Abstract:
A gas valve for controlling the flow of gas to a burner. An actuator controls the flow of gas through the valve. A stepper motor operates the actuator. A first temperature sensor senses temperature of gas entering the valve. A second temperature sensor senses temperature of gas leaving the valve. A controller controls the stepper motor in response to the sensed temperatures. This gas valve provides universal single-stage, multi-stage and modulating gas flow control for appliances and furnaces.

Description:
FIELD OF THE INVENTION 
   The present invention relates to gas furnaces and appliances and, more particularly, to controls for gas input to gas furnaces and appliances. 
   BACKGROUND OF THE INVENTION 
   In gas appliances and furnaces, diaphragms and/or solenoids are commonly used for controlling the level of gas flow through a gas valve to a burner. Flow-control solenoids typically are actuated by continuous signals from a low-voltage power source. For this reason and for other reasons, valve control via diaphragms and solenoids tends to be complex and costly. In gas fireplace units, gas flow control may be via a stepper-motor-controlled valve, which can vary gas flow without a diaphragm and is powered by intermittent low-voltage signals. Such valves can vary gas flow to vary fireplace flame, but cannot sense outlet flow rate or adjust outlet flow to a desired flow rate value. 
   SUMMARY OF THE INVENTION 
   The present invention, in one embodiment, is directed to a gas valve for controlling the flow of gas to a burner. The gas valve includes an actuator that controls the flow of gas through the valve. A stepper motor operates the actuator. A first temperature sensor senses temperature of gas entering the valve. A second temperature sensor senses temperature of gas leaving the  valve. A controller controls the stepper motor in response to the sensed temperatures. 
   Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating various embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
       FIG. 1  is a longitudinal cross-sectional view of a gas valve in accordance with one embodiment of the present invention; 
       FIG. 2  is a cross-sectional view of the valve embodiment shown in  FIG. 1 , taken along the plane of line  2 — 2  in  FIG. 1 ; 
       FIG. 3  is a cross-sectional view of a floor of the valve embodiment shown in  FIG. 1 , taken along the plane of line  3 — 3  in  FIG. 1 ; 
       FIG. 4A  is a partial schematic diagram of an embodiment of a gas valve control system; and 
       FIG. 4B  is continuous with  FIG. 4A  and is a partial schematic diagram of the embodiment of a gas valve control system shown in  FIG. 4A .  
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The following description of various embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
   A gas valve according to one embodiment of the present invention is indicated generally in  FIG. 1  and  FIG. 2  by reference number  10 . The gas valve  10  is used, for example, to control gas flow to a burner in a gas appliance or gas furnace. The valve  10  has a body  14  fabricated, for example, of cast aluminum. The valve body  14  has a top plate  18 , a bottom plate  22 , two side plates  24 , and an inlet plate  28  from which extends an inlet block  32 . A gas inlet  36  extends through the inlet block  32  and opens into an inlet chamber  40  in the body  14 . An outlet block  44  extends from an outlet plate  46  of the valve body  14 . An outlet chamber  50  is fluidly connected with a gas outlet  54  extending through the outlet block  44 . 
   A bracket  56  extends within the body  14  from the outlet plate  46 . The bracket  56  is integral with a separator plate  60  that separates the inlet chamber  40  from the outlet chamber  50 . The separator plate  60  has a central, generally circular opening  62  that fluidly connects the inlet and outlet chambers  40  and  50  when a poppet  64  operable by a linear actuator  66  is in an open position as further described below. 
     FIG. 3  is a plan view of the separator plate  60 , taken along the plane of line  3 — 3  in  FIG. 1 . The opening  62  has a chamfered edge  66  against which the poppet  64  fits snugly when in a closed position as shown in  FIG. 1 .  Another opening  70  in the separator plate  60  opens into a passage  72  through the bracket  56  that fluidly connects the outlet chamber  50  with the gas outlet  54 . 
   The poppet  64  is mounted on a lower end  74  of a poppet shaft  76 . A key-shaped upper end  78  of the poppet shaft  76  is movably mounted in a vertical key-shaped channel  80  in an arm  82  of the bracket  56 . The poppet shaft  76  can be driven up and/or down by a stepper motor  84  mounted on the top plate  18 . Specifically, a threaded shaft end  86  of the motor  84  extends through the top plate  18  into a threaded sleeve  88  such that rotational movement of the motor  84  is translated into linear movement of the poppet shaft  76 . The keyed shapes of the channel  80  and shaft end  78  keep the poppet shaft  76  from rotating while the shaft  76  is moved up or down. It is contemplated that in other embodiments, other linear actuating elements could be utilized to move the poppet shaft  76  up and/or down. 
   The poppet shaft  76  and poppet  64  are concentrically aligned with the opening  62 . The poppet  64  has a top portion  90  fabricated, for example, of rubber, and a lower plate  92  fabricated, for example, of aluminum. The plate  92  is affixed to the lower end  74  of the poppet shaft  76  and supports and stabilizes the rubber portion  90  relative to the poppet shaft  76 . The poppet  64  is shaped so as to fit snugly against the chamfered edge  66  of the opening  62  when the poppet  64  is in the closed position. 
