The present invention refers to an electric thermal fuse, the features of which are presented in more detail in a subsequent description. Pursuant to the International Patent Classification such inventions belong to electricity, namely to basic electric components, in particular to electric switches and protecting components, in which the current flows through a part of melting material and is interrupted as soon as said melting material is displaced due to excessive current, wherein the casing is filled with a filling materiel in powder form. Consequently, such invention belongs to the class A 01 H 85/18.

The underlying problem of the invention is how to create such electric thermal fuse, in which the electric circuit through the fuse is interrupted in a shortest possible time, as soon as even relatively high voltage or current is exceed, and regardless to position/orientation of the fuse, while at the same time it should also be assured that each generated electric arc, whenever occurs, would have any essential impact neither to the fuse nor to each surrounding area in the adjacency thereof. Electric thermal fuse is intended for protection of en electric circuit, and in particular of each particular components integrated therein, e.g. varistor fuses as well as of other over-voltage protecting components. This means that the electro thermal fuse react to a heat, which is sue to electric overloads generated either within the fuse as such or also in each neighboring electric components within the same electric circuit. Such fuse is disclosed in JP 2016-162683 A and comprises a tubular casing, which consists of an electric insulating material and is on its both terminal portions furnished with contact members, by means of which said fuse is electrically connectable to each disposable electric circuit. An electric conductor extends through the passage within said casing, and is by means of solder connected on the one hand with one of said contact members and on the other hand with a tension helical spring, which is attached to the other contact member. As soon as in certain circuit an overload occurs, the heat is generated and transferred towards the interior of the fuse and up to said soldered contact between the electric conductor and corresponding contact member. Said solder is then molten at a pre determined temperature, upon which said interconnection between said conductor and corresponding contact member is interrupted, and the connector is by means of said spring displaced apart from said contact member. In particular in high-voltage circuits such displacement of the conductor apart from the contact member results in formation of a very intensive arc, which may quickly and seriously damage the casing and objects in the neighborhood of the fuse, or initiate the fire.

Electro thermal fuse according to the invention comprises a tubular casing consisting of electric insulating material, which is on each of its terminal portions closed by a cover, which is also functioning as a contact member consisting of an electric conductive material, which is suitable for integration of the fuse into each disposable electric circuit. An electric conductor is inserted throughout the passage within said hollow casing and is during the normal operation of the fuse, namely when the electric current is allowed to flow through said electric conductor, via at least one contact established by solder electrically interconnected with said contact members, but is in the case of the electric overload within said circuit and generated heat and consequently melting and interruption of said at least one soldered contact displaceable away from at least one of said contact members by means of a spring, by which the electric current through the fuse is then interrupted.

The invention provides that said tubular casing consists of ceramics, and each of said contact members is furnished with at least approximately centrally arranged throughout passage, so that the electric conductor is inserted through said passages within said contact members and is by means of solder, which is located on the external side of the fuse, firmly and electric conductively connected with each of said contact members. Said conductor is in the one terminal area of the fuse extended and ended with appropriate thicker portion, so that a spring is placed around said conductor and is inserted between said thicker portion and the belonging contact member with said solder. Each residual volume within said passage in the casing of the fuse, namely the area between said conductor and the casing as well as between said contact members, is filled with a pre-determined quantity of arc preventing filler on the basis of properly granulated silica.

In a preferred embodiment of the invention said conductor is a wire consisting of copper and having a pre-determined circular cross-section, an said spring is a compression helical spring. Moreover, a washer, which is suitable for supporting said spring, can be inserted between said spring and said thicker portion on the conductor. A suitable quantity of filler on the basis of properly granulated silica is determined in such manner is such, that the volume of the filler as such corresponds to approximately 90% of the whole disposable volume around the conductor within said passage within the casing. Said solder, which is foreseen for connection of the conductor with each corresponding contact member, is selected in such manner that its melting point is adjusted within the range 105 - 1 15°C.

The invention will also be explained in more detail on the basis of an embodiment, which is presented in the attached drawings, in which

Fig. 1 is an electric thermal fuse in isometric view;

Fig. 2 is the fuse according to Fig. 1 in front view; and

Fig. 3 the fuse according to Figs. 1 and 2 in longitudinal cross-section in its diametrical plane.

Electro thermal fuse generally, and also in the embodiment according to Figs. 1 - 3, comprises a tubular casing 1 , which is made of an electric insulating material, and is on each of its terminal portions 1 1, 12 closed by a cover, which is in fact also functioning as a contact member 1 10, 120 consisting of an electric conductive material, which is suitable for integration of the fuse into each disposable electric circuit. An electric conductor 2 is inserted throughout the passage 10 within said hollow casing 1.

