to a load

127

via an electric wire

126

constituting a wire harness

125

, an electric wire

131

constituted by a fusible conductive wire

129

obtained by forming metal having a low melting point in a U shape and a heat resisting coat

130

formed so as to cover the fusible conductive wire

129

, one end being connected to an upper end of the power source terminal

124

and another end being connected to an upper end of the load terminal

128

, a coil

132

constituted by a shape-memory alloy formed in a shape wound around the electric wire

131

as shown in

FIG. 2

under a martensite phase and returning to a base phase in a shape of fastening the electric wire

131

when heated to a temperature between120° C. and 170° C., and an external terminal

133

provided in an outer portion of the housing

122

and having an upper end connected to one end of the coil

132

and a lower end connected to the minus terminal of the battery

123

.

Then, in the case that an ignition switch or the like of a vehicle is operated, and current flows along a path comprising the plus terminal of the battery

123

, the power source terminal

124

, the fusible body

129

of the electric wire

131

, the load terminal

128

, the electric wire

126

of the wire harness

125

, the load

127

and the minus terminal of the battery

123

, when a certain abnormality is generated in the load

127

or the wire harness

125

connecting the load

127

to the protecting apparatus

121

and the current equal to or more than an allowable value flows through the fusible body

129

, the fusible body is melted and broken due to the heat generation, thereby protecting the load

127

, the wire harness

125

and the like.

Further, even in the case that a certain abnormality is generated in the load

127

or the wire harness

125

connecting the load

127

to the protecting apparatus

121

and a great current flows through the fusible conductive wire

129

, when the current is not over the allowable value, the fusible conductive wire

129

generates heat due to the current flowing through the fusible conductive wire

129

and the temperature of the coil

132

is increased. Then, at a time when a predetermined time has elapsed after the great current starts flowing through the fusible conductive wire

129

and the temperature of the coil

132

is increased to a temperature between 120° C. and 170 °C., the coil

132

transits from the martensite phase to the base phase, eats into the heat resisting coat

130

softened due to the heat, and is brought into contact with the fusible conductive wire

129

, and a great short circuiting current flows through the fusible conductive wire

129

along the path comprising the plus terminal of the battery

123

, the power source terminal

124

, the fusible conductive wire

129

, the coil

132

, the external terminal

133

and the minus terminal of the battery

123

, so that the fusible conductive wire

129

is melted and broken.

Accordingly, even when the current equal to or less than the allowable value flows for a time equal to or more than the predetermined time, the circuit is broken and the wire harness

125

and the load

127

are protected.

Further,

FIG. 3

is a perspective view of a fusible conductor for a fusible link. The fusible conductor

201

for the fusible link is structured such that a fusible conductor piece

203

made of metal having a low melting point is held in an intermediate portion of a fusible conductor main body

202

made of metal having a high melting metal via a gripping piece

202

a,

thereby improving a melting property due to generation of an alloy according to a diffusion of the metal having a low melting point.

In accordance with the structure mentioned above, when an excessive current flows through the fusible conductor main body

202

, the melting of the fusible conductor piece

203

is generated due to the heat of generation, whereby it is possible to melt down and break the fusible conductor

201

.

However, in the conventional protecting apparatuses

101

and

121

mentioned above, there are problems mentioned below.

At first, in the protecting apparatus shown in

FIG. 1

, since it is detected by using the bimetal

112

obtained by sticking two kinds of metals having different coefficients of thermal expansion to each other whether or not a great current flows through the fusible body

110

, the bimetal

112

is deformed when a magnitude of the current flowing through the fusible body

110

is changed, so that a time required for breaking the circuit is changed.

Accordingly, when a trouble that a great current intermittently flows is generated, the temperature of the fusible body

110

is increased only to a certain degree, so that there is a risk that the wire harness

106

, the load

108

or the like starts burning before the protecting apparatus

101

breaks the circuit.

On the contrary, the protecting apparatus

121

shown in

FIG. 2

, since it is detected by using the coil

132

constituted by the shape-memory alloy whether or not a great current flows through the fusible conductive wire

129

, the coil

132

is deformed when the magnitude of the current flowing through the fusible conductive wire

129

is changed, so that a time required for breaking the circuit is changed.

