Protection Devices

Abstract

To provide a protection device having a new mechanism.SOLUTION: A protection device has a movable arm (12), a fixed terminal (14), a bimetal member (16), and a casing (18) for accommodating them. The bimetal member (16) is located one of above and below the movable arm (12). One end (36) of the bimetal member (16) exerts force on one end (34) of the movable arm (12), whereby the one end (34) of the movable arm and the fixed terminal (14) are held in a contact state.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a protection device, and more particularly to a device used for protecting an electric circuit, protecting an electric device, etc. For example, such a device is incorporated into an electric circuit of an electric device, and when an abnormal current flows in the electric circuit due to a failure of the electric device, etc., the device functions as a so-called circuit breaker that blocks the flow of current to protect all downstream electric loads. In another embodiment, the device functions as a so-called circuit protector that blocks abnormal current to individual electric loads to protect the electric loads. [Background technology]

[0002] A protective device is known that is configured to open an electric circuit by utilizing the phenomenon in which a bimetal member is heated and reversely deformed by heat generated by the flow of abnormal current, thereby interrupting the abnormal current (see, for example, Patent Document 1 below). This protective device has a bimetal member below a movable arm in a state in which a contact provided on the movable arm of a terminal into which current flows and a contact provided on a fixed terminal of a terminal from which current flows are in contact. The movable arm is configured to use metallic elasticity to press (i.e., bias) its contact against a contact on the fixed terminal, thereby maintaining the contact state between the contacts.

[0003] When a normal current flows through the electric circuit of an electric device in which this protection device is installed, both contacts are in contact, closing the circuit, and the bimetal member is located below the movable arm. When an abnormal current flows through the electric circuit, the current heats the movable arm, the fixed terminal, etc., and the bimetal member is heated and reversed in shape. As a result, the bimetal member pushes up the movable arm, causing the contacts of the movable arm to move upward, separating the previously in contact contacts and opening the electric circuit.

[0004] When such a protection device is used in an electrical device, for example, when an abnormality occurs in the device that generates an abnormal current, and the abnormality is then eliminated, the contacts of the protection device separate and then come into contact. When such separation and contact are repeated, the contacts may wear out due to arcing caused by the opening and closing of the contacts. This wear requires the movable arm to be pressed more downward, but this, combined with the fact that the pressing force of the movable arm changes over time (so-called "sag") and the pressing force against the fixed terminal may become insufficient, may reduce the contact force between the contacts. In addition, wear powder may be generated due to wear, causing fine irregularities on the surface of the contacts. When the contacts open and close under such conditions, arc discharge is more likely to occur.

[0005] The arc discharge that occurs as described above may eventually cause the contacts to fuse together. If the contacts fuse together, the contacts will remain in contact and will not open even if an abnormal current flows (therefore, the electric circuit will remain in a closed state and will not open), making it impossible to interrupt the abnormal current, resulting in a failure state in which the protective device does not perform its function, and it may not be able to protect electrical equipment, electrical circuits, etc. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2003-297204 A Summary of the Invention [Problem to be solved by the invention]

[0007] The problem to be solved by the present invention is to provide a new mechanism for opening and closing the contacts in the above-mentioned protection device. [Means for solving the problem]

[0008] In a first aspect, the present invention provides a protection device including a fixed terminal, a movable arm and a bimetal member located above the fixed terminal, and a casing that houses these members, the protection device comprising: the bimetal member is located at one of the upper and lower sides of the movable arm; One end of the bimetal member applies a force to one end of the movable arm, thereby holding the one end of the movable arm in contact with the fixed terminal.

[0009] In such a protective device of the present invention, both the movable arm and the bimetal member are located above the fixed terminal, and when no force is applied by that one end of the bimetal member, that one end of the movable arm is in its original state spaced apart from the fixed terminal, but when force is applied by that one end of the bimetal member, that one end of the bimetal member holds that end of the movable arm in contact with the fixed terminal, resisting the elastic force of the movable arm.

[0010] Therefore, when the force that the one end of the bimetal member applies to the one end of the movable arm is reduced, preferably substantially eliminated, and the elastic force of the movable arm becomes greater than the reduced force, the one end of the movable arm is permitted to move upward, and as a result, it moves away from the fixed terminal, forming a gap therebetween. The reduction in the force applied by the one end of the bimetal member described above is caused by the reversal of the bimetal member.

[0011] In one embodiment, the force applied by the one end of the bimetal member to the one end of the movable arm can be a pressing force by the one end of the bimetal member pressing (or pushing down) the one end of the movable arm toward the fixed terminal, or in another embodiment, a pulling force by the one end of the bimetal member pulling (or pulling down) the one end of the movable arm toward the fixed terminal.

[0012] In a first preferred embodiment, in the protection device of the present invention, the bimetallic member is located above the movable arm, and said one end of the bimetallic member applies a force, i.e. a pressing force, to said one end of the movable arm, thereby pressing said one end of the movable arm towards and holding them in contact with the fixed terminal (thereby providing electrical continuity between the movable arm and the fixed terminal).

[0013] In this embodiment, the protective device (10) comprising the movable arm (12), the fixed terminal (14), and the bimetal member (16) as well as the casing (18) housing them has the fixed terminal (14) below the movable arm (12) and the bimetal member (16) above the movable arm (12). When the bimetal member is inverted, it allows the one end of the movable arm to move upward, whereby the one end of the movable arm moves away from the fixed terminal to form a gap between the one end of the movable arm and the fixed terminal (so that electrical continuity between them can be interrupted).

[0014] In a second preferred embodiment, in the protection device of the present invention, the bimetallic member is located below the movable arm, and said one end of the bimetallic member applies a force, i.e. a pulling force, to said one end of the movable arm, thereby pressing said one end of the movable arm towards and holding them in contact with the fixed terminal (thereby providing electrical continuity between the movable arm and the fixed terminal).

