Method of cleaning a cooking appliance and cooking appliance

Abstract

This invention relates to a method for cleaning cooking appliances and the cooking appliances themselves. A method for cleaning a cooking appliance includes a cooking chamber and a heating device having a heating element, wherein the heating element has a first section that can be actively heated and a second section adjacent to the first section that cannot be actively heated, wherein during normal operation of the cooking appliance, impurities are deposited and burned onto a burning area in the second section, wherein the method includes the steps of: a) selecting a cleaning program; b) turning on the heating device such that the first section of the heating element is heated; c) operating the heating device at a power level during the cleaning period such that heat transfer through the burning area reaches a temperature that causes impurities adhering to the burning area to detach within a combustion period of at least 1 minute and preferably at least 5 minutes, while simultaneously preventing the temperature in the cooking chamber from exceeding the maximum permissible cooking chamber temperature.

Description

Technical Field

[0001] This invention relates to a method for cleaning cooking appliances, the cooking appliances including a cooking chamber and a heating device having a heating element. The invention also relates to a cooking appliance for implementing the method. Background Technology

[0002] Cooking appliances with heating elements are typically used for cooking food in gourmet dishes. Depending on their use and when cooking certain foods, a significant amount of impurities may appear in the cooking chamber, distributed throughout the chamber and adhering to surfaces.

[0003] Common cleaning methods are based on chemical surface cleaning. This involves adding water and chemicals to form a detergent solution, which may be additionally heated and then typically circulated in the cooking appliance for a period of time or the cooking chamber is rinsed at least once.

[0004] However, chemical cleaning is insufficient in some areas. In particular, heating devices with one or more heating elements cannot always be thoroughly cleaned chemically because these elements have areas that are difficult for detergent to reach. Additionally, the varying temperatures the heating elements receive during cooking also affect the cleaning results. In the unheated sections, which typically reach at most the ambient temperature of the cooking chamber, impurities (such as grease and other residues from cooked food) do not adhere strongly, making them easily removable by chemical cleaning. In the actively heated sections, the significantly higher temperatures cause impurities to chemically decompose, resulting in similarly weak adhesion. However, between the actively heated and unheated sections, there exists a region where the temperature during cooking falls between the active and unheated sections. The thermal effects in these areas cause impurities to adhere particularly strongly, accompanied by chemical transformation and adhesion through combustion. Therefore, these impurities cannot be adequately removed by chemical cleaning.

[0005] Over time, increasingly thick layers of various impurities accumulate in what's known as the burnt-on zone. This can lead to fumes in the cooking chamber, altering the taste of food, severely damaging air quality in the kitchen, and harming cooking appliances. Summary of the Invention

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

[0007] According to the present invention, this objective is achieved by a method for cleaning a cooking appliance, the cooking appliance comprising a cooking chamber and a heating device having a heating element. The heating element has a first section that can be actively heated and a second section adjacent to the first section that cannot be actively heated. During normal operation of the cooking appliance, impurities deposit and burn onto a burning area in the second section. The cleaning method includes the following steps: First, a cleaning program is selected. Then, the heating device is turned on so that the first section of the heating element is heated. Then, the heating device is operated at a certain power during the cleaning period, such that heat transfer through the burning area reaches a temperature that causes the impurities adhering to the burning area to detach within a combustion period of at least 1 minute, and preferably at least 5 minutes. Simultaneously, the temperature in the cooking chamber is prevented from exceeding the maximum permissible cooking chamber temperature.

[0008] This invention is based on the following fundamental concept: by heating the first section of the heating tube more intensely and / or for a longer period, the burn-off area of ​​the second section of the heating tube is heated to the point where impurities adhering to the burn-off area are thermally oxidized. In other words, the burn-off area is temporarily transferred during the cleaning process from the actual burn-off area generated by normal operation, and is located at a different point on the heating tube during the cleaning process than during normal operation. However, it is important not to exceed the maximum permissible temperature in the cooking chamber to protect temperature-sensitive components in the cooking chamber, such as the cooking chamber seals, from damage. Using the method according to the invention, the heating device is thus heated particularly intensely while the cooking chamber remains relatively "cool". The walls and cooking chamber door and / or sensors installed in the cooking chamber are not heated to the point where any impurities adhering to them are oxidized. Therefore, there is no cleaning of the entire cooking chamber, including the cooking chamber walls, bottom, and cooking chamber door; instead, only the heating device is cleaned, and if necessary, any supports and / or nozzles located in its immediate vicinity are cleaned.