Accordingly, when a trouble that a great current intermittently flows is generated, the temperature of the fusible conductive wire

129

is increased only to a certain degree, so that there is a risk that the wire harness

125

, the load

127

or the like is excessively heated before the protecting apparatus

121

breaks the circuit.

Further, in the protecting apparatus shown in

FIGS. 1 and 2

, the thermal reaction time of the bimetal

112

and the coil

132

corresponding to the heat deforming conductive member is affected by an energizing current. Further, there is a case that the thermal reaction of the heat deforming conductive member is not timely operated at a time of abnormality (an excessive current flow).

Further, in the fusible conductor

201

shown in

FIG. 3

, since a time of diffusing the metal having a low melting point into a copper alloy is affected by the energizing current and a lot of time is required for diffusing the metal having a low melting point, there is a case that the fusible conductor does not operate timely at a time of abnormality (an excessive current flow).

Then, as a circuit breaker timely operating at a time of abnormality (an excessive current flow), the applicant of the present invention filed a circuit breaker described in Japanese Patent Application No. 11-64055 (which was filed on Mar.10, 1999 and has not been laid open). The circuit breaker is schematically structured such as to provide a pair of connection terminals constituted by a battery connection terminal (for example, a bus bar) and a load connection terminal, provide a conductive member (for example, a thermit case) electrically brought into contact with each of the pair of connection terminals, move the conductive member upward by a compression spring or the like in response to the abnormality signal input from the control circuit or the like at a time when the vehicle is abnormal, and shut an electrical connection between one connection terminal and another connection terminal so as to break the circuit.

However, in this circuit breaker, there is a problem that it is impossible to break the circuit in the case that the abnormality signal is not sent to the circuit breaker because a wire breaking is generated in the control circuit or the like or the current sensor or the like is broken.

Taking the matter mentioned above into consideration, the applicant of the present invention provides an improvement of a circuit breaker which can securely break the circuit for a short time so as to protect the electrical parts, and securely break the circuit for a short time even in the case that an abnormality signal is not sent due to a trouble of the control portion or the like. A description will be in detail given below of the apparatus as a third embodiment with reference to

FIGS. 4

to

9

.

The circuit breaker according to the third embodiment is particularly characterized in that the circuit is broken due to a heat generated by a temperature increase of the bus bar in response to an excessive current even in the case that the circuit can not be broken because the abnormality signal is not input to the ignition portion due to the trouble in the control portion or the like.

In the circuit breaker shown in

FIG. 4

, a plate-like long first bus bar

11

a

is made of, for example, copper or copper alloy, and is connected to a battery

1

. Further, a plate-like long second bus bar

19

a

is also made of, for example, copper or copper alloy, and is connected to a load (not shown) or the like.

In

FIG. 5

, an extended portion

50

having a rectangular groove portion

51

is formed in a cap

14

a,

and a wedge-like engaging portion

55

is formed in a resin case

14

b,

so that the structure is made such that the engaging portion

55

is fitted to the groove portion

51

, whereby the cap

14

a

is covered on the resin case

14

b.

The cap

14

a

and the resin case

14

b

constitute an outer container, and is constituted by a container made of an insulating material such as a resin (a thermoplastic resin) or the like.

A cylindrical thermit case

26

is received in an opening portion

53

formed in the resin case

14

b,

an ignition portion

29

to which a heating agent

27

and a lead wire

31

are connected is received in the thermit case

26

, and an upper lid

24

is put on an upper portion of the heating agent.

The thermit case

26

preferably employs a material having a good heat conductivity and infusible due to a heat generation of the heating agent

27

, for example, a brass, a copper, a copper alloy, a stainless steel or the like. The thermit case

26

is formed by a metal drawing or the like, and is formed in a cylindrical shape of a rectangular parallelepiped.

The ignition portion

29

is structured so as to ignite an ignition agent

30

a

due to a heat generated by the current flowing through the lead wire

31

at a time of abnormality of the vehicle such as a collision of the vehicle or the like so as to generate a thermit reaction heat in the heating agent

27

.

