JP2005174814A - Thermosensitive operation element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermosensitive operation element capable of cutting off a circuit in response to a temperature rise and an excessive current. <P>SOLUTION: A bimetal 8 is installed in a space formed between a fixed electrode 2 and a movable electrode 3 brought into contact with the fixed electrode 2 through a contact 3a formed at one end. When the bimetal 8 is deformed by temperature rise, the movable electrode 3 is pressed up to separate the contact 3a from the fixed electrode 2. When this thermosensitive operation element 1 is installed with the movable electrode 3 and the fixed electrode 2 serially connected to a circuit, the circuit can be cut off when temperature rises. When an excessive current flows through the circuit, the movable electrode 3 generates heat by its electric resistance and the heat is transmitted to the bimetal 8, whereby the movable electrode 3 is separated from the fixed electrode 2 by its contact 3a by deformation of the bimetal 8, so that the excessive current flowing through the circuit is cut off. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a heat-sensitive actuating element that is activated by an increase in temperature and an excessive current to interrupt circuit connection.

  A thermostat is known as an element that cuts off a circuit in response to a temperature rise, and a small thermostat is applied to a battery pack using a secondary battery. In the battery pack, when the secondary battery temperature rises due to overcharge, etc., the charging circuit is shut off by a thermostat sensitive to the rising temperature, preventing accidents where the secondary battery is ignited due to excessive temperature rise To do.

As a conventional technology that applies a thermostat to such a battery pack, a thermal protector is known in which a bimetal is attached to a movable plate forming a switch structure, and the movable plate is separated from the fixed plate by deformation of the bimetal due to temperature rise. (See Patent Document 1).
Japanese Patent Laid-Open No. 11-260220 (pages 2 and 3, FIG. 2)

  In a battery pack using a lithium ion secondary battery, a means for protecting the secondary battery from overcharge, overdischarge and excessive current is provided, and the safety of the lithium ion secondary battery using a flammable organic solvent as an electrolyte. The structure which secures property is adopted. For overcharge and overdischarge, means for detecting overcharge and overdischarge by the battery protection circuit and shutting down the charge / discharge circuit is used. For overcurrent due to an external short circuit or the like, the PTC ( Double temperature measures have been taken in which a positive temperature coefficient) element or thermostat is connected in series with the charge / discharge circuit. In this case, the PTC or thermostat prevents overcharge due to failure of the battery protection circuit, overcurrent due to improper connection of the charger or external short circuit, the battery temperature rises due to them, It is because it operates to cut off the charge / discharge circuit at that temperature. Such a configuration is an indispensable and effective means for constructing a battery pack using a lithium ion secondary battery. The circuit board constituting the battery protection circuit is packaged together with the secondary battery, and the wiring process is performed. It is necessary, and it becomes a factor that hinders downsizing and cost reduction of the battery pack.

  As the performance of the secondary battery is improved, the battery protection configuration as described above may become an excessive configuration, which increases the cost. Therefore, a configuration that can easily protect the battery is required. If a temperature rise or an excessive current that adversely affects the secondary battery can be detected and the charge / discharge circuit can be promptly shut off, battery protection can be achieved in a battery pack having a normal configuration.

  By using a thermostat, when the charge / discharge circuit is shut down for both the battery temperature above a predetermined value and the charge / discharge current above a predetermined value, the thermostat is closed due to the deformation of the bimetal constituting the thermostat. Since it works to open the contacts, if the current flows through the bimetal, the Joule heat exceeding the predetermined value due to the electrical resistance of the bimetal generated when an excessive current flows, and the battery exceeding the predetermined value It is conceivable that the contacts can be configured to open at any temperature.

  However, it is difficult to select a bimetal material that simultaneously satisfies an operation that deforms due to heat generation by a current exceeding a predetermined value and an operation that deforms due to an ambient temperature that exceeds a predetermined value, and the temperature of the battery is increased by one thermostat. And overcurrent could not be dealt with.

  An object of the present invention is to provide a heat-sensitive actuating element capable of breaking a circuit in response to a temperature rise and an excessive current.

  In order to achieve the above object, in the thermosensitive operating element according to the present invention, a temperature rise occurs in a gap formed between the fixed electrode and the movable electrode contacting the fixed electrode by a contact provided at one end. A bimetal that is deformed so as to separate the contact from the fixed electrode, and the movable electrode is formed of a material that generates heat to a temperature at which the bimetal can be deformed when an excessive current flows therethrough. To do.

