Patent Description:
Convection ovens can improve cooking speed by dispersing stagnant air that can provide an insulating blanket around food in an oven. Such ovens normally provide a blower blowing heated air through an opening in the wall of the cooking cavity, the opening positioned in a way to increase air turbulence so as to provide even cooking.

One drawback to convection ovens is that different volumes of food as well as different food loading arrangements can radically change the airflow pattern and hence the cooking process. This can require a chef to develop extensive experience in how to load and operate the oven when different types of food items, different volumes of food or different placement of food within the cook cavity are used.

Higher cooking speeds and more consistent cooking can often be obtained by reducing the length of the path between the heated air and the food, for example, by delivering the heat through an array of horizontally dispersed openings positioned directly above and/or below the food, thereby increasing the surface area of food that is directly contacted by the delivered heat. This proximate-air delivery can improve the uniformity of cooking in a variety of different food loading patterns and for different types of food. In this regard, the short air delivery distance provides more predictable tractable airflow patterns. Common ovens of this type provide a set of upward and downward facing airstream openings in opposition on upper and lower walls of the oven cavity.

It would be desirable to provide ovens using this proximate-air delivery that could simultaneously cook a variety of different foods at different temperatures. Two-cavity proximate-air ovens are relatively simple to construct by simply stacking two single cavity ovens one on top of the other. Unfortunately, additional cavities can unduly increase the height of the oven or reduce the cooking volume because of the substantial space between cavities necessary for insulation between the cavities and for the plenums necessary for the air delivery. <CIT>, <CIT> and <CIT> disclose various arrangements of ovens.

The present invention provides a compact, multi-zone oven using proximate-air delivery, enabled by using extremely low profile separators between the cavities. The present inventors have recognized that absolute isolation between the cavities is not required and that substantial leakage can be managed by the active feedback control of cavity temperature and proper management of cavity loading, among other techniques. In addition, an innovative air distribution plate design operates with relatively thin plenums. By radically reducing the thickness of the separation between the different cavities, three- and four-zone ovens can be readily obtained while still satisfying desired ergonomic height restrictions.

Specifically then, at least one embodiment of the invention provides a multi-cavity oven having a housing defining an interior cooking volume surrounded by insulated outer walls and at least one door that may open and close to provide access to the interior cooking volume. A set of shelves subdivides the cooking volume into cooking cavities, the shelves providing separate upper and lower air channels each leading from respective air inlets to respective upwardly directed airstream openings and downwardly directed airstream openings. Each cavity provides a separate blower circulating air from the cavity into a lower air channel of a shelf above the cavity and an upper air channel of the shelf below the cavity, and each cavity provides a separate heater and a thermal sensor placed in the circulated air after the airstream openings but before the heater. A controller receives a control set point and a signal from the thermal sensor to control the heater.

It is thus a feature of at least one embodiment of the invention to provide a proximate-air, multi-zone oven in which the cavity shelves alone separate the oven cavities thereby greatly reducing the oven height and increasing usable cooking volume.

In this regard the shelves may have a vertical thickness of less than <NUM> (three inches) or preferably less than <NUM> (two inches) measured between an uppermost extent of airstream openings of the upper air channels and the lowermost extent of airstream openings of the lower air channels, and/or the upper and lower air channels of each shelf may have an average separation of less than <NUM> (one inch) or preferably less than <NUM> (one half inch). Alternatively or in addition, the effective resistance between the upper and lower channels may be less than half of that through the outer oven wall.

It is thus a feature of at least one embodiment of the invention to accommodate increased heat leakage between the cavities in order to maximize cooking volume while reducing the height of a multi-zone oven having proximate-air delivery. This design may be contrasted from conventional wisdom that requires standard oven wall-grade insulation between cavities that operate at different temperatures. In addition, the inventors have recognized that it is possible to construct an air distribution plate system operable using relatively narrow shelf channels.

The controller may operate to control the airspeed through the channel to prevent an air temperature gain or loss from air passing through the channel, from inlet to airstream openings caused by thermal transfer with an adjacent air channel, of greater than <NUM> (five degrees Fahrenheit).

It is thus a feature of at least one embodiment of the invention to manage heat transfer between cavities to within values that can be actively compensated for by the independent temperature controls of the cavities.

The shelves may be replaceably removable from the interior cooking volume.

It is thus a feature of at least one embodiment of the invention to provide a multi-zone oven having compact partitions enabling ready removal useful for cleaning or changing cavity sizes.

The shelves may consist of a separately removable lower plenum providing lower air channels and a separately removable upper plenum providing upper air channels, at least one plenum providing a barrier wall separating the upper and lower air channels.

It is thus a feature of at least one embodiment of the invention to reduce the weight and bulk of the shelf by allowing it to be separated into different plenums. It is another object of the invention to provide a plenum component that can be used both for the shelves and also for the top and bottom of the cooking volume where only single directions of airflow are required.

The interior cooking volume may provide inwardly extending shelf supports supporting the lower plenum, and the upper plenum may rest directly on the lower plenum to be supported thereby.

It is thus a feature of at least one embodiment of the invention to minimize shelf height by ensuring close plenum abutment simplified by direct support.