The first bus bar

11

a

having a round hole portion

12

and the second bus bar

19

a

having a round hole portion

20

are upward bent so as to form a substantially vertical angle, the bent portion passes through the resin case

14

b,

and bus bar front end portions

13

a

and

16

a

are brought into contact with right and left side wall portions of the thermit case

26

via metal having a low melting point

23

corresponding to the material having a low melting point such as a solder (for example, having a melting point of 200° C. to 300° C.) or the like.

The right and left side wall portions of the thermit case

26

are bonded to the bus bar front end portions

13

a

and

16

a

by the metal having a low melting point

23

, whereby the first bus bar

11

a

and the second bus bar

19

a

can be electrically connected via the metal having a low melting point

23

and the thermit case

26

.

The metal having a low melting point

23

is, for example, made of at least one kind of metal selected from the group of Sn, Pb, Zn, Al and Cu.

The heating agent

27

is, for example, constituted by metal oxide powders such as iron oxide (Fe

2

O

3

) or the like, and aluminum powders, and corresponds to a thermit agent which generates a thermit reaction due to a heat generation of the lead wire

31

so as to generate a high heat. The thermit agent is sealed in the thermit case

26

corresponding to a metal container for preventing moisture. In this case, in place of employing the iron oxide (Fe

2

O

3

), a chrome oxide (Cr

2

O

3

), a manganese oxide (MnO

2

) or the like may be employed.

Further, as the heating agent

27

, it is possible to employ at least one kind of mixture constituted by at least one kind of metal powders selected from the group of B, Sn, FeSi, Zr, Ti and Al, at least one kind of metal oxide selected from the group of CuO, MnO

2

, Pb

3

O

4

, PbO

2

, Fe

3

O

4

and Fe

2

O

3

, and an additive made of an alumina, a bentonite, a talc or the like. In accordance with the heating agent mentioned above, it is possible to easily ignite by the ignition portion

29

and it is possible to melt the metal having a low melting point

23

a short time.

Further, a retainer

45

constituted by a resin member is arranged within an opening portion

53

of the resin case

14

b and in a lower portion of the thermit case

26

. The retainer

45

constitutes an attaching and detaching member which mounts a compression spring

39

a

in a compression state, is freely attached to and detached from the resin case

14

b,

is arranged near or in contact with the thermit case

26

when being mounted to the resin case

14

b,

and melts due to heat of the heating agent

27

.

The retainer

45

is structured, as shown in

FIG. 8

, so as to have a base portion

61

, a notch portion

63

formed in the base portion

61

, a retainer body portion

65

standing from the notch portion

63

and the base portion

61

, and a pair of retainer engaging portions

67

formed at a front end of the retainer body portion

65

, and the structure is made such that a pair of retainer engaging portions

67

are mounted to the resin case

14

b.

The compression spring

39

a

spirally wound around the retainer body portion

65

is arranged in an outer side of the retainer body portion

65

, and a front end portion of the compression spring

39

a

is engaged with the retainer engaging portion

67

. That is, the compression spring

39

a

is held in the retainer

45

in a compressed state.

The ignition portion

29

has a pair of ignition portion terminals

30

c

and

30

d,

a resistance

30

b

provided between the pair of ignition portion terminals

30

c

and

30

d,

and an ignition agent

30

a

arranged near or in contact with the resistance

30

b.

Further, there is provided a heat conduction terminal

32

corresponding to a heat conduction member brought into contact with the bent portion of the first bus bar

11

a

and the ignition portion terminal

30

c,

and made of, for example, a copper, a copper alloy or the like. The heat conduction terminal

32

is, as shown in

FIG. 6

, formed substantially in an L shape, and is structured such as to form a heat conduction terminal main body

32

a,

a bus bar contact piece

32

c

protruding in a circular arc shape so as to be press contact with the first bus bar

11

a,

and an ignition portion contact piece

32

b

being surface contact with the ignition portion terminal

30

c

and be inserted from a lower portion of the resin case

14

b.

The ignition portion terminal

30

d

is connected to a control portion

70

shown in

FIG. 7

via a lead wire

31

.