  According to the above configuration, when the bimetal is deformed due to a temperature rise, the deformation reaches the movable electrode and acts so that the contact provided at one end of the movable electrode is separated from the fixed electrode. If the thermosensitive operating element is disposed in a state where the movable electrode and the fixed electrode are connected in series with the charge / discharge circuit, the circuit can be shut off when the temperature rises to a temperature at which the bimetal is deformed. In addition, when an excessive current flows in the circuit, the movable electrode generates heat due to its electric resistance, and the generated heat is transferred to the bimetal with which part of the movable electrode comes into contact. Since it acts so as to be separated from the fixed electrode, an excessive current flowing in the circuit is cut off.

  In the above configuration, in order for the movable electrode to generate heat due to an excessive current, the movable electrode has a required electrical resistance, and the electrical resistance needs to be negligible as a circuit resistance in normal times. SUS304 is suitable as a material of the movable electrode that realizes this, and a material having elasticity that forms a switch structure can be obtained.

  According to the present invention, a thermosensitive actuating element configured to shut off a circuit in response to a temperature rise and an excessive current is configured, and is charged against a temperature rise when a secondary battery is overcharged like a battery pack. Individual protection to shut off the discharge circuit to stop overcharge and shut off the charge / discharge circuit to prevent overcurrent flow when overcurrent flows due to external short circuit or improper charger connection The conventional configuration provided with the means can be realized by one heat-sensitive operating element, and the battery pack can be simply configured to reduce the size and the cost.

  Fig.1 (a) shows the structure of the thermosensitive operating element 1 which concerns on this embodiment, and was assembled using the component shown disassembled in FIG. This heat-sensitive actuating element 1 has a structure suitable for application to a battery pack using a lithium ion secondary battery. When the secondary battery rises abnormally or due to an external short circuit or the like in the charge / discharge circuit. When an excessive current flows, it is used for the purpose of blocking the charge / discharge circuit and protecting the secondary battery.

  As shown in FIGS. 1 and 2, the base case 5 constituting the housing 10 is inserted into the fixed electrode 2 and the movable electrode lead 4 by resin molding, and a member accommodating chamber 11 which is a space for accommodating the constituent elements in the center. Is formed. A heat transfer seat plate 9 is arranged in a circular recess 11a in which the surface of the fixed electrode 2 is exposed in the center of the member accommodating chamber 11, and a bimetal 8 curved in an arc shape is stacked thereon, and the bimetal 8 is movable on the bimetal 8. An electrode 3 is provided. Since the fixed wing 3b provided on the movable electrode 3 fits in the positioning frame 12 provided on the base case 5, one end of the movable electrode 3 is spot welded to the movable electrode lead 4 exposed in the positioning frame 12. The The lid case 6 formed by inserting the pressing plate 7 by resin formation is put on the base case 5 to which the constituent members are attached in this way, and ultrasonic welding is performed between the lid case 6 and the base case 5. Thus, the heat-sensitive operating element 1 is formed by sealing the constituent members in the internal space of the base case 5. The heat transfer seat plate 9 serves to hold the bimetal 8 in a predetermined position and transfer heat from the outside to the bimetal 8, but can be formed integrally with the base case 5.

  As shown in FIG. 1 (a), the movable electrode 3 disposed in the base case 5 is pressed at the center portion by the protruding portion of the pressing plate 7 inserted on the inner surface of the movable electrode 3 when the cover case 6 is covered. Then, the contact 3 a provided at the tip is brought into contact with the fixed electrode 2.

  As shown in FIG. 3, the heat-sensitive operating element 1 having the above-described configuration is disposed in a state of being connected in series with the secondary battery B in the battery pack A. As shown in FIG. 4, the heat-sensitive operating element 1 is attached so that the bottom surface of the base case 5 comes into contact with the surface of the secondary battery B via the insulating paper C.

  When the secondary battery B is overcharged or when the battery pack A is exposed to a high temperature environment, the temperature of the secondary battery B rises. Since the heat of the secondary battery B is transferred to the bimetal 8 through the fixed electrode 2 and the heat transfer seat plate 9, when the bimetal 8 is heated to a predetermined temperature or higher, as shown in FIG. Deform to reverse the bulging direction. Since the bimetal 8 is formed by bonding two types of metal plates having different thermal expansion coefficients, the expansion direction is reversed because the expansion coefficients of both surfaces are different when the temperature rise exceeds a predetermined temperature.

