Methods for the safe operation of a combination cooking appliance and combination cooking appliance

Abstract

The invention relates to a method for the safe operation of a combination cooking appliance (10) comprising a cooking chamber (14) and a microwave source (26) with a microwave power output. The cooking chamber temperature (14) is measured. A convection-relevant parameter is determined. The measured cooking chamber temperature and the convection-relevant parameter are evaluated to determine a maximum permissible microwave power output. The microwave power output of the microwave source (26) is limited to the maximum permissible microwave power output. Furthermore, a combination cooking appliance (10) is described.

Description

The invention relates to a method for safe operation of a combination cooking appliance. The invention further relates to a combination cooker.Cooking devices which are used in professional or large gastronomy typically have, in addition to a heating device for generating hot air, also a steam generator for generating steam in order to cook a product to be cooked introduced into the cooking chamber of the cooking device. The heating device and the steam generator generate a cooking chamber atmosphere in the cooking chamber, which can also be referred to as cooking chamber climate. A item to be cooked exposed to the cooking chamber climate in the cooking chamber is cooked by the latter in a corresponding manner by introducing energy in a convection-based manner into the item to be cooked.In addition, such cooking devices can also have, in addition to the heating device and the steam generator, a microwave source which serves to accelerate the cooking process of the item to be cooked by (additional) energy in the form of microwaves being introduced into the item to be cooked. In principle, cooking appliances which have a microwave source in addition to a heating device and an optional steam generator are also referred to as combination cooking appliances.It has been found that if no item of cooking is present in the cooking chamber, the microwave radiation fed into the cooking chamber interacts predominantly with the cooking chamber itself, that is to say couples it into components of the cooking device which delimit the cooking chamber, that is to say for example the walls of the cooking chamber or a pane in a cooking chamber door. However, the microwave radiation can also be partially absorbed by components in the cooking chamber which have additionally been introduced, for example cooking accessories or a core temperature sensor, in particular a cable of a cable-bound core temperature sensor.The absorption of the microwave radiation fed into the cooking chamber can lead to damage thereof depending on the material and composition of the components. In order to avoid such damage, it is contemplated in the prior art to equip cooking devices with automatic safety shutdowns. These recognize an idle operation, i.e. an operation of the cooking appliance with an empty cooking chamber, whereupon the microwave feed is automatically switched off.For example, DE 10 2004 015 993 A1 discloses a microwave appliance which automatically determines the idling mode and automatically switches off a device for generating microwaves if idling of the cooking appliance has been detected.Also known in DE 102014 112 590 A1 is a microwave apparatus which recognizes an idle operation by detecting a temperature of a component of the high-frequency heating device.DE 10 2021 106 703 A1 discloses a cooking appliance and a method for controlling a cooking appliance, in which a current behavior of a conventional heating device is compared with the behavior of the conventional heating device in empty operation.DE 10 2004 015 993 A1 shows a microwave device which has a microwave source and a temperature sensor, wherein the temperature detected by means of the temperature sensor is evaluated in microwave operation.However, it has been found that under certain circumstances even with low or even medium loads of the cooking appliance wear or damage of components of the cooking appliance can occur, that is to say when microwave operation is generally permitted. The closing or damage is undesirable since the corresponding components have to be replaced early, as a result of which the costs increase.In this respect, the object of the present invention is to eliminate the disadvantages from the prior art and to provide a method with which a cooking appliance can be operated reliably.The object is achieved according to the invention by a method for the safe operation of a combination cooking appliance which has a cooking chamber and a microwave source with a microwave power, wherein the method comprises the following steps:detecting a cooking chamber temperature present in the cooking chamber,determining a convection-relevant parameter,evaluating the sensed cooking chamber temperature and the convection-relevant parameter in order to determine a maximum permissible microwave power, andlimiting the microwave power of the microwave source to the maximum permissible microwave power, in particular to a maximum permissible microwave power for the detected cooking chamber temperature and the determined convection-relevant parameter.The invention is based on the basic idea that the combination cooking appliance can be operated reliably with the microwave source by limiting the microwave power of the microwave source to the maximum permissible microwave power for the determined convection-relevant parameter and the detected cooking chamber temperature.The maximum permissible microwave power can accordingly be lower than the basically possible microwave power (rated power of the microwave source). The actually maximum permissible microwave power thus depends on the sensed cooking chamber temperature and the determined convection-relevant parameter. In other words, the maximum permissible microwave power is predefined by control technology, namely as a function of the detected cooking chamber temperature and