Variably adjustable clock ratio

Abstract

The method involves adjusting a duty ratio of a fan of a cooking device in a standstill operating phase based on a function of temperature drop in a cooking chamber of the cooking device, where the duty ratio depends on a program that provides prolonged standstill phases for dry cooking or prolonged halt phases, cooking chamber temperature (T), or charging of the cooking device. The temperature drop is determined based on course of temperatures (T1-T3) in the cooking chamber during a standstill phase of the fan.

Description

[0001] The invention relates to a method for cooking a food in a cooking appliance having a heater and a fan that can be operated at intervals.

[0002] Such a method is known from DE 10 2010 012 368 A1. For energy savings, the fan is always switched off when a hot-air heater intended for heating the cooking chamber is switched off. However, the method disclosed in this document is not variable, since a fixed cycle time, i.e., a fixed ratio of operating to standstill phases of the fan, is provided.

[0003] From DE 43 19 613 C1 a method is known in which a fan switches between two operating modes with an active fan, a recirculation mode and a top and bottom heat mode, depending on the cooking chamber temperature.

[0004] DE 10 2009 024 546 A1 shows a method which includes an energy saving mode in which a fan can be switched to a standstill phase and yet the standby temperature in the cooking chamber is maintained.

[0005] DE 10 2008 040 981 A1 describes a process in which a fan actively blows cold air onto a temperature sensor so that it measures a lower temperature than the actual temperature in the cooking chamber.

[0006] DE 26 21 927 discloses a method for cooking food in which a circulating air fan is switched on and off depending on fixed temperature thresholds.

[0007] EP 2 287 533 A1 describes a method for operating a cooking appliance in which a cooling fan is controlled which is assigned to a control unit, the control being carried out via a temperature sensor provided in an installation space.

[0008] DE 20 2004 015 290 U1 describes a method and a device in which the energy input into the food to be cooked is to be carried out evenly by applying an air stream evenly to the food.

[0009] The object of the invention is to further develop the cooking process so that a better, reproducible quality of the cooked food is achieved.

[0010] To achieve this object, the invention provides a method according to claim 1.

[0011] Depending on the cooking program, a drying program for almonds, for example, can use a cycle time with long fan idle periods to ensure a quiet cooking chamber climate. The idle periods are only interrupted by short fan operating phases, which ensure minimum air circulation, thus ensuring sufficient energy input to the almonds.

[0012] For a cooking program that requires longer holding phases, a cycle time with longer standstill phases can also be used. This ensures that the food doesn't dry out.

[0013] Falling below the predetermined threshold indicates that the core temperature of the product to be cooked is approaching the setpoint, so that the proportion of phases during which energy is supplied to the cooking chamber can be reduced.

[0014] The cycle rate therefore depends on the temperature. For example, at cooking temperatures below 100 °C, such as those used for drying food, longer standstill periods can be used. At temperatures above 240 °C, however, either short standstill periods or no standstill periods at all are used, since in these temperature ranges, maximum energy input into the food being cooked is essential, for which air circulation is advantageous.

[0015] For example, the proportion of downtimes increases as the cooking chamber temperature rises. A rise in the cooking chamber temperature indicates that sufficient energy is currently being supplied to the cooking chamber. This allows the fan to be temporarily switched off.

[0016] Preferably, the proportion of standstill phases is initially doubled, then the cooking chamber temperature curve is evaluated over a certain period of time, and then the proportion of standstill phases is doubled again if the cooking chamber temperature continues to rise. With such a control strategy, the cycle rate can be very quickly adapted to the respective requirements by extending the standstill phases in very large increments until the desired effect on the cooking chamber temperature is achieved.

[0017] The cycle rate can depend on the derivative of the measured temperature with respect to time, i.e., the slope of the temperature curve. This allows additional parameters to be used to adapt the currently used cooking program to the requirements. For example, if the slope of the temperature curve is low and the measured temperature, such as the core temperature, is still far from the setpoint, the proportion of downtime phases can be reduced to prevent the cooking process from taking too long.

