Abstract:
A gas-fired smoker constitutes a cabinet for holding food products to be cooked. A gas burner in the cabinet is connected to a source of flammable gas by means of a valve. The gas burner heats the cabinet and thereby cooks the food products. In one embodiment a pilot light ignites the flammable gas at the gas burner. A control circuit powered by a DC source controls the operation of the gas-fired smoker including igniting and extinguishing the gas burner in order to maintain a cooking temperature in the cabinet. A battery powers the control system. In another embodiment a rechargeable battery is recharged by a Seebeck thermal electric generator that is exposed to the heat from the gas burner.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to a smoker for slowly cooking food while imparting a smoked flavor to the food, and more particularly to controlling the temperature and smoking process of a gas-fired smoker. 
       BACKGROUND OF THE INVENTION 
       [0002]    A conventional smoker assembly includes an cabinet containing one or more grill racks spaced vertically within the cabinet, a drip pan positioned below the grill for collecting food drippings, a water pan in the bottom of the cabinet, a heat source at the bottom of the cabinet, and a tray, placed adjacent the heat source, to hold the smoke generating material. Typical smoke generating material is wood and may include hickory, alder, and mesquite wood in a variety of forms including chips, briquettes, pellets, and saw dust. The heat source may include an electric heating element, a gas-fired burner, or combustible materials such as charcoal. 
         [0003]    Smokers for slowly cooking food while imparting a smoke flavor to the food are illustrated, for example, in U.S. Pat. Nos. 7,426,885; 7,703,389; 5,713,267; 4,417,748; 4,309,938; 4,020,322; and 3,776,127. In addition, smokers that are designed as an added feature to a grill assembly are disclosed in U.S. Pat. Nos. 5,891,498; 5,718,165; 5,167,183; and 4,770,157. In addition, the prior art discloses a variety of apparatus for generating smoke and conveying the smoke to the food being smoked including U.S. Pat. Nos. 4,321,857; 6,209,533; and 5,138,939. 
         [0004]    The smoking process is generally carried out at low to moderate temperatures over an extended period of time. For example, the internal temperature of the smoker is generally about 220° F.-230° F. At such temperatures, the smoking process generally takes about six hours. One smoking method, the 3-2-1 method, is often employed to smoke meat. For the first three hours, the meat is left uncovered on the smoker&#39;s grill rack so that the meat is surrounded by the smoke and thereby absorbs the smoke flavor from the heated wood chips. For the next two hours, the meat is wrapped in aluminum foil in order to steam and tenderize the meat. For the last hour, the meat is again left uncovered. The smoking process may also include basting the meat as the juices from the meat are caught in the drip pan and reapplied to the meat to keep the meat moist. In addition, the juices caught in the drip pan vaporize to maintain a moist atmosphere within the smoker cabinet thereby keeping the meat hydrated. The water pan also holds water or other flavor imparting liquids which, in conjunction with the heat source, add moisture to the atmosphere inside the smoker. 
         [0005]    During the smoking a process, the internal temperature of the meat slowly rises, as a result of the heat created by the heat source at the bottom of the smoker, until the internal temperature of the meat reaches at least a safe level for consumption or to a higher level to suit the taste of the user. 
         [0006]    Maintaining a constant set temperature in a smoker is important to ensure consistent results during the extended smoking process. Maintaining a constant temperature is affected by several factors including changes in atmospheric conditions outside of the smoker such as the presence of wind or rain, the temperature variation created by the introduction of the food products such as meat into the smoker, and the opening and closing of the door of the smoker to baste the meat, to add smoke generating material to the tray, or to check on the progress of the smoking process. 
         [0007]    For gas-fired smokers, controlling the internal temperature of the smoker cabinet within an acceptable range of variation is more difficult than controlling the temperature of an electric smoker. Several considerations are present when controlling the internal temperature of a gas-fired smoker. The control system for a gas-fired smoker must react quickly to changes in internal temperature of the smoker cabinet to maintain a relatively constant temperature while conserving gas, particularly when the smokers are used at a remote location. Consequently, the gas-fired smoker should relieve the user from constantly adjusting the temperature of the smoker cabinet as the environment around the gas-fired smoker changes over the extended duration of the smoking process. 