  When the bulging direction of the bimetal 8 is reversed, the jumped peripheral edge pushes up the distal end side of the movable electrode 3, so that the contact 3 a provided at the distal end is separated from the fixed electrode 2, the charge / discharge circuit is interrupted, and overcharge When the battery is in the state, overcharge is stopped, and when the battery is exposed to a high temperature environment, the secondary battery B in the high temperature state can be prevented from being charged or discharged. When the temperature of the secondary battery B decreases, the temperature of the bimetal 8 also decreases accordingly. Therefore, the bulging direction is reversed to the original state, and the state shown in FIG. Thus, the original state is restored, and the contact 3a comes into contact with the fixed electrode 2 so that the charge / discharge circuit becomes conductive.

  In addition, when an external current is short-circuited between the positive electrode and the negative electrode of the external input / output terminal D of the battery pack A, a secondary battery is supplied if an excessive current flows from the secondary battery B or an inappropriate charger is connected. An excessive current flows into B, and the temperature of the secondary battery B rises. Before that, when an excessive current flows through the heat-sensitive operating element 1, the movable electrode 3 generates Joule heat due to its electric resistance, and the temperature rises. In this configuration, SUS304 is applied as the material of the movable electrode 3, and the electrical resistance of a copper alloy generally applied to this type of member is about 7 mΩ, whereas the electrical resistance of SUS304 is about 40 mΩ. The amount of heat generated when excessive current flows increases. The heat generated by the movable electrode 3 is transferred to the bimetal 8 that is partially in contact therewith, and when the bimetal 8 is heated to a predetermined temperature or more, the bimetal 8 reverses the bulging direction as shown in FIG. It transforms so that

  When the bulging direction of the bimetal 8 is reversed, the peripheral edge that has jumped up pushes up the distal end side of the movable electrode 3 in the same manner as before, so that the contact 3a provided at the distal end is separated from the fixed electrode 2 and flows into the charge / discharge circuit. Excessive current is cut off. When the state such as the external short circuit is eliminated, the excessive current disappears, so the temperature of the movable electrode 3 is lowered, and the temperature of the bimetal 8 is also lowered accordingly, so that the bulging direction is reversed to the original state. 1 (a), the movable electrode 3 returns to its original state due to its elasticity, the contact 3a contacts the fixed electrode 2, and the charge / discharge circuit becomes conductive.

  As described above, by selecting the material of the movable electrode 3 that has an electric resistance that does not cause a large loss due to the charge / discharge current that flows during normal use and has appropriate elasticity, the temperature rise and the excessive current It is possible to configure the thermosensitive operating element 1 that is sensitive to the above.

  The embodiment described above has been described with respect to a configuration suitable for application to a battery pack. However, the present invention is not limited to this, and it is needless to say that the embodiment can be widely applied to applications in which a circuit is cut in response to a temperature rise and an excessive current. Yes.

  Since the heat-sensitive operating element according to the present invention can shut down the circuit in response to a temperature rise and an excessive current, the charge / discharge circuit is cut off against a temperature rise when the secondary battery is overcharged. And means for stopping overcharging, and means for interrupting the flow of excessive current by shutting off the charge / discharge circuit when excessive current flows due to an external short circuit or improper charger connected. Can be realized by one heat-sensitive actuating element, and the configuration of the battery pack or the like can be simplified to reduce the size and the cost.

Sectional drawing which shows the structure of the thermosensitive operating element which concerns on embodiment in the state at the time of the normal time of (a), and (b). The disassembled perspective view which decomposes | disassembles and shows the component of a thermosensitive operating element same as the above. The circuit diagram which shows the example applied to the battery pack. The side view which shows the attachment state with respect to a battery pack.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Thermal sensing element 2 Fixed electrode 3 Movable electrode 3a Contact 8 Bimetal

Claims (2)

A bimetal that deforms so as to separate the contact from the fixed electrode when the temperature rises is disposed in a gap formed between the fixed electrode and the movable electrode that contacts the fixed electrode by a contact provided at one end. The heat-sensitive actuating element, wherein the movable electrode is formed of a material that generates heat to a temperature at which the bimetal can be deformed when an excessive current flows through the movable electrode. The heat-sensitive operating element according to claim 1, wherein the material of the movable electrode is SUS304.

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