Each plenum may provide an air distribution plate holding the airstream openings and an opposed barrier wall together with the air distribution plate defining the channel, and the air distribution plate and barrier wall may be user-separable components.

It is thus a feature of at least one embodiment of the invention to provide plenums (and shelves) with interior air channels that are nevertheless easily cleaned by separating the plenums and channel components.

The upper and lower plenums may provide different air distribution plates providing a different configuration of openings.

It is thus a feature of at least one embodiment of the invention to permit tailoring of the air distribution plate openings to the airflow within the shelves to provide even cooking.

The oven may include a manifold communicating between each blower and two channels to provide greater airflow through an upper channel of the lower plenum than to the corresponding lower channel of the upper plenum flanking a cavity.

It is thus a feature of at least one embodiment of the invention to manage airflow ratios through the agency of the manifold to optimize cooking performance while simplifying construction of the shelves and minimize their thickness. The multi-cavity oven may provide a single plenum at the top and bottom of the interior cooking volume providing an upper surface of the uppermost cavity and a lower surface of the lowermost cavity.

It is thus a feature of at least one embodiment of the invention to employ the plenum design to provide the uppermost downward airstream openings and lowermost upward airstream openings without requiring a full shelf or new part.

The multi-cavity oven may include at least one rack positionable on an upper surface of at least one shelf, the rack supported by the shelf to be stationary with respect to the shelf in spaced relationship from the upwardly directed airstreams.

It is thus a feature of at least one embodiment of the invention to provide a simple method of ensuring airflow out of the lower airstream openings is unobstructed by food placed on the shelf such as can be a problem with stationary positioning of the rack.

The temperature probe may be positioned in a wall of the oven communicating with the cavity through intake apertures to be upstream from the heater of the cavity and downstream from the airstreams.

It is thus a feature of at least one embodiment of the invention to place the temperature probe so as to permit compensation for heat transfer between different temperature cavities. As so positioned (in contrast from being directly downstream from the heater and upstream from the airstreams), the temperature sensor can provide guidance with respect to sensing and compensating for inter-cavity heat transfer.

The multi-cavity oven may further include a compliant seal positioned between the inner surface of the at least one door and a front edge of the shelf to block airflow past the shelf between adjacent cavities.

It is thus a feature of at least one embodiment of the invention to minimize airflow between the cavities, such airflow potentially resulting in undesirable heat transfer as well as potential flavor transfer.

An upper wall of the lower air channel of each shelf may slope downwardly from the air inlet and a lower wall of the upper air channel of each shelf may slope upwardly from the air inlet to provide an increasing air gap between the upper and lower channels possible with reduced airflow through the channels as one moves away from the air inlets.

It is thus a feature of at least one embodiment of the invention to increase the insulating space between the shelves when shelf channel thickness can be reduced as a result of reduced airflow toward its tip.

The controller may communicate with a display guiding the user in loading of food into cavities currently not used for cooking food based on temperatures of cavities currently used for cooking food.

It is thus a feature of at least one embodiment of the invention to manage "smart" loading of the oven to minimize temperature flow between the cavities and thus heat transfer.

The multi-cavity oven may provide for at least three cavities, and a separation between the upper wall of the interior cooking volume and a lower wall of the interior cooking volume may be less than <NUM> (<NUM> inches). Each cooking cavity may be at least <NUM> (five inches) in height between a lower surface of the airstream openings of the upper shelf in an upper surface of the airstream openings of the lower shelf.

It is thus a feature of at least one embodiment of the invention to provide a multi-zone oven using proximate-air delivery having a compact height for improved ergonomic use.

In one embodiment, the set of shelves subdividing the cooking volume into cooking cavities may provide separate upper and lower air channels divided by at least one interior barrier wall and the barrier wall and jet plate may intercommunicate mechanically through a floating mounting adapted to resist warpage of the shelf with variations in thermal expansion of the barrier wall and jet plate.

It is thus a feature of at least one embodiment of the invention to permit extremely thin shelves without risk of disruptive warpage caused by oven temperatures. This is particularly important when the jet plate and barrier walls are of different lengths caused by intentional sloping of one or the other.

In at least one embodiment of the invention the blowers may communicate with the shelves through a bifurcated manifold providing extended transition sections of smoothly varying cross-section reducing a height of the transition section from an inlet to an outlet by no less than <NUM> percent.

It is thus a feature of at least one embodiment of the invention to provide for high airflow and low airflow resistance with extremely narrow high aspect ratio shelf inlets. Introduction of the transition section allows these narrow shelves to receive air with minimized air back resistance.

The transition sections may simultaneously provide a smoothly varying cross-section increasing a width of the transition section from the inlet to the outlet by at least <NUM> percent. It is thus a feature of at least one embodiment of the invention to minimize velocity changes in the airflow such as could cause turbulence by minimizing cross-sectional area variation to the extent possible.

These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention.