the determined convection-relevant parameter. The maximum permissible microwave power is therefore variable, in particular during a cooking process which is taking place, since the cooking chamber temperature and / or the convection-relevant parameter change or change during the cooking process.As a result, the energy fed into the cooking chamber can be limited in the form of microwaves, as a result of which less microwave energy can interact with the components of the combination cooking appliance, so that damage to the components due to the microwaves is effectively prevented.It has been found that the energy of the microwaves can couple into components of the combination cooking appliance which are present in the cooking chamber or limit it, as a result of which these components are heated. This resulted in increased wear or even damage to the components, which is now effectively prevented, thereby enabling reliable and safe operation of the combination cooking appliance. The components present in the cooking chamber are in particular core temperature sensors which are wired and which should not exceed a specific temperature.If convection takes place at the respective component, i.e. there is a flow around the component, this can be cooled as a result, which is why the component heats up to a lesser extent. In the case of strong convection or flow around the component, more thermal energy can be transported away than in the case of low convection. If more thermal energy can be transported away, i.e. there is a higher convection, more microwave energy can in principle also be fed in under otherwise identical circumstances. For this reason, in addition to the cooking chamber temperature, the convection-relevant parameter is also determined and taken into account in the evaluation.Both parameters, i.e. the cooking chamber temperature present in the cooking chamber and the convection-relevant parameter, accordingly have an influence on how high the energy input by microwaves may still be, which results in the maximum permissible microwave power of the microwave source. Based on these parameters, i.e. the cooking chamber temperature and the convection-relevant parameter, it is thus possible to determine or estimate how much energy the respective component is still allowed to absorb at most in order not to be damaged. In this respect, a maximum permissible microwave power can be determined, which is permitted for the operating state. The operating state is determined by the cooking chamber temperature and the convection-relevant parameter.In other words, it is possible to determine how high an additional energy input by the microwave source into the component may be at a maximum, so that a threshold value or limit value for the temperature of the component is not reached and / or exceeded.The microwave power which can actually be introduced to the maximum and is defined by the maximum permissible microwave power can therefore be regulated as a function of the cooking chamber temperature and the convection-relevant parameter.In contrast to safety shutdowns known from the prior art, which merely provide for completely disabling microwave operation, the method according to the invention provides for regulating or reducing the microwave power of the microwave source, if necessary. The (theoretically possible) microwave power of the microwave source, i.e. the rated power, is therefore reduced according to the invention to the maximum permissible microwave power (situationally) instead of being set completely to zero. A situational reduction is understood here to mean a reduction which depends on the detected or determined parameters, namely the cooking chamber temperature and the convection-relevant parameter. As a result, the combination cooking appliance can be operated reliably without necessarily switching off the microwave source. In other words, microwave operation of the combination cooking appliance is nevertheless possible.The maximum permissible microwave power is in particular dependent on the component taken into account. If several components are taken into account, the maximum permissible microwave power can be selected on the basis of the component which permits the lowest maximum permissible microwave power. This ensures that none of the components considered is damaged. In this respect, a globally maximum permissible microwave power can be determined.The loading state of the combination cooking appliance can also play no role for the regulation of the microwave power, so that a regulation of the microwave power is present which is independent of the loading of the combination cooking appliance. Instead of using the load as a further parameter, the convection-relevant parameter is namely used, which allows a statement about any cooling effect of the component on account of convection.During the evaluation, a maximum permissible energy input into a component of the combination cooking appliance and / or a maximum permissible temperature of a component of the combination cooking appliance can be taken into account. The maximum permissible microwave power is determined in such a way that, during operation of the microwave source with the maximum permissible microwave power, the maximum permissible energy input into the component of the combination cooking appliance and / or the maximum permissible temperature of the component of the combination cooking appliance are not exceeded or is not exceeded.The maximum permissible energy input is understood to mean the input of an energy to which a component of the combination cooking appliance can be supplied without the component being damaged by the absorption of the energy or reaching the maximum permissible temperature.The maximum permissible temperature is understood to mean that temperature which should not exceed a component of the combination cooking appliance, in particular during operation of the microwave source with the maximum permissible microwave power, for example in the case of an empty cooking chamber.The component of the