         [0008]    In addition, the gas-fired smoker should have the capability of terminating the smoking process either after a pre-determined time period has elapsed or when the internal temperature of the food product reaches a pre-determined internal temperature. 
         [0009]    Because of the smoker is gas-fired, safety measures should be implemented to ensure that gas cannot build up in or around the smoker and create a fire or explosion hazard. 
       SUMMARY OF THE INVENTION 
       [0010]    The gas-fired smoker of the present invention has a digital control system that controls the internal temperature of the cabinet of the gas-fired smoker within an acceptable temperature range. The gas-fired smoker of the present invention also terminates the smoking process either at the end of a predetermined time or when the internal temperature of the food product reaches a predetermined internal temperature. The gas-fired smoker of the present invention further employs a safety mechanism to ensure that gas cannot build up in the cabinet of the smoker thereby leading to a fire or explosion hazard. 
         [0011]    In a first embodiment of a gas-fired smoker of the present invention, the stand-alone gas-fired smoker includes a control circuit with a controller. The controller controls the startup, operation, and shutdown of the stand-alone gas smoker. The gas burner is lit by means of a gas pilot light. The pilot light is initially ignited either by means of a piezo igniter or an electronic spark device. The controller cycles the gas burner on and off by opening and closing a gas solenoid valve between the gas source and the gas burner in order to maintain a preset cooking temperature within the cabinet of the smoker. The control circuit includes a display and input panel for displaying the status of the operation of the gas-fired smoker and for accepting user input, a timer set module for setting the cooking time for the gas-fired smoker, a cabinet temperature set module for setting the temperature inside the smoker cabinet, a temperature sensor for determining the temperature inside the cabinet, a probe temperature set module for setting the final internal temperature for the food, particularly meat, and a food probe for determining the internal temperature of the food. The cabinet temperature sensor is located in the cabinet at a position that accurately reflects the average temperature within the cabinet. 
         [0012]    In a second embodiment of a gas-fired smoker in accordance with the present invention, the gas-fired smoker has a digital control circuit with a controller that controls the startup, operation, and shutdown of the stand-alone gas smoker. The second embodiment of the gas-fired smoker is similar to the first embodiment of the gas-fired smoker except the control circuit of the second embodiment includes a rechargeable battery for powering the control circuit and means for recharging the battery. In order to maintain the rechargeable battery over an extended period of time during the smoking process, the second embodiment gas-fired smoker of the present invention includes a thermal electric generator, such as a Seebeck thermal electric generator, to convert the heat from the gas-fired smoker into electric current to recharge the battery for the control circuit including the electric igniter. The Seebeck thermal electric generator also can provide current for an external USB port, for lighting, and for charging electronic devices such as cell phones, tablets, or MP 3  players. 
         [0013]    Further objects, features and advantages will become apparent upon consideration of the following detailed description of the invention when taken in conjunction with the drawings and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a front perspective view of a stand-alone gas smoker in accordance with the present invention. 
           [0015]      FIG. 2A  is a front elevation view of the stand-alone gas smoker in accordance with the present invention and with the doors and the burner control mechanism panel removed to reveal internal detail of the smoker cabinet and the gas burner control mechanism. 
           [0016]      FIG. 2B  is an enlarged front elevation view of the gas burner control mechanism of the stand-alone gas smoker in accordance with the present invention. 
           [0017]      FIG. 2C  is an enlarged back elevation view of the gas burner control mechanism of the stand-alone gas smoker in accordance with the present invention. 
           [0018]      FIG. 3  is a right side elevation view of the stand-alone gas smoker in accordance with the present invention. 
           [0019]      FIG. 4  is a back elevation view of the stand-alone gas smoker in accordance with the present invention. 
           [0020]      FIG. 5  is a left side elevation view of the stand-alone gas smoker in accordance with the present invention. 
           [0021]      FIG. 6  is a top plan view of the stand-alone gas smoker in accordance with the present invention. 
           [0022]      FIG. 7  is a bottom plan view of the stand-alone gas smoker in accordance with the present invention and with the heat shield and burner bracket removed to reveal internal detail of the gas burner control mechanism. 
