Method for cleaning a cooking device and cooking device

Abstract

A method for cleaning a cooking appliance (10) with a cooking chamber (12) and a heating device (22) with a heating tube (24), wherein the heating tube (24) has a first actively heated section (26) and a second section (28) adjacent to the first section (26) which is not actively heated, wherein, during normal operation of the cooking appliance (10), contaminants accumulate and burn onto the second section (28) in a solid burn area (30), the method comprising the following steps: a) selecting a cleaning program; b) switching on the heating device (22) so that the first section (26) of the heating tube (24) is heated; c) operating the heating device (22) for a cleaning period at such a power that, through heat transfer in the solid burn area (30), a temperature is reached for a burn-off period of at least 1 min and preferably at least 5 min.adjusts so that the impurities adhering in the solid burn area (30) are dissolved, while at the same time preventing the temperature in the cooking chamber (12) from exceeding a maximum permissible cooking chamber temperature.

Description

[0001] The present invention relates to a method for cleaning a cooking appliance comprising a cooking chamber and a heating device with heating tubes. The invention also relates to a cooking appliance that performs the method.

[0002] Cooking appliances with heating elements are commonly used for cooking food in the catering industry. Depending on usage and when cooking certain foods, a large amount of impurities can accumulate in the cooking chamber, which are then distributed throughout the chamber and adhere to the surfaces.

[0003] Common cleaning methods are based on the chemical cleaning of surfaces. A cleaning solution is created by adding water and chemicals, which can also be heated and is then usually circulated in the cooking appliance for a certain period of time or at least rinsed once through the cooking chamber.

[0004] However, chemical cleaning is not always sufficient. Heating appliances with one or more heating elements, in particular, cannot always be completely cleaned using chemical methods, as the heating elements sometimes have areas that are difficult for the cleaning solution to reach. Furthermore, the heating elements are heated to varying degrees during cooking, which also affects the cleaning result. In unheated sections, which generally reach no more than the ambient temperature in the cooking chamber, contaminants (such as grease and other residues from cooked food) adhere less strongly and can therefore be removed very effectively by chemical cleaning. In actively heated sections, the significantly higher temperatures cause the chemical decomposition of the contaminants, so they also do not adhere strongly.However, between actively heated and unheated sections, there are areas where the cooking temperatures are intermediate. In these areas, the thermal effect causes a particularly strong adhesion of contaminants, which is accompanied by a chemical transformation and their hardening. As a result, the contaminants can no longer be adequately removed by chemical cleaning.

[0005] Over time, a thickening layer of various contaminants can accumulate in the so-called "permanently burned" areas. This can lead to smoke development in the cooking chamber, which alters the taste of the food, significantly impairs kitchen air quality, and can damage the cooking appliance.

[0006] The object of the present invention is to provide a method for cleaning a cooking appliance that overcomes the disadvantages described above and reliably cleans the cooking chamber of the cooking appliance.

[0007] The problem is solved according to the invention by a method for cleaning a cooking appliance with a cooking chamber and a heating device with a heating tube. The heating tube has a first, actively heated section and a second section adjacent to the first section, which is not actively heated. During normal operation of the cooking appliance, contaminants accumulate and become baked on in a solid-on area in the second section. The cleaning method comprises the following steps. First, a cleaning program is selected. Then, the heating device is switched on so that the first section of the heating tube is heated. Subsequently, the heating device is operated at a power level for a cleaning period such that, through heat transfer in the solid-on area, a temperature is reached for a combustion period of at least 1 minute and preferably at least 5 minutes, such that the contaminants adhering to the solid-on area are dissolved.At the same time, it prevents the temperature in the cooking chamber from exceeding a maximum permissible cooking chamber temperature.

[0008] The invention is based on the fundamental idea that by heating the first section of the heating tube more intensely and / or for a longer period, the stubborn residue area of ​​the second section of the heating tube is heated to such an extent that the adhering contaminants thermally oxidize. In other words, the stubborn residue area is temporarily shifted during the cleaning process from the actual stubborn residue area resulting from normal operation and is located at a different position on the heating tube during the cleaning process than during normal operation. It is important, however, that the maximum permissible temperature in the cooking chamber is not exceeded in order to protect temperature-sensitive components in the cooking chamber, such as the cooking chamber seal, from damage. With the method according to the invention, the heating device is therefore heated particularly intensely, while the cooking chamber remains relatively "cold".Neither the walls nor the oven door and / or the sensors installed in the oven are heated to such an extent that any adhering dirt is oxidized. Therefore, the entire oven cavity, including the walls, floor, and door, is not cleaned; only the heating element and any brackets and / or nozzles located in its immediate vicinity are cleaned.

[0009] This method ensures that heavily contaminated areas of the heating pipes are effectively cleaned without damaging temperature-sensitive components in the cooking chamber.

[0010] Even if, during normal operation, a temperature of, for example, 400°C is exceeded in certain areas of the solid combustion zone, the impurities are not sufficiently removed. For adequate removal, the temperature must be exceeded for at least 5 minutes.