[0015] In this embodiment, the protective device (10) comprising the movable arm (12), the fixed terminal (14), and the bimetal member (16) as well as the casing (18) housing them has the fixed terminal (14) below the movable arm (12) and the bimetal member (16) between the fixed terminal and the movable arm (12). When the bimetal member is inverted, it allows the one end of the movable arm to move upward, whereby the one end of the movable arm moves away from the fixed terminal to form a gap between the one end of the movable arm and the fixed terminal (as a result, electrical continuity between them can be interrupted).

[0016] In either embodiment, the rigidity of the bimetallic member is utilized so that the one end of the bimetallic member applies a force to the one end of the movable arm to forcibly bring it closer to the fixed terminal and maintain the state of contact between them. Also, when the bimetallic member reaches a threshold temperature and reverses, the one end of the bimetallic member is displaced in a direction away from the fixed terminal, and this is utilized to reduce, preferably to zero, the force applied to the one terminal of the movable arm, thereby allowing the one end of the movable arm to move away from the fixed terminal.

[0017] In the protective device of the present invention, the movable arm and the bimetal member may have a so-called cantilever structure in which one end of each of them is a free end and the other end is a fixed end (or fulcrum). The other end is, for example, integrally held within the casing. The movable arm and the fixed terminal may be made of the same or different types of electrically conductive materials, such as copper, phosphor bronze, beryllium copper, nickel silver, brass, and stainless steel, as necessary to form part of the electric circuit in which the protective device is arranged. In another embodiment, they may be made of various clad materials of such materials.

[0018] In the protection device of the present invention, the state in which electrical continuity between the movable arm and the fixed terminal is provided as described above is also referred to as the "closed state (including the action of closing the circuit and the state in which the circuit is closed)," and the state in which electrical continuity between the movable arm and the fixed terminal is interrupted as described above is also referred to as the "open state (including the action of opening the circuit and the state in which the circuit is open)." The protection device of the present invention is manufactured and supplied as a product in the closed state, and can be incorporated into a given electric circuit or electric device in that state.

[0019] Normally, when a normal current flows in an electrical device having an electrical circuit in which the protective device is installed, the protective device is in a closed state. When an abnormal current flows, the bimetallic member is heated above a certain threshold temperature by heat generated by the abnormal current, and the protective device reverses to an open state, thereby interrupting the flow of current. When the temperature of the bimetallic member, which is no longer heated by the interruption of the current, drops below the threshold temperature, the bimetallic member returns to its original shape (i.e., recovers), and the protective device returns to a closed state, causing the abnormal current to flow through the electrical circuit again.

[0020] In a preferred embodiment of the invention, the movable arm has a contact at one end thereof which contacts the fixed terminal, the contact being a protrusion formed of an electrically conductive material.

[0021] In a preferred embodiment of the present invention, the fixed terminal has a contact, and the end of the movable arm preferably contacts this contact. In a particularly preferred embodiment, when the protective device is in the closed state, the contact on the movable arm abuts against the contact on the fixed terminal.

[0022] In the protective device of the present invention, under normal current flow, the movable arm is in a closed state in contact with the fixed terminal due to the pushing or pulling force of the bimetal. When the bimetal member is reversed under abnormal current, the end of the bimetal member applying a force to the movable arm moves upward, and the pushing force is reduced, preferably substantially eliminated, so that the movable arm tries to return to its original shape based on its elasticity, and the one end of the movable arm also moves upward.

[0023] When the protective device is in the closed state, the one end of the bimetal member applies a pushing or pulling force to the one end of the movable arm, thereby elastically deforming the one end of the movable arm against the elasticity of the movable arm, and pressing and holding the one end of the movable arm downward toward the fixed terminal. More specifically, the one end of the bimetal member applies a downward force to the one end of the movable arm that is greater than the upward force (upward elastic force) that the one end of the movable arm tries to move upward due to its elasticity, thereby causing the movable arm to contact the fixed terminal and to maintain that state. This state corresponds to a closed state in which the electrical equipment in which the protective device is installed operates normally and normal current flows through the electrical circuit.

[0024] The bimetal member is a well-known member formed from a bimetal material made by bonding together metals with different thermal expansion coefficients. Bimetal materials are used, for example, in relays, switches, etc. As is well-known, when a bimetal member is heated and exceeds a certain threshold temperature, it is suddenly deformed. As is well-known, such deformation is also called "reversal," and the term "reversal" is also used in this specification.

[0025] This reversal of the bimetallic member to change configuration is also known as a snap action. The bimetallic member may be of any suitable configuration so long as the protection device of the present invention is able to use the reversal of the bimetallic member to change from a closed state, in which a force is applied, to an open state, in which the force is reduced, preferably to zero, as described above.

[0026] In the protection device of the present invention, the bimetallic member may, for example, be suddenly deformed from a flat plate shape and inverted to a downwardly convex plate shape, so that the end of the bimetallic member in contact with the fixed terminal moves upward and is in an open state. In another embodiment, the bimetallic member may be inverted from a downwardly concave plate shape to a flat plate shape or a downwardly convex plate shape, so that the end of the bimetallic member in contact with the fixed terminal moves upward and is in an open state.

[0027] In addition, the bimetal member is reversed, and the one end of the bimetal member moves upward, but this movement may be stopped by the complete reversal of the bimetal member (i.e., reversal when there is nothing obstructing the reversal). In another embodiment, the one end of the bimetal member that moves upward by reversal may come into contact with a member located above it, such as the wall surface of the casing (for example, the inner surface of the portion that constitutes the ceiling of the casing), and may be stopped without being able to move further upward. In yet another embodiment, a contact member (for example, a plate arranged inside the ceiling of the casing) may be provided as a stopper on the inside of the casing, and the one end of the bimetal member may come into contact with it to stop it. In yet another embodiment, instead of the one end of the bimetal member, the one end of the movable arm may be stopped from moving upward. In any case, it is necessary to ensure that the one end of the movable arm or a contact provided thereon is separated from the fixed terminal or a contact provided thereon.

