JP2005174816A - 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 between a fixed electrode 2 and a movable electrode 3, and an inactive gas is enclosed in a casing 10. Oxidization and contamination of a contact part can be prevented by enclosing the gas; when the bimetal 8 is deformed by temperature rise, the movable electrode 3 is pressed up to separate a contact 3a from the fixed electrode 2; and 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 to heat and deform the bimetal 8, whereby the contact 3a is separated from the fixed electrode 2 to cut off the excessive current. <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 technique 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 a temperature rise. (See Patent Document 1).

However, when the charging circuit is interrupted by the thermostat, the temperature of the secondary battery is lowered, and the thermostat closes the charging circuit, so that the charging current flows again and the battery is overcharged. In order to solve this problem, there is known a self-holding thermostat in which a heating resistor is connected in parallel to a thermostat and the thermostat and the heating resistor are integrated. In this self-holding thermostat, when a thermostat that responds to the temperature rise of the secondary battery opens the charging circuit, current flows through the heating resistor connected in parallel, and the thermostat is heated by the heat generated by the heating resistor. Heated and maintained in a circuit interrupted state. Since the resistance value of the heating resistor is set to be large, the current required for the thermostat to keep itself in a state where the thermostat is cut off is small, and the secondary battery is not overcharged by the current (see Patent Document 2).
Japanese Patent Laid-Open No. 11-260220 (pages 2 and 3, FIG. 2) Japanese Patent No. 3416229 (pages 2 and 3, FIG. 8)

  However, since the thermostat is an element that opens and closes a circuit by opening and closing the contact portion, contact resistance increases when a non-conductive layer such as oxide or dirt is formed on the contact due to change over time. Since the thermostat applied to the battery pack is connected in series with the charge / discharge circuit, the charge / discharge current flows through the contact part, and when the amount of current increases, the increase in contact resistance leads to power loss associated with an increase in wasted thermal energy. There was a problem of increasing the internal resistance of the battery pack.

  An object of the present invention is to provide a heat-sensitive actuating element having a structure that suppresses a change with time in a contact portion.

  In order to achieve the above object, a thermosensitive operating element according to the present invention includes at least a fixed electrode, a movable electrode that is deformed into a state in which the movable contact is in contact with the fixed electrode, and a state in which the movable contact is separated from the fixed electrode, and a temperature rise. The movable contact accommodates a bimetal that exerts a deformation action on the movable electrode in a state separated from the state in which the movable contact is in contact with the fixed electrode, draws out the lead portion connected to the fixed electrode and the movable electrode to the outside, and encloses the inert gas, The inside of the housing is sealed.

  According to the above configuration, when a thermosensitive operating element is attached to an object for detecting an increase in temperature, the bimetal is heated and deformed by heat transfer from the object, and the movable electrode is deformed. If the leads of the fixed electrode and the movable electrode are connected in series with the circuit in a separated state, the circuit is interrupted due to the temperature rise. In the temperature state where the movable electrode is not deformed, the connection between the movable contact and the fixed electrode is required to be maintained at a contact resistance that does not cause a loss in circuit connection. As the contact resistance increases with time due to oxides and dirt on the contacts, a change with time will occur at each contact if an inert gas is enclosed in the housing as in this configuration. Must not.

  In the above configuration, the movable electrode can be formed of bimetal, and the circuit can be interrupted by separating the movable contact from the fixed electrode by its own thermal deformation.

  In addition, since the movable electrode is made of a material that generates heat when an excessive current flows, the bimetal can be heated by heating due to an excessive current due to a short circuit, etc. Thus, a heat-sensitive operating element that cuts off the circuit can be obtained. SUS304 is a suitable material for the movable electrode that can cope with an excessive current.

  In addition, the inert gas can be sealed in the casing by at least sealing the casing in an inert gas atmosphere, and it is also possible to assemble the thermal element in an inert gas atmosphere. It is.

  According to the present invention, the change over time of the thermosensitive operating element that shuts down the circuit in response to a temperature rise or an excessive current is suppressed, and the circuit connection is made with a contact resistance that does not cause a loss in the circuit connection under normal conditions, resulting in a temperature rise. No change occurs in the heat sensitive operation that interrupts the circuit when an overcurrent or excessive current flows, and safety measures such as battery packs can be taken reliably.

  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. The detailed structure and operation will be described below with reference to FIGS.

  As shown in FIGS. 1 and 2, the base case 5 constituting the casing 10 of the thermosensitive operating element 1 is a member housing in which the fixed electrode 2 and the movable electrode lead 4 are inserted by resin molding and the constituent members are housed in the center. A chamber 11 is formed. A circular recess 11a in which the surface of the fixed electrode 2 is exposed is formed in the center of the member accommodating chamber 11, and a PTC element 9 formed in a disk shape is disposed therein, and is curved in an arc shape thereon. The bimetal 8 is stacked, and the movable electrode 3 is disposed on the bimetal 8. Since the fixed wing 3b provided on the movable electrode 3 fits a pair of positioning frames 12 formed on the base case 5, the movable electrode 3 is positioned and disposed, and one end of the movable electrode 3 is placed in the positioning frame 12. Spot welding is performed on the exposed movable electrode lead 4. 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. As a result, the structural member is sealed in the member housing chamber 11 of the housing 10 in which the lid case 6 is joined to the base case 5, thereby forming the heat-sensitive operating element 1.

  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 movable contact 3 a provided at the tip is brought into contact with the fixed electrode 2.