[0018] If the temperature is measured at the shaft of a core temperature probe and the gradient of the temperature curve is negative, the proportion of standstill phases can be reduced. In this case, negative values ​​of the temperature derivative with respect to time indicate that the product is transferring heat to the cooking chamber.

[0019] According to one embodiment, the cycle rate depends on the cooking appliance's load. A high load leads to high heat dissipation in the cooking appliance, so a lower proportion of downtimes is generally advisable.

[0020] It can be provided that, when the cooking appliance is loaded above an upper threshold, the proportion of idle phases is reduced, in particular halved. This results in an approximately adjusted starting value for the cycle rate, which can, however, be further individually adjusted depending on other parameters, such as the cooking temperature profile. The same applies when the cooking appliance is loaded below a lower threshold; in this case, the proportion of idle phases is increased, in particular quadrupled.

[0021] The cycle rate can also be set to depend on the size of the products to be cooked in the cooking chamber. For example, a higher proportion of downtimes can be used for larger products, for example, by quadrupling the pause times.

[0022] To determine the caliber, the core temperature can be evaluated over time. This can be easily integrated into intelligent cooking programs.

[0023] The calibre of the products to be cooked can be taken into account by using a greater proportion of standstill phases when the calibre is above a predetermined threshold.

[0024] Preferably, the core temperature is also taken into account, meaning that the caliber-dependent extension of the standstill phases is only permitted once the core temperature has already risen. Otherwise, the cooking process would take too long.

[0025] Preferably, the heat loss in the cooking chamber is determined based on the temperature profile during a fan standstill phase. This eliminates disruptive factors, such as energy input from the fan.

[0026] Preferably, the proportion of idle phases is reduced when heat loss exceeds a predetermined threshold. A higher proportion of fan operating phases ensures that a large amount of energy can be supplied to the cooking chamber, thus compensating for the high heat loss in the cooking chamber.

[0027] According to one embodiment, it is provided that the amount of energy required to supply the cooking chamber until a target temperature is reached is determined, and that the proportion of downtime phases is subsequently reduced if the required energy was above a predetermined threshold. This also makes it possible to adapt the cycle rate to the heat loss in the cooking chamber with minimal effort, thus achieving high, reproducible quality in the cooked products.

[0028] According to one embodiment of the invention, an energy-saving button is provided on the cooking appliance, whereby the proportion of idle phases is increased, in particular doubled, when the energy-saving button is pressed. This allows an operator to influence the currently used cooking process in such a way that the focus is on energy savings, while, in return, an extension of the cooking time is tolerated.

[0029] It can also be provided that the operator can select a quieter operating phase, in which case the proportion of idle phases is increased. This allows a quieter operating mode to be temporarily set if the operating noise generated by the cooking appliance is perceived as disturbing by the operator.

[0030] According to one embodiment of the invention, the proportion of idle phases is reduced when the temperature in the electrical installation compartment of the cooking appliance is above a predetermined threshold. This ensures that a high proportion of fan idle phases, which are desirable for the current cooking program, does not lead to heat buildup in the electrical installation compartment of the cooking appliance.

[0031] According to one embodiment of the invention, the fan can be operated with alternating directions of rotation, and standstill phases are synchronized with a change in the direction of rotation. This prevents the fan from restarting after a standstill phase and then, shortly thereafter, decelerating and then starting again in the opposite direction because the direction of rotation is reversed. Instead, in such a case, the fan would immediately start operating in the new direction of rotation.

[0032] According to one embodiment of the invention, two or more temperature sensors are evaluated, and the standstill phases are shortened or aborted if the difference between the temperatures detected by the two temperature sensors, in particular the shaft temperature and the cooking chamber temperature, exceeds a threshold value. Exceeding the threshold value indicates an uneven temperature distribution in the cooking chamber, which is counteracted by longer fan operating phases.

[0033] The invention is described below with reference to an embodiment shown in the attached single drawing.