Referring now to <FIG>, a multi-zone, proximate-air delivery oven <NUM> may provide for a housing <NUM> having upstanding insulated outer sidewalls 14a and 14b and an upstanding outer insulated rear wall 14c extending between and joining opposed generally horizontal insulated outer upper walls 14d and 14e. The resulting cooking volume <NUM> is open on the front and this opening may be covered by hinged door <NUM> when the door <NUM> is in a closed position or accessible through the hinged door <NUM> when the door <NUM> is in an open position as is generally understood in the art. The housing <NUM> may be supported on one or more legs <NUM> extending downwardly from a bottom surface of the bottom wall 14e.

The cooking volume <NUM> may be divided into multiple cooking cavities 20a-d. Although four cooking cavities are shown, the invention contemplates a range from <NUM> to <NUM> cooking cavities <NUM> in vertical, spaced separation. Each of the cooking cavities <NUM> is separated by a thin shelf 22a-c with shelf 22a separating cavities 20a and 20b, shelf 22b separating cavities 20b and 20c and shelf 22c separating cavities 20b and 20d.

Referring also to <FIG>, each shelf <NUM> comprises a separate upper and lower generally rectangular plenum 24a and 24b fitting horizontally in the cooking volume <NUM>. When the shelf <NUM> is installed, a lower edge of the plenum 24b may rest on rails <NUM> extending inwardly from the inner surface of the walls 14a and 14b and the upper plenum 24a may rest directly on top of the lower plenum 24b for reduced total height.

Each plenum <NUM> provides an outer, horizontally extending air distribution plate <NUM> having a set of airstream openings <NUM> distributed over its area to provide for substantially even airflow therethrough. The air distribution plate <NUM> may be substantially planar and may have one or more reinforcing ribs <NUM> attached along its inner surface to prevent thermal warping of opposed edges of the slot-like airstream openings <NUM> in the air distribution plate <NUM> as will be described below. The reinforcing ribs <NUM> may be relatively thin as measured along the length of the airstream openings <NUM>, for example, less than <NUM> (<NUM>/<NUM> of an inch) or less than <NUM> (<NUM>/<NUM> of an inch), to minimize disruption of air through the airstream openings <NUM>.

Air enters through sidewalls of each of the plenums 24a and 24b at air inlets 32a and 32b, respectively. These air inlets <NUM> may be as little as <NUM> (<NUM><NUM>/<NUM> inches) tall and preferably less than <NUM> (one inch) tall. From the air inlets 32a and 32b, the air then passes through a horizontally extending channel <NUM> defined by an inner surface of the air distribution plates <NUM> and inner surface of a barrier wall <NUM> opposite the air distribution plate <NUM> about the channel <NUM>. The barrier wall <NUM> has a maximum separation from the air distribution plate <NUM> at the air inlet <NUM> and then curves inward toward the air distribution plate <NUM> as air conducted in the channel <NUM> escapes through the airstream openings <NUM> and less channel height is needed. This inward sloping of the barrier walls <NUM> for each of the plenums 24a and 24b together provides an additional insulation zone <NUM> between the barrier walls <NUM> of the upper and lower plenums 24a and 24b, respectively, minimizing shelf height but maximizing insulation value. The average separation of the barrier walls <NUM> may be approximately <NUM> (one inch) varying from contact between the barrier walls to nearly <NUM> (<NUM> inches) in separation. Invention contemplates an average separation of at least <NUM> (one-quarter inch) and preferably at least <NUM> (one inch).

A peripheral wall <NUM> of each plenum <NUM> surrounds the air distribution plate <NUM> and the barrier wall <NUM> to corral air within the channel <NUM> in all directions except through the inlets <NUM> and the airstream openings <NUM>. Peripheral wall <NUM> also provides inwardly horizontally extending tabs <NUM> which may support a wire rack <NUM> at a separation of approximately <NUM> (<NUM>/<NUM> inch) and at least <NUM> (<NUM>/<NUM> inch) above the upper extent of the air distribution plate <NUM> of the upper plenum 24a. In one embodiment the wire rack <NUM> may be supported by more than <NUM> (one inch) above the air distribution plate <NUM> and desirably more than <NUM> (<NUM> inches) above the air distribution plate either through the use of a special wire rack <NUM> or extender tabs <NUM> (not shown). In this way, a cooking sheet or pan set on top of the shelf <NUM> rests on the wire rack <NUM> and does not block the airstream openings <NUM>. In a preferred embodiment, a separation <NUM> (shown in <FIG> and <FIG>) between the uppermost extent of the airstream openings <NUM> of the air distribution plate <NUM> of the upper plenum 24a and the lowermost extent of the airstream openings <NUM> of the air distribution plate <NUM> of the lower plenum 24b will be less than <NUM> (four inches), preferably less than <NUM> (three inches) and desirably less than <NUM> (two inches) providing an extremely compact shelf maximizing cavity space and minimizing total height. The cavities <NUM> (shown in <FIG> and <FIG>) will have a nominal height <NUM> of from between <NUM> and <NUM> (four and nine inches) and preferably <NUM> (five inches) or more defined by the distance between air distribution plates <NUM> bounding the upper and lower extent of the cavity <NUM>. In one nonlimiting example, each cavity may add a height of about <NUM> (seven inches) to the oven so that three cavities may have a height of no more than <NUM> (<NUM> inches) or at least no more than <NUM> (<NUM> inches), and four cavities may have a nominal height of <NUM> (<NUM> inches) and no more than <NUM> (<NUM> inches).