[0028] As described above, when the one end of the bimetal member moves upward, the movable arm elastically tries to return to its original shape (i.e., the shape of the movable arm when no external force is applied), and the one end of the movable arm moves upward, i.e., the one end of the movable arm moves away from the fixed terminal. As a result, a gap is formed between them, and the electrical continuity between them is interrupted, resulting in an open state.

[0029] The protective device of the present invention is provided as a product in a closed state in which one end of the movable arm is pressed downward by one end of the bimetal member to provide electrical continuity as described above, and this protective device is placed in, for example, an electrical device and operated. When the electrical device is operating normally, i.e., when a normal current flows through the electrical circuit, electrical continuity is provided between the fixed terminal and the movable arm of the protective device, so that a normal current passes between them.

[0030] For example, if an excessively large abnormal current flows due to a malfunction of an electrical device, the heat generated will cause the bimetal member to reverse, causing the one end of the movable arm to move away from the fixed terminal and enter an open state, as described above, thereby cutting off electrical continuity and protecting the electrical device, electrical circuit, etc. from the abnormal current. Effect of the Invention

[0031] In the protective device of the present invention, the shape of the movable arm is originally formed such that the end of the movable arm is spaced upward from the fixed terminal, and the other end is fixed integrally with the bimetal member inside the casing, and is configured so that the force applied by the one end of the bimetal member causes the movable arm to elastically deform and contact the fixed terminal. If the bimetal member is removed from this configuration, the one end of the movable arm, which is the free end (because no force is applied), elastically moves toward its original shape (i.e., upward) and returns to a state spaced apart from the fixed terminal as a predetermined position.

[0032] By appropriately selecting the material, shape, dimensions, etc. of the movable arm, the movable arm can be formed so that the one end of the movable arm is inherently spaced apart from the fixed terminal in a predetermined manner. The bimetal member is configured so that a downward pushing or pulling force is applied to such a movable arm, forcibly and elastically moving the one end of the movable arm downward to abut against the fixed terminal and maintain a contact state.

[0033] When the bimetal member is heated above the threshold temperature by heat generated when an abnormal current flows through the movable arm, etc., it reverses as described above, and the one end of the bimetal member moves upward and (instantly) reduces or releases the force acting on the one end of the movable arm, so that it can no longer maintain contact with the fixed terminal, and the one end of the movable arm moves upward and separates from the fixed terminal.

[0034] In a conventional protective device in which a bimetallic member is disposed below a movable arm, the bimetallic member must reverse its position to push up the movable arm, which itself presses the fixed terminal downward, and forcibly separate it from the fixed terminal. In order to push up the movable arm in this manner, it is necessary to design the bimetallic member so that, by reversing, it applies an upward force to the movable arm that is greater than the downward pressing force of the movable arm acting on the fixed terminal.

[0035] In contrast, in the protective device of the present invention, the bimetal member only needs to be reversed in order to separate the movable arm from the fixed terminal. That is, in the protective device of the present invention, when the bimetal member is reversed at a threshold temperature, the movable arm naturally (i.e., by its own nature) elastically returns to its original shape, and the one end of the movable arm automatically moves upward from the fixed terminal. Therefore, in the protective device of the present invention, the bimetal member only needs to be reversed, and it is considered that it is not necessary to precisely consider the force that pushes up the movable arm, i.e., the upward force of the bimetal, that is generated by the reversal. Therefore, it is considered that the design can be simplified with regard to the reversal of the bimetal member in the protective device. At least, a protective device based on a concept completely different from conventional protective devices is provided in that the nature of the movable arm that returns to its original shape is utilized. [Brief description of the drawings]

[0036] [Figure 1] FIG. 1 is a schematic, partially exploded perspective view of a first preferred embodiment of a protection device of the present invention (in a closed state). [Diagram 2] FIG. 2 is a perspective view showing the original state of the protection device of the present invention shown in FIG. 1 (ie, before being disassembled as in FIG. 1). [Diagram 3] FIG. 3 shows a schematic longitudinal cross-sectional view of the protection device of the present invention shown in FIG. 2 (in a closed state). [Figure 4] FIG. 4 is a schematic cross-sectional view similar to FIG. 3 showing the state in which the protection device of the present invention shown in FIGS. 1 to 3 is in an open state. [Diagram 5] FIG. 5 is a schematic perspective view showing only the movable arm, the bimetal member, the fixed terminal, the first connection terminal and the second connection terminal of the protective device in the closed state of FIG. 4, disassembled and separated in the vertical direction. [Figure 6] FIG. 6 is a schematic perspective view showing a bimetal member having a weakened portion in a protective device according to one preferred embodiment of the present invention. [Figure 7] Fig. 7 shows a schematic cross-sectional view of the above-mentioned second preferred embodiment of the protection device of the present invention (an embodiment in which the bimetal member is disposed below the movable arm) similar to Fig. 3 and Fig. 4. Fig. 7(a) shows the protection device in a closed state, and Fig. 7(b) shows the state after changing from that state to the closed state. [Figure 8] FIG. 8 shows, in a schematic plan view, another form of bimetal member that can be used in the protection device of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] The protective device of the present invention will be described in more detail below with reference to the accompanying drawings. Note that the protective device of the first preferred embodiment will be mainly described as an example, but such description also applies to the protective device of the second preferred embodiment, except for the description related to the bimetal member pulling down the movable arm. Note that the features that apply only to the protective device of the second preferred embodiment will be described with reference to FIG. 7.

[0038] In the schematic perspective view of FIG. 1, which shows a first preferred embodiment of the protective device of the present invention in a partially exploded manner, the protective device 10 has a plate-shaped movable arm 12 made of a conductive metal, a plate-shaped fixed terminal 14 made of a conductive metal, and a plate-shaped bimetallic member 16. In this protective device, the bimetallic member 16 and the movable arm 12 are located above the fixed terminal 14, and the bimetallic member 16 is located above the movable arm 12. In the illustrated embodiment, the protective device 10 further has an end molding 22 that fits into the illustrated casing 18 and its front end opening 20. The arrows shown in FIG. 1 diagrammatically indicate the directions of "front", "back", "right", "left", "up" and "down" used in the description herein. Also, a longitudinal cross section of the protective device of FIG. 2 is diagrammatically shown in FIG. 3.

