Patent Abstract:
A damper mechanism for a gas-fired appliance is disclosed. The damper mechanism is mechanically operated in response to changes in pressure within a portion of the appliance. Changes in gas pressure operate to displace a diaphragm, thereby moving a linkage attached to a flue damper, such that the damper can be moved between open and closed positions. An interim damper control activation arm can pivot in response to movement of the linkage to actuate electrical switches, which act to close a magnetic pilot valve when the damper is in a partially-opened or partially-closed position.

Full Description:
TECHNICAL FIELD 
       [0001]    The present invention relates generally to gas-fired appliances, and, more particularly, to a damper control mechanism for a water heater or other gas-fired appliance. 
       BACKGROUND OF THE INVENTION 
       [0002]    Many gas-fired appliances, such as boilers or water heaters, include burners that fire to raise the temperature of materials, such as water, contained within a tank. In many such appliances, the burners periodically cycle on and off. When the contents of the tank fall below a desired minimum temperature, a call for heat is triggered, which initiates the firing of a main gas burner assembly. The resulting heat generated by the burner acts to raise the tank temperature. When the tank temperature reaches a desired maximum threshold, the main burner is deactivated, until such time as the tank cools and again falls below the minimum desired temperature. A small pilot burner can be provided to maintain a small flame under normal operation, which flame is used to ignite the main burner when desired. 
         [0003]    To increase the energy efficiency of such gas-fired appliances, many systems include one or more dampers. For example, a flue damper can be provided within an exhaust flue near the top of a gas fired appliance. The flue damper is opened during operation of the main burner, to permit the venting of heat and exhaust gases generated during operation of the main burner. However, once the main burner is shut off, the flue damper closes the flue, thereby reducing heat loss out the flue and retaining heat within the appliance to improve the overall energy efficiency of the appliance. 
         [0004]    Conventionally, dampers can be operated using an electric motor supplied by 24 volt or 120 volt power sources. However, such designs typically require the routing of a power source to the location of the gas-fired appliance, potentially increasing installation costs. More recently, gas fired appliances have been designed using thermoelectric devices such as one or more 750 millivolt thermopiles, operating using heat from the pilot flame, to power a low-power motor. The low-power motor in turn operates the flue damper. 
         [0005]    However, many gas-fired appliances, particularly residential water heaters, do not include power sources having sufficient voltage to reliably operate a damper motor. As a result, many residential water heaters are primarily mechanically operated. While some such water heaters may utilize a thermocouple to operate a magnetic pilot safety switch, such thermocouples typically generate only 10 to 30 millivolts, and do not supply sufficient power to drive a damper motor. Because of such control limitations, flue dampers are often not provided on residential water heaters, thereby sacrificing potential improvements in energy efficiency. 
       SUMMARY OF THE INVENTION 
       [0006]    In accordance with one exemplary form of the invention, a gas-fired appliance is provided, having a burner which is configured to receive and burn pressurized gas, such as natural gas, during operation. A diaphragm device includes an inlet which is exposed to the gas pressure during operation of the burner. The diaphragm device also includes a moveable member, such as a flexible diaphragm exposed to ambient pressure on one side and the pressure of the pressurized gas on the other, such that it moves in response to the application of pressurized gas at the diaphragm device inlet. A linkage, which may be directly or indirectly connected to the diaphragm device, moves in response to movement of the moveable member. In some embodiments, the linkage may be comprised of a metal cable sliding within a stationary sheath, or a shaft. The linkage is connected to a damper assembly, which includes a damper that is movable between open and closed positions in response to movement of the linkage. The damper assembly may also include a rotatable damper shaft on which the damper is mounted, and a lever arm secured to the rotatable damper shaft at a first location and secured to the linkage at a second location. 