Generally the shelves <NUM> may be constructed entirely of stainless steel for durability and ease of cleaning, and although the invention contemplates that thin insulating materials may also be incorporated into the shelves <NUM> in some embodiments, the invention contemplates that no nonmetallic shelf construction materials are required. The barrier walls <NUM> may be held within each plenum <NUM> with a "floating mounting" allowing sliding of the barrier walls <NUM> with respect to the other structures of the plenums <NUM>, for example, by creating a sliding fit between these components augmented by a natural flexure of the metal of the barrier walls <NUM> providing a light pressure between the barrier walls <NUM> and the ribs <NUM> and inwardly extending lips of the peripheral walls <NUM>. In this way, extremely thin plenums <NUM> may be developed without warpage at high temperature by preventing warpage forces produced by the barrier walls <NUM> on the plenums <NUM> such as is relieved by sliding. This sliding feature may be extended to allow the barrier walls <NUM> to be removed horizontally through the inlets <NUM> to eliminate any enclosed pockets for easy cleaning of the plenums <NUM> when removed from the oven <NUM>. Other "floating mountings" are contemplated by the invention including those which provide for flexible or spring-loaded mounting that allows relative different expansion and contraction rates of the broad area air distribution plate <NUM> and barrier walls <NUM> to prevent warping and buckling of either or both or the plenum <NUM> such as can be particularly acute for extremely thin shelves <NUM> and plenums <NUM> at higher temperatures such as above <NUM> (<NUM> degrees Fahrenheit).

Referring now to <FIG> each of the cavities <NUM> may be associated with a temperature sensor <NUM> communicating with a controller <NUM>, for example, being a microcontroller having one or more processor <NUM> executing programs and communicating with an associated memory <NUM>, holding an operating program <NUM> and various recipe schedules <NUM> as will be discussed in more detail below. The temperature sensors <NUM> may be thermistors, resistive temperature sensors or the like.

Each cavity <NUM> is associated with an airflow system <NUM> comprising a heater system, blower motor and variable speed motor controller so that the controller <NUM> may independently control the airflow circulating through each cavity <NUM> through a continuous range and may control the temperature of that air through a continuous range of temperatures. The heater system may be, for example, an electric resistance heater such as a "cal" rod controlled by a solid-state relay or may be a heat exchanger of an electrically controllable gas burner system.

Optionally, each cavity <NUM> may have an electrically controllable valve <NUM> communicating with a common water supply <NUM> (either sourced from a self-contained water source or external plumbing) so that moisture may be introduced into the cavity by a signal to the controllable valve <NUM> from the controller <NUM> to allow independent control of moisture according to a cooking schedule. Mechanisms for the introduction of controlled moisture into an oven cavity <NUM> suitable for the present invention are described, for example, in <CIT>; <CIT>; <CIT> and <CIT> assigned to the assignee of the present application.

The controller <NUM> may also receive a signal from a door close sensor <NUM> (such as a limit switch or proximity switch) and may provide for input and output to an oven user through a user interface <NUM> such as a touch screen, graphic display, membrane switch or the like such as are well known in the art. A data connector <NUM> may communicate with the controller <NUM> to allow for the readily uploading of cooking schedules <NUM> over the Internet or by transfer from a portable storage device or the like.

One or more of the cavities <NUM> may also include a smoker <NUM>, for example, providing a compartment that may hold woodchips or the like to be heated by an electric element controlled by the controller <NUM> through corresponding solid-state relays. The construction of a smoker <NUM> suitable for the present invention is described, for example, in <CIT>; <CIT>; and <CIT> each assigned to the assignee of the present invention.

Referring now to <FIG> and <FIG>, the thermal resistance of each shelf <NUM> will be substantially less than that necessary to provide for thermal isolation of each oven cavity <NUM> and equal to the isolation between the cooking volume <NUM> and the kitchen as is provided by the insulation values in the walls <NUM>. For example, the walls <NUM> may have <NUM> (one inch) of fiberglass mat with a reflective aluminum foil providing thermal resistance R-value of <NUM>-<NUM> (<NUM> (one inch) material having a k-value of approximately <NUM>. In contrast, the effective thermal resistance between the upper and lower channels when separated by an average <NUM> (one-inch) air gap is estimated to have an R-value of approximately <NUM> (<NUM> (one inch) material having a k-value of approximately <NUM>). Accordingly the effective thermal resistance between the upper and lower channels will be less than one half of that through the outer oven walls <NUM>. This is in contrast to existing practice of multi-cavity ovens to make the thermal resistance between the oven cavities substantially equal to that between the cavities and the kitchen.

Lower R-value shelves <NUM> provide improved oven cavity utilization and, importantly, ergonomically improved oven height when multiple cavities are desired and offer an improved ability to remove the shelves <NUM> for cleaning or changing cavity size. Nevertheless, the lower R-value shelves provide significant inter-cavity thermal transfer <NUM> in contrast with normal levels of thermal transfer <NUM>' through isolating insulation of the walls <NUM>. For example, with <NUM> (<NUM> degree Fahrenheit) air moving through an upper plenum 24a, the still air of adjacent lower plenum <NUM> of an unused cavity <NUM> beneath the lower plenum <NUM> will asymptotically approach temperatures over <NUM> (<NUM> degrees Fahrenheit) without activating the heater of the unused cavity <NUM>.

