JP2020024852A - Breaker and safety circuit - Google Patents

Abstract

To attain reduction in height while securing an interval between a stationary contact and a movable contact in a cut-off state.SOLUTION: A breaker 1 comprises: a stationary contact 21; a movable piece 4 including an elastic part 44 which is formed tabular and elastically deformed and a movable contact 41 at a tip end of the elastic part 44, and pressing and bringing the movable contact 41 into contact with the stationary contact 21; a thermally-actuated element 5 which shifts a state of the movable piece 4 from a conduction state to a cut-off state by being deformed with a temperature change; a case body 7 in which the stationary contact 21, the movable piece 4 and the thermally-actuated element 5 are accommodated; and a lid member 8 which is mounted over the case body 7 while at least partially covering the movable element 4 and the thermally-actuated element 5. On an inner surface of the lid member 8 directed to the side of the movable piece 4, a retraction part 82 which is retracted in a direction away from the stationary contact 21 is locally formed in a region opposed to the stationary contact 21 via the movable piece 4.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a small breaker and the like suitable for use in a safety circuit of an electric device.

  Conventionally, a breaker has been used as a protection device (safety circuit) for a secondary battery, a motor, and the like of various electric devices. The breaker is activated when the temperature of the secondary battery during charging / discharging rises excessively, or when an abnormal condition occurs, such as when an overcurrent flows through a motor or the like provided in a device such as an automobile or a home appliance. Cut off the current to protect the secondary battery and motor. The breaker used as such a protection device operates accurately (has good temperature characteristics) in accordance with the temperature change and has a stable resistance value when energized in order to ensure the safety of the equipment. Is required.

  The breaker is provided with a thermoresponsive element that operates in response to a temperature change and conducts or interrupts current. Patent Literature 1 discloses a breaker to which a bimetal is applied as a thermally responsive element. A bimetal is an element in which two types of plate-like metal materials having different coefficients of thermal expansion are laminated, and the shape of the metal material is changed according to a temperature change to control the conduction state of the contact. The breaker disclosed in the document has components such as a fixed piece, a terminal piece, a movable piece, a thermoresponsive element, and a PTC thermistor housed in a case, and the terminals of the fixed piece and the terminal piece protrude from the case. Used by being connected to the electric circuit of the equipment.

WO2011 / 105175

  Further, when the breaker is used as a protective device such as a secondary battery mounted on an electric device such as a notebook personal computer, a tablet-type portable information terminal device, or a thin multi-functional mobile phone called a smartphone, In addition to ensuring safety, miniaturization is required. In particular, in recent mobile information terminal devices, users are keen on miniaturization (thinning or reduction in height), and devices newly released from each company are required to secure superiority in design. There is a remarkable tendency to be designed in a small size. Against this background, as a component of a portable information terminal device, a breaker mounted together with a secondary battery is also required to be further reduced in size.

  In the above-mentioned breaker, when an impact or the like is applied to the breaker in which the movable piece is in the cut-off state for some reason, instantaneous conduction between the fixed contact and the movable contact may occur. Such instantaneous conduction can be suppressed by ensuring a sufficient gap between the fixed contact and the movable contact in the interrupted state. However, in order to ensure a sufficient gap between the fixed contact and the movable contact in the interrupted state, it is necessary to increase the internal space of the case, which is one of the factors that hinder the reduction in height of the case.

  The present invention has been made to solve the above problems, and provides a breaker that can easily reduce the height while sufficiently securing a gap between a fixed contact and a movable contact in a disconnected state. The purpose is to.

  In order to achieve the above object, a breaker according to the present invention has a fixed contact, an elastic portion formed in a plate shape and elastically deformed, and a movable contact at a tip end of the elastic portion, and the movable contact is pressed against the fixed contact. The movable piece is brought into contact with the movable contact, and the state of the movable piece is changed from a conduction state in which the movable contact comes into contact with the fixed contact to a cut-off state in which the movable contact is separated from the fixed contact by being deformed with a change in temperature. The thermal response element to be shifted, the first case accommodating the fixed contact, the movable piece and the thermal response element, and the first case covering the movable piece and the thermal response element and being mounted on the first case. A breaker provided with a second case, wherein an inner surface facing the movable piece of the second case has a direction facing away from the fixed contact in a region facing the fixed contact via the movable piece. To Retracting section to avoid is locally formed, a breaker, characterized in that.

