Breaker

Abstract

[Problem] To provide a breaker that makes it possible to easily return a thermally actuated element to an initial state. [Solution] A breaker 1 comprises: a fixed piece 2 that has a fixed contact 21; a movable piece 3 that has a movable contact 31 and that presses the movable contact 31 against the fixed contact 21 to be brought into contact with each other; a thermally actuated element 4 that deforms, due to temperature change, from a curved first shape to a reversely-curved second shape to thereby actuate the movable piece 3 so as to separate the movable contact 31 from the fixed contact 21; a case 6 that has an accommodation part 60 in which the fixed piece 2, the movable piece 3, and the thermally actuated element 4 are accommodated; and a return switch 5 that physically returns the thermally actuated element 4 from the second shape to the first shape. The return switch 5 has a plurality of protrusions 52 that protrude toward the thermally actuated element 4.

Description

breaker

[0001] The present invention relates to a circuit breaker that interrupts current when the ambient temperature becomes abnormally high.

[0002] Conventionally, secondary batteries, motors, etc. of electrical devices are provided with temperature protection devices (breakers) that cut off current when the ambient temperature becomes abnormally high. In particular, secondary battery packs containing lithium-ion batteries can become extremely hot when charged under abnormal conditions such as overcharging, posing a risk of fire, so temperature protection devices such as the breakers are generally provided to ensure safety.

[0003] Known examples of this type of breaker include a fixed piece having a fixed contact, a movable piece having a movable contact that presses the movable contact against the fixed contact to bring it into contact, and a thermally responsive element that deforms with temperature changes to activate the movable piece so that the movable contact moves away from the fixed contact (see, for example, Patent Document 1).

[0004] The breaker described in Patent Document 1 uses a bimetal as a thermally responsive element. The bimetal is made of a laminate of multiple types of plate-shaped metal materials with different thermal expansion coefficients, and can change shape in response to temperature changes. The thermally responsive element is initially curved, for example, in a circular arc when viewed from the side. When the element reaches its operating temperature due to overheating, the curved shape of the thermally responsive element reverses with a snap motion. The breaker utilizes this shape change of the thermally responsive element to separate the movable contact from the fixed contact, thereby interrupting current flow. Furthermore, when the thermally responsive element cools down below its reset temperature, it returns to its initial shape, and the movable contact and the fixed contact return to their contact state.

[0005] WO2011 / 105175

[0006] Although circuit breakers interrupt current in response to abnormal ambient temperatures, there are cases where, for example, if the cause of the abnormality has not been resolved, they cannot immediately resume power even if the ambient temperature drops. Electrical equipment that is susceptible to such situations uses so-called one-shot circuit breakers, which do not return to a conductive state even if the ambient temperature drops after interrupting the current. One-shot circuit breakers are designed so that the reset temperature of the thermally responsive element is set to a low temperature below 0°C and the thermally responsive element does not return to its initial state at room temperature (5-35°C).

[0007] However, in product testing of one-shot breakers, after confirming that the product properly interrupts current when it reaches its operating temperature, returning the thermally responsive element to its initial state requires a time-consuming and equipment-intensive process, such as cooling the tested product in a freezer. Furthermore, for example, safety testing may be performed with the breaker mounted in electrical equipment, and it may be preferable for the user to be able to return the thermally responsive element to its initial state.

[0008] The present invention has been made to solve the above problems, and has an object to provide a breaker that can easily return a thermally responsive element to its initial state.

[0009] In order to achieve the above-mentioned object, the breaker of the present invention comprises a fixed piece having a fixed contact, a movable piece having a movable contact and pressing the movable contact against the fixed contact to bring it into contact, a thermally responsive element that operates the movable piece so that the movable contact moves away from the fixed contact by deforming from a curved first shape to a reversely curved second shape in response to a temperature change, a case having a housing portion that houses the fixed piece, the movable piece, and the thermally responsive element, and a reset switch that physically returns the thermally responsive element from the second shape to the first shape, and is characterized in that the reset switch has a plurality of protrusions that protrude toward the thermally responsive element.

[0010] In the above-described breaker, it is preferable that the thermally responsive element has a polygonal shape in a plan view, and the plurality of protrusions protrude toward two or more corners that are diagonally opposite each other of the thermally responsive element.

