JP2013020864A - Thermal protector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a self-holding circuit in which an interruption state can be generated quickly and reliably when the current must be interrupted and can be maintained, by preventing excessive heat radiation from a fixed piece while composing the fixed piece of an alloy of good conductivity for a high capacity thermal protector.SOLUTION: A fixed piece having a fixed contact, a movable piece having a movable contact and a thermally-actuated element are disposed in the housing. The fixed piece and/or the movable piece is a copper alloy member having a conductivity of 60%IACS or higher and has a surface subjected to nickel plating, for example, in the vicinity of the contact. The fixed piece and/or the movable piece is buried in the housing and has a terminal extending to the outside of the housing, and holds a positive characteristic thermistor together with the thermally-actuated element.

Description

  The present invention relates to a thermal protector for preventing overheating in a battery pack of a form device. More specifically, the present invention relates to a thermal protector that forms a self-holding circuit by incorporating a PTC (positive characteristic thermistor).

  A portable device such as a notebook personal computer, a tablet personal computer, or a mobile phone is usually equipped with a battery pack such as a lithium secondary battery and used as a power source. In many cases, this type of battery pack uses a thermal protector that uses a thermally responsive element such as a bimetal, which is a safety device. In recent years, since these portable devices have become highly functional, the current during charging and discharging of the battery pack is increased along with the power consumption, and it is also desired for the thermal protector to increase the capacity of the current.

  In response to these requirements, Patent Document 1 includes means for increasing the electrical resistance provided in the vicinity of the thermally responsive member (bimetal) and means for reducing the electrical resistance provided in a portion other than the thermally responsive means. A thermal protector is described. In Patent Document 1, pure copper, phosphor bronze, and brass are used as means for reducing the resistance of the movable piece. On the other hand, SUS304, SUS301, 6 mass% Al-4 mass% V- In addition to Ti, combinations of Cu—Ni—Mn and Ni—Fe, combinations of Ni—Cr—Fe and Ni—Fe, and the like are exemplified.

  In order to reduce the size of the thermal protector and form a self-holding circuit, as in Patent Document 2, it is the simplest and most reliable method to place the PTC in contact with the movable piece and the fixed piece. Here, once the bimetal is reversed, the PTC is located between the movable piece and the fixed piece and causes a leakage current to flow through itself to generate heat, thereby maintaining the inverted state of the bimetal and forming a self-holding circuit.

JP 2006-331893 A JP 2005-185749 A JP 2006-338952 A

  However, in the prior art as described above, the number of parts is increased and the conduction of the entire thermal protector is impaired, so that there is a limit to the reduction in construction cost and the increase in capacity. On the other hand, if the fixed piece is made of only a highly conductive alloy without having a high resistance portion, the following problem may occur. Since a metal having high conductivity has high heat conductivity, if at least a part of the fixed piece becomes a terminal and is exposed to the outside, heat radiation from the terminal becomes excessive. Therefore, since the heat generated by the PTC is not sufficiently transmitted to the bimetal, there is a possibility that the inverted state of the bimetal cannot be maintained when it should be shut off.

  The purpose of the present invention is to form a fixed piece with a highly conductive alloy for a high-capacity thermal protector, while suppressing excessive heat dissipation as described above and maintaining a cut-off state when the current should be cut off. It is to ensure certainty.

In order to solve this problem, the present inventor has found the following configuration after intensive studies.
According to a first aspect of the present invention, a fixed piece having a fixed contact and a movable piece having a movable contact are contacted or separated from each other by a thermally responsive element that reverses in response to a temperature change. The fixed piece and / or the movable piece, which is arranged inside the body, is a copper alloy member having a conductivity of 60% IACS or more plated with nickel or chromium on the surface, embedded in the case, and further outside the case. It has an extended terminal, and is held by sandwiching a positive temperature coefficient thermistor together with a thermally responsive element or a movable piece.