           [0023]      FIG. 8  is a schematic diagram of a control circuit for a first embodiment of a stand-alone gas smoker in accordance with the present invention. 
           [0024]      FIG. 9  is a flowchart showing the operation of the control circuit for the first embodiment of the stand-alone gas smoker in accordance with the present invention. 
           [0025]      FIG. 10  is a schematic diagram of a control circuit for a second embodiment of a stand-alone gas smoker in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0026]      FIGS. 1-7  illustrate a stand-alone gas smoker  10  having control features in accordance with the present invention. The stand-alone gas smoker  10  includes a cabinet  12  mounted on legs  14 . The cabinet  12  has a top  2 , a bottom  3 , a back  4 , and sides  5 . An upper front door  15  provides access to the interior of the cabinet  12  where food to be cooked is supported on vertically spaced grill racks  17 . The food in the smoker  10  is heated and slowly cooked by heat from a gas burner  20  located near the bottom  3  of the smoker  10 . The gas burner  20  is connected to a source (tank)  18  of flammable gas through a burner control mechanism  100  that includes a gas solenoid valve  22  that controls the on/off flow of gas to the gas burner  20  during the smoking process. 
         [0027]    The stand-alone gas smoker  10  has a wood tray  24  that holds woodchips that, when heated by the gas burner  20 , produce smoke to impart a smoked flavor to the food within the cabinet  12  as the food is slowly cooked. In addition, the gas smoker  10  may include a drip pan  28  adjacent the bottom  3  of the cabinet  12  to catch drippings from the food. A liquid pan  26  adjacent the gas burner  20  is filled with liquid that may include water or other flavor imparting liquids. As the liquid in the liquid pan  26  is heated, the resulting liquid vapor serves to impart additional flavoring to the food and to maintain a moist atmosphere inside the cabinet  12  and thus keeps the food from drying out during the slow cooking process. A lower front door  16  provides access to the wood tray  24 , the liquid pan  26 , the drip pan  28 , and the gas burner  20 . The wood tray  24  is attached to the inside of the lower front door  16  and swings outwardly with the lower front door  16  for easy access to replenish the smoke producing material. A heat shield  19  is located below the burner control mechanism  100 . 
         [0028]    With reference to  FIGS. 2A, 2B, and 3C , the burner control mechanism  100 , located behind burner control mechanism panel  13 , includes an igniter  34 , a flame sensor  36  with male connector  112 , a gas solenoid valve  22 , a gas inlet  104 , a gas outlet  102 , a pilot light connection  106 , a normally closed safety/ignition valve  114 , and a control knob (stem)  21 . The gas source  18  is connected through the manual control valve  23  to the gas inlet  104  of the burner control mechanism  100  by means of a flexible conduit (not shown). The gas inlet  104  connects the gas to the normally closed safety/ignition valve  114 . When the safety/ignition valve  114  is open, gas flows to the pilot light  35  through the pilot light connection  106  and is also connected to the gas solenoid valve  22 . When the gas solenoid valve  22  is opened, the gas can flow through the gas solenoid valve  22  to the gas outlet  102 . The gas outlet  102  is connected to the burner tube  82  which in turn conducts the gas to the burner  20 . The male sensor connector  112  is connected to the safety/ignition valve  114  through female sensor connector  108 . The igniter  34  is either a piezo igniter that creates an ignition spark by mechanical force applied to the piezo crystal or the igniter  34  may be an electronically controlled spark device. 
         [0029]    The thermocouple temperature sensor  36  determines if the pilot light  35  is lit or not. 
         [0030]    When the pilot light  35  is lit, the thermocouple temperature sensor  36  sends a pilot light signal to the safety/ignition valve  114  indicating that the pilot light  35  is lit. As long as the pilot light signal persists, the safety/ignition valve  114  remains open, and gas is delivered to the pilot light  35  through the pilot light connection  106 . If the pilot light  35  goes out, the pilot light signal from the thermocouple temperature sensor  36  ceases, and the safety/ignition valve  114  reverts to its normally closed condition thereby including gas flow from the gas source  18  to the pilot light  35  and to the gas burner  20 . Consequently, gas cannot build up inside the cabinet  12  thereby creating a fire and explosion hazard. 