  In the breaker according to the present invention, it is preferable that the second case includes a plate-shaped cover piece disposed to face the movable piece.

  In the above-mentioned breaker according to the present invention, it is preferable that the retreat portion penetrates the cover piece.

  In the above-described breaker according to the present invention, it is preferable that the retreat portion penetrates the second case.

  In the breaker according to the present invention, the movable piece has a fixing portion fixed by the first case and the second case on a base end side of the elastic portion, and the retreating portion includes a fixing portion of the elastic portion. It is desirable to extend from the area facing the fixed contact to the base end side along the longitudinal direction.

  In the breaker according to the present invention, it is preferable that an end edge of the retreating portion on the base end side is disposed at a position 70% or less of a length of the elastic portion from the base end.

  In the breaker according to the present invention, the movable piece has a fixing portion fixed by the first case and the second case on a base end side of the elastic portion, and the retreating portion includes a fixing portion of the elastic portion. Extending along the longitudinal direction from the region facing the fixed contact to the base end, the base end edge of the retreating portion is located at a position at least 48% of the length of the elastic portion from the base end. It is desirable to be arranged.

  In the breaker according to the present invention, it is preferable that a protrusion protruding toward the elastic portion is formed on the inner surface.

  In the breaker according to the present invention, it is preferable that the elastic portion is plastically deformed by the thermoresponsive element deformed by an overcurrent.

  A safety circuit according to the present invention includes the above-described breaker.

  The breaker according to the present invention includes a first case accommodating the fixed contact, the movable piece, and the thermoresponsive element, and a second case that covers at least a part of the movable piece and the thermoresponsive element and is attached to the first case. On the inner surface of the second case, a retreating portion is formed to retreat in a direction away from the fixed contact in a region facing the fixed contact via the movable piece. Therefore, when the movable piece is in the blocking state, the distal end of the elastic portion is accommodated in the retracting portion, so that interference between the distal end and the lid member is suppressed, and the distance between the fixed contact and the movable contact is sufficiently ensured. You. Thus, even if, for some reason, an impact or the like is applied to the breaker in which the movable piece is in the cutoff state, instantaneous conduction between the fixed contact and the movable contact is suppressed. Further, since the retracting portion is locally formed in a region facing the fixed contact, the height can be easily reduced without enlarging the entire case.

BRIEF DESCRIPTION OF THE DRAWINGS The perspective view before assembling which shows the schematic structure of the breaker by one Embodiment of this invention. Sectional drawing which shows the breaker of FIG. 1 in a normal charge or discharge state. Sectional drawing which shows the breaker of FIG. 1 in an overcharge state or at the time of abnormality. It is the perspective view which looked at the cover member of the above-mentioned breaker from the 1st surface side. It is a top view of the said breaker. It is sectional drawing which shows the internal structure of the said breaker. The top view which shows the structure of the secondary battery pack provided with the said breaker of this invention. The circuit diagram of the safety circuit provided with the above-mentioned breaker of the present invention.

  A breaker according to an embodiment of the present invention will be described with reference to the drawings. 1 to 3 show the configuration of the breaker. As shown in FIGS. 1 and 3, the breaker 1 includes a pair of terminals 22 and 42 that are partially exposed to the outside from the case 10. When the terminals 22 and 42 are electrically connected to an external circuit (not shown), the breaker 1 forms a main part of a safety circuit of the electric device.

  As shown in FIG. 1, the breaker 1 includes a fixed piece 2 having a fixed contact 21 and a terminal 22, a movable piece 4 having a movable contact 41 at a distal end, a thermally responsive element 5 deformed with a temperature change, and the like. It is constituted by.

