Electricity: electrothermally or thermally actuated switches – Thermally actuated switches – With longitudinally expansible solid element
Reexamination Certificate
1999-08-06
2001-05-29
Picard, Leo P. (Department: 2835)
Electricity: electrothermally or thermally actuated switches
Thermally actuated switches
With longitudinally expansible solid element
C337S123000, C337S298000, C337S383000, C337S398000, C337S139000, C337S140000, C060S528000
Reexamination Certificate
active
06239686
ABSTRACT:
BACKGROUND OF THE INVENTION
This application relates to the art of switches and, more particularly, to temperature actuated switches that use actuators of shape memory alloy. The invention is particularly applicable to very small relays or thermostats having a resilient switch blade that extends generally perpendicular to an elongated actuator of shape memory alloy and will be described with specific reference thereto. However, it will be appreciated that the invention has broader aspects, and that it can be used in other types of temperature actuated switches that have other arrangements of the actuator and switch blade.
Extremely small relays and thermostats are very complicated due to the use of a relatively large number of parts and the difficulty of reliably producing the parts in very small sizes. The same considerations make such relays and thermostats relatively difficult to manufacture and assemble, and makes them relatively expensive. It would be desirable to have a temperature actuated switch that is capable of being manufactured in extremely small sizes with a minimum number of parts, and that can be manufactured and assembled in a relatively efficient and reliable manner.
SUMMARY OF THE INVENTION
A polymeric housing for a relay has a cavity therein receiving a resilient switch blade and an elongated actuator of shape memory alloy that provides movement of the switch blade between open and closed positions. A pair of terminal members have fixed terminal contacts positioned in the cavity and terminal leads that extend externally of the housing from the terminal contacts. The switch blade has a movable blade contact for cooperation with one of the fixed terminal contacts as the switch blade moves between its open and closed positions.
The elongated actuator of shape memory alloy has an extended deformed shape at normal temperatures and a contracted recovered shape at an elevated temperature. An end portion of the actuator is attached to the switch blade to provide movement of the switch blade between its open and closed positions with variations in the actuator length as the actuator changes between its deformed and recovered shapes.
In a preferred arrangement, the relay is normally closed with the movable contact being biased into engagement with the one terminal contact by the force of bending stress in the resilient switch blade. When the actuator changes to its recovered shape at an elevated temperature, the actuator length contracts and pulls the switch blade in a direction to move the movable contact away from the one fixed terminal contact. Upon cooling, the actuator preferably reverts to its extended deformed shape to allow the switch blade to return to its closed position with the movable contact engaging the one fixed terminal contact.
In one arrangement, the switch blade extends generally perpendicular to the elongated actuator of shape memory alloy, and the actuator is attached to the switch blade at a point intermediate its opposite ends.
In another arrangement, the actuator has the shape of a coil spring with a plurality of coil turns and the spring actuator is attached to the resilient switch blade by extending the blade between adjacent coils in an end portion of the spring actuator.
In another arrangement, an anchor projection in the housing cavity is attached to a distal end portion of the actuator remote from the switch blade. In a preferred arrangement, the anchor projection is molded integrally in one piece with the housing and extends between adjacent coils in the distal end portion of the spring actuator.
In accordance with another aspect of the application, the resilient switch blade is on a generally U-shaped switch blade member that has a pair of substantially parallel arms connected by a base portion. One of the arms is longer than the other arm and defines the resilient switch blade, and the other arm engages the other terminal contact.
The polymeric housing has opposite ends, opposite sides, and opposite front and rear surfaces. The cavity includes opposite end cavity portions located adjacent the housing opposite ends and a cavity connecting portion that is adjacent one of the housing sides and extends between the cavity end portions. The generally U-shaped switch blade member has its arms received in the cavity end portions and its base portion received in the cavity connecting portion.
The cavity includes a generally T-shaped portion that has a crossing portion with a leg portion extending therefrom in a direction longitudinally between the opposite ends of the polymeric housing. The resilient switch blade is received in the cavity crossing portion while the actuator is received in the cavity leg portion.
The front surface of the housing has a pair of notches extending between the cavity and the opposite end portions of the housing for receiving the terminal leads. The notches are centrally located between the opposite sides of the housing although other locations are possible.
A plurality of fastener projections are ultrasonically welded to the front surface of the housing and extend upwardly therefrom for reception in a plurality of fastener receiving holes in a flat cover to attach the cover to the plane front surface of the housing for closing the cavity and securing the terminals to the housing.
It is a principal object of the present invention to provide an improved temperature actuated switch having an actuator of shape memory alloy.
It is another object of the invention to provide such a switch that has a minimum number of parts and is relatively simple to manufacture and assemble.
It is also an object of the invention to provide such a switch that allows the use of a thicker and stronger switch blade material to minimize fatigue failure.
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Clow David W.
Eder Philip B.
Quinn William F.
Roberts Mark A.
Welch Richard E.
Harness Dickey & Pierce
Picard Leo P.
Therm-O-Disc Incorporated
Vortman Anatoly
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