[0039] For ease of understanding, in the state shown in Fig. 1, the casing 18 and the end molding 22 are shown in a state moved along the longitudinal direction from the original state of the protection device 10 shown in a schematic perspective view in Fig. 2. More specifically, the casing 18 is shown in a state moved in the direction of arrow A (i.e., rearward), and the end molding 22 is shown in a state moved in the direction of arrow B (i.e., forward).

[0040] The bimetal member 16 is positioned above the movable arm 12, and the front end 36 of the bimetal member 16 applies a downward pressing force to the front end 34 of the movable arm 12, pressing the movable arm 12 toward the fixed terminal 14, and as can be seen particularly from Fig. 3, the contact 32 provided at the front end 36 is held in contact with the contact 30 provided at the fixed terminal. In the original state in which no such pressing force is applied, the movable arm 12 is designed so that its end 34 is spaced from the fixed terminal 14, but the pressing force forcibly elastically deforms it to bring it into contact as shown in the figure.

[0041] The protection device 10 of the present invention has a first connection terminal 24 and a second connection terminal 26. The first connection terminal 24 is electrically connected to the fixed terminal 14, and in one preferred embodiment, the first connection terminal 24 and the fixed terminal 14 may form a single member as shown in the figure, and each is a part of a single member. The second connection terminal 26 has an extension member 27 at its rear, which may also form a single member as shown in the figure. For details regarding such a single member, refer to FIG. 5 described later. In the illustrated embodiment, the extension member 27 is electrically connected to the rear end 13 of the movable arm 12 in a state where it overlaps with the rear end 13. For example, the rear end 13 of the movable arm 12 (corresponding to the "other end") and the extension member 27 are in contact with each other and fastened together in a stacked state, for example by crimping 50. As shown in the figure, the bimetal member 16 is also fastened together with the movable arm 12, specifically, with its rear end 13, at its rear end 37.

[0042] 1 also shows a pre-assembly 28 in which the first connecting terminal 24 integral with the fixed terminal 14 and the second connecting terminal integral with the extension member 27 are assembled in a state where they pass through an opening located in the front face of the end molding portion 22. The movable arm 12 and the bimetal member 16 are placed on this pre-assembly 28 and crimped 50 to form an assembly in which these are assembled together, and the assembly is inserted through the opening 20 of the casing 18 to form the protection device of the present invention shown in FIG.

[0043] In the illustrated embodiment, the fixed terminal 14 has a contact 30 on its upper side, and the movable arm 12 has a contact 32 on its lower front end 34. In the closed state of such a protection device, the contacts 30 and 32 abut against each other to provide electrical continuity, as shown in Figure 3. In the open state, the contact 32 moves away from the contact 30 to interrupt electrical continuity, as shown in Figure 4, which will be described later.

[0044] The movable arm 12 is formed such that, if the bimetal member 16 is not present above it (i.e., if the movable arm 12 is in its original shape (also called the "original shape") when no pressing force from the bimetal member 16 is acting on it), the end 34 of the movable arm 12 is located higher than the position shown in Fig. 3. For example, when the protective device is in the closed state as shown in Fig. 3, the end 36 of the bimetal member 16 abuts on the end 34 of the movable arm 12 and applies a pressing force to the movable arm 12, elastically deforming the movable arm 12 and pushing down the end 34 so that the contact 32 comes into contact with the contact 30.

[0045] In this manner, the bimetal member 16 elastically deforms the movable arm 12, so that the bimetal member 16 has a rigidity that allows the original shape before reversal to be maintained such that the front end 34 of the movable arm 12 moves downward and remains in contact with the fixed terminal 14, for example, with the contact 32 provided thereon, as shown in FIG.

[0046] More specifically, by fastening the movable arm 12 and the bimetal member 16 together at their respective rear ends, for example by means of a crimp 50, the bimetal member 16 maintains a state in which it presses the end 34 of the movable arm 12 downward with a pressing force F1. In this case, even if a reaction force F2 (corresponding to the elastic force of the movable arm 12 against the pressing force of the bimetal member) acts on the end 34 to press the end 36 of the bimetal member 16 upward, the bimetal member 16 has a rigidity that is not substantially deformed, and the pressing state of the movable arm 12 can be maintained.

[0047] In order to maintain the pressing state in this way, it is possible to prevent the bimetal member from deforming by, for example, appropriately selecting the shape and dimensions (particularly the length, width and thickness) of the bimetal member, the constituent material, etc. In the closed state, the pressing force F1 is substantially greater than the elastic force F2, and the bimetal member 16 does not substantially deform, and the movable arm 12 is elastically deformed to enter the closed state as shown in FIG.

[0048] As described above, the bimetal member 16 that applies a pressing force in the closed state is reversed when its temperature exceeds a predetermined threshold value (e.g., 170°C). The state of the bimetal member 16 immediately after it is reversed in this way is shown in Fig. 4, a schematic cross-sectional view similar to Fig. 3. Comparing Fig. 3 and Fig. 4, it can be seen that the bimetal member 16 shown in Fig. 3, which is substantially flat and plate-like or has a (slightly) upwardly convex shape, is reversed and becomes a (slightly) downwardly convex shape as shown in Fig. 4.

[0049] As a result of this reversal, the position of the end 36 of the bimetal member 16 in Fig. 3 moves quickly upward as shown in Fig. 4. As a result, the movable arm 12, which was pressed by the bimetal member 16, can elastically deform toward its original shape, and therefore its end 34 can move upward. As is clear from Fig. 4, the contact 32 provided on the end 34 of the movable arm 12 is separated from the contact 30 of the fixed terminal. Therefore, this state corresponds to an open state in which electrical continuity between the movable arm 12 and the fixed terminal 14 is interrupted.