[0011] In principle, the area affected by stubborn residue can extend slightly into the actively heated first section of the heating element. This depends on how the temperature transfer from the first to the second section develops during normal operation of the cooking appliance. Due to heat conduction, a temperature drop can occur in the second section, even at the edge of the first section, compared to the area of ​​the first section that is not affected by heat conduction due to the greater distance to the second section. Furthermore, the stubborn residue area may not directly adjoin the first section, so a short portion of the second section is adequately cleaned during normal operation. The precise nature of the temperature transfer, and thus the location of the stubborn residue area, depends on several factors, such as the cooking chamber temperature, the typical temperature in the actively heated area, and possibly the composition of the dirt, etc.

[0012] The heating device can be an electric resistance heater if it is an electrically operated cooking appliance. If the cooking appliance is gas-powered, the heating device has a gas burner that heats the first section of the heating tubes. An electric resistance heater typically has several heating tubes arranged approximately in parallel, while a heat exchanger, on the other hand, has a long, coiled heating tube.

[0013] In electric resistance heating systems, the heating tubes are generally only heated at a defined distance inside the cooking chamber after passing through the chamber wall. This prevents overheating of the connections and the chamber wall, and thus reduces heat loss. The unheated sections, particularly near where the tubes pass through the chamber wall, form the second section. Furthermore, several brackets along the heating tubes, which are in contact with the first section but are not themselves heated, secure the tubes to each other and to the chamber wall. It is conceivable that the inventive method could also be used to clean other areas and components within the cooking appliance that either border the first section or are located in close proximity to it. In this case, cleaning would occur through convective heat transfer and / or radiation.

[0014] In gas-fired cooking appliances with heat exchangers, significant temperature differences along the heating tube are unavoidable, depending on the exhaust gas temperature, the internal flow velocity, and the cooling (in the sense of "heat dissipation") on the outside of the heating tube. This results in such low temperatures in areas upstream of the gas burner and in areas far downstream of the gas burner that the burning of contaminants is inevitable.

[0015] In the following, combustion time refers to the period of time typically sufficient to thermally and oxidatively decompose the adhering contaminants. The combustion time is at least 5 minutes. After this time, the contaminants in the solid combustion area begin to glow independently.

[0016] The cleaning time refers to the duration for which the heating device must operate until the desired temperature, for example, at least 400°C, is reached. This includes the subsequent combustion time. The cleaning time is therefore the time from the start of the process until the end of the cleaning. The cleaning time varies depending on the degree and type of contamination, as well as the temperature achieved in the solid residue zone. For example, a cleaning time of 15 minutes is sufficient to achieve a good cleaning result with an average level of contamination. The combustion time may, for instance, account for half of the cleaning time.

[0017] In the following, "actively heated" refers to heating using a heat source. Non-active or passive heating occurs when the second section is only heated by heat transfer from the first section or by the hot medium flowing through it. The second section then has a lower flow velocity and / or a lower exhaust gas temperature, which can result in temperatures in the critical range. The flow around and cooling of the second section also play a role. The second section does not have its own heat source.

[0018] In normal operation, the cooking appliance performs any cooking method for food. Normal operation represents the typical cooking mode. During normal operation, the temperature in the solid-burn range remains below 400°C. The range between 300°C and 400°C is referred to as the medium or critical temperature range, as particularly stubborn, burnt-on residues adhere to the heating element in this range.

[0019] The temperature set in step c) in the solid firing zone can be at least 400°C. Above this temperature, effective and particularly reliable cleaning of the solid firing zone occurs.

[0020] According to one aspect of the invention, step c) is followed by step d), in which the cooking chamber is rinsed with a cleaning solution or clean water. This rinsing step removes the dirt that has fallen from the baked-on area and accumulates, for example, on the cooking chamber floor. This prevents the dirt from baking on again. The cleaning solution can be, for example, an alkali or an acid.

[0021] If a high-temperature cleaning step is integrated into the middle of a chemical cleaning program, then a cooling phase, such as an accelerated cooldown, is usually necessary afterward. This is because further cleaning steps typically follow, which again involve water or a chemically treated cleaning solution in the cooking chamber. The high temperature in the cooking chamber would cause sudden evaporation with potentially serious consequences. Therefore, the cooking chamber and the heating element must first be cooled down before the subsequent steps can begin. This cooling phase must therefore also be integrated into such a combined cleaning process. In other cases, such as when using thermal oxidative cleaning at the end of the cleaning cycle, the cooling phase is not strictly necessary.

[0022] According to another aspect of the invention, the heating device is operated at maximum power in step c). The cleaning time is, in particular, at least 15 minutes. The combination of maximum power and a sufficiently long cleaning time leads to optimal cleaning results. However, it is important to note that the maximum cooking chamber temperature must not be exceeded. Therefore, the heating device may only be operated at maximum power if, for example, a thermal load is introduced into the cooking chamber or if the cooking chamber is actively or passively cooled. Essentially, the aim is to operate the heating device at maximum power, or alternatively at a moderately high power, for a sufficient duration.