  Furthermore, the second aspect of the present invention is characterized in that the copper alloy member has a conductivity of 70% IACS or higher.

  Furthermore, the third aspect of the present invention is characterized in that the plating is performed between the fixed contact and the fixed piece in the vicinity of the fixed contact.

  Furthermore, the fourth aspect of the present invention is characterized in that the nickel or chromium plating is 2.0 to 3.0 μm.

  According to the first aspect of the present invention, it is possible to increase the current capacity and suppress the excessive heat radiation from the fixed piece and the terminal, thereby ensuring the reliability of the self-holding circuit.

  Furthermore, according to the second to fourth aspects of the present invention, it is possible to equip a thermal protector having an allowable current of 10 A or more with a self-holding circuit that is quick and reliable in operation.

Sectional view conceptually showing the overall structure of the thermal protector Enlarged sectional view conceptually showing the layer structure of the fixed piece

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1, the thermal protector 1 is configured by disposing a movable piece 2, a fixed piece 3, a bimetal 4 (thermally responsive element) and a PTC 5 (positive characteristic thermistor) inside a resin case 6 (housing). Has been. The case 6 includes a cover 61 and a base 62.

  The movable piece 2 is an elongated plate-like metal member having a movable contact 21 at one end. The movable contact 21 is formed from an alloy whose main component is a metal having good conductivity such as gold or silver, and is joined to the movable piece 2 by welding or other known methods. The movable piece 2 is formed by processing a metal plate material into a predetermined shape by press molding. Another tip of the movable piece 2 is extended to the outside of the case and serves as a first terminal 22. The movable piece 2 is preferably made of a highly conductive alloy and has a conductivity of 60% IACS or higher in order to increase the capacity of the thermal protector. The form of the first terminal 22 is not limited to one that is integrally continuous with the portion of the movable piece 2 that is housed inside the case 6, but may be one in which a plurality of members are joined.

  Similarly to the movable piece 2, the fixed piece 3 forms a part of the base 62 by processing a metal plate material into a predetermined shape by press molding and then embed it in resin by insert molding. A fixed contact 31 is applied to a portion of the fixed piece 3 that contacts the movable contact 21. The fixed contact 31 is configured by joining a metal having good conductivity such as gold or silver or an alloy containing these metals as a main component to the fixed piece 3 by clad, plating, or other known methods. One end of the fixed piece 3 is extended outside the base 62 to form the second terminal 32. Another end and an intermediate portion of the fixed piece 3 form the bottom surface of the hole portion that accommodates the PTC 5.

  The bimetal 4 is a flat plate member in which a plurality of types of metal materials having different expansion rates are laminated. The shape of the bimetal 4 is not particularly limited as long as it is a rectangle or a circle and is a thin flat plate. The bimetal 4 is inverted or returned to its original shape according to the temperature change. Due to such deformation, the bimetal 4 pushes up the movable piece 2 or returns it to the original shape as shown in FIG.

  The PTC 5 is a thermal element formed in a flat plate shape or a disk shape with barium titanate or the like as a main component, for example, and generates heat to rapidly increase electric resistance when conducting. The PTC 5 is disposed along the vicinity of the bimetal 4 or the movable piece 2 and is sandwiched and held between the bimetal 4 and the fixed piece 3. In a state in which the bimetal 4 is inverted due to a temperature rise and the movable piece 2 is pushed up as shown in FIG. 1B, a leakage current L flows between the movable piece 2 and the fixed piece 3 to generate heat, and the bimetal 4 is heated. To maintain the bimetal 4 in an inverted state. Thus, a self-holding circuit is formed.

  The fixed piece 3 and the movable piece 2 are preferably formed of the same material because the manufacturing process is easy. Therefore, in order to constitute the high-capacity thermal protector 1, the fixed piece 3 is formed of a copper alloy member having a conductivity of 60% IACS or more. Further, the fixed piece 3 preferably has a conductivity of 70% IACS or more in order to expand the current capacity to 10 A or more. However, this does not exclude the difference in material between the movable piece 2 and the fixed piece 3.