  The fixed piece 2, the movable piece 4, and the thermally responsive element 5 are housed in a case 10. The case 10 includes a case body (first case) 7, a lid member (second case) 8 mounted on the upper surface of the case body 7, and the like.

  The fixing piece 2 is formed in a plate shape by, for example, pressing a metal plate containing copper or the like as a main component (in addition, a metal plate of copper-titanium alloy, nickel silver, brass, or the like). It is embedded by insert molding.

  The fixed contact 21 is formed by cladding, plating, coating, or the like of a material having good conductivity such as a copper-silver alloy, a gold-silver alloy, or the like, in addition to silver, nickel, and a nickel-silver alloy. The fixed contact 21 is formed at a position facing the distal end of the fixed piece 2, that is, the movable contact 41, and is exposed to an internal space defined by a concave portion 73 formed inside the case body 7.

  A terminal 22 that is electrically connected to an external circuit is formed at the other end of the fixed piece 2. The terminal 22 is exposed from the side wall of the case body 7 and is connected to an external circuit by welding or soldering. The fixed piece 2 has a buried portion 23 between the fixed contact 21 and the terminal 22. The fixing piece 2 is embedded in the case main body 7 at the embedded portion 23.

  The movable piece 4 is formed in a plate shape by pressing a metal material mainly containing copper or the like. The movable piece 4 is formed in an arm shape symmetric with respect to a longitudinal center line.

  A movable contact 41 is formed at the tip of the movable piece 4. The movable contact 41 is formed of a material equivalent to that of the fixed contact 21 by plating or coating.

  The other end of the movable piece 4 is formed with a terminal 42 that is electrically connected to an external circuit. The terminal 42 is exposed from the side wall of the case main body 7 and is connected to an external circuit by a method such as welding or soldering.

  The movable piece 4 has a fixed part 43 and an elastic part 44 between the movable contact 41 and the terminal 42. The fixing part 43 is formed between the terminal 42 and the elastic part 44. The fixing portion 43 is embedded and fixed in the case 10 by being sandwiched between the case main body 7 and the lid member 8. The fixed portion 43 has a protruding portion 43 a that protrudes in a wing shape in the lateral direction of the movable piece 4 between the terminal 42 and the elastic portion 44. By providing the protruding portion 43a, the fixing portion 43 is sandwiched between the case main body 7 and the cover member 8 in a wide and large area, and the movable piece 4 is firmly fixed to the case 10.

  The elastic part 44 extends from the fixed part 43 to the movable contact 41 side. The elastic portion 44 has a base portion 44s on the side of the fixing portion 43 and a tip portion 44e on the opposite side. The movable contact 41 is formed at the tip 44 e of the elastic portion 44. The elastic part 44 and the movable contact 41 are exposed to the internal space by the recess 73.

  The fixed portion 43 is fixed by being embedded in the case 10, and the elastic portion 44 is elastically deformed, so that the movable contact 41 formed at the end thereof is pressed against the fixed contact 21 and comes into contact with the fixed contact 2. And the movable piece 4 can be energized.

  The movable piece 4 is curved or bent at the elastic portion 44 by press working. The degree of bending or bending is not particularly limited as long as the thermoresponsive element 5 can be accommodated, and may be appropriately set in consideration of the operating temperature, the pressing force of the movable contact 41, and the like. The elastic portion 44 has a pair of protrusions (contact portions) 44 a and 44 b protruding toward the thermoresponsive element 5. The protrusions 44a and 44b are in contact with the thermoresponsive element 5, and the deformation of the thermoresponsive element 5 is transmitted to the elastic portion 44 via the protrusions 44a and 44b (see FIGS. 1 and 3).

  In the present application, unless otherwise specified, the surface of the movable piece 4 on which the elastic portion 44 faces the thermally responsive element 5 (that is, the lower surface in FIGS. 1 to 3) is the first surface. The opposite surface is described as the second surface. The same applies to other components arranged along the movable piece 4, for example, the fixed piece 2, the thermally responsive element 5, the case 10, and the like.

