Abstract:
An automatic temperature control device for solid fuel fired food cooker fueled by wood, charcoal, or other solid fuels which is capable of operation with any type of cooker without utilization of different sized blowers and conserves solid fuel usage. The present invention serves to regulate cooking temperature by controlling or optimizing the amount of combustion air reaching the fuel. The present invention also allows an outdoor barbecue grill or smoker of any reasonable size to be retrofitted with the invention in order to allow a chef to cook foods at stable and precise temperatures. The core components of the invention are an air blower to provide combustion air to the burning fuel, an electronic controller to control the amount of air delivered by the air blower via a unique algorithm embedded within the electronic controller, a temperature sensor to sense the temperature inside of the cooker in the vicinity of the cooking food and provide feedback to the electronic controller, and an air tube and air manifold to get or direct the combustion air from the air blower inside the blower box to the burning fuel inside the cooker. Alternative embodiments utilize an automatic damper connected with said electronic controller whereby convection air currents may be precisely controlled.

Description:
This application claims priority of U.S. Provisional Patent Application No. 61/399,971, filed Jul. 20, 2010, entitled Automatic Temperature Control Device for Solid Fuel Fired Food Cooker. 
    
    
     BACKGROUND OF THE INVENTION 
     The art of the present invention relates to temperature controllers for fuel fired cooking equipment in general and more particularly to an apparatus and method of use which automatically controls the air feeding the fuel (typically charcoal or wood) of a barbeque grill, smoker, or cooker and which is easily installed upon commercially available equipment without modification. 
     Currently there are a number or plurality of prior art solutions for automatically controlling the cooking temperature of a solid fueled food cooker. These inventions or prior art attempts to provide a solution that is easy to use, fail to meet the needs of the marketplace because they are difficult to configure and to connect to the cooker and because of their increased cost. Primarily, this is because they are composed of independent components that must be connected together during installation. Specifically, these prior art systems are composed of physically separated components that must be attached and/or connected by the user. These components include the air blower assembly, the cooker adapter, the electronic controller, and the cooking temperature probe. In using said prior art solutions, the user attaches the cooker adapter directly to the cooker with tools such as wrenches, screwdrivers, or other specialty tools. The prior art air blower assembly, consisting of an air blower and a housing, is then attached to the cooker adapter, again typically using tools. The air blower assembly power cable is then connected to the electronic controller box that typically rests on the ground or on a table. The cooking temperature sensor cable is then plugged into the electronic controller box and the cable is routed into the cooker under the cooker&#39;s lid or through a door, often causing physical abrasion, pinching, and mechanical stresses on the wires inside the cable. In addition, these systems require the user to select both a cooker adapter and an air blower assembly that is sized specifically for a single cooker size. The prior art user-chosen air blower (which is commercially available) is not modulated with a variable voltage to control its speed between full off and full on, thus a specific air blower size is required for a specific cooker size. When the user moves the prior art controller solution or system to another cooker, it is commonly required that the user purchase both a different size air blower assembly and a different cooker adapter. Additionally, no means or apparatus is provided to hang the electronic controller from handles present on the cooker nor is an internal battery pack offered for these solutions. Also, the increased complexity of these prior art solutions unnecessarily increases both the user&#39;s time required to attach and to connect them to a cooker as well as the system cost. 
     The present invention provides a self contained blower and blower controller which attaches with a cooker, grill, or smoker via a flexible hose, measures the ambient air temperature within the cooker, and adjusts the air flow into the cooker via a unique algorithm, all in a compact device which may be easily hung onto the cooker. The present art may be installed upon commercially available cookers without the requirement of specialty tools. The unique algorithmic control allows for a minimal use of fuel (typically charcoal or wood) to provide optimum cooking thereby minimizing energy consumption and also adaptively learns the thermal mass parameters of the cooker in order to meet the desired temperature quickly with a minimum of overshoot. 
     The present art provides stable and precise temperature control of a wood or charcoal fired barbecue grill or smoker. It also easily attaches to a cooker already in the possession of the user without modification. The preferred embodiment present art apparatus is a single assembly which attaches to the user&#39;s cooker without the use of any tools. The present art is also simpler, easily configured, and of a lower cost than other solutions in the marketplace which allows owners of low cost food cookers to retrofit their cooker with automatic temperature control. 
     Accordingly, it is an object of the present invention to provide an automatic temperature control device for solid fuel fired food cooker representing an apparatus and method of use which provides the necessary air for combustion to the solid fuel in a self contained compact unit which may be quickly adapted to any cooker without the requirement of specialty tools and that does not suffer from any of the problems or deficiencies associated with prior art solutions. 
     Another object of the present invention is to provide an automatic temperature control device and method of use for barbecue grills and smokers that is easily installed on the user&#39;s grill or smoker in under one minute without the use of any tools, is simple to understand, does not require the user to select a specific separate air blower, and does not require the user to select a specific cooker adapter to mount the air blower to the cooker. 