The control portion

70

has, as shown in

FIG. 7

, a current sensor

71

for detecting a current flowing through each of the first bus bar

11

a

and the second bus bar

19

a,

a collision sensor (a G sensor)

73

for detecting a collision of the vehicle, a control circuit

75

for outputting a drive control signal as an abnormality signal to a drive circuit

77

in the case that a detected current value detected by the current sensor

71

becomes equal to or more than a threshold value or outputting a drive control signal to an electromagnetic relay

77

in the case that a detected acceleration value detected by the G sensor

73

becomes equal to or more than a predetermined value, and the electromagnetic relay

77

driven according to a drive control signal from the control circuit

75

.

The electromagnetic relay

77

has an electromagnetic coil

78

through which an exciting current flows according to the abnormality signal (here, corresponding to the drive control signal), and a switch

79

whose one end a is connected to the ignition portion terminal

30

d

via the lead wire

31

and another end b is grounded, thereby being turned on according to the exciting current.

In this case, the circuit breaker may be structured such a voltage sensor for detecting an excessive voltage and a temperature sensor for detecting a temperature are provided so a as to output an output from the voltage sensor and an output from the temperature sensor to the control circuit

75

.

The abnormality signal is input to the ignition portion

29

in the case that the value of the current mentioned above becomes equal to or more than a threshold value, and the value of the current when the heating agent

27

generates heat due to the heat from the heat conduction terminal

32

via the first bus bar

11

a

is set to a value over the threshold value mentioned above.

Next, a description will be given of an operation of the circuit breaker according to the embodiment structure in this manner with reference to the accompanying drawings.

At first, in a normal state, the first bus bar

11

a

and the second bus bar

19

a

are electrically connected to each other via the metal having a low melting point

23

and the thermit case

26

, and a current is supplied to a load (not shown) from the battery

1

.

Next, a description will be given of an operation in the case that the current sensor

71

, the G sensor

73

, the control circuit

75

and the like are normal -and the abnormality signal is sent to the ignition portion

29

when the vehicle is abnormal. When the abnormality is generated in the vehicle and the excessive current flows through the first bus bar

11

a

and the second bus bar

19

a,

the current sensor

71

detects the current. In the case that the detected current value detected by the current sensor

71

becomes equal to or more than the threshold value, the control circuit

75

outputs the drive control signal to the electromagnetic coil

78

, so that the exciting current flows through the electromagnetic coil

78

and the switch

79

turns on due to the exciting current.

Then, the current flows from the buttery (the power source)

1

along the path comprising the first bus bar

11

a,

the heat conduction terminal

32

, the ignition portion terminal

30

c,

the resistance

30

b,

the ignition portion terminal

30

d,

the lead wire

31

, the switch

79

and the earth. Accordingly, the resistance

30

b

generates heat. When the temperature of the resistance

30

b

becomes 350° C. or more, the ignition agent is ignited and the heating agent

27

which is the thermit agent generates a thermit reaction heat according to the following reaction formula.

Fe

2

O

3

+2AL→AL

2

O

3

+2Fe+386.2Kcal

The thermit case

26

is heated due to the thermit reaction heat and the metal having a low melting point

23

is heated due to the heat generation of the heating agent

27

and the heat of the thermit case

26

, thereby being melted. Further, at the same time of this, the resin retainer engaging portion

67

compressing and fixing the compression spring

39

a

to the retainer

45

is melted due to the heat mentioned above. Then, as shown in

FIG. 6

, since the compression spring

39

a

is extended, the thermit case

26

jumps up in a direction of the cap

14

a.

Accordingly, an electrical connection between the thermit case

26

, and the first bus bar

11

a

and the second bus bar

19

a

is shut. That is, the electrical circuit of the vehicle is securely broken for a short time. Further, it is possible to break the circuit according to the abnormality signal by utilizing the power source voltage from the buttery

1

.

Next, a description will be given of an operation in the case that breaking of the current sensor

71

and the G sensor

73

, breaking of the control circuit

75

or the like is generated and the abnormality signal is not sent to the ignition portion

29

when the vehicle is abnormal. In this case, the switch

79

in the electromagnetic relay

77

is in an off state.