[0023] In step c), the temperature in the cooking chamber can reach a maximum of 300°C, and the temperature in the first section of the heating element can range between 500°C and 850°C. The maximum cooking chamber temperature depends on the thermally sensitive components installed in the cooking chamber, such as the chamber seal or sensors, which must not be damaged by the cleaning process. The maximum temperature in the first section of the heating element must also be within a temperature range that does not cause any damage to the heating element.

[0024] The heating device can be either an electric heater, in which the first section is actively heated electrically and the second section is not actively heated and is heated indirectly via conduction, convection, and / or radiation. Alternatively, the heating device can also be a heat exchanger, in which the first section is actively heated by a burner, in particular a gas burner, and the second section is located downstream of the first section and is not actively heated by combustion, but "only" by the combustion gases. The cleaning method according to the invention can thus be applied to both electrically operated and gas-operated cooking appliances. In other words, hot exhaust gas is generated at the burner by combustion, which flows through the heat exchanger. In the first section, which is located in the area of ​​the burner, the heat transfer is sufficient to remove contaminants from the heating tube.In the second section, the heat transfer is insufficient because, for example, low flow velocities or low exhaust gas temperatures are present to generate sufficiently high temperatures for the thermal oxidation of the contaminants during normal operation.

[0025] According to a further aspect of the invention, the cooking chamber can be actively cooled during the cleaning process, in particular by introducing steam from a steam generator into the cooking chamber and / or introducing water from a nozzle into the cooking chamber and / or opening a cooking chamber vent. Active cooling has the advantage that it maximizes the heating power of the heating device without the temperature in the cooking chamber exceeding the maximum permissible cooking chamber temperature. In this way, the temperature in the stubborn food residue zone can be raised sufficiently to thermally oxidize the residues, while simultaneously keeping the cooking chamber temperature below the maximum permissible cooking chamber temperature. The faster, longer, and further the temperature in the stubborn food residue zone remains above 400°C, the faster the cleaning program is completed.Thus, active cooling (i.e., heat dissipation) leads to a better cleaning result and a shorter cleaning time.

[0026] The cooking appliance or cooking chamber can also be cooled during the cleaning process by opening the oven door. Alternatively or additionally, the thermal load in the cooking chamber can be increased and / or the speed of a rotating fan in the cooking chamber can be reduced. Opening the oven door allows hot air to escape from the cooking chamber, thus cooling it. A thermal load in the cooking chamber causes it to heat up more slowly. A slower-rotating fan reduces the air velocity near the heating elements, so that the heat released there is used more effectively to heat the other sections and is not dissipated into the cooking chamber. In combination with other methods of cooling the cooking chamber, such as opening the oven vent, the optimal fan speed can be in the middle range.Under certain circumstances, a higher fan speed can even lead to higher temperatures in the burnt-on area, thus improving the cleaning result. In addition to changing the fan speed and maintaining a high cooking chamber temperature, cooling can be reduced by restricting the fan's reversing rotation to the direction that generates the highest temperatures in the areas being cleaned.

[0027] The heating element's power in step c) can be temporarily reduced, creating a heating pause. The heating element's power can then be increased again, resulting in a heating peak. With a longer heating pause than during normal operation of the cooking appliance, a longer phase at maximum heating power (the heating peak) can then occur, as the cooking chamber has cooled down somewhat, without reaching excessively high temperatures in the cooking chamber. The high temperatures reached at the heating elements during this time reliably remove accumulated contaminants. By using heating pauses and heating peaks, the cooking chamber is heated less overall, thus requiring less or no cooling and introducing little to no thermal load into the cooking chamber.

[0028] According to a further aspect of the invention, the first section of the heating tubes is heated to such an extent that contaminants located on one or more supports of the heating tube and / or on a steam nozzle and / or on other indirectly heated components in the cooking chamber are loosened. Both the support and the steam nozzle are heated by heat transfer from the first section to such an extent that baked-on contaminants decompose thermally and oxidatively.

[0029] The cleaning process can be a standalone program that can be selected separately by the operator of the cooking appliance, or one that the appliance performs automatically after a certain period of time. Alternatively or additionally, the cleaning program can be combined with other cleaning programs. For example, cleaning programs that clean the cooking chamber with chemical cleaning agents are suitable for this purpose. If the burnt-on food area, the rack, and the steam nozzle are first heated sufficiently to loosen the burnt-on residue, any remaining residue can be easily removed with the chemical cleaning agent in the subsequent chemical cleaning step. It is also possible to create entirely new, combined cleaning sequences into which the cleaning program is integrated.If the process is integrated into an existing cleaning program, it is preferably carried out after a cleaning step with alkali and before a cleaning step with acid. The cleaning step with acid then corresponds to the optional step d), in which the cooking chamber is rinsed with a cleaning solution.

[0030] According to the invention, a cooking appliance is also provided, comprising a cooking chamber and a heating device with at least one heating tube. The heating tube has a first, actively heated section and a second, non-actively heated section adjacent to the first section, with a solid-burn area in which burnt-on impurities can accumulate. The cooking appliance has a control unit designed and configured to control the cooking appliance and the heating device so that they execute the method according to one of the preceding claims. The control unit not only controls the heating device itself, but can also additionally control a steam generator, the steam nozzle, or the cooking chamber ventilation to cool the cooking chamber. Furthermore, the control unit can also receive signals from various sensors, such as a temperature sensor, and thus control the heating device and other components of the cooking appliance accordingly.The control system can also prompt a user via a user interface to introduce a thermal load into the cooking chamber, for example, a container filled with water.

