JP3731337B2 - Current limiter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a current limiter used to limit, for example, a short circuit current or an overcurrent, using a conductive polymer having a positive temperature coefficient resistance value (hereinafter referred to as a PTC polymer).
[0002]
[Prior art]
FIG. 5 is a side view showing a conventional current limiter disclosed in, for example, Japanese Patent Application No. 8-223945. In FIG. 5, 1 is a plate-like PTC polymer having a PTC (positive temperature resistance coefficient) characteristic, 2 and 3 are a pair of plate-like electrodes, and PTC polymer 1 and electrodes 2 and 3 are in electrical contact with each other. ing. As shown in FIG. 6, the resistivity of the PTC polymer 1 is low until the transition start temperature T1, and increases rapidly when the transition start temperature T1 is exceeded. Some PTC polymers increase slowly but gradually decrease above the transition end temperature T2. In one example of a PTC polymer, T1 is 125 ° C., T2 is 135 ° C., and the resistivity at T2 is 1000 times the resistivity at T1.
[0003]
FIG. 7 shows a top view of the electrodes 2 and 3 in FIG. FIG. 8 shows a cross section taken along line AA of FIG. In FIG. 8, reference numeral 2 </ b> A denotes an edge portion formed on the electrode 2, and this edge 2 </ b> A contacts the PTC polymer 1. A perspective view of the electrode 2 and the PTC polymer 1 is shown in FIG. In the conventional current limiting device, as shown in FIG. 9, the edge part (periphery 2 </ b> A) of the electrode 2 is pressed against the PTC polymer 1.
[0004]
Reference numeral 4 denotes an interface between the PTC polymer 1 and the electrodes 2 and 3, and contact resistance exists at the interface between the PTC polymer 1 and the electrodes 2 and 3. The PTC polymer 1 may be pressed against the electrodes 2 and 3 or may be heat-sealed. When heat-sealed, the contact resistance at the interface between the PTC polymer 1 and the electrodes 2 and 3 is reduced. A pair of terminal plates 6 and 7 are provided outside the electrodes 2 and 3, and the terminal plates 6 and 7 are connected to the external electric wires 13 and 14, respectively. The terminal plates 6 and 7 may be integrated with the electrodes 2 and 3, and the terminal plates 6 and 7 may also serve as the electrodes 2 and 3. 8 is an elastic body, for example, a leaf spring, a disc spring or the like is used. The elastic body 8 presses the terminal plates 6 and 7, the electrodes 2 and 3, and the PTC polymer 1. 9 and 10 are a pair of insulating plates. The insulating plates 9 and 10 are provided with holes 9a and 10a, respectively, the holes 9a and 10a are provided with screws 11 penetrating them, and the screws 11 are tightened with nuts 12. The elastic body 8 is compressed.
[0005]
The current flows through one electric wire 13, one terminal plate 6, one electrode 2, the PTC polymer 1, the other electrode 3, the other terminal plate 7, and the other electric wire 14.
[0006]
Next, the operation will be described. The load current flows to the PTC polymer 1 through the electrodes 2 and 3. When the load current flows, the temperature of the PTC polymer 1 rises due to Joule heating, but since the energization current is small, the temperature of the PTC polymer 1 is lower than the transition start temperature T1. When a short circuit current or an overcurrent flows, the temperature rise of the PTC polymer 1 becomes large, the temperature of the PTC polymer 1 becomes higher than the transition start temperature T1, and the resistivity of the PTC polymer 1 increases rapidly. Therefore, short circuit current or overcurrent is suppressed. The suppressed current is interrupted by a switch (not shown). When the current is cut off, no heat is input to the current limiter, and the temperature of the PTC polymer 1 becomes equal to or lower than the transition start temperature T1, the load current can be re-energized.
[0007]
[Problems to be solved by the invention]
In the conventional current limiter, as shown in FIG. 5, since the edge part (periphery 2 </ b> A) of the electrode 2 is pressed against the PTC polymer 1, strong stress is concentrated on the electrode peripheral contact part of the PTC polymer 1 Works. When a short-circuit current flows, an electromagnetic force is generated in the electrode and the terminal plate, and the element is further subjected to mechanical stress due to the electromagnetic force. This mechanical stress also gives concentrated strong stress to the electrode peripheral edge contact portion of the PTC polymer 1. These stresses combine to cause a problem that the PTC polymer is easily damaged during the current limiting operation.