[0034] Generally speaking, the method according to the invention provides that the fan's duty cycle, i.e. the ratio of operating to idle phases, can be variably adjusted to suit the respective requirements. The main parameter that determines the selected duty cycle is the heat loss in the cooking chamber, i.e. the amount of heat absorbed by the food in the cooking chamber, the accessories located in the cooking chamber, and the boundaries of the cooking chamber (i.e., side walls, floor, ceiling, and door). In other words, the heat loss in the cooking chamber corresponds to the amount of energy that must be supplied to the cooking chamber to maintain a constant temperature. Other parameters that influence the duty cycle are the cooking chamber temperature, the food being cooked, the cooking program, and various temperature profiles.

[0035] The duty cycle can generally be freely adjusted. Examples include an on-time of 25 seconds and an off-time of 360 seconds, or an on-time of 15 seconds and an off-time of 1,000 seconds. Additionally, the fan speed can be varied during operation, either continuously or in predefined steps. The respective duty cycle can be saved in the cooking appliance's control system and integrated into a cooking program or process as needed.

[0036] The particular advantage of an automatically adjusting cycle rate becomes clear when considering the effects of varying load volumes. Surprisingly, it was found that, with smaller load volumes, it is advantageous to use a larger proportion of idle phases in the cycle rate. This not only reduces energy consumption, as the fan drive motor operates less frequently, but also reduces heat loss through the cooking chamber walls and door. With maximum loads, however, the proportion of idle phases should be reduced, as otherwise, temperature stratification can occur in the cooking chamber, leading to uneven cooking (the items positioned at the top receive more energy).

[0037] The load quantity can be detected based on existing load detections (e.g. based on the temperature drop after loading, based on the gradient of the temperature rise after loading or by weight measurement, customer input or other data input such as barcode scanning, moisture development in the cooking chamber, energy decrease and / or energy consumption).

[0038] For example, half the cooking chamber load can be considered a standard value. A high load would then halve the fan idle periods, while a low load would quadruple the fan idle periods. In concrete terms, this could mean that a low load would result in an operating phase of 10 seconds followed by an idle phase of 440 seconds.

[0039] Another parameter that influences the cycle rate is the type of food being cooked. For example, when roasting almonds or drying moist fruit slices, such as apple rings or orange slices, it is preferable to have a short period of standstill at the beginning of the drying process to remove the moisture from the surface of the food so that the moisture from the inside can flow in and is then removed. In order to quickly remove the high level of moisture present at the beginning of a drying process, it is best to have the fan running continuously. However, once the drying process is further advanced, the limiting parameter for the drying speed is the inflow of moisture from the inside of the food. Therefore, during this phase the fan is reduced or operated in cycles, i.e. with a high proportion of standstill phases, in order to maintain a calm cooking chamber climate.Only a small minimum proportion of fan operating phases is used, which ensures sufficient energy transfer but prevents over-drying of the food surface, which could lead to a porous structure.

[0040] Another parameter that influences the cycle time is the cooking method. For example, low-temperature cooking requires less air circulation, meaning a higher proportion of fan idle phases, to prevent the surface of the food from drying out. Furthermore, in drying processes, it is not necessary to constantly maintain an airflow on the surface of the product being dried, as moisture removal from the surface is limited by water transport inside the cooking appliance, at least in an advanced drying phase. If a high airflow were to force a high level of moisture removal from the surface, this would lead to a brittle end product. Even with weight-saving cooking, it is desirable that the product being cooked does not dry out. In this case, a high proportion of fan idle phases is advantageous so as not to disturb the microclimate around the food.

[0041] Preferably, it is provided that the user can save the timing ratios he has tested and found to be good and integrate them into the cooking programs or processes, individually for each cooking program step.

[0042] The cooking program currently in use also fundamentally influences the appropriate cycle ratio. For example, when steaming, a small proportion of fan idle phases are used, as otherwise steam mixing in the cooking chamber cannot be guaranteed. During the searing and crusting phases of a cooking program, however, only short fan idle phases are advisable in order to ensure maximum energy input into the product being cooked. During the holding phases of a cooking program, however, long idle phases can be inserted without this negatively affecting the quality of the products being cooked. During a cleaning program, idle phases can be used if excessive foaming is detected.

[0043] In principle, the respective duty cycle is not linked to the switching on and off of the cooking appliance's heater. In other words, there is no mandatory link that requires the fan to be switched on when the heater is switched on, or that requires the heater to be switched on when the fan is switched on.

