Breaker, safety circuit for electric apparatus, and secondary battery pack

Abstract

A breaker 1 comprises: a stationary piece 2 that has a stationary contact 21; a movable piece 4 having an elastic portion 43 that is formed in a plate shape and is capable of elastic deformation, and a movable contact 41 on one end portion of the elastic portion 43, the movable piece 4 pressing the movable contact 41 against the stationary contact 21 to make contact therewith; and a thermally responsive element 5 that deforms in accordance with a temperature change, thereby causing a transition of the movable piece 4 from a conduction state in which the movable contact 41 is in contact with the stationary contact 21 to an interruption state in which the movable contact 41 is separated from the stationary contact 21. The movable piece 4 has, in the thickness direction thereof, a thin portion 45 that is recessed in a direction opposite that of the thermally responsive element 5.

Description

Breakers, safety circuits for electrical equipment, and secondary battery packs

[0001] The present invention relates to a small breaker or the like that is built into a secondary battery pack or the like of an electrical device.

[0002] 2. Description of the Related Art Conventionally, a breaker is known that includes a fixed contact, a movable piece having a movable contact, a thermally responsive element, and a positive temperature coefficient thermistor (see, for example, Patent Document 1).

[0003] WO2011 / 105175 publication

[0004] In a breaker, the thermally responsive element is curved so that its center protrudes toward the movable contact. When the temperature of this thermally responsive element rises, the peripheral part pushes up the movable contact, separating the movable contact from the fixed contact.

[0005] However, when electrical equipment is exposed to extremely low temperatures, the degree of bending of the thermally responsive element increases, and its center pushes up the movable piece, potentially separating the movable contact from the fixed contact. Even if the movable contact is prevented from separating, the contact pressure between the movable and fixed contacts decreases, increasing the resistance across the breaker.

[0006] The present invention has been devised in view of the above circumstances, and has as its main object to provide a breaker that can maintain a stable conduction state even when used at extremely low temperatures.

[0007] The present invention is a breaker comprising: a fixed piece having a fixed contact; a movable piece formed in a plate shape and having an elastic portion that elastically deforms and a movable contact at one end of the elastic portion, and pressing the movable contact against the fixed contact to bring it into contact; and a thermally responsive element that deforms in response to temperature changes, thereby transitioning the movable piece from a conductive state in which the movable contact is in contact with the fixed contact to a cut-off state in which the movable contact is separated from the fixed contact, wherein the movable piece has a thin portion in its thickness direction that is recessed in the opposite direction to the thermally responsive element.

[0008] Because the breaker of the present invention has the above-mentioned configuration, even when used at extremely low temperatures, the center of the thermally responsive element is prevented from pushing up the movable piece, and a stable conductive state can be maintained between the movable contact and the fixed contact.

[0009] 1 is a perspective view showing a state before assembly of a breaker according to an embodiment of the present invention; a cross-sectional view showing the breaker in a normal charging or discharging state; a cross-sectional view showing the breaker in an overcharged state or in an abnormal state; a perspective view showing the configuration of the movable piece of FIG. 1, with a portion cut away; a cross-sectional view showing the breaker in an extremely low temperature state; a plan view of the movable piece and thermally responsive element of FIG. 1; a perspective view showing the configuration of a modified example of the movable piece 4 of FIG. 4, with a portion cut away; a front view of a secondary battery pack including the breaker of FIG. 1, etc.; a circuit diagram of a safety circuit including the breaker of FIG. 1, etc.

[0010] A circuit breaker according to an embodiment of the present invention will be described with reference to the drawings. Figures 1 to 3 show the configuration of a circuit breaker 1 according to the present invention. The circuit breaker 1 is mounted in an electrical device or the like and protects the electrical device from excessive temperature rise or overcurrent.

