Thermal fuse with heat-sensitive pellet

Abstract

Thermal fuse with heat-sensitive pellet, comprehensive a metal housing of cylindrical shape with a hollow interior, a first conductor electrically connected to the first bottom surface of the metal housing, a second conductor which is guided through a through-hole in the second bottom surface of the metal housing and at whose tip located in the interior of the housing a fixed contact is attached, a movable electrode comprising a movable contact opposite the fixed contact and a contact edge abutting the inner surface of the metal casing, which is displaceable in the axial direction of the metal casing when the contact edge abuts the inner surface of the metal casing; a heat-sensitive pellet arranged closer to the first conductor than to the movable electrode in the interior of the casing and melting at a prescribed temperature; a first spring element which is pre-tensioned between the heat-sensitive pellet and the movable electrode and presses the movable contact towards the fixed contact by applying tension to the movable electrode, and a second spring element which is prestressed on the movable electrode opposite to the first spring element and presses the movable contact away from the fixed contact by applying tension to the movable electrode, whose metal housing is characterized in that the ratio of its length in the axial direction to the outer diameter is between 1.4 and 2.0.

Description

[0001] The present invention relates to a thermal fuse with a heat-sensitive pellet.

[0002] According to the state of the art, so-called thermal fuses with heat-sensitive pellets are known for use in household and other electrical appliances as a means of interrupting electrical circuits upon detection of irregular heating, for example in the event of device damage or a short circuit in the internal circuits. Their design enables circuit interruption. In these cases, heat-sensitive pellets are housed in a metal housing, on each side of which are formed a first conductor and a second conductor, each of which is connected to the circuit. These pellets melt when the prescribed trigger temperature is reached, thereby disconnecting the electrical contacts inside the housing (e.g., JP 2021 168258 A). Such thermal fuses with heat-sensitive pellets require further miniaturization and cost reduction.

[0003] Against this background, the main object of the present invention is to provide a thermal fuse with a heat-sensitive pellet, which can be manufactured more compactly and at lower costs due to material savings compared to the prior art.

[0004] The above-mentioned object is achieved with a thermal fuse having the features of claim 1. Advantageous further developments are specified in the subclaims.

[0005] The thermal fuse with a heat-sensitive pellet according to the invention comprises a cylindrical metal housing with a hollow interior, a first conductor electrically connected to the first bottom surface of the metal housing, a second conductor guided through a through-hole in the second bottom surface of the metal housing and having a fixed contact attached to its tip located in the interior of the housing, a movable electrode comprising a movable contact opposite the fixed contact and a contact edge abutting the inner surface of the metal housing, and which, when the contact edge abuts the inner surface of the metal housing, is displaceable in the axial direction of the metal housing, a heat-sensitive pellet arranged closer to the first conductor than to the movable electrode in the interior of the housing and which melts at a prescribed temperature, a first spring element,which is prestressed between the heat-sensitive pellet and the movable electrode and presses the movable contact towards the fixed contact by applying tension to the movable electrode, and a second spring element which is prestressed opposite to the first spring element on the movable electrode and presses the movable contact away from the fixed contact by applying tension to the movable electrode, wherein the metal housing is characterized in that the ratio of its length in the axial direction to the outer diameter is between 1.4 and 2.0.

[0006] According to the prior art, no thermal fuses with heat-sensitive pellets are known in which the ratio of the axial length to the outer diameter is between 1.4 and 2.0 in the metal housing. By constructing the metal housing with a ratio of the axial length to the outer diameter of between 1.4 and 2.0, the present invention enables the provision of thermal fuses with heat-sensitive pellets that are more compact than the prior art and can be manufactured at lower costs due to material savings. In such compact thermal fuses, the heat-sensitive pellets themselves housed in the metal housing are also smaller, thus shortening the time required for the pellets to break the circuit by separating the movable contact from the fixed contact when they reach the trigger temperature.

[0007] The invention will be described in more detail below with reference to the figures, without limitation. Like reference numerals designate like or similar elements. Fig. 1: Schematic drawing of a thermal fuse according to an embodiment of the present invention in perspective view Fig. 2: Schematic sectional drawing of the internal structure of a thermal fuse according to the same embodiment Fig. 3: Drawing to explain the function of a thermal fuse according to the same embodiment Fig. 4: Drawing to explain the dimensions of the parts of a thermal fuse according to the same embodiment in normal condition Fig. 5: Drawing to explain the dimensions of the parts of a thermal fuse according to the same embodiment in a completely melted state

[0008] The thermal fuse 100 according to an embodiment of the present invention will be explained below with reference to the drawings.