[0008]
An object of the present invention is to provide a current limiting device in which the PTC polymer 1 is not easily damaged.
[0009]
[Means for Solving the Problems]
The current limiting device according to the present invention is a current limiting device having a PTC polymer, a pair of electrodes in contact with the PTC polymer, and a means for pressurizing the electrode and the PTC polymer. The peripheral edge is processed to remove the edge.
[0010]
The current limiting device according to the present invention may be one in which the edge is removed by chamfering the periphery of the electrode.
[0011]
The current limiting device according to the present invention may be one in which the edge is removed by R-chamfering the periphery of the electrode.
[0012]
The current limiting device according to the present invention may be one in which the edge is removed by pressing the peripheral edge of the electrode.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In FIG. 1, 1 is a plate-like PTC polymer having PTC characteristics, 2 and 3 are a pair of plate-like electrodes, and the PTC polymer 1 and the electrodes 2 and 3 are in electrical contact. FIG. 2 shows a cross-sectional view of the electrodes 2 and 3, and a chamfering process is performed on the periphery of the electrodes 2 and 3. As shown in FIG. 6, the resistivity of the PTC polymer is low until the transition start temperature T1, and increases rapidly when the transition start temperature T1 is exceeded. Some PTC polymers increase slowly but gradually decrease above the transition end temperature T2. In one example of a PTC polymer, T1 is 125 ° C., T2 is 135 ° C., and the resistivity at T2 is 1000 times the resistivity at T1.
[0014]
Reference numeral 4 denotes an interface between the PTC polymer 1 and the electrodes 2 and 3, and contact resistance exists at the interface between the PTC polymer 1 and the electrodes 2 and 3. The PTC polymer 1 may be pressed against the electrodes 2 and 3 or may be heat-sealed. When heat-sealed, the contact resistance at the interface between the PTC polymer 1 and the electrodes 2 and 3 is reduced. A pair of terminal plates 6 and 7 are provided outside the electrodes 2 and 3, and the terminal plates 6 and 7 are connected to the external electric wires 13 and 14, respectively. The terminal plates 6 and 7 may be integrated with the electrodes 2 and 3, and the terminal plates 6 and 7 may also serve as the electrodes 2 and 3. 8 is an elastic body, for example, a leaf spring, a disc spring or the like is used. The elastic body 8 presses the terminal plates 6 and 7, the electrodes 2 and 3, and the PTC polymer 1. 9 and 10 are a pair of insulating plates. The insulating plates 9 and 10 are provided with holes 9a and 10a, respectively, the holes 9a and 10a are provided with screws 11 penetrating them, and the screws 11 are tightened with nuts 12. The elastic body 8 is compressed.
[0015]
The current flows through one electric wire 13, one terminal plate 6, one electrode 2, the PTC polymer 1, the other electrode 3, the other terminal plate 7, and the other electric wire 14.
[0016]
Next, the operation will be described. The load current flows to the PTC polymer 1 through the electrodes 2 and 3. When the load current flows, the temperature of the PTC polymer 1 rises due to Joule heating, but since the energization current is small, the temperature of the PTC polymer 1 is lower than the transition start temperature T1. When a short circuit current or an overcurrent flows, the temperature rise of the PTC polymer 1 becomes large, the temperature of the PTC polymer 1 becomes higher than the transition start temperature T1, and the resistivity of the PTC polymer 1 increases rapidly. Therefore, short circuit current or overcurrent is suppressed. The suppressed current is interrupted by a switch (not shown). When the current is cut off, no heat is input to the current limiter, and the temperature of the PTC polymer 1 becomes equal to or lower than the transition start temperature T1, the load current can be re-energized.
[0017]
In this embodiment, as shown in FIG. 1 and FIG. 2, the chamfering process is performed on the peripheral edge of the electrodes 2 and 3 on the side in contact with the PTC polymer 1, and the sharp edge is removed. Sometimes, the concentrated stress acting on the PTC polymer 1 can be reduced. As a result, the number of times the PTC polymer 1 can withstand the current-limiting operation is 1.5 to 2 times.
Therefore, it is possible to obtain a current limiting device in which the PTC polymer 1 is not easily damaged at the time of a short circuit accident. In addition, in this Embodiment, since the process of the peripheral edge 2A of the electrodes 2 and 3 is a C chamfering process, there exists a merit that a process is easy.