  A part of the fixed piece 3 becomes the second terminal 32 or is joined to a member to be a terminal and exposed to the outside. Further, as shown in FIG. 1, the base 62 has a portion that forms the bottom surface 64 of the hole portion that accommodates the PTC 5, and the fixing piece 3 is exposed to the outside from the resin portion 63 of the case 6. The fixing piece 3 is in contact with the PTC 5 at the bottom surface 64 of the hole and holds the PTC 5 together with the bimetal 4. That is, since the PTC 5 is in contact with the fixed piece 3, the heat generated in the PTC 5 in the inverted state of the bimetal 4 in FIG. 1B is released from these exposed portions to the outside of the thermal protector 1. If this heat radiation is excessive, the bimetal 4 cannot obtain sufficient heat, and the inverted state is desirably generated and cannot be maintained.

  In order for the allowable current of the thermal protector 1 to exceed 5A, it is desirable that the fixed piece 3 and the movable piece 2 be a copper material having a conductivity of 60% IACS or higher. In order to further increase the current capacity and obtain an allowable current exceeding 10 A at room temperature (25 ° C.), it is preferable to mold the fixed piece 3 and the movable piece 2 with a copper alloy of at least 70% IACS or more. In order to obtain the material having the above conductivity, the copper component ratio is preferably 90% by weight or more, more preferably 99% by weight or more. In general, in metal materials, there is a positive correlation between conductivity and heat dissipation. Therefore, if the current used by the thermal protector 1 is set to a high capacity, there is a risk that the heat dissipation will be excessive.

  In order to suppress inconvenience such as excessive heat dissipation, the surface of the fixed piece 3 is plated for heat insulation as shown in FIG. The heat insulating plating 33 of the fixed piece 3 may be applied by breath-molding a plated material on the fixed piece 3 or may be plated after forming the fixed piece 3. The fixed contact 31 is obtained by attaching gold, gold alloy, silver or silver alloy to the fixed piece 3 by plating, clad, welding or the like. The fixed contact 31 is preferably applied on the heat insulating plating 33 after plating the fixed piece 3 from the viewpoint described later. However, after providing the fixed contact 31 first, it can also attach by avoiding the location of the fixed contact 31 and plating.

  Hereinafter, the fixed piece 3 and the fixed contact 31 are described in the place where the heat insulation plating 33 is applied. In this description, the fixed piece 3 and the fixed contact 31 are replaced with the movable piece 2 and the movable contact 21, respectively. However, if there is a possibility that the terminal is exposed to the outside and excessive heat dissipation occurs, it is similarly useful to apply the heat insulation plating of the present invention. Applying the heat insulating plating 33 between the fixed contact 31 and the fixed piece 3 is more useful from the following viewpoint when the fixed plate 3 or the vicinity of the fixed contact 31 is used.

  Nickel or chromium is preferably used as the material of the heat insulating plating 33 from the viewpoint of availability and the like. The plating with nickel or chromium may be a simple substance or may take the form of an alloy with another metal having these metals as a main component. Nickel is particularly preferable from the viewpoint of easy plating. The inversion state in which the bimetal 4 is reversed is realized by the heat generated by the movable piece 2 being transmitted to the bimetal 4, particularly during overdischarge. Since the contact resistance is generated at the place where the fixed contact 31 and the movable contact 21 are in contact, it becomes a heat source when energized. The heat generated from this heat source is transmitted to the movable piece 2, and the bimetal 4 is reversed when overheated. Therefore, in order to prevent this heat from escaping from the fixed piece 3, it is preferable to apply the heat insulating plating 33 between the fixed contact 31 and the fixed piece 3. By such heat insulation plating 33, a quick reversing operation of the bimetal 4 can be realized.