[0031] Further features and characteristics of the invention will become apparent from the following figures and the accompanying description. The figures show: Figure 1 a schematic representation of a cooking appliance according to the invention with a schematically represented heating device; Figure 2 a section of a cooking appliance according to the invention with a fan wheel and an electric heating device; Figure 3 a section of a cooking appliance according to the invention with two fan wheels and an electric heating device; Figure 4 a heating device according to the invention for a gas-powered cooking appliance; Figure 5a diagram with two curves showing the temperature distribution along a heating tube, wherein curve A shows the temperature distribution during normal operation of a cooking appliance according to the invention and curve B shows the temperature distribution during a cleaning process according to the invention; Figure 6 a diagram with two curves showing a temperature profile at a solid combustion area of ​​a heating device according to the invention, wherein curve A shows the temperature profile during normal operation of a cooking device according to the invention and curve B shows an ideal temperature profile during a cleaning process according to the invention; Figure 7a diagram with two curves showing a temperature profile at a solid combustion area of ​​a heating device according to the invention, wherein curve A shows the temperature profile during normal operation of a cooking device according to the invention and curve B shows a temperature profile with heating breaks during a cleaning process according to the invention; and Figure 8 a schematic representation of the procedure for cleaning the cooking appliance Figure 1 .

[0032] Figure 1 Figure 10 shows a cooking appliance 10 for professional use in restaurants, canteens, and large-scale catering establishments. The cooking appliance 10 has a cooking chamber 12, which is bounded by walls 14. A fan 18 is attached to a side wall 16 of the cooking chamber 12. The fan 18 is rotatably mounted on the side wall 16 about an axis of rotation by means of a motor (not shown). An air deflector 20 is provided to shield the fan from the cooking chamber 12.

[0033] In the area of ​​the fan wheel 18, in the Figure 1 To the left of the air guide plate 20 is a heating device 22, which is shown only schematically. Figure 2, 3 and 4 show the respective heating device 22 in detail.

[0034] The heating device 22 has a heating pipe 24.

[0035] When food is cooked in the cooking chamber 12, the resulting impurities are distributed in the cooking chamber 12, so that impurities also accumulate on the heating device 22 and the heating tube 24.

[0036] Depending on how much the heating tube 24 is heated during a cooking process, different levels of impurities adhere to the heating tube 24.

[0037] In the first section 26 of the heating tube 24, which is actively heated, strongly adhering contaminants do not accumulate, as the contaminants that come into contact with it are thermally oxidized during normal operation and fall off the first section 26. Depending on whether the cooking appliance 10 is electrically operated or gas-operated, the first section 26 is heated either by an electric resistance heater or by a gas burner.

[0038] The first section 26 is followed by a second section 28. However, this second section is not actively heated, but only partially warmed by heat transfer from the first section 26 to the second section 28 (i.e., by conduction in the case of electric heating, or by the combustion gas in the case of gas heating). Consequently, the second section 28 does not reach temperatures as high as those of the first section 26, and impurities are not removed by thermal oxidation as they are in the first section 26 during normal operation.

[0039] In the second section, two different areas can be identified with regard to temperature distribution and consequently with regard to impurities.

[0040] A first section 29 of the second section 28, located far from the first section 26, has essentially the same temperature as the cooking chamber 12, i.e., between 250°C and 300°C, since, due to the spatial distance, there is no or only negligible heat transfer from the first section 26 to the first section 29 of the second section 28. As a result, contaminants adhere only weakly and can therefore be removed very effectively by chemical cleaning.

[0041] A second area of ​​the second section 28, which is hereinafter referred to as the solid combustion area 30, has a mean temperature in the range between 300°C and 400°C during normal operation of the cooking appliance.

[0042] The temperatures reached in the solid combustion zone 30 during normal operation result in the contaminants adhering particularly strongly to the surface of this zone ("baking on"). Thermal oxidation of the contaminants does not yet occur, and they are difficult and only partially removed with chemical cleaning agents.

[0043] The spatial extent of the solid residue area 30 on the heating tube 24 depends on the cooking methods or programs typically used with the cooking appliance. Depending on how long and at what temperature the first section 26 is heated during a cooking process, the solid residue area 30 shifts on the second section 28. Generally speaking, the hotter the first section 26, the greater the distance between the solid residue area 30 and the first section 26. It is also possible that the solid residue area 30 may extend partially into the first section 26. In any case, it is not possible to completely clean the solid residue area 30 of impurities during normal operation.

[0044] The cooking appliance 10 has a control unit 32 which is designed, among other things, to control the heating device 22.