  The thermally responsive element 5 changes the state of the movable piece 4 from a conductive state in which the movable contact 41 contacts the fixed contact 21 to a cutoff state in which the movable contact 41 is separated from the fixed contact 21. The thermally responsive element 5 has an initial shape curved in an arc shape and is formed by laminating thin plates having different coefficients of thermal expansion. When the operating temperature is reached due to overheating, the curved shape of the thermoresponsive element 5 reversely warps with snap motion, and is restored when the temperature falls below the return temperature due to cooling. The initial shape of the thermally responsive element 5 can be formed by press working. The material and the shape of the thermally responsive element 5 are not particularly limited as long as the thermal responsive element 5 is reversely deformed at an intended temperature. It is desirable that the shape be a rectangle close to a square in order to push up the portion 44 efficiently. In addition, as a material of the thermal response element 5, for example, copper-nickel-manganese alloy or nickel-chromium-iron alloy on the high expansion side, iron-nickel alloy on the low expansion side, nickel silver, brass, stainless steel, etc. Two kinds of materials having different coefficients of thermal expansion made of various alloys such as steel are laminated and used in combination according to required conditions.

  The case body 7 and the lid member 8 constituting the case 10 are formed of a thermoplastic resin such as flame-retardant polyamide, polyphenylene sulfide (PPS), liquid crystal polymer (LCP), and polybutylene terephthalate (PBT) having excellent heat resistance. Have been. An insulating material other than the resin may be applied as long as characteristics equivalent to or higher than those of the resin described above can be obtained.

  The case body 7 has a concave portion 73 that forms an internal space for accommodating the fixed contact 21, the movable contact 41, the elastic portion 44, the thermoresponsive element 5, and the like. The concave portion 73 is formed in a shape along the outer edges of the movable piece 4 and the thermally responsive element 5 in plan view. Since the concave portion 73 is formed in the case body 7, the elastic portion 44 can be elastically deformed, and the thermally responsive element 5 can be reversely warped.

  The cover member 8 is attached to the case main body 7 so as to cover at least a part of the movable piece 4 and the thermally responsive element 5. A cover piece 9 is embedded in the lid member 8 of this embodiment by insert molding. The cover piece 9 is formed in a plate shape by pressing the above-described metal containing copper or the like as a main component or a metal such as stainless steel. The cover piece 9 contributes to the downsizing of the breaker 1 while increasing the rigidity and strength of the cover member 8 and thus the case 10 as a housing. When sufficient rigidity and strength can be obtained by the resin or the like forming the lid member 8, the cover piece 9 may be omitted from the lid member 8.

  As shown in FIG. 1, a lid member 8 is attached to the case main body 7, which houses the fixed piece 2, the movable piece 4, the thermoresponsive element 5, and the like. The case body 7 and the lid member 8 are joined to each other by, for example, ultrasonic welding. At this time, the case body 7 and the lid member 8 are continuously joined over the entire periphery of each outer edge, and the strength and rigidity of the case 10 are improved.

  FIG. 2 shows the operation of the breaker 1 in a normal charge or discharge state. In a normal charge or discharge state, the thermally responsive element 5 maintains an initial shape (before reverse warpage). When the movable contact 41 is pressed toward the fixed contact 21 by the elastic portion 44, the movable contact 41 and the fixed contact 21 come into contact with each other, and the fixed piece 2 and the movable piece 4 of the breaker 1 are brought into a conductive state. You.

  FIG. 3 shows an operation of the breaker 1 in an overcharged state or in an abnormal state. When the temperature reaches a high temperature state due to overcharging or an abnormality, the thermoresponsive element 5 that has reached the operating temperature reversely warps, the elastic portion 44 of the movable piece 4 is pushed up, and the fixed contact 21 and the movable contact 41 are separated. The operating temperature of the thermally responsive element 5 when the thermally responsive element 5 is deformed inside the breaker 1 and pushes up the movable piece 4 is, for example, 70 ° C. to 90 ° C. At this time, the current flowing between the fixed contact 21 and the movable contact 41 is cut off.

