JPS6028086B2 - Overcurrent protection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an overcurrent protection device that opens contacts by reversing a bimetal when an overcurrent such as a short circuit current or an overload current flows.

In the prior art, if contacts weld or mechanical components such as bimetals break, normal operation is no longer achieved. Such a state cannot be easily determined from the outside, and if the product is used as it is, there is a risk that it will lead to a major accident. To solve this problem, for example, Utility Model Application No. 51-102760 developed a bimetal for temperature control in which the movable contact deforms in the direction away from the fixed contact due to temperature rise, and A configuration is shown in which a thermal fuse that melts when the temperature rises is integrally incorporated.

This prevents an abnormal temperature rise due to melting of the thermal fuse even if the movable contact and the fixed contact contact each other.
Instead of a thermal fuse, for example, JP-A-54-8267
9, the bimetal is deformed due to temperature rise, the movable contact separates from the fixed contact and opens, and the open state is maintained by a spring. At this time, a new problem arises that must be solved.

That is, a first bimetal whose movable contact deforms in the direction of moving away from a fixed contact due to temperature rise, and a second bimetal connected in series with this first bimetal and used in place of a thermal fuse are separately provided. Therefore, when the contact between the first and second bimetals is established, the resistance becomes large, and the temperature rise becomes significant during normal operation. Also, the configuration is obviously complex. Furthermore, it is necessary to individually adjust the setting of the temperature at which the first and second bimetals conduct their opening operations, resulting in poor reliability. The purpose of the present invention is to reduce the resistance when the contacts are connected as much as possible to prevent temperature rise during normal operation, thereby preventing malfunctions, simplifying the configuration, and improving reliability. An object of the present invention is to provide a current protection device.

FIG. 1 is a sectional view of one embodiment of the present invention.

A substrate 1 made of an electrically insulating material has two electrodes spaced apart from each other.
Two fixed contacts 2, 3 are provided. The fixed contact 2 is fixed to a terminal 4 fixed to the substrate 1. Another fixed contact 3 is a bulge formed on the terminal 5. Contact 2
, 3, a support step 6 is provided in a protruding manner. Spring means 7 are fixed to the support step 6 . A bimetal 8 is connected to the spring means 7. FIG. 2 is a perspective view of the bimetal 8 shown in the first diagram.

The bimetal 8 is constructed symmetrically in its longitudinal direction (left-right direction in FIG. 2). Attachment holes 9 and 10 are bored at both ends of the bimetal 8.
Movable contacts 11 and 12 facing fixed contacts 2 and 3, respectively
are fixed respectively. At the longitudinal center position of the bimetal 8, there is a mounting hole 13 for mounting the spring means 7.
, 14 are drilled. Holding pieces 15 and 16 are formed by punching on both sides of the mounting holes 13 and 14 in the longitudinal direction (left and right in FIG. 2). The holding pieces 15 and 16 are formed with engaging portions 15a and 16a. The holding pieces 15 and 16 extend in the longitudinal direction (left-right direction in FIG. 2). Engagement part 15
a and 16a are formed at the tips of the holding pieces 15 and 16, and are located near the center of the bimetal 8 in the longitudinal direction. FIG. 3 is a perspective view of the spring means 7.

The spring means 7 is arranged on both sides of the bimetal 8 in the longitudinal direction (left and right in FIG.
The curved spring portion 17 protrudes above
, 18. The free ends of the spring parts 17 and 18 have cutouts 17 for engaging with the engaging parts 15a and 16a, respectively.
a, 18a are formed. Legs 19, 20 of spring means 7
is fixed to the support step 6. The spring forces F1 and F2 that can be applied to the holding pieces 15 and 16 by the spring parts 17 and 18 are as follows:
It is determined to satisfy the relationship of the first formula, and for this purpose, the width minor 1, d2 of the spring portions 17, 18 is determined as shown in the second formula. F1<F2 ``E, dl<d2...[2' The bimetal 8 has two stable states in which the movable contact 11 contacts and separates from the fixed contact 2 due to the action of the spring means 7.
There are two stable states in which the movable contact 12 contacts and separates from the fixed contact 3.

The displacement history of the bimetal 8 when the movable contact 11 is displaced away from the fixed contact 2 is limited by the stopper 21. Therefore, when the temperature of the bimetal 8 decreases, the movable contact 11 can return to the stable state in which it is in contact with the fixed contact 2. Once the other movable contact 12 is displaced away from the fixed contact 3, it will not come into contact with the fixed contact 3 and return to its original stable state. Instead of configuring the spring sections 17 and 18 to satisfy the second equation, another embodiment is to form the spring sections 17 and 18 to have the same width, and to make one spring section 17 wider than the other spring section 18. It may be formed thin to satisfy the first formula.

The present overcurrent protection device is interposed between the power source and the load by connecting terminals 4 and 5 in series.