The present inventors have recognized such increased heat transfer can be accommodated through a combination of one or more of: (<NUM>) managing the cavity temperatures to minimize temperature differences between cavities; (<NUM>) ensuring sufficient airflow through the shelves to minimize absolute temperature gain in the air as it passes through the shelves; (<NUM>) offsetting heat gain and heat loss through the separate independent feedback control systems for each cavity; (<NUM>) managing airflow to increase thermal resistance to unused cavities; and (<NUM>) maximizing separation between airflows within a shelf through sloped barrier walls described above. With respect to (<NUM>) the problems associated with forced air in increasing thermal transfer through low R-value shelves can in fact be exploited, as will be described, to manage that thermal transfer effectively.

Referring now to <FIG>, as discussed above, the airflow system <NUM> of each cavity <NUM> (indicated generally by separating dotted lines) may include a separate blower <NUM> independently controlled by a variable speed motor and motor drive <NUM>. The blower <NUM> may be, for example, a squirrel cage blower and the motor a DC synchronous motor driven by a solid-state motor controller of a type known in the art. The use of separate blowers <NUM> permits full segregation of the airflows within each cavity <NUM>. The use of a separate motor and motor drive <NUM> allows independent airspeed control of the air in each cavity <NUM>.

The airflow system <NUM> may also include a heater unit <NUM> and the air from each blower <NUM> may pass through a heater unit <NUM> to be received by a bifurcated manifold <NUM> which separates the heated airstream into an upper airstream <NUM> and lower airstream <NUM>. The upper airstream <NUM> passes into the channel <NUM> (shown in <FIG>) of a lower plenum 24b of an upper shelf <NUM> defining an upper wall of the cavity <NUM> and then exits from the channel <NUM> as a set of downwardly directed airstreams 72a from each of the airstream openings <NUM> (shown in <FIG>) distributed over the lower area of the plenum 24b. The lower airstream <NUM> passes into the upper channel <NUM> of upper plenum 24a of a lower shelf <NUM> defining a lower wall of the cavity <NUM> to exit from the channel <NUM> as a set of upwardly directed airstreams 72b from each of the airstream openings <NUM> (shown in <FIG>) distributed over the upper area of the plenum 24a.

The bifurcated manifold <NUM> may be designed to provide substantially greater airflow in the upper airstream <NUM> than the airflow of the lower airstream <NUM>, for example, by constrictions or orientation of the branches of the bifurcated manifold <NUM> with respect to the natural cyclic flow of the blower. In one example, the air may be split so that <NUM> to <NUM> percent of the heated air is allocated to the lower shelf sending air upward, and <NUM>-<NUM> percent of the heated air is allocated to the upper plenum pulling downward as described in <CIT> cited above.

Significantly, the location of the exit of the blower <NUM> is located approximately midway between the shelves <NUM> so that each leg of the manifold may provide an aerodynamic reducer/expander <NUM> of approximately <NUM> (<NUM> inches) and at least <NUM> (three inches) long for gradually reducing the exit area height of the blower <NUM> to the extremely narrow inlet <NUM> of the plenums <NUM> and expanding its width to the much wider plenums <NUM>. Without this reducer/expander <NUM>, an extremely high air resistance would be generated in attempting to force air into the extremely high aspect ratio plenums <NUM> such as would resist effective air conduction. For example, each manifold <NUM> may receive air at an area having a height of approximately <NUM> (four inches) which will be split into two <NUM> (<NUM>-inch) high branches and then smoothly reduced to the approximately <NUM> (one inch) high area of each plenum <NUM>. At the same time, the approximately <NUM> (<NUM> inch) wide area at which air is received by the manifold <NUM> may be expanded to the full width of the shelf (approximately <NUM> (<NUM> inches) and at least <NUM> (<NUM> inches)) through a smoothly transitioning expander. Importantly, <NUM> degree turns such as creates significant turbulence and back resistance are avoided and the change in air velocity through the reducer/expander <NUM> is minimized. Generally the walls of each reducer/expander <NUM> may be constructed of planar sheets of sheet metal for simplified manufacturing and reduced air turbulence.

This arrangement of blowers, airflow systems <NUM> and bifurcated manifold <NUM> is duplicated for each cavity <NUM>. In the uppermost cavity 20a only a single lower plenum 24b is provided at the top of that cavity 20a and in the lowermost cavity 20d only a single upper plenum 24a is provided, each being effectively one half of shelf <NUM>.