[0011] 1, the breaker 1 is composed of a fixed piece 2 having a fixed contact 21 and a terminal 22, a terminal piece 3 having a terminal 32, a movable piece 4 having a movable contact 41 at its tip, a thermally responsive element 5 that deforms with temperature changes, a PTC (Positive Temperature Coefficient) thermistor 6, and a case 10 that houses the fixed piece 2, terminal piece 3, movable piece 4, thermally responsive element 5, and PTC thermistor 6. The case 10 is composed of a case main body (first case) 7, a cover member (second case) 8 attached to the case main body 7, and the like.

[0012] The fixing piece 2 is formed, for example, by pressing a metal plate whose main component is copper or the like (other metal plates include copper-titanium alloy, nickel silver, brass, etc.), and is embedded in the case body 7 by insert molding.

[0013] The fixed contact 21 is formed by cladding, plating, or coating a highly conductive material such as silver, nickel, nickel-silver alloy, copper-silver alloy, gold-silver alloy, etc. The fixed contact 21 is formed in a position facing the movable contact 41 of the fixed piece 2, and is exposed to the housing portion 73 of the case body 7 from a part of a recess 73a formed inside the case body 7.

[0014] In this application, unless otherwise specified, the surface of the fixed piece 2 on which the fixed contact 21 is formed (i.e., the upper surface in FIG. 1) is referred to as the top surface, and the opposite surface is referred to as the bottom surface. The same applies to other components, such as the terminal piece 3, the movable piece 4, the thermally responsive element 5, the case 10, the cover piece 9, etc.

[0015] The terminals 22 protrude from the side walls of the case body 7 and are connected to lands on a circuit board or tabs on a secondary battery circuit, etc. The terminals 22 may be configured to be exposed from the bottom wall of the case body 7.

[0016] 2 , the fixed piece 2 has a support portion 23 that supports the PTC thermistor 6, and a stepped bent portion 25 that is bent in a stepped manner (crank-shaped in side view). The stepped bent portion 25 connects the fixed contact 21 and the support portion 23, and positions the fixed contact 21 and the support portion 23 at different heights. The PTC thermistor 6 is placed on and supported by convex protrusions (dowels) 24 formed in three locations on the support portion 23. By bending the fixed piece 2 in a stepped manner and positioning the fixed contact 21 and the support portion 23 at different levels, a space for accommodating the PTC thermistor 6 can be easily secured.

[0017] Like the fixed piece 2, the terminal piece 3 is formed by pressing a metal plate whose main component is copper or the like, and is embedded in the case body 7 by insert molding. The terminal piece 3 has a connection portion 31 connected to the movable piece 4, and a terminal 32.

[0018] The connection portion 31 is exposed to the accommodation portion 73 of the case body 7 from a part of the recess 73b formed inside the case body 7, and is electrically connected to the movable piece 4. On the other hand, the terminal 32 protrudes from the side wall of the case body 7 on the opposite side to the terminal 22, and is connected to a land portion of the circuit board, a tab of the secondary battery circuit, or the like. The terminal 32 may be configured to be exposed from the bottom wall of the case body 7.

[0019] The movable piece 4 is formed into a plate shape by pressing a metal material whose main component is copper, etc. The movable piece 4 is formed into an arm shape symmetrical with respect to the center line in the longitudinal direction.

[0020] As in the breaker disclosed in the above-mentioned Patent Document 1, the movable piece 4 may be formed integrally with the terminal piece 3. In this case, a terminal 32 is formed on a part of the movable piece 4 (on the side of a connection portion 42 described later), and the terminal 32 protrudes from the side wall of the case body 7.

[0021] A movable contact 41 is formed at one end of the movable piece 4. The movable contact 41 is formed on the bottom surface of the movable piece 4 using the same material as the fixed contact 21, and is joined to the tip of the movable piece 4 by welding, cladding, crimping, or other methods.

[0022] A connection portion 42 that is electrically connected to the connection portion 31 of the terminal piece 3 is formed at the other end of the movable piece 4. The top surface of the connection portion 31 of the terminal piece 3 and the bottom surface of the connection portion 42 of the movable piece 4 are fixed together by, for example, laser welding. Laser welding is a welding technique in which workpieces (corresponding to the terminal piece 3 and the movable piece 4 in this embodiment) are irradiated with laser light to locally melt and solidify the workpieces, thereby joining them together. Laser weld marks are formed on the surface of the workpiece irradiated with laser light, which have a form different from weld marks formed by other welding techniques (for example, resistance welding that utilizes Joule heat).