     Another object of the present invention is to provide an automatic temperature control device for solid fuel fired food cooker representing an apparatus and method of use which adaptively senses or measures the thermal parameters of the cooker and adjusts the airflow of combustion to rapidly and precisely meet the set temperature with a minimum of overshoot. 
     A further object of the present invention is to provide an automatic temperature control device for solid fuel fired food cooker representing an apparatus and method of use which utilizes a blower time proportioning algorithm and/or a blower speed control algorithm in conjunction with a take back half proportional integral derivative (PID) algorithm in order to optimally meet the desired cooking environment temperature. 
     A yet further object of the present invention is to provide an automatic temperature control device for solid fuel fired food cooker representing an apparatus and method of use which utilizes an automatic or manual damper system to allow control of naturally occurring convection currents. 
     A still further object of the present invention to provide an automatic temperature control device and method of use for barbecue grills and smokers that senses the combustion air volume requirements of the cooker and adjusts the air blower speed accordingly, thereby allowing a larger air blower to satisfy the combustion air requirements of both large and small cookers alike. 
     SUMMARY OF THE INVENTION 
     To accomplish the foregoing and other objects of this invention, there is provided an automatic temperature control device for solid fuel fired food cooker representing an apparatus and method of use having a micro-controller based electronic controller and blower in a single blower box housing, an air tube, an air manifold, a temperature sensor connected with said blower box via a cable, and a power supply. For an alternative embodiment, a damper is attached with an inlet of said blower box and automatically or manually controls the natural convection currents. The controller utilizes a take back half proportional integral derivative (PID) algorithm to control the blower speed, the blower on time, and the damper opening or closing. 
     The present invention advantageously fills the aforementioned deficiencies by providing an automatic temperature control device for a solid fuel fired food cooker which provides precise and stable temperature control for barbecue grills and smokers in an easy to use and low cost solution. 
     The present art represents an automatic temperature controller for solid fuel fired cookers, comprising a blower box, an air tube, an air manifold, a temperature sensor, a temperature sensor cable, and a power supply. In an alternative embodiment, a damper in the form of a rotary vane or other vent closing apparatus is attached with said blower box to allow more precise control of the air flow onto the solid fuel. The blower box contains an air blower and an electronic controller that both controls operation of the air blower and interprets the electrical signal from the temperature sensor. The air tube delivers air from the blower box to the air manifold. The air manifold attaches to the food cooker to inject combustion air delivered by the air tube into the food cooker. The electronic controller uses the measured cooking temperature to adjust the instantaneous and average air which is forced into the air tube in order to adjust the temperature of the fire, all by modulating the voltage to the air blower. In a preferred embodiment, the electronic controller has a rotary control that protrudes though the blower box&#39;s enclosure. A knob with a pointer is attached to the protruding shaft of the rotary control. The desired cooking temperature is set by turning the knob&#39;s pointer to point at or in between a temperature number printed on the graphic overlay that is adhered to the face of the blower box. For the preferred embodiment, the electronic controller also provides a light emitting diode (LED) (or other light or visual indication) for visual feedback indicating if the cooking temperature is near the selected temperature, too cold, slightly hot, very hot, or if the controller has detected an error condition. For safety, the blower box has an air intake grate that prevents the user&#39;s fingers from touching moving parts inside. 
     The blower box connects to the temperature sensor via the temperature sensor cable. For an alternative embodiment of the present art, the temperature sensor cable is routed through the air tube and the air manifold into the food cooker. During utilization, the temperature sensor clip is preferably attached with the cooker in the vicinity of the food cooking area. The power supply connects to the blower box to provide electrical power. The flow of combustion air to the burning fuel is delivered by the blower box through the air tube and air manifold into the cooker and is modulated by the blower box to control the rate of fuel burn and thus the average temperature near the food area of the cooker. For the preferred embodiment, the blower box has a hanger that allows it to hang from the food cooker&#39;s handle or other extending elements of the cooker. 
     Alternative embodiments of the present art invention may also have one or more of the following: (1) standoffs attached to the back of the blower box to hold the device away from the cooker, (2) a magnetic attachment mechanism to mount the blower box to the cooker, (3) a water resistant version of the blower box; (4) a heat resistant version of the blower box, (5) a variable speed capability to automatically control the speed of the air blower to allow a more powerful air blower to be used and its speed adjusted automatically when the electronic controller senses that more or less air blower capacity is needed, (6) a temperature sensor inside the blower box to shut down the airflow when the blower box is too close to a surface that is too hot, (7) detection of excessive air blower motor current flow and subsequent shutdown of air flow, (8) a manual, passive, or microcontroller controlled active damper to prevent combustion air from being drawn through the system with the air blower off, (9) a character or graphic display for presentation of cooking variables and settings of cooking parameters, (10) discrete or membrane key switches for selection of cooking options and manipulation of cooking parameters, (11) a touch screen for selection of cooking options and manipulation of cooking parameters, (12) multiple discrete visual indicators (LEDs or other visual elements) for presentation of