JPH04517Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a temperature-sensitive circuit breaker that uses an omnidirectional shape memory alloy and a heat sink to detect both temperature and current.

As an example of the circuit breaker used in the present invention, a case will be described in which the voice coil of a speaker system is prevented from being burnt out.

Since the acoustic conversion efficiency of electroacoustic transducers such as speakers is extremely low at a few percent, most of the energy is generated by Joule heat. Therefore, if an excessive input is applied to the speaker, there is a risk that the voice coil will burn out due to the generated Joule heat. Conventionally, to protect the voice coil, a bimetallic circuit breaker or fuse is used to prevent damage due to excessive input in a relatively short period of time. However, these methods of over-input protection do not take into account the temperature conditions of the voice coil, which is the source of heat generation, and its vicinity, which is inconvenient in setting the current limit value.
If the current limit value of the breaker is set low in consideration of the temperature rise in the vicinity of the voice coil, there will be an inconvenience that the protective operation will be activated repeatedly at the peak of the sound source even if the input value does not yet cause a burnout under normal usage conditions. . On the other hand, if the limiting current value is set in the initial state of use or when the temperature near the voice coil is close to room temperature, even if the current value is less than that, the temperature will reach sufficient to burn out the voice coil with continuous input signals. As described above, the permissible input conditions for speakers, etc. include the strength, weakness, and intermittent input signals, and because they change from moment to moment, it is difficult to protect them by simply limiting the current value using bimetals, etc. Therefore, in order to perform more reliable protection, it is necessary to detect the temperature rise near the voice coil and attenuate or cut off the input signal if the temperature exceeds the set temperature condition.

As a conventional example of a temperature sensor, an electronic circuit system using a temperature sensing element such as a thermistor or a varistor and a relay circuit can be considered, but it requires a power source to operate the circuit. Furthermore, it requires a large number of parts and expensive parts such as relays, and is currently not commercially available because it is not reasonably priced.

Therefore, in order to eliminate these drawbacks, the present invention aims to provide a new type of temperature-sensitive circuit protector that has the dual functions of a temperature-sensitive switch and a current circuit breaker.

The present invention consists of a temperature-sensing section made of an omnidirectional shape memory alloy whose outer shape changes rapidly when a predetermined temperature is reached, and a heat collecting section for external temperature detection installed close to the temperature-sensing section. A plate, a bay-shaped spring member with one end fixed to support the shape memory alloy, an electric contact that snaps and moves due to a change in shape of the shape memory alloy, a fixed contact therefor, and a stopper for the electric contact that snaps and moves. A temperature-sensitive circuit protector configured to open and close the contacts based on changes in the outer shape of the temperature-sensing section due to self-heating caused by energizing the temperature-sensing section and heat conduction of the heat collecting plate. By using the shape memory alloy, which is a temperature sensing element, as a current path, it also works as a circuit breaker. In addition, the set current value changes depending on the external temperature due to the heat transferred from the heat sink, and when the temperature in the vicinity exceeds the set value, the temperature-sensitive switch and current sensor break the input signal, regardless of the current value. It has the advantage of having two functions of a kit breaker.

The omnidirectional shape memory alloy used in this invention is 1 mm x 15
FIG. 1 shows the relationship between the temperature of the free end and the displacement D when the size is mm x 50 mm. Omnidirectional shape memory alloys include Ti-Ni alloys and copper-zinc alloys, but Ti-Ni alloys are superior in properties such as fatigue strength and corrosion resistance. When the omnidirectional shape memory alloy is cooled, it transforms from the parent phase to the martensitic phase at a temperature called the martensitic transformation point expressed by Ms, and deforms into the first shape memorized in advance.