[0011] In the above-mentioned breaker, it is preferable that the return switch further has a rectangular, flat base portion and a return button protruding from approximately the center of one face of the base portion, and that the case has an opening that exposes the return button to the outside.

[0012] In the above breaker, it is preferable that a part of the reset button protrudes outward from the outer surface of the case when the thermally responsive element is in the second shape.

[0013] In the above breaker, it is preferable that the reset button is colored differently from the case.

[0014] In the above-mentioned breaker, it is preferable that the return switch has a pair of protrusions protruding in a planar direction from two opposing sides of the base portion, and that the accommodating portion has a groove portion into which the protrusions are fitted to regulate the operating range of the return switch.

[0015] According to the present invention, by operating the return switch, the thermally responsive element can be physically returned from the second shape to the first shape, so that the thermally responsive element can be easily returned to its initial state.

[0016] 2A and 2B are exploded perspective views of a breaker according to an embodiment of the present invention. (a) is a plan view of the breaker, (b) is a side view of the breaker when the thermally responsive element is in a first shape (conductive state), and (c) is a side view of the breaker when the thermally responsive element is in a second shape (abnormal state). (a) is a perspective view mainly showing the top of a return switch used in the breaker, and (b) is a perspective view mainly showing the bottom. (a) is a cross-sectional view taken along line A-A in FIG. 2A when the thermally responsive element is in the first shape (conductive state), and (b) is a cross-sectional view taken along line B-B in FIG. 2A when the thermally responsive element is in the first shape (conductive state), and (b) is a cross-sectional view when the thermally responsive element is in the second shape (abnormal state). 10A is a perspective view mainly showing the top surface of a modified example of the return switch, and FIG. 10B is a perspective view mainly showing the bottom surface.

[0017] A circuit breaker according to one embodiment of the present invention will be described with reference to the drawings. The circuit breaker 1 of this embodiment includes a current interruption device that interrupts current in response to temperature changes. As shown in FIGS. 1 and 2(a) to 2(c), the current interruption device is primarily composed of a fixed piece 2 having a fixed contact 21, a movable piece 3 having a movable contact 31 at its tip, and a thermally responsive element 4 that deforms in response to temperature changes. The circuit breaker 1 also includes a reset switch 5 that physically returns the thermally responsive element 4 from its activated state (second shape) to its initial state (first shape), and a case 6 that houses the current interruption device. While a typical circuit breaker includes a PTC thermistor between the fixed piece 2 and the thermally responsive element 4, the circuit breaker 1 of this embodiment is designed as a one-shot circuit breaker that does not return to a conductive state at room temperature, and therefore does not include a PTC thermistor.

[0018] The fixed piece 2 is formed, for example, by pressing a metal plate whose main component is copper, and a part of it is embedded in the case 6 by insert molding (see also FIGS. 5(a) and 5(b)). The fixed contact 21 is formed in a position opposite the movable contact 31 by cladding, plating, crimping, or coating with a highly conductive material such as silver, a copper-silver alloy, or a gold-silver alloy. A terminal 22 that is electrically connected to an external circuit is formed on one end of the fixed piece 2, and the terminal 22 protrudes outward from the edge of the case 6.

[0019] The movable piece 3 is formed by pressing a strip-shaped metal plate into an arm shape symmetrical about the longitudinal centerline. The width of the movable piece 3 in the transverse direction is smaller than the width of the thermally responsive element 4 and narrower than the spacing between the protrusions 52 of the return switch 5 (see also FIGS. 4( a ) and 4 ( b )). The material of the movable piece 3 is preferably a material mainly composed of copper, similar to that of the fixed piece 2. The movable contact 31 is formed of the same material as the fixed contact 21 and is bonded near one end of the movable piece 3, which forms a free end. A fixed portion 32 is formed on the portion of the movable piece 3 opposite the free end where the movable contact 31 is provided, and is fixed to the case 6. The portion between the movable contact 31 and the fixed portion 32 forms an elastic portion 34. The movable piece 3 extends further outward from the fixed portion 32, forming a terminal 33 that is electrically connected to an external circuit. Furthermore, the movable piece 3 has a protrusion 35 on the surface of the elastic part 34 that faces the thermally responsive element 4, making it easier for the elastic part 34 to be pushed up by changes in the shape of the thermally responsive element 4. With this configuration, the elastic part 34 of the movable piece 3 elastically deforms, and the movable contact 31 formed at its free end is pressed against and comes into contact with the fixed contact 21, thereby enabling electrical conduction between the fixed piece 2 and the movable piece 3.

