JPH11111135A - Temperature fuse - Google Patents

Abstract

PROBLEM TO BE SOLVED: To isolate a lead wire from a movable electrode by transformation of a highly compressed spring and to cut off a current at a transformation temperature even if the lead wire and the movable electrode are not isolated due to an actuation failure at an operation temperature by using the highly compressed spring consisting of a shape memory alloy having a characteristic that the transformation temperature is higher than the operating temperature. SOLUTION: Lead wires 3a and 3b are provided at the left and right, and an auxiliary spring 6, a temperature sensing pellet 5, a movable electrode 4, and a compressed spring 2 for isolating the movable electrode 4 from the left lead 3a during operation are provided therein. That is, the temperature sensing pellet 5 is melted at an operating temperature, the compressed spring 2 is unloaded, and the compressed spring 2 expands, and thereby, the movable electrode 4 pressure-contacted to the lead wires 3a and 3b is isolated from the lead wires 3a and 3b, and cut off the current. In the case, the compressed spring 2 consists of a shape memory alloy having a characteristic that the transformation temperature is higher than the operating temperature, and even in the case of an actuation failure, current is cut-off by a transformation force at the transformation temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal fuse to be installed in an electronic device or a household electric appliance to prevent the device from becoming abnormally high temperature. It relates to a thermal fuse having a characteristic.

[0002]

2. Description of the Related Art A conventional thermal fuse technique will be described below with reference to the drawings. Conventional thermal fuses are classified into a fusible alloy type and a thermosensitive pellet type using a fusible pellet. The present invention particularly relates to a thermal fuse of a type using a thermosensitive pellet. Will be described. A conventional thermal fuse of this type has a structure as shown in FIG. That is, the entire structure before the operation is such that at least the lead terminals 43a and 43b are provided at both ends of a cylinder whose inner surface is covered with a conductive material, that is, for example, a metal case 47, and the current is interrupted inside. There is provided a movable electrode 44 to be moved for the purpose.

[0003] The movable electrode 44 is pressed against the lead 43a, and before operation, the circuit is maintained in a conductive state, that is, a state in which current flows from the left lead 43a to the right lead 43b. The path through which the current flows passes through at least the inner wall surface of the metal case 47 from the left lead 43a through the movable electrode 44 and passes through the right lead 43a.
When the current reaches b, the current passes through the thermal fuse 41. The rectangular solid portion provided in contact with the right lead 43b is a temperature-sensitive pellet 45, which melts at a predetermined operating temperature and unloads the auxiliary spring 46 pressing the movable electrode 44. The movable electrode 44 is separated from the lead 43a by the expansion of the compression spring 42, and the current is interrupted.

[0004] Here, the role of the compression spring 42 and the auxiliary spring 46 will be briefly described. When the pressing force applied to the movable electrode 44 by the auxiliary spring 46 is released, the compression spring 42 is shown in the figure. Move to the right to move the left lead 43a
And the movable electrode 44. Conversely, the auxiliary spring 46 is placed on the temperature-sensitive pellet 45 and presses the movable electrode 44 against the left lead 43a. Before the operation, a current flows from the left lead 43a to the right lead 43b. Is to be secured.

[0005] The reason why the auxiliary spring 46 is particularly necessary is that the melting of the thermosensitive pellet 45 does not have such a property that the melting of the thermosensitive pellet 45 is started at a time as the operating temperature approaches, and that the melting of the thermosensitive pellet 45 is performed at once. Even if the temperature-sensitive pellet 45 approaches the operating temperature and slightly melts, the auxiliary spring 4
6 expands and serves to press the movable electrode 44 still against the left lead 43a, and when the thermosensitive pellet 45 is completely melted, the movable electrode 44 is separated from the left lead 43a by the compression spring 42. In this way, the current can be interrupted. In short, the movable electrode 44 is separated to the right at a time only in a completely melted state of the temperature-sensitive pellet 45 so as to cut off the current flowing under the lead 43b and the movable electrode 44.