On the other hand, when heated to a temperature above the reverse transformation point Af,
It transforms into a second shape stored in advance. In other words,
At temperatures above the transformation point Af, it assumes the second shape,
At an intermediate temperature between the transformation point Ms and the reverse transformation point Af, there is hysteresis. The tensile strength when in the matrix state above the Af point is several times that of the martensitic state for the same amount of strain. In other words, the omnidirectional shape memory alloy has the reverse transformation point Af
It has the property that the shape changes rapidly and significantly after the boundary.

Omnidirectional shape memory alloys have the characteristics shown by the solid line in the characteristic curve showing the amount of displacement D with respect to temperature T in Figure 1, and the continuous shape like bimetal, shown by the broken line in Figure 1. Don't change,
The shape changes rapidly at the point when the temperature T exceeds the reverse transformation point Af, and the rate of change is approximately nine times that of bimetallic material. Bimetal: 0.04mm per 1°C
Shape memory alloys have a property that changes rapidly near the reverse transformation point Af, so the variation in operating temperature can be reduced with respect to assembly accuracy.
Further, it is possible to reduce the amount of variation in operating temperature due to variation in the positional relationship of the members used during long-term use.

FIG. 2 shows an embodiment of a temperature-sensitive circuit protector using a shape memory alloy according to the present invention.

In FIG. 2, a temperature sensing element 6 is made of a shape memory alloy, one end of which is connected to a terminal plate 3, and is fixed together with the terminal plate 3 to a case 1 made of insulating resin. The joint portion is in contact with a heat sink plate 8 made of aluminum, copper, etc. provided at the bottom of the case via an insulating sheet 9. The other end of the temperature sensing element 6 is processed as shown in Fig. 2 d.
It is configured to be inserted into a small hole provided in a semicircular bias spring 7 as shown in FIG. Further, an electrical contact 4 is provided on the terminal plate 2 held in the case 1, with which the electrical contact 5 provided at the center of the temperature sensing element 6 comes into contact, and a stopper 10 for the temperature sensing element 6 is provided on the opposite side. is provided. Further, when the detected portion in contact with the heat sink plate 8 is not electrically insulated, the insulating sheet 11 can be combined with the lower part of the heat sink plate 8.

When the current flowing through the thermosensor 6 is below the set value, the temperature of the thermosensor 6 due to Joule heat is less than the reverse transformation point Af, and the thermosensor 6 assumes a linear shape as shown in Fig. 2a, and the spring 7 Electrical contacts 5 and 4 maintain contact. However, when the current exceeds the set value, the thermosensor 6 rapidly generates Joule heat, and when the temperature reaches the reverse transformation point, it curves as shown by the broken line in FIG. 2a. Due to the curvature, when the contact between the spring 7 and the temperature sensing element 6 passes the critical point shown by the chain line in FIG. The power supply is cut off when the power is reached. When the temperature of the temperature sensing element 6 decreases by cutting off the current and becomes less than the martensitic transformation point Ms, the temperature sensing element 6 curves upward as shown by the broken line in FIG. When the junction exceeds the critical point, the contact 5 automatically returns to its original state. Further, when the temperature sensing element 6 is in contact with the heat sink plate 8 through the insulating sheet 9 as shown in FIG. 2a, the set current value will automatically decrease as shown in FIG. 3 when the temperature of the mounting portion increases. Furthermore, when the temperature in the vicinity exceeds the break setting value, the input signal is cut off regardless of the current value. In this way, the limited current is repeatedly cut off automatically according to the temperature near the installation. In addition, by utilizing the properties of a spring at a critical point, a snap action can be performed to reduce the wear and tear on the contacts that occurs when the contacts open and close, and at the same time, it is possible to reduce the variation in operating temperature due to the adhesive phenomenon of the contacts. Note that it is not necessary to install the insulating sheet 9 if the mounting portion of the temperature-sensitive circuit breaker is electrically insulated or if there are no defects according to safety standards.

4 and 5 show the case where the temperature-sensitive circuit breaker according to the present invention is applied to a dome-shaped speaker or a cone-shaped speaker.

