Combination oven with peak power control

A commercial oven, such as a combination oven providing steam and convection heating, may provide for two different peak power modes and for steam cooking. A temperature sensor sampling temperature from a region of the oven may be used to detect a complete filling of the oven with steam. The temperature of the temperature sensor is compared against different temperature thresholds depending on the selected peak power so that temperature may be used to discriminate steam filling for different peak power levels.

BACKGROUND OF THE INVENTION

The present invention relates to ovens for preparing food and in particular to a “combination” oven that may cook food with steam and convection airflow and that further provides for the adjustment of peak oven heating power.

High-end commercial ovens may provide for multiple cooking modes including heat augmented with forced airflow (convection) and heat augmented with steam. Generally, convection cooking uses a fan to disrupt the insulating effect of stagnant air around the food, increasing the heat flow to the food. This increased peak flow may be used, for example, to promote surface browning of the food. In contrast, the application of steam (typically also with operation of the convection fan) can provide for fast cooking while retaining food moisture, flavors, and nutrients. Steam cooking generally prevents surface browning. These different modes may be combined in sequence during a cooking cycle, for example, to rapidly cook meat and then to brown its surface.

Different heat sources are commonly used for ovens including electrical heating elements, which employ electrical current passing through a resistance in communication with the oven cavity, and gas heating elements, which provide for the combustion of gas and the circulation of the combustion exhaust through a heat exchanger in communication with the oven cavity. Temperature control of the oven is typically provided by switching the electrical current or the gas on and off according to a sensed temperature of the oven cavity. Such switching between on and off states greatly simplifies the control of the electrical current and gas elements.

Ovens of this type are commercially available from the Alto-Shaam Inc. of Menomonee Falls, Wis. and are described generally in U.S. Pat. No. 6,188,045, entitled “Combination Oven with Three Stage Water Atomizer” hereby incorporated by reference.

The speed with which an oven can attain a given temperature when loaded with food is normally determined by the peak power that may be delivered to the heating element when the heating element is continuously operating. Normally, this peak power of the heating element is selected to effect a desired trade-off between energy usage and oven performance.

The need to compromise between energy usage and oven performance can be relaxed by the use of the so-called “turbo” mode in which the peak power of the heating element is adjusted. Turbo mode may be desired when fast cooking speeds are of great importance.

SUMMARY OF THE INVENTION

The present invention provides improved integration of “turbo” mode adjustment of heater peak power into a combination oven providing steam cooking. In this regard, the inventors have determined that changing the peak power of the oven operation can adversely affect the ability to detect the presence of steam filling the oven cavity normally done with a temperature probe. If the filling of the oven cavity with steam is not accurately detected, food may dry or brown undesirably or prematurely in the steam cooking process. By modifying the steam sensing temperature threshold according to peak power setting, accurate control of steam cooking may be obtained and high peak power cooking can work smoothly with steam cooking.

In one embodiment, the present invention provides a combination oven having an insulated housing including a door closing to define an interior cooking cavity and an opening to provide access to the cooking cavity. A cooking cavity heater communicates with the cooking cavity to heat the cooking cavity, the cooking cavity heater providing at least two power settings according to a power signal. A steam generator produces steam within the cooking cavity according to a steam production signal. A first temperature sensor samples a temperature of the cooking cavity to provide a temperature signal and a second temperature sensor located near an outlet from the interior cooking cavity produces a second temperature signal. A controller communicates with the cooking cavity heater, steam generator and first and second temperature sensors, and executes a program stored in memory to (i) generate a steam detection signal as a function of the second temperature signal and the power signal and indicating the presence of steam filling the cooking cavity; and (ii) control at least one of the steam production signal and power signal according to a stored program according to the temperature signal and the steam detection signal.

It is thus a feature of at least one embodiment to accurately detect the presence of steam in the cooking cavity regardless of the power level of the heating elements.

The second temperature sensor may be at a bottom end of the cooking cavity.

It is thus a feature of at least one embodiment to detect when steam fills the entire oven cavity by situating the sensor away from the upper area where steam will naturally congregate.

