WO2013116946A1

WO2013116946A1 - Pellet kamado cooker

Info

Publication number: WO2013116946A1
Application number: PCT/CA2013/050100
Authority: WO
Inventors: Shawn Harper
Original assignee: Sherwood Industries Ltd.
Priority date: 2012-02-08
Filing date: 2013-02-08
Publication date: 2013-08-15

Abstract

A cooker includes a cooking chamber having a high heat capacity and a heating assembly that generates heat energy by combusting pellets. The cooking chamber and the heating assembly are connected such that the heat energy generated by the heating assembly transfers from the heating assembly to the cooking chamber. The heating assembly may be outside the cooking chamber.

Description

PELLET KAMADO COOKER

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from United States Provisional Patent Application Serial Number US61/596,633 filed on February 8, 2012, entitled Pellet Kamado Cooker, which is expressly incorporated by reference herein to the fullest extent permitted by law.

BACKGROUND

1. Field

The present invention relates to cookers. 2. Description of Related Art

Kamado Cookers

Grills, barbeques and smokers having earthen cooking chambers - often called kamado cookers or more fully mushikamado cookers - historically have burned charcoal, whole wood or the like as fuel. The term earthen includes: pottery, earthenware, stoneware, porcelain, clay, refractory, and fired wares in general, which are more broadly classified as traditional or industrial ceramics (as opposed to advanced ceramics).

As shown in Figure 1, the cooking chamber is typically elongated along its vertical axis, having a base portion and a lid portion. Fuel is placed deep at the bottom of the base portion and food is placed on a grate mounted toward the top of the base portion. As the fuel is combusted, it transfers its heat to the earthen cooking chamber, which in combination with the combusting fuel, transfers heat to the food from below and from all around the food.

The high heat capacity of the earthen cooking chamber helps the kamado to maintain a steady temperature with a modest amount of fuel when the lid portion remains generally closed. The temperature is controlled by incrementally opening or closing vents or dampers located at the top and/or bottom of the cooking chamber, to create a chimney effect. The kamado does however have a number of disadvantages. If fuel must be replenished during cooking, typically the lid portion must be opened, the hot grate with the food moved or removed, and then fresh fuel placed deep at the bottom of the chamber. Not only is this process cumbersome, but also it presents an opportunity for a person to be burned while reaching deep into the cooking chamber, which remains hot because of its high heat capacity. If one were to place a side-hole in the base portion sufficiently large to receive fuel replenishment, the hole could allow heat to escape the cooking chamber and could jeopardize the structural integrity of the fragile earthen cooking chamber. It can also be challenging to master the art of kamado temperature control by setting vents or dampers. This challenge is made still more difficult by the high heat capacity of the earthen cooking chamber, because once heated, the chamber can take a significant amount of time cool back down; users of kamado cookers are commonly advised not to overshoot their desired cooking temperature, lest they have to postpone cooking while the kamado cools. Even when mastered, kamado cookers can take a relatively long time to heat up to cooking temperature.

It can be particularly challenging to achieve predictable and reproducible cooking temperatures from use to use, when fuel amounts, fuel geometries and fuel compositions are difficult to control, and the correlation that these properties (along with vent/damper settings and elapsed time) have to temperature is difficult to appreciate. Furthermore, air paths between the vents/dampers can become blocked, preventing proper airflow to the fuel, presenting the opportunity for fuel to be incompletely or inefficiently combusted, or worse for toxic fumes to build up.

Finally, during cooking the fuel in a kamado is vulnerable to flame flare- ups because the fuel is located in the cooking chamber directly below the food, exposed to hot dripping fat. Pellet Cookers

A comparatively new type of cooker is the pellet grill / barbeque / smoker, perhaps pioneered by Traeger Industries, Inc. as shown in Figure 2 and United States patent 4,823,684 granted April 25, 1989 for a Pellet-fired Barbecue. As shown in Figure 2 this pellet barbeque closely resembles a conventional propane or natural gas grill. An alternative configuration is shown in Figure 3, which more closely resembles a conventional horizontal smoker. Generally these cookers are made from metal, typically stainless steel.