         [0031]    With reference to  FIG. 8 , a first embodiment of the stand-alone gas smoker  10  has a control circuit  8  that includes a controller  30 . The controller  30  controls the startup, operation, and shutdown of the stand-alone gas smoker  10 . Particularly, the controller  30  cycles the gas burner  20  on and off in order to maintain a preset cooking temperature within an acceptable range within the cabinet  12 . The control circuit  8  also includes a direct current (DC) power source  32 , a display and input panel  42  for displaying the status of the operation of the smoker  10  and for accommodating user input, a cabinet temperature sensor  38  for determining the temperature inside the cabinet  12 , a probe temperature sensor  90  for determining the internal temperature of the food being cooked, a timer set module  74  for setting the cooking time for the smoker  10 , a probe temperature set module  86  for setting the internal temperature of the food product based on the user&#39;s preference for the cooked food, a display control relay  46  for powering the display and input panel  42 , and a burner control relay  44  for cycling the gas burner  20  on and off. 
         [0032]    The control circuit  8  is powered by the DC power source  32  with a positive terminal  60  and a negative terminal  62 . An on-off switch  52  connects the power source  32  to the control circuit  8 . The DC power source  32  may comprise standard batteries, a rechargeable battery pack, an alternating current (AC) converter, or a universal serial bus (USB) connection. 
         [0033]    With respect to the controller  30 , positive voltage from the power source  32  is connected to the controller  30  on controller input  68 , and negative voltage from the power source  32  is connected to the controller  30  on controller input  70 . Inputs to the controller  30  include a cabinet temperature set input  96  from a cabinet temperature set module  94 , a cabinet temperature sensor input  72  from a cabinet temperature sensor  38 , a probe temperature set input  88  from a probe temperature set module  86 , a probe temperature sensor input  92  from a probe temperature sensor  90 , and a timer set input  76  from a timer set module  74 . Outputs from the controller  30  include a burner control output  54 , a display control output  56 , and a display data output  58 . The cabinet temperature set module  94 , the probe temperature set module  86 , and the timer set module  74  are connected to the display and input panel  42  in order to accommodate user input. 
         [0034]    In order to set the cabinet cooking temperature, normally 220° F.-230° F., the user, using the display and input panel  42 , selects the cabinet temperature in that range by means of the cabinet temperature set module  94 . The controller  30  receives an electrical signal from the cabinet temperature set module  94  on cabinet temperature set input  96  thereby setting the cooking temperature for the cabinet  12 . The controller  30  receives an electrical signal from the cabinet temperature sensor  38  on the cabinet temperature sensor input  72  indicative of the temperature in the cabinet  12 . Based on comparing the cabinet temperature to the cabinet set temperature, the controller  30  cycles the gas burner  20  on and off to maintain a cabinet temperature within an acceptable range including the temperature value set by the user. 
         [0035]    In order to maintain that temperature in the cabinet  12  within an acceptable range of temperature, the cabinet temperature sensor  38  is located in the cabinet at a position where the sensed temperature reflects the average temperature within the cabinet  12 . The cabinet  12  has a range of internal temperatures within the volume defined by the cabinet  12 . In order to ensure consistent temperature sensing by the cabinet temperature sensor  38 , the position of the average cabinet temperature is determined empirically for the cabinet  12  by positioning temperature sensors throughout the cabinet  12  and finding the location that accurately reflects the average of all of the temperatures found in the cabinet  12 . Once the average temperature position has been determined, the temperature sensor  38  is placed at that location inside the cabinet  12 . 
         [0036]    The controller  30  controls the duration of the smoking process in two ways. In a probe temperature mode, the user, using the display and input panel  42 , selects the internal temperature for the food product relating to the user&#39;s preference. Based on that input from the user, the probe temperature set module  86  sends an electrical signal proportional to that selected temperature on probe temperature set input  88  to the controller  30 . The controller  30  receives the electrical signal from the probe temperature set module  86  on the probe temperature set input  88  corresponding to a temperature selected by the user for the final internal temperature of the food product based on the user&#39;s preference. The controller  30  receives an electrical signal from the probe temperature sensor  90  on probe temperature sensor input  92  indicative of the internal temperature of the food product being cooked and displays that sensed temperature on the display and input panel  42 . Once the internal temperature of the food product reaches the value of the temperature set by the user using the probe temperature set module  86 , the controller  30  terminates the smoking process by closing the gas solenoid valve  22  to extinguish the gas burner  20 . 