When a normal current is flowing, the current path is, as shown in the first diagram, terminal 4, fixed contact 2, movable contact 11,
It is formed by a bimetal 8, a movable contact point 12, a fixed contact 3, and a terminal 5. When the load current becomes excessive, the temperature of the bimetal 8 increases, and as a result, the movable contact 11 first separates from the fixed contact 2 and becomes open, as shown in the fourth figure.

This cuts off the supply of power to the load. Therefore, the temperature of the bimetal 8 decreases. Therefore, movable contact 1
1 comes into contact with the fixed contact 2 and returns to the conductive state shown in the first figure. Such action prevents excessive flow from flowing to the load. When the fixed contact 2 and the movable contact 11 remain in contact with each other due to welding or the like, the fixed contact 2 and the movable contact 11 are not electrically connected and overcurrent continues to flow.

As a result, the bimetal 8 has a movable contact 11 and a fixed contact 2.
It is heated to a temperature even higher than the temperature at which it is exposed. As a result, the movable contact 12 is opened from the fixed contact 3. Once the movable contact 12 is separated from the fixed contact 3, its stable state is maintained. This prevents overcurrent from continuing to flow through the load. FIG. 5 is a cross-sectional view of another embodiment of the invention.

Although this embodiment is similar to the previous embodiment, a notable feature is that the spring means 26 has two spring parts 23, 24 at their bases 23a, 24a fixed to the support step 6. It is fixed to the support body 25 and these base parts 23a, 2
4a provides a distance difference 6 with respect to the bimetal 8, and the fifth
In the figure, the base 24a of the copying part 24 is made higher than the base 23a of the spring part 23 by a difference of 6. As a result, the spring force F2 that suppresses the holding piece 16 by the spring portion 24 is
is the force F that holds down the holding part 15 by the spring part 23.
It can be larger than I. As described above, according to the present invention, in addition to the movable contact that repeatedly opens and closes due to overcurrent, another movable contact that opens at a temperature higher than that of the movable contact is provided, and this other movable contact Since the contact state is maintained when the contacts open, even if one movable contact remains closed due to falling, abnormal overcurrent is prevented from continuing to flow to the load. It's safe. In particular, in the present invention a single bimetal 8 is used, so that two pairs of contacts 2, 11
;The resistance when the contacts 3 and 12 are in contact can be reduced. Therefore, bimetal 8 under normal conditions
temperature rise is suppressed. Therefore, malfunctions are prevented. Furthermore, the configuration is simplified. Furthermore, by selecting one spring force FI to be smaller than the other spring force F2, the temperature of the bimetal 8 at which one fixed contact 2 and one movable contact 11 are separated is lowered by the temperature at which the other fixed contact 3 and the other movable contact 11 separate. The temperature can be set lower than the temperature at which the movable contact 12 separates.

In this way, the adjustments described above in connection with the prior art are not required and reliability is thus improved.

[Brief explanation of the drawing]

1 is a sectional view of an embodiment of the invention, FIG. 2 is a perspective view of the bimetal 8, FIG. 3 is a perspective view of the spring means 7, and FIG. 4 is another operating state of the embodiment shown in the first figure. FIG. 5 is a cross-sectional view of another embodiment of the present invention. 1... Board, 2, 3... Fixed contact, 4, 5
...Terminal, 6...Support step, 7, 26
... Spring means, 8 ... Bimetal, 11, 12
......Movable contact, 21...Stopper. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. A substrate 1 made of an electrically insulating material on which a pair of spaced apart fixed contacts 2 and 3 are provided, and one and the other movable contacts facing the one and the other fixed contacts 2 and 3, respectively. Contacts 11 and 12 are fixed to both ends in the longitudinal direction, and the center position in the longitudinal direction is fixed to the board 1 between the fixed contacts 2 and 3, and holding pieces 15 and 16 are mounted on both sides of this center position, respectively. The holding pieces 15, 16 extend in the longitudinal direction, and the holding pieces 15, 16 extend in the longitudinal direction.
The engaging portions 15a, 16a formed at the tips of the bimetal 8 are located closer to the center position, and the engaging portions 15a, 16a are fixed to the center position of the substrate 1.
16a, and biases the engaging portions 15a, 16a in directions away from each other with spring forces F1, F2, respectively;
The one spring force F1 is selected to be smaller than the other spring force F2, and the one fixed contact 2 and the one movable contact 11 corresponding to the one spring force F1 are such that a normal current flows through the bimetal 8. When the bimetal 8 is in stable contact with the bimetal 8 and an excessive current flows through the bimetal and the temperature of the bimetal rises, the bimetal 8 becomes separated, and when the temperature of the bimetal 8 falls after reaching the separated state, the bimetal 8 becomes separated. One fixed contact 2 and the other movable contact 1 were separated.
A stopper 21 is provided on the substrate 1 to limit the displacement of the other movable contact 11 so that the other movable contact 11 comes into contact with the other fixed contact 3 and the other movable contact 12 corresponding to the other spring force F2. An overcurrent protection device characterized by being stable in a separated state.