[0009] The thermal fuse 100 according to the present embodiment is used in household appliances, motor vehicles, and office equipment, for example, as a means for interrupting electrical circuits upon detection of irregular heating, such as in the event of device damage or a short circuit of the internal circuits. The thermal fuse 100 according to the present embodiment is a so-called heat-sensitive pellet thermal fuse, the structure of which enables circuit interruption. Heat-sensitive pellets 5 are housed in a metal casing 1, on each side of which a first conductor 2 and a second conductor 3 are formed, which are connected to the circuit. These pellets melt when the prescribed trigger temperature is reached, thereby breaking the electrical contacts inside the casing.

[0010] Specifically, this thermal fuse includes 100, as shown in the Fig. 1 and Fig. 2, a metal housing 1 of approximately cylindrical shape with a hollow interior 1s, a first conductor 2 which is electrically connected to the first bottom surface 11 of the metal housing 1, a second conductor 3 which is guided through a through-hole 12o in the second bottom surface 12 of the metal housing 1 and at whose tip located in the interior 1s a fixed contact 31 is attached, a movable electrode 4 which comprises a movable contact 41 opposite the fixed contact 31 of the second conductor 3 and a contact edge 42 which bears against the inner surface of the metal housing 1 and which, when the contact edge 42 bears against the inner surface of the metal housing 1, is arranged in the interior 1s so as to be displaceable in the axial direction of the metal housing 1, a heat-sensitive pellet 5 which is arranged closer to the first conductor 2 than to the movable electrode 4 in the interior 1s, a first spring element 6,which is prestressed between the heat-sensitive pellet 5 and the movable electrode 4 and presses the movable contact 41 towards the fixed contact 31 by applying tension to the movable electrode 4, and a second spring element 7 which is prestressed opposite to the first spring element 6 on the movable electrode 4 and presses the movable contact 31 away from the fixed contact 31 by applying tension to the movable electrode 4.

[0011] This thermal fuse 100 is, as in the Fig. 3, the spring element 6 is constructed such that, in the normal state when the temperature of the heat-sensitive pellet 5 is below the trigger temperature (when the heat-sensitive pellet 5 is not melted), the tension force of the first spring element 6 is greater than the tension force of the second spring element 7, so that the movable contact 41 is pressed against the fixed contact 31. In the normal state, the electric current can pass through the first conductor 2, the metal casing 1, the movable electrode 4, and the second conductor 3 in this order (or in the reverse order).

[0012] If, however, an increase in the ambient temperature causes the temperature of the heat-sensitive pellet 5 to reach the trigger temperature, the heat-sensitive pellet 5 melts, causing the first spring element 6 and the second spring element to move, as shown in Fig. 3 (b) (tripped state). The thermal fuse 100 is constructed such that the tension force of the second spring element 7 now gradually becomes greater than the tension force of the first spring element 6 and pushes the movable contact 41 away from the fixed contact 31, thereby breaking the circuit (fully melted state).

[0013] The structure of the individual parts will be explained below.

[0014] The metal housing 1 consists of a metallic material, such as copper, iron, or a copper or iron alloy; a particularly electrically conductive coating, such as silver plating, can also be applied to its surface. Through holes 11o and 12o, through which the first conductor 2 and the second conductor 3 are respectively guided, are formed in the bottom surfaces 11 and 12 of the metal housing 1, which overlap in the axial direction.

[0015] An insulating tube 9 is attached to the second base surface 12 in the interior space 1s of the metal housing 1 to secure and stabilize the second conductor 3 passing through. This insulating tube 9 is made of ceramic, for example, and is also referred to as a bushing insulator. The insulating tube 9 is housed in the interior space 1s such that its axis coincides with the central axis of the metal housing 1.

[0016] The first conductor element is made of silver-plated or tin-plated copper, for example. This first conductor element is guided through the through-hole in the first bottom surface 11 of the metal housing 1, fixed with its edge to the bottom surface 11, and electrically connected.