  FIG. 4 is a perspective view of the lid member 8 as viewed from the first surface side. On the first surface of the lid member 8, that is, on the inner surface 81 facing the movable piece 4, a retreat which retreats in the thickness direction of the lid member 8 (thickness direction of the movable piece 4), that is, in the direction D1 away from the fixed contact 21. A portion 82 is formed. The retracting portion 82 is locally formed in a region opposed to the fixed contact 21 (the distal end portion of the movable piece 4) via the movable piece 4.

  By forming the evacuation portion 82 in the cover member 8, as shown in FIG. 3, when the movable piece 4 is in the blocking state, the distal end portion 44 e of the elastic portion 44 is housed in the evacuation portion 82. Thereby, interference between the distal end portion 44e and the lid member 8 is suppressed, and the distance between the fixed contact 21 and the movable contact 41 is sufficiently ensured. Therefore, even if, for some reason, an impact or the like is applied to the breaker 1 in which the movable piece 4 is in the cutoff state, instantaneous conduction between the fixed contact 21 and the movable contact 41 is suppressed. Further, since the retracting portion 82 is locally formed in a region opposed to the fixed contact 21, the height can be easily reduced without enlarging the entire case 10.

  It is desirable that the retracting portion 82 penetrates a part of the cover piece 9. This makes it possible to easily secure the depth of the retracting portion 82, and to further increase the distance between the fixed contact 21 and the movable contact 41. In the present embodiment, the notch is formed at the edge of the cover piece 9 to realize the retreat portion 82, but the cover piece 9 extends to the terminal 22 side beyond the area facing the fixed contact 21. In the embodiment described above, the retracting portion 82 may be realized by a through hole formed in the cover piece 9.

  In the lid member 8 of the present embodiment, a concave portion 85 is formed on the inner surface 81 of the lid member 8 to avoid interference with the thermally responsive element. The second surface of the cover piece 9 is exposed to the internal space of the case 10 by the recess 85. The evacuation section 82 is further depressed from the recess 85. Thereby, the interference between the distal end portion 44e and the lid member 8 is further suppressed.

  FIG. 5 is a plan view of the breaker 1. In order to avoid interference between the elastic part 44 and the cover member 8 in which the movable piece 4 is in the cut-off state, the retracting part 82 is desirably formed along the outer edge of the elastic part 44. The expression "along the outer edge of the elastic portion 44" means that a clearance (for example, 0.03 mm to 0.30 mm) is formed with a clearance that does not interfere with the outer edge of the elastic portion 44, The form along the outer edge of the thermally responsive element 5 far away from the outer edge of the elastic portion 44 (for example, about 0.80 mm) is excluded.

  It is desirable that the retracting portion 82 penetrates the lid member 8. In the present embodiment, the retracting section 82 is configured by a through hole 83 that penetrates the lid member 8 in the thickness direction. Thereby, the interference between the distal end portion 44e and the lid member 8 is more easily suppressed, and the distance between the fixed contact 21 and the movable contact 41 can be further increased in the cutoff state shown in FIG.

  In the present breaker 1, since the interference between the distal end portion 44e and the lid member 8 is suppressed by the retracting portion 82, the thermally responsive element 5 having a large amount of deformation (that is, the amount of pushing up the movable piece 4) at the time of reverse warpage is applied. Thereby, the deformation of the elastic portion 44 can be expanded to the plastic region. The elastic portion 44 is plastically deformed, so that in the shut-off state shown in FIG. 3, even after the thermoresponsive element 5 is restored to the shape shown in FIG. The reverse warpage of the elastic portion 44 is maintained. Therefore, since the movable contact 41 is kept in the cut-off state away from the fixed contact 21, the self-holding function of the breaker 1 for holding the cut-off state of the movable piece 4 uses the PTC thermistor disclosed in Patent Document 1. And is realized with a simple configuration. Further, with the configuration in which the PTC thermistor is omitted, further reduction in the height of the breaker 1 can be easily realized.