information, (13) an audible alarm for annunciation of alarm conditions, (14) a rigid or flexible air tube of any length and of any suitable material, (15) a wing bolt and toggle nut attachment method for attachment of the air manifold without the need for tools, (16) a magnetic attachment method for attachment of the air manifold without the need for tools, (17) a temperature sensor cable that can be detached at the air manifold to permit removal or replacement of the temperature sensor and its portion of the split temperature sensor cable, (18) an alternate connection point on the blower box for the temperature sensor cable, (19) a spring clip or hanger on the temperature sensor to secure it in the desired location, (20) an internal or external rechargeable or disposable battery pack to be used in addition to or in lieu of an external power source, and (21) an air manifold consisting of a curved metal plate with a hole designed to directly retain the air tube by surrounding the air tube&#39;s corrugations. 
     The present invention is unique when compared with other known devices and solutions as the present invention provides: (1) a single, interconnected, ready-to-use assembly right out of the box, (2) a solution that is simpler to understand because it does not require choosing a specific air blower size nor a specific cooker adapter for a specific cooker, (3) a tool free installation, (4) a much faster installation that can be completed in under one minute, (5) a system that attaches with a single wing bolt and toggle nut using only finger pressure, (6) the capability to hang the blower box from a cooker&#39;s handle, (7) lower cost through reduced complexity and fewer components, (8) lower cost through the use of a single housing for both the electronic controller and the air blower, (9) lower cost when moving the present invention to a different size cooker because a different size air blower does not need to be purchased, (10) easier movement of the present invention between different cookers as there is no need to change the air blower or the cooking adapter, and (11) adaptive control of the air flow via blower and damper control and a unique implementation of a specialized algorithm within the electronic temperature controller. 
     The present invention is unique in that it is structurally different from other known devices or solutions. More specifically, the present invention has structurally unique elements which include but are not limited to: (1) encasement of the electronic controller and air blower in a single housing, (2) the electronic controller is pre-wired or factory wired to the air blower, (3) the combustion air delivered into the cooker via the air tube/air manifold combination, (4) attachment of the air tube to the air manifold, (5) a large capacity air blower utilized for all applications and a plurality of cooker sizes, (6) the air blower electrical power being modulated with a variable duty cycle pulse width modulation (PWM) signal as well as time and damper control; (7) the air blower&#39;s speed being controlled continuously anywhere between full-off and full-on, (8) the air blower&#39;s speed being chosen by the electronic controller based on the rate of temperature rise (dT/dt) in the cooker, (9) the inclusion of a hanging mechanism to hang the blower box from the cooker&#39;s handle or other extremities, (10) the air manifold mounting hardware consisting of magnets or a single wing bolt with toggle nut, (11) the integrated design allows the system to arrive pre-assembled or factory assembled, and (12) the integration of a rechargeable battery pack to be used in addition to or in lieu of external power. 
     The art of the present invention may be manufactured from a variety of materials provided that said materials are able to withstand the heat and stresses applied during operation of the apparatus. Said materials include but are not limited to various metals and their alloys, woods, rubbers, plastics, or composites. For the preferred embodiment, the air tube is an ethylene propylene diene monomer (EPDM) rubber, the manifold is of a steel metal, and the temperature sensor is a resistive thermal device or resistance temperature detector (RTD), and the automatic temperature controller is based upon a PIC 16F616 micro-controller with associated interface circuitry. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Numerous other objects, features and advantages of the invention should now become apparent upon a reading of the detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a front perspective view of an automatic temperature control device for solid fuel fired food cooker hung with a kettle type cooker. 
         FIG. 2  is a front perspective view of an automatic temperature control device for solid fuel fired food cooker hung with a bullet type cooker, 
         FIG. 3  shows a front plan diagrammatic view of the overall automatic temperature control device not attached with a cooker. 
         FIG. 4  shows a front plan diagrammatic view of the blower box with the top cover removed allowing the air blower and electronic controller to be seen. 
         FIG. 5  shows a front plan diagrammatic view of a typical installation of the automatic temperature control device on a kettle style cooker. 
         FIG. 6  shows a front plan view of an automatic temperature control device for solid fuel fired food cooker having a manual damper in a fully open position. 
         FIG. 7  shows a front plan view of an automatic temperature control device for solid fuel fired food cooker having a manual damper in a partially open position. 
         FIG. 8  shows a front perspective view of an automatic temperature control device for solid fuel fired food cooker having an automatic damper in a partially open position. 
         FIG. 9  shows a schematic circuit diagram for the electronic controller of an automatic temperature control device for solid fuel fired food cooker showing a first embodiment for use with a two terminal air blower. 
         FIG. 10  shows a schematic circuit diagram for the electronic controller of an automatic temperature control device for solid fuel fired food cooker showing a second embodiment for use with a two terminal air blower. 
         FIG. 11  shows a schematic circuit diagram for the electronic controller of an automatic temperature control device for solid fuel fired food cooker showing a first embodiment for use with a four terminal air blower. 
         FIG. 12  shows a control loop block diagram for the electronic controller of an automatic temperature control device for solid fuel fired food cooker. 
     