Pellet cookers combust pellets as fuel. Pellets are produced by compressing combustible material, most commonly wood, which has typically first passed through a hammer mill to provide a uniform dough-like mass. Pellets are often made from compacted sawdust or other wastes from sawmilling and other wood products manufacture, or from sources such as whole-tree removal or tree tops and branches leftover after logging. This mass is fed to a press where it is squeezed through a die having holes of the size required (typically ¼ inch diameter, but sometimes larger). The high pressure of the press causes the temperature of the wood to increase greatly, and the lignin plasticizes slightly forming a natural "glue" that holds the pellet together as it cools. Pellets have a regular geometry and small size, allowing automatic feeding with very fine calibration. Pellets are extremely dense and can be produced with a low moisture content (generally below 10%) that allows them to be burned with very high combustion efficiency. They have a uniform density, typically higher than 1 ton per cubic meter and bulk density of about 0.6-0.7 ton per cubic meter. They have good structural strength, and low dust and ash content. It has been estimated that the energy required to manufacture and transport pellets is less than 2% of the energy content of the pellets, so some see them as an environmentally responsible fuel.

Conventionally, the cooking chamber of a pellet cooker is elongated along its horizontal axis, having a base portion and a lid portion. Fuel is placed in a hopper at one edge of the base portion and conveyed by an auger to a firepot located in the middle of the base portion of the cooking chamber.

Generally an igniter and a combustion fan (air blower) are located with respect to the firepot such that the igniter can ignite the pellets in the firepot and the combustion fan can direct air across the ignited pellets. Both the igniter and the combustion fan are typically thermostatically-controlled electrical devices, the igniter being for example a high-resistance material connectable to a source of electric power and having an exposed surface that exceeds the fuel's ignition temperature when the igniter is powered. Conventional pellet cookers suffer from a number of disadvantages.

Conventional pellet cookers typically must combust a high amount of fuel to maintain a reasonable cooking temperature in the cooking chamber - typically in the neighborhood of four pounds per hour. Even then, pellet cookers have a reputation for a low maximum temperature (typically no more than 500 degrees Fahrenheit) that is insufficient to sear food well.

Additionally, because it can be difficult to maintain efficient combustion of pellet fuel, conventional pellet grills require fans and thermostatic control systems that add to cost and are subject to failure.

Furthermore, the fuel delivery system and the firepot are typically located in the cooking chamber, subject to flame flare-ups and unintended (and perhaps dangerous) combustion. In cases where the hopper is located outside the cooking chamber, the opening between the hopper and the cooking chamber can steal heat from the cooking chamber and compromise the structural integrity of the cooking chamber. Accordingly, what is needed is a cooker that provides at least some of the benefits of kamado and pellet cookers without at least some of their disadvantages. SUMMARY

The present invention is directed to this need.

According to one aspect of the present invention, there is provided a apparatus for cooking, having a cooking chamber having a high heat capacity, and a heating assembly that generates heat energy by combusting pellets, wherein the heating assembly is adapted to connect to the cooking chamber such that the heat energy generated by the heating assembly transfers from the heating assembly to the cooking chamber.

The cooking chamber may be made from a material having a specific heat capacity at constant pressure that is greater than that of steel, for example greater than 0.7, for example a ceramic material. The cooking chamber may be a kamado.

The heating assembly may be outside the cooking chamber and may be clad to protect users from contacting heat sources. The heating assembly may include a fire tube adapted to connect to the cooking chamber such that the heat energy generated by the heating assembly transfers from the heating assembly to the cooking chamber via the fire tube.

The cooking chamber may include a reinforcement collar adapted to receive the fire tube and a flame diffuser proximate the reinforcement collar. The fire tube may include a burn grate at one end, for example a removable burn grate. The fire tube may have sides that are perforated with air holes.

The heating assembly may include a combustion fan connected to the fire tube to urge ambient air into the fire tube. The combustion fan may be connected to the fire tube to urge ambient air into the fire tube through the burn grate or through the air holes in the perforated sides. The heating assembly may further include a thermostatic switch adapted to detect a temperature and connected to the combustion fan so as to switch off the combustion fan when the detected temperature is less than a threshold temperature. The heating assembly may also include a pellet drop tube connected to the fire tube to deliver a plurality of pellets into the fire tube for combustion therein and an ash pan connected to the fire tube to collect ash resulting from the combustion of the plurality of pellets in the fire tube.

The fire tube may be adapted to urge the delivered plurality of pellets to mound. The fire tube and the cooking chamber may form a chimney.

The cooking chamber may include at least one of a vent and a chimney stack.

The heating assembly may include a feed auger connected to the pellet drop tube to receive the plurality of pellets and deliver the plurality of pellets to the pellet drop tube.

The apparatus may further include a hopper connected to the feed auger to store and deliver the plurality of pellets to the feed auger. The feed auger may include a motor connected to drive the auger.