In FIG. 1B, the temperature fuse 41 rises to a predetermined temperature and the temperature-sensitive pellet 45 melts.
Indicates a state in which is operated. In such a case, as described above, the compression spring 42 is unloaded, and as the compression spring 42 expands, the movable electrode 44 pressed against the left lead wire 43a is separated from the lead wire 43a and the left lead wire 43a is separated. The current flowing from the lead 43a to the right lead 43b is cut off. In addition, various temperature-sensitive pellets 45 are selected depending on how the operating temperature is set as such a temperature-sensitive pellet 45.

Conventionally, the operating temperature of the device manufactured by the applicant is about 70 ° C. to 240 ° C., and the operating accuracy under normal operation is generally about ± 2 ° C. The rated current is 10 amps and the rated voltage is 2
Those having a voltage of about 50 volts are generally used. The outer diameter of this type of thermal fuse is about 60 mm to 80 mm in total length including the lead.
About 0 mm. The metal case is generally cylindrical, and the outer diameter of the metal case is about 4.2 mm, and the length of the main body of the metal case is about 11 mm. Therefore, this type of thermal fuse is small, so it operates sensitively to temperature changes.It is made of a metal case in an airtight structure, has little change over time in characteristics and high operating accuracy. Once operated, it is in a form that does not recover even if the temperature drops.

For example, this type of thermal fuse is used for electric stoves and electric kotatsu, electric carpets, irons and trouser presses, air conditioners and ventilation fans, gas baths and gas water heaters,
It is used in pencil sharpeners, liquid crystal televisions, color televisions, refrigerators, electric rice cookers, fluorescent lamps, desk lamps, transformers, rechargeable batteries, hot water toilet seats, copiers, printers, and the like. In particular, in recent years, the demand for safety for products has been increasing, and the products are extremely high in social needs. From such a viewpoint, the thermal fuse is required to have extremely high reliability. This is because if the thermal fuse does not operate with a high degree of accuracy, a fire may occur, thereby injuring a person or, in the worst case, causing death.

On the other hand, as described above, as can be seen from the general structure of the thermal fuse and its operating condition, in this type of thermal fuse, the movable electrode and the lead are merely pressed against each other. The structure is such that the lead and the movable electrode are easily separated from each other. Therefore, there is a small gap between the lead and the movable electrode, but when a high current flows, a spark occurs in this part, and the phenomenon that the movable electrode and a part of the lead are melted by the spark also occurs. ing. Further, when the leads and the movable electrode are microscopically viewed, they are not necessarily finished to be smooth, so that the movable electrode and the lead may be mechanically and microscopically fitted.

In order to eliminate the malfunction of the movable electrode by welding or mechanically fitting the movable electrode and the lead, the present inventors have developed a structure in which the movable electrode is separated using a shape memory alloy. Provide the adopted thermal fuse. Therefore, a conventional thermal fuse using a shape memory alloy will be briefly described. FIG. 5 shows an example of a thermal fuse 51 using a shape memory alloy.

To briefly explain this type of thermal fuse, shape memory alloys are notable for latching unlike bimetals because they have a large operation stroke, and are advantageous for miniaturization. As shown in the figure, the lead 53a and the lead 53b are connected by a shape memory alloy because they have an integration effect on the surge current, and when a predetermined temperature is reached, the shape memory alloy returns to its original shape, A structure in which the connection between the leads 53a and 53b is opened to interrupt the current is considered.

Such a thermal fuse is suitable for a high-power and high-voltage thermal fuse because the cut portion is separated by a strong force. In addition to the above, a thermal fuse made of a shape memory alloy having a simple structure in which the compression spring is formed of a shape memory alloy in the thermal fuse having a shape as shown in FIG. Have been.