[0044] The attached figure shows how the fan's timing changes depending on the heat dissipation in the cooking chamber. The lower part of the diagram shows the fan's operation; for simplicity, it is assumed that the fan is operating at a constant speed. Thus, the state changes between an operating phase (the curve has the value "1") and a standstill phase (the curve has the value "0"). The cooking chamber temperature T is used here as a specific parameter that correlates with the heat dissipation in the cooking chamber. During an initial standstill phase of the fan, the temperature in the cooking chamber drops from temperature level T 1 to temperature T 2 . The difference between these two temperatures is detected as being above a predefined threshold.In a subsequent operating phase, the duty cycle is then changed so that longer operating phases and shorter fan standstill phases are used. After three fan operating phases, a longer standstill phase is inserted again, as a test, to check the extent of the heat loss in the cooking chamber (and thus the temperature drop). After the standstill phase is over, the temperature in the cooking chamber has dropped to a value T 3, with the difference between the temperatures T 1 and T 3 being below a predetermined threshold. This tells the cooking appliance's control system that a duty cycle with a larger proportion of standstill phases can now be used.

[0045] Alternatively, the timing ratio can be adjusted by evaluating how much energy is required to reach a target temperature again after a standstill period. The fan is preferably operated continuously until the target temperature is reached again.

[0046] With the method according to the invention, the energy of the resulting moisture (heat of vaporization) can also be determined by measuring the humidity in the cooking chamber and / or the evaporation rate. This moisture originates from the food. The fan is then controlled so that the heat loss is reduced by the heat of vaporization.

[0047] Heat loss in the cooking chamber can also be determined by the core temperature. By measuring the core temperature, a heat gradient in the food can be determined. The lower the gradient, the less energy flows into the food. Therefore, heat loss in the cooking chamber must be reduced.

[0048] It may also be planned to compare the change or absolute value of weight loss during a standstill phase with that of an active phase. The heat loss is adjusted so that they are identical.

[0049] Heat dissipation can also be adjusted for frozen products. If the appliance receives information that a frozen product is in the cooking chamber (this has lower thermal conductivity than a product with an initial temperature above freezing), the heat dissipation is reduced.

Claims

1. A method of cooking a food in a cooking appliance which includes a heater and a fan that can be operated at intervals, wherein the ratio between operating phases and standstill phases of the fan (clock ratio) is varied as a function of the decrease in heat in the cooking chamber of the cooking appliance, the clock ratio being dependent on the cooking program, characterized in that the core temperature of a product to be cooked is monitored and the portion of the standstill phases is increased when the difference between the actual core temperature and either the cooking chamber temperature and / or the shank temperature of a temperature sensor falls below a predetermined threshold.

2. The method according to claim 1, characterized in that longer standstill phases are used in a cooking program that provides a dry cooking.

3. The method according to claim 2, characterized in that longer standstill phases are used in a cooking program that provides long holding phases.

4. The method according to any of the preceding claims, characterized in that it is determined how much energy has to be supplied to the cooking chamber until a set-point temperature is reached again, and in that subsequently the portion of the standstill phases is reduced if the required energy was above a predetermined threshold.

5. The method according to any of the preceding claims, characterized in that the gradient of the profile of the core temperature of a product to be cooked is monitored and the portion of the standstill phases is reduced if the gradient is below a predetermined threshold at a pre-defined distance between the actual core temperature and the set-point core temperature.

6. The method according to any of the preceding claims, characterized in that a power save key is provided and in that the portion of the standstill phases is increased, in particular doubled, when the power save key has been pressed.

7. The method according to any of the preceding claims, characterized in that a low-noise operating phase can be selected and in that the portion of the standstill phases is increased when the low-noise operating phase has been selected.

8. The method according to any of the preceding claims, characterized in that the fan can be operated with alternating directions of rotation and in that standstill phases are coordinated with a change of the direction of rotation.

9. The method according to any of the preceding claims, characterized in that two or more temperature sensors are evaluated and the standstill phases are shortened or discontinued if the difference between the temperatures detected by the two temperature sensors, in particular the shank temperature and the cooking chamber temperature, exceeds a threshold value.

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