Thermal cut-off fuse

• US 4,198,617 A
• Filed: 09/06/1978
• Issued: 04/15/1980
• Est. Priority Date: 09/12/1977
• Status: Expired due to Term

• Current Assignee: Nifco Incorporated
• Original Assignee: Nifco Incorporated
• Inventors: Hara, Kunio
• Primary Examiner(s): Harris, George
• Application Number:
  US05/939,971
• Time in Patent Office: 587 Days
• Field of Search: 337/403, 337/404, 337/405, 337/407, 337/408, 337/409
• US Class Current: 337/403
• CPC Class Codes: H01H 37/761 with a fusible element forming part of the switched circuit H01H37/767 takes precedence

Abstract

A thermal cut-off fuse of the class wherein the electric continuity between electrodes disposed inside a housing is maintained by conductor means at normal service temperatures and broken by the conductor means being fractured when the ambient temperature reaches a fixed level is improved by having the conductor means made of a metal capable of liquefying before the ambient temperature reaches the fixed level mentioned above and providing a thermal pellet faithfully fusible at the fixed level of temperature for the purpose of supporting in position the conductor means serving to maintain the electric continuity between the electrodes at normal service temperatures and thereby allowing the electric continuity between the electrodes to be broken at the fixed level of temperature by the thermal pellet being melted and deprived of its role of supporting the conductor means.

Claims

1. A thermal cut-off fuse, comprising in combination:

a housing having a pair of lead wires withdrawn outwardly therefrom and having the terminals of the lead wires forming a pair of opposed electrodes;

a thermal pellet made of a substance capable of assuming a solid state at normal service temperatures and faithfully melting in response to the rise of the ambient temperature to a fixed level and placed inside said housing; and

a conductor means made of a substance capable of assuming a liquid state at least before the ambient temperature reaches the fixed level and adapted to be retained by said thermal pellet in a position for maintaining the electric continuity between the pair of electrodes until the ambient temperature reaches the fixed level.

2. The thermal cut-off fuse according to claim 1, wherein protuberances are formed inwardly in the housing interior by having the housing constricted in the middle, the protuberances serving to facilitate the separation of the conductor means melted at the fixed level of temperature.

3. The thermal cut-off fuse according to claim 1, wherein mercury is used as the conductor means.

4. The thermal cut-off fuse acccording to claim 1, wherein a fusible alloy capable of assuming a liquid state before the ambient temperature reaches the fixed level is used as the conductor means.

5. The thermal cut-off fuse according to claim 1, wherein the two electrodes are provided one each with auxiliary electrode means disposed in mutually approaching directions.

6. The thermal cut-off fuse according to claim 1, wherein the lead wires are withdrawn parallelly to each other out of the housing.

7. The thermal cut-off fuse according to claim 1, wherein the lead wires are withdrawn in mutually opposite direction in one straight line.

8. The thermal cut-off fuse according to claim 1, wherein the housing is provided with a flange adapted to have the thermal cut-off fuse attached to the base plate by fastening means.