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

[0010] Even when temperatures exceed, for example, 400°C at locations within the burn-in zone during normal operation, impurities at those locations cannot be adequately removed. For adequate removal, a temperature exceeding 400°C must be maintained for at least 5 minutes, for example.

[0011] In principle, the burnt-on area can extend slightly into the first section of the actively heated heating element. This depends on how the temperature transition from the first section to the second section develops during normal operation of the cooking appliance. Due to heat conduction, a temperature drop may have occurred in the second section at the edge of the first section compared to the area in the first section, while the area in the first section is unaffected by heat conduction due to the greater distance to the second section. Furthermore, the burnt-on area may not be directly adjacent to the first section, allowing the shorter portion of the second section to be adequately cleaned during normal operation. The exact formation of the temperature transition and therefore the location of the burnt-on area depend on several factors, such as the cooking chamber temperature used, the typical temperature in the actively heated area, and the possible composition of the contaminants.

[0012] If the cooking appliance is electrically operated, the heating device may be a heating device with a resistance heater. If the cooking appliance is gas-powered, the heating device includes a gas burner that heats a first section of the heating element. Typically, the resistance heater has multiple heating elements arranged approximately parallel to each other, while the heat exchanger has long, multi-coiled heating elements.

[0013] In resistance heaters, the heating element is typically heated only a limited distance after passing through the cooking chamber wall inside the cooking chamber to prevent overheating of the connectors and the cooking chamber wall, and thus to prevent higher heat loss. Unheated sections, particularly those near the passage through the wall of the cooking chamber, form a second section. Additionally, multiple supports exist along the heating element for securing it to each other and also to the wall of the cooking chamber; these supports contact the first section of the heating element but are not heated themselves. In principle, it is conceivable that the method according to the invention can also be used to clean other areas and components in the cooking appliance that are adjacent to or spatially located near the first section. Cleaning is then performed by convective heat transfer and / or radiation.

[0014] In gas-fired cooking appliances with heat exchangers, significant temperature differences along the heating elements are unavoidable due to exhaust gas temperature, internal flow velocity, and external cooling (in the sense of "heat dissipation") of the heating elements. This results in temperatures so low in the area in front of the gas burner and in areas far downstream of it that it becomes impossible to prevent impurities from adhering during combustion.

[0015] In the following text, burning time refers to the length of time generally sufficient for the adhering impurities to decompose through thermal oxidation. The burning time is at least 5 minutes. After this time, the impurities in the burned area begin to self-heat.

[0016] Cleaning time refers to the length of time the heating device must operate until the desired temperature, for example, at least 400°C, is reached. This also includes the subsequent combustion time. Therefore, cleaning time is the time from the start of the process to the end of cleaning. Cleaning time varies depending on the severity of contamination, the type of impurities, and the temperature reached in the burning zone. For example, for average contamination, a cleaning time of 15 minutes is sufficient to achieve good cleaning results. The combustion time can, for example, be half the cleaning time.

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

[0018] During normal operation, the cooking appliance performs any cooking process used to cook food. Normal operation refers to typical cooking operations. During normal operation, the temperature in the burnt zone is below 400°C. The range between 300°C and 400°C is called the intermediate temperature range or critical temperature range because this range causes burnt impurities to adhere particularly strongly to the heating element.

[0019] The temperature set in step c) in the sintering zone can be at least 400°C. Starting from this temperature, the sintering zone is effectively and reliably cleaned.

[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 water. The rinsing step removes impurities that have detached from the burnt area and deposited, for example, on the bottom plate of the cooking chamber. This prevents impurities from re-burning onto it. The cleaning solution may be, for example, an alkaline solution or an acid.