A water trap may define a volume for holding water and providing a drain pipe communicating between the cooking cavity and the volume, wherein the second temperature sensor is located within the volume. Excess pressure or steam from the cooking cavity may escape through the drain pipe into the volume and exit through the outlet.

It is thus a feature of at least one embodiment to locate the steam sensor in an environment that will experience a significant temperature change for both high and low power levels. Trapped water which cools the steam and prevents excess heat from passing out of the oven cavity also cools the probe when steam is not present. Gases also pass the second temperature sensor to provide a continuous sampling of air steam.

The steam detection signal may be generated by comparing the second temperature signal against a threshold temperature linked to the power signal according to a stored program. The threshold temperature may be a higher temperature when at a higher power level compared to a lower power level.

It is thus a feature of at least one embodiment to provide a simple function for detecting steam from air temperature for different power levels. The threshold temperature is adjusted to deal with changes that occur when cooking at a “turbo” mode.

The at least two power signals may include at least two ON power signals which heat the cooking cavity at different heating levels.

It is thus a feature of at least one embodiment to provide a combination oven that cooks at at least two power output modes, such as normal and “turbo” modes.

The steam generator may be a boiler element having a volume for holding water and a boiler heating element. The steam generator may be a water nozzle directing water into a heating element.

It is thus a feature of at least one embodiment to provide a system that works with a variety of steam generation techniques.

A steam bypass conduit may communicate between the cooking cavity and the volume. Excess pressure or steam from the cooking cavity may escape through the steam bypass conduit into the volume and exit through the outlet.

It is thus a feature of at least one embodiment to provide a constant sampling of oven atmosphere for the detection of steam.

The first temperature sensor may be located within the interior cooking volume.

It is thus a feature of at least one embodiment to provide a separate temperature probe for detecting the cooking cavity temperature for determining on-off function of the heating element.

An alternative embodiment of the present invention provides a combination oven having an insulated housing including a door closing to define an interior cooking cavity and an opening to provide access to the cooking cavity. A cooking cavity heater communicates with the cooking cavity to heat the cooking cavity, the cooking cavity heater providing at least two power settings according to a power signal. A steam generator produces steam within the cooking cavity according to a steam production signal. A first temperature sensor samples a temperature of the cooking cavity to provide a temperature signal and a second temperature sensor located near an outlet from the interior cooking cavity produces a second temperature signal. A controller communicates with the cooking cavity heater, steam generator and first and second temperature sensors, and executes a program stored in memory to (i) generate a steam detection signal as a function of the second temperature signal and the power signal and indicating the presence of steam filling the cooking cavity when the second temperature signal is above a temperature threshold linked to the power signal; and (ii) control at least one of the steam production signal and power signal according to a stored program according to the temperature signal and the steam detection signal.

A first power setting is higher than a second power setting, and a temperature threshold correlating to the first power setting is higher than a temperature threshold correlating to the second power setting.

It is thus a feature of at least one embodiment to provide more than one cooking power modes and more than one temperature thresholds correlating to the power modes.

A first lower temperature threshold is used during steam generation and a second higher temperature threshold is used during cooking.

It is thus a feature of at least one embodiment to correct for the detection of the exhaustion of steam being delayed.

Still another embodiment of the present invention provides a method for operating a combination oven having the steps of providing a combination oven, as described herein, and inputting a user command into a control panel for setting the power signal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now toFIG. 1, a turbo-mode combination oven10according to one embodiment of the present invention may provide a housing12defining an oven cavity14with sidewalls of the oven cavity14providing for rack supports11holding conventional cooking racks for supporting pans or trays of food.

The oven cavity14may be accessed through a door16connected by a hinge at one vertical side of the oven cavity14. The door16may close over the oven cavity14during the cooking operation as held by a latch assembly15(visible on the door16only). In the closed position, the door16may substantially seal against the oven cavity14by compressing a gasket17surrounding an opening of the oven cavity14in the housing12.

At one side of the oven cavity14, the housing12may support a control panel22accessible by a user standing at a front of the oven10. The control panel22may provide conventional electronic controls such as switches, buttons, a touchscreen or the like that may receive oven control data from the user as will be described below.