A first element of the active insulation process of the present invention may be understood by considering a cooking schedule <NUM> held in the memory <NUM> of the controller <NUM>; the cooking schedule <NUM> requires a given time for a cooking cavity command temperature of T<NUM>. Initially, the upper airstream delivered to the cavity 20b, for example, may be heated by the heater unit <NUM> to a command temperature T<NUM> through a feedback control structure in which the temperature of the air in the cavity 20b is sensed by the sensor <NUM>. A difference between the command temperature of T<NUM> and the temperature measured by the temperature sensor <NUM> provides a control signal that controls the heater unit <NUM>, for example, by pulse width modulation. Under this control strategy, when the temperature of the cavity 20b sensed by the sensor <NUM> rises above command temperature T<NUM>, the heater unit <NUM> will be deactivated, and conversely when the temperature of the cavity 20b sensed by the sensor <NUM> falls below command temperature T<NUM>, the heater may be activated by the controller <NUM>. It will be appreciated that this is a simplified description of feedback control which may provide more sophisticated proportional/integral/derivative type control mechanisms as are understood in the art further modified as will be discussed below.

Consider now the introduction of food into the adjacent upper cavity 20a for cooking at a temperature substantially above the command temperature T<NUM>. The heating of the cavity 20a results in heat leakage <NUM> from the upper plenum 24a of the upper shelf <NUM> into the lower plenum 24b where it heats airstream <NUM> to a higher temperature than desired resulting in air exiting in airstreams 72a at a temperature T<NUM>+ΔT. The temperature of this air will then be sensed by the thermal sensor <NUM> resulting in a deactivation of the heater unit <NUM> until the upper airstream <NUM> from the manifold <NUM> effectively reaches a temperature of T<NUM>-ΔT. This cool air at T<NUM>-ΔT will then enter the channel <NUM> and be heated by an amount ΔT from leakage heat. The result is that the exiting air of airstreams 72a will be raised exactly to the desired regulated temperature of T<NUM> despite heat leakage.

The ability to implement this "active insulation" by using a feedback control system requires that the ΔT component be kept relatively small so that it does not adversely affect the cooking process before a correction can be undertaken. In this regard, the invention employs the movement of the air through the channel <NUM> (such as could otherwise exacerbate the effects of heat leakage between the plenums <NUM>) to ensure sufficient velocity of airflow through the channel <NUM> of the lower plenum 24b at all times to so constrain the ΔT value to within a predetermined value that can be readily compensated by control of the heater unit <NUM>. By keeping the value of ΔT small by ensuring a given air velocity and thus reduced dwell time of air within the channel <NUM>, the effects of heat leakage can be greatly mitigated.

Settings of the parameters of feedback control, for example, in a proportional/integral/derivative controller may be adjusted using the controller's "knowledge" of the regulated temperatures to estimate heat leakage and adjust the control loop parameters (integral, proportional, and derivative terms) appropriately to ensure proper control loop accuracy. Thus, for example, the controller <NUM> may anticipate additional heat loads from leakage knowing the control temperature profile of the adjacent cavities by introducing feedforward terms between cavities. In addition or alternatively, each schedule <NUM> may be modified according to knowledge held in the controller <NUM> with respect to the adjacent cavity temperatures.

The implementation of the above-described active insulation is further complicated by heat leakage <NUM> through the lower shelf of cavity 20b which, like the heat leakage <NUM> in the upper shelf <NUM>, may be in either direction. Accordingly, the controller <NUM> must accommodate the net effect of heat leakage through the upper and lower shelves <NUM> associated with a given cavity <NUM>. The use of a single sensor <NUM> positioned appropriately can automatically implement a control strategy based on a weighted temperature of the airstreams 72a and 72b when compared to the command temperature T<NUM>. Alternatively, multiple sensors <NUM> may be used to measure the temperatures of airstream 72a and 72b separately, and the signals may be weighted, for example, allowing the airstreams 72b to run somewhat cooler or hotter than the desired cooking temperature.

In this regard, it is important that the sensors <NUM> be placed after the openings and before the heater unit <NUM>. Referring now to <FIG>, generally a return air passage <NUM> may be provided on either the left or right side of the cavity <NUM> and/or at the rear of the cavity <NUM> providing a path of return air back to the blower <NUM> after the air exits through air distribution plate airstream openings <NUM>. The asymmetry in airflow from the introduction of air at inlets <NUM> at one end of each shelf <NUM> and the withdrawal of air, for example, from the side of the cavity <NUM> and its rear wall through the return air passage <NUM> can be compensated for by graduating the size of the airstream openings <NUM>, for example, to generally increase in size away from the return air port <NUM> (from <FIG>) and return air passage <NUM> and decreasing the hole sizes as one moves away from the air inlets <NUM> as depicted to establish a two-dimensional gradient indicated by arrows <NUM>. In one embodiment the temperature sensor <NUM> may be placed in this return air passage <NUM> to be protected from damage but to monitor excess heat introduced into the air from adjacent cavities.

Referring now to <FIG> and <FIG>, when a single door <NUM> is used on the oven <NUM>, it may be divided into a set of glass panels <NUM> separated from each other within a framework having horizontal separator mullions <NUM> generally aligned with a front edge of each shelf <NUM>. The glass panels <NUM> may provide for at least one insulating air layer (two separate spaces can be produced using an additional glass panel <NUM> not shown) that is vertically continuous to allow convection airflow through openings in the bottom of the door and out of openings at the top of the door (neither shown) to preserve a temperature to the outer surface of the frontmost glass panel <NUM> for safety. For this purpose, the mullions <NUM> may provide for a free passage of air upward between the glass panels <NUM>. A pliable gasket or compliant sealing flange <NUM> may be attached to the inner surface of the mullions <NUM> to fill the gap between the front edge of the shelf <NUM> and the door when the door <NUM> is closed reducing the flow of air or moisture between cavities <NUM>.

