Electricity: magnetically operated switches – magnets – and electr – Electromagnetically actuated switches – Automatic circuit-interrupting devices
Reexamination Certificate
1999-08-27
2001-07-10
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Electromagnetically actuated switches
Automatic circuit-interrupting devices
C335S172000
Reexamination Certificate
active
06259341
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to circuit interrupters generally and, more specifically, to those kinds of circuit interrupters having a trip mechanism including an automatic trip assembly with a bimetal for generating a thermally-induced tripping operation.
2. Description of the Prior Art
Molded case circuit breakers and interrupters are well known in the art as exemplified by U.S. Pat. No. 4,503,408 issued Mar. 5, 1985, to Mrenna et al., and U.S. Pat. No. 5,910,760 issued Jun. 8, 1999 to Malingowski, et al., each of which is assigned to the assignee of the present application and incorporated herein by reference.
A continuing industry objective with respect to many types of circuit interrupters is to be able to reduce the size and/or footprint of the interrupter housing while at the same time providing the same or improved performance capabilities. A major advantage of creating such a “smaller package” is that it provides increased flexibility in installation. However, a consequence of this objective is that the internal space constraints of such interrupters have become much more limiting, posing certain design obstacles that need to be overcome.
Circuit interrupters advantageously provide for automatic circuit interruption (opening of the contacts) when an overcurrent condition is determined to exist. One way of determining whether or not an overcurrent condition exists is to provide a trip mechanism with an automatic trip assembly having a bimetal through which current flows. The bimetal reacts to overcurrent conditions by heating up and bending so as to set in motion a tripping operation. Another way of determining whether or not an overcurrent condition exists is to enable the automatic trip assembly to react to a magnetic field generated by the condition. The reaction to the magnetic field is often in the form of a movement of an armature that, in turn, sets in motion a tripping operation. The movement of the armature normally is either away from or towards a magnetic structure from which the magnetic field emanates.
In some circuit interrupters, both a thermally-induced and a magnetically-induced tripping operation is provided. In such interrupters, the bimetal is frequently positioned such that a portion thereof extends between portions of the magnetic structure. This “extending portion” of the bimetal is normally thinner than the rest of the bimetal in order to provide for a proper fit between the magnetic structure portions. In the prior art, the bimetal configuration of such interrupters does not provide for clearance of other internal circuit components, resulting in a bimetal that occupies more internal space than desired. The prior art bimetal configuration also suffers from current flow difficulties near the top of the thinner “extending portion” due to the narrowing of the flow path of current. These flow difficulties can increase the current density to the point where the bimetal material could undesirably melt and erode.
It would be advantageous if a bimetal configuration existed that could provide clearance for other internal components and therefore aforementioned space constraints. It would also be advantageous if a bimetal configuration existed that did not suffer from current flow difficulties that could lead to melting and erosion.
SUMMARY OF THE INVENTION
The present invention provides a circuit interrupter that meets all of the above-identified needs.
In accordance with the present invention, a circuit interrupter is provided which includes a housing, separable main contacts disposed in the housing, and an operating mechanism disposed in the housing and interconnected with the contacts. Also provided is a trip mechanism disposed in the housing and having an automatic trip assembly that selectively generates a tripping operation which causes the operating mechanism to open the contacts upon a predetermined current threshold. The automatic trip assembly includes a substantially planar bimetal, an electrical terminal, and a magnetic yoke. The bimetal has a first cutout region and a second cutout region on opposite sides thereof which form a neck portion and define a head portion. The head portion is connected to an end of the terminal. The magnetic yoke has a substantially planar portion and two arm portions. The bimetal is positioned substantially parallel with the planar portion with the neck portion positioned between the arm portions. The first cutout region terminates approximately just below the arm portions, and the second cutout region is longer than the first cutout region and terminates farther below the arm portions.
A circuit interrupter is also provided which includes a housing, separable main contacts disposed in the housing, and an operating mechanism disposed in the housing and interconnected with the contacts. Also provided is a trip mechanism disposed in the housing and having an automatic trip assembly that selectively generates a tripping operation which causes the operating mechanism to open the contacts upon a predetermined current threshold. The automatic trip assembly includes a substantially planar bimetal, an electrical terminal, and a magnetic yoke. The bimetal has a first cutout region and a second cutout region on opposite sides thereof which form a neck portion and define a head portion. The head portion is connected to an end of the terminal. The magnetic yoke has a substantially planar portion and two arm portions. The bimetal is positioned substantially parallel with the planar portion with the neck portion positioned between the arm portions. The bimetal has rounded inner corners between the neck portion and the head portion.
This and other objects and advantages of the present invention will become apparent from a reading of the following description of the preferred embodiment taken in connection with the attached drawings.
REFERENCES:
patent: 4105986 (1978-08-01), Gogniat et al.
patent: 5313033 (1994-05-01), Link et al.
patent: 5329264 (1994-07-01), Toda et al.
patent: 5381120 (1995-01-01), Arnold et al.
Gundy Raymond P.
Hood Teresa I.
Juds Mark A.
Donovan Lincoln
Eaton Corporation
Kosinski Charles E.
Nguyen Tuyen T.
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