Referring now also toFIG. 2, a motor-driven convection fan18may be positioned within the housing12to direct a stream of air across a heater element20into the oven cavity14. The heater element20may be an electric heating element or a heat exchanger receiving heat from a gas flame or the like and may surround the convection fan18.

Steam may be introduced into the oven cavity14, for example, by a valve-controlled water nozzle19directing a spray of water on the fan18and the heater element20proximate to the fan18. Alternatively, steam may be provided by a separate boiler21having a dedicated heater element23and communicating with the oven cavity14.

Ovens of this type are commercially available from the Alto-Shaam Inc. of Menomonee Falls, Wis. and are described generally in U.S. Pat. No. 6,188,045, entitled “Combination Oven with Three Stage Water Atomizer” hereby incorporated by reference.

Referring still toFIG. 2, a bottom wall31of the oven cavity14may expose a channel to a drainpipe25extending downwardly from the bottom wall31to a condenser chamber30positioned beneath the bottom wall31. The drainpipe25may extend vertically (as shown) or may extend horizontally for a short distance before or after it is received within the condenser chamber30. In either case, the drainpipe25allows steam and water vapor to enter the condenser chamber30which provides a generally enclosed box whose upstanding sidewalls retain a pool of water having a water level36. The lower end of the drainpipe25passing into the condenser chamber30stops above the bottom wall33and above a water level36.

An opposite end of the condenser chamber30provides an exit port32leading to the outside atmosphere. A baffle plate38extends downward from an upper surface of the chamber30below the water level36to separate the drainpipe25from the exit port32except by a path passing through the contained water. Excess pressure from cooking or from steam may escape through the drainpipe25bubbling through the water under the baffle plate38to the exit port32. This process cools the steam and prevents excess heat from passing out of the oven cavity14as might occur if there were a direct path to the outer atmosphere.

A variation on this design of the condenser chamber30is shown in U.S. patent application Ser. No. 13/306,687 filed Nov. 29, 2011, entitled “Grease Handling Apparatus for Closed-system Oven” assigned to the same assignee as the present invention and hereby incorporated by reference.

Referring still toFIG. 2, a steam bypass conduit40may also lead from within the oven cavity14to condenser chamber30to a temperature sensor42, for example, positioned on the same side of the baffle plate38as the drainpipe25. The steam bypass conduit40and the drainpipe25may be situated at slightly different regions of pressure within the oven cavity14when the fan18is operated, so that the gases near the bottom of the oven cavity14flow past the temperature sensor42to provide a continuous sampling of air or steam from near the bottom of the oven cavity14.

An internal controller37may be positioned within an equipment cavity adjacent to the oven cavity14but maintained at a cooler temperature. The controller37provides a computer processor providing a processor and associated memory, for example, flash memory, for executing a program held in the associated memory. Execution of the program may generate control signals output by interface circuitry of the controller37to components of the oven10and may read sensed signals from the user and various sensors within the oven10. For example, the controller37may receive signals from temperature sensor42in the condenser chamber30, one or more internal oven temperature sensors45in the oven cavity14, each providing temperature signals (X1), as well as signals from the control panel22providing user commands. The controller37may output convection control signals to a motor43operating the fan18(to control a convection mode of the oven10). In addition, the controller37may output steam control signals to a valve44communicating between a water supply and the nozzle19to generate steam, or alternatively to electrically controlled switch47communicating between line power and the heater element23to generate steam. In addition the controller37may provide a heat power signal to a heater controller46controlling heating elements20according to four states of peak power output including: off, a first peak power level, and a second peak power level greater than the first peak power level and a third power level greater than the second power level. Typically, the third peak power level will be at least 10% larger than the second peak power level, for example, boosting the peak power of the heating elements from 10 kilowatts to 14 kilowatts.

Referring now toFIGS. 2, 3 and 5, the program50executing on the controller37may receive a mode input command from a user, for example, as entered through control panel22and as represented by decision block52. This mode input will generally indicate a desired peak operating power either directly or as linked to the identification of a predetermined “recipe” by the user, the recipe also providing a schedule of cooking temperatures and cooking modes (convection, steam) in turn associated, for example, with an identified type of food preparation. When the operating power is designated directly, the user may also input other operating parameters such as the cooking mode and temperature directly.