Referring now to <FIG>, <FIG> and <FIG>, as noted, the memory <NUM> of the controller <NUM> may hold a series of cooking schedules <NUM> (recipes) each providing cooking schedules <NUM> describing cooking parameters as a function of time. The schedules <NUM> may include a moisture schedule <NUM>, a temperature schedule <NUM>, and a blower speed schedule <NUM>. A schedule similar to the moisture schedule <NUM> (not shown) may control a smoker feature. The blower speed schedule <NUM> may include an average blower speed 104a (indicated by the dotted line) having a superimposed blower fluctuation function 104b, for example, increasing and decreasing blower speed so as to break up stagnant air patterns from the airstream openings <NUM> such as may contribute to uneven heating. By fluctuating the blower speed of the blowers <NUM>, hotspots in the food when the food is stationary with respect to the airstream openings <NUM> may be further reduced eliminating the need for conveyor systems or rotary platforms on which the food is placed to prevent localized burning of the food as opposed to a desired even cooking.

This schedule information is accessible by the controller <NUM> for all cavities <NUM> and may be used to accommodate the thermal interaction between cavities <NUM> (as has been discussed) and to instruct the user with respect to optimal loading of the oven <NUM>. More generally, the schedule information is used by the controller <NUM> to permit complex changes of temperature, moisture and airflow during cooking tailored to particular recipes. In this regard, the user may identify a recipe, for example, and the cooking of a certain food item in this recipe may be linked to a schedule developed for that food item without the need for the user to directly program the actual schedule.

Referring now to <FIG>, the airstream openings <NUM> in the air distribution plate <NUM> may provide a series of holes <NUM> of the variable size as discussed generally with respect to <FIG> joined by slots <NUM>. The airstream openings <NUM>, comprising both the holes <NUM> and slots <NUM>, create a slot-form extending the full width or depth of the oven (or diagonally between sidewalls of the oven) as described in <CIT> referenced above. Generally a width <NUM> of the slots <NUM> will be less than <NUM> (<NUM> inches) and preferably less than <NUM> (<NUM> inches) to reduce pressure loss in the channel <NUM> that could result from high slot area. The holes <NUM> are much larger than the slot <NUM> and maybe circular and may have a diameter ranging from <NUM> to <NUM> (<NUM> inches to <NUM> inches) to provide airstreams that help shepherd the air from the slots <NUM> while also minimizing loss of air pressure. Slot lengths may vary between <NUM> to <NUM> (<NUM> to <NUM> inches) and are preferably approximately <NUM> (<NUM> inches). The air distribution plate <NUM> is a thin sheet of metal, for example, stainless steel, with a thickness less than <NUM> (<NUM>/<NUM> inch) and typically less than <NUM> (<NUM>/<NUM> inch), such as may be easily formed using laser cutting techniques.

Referring now to <FIG>, the compact shelf arrangement of the present invention is facilitated through the use of a control program that helps allocate different cooking recipes to the proper cavities <NUM>. In this respect, the user interface <NUM> may provide for a graphic indications, for example, providing an icon 114a-c associated with each of the cavities 20a-d and arranged vertically in a manner similar to the cavities <NUM>. Any given cooking schedule <NUM> being implemented by a cavity may be identified, for example, by a recipe label name <NUM>.

In a first case, if there are no other cavities <NUM> being used, the user may enter a new desired recipe (associated with a schedule <NUM>) at process block <NUM>. For example, the user may indicate a desire to cook bacon strips having a peak cooking temperature of <NUM> (<NUM> degrees Fahrenheit). Using one or more of the peak and average temperature of identified schedule <NUM>, an operating program <NUM> of the controller <NUM> will recommend one or more of the four cavities <NUM> to the user for placement of the desired food item of bacon strips. In making this recommendation, the operating program <NUM>, in the absence of other schedules of cooking items, operates to place high temperature recipes in the higher cavities <NUM> to take advantage of natural temperature gradients established by convective effects thereby conserving power and improving compatibility between possible additional recipes. In one embodiment, schedules <NUM> having an average or peak temperature above <NUM> (<NUM> degrees Fahrenheit) are preferentially placed in the top or upper two cavities 20a and 20b and this recommendation is enforced by a graying out on user interface <NUM> of the icons <NUM> for lower cavities 20c and 20d. Conversely, schedule <NUM> having an average or peak temperature of less than <NUM> (<NUM> degrees Fahrenheit) is preferentially placed in the bottom or lower two cavities 20c and 20d.