The heating assembly may include an igniter connected to the fire tube to ignite pellets within the fire tube. The heating assembly may include an igniter tube that houses the igniter. The heating assembly may include an air pump connected to pump air toward the igniter, for example through the igniter tube.

The heating assembly may further include a user-operable control for activating at least one of: the auger motor, the igniter, the air pump and the combustion fan, for example switching from an off-state to an on-state or varying output magnitude, including varying output magnitude over a user-selectable range. Further aspects and advantages of the present invention will become apparent upon considering the following drawings, description, and claims.

DESCRIPTION

The invention will be more fully illustrated by the following detailed description of non-limiting specific embodiments in conjunction with the accompanying drawing figures. In the figures, similar elements and/or features may have the same reference label.

1. Brief Description of the Drawings

Figure 1 Is a front sectional view of a prior art kamado cooker.

Figure 2 Is a top front left oblique outline view of a first prior art pellet cooker.

Figure 3 Is a top front left oblique sectional view of a second prior art pellet cooker.

Figure 4 Is a top front right oblique sectional view of an embodiment of a pellet kamado cooker according to aspects of the present invention, the cooker having a cooking chamber with a base portion and a lid portion and having a hopper and a heating assembly located outside the cooking chamber.

Figure 5 Is a top front right oblique view the cooker of Figure 4, the lid portion and the hopper being in a closed position.

Figure 6 Is a top front right oblique view the cooker of Figure 4, the lid portion and the hopper being in an open position.

Figure 7 Is a front elevation view of the cooker of Figure 4. Figure 8 Is a rear elevation view of the cooker of Figure 4. Figure 9 Is a top plan view of the cooker of Figure 4. Figure 10 Is a left elevation view of the cooker of Figure 4.

Figure 11 Is a right elevation view of the cooker of Figure 4.

Figure 12 Is a front elevation sectional view of the cooker of Figure 4.

Figure 13 Is a right elevation sectional view of the cooker of Figure 4.

Figure 14 Is a front elevation sectional view of the heating assembly of

Figure 4.

Figure 15 Is a top front right oblique detail sectional view of the heating assembly of Figure 4.

Figure 16 Is a top plan sectional view detailing the heating assembly of

Figure 4, showing an igniter in an igniter tube, and further including an auger timing module, an igniter air pump and a combustion fan.

Figure 17 Is a schematic view of the electrical interconnection of the igniter the auger timing module with the auger motor, the igniter, the air pump, and the combustion fan in the heating assembly.

2. Detailed Description of Specific Embodiments

(a) Structure of Specific Embodiments

The structure of aspects of the invention will now be illustrated by explanation of specific, non-limiting, exemplary embodiments shown in the drawing figures and described in greater detail herein.

Element Reference Number Element Name

100 cooker

102 cooking chamber

104 base portion

106 lid portion

108 hinge

1 10 handle

Figures 4-17 show a cooking apparatus (hereinafter a "cooker") 100 according to embodiments of the present invention. The cooker 100 is suitable for barbequing, smoking (hot, cold or otherwise), grilling, searing, roasting, baking and the like, among other uses, and terms such as "cook' and "cooking" will be used herein to have any and all such meanings unless otherwise specified, and a cooker 100 will be such an apparatus for cooking. Referring first to Figures 4-13, the cooker 100 includes a kamado-style cooking chamber 102, in this embodiment formed from an earthen material, for example a ceramic shell bottom (hereinafter base portion 104) and a mating ceramic shell top (hereinafter lid portion 106) connected together by a hinge 108, the lid portion 106 having a handle 110 to assist a user to move the lid portion 106 between a closed position (Figure 5) and an open position (Figure 6).

In this regard, the term kamado-style connotes a cooking chamber 102 with a high heat capacity; those skilled in the art will recognize that such a cooking chamber 102 might be constructed with other than earthen material. As used herein, the term high heat capacity denotes a specific heat capacity at

J

constant pressure (c_p ) greater than 0.7. Those skilled in the art will recognize that a suitable material for the cooking chamber 102 must also have a melting temperature, a sublimation temperature and a combustion temperature greater than the operating temperature inside the cooking chamber 102. Those skilled in the art will also recognize that a suitable material will not have a high thermal conductivity; for example, although aluminum has a specific heat capacity greater than 0.7 (0.9), its low melting temperature (660 °C) and its high

w

thermal conductivity 1 = 237 would make it an unsuitable material for this

m^° K

purpose.