[0021] If a high-temperature cleaning step is incorporated into a chemical cleaning process, cooling, such as accelerated cooling, is typically required afterward. This is because further cleaning steps are usually followed, in which water or chemical cleaning solutions are used again in the cooking chamber. The high temperatures in the cooking chamber can cause sudden evaporation, leading to further serious consequences. Therefore, the cooking chamber and heating elements must be cooled again before proceeding to the next step. Thus, this cooling must also be incorporated into such combined cleaning processes. In other cases, such as when thermal oxidative cleaning is used at the end of a cleaning process, cooling is not necessarily required.

[0022] According to another aspect of the invention, the heating device operates 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 results in optimal cleaning results. However, it should be noted that the maximum cooking chamber temperature must not be exceeded. Therefore, if necessary, for example when a heat load is introduced into the cooking chamber or when the cooking chamber is actively or passively cooled, the heating device operates only at maximum power. Essentially, the heating device must operate at maximum heating power or alternatively at medium to high heating power for a sufficient period of time.

[0023] In step c), the temperature in the cooking chamber can be a maximum of 300°C, and the temperature in the first section of the heating element can be between 500°C and 850°C. The maximum cooking chamber temperature depends on the heat-sensitive components installed in the cooking chamber, such as the cooking chamber seals 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 will not damage the heating element.

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

[0025] According to another aspect of the invention, the cooking chamber can be actively cooled during the cleaning process, particularly by introducing steam from a steam generator into the cooking chamber and / or introducing water from a nozzle into the cooking chamber and / or activating the cooking chamber ventilation system in a further step. Active cooling has the advantage of maximizing the heating power of the heating device while ensuring that the temperature in the cooking chamber does not exceed the maximum permissible cooking chamber temperature. In this way, the temperature in the burnt zone can be raised to a level that thermally oxidizes impurities while simultaneously maintaining the cooking chamber temperature below the maximum permissible cooking chamber temperature. The faster, longer, and further the temperature in the burnt zone exceeds 400°C, the faster the cleaning process is completed. Therefore, active cooling (i.e., heat dissipation) results in better cleaning outcomes and a shorter cleaning duration.

[0026] During the cleaning process, the cooking appliances or cooking chamber can also be cooled by opening the cooking chamber door. Alternatively or additionally, the heat load in the cooking chamber can be increased and / or the speed of the rotating fan impeller in the cooking chamber can be reduced. Due to the open cooking chamber door, hot air can escape from the cooking chamber, thus cooling it. The heat load arranged in the cooking chamber causes it to heat up more slowly. A slower rotating fan impeller reduces the air velocity near the heating elements, so that more heat released near the heating elements is used to heat the secondary section and not dissipated into the cooking chamber. Combined with other methods of cooling the cooking chamber, such as an open cooking chamber ventilation system, the optimal fan impeller speed can be found in the intermediate range. In some cases, a higher fan impeller speed may even result in higher temperatures in the burnt areas, thus improving cleaning results. In addition to altered fan impeller speed and higher cooking chamber temperatures, cooling can also be reduced by reversing the fan impeller's rotation to a direction that generates higher temperatures at the point to be cleaned.

[0027] In step c), the power of the heating element can be temporarily reduced, resulting in a heating pause. The heating power can then be increased again, generating a heating peak. By pausing the heating for a longer period than during normal operation of the cooking appliance, a longer phase with maximum heating power (heating peak) can then occur without reaching unacceptably high temperatures in the cooking chamber, as the chamber has cooled slightly again. Due to the high temperatures reached on the heating element during this process, any deposited impurities can be reliably removed. The use of heating pauses and heating peaks typically results in the cooking chamber being heated less intensely, requiring little or no cooling, and necessitating the introduction of a heat load or only a low heat load into the cooking chamber.