         [0037]    Alternatively, in a time mode, the controller  30  controls the duration of the cooking process based on elapsed time. In the time mode, the user, using the display and input panel  42  selects the time required to cook the food products to the user&#39;s taste. Based on that input from the user, the time set module  74  sends an electrical signal proportional to that selected time on time set input  76  to the controller  30 . The controller  30  receives the electrical signal from the timer set module  74  indicative of a time value entered by the user for the duration of the cooking process. The timer set module  74  can either allow the user to manually set a time value for the duration of the cooking process, or the time set module  74  can determine a time value for the duration of the cooking process by using the computational capability of the controller  30 . Particularly, cooking process inputs, such as the kind of food (beef, pork, poultry, etc.), the weight of the food, and the user preference (rare, medium, well done, etc.), can be entered by means of the display and input panel  42  and the time set module  74 . Based on the input from time set module  74 , the controller  30  can determine the time duration for the cooking process based on the selected cabinet temperature. The determination of the cooking time made by the controller  30  is based on empirically derived lookup tables that include, among others, the parameters listed above, namely kind of food, weight of the food, user preference, and cabinet temperature. Once the cooking time set by the timer set module  74  has elapsed, the controller  30  terminates the cooking process by closing the gas solenoid valve  22  and thereby extinguishing the gas burner  20 . 
         [0038]    During the smoking process, the controller  30  controls the gas burner  20  and the display and input panel  42  in accordance with the method illustrated by the flowchart shown in 
         [0039]      FIG. 9 . An output signal on the burner control output  54  from the controller  30  turns on transistor  48 , which in turn energizes the relay coil  44 . The relay coil  44  operates the relay contacts R 1 . The relay contacts R 1 , when operated by the relay coil  44 , open the gas solenoid valve  22  allowing gas to flow from the gas source  18  through gas line  84  and a burner tube  82  to the burner  20 . The pilot light  35  then lights the gas at the gas burner  20 . 
         [0040]    An output signal on display control output  56  of the controller  30  turns on transistor  50 , which in turn energizes the relay coil  46 . The relay coil  46  operates the relay contacts R 2 , and the closed contacts R 2  energize the display and input panel  42 . The display on the display and input panel  42  is controlled by data transmitted from the controller  30  to the display and input panel  42  from display data output  58 . The data transmitted from the controller  30  to the display and input panel  42  may display, for example, the cabinet temperature, the status of the gas burner  20 , the status of the pilot light  35 , the amount of flammable gas in the gas source  18 , the status of the DC power source, the amount of time elapsed since the beginning of the cooking process, the amount of time remaining in the cooking process, and the internal temperature of the food product measured by the probe temperature sensor  90 . 
         [0041]      FIG. 9  illustrates the operating method  900  for the control circuit  8  ( FIG. 8 ). The operating method  900  begins at step  901  and proceeds to step  902  where the user opens the manual gas valve  23  ( FIGS. 1, 2, 3, 4, and 6 ) on the gas source  18 . At step  904 , user lights the pilot light  35  by pushing in the control knob  23  and turning the control knob  23  to the pilot position. Gas from the gas source  18  flows through the safety/ignition valve  114 , through the pilot light connection  106 , and to the pilot light  35 . The igniter  34  ignites the gas at the pilot light  35 . The user holds the gas control knob  23  in the pilot position until the thermocouple flame sensor  36  is sufficiently heated by the pilot light  35  to maintain gas flow through the safety/ignition valve  114  to the pilot light  35 . With the pilot light  35  lit, at step  906 , the user turns the control knob  23  from the pilot position to the on position, which in turn closes switch  52  and connects power to the controller  30  and allows gas to enter to the closed solenoid valve  22 . 