The cooking chamber 102 is elongated along its vertical axis, with a chimney stack 112 in its lid portion 106, in this embodiment shown protected with a rain cap 114, and a vent 116, in this embodiment having a damper 118, in its base portion 104, in this embodiment in a sidewall proximate the bottom. This orientation and arrangement of venting encourages chimney effect airflow, to encourage fuel combustion and heat transfer from the combusting fuel to the cooking chamber 102. The cooking chamber 102 conveniently supports opposing side shelves 120 and is supported itself by a wheeled cart 122. The cooker 100 may include a thermometer having a display mounted on the outside of the cooking chamber 102 and a probe that extends into the cooking chamber 102 for measuring the temperature therewithin.

As best seen in Figures 4, 12 and 13, the base portion 104 supports within it a cooking grill 124, a heat diffuser 126 below the cooking grill 124, and a flame diffuser 128 below the heat diffuser 126. In this embodiment, the cooking grill 124 and the heat diffuser 126 are proximate the top of the base portion 104 and the flame diffuser 128 is proximate the bottom of the base portion 104.

As best seen in Figures 4, 12-16, the cooker 100 also includes a fuel hopper 130 and a heating assembly 132 that includes a feed auger 134, a pellet drop tube 136, a fire tube 138 and an ash pan 140. The cooking chamber 102 and the fire tube 138 are adapted so that the narrow fire tube 138 passes into the cooking chamber 102 through a mating small passage in its base portion 104, proximate the flame diffuser 128. As illustrated, the passage is soundly located at the centre of the bottom of the base portion 104 and is reinforced, in this embodiment with a reinforcement collar 142. The flame diffuser 128 provides further reinforcement to the base portion 104.

Those skilled in the art will recognize that this external arrangement of the hopper 130 and the heating assembly 132 provides a convenient way to transfer the heat energy generated from pellet combustion into the cooking chamber 102 without having to fit either the hopper 130 or the heating assembly 132 (or a significant portion thereof) into the cooking chamber 102, which would take up space within the cooking chamber 102 and raise safety concerns about grease fires, among other issues. Locating only the hopper 130 outside the cooking chamber 102 is more safe and convenient for the user than locating it inside; however, that arrangement is still less desirable than externally locating both the hopper 130 and the heating assembly 132, because for pellet combustion to occur within the cooking chamber 102, the pellets would have to be conveyed from the hopper 130 into the cooking chamber 102 to the heating assembly 132 through a wall in the cooking chamber 102, which arrangement would require a sufficiently significant hole in the wall as to steal heat from the cooking chamber 102 and undermine the structural integrity of the fragile earthen material. In this embodiment, the hopper 130 extends steeply downward from one of the side shelves 120 to a location below the base portion 104 of the cooking chamber 102. At its top end, the hopper 130 includes a hopper lid 144 in the one of the side shelves 120, openable to allow a user to load pellets into the hopper 130 and closeable to protect the pellets in the hopper 130 from contamination and to provide a work surface on the one of the side shelves 120. At its bottom end, the hopper 130 includes a dump gate 146 for unloading unused pellets, for example for winterizing the cooker 100.

The feed auger 134 inclines upward from the bottom of the hopper 130 toward the base portion 104 of the cooking chamber 102. The bottom of the auger 134 is connected to receive pellets from the hopper 130 and the top of the auger 134 is connected to a drive motor 148. The drive parameters of the motor 148 (for example speed or duty cycle) - and hence the pellet feed rate of the driven auger 134 - are set by a user-operable control, for example a knob 150 conveniently mounted on one of the side shelves 120 (Figure 5-7, 9). As will be described more fully below, the knob 150 has an "off' position and a range of "on" positions corresponding to a range of auger 134 feed rates, and as a consequence corresponding to a range of cooking chamber 102 temperatures. For convenience, a scale of the corresponding temperatures can be located adjacent the knob 150. In this embodiment, the user-operable control also includes a range switch 152, for selecting among predetermined ranges for the knob, for example a range of low values and a range of high values. Those skilled in the art will recognize that switching between ranges is one way to provide finer resolution and control. For example, the low range might cover values that correspond to smoking temperatures and the high range might cover values that correspond to grilling temperatures. Those skilled in the art will recognize that the knob 150 could be implemented in a number of ways, for example as a combination of an on/off switch and a potentiometer for supplying varying amounts of electricity to drive the motor 148. As best seen in Figure 16, one implementation of the user- operable control includes an auger timing module 154 that is connected to receive an input signal from the knob 150 and range switch 152 and to generate an output signal to the motor 148 to set a duty cycle for the pellet feed. In this embodiment, the timer module includes a model TRS51 A1 1 S2 digital encapsulated repeat cycle time delay module by Infitec Inc., having a place of business at 6500 Badgley Road, East Syracuse, NY 13057 USA. Attached as Appendix A to this specification is a manufacturer's data sheet for the Infitec TRS51A1 1 S2 digital encapsulated repeat cycle time delay module.