[0013]

As described above, in the conventional temperature-sensitive pellet type thermal fuse, a spark is generated between the lead and the movable electrode, and the heat generated by the spark causes the lead and the movable electrode to be welded. As shown in FIG. 6B, even if the thermosensitive pellet 65 is melted at a predetermined temperature, and the movable electrode 62 pressed against the lead wire 63a is released from the pressing force of the auxiliary spring 66, the movable electrode 64 remains An operation failure has occurred such that current continues to flow without leaving the left lead 63a. In such a case, as described above, the temperature of the device may be steadily increased, and eventually, other important parts of the device may be destroyed or a fire may occur, resulting in personal injury.

Although a temperature fuse using a shape memory alloy as described in the prior art appears to be reasonable at first glance, the shape memory alloy does not always reproduce its operating temperature with high accuracy. Has a temperature hysteresis of about 30 degrees. Therefore, as described above, it is extremely difficult to guarantee the operating temperature accuracy of about ± 2 degrees of the thermal fuse manufactured and sold by the present applicant in the thermal fuse using only the shape memory alloy. I can't get it.

[0015]

In order to solve the above-mentioned problems, a thermosensitive pellet is melted at an operating temperature to unload a compression spring, and the compression spring is expanded to be pressed against a lead wire. Wherein the movable electrode is separated from a lead wire to interrupt a current, wherein the spring is made of a shape memory alloy having a transformation temperature characteristic higher than the operating temperature. Even when the wire and the movable electrode are not separated due to a malfunction even at the operating temperature, the lead wire is separated from the movable electrode by the transformation force of the spring at the transformation temperature, and the current is interrupted. Temperature fuse.

Also, the transformation temperature provides a temperature fuse 5 ° C. to 25 ° C. higher than the operating temperature of the thermosensitive pellet. The spring is made of Ti having a wire diameter of 0.3 to 1.2 mm.
A temperature fuse made of a Ni alloy and having a transformation temperature of 60 ° C to 100 ° C is provided. The spring has a wire diameter of 0.3.
Ｍｎ1.2 mm MnCu alloy with transformation temperature of 100
A temperature fuse is provided that is between ℃ and 180 ° C.

[0017]

Embodiments of the present invention will be described below in the order of claims with reference to the drawings. According to the first aspect of the present invention, as described above, the temperature-sensitive pellet is melted at the operating temperature to unload the compression spring, and the compression spring expands, so that the movable electrode pressed against the lead wire is removed. A temperature fuse of a type which cuts off current from a lead wire, wherein the spring is made of a shape memory alloy having a transformation temperature characteristic higher than the operating temperature, and the lead wire and the movable electrode However, even at the operating temperature, even if the separation is not performed due to a malfunction, the lead wire and the movable electrode are separated by the transformation force of the spring at the transformation temperature,
Temperature fuse for interrupting the current.

That is, the present invention uses a spring made of a shape memory alloy to eliminate the malfunction even if the conventional temperature-sensitive type thermal fuse malfunctions, and the movable electrode is connected to the lead wire by its transformation force. It is a type of thermal fuse that separates from the fuse and eventually cuts off the current to achieve the purpose. Thus, comparing the conventional thermal fuse with the thermal fuse of claim 1 of the present application, the difference is that the material of the compression spring is a shape memory alloy or not a shape memory alloy. The function and effect of the invention described in claim 1 can be obtained by using it as a compression spring.

Here, the basic characteristics of the shape memory alloy will be briefly described. Table 1 shows the composition and various properties of the alloy exhibiting the shape memory effect. These alloys generally have a thermoelastic martensitic transformation. The interface between the mother phase and the martensitic phase is well-matched, so that the transformation latent heat is small and the transformation is crystallographically reversible. As described above, the cause of the crystallographic reversibility is that the parent phase and the martensite phase both have an ordered structure, and that the martensite phase returns to the parent phase with a single lattice structure between the two. The process of breaking the structure increases the free energy of the mother phase, so that it returns to the mother phase by following the original path.