[0028] According to another aspect of the invention, a first section of the heating tube is heated to the extent that impurities located on one or more supports of the heating tube and / or on the steaming nozzles and / or other indirect heating components in the cooking chamber are removed. Both the supports and the steaming nozzles are heated by heat transfer from the first section to the extent that any burnt impurities are decomposed by thermal oxidation.

[0029] This process can be a standalone cleaning procedure, which can be selected individually by the operator of the cooking appliance, or the cooking appliance can perform the process automatically and independently after a period of time. Alternatively or additionally, the cleaning procedure can also be combined with other cleaning procedures. For example, a cleaning procedure using chemical cleaners to clean the cooking chamber is suitable for this purpose. If the burnt areas, supports, and spray nozzles are first heated to the point that burnt impurities are detached, the remaining impurities can be easily removed using chemical cleaners in the subsequent chemical cleaning step. Novel combined cleaning sequences incorporating cleaning procedures can also be created. If this process is incorporated into an existing cleaning procedure, it is preferably performed after a cleaning step using alkali and before a cleaning step using acid. The cleaning step using acid then corresponds to optional step d), in which the cooking chamber is rinsed with a cleaning solution.

[0030] According to the present invention, a cooking appliance is also provided, comprising a cooking chamber and a heating device having at least one heating tube. The heating tube has a first section that can be actively heated and a second section adjacent to the first section that cannot be actively heated, and the heating tube has a burning area on which burning impurities can be deposited. The cooking appliance has a control unit configured and set to operate the cooking appliance and the heating device such that the cooking appliance and the heating device perform the method according to any of the foregoing aspects. The control unit controls not only the heating device itself, but can also additionally control a steam generator, spray nozzles, or a cooking chamber ventilation system to cool the cooking chamber. Furthermore, the control unit can receive signals from various sensors, such as temperature sensors, and thus control the heating device and other components of the cooking appliance accordingly. The control unit can also prompt a user via a user interface to place a heat load in the cooking chamber, for example, a container filled with water. Attached Figure Description

[0031] Other features and characteristics of the invention will become apparent from the following drawings and related description, in which:

[0032] - Figure 1 A schematic diagram of a cooking appliance with a heating device according to the present invention is shown;

[0033] - Figure 2 Details of a cooking appliance with a fan impeller and an electric heating device according to the present invention are shown;

[0034] - Figure 3 Details of a cooking appliance with two fan impellers and an electric heating device according to the present invention are shown;

[0035] - Figure 4 A heating device for a gas-powered cooking appliance according to the present invention is shown;

[0036] - Figure 5 A graph with two curves is shown, which show the temperature distribution along the heating element. Curve A shows the temperature distribution during normal operation of the cooking appliance according to the invention, and curve B shows the temperature distribution during the cleaning method according to the invention.

[0037] - Figure 6 A graph with two curves is shown, which show the temperature distribution in the burning area of ​​the heating device according to the invention. Curve A shows the temperature distribution during normal operation of the cooking appliance according to the invention, and curve B shows the ideal temperature distribution during the cleaning method according to the invention.

[0038] - Figure 7 A graph showing two curves illustrates the temperature distribution at the burning zone of the heating device according to the invention. Curve A shows the temperature distribution during normal operation of the cooking appliance according to the invention, and curve B shows the temperature distribution during a heating pause in the cleaning method according to the invention.

[0039] - Figure 8 A diagram showing the cleaning process from Figure 1 A diagram illustrating the cooking methods using cooking utensils. Detailed Implementation

[0040] Figure 1 A cooking appliance 10 is shown for professional use in restaurants, canteens, and large-scale cooking methods. The cooking appliance 10 has a cooking chamber 12 defined by a wall 14. A fan impeller 18 is attached to a side wall 16 of the cooking chamber 12. The fan impeller 18 is mounted on the side wall 16 and is capable of rotating about a rotation axis by means of a motor (not shown). An air baffle 20 is provided to protect the fan impeller from the influence of the cooking chamber 12.

[0041] exist Figure 1 A heating device 22, shown only schematically, is provided on the left side of the air baffle 20 in the area of ​​the fan impeller 18. Figure 2 , Figure 3 and Figure 4 The corresponding heating device 22 is shown in detail.