         [0007]    In accordance with some embodiments, the gas-fired appliance further includes a pilot burner, and a thermoelectric device, such as a thermocouple or thermopile, positioned near the pilot burner, such that the thermoelectric device generates an electrical voltage differential when exposed to heat from the pilot burner. A magnetic pilot valve controls gas flow to the pilot burner, and features an electrical input. The magnetic pilot valve is maintained in an open position in response to the maintenance of the voltage generated by the pilot flame. A switch circuit is interposed in an electrical conduction path between the thermoelectric device and the magnetic pilot valve electrical input, whereby it can operate to control the transmission of the electrical voltage differential generated by the thermoelectric device to the magnetic pilot valve electrical input. The switch circuit is movable between an open state and a closed state in response to movement of the linkage. Accordingly, if the linkage becomes resident in an intermediate state, corresponding to a partially-opened or partially-closed damper position, the switch circuit can be configured to assume an open state, thereby cutting off the application of electrical voltage to the magnetic pilot valve and thus stopping the supply of gas to the pilot burner. 
         [0008]    The linkage may include a damper control activation arm, which pivots between a first position and a second position in response to movement of the linkage. In some embodiments, the damper control activation arm moves throughout a predetermined range of motion, in which the first position comprises a range from zero to about 20 percent of the predetermined range of motion, and the second position comprises a range from about 80 percent to 100 percent of the predetermined range of motion. 
         [0009]    The damper control activation arm can interact with the switch circuit to control the state thereof. For example, the switch circuit can include a first switch and a second switch, electrically connected in parallel. The first switch is closed by the damper control activation arm when the damper control activation arm is in the first position, while the second switch is closed when the damper control activation arm is in the second position. Accordingly, the switch circuit can operate to provide a closed electrical path when the damper control activation arm is in either the first position or the second position. 
         [0010]    In such an embodiment, additional components can be provided to maintain an electrical voltage differential at the magnetic pilot valve input for a period of time when the damper control activation arm transitions between the first and second positions. Such components may include a resistor and a capacitor, whereby the capacitor is connected between a signal path leading to the pilot valve electrical input and a ground reference voltage. Accordingly, the capacitor can become charged by the electrical voltage differential provided by the thermoelectric device when the switch circuit is in a closed state, and the capacitor can discharge to provide an electrical voltage differential to the magnetic pilot valve switch when the switch circuit is in an open state. 
         [0011]    The damper control activation arm can include a first arm portion and a second arm portion. The first arm portion depresses a contact on the first switch when the damper control activation arm is in the first position. The second arm portion depresses a contact on the second switch when the damper control activation arm is in the second position. 
         [0012]    A damper control mechanism for an appliance that operates through combustion of gas having a pressure greater than ambient pressure is also provided. The control mechanism includes a diaphragm device having an inlet that is exposed to the gas pressure during operation of the appliance. The diaphragm device further includes a moveable diaphragm having a first side and a second side. The moveable diaphragm is exposed to pressure conditions of the inlet on the first side, and ambient pressure conditions on the second side. Accordingly, the moveable diaphragm moves in response to change of pressure at the inlet. The moveable diaphragm occupies a first position when the inlet is under ambient pressure conditions, and a second position when the inlet is exposed to the gas pressure. The damper control mechanism also includes a linkage which is operably connected to the diaphragm device and the damper, whereby the linkage imparts movement on the damper in response to movement of the moveable diaphragm. 
         [0013]    The damper control mechanism may also include a thermoelectric device having an output capable of generating an electrical voltage differential. A circuit which includes one or more electrical switches electrically connects the thermoelectric device and a magnetic pilot valve. The linkage contacts the one or more electrical switches to disconnect the thermoelectric device from the magnetic pilot valve when the movable diaphragm is not within either the first or the second position. A capacitor can be provided, having a first term terminal electrically connected with the thermoelectric device and the magnetic pilot valve, and a second terminal connected to a ground reference voltage. Accordingly, if, for example, the one or more switches are placed into an open position to disconnect the capacitor from the thermoelectric device, the capacitor can temporarily apply an electrical voltage differential to the magnetic pilot valve. 
         [0014]    The linkage may include an arm attached to a pivot, such that the arm pivots between a first position and a second position during movement of the linkage. The arm can be mounted proximate the one or more electrical switches, such that it contacts the switches to change their state during movement of the arm. 
