JP3754726B2 - Thin temperature fuse - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an alloy type thin temperature fuse.
[0002]
[Prior art]
Alloy types are well known as temperature fuses for protecting electrical and electronic devices from abnormal heat generation due to overcurrent.
As is well known, in the temperature fuse of this alloy type, the low melting point metal piece, which is a fuse element, is melted by the abnormal heat generated by the equipment and the power supply to the equipment is cut off, depending on the allowable temperature of the equipment. A low melting point metal piece having a set melting point is used as a fuse element.
[0003]
[Problems to be solved by the invention]
In recent years, with the miniaturization of electric / electronic devices, there has been a demand for miniaturization, in particular, thinning, in the temperature fuse used by being mounted on these devices.
In a conventional alloy type temperature fuse, a low melting point metal piece is connected between the tips of a pair of lead conductors, the low melting point metal piece is surrounded by a case, and the lead is then removed from the case. Since the lead conductor is hermetically drawn through the sealant and the space in the case needs to be thick enough to accept the lead conductor, there is a limit to the reduction in thickness.
However, in the current fuse, a configuration in which both cover plates of the flat case are constituted by electrode plates, and both ends of the low melting point metal pieces accommodated in the flat case are connected to each electrode plate is known. (Japanese Utility Model Laid-Open No. 50-60530). However, even in this configuration, the space thickness in the flat case must be equal to or larger than the wire diameter of the fuse element, and the cross-sectional area of the low melting point metal piece must be increased (rated current) In the case of an alloy type temperature fuse of 10 amperes or more, the wire diameter of the low melting point metal piece becomes large, and thus the case is forced to be considerably thickened. Also, if the gap between the low melting point metal piece in the flat case and the inner surface of the case cover plate is very small, even if the low melting point metal piece is melted, the molten metal bridges between the inner surface of both cover plates and immediately Therefore, it takes a long time until the low melting point metal piece is melted and then divided, and it is difficult to guarantee the quick operation.
[0004]
Conventionally, it is known that a low melting point metal piece is subjected to a load by a spring or a spring, and the low melting point metal piece is forcibly broken at the same time as melting to ensure quick operation. In this case, a large space in the case is required for housing the spring and the spring, and it is difficult to apply to a thin temperature fuse.
[0005]
An object of the present invention is to provide an alloy-type thin temperature fuse that is sufficiently thin even at a high current capacity and can guarantee quick operation.
[0006]
[Means for Solving the Problems]
In the thin thermal fuse according to the present invention, a low melting point metal piece is vertically penetrated through a flat case, both ends of the low melting point metal piece are connected to respective electrodes on both sides of the case, and an annular elastic member is provided in the case. Is housed against the reaction force of the low melting point metal piece, using a circular case for the flat case and an annular body with an outer diameter smaller than the inner diameter of the case for the annular elastic material can do.
[0007]
[Action]
Under normal conditions, the low melting point metal piece is unmelted, and the low melting point metal piece has a high breaking strength. The metal piece is held stably. When the low melting point metal piece is heated to the melting point due to heat generation due to the overcurrent of the equipment, the breaking strength of the low melting point metal piece suddenly decreases, and the low melting point metal piece is based on the reaction force of the elastic material. The device breaks without being able to withstand the force and power to the equipment is immediately cut off.
[0008]
In this case, even if the rated current is large and the cross-sectional area of the low melting point metal piece is large, a reaction force that can cause the low melting point metal piece below the melting point to break instantaneously is applied to the elastic material. This elastic material can be easily obtained by increasing the cross-sectional secondary moment of the annular elastic body even if the thickness of the space in the flat case is reduced.
Therefore, it is possible to provide an alloy-type thin temperature fuse that is sufficiently thin even with a large current capacity and that can guarantee quick operation.
[0009]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
1A is an explanatory view showing an embodiment of a thin temperature fuse according to the present invention, and FIG. 1B is a cross-sectional view of FIG.
In FIG. 1A and FIG. 1B, reference numeral 1 denotes an insulator, for example, a flat case made of ceramics or plastic, and upper and lower cover plate portions 11 and 12 are integrated with the body frame portion 10. ing. The inner and outer circumferences of the flat case 1 are usually circular. Reference numerals 21 and 22 denote electrodes provided on the outer surface of the cover plate portions 11 and 12 of the flat case 1, adhesion of conductive metal plates and conductive metal foils, application and baking of conductive paste, It can be formed by vapor deposition or plating. 3 is an annular elastic body housed in the flat case 1, 4 is a low melting point metal piece penetrating in the thickness direction of the flat case 1, and the low melting point metal piece 4 is the flat case 1. The annular elastic body 3 is flattened and flattened by the low melting point metal piece 4 at the position along the movement along the slit s, and both ends of the low melting point metal piece 4 are opposite to the flattened annular elastic body 3. It is fixed to each of the electrodes 21 and 22 by welding or the like against the force.
[0010]
In order to manufacture the above-described thin temperature fuse, for example, the lower electrode plate 22, the plastic lower lid plate 12, the plastic body frame 10, and the plastic upper side which are arranged as shown in FIG. The lid plate 11 and the upper electrode 21 are laminated and integrated by heat fusion or the like, and the annular elastic body 3 is accommodated in the body frame 10, and the flat case containing the annular elastic body thus manufactured [(( B)], a linear low melting point metal 40 is inserted into the slit s as shown in FIG. 3C, and the linear low melting point metal 40 is moved along the slit s, as shown in FIG. The annular elastic body 3 is flattened and flattened, and both ends of the linear low melting point metal 40 are connected to the electrode plates 21 as shown in FIG. 3E against the crushing flattening reaction force of the annular elastic body 3. As shown in FIG. 3 (f), the excess end portion of the linear low-melting-point metal is welded. How to cut can be used.