Upon completion of that peak power mode entry, the program50moves to a process block that sets the peak operating power of the oven10, the mechanics of which will be discussed below and as may vary depending on the source of heating energy. As shown generally inFIG. 5, “Power0” of process block88will generally be a low-power, “Power1” of process block54will be a normal power and “Power2” process block83will be a high or turbo power.

For example, the user may select a standard operating mode “Power1” in which the peak power is set at process block54to a standard power level for example of approximately 10 kilowatts. The cooking cycle than proceeds to a steam generation stage indicated by process block56where steam is generated either by activation of the boiler21(and dispersed by the fan18with additional heat added by the heater element20) or activation of the nozzle19to direct water against a heater element20under the guidance of the fan18.

During steam generation stage of process block56, the temperature (X1) in the oven cavity14is moderated to prevent a high temperature cooking of the food until the oven cavity14is filled with steam.

This moderation is a simple matter if the oven cavity temperature intended for cooking is below the steam point of 212 degrees Fahrenheit, and simply requires that the oven cavity temperature probe45be monitored to moderate the temperature of the oven cavity by switching the heater elements20on and off.

On the other hand, if the oven cavity temperature intended for cooking is above 212 degrees Fahrenheit, the oven temperature must be moderated until the oven has filled with steam. If steam is being generated by the nozzle19, the nozzle is activated during this period so that the formation of steam limits the temperature to approximately 212 degrees. If the boiler21is being used for steam production, the temperature is moderated by overriding the setpoint temperature of the oven (preventing the use of the highest power level as will be described) and relying on the stabilizing effects of the introduced steam during this steam generation time.

As shown diagrammatically inFIG. 3, during this filling stage58steam60may partially fill the oven cavity14concentrating in its upper portion because of its relative temperature and/or shielding by food on the racks (not shown) and thus the high temperature of the steam60is removed from the condenser chamber30and thus from temperature sensor42. A low temperature on temperature sensor42, then generally indicates that the oven cavity has not fully filled with steam. Specifically, during the initial stages of steam generation, a temperature signal62from the temperature sensor42(as monitored by decision block66) will remain below an empirically determined steam overflow temperature64(B1), although generally rising over time slightly with increased heating of the oven cavity14. As will be discussed further below, the steam overflow temperature64is linked to the peak power of process block54.

When steam60completely fills the oven cavity14, it is drawn into the condenser chamber30to contact the temperature sensor42and the temperature signal62rises above the steam overflow temperature64of B1. This rise is relatively rapid in part because of the high specific heat of the steam60, and is detected at decision block66. For as long as the temperature signal62is below the steam overflow temperature64, the program50loops from decision block66back to the steam process block56, however when the temperature signal62rises above the steam overflow temperature64, the program proceeds to a cooking stage indicated by process block68.

Referring toFIG. 6, the cooking stage of process block68resets the set point temperature of the oven10from any lower temperature (X1) used during steam formation temperature to a desired cooking temperature (X2) as indicated by process block72and sets a timer for the desired cooking time based on the user's input entered either directly or indirectly through recipe designation. Periodically, the timer is checked to see if the time value has expired as indicated by decision block74. If the timer has expired, then the program passes to an exit block76terminating the cooking process. If the timer has not expired, however, the program50proceeds to decision block70and the temperature of the oven cavity14is compared against the cooking temperature (X2) set at process block72. If the temperature of the oven cavity14as determined from temperature sensor45is above the cooking temperature X2, then the heating elements20are turned on as indicated by process block80to provide the selected peak power. On the other hand, if the temperature of the oven cavity14is below the cooking temperature X2, the heating elements20are turned off as indicated by process block82. A dead band providing a few degrees of temperature hysteresis may be implemented to prevent rapid on-off switching of the heater element20. This dead band, for example, may provide for two slightly displaced thresholds, a higher one used when the heater element20is on to determine when the heater element20should be switched off and a lower one used when the heater element20is off to determine when the heating element should be switched on. This temperature control is thus provided by a simple on and off switching of the heater element20whose peak power is independently controlled by the mode setting of process block54.

