Thermal fuse

Abstract

A thermal fuse for an electrical circuit is described, with a contact arm by way of which two electrical conductors are electrically conductively connected to each other, wherein the connection of the contact arm to at least one of the two conductors is a soldered joint, which loses its strength when a activation temperature of the fuse is reached. In accordance with this disclosure a permanent magnet is provided, which generates a magnetic force, which lifts the contact arm from at least one of the two conductors as soon as the soldered joint loses its strength.

Claims

1. A thermal fuse for an electrical circuit, comprising: a contact arm that electrically and conductively connects two electrical conductors; a soldered joint connecting the contact arm to one of the two electrical conductors, wherein the soldered joint loses its strength when an activation temperature of the fuse is reached; and a permanent magnet configured to generate a magnetic force which lifts the contact arm as soon as the soldered joint between the contact arm and the one of the two conductors loses its strength.

2. The thermal fuse in accordance with claim 1, further comprising a second soldered joint connecting the contact arm to the other of the two electrical conductors.

3. The thermal fuse in accordance with claim 1, wherein the contact arm is made of iron or ferromagnetic steel.

4. The thermal fuse in accordance with claim 1, wherein the contact arm is mechanically preloaded, wherein a spring force is applied to the soldered joint.

5. The thermal fuse in accordance with claim 1, wherein the contact arm is a leaf spring.

6. The thermal fuse in accordance with claim 5, wherein the conductor soldered to the contact arm is a preloaded leaf spring whose spring force is applied to the soldered joint.

7. The thermal fuse in accordance with claim 6, wherein the two leaf springs are of the same shape.

8. The thermal fuse in accordance with claim 1, wherein the contact arm is arranged in a housing to which the permanent magnet is attached.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above-mentioned aspects of exemplary embodiments will become more apparent and will be better understood by reference to the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

(2) FIG. 1 shows an example of embodiment of a thermal fuse; and

(3) FIG. 2 shows another view relative to FIG. 1.

DESCRIPTION

(4) The embodiments described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of this disclosure.

(5) FIGS. 1 and 2 schematically illustrate a thermal fuse in an open state. The fuse comprises a contact arm 4, which, when the fuse is closed, electrically connects two electrical conductors, e.g., a conductor 2 and a leaf spring 5. When the fuse is closed, the contact arm 4 is soldered to one of these two conductors by way of a soldered joint 8.

(6) A magnetic force of a permanent magnet 6 of the fuse acts on the contact arm 4. When the fuse reaches its activation temperature, the soldered joint loses its strength. Under the action of the magnetic force the contact arm 4 is then lifted from the conductor that was soldered to it, e.g., the leaf spring 5, so that the fuse opens. For this purpose the contact arm 4 can be made of iron or ferromagnetic steel, for example. However, it is also possible to manufacture the contact arm from a non-ferromagnetic material, and to attach a second permanent magnet or a ferromagnetic part, such as a rivet, to the contact arm.

(7) To aid the opening movement, the contact arm 4 can be mechanically preloaded, such that a spring force is also applied to the soldered joint in addition to the magnetic force. When the activation temperature is reached, the fuse can thus open even faster and an even greater opening gap can be achieved. Since the conductor soldered to the contact arm 4 is a leaf spring 5, the opening speed and the opening gap can be further increased by preloading the leaf spring 5.

(8) The fuse shown has a housing 1 from which two conductors 2, 3 protrude. The conductors 2, 3 are electrical conductors, which, at their ends protruding from the housing 1, can have plug-in contacts, for example for insertion into the holes of a printed circuit board, or can be fitted with a stranded cable for purposes of soldering or welding. The conductor 2 is connected, for example welded, to the contact arm 4. The connecting conductor 3 can be soldered directly to the contact arm 4, but in the example shown it is electrically connected to the contact arm 4 via the leaf spring 5. The leaf spring 5 can, for example, be welded to the connecting conductor 3.

(9) In the example embodiment illustrated in the figures, the contact arm 4 is soldered at one end to a conductor, e.g., a leaf spring 5, by way of the soldered joint 8, and is welded at its other end to a conductor, e.g., the connecting conductor 2. However, it is also possible to solder the contact arm 4 at both ends, i.e., both with the leaf spring 5 and also with the connecting conductor 2, or with both connecting conductors 2, 3. If the soldered joint then loses its strength, the entire contact arm 4 can be lifted from both conductors that were soldered to it by the magnetic force of the permanent magnet 6. In this way, a particularly large opening gap can be achieved. Also with this embodiment, the opening movement can be aided by preloading the contact arm 4 and/or a conductor soldered to it, e.g., a leaf spring 5.

(10) In the example of embodiment illustrated, the contact arm 4 and the leaf spring 5 have the same shape, but are preferably made from different materials. Ferromagnetic materials such as iron or a ferromagnetic steel are advantageous for the contact arm 4, while non-magnetic materials such as aluminium or brass are more suitable for the leaf spring 5. In this way it is possible to prevent the leaf spring 5 from being attracted to the contact arm 4 by magnetic force.

(11) While exemplary embodiments have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of this disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

REFERENCE LIST

(12) 1 Housing 2 Connecting conductor 3 Connecting conductor 4 Contact arm Leaf spring 7 Permanent magnet 8 Soldered joint