As best seen in Figures 4, 12-16, the pellet drop tube 136 is connected between the top of the feed auger 134 and the fire tube 138, to supply pellets from the auger 134 to the fire tube 138. The bottom of the fire tube 138 is formed as a removable burn grate 156 that provides primary air holes 158 to aid combustion. The sides of the fire tube 138 are perforated with secondary air holes 160 to further aid combustion. The ash pan 140 is located beneath the fire tube 138 to catch uncombusted ash that falls through the burn grate 156. As best seen in Figure 16, the heating assembly 132 can further include an igniter 162, shown located near the burn grate 156 in the fire tube 138 and housed within an igniter tube 164. In this embodiment, an air pump 166 is connected to pump ambient air toward the igniter 162, for example through the igniter tube 164, to improve the combustion environment proximate the igniter 162 to encourage faster pellet ignition.

Also shown in Figure 16, a combustion fan 168 may be located proximate the fire tube 138 to urge ambient air through the primary air holes 158 and/or secondary air holes 160 to improve the combustion environment in the fire tube 138 and/or to pressurize the fire tube 138 to encourage convection and to pressurize the ash pan 140 to trap ash. The igniter 162, the air pump 166 and the combustion fan 168 may be connected to an electricity source by a user-operable control, in this embodiment the control knob 150, such that the three devices are powered on whenever the knob 150 is in a position other than its off position. The combustion fan 168 may additionally include a thermostatic switch 170 that prevents the combustion fan 168 from operating below a threshold temperature; for example, the thermostatic switch 170 might detect the temperature on, near or in the fire tube 138 or the igniter tube 164 and the threshold temperature might be 160 degrees Fahrenheit. One advantage of this control arrangement for the combustion fan 168 is improved initial pellet ignition.

It has been found that a system so embodied consumes 500 watts, drawings 4 amperes of line current at 120 volts; of which the igniter 162 consumes 400 watts and the auger motor 148, the combustion fan 168, and the air pump 166 consume in combination 100 watts, all these quantities being nominal values.

In this embodiment, the igniter 162, the air pump 166 and the combustion fan 168 are controlled in a simple "on" or "off' manner; however, those skilled in the art will recognize that they could be controlled to have variable output magnitude depending on system parameters, for example temperature, air flow or concentration of combustion chemicals, for example as measured in the fire tube 138 or the cooking chamber 102.

Figure 17 illustrates one suitable electrical interconnection of the auger timing module 154 with its inputs and its outputs in the heating assembly 132, namely the knob 150 and range the range switch 152 (the user-operable controls) and the thermostatic switch 170 as inputs and the auger motor 148, the igniter 162, the air pump 166, and the combustion fan 168 as outputs.

In embodiments without a combustion fan 168 and/or an air pump 166, airflow for combustion can be encouraged by (a) configuring the fire tube 138 and in particular the burn grate 156 to urge the pellets to mound in a formation that permits good airflow between pellets and (b) configuring the cooking chamber 702 (and its chimney stack 112, vent 116, heat diffuser 726 and flame diffusers 728) and the fire tube 738 (and its primary air holes 758 and secondary air holes 760) for strong chimney effect. As illustrated, the heating assembly 732 is clad for protection and to protect the user from contacting heat sources.

(b) Operation of Specific Embodiments

With reference again to the figures, the operation of these exemplary embodiments of the present invention will now be described. To operate the cooker 700, a user lifts the hopper lid 744 and fills the hopper 730 with fuel pellets, closing the hopper lid 744 when he is finished. Typically, a user might wish to fill the hopper 730 with at least the amount of fuel he expects to use for the current cooking tasks. Nevertheless, if additional pellets were to be needed, it is simple and safe to add more fuel pellets to the hopper 730, even in the middle of cooking. Gravity draws the pellets to the bottom of the hopper 730, thus supplying pellets to the auger 734 at its lower end.

The user then ensures the cooker 700 is connected to receive electrical power, typically from mains but alternatively from local sources such as batteries.