[0023] The movable piece 4 has an elastic portion 43 between the movable contact 41 and the connecting portion 42. The elastic portion 43 extends from the connecting portion 42 toward the movable contact 41. As a result, the connecting portion 42 is provided on the opposite side of the elastic portion 43 from the movable contact 41.

[0024] The movable piece 4 is fixed by being fixed to the connection part 31 of the terminal piece 3 at the connection part 42, and as the elastic part 43 elastically deforms, the movable contact 41 formed at the tip thereof is pressed against the fixed contact 21 and makes contact, thereby enabling electrical conduction between the fixed piece 2 and the movable piece 4. The movable piece 4 and the terminal piece 3 are electrically connected at the connection parts 31 and 42, so that electrical conduction between the fixed piece 2 and the terminal piece 3 is possible.

[0025] The movable piece 4 is curved or bent by press working at the elastic portion 43. There are no particular limitations on the degree of curvature or bending as long as it can accommodate the thermally responsive element 5, and it may be set appropriately taking into consideration the elastic force at the operating temperature and the return temperature, the pressing force of the contacts, etc. Also, a pair of protrusions (contact portions) 44a, 44b are formed on the bottom surface of the elastic portion 43 so as to face the thermally responsive element 5. The protrusions 44a, 44b contact the thermally responsive element 5, and deformation of the thermally responsive element 5 is transmitted to the elastic portion 43 via the protrusions 44a, 44b (see FIGS. 1 and 3).

[0026] The thermally responsive element 5 transitions from a conductive state in which the movable contact 41 contacts the fixed contact 21 to a disconnected state in which the movable contact 41 is separated from the fixed contact 21. The thermally responsive element 5 has an initial shape with an arc-shaped cross section that is convex toward the movable piece 4, and is formed by laminating thin plates with different thermal expansion coefficients. When heated to an operating temperature, the curved shape of the thermally responsive element 5 reverses with a snap motion and returns to its original shape when cooled below the recovery temperature. The initial shape of the thermally responsive element 5 can be formed by press working. The material and shape of the thermally responsive element 5 are not particularly limited, as long as the reverse bending action of the thermally responsive element 5 pushes up the elastic portion 43 of the movable piece 4 at the desired temperature and the elastic force of the elastic portion 43 returns it to its original state. However, a rectangular shape is preferable from the standpoint of productivity and efficiency of the reverse bending action, and a rectangular shape close to a square is preferable to efficiently push up the elastic portion 43 while maintaining a small size. The material of the thermally responsive element 5 may be a laminate of two materials with different thermal expansion coefficients, for example, a copper-nickel-manganese alloy or a nickel-chromium-iron alloy on the high expansion side, and an iron-nickel alloy or various alloys such as nickel silver, brass, and stainless steel on the low expansion side, and these materials may be combined according to the required conditions.

[0027] The PTC thermistor 6 establishes electrical continuity between the fixed piece 2 and the movable piece 4 when the movable piece 4 is in an interrupted state. The PTC thermistor 6 is disposed between the support 23 of the fixed piece 2 and the thermally-activated element 5. That is, the support 23 is located directly below the thermally-activated element 5, sandwiching the PTC thermistor 6 therebetween. When the thermally-activated element 5 reversely bends, interrupting electrical continuity between the fixed piece 2 and the movable piece 4, the current flowing through the PTC thermistor 6 increases. The PTC thermistor 6 can be selected based on operating current, operating voltage, operating temperature, and recovery temperature, as long as it is a positive temperature coefficient thermistor that limits current by increasing its resistance with increasing temperature. The material and shape of the PTC thermistor 6 are not particularly limited as long as these characteristics are not impaired. In this embodiment, a ceramic sintered body containing barium titanate, strontium titanate, or calcium titanate is used. In addition to a ceramic sintered body, a so-called polymer PTC, in which conductive particles such as carbon are incorporated into a polymer, may also be used.