[0045] When the cooking appliance 10 is switched to a cleaning mode, the control unit 32 controls the heating device 22 in such a way that the first section 26 is heated to such an extent that, by means of heat transfer, the second section 28 and thus also the solid combustion area 30 is heated to such an extent that the impurities present on the solid combustion area 30 are removed from the heating tube 24 by means of thermal oxidation.

[0046] The control unit 32 is additionally configured to monitor the cooking chamber temperature and control the cooking appliance so that the cooking chamber temperature always remains below a maximum temperature of, for example, 300°C, even during cleaning operation. If necessary, the control unit 32 ensures that the cooking chamber 12 is cooled so that the heating element 22 can operate at maximum power for the desired cleaning duration under optimal conditions.

[0047] For example, the control unit 32 can control the fan wheel 18 accordingly and reduce its speed, so that the heating element is cooled less by air circulation. Alternatively or additionally, the control unit 32 can also control and open a cooking chamber ventilation, control a steam generator so that it produces steam which is introduced into the cooking chamber, and / or activate a steam nozzle.

[0048] Figure 2 Figure 1 shows in detail a first embodiment of a cooking device 10 with a single fan wheel 18 around which several heating tubes 24 are arranged.

[0049] The heating pipes 24 are inserted from a technical room into the cooking chamber 12 through a penetration 34. The heating pipes 24 are not heated in this area to prevent overheating of the connections, undesirable heating of the cooking chamber wall, and consequently, higher heat losses. The second section 28 is therefore located in the area of ​​the penetration 34; more precisely, the first section 29 of the second section 28 is located at the penetrations, and the fixed-burning section 30 is located near the first section 26.

[0050] Following the second section 28 is the first section 26, which is actively heated by means of an electric resistance heater.

[0051] On the side of the heating pipes 24 diametrically opposite the passage 34 there is a bracket 36 which secures the heating pipes 24 to the side wall 16 of the cooking appliance 10.

[0052] In the area of ​​the opening 34, there is also a steam injection nozzle 38, with which water can be sprayed into the cooking chamber 12. Neither the bracket 36 nor the steam injection nozzle 38 are directly heated, so that, similar to the solid combustion area 30, stubborn impurities can accumulate there.

[0053] Figure 3 Figure 1 shows a second embodiment of a cooking appliance with two fan wheels 18, around which two heating tubes 24 are also arranged. The heating tubes 24 emerge from the opening 34 and are fixed to the corresponding side wall 16 of the cooking appliance 10 by means of brackets 36. These two heating tubes also have, in the area of ​​the opening 34, the unheated second section 28 with the first section 29 near the opening and the fixed firing section 30 near the first section 26, while the first section 26 is electrically heated by means of a resistance heater.

[0054] In this embodiment of the cooking device 10, strongly adhering contaminants also occur in the solid combustion area 30, in the area of ​​the feedthrough 34, on the holder 36 and the steam nozzle 38.

[0055] Figure 4 Figure 1 shows a heating device 22 with a heat exchanger 40, which is installed in a gas-powered cooking appliance 10.

[0056] In the first section 26 of the heating device 22, a gas burner 42 is arranged, which actively heats the first section 26. In the present heating device 22, a fuel gas-air mixture is conveyed by a blower (not shown) into the gas burner 42 via a heating tube 24. The hot combustion gases produced during combustion then flow through the heating tube 24, which forms the second section 28. The gas burner 42 is supplied with a fuel gas-air mixture via the blower, which exits the gas burner 42 and is combusted there. The exhaust gas thus generated flows through the inside of the heating tube 24 and transfers the heat to it. However, the heat transfer is not uniform, as the flow rate does not vary across all areas and the exhaust gas temperature decreases towards the end of the heating tube.

[0057] Both upstream of the first section 26 with the gas burner 42 and downstream of the first section 26, the heating tube 24 has fixed combustion zones 30. These fixed combustion zones 30 are located at the points on the heating tube 24 where it is either just being inserted into the cooking chamber 12 or shortly before it exits the cooking chamber 12. The exact position of the fixed combustion zone 30 depends on the flow velocity, the exhaust gas temperature, and the heat dissipation on the outside of the heating tube 24.

[0058] In electric heating devices, the temperature in the first section 26 is usually similar because the heating tubes 24 are generally heated everywhere with approximately the same power density.

[0059] In the heat exchangers of a gas-fired cooking appliance 10, much greater temperature differences occur, particularly due to the decreasing exhaust gas temperature downstream. However, there are also areas with locally stronger heat transfer (e.g., increased turbulence, bending flow, or similar flow effects) or locally weaker heat transfer (e.g., dead zones), which locally increase or decrease the heat transfer. Depending on the heating pipe configuration and other boundary conditions, this can lead to the formation of further areas of stuck combustion 30.

[0060] In order to loosen the strongly adhering contaminants in the solid combustion areas 30 of all previously shown embodiments, the heating device 22 is controlled with such power for a cleaning period of, for example, 15 min that a temperature of, for example, at least 400°C is established in the solid combustion area 30 for a combustion period of, for example, at least 5 min. At the same time, a temperature of 300°C in the cooking chamber is not exceeded.