[0020]

[Table 1]

FIG. 2 schematically shows a state of a crystal structure change accompanying a change of a parent phase, that is, an austenite phase and a twin martensite phase, a deformed martensite phase, and a parent phase in a typical shape memory alloy. It is a thing.
In the figure, the state (a) is an austenite phase, which is stable at a temperature equal to or higher than the Af point, and has a cubic crystal structure. (B) shows twin martensite, which is transformed into a martensite phase if the mother phase is cooled to a temperature below the Mf point. In general, the martensite phase is not cubic, but has lattice deformation.

In this figure, the shape is a rhombic lattice, and the lattice deformation is exaggerated. In addition to the lattice deformation, a lattice invariant deformation occurs, and as a result, the martensite phase is accompanied by twins. Such twins are called internal twins and are indispensable for the heat-cutting martensite phase. Since the martensite phase contains such twins, the outer shape is substantially similar to the outer shape of the parent phase, and the increase in strain energy of the entire system due to the transformation is suppressed. Such a suppression effect due to lattice invariant deformation is called self-correction. FIG. 3C shows deformed martensite, which is generated when an external force is applied to the above-described twinned martensite to deform it.

As a result of shearing deformation due to external force, twins of martensite disappear and become a single variant. This is a deformation based on another mechanism completely different from that in which the plastic deformation of a normal metal or alloy occurs by the slip of the lattice plane due to the movement of the sliding dislocation. In the context of the present invention, the process of forming deformed martensite is a process of compressing a spring, and the state of twinned martensite is a process of forming a spring made of a shape memory alloy. Deformation of a shape memory alloy is characterized as a process in which twin martensite having a large number of variants is converted into a single variant to form a deformed martensite phase.

Finally, consider a case in which such a deformed martensite phase is heated to a temperature equal to or higher than the Af point to cause reverse martensitic transformation and return to the parent phase. As the martensite returns to the parent phase and the crystal becomes cubic, both the lattice deformation and the lattice invariant deformation disappear. Along with this, the deformation given by twinned martensite also disappears, and the outer shape returns to its original shape. This is the principle of the shape memory effect. According to the present invention, in accordance with the present invention, a compression spring formed in a stretched state by a shape memory alloy undergoes reverse martensitic transformation as the temperature rises, and the original shape, that is, the spring is initially formed by the reverse martensitic transformation. It returns to the formed stretched state.

At this time, the force accompanying the reverse martensitic transformation to return to the stretched state is the transformation force. The feature of the present invention is that the transformation force causes welding or mechanical fitting to the lead wire due to malfunction. To separate the movable electrode. The invention according to claim 1 will be described with reference to FIG. The basic structure of the thermal fuse 1 of the present invention is the same as that of a conventional thermal pellet type thermal fuse, but the difference is that the compression spring 2 is made of a shape memory alloy.

As described above, the shape memory alloy stores the shape when the compression spring 2 is fully extended, and when the temperature reaches a predetermined temperature, the compression spring 2 is fully extended due to the shape memory effect. Try to return to. Unlike the conventional temperature-sensitive pellet-type thermal fuse, the transforming force at this time acts to separate the movable electrode 4 from the lead wire 3a by applying a transforming force in addition to the force for expanding the spring.

The other components are the same as those of the conventional temperature-sensitive pellet type thermal fuse. Lead wires 3a and 3b are provided on the left and right, and an auxiliary spring 6 for compressing the movable electrode 4 from the temperature-sensitive pellet 5 side. A compression spring 2 for separating the movable electrode 4 from the left lead 3a during operation is provided on the left side of the temperature-sensitive pellet 5 and the movable electrode 4, and the entirety of the compression spring 2 is housed in the metal case 7. The metal case 7 is generally cylindrical, and such a shape is sufficient in the present invention.

FIG. 2B shows a state in which the thermal fuse 1 according to claim 1 using such a shape memory alloy is operated. As can be seen from the operation shown in FIG. 3B, the compression spring 2 is unloaded, and at a temperature higher than the transformation temperature of the shape memory alloy, a force for pushing the movable electrode 4 to the right with a transformation force acts. Even if the lead 3a is not separated from the lead 3a by a normal spring force due to welding by an arc or mechanical fitting, this is guaranteed and the current is reliably cut off.

