Electricity: magnetically operated switches – magnets – and electr – Permanent magnet-actuated switches – Plural magnets
Reexamination Certificate
2002-08-26
2004-04-13
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Permanent magnet-actuated switches
Plural magnets
C337S090000
Reexamination Certificate
active
06720852
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to electro-mechanical switches. The present invention also generally relates to thermostats. In addition, the present invention relates to electro-mechanical switches, which can be adapted for use with thermostats.
BACKGROUND OF THE INVENTION
Electro-mechanical switches are utilized in a variety of industrial, consumer and commercial applications. Certain types of electrical switching applications require a mechanical switch that can operate property with a slowly-applied, low-actuation force. Such a switch must also be extremely reliable and generate an accurate, repeatable response, while possessing a small actuation differential. These requirements arise perhaps most commonly in applications involving electro-mechanical thermostats, which are utilized for controlling heating and cooling in homes and buildings where coils of standard bi-metal strips form the switch actuation elements. For many years this thermostatic switching function has been performed by mercury bulb switch elements.
Due to the environmental concerns associated with the use of mercury, it is anticipated that electro-mechanical switches will eventually replace mercury-based switches. Legislation currently being drafted and passed in a variety of countries, including the United States, is aimed at banning the use of mercury in most consumer-based applications. Thus, non-mercury based switches must be developed to replace such mercury-type switching mechanisms.
Some attempts have been made at replacing mercury-switching devices, but such attempts have not been very successful. For example, so-called “snap action” switches have been designed to address the environmental concerns that mercury bulb switch elements raise. As utilized herein, the term “snap action switch” generally refers to a low actuation force switch, which utilizes an internal mechanism to rapidly shift or snap the movable contact from one position to another thus making or breaking electrical conduction between the movable contact and a fixed contact in response to moving an operating element of the switch, such as a plunger, a lever, a spring, or the like from a first to a second position. Typically, these switches require only a few millimeters of movement by the operating element to change the conduction state of the switch.
Such switches can safely and reliably operate at a current level of several amperes using the standard 24 VAC power that thermostats control. However, when actuated by a slowly-applied, low-actuation force such as is provided by a thermostat's coiled bi-metal strip, snap action switches may occasionally hang in a state between the two conducting states, or may switch so slowly between the two conducting states that unacceptable arcing and/or heat-rise can occur when entering the non-conducting state. Either condition gives rise to unacceptable reliability and predictability of operation. Furthermore, these switches frequently have unacceptably large differentials, which means that the position of the operating element at which actuation of the switch to one state occurs differs substantially from the position of the actuation element at which actuation of the switch to the other state occurs. If the differential is too large, then the temperature range that the controlled space experiences is also too large. Accordingly, the use of snap action switches in thermostat-type applications has not been particularly successful.
Electronic thermostats are generally known in the art. An example of an electro-mechanical thermostat that has been utilized in commercial, consumer and industrial applications is the T87 thermostat produced by Honeywell International, Inc. (“Honeywell”). An example of the T87 thermostat is disclosed in the publication “Thermostats T87F,” Form Number 60-2222-2, S. M. Rev. 4-86, which is incorporated herein by reference. Another example of the T87F thermostat is disclosed in the publication “T87F Universal Thermostat,” Form Number 60-0830-3, S. M. Rev. 8-93, which is also incorporated herein by reference. The T87F thermostat, in particular, provides temperature control for residential heating, cooling or heating-cooling systems. U.S. Pat. No. 5,262,752, which is incorporated by reference, is an example of an electrical switch assembly that forms the temperature responsive element in a thermostat.
A typical construction of an electronic thermostat
10
is illustrated in prior art
FIG. 1. A
processor
15
, usually a microprocessor, is connected to a memory
20
, a sensor
25
, a display
30
and an input/output (I/O) device
35
. The processor
15
controls overall operation of the thermostat and produces a control signal, which is generally passed through input/output (I/O) device
35
to the Heating, Ventilating and Air-Conditioning (HVAC) plant for controlling the operation of the plant. The memory
20
stores instructions by which processor
15
operates. Sensor
25
generates a temperature signal representative of the temperature of the air in the vicinity of the sensor
25
. Display
30
displays information to an operator of the thermostat. This information may include the current set point, the actual temperature sensed by the sensor
25
, the operating status of the HVAC plant and the like.
I/O device
35
receives one or more signals intended for the HVAC plant from the processor
15
and converts such signals into control signals for the HVAC plant. I/O device
35
also receives signals from the HVAC plant and converts those signals into signals which processor
15
can interpret. Electronic thermostats require an external power source to operate. Electro-mechanical thermostats (e.g., the Honeywell T87), on the other hand, control the HVAC plant utilizing only the physical movement of the bi-metal coil. Thus, the successful application of electro-mechanical thermostats is independent of the availability of an adequate power supply. Retrofitting an electronic thermostat into an existing electro-mechanical thermostat installation may require routing and running additional wires from the HVAC plant to the thermostat location.
One of the problems encountered in the efficient utilization of many thermostats in use today is the problem of actuating an electro-mechanical switch with a slow-moving actuator, such as a bi-metal coil, without sacrificing the switch's electrical life. For example, mechanical thermostats, such as the T87 line of thermostats manufactured by Honeywell, utilize a bi-metal coil as the temperature-sensing device. In the operation of the thermostat, the bi-metal coil moves a small amount at a slow rate. Actuating a switch directly off the bi-metal coil results in an inordinate amount of time spent, during the switching cycle, at or near snap-over. Electro-mechanical switches have low contact forces near snap-over and zero contact forces at snap-over. When the switch contact forces are low or zero, the amount of electrical resistance at the contact interface increases. As the electrical resistance to current passing through the switch increases, the heat also increases. The electrical life of an electro-mechanical switch is reduced with time as the current is carried at or near the snap-over points.
The present inventors have thus concluded, based on the foregoing, that a need exists for an improved apparatus, including a method thereof, for effectively actuating or deactuating an electro-mechanical switch. The present invention, which is described in greater detail herein, offers a unique solution to the aforementioned problems.
BRIEF SUMMARY OF THE INVENTION
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
It is, therefore, one aspect of the present invention to provide an improved electro-mechanical switch.
It is an
Farrey Michael P.
Marchini Michael G.
Donovan Lincoln
Fredrick Kris T.
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