[0061] In Figure 5 Two curves are schematically depicted, showing a temperature distribution along a heating tube 24 during a normal cooking program in a cooking appliance 10 during normal operation (curve A) and during the cleaning process (curve B). The x-axis represents the length of the heating tube 24 and the y-axis represents the temperature at that point.

[0062] The two curves each represent a snapshot in time, as the distribution is not constant during a cooking or cleaning cycle. Crucially, the distribution during cooking generally corresponds more closely to curve A for most of the time, while during cleaning, particularly during the combustion phase, it more closely resembles curve B.

[0063] Below the graph, two schematic heating pipes 24 are additionally shown, wherein the upper heating pipe 24a and the positions of the sections and areas drawn therein correspond to a heating pipe 24 that is operated in normal operation, and the sections and areas of the lower heating pipe 24b correspond to a heating pipe 24 during the cleaning process.

[0064] The temperatures established on the two heating tubes 24a, 24b can be divided into three areas: One area of ​​the heating tube 24a, 24b has a temperature within a temperature range T1, which essentially corresponds to the temperature in the cooking chamber. This part is the first area 29 of the second section 28 of the heating tube 24a, 24b.

[0065] The subsequent area is the solid firing zone 30, which has a temperature in temperature range T2. Temperature range T2 is shown hatched for clarity and represents the critical or middle temperature range in which strong adhesion of contaminants occurs.

[0066] The first section 26, which follows the second section 28, has a temperature above the temperature range T2 and is therefore in the temperature range T3, in which a thermal-oxidative decomposition of the impurities takes place.

[0067] When comparing the two curves A and B and the heating tubes 24a, 24b shown below, it is noticeable that the temperature at the first section 26 is significantly higher during the cleaning process (curve B) than during the cooking process (curve A).

[0068] This leads to a spatial shift of the solid combustion zone 30 on the heating tube 24b compared to the heating tube 24a, further towards the first zone 29. The solid combustion zone 30 is located further to the left on the heating tube 24b than on the heating tube 24a. As a result, the actual solid combustion zone 30 on the heating tube 24b has a temperature in the temperature range T3, and thus thermal oxidation takes place there.

[0069] Simultaneously, in the first area 29 of the second section 28, both heating tubes 24a and 24b are at the same temperature. Therefore, the cooking chamber temperature is the same during the cleaning process (curve B) as during normal operation (curve A).

[0070] By raising the temperature in the original solids area 30 for a sufficient duration, for example over a cleaning period of at least 15 minutes, the adhering impurities undergo thermal oxidation, causing them to fall off. The necessary cleaning time depends on the cooking system used as well as the quantity and severity of the impurities.

[0071] Figure 6 represents the temperature profile in the solid combustion zone 30 of a heating tube 24 and compares the temperature profile during a normal cooking process (curve A) and the temperature profile at the solid combustion zone 30 during the cleaning process (curve B).

[0072] At the beginning of the cooking process (curve A), when the cooking chamber temperature is below a set temperature, the cooking chamber 12 is still cold. Therefore, the heating element 22 is initially continuously active and heats very intensely. This causes the food-stick area to heat up, initially reaching temperature range T1 and subsequently temperature range T2. For a brief period, the temperature also exceeds T2, briefly reaching temperature range T3 in the food-stick area 30. However, not every cooking process necessarily results in a temperature peak in temperature range T3. Depending on the cooking process, it is also possible for the peak to occur only in range T2. Temperatures only in T1 are also possible, but in this case, the heavy food sticking does not occur.

[0073] Once the target temperature in the cooking chamber 12 is reached, the heating element 22 switches to intermittent operation. The control unit 32 regulates the heating element 22 to maintain the cooking chamber temperature as close as possible to the target temperature. When the target temperature is first reached, the heating element 22 is deactivated, causing the temperature in the heating tube 24 to drop. The cooking chamber temperature also drops with a slight delay, so that the heating element 22 is reactivated when a lower threshold for the cooking chamber temperature is reached. The temperature of the heating tube 24 then rises again. This process creates repeated small heating peaks.

[0074] As long as the target temperature of the cooking chamber 12 is not changed, for example by a user, the cycle operation continues, since maintaining the target temperature in the cooking chamber 12 usually does not require a constant maximum heating power of the heating device 22.

[0075] The highest temperature of the heating element 24 in the solid combustion zone 30 occurs only once, when the target temperature of the cooking chamber 12 is first reached (first peak of curve A on the far left). Subsequently, the temperature level drops more or less significantly depending on the cooking process until it stabilizes at a roughly constant level. The temperature level at which the heating element 24 stabilizes lies precisely within the critical temperature range T2, where increased adhesion of contaminants occurs. In principle, it is also conceivable that the temperature does not remain within temperature range T2 continuously, but briefly falls below or exceeds it. Significant adhesion is also possible in these cases. The crucial factor is that the temperature remains within temperature range T2 for an extended period and only rarely, and above all, never for a prolonged time, enters temperature range T3.

[0076] The reason for the gradual drop in temperature after the first higher peak is that even if the cooking chamber temperature has already reached the target temperature, due to the inertia of the cooking appliance the temperature in the heating tube 24 continues to rise slightly until the entire cooking appliance is thoroughly heated.