In a second case, where there is already food being cooked, the operating program <NUM> makes recommendations of cavity loading based on the schedules <NUM> of the food being currently cooked and the new food to be cooked at process block <NUM>. The operating program <NUM> then recommends a cavity <NUM> for the new food necessary to ensure that the difference in temperature between two adjacent cavities does not exceed the maximum temperature difference practical with the shelves <NUM> using active insulation. For example, the maximum temperature difference may be <NUM>,<NUM> (<NUM> degrees Fahrenheit) or another predetermined value for example <NUM> (<NUM> degrees Fahrenheit) depending on the characteristics of the oven, and the operating program <NUM> may review each cavity <NUM> to test whether this maximum temperature difference would be exceeded and if so to gray-out those cavities preventing the user from using them for the new recipe. Thus, for example, if bacon strips are being cooked in cavity 20b at <NUM> (<NUM> degrees Fahrenheit) and the new food to be cooked is cheesecake at a cooking temperature of <NUM> (<NUM> degrees Fahrenheit), the operating program <NUM> will require the user to select cavity 20d separated from cavity 20b by cavity 20c. Specifically adjacent icons 114a and 114c may be grayed out as indicated by process block <NUM> to indicate those cavities <NUM> are not available and control for those cavities <NUM> may be locked out from the user. Instead, a lower cavity 114d is identified for a low temperature cheesecake recipe providing sufficient thermal isolation between cavities associated with the cheesecake.

Conversely if the temperatures of the schedule of the new recipe is within the necessary temperature difference required of adjacent cavities <NUM>, the new food item is placed in a cavity closest to the currently cooking food item so as to reduce energy usage by reducing the temperature difference across the partitioning shelf and thus heat transfer through the partitioning shelf.

Once the proper cavity is selected, the user may then press a start button (implemented on user interface <NUM>) as detected by decision block <NUM>. As part of this process, the user may acknowledge that he or she is using the cavity location recommended by the control program <NUM> at decision block <NUM>. After this acknowledgment, cooking is begun as indicated by process block <NUM>. Failure to acknowledge the correct cavity provides an error message to the user at process block <NUM> and allows a reentry of the necessary recipe data.

During the cooking process of process block <NUM>, the control system controls the heater, blower, moisture, and smoker as provided by the cooking schedules <NUM> of <FIG>.

When the door <NUM> is opened, for example, and is detected by sensor <NUM>, the speed of the blowers <NUM> may be moderated to reduce air escape through the open door. For example, the blowers <NUM> may be operated at a low level but a level sufficient for the suction force of the return air to generally prevent heated air from escaping out the open door, and the schedules <NUM> may be halted to account for lost cooking time. As noted above, at all times during the cooking of food in adjacent cavities <NUM>, a predetermined minimum airflow is provided through the channels <NUM> of the shelves <NUM> to prevent excess heating of the air flowing through the channels <NUM> such as could not readily be corrected or compensated for using the temperature control system. This airflow may be selected, for example, to ensure less than a <NUM> (<NUM> degree Fahrenheit) increase in temperature of the air flowing through the air channel <NUM> based on knowledge of the temperature of the adjacent air in the adjacent air channel.

Referring again to <FIG>, the invention contemplates that a complex schedule for multiple foods cooked at different temperatures having different schedules <NUM> may be entered into the control program <NUM> at process block <NUM>. In this case, the program <NUM> may have an overview of the entire cooking process for improved cooking control. The program <NUM> may make use of the same compatibility rules described above and knowledge of the cooking times to completely schedule start times and cavity locations of foods to provide both compatibility of cooking temperatures and simultaneous or scheduled completion of each food item. Because the scheduled start times of the cooking of each food item is known, more sophisticated matching of cavities to recipes may be performed by looking not at peak or average cooking temperatures over the entire cooking process but rather only peak or average cooking temperatures during the period of overlap of cooking between the two cavities.

Certain terminology is used herein for purposes of reference only, and thus is not intended to be limiting. For example, terms such as "upper", "lower", "above", and "below" refer to directions in the drawings to which reference is made. Terms such as "front", "back", "rear", "bottom" and "side", describe the orientation of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms "first", "second" and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context.

When introducing elements or features of the present disclosure and the exemplary embodiments, the articles "a", "an", "the" and "said" are intended to mean that there are one or more of such elements or features. The terms "comprising", "including" and "having" are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It is further to be understood that the method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance.

Claim 1:
A multi-cavity oven (<NUM>) comprising:
a housing (<NUM>) defining an interior cooking volume (<NUM>) surrounded by insulated outer walls (14a, 14b, 14c, 14d, 14e) and at least one door (<NUM>) that may open and close to provide access to the interior cooking volume;
a set of shelves (22a, 22b, 22c) subdividing the cooking volume into cooking cavities (20a, 20b, 20c, 20d), the shelves comprising separate upper and lower air channels (24a, 24b) divided by at least one interior barrier wall, each air channel leading from respective air inlets (32a, 32b) to respective upwardly directed airstream openings (<NUM>) and downwardly directed airstream openings (<NUM>) through a jet plate (<NUM>), wherein the set of shelves are removable from the interior cooking volume;
the multi-cavity oven (<NUM>) further characterized by comprising:
electrically controllable water valves (<NUM>) for introducing moisture into each of the cooking cavities; and
a controller (<NUM>) configured to provide independent control of moisture according to the cooking schedule in each of the cooking cavities;
wherein each of the cavities (20a, 20b, 20c, 20d) is associated with an airflow system (<NUM>) comprising a heater system, blower motor and variable speed motor controller so that the controller (<NUM>) independently controls the airflow circulating through each cavity <NUM> and the temperature of said airflow.