[0011]
In the thin temperature fuse according to the present invention, the normal rupture strength of the low melting point metal piece is sufficiently higher than the normal stress based on the elastic reaction force in the normal state. It is kept stable.
Therefore, when the low melting point metal piece is heated to the melting temperature due to heat generation due to the overcurrent of the equipment, the low melting point of the low melting point metal piece instantaneously decreases, and the molten low melting point metal piece becomes an elastic body. The elastic body 3 is restored to the initial state as shown in FIG.
[0012]
The normal stress τ (cross-sectional average value) acting on the low melting point metal piece in normal times is P, the force required to deform the annular elastic body 3 from the circular shape to the flat shape shown in FIG. If the cross-sectional area of the piece 4 is S,
τ = P / S (1)
In order to achieve instantaneous fracture at the melting temperature of the low melting point metal piece, the stress τ is made sufficiently larger than the shear breaking strength of the low melting point metal piece at the melting temperature. It is essential to keep it.
Therefore, the relationship between the P and the deflection amount δ of the annular elastic body is the relationship between P and the deflection amount δ when the annular beam is flattened by the one-point action load P [P = (δEI) / (0.149R]. ³ ), where R is the radius of the circular beam, E is the Young's modulus of the beam, and I is the secondary moment of the cross section of the beam.
P∝Iδ ▲ 2 ▼
In the formula (1), even if the cross-sectional area S of the low melting point metal piece is large, in the formula (2), by increasing the cross-sectional secondary moment I of the annular elastic body and increasing P, The stress τ acting on the low melting point metal piece can be maintained at a desired value.
Therefore, when the cross-sectional area of the low-melting point metal piece is increased to increase the current capacity, the thickness and diameter of the low-melting point metal piece are left as they are, and the width b of the annular elastic body (see (b) in FIG. 1 for the width b). ] To increase the cross-sectional secondary moment of the annular elastic body, the above-mentioned rapid breaking operation can be guaranteed.
[0013]
In the thin temperature fuse according to the present invention, the thickness a of the space in the flat case (see FIG. 1A) is set to about several millimeters for a thick one and about several hundred μm for a thin one. When the cross section of the annular elastic body is a square having a width a ′ (slightly smaller than a) and a thickness b, the secondary moment I of the cross section
I = a'b 3/12 ( ³⁾
When the cross section of the annular elastic body is an oval having a width a ′ and a thickness b, the secondary moment I of the cross section is
^{I = πa'b 3/4 ▲ 4} ▼
In the thin temperature fuse according to the present invention, even if the cross-sectional areas of the low melting point metal pieces are different, the dimension a ′ is constant, so that the cross-section of the annular elastic body is left unchanged. By adjusting the secondary moment I by changing only its thickness b, the above-described quick breaking operation can be guaranteed.
[0014]
In the present invention, a flat coil-like elastic body as shown in FIG. 4 (a) (plan view) and FIG. 4 (b) (side view) can also be used as the annular elastic body 3. The outer diameter (diameter) d of the annular elastic body is normally set to 2D / 3 ≦ d <D with respect to the inner diameter (diameter) D of the flat circular case. Furthermore, as the material (Young's modulus) of the annular elastic body, engineering plastic, silicon rubber, etc. can be used in addition to the spring material.
[0015]
【The invention's effect】
In the temperature fuse of the alloy type according to the present invention, the low melting point metal piece is penetrated in the thickness direction of the flat case, so that the cross-sectional area of the low melting point metal piece is left as it is. In addition, the increase in the shear reaction force of the annular elastic body for breaking the low melting point metal piece at the melting temperature according to the increase in the cross-sectional area of the low melting point metal piece is due to the increase in the thickness of the annular elastic body. Since it can be performed only by increasing the secondary moment of the cross section (and not depending on the thickness of the flat case), the cross-sectional area of the low melting point metal piece is increased in order to increase the current capacity. Even in such a case, it is possible to provide an alloy-type thin temperature fuse that is sufficiently thin and can guarantee quick operation.
[Brief description of the drawings]
FIG. 1 (a) is an explanatory view showing an embodiment of a thin temperature fuse according to the present invention, and FIG. 1 (b) is a cross-sectional view of FIG. 1 (b). .
FIG. 2 is an explanatory view showing an operating state of a thin temperature fuse according to the present invention.
FIG. 3 is an explanatory view showing a method of manufacturing a thin temperature fuse according to the present invention.
4A is a plan view showing another example of the annular elastic body used in the present invention, and FIG. 4B is a side view of the same.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Flat case 21 Electrode 22 Electrode 3 Elastic body 4 Low melting metal piece

Claims (2)

A low melting point metal piece is vertically penetrated through the flat case, both ends of the low melting point metal piece are connected to the electrodes on both sides of the case, and an annular elastic material is inserted into the case to cause the low melting point metal piece. A thin thermal fuse characterized by being stored against the reaction force. The flat case is a circular case, and the annular elastic member is an annular body having an outer diameter smaller than the inner diameter of the case, and the annular elastic body is elastically deformed by a reaction force of a low melting point metal piece. The thin thermal fuse according to 1.

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