[0020] The thermally actuated element 4 has a polygonal shape (approximately rectangular in this embodiment) in plan view and a first shape (initial shape) that is curved like an upwardly convex arc in side view. It is formed by stacking thin plates with different thermal expansion coefficients. Note that in Figures 4(a) and 4(b) and Figures 5(a) and 5(b), the thermally actuated element 4 is highlighted with dashed lines. When heated to an operating temperature, the curved shape of the thermally actuated element 4 snaps into a downwardly convex, reversely warped second shape. Upon cooling below the recovery temperature, the thermally actuated element 4 returns to its first shape. The first shape of the thermally actuated element 4 is formed by press working. The shape of the thermally actuated element 4 is preferably a rectangle close to a square to efficiently push up the elastic portion 34 while maintaining a compact size. Note that the thermally actuated element 4 of this embodiment is formed so that, when incorporated into the breaker 1, the direction along the longitudinal direction of the movable piece 3 is slightly longer than the direction perpendicular thereto. The width of the thermally responsive element 4 in the lateral direction is larger than the width of the movable piece 3 in the lateral direction.

[0021] The material of the thermally responsive element 4 is, for example, a laminate of two materials with different thermal expansion coefficients, such as 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, or stainless steel on the low expansion side, which are used in combination according to the required conditions. Note that the breaker 1 of this embodiment is intended to be a so-called one-shot breaker that does not return to a conductive state even when the ambient temperature drops below its operating temperature after interrupting the current, and the return temperature is preferably set to 0°C or below.

[0022] 3(a) and 3(b), the return switch 5 has a rectangular flat base 51, a plurality of protrusions 52 protruding toward two or more diagonally opposite corners of the thermally actuated element 4, and a return button 53 protruding from approximately the center of one surface of the base 51. In the return switch 5 of this embodiment, four protrusions 52 are provided at the four corners of the other surface of the base 51, respectively, but the number of protrusions 52 is not limited to four, as in a modified example described later. The return switch 5 is formed from a hard resin that is resistant to elastic deformation, such as a thermoplastic resin composition such as flame-retardant polyamide, polyphenylene sulfide (PPS), liquid crystal polymer (LCP), or polybutylene terephthalate (PBT) that has excellent heat resistance.

[0023] The base portion 51 is a plate-like member having a predetermined strength, and is formed into a substantially rectangular shape with one side slightly longer than the other so that its planar shape is substantially the same as that of the thermally actuated element 4. The four corners of the base portion 51 are rounded. The protrusions 52 are thin, cylindrical members that are erected at the four corners of the base portion 51. The reset button 53 is a cylindrical member that is thicker than the protrusions 52, and is erected at the center of the surface opposite the protrusions 52 so that the distances between the reset button 53 and the four protrusions 52 are equal. Therefore, when the reset button 53 is pressed from above, the pressing force is equally distributed and transmitted to the four protrusions 52.

[0024] The return switch 5 also has a pair of protrusions 54 that protrude in a planar direction from two opposing sides of the base part 51. In this embodiment, the protrusions 54 are provided on two longitudinal sides of the base part 51, respectively, and the upper and lower surfaces of the protrusions 54 are flush with the upper and lower surfaces of the base part 51.

[0025] The case 6 is a box-shaped member that is approximately rectangular in plan view and includes a resin base 61 that houses the thermally responsive element 4 and other components, and a resin cover 62 that is welded to the resin base 61 (see FIG. 1 again). In this embodiment, of the resin base 61 and the resin cover 62, an accommodation section 60 that houses the main components of the current interruption means is formed on the resin base 61 side. On the other hand, the resin cover 62 is the member that has a small accommodation section volume and is relatively thin. Like the return switch 5, the resin base 61 and the resin cover 62 are formed from a thermoplastic resin composition such as flame-retardant polyamide, or excellent heat-resistant polyphenylene sulfide (PPS), liquid crystal polymer (LCP), or polybutylene terephthalate (PBT).