[0050] Fig. 5 is a perspective view showing only the movable arm 12, the bimetal member 16, the fixed terminal 14 and the first connecting terminal 24 integral therewith, and the second connecting terminal 26 and the extending member 27 integral therewith of the protective device in the state shown in Fig. 3, separated in the vertical direction. Note that Fig. 5 also shows the crimping tab 50 provided at the rearmost end of the extending member 27, which stacks and holds the rear end 37 of the bimetal member 16 and the rear end 13 of the movable arm (see Fig. 1).

[0051] As can be seen from Fig. 5, in a preferred embodiment of the protection device of the present invention shown in Figs. 1 to 5, the front end 38 of the movable arm 12 may have an upwardly bent portion (for example, a tip portion of an L-shaped cross section as shown in the figure). The front end 38 has a through opening 40, and the front end 42 of the bimetal member 16 is adapted to fit into the through opening 40. By configuring the movable arm 12 and the bimetal member 16 in this manner, when the bimetal member 16 is turned over and its end 36 moves upward as described above, the front end 42 of the bimetal member 16 fitted into the through opening 40 can pull up the end 34 of the movable arm 12.

[0052] The upward movement of the end 36 of the movable arm 12 when the bimetal member 16 is reversed is essentially possible because the movable arm 12 elastically tries to return to its original shape (i.e., undergoes recovery deformation). However, even if the elastic return is insufficient for some reason (e.g., creep phenomenon), the pulling up of the end 34 of the movable arm 12 by the bimetal member 16 can promote the elastic return of the movable arm 12. As a result, the end 34 of the movable arm 12 can be moved upward sufficiently, further ensuring the interruption of electrical continuity.

[0053] In the protective device of this type, when the bimetal member 16 is reversed, the upward movement of the bimetal member and the movable arm (more specifically, their ends 34) is stopped by the front end 38 of the movable arm 12 abutting against a strip-shaped stopper 44 provided on the end molding portion 22 that fits into the front end opening 20 of the casing 18, as can be seen in FIG.

[0054] In the protective device of the present invention, it is not always necessary to provide the through opening 40 at the front end 38 of the movable arm, and in this embodiment, the front end 38 of the movable arm 12 is located below the front end 42 of the bimetal member. In this case, the upward movement of the end 34 of the movable arm occurs when the bimetal member 16 is reversed, releasing the pressing force on the movable arm and causing the movable arm to return to its original shape. In this embodiment, the upward movement of the bimetal member 16 is stopped by the end 36 of the bimetal member 16 abutting against the stopper 44, and the upward movement of the movable arm 12 is stopped by the end 34 of the movable arm 12 abutting against the end 36.

[0055] Although the illustrated protective device is provided with a stopper 44, in one embodiment of the present invention, the stopper is omitted and the upward movement is stopped by the tip of the movable arm or the tip of the bimetal member abutting against the inside of the front end of the wall that defines the upper surface of the casing. This makes it possible to reduce the number of parts that make up the protective device.

[0056] The protection device of the present invention can be manufactured, for example, by forming a preassembly 28 in which the fixed terminal 14 and the first connecting terminal 24 integral therewith, and the second connecting terminal 26 and the extending member 27 integral therewith are fixed by the end forming portion 22 as shown in Fig. 1, and then assembling an assembly in which the movable arm 12 and the bimetal member 16 are fastened together at the rear end of the extending member 27 by, for example, crimping or clamping means, and inserting and fixing the assembly into the casing 18 so that the first connecting terminal and the second connecting terminal protrude from the opening 20. When assembling the assembly in this manner, in the case of the protection device of Fig. 1, it is preferable to fasten the assembly in a state in which the front end 42 of the bimetal member 16 is pre-inserted into the through opening 40 of the movable arm 12.

[0057] Incidentally, the casing 18 and the end molding 22 may be made of resin, and when the assembly is inserted into the casing 18 with the rear end closed, a protrusion (not shown) provided on the bottom of the resin casing 18 may be snap-fitted or press-fitted into recesses (not shown) provided in the fixed terminal 14 and the extension member 27 to secure them in place. Similarly, the end molding 22 may be snap-fitted or press-fitted into the opening 20.

[0058] Except for matters specifically described in this specification in relation to the present invention, the members constituting the protection device of the present invention (e.g., the movable arm, the bimetal member, the fixed terminal, etc.), particularly their shapes, materials, etc., can all be similar to those used in conventional protection devices. The same can be said about the manufacture of the protection device.

[0059] In one embodiment of the protective device of the present invention, the bimetal member further comprises a weakened portion. When the protective device is used in an electric device, the protective device in a closed state may become an open state due to an abnormal current, and then the bimetal cools down and becomes a closed state again, and then again becomes an open state due to the continuation of the abnormal current, and then the bimetal cools down and becomes a closed state, and so on. In other words, while the abnormal current of the electric device is not eliminated, the protective device incorporated therein may change states in the order of "closed state → open state → closed state → open state → ... → open state → closed state."

[0060] Ideally, a protective device would be able to cycle through these state changes indefinitely, but in electrical equipment using conventional protective devices, for example, as the protective device ages, creep of the movable arm can reduce the compressive force it inherently exerts on the fixed terminal, increasing the contact resistance between them.

[0061] Furthermore, the repeated changes in state cause the arcing to wear down the contacts (hence the reduction in contact thickness), which requires the movable arm to be pressed further downward, which can increase contact resistance because the margin of pressure (over the minimum pressure required to ensure contact) that keeps the movable arm (specifically its contact) in contact with the fixed terminal (specifically its contact) is reduced.

[0062] As a result of this possibility, an arc may occur, eventually causing the contacts to weld (i.e., close), causing the protective device itself to fail. When a conventional protective device fails in the closed state in this way, even if an abnormal current occurs, the welded contacts are in a conductive state and the current cannot be interrupted, resulting in a problem that the protective device cannot perform its function.