  In the present embodiment, since the retracting portion 82 is constituted by the through hole 83, the interference between the distal end portion 44e and the cover member 8 is further suppressed, and the elastic portion 44 can be easily plastically deformed. The thermally responsive element 5 having a large amount of deformation at the time of reverse warpage can be easily realized, for example, by laminating the above-described thin plate materials having a significantly different coefficient of thermal expansion.

  FIG. 6 shows an enlarged cross section of the breaker 1. The retracting section 82 is formed along the longitudinal direction of the elastic section 44. More specifically, the retracting portion 82 extends from the region of the elastic portion 44 facing the fixed contact 21 toward the fixed portion 43, that is, toward the base end 44s of the elastic portion 44. With such a retracting portion 82, the distal end portion 44e of the elastic portion 44 in the shut-off state is efficiently accommodated.

  It is desirable that the distance L1 in the longitudinal direction of the movable piece 4 from the base end 44s of the elastic portion 44 to the end edge 82e of the retracting portion 82 is 70% or less of the length L2 of the elastic portion 44 from the base end 44s. That is, it is desirable that the edge 82e is arranged at a position that is 70% or less of the length L2 from the base end 44s. The “length L2 of the elastic portion 44” is a distance from the base end 44s to the distal end of the movable piece 4 on the terminal 22 side. Since the edge 82e is disposed at a position 70% or less of the length L2 from the base end 44s, a sufficient distance between the fixed contact 21 and the movable contact 41 is secured in the cutoff state shown in FIG. It becomes possible.

  Further, as in the present embodiment, in the breaker 1 in which the retreat portion 82 is formed by the through holes 83, the distance L1 is desirably equal to or greater than 48% of the length L2. That is, it is desirable that the edge 82e is disposed at a position that is at least 48% of the length L2 from the base end 44s. Since the end edge 82e is arranged at a position 48% or more of the length L2 from the base end 44s, the distal end portion 44e of the elastic portion 44 is moved to the second surface of the lid member 8 in the cutoff state shown in FIG. (Outer surface) is suppressed.

  It is desirable that a projection 84 projecting toward the elastic portion 44 be formed on the inner surface 81 of the lid member 8. In the present embodiment, the protrusion 84 is realized by the protrusion 91 formed on the first surface of the cover piece 9.

  The protruding portion 91 abuts on the second surface of the elastic portion 44 in the blocking state shown in FIG. Thereby, the movable piece 4 is pushed up with the contact point between the elastic portion 44 and the protruding portion 91 as a fulcrum, and the distance between the fixed contact 21 and the movable contact 41 is easily maintained. In addition, stress applied to the elastic portion 44 is concentrated around the portion where the elastic portion 44 is in contact with the protruding portion 91, and plastic deformation of the elastic portion 44 is likely to occur. From such a viewpoint, it is desirable that the protruding portion 91 is provided at or near the edge 82e.

  The breaker 1 of the present invention is not limited to the configuration of the above-described embodiment, but can be implemented in various modes. That is, the breaker 1 has at least the fixed contact 21, the elastic portion 44 formed in a plate shape and elastically deformed, and the movable contact 41 at the tip of the elastic portion 44, and the movable contact 41 is pressed against the fixed contact 21. The movable piece 4 to be brought into contact with the movable piece 4 is deformed in accordance with a change in temperature, thereby changing the state of the movable piece 4 from a conduction state in which the movable contact 41 contacts the fixed contact 21 to a cut-off state in which the movable contact 41 is separated from the fixed contact 21. The thermal responsive element 5 to be made, the fixed contact 21, the movable body 4 and the case main body 7 accommodating the thermal responsive element 5, and the cover which covers at least a part of the movable movable part 4 and the thermal responsive element 5 and is attached to the case main body 7. A breaker 1 including a member 8, and a direction away from the fixed contact 21 in a region facing the fixed contact 21 via the movable piece 4 on an inner surface 81 facing the movable piece 4 of the lid member 8. Evacuate to Saving unit 82 only need to be locally formed.