combination cooking appliance can be any component or any component of the combination cooking appliance within the cooking chamber, for example a cooking chamber wall, a core temperature sensor provided in the cooking chamber, a cable of the core temperature sensor, a sensor, a frame, a lighting and / or a viewing window of the cooking chamber door, in particular a pane. The components of the combination cooking appliance all have a maximum permissible energy input or a maximum permissible temperature, from which damage to the components can occur. The maximum permissible energy input is thus individual for each of the components. This applies in the same way to the maximum permissible temperature.For example, the maximum permissible temperature for the core temperature sensor, in particular its cable, is the melting point of a sheathing. In the case of the viewing window of the cooking chamber door, the transition temperature of the pane installed in the viewing window, in particular glass pane, can be defined as the maximum permissible temperature.By taking into account the maximum permissible energy input and / or the maximum permissible temperature, damage to a component during operation can be prevented in a simple manner.One aspect provides that the cooking chamber temperature is detected by a temperature sensor which is arranged in a core temperature sensor, and / or that the cooking chamber temperature is detected by a temperature sensor which is arranged in the cooking chamber of the combination cooking appliance. The temperature sensor may be provided in a grip portion or a measurement portion of the core temperature sensor. If the core temperature sensor is in a parking position, i.e. is not inserted into the item to be cooked, any temperature sensor of the core temperature sensor can be used if it is not thermally insulated in the parking position. If the core temperature sensor is inserted into a food item to be cooked, i.e. is used, the temperature sensor provided in the grip section can nevertheless be used. Alternatively or additionally, a temperature sensor can be used which is assigned to the cooking chamber but is provided outside the core temperature sensor.Furthermore, the determined convection-relevant parameter can be a rotational speed of a fan wheel, a rotational speed of a fan wheel, a volume per unit time of exchanged air in the cooking chamber or a circulation flow in the cooking chamber. In particular, the rotational speed of the fan wheel is detected by sensors, based on which the rotational speed, the volume per unit time of exchanged air in the cooking chamber or the circulation flow in the cooking chamber is then determined. However, the rotational speed of the fan wheel detected by the sensor can also be taken into account directly in the evaluation in order to then determine the maximum permissible microwave power, inter alia, on the basis of the rotational speed.A further aspect provides that a model, a functional relationship or a table has been determined, in particular empirically, on the basis of which the maximum permissible microwave power is determined as a function of the convection-relevant parameter and the cooking temperature. The model, the functional relationship or the table is determined in particular for the respective component. If a plurality of components are included in order to situatively limit the microwave power of the microwave source, a plurality of models, functional relationships or tables are correspondingly used.The model, functional relationship or table is preferably based on data previously determined. For example, the data have been obtained from test series in which the influence of varying microwave powers on a cooking chamber is examined with different convection-relevant parameters and / or different cooking chamber temperatures. Here, for different combinations of a convection-relevant parameter and a cooking chamber temperature, a maximum permissible microwave power can be determined empirically, which can be fed into the cooking chamber without a maximum permissible energy input into a component of the combination cooking appliance and / or a maximum permissible temperature of a component of the combination cooking appliance being exceeded. The data obtained in this way can be used as the basis for the model, the functional relationship or the table in order to determine on the basis thereof the maximum permissible microwave power as a function of the convection-relevant parameter and the cooking chamber temperature, that is to say as a function of the operating state of the combination cooking appliance, which is determined inter alia by means of the convection-relevant parameter and / or the cooking chamber temperature.In particular, at least one predetermined threshold value is provided for the convection-relevant parameter, wherein exceeding and / or falling below the threshold value results in a changed dependence of the maximum permissible microwave power. For example, the threshold value for the rotational speed of the fan wheel can be provided, since a convection is only established starting from a specific rotational speed, which results in a cooling of the component. Also, starting from a certain rotational speed of the fan wheel, such a large convection can already be present that a higher rotational speed would no longer result in better cooling. Furthermore, a different threshold value may be present depending on the respective component. The respective threshold value may have been determined empirically. For the sheathing of a core temperature sensor, in particular its cable, a threshold value for the rotational speed of the fan of 1,000 revolutions per minute (rpm / min) can be provided. The dependence of the maximum permissible microwave power on the rotational speed of the fan, which serves as a convection-relevant parameter, is therefore different below a rotational speed of 1,000 U / min than at a rotational speed above 1,000 U / min.For example, the maximum permissible microwave power is determined