[0028] The case body 7 and the lid member 8 that constitute the case 10 are molded from a thermoplastic resin such as flame-retardant polyamide, polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polybutylene terephthalate (PBT), or other thermoplastic resins that have excellent heat resistance. Materials other than resins may also be used as long as they have properties equivalent to or better than those of the above-mentioned resins.

[0029] The top surface of the case body 7 is formed with a housing section 73, which is an internal space for housing the movable piece 4, the thermally responsive element 5, the PTC thermistor 6, etc. The housing section 73 is recessed from the joint surface with the lid member 8 (the top surface of the case body 7) toward the bottom surface of the case body 7. The housing section 73 has recesses 73a and 73b for housing the movable piece 4, a recess 73c for housing the movable piece 4 and the thermally responsive element 5, and a recess 73d for housing the PTC thermistor 6. The edges of the movable piece 4 and the thermally responsive element 5 incorporated in the case body 7 are abutted by frames that constitute the housing section 73, and are guided during reverse warpage deformation of the thermally responsive element 5.

[0030] A cover piece 9 is embedded in the lid member 8 by insert molding. The cover piece 9 is formed into a plate shape by pressing a metal such as the above-mentioned copper-based metal or a metal such as stainless steel. The cover piece 9 increases the rigidity and strength of the lid member 8 and, in turn, the case 10 serving as the housing, while contributing to the miniaturization of the breaker 1.

[0031] As shown in FIG. 1 , a cover member 8 is attached to the case body 7 so as to cover recesses 73a, 73b, 73c, etc., of the case body 7, which houses the fixed piece 2, terminal piece 3, movable piece 4, thermally-activated element 5, PTC thermistor 6, etc. The case body 7 and cover member 8 are joined together by, for example, ultrasonic welding. At this time, the case body 7 and cover member 8 are continuously joined around the entire periphery of their respective outer edges, improving the airtightness of the case 10. This seals the internal space of the case 10 defined by the housing portion 73, protecting the movable piece 4, thermally-activated element 5, PTC thermistor 6, and other components from the atmosphere outside the case 10. In this embodiment, resin is entirely disposed on the top surface of the cover member 9, further enhancing the airtightness of the housing portion 73.

[0032] 2 shows the operation of the breaker 1 under normal charging or discharging conditions. Under normal charging or discharging conditions, the thermally responsive element 5 maintains its initial shape (before reverse bending). At this time, electrical continuity exists between the fixed piece 2 and the terminal piece 3 of the breaker 1 through the elastic portion 43 of the movable piece 4. The elastic portion 43 of the movable piece 4 may contact the thermally responsive element 5, and the movable piece 4, thermally responsive element 5, PTC thermistor 6, and fixed piece 2 may be electrically connected as a circuit. However, because the resistance of the PTC thermistor 6 is overwhelmingly greater than the resistance of the movable piece 4, the current flowing through the PTC thermistor 6 is substantially negligible compared to the current flowing through the fixed contact 21 and the movable contact 41.

[0033] FIG. 3 illustrates the operation of the breaker 1 during an overcharge or other abnormal condition. When a high temperature occurs due to overcharge or other abnormality, the thermally responsive element 5 reaches its operating temperature and bends backward, pushing up the elastic portion 43 of the movable piece 4 and separating the fixed contact 21 and the movable contact 41. The operating temperature of the thermally responsive element 5, when it deforms 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 interrupted, and a small leakage current flows through the thermally responsive element 5 and the PTC thermistor 6. The PTC thermistor 6 continues to generate heat as long as this leakage current flows, maintaining the thermally responsive element 5 in a bent state and dramatically increasing its resistance. Therefore, current does not flow through the path between the fixed contact 21 and the movable contact 41, and only the small leakage current described above exists (forming a self-holding circuit). This leakage current can be used for other functions of the safety device.