[0077] Curve B shows the idealized temperature profile of the heating tube 24, in which the heating device 22 is continuously active. For example, the thermal load in the cooking chamber 12 may have been increased, such as by placing a container of water in the cooking chamber 12. This requires a consistently high power output from the heating device 22 to achieve the same (high) target temperature in the cooking chamber 12.

[0078] The temperature of the heating tube 24 initially rises more slowly due to the higher load in the cooking chamber 12, but then exceeds the highest temperature of curve A (first peak) and remains at approximately its maximum temperature in temperature range T3 after reaching the target temperature in the cooking chamber 12, since the heating device 22 is permanently active.

[0079] If the heating power of the heating device 22 is constantly at its maximum, the temperature of the heating tube 24 can be kept permanently above the temperature range T2 and the solid combustion area 30 can be cleaned by thermal oxidation.

[0080] The curve shown here represents the highest possible temperature profile during cleaning. Cleaning can also be successful if the heating device 22 is not continuously active, i.e., if it operates intermittently, but is active for a significantly longer average time (higher average power) than in normal operation. The crucial factor is that the temperature remains within temperature range T3 for an extended period, even during intermittent operation. In such a hotter, intermittent mode, the individual heating phases are longer and the heating breaks shorter than in normal operation.

[0081] It can even be advantageous to set the temperature only slightly above temperature range T2. Ideally, this allows for a lower thermal load or less cooling of the cooking chamber, which is generally easier to achieve. Furthermore, the temperature stress on some components is then not quite as high, thus avoiding an unnecessary reduction in their lifespan.

[0082] Alternatively or additionally to increase the thermal load in the cooking chamber 12, a cooking chamber door of the cooking appliance 10 can be opened so that the heat introduced into the cooking chamber 12 can be released into the surroundings. A cooking chamber vent can also be opened so that cool air flows into the cooking chamber, or the cooking chamber can be actively cooled with a water source such as steam from a steam generator and / or water from a steam nozzle. Furthermore, it is advantageous to utilize the maximum possible temperature of the cooking chamber, so the heating element 22 is set to always maintain the maximum permissible cooking chamber temperature.

[0083] Additionally, the speed of the fan wheel 18 can be reduced. Besides a lower fan wheel speed and a high cooking chamber temperature, cooling can be reduced by restricting the reversing operation of the fan wheel 18 to the direction of rotation that generates the higher temperatures at the areas to be cleaned.

[0084] The highest possible temperature at the heating element 24 is achieved when the thermal load exactly matches the maximum power of the heating device 22. The thermal load is the consumer of the generated heat. The heating device 22 is controlled so that, on average, only as much heat is generated at the heating element 24 as the consumers draw; otherwise, the cooking chamber temperature would, in most cases, rise significantly above the maximum cooking chamber temperature. With an empty cooking chamber 12, initially only the air and the components of the cooking appliance 10 need to be heated. Once the cooking appliance 10 is heated, only the energy required to compensate for its heat losses needs to be supplied, so that, on average, very little power is required. By increasing the thermal load, the cooking appliance 10 requires a consistently higher average heat supply. The type of consumer does not affect the required heating power.With open oven ventilation, the fresh, cold air must be heated additionally. If a water container is used, the water must also be heated and may later evaporate. With an open oven door, air exchange occurs with the cold ambient air, so the incoming cold air must also be heated.

[0085] If the thermal load is lower than the maximum heating power, the cooking appliance 10 enters cycle mode, which is previously determined based on Figure 6 As described above, at even higher loads the heating power is insufficient to reach the target temperature of the cooking chamber 12. This increases heat loss, and the temperature of the heating tube 24 is lower despite the heating device being continuously active.

[0086] In addition to generating a permanently high thermal load, the necessary temperature in the solid combustion area 30 can also be achieved by alternately heating and cooling the cooking chamber 12.

[0087] This is in Figure 7 shown, where curve A again shows the temperature profile at the solid combustion area 30 during normal operation and curve B shows the cycle operation of a possible cleaning process.

[0088] During the cleaning process, after heating up and reaching the target temperature in cooking chamber 12, there is a heating pause, resulting in a longer cooling period for the cooking chamber 12. This also causes the temperature of the heating element 24 to drop more significantly (curve B) compared to the temperature during normal operation (curve A). Subsequently, when reheating to the target temperature of the cooking chamber 12 in curve B, the heating element 22 must heat for a longer period, resulting in a higher heating peak compared to the heating peak that occurs during normal operation.

[0089] The sum of the peaks ensures that the temperature required for the thermo-oxidative decomposition of contaminants in the solid burnt area 30 is reached for a sufficient duration. This method is particularly suitable when a continuous thermal load cannot be introduced into the cooking chamber 12. However, this results in a longer cleaning time.

[0090] Figure 8 shows an overview of the cleaning method according to the invention.

[0091] In the first step S1, a cleaning program is selected.

[0092] In a second step, S2 then switches on the heating device, so that the first section 26 of the heating pipe 24 is heated.