At first, when an excessive current exceeding the threshold value flows through the first bus bar

11

a,

the temperature of the first bus bar

11

is increased, the temperature becomes, for example, equal to or more than 350° C., and the heat due to the temperature increase is conducted to the first bus bar

11

a,

the heat conduction terminal

32

, the ignition portion terminal

30

c,

the resistance

30

b

and the ignition agent

30

a.

Accordingly, the ignition agent

30

a

is ignited due to the heat (for example, when the temperature becomes equal to or more than 350° C.), the heating agent

27

generates heat, the thermit case

26

is heated due to the heat, and the metal having a low melting point

23

is heated due to the heat generated by the heating agent

27

and the heat of the thermit case

26

and melted. Further, at the same time of this, the resin retainer engaging portion

67

compressing and fixing the compression spring

39

a

to the retainer

45

is melted due to the heat mentioned above. Then, as shown in

FIG. 6

, since the compression spring

39

a

is expanded, the thermit case

26

jumps up in a direction of the cap

14

a.

Accordingly, the electrical connection between the thermit case

26

, and the first bus bar

11

a

and the second bus bar

19

a

is shut. That is, even in the case that the circuit can not be broken due to the trouble of the control portion

70

or the like, it is possible to securely break the circuit for a short time due to the heat generated by the temperature increase of the bus bar at a time of the excessive current.

Further, even when there is no sensor such as the current sensor

71

or the like, it is possible to break the circuit by detecting the temperature. Further, in comparison with the method of melting down the circuit member shown in

FIG. 3

, since the circuit breaker according to the third embodiment employs the heat conduction terminal

32

, it is possible to reduce the circuit resistance of the fuse, so that there is no natural breaking or the like, and it is possible to improve a safety.

Further, since the abnormality signal is input to the ignition portion

29

in the case that the value of the current becomes equal to or more than the threshold value, and the value of the current when the heating agent

27

generates heat by the heat from the heat conduction terminal

32

via the first bus bar

11

a

is set to a value over the threshold value, it is possible to break the circuit due to the heat from the heat conduction terminal

32

via the first bus bar

11

a

in the case that it is impossible to break the circuit according to the abnormality signal from the control portion

70

, and the circuit is not broken due to the heat from the heat conduction terminal

32

before the circuit is broken according to the abnormality signal.

Further, since the retainer engagement portion

67

is placed in the inner side of the compression spring

39

a,

the retainer engagement portion

67

tends to be inclined inward due to the reaction force of the compression spring

39

a,

whereby the thermit case

26

and the retainer

45

are brought into strong contact with each other. Accordingly, since the heat conduction is well performed from the thermit case

26

to the retainer

45

, it is possible to effectively melt the retainer engagement portion

67

.

Further, it is possible to easily assemble the compression spring

39

a

in the retainer

45

only by inclining the retainer engagement portion

67

inward and pressing the compression spring

39

a

to the retainer

45

, and it is possible to easily mount the retainer

45

to the resin case.

14

b.

Further, since the compression spring

39

a

is held by the retainer

45

, no external force is applied to the bonding portion between the first bus bar

11

a

and the second bus bar

19

b,

and the thermit case

26

, that is, the metal having a low melting point

23

. Accordingly, it is possible to improve a reliability of the bonding portion.

Further, since the sub-assembly between the compression spring

39

a

and the retainer

45

is inserted from the lower surface of the fuse, that is, the opening portion

53

f

of the resin case

14

b,

a total assembly of the circuit breaker is easily performed. Further, after the circuit is broken, the resin case

14

b

can be reused as the fuse in the existing state only by replacing the retainer

45

and the thermit case

26

.

Further, since the cap

14

a

is put on the resin case

14

b,

the thermit case

26

does not go out from the cap

14

a

when the circuit is broken, whereby it is possible to prevent a burn due to the heat or the like.

In this case, the present invention is not limited to the circuit breaker according to the embodiments mentioned above. In the embodiments, the structure is made such that the compression spring

39

a

and the metal having a low melting point

23

are provided and the circuit is broken when the retainer

45

and the metal having a low melting point

23

are melted down, however, the structure may be made, for example, such that only the retainer