  For example, the joining method of the case body 7 and the lid member 8 is not limited to the ultrasonic welding, and may be appropriately applied as long as both are firmly joined. For example, both may be adhered by applying and filling a liquid or gel adhesive and curing the adhesive. In addition, the case 10 is not limited to the form constituted by the case main body 7 and the lid member 8 and the like, but may be constituted by two or more parts.

  Further, the movable piece 4 and the thermally responsive element 5 may be integrally formed by forming the movable piece 4 from a laminated metal such as a bimetal or a trimetal. In this case, the configuration of the breaker 1 and the like is simplified, and the size can be reduced.

  Further, the breaker 1 and the like of the present invention can be widely applied to a secondary battery pack, a safety circuit for electric equipment, and the like. FIG. 7 shows a secondary battery pack 500. The secondary battery pack 500 includes a secondary battery 501, a breaker 1 provided in an output terminal circuit of the secondary battery 501, and the like. FIG. 8 shows a safety circuit 502 for an electric device. The safety circuit 502 includes a breaker 1 and the like in series in the output circuit of the secondary battery 501. A part of the safety circuit 502 may be configured by a cable including a connector including the breaker 1 and the like.

1: Breaker 4: Movable piece 5: Thermal response element 7: Case body (first case)
8: Lid member (second case)
9: cover piece 21: fixed contact 41: movable contact 43: fixed part 44: elastic part 44e: tip part 44s: base end 81: inner surface 82: retreat part 82e: edge 83: through hole 84: projecting part 91: Protruding part 500: secondary battery pack 502: safety circuit D1: direction

Claims (10)

Fixed contacts,
An elastic portion formed in a plate shape and having a movable contact at a distal end portion of the elastic portion and a movable piece that presses the movable contact to the fixed contact to make contact therewith;
By being deformed with a change in temperature, a thermally responsive element that shifts the state of the movable piece from a conductive state in which the movable contact contacts the fixed contact to an interrupted state in which the movable contact is separated from the fixed contact,
A first case accommodating the fixed contact, the movable piece and the thermoresponsive element;
A second case mounted on the first case and covering the movable piece and at least a part of the thermally responsive element,
On the inner surface of the second case facing the movable piece, a retreating portion is formed locally in a region facing the fixed contact via the movable piece, and retracts away from the fixed contact. A breaker.   2. The breaker according to claim 1, wherein the second case includes a plate-shaped cover piece disposed to face the movable piece. 3.   The breaker according to claim 2, wherein the retreating portion penetrates the cover piece.   The breaker according to any one of claims 1 to 3, wherein the retreat portion penetrates the second case. The movable piece has a fixed portion fixed by the first case and the second case on a base end side of the elastic portion,
5. The breaker according to claim 1, wherein the retreating portion extends from a region facing the fixed contact to the base end along a longitudinal direction of the elastic portion. 6.   The breaker according to claim 5, wherein the base end side edge of the retreating portion is arranged at a position which is 70% or less of a length of the elastic portion from the base end. The movable piece has a fixed portion fixed by the first case and the second case on a base end side of the elastic portion,
The retracting portion extends from the region facing the fixed contact to the base end side along the longitudinal direction of the elastic portion,
The breaker according to claim 4, wherein an edge of the retreating portion on the base end side is disposed at a position at least 48% of a length of the elastic portion from the base end.   The breaker according to any one of claims 5 to 7, wherein a protrusion protruding toward the elastic portion is formed on the inner surface.   The breaker according to any one of claims 1 to 8, wherein the elastic portion is plastically deformed by the thermally responsive element deformed by an overcurrent.   A safety circuit comprising the breaker according to any one of claims 1 to 9.

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