[0063] Considering such problems, it may be preferable to configure the protective device so that when the number of state changes (for convenience, one cycle of state changes from "closed state → open state → closed state" is considered to be one change) exceeds a predetermined number of times, the protective device intentionally goes into an open state and maintains that state to prevent the occurrence of a conductive state between the contacts (i.e., maintains the contacts separated from each other), and therefore fails in the open state.

[0064] When such a protective device is used, in one embodiment, when the number of state changes reaches a predetermined number or a number close to that number (for example, ±20% of the predetermined number, preferably ±5% of the predetermined number), the force with which the bimetal member presses the movable arm is reduced by the weakened portion, so that the end of the movable arm moves upward and is maintained in a spaced-apart state from the fixed terminal, making it impossible for it to abut against the fixed terminal.

[0065] When such a protection device is used, in another embodiment, the number of state changes is a predetermined number or or a number close to that number (for example, ±20% of the specified number, preferably ±5% of the specified number), the force with which the bimetal member presses the movable arm can be made substantially zero by the weakened portion, so that the end of the movable arm moves upward and is maintained in a separated state from the fixed terminal, making it impossible for it to abut against the fixed terminal.

[0066] The protective device of the present invention has a bimetallic member that can assume an upper limit of permissible state changes according to the actual electrical equipment incorporating the protective device, and can enter and maintain an open fault state when the state changes reach the upper limit. For example, in one embodiment, the number of state changes in the electrical equipment is counted, and when the count reaches the upper limit, preferably 90% of the upper limit, more preferably 80% of the upper limit, the protective device in use is replaced with a new protective device. In another case, when the protective device fails in an open state, the protective device in use is replaced with a new protective device as necessary.

[0067] The upper limit of the number of state changes is assumed depending on the electric equipment in which the protective device is incorporated. In one embodiment, when the protective device is used, for example, to prevent the windings of a small to medium-sized motor from burning out when the motor is locked, it is sufficient for the protective device to repeat, for example, about 15,000 state changes, after which the protective device may fail in an open state. In this case, the predetermined upper limit of the number of state changes is 15,000, and after about 15,000 reversals / reversals recoveries, the bimetal member fails in an open state in which the bimetal member can no longer sufficiently press the movable arm due to the weakened portion, and the end of the movable arm is separated from the fixed terminal.

[0068] The number of state changes that may cause the contacts to weld as described above is predicted in advance (also referred to as the "predicted number of welds"), and in one embodiment of the protection device of the present invention, an upper limit number is assumed to be sufficiently smaller than the "predicted number of welds." It is preferable to configure the bimetal so that, when such an upper limit number of state changes occurs, the weakened portion can be used to intentionally cause the bimetal member to lose its function of pressing the movable arm.

[0069] The "predicted number of weldings" can be determined by incorporating a protective device without a weakened portion into an assumed electric circuit, intentionally passing an abnormal current through it to change the state, and repeating this process until the terminals are welded. As described below, the protective device of the present invention, which is provided with a bimetal member having a weakened portion, is incorporated into an assumed electric circuit, and the number of times that it will fail in an open state is measured by intentionally passing an abnormal current through it to change the state, and this number is set as the upper limit number. This upper limit number can be set to a predetermined value through trial and error by changing the characteristics of the weakened portion (e.g., the constituent material, shape, specific form of the weakened portion, etc.).

[0070] The weakened portion, which prevents the end of the bimetal member from sufficiently pressing against the end of the movable arm after a predetermined upper limit number of state changes, is designed so that the pressing force that the bimetal member applies to the movable arm is smaller than the upward elastic force caused by the movable arm trying to return to its original shape. Specifically, the bimetal member repeatedly reverses from a state in which it presses the movable arm and returns to its original shape (i.e., recovers), i.e., the bimetal member repeatedly deforms, so that the stress generated in the bimetal member tends to concentrate in a specific area, and that area is provided in the bimetal member as the weakened portion.

[0071] In one embodiment of the protection device, as shown in the figure, the bimetal member and the movable arm are fastened together at their respective ends by, for example, a crimping member, and the bimetal member is in the form of a so-called cantilever beam.

[0072] Therefore, stress is likely to concentrate near the rear end of the bimetal member, which is the fastening point (i.e., a point that is likely to become a fulcrum during deformation). In one embodiment, specifically, stress is likely to concentrate at a point slightly forward of the fastening point. Therefore, a weakened portion may be provided at such a point. In another embodiment, the point where stress is likely to concentrate is intentionally provided as a weakened portion in the bimetal member.

[0073] One embodiment of the bimetal member 16 is shown in a perspective view. As shown in the figure, when the state changes are repeated with a point slightly forward of the rear end 37 as the fulcrum, stress is likely to concentrate at the portion indicated by the dashed line 52. Therefore, it is preferable to provide a weakened portion at this portion to actively promote stress concentration. If stress concentration is promoted in this manner, metal fatigue will progress and the bimetal member will no longer be able to apply the force required to press the end of the movable arm. In one case, metal fatigue will cause cracks to occur at the weakened portion, and in some cases, the weakened portion will break.

[0074] Specifically, the weakened portion may be a fatigue promoting means 54, such as a V-shaped or U-shaped notch, groove, etc., extending, for example, along dashed line 52 at rear end 37 of the bimetallic member. As shown, the weakened portion indicated by dashed line 52 extends along a left-right direction perpendicular to the longitudinal direction (i.e., the front-to-rear direction) of the bimetallic member.

[0075] In such weakened portions, the thickness (i.e., the vertical dimension) of the bimetal member can be locally reduced, thereby concentrating stress. By varying the depth, length, and width of the notches (corresponding to the vertical dimension, left-right dimension, and front-rear dimension perpendicular to these dimensions of the plate-shaped bimetal member, respectively), and the cross-sectional shape of the notches along the front-rear direction, and by changing the bimetal material that constitutes the bimetal member, it is possible to control the upper limit of the number of times the bimetal member can be pressed against the movable arm before it loses its function of pressing the movable arm.

