JPS6238809B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention is arranged at an appropriate position inside a high temperature device such as an exhaust gas purification device for an internal combustion engine, and when the temperature inside the device rises abnormally, the tip of the lead wire is fixed at a constant temperature. The present invention relates to an improvement in a fuse plug used to open an electrical closed circuit connected to an alarm or protection device and emit an electrical signal by blowing a fusible metal wire portion.

This type of fuse plug has not been used much in the past due to concerns that it would need to be replaced, but it was initially thought that as a result of actual use of an exhaust gas purification device, the temperature inside the device would rise to an abnormal level. It has become known that the phenomenon of temperature rise occurs infrequently and does not occur as frequently as in the past. Therefore, the low price of fuse plugs that cannot be used repeatedly is being reconsidered, and there are signs that their use will be rapidly expanded recently. However, there were problems with the physical durability of the fuse plug and the stability of the fusing temperature, which prevented it from becoming more widespread. For this reason, one and two proposals have been made. One is to join a fusible metal to the end of a lead wire sealed with an insulator in a metal protection tube, and to cover the area around the fusible metal with an insulating tube. One with a void around it has been proposed. On the other hand, in Japanese Patent Application Laid-Open No. 51-143857, which was previously proposed by the applicant, a fusible metal is connected to the tip of the metal tube via a lead wire, and the fusible metal part is used for high-temperature brazing, for example. An insulating solvent such as paste flux is applied to the fusible metal wire, dried, and the voids inside the tube are filled with insulating powder. The former has the disadvantage that when installed in equipment such as internal combustion engines that are subject to high temperatures and large vibrations, problems such as breakage of the fusible metal wire are likely to occur because there is a void around the fusible metal wire. .

In the latter case, the drying is caused by vibration when the solvent applied to the fusible metal wire is inserted into the metal tube after drying, and when the insulating powder is uniformly filled to the tip of the metal protection tube using a vibrator. There was a risk that some of the solvent would fall off or be missing, which would eliminate the oxidation-preventing effect in that area, change the melting temperature, and make the fuse performance unstable.

Therefore, the present invention has been made in view of the above, and aims to provide a fuse plug that completely protects the fusible metal wire from vibrations during the manufacturing process or at high temperatures, and whose fusing temperature is stabilized. .

That is, the two lead wires and a part of the U-shaped fusible metal wire connected to the tip of the lead wire are housed in two small holes in the axial direction of the insulating tube, and the fusible metal wire is inserted into the tip of the insulating tube. The bent part of the wire is exposed to form a slit with a volume sufficient for the molten metal to become spherical, and the solvent is applied around the metal wire to fill the gap in the slit and fix the insulating tube. It is housed in a protective metal tube and the gaps are filled with insulating powder.