[0034] 4 shows a partially cutaway view of the configuration of the movable piece 4. The movable piece 4 has a thin-walled portion 45 that is thinner than the surrounding area in the elastic portion 43. The thin-walled portion 45 is formed by recessing the bottom surface of the movable piece 4 in the thickness direction of the movable piece 4, in the opposite direction to the thermally responsive element 5.

[0035] 5 shows the circuit breaker 1 in a cryogenic state. The cryogenic state refers to a state in which the ambient temperature around the electrical device in which the circuit breaker 1 is mounted is -10°C or lower, for example.

[0036] 5, in the breaker 1 at an extremely low temperature, the degree of curvature of the thermally responsive element 5 increases, and its central portion 51 approaches the bottom surface of the movable piece 4. However, in the movable piece 4 of this embodiment, a thin-walled portion 45 that is recessed in the opposite direction to the thermally responsive element 5 is formed on the bottom surface of the elastic portion 43, so that the central portion 51 of the thermally responsive element 5 is prevented from coming into contact with the movable piece 4. As a result, even in an extremely low temperature state, the central portion 51 of the thermally responsive element 5 is prevented from pushing up the elastic portion 43 of the movable piece 4, and a stable conductive state can be maintained between the movable contact 41 and the fixed contact 21.

[0037] Furthermore, as shown in FIG. 1, a thin portion 45 is formed in the area of ​​the movable piece 4 facing the central portion 51 of the thermally responsive element 5, so that the movable piece 4 can be positioned close to the thermally responsive element 5, making it possible to easily make the breaker 1 thinner.

[0038] At the thin-walled portion 45, it is desirable that the top surface of the movable piece 4 is substantially flat. "Substantially flat" does not necessarily mean a completely flat shape, but rather means that a slight curvature originally formed in the elastic portion 43 around the thin-walled portion 45 is allowed. In other words, it is desirable that the thin-walled portion 45 is configured so that the top surface of the movable piece 4 does not protrude as the bottom surface of the movable piece 4 is recessed. With this configuration, the cover piece 9 can be disposed close to the movable piece 4, making it possible to easily reduce the thickness of the breaker 1.

[0039] 4, the movable piece 4 has a longitudinal direction DL in which the elastic portion 43 extends toward the movable contact 41, and a lateral direction DS that is perpendicular to the longitudinal direction DL. When the longitudinal direction DL and the lateral direction DS are defined as above, FIGS. 2, 3, and 5 show cross sections perpendicular to the lateral direction DS that pass through the center of the breaker 1 in the lateral direction DS.

[0040] The thin-walled portion 45 is preferably disposed in a region where the distance between the elastic portion 43 and the thermally responsive element 5 is minimum when viewed from the short side direction DS. This configuration further prevents the center portion 51 of the thermally responsive element 5 from pushing up the elastic portion 43 of the movable piece 4, even in an extremely low temperature state, thereby maintaining a stable electrical connection between the movable contact 41 and the fixed contact 21. Furthermore, the movable piece 4 can be disposed even closer to the thermally responsive element 5, making it easier to reduce the thickness of the breaker 1. The distance between the elastic portion 43 and the thermally responsive element 5 is measured with the breaker 1 placed in an atmosphere at room temperature (e.g., 20°C).

[0041] FIG. 6 is a plan view of the movable piece 4 and the thermally responsive element 5 as viewed from the thickness direction of the movable piece 4. As shown in FIG.

[0042] 4 and 6 , the elastic portion 43 has a maximum width portion 46 having a maximum length L1 in the short-side direction DS. The maximum width portion 46 is formed by expanding the central region of the elastic portion 43 in the longitudinal direction DL in the short-side direction DS. The maximum width portion 46 easily increases the elastic force generated by the elastic portion 43, improving the contact pressure between the movable contact 41 and the fixed contact 21 and reducing the contact resistance therebetween.

[0043] In this embodiment, it is desirable that the thin-walled portion 45 is formed in the maximum width portion 46. With this configuration, the reduction in elastic force caused by the formation of the thin-walled portion 45 in the elastic portion 43 is compensated for by the maximum width portion 46, making it possible to easily maintain the contact pressure between the movable contact 41 and the fixed contact 21 at an appropriate value or higher. Furthermore, the formation of the thin-walled portion 45 in the elastic portion 43 suppresses an increase in conductor resistance, making it possible to suppress voltage drop in the movable piece 4.