Referring in particular toFIG. 3, as the cooking stage of process block68continues, steam60may be lost or absorbed by the food product raising the risk of undesired food burning or browning. This loss of steam60withdraws steam60from temperature sensor42causing temperature signal62to fall. This fall in temperature is detected by decision block70triggering the program50to return to the steam mode of process block56so that more steam60is generated in a refilling mode69as shown diagrammatically inFIG. 3. Typically, return to the steam mode of process block56does not reset the oven cavity temperature to its moderated value of X1because steam60can be replenished rapidly enough to prevent significant change in the cooking environment with respect to drying or browning.

WhileFIG. 3depicts a relatively sharp stratification of the steam60, it will be appreciated that this represents a simplified interpretation of the mechanism for rapid temperature rise at temperature signal62which may also in part reflect a relative average change in the humidity within the oven cavity14as sampled by the condenser chamber30, transport delays of the steam into the condenser chamber30and other mechanisms and the invention should not be limited by this interpretation of the underlying mechanism.

Referring now toFIGS. 3, 4 and 5, in an alternative mode of operation, the user may select a turbo mode of operation at decision block52causing the program50to proceed to process block83where the peak power available to the heater elements20is increased to a power level greater than that provided at process block54. The mechanism for increasing this power level will be described later.

After adjusting the peak power level, the program50proceeds to a steam generation stage of process block56′ substantially identical to that described with respect to process block56with the following exception. If the cooking temperature X2is above 212 degrees Fahrenheit and steam is being generated by the boiler21, the peak power level is set back to the standard level for the steam generation process only. Otherwise the higher setting of peak power is used when steam is generated using the nozzle19.

The filling of the oven cavity14with steam60is assessed periodically at decision block66′ which evaluates the temperature signal62′ (shown inFIG. 4) of the temperature sensor42to determine whether the oven cavity14is filled with steam. During the steam generation process, the turbo mode operation with its higher power output may result in a faster rise in temperature signal62′ exceeding steam overflow temperature64even before the oven cavity14is filled with steam60. Accordingly, the inventors have determined that a higher temperature threshold84(B2) must be adopted at decision block66′. It will be appreciated fromFIG. 4that without a change in this threshold, the cooking stage of process block68would occur early, at time86, possibly causing undesired cooking of food positioned near the bottom of the oven cavity14.

At the conclusion of the steam cycle of process block56′, the program again switches to the cooking cycle of process block68′ substantially identical to process block68and cooking temperature is boosted for cooking. If the peak power was reset in the steam generation of process block56, it is returned to its boosted state. The turbo mode of higher peak heating power results in a rapid rise in the temperature signal62′ beyond that which was experienced in the non-turbo mode of process block54and as is desired for rapid cooking.

Upon the exhaustion of steam during cooking, the temperature signal62′ begins to fall, however, it has been determined that if the temperature threshold84is used, detection of the exhaustion of steam60will be erroneously delayed. Accordingly, a third temperature threshold90above temperature threshold84(designated B3) is established for use at decision block70′ (corresponding approximately to previously described decision block70) to determine when the steam mode should be reinitialized at process block56. In this way the implicit tuning that controls the detection of steam60through a temperature sensor42in the chamber30may be for non-turbo mode may also accommodate the significant peak power increase of turbo mode. This selection of the temperature thresholds84and90is triggered by the higher power level selected at process block83

Referring again toFIG. 5, the oven10may also provide a reduced power mode may also be provided by the controller as indicated by process block88. In this reduced power mode the heating elements20may be constrained to operate at a reduced peak power level lower than the power levels set at process blocks54and84. In this reduced power mode, steam is generated as indicated by process block56″, a steam fill is detected at decision block66″, cooking is controlled at process block68″ and steam refreshing is controlled at process block70″ corresponding to the similarly numbered process blocks used for standard cooking of56,66,68, and70. In this regard, the temperature threshold64is used for the detection of steam before and after the cooking stage, similar to process block54.