    
    
     DETAILED DESCRIPTION 
     The preferred embodiment of the present art automatic temperature control device for solid fuel fired food cooker  30  comprises a blower box  2  having an electronic controller  18  within an inside, an air manifold  9  outside of said blower box  2 , an air tube  7  connecting the blower box  2  to the air manifold  9 , a cooking temperature sensor  5 , a cooking temperature sensor cable  6 , a cooking temperature sensor retaining clip  4 , and a power supply  14 . Alternative embodiments may utilize a wireless remote control module and one, two, or more food temperature sensing probes. 
     The blower box houses an air blower  19  that draws or ingests atmospheric air through a finger safe grate  3  and forces it into the air tube  7 . The air tube  7  passes into or onto the blower box housing and connects directly or indirectly with the air blower&#39;s discharge port  20 . The air tube  7 , which is preferably made of rubber and has corrugations to keep it from kinking when bent tightly, is preferably retained by the blower box  2  housing by gripping it between the first and second corrugations. Alternative embodiments may utilize a plurality of air tube  7  retention techniques including but not limited to nipples, adhesives, clamps, or integral molding. Alternative embodiments may also utilize a plurality of forms of air tubes  7 , including but not limited to flexible hoses, pipes, or heat resistant molded assemblies. 
     For the preferred embodiment, the air blower  19  receives its electrical power from the electronic controller  18  also housed in the blower box  2 . The electronic controller  18  varies the electrical power to the air blower  19  in order to control the instantaneous and average amount of air forced into the air tube  7 . For the preferred embodiment, the electrical power to the air blower  19  is controlled by pulse width modulating (PWM) its voltage between two direct current (DC) voltages. The modulation duty cycle varies continuously between 0%, which is completely off, and 100%, which is completely on, provided the blower  19  utilized will support a near 0% duty cycle. The modulation duty cycle is chosen by software algorithms in the electronic controller  18  with the goal of keeping the cooking temperature at the temperature set point and assuring that the air blower  19  has a sufficient duty cycle to begin operation. If the blower  19  will only support a duty cycle greater than near 0%, the minimum supported blower  19  duty cycle is utilized as the minimum blower  19  drive value. 
     The electronic controller  18  connects to the cooking temperature sensor  5  via the temperature sensor cable  6  in order to measure the cooking temperature. The electronic controller  18  uses the measured cooking temperature to adjust the instantaneous and average air amount or volume forced into the air tube  7  in order to adjust the temperature of the burning solid fuel by modulating the voltage to the air blower  19 . The preferred embodiment of the electronic controller  18  has a status LED  10  (or other indicator light) and a rotary temperature selection knob  11  for temperature control. For the preferred embodiment, the LED  10  is visible through the blower box&#39;s enclosure, is bicolored red and green (based upon bias direction), and represents the following: 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 LED COLOR 
                 MEANING 
               
               
                   
                   
               
             
             
               
                   
                 Flashing Green 
                 Actual temp 10° F. or more below 
               
               
                   
                   
                 temperature set point 
               
               
                   
                 Solid Green 
                 Actual temp within 10° F. of set temp 
               
               
                   
                   
                 (i.e. close to said temperature set point) 
               
               
                   
                 Alternating 
                 Multiple meanings: 
               
               
                   
                 Red/Green 
                 1) lid off delay in effect 
               
               
                   
                   
                 2) blower box overheated 
               
               
                   
                   
                 3) temperature probe failure (short or 
               
               
                   
                   
                 open circuit) 
               
               
                   
                 Solid Red 
                 Actual temp 10° F. or more over set 
               
               
                   
                   
                 temp 
               
               
                   
                 Flashing Red 
                 Actual temp 50° F. or more over 
               
               
                   
                   
                 temperature set point 
               
               
                   
                   
               
             
          
         
       