[0026] The resin base 61 has a rectangular shape in a plan view, and the terminals 22 of the fixed piece 2 extend in the longitudinal direction of the resin base 61. The resin base 61 also holds the fixed piece 2 with the outer surfaces of the support portions 23 of the fixed piece 2 (the surfaces opposite to the surfaces on which the fixed contacts 21 are provided) exposed to the outside on the bottom surface (outside) of the resin base 61 (see FIGS. 5( a) and 5(b)).

[0027] The accommodation portion 60 of the resin base 61 is formed in a shape corresponding to the return switch 5 in a plan view. The accommodation portion 60 also has a groove 63 into which the protrusion 54 of the return switch 5 is fitted to restrict the operating range of the return switch 5. The groove 63 has a shape corresponding to the protrusion 54 in a plan view, and fitting the protrusion 54 into the groove 63 prevents the return switch 5 from shifting in the longitudinal direction of the case 6. The depth of the groove 63 is shallower than the bottom of the accommodation portion 60. Even if the return button 53 is pressed hard, the protrusion 54 abuts against the underside of the groove 63, so the return switch 5 can only be pressed within the depth range of the groove 63, preventing excessive load from being applied to the thermally responsive element 4. In addition, a dish-shaped mounting portion 66 on which the thermally responsive element 4 is placed is provided in the center of the bottom surface of the accommodating portion 60, and the mounting portion 66 supports the lower surface of the thermally responsive element 4, which has a second shape that is convex downward.

[0028] The resin cover 62 has a recess 64 that serves as a space for accommodating the return switch 5, and a groove 63 that partially fits over the protrusion 54 is formed around the periphery of the recess 64 (see FIG. 4A). The resin cover 62 also has an opening 65 that exposes the return button 53 to the outside. The opening 65 is formed so that the diameter near the inner surface corresponds to the outer diameter of the return button 53, and the diameter near the outer surface is wider than that near the inner surface so that the return button 53 can be easily pressed in with a finger.

[0029] A reinforcing member 7 is embedded in the resin cover 62. The reinforcing member 7 is a rectangular, flat metal plate, formed by pressing, for example, a metal plate primarily composed of copper or stainless steel. The reinforcing member 7 contributes to the miniaturization of the breaker 1 while increasing the rigidity and strength of the case 6 as a housing. The reinforcing member 7 in this embodiment is insert-molded into the resin cover 62, with one end protruding outside the case. The reinforcing member 7 also has a round hole formed therein corresponding to the opening 65 of the resin cover 62 so that the reset button 53 can be inserted therethrough.

[0030] 2(b), 4(a), and 5(a) show the states of the breaker 1 when the normal current path is operating. In the conductive state, the thermally responsive element 4 maintains its first shape (initial shape) that is convex upward, the fixed contact 21 and the movable contact 31 are in contact, and current flows between the two terminals 22 and 33 of the breaker 1 through the elastic portion 34 of the movable piece 3, etc.

[0031] In the conductive state, the thermally responsive element 4 is in the first shape, and its peripheral portion is positioned lower than the upwardly convex central portion, so that the return switch 5 placed via the protrusions 52 on the four corners of the thermally responsive element 4 is placed in the lower position, and the return button 53 is housed within the case 6. Note that a weak biasing force that does not prevent the deformation of the thermally responsive element 4, or contact resistance between the case 6 and the return switch 5, may be applied to the return switch 5 so as to keep it in the lower position in the conductive state.

[0032] 2(c), 4(b), and 5(b) show the state of the breaker 1 when an abnormality occurs. When the temperature rises due to an abnormality, the thermally responsive element 4 reaches its operating temperature and warps inward, forming a second shape that is convex downward, pushing up the elastic portion 34 of the movable piece 3, separating the fixed contact 21 and the movable contact 31.

[0033] In an abnormal state, the peripheral portion of the thermally responsive element 4 is raised relative to the center portion, so that the reset switch 5 is pushed up to an upper position and the reset button 53 protrudes outward from the outer surface of the case 6. Therefore, in the breaker 1, whether or not an abnormal state is present can be visually confirmed by whether or not the reset button 53 protrudes. In addition, it is preferable that the reset button 53 be colored differently from the case 6. For example, if the case 6 is black and the outer periphery of the cylindrical portion of the reset button 53 is colored red, it becomes easy to identify that the reset button 53 is protruding, and it becomes possible to confirm at a glance whether or not an abnormal state is present.