The user would then turn the control knob 750 from the "off' position to an "on" position that corresponds to the desired temperature for the cooking chamber 702 - and more directly, that corresponds to the auger 734 feed rate that delivers sufficient pellet fuel for combustion to produce that temperature. Thus, electricity would be supplied to the auger motor 748 (in this embodiment via the auger timing 754 module) such that the auger 734 would be engaged to feed substantially uniform pellets at that predetermined feed rate. Operation of the knob 150 would also cause electricity to be supplied to the igniter 162, causing the igniter 162 to heat to a temperature sufficient to ignite proximate pellets dropped by the auger 134 into the fire tube 138 via the pellet drop tube 136. In embodiments with an air pump 166, electricity would also be supplied to the air pump 166, causing it to supply air to the region around the igniter 162 to encourage combustion of proximate pellets.

In embodiments with a combustion fan 168, operation of the knob 150 would also cause electricity to be supplied to the combustion fan 168, such that the combustion fan 168 would supply still more air to the fire tube 138 via the primary air holes 158 and/or secondary air holes 160. In embodiments with a thermostatic switch 170, the combustion fan 168 would only supply air when a threshold temperature (for example 160 degrees Fahrenheit) in a region (for example inside the igniter tube 164 adjacent the igniter 162) had been exceeded, such that the combustion fan 168 was activated when most useful. In some embodiments, there might be a designated ignition position for the control knob 150 that corresponds to operating parameters for the auger 134 (motor 148), the igniter 162, the air pump 166, the combustion fan 168 that particularly encourage initial ignition of the pellets.

In some embodiments, the knob 150 might have a setting that supplies electricity to the combustion fan 168 but not the auger 134, the igniter 162 and the air pump 166, this knob 150 setting would correspond to a cool down mode where no further pellets are being supplied to the fire tube 138 but the combustion fan 168 encourages the pellets currently in the fire tube 138 to combust as fully and efficiently as practical. The user might further adjust the operating parameters of the heating assembly 132 by toggling the thermostatic switch 170, thereby selecting a range for the knob 150.

These simple, predicable, reliable, repeatable arrangements for achieving a desired temperature makes using an earthen cooking chamber 102 less frustrating for a user than is the case with conventional kamado cookers; a user doesn't have to fiddle with confusing vent/damper settings and is less likely to overshoot a desired temperature, which can be time-consuming to recover from when using a cooking chamber 102 with a high heat capacity. Although the present embodiment cooker 100 has a damper 118 in the lower portion of the cooking chamber 102, it has been found that this control affects the completeness of combustion more than the temperature of the cooking chamber 102

Through experimentation with a cooker 100 built in accordance with such an embodiment of the invention, wherein:

• the ceramic cooking chamber 102 had silicate walls with a nominal thickness of 0.875 inches that contained a nominal volume of 3.9 cubic feet,

• the auger 134 had a maximum nominal feed rate of 5.85 pounds of pellets per hour,

• the pellets used were food-grade wood pellets that are believed to have had an energy density in a range between 7500 British thermal units per pound and 9200 British thermal units per pound, and more particularly were Traeger^® brand hickory pellets from Traeger Pellet Grills, LLC, having a place of business at 9445 SW Ridder Rd, Wilsonville, OR 97070, United States of America, and

• the heating assembly 132 included both an air pump 166 and a combustion fan 168 with a thermostatic switch 170 having a threshold temperature of 160 degrees Fahrenheit, the following results were observed: Pel let Result in

Auger Feed Duty Cycle

Feed Rate Cooking Chamber

Feed On [s] Feed Off [s] Mass/Time [Ib/hr] Temperature [F]

1 9.0 0.59 250

1 8.0 0.65 260

1 7.0 0.73 270

1 6.0 0.84 330

1 5.0 0.98 400

1 4.0 1 .17 470

1 3.0 1 .46 550

1 2.0 1 .95 625

1 0.3 4.50 675

As used herein, the term ceramic means a traditional or industrial ceramic material such as clay, earthenware, stoneware, porcelain, refractory, pottery, and fired wares in general, and includes functional equivalents that have traditional ceramic properties that support the present teaching (for example high specific heat capacity, high melting point, low thermal conductivity), including advanced ceramic materials and non-ceramic materials.

It was observed that during normal use of the cooker 100, including opening and closing the lid portion 106 of the cooking chamber 102, these settings produced temperatures within the cooking chamber 102 that held steady within ±25 degrees Fahrenheit, with a minimum observed steady temperature of 225 degrees Fahrenheit and a maximum observed steady temperature of 700 degrees Fahrenheit. It was observed that temperature increased at a nominal rate of 100 degrees Fahrenheit per minute and decreased from 700 degrees Fahrenheit to 500 degrees Fahrenheit in a nominal time of five minutes.