Next, the second aspect of the present invention will be described. As described above, in the invention of claim 2, the transformation temperature is:
2. The temperature fuse according to claim 1, wherein the temperature is higher by 5 DEG C. to 25 DEG C. than the operating temperature of the thermosensitive pellet. As described above, the difference between this invention and the invention using the conventional shape memory alloy is that the shape memory alloy is not set to be transformed by the operating temperature. The basic operation of this thermal fuse is the same as that of the conventional thermal fuse. The temperature sensitive pellet melts and the movable electrode is unloaded, so the left compression spring expands and the movable electrode is separated from the left lead wire. And acts to interrupt the current.

However, in a very rare case, only when the movable electrode is welded or mechanically fitted to the left lead, the compression spring is made of a shape alloy to prevent a further rise in temperature. It is intended to provide a thermal fuse based on a so-called fail-safe design concept. From such a viewpoint, it is not appropriate to use the transformation temperature of the shape memory alloy as the basic operating temperature of the thermal fuse. Because, as described above, the reproducibility of the transformation temperature of the shape memory alloy is not always sufficient, and when the transformation temperature is several degrees or more, it has a temperature hysteresis of about 30 degrees, so that it is possible to provide a thermal fuse having accurate characteristics. It is because it disappears.

Therefore, in a thermal fuse using a shape memory alloy for this kind of compression spring, the operating temperature of the shape memory alloy should be higher than the operating temperature of the original thermal fuse. It is appropriate to use a shape memory alloy having a transformation temperature as high as about 25 degrees. 5
The range of degrees to 25 degrees is determined by design depending on the transformation temperature of the shape memory alloy and the temperature hysteresis at which actual transformation starts, that is, the type of shape memory alloy used. Since the shape memory alloy has a temperature hysteresis of about 5 degrees, a transformation temperature about 5 degrees higher than the operating temperature is required.

If the transformation temperature is higher than 25 ° C., there is a possibility that the performance of the device will be impaired. Therefore, it is necessary to operate the shape memory alloy as a fail safe at a temperature as low as possible. 25 from a perspective
It is preferable to set the transformation temperature of the shape memory alloy at a temperature lower than the temperature. From this viewpoint, the transformation temperature is preferably about 5 to 25 degrees higher than the operating temperature of the thermosensitive pellet, and if a shape memory alloy having such a transformation temperature is applied to the thermal fuse according to claim 1, it is unlikely that Thus, it is possible to provide a highly reliable thermal fuse that can avoid malfunctions.

Next, the third aspect of the present invention will be described. As described above, the invention according to claim 3 is characterized in that:
3. The temperature fuse according to claim 1, wherein the temperature fuse is made of a TiNi alloy having a wire diameter of 0.3 to 1.2 mm, and has a transformation temperature of 60 ° C. to 100 ° C. In order for a thermal fuse using a shape memory alloy to have predetermined characteristics as described above, it is necessary that a spring using the shape memory alloy has a predetermined elasticity in a normal operation state.

From such a viewpoint, the present inventors have found a TiNi alloy as an alloy that can also be used as a spring material having a predetermined elasticity. FIG. 3 shows the relationship between the stress and strain of the TiNi alloy. In this case, the linearity is set to 0.
It is appropriate to set it to about 3 to 1.2 mm. 0.3mm
If it is smaller than this, a sufficiently large spring repulsion force cannot be obtained, and if the linearity is larger than 1.2 mm, the thermal fuse itself cannot be miniaturized, so that various factors such as variations in response to temperature will occur. It is not reasonable to cause problems.