In operation, a mode input command is entered by the user, for example through a control panel22, for indicating a peak operating power. The peak operating power may correlate to the normal54, turbo83, or reduced88power modes described above and indicated by process blocks54,83, and88, respectively. Alternatively, the user may input a “recipe” which is linked to a schedule of cooking temperatures and cooking modes.

The controller37receives the mode input command or “recipe” from the user correlating to a desired peak operating power and the oven cavity14proceeds to fill with steam, e.g., by nozzle19or boiler21described above, and shown by process blocks56,56′,56″. The controller37then monitors a temperature signal from temperature sensor42indicating the temperature at a lower end of the cavity14. The controller37executes the stored program50to generate a steam detection signal indicating that the oven cavity14is fully filled with steam as a function of (1) the temperature signal from temperature sensor42and (2) the mode input command. A predetermined threshold temperature is linked as a function of the particular mode input command. The temperature signal from temperature sensor42is compared to the threshold temperature. A temperature signal from temperature sensor42that is higher than the threshold temperature indicates the presence of steam sufficiently filling the cavity and a steam detection signal is generated.

The threshold temperature will be higher for mode input command set at the “turbo” power mode83, and the threshold temperature will be lower for mode input commands set at the normal54power mode (or reduced88power mode), as the faster rise in temperature during “turbo” mode83may result in an inaccurate steam indication and must be adjusted accordingly.

The steam detection signal indicating that sufficient steam is present in the oven cavity14allows the controller37to proceed to the cooking process, shown by process blocks68,68′,68″, and sends a power signal to heating elements20to begin cooking. The controller37will periodically receive a temperature signal from temperature sensor45within the oven cavity14to indicate whether heating elements20should be turned on or off to provide the desired peak operating power, as shown by program50inFIG. 6.

As the cooking process continues and steam within the oven cavity14is lost, the temperature sensor42will indicate a declining temperature signal so that steam must be regenerated. The loss of steam is again indicated as a function of (1) the temperature signal from temperature sensor42and (2) the mode input command, as provided by program50executed by controller37. When the temperature signal falls below a predetermined threshold temperature, the steam generation stage is reentered.

The threshold temperature may be the same or different as the threshold temperature provided during the steam generation stage. For example, in “turbo” mode, the threshold temperature (designated B3) during the cooking stage may be higher than the threshold temperature (designated B2) during the steam generation stage in order to correct for the erroneous delay of the exhaustion of steam.

If it is indicated that steam has been lost below an acceptable level, the steam generation stage, shown by process blocks68,68′,68″, is repeated until (1) the temperature signal from temperature sensor42and (2) the mode input command indicate the presence of sufficient steam filling the cavity, as provided by program50executed by controller37, as previously described above. Referring now toFIG. 7, when the heater element20is an electrical heating element, the ability to set different peak heating powers at process blocks54,84, and88may be implemented by selectively connecting either or both of two switchable resistive elements92in parallel with a base heating element93(being a parallel connected pair of elements) for heating of the oven cavity14. All resistive heating elements92and93may be switched in tandem by means of an electrically controllable switch94opened and closed by the program operations of process blocks80and82. A first switch96in series with only one of the resistive elements92and a second switch97in series with the other of the resistive elements may be controlled by the power setting process blocks54,84, and88switching from a low power level of process block88by opening both of switches96and97, to a standard power level of process block54by closing switch96and keeping switch97open, and switching to the high-power level of process block83by closing both switches97and96and a high power level of process block83by closing switch96. Each of these switches94,96and97may be directly controlled by the controller37.

Referring now toFIG. 8, when the heater element20is a gas heating element, a four state valve98may deliver three nonzero flow levels of gas to a gas jet100with a lowest gas flow used for power setting of process block88and a highest gas flow used for turbo mode of process block83. The valve98may also shut the gas off completely so as to provide for temperature control of process blocks80and82. The gas jet100releases the gas flow into a combustion chamber102where the gas is burned. The exhaust is then released into exhaust pipe104which directs the exhaust away from the heater element20.