Electricity: electrothermally or thermally actuated switches – Thermally actuated switches – With bimetallic element
Reexamination Certificate
1999-03-18
2001-06-26
Tolin, Gerald (Department: 2835)
Electricity: electrothermally or thermally actuated switches
Thermally actuated switches
With bimetallic element
C337S368000, C337S319000, C337S347000, C337S375000, C200S407000, C200S448000
Reexamination Certificate
active
06252492
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to condition-responsive controls and, particularly, to a condition-responsive electric switch mechanism having an alarm or an alarm and line switch.
Switches that are responsive to temperature changes, commonly known as thermostats or cold controls, are used in refrigeration appliances, such a refrigerators and freezers, to control the temperatures therein. These thermostats regulate the switching cycle of the refrigeration compressor in response to the temperature of the air contained at some location within the appliance. When the temperature exceeds a certain “turn-on” point, the switch contacts are closed and the compressor is switched on to cool the appliance. When the temperature drops below a certain “turn-off” point, the switch contacts are opened and the compressor is switched off.
Thermostats of the type to which this invention relates typically employ a bellows communicating with a capillary tube in thermal contact with the location to be cooled. Expansion and contraction of a gas within the capillary tube and bellows causes corresponding expansion and contraction of the length of the bellows. The motion of the bellows is transmitted via an actuator to a switch element such as a bistable spring switch element which is capable of snapping between two stable positions, one of which closes a circuit and activates the compressor to cool the appliance and the other of which opens the circuit to deactivate the compressor. The spring switch element is fixed to one circuit element and extends outwardly toward another circuit element and carries a electrical contact on its free end. In the circuit open position of the spring switch element, the spring switch element is spaced away from the other circuit element. In the circuit closed position, the contact on the spring switch element engages a contact fixed to the other circuit element and the circuit is completed. Snapping of the spring switch element is controlled by the actuator in the thermostat which presses against the spring switch element with a force increasing with the increase in temperature above the set point detected within the appliance. Eventually, the force reaches a switch point at which the spring switch element snaps from one position to another to open or close the circuit.
Under certain circumstances, the temperature in an appliance compartment, for example, can continue to rise above the temperature set point even though the cold control has called for the compressor to cool the compartment. In these instances, an audio or visual indication of the excessive temperature condition is desired. Unfortunately, presently available alarm circuits require an increase in force to close the alarm circuit and cause additional electrical loading during closure of the circuit. This prevents the user from calibrating the alarm threshold temperature very closely to the thermostat's temperature set point for turning on the compressor.
Commonly assigned U.S. Pat. Nos. 3,065,320, 3,065,323, 3,648,214, 4,490,708, 5,142,261 and 5,585,774, the entire disclosures of which are incorporated herein by reference, are examples of thermostats for refrigeration appliances.
SUMMARY OF THE INVENTION
It is therefore seen to be desirable to provide responsive electric switch mechanism that permits temperature control of a compressor; such a switch mechanism generates an alarm signal when a detected temperature exceeds a threshold; the provision of such a switch mechanism that permits substantial sensitivity adjustment of the mechanism by changing the gap between fixed and movable contacts; and such a switch mechanism that is economically feasible and commercially practical.
Briefly described, a condition-responsive electric switch mechanism embodying aspects of the invention includes a housing with first, second and third terminals projecting outwardly from the housing for connection in an external electric circuit. The switch mechanism also includes an actuator movable as a function of a detected condition and a bistable spring switch element electrically connected to the first terminal. The spring switch element includes a movable contact and is adapted for snap-acting movement between a circuit open position and a circuit closed position. In the circuit open position, the movable contact of the spring switch element is spaced apart from a fixed contact mounted on the second terminal. In the circuit closed position, the movable contact engages the fixed contact to electrically connect the first and second terminals. The spring switch element also includes a toggle blade operable by engagement with the actuator for motion through a first switch point. At the first switch point, the spring switch element snaps between the circuit open position and the circuit closed position. The toggle blade is operable by further engagement with the actuator for motion past the first switch point to a second switch point for electrically connecting the first and third terminals.
In one embodiment of the invention, the condition-responsive switch mechanism is adapted for use with a refrigeration appliance. The appliance includes a compartment and a compressor for cooling the compartment. The appliance also includes an alarm and the switch mechanism is responsive to temperature in the compartment for controlling operation of the compressor.
Alternatively, the invention may comprise various other methods or systems.
Other objects and features will be in part apparent and in part pointed out hereinafter.
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Frank James P.
Poling Ronald W.
Struttmann Ted P.
Tolin Gerald
Vortman Anatoly
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