Also, as can be seen from Table 1, in the case of TiNi, the transformation temperature is about 60 to 100 degrees, which is considered to be about 5 to 25 degrees higher than the operating temperature of the thermosensitive pellet. For example, it is possible to use a spring using this type of shape memory alloy for a thermal fuse whose operating temperature is about 70 to 80 degrees among thermal fuses conventionally manufactured or sold by the present applicants. Thus, the object of the present invention can be reliably achieved.

Next, the invention according to claim 4 will be described. According to a fourth aspect of the present invention, as described above, the spring is made of a MnCu alloy having a wire diameter of 0.3 to 1.2 mm, and has a transformation temperature of 100 to 180 ° C. It is. According to the present invention, a spring made of a shape memory alloy has a predetermined elasticity under normal operating conditions, that is, the movable electrode is sufficiently separated from the lead when the temperature-sensitive pellet is in a molten state. It has been invented in view of the case where it has a repulsive force that can be separated to the
The alloy was also found to satisfy such conditions.

In the case of the MnCu alloy, unlike the TiNi alloy according to claim 3, the transformation temperature is 100 ° C. to 1 ° C.
A temperature of about 80 ° C. can be realized. In view of this point, it is possible to select a spring made of a shape memory alloy that is optimal for a temperature fuse of about 120 to 200 out of operating temperatures of thermal fuses manufactured or sold by the applicant and the like. Becomes Therefore, it is possible to provide an extremely reliable thermal fuse using a shape memory alloy as a compression spring material in a very wide operating temperature range in combination with the above-described third aspect of the present invention.

[0038]

As described above, according to the present invention, even when the movable electrode is welded or mechanically fixed by spark or mechanical fitting generated between the movable electrode and the lead, the operating temperature is maintained. By using a shape memory alloy having a higher transformation temperature for the compression spring,
With the transformation force, the movable electrode is separated from the lead wire, and as a result, the current flowing through the thermal fuse can be cut off,
An extremely reliable thermal fuse can be provided. In addition, such a thermal fuse operates in exactly the same manner as a conventional thermal pellet-type thermal fuse when no failure occurs, and thus is considered to be a thermal fuse using only a shape memory alloy, which has a poor operating sensitivity. The disadvantages that have been solved have also been eliminated.

[Brief description of the drawings]

FIG. 1 is a sectional view of a thermal fuse of the present invention.

FIG. 2 is a schematic view of a crystal change in a shape memory alloy.

FIG. 3 is a diagram showing a relationship between stress and strain of a TiNi alloy.

FIG. 4 is a cross-sectional view of a conventional thermal fuse.

FIG. 5 is a cross-sectional view of a thermal fuse using a shape memory alloy.

FIG. 6 is a sectional view showing a malfunction of a conventional thermal fuse.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thermal fuse 2 Compression spring 3a, 3b Lead wire 4 Movable electrode 5 Thermosensitive pellet 6 Auxiliary spring 7 Metal case

Claims (4)

[Claims] The movable electrode, which has been pressed against the lead wire, is separated from the lead wire by the thermosensitive pellet melting at the operating temperature to unload the compression spring and expand the compression spring. A temperature fuse of a type for interrupting an electric current, wherein the spring is made of a shape memory alloy having a transformation temperature characteristic higher than the operating temperature, and the lead wire and the movable electrode are kept at the operating temperature. A temperature fuse that separates the lead wire and the movable electrode by the transformation force of the spring at the transformation temperature and cuts off current even when the separation is not performed due to a malfunction. 2. The temperature hue according to claim 1, wherein said transformation temperature is 5 ° C. to 25 ° C. higher than the operating temperature of said thermosensitive pellet.
Z. 3. The spring according to claim 1, wherein said spring has a wire diameter of 0.3 to 1.2 mm.
3. The temperature fuse according to claim 1, which is made of an iNi alloy and has a transformation temperature of 60 to 100.degree. 4. The spring according to claim 1, wherein said spring has a wire diameter of 0.3 to 1.2 mm.
3. The temperature fuse according to claim 1, wherein the temperature fuse is made of an nCu alloy and has a transformation temperature of 100.degree.