Those skilled in the art will appreciate that this cooking chamber 702 has a high heat capacity in comparison to non-kamado-style cookers 100, such as kettle barbeques, bullet smokers, gas grills, and pellet cookers 100 fabricated from sheets of stainless steel and the like. The cooking chamber 102 had a

J

mass of 55 kg. For a nominal specific heat capacity c_p for silicate of 0.8 kJ

the heat capacity of the cooking chamber 102 is nominally 44

Those skilled in the art will recognize that a closed-loop control system, for example including a PID (Proportional/lntegral/Derivative) controller, could be added to control at least some of the auger motor 748, the igniter 762, the air pump 766, and the combustion fan 768 (perhaps as variable-output devices), if it were decided that tighter temperature tolerances warranted the additional cost and complexity. However, the simple open-loop embodiments described in combination with the high heat capacity of the cooking chamber 702 cooperate to produce predictable and steady cooking temperatures for many applications.

The fuel combustion will now be described in more detail. Pellets fed into the fire tube 738 and mounding on the burn grate 756 are ignited by the igniter 762 or adjacent ignited pellets, their combustion drawing outside air through the primary air holes 758 in the burn grate 756 and secondary air holes 760 in the walls of the fire tube 738 to encourage the combustion. Uncombusted waste product, such as ash, falls through the burn grate 756 into the ash pan 740.

Heat energy, for example in the form of hot flue gases, flame, and the heated fire tube 738 itself, is transferred by the fire tube 738, for example by convection, radiation and conduction, from the heating assembly 732 into the base portion 704 of the cooking chamber 702 proximate the flame diffuser 728, where at least some of that heat energy is transferred to the walls of the cooking chamber 102 and to the heat diffuser 126 and ultimately to food on the cooking grill 124. The heat is distributed substantially evenly due to the round shape of the cooking chamber 102 and the elongated vertical distance between the fire tube 138 and the cooking grill 124. The elongated vertical distance also encourages a chimney effect to urge upward convection currents. The high heat capacity of the cooking chamber 102 walls encourages temperature stability within the cooking chamber 102.

This arrangement of locating the heating assembly 132 outside of (but in communication with) the cooking chamber 102 produces a safer cooking environment within the cooking chamber 102, reducing the chance and severity of grease fires or flame flare-ups. The flame diffuser 128, the heat diffuser 126 and the extension of the top end of the fire tube 138 above the bottom inside surface of the cooking chamber 102, where grease might pool, provide further safety in this regard. Furthermore, this placement of the heating assembly 132 below the cooking chamber 102 and behind cladding keeps hot sources further away from human contact than a regular outdoor cooker, such as a charcoal grill.

To adjust the desired cooking temperature, the user adjusts the control knob 150 and/or the range switch 152 to adjust the feed of pellets into the fire tube 138 and allows the cooking chamber 102 to settle at the corresponding temperature.

When the user is finished the cooking tasks, he turns the knob 150 to the off position which turns off both the auger 134 and the igniter 162. He may wish to disconnect the cooker 100 from the electrical supply, for example the mains. If he wishes, he can open the hopper 130 dump gate 146 to remove the pellets that remain in the hopper 130. Once the cooker 100 has sufficiently cooled, he can remove the ash pan 140 to dispose of the unburned ash from the pellet combustion. Furthermore, the auger 134 and hopper 130 are easy to clean when not in use and the burn grate 156 can be removed for easy cleaning. (c) Description Summary

Thus, it will be seen from the foregoing embodiments and examples that there has been described a novel and inventive pellet kamado cooker 100.

While specific embodiments of the invention have been described and illustrated, such embodiments should be considered only illustrative of the invention and not as limiting the invention as construed in accordance with the accompanying claims. In particular, all quantities described have been determined empirically and those skilled in the art might well expect a wide range of values surrounding those described to provide similarly beneficial results.

It will be understood by those skilled in the art that various changes, modifications and substitutions can be made to the foregoing embodiments without departing from the principle and scope of the invention expressed in the claims made herein. For example, the cooking chamber 102 may be made using non-earthen materials that have functional similarities.

While the invention has been described as having particular application for cooking, those skilled in the art will recognize it has wider application.