     
     Alternative embodiments may utilize various types of user interfaces, including but not limited to, the most sophisticated of which consists of a graphic liquid crystal display (LCD), four membrane key switches, and five light emitting diodes (LEDs) which are visible through the blower box&#39;s enclosure. Said membrane key switches are integrated into the graphic overlay  12  that is adhered to the face of the blower box  2 . Numerous cooking variables and parameters, the most obvious of which are the desired and actual cooking temperatures, are viewable or modifiable through this alternative user interface. The LEDs convey system status including: too cool; too warm; at desired temperature; error condition present; and battery charging status. Further alternative embodiments allow the electronic controller  18  to also connect to two food temperature probes through jacks mounted to the blower box  2  housing. The food temperature probes are used to view the food temperature through the user interface and also to automatically adjust the cooking temperature at preset food temperatures. 
     For the preferred embodiment, the air manifold  9  attaches to the user&#39;s cooker  21  at points on the cooker  21  designed for the ingestion of combustion air. For the preferred embodiment, the air manifold  9  is a cup shaped element having an exiting hose barb  8  or equivalent member to attach the air tube  7 . Alternative embodiments may utilize manifolds  9  which are bowl, rectangular, or plate shaped or simply represent a ball valve, pipe, or hose barb type element which exits or is attached with the cooker  21 . For the preferred embodiment, the method of attachment consists of a threaded bolt  15  with a fixed wing head (wing bolt)  15  on the end of the bolt  15  that is visible on the outside of the air manifold  9 . The end of the wing bolt  15  is visible from the inside of the air manifold  9  and is screwed or threaded into a folding toggle nut  16 . During installation, the air manifold  9  is mounted to the user&#39;s cooker  21  by folding the toggle nut  16 , pushing it though an existing air intake hole on the cooker  21 , allowing the toggle nut  16  to unfold, and then turning the wing bolt  15  with finger pressure until the air manifold&#39;s  9  edges are held tightly against the cooker  21 . The closed end of the air manifold  9 , i.e., the end that does not attach to the cooker, preferably has a hose barb  8  mounted to it which is designed to retain the air tube  7 . Alternative embodiments may mount said manifold  9  in a plurality of ways, including but not limited to adhesives, screws, pins, magnets, wire, or hooks. 
     For the preferred embodiment, the air tube  7  is a rubber corrugated tube that connects the blower box  2  to the air manifold  9 . Its primary purpose is to channel the air forced into it by the air blower  19  into the cooker  21  through the air manifold  9 . It is corrugated in an annular fashion to both allow mechanical retention by the blower box  2  enclosure and to prevent it from kinking as it is bent. An alternative embodiment also utilizes the air tube  7  in order to pass the temperature sensor cable  6  from the inside of the blower box  2  through the air manifold  9  and into the cooker  21 . For said alternative embodiment, the cooking temperature sensor cable  6  is split in the interior of the air manifold  9  to permit attachment of mating electrical connectors. This allows the portion of the temperature sensor cable  6  that enters the cooker, that portion with the temperature sensor  5  attached to it, to be replaced as necessary or to be removed for convenience. The preferred embodiment simply places the cooking temperature sensor  5  and cable  6  between a lid and body of the cooker  21 . 
     For the preferred embodiment, the portion of the temperature sensor cable  6  that enters the cooker  21  is designed to sustain the heat of the fire from a distance of three inches without damage. The cable  6  terminates into a metal housing that contains an electrical temperature sensing device or cooking temperature sensor  5 , preferably an RTD, although alternative embodiments may utilize thermocouples, thermistors, or other semiconductor type sensors. The metal housing is attached to a spring retaining clip  4  that allows it to be attached where the user desires inside the cooker  21 . The cooking temperature sensor  5  is represented on the schematics by the feed at connector J1, lines 5 &amp; 6 and represents the feedback signal for the PIC16F616. 
     For the preferred embodiment, the power supply  14  attaches to the blower box  2  with a jack  13  connected to the blower box&#39;s  2  housing. The power supply  14  supplies the electricity needed to run the present invention  30  while connected to an external power source. Additionally for alternative embodiments, the power supply  14  recharges a battery pack inside the blower box  2 . The battery pack powers the present invention  30  when it is desired to operate without an external power source or when the external power source is temporally interrupted. 
     An alternative embodiment of the electronic controller  18 , inside the blower box  2 , contains a wireless two-way communication radio capability designed to communicate with a remote radio module. The remote radio module is designed to both provide two-way communications with the blower box  2  and to provide communications with a computer. A computer program allows the user to interact with and control the system from their computer or from other computers connected to said computer through any network means. 