[0044] 6, it is desirable that the center 45c of area of ​​the thin portion 45 is located closer to the movable contact 41 than the center 5c of area of ​​the thermally responsive element 5. With this configuration, it becomes possible to easily maintain the contact pressure between the movable contact 41 and the fixed contact 21 at an appropriate value or higher.

[0045] As shown in FIG. 4 , the thin-walled portion 45 is formed by providing a hole 45A in the movable piece 4. The bottom of the hole 45A constitutes the thin-walled portion 45. The hole 45A is formed on the bottom surface of the movable piece 4 so as to face the central portion 51 of the thermally responsive element 5. In a breaker 1 in an extremely low temperature state, the central portion 51 of the thermally responsive element 5 is accommodated in the hole 45A formed in the movable piece 4, preventing the central portion 51 of the thermally responsive element 5 from pushing up the elastic portion 43 of the movable piece 4. Note that the hole 45A should be large enough to accommodate the central portion 51 of the thermally responsive element 5, which increases in degree of curvature in an extremely low temperature state, and is preferably formed in a size that does not reach the edge of the elastic portion 43 in the short-side direction DS.

[0046] The hole 45A is preferably formed in a tapered shape such that the area in a plan view seen from the thickness direction of the movable piece 4 increases toward the thermally responsive element 5. With this configuration, even in an extremely low temperature state, the central portion 51 of the thermally responsive element 5 is further prevented from pushing up the elastic portion 43 of the movable piece 4.

[0047] The thin-walled portion 45 may be formed in an elliptical shape with a major axis in the longitudinal direction DL. By combining such a thin-walled portion 45 with a rectangular thermally responsive element 5 with long sides in the longitudinal direction DL, the central portion 51 of the thermally responsive element 5 is further prevented from pushing up the elastic portion 43 of the movable piece 4, even in an extremely low temperature state. Furthermore, the formation of the thin-walled portion 45 in the elastic portion 43 prevents a decrease in elastic force, making it possible to easily maintain the contact pressure between the movable contact 41 and the fixed contact 21 at an appropriate value or higher. Furthermore, the formation of the thin-walled portion 45 in the elastic portion 43 prevents an increase in conductor resistance, making it possible to suppress voltage drop in the movable piece 4.

[0048] 6, in the elastic portion 43, the difference W1A-W1B between the width W1A in the short-side direction DS of the first portion 47 where the thin-walled portion 45 is formed and the width W1B in the short-side direction DS of the thin-walled portion 45 is preferably equal to or greater than the width W2 in the short-side direction DS of the second portion 48 where the movable contact 41 is formed. With this configuration, the reduction in elastic force due to the formation of the thin-walled portion 45 in the elastic portion 43 is suppressed, making it possible to easily maintain the contact pressure between the movable contact 41 and the fixed contact 21 at an appropriate value or higher. Furthermore, the formation of the thin-walled portion 45 in the elastic portion 43 is suppressed, making it possible to suppress the voltage drop in the movable piece 4.

[0049] The thickness of the elastic portion 43 is preferably 0.05 to 0.2 mm. By making the thickness of the elastic portion 43 0.05 mm or more, a decrease in elastic force due to the formation of the thin-walled portion 45 in the elastic portion 43 is suppressed, making it possible to easily maintain the contact pressure between the movable contact 41 and the fixed contact 21 at an appropriate value or higher. In addition, an increase in conductor resistance due to the formation of the thin-walled portion 45 in the elastic portion 43 is suppressed, making it possible to suppress voltage drop in the movable piece 4. On the other hand, by making the thickness of the elastic portion 43 0.2 mm or less, it is possible to easily make the breaker 1 thinner.

[0050] Fig. 7 is a perspective view, with a portion cut away, of a movable piece 4A, which is a modified example of the movable piece 4 in Fig. 4. The configuration of the movable piece 4 described above can be adopted for portions of the movable piece 4A that are not described below.