         [0015]    A method for controlling a damper in a gas-fired appliance is also provided. The method includes the steps of applying pressurized gas to a first portion of the gas-fired appliance which includes a main burner. The method further includes the step of opening a damper by moving a linkage connected to the damper via an application of mechanical force generated by the introduction of pressurized gas into the first portion of the gas-fired appliance. The step of applying pressurized gas to a first portion of the gas-fired appliance may include the step of applying pressurized gas to a diaphragm device to cause movement of said diaphragm device. The step of opening a damper by moving a linkage may include the step of moving the linkage in response to said movement of the diaphragm device. 
         [0016]    In other embodiments, the step of opening a damper via movement of the linkage can include the steps of: providing a magnetic pilot valve which maintains an open position in response to the maintenance of an electrical signal at an input terminal; applying the electrical signal to the magnetic pilot valve input terminal when the damper is in an open or closed position; and removing the electrical signal from the magnetic pilot valve input terminal when the damper occupies a partially-opened position for at least a predetermined period of time. The predetermined period of time can be zero or greater. In some embodiments, the predetermined period of time is at least about 2 seconds. In other embodiments, the predetermined period of time is between about two seconds and about three seconds. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a diagrammatic view of a portion of a gas-fired appliance, having a manually-operated damper and pilot power control switch, in accordance with one embodiment of the invention. 
           [0018]      FIG. 2  is a schematic block diagram of a flue damper control circuit. 
           [0019]      FIG. 3  is a perspective view of a pilot power control switch. 
           [0020]      FIG. 4  is an elevation view of a portion of a pilot power control switch, in a position corresponding to an open damper condition. 
           [0021]      FIG. 5  is an elevation view of a portion of a pilot power control switch, in a position corresponding to a closed damper condition. 
           [0022]      FIG. 6  is a perspective view of a damper. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    While this invention is susceptible of embodiment in many different forms, there are shown in the drawings and will herein be described in detail, certain specific embodiments with the understanding that the present disclosure should be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiments so illustrated or described. 
         [0024]    Referring initially to  FIG. 1 , a portion of a gas-fired appliance, such as a water heater, is illustrated. Gas fired appliance  100  receives combustible gas, such as natural gas, via supply line  110 . The gas is supplied at a pressure greater than the ambient air pressure in which the main appliance burners  112  (shown schematically) operate. Gas is fed into control body  120  and through pilot valve  130 , which supplies gas to a pilot burner  132  (shown schematically). Once pilot burner  132  is ignited, pilot valve  130  is maintained in an open position by pilot valve magnet  140 , which is energized by voltage received at thermoelectric device connection  150 . Thermoelectric device connection  150  is energized by thermoelectric device  160  (illustrated in  FIG. 2 ). In exemplary embodiments, thermoelectric device  160  may include a thermocouple or a thermopile. Thermoelectric device  160  is positioned adjacent pilot burner  132  to generate voltage when exposed to the heat of the pilot flame. If the pilot flame is extinguished, thermoelectric device  160  ceases generation of sufficient voltage for pilot valve magnet  140  to maintain pilot valve  130  in an open position, thereby stopping the flow of gas to pilot burner  132  via supply tube  170  and preventing unintentional flooding of unburned gas. 
         [0025]    Control body  120  further includes gas pressure regulator  180 , which operates to regulate the gas pressure within control body  120 . Temperature controlled burner valve  190  operates to limit the conditions under which gas is supplied to primary appliance burners  112  via burner supply tube  200 . For example, in an embodiment in which gas fired appliance  100  is a water heater, a temperature sensor can be provided within the water tank, such that a call for heat is issued when the water temperature falls below a desired level. In response to a call for heat, burner valve  190  is opened, thereby supplying gas to main burner  112  through burner supply tube  200 . When burner  112  acts to raise the monitored temperature above a desired maximum level, burner valve  190  is closed, thereby shutting off the flow of gas to burner  112 . 
         [0026]    In addition to providing gas feeds to pilot burner supply tube  170  and main burner supply tube  200 , control body  120  further includes a gas pressure tap port  210 . Gas pressure tap port  210  is connected to a diaphragm device  220  via tube  230  to communicate pressure within control body  120  therethrough. Thus, when pilot valve  130  and main burner valve  190  are both open, the resulting flow of gas pressurizes a chamber to which gas pressure tap port  210  is connected. When main burner valve  190  is closed, gas pressure tap port  210  and thus diaphragm device  220  are exposed to ambient pressure conditions. 