via the detected cooking chamber temperature and a microwave factor which depends on the at least one predetermined threshold value. The threshold value can thus be used first to determine a microwave factor which is then used in turn for calculating the maximum permissible microwave power. In particular, the microwave factor depends linearly on the at least one predetermined threshold value when the at least one predetermined threshold value is undershot, whereas the microwave factor is otherwise a constant, that is to say when the at least one predetermined threshold value is exceeded.For example, the dependence of the microwave factor MW Faktor is as follows when the predetermined threshold value for the convection-relevant parameter is undershot: wherein Prop Faktor is a proportionality factor which has been determined or simulated empirically, for example, parameter konvektionsrelevant is the convection-relevant parameter, and offset is a compensation value which determines the microwave factor when the convection-relevant parameter is 0.By contrast, the microwave factor MW Faktor is a constant (constant) if the predetermined threshold value for the convection-relevant parameter is exceeded:Furthermore, a temperature limit value can be provided, wherein the maximum permissible microwave power is zero when the detected cooking chamber temperature reaches the temperature limit value. This results in an additional safety level, since it is ensured that microwave energy is not additionally introduced if the cooking chamber temperature is already so high that the maximum permissible temperature of the component of the combination cooking appliance should already be reached or there is only a difference between the cooking chamber temperature and the maximum permissible temperature of the component which is less than a safety margin. The temperature threshold may be 300° C. In this respect, starting from a cooking chamber temperature of 300° C., no further microwave energy can be introduced into the cooking chamber any longer.In particular, it is provided that the microwave source is operated at most with the maximum permissible microwave power, so that microwaves generated by the microwave source are fed into the cooking chamber. The microwave power that can actually be introduced at a maximum is thus changed depending on the situation. The microwave source can be operated with a microwave power that is less than the maximum permissible microwave power. In any case, the microwave power emitted by the microwave source cannot be above the maximum permissible microwave power.The maximum permissible microwave power can be greater than or equal to 0% and less than or equal to 100% of the rated power of the microwave source. If the operating state of the combination cooking appliance (and a power connection of the combination cooking appliance) allows, the entire rated power of the microwave source can thus be utilized. In other words, the maximum permissible microwave power can be between 0% and 100% of the rated power of the microwave source, wherein this depends on the operating state of the combination cooking appliance, which depends on the sensed cooking chamber temperature and the convection-relevant parameter.A further aspect provides that the maximum permissible microwave power is determined several times during a cooking process, in particular regularly or periodically. Thus, the currently present operating state of the combination cooking appliance is constantly monitored, as a result of which the maximum permissible microwave power is adapted (periodically or periodically).A control of the combination cooking appliance can take into account the maximum permissible microwave power, which has been determined beforehand, when driving the microwave source, in particular when specifying the power for the microwave source. As explained above, the maximum permissible microwave power is not necessarily the actual microwave power of the microwave source, but rather a limit value which cannot be exceeded or (by control technology) can be exceeded.When processing a cooking program, it can also be provided that the controller of the combination cooking appliance takes into account the specifications for the cooking chamber temperature (setpoint cooking chamber temperature) and the convection-relevant parameter (setpoint for the convection-relevant parameter). This allows the cooking processes to be adapted, for example a cooking time adjustment, provided it is determined that the maximum permissible microwave power is low for a certain period of time, so that a shortening of the cooking time is not possible due to additionally introduced microwave energy.The invention further relates to a combination cooking appliance for cooking food. The combination cooking appliance comprises a cooking chamber, a microwave source assigned to the cooking chamber for feeding microwaves with a specific microwave power into the cooking chamber, a temperature sensor for detecting a cooking chamber temperature and at least one sensor for detecting a convection-relevant parameter. The combination cooking appliance has an evaluation unit which is connected to the temperature sensor and the at least one sensor in a signal-transmitting manner. The evaluation unit is configured to determine a maximum permissible microwave power for the microwave source on the basis of the cooking chamber temperature detected by the temperature sensor and the convection-relevant parameter determined by the sensor. The combination cooking appliance has a controller which is connected to the evaluation unit and the microwave source in a signal-transmitting manner. The controller is configured to receive the maximum permissible microwave power determined by the evaluation unit and on the basis of which limit the microwave power of the microwave source. The combination cooking appliance is basically designed and configured to carry out the aforementioned method. The corresponding properties and advantages result in an analogous manner for the