[0051] 7, the movable piece 4A differs from the movable piece 4 in that the hole 45A penetrates the elastic portion 43. By having the hole 45A penetrate the elastic portion 43, the movable piece 4A has a configuration in which the thickness of the thin-walled portion 45 is zero.

[0052] The movable piece 4A further prevents the center portion 51 of the thermally responsive element 5 from pushing up the elastic portion 43 of the movable piece 4, even at extremely low temperatures, and maintains a stable electrical connection between the movable contact 41 and the fixed contact 21. Furthermore, the movable piece 4 can be positioned even closer to the thermally responsive element 5, making it easier to reduce the thickness of the breaker 1. Furthermore, the movable piece 4A can be manufactured more cheaply and easily than the movable piece 4.

[0053] The breaker 1 and the like of the present invention can also be widely applied to secondary battery packs, safety circuits for electrical equipment, and the like. FIG. 8 shows a secondary battery pack 500. The secondary battery pack 500 includes a secondary battery 501 and a breaker 1 and the like provided in the output circuit of the secondary battery 501. FIG. 9 shows a safety circuit 502 for electrical equipment. The safety circuit 502 includes a breaker 1 and the like connected in series in the output circuit of the secondary battery 501. A part of the safety circuit 502 may be formed by a cable including a connector equipped with a breaker 1 and the like. By using a secondary battery pack 500 or a safety circuit 502 equipped with a breaker 1 and the like, it is possible to manufacture a secondary battery pack 500 or a safety circuit 502 that can maintain a stable conduction state even at extremely low temperatures.

[0054] Although the breaker 1 of the present invention has been described in detail above, the present invention is not limited to the above-mentioned specific embodiment and can be modified and implemented in various aspects. [Note] The present invention includes the following aspects.

[0055] [Invention 1] A breaker comprising: a fixed piece having a fixed contact; a movable piece formed in a plate shape and having an elastically deformable elastic portion and a movable contact at one end of the elastic portion, pressing the movable contact against the fixed contact to bring it into contact; and a thermally responsive element that deforms in response to a change in temperature to transition the movable piece from a conductive state in which the movable contact is in contact with the fixed contact to a cut-off state in which the movable contact is separated from the fixed contact, wherein the movable piece has a thin-walled portion in its thickness direction that is recessed in the opposite direction to the thermally responsive element. [Invention 2] The breaker according to Invention 1, wherein the thin-walled portion is formed by providing a hole in the movable piece, and the hole penetrates the movable piece in the thickness direction. [Invention 3] The breaker according to Invention 1, wherein the thermally responsive element is formed in a curved shape convex toward the movable piece, the movable piece has a longitudinal direction in which the elastic part extends toward the movable contact and a lateral direction perpendicular to the longitudinal direction, and the thin-walled part is arranged in a region where the distance between the elastic part and the thermally responsive element is shortest when viewed from the lateral direction. [Invention 4] The breaker according to Invention 1, wherein the movable piece has a longitudinal direction in which the elastic part extends toward the movable contact and a lateral direction perpendicular to the longitudinal direction, the elastic part has a maximum width part where the length in the lateral direction is maximum, and the thin-walled part is formed in the maximum width part. [Invention 5] The breaker according to Invention 1, wherein, in a plan view viewed from the thickness direction of the movable piece, the center of area of ​​the thin-walled part is located closer to the movable contact than the center of area of ​​the thermally responsive element. [Invention 6] The breaker according to Invention 1, wherein the thin-walled portion is formed by providing a hole in the movable piece, and the hole is formed in a tapered shape such that the area in a plan view seen from the thickness direction increases toward the thermally responsive element. [Invention 7] The breaker according to Invention 1, wherein the movable piece has a longitudinal direction in which the elastic portion extends toward the movable contact and a lateral direction orthogonal to the longitudinal direction, and the thin-walled portion is formed in an elliptical shape having a major axis in the longitudinal direction.[Invention 8] The breaker according to Invention 1, wherein the movable piece has a longitudinal direction in which the elastic portion extends toward the movable contact and a lateral direction perpendicular to the longitudinal direction, and in the elastic portion, a difference W1A-W1B between a width W1A in the lateral direction of a first portion in which the thin portion is formed and a width W1B in the lateral direction of the thin portion is equal to or greater than a width W2 in the lateral direction of a second portion in which the movable contact is formed. [Invention 9] The breaker according to Invention 1, wherein a thickness of the elastic portion is 0.05 to 0.2 mm. [Invention 10] A safety circuit for an electrical device, comprising the breaker according to any one of Inventions 1 to 9. [Invention 11] A secondary battery pack, comprising the breaker according to any one of Inventions 1 to 9.