         [0027]    Diaphragm device  220  is a mechanism having an inlet  231 , which is alternatively exposed to pressure of the gas or ambient pressure conditions, depending upon the state of main burner valve  190 . Diaphragm device  220  also includes a movable member  232 , which is a structural component displaced in response to the application of gas pressure to an inlet portion of the device. Moveable member  232  includes a first surface  233  which is exposed to the pressure conditions of the inlet, and a second surface  234  that is exposed to ambient pressure conditions. Accordingly, moveable member  232  is displaced in response to changes in inlet pressure. For example, in some embodiments, moveable member  232  may include a diaphragm, such as a thin, flexible membrane, spanning inlet and ambient conditions. 
         [0028]    Moveable member  232  within diaphragm device  220  is operably interconnected with intermediate shaft  235  and damper control activation arm  240 , forming a portion of an operable linkage with device  220 . When gas pressure is applied to the inlet side of diaphragm device  220 , intermediate shaft  235  moves upwards, causing damper control activation arm  240  to pivot about pivot point  250  in the direction of the illustrated arrow  251 . When gas pressure is released from diaphragm device  220 , intermediate shaft  235  returns to a lowered position and activation arm  240  pivots oppositely to the direction indicated by arrow  251 . 
         [0029]    Damper control activation arm  240  is illustrated in perspective view in  FIG. 3 . In the illustrated embodiment, damper control activation arm  240  is made with first arm portion  240   a  and second arm portion  240   b , which are mechanically connected. One end  252  of damper control activation arm  240  interacts with a switch circuit  260  that includes pilot power control switches  260   a  and  260   b , which are mounted adjacent to one another. 
         [0030]    Pilot power control switches  260   a  and  260   b  are further illustrated in  FIGS. 4 and 5 . Pilot power control switches  260   a  and  260   b  include switch arms  265   a  and  265   b , respectively. Switch arm  265   a  extends downwards from the point at which it is attached to switch  260   a . Switch arm  265   b  extends upwards from the point at which it is attached to switch  260   b . Damper control activation arm  240   a  is aligned to interact with pilot power control switch  260   a , such that switch arm  265   a  is depressed when activation arm  240  is moved to a first position, as shown in  FIG. 4 , and released when activation arm  240  is moved to a second position, as shown in  FIG. 5 . Damper control activation arm  240   b  is aligned to interact with pilot power control switch  260   b , such that switch  265   b  is depressed when activation arm  240  is in the second position, shown in  FIG. 5 , and released when activation arm  240  is in the first position of  FIG. 4 . In the exemplary embodiment of  FIGS. 4 and 5 , the first activation arm position ( FIG. 4 ) is maintained over a range from about 80% to about 100% of the normal range of travel of activation arm  240 , in which gas is being supplied to the main burner and the flue damper is substantially open. The second activation arm position ( FIG. 5 ) is maintained over a range from about zero to about 20% of the normal range of travel of activation arm  240 , in which the supply of gas to the main burner has been shut off and the flue damper is substantially closed. 
         [0031]    Damper control activation arm  240  is further connected to link  270 , which extends to control the opening and closing of flue damper  280 , illustrated in  FIG. 6 . In an exemplary embodiment, link  270  may incorporate a cable structure, such as a metal cable that slides freely within a polymer sheath. Alternatively, it is understood that other varieties of mechanical links that are known in the art could be implemented, such as a rod or shaft. The end of link  270  opposite damper control activation arm  240  is attached to lever arm  290 , which is secured to damper control shaft  300 . Damper  280  is mounted on control shaft  300 . Accordingly, movement of link  270  results in pivoting of control shaft  300  and damper  280  between open and closed positions. 