[0018]
Embodiment 2. FIG.
Next, a second embodiment will be described. A sectional view of the electrodes 2 and 3 in this embodiment is shown in FIG. In this embodiment, as shown in FIG. 3, the edge 2A of the electrodes 2 and 3 is subjected to R chamfering to remove sharp edges, so that this embodiment is compared with the case of the first embodiment. In the embodiment, the concentrated stress acting on the PTC polymer 1 at the time of a short circuit accident is greatly reduced, so that the PTC polymer 1 can be more difficult to break. As a result, the number of times the PTC polymer 1 can withstand the current-limiting operation is 2 to 2.5 times.
[0019]
Embodiment 3 FIG.
In this embodiment, the electrodes 2 and 3 are manufactured by press working. FIG. 4 shows a cross-sectional view of the electrode manufactured by press working. The electrode shown in FIG. 4 is pressed in the direction from A to B shown in FIG. In this embodiment, since the electrodes 2 and 3 are manufactured by press working, there is an advantage that the manufacturing is easy. Since the cross section of the pressed electrode is as shown in FIG. 4, the concentrated stress acting on the PTC polymer 1 in the event of a short circuit accident is brought into contact with the PTC polymer by contacting the surface C of the electrodes 2 and 3 with the sharp edges removed. Is reduced, the PTC polymer 1 can be more difficult to break. Thereby, the lifetime of the PTC polymer 1 was 1.5 to 2 times.
[0020]
【The invention's effect】
According to the current limiter according to the present invention, in the current limiter having the PTC polymer, the pair of electrodes in contact with the PTC polymer, and the means for pressurizing the electrode and the PTC polymer, the PTC polymer is in contact with the PTC polymer. Since the peripheral edge of the electrode is removed, the concentrated stress acting on the PTC polymer 1 can be reduced at the time of a short circuit accident. Therefore, it is possible to obtain a current limiting device in which the PTC polymer 1 is not easily damaged at the time of a short circuit accident.
[0021]
Moreover, according to this invention, since the edge was removed by chamfering the periphery of the electrode, the concentrated stress acting on the PTC polymer 1 at the time of a short circuit accident can be reduced. Therefore, it is possible to obtain a current limiting device in which the PTC polymer 1 is not easily damaged at the time of a short circuit accident.
[0022]
Moreover, according to this invention, since the edge was removed by carrying out R chamfering of the periphery of an electrode, the concentrated stress which acts on the PTC polymer 1 at the time of a short circuit accident can be reduced. Therefore, it is possible to obtain a current limiting device in which the PTC polymer 1 is not easily damaged at the time of a short circuit accident.
[0023]
Further, according to the present invention, the edge of the periphery is removed by pressing the periphery of the electrode, and the surface of the electrode from which the sharp edge has been removed is brought into contact with the PTC polymer. The concentrated stress acting on 1 can be reduced. Therefore, it is possible to obtain a current limiting device in which the PTC polymer 1 is not easily damaged at the time of a short circuit accident.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of a current limiter according to the present invention.
2 is a cross-sectional view showing an electrode of the current limiting device of FIG.
FIG. 3 is a cross-sectional view showing an electrode according to another embodiment of the current limiting device of the present invention.
FIG. 4 is a cross-sectional view showing an electrode of another embodiment of the current limiting device according to the present invention.
FIG. 5 is a cross-sectional view of a conventional current limiting device.
FIG. 6 is a graph showing PTC characteristics of a PTC polymer.
FIG. 7 is a top view showing an electrode of a conventional current limiting device.
FIG. 8 is a cross-sectional view of a conventional current limiting electrode.
FIG. 9 is a perspective view of a PTC polymer and electrodes of a conventional current limiting device.
[Explanation of symbols]
1 PTC polymer, 2 electrodes, 3 electrodes, 6 terminal plate, 7 terminal plate, 8 elastic body, 11 screw, 12 nut, 13 electric wire, 14 electric wire

Claims (4)

In a current limiting device having a PTC polymer, a pair of electrodes in contact with the PTC polymer, and a means for pressurizing the PTC polymer, the edge of the electrode on the side in contact with the PTC polymer is processed to remove the edge. A current limiting device characterized by that. The current limiting device according to claim 1, wherein the machining is C chamfering. The current limiting device according to claim 1, wherein the machining is R chamfering. 2. The current limiting device according to claim 1, wherein the processing is press processing.

Images