[0056] 1: Breaker 2: Fixed piece 4: Movable piece 4A: Movable piece 5: Thermally responsive element 5c: Center of area 21: Fixed contact 41: Movable contact 43: Elastic portion 45: Thin portion 45A: Hole 45c: Center of area 46: Maximum width portion 47: First portion 48: Second portion 500: Secondary battery pack 501: Secondary battery 502: Safety circuit DL: Longitudinal direction DS: Shortitudinal direction W1A: Width W1B: Width W2: Width

Claims

1. A breaker comprising: a fixed piece having a fixed contact; a movable piece formed in a plate shape and having an elastic portion that elastically deforms and a movable contact at one end of the elastic portion, the movable contact being pressed against the fixed contact to bring it into contact; and a thermally responsive element that deforms in response to a change in temperature, thereby transitioning the movable piece from a conductive state in which the movable contact is in contact with the fixed contact to a cut-off state in which the movable contact is separated from the fixed contact, wherein the movable piece has a thin portion in its thickness direction that is recessed in the opposite direction to the thermally responsive element.

2. The breaker according to claim 1, wherein the thin-walled portion is formed by providing a hole in the movable piece, the hole penetrating the movable piece in the thickness direction.

3. A breaker as described in claim 1, wherein the thermally responsive element is formed in a curved shape that is convex toward the movable piece, the movable piece has a longitudinal direction in which the elastic portion extends toward the movable contact and a lateral direction perpendicular to the longitudinal direction, and the thin-walled portion is arranged in a region where the distance between the elastic portion and the thermally responsive element is minimum when viewed from the lateral direction.

4. A breaker as described in claim 1, wherein the movable piece has a longitudinal direction in which the elastic portion extends toward the movable contact and a lateral direction perpendicular to the longitudinal direction, the elastic portion has a maximum width portion whose length in the lateral direction is maximum, and the thin portion is formed in the maximum width portion.

5. A breaker as claimed in claim 1, wherein in a plan view seen from the thickness direction of said movable piece, the centre of area of ​​said thin-walled portion is located on the side of said movable contact relative to the centre of area of ​​said thermally responsive element.

6. A breaker as described in claim 1, wherein the thin-walled portion is formed by providing a hole in the movable piece, and the hole is formed in a tapered shape such that the area in a plan view viewed from the thickness direction increases toward the thermally responsive element.

7. A breaker as claimed in claim 1, wherein said movable piece has a longitudinal direction in which said elastic portion extends towards said movable contact and a lateral direction perpendicular to said longitudinal direction, and said thin-walled portion is formed in an elliptical shape having a major axis in said longitudinal direction.

8. The breaker as described in claim 1, wherein the movable piece has a longitudinal direction in which the elastic portion extends toward the movable contact and a lateral direction perpendicular to the longitudinal direction, and in the elastic portion, a difference W1A-W1B between a width W1A in the lateral direction of a first portion in which the thin portion is formed and a width W1B in the lateral direction of the thin portion is equal to or greater than a width W2 in the lateral direction of a second portion in which the movable contact is formed.

9. The breaker according to claim 1, wherein the thickness of said elastic portion is 0.05 to 0.2 mm.

10. A safety circuit for electrical equipment comprising a circuit breaker according to any one of claims 1 to 9.

11. A secondary battery pack comprising a breaker according to any one of claims 1 to 9.

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