[0017] The second conductor 3 is made of silver-plated or tin-plated copper, for example. This second conductor 3 is guided through the through-hole 12o in the second bottom surface 12 of the metal housing 1, guided through the insulating tube 9 in the interior space 1s, and stabilized on its outer surface by the wall of the insulating tube 9. The fixed contact 31 is attached to the tip of the second conductor 3, which protrudes from the insulating tube 9. The interior space 1s is hermetically sealed from the outside by sealing the through-hole 12o in the second bottom surface 12 of the metal housing 1, through which the second conductor 3 is guided, with a sealant 8, which consists, for example, of organic adhesives.

[0018] The movable electrode 4 is normally in contact with both the second conductor 3 and the metal housing 1, thus establishing an electrical connection between them. This movable electrode 4 is made of metallic materials, such as silver alloys, and is approximately cup-shaped. Specifically, this movable electrode 4 comprises a disc 4a opposite the tip of the second conductor 3, which functions as a movable contact 41, and a bulge 4b extending from the outer edge of the disc 4a in the axial direction of the metal housing 1 and resting against the inner surface of the metal housing 1.

[0019] The heat-sensitive pellet 5 can be formed from a known organic material that melts upon reaching a predetermined trigger temperature. Preferably, cylindrical and prismatic pellets made of thermoplastic resins or other organic materials, as well as organic chemicals in tablet form, can be used for the heat-sensitive pellet 5. However, the heat-sensitive pellet 5 does not have to be formed from organic materials; it can also consist of insulating materials that melt upon reaching a predetermined trigger temperature. This heat-sensitive pellet 5 is approximately cylindrical in shape and arranged at the edge of the interior space 1s facing the first conductor 2 such that its central axis coincides with the central axis of the metal housing 1.

[0020] Both the first spring element 6 and the second spring element 7 are compression springs. These spring elements are arranged on both sides of the movable electrode so that their central axes coincide with each other and simultaneously coincide with the central axis of the metal housing 1. The first spring element 6 is clamped between the movable electrode 4 and the heat-sensitive pellet 5 via the two disc-shaped pressure plates 61 and 62.

[0021] In order to realize a miniaturization of the thermal fuse 100 according to the present embodiment, its individual parts are dimensioned as follows. The dimensions of the individual parts are described below based on the Fig. 4 and Fig. 5 will be explained. (Dimensions of the metal housing 1)

[0022] For the metal casing 1 according to the present embodiment, the ratio of the axial length (also referred to as casing length) D2 to the outer diameter D1 (D2 / D1) is between about 1.4 and about 2.0, preferably between about 1.4 and about 1.8, with the range between about 1.4 and about 1.6 being more preferable, and a value of about 1.5 being most preferable. Specifically, for the metal casing 1 according to the present embodiment, the outer diameter D1 is 4 mm and the casing length D2 is 6.1 mm, so D2 / D1=1.525. (Dimensions of the first spring element 6)

[0023] For the first spring element 6 according to the present embodiment in a normal state, the ratio of the length in the axial direction (length of the first spring) d1 to the outer diameter D1 of the metal housing 1 is between about 0.30 and about 0.5, preferably between about 0.35 and about 0.45, with a value of about 0.375 being even more advantageous.

[0024] For the first spring element 6, the ratio of the axial length (first spring length) d1' to the outer diameter D1 of the metal shell 1 when the pellet is fully melted is between about 0.45 and about 0.80, preferably between about 0.45 and about 0.6, with a value of about 0.52 being more preferable. Specifically, for the first spring element 6 according to the present embodiment, the length of the first spring in the normal state d1 is about 1.5 mm, and the length of the first spring when the pellet is fully melted d1' is about 2.1 mm. (Dimensions of the second spring element 7)

[0025] For the second spring element 7 according to the present embodiment in a normal state, the ratio of the length in the axial direction (length of the second spring) d2 to the outer diameter D1 of the metal housing 1 is between about 0.25 and about 0.4, preferably between about 0.25 and about 0.35, with a value of about 0.3 being even more advantageous.

[0026] For the second spring element 7, the ratio of the axial length (second spring length) d2' to the outer diameter D1 of the metal shell 1 when the pellet is fully molten is between about 0.40 and about 0.80, preferably between about 0.45 and about 0.56, with a value of about 0.465 being more preferable. Specifically, for the second spring element 7 according to the present embodiment, the length of the second spring in the normal state d2 is about 1.2 mm, and the length of the second spring when the pellet is fully molten is about 1.88 mm. (Dimensions of the heat-sensitive pellet 5)

[0027] For the heat-sensitive pellet 5 according to the present embodiment in a normal state, the ratio of the axial length (pellet length) d3 to the outer diameter D1 of the metal shell 1 is between about 0.25 and about 0.60, preferably between about 0.25 and about 0.35, with a value of about 0.3 being more preferable. Specifically, for the heat-sensitive pellet 5 according to the present embodiment, the pellet length in a normal state is about 1.2 mm.

[0028] The thermal fuse 100 according to the present embodiment, with the described structure in which the ratio of the axial length of the metal casing 1 to the outer diameter is between 1.4 and 2.0, enables the provision of thermal fuses with heat-sensitive pellets 100 that are more compact than the prior art and can be manufactured at a lower cost due to material savings. Furthermore, with such compact thermal fuses 100, the heat-sensitive pellets 5 themselves housed in the metal casing 1 are smaller, thus shortening the time required for the pellets 5 to reach the triggering temperature and break the circuit by removing the movable contact 41 from the fixed contact 31.

[0029] Notwithstanding this, the present invention is not limited to the described embodiment, but may be modified in various ways, provided that the spirit thereof is not deviated from. The thermal fuse 100 according to the present invention may include, for example, the variants 1 to 9 described below. (Variant 1)

[0030] Thermal fuse with heat-sensitive pellet, comprising a metal housing of cylindrical shape with a hollow interior, a first conductor electrically connected to the first bottom surface of the metal housing, a second conductor which is guided through a through-hole in the second bottom surface of the metal housing and at whose tip located in the interior of the housing a fixed contact is attached, a movable electrode comprising a movable contact opposite the fixed contact and a contact edge resting on the inner surface of the metal housing, and which is displaceable in the axial direction of the metal housing when the contact edge rests on the inner surface of the metal housing, a heat-sensitive pellet which is arranged closer to the first conductor than to the movable electrode in the interior of the housing and which melts at a prescribed temperature, a first spring element which is pre-tensioned between the heat-sensitive pellet and the movable electrode and presses the movable contact towards the fixed contact by applying tension to the movable electrode, as well as a second spring element which is prestressed on the movable electrode opposite to the first spring element and presses the movable contact away from the fixed contact by applying tension to the movable electrode, whose metal housing is characterized in that the ratio of its length in the axial direction to the outer diameter is between 1.4 and 2.0. (Variant 2)

[0031] Thermal fuse with heat-sensitive pellet according to variant 1, the metal housing of which is characterized in that the ratio of its length in the axial direction to the outer diameter is between 1.4 and 1.8. (Variant 3)

[0032] Thermal fuse with heat-sensitive pellet according to variant 2, the metal housing of which is characterized in that the ratio of its length in the axial direction to the outer diameter is between 1.4 and 1.6. (Variant 4)

[0033] Thermal fuse with heat-sensitive pellet according to one of variants 1 to 3, the first spring element of which is characterized in that the ratio of its length in the axial direction to the outer diameter of the metal housing is between 0.30 and 0.5 when the heat-sensitive pellet is not melted and between 0.45 and 0.80 when the heat-sensitive pellet is completely melted. (Variant 5)

[0034] Thermal fuse with heat-sensitive pellet according to variant 4, the first spring element of which is characterized in that the ratio of its length in the axial direction to the outer diameter of the metal housing is between 0.35 and 0.45 when the heat-sensitive pellet is not melted and between 0.45 and 0.6 when the heat-sensitive pellet is completely melted. (Variant 6)

[0035] Thermal fuse with heat-sensitive pellet according to one of variants 1 to 5, the second spring element of which is characterized in that the ratio of its length in the axial direction to the outer diameter of the metal housing is between 0.25 and 0.4 when the heat-sensitive pellet is not melted and between 0.40 and 0.80 when the heat-sensitive pellet is completely melted. (Variant 7)

[0036] Thermal fuse with heat-sensitive pellet according to variant 6, the second spring element is characterized in that the ratio of its length in the axial direction to the outer diameter of the metal housing is between 0.25 and 0.35 when the heat-sensitive pellet is not melted and between 0.45 and 0.56 when the heat-sensitive pellet is completely melted. (Variant 8)

[0037] Thermal fuse with heat-sensitive pellet according to one of variants 1 to 7, whose heat-sensitive pellet is characterized in that the ratio of its length in the axial direction to the outer diameter of the metal housing when the heat-sensitive pellet is not melted is between 0.25 and 0.60. (Variant 9)

[0038] Thermal fuse with heat-sensitive pellet according to variant 8, whose heat-sensitive pellet is characterized in that the ratio of its length in the axial direction to the outer diameter of the metal casing is between 0.25 and 0.35 when the heat-sensitive pellet is not melted.

[0039] Although the present invention has been described using preferred embodiments, it is not limited thereto but can be modified in many ways. List of reference symbols 100 thermal fuses 1 metal housing 1s interior 11 first floor area 11o Through hole 12 second floor area 12o through hole 2 first leader 3 second conductor 31 fixed contact 4 movable electrodes 41 movable contact 42 contact surface 4a disc 4b Curvature 5 heat-sensitive pellets 6 first spring element 61 Pressure plate 62 pressure plate 7 second spring element 8 Sealant 9 Insulating pipe QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2021 168258 A

[0002]

Claims

[1] Thermal fuse with heat-sensitive pellet, comprehensive a metal housing of cylindrical shape with a hollow interior, a first conductor electrically connected to the first bottom surface of the metal housing, a second conductor which is guided through a through-hole in the second bottom surface of the metal housing and at whose tip located in the interior of the housing a fixed contact is attached, a movable electrode comprising a movable contact opposite the fixed contact and a contact edge abutting the inner surface of the metal casing, which is displaceable in the axial direction of the metal casing when the contact edge abuts the inner surface of the metal casing; a heat-sensitive pellet arranged closer to the first conductor than to the movable electrode in the interior of the casing and melting at a prescribed temperature; a first spring element which is pre-tensioned between the heat-sensitive pellet and the movable electrode and presses the movable contact towards the fixed contact by applying tension to the movable electrode, and a second spring element which is prestressed on the movable electrode opposite to the first spring element and presses the movable contact away from the fixed contact by applying tension to the movable electrode, their metal housing characterized by is that the ratio of its length in the axial direction to the outer diameter is between 1.4 and 2.

0. [2] Thermal fuse with heat-sensitive pellet according to claim 1, whose metal housing characterized by is that the ratio of its length in the axial direction to the outer diameter is between 1.4 and 1.

8. [3] Thermal fuse with heat-sensitive pellet according to claim 2, whose metal housing characterized byis that the ratio of its length in the axial direction to the outer diameter is between 1.4 and 1.

6. [4] Thermal fuse with heat-sensitive pellet according to claim 1, the first spring element characterized by is that the ratio of its length in the axial direction to the outer diameter of the metal casing is between 0.30 and 0.5 for the unmelted heat-sensitive pellet and between 0.45 and 0.80 for the fully melted heat-sensitive pellet. [5] Thermal fuse with heat-sensitive pellet according to claim 4, the first spring element characterized by is that the ratio of its length in the axial direction to the outer diameter of the metal casing is between 0.35 and 0.45 when the heat-sensitive pellet is not melted and between 0.45 and 0.6 when the heat-sensitive pellet is completely melted. [6] Thermal fuse with heat-sensitive pellet according to claim 1, the second spring element characterized byis that the ratio of its length in the axial direction to the outer diameter of the metal casing is between 0.25 and 0.4 for an unmelted heat-sensitive pellet and between 0.40 and 0.80 for a completely melted heat-sensitive pellet. [7] Thermal fuse with heat-sensitive pellet according to claim 6, the second spring element characterized by is that the ratio of its length in the axial direction to the outer diameter of the metal casing is between 0.25 and 0.35 for the unmelted heat-sensitive pellet and between 0.45 and 0.56 for the fully melted heat-sensitive pellet [8] Thermal fuse with heat-sensitive pellet according to claim 1, the heat-sensitive pellet characterized by is that the ratio of its axial length to the outer diameter of the metal casing in the case of a non-melted heat-sensitive pellet is between 0.25 and 0.

60. [9] Thermal fuse with heat-sensitive pellet according to claim 8, the heat-sensitive pellet characterized by is that the ratio of its length in the axial direction to the outer diameter of the metal casing in the case of a non-melted heat-sensitive pellet is between 0.25 and 0.35.

Images