     In operation, the user connects the automatic temperature control device for solid fuel fired food cooker  30  system to their solid fuel cooker  21 , typically burning charcoal and/or wood, as described. The user next starts a fire burning in the cooker  21 , places the food to be cooked on the cooking grate, and then places the cooking temperature sensor  5  in or at the vicinity of the food to be cooked. For an alternative embodiment, the user then places one or two food temperature probes in the food being cooked. The cooker  21  is then closed and the desired cooking and food temperatures are programmed into the electronic controller  18  via the user interface. The electronic controller  18  operates the air blower  19  as necessary to maintain the desired cooking temperature up to the point where the desired food temperature is achieved. Cooking temperature is increased by forcing more air into the air tube  7  through increasing the electrical duty cycle to the air blower  19  and reduced by reducing the electrical duty cycle to the air blower  19 . When the desired food temperature is reached, the cooking temperature is automatically adjusted to a programmed level, typically lower to hold the food at a desired temperature without increasing it further. 
     The preferred embodiment of the electronic controller  18  has a rotary control  17  that protrudes though the blower box&#39;s  2  enclosure. A knob  11  with a pointer is attached to the protruding shaft of the rotary control  17 . The desired cooking temperature is set by turning the knob&#39;s pointer  11  to point at or in between a temperature number printed on the graphic overlay  12  that is adhered to the face of the blower box  2 . The rotary control  17  is represented by the potentiometer R8 on the schematic and the output of said potentiometer (which feeds the PIC16F616) represents the setpoint input for the PID control system. The electronic controller  18  also provides a light emitting diode (LED)  10  (or other visual indication) for visual feedback indicating if the cooking temperature is near the selected temperature, too cold, slightly hot, very hot, or if the controller  18  has detected an error condition as afore described. 
     Referring to the Figures,  FIG. 3  shows a front view of the overall device. It is shown how the handle  1  attaches to the blower box  2 , how the air tube  7  connects to the blower box  2 , and how the air manifold  9  connects to the air tube  7  via the hose barb  8 . Also shown is the cooking temperature sensor cable  6  and how it connects to the temperature sensor  5 , how it is routed through the air tube  7  and air manifold  9  for an alternative embodiment, and how the temperature sensor  5  connects to the temperature sensor spring clip  4 . Shown as well are the finger-safe grate  3 , the graphic overlay  12 , and the most basic of the electronic controller configurations consisting of a status LED  10  and a rotary temperature selection knob  11 . 
       FIG. 4  shows the blower box  2  with the top cover of the blower box  2  housing removed. Visible inside are the air blower  19 , the electronic controller  18 , and, for the alternative embodiment, the routing of the cooking temperature sensor cable  6  is out of the air tube  7  and to the electronic controller  18 . Also shown is how the enclosure is used to provide a method of securely holding the air tube  7  in place by surrounding the air tube  7  lesser diameter between its annular corrugations. 
       FIG. 5  shows the attachment of the device to a typical kettle style grill  21 . For an alternative embodiment and not explicitly shown, the cooking temperature sensor  5  and cable  6  are passed through an air hole in the bottom of the cooker  21 . The toggle nut  16  is folded and passed through an air hole, and the wing bolt  15  is turned hand tight until the air manifold  9  is held securely against the cooker  21 . The blower box&#39;s handle  1  is then placed over the cooker&#39;s handle  25 . Preferably said handle  1  is of a flexible inverted “U” shaped form connected with a portion of the blower box  2  whereby it may be placed onto or around a portion or extension of the cooker  21 . 
     The present art algorithmic control of airflow is based upon controlling the speed of the blower  19  and the amount of time said blower  19  is turned on within a fixed time window. As relating to this specification, varying the blower  19  speed or blower speed control (BSC), and controlling the time the blower  19  is on vs. the time the blower  19  is off is the blower time proportioning (BTP). The combination of BSC and BTP allows the average airflow from the blower  19  to be adjusted between 0% and 100%. For the preferred embodiment, a combination of BSC and BTP work in conjunction to produce the desired cooking temperature with a minimum of solid fuel usage. 
     Control of the average airflow from the blower  19  between 0% and 100% maximizes the ability of the control system (i.e. incorporated into the electronic controller  18 ) to regulate the temperature within the cooker  21 . Control of the speed of the blower  19  also allows a continuous airflow through the cooker  21  which allows the instantaneous and average airflow to remain the same. As understood within the arts, it is not possible to continuously adjust the speed of all blowers  19  from 0% to 100%. For some blowers  19 , it is only possible to continuously adjust the speed from some midpoint speed or flow to a full speed or flow while others allow only full on or full off speeds or flows. For the preferred embodiment, the speed or flow of the blower  19  can be reliably adjusted from 50% to 100% whereby the present art algorithmic control utilizes a combination of BSC/BTP control. Alternative embodiments of the present art may utilize a full BSC control algorithm, provided the blower  19  supports a full 0% to 100% control. This is especially true for a four terminal blower  19 . 