         [0032]    In operation, when appliance  100  initiates a call for heat, temperature controlled burner valve  190  opens, which permits the flow of pressurized gas to main burner  112 , gas pressure tap port  210 , tube  230  and diaphragm device  220 . The resulting displacement of diaphragm device  220  causes movement of intermediate shaft  235 , pivoting of damper control activation arm  240  and movement of link  270 , which in turn pivots damper  280  into an open position, so that exhaust is vented while main burner  112  is ignited. When continued activation of main burner  112  is no longer required, temperature controlled burner valve  190  closed, thereby depressurizing gas pressure tap port  210  and diaphragm device  220 . Shaft  235  is displaced downwards, which pivots damper control activation arm  240  and moves link  270 , which in turn pivots damper  280  into a closed position, so that heat loss from appliance  100  is reduced. 
         [0033]    Damper switches  260   a  and  260   b  operate to provide added safety measures in the event that damper  280  becomes stuck in a partially-opened position. In such a position, the flue may be opened sufficiently to permit operation of main burner  112  without tripping a flame safety switch in the burner chamber, but it may not provide enough venting of the flue to eliminate the creation of high levels of carbon monoxide. Accordingly, a further safety feature is provided to address partial opening of the damper. 
         [0034]    In the embodiment illustrated in the schematic diagram of  FIG. 2 , pilot power control switches  260   a  and  260   b  are wired in parallel, between thermoelectric device  160  and pilot magnet  140 , such that voltage generated by thermoelectric device  160  is applied to pilot magnet  140  when activation arm  240  is in a raised or lowered position. However, if damper  280  becomes stuck in a partially-opened or partially-closed position, activation arm  240  is likewise placed into an intermediate position, such that neither of switches  260   a  and  260   b  is closed. As a result, power to pilot magnet  140  is interrupted, such that pilot valve  130  is closed and the flow of gas to main burner supply tube  200  and pilot burner supply tube  170  is interrupted, thereby shutting off the main burner  112  and pilot burner  132  and avoiding misoperation that might otherwise be caused by partial closure of damper  280  during firing of main burner  112 . Further safety measures can be implemented through the operation of spill switch  302 , interposed between damper switches  260   a ,  260   b  and thermoelectric device  140 , and flame safety switch  304 , interposed in the connection of thermoelectric device  140  to ground. These components interrupt burner operation, thereby to avoid excessive heat generation in the combustion chamber, as may be caused by potentially a number of different conditions. 
         [0035]    While the above-described termination of power to pilot valve magnet  140  can avoid undesired operating conditions if damper  280  sticks in a partially-open or partially-closed position, even during the intended operation, damper control activation arms  240  will inherently move momentarily through an intermediate position, in which neither of switches  260   a  and  260   b  is closed, when transitioning normally between elevated and lowered states. In some embodiments, gas pressure tap port  210  will fully pressurize in about 2 to 3 seconds after opening of burner valve  190 , during which period damper control activation arm  240  and flue damper  280  are moved between open and closed positions. In order to avoid unintentional closure of pilot valve  130  during this transition period, a lowpass filter or timer circuit is provided between damper switches  260   a  and  260   b , and pilot magnet  140 . In the embodiment of  FIG. 2 , a series RC circuit with resistor  310  and capacitor  320  is provided. Resistor  310  and capacitor  320  operate to temporarily maintain the voltage level present at pilot magnet  140  when both of switches  260   a  and  260   b  are opened. 
         [0036]    Capacitor  320  can be sized to accommodate the target switching time, voltage levels and circuit resistance. For example, in an embodiment utilizing a thermocouple having a nominal minimum operating voltage of 10 millivolts and a circuit resistance of 0.017 Ohms, and requiring at least 5 millivolts applied to pilot magnet  140  to maintain pilot valve  130  in an open position, it can be determined that a 220 Farad capacitor would maintain the required voltage level for around 2.6 seconds. In embodiments utilizing a thermopile in place of a thermocouple, the higher operating voltages would allow for a smaller capacitor to maintain the required pilot magnet voltage for a given period of time. 
         [0037]    The foregoing description and drawings merely explain and illustrate the invention and the invention is not limited thereto, inasmuch as those skilled in the art, having the present disclosure before them will be able to make modifications and variations therein without departing from the scope of the invention.

Technology Classification (CPC): 5