[0093] In the third step S3, the heating device 22 is operated for a cleaning period of, for example, 15 minutes at a power level such that heat transfer in the solids area 30 results in a temperature of at least 400°C for a combustion period of at least 5 minutes, thus dissolving the contaminants adhering to the solids area 30. At the same time, the maximum permissible cooking chamber temperature of, for example, 300°C is not exceeded. In step S2, the power of the heating device 22 can be temporarily reduced, creating one or more heating pauses. After these heating pauses, the power of the heating device 22 is increased again, resulting in a heating peak.

[0094] Parallel to or following the heating of the cooking chamber 12 with the heating device 22, the cooking chamber 12 can be actively cooled in an additional step S4, for example by introducing steam from a steam generator into the cooking chamber 12, and / or by introducing water from a steam nozzle 38 into the cooking chamber 12, and / or by opening a cooking chamber vent. Additionally, the process can be carried out with the cooking chamber door open, and / or the thermal load in the cooking chamber 12 can be increased, and / or the speed of a rotating fan wheel 18 in the cooking chamber 12 can be reduced.

[0095] In a further step S5, the cooking chamber 12 is rinsed with a cleaning solution such as an alkali or acid.

[0096] The cleaning process can either be carried out as a standalone cleaning program or it can be combined with an existing cleaning program of the cooking appliance 10, which, for example, cleans the cooking chamber 12 using chemical cleaning agents.

Claims

1. A method for cleaning a cooking appliance (10) with a cooking chamber (12) and a heating device (22) with a heating tube (24), wherein the heating tube (24) has a first actively heated section (26) and a second section (28) adjacent to the first section (26) which is not actively heated, wherein, during normal operation of the cooking appliance (10), contaminants accumulate and burn onto the second section (28) in a solid burn area (30), the method comprising the following steps: a) selecting a cleaning program; b) switching on the heating device (22) so that the first section (26) of the heating tube (24) is heated; c) operating the heating device (22) for a cleaning period at such a power that, through heat transfer in the solid burn area (30), a temperature is reached for a burn-off period of at least 1 min and preferably at least 5 min.adjusts so that the impurities adhering in the solid burn area (30) are dissolved, while at the same time preventing the temperature in the cooking chamber (12) from exceeding a maximum permissible cooking chamber temperature.

2. Method according to claim 1, characterized by the fact that step c) a temperature of at least 400°C is reached in the solid firing range (30).

3. Method according to one of claims 1 and 2, characterized by the fact that Step c) is followed by step d), in which the cooking chamber (10) is rinsed with a cleaning solution.

4. Method according to any one of the preceding claims, characterized by the fact that the heating device (22) in step c) is operated at maximum power, in particular the cleaning time being at least 15 min.

5. Procedure according to any of the preceding claims, characterized by the fact thatIn step c) the temperature in the cooking chamber (12) is at a maximum of 300°C and the temperature in the first section (26) of the heating tube (24) is between 500°C and 850°C.

6. Method according to any one of the preceding claims, characterized by the fact that The heating device (22) is either an electric heater, wherein the first section (26) is actively heated electrically and the second section (28) is not actively heated and is heated indirectly via heat transfer, or a heat exchanger (40), wherein the first section (26) is actively heated via a burner, in particular a gas burner (42), and the second section (28) is arranged downstream of the first section (26), is not actively heated, and is heated indirectly via heat convection.

7. Method according to any of the preceding claims, characterized by the fact thatthe cooking chamber (12) is actively cooled during the cleaning process, in particular by introducing steam from a steam generator into the cooking chamber (12) in a further step and / or introducing water from a nozzle into the cooking chamber (12) and / or opening a cooking chamber ventilation.

8. Method according to any one of the preceding claims, characterized by the fact that a cooking chamber door of the cooking appliance (10) is open during the cleaning process and / or a thermal load in the cooking chamber (12) is increased and / or in a further step the speed of a rotating fan wheel (18) in the cooking chamber (12) is reduced and / or the reversing operation of the fan wheel (18) is restricted.

9. Method according to any one of the preceding claims, characterized by the fact that The power of the heating device (22) is temporarily reduced in step c) so that a heating pause occurs, and after the heating pause the power of the heating device (22) is increased again so that a heating peak occurs.

10. Method according to any one of the preceding claims, characterized by the fact that the first section (26) of the heating tubes (24) is heated to such an extent that impurities located on a support (36) of the heating tube (24) and / or on a steam nozzle (38) and / or on other components in the cooking chamber (12) are dissolved.

11. Method according to any of the preceding claims, characterized by the fact that the procedure is a standalone cleaning program and / or is combined with a cleaning program of the cooking appliance (10) with which the cooking chamber is cleaned using chemical cleaning agents.

12. Cooking appliance (10) with a cooking chamber (12) and a heating device (22) with at least one heating tube (24), which has a first, actively heated section (26) and a second, non-actively heated section (28) adjacent to the first section (26) with a solid burn area (30) on which burnt-on impurities can accumulate, wherein the cooking appliance (10) has a control unit (32) which is designed and configured to control the cooking appliance (10) and the heating device (22) so that they perform the method according to one of the preceding claims.

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