combination cooker.As already explained above, the microwave source is controlled by the controller in such a way that the actual microwave power is less than or equal to the maximum permissible microwave power, which depends on the operating state of the combination cooking appliance. In the event of a change in the operating state, i.e. the cooking chamber temperature and / or the convection-relevant parameter, a different maximum permissible microwave power is thus also obtained.In particular, during a cooking process, the maximum permissible microwave power is determined multiple times, in particular regularly or periodically.Further advantages and properties of the invention will become apparent from the following description and the drawings to which reference is made. In the drawings, there are shown:FIG. 1 is a schematic representation of a combination cooking appliance according to the invention,FIG. 2 shows the steps of a method according to the invention for safe operation of the combination cooking appliance from FIG. 1, andFIG. 3 is an overview illustrating the maximum permissible microwave power as a function of the cooking chamber temperature and the convection-relevant parameter.FIG. 1 shows a combination cooking appliance 10 for cooking items 12 to be cooked which have been introduced into a cooking chamber 14 of the combination cooking appliance 10 in order to be cooked there.Furthermore, a cooking chamber door 16 is assigned to the cooking chamber 14, which door closes the cooking chamber 14 with respect to the environment, so that a defined cooking chamber climate for cooking the item to be cooked 12 can be generated within the cooking chamber 14. The cooking chamber door 16 also has a viewing window 18 which serves to ensure a free view of the item to be cooked 12 from outside during the cooking process. The viewing window 18 is in particular a glass pane.A technical space 20 is provided, separate from the cooking chamber 14, in which, among other things, components are at least partially accommodated, which are necessary for generating and setting the cooking chamber climate, i.e. a cooking chamber atmosphere, in the cooking chamber 14 or which provide energy for cooking the item to be cooked 12.In the embodiment shown, the combination cooking appliance 10 comprises a heating device 22, a steam generator 24, a microwave source 26 and a fan wheel 28.The steam generator 24 and the heating device 22 are at least partially accommodated in the technical room 20 and serve, among other things, to provide the defined cooking chamber atmosphere in the cooking chamber 14, in particular the cooking chamber temperature and humidity. The cooking chamber atmosphere or cooking chamber climate generated in the cooking chamber 16 is thus defined, among other things, as a specific temperature in combination with a specific humidity. In addition, a flow speed and / or a pressure can also be provided with respect to the cooking chamber atmosphere, provided that the fan wheel 28 is operated accordingly. In principle, the fan wheel 28 can therefore also contribute to the cooking chamber atmosphere or to the cooking chamber climate, since a convection within the cooking chamber 14 is set thereby.The microwave source 26 has at least one antenna 30, which faces the cooking chamber 14, in order to couple microwaves generated by the microwave source 26 into the cooking chamber 14 and thus to apply (additional) energy to the item to be cooked 12.The combination cooking appliance 10 also has at least one cooking chamber temperature sensor 32 which is configured to measure the cooking chamber temperature in the cooking chamber 14. The cooking chamber temperature sensor 32 can also be referred to as a cooking chamber sensor. In the exemplary embodiment shown, two cooking chamber temperature sensors or cooking chamber sensors 32 are shown, which can be arranged in particular distributed in the cooking chamber 14. Then, for example, an average value of the cooking chamber temperatures detected by the respective cooking chamber sensors 32 is used for the further processing.Furthermore, a core temperature sensor 34 is provided in the cooking chamber 14, which has at least one temperature sensor 36.If the core temperature sensor 34 is not inserted into the item to be cooked 12, the temperature sensor 36, which is integrated in the core temperature sensor 34, could also be used to detect a cooking chamber temperature present in the cooking chamber 14, in particular as an aid if the cooking chamber sensor 32 fails.The cooking chamber temperature present in the cooking chamber 14 can thus be detected by the cooking chamber sensor 32 and / or the core temperature sensor 34, in particular its temperature sensor 36.In the embodiment shown, the core temperature sensor 34 is a cable-bound core temperature sensor which has a cable 38 arranged in the cooking chamber 14 and which, like the core temperature sensor 34 itself, is exposed to the cooking chamber climate, that is to say to the cooking chamber temperature.In addition, a sensor 40 is assigned to fan wheel 28, via which a convection-relevant parameter can be ascertained. The sensor 40 can be configured to measure the rotational speed of the fan impeller 28, which corresponds to the convection-relevant parameter, since the convection generated by the fan impeller 28 depends on its rotational speed.Furthermore, the combination cooking appliance 10 has an evaluation unit 42 which is arranged in the technical room 20 and is connected to the aforementioned components in a signal-transmitting manner, that is to say in particular the cooking chamber sensor 32, the core temperature sensor 34 and the sensor 40.The evaluation unit 42 can also be configured to determine another convection-relevant parameter based on the rotational speed detected by the sensor 40, for example a rotational speed of the fan wheel 28, a volume per unit time of exchanged air in the cooking chamber 14 or a circulating flow in the cooking chamber 14.The evaluation unit 42 can in principle