[0076] In another embodiment, the weakened portion may be a notch, a corner, a gap, or any combination thereof formed in the plate-shaped bimetal member (when viewed from above). For example, the plate member may have a constricted portion (a portion where the width of the plate is narrow), and stress may be concentrated in that portion. For example, as shown in FIG. 6, the weakened portion may be formed by appropriately selecting the shape, dimensions, etc. of the notch 56.

[0077] The weakened portion described above does not necessarily have to be provided in a portion where stress is likely to concentrate, and in another embodiment, it may be provided in another portion of the bimetal member, and the weakened portion is provided so as to actively concentrate stress in that portion. Figure 6 shows a weakened portion 58 provided near the center of the bimetal member. This weakened portion may be in the form of a notch extending in the left-right direction as described above, and a portion of it is enlarged to show a schematic V-shaped cross section.

[0078] The weakened portions as described above may be used in various combinations as desired, for example a combination of notches and waists.

[0079] The notch may be formed by any suitable method. For example, a groove, notch, etc. may be formed on the upper surface of the bimetal member by laser processing, press processing, etc. For example, a notch 58 shown in FIG. 6 was formed as a weakened portion by press processing on a plate-shaped (approximately rectangular in plan view) bimetal member (10 mm in the front-rear (longitudinal) dimension (length), 6 mm in the left-right dimension (width), and 0.13 mm in the up-down dimension (thickness)) in a plate shape. The bimetal material constituting this bimetal member was Ni-Cr-Fe on the high expansion side and Ni-Fe (BL-51 manufactured by Hitachi Metals Neomaterial) on the low expansion side. The dimensions of the notch were 0.1 mm in the front-rear dimension, 0.05 mm in the up-down dimension, and 1.8 mm in the left-right dimension.

[0080] A current was passed through the movable arm to rotate the bimetallic member in a repeated cycle (corresponding to twice the amplitude of the vertical movement of the end of the bimetallic member). After 10,000 cycles, it was confirmed that a crack had appeared in the notch. It is believed that this crack significantly reduced the force with which the bimetallic member presses the movable arm, and therefore the end of the movable arm or a contact attached to it could no longer be pressed against and held in contact with the fixed terminal or a contact attached to it.

[0081] In one embodiment of the protection device of the present invention, the front end of the housing member or the base molding 22 may further include a stopper for limiting excessive downward movement of the front end 36 of the bimetal member 16. For example, as shown in FIG. 3, the base molding 22 may have such a protrusion 60 as a stopper. In the illustrated embodiment, the protrusion 60 is slightly spaced from the lower surface of the front end 42 of the bimetal member. Note that only in FIG. 3 is an embodiment having the protrusion 60 shown for the purpose of explaining such a protrusion (or step portion) 60, and the vicinity of the protrusion 60 is shown in an enlarged manner for easy understanding.

[0082] Repeated opening and closing of the contacts causes wear of the contacts, and the thickness of the contacts decreases due to abnormal wear caused by large arcs, which may cause the positions of the front end 36 of the bimetal member 16 and the front end 34 of the movable arm 12 at the time of closing to become lower. As a result, the slight gap between the protrusion 60 and the lower surface of the bimetal end 42, which was in the initial state, may disappear. In this case, the possibility of the contacts welding due to contact wear increases, but the front end 42 of the bimetal member 16 abuts against the protrusion 60 before that happens. As a result, the bimetal member 16 cannot move further downward, so that the above-mentioned welding of the contacts can be prevented in advance. In addition, this abutment weakens the pressing force of the bimetal member 16 against the movable arm 12. As a result, the elastic force of the movable arm 12 trying to return to its original shape becomes relatively large, and the open state of the contacts can be maintained.

[0083] By providing the protrusion in this manner, even if the protective device fails in the open state, the possibility of the movable arm 12 coming into contact with the fixed terminal 14 for some reason is significantly reduced, and failure in the open state can be prevented. Note that, since it is only necessary to ensure that the tip of the protrusion 60 (the uppermost end in the drawing) does not impede the end of the movable arm from contacting the fixed terminal (or a terminal provided thereon) in the closed state, the tip of the protrusion 60 may be located lower than the position shown in FIG. 3.

[0084] In the illustrated embodiment, the tip of the protrusion 60 is spaced from the movable arm 12 so that a gap exists therebetween. To allow some degree of wear of the contacts caused by the reversing and returning cycles of the bimetal member 16, it is preferable to provide the protrusion 60 so that such a gap exists.

[0085] FIG. 7 shows a schematic cross-sectional view of a second preferred embodiment of the protection device of the present invention (an embodiment in which the bimetal member pulls down the movable arm in the closed state) with the casing omitted. Note that FIG. 7(a) shows the protection device in the closed state, and FIG. 7(b) shows the state after changing from that state to the closed state. In this protection device,

[0086] As shown in Fig. 7(a), the bimetal member 16 and the movable arm (12) are located above the fixed terminal 14, and the bimetal member 16 is located below the movable arm 12. The movable arm has an engagement portion 70 behind the contact 32, and the front end 36 of the bimetal member 16 can engage with the engagement portion 70. For example, the engagement portion 70 may be a hook-shaped portion on which the end can be hooked. More specifically, in the illustrated embodiment, the engagement portion 70 has an L-shaped cross section.

[0087] As shown in Fig. 7(a), when the front end 36 of the bimetal member 16 is engaged with the engagement portion 70, it forcibly holds the movable arm 12, whose original shape is as shown in Fig. 7(b), in the shape shown in Fig. 7(a). That is, the bimetal member 16 has a rigidity that does not substantially deform against the elastic force that causes the movable arm 16 to return to its original shape, and as a result, the bimetal member 16 applies a force that pulls down the front end 34 of the movable arm 12, i.e., a pulling force. Thereby, in the illustrated embodiment, the contact 32 located at the front end 34 of the movable arm 12 is pressed against the contact 30 of the fixed terminal 14 and held in contact therewith.

