Electricity: electrothermally or thermally actuated switches – Thermally actuated switches – With bimetallic element
Reexamination Certificate
2001-09-27
2004-03-16
Vortman, Anatoly (Department: 2835)
Electricity: electrothermally or thermally actuated switches
Thermally actuated switches
With bimetallic element
C337S343000, C337S300000
Reexamination Certificate
active
06707372
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to temperature sensors and, more particularly, to snap-action thermal switches and resistance thermal sensors.
BACKGROUND OF THE INVENTION
Snap-action thermal switches are utilized in a number of applications, such as temperature control and overheat detection of mechanical devices such as motors and bearings. In some applications, multiple thermal switches are located at different positions around the equipment. For example, in some aircraft wing, fuselage, and cowling overheat detection applications, multiple thermal switches located just behind the leading edge flap, while other thermal switches are spaced along the length of each wing. Additional thermal switches are located in the engine pylon and where the wing attaches to the fuselage. In this example, the multiple thermal switches are connected electrically in parallel, such that just two wires are used to interface between all of the switches on each wing and an instrument that monitors the temperature of the aircraft's wing, fuselage, and cowling.
Current snap-action thermal switch designs typically provide open and closed functions only. Typically, all of the thermal switches in the aircraft wing, fuselage, and cowling overheat detection applications are operated in the normally open state. The thermal switches are thus all in the “open” state until an overheat condition is detected, at which time one or more of the switches change to the “closed” state, thereby completing the circuit causing a “right wing,” “left wing” or “fuselage” overheat indication to appear in the cockpit. The pilot then follows the appropriate procedure to reduce the overheat condition.
Current snap-action thermal switches used in parallel operation, multiple thermal switch overheat detection systems suffer from various drawbacks. The integrity of the wire harness between the cockpit and the wing tip cannot be assured because the circuit is always open under normal operating conditions. If a switch connector is not engaged or the wire harness contains a broken lead wire, a malfunction indication will not occur, but neither will the overheat detection system operate during an actual in-flight overheat condition. Furthermore, if an overheat condition does occur, current snap-action thermal switches are not equipped to provide information describing the exact location of the overheat. In both instances, flight safety is compromised, and later correction of the problem that caused the overheat condition is made more difficult because of the inability to pinpoint the overheat fault.
SUMMARY OF THE INVENTION
The present invention overcomes the limitations of the prior art by providing a device that provides a self-test function in combination with a thermal overheat detection function.
According to one embodiment of the invention, a snap-action thermal switch structured in a normally open configuration is combined with a resistance element integral with the snap-action thermal switch and coupled to an output thereof.
According to one embodiment of the invention, the resistance element and the snap-action thermal switch share one or more common terminals. For example, the snap-action thermal switch is structured having a pair of terminals being mutually electrically isolated when the snap-action thermal switch structured in the normally open configuration, and the integral resistance element is electrically coupled to provide an output on the pair of electrically isolated terminals. According to different embodiments of the invention, the resistance element is mounted either internally or externally to the snap-action thermal switch.
According to another embodiment, the invention is embodied as a three-terminal, snap-action thermal switch having first, second and third electrical terminals mounted in a header, the first, second and third terminal being mutually spaced apart and electrically isolated; a fixed electrical contact being positioned on the first terminal; a movable electrical contact being positioned on the second terminal and being biased into electrical contact with the fixed electrical contact; a bi-metallic actuator being convertible as a function of temperature between a first state wherein an actuation portion is positioned to space the movable electrical contact away from the fixed electrical contact and a second state wherein the actuation portion is positioned to permit electrical contact between the movable electrical contact and the fixed electrical contact; and an electrically resistive element coupled between the third electrical terminal and one of the first and second electrical terminals.
The invention also provides methods of accomplishing the same. For example, the method of the invention includes structuring a pair of electrical contacts in a normally open configuration; electrically interconnecting an electrically resistive element with at least one of the pair of contacts; and detecting a minimum electrical resistance of the electrically resistive element.
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Davis George D
Scott Byron G
Honeywell International , Inc.
Rupnick Charles J.
Vortman Anatoly
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