Said conductor 2 is during the normal operation of the fuse, namely when the electric current is allowed to flow through said electric conductor 2, via at least one soldered contact 3, 3' electrically interconnected with said contact members 1 10, 120, but is in the case of the electric overload within said circuit and generated heat and consequently melting and interruption of said at least one soldered contact 3, 3' displaceable away from at least one of said contact members 1 10, 120 by means of a spring 4, by which then the electric current through the fuse is then interrupted.

In accordance with the present invention said tubular casing 1 consists of ceramics, and is therefore not only electric insulating but also highly temperature resistant and inflammable.

Each of said contact members 1 10, 120 is furnished with at least approximately centrally arranged throughout passage 111, 121, so that said electric conductor 2 is inserted through said passages 1 1 1 , 121 within said contact members 1 10, 120 and is by means of solder 3, 3’, which is located on the external side of the fuse, firmly and electric conductively connected with each of said contact members 1 10, 120. Said conductor 2 is in the one terminal area of the fuse extended and ended with appropriately thicker portion 20, so that a spring 4 can be placed around said conductor 2 and is then jammed between said thicker portion 20 and the belonging contact member 120 with said solder 3’.

Each residual volume within said passage 10 in the casing 1 of the fuse, namely the area between said conductor 2 and the casing 1 as well as between said contact members 1 10, 120, is filled with a pre-determined quantity of arc preventing filler 5 of the basis of silica, wherein the granulation of the last is preferably 0,2 to 0,4 mm. Quantity of said filler 5 on the basis of silica is determined in such manner, that the volume of the filler 5 as such corresponds to approximately 90% of the whole disposable volume around the conductor 2 within said passage 10 within the casing 1.

In the shown embodiment of the invention said spring 4 is a compression helical spring, and a washer 6, which is suitable for supporting said spring 4, is inserted between said spring 4 and said thicker portion 20 on the conductor 2. As a result of such concept, as soon as the spring 4 is placed around the conductor 2 and compressed, and subsequently also the washer 6 is set in position, said thicker portion 20 can be easily realized by locally flattening said conductor 2, by which said spring 4 is maintained in compressed state until the solder 3, 3’ is molten.

In a preferred embodiment of the fuse according to the invention said conductor 2 is a wire consisting of copper and having a pre-determined circular cross-section of e.g. 1,5 mm . For such conductor 2 it is then quite satisfactory, if the diameter of passages 1 1 1, 121 in said contact members 1 10, 120 is approximately 1,5 mm. Suitable solder 3, 3’ for connecting said conductor 2 with each belonging contact member 1 10, 120 is selected in such way, that its melting point is adjusted within the range 105 - 1 15°C, and e.g. for the purpose of protection of varistors in the adjacency substantially around 109 or 1 10°C.

As soon as such fuse is integrated within an electric circuit, the electric current starts flowing through the first contact member 1 10, the solder 3, the electric conductor 2, the solder 3’ and the second contact member 120. The electric conductor is surrounded with a filler 5. As soon as excessive current occurs within said electric circuit and the temperature increases above a pre-determined value, which corresponds to the melting point of each solder 3, 3’ like e.g. 105°C or e.g. 109°C, if chemical ingredients in the solder are correspondingly adjusted, the solder 3, 3’ starts melting, upon which the previously compressed spring 4 may be released, which then results in displacement of the conductor away from at least one contact member 1 10, 120. Since such displacement of said conductor 2 apart from the contact member 1 10, 120 may, in particular in a high-voltage circuit, might lead to formation of arc between the conductor 2 and the contact member 1 10, 120, the invention provides that each disposal volume within the casing 1 , namely between the last and the conductor 2, is properly i.e. in certain extent filled by a filler on the basis of silica. Adjusting each suitable granulation of sand in said filler 5 is important for two reasons. Namely, on the one hand is herewith prevented that by introduction of too much filler 5, the silica sand, which is in general quite similarly like ceramics resistant against high temperature and inflammable, by axially displacing the conductor 2 in each possible position of the fuse, e.g. in vertical or horizontal or slanted position of the fuse, due to its abrasive properties, hinder said displacing in such extend that despite to sufficiently strong spring 4 said displacement would be decelerated, which could have negative impact to reacting ability of the fuse to each overload, since the time required for interruption of circuit, into which the fuse is integrated, could be herewith essentially prolonged. On the other hand, appropriate quantity and granulation of said in the filler 5 is also important for another reason, since during displacing the conductor 2 the sand is immediately and successively filling the space, which is formed behind the conductor 2 by displacing thereof and in which otherwise said arc could appear, so that said released space is promptly filled with a non flammable and temperature resistant filler 5.

Thanks to such concept such fuse according to the invention is extremely efficient even in high-voltage electric circuits and regardless to each current position of the mounted fuse.