  The thickness of the heat insulating plating 33 is preferably 2.0 to 3.0 μm from the viewpoint of achieving both conductivity and heat insulating performance. Below this range, there is a risk that the heat retention effect will not be sufficient. On the other hand, if it exceeds this range, when the copper alloy material of the fixed piece 3 is processed (particularly bending), the nickel is easily cracked, and at the same time, the copper alloy layer of the base material may be cracked. Therefore, the thickness of the heat insulating plating 33 is preferably within the above-mentioned range. The heat insulating plating 33 does not need to exist over the entire surface of the fixed piece 3, and may be applied only to a portion exposed to the outside of the resin portion 63 of the case 6. It is only necessary that the generated heat is not excessively released to the outside of the thermal protector 1.

  The fixed contact 31 is preferably a silver or silver alloy stripe plating from the viewpoint of saving the process and reducing the construction cost. The thickness of the fixed contact 31 is preferably 3.5 to 4.5 μm, more preferably 2.0 to 3.0 μm. However, the layer thickness of the fixed contact 31 is not particularly limited as long as it functions to reduce contact resistance. By defining the thickness of the heat insulating plating 33 as described above, the fixed contact 31 can be provided on the heat insulating plating 33. Since the fixed contact 31 can be plated on the heat insulating plating 33, the fixed contact 31 can be obtained at a lower cost by clad or the like.

  From the viewpoint of plating adhesion, the silver plating layer of the fixed contact 31 is preferably applied directly to the surface of the heat insulation plating 33. Furthermore, in the fixed contact 31, it is more preferable to perform strike plating with the same material or main component as the fixed contact 31 between the layer of the heat insulating plating 33 and the layer of the fixed contact 31. Silver, nickel or chromium may be in the form of an alloy as long as a sufficient blending ratio is maintained. About the process of plating, although you may process as normal functional plating, it is desirable that the said nickel or chromium is not the alloy (black plating) containing zinc.

  In the present invention, a specific mode in which the fixed contact and the movable contact are brought into contact with or separated from each other by the thermally responsive element inside the casing is not limited. For example, the shape of the movable piece 2 is not limited to the one in which the movable contact is provided only at one end as in the present embodiment, but the movable contact is provided at both ends of the movable piece so as to contact the two fixed contacts by flapping-like operation. Alternatively, they may be separated. The thermally responsive element need not be a member independent of the movable piece, and may be formed integrally with the movable piece. The positive temperature coefficient thermistor is not limited to the form sandwiched between the thermally responsive element and the fixed piece, and may be formed between the movable piece and the fixed piece. Even if the latter is sandwiched between the movable piece and the fixed piece, the thermoresponsive element and the positive temperature coefficient thermistor can be arranged in parallel.

1 Thermal protector,
2 movable pieces,
21 movable contact, 22 first terminal,
3 fixed pieces,
31 fixed contact, 32 second terminal, 33 heat insulation plating,
4 Bimetal,
5 PTC (positive thermistor),
6 Case (housing),
61 Cover, 62 Base, 63 Resin part, 64 Bottom of hole part,
L leakage current,

Claims (4)

A fixed piece having a fixed contact and a movable piece having a movable contact are arranged inside the housing so that the fixed contact and the movable contact are brought into contact with or separated from each other by a thermally responsive element that reverses in response to a temperature change.
A copper alloy member having a conductivity of 60% IACS or more plated on the fixed piece and / or the movable piece with nickel or chromium or an alloy containing these as a main component, embedded in the case, and further A thermal protector having a terminal extended outside and holding a positive temperature coefficient thermistor together with the thermal responsive element or the movable piece.   The thermal protector according to claim 1, wherein the copper alloy member has a conductivity of 70% IACS or more.   3. The thermal protector according to claim 1, wherein the plating is performed between the fixed contact and the fixed piece in the vicinity of the fixed contact.   4. The thermal protector according to claim 1, wherein the plating is 2.0 to 3.0 [mu] m.

Images