also be connected in a signal-transmitting manner to the heating device 22, the steam generator 24 and the microwave source 26 in order to obtain information or data from these components.In principle, the evaluation unit 42 is designed and configured to evaluate the detected cooking chamber temperature and the convection-relevant parameter in order to determine a maximum permissible microwave power, as will be explained in more detail below with reference to FIGS. 2 and 3.The evaluation unit 42 is additionally connected in a signal-transmitting manner to a controller 44 which in turn is connected in a signal-transmitting manner at least to the microwave source 26 in such a way that the microwave source 26 can be controlled by the controller 44. In other words, the controller 44 is designed and configured to actuate the microwave source 26, in particular depending on an evaluation result of the evaluation unit 42.Accordingly, the controller 44 is configured to limit a microwave power of the microwave source 26 to the maximum permissible microwave power, as will be explained in the following.The controller 44 can also be connected to the heating device 22, the steam generator 24 and / or the fan wheel 28 in a signal-transmitting manner in such a way that the corresponding components can be controlled by the controller 44. These corresponding compounds are not shown here for the sake of better overview.In principle, it is conceivable for the evaluation unit 42 and the controller 44 to be designed as a common combined unit, namely a control and / or evaluation unit.The combination cooking appliance 10 is configured to execute the method according to the invention for safe operation of the combination cooking appliance 10 explained below.In a first step, the cooking chamber temperature present in the cooking chamber 14 is detected (step S 1). For this purpose, the cooking chamber sensor 32 and / or the core temperature sensor 34 measure the cooking chamber temperature present in the cooking chamber 14.The measured cooking chamber temperature is transmitted to the evaluation unit 42.In a second step, the convection-relevant parameter is determined (step S 2). For this purpose, in the present exemplary embodiment according to FIG. 1, the sensor 40 measures the rotational speed of the fan wheel 28, which is the convection-relevant parameter.The rotational speed is transmitted to the evaluation unit 42. The evaluation unit 42 can calculate another convection-relevant parameter on the basis of the rotational speed detected by the sensor, provided that this parameter can be used for a later evaluation.In a third step, the detected cooking chamber temperature and the convection-relevant parameter are evaluated by the evaluation unit 42 in order to determine a maximum permissible microwave power (step S 3). During the evaluation, the evaluation unit 42 takes into account a maximum permissible energy input into at least one component of the combination cooking appliance 10 and / or a maximum permissible temperature of at least one component of the combination cooking appliance 10.The maximum permissible microwave power is determined in such a way that, during operation of the microwave source 26 with the maximum permissible microwave power, the maximum permissible energy input into the component of the combination cooking appliance 10 and / or the maximum permissible temperature of the component of the combination cooking appliance 10 are not exceeded or is not exceeded.The corresponding component is, for example, the viewing window 18 or the core temperature sensor 34, in particular the cable 38 of the core temperature sensor 34.In principle, a plurality of components can be taken into account if the maximum permissible microwave power is determined, each component having its own individual maximum permissible microwave power. The component that has the lowest individual maximum permissible microwave power then specifies, for example, the maximum permissible microwave power in order to ensure that no component of the combination cooking appliance 10 is damaged.In particular, the evaluation unit 42 uses a model, a functional relationship or a table for the respective component of the combination cooking appliance 10. The model, the functional relationship or the table has been determined in particular on the basis of data which have been determined empirically in advance on a component of the combination cooking appliance 10. Using these data, the model, the functional relationship or the table can then be used to determine the maximum permissible microwave power as a function of the currently determined convection-relevant parameter and the currently detected cooking chamber temperature. In other words, the cooking chamber temperature and the convection-relevant parameter serve as input values, which the evaluation unit 42 uses to determine the maximum permissible microwave power with the aid of an algorithm or logic.The maximum permissible microwave power is greater than or equal to 0% and less than or equal to 100% of the rated power of the microwave source 26; this depends on the operating state of the combination cooking appliance 10, namely on the detected cooking chamber temperature and the convection-relevant parameter, for example the rotational speed.FIG. 3 shows diagrams which illustrate how the maximum permissible microwave power depends on the cooking chamber temperature and the convection-relevant parameter.In the first diagram, the maximum permissible microwave power (in %), referred to there as "available MW", is shown with respect to the detected cooking chamber temperature GT ist( in ° C.) for three different convection-relevant parameters, namely for a rotational speed of the fan wheel 28 ("LR") of 500 U / min, 750 U / min and >1000 U / min.In the second diagram, the maximum permissible microwave power (in %), referred to there as "available MW", is shown compared to the convection-relevant parameter in the form of the rotational speed of the fan wheel 28 LRDre (in U / min) for five