[0034] In this embodiment, the return temperature for the thermally responsive element 4 to return from the second shape to the first shape is set lower than the operating temperature. Therefore, after interrupting the current, the breaker 1 does not return to a conductive state even when the ambient temperature drops below the operating temperature. However, when an operator presses the reset button 53 with their finger, the protrusions 52 press the four corners of the thermally responsive element 4, physically returning the thermally responsive element 4 from the second shape to the first shape. Thus, with the breaker 1, the thermally responsive element 4 can be easily returned to its initial state by operating the reset switch 5. This simplifies the product inspection process, eliminating the need to freeze the inspected product after confirming that it properly interrupts the current when it reaches the operating temperature. Furthermore, users can easily perform safety inspections of electrical equipment incorporating the breaker 1.

[0035] 6(a) and 6(b) show a modified return switch 5'. In this modified return switch 5', protrusions 52 are provided at two diagonally opposite corners of the base 51. The thermally actuated element 4 is formed symmetrically about its longitudinal centerline, so that pressing the two diagonally opposite corners returns the switch to its initial state. This modified return switch 5' requires less resin material than the return switch 5 having four protrusions 52. Furthermore, the fewer protrusions 52 create more free space within the case 6, making it suitable for incorporating additional components within the case 6. While the above embodiment and modified examples illustrate configurations in which the thermally actuated element 4 and the base 1 are generally rectangular, the shape of the thermally actuated element 4 is not limited to a generally rectangular shape and can be any polygonal shape as long as the thermally actuated element 4 can be returned from the second shape to the first shape by physical pressure. Furthermore, the shape of the base 51 and the arrangement of the protrusions 52 can be appropriately configured and arranged to correspond to the shape of the thermally actuated element 4.

[0036] The present invention is not limited to the above embodiment, and various modifications are possible as long as the breaker 1 is configured to include a reset switch 5 that physically returns the thermally responsive element 4 from the second shape (abnormal state) to the first shape (conducting state). In the breaker 1 of the above embodiment, the reset switch 5 is also housed in the case 6, but the reset switch 5 may not be housed in the case 6. For example, the case 6 may be formed with a plurality of holes through which the protrusions 52 of the reset switch 5 are inserted, and these holes may be connected to the four corners of the thermally responsive element 4, so that the reset switch 5 is attached and the thermally responsive element 4 is pushed in from outside the case 6 when returning the thermally responsive element 4 from the second shape to the first shape.

[0037] REFERENCE SIGNS LIST 1 breaker 2 fixed piece 21 fixed contact 3 movable piece 31 movable contact 4 thermally responsive element 5 return switch 51 base portion 52 protrusion portion 53 return button 54 convex portion 6 case 60 storage portion 63 groove portion 65 opening

Claims

1. A breaker comprising: a fixed piece having a fixed contact; a movable piece having a movable contact and pressing the movable contact against the fixed contact to bring them into contact; a thermal responsive element that deforms in accordance with a temperature change from a curved first shape to a second shape that is reverse to the first shape, thereby operating the movable piece so that the movable contact is separated from the fixed contact; a case having a housing portion for housing the fixed piece, the movable piece, and the thermal responsive element; and a return switch for physically returning the thermal responsive element from the second shape to the first shape, wherein the return switch has a plurality of protrusions protruding toward the thermal responsive element.

2. The breaker according to claim 1, wherein the thermal responsive element is polygonal in plan view, and the plurality of protrusions respectively protrude toward two or more corners that are in a diagonal relationship with respect to the thermal responsive element.

3. The breaker according to claim 2, wherein the return switch further has a rectangular flat base portion and a return button protruding substantially at the center of one surface of the base portion, and the case has an opening for exposing the return button to the outside.

4. The breaker according to claim 3, wherein when the thermal responsive element is in the second shape, a part of the return button protrudes outside the outer surface of the case.

5. The breaker according to claim 3 or claim 4, wherein the return button is colored differently from the case.

6. The breaker according to claim 3 or claim 4, wherein the return switch has a pair of convex portions protruding in a planar direction from two opposing sides of the base portion, and the housing portion has a groove portion into which the convex portions are fitted to restrict the operating range of the return switch.

Images