  The assembly process of the thermosensitive operating element 1 is performed in a chamber filled with an inert gas, whereby a state in which the inert gas is sealed in the housing 10 of the completed thermosensitive operating element 1 is obtained. Even if only the step of joining the lid case 6 to the base case 5 on which the components are arranged is performed in a chamber filled with an inert gas, the inert gas can be enclosed in the housing 10.

  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 PTC element 9, when the bimetal 8 is heated to a predetermined temperature or more, the bimetal 8 swells as shown in FIG. Deform to reverse 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 movable contact 3 a provided at the distal end is separated from the fixed electrode 2 and the charge / discharge circuit is interrupted. Overcharging is stopped when in a charged state, and charging / discharging of the secondary battery B in a high temperature state can be prevented when exposed to a high temperature environment. When the movable contact 3 a of the movable electrode 3 moves away from the fixed electrode 2, a current path is formed from the movable electrode 3 to the fixed electrode 2 through the bimetal 8 and the PTC element 9, and a current having a current value corresponding to the resistance value of the PTC element 9. Flows. The PTC element 9 has a characteristic that a resistance value rapidly increases when a predetermined temperature (trip temperature) is exceeded. Once the trip state is reached, the resistance value is maintained until the current is cut off. The Therefore, the bimetal 8 is heated by the temperature rise of the PTC element 9 due to the Joule heat caused by the current flowing at a high resistance value, and the state where the bulging direction is reversed is maintained.

  Since the inversion state is maintained in the bimetal 8 by the heating by the PTC element 9, when the overcharge state is stopped and the temperature of the secondary battery B is lowered, the temperature of the bimetal 8 is also lowered accordingly, and the bulging direction is changed. Inverted to the original state, the movable electrode 3 returns to its original state due to its elasticity, and the movable contact 3a comes into contact with the fixed electrode 2 to be in the state shown in FIG. 1A, the charge / discharge circuit becomes conductive, and charging starts again. Thus, the state in which overcharge continues is not repeated.

  Further, when the positive and negative electrodes of the external input / output terminal D of the battery pack A are externally short-circuited, an excessive current flows from the secondary battery 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 movable contact 3 a provided at the distal end is separated from the fixed electrode 2 and is connected to the charge / discharge circuit. The excessive current that flows is cut off. When the movable contact 3 a is separated from the fixed electrode 2, a current path is formed from the movable electrode 3 to the fixed electrode 2 through the bimetal 8 and the PTC element 9, and a current having a current value corresponding to the resistance value of the PTC element 9 flows. Since the temperature of the PTC element 9 rises due to Joule heat caused by current flowing at a high resistance value, the bimetal 8 is heated and the state where the bulging direction is reversed is maintained.

  Since the inversion state is maintained in the bimetal 8 by the heating by the PTC element 9, when the excessive current is prevented and the temperature of the secondary battery B is lowered, the temperature of the bimetal 8 is also lowered accordingly, and the bulging direction is the original. The movable electrode 3 returns to its original state due to its elasticity, and the movable contact 3a comes into contact with the fixed electrode 2 to be in the state shown in FIG. 1 (a), the charge / discharge circuit becomes conductive, and an excessive current flows again. The state will not be repeated. When a cause such as an external short circuit in which an excessive current flows is eliminated, no current flows in the charge / discharge circuit, so that the PTC element 9 is released from the trip state and returns to the original low resistance state.

  In the above configuration, the PTC element 9 is applied in order to maintain the movable contact 3a of the movable electrode 3 separated from the fixed electrode 2. Instead, a resistor having a predetermined resistance value is used. However, the same effect can be obtained. In addition, when a fixed contact is provided on the fixed electrode 2 with which the movable contact 3a contacts, it can be configured such that the contact resistance is smaller and stable contact can be obtained.

  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.

  Further, when a simpler configuration is sufficient, the movable electrode 3 itself can be formed of a bimetal material. In this configuration, when the temperature of the thermosensitive operating element 1 rises, the movable electrode 3 formed of the bimetal material is deformed, and the movable contact 3a provided at the tip is separated from the fixed electrode 2 and the circuit is interrupted.

  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.

  In the heat-sensitive actuating element according to the present invention, the inert gas is sealed in the internal space of the housing that accommodates the component that operates due to temperature rise and / or excessive current, so that oxide and dirt are generated at the contact portion. Therefore, it is possible to configure a heat-sensitive operating element with little secular change.

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 Movable contact 5 Case 6 Lid case 8 Bimetal 10 Case 11 Member accommodation chamber

Claims (5)

In the housing, at least a fixed electrode, a movable electrode that is deformed into a state in which the movable contact is in contact with the fixed electrode, and a state in which the movable contact is separated from the fixed electrode, and a state in which the movable contact is separated from a state in which the movable contact is in contact with the fixed electrode due to temperature rise A thermosensitive actuating element comprising: a bimetal that exerts a deforming action on an electrode; a lead portion connected to the fixed electrode and the movable electrode is drawn to the outside; and the inside of the casing is sealed with an inert gas sealed . The heat-sensitive operating element according to claim 1, wherein the movable electrode is made of bimetal. The heat-sensitive operating element according to claim 1, wherein the movable electrode is formed of a material that generates heat when an excessive current flows. The heat-sensitive operating element according to claim 3, wherein the movable electrode is made of SUS304. The heat-sensitive operating element according to claim 1, wherein at least sealing in the housing is performed in an atmosphere of an inert gas.

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