Embodiments of the present invention will be described below based on the drawings. A lead wire 1 leading to an electric circuit is installed in the purification apparatus and is made of a sufficiently heat-resistant metal such as a nickel alloy wire, and its two ends are connected by a U-shaped fusible metal wire 2. This fusible metal wire is made of an alloy that melts at a predetermined ambient temperature of 700 to 1000°C, such as a eutectic alloy of silver and copper, silver and palladium, etc. Two lead wires 1 and a part of the fusible metal wire 2 connected to the ends of the lead wires are formed by two parallel thin holes bored through the axial direction of an unglazed ceramic insulating tube 3. 4 respectively. This insulating tube 3 has a slit 5 formed in the axial direction at its tip, and the U-shaped bent portion of the fusible metal wire is located and exposed in this slit. The width of this slit is about 2 to 3 times the diameter of the fusible metal wire, and the volume of the slit is large enough for the fusible metal wire to melt and become spherical due to surface tension. Therefore, the width and depth of this slit are determined by the diameter and length of the fusible metal wire. The bent portion of the fusible metal wire is accommodated so as not to protrude from inside the slit 5, and the exposed portion is coated with a paste-like solvent 7, such as a flux containing boric acid and a borate, and the flux filled in the slit is applied. This prevents the fusible metal wire from oxidizing, ensures reliable melting, and protects it from breakage due to vibrations, etc. This flux melts at a temperature approximately 50°C to 300°C lower than the fusing temperature of the fusible metal wire, and prevents the oxidation of the fusible metal wire. It also maintains electrical insulation properties in the molten state and has other electrical insulating properties. A material is selected that provides a fluid with good wettability to the powdered filler. After the flux has been applied and dried, the insulating tube 3 is inserted into a metal protective tube 6 made of stainless steel whose tip is closed by argon welding or the like. An inert heat-resistant material such as magnesia powder 8 is placed between the metal protection tube 6 and the insulation tube 3.
is filled without any gaps by a vibrating filling device. A glass powder layer 9 is sequentially filled between the lead wire protruding from the insulating tube 3 and the metal protection tube 6.
The mouth of the metal protection tube 6 is closed with a rubber stopper 10, and then this metal protection tube 6 is compressed from the radial direction by a known method to increase the strength of the protection tube, and after that, the metal protection tube 6 is compressed in a furnace for about 500 min. Heat treatment is performed at ~700°C to soften and seal the glass material 9. The lead wire 1 is connected to an electrical circuit by means of a terminal. When the metal protection tube 6 filled with a series of substances is installed with the tip facing downward, for example, in an automobile exhaust gas purification device via a mounting bracket, the temperature inside the purification device is 300°C below the melting temperature of the fusible metal wire. When the temperature is raised to within 0.degree. C., the flux exhibits fluidity and melts, forming voids in the slit around the fusible metal wire. When the fusible metal wire reaches a predetermined fusing temperature and is fused, the molten metal flows out and accumulates in the slit 5, where it becomes spherical due to surface tension and breaks. Therefore, both ends of the lead wire 1 are completely open and a signal is sent to the electric circuit.

As detailed above, the lead wire and part of the fusible metal wire are inserted into the two thin holes of the insulating tube, the bent part of the fusible metal wire is accommodated in the slit at the end of the insulating tube, and the slit is filled with flux. Because it is fixed in place, it will not fall off due to vibration when inserting the insulating tube into the metal protection tube or when vibrating and filling the gap with insulating powder, and will not break or break even when the vehicle body vibrates at high temperatures. All of them disappeared. In addition, the manufacturing process becomes easier, the strength of the metal protection tube is increased, and the durability and quality stability can be further improved.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional view of the fuse plug of the present invention, Fig. 2 is a sectional view taken along the line A-A in Fig. 1, Fig. 3 is a sectional view taken along the line B-B in Fig. 1, and Fig. 4 is a sectional view of the insulating tube. vertical front view of
FIG. 5 is a bottom view of FIG. 4. 1...Lead wire, 2...Fusible metal wire, 3...Insulating tube, 4...Small hole, 5...Slit, 6...Metal protective tube, 7...Solvent, 8...Inert heat resistant Sex material.

Claims (1)

[Claims] 1. In a covered type fuse plug in which two lead wires with fusible metal wires connected to the distal ends are housed in a metal tube for protective coating with a closed end, the two lead wires are connected to these ends. Two small holes are drilled in parallel to the axial direction that are sufficient to insert a part of the U-shaped fusible metal wire while insulating it from each other, and the bent part of the fusible metal wire is exposed at the tip and is fusible. The lead wire is inserted into each of the two small holes in an insulating tube made of unglazed ceramic material, in which a slit with a volume sufficient for the metal wire to become spherical when melted is formed on a diameter including the two small holes. The fusible metal wire in the slit was covered and fixed with an electrically insulating solvent, the insulating tube was housed in the metal tube, and the gap between the metal tube and the insulating tube was filled with insulating powder of a heat-resistant substance. A fuse plug characterized by: