TEMPERATURE-SENSITIVE PELLET TYPE THERMAL FUSE

Abstract

A temperature-sensitive pellet type thermal fuse having a cylindrical metal case (11), a first lead (1) fixedly installed and insulated from the case (11) and a second lead (2) electrically connected to the case (11). A temperature-sensitive pellet (12) is installed by melting inside the case (11) and has a variable height. A moving terminal (16) is elastically coupled by a first spring (17) to the temperature-sensitive pellet (12) and an activating member (15) moves in a height decrease direction of the temperature-sensitive pellet (12) by an elastic repulsive force of a second spring (18). When the temperature-sensitive pellet (12) is melted and thereby is reduced in height, a first moving contact (16b) of the moving terminal (16) is separated from a first contact (1a) of the first lead (1).

Claims

1. A temperature-sensitive pellet type thermal fuse comprising: a cylindrical metal case (11); a first lead (1) fixedly installed on one end of the case (11) to be insulated from the case (11) by an insulating bushing (20); a second lead (2) electrically connected to the other end of the case (11); a temperature-sensitive pellet (12) installed inside the case (11) and having a height varied while being melted at a predetermined temperature or higher; and a moving terminal (15), one end of which is elastically supported by a first spring (17) to the temperature-sensitive pellet (12), and electrically separating the first lead and the second lead from each other in accordance with height decrease of the temperature-sensitive pellet (12), wherein the temperature-sensitive pellet type thermal fuse further comprises: a fixed terminal plate (19) fitted in the case (11) under the insulating bushing (20) to slidably guide and electrically connect the moving terminal (16) with the case (11); and an activating member (15) moving in the direction of a height decrease direction of the temperature-sensitive pellet (12) by an elastic repulsive force of a second spring (18) acting toward the temperature-sensitive pellet (12) when the temperature-sensitive pellet (12) is melted and thereby is reduced in height, and actuating the moving terminal (16) to separate a first moving contact (16b) of the moving terminal (16) from a first fixed contact (1a) of the first lead (1) at the time when the temperature-sensitive pellet (12) is reduced to a predetermined height.

2. The temperature-sensitive pellet type thermal fuse according to claim 1, wherein the fixed terminal plate 19 has a hole (19a) perforated coaxially with a through-hole (21) of the insulating bushing (20); the moving terminal (16) is slidingly guided into the hole (19a) of the fixed terminal plate (19); and an inner wall surface of the hole (19a) serves as a second fixed contact electrically connecting the first fixed contact (1a) of the first lead (1) and the case (11) on the second lead (2) side while slidingly contacting an outer circumferential surface of the moving terminal (16) until the temperature-sensitive pellet (12) arrives at an activation height H2 at which a switch is turned off.

3. The temperature-sensitive pellet type thermal fuse according to claim 1, wherein the moving terminal (16) has a head part (16c) provided on a lower end of a body 16a and expanded at a relatively greater diameter than the diameter of the body (16a), and the first spring (17) is compressedly installed between a lower surface of the head part (16c) of the moving terminal (16) and an upper surface of the temperature-sensitive pellet (12), and wherein the activating member (15) has a through hole (15a) defined in an upper end sidewall (15c) thereof such that the body (16a) of the moving terminal (16) passes therethrough, a lower surface (15d) of the upper end sidewall (15c) contacts an upper surface (16d) of the head part (16c) of the moving terminal (16) when the height change amount of the temperature-sensitive pellet (12) arrives at a predetermined level, and the activating member (15) moves the moving terminal (16) when the temperature-sensitive pellet (12) is excessively melted beyond the predetermined level specified as the height (H2) change amount of the temperature-sensitive pellet (12).

4. The temperature-sensitive pellet type thermal fuse according to claim 1, wherein the base plate (13) has a hole (13a) such that, when the temperature-sensitive pellet (12) is melted, a melted portion (12a) of the temperature-sensitive pellet (12) is introduced in the inside of the activating member (15).

5. The temperature-sensitive pellet type thermal fuse according to claim 2, wherein the case (11) has a stepped portion formed at a border between an upper region having a relatively greater inner diameter and a lower region having a relatively less inner diameter, and wherein the fixed terminal plate (19) is placed on and fixed by the stepped portion of the case (11), and the insulating bushing (20) is placed on and fixed by an upper surface of the fixed terminal plate (19).

6. The temperature-sensitive pellet type thermal fuse according to claim 3, further comprises a base plate (13) placed between the bottom of the activating member (15) and an upper surface of the temperature-sensitive pellet (12) to support the bottom of the first spring (17).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:

[0019] FIG. 1 is an exploded perspective view schematically illustrating an overall configuration of a temperature-sensitive pellet type thermal fuse according to an embodiment of the present invention;

[0020] FIG. 2 is a cross-sectional assembly view in a longitudinal direction of a temperature-sensitive pellet type thermal fuse according to an embodiment of the present invention when temperatures inside and outside a case are in a switched on state;

[0021] FIG. 3 is a cross-sectional assembly view in a longitudinal direction of the temperature-sensitive pellet type thermal fuse at an initial state that melting of the temperature-sensitive pellet begins;

[0022] FIG. 4 is a cross-sectional assembly view in a longitudinal direction of the temperature-sensitive pellet type thermal fuse in a state right before a moving terminal is separated from a first lead; and

[0023] FIG. 5 is a cross-sectional assembly view in a longitudinal direction of the temperature-sensitive pellet type thermal fuse in a state when the moving terminal is separated from the first lead.

DETAILED DESCRIPTION OF THE INVENTION

[0024] Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. Hereinafter, a temperature-sensitive pellet type thermal fuse according to embodiments of the present invention will be described in detail with reference to accompanying drawings.

[0025] As shown in FIGS. 1 and 2, a temperature-sensitive pellet type thermal fuse according to an embodiment of the present invention includes a metal case 11, one end of which is opened while the other end has a floor 11c. The case 11 is divided into an upper region having a relatively greater inner diameter and a lower region having a relatively less inner diameter, and a stepped portion is defined on a border of the upper and lower regions.

[0026] In the lower region of the case 11, a temperature-sensitive pellet 12, a base plate 13, a first spring 17, a moving terminal 16, an activating member 15 and a second spring 18 are insertedly installed in a sequential manner from the floor 11c side of the case 11, and in the upper region of the case 11, a fixed terminal plate 19 and an insulating bushing 20 are insertedly provided in a sequential manner.

[0027] The fixed terminal plate 19 is preferably provided in a disc type made of metal. The fixed terminal plate 19 is placed on and fixed by the stepped portion while contacting an inner wall surface of the case 11 along a perimeter of a side surface so as to be electrically connected to the case 11. The fixed terminal plate 19 has a hole 19a such that the moving terminal 16 moves in a central axis direction while slidingly contacting the hole 19a. Thus, the fixed terminal plate 19 is electrically connected to the case 11 by contacting the inner wall surface of the case 11 and/or the stepped portion, and is also electrically connected to the moving terminal 16 slidingly contacting the hole 19a, and at the same time, the fixed terminal plate 19 also serves a role to guide the moving terminal 16, so that the moving terminal 16 moves while slidingly contacting an inner wall of the hole 19a.

[0028] The temperature-sensitive pellet 12 is made by compressing and molding a non-conductive organic material in a pellet shape. The temperature-sensitive pellet 12 has an initial height H0, and is installed to be loaded on the floor 11c inside the cabinet 11, and as illustrated in FIG. 5, when a periphery temperature of the case 11 is equal to or greater than a predetermined preset activation temperature (a switch off activation temperature that a thermal fuse shuts off a circuit), the temperature-sensitive pellet 12 is melted and reduced in height to a predetermined height H2 or less at which the switch performs a shut off operation.

[0029] A first lead 1 passes through a through-hole 21 of the insulating bushing 20, such that one end of which extends to the outside of the case 11 while a surface of the other end provides a first fixed contact 1a inside the through-hole 21. On the floor 11c of the case 11, a second lead 2 is electrically connected to the case 11 while facing the first lead 1. An opened upper side of the insulating bushing 20 is sealed with a sealing material 3.

[0030] The moving terminal 16 has, on one end, a first moving contact 16b contacting a first fixed contact 1a of the first lead 1 and, on the other end, a head part 16c expanded at a relatively greater diameter than the diameter of a body 16a. As illustrated in FIGS. 2 and 3, the moving terminal 16 having the aforementioned structure is installed such that the body 16a passes through the hole 19a of the fixed terminal plate 19 to be slidingly guided on an inner surface of the hole 19a, and the head part 16c expanded in a relatively greater diameter than the diameter of the body 16a is provided on a lower end of the body 16a. The moving terminal 16 is elastically supported by the first spring 17 compressedly installed between a lower surface of the head part 16c and an upper surface of the temperature-sensitive pellet 12. That is, at least until the temperature-sensitive pellet 12 is melted and is reduced in height to a predetermined level or less, the first spring 17 elastically supports the lower surface of the head part 16c of the moving terminal 16 such that the first moving contact 16b of the moving terminal 16 remains in contact with the first fixed contact 1a of the first lead 1.

[0031] The base plate 13 is disposed between the first spring and the temperature-sensitive pellet 12 so as to stably support one end of the first spring 17 even in the case that the temperature-sensitive pellet 12 is deformed by molten deformation or damage. The base plate 13 has a hole 13a such that a melted portion 12a may escape therethrough when the temperature-sensitive pellet 12 is deformed by being melted.

[0032] The thermal fuse according to an embodiment of the present invention has the activating member 15 configured to separate a first moving contact 16b of the moving terminal 16 from the first fixed contact 1a of the first lead 1 such that a switch performs an off operation when the temperature-sensitive pellet 12 is melted, in accordance with the rise of the periphery temperature, and is reduced in height from the initial height H0 to a predetermined height H2 or less at which the switch performs an off operation.

[0033] The activating member 15 is provided in a cylindrical shape having an opened lower end, an upper end having an upper end sidewall 15c, and a spring support step 15b on an outer surface of the lower end. The activating member 15 is placed on and supported by the base plate 13 and receiving the moving terminal 16 and the first spring 17 in an internal space thereof, wherein the body 16a of the moving terminal 16 passes through a through-hole 15a of the upper end sidewall 15c to extend towards the first lead 1, and the head part 16c is elastically supported by the first spring 17 in the internal space of the activating member 15. The second spring 18 having a relatively greater modulus of elasticity than the first spring 17 is elastically installed on the outside of the activating member 15 to elastically deflect the activating member 15 towards the temperature-sensitive pellet 12 in response to a height decrease due to melting of the temperature-sensitive pellet 12.

[0034] As illustrated in FIGS. 2 and 3, when the temperature-sensitive pellet 12 is melted and is reduced in height, the activating member 15 moves towards the temperature-sensitive pellet 12 by an elastic repulsive force of the second spring 18 elastically installed between a lower surface 19b of the fixed terminal plate 19 and the spring support step 15b, and when the temperature-sensitive pellet 12 is reduced in height to a predetermined height H2 or less, the activating member 15 moves the moving terminal 16 in a state in which a lower surface 15d of the upper end sidewall 15c remains in contact with the upper surface 16d of the head part 16c of the moving terminal 16, and separates the first moving contact 16b of the moving terminal 16 from the first fixed contact 1a of the first lead 1 to turn the switch off.

[0035] As described above, when the moving terminal 16 moves in the same direction as a sliding movement direction of the activating member 15 by interlocking with a sliding movement of the activating member 15, the moving terminal 16 is guided by the body 16a slidingly contacting an inner wall of the hole 19a of the fixed terminal plate 19, so it is possible to prevent a phenomenon in which the moving terminal 16 is tilted and caught by an inner wall of the case to cause a malfunction.

[0036] Hereinafter, an operating mechanism of the thermal fuse according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0037] Normal State: Switched on State (FIGS. 2 and 3)

[0038] As illustrated in FIG. 2, if the periphery temperature of the case 11 is equal to or less than a predetermined fuse activation temperature, the temperature-sensitive pellet 12 is not melted, so the temperature-sensitive pellet 12 is not changed in height. Thus, the moving terminal 16 maintains a contact state between the first moving contact 16b and the first fixed contact 1a of the first lead 1 by a spring force of the first spring 17, and an outer surface of the body 16a of the moving terminal 16 maintains a contact state with the inner wall of the hole 19a of the fixed terminal plate 19 connected to the case 11. That is, in the state exhibited in FIG. 2, the first lead 1 is electrically connected to the second lead 2 through a path of the moving terminal 16—the fixed terminal plate 19—the case 11, and thus a switch on state is maintained.

[0039] From the state exhibited in FIG. 2, when the temperature-sensitive pellet 12 is partially melted and is reduced in height as the temperature rises, and before a height H1 of the temperature-sensitive pellet 12 is reduced to the height H2 at which the switch substantially initiates operation (H1>H2), as illustrated in FIG. 3, the temperature-sensitive pellet 12 is reduced in height due to melting of the temperature-sensitive pellet 12, and the base plate 13 is also accordingly lowered by the height reduction amount (H0−H1) of the temperature-sensitive pellet 12. Thereby, while the second spring 18 expands and pushes the activating member 15 away such that the activating member is in close contact with the temperature-sensitive pellet 12, the first spring 17 pushes the moving terminal 16 up in an opposite direction, and thus the first moving terminal contact 16b of the moving terminal 16 maintains a close contact state with the first fixed contact 1a of the first lead 1.

[0040] Switched Off State (FIGS. 4 and 5)

[0041] The temperature-sensitive pellet 12 is continuously melted as the periphery temperature rises, and is continuously reduced in height, and accordingly, the activating member 15 also moves towards the floor 11c of the case 11. However, after a time point (G=0) when the lower surface 15d of the upper-end sidewall 15c of the activating member 15 contacts the upper surface 16d of the head part 16c of the moving terminal 16, the activating member 15 moves the moving terminal 16 towards the temperature-sensitive pellet 12 by the force of the second spring 18, which is greater than the force of the first spring 17, to separate the first moving contact 16b from the first fixed contact 1a of the first lead, and thus a switch off operation is performed.

[0042] While the activating member 15 moves the moving terminal 16 for the switch off operation, the body 16a of the moving terminal 16 is linearly guided while sliding into the hole 19a of the fixed terminal plate 19, thus the moving terminal 16 performs a linear movement without shaking, and thus it is possible to prevent an inoperability or malfunction in that the moving terminal 16 is deflected in any one direction and caught by the inner wall of the case due to an uneven force of the spring which gives a moving force when the moving terminal 16 moves for the switch off operation.

[0043] According to the configuration set forth herein, when the moving terminal moves in accordance with melting of the temperature-sensitive pellet, the moving terminal is guided along the inner wall surface of the hole of the fixed terminal plate, and a separation of the moving terminal from the fixed contact is stably performed, so the switch operation is accurately performed within the predetermined temperature range without malfunction.

[0044] Also, the switching operation is performed only when the temperature-sensitive pellet is melted and deformed by a predetermined amount by rise of the periphery temperature without being directly affected by deformation of the temperature-sensitive pellet caused by unexpected factors such as external vibration or impact, thereby ensuring high operation reliability.

[0045] It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.