[0088] In the protection device of Fig. 7(a), when the temperature of the bimetal member 16 exceeds the threshold value, the bimetal member 16 reverses as shown in Fig. 7(b), and the engagement between the engagement portion 70 and the front end 36 of the bimetal member is released. As a result, the downward force applied by the bimetal member 16 is no longer applied, the movable arm 12 tries to return to its original shape, and the front end 34, in the illustrated embodiment, the contact 32 provided thereon, moves away from the fixed terminal 14, in the illustrated embodiment, the contact 30 provided thereon, and the protection device is in an open state.

[0089] As can be easily understood, in the embodiment where the bimetal member is located below the movable arm, the above-described description of the first preferred embodiment of the protection device of the present invention (the embodiment where the bimetal member presses down on the movable arm in the closed state) is applicable, except for matters related to the bimetal member pulling down on the movable arm.

[0090] 8 shows a schematic plan view of another preferred embodiment of the bimetal member of the protection device of the present invention. This bimetal member 16' is composed of a portion 88 and a portion 90, and has a substantially elongated, generally rectangular, flat plate shape, similar to the bimetal member 16 described above.

[0091] The bimetal member 16' shown in FIG. 8 has a substantially U-shaped through opening 80 in a right portion 88, and a tongue portion 86 protruding forward (to the left in the drawing) from a base portion 82 at the right end of the right portion 88. In the illustrated embodiment, the tongue portion 86 has a through opening 84 adjacent to its end 92. The through opening 84 can be aligned with the through openings provided in the arm member to be fastened to the bimetal member and the extension member 27 of the second connection terminal, and then crimped to fasten the bimetal member, the movable arm, and the extension member together. Thus, the end 92 corresponds as if to the rear end 37 of the bimetal member 16.

[0092] The illustrated bimetal member 16' may have a contact point on the underside of the front end 94 of the left portion 90 (corresponding to the front end 36 of the bimetal member 16), which applies a force to the movable arm. In the case of such a bimetal member 16', it can be considered that a beam having a length equal to the sum of the length a1 of the portion 90 and the length a2 of the portion 88 plus the length a3 of the tongue portion 86 is crimped in the opening 84 acting as a fulcrum. In other words, the bimetal member shown in FIG. 8 is also a type of cantilever beam.

[0093] When the bimetal member 16' is inverted, the front end 94 moves upward, and the front end of the movable arm moves upward, forming a gap between the fixed terminal and the bimetal member 16', and the bimetal member 16' is in an open state. When such a bimetal member 16' is used, the length a3 of the tongue portion 86 can be additionally included in the length of the beam. Therefore, even though the total length of the bimetal member is a1+a2, the length a3 of the tongue portion can also be included in the length of the beam of the bimetal member. That is, the bimetal member having the structure shown in FIG. 8 can contribute to the compactness of the bimetal member. Specifically, for example, the bimetal member used in Otter's small circuit breaker (PBA type) can be used as the bimetal member shown in FIG. 8. [Industrial Applicability]

[0094] As can be seen from the above description, the protection device of the present invention has a novel mechanism for moving the end of a movable arm away from a fixed terminal to transition from a closed state to an open state, and can be used to protect electrical equipment, electrical circuits, and the like. [Explanation of symbols]

[0095] 10:Protection Devices 12: Movable arm 13: Rear end of movable arm 14:Fixed terminal 16 and 16': Bimetallic members 18: Casing 20:Opening 22: End forming part 24: First connection terminal 26: Second connection terminal 27: Extension member 28: Pre-assembly 30: Fixed terminal contact 32: Contact point of movable arm 34: Front end of movable arm 36: Front end of bimetal member 37: Rear end of bimetal member 38: Front end of movable arm 40:Through opening 42: Front end of bimetal member 44: Stopper 50: Clamping tab 52: Weakened part 56: Notch 58: Weakened area (V-shaped notch) 60:Protrusion 70: Engagement part 80:Through opening 82: Base 84:Through opening 86: Tongue-shaped part 88: Right side part 90:Left side part 92: Rear end 94: Front end

Claims

1. A protection device comprising a fixed terminal, a movable arm and a bimetal member located above the fixed terminal, and a casing that houses these, the bimetal member is located at one of the upper and lower sides of the movable arm; one end of the bimetal member applies a force to one end of the movable arm, thereby holding the one end of the movable arm in contact with the fixed terminal; the bimetal member applies a force to the one end of the movable arm so that the one end of the movable arm and the fixed terminal are held in contact with each other against an elastic force that tends to separate the one end of the movable arm from the fixed terminal. Protection devices.

2. 2. The protection device of claim 1, wherein when the bimetal member is inverted, it allows the one end of the movable arm to move upward, thereby separating the one end of the movable arm from the fixed terminal to form a gap between the movable arm and the fixed terminal.

3. The bimetal member is located above the movable arm, 3. A protection device according to claim 1 or 2, characterized in that the one end of the bimetallic member applies a pressing force to the one end of the movable arm.

4. The bimetal member is located below the movable arm, 3. A protection device as claimed in claim 1 or 2, characterized in that said one end of the bimetallic member exerts a downward force on said one end of the movable arm.

5. A protection device according to any one of claims 1 to 4, characterized in that the movable arm and the bimetallic member are in the form of a cantilever beam fastened together at their other ends.

6. A protection device according to any one of claims 1 to 5, characterized in that the bimetallic member has a weakened portion.

7. 7. A protection device according to claim 6, characterized in that the weakened portion is in the form of a notch.

8. A protection device as claimed in any preceding claim, wherein the movable arm has a contact at said one end, the contact being pressed towards the fixed terminal.

9. 9. The protection device according to claim 1, wherein the fixed terminal has a contact that contacts the one end of the movable arm or a contact provided thereon.

10. The protection device according to any one of claims 1 to 9, wherein the bimetal member has a flat plate shape or a downwardly concave plate shape before being inverted.

11. 11. The protection device according to claim 1, further comprising a stopper at the front end of the housing member for limiting excessive downward movement of said one end of the bimetal member.

12. An electrical apparatus comprising a protection device according to any one of claims 1 to 11.

13. An electric circuit comprising a protection device according to any one of claims 1 to 11.

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