     For the preferred embodiment, during low cooker  21  air demands, the blower  19  is operated at its minimum allowed speed via pulse width modulation (PWM) of the blower  19  input drive potential at the blower  19  input terminals. For enablement purposes only and by no means a limitation, as seen in the schematic Figures, this is accomplished by gate modulation of the N-channel enhancement mode MOSFET labeled as Q4B by the electronic controller  18  via an output port on the PIC 16F616 micro-controller. Blower  19  speeds below the minimum allowed will result in erratic operation unless the blower  19  allows speed control for a near zero duty cycle drive potential. For the preferred embodiment, during a period of low air demand, the average airflow is controlled using BTP. For BTP, the average airflow is controlled by controlling the amount of time the blower  19  is operated in a fixed time window. For the preferred embodiment, the fixed time window is approximately 20 seconds but may comprise a plurality of time window sizes in alternative embodiments. For the preferred embodiment and by way of example only and not limitation, for a very low air demand, the blower  19  may be operate for 5 seconds out of the 20 seconds possible which provides a remnant off time of 15 seconds. Also for the preferred embodiment and by way of example only and not limitation, if slightly more airflow is required in order to regulate temperature, the blower  19  may be operated for 18 seconds out of the possible 20 with 2 seconds off. Again, during the BTP period, the blower  19  is operated at the minimum speed or flow allowed for the specific blower  19  utilized. 
     For the preferred embodiment, when the on time for the blower  19  increases to 20 seconds, meaning it is continuously on, and still more air is required to regulate temperature, then the blower  19  speed or air flow is increased utilizing BSC. In this mode, the blower  19  runs continuously and its speed is increased or decreased between 50% and 100% in an attempt to keep the cooking temperature stable. Again for the preferred embodiment with a blower  19  that is incapable of operating below a 50% speed or flow, when operating in BSC with the blower  19  speed dropping and reaching the 50% speed point, the control algorithm switches back to BTP. 
     For the preferred embodiment, the blower  19  speed or flow is controlled by adjusting the average voltage presented to its power terminals. As afore described, the system DC voltage is pulse width modulated (PWM) to control the average voltage as seen by the blower  19  power terminals. For the preferred embodiment, the PWM frequency is 20 kHz, and the duty cycle is varied between 50% and 100% with alternative embodiments utilizing PWM frequencies of any desired frequency capable of supporting PWM for the blower  19 . 
     An alternative embodiment of the present art utilizes a blower  19  having four terminals. In addition to the blower  19  power input terminals, a third terminal is provided to command the electronics contained within the blower  19  to operate the blower  19  at a specific speed. The third terminal is driven with the PWM signal and controls commutation of the blower  19 . Further alternative embodiments may utilize a third terminal speed control which relies upon a direct current value or digital input value. For the alternative embodiment, a fourth terminal is commonly provided to feed back the actual blower speed to the controller, so that the actual blower speed can be reliably controlled between 0% and 100%. 
     For the preferred embodiment, a computation of the average airflow command is based upon the present average airflow, the actual cooking temperature (typically sampled at 10-15 second intervals, with a plurality of other sample rates allowable), and the desired cooking temperature or set point. By way of example, if the actual cooking temperature is below that desired, then the commanded average airflow would be increased. In order to compute the airflow command, a modified proportional integral derivative (PID) control (as understood within the arts) is utilized with adaptive PID gain adjustments. The PID gains are adapted according to the speed of the cooker&#39;s response to airflow changes. By way of example, a smaller cooker  21  will have less thermal mass and will respond more quickly to airflow changes than will a larger cooker  21  with increased thermal mass. By modifying the PID gains (i.e. multiplier constants before the error term, integrated error term, and differentiated error term; the error term being the difference between the temperature selection knob  11  setpoint and the cooking temperature sensor  5  temperature), the control algorithm matches its reaction time to match that of the cooker  21 , minimizing undershoots, overshoots, and conserves the amount of solid fuel utilized. By way of example, when the cooker&#39;s response time is above a threshold, then the PID gains are modified or increased to speed up the PID&#39;s response time to match the cooker. The PID controller is seen in the block diagram control system  FIG. 12  drawing and represents three parallel paths there through which represent a linear path, an integrated path, and a differentiated path respectively which sum at the output and feed the PWM control of the PID electronic controller  18 . 
     For the preferred embodiment, a novel approach is employed to increase control loop robustness and to hasten the time the control algorithm settles in on the desired cooking temperature. A modified take-back-half (TBH) algorithm is used to modify the PID integrator variable. In operation, when the actual cooking temperature variable (i.e temperature equivalent) crosses through the desired cooking temperature, the integrator&#39;s memory variable is reset to the mathematical average of its present value and the previous value during the last time the actual temperature passed through the set point. That is, if the present value of the integrator output when the cooking temperature sensor reaches the setpoint on the temperature selection knob is represented by IV present  and the prior stored value of the integrator output when the cooking temperature sensor previously reached the setpoint on the temperature selection knob (i.e. the last time) is represented by IV prior  and the reset value of the integrator&#39;s memory variable is IV reset , the running output value of the PID integrator is reset to (i.e. current value replaced in memory) the value of: 
               IV   reset     =         IV   present     +     IV   prior       2           
The technique is used to ensure control loop convergence on the desired cooking temperature, even in the presence of marginal stability situations and further conserves or minimizes solid fuel usage. The aforesaid TBH-PID is used to compute an airflow command utilized by the electronic controller  18 . In practice, the airflow command is typically limited to be between 0% and 100%.
 