APPENDIX A ηιΐΏΡΐιιιι TRS SERIES

■ I n i h rrr DIGITAL ENCAPSULATED REPEAT

■ I I I I II L^L^f CYCLE TIME DELAY MODULE

Claims

CLAIMS We claim:

1 . An apparatus for cooking, comprising: a. a cooking chamber having a high heat capacity, and b. a heating assembly that generates heat energy by combusting pellets, wherein the heating assembly is adapted to connect to the cooking chamber such that the heat energy generated by the heating assembly transfers from the heating assembly to the cooking chamber.

2. The apparatus as claimed in claim 1 , wherein the cooking chamber is made from a material having a specific heat capacity at constant pressure that is greater than that of steel.

3. The apparatus as claimed in claim 2, wherein the cooking chamber is made from a material having a specific heat capacity at constant pressure that is greater than 0.7

4. The apparatus as claimed in claim 1 , wherein the cooking chamber is made from a ceramic material.

5. The apparatus as claimed in claim 1 , wherein the cooking chamber is a kamado.

6. The apparatus as claimed in claim 1 , wherein the heating assembly is outside the cooking chamber.

7. The apparatus as claimed in claim 6, wherein the heating assembly is clad to protect users from contacting heat sources.

8. The apparatus as claimed in claim 6, wherein the heating assembly

includes a fire tube adapted to connect to the cooking chamber such that the heat energy generated by the heating assembly transfers from the heating assembly to the cooking chamber via the fire tube.

9. The apparatus as claimed in claim 8, wherein the cooking chamber

includes a reinforcement collar adapted to receive the fire tube.

10. The apparatus as claimed in claim 8, wherein the cooking chamber

includes a flame diffuser proximate the reinforcement collar.

1 1 . The apparatus as claimed in claim 8, wherein the fire tube includes a burn grate at one end.

12. The apparatus as claimed in claim 1 1 , wherein the burn grate is

removable.

13. The apparatus as claimed in claim 1 1 , wherein the fire tube has sides that are perforated with air holes.

14. The apparatus as claimed in claim 13, wherein the heating assembly includes a combustion fan connected to the fire tube to urge ambient air into the fire tube.

15. The apparatus as claimed in claim 14, wherein the combustion fan is connected to the fire tube to urge ambient air into the fire tube through the burn grate.

16. The apparatus as claimed in claim 15, wherein the combustion fan is connected to the fire tube to urge ambient air through into the fire tube through the air holes in the perforated sides.

17. The apparatus as claimed in claim 14, wherein the heating assembly further includes a thermostatic switch adapted to detect a temperature and connected to the combustion fan so as to switch off the combustion fan when the detected temperature is less than a threshold temperature.

18. The apparatus as claimed in claim 8, wherein the heating assembly includes: a. a pellet drop tube connected to the fire tube to deliver a plurality of pellets into the fire tube for combustion therein, and b. an ash pan connected to the fire tube to collect ash resulting from the combustion of the plurality of pellets in the fire tube.

19. The apparatus as claimed in claim 18, wherein the fire tube is adapted to urge the delivered plurality of pellets to mound.

20. The apparatus as claimed in claim 18, wherein the fire tube and the cooking chamber form a chimney.

21 . The apparatus as claimed in claimed in claim 20, wherein the cooking chamber includes at least one of a vent and a chimney stack.

22. The apparatus as claimed in claim 18, wherein the heating assembly includes a feed auger connected to the pellet drop tube to receive the plurality of pellets and deliver the plurality of pellets to the pellet drop tube.

23. The apparatus as claimed in claim 22, further including a hopper

connected to the feed auger to store and deliver the plurality of pellets to the feed auger.

24. The apparatus as claimed in claim 22, wherein the feed auger includes a motor connected to drive the auger.

25. The apparatus as claimed in claim 8, wherein the heating assembly includes an igniter connected to the fire tube to ignite pellets within the fire tube.

26. The apparatus as claimed in claim 25, wherein the heating assembly includes an igniter tube that houses the igniter.

27. The apparatus as claimed in claim 26, wherein the heating assembly includes an air pump connected to pump air toward the igniter.

28. The apparatus as claimed in claim 27, wherein the air pump is connected to pump air toward the igniter through the igniter tube.

29. The apparatus as claimed in all of claims 14, 24 and 27 combined,

wherein the heating assembly further includes a user-operable control for activating at least one of: a. the auger motor, b. the igniter, c. the air pump, and d. the combustion fan.

30. The apparatus as claimed in claim 29, wherein activate includes

switching from an off-state to an on-state.

31 . The apparatus as claimed in claim 30, wherein activate includes varying output magnitude.

32. The apparatus as claimed in claim 30, wherein varying output magnitude includes varying output magnitude over a user-selectable range.