different cooking chamber temperatures GT ist namely for cooking chamber temperatures GT ist of 270° C., 280° C., 285° C., 290° C. and 295° C.A three-dimensional diagram is shown in the third diagram, wherein the maximum permissible microwave power (in %), referred to there as "available MW", is shown in relation to the detected cooking chamber temperature GT ist( in ° C.) and the rotational speed of the fan wheel 28 LRDre(in U / min).As already explained above, the maximum admissible microwave power is a limit value for the microwave source 26, which does not necessarily have to correspond to the microwave power actually introduced by the microwave source 26. Rather, the theoretically possible microwave power is limited under certain circumstances, namely as a function of the cooking chamber temperature and the convection-relevant parameter, as can be seen clearly from FIG. 3.It becomes clear from this in particular that a temperature limit value is provided, wherein the maximum permissible microwave power is zero when the detected cooking chamber temperature reaches the temperature limit value. In the exemplary embodiment shown, the temperature limit value is provided at 300° C.It can also be seen from the diagrams that at least one predetermined threshold value is provided for the convection-relevant parameter, wherein exceeding and / or falling below the threshold value results in a changed dependence of the maximum admissible microwave power. In the exemplary embodiment shown, the threshold value corresponds to a rotational speed of the fan of 1,000 revolutions per minute (U / min). Above this rotational speed, i.e. the threshold value of 1,000 U / min, the maximum permissible microwave power is namely 100%, whereas below this rotational speed the maximum permissible microwave power decreases with decreasing rotational speed.In addition, it can be seen from the diagrams that a linear relationship exists between the cooking chamber temperature and the maximum permissible microwave power, wherein the linearity in turn depends on the convection-relevant parameter, i.e. the rotational speed.In principle, the maximum permissible microwave power can be determined via the detected cooking chamber temperature and a microwave factor which depends on the at least one predetermined threshold value. This can result in a functional relationship for the maximum permissible microwave power MW max which can be expressed as follows: wherein GT ist is the detected cooking chamber temperature. In addition, the microwave factor MW Faktor is provided in the functional relationship, which describes the linear dependence of the maximum permissible microwave power on the cooking chamber temperature and itself depends on the convection-relevant parameter, as already explained above with reference to the diagrams. The microwave factor MW Faktor can be represented as follows:If the predetermined threshold value (1,000 U / min) for the convection-relevant parameter is undershot, the following relationship results for the microwave factor MW Faktor wherein Prop Faktor is a proportionality factor which has been determined or simulated empirically, for example, parameter konvektionsrelevant is the convection-relevant parameter, for example the rotational speed. The parameter offset is a compensation value which determines the microwave factor MW Faktor if the convection-relevant parameter, for example the rotational speed, is 0.By contrast, the microwave factor MW Faktor is a constant (constant) if the predetermined threshold value (1,000 U / min) for the convection-relevant parameter is exceeded:In addition, the evaluation unit stores that the maximum permissible microwave power has a value of 100 if a value greater than 100 would result from the above functional relationship, and a value of 0 if a value less than 0 would result from the above functional relationship. This ensures that the maximum permissible microwave power lies between 0% and 100% of the rated power of the microwave source 26, as already explained above.If the evaluation unit 42 has determined the maximum permissible microwave power, this is then sent to the controller 44.The controller 44 then limits the actually output microwave power of the microwave source 26 to the maximum allowable microwave power (step S 4). In this case, the microwave source 26 can either be controlled or regulated accordingly, or an attenuation element is connected which limits the microwave power. The microwave power can be controlled or regulated via pulse width modulation by setting time intervals between microwave pulses, for example a PWM of 20%, in particular a pulse duration of 200 ms and a pause of 800 ms. The microwave source 26 is then operated in such a way that its actually emitted microwave power never exceeds the currently present maximum permissible microwave power. The actually emitted microwave power can, however, be below the maximum permissible microwave power, since this merely represents a limit value for the microwave source 26, which limit value must not be exceeded in order to ensure that the component of the combination cooking appliance 10 is not damaged, for example a sheathing of the core temperature sensor 34, in particular of the cable 38.The method described here can be carried out both at the start of a cooking process and at regular time intervals during the cooking process.In other words, the maximum permissible microwave power can be determined several times during a cooking process. First, the operating state of the combination cooking appliance 10, i.e. the cooking chamber temperature and the convection-relevant parameter, is detected several times during the cooking process, in particular regularly or periodically, so that on the basis thereof the evaluation of these values can take place in order thus to determine the maximum permissible microwave power. In this respect, it is ensured that the efficiency and the safety are both maximized, since the theoretically maximum possible microwave power is adapted depending on the situation.