   Examples of such system-controlled printing and promotional tickets may be found I co-pending U.S. patent application Ser. No. 10/349,874, titled “System and Method for Electronic Game Promotion,” filed Jan. 22, 2003; and U.S. patent application Ser. No. 10/308,768, titled “System for Electronic Game Promotion,” filed Dec. 2, 2002; incorporated by reference herein. 
   When the stepper motor  84  is activated to lower the poppet shaft  76 , the poppet  64  is lowered from the closed position. When the poppet  64  is in an open position, gas can pass from the inlet chamber  40  through the  opening  62  into the outlet chamber  50 , at a flow rate determined by how far the poppet  64  is lowered from the closed position. In the embodiment shown in  FIG. 1 , the poppet  64  is hemispherically shaped, although embodiments are contemplated wherein the poppet and/or opening between the chambers may have other shapes and/or contours. 
   An inlet temperature sensor  104 , e.g., a thermistor, is mounted in the inlet block  32  and connected to terminals  108  and  112 . A lead  114  of the inlet thermistor  104  extends through a passage  116  into the gas inlet  36 . An outlet temperature sensor  120 , e.g., a thermistor, is mounted in the outlet block  44  and connected to terminals  122  and  126 . A lead  130  of the outlet thermistor  120  extends through a passage  132  into the gas outlet  54 . The temperature sensors  104  and  120  are, for example, thermistors having part number 2322 626 23102, available from BC Components International B.V., Alpharetta, Ga. 30076. It is contemplated that, in other embodiments, other temperature-sensing devices, including but not limited to transistors and/or resistance temperature detectors, could be used to sense gas temperature(s) in the gas inlet and outlet. In other embodiments, temperature sensor  104  may be different from temperature sensor  120 . 
   An embodiment of a control system for controlling gas flow through the valve  10  is indicated generally in  FIGS. 4A and 4B  by reference number  200 . The controller  200  includes a half-wave rectifier circuit indicated generally by reference number  204 , a processor power supply circuit indicated generally by reference number  208 , and a processor  212 , e.g., an erasable  programmable read-only memory (EPROM) 68HC705P6A, available from Motorola, Inc., http://www.motorola.com. The stepper motor  84  is driven in forward and/or reverse directions via a pair of driver circuits  216  under control of the processor  212 . The processor  212  controls a signal that indicates a number of angular steps through which the motor shaft  86  is to rotate and thereby drive the poppet shaft  76 . Mechanical switches, indicated schematically by reference number  220 , are used to provide manual test control for starting, stopping and/or changing direction of the stepper motor  84 . The stepper motor  84  is, for example, a 1.8-degree, size  23  single-shaft hybrid motor available from Source Engineering Inc. of Santa Clara, Calif. 
   As shown in  FIG. 4A , the inlet thermistor  104  is electrically connected between a terminal E 4  and a grounded terminal E 5 . In the present exemplary embodiment, wherein the pins  108  and/or  112  (shown in  FIG. 2 ) are insulated from ground, the terminal E 5  provides grounding, for example, through the valve  10  aluminum casting. The inlet thermistor  104  receives a constant current supply of, for example, about 0.0001 ampere, a current sufficiently low to prevent the inlet thermistor  104  from self-heating. The outlet thermistor  120  is electrically connected between a terminal E 3  and the ground E 5 . The outlet thermistor  120  receives a constant current supply of, for example, about 0.05 ampere, a current sufficiently high to allow the outlet thermistor  120  to self-heat to a predetermined level. 
   A resistor R 26  is configured with the inlet thermistor  104  such that a voltage drop across the resistor R 26  corresponds to a temperature sensed  by the inlet thermistor  104 . A resistor R 27  connected across the outlet thermistor  120  is configured with the outlet thermistor  120  such that a voltage drop across the resistor R 27  corresponds to a temperature sensed by the outlet thermistor  120 . Resistors R 26  and R 27  preferably have equal resistance, for example, 8.2 kΩ. 
   During operation of the gas valve  10 , as gas enters the inlet  36 , the inlet thermistor  104  senses temperature of the gas in the inlet  36 . The temperature is signaled to the processor  212  via resistor R 26 . When the poppet  24  is in an open position, gas flows from the inlet chamber  40  to the outlet chamber  50  and through the outlet  54 . The outlet thermistor  120  senses heat removed by gas flow at the outlet  54 . The thermistor temperature is signaled to the processor  212  via resistor R 27 . 
   As gas flows through the valve  10 , it tends to draw heat from the self-heated outlet thermistor  120 . The amount of heat drawn by the gas from the thermistor  120  corresponds to a gas flow rate through the valve  10 . The processor  212  periodically compares the temperature of the inlet thermistor  104  with the temperature of the outlet thermistor  120  and uses the temperatures to determine a gas flow rate through the valve  10 . Based on the determined gas flow rate, the processor  212  signals the stepper motor  84  to operate the poppet  64  so as to adjust the flow rate through the valve  10  in accordance with a desired flow rate. 
   It can be appreciated that an embodiment of a gas valve that includes a stepper motor and differential thermistor flow sensing as described  above can provide universal single-stage, multi-stage and modulating gas flow control in a gas appliance or furnace. The above described gas valve is capable of sensing a gas flow rate, and of maintaining a selected outlet gas flow rate, for single-stage, multi-stage and/or modulated burner applications. 
   The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.