     For the preferred embodiment, upon computation of the desired airflow command, the electronic controller  18  converts the airflow command to the required BSC/BTP values. That is, once the control algorithm has computed the airflow command using the TBH-PID, it must be converted to actual BSC PWM values and BTP time-on values so that the average airflow from the blower can be adjusted to match that desired by the control algorithm. For the preferred embodiment, a look up table (LUT) is employed with alternative embodiments utilizing a plurality of conversion techniques including but not limited to a fixed constant, linear or nonlinear equation computations, or state variables. For enablement purposes only and by no means a limitation of the preferred embodiment LUT, the below table represents a LUT utilized for the present art. 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Airflow  
                   
                   
               
               
                   
                 Command 
                 BSC 
                 BTP 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                  0% 
                 50% 
                  0 s 
               
               
                   
                 10% 
                 50% 
                  4 s 
               
               
                   
                 20% 
                 50% 
                  8 s 
               
               
                   
                 30% 
                 50% 
                 12 s 
               
               
                   
                 40% 
                 50% 
                 16 s 
               
               
                   
                 50% 
                 50% 
                 20 s 
               
               
                   
                 60% 
                 60% 
                 20 s 
               
               
                   
                 70% 
                 70% 
                 20 s 
               
               
                   
                 80% 
                 80% 
                 20 s 
               
               
                   
                 90% 
                 90% 
                 20 s 
               
               
                   
                 100%  
                 100%  
                 20 s 
               
               
                   
                   
               
             
          
         
       
     
     For the preceding LUT, the airflow command is computed by the TBH-PID and is used to index the BSC and BTP values. The BSC value represents the average potential or voltage presented to the blower  19  power terminals, and the BTP represents the time the blower  19  is turned on within the afore described 20 second window. As understood within the arts, for both BSC and BTP, the average potential or voltage presented to the blower is construed, or effectively controlled or modified, as being an integral of potential value over shorter or longer periods of time. For a four terminal blower  19  having on-board electronics, the blower  19  on-board electronics linearize the airflow generated to the average voltage at its power terminals, but in other embodiments, the LUT can include or capture the desired linearization in order to implement a full BSC 0% to 100% control. 
     An alternative embodiment of the present art utilizes an automatic damper  22  control for optimal control of convection currents. In addition to the afore described control techniques, it is further possible to enhance control and temperature regulation with an automatic damper  22 . During the blower  19  off period in the BTP control mode, there exists a natural convection current that flows upwards in the cooker  21  causing a draft to flow into the blower box  2  and through the grate  3 , air tube  7 , and air manifold  9  and eventually into the cooker  21  acting as combustion air and feeding the solid fuel fire. This effect is undesirable and can be controlled with the damper  22 . 
     For this alternative embodiment, the damper  22  is preferably a rotary vane  23  type that blocks a portion or percentage of the blower  19  air intake grate  3 , thereby allowing unrestricted airflow, complete blocking of airflow, or a flow in between the aforesaid. Alternative embodiments may utilize a plurality of damper  22  configurations, including but not limited to iris types, shutter types, or register types and may further utilize a restriction or damper at the output of the air blower  19  or within the air tube  7  or at the air manifold  9 . For the alternative embodiment described, the electronic controller  18  utilizes the computed airflow command to position the automatic damper  22  to an appropriate position in order to keep the convection current at a manageable level. That is, if the blower  19  is off and the electronic controller  18  senses that the cooker  21  temperature is rising, i.e. via natural convection, it will close the damper  22  to a partially or eventually fully closed position. The controller  18  preferably positions the damper  22  using an attached electromechanical damper servo  24  such as found on radio controlled hobby cars and planes. The damper servo  24  is electrically connected with the electronic controller  18  and controlled thereby. Alternative embodiments may utilize servos  24  or damper  22  controls which take a plurality of forms, including but not limited to motors, linear motors, geared motors, electro-mechanical linear actuators, pneumatic actuators, or hydraulic actuators. By way of example only, when the airflow command is 50%, the automatic damper  22  would be set to 25% open in order to reduce convection currents during the blower  19  off time. The manual damper  22  shown in  FIGS. 6 &amp; 7  requires user closure to achieve the same results. That is, if the status LED  10  is solid or flashing red and the blower  19  is off, the user may close the damper  22  to minimize convection feed of the solid fuel. For this embodiment a tab  27  is attached with the rotary vane  23  and extends through a slot  26  in the face or front of the blower box  2  and the graphic overlay  12 . The user simply moves the tab  27  within the slot  26  in order to open or close the damper  22 . 
     Although described for enablement purposes, the electronic component part numbers or values, lengths, widths, geometric shapes, gains, constants, and other dimensional or parameter attributes may depart significantly from those specified. The shape, size, location, component numbers, mounting methods, and LUT values utilized for the components described may take a plurality of forms as recognized within the pertinent arts without departing from the scope and spirit of the present invention. 
     Having described the invention in detail, those skilled in the art will appreciate that modifications may be made to the invention and its method of use without departing from the spirit herein identified. Therefore, it is not intended that the scope of the invention be limited to the specific embodiments illustrated and described. Rather, it is intended that the scope of this invention be determined by the appended claims and their equivalents.