The temperature-sensitive circuit protector 58 is attached near the voice coil 55, which is the part to be measured, and the current flowing through the voice coil flows through the temperature-sensitive element of the temperature-sensitive circuit protector. In the figure, 51 is a magnet, 52 is a yoke, 53 is a top plate, 54 is a frame, 60 is a damper,
56 is a diaphragm, 57 is an edge, 59 is a gap,
61 indicates a speaker input terminal.

As explained above, the temperature-sensitive circuit breaker of the present invention has both temperature detection and current detection functions, and the limiting current value changes automatically depending on the temperature of the installation part, so it can be used as a circuit breaker for speakers. In this case, when the temperature near the voice coil increases, the current limit value decreases and the voice coil does not burn out. Furthermore, when the temperature in the vicinity exceeds the break setting value, the break occurs with a snap operation, regardless of the current value, and a reliable protection operation begins.

In addition, the Ti-Ni alloy used in this invention is paramagnetic, which is a necessary condition for sound quality and distortion for audio equipment, so it is a device with low distortion and good sound quality, and the sound quality is slightly better than conventional products using bimetals. Problems with distortion and distortion have been improved.

Furthermore, as shown in Figure 1, omnidirectional shape memory alloys exhibit rapid and large changes in shape past the reverse transformation point Af, which makes it possible to instantly connect and disconnect contacts, as well as to make them work like bimetals. The operating temperature does not fluctuate significantly depending on the processing and assembly accuracy of the parts, making it possible to supply highly reliable temperature-sensitive circuit protectors with stable operating temperatures.

The temperature-sensitive circuit protector of this invention prevents accidents caused by overheating and overcurrent in the event of an abnormality in electrical equipment or heat source application equipment, and maintains the safety of the equipment.It is a temperature-sensitive circuit breaker for speakers and amplifiers. Not only as a fluorescent light ballast,
It can also be used as temperature-sensitive circuit breakers for motors, small transformers, their applied equipment, and other electric heating equipment.

[Brief explanation of the drawing]

FIG. 1 shows the amount of displacement of the free end of the Ti--Ni shape memory alloy with respect to temperature. Figures 2a and b are front sectional views of an embodiment of the temperature-sensitive circuit breaker according to the present invention, Figure 2c is a perspective view of the spring material, Figure 2d is a front view of the temperature-sensitive element, and Figure 3. is a curve showing the relationship between the external temperature and the limiting current value of the temperature-sensitive circuit breaker according to the present invention. Furthermore, FIGS. 4 and 5 are cross-sectional views of a cone-shaped speaker and a dome-shaped speaker, respectively, in which the temperature-sensitive circuit breaker of the present invention is attached. In the figure, 1...resin case, 2, 3...
Input end, 6... Temperature sensing element (shape memory alloy), 4,
5... Electric contact, 8... Heat sink plate, 7... Spring,
9, 11...Insulating sheet, 10...Stopper,
51...Magnet, 52...Yoke, 53...
Top plate, 54...Frame, 55...Voice coil, 56...Diaphragm, 57...Edge,
58... Temperature sensitive circuit protector, 59...
Cap, 60...damper, 61...speaker input terminal.

Claims (1)

[Scope of utility model registration request] a temperature-sensing section made of an omnidirectional shape-memory alloy that has the characteristic of rapidly changing its external shape when a predetermined temperature is reached; a heat collecting plate for external temperature detection provided in proximity to the temperature-sensing section; It is composed of a bay-shaped spring member with one end fixed to support a shape memory alloy, an electrical contact that snaps and moves as the shape memory alloy changes, a fixed contact for this, and a stopper for the electrical contact that snaps and moves, and A temperature-sensitive circuit protector, characterized in that the contacts are opened and closed based on changes in the external shape of the temperature-sensing section due to self-heating caused by energizing the temperature-sensing section and heat conduction of the heat collecting plate.