         [0042]    At subsequent step  908 , the user sets the cooking time for the stand-alone gas smoker  10  by means of the display and input panel  42  and the time set module  74 . Alternatively, at step  909 , the user sets the probe temperature, by means of the display and input panel  42  and the set probe temperature set module  86 , to a value relating to the user&#39;s preference for the internal temperature of the food product when done. At step  910 , the user sets the temperature for the cabinet  12  by means of the display and input panel  42  and the cabinet temperature set module  94 . 
         [0043]    From step  910 , the method moves to step  912  where the solenoid gas valve  22  is opened by the R 1  contacts, and gas flows to the gas burner  20 . At step  914 , the pilot light  35  lights the gas burner  20 . 
         [0044]    From step  914 , the method moves to decision step  916 . At decision step  916 , the method determines if the cabinet  12  has reached the set cabin temperature (set at step  910 ) based on information provided by the cabinet temperature sensor  38 . If the cabinet temperature has not reached the set temperature, the method then follows the “no” branch and cycles back to decision step  916 . If, on the other hand, the temperature in the cabinet has reached the set temperature (set at step  910 ), the method follows the “yes” branch to step  818  where the solenoid gas valve  22  is closed thus extinguishing the burner  20  but leaving the pilot light  35  burning. 
         [0045]    From step  918  the method proceeds to decision step  920 . At decision step  920 , the controller  30  determines if the temperature in the cabinet  12  has dropped to a predetermined low threshold temperature requiring restart of the burner  20 . The low threshold temperature is a temperature value preprogrammed into the controller  30  and relates to the cabinet temperature set by the user. If the cabinet temperature has not dropped to the low threshold temperature, the method then follows the “no” branch and cycles back to decision step  920 . Once the temperature in the cabinet  12  has dropped to the low threshold temperature, the method follows the “yes” branch to decision step  922 . 
         [0046]    At decision step  922 , the method determines if the control knob  21  has been set to off by the user. If the control knob  21  has been set to off, the method follows the “yes” branch to step  926  where the control sequence ends with the gas burner  20  turned off. If on the other hand the control knob and  21  has not been set to off, the method follows the “no” branch to decision step  924 . 
         [0047]    At decision step  924 , the controller  30  determines if the time set at step  908  has expired. If the time has expired, the method follows the “yes” branch, and the method ends at step  926 . If the other hand the time has not expired, the method follows the “no” branch from step  924  to decision step  928 . At decision step  928 , the method determines whether the set probe temperature (set at step  909 ) has been reached. If the set probe temperature has been reached, the method follows the “yes” branch and ends at step  926 . If on the other hand, the set probe temperature has not been reached at step  928 , the method follows the “no” branch to step  912 . At step  912 , the controller  30 , via a signal on the burner control output  54 , opens the gas valve  22  in order to relight the burner  20  to bring the cabinet  12  back up to the set temperature (set at step  910 ). 
         [0048]      FIG. 10  illustrates a second embodiment of the invention having a control circuit  108  for the gas-fired gas smoker  10 . In  FIG. 10 , the same reference numerals refer to the same parts that are used with the control circuit  8  shown in  FIG. 8 . The control circuit control circuit  108  is the same as control circuit  8  of  FIG. 8  except for the inclusion of a thermal electric generator  40 . The thermal electric generator  40  is implemented by a Seebeck thermal electric generator. The thermal electric generator  40  charges the rechargeable battery pack of the DC power source  32  and provides power for auxiliary lighting or for recharging electronic devices. 
         [0049]    Particularly, the Seebeck thermal electric generator  40  has a positive terminal  64  and a negative terminal  66 . The Seebeck thermal electric generator  40  converts the heat of the gas-fired smoker  10  into electric energy at the terminals  64  and  66 . The positive terminal  64  and the negative terminal  66  of the Seebeck thermal electric generator  40  are connected through the controller  30  to the rechargeable battery pack of the power source  32 . The controller  30  controls the delivery of electric energy from the Seebeck thermal electric generator  40  to the rechargeable battery to protect against overcharging the rechargeable battery of the power source  32  and to regulate the power available for auxiliary lighting and for other electronic devices. 
         [0050]    While this invention has been described with reference to preferred embodiments thereof, it is to be understood that variations and modifications can be affected within the spirit and scope of the invention as described herein and as described in the appended claims.