Thermal switch assembly

Details Thermal switch assembly Thermal switch assembly

2000-04-21

2001-09-25

Tolin, Gerald (Department: 2835)

Electricity: electrothermally or thermally actuated switches

Electrothermally actuated switches

With longitudinally expansible solid element

C337S139000, C337S395000, C337S396000, C429S061000, C429S122000

Reexamination Certificate

active

06294977

ABSTRACT:

BACKGROUND OF THE INVENTION
This application relates to the art of thermal switches and, more particularly, to thermal switches that use a contact member of temperature sensitive shape memory alloy for making and breaking a circuit. The thermal switch of the present invention is particularly applicable for use in batteries and will be described with specific reference thereto. However, it will be appreciated that the invention has broader aspects and can be used in other devices.
Shape memory alloys can be used to replace bimetals in thermal switches. A switch contact arm of shape memory alloy has a deformed shape at normal temperatures and changes to a recovered shape at elevated temperatures. These changes in shape of a shape memory alloy contact arm provide different contact arm positions that can be used to open and close an electrical circuit.
Electrical switch components of shape memory alloy have been incorporated in batteries to open the battery circuit when the battery overheats. It is difficult to incorporate a switch component of shape metal alloy into the battery construction in a manner that provides reliable operation and protects the shape memory alloy from the corrosive battery environment. Therefore, it would be desirable to have a self-contained unitary sealed thermal switch assembly that can be incorporated into batteries and other devices in a convenient and reliable manner.
SUMMARY OF THE INVENTION
A self-contained sealed thermal switch assembly includes a contact member of shape memory alloy sandwiched between a pair of electrically conductive metal outer members. The contact member has a contact arm that completes or opens a current path between the pair of outer members by changing between a deformed shape at normal temperatures and a recovered shape at elevated temperatures.
In a preferred arrangement, the contact member of shape memory alloy is substantially E-shaped in plan view, and the elongated contact arm is defined by the center leg of the E.
In accordance with a preferred arrangement, the peripheral portion of the contact member is circumferentially interrupted so that its circumferential extent is substantially less than 360° but at least 270°.
An electrical insulator is positioned between a peripheral portion of the contact member and one of the outer members. The contact arm engages the one outer member when it is in its deformed shape at normal temperatures, and moves out of engagement with the one outer member when it is in its recovered shape at an elevated temperature.
The pair of outer members have a cavity therebetween in which the elongated contact arm is located, and the one outer member has a depression therein facing the cavity.
The outer members have outwardly extending circumferential flanges surrounded by a sealing ring of electrical insulating material. A metal clamping ring surrounds the sealing ring and is crimped over the flanges on the-outer members for holding same together while firmly compressing the sealing ring against the flanges to seal the cavity.
In a preferred arrangement, the pair of outer members include a cap member and a base member. The base member is of aluminum and the cap member is of cold rolled steel that is plated with a precious metal.
The contact member of shape memory alloy preferably is plated with a precious metal.
It is a principal object of the present invention to provide a self-contained sealed thermal switch assembly that has a contact member of shape memory alloy.
It is also an object of the invention to provide a unitary thermal switch assembly that can be installed in batteries and other devices.
It is also an object of the invention to provide a thermal switch assembly of the type described that is reliable in operation and relatively easy to manufacture and assemble.


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