Claims

Method for safe operation of a combination cooking appliance (10) which has a cooking chamber (14) and a microwave source (26) with a microwave power, wherein the method comprises the following steps: - detecting a cooking chamber temperature present in the cooking chamber (14), - determining a convection-relevant parameter, - evaluating the detected cooking chamber temperature and the convection-relevant parameter in order to determine a maximum permissible microwave power, and - limiting the microwave power of the microwave source (26) to the maximum permissible microwave power.Method according to claim 1, characterised in that the cooking chamber temperature is detected by a temperature sensor (36) which is arranged in a core temperature sensor (34), and / or in that the cooking chamber temperature is detected by a temperature sensor (32) which is arranged in the cooking chamber (14) of the combination cooking appliance (10).Method according to Claim 1 or 2, characterized in that the determined convection-relevant parameter is a rotational speed of a fan wheel (28), a rotational speed of a fan wheel (28), a volume per unit time of exchanged air in the cooking chamber (14) or a circulation flow in the cooking chamber (14).Method according to one of the preceding claims, characterized in that a model, a functional relationship or a table has been determined, in particular empirically, on the basis of which the maximum permissible microwave power is determined as a function of the convection-relevant parameter and the cooking chamber temperature.Method according to one of the preceding claims, characterized in that at least one predetermined threshold value is provided for the convection-relevant parameter, wherein exceeding and / or falling below the threshold value results in a changed dependence of the maximum admissible microwave power.Method according to claim 5, characterised in that the maximum permissible microwave power is determined via the detected cooking chamber temperature and a microwave factor which depends on the at least one predetermined threshold value.Method according to one of the preceding claims, characterized in that a temperature limit value is provided, wherein the maximum permissible microwave power is zero when the detected cooking chamber temperature reaches the temperature limit value.Method according to one of the preceding claims, characterized in that the microwave source (26) is operated at most with the maximum permissible microwave power, so that microwaves generated by the microwave source (26) are fed into the cooking chamber (14), and / or in that the maximum permissible microwave power is greater than 0% and less than or equal to 100% of the rated power of the microwave source (26).Method according to one of the preceding claims, characterized in that the maximum permissible microwave power is determined a number of times during a cooking process.Combination cooking appliance (10) for cooking items (12), wherein the combination cooking appliance (10) comprises a cooking chamber (14), a microwave source (26) assigned to the cooking chamber (14) for feeding microwaves with a specific microwave power into the cooking chamber (14), a temperature sensor (32, 36) for detecting a cooking chamber temperature and at least one sensor (40) for detecting a convection-relevant parameter, wherein the combination cooking appliance (10) has an evaluation unit (42) which is connected to the temperature sensor (32, 36) and to the at least one sensor (40) in a signal-transmitting manner, wherein the evaluation unit (42) is configured to determine a maximum permissible microwave power for the microwave source (26) on the basis of the cooking chamber temperature detected by the temperature sensor (32, 36) and the convection-relevant parameter determined by the sensor (40), and wherein the combination cooking appliance (10) has a controller (44), which is connected to the evaluation unit (42) and the microwave source (26) in a signal-transmitting manner, wherein the controller (44) is configured to receive the maximum permissible microwave power determined by the evaluation unit (42) and on the basis of which to limit the microwave power of the microwave source (26).

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