[0042] The heating device 22 has a heating tube 24.

[0043] When food is cooked in the cooking chamber 12, the resulting impurities are distributed throughout the cooking chamber 12, causing the impurities to also deposit on the heating device 22 and the heating tube 24.

[0044] Depending on the intensity of heating of the heating element 24 during the cooking process, impurities adhere to the heating element 24 to varying degrees.

[0045] Firmly adhered impurities will not deposit in the actively heated first section 26 of the heating element 24 because impurities impacting the first section 26 have been thermally oxidized and detached from the first section 26 during normal operation. Depending on whether the cooking appliance 10 is an electrically operated or gas-operated cooking appliance 10, the first section 26 is heated by a resistance heater or by a gas burner.

[0046] The first section 26 is followed by the second section 28. However, the second section 28 is not actively heated, but is only partially heated by heat transfer from the first section 26 to the second section 28 (i.e., by heat conduction in the case of an electric heater or by combustion gas in the case of a gas heater). The second section 28 does not reach the same temperature as the first section 26, and impurities are not removed by thermal oxidation during normal operation as in the first section 26.

[0047] In the second section, two distinct regions can be identified in terms of temperature distribution and therefore impurities.

[0048] The first region 29 of the second segment 28, located away from the first segment 26, has a temperature substantially the same as that present in the cooking chamber 12, i.e., between 250°C and 300°C, because due to the spatial distance, there is no or only negligible heat transfer from the first segment 26 to the second segment 28 in the first region 29. Therefore, impurities adhere only slightly and can thus be removed very easily by chemical cleaning.

[0049] The second region of the second section 28, hereinafter referred to as the burnt region 30, has an average temperature in the range of 300°C to 400°C during normal operation of the cooking appliance.

[0050] The temperatures that occur in the burn-on zone 30 during normal operation cause impurities to adhere (“burn-on”) particularly firmly to the surface of the burn-on zone 30. Thermal oxidation of the impurities has not yet occurred, and the impurities are difficult to completely remove with chemical cleaning agents.

[0051] The extent of the burn-in zone 30 on the heating element 24 depends on the cooking process or procedure typically performed with the cooking appliance. Depending on the time and temperature at which the first section 26 is heated during the cooking process, the burn-in zone 30 shifts onto the second section 28. Generally, the hotter the first section 26, the greater the distance between the burn-in zone 30 and the first section 26. It is also possible that the burn-in zone 30 partially extends into the first section 26. However, under no circumstances can impurities in the burn-in zone 30 be completely cleaned during normal operation.

[0052] The cooking appliance 10 has a control unit 32, which is specifically configured to operate the heating device 22.

[0053] If the cooking appliance 10 is switched to cleaning mode, the control unit 32 controls the heating device 22 so that the first section 26 is heated to the extent that the second section 28 and thus the burnt area 30 are heated by means of heat transfer to the extent that impurities present on the burnt area 30 are removed from the heating tube 24 by thermal oxidation.

[0054] The control unit 32 is also configured to monitor the cooking chamber temperature and control the cooking appliances so that the cooking chamber temperature is always kept below, for example, the maximum cooking chamber temperature of 300°C, even during cleaning operations. If necessary, the control unit 32 ensures that the cooking chamber 12 is cooled so that, under optimal conditions, the heating device 22 can operate at maximum power for the desired cleaning time.

[0055] For this purpose, for example, the control unit 32 may accordingly drive the fan impeller 18 and reduce the speed of the fan impeller 18, so that the heater is cooled less by air circulation. Alternatively or additionally, the control unit 32 may also operate and turn on the cooking chamber ventilation system, control the steam generator to produce steam to be introduced into the cooking chamber, and / or activate the spray nozzles.

[0056] Figure 2 A first embodiment of a cooking appliance 10 with a single fan impeller 18 is shown in detail, with a plurality of heating tubes 24 arranged around the single fan impeller 18.

[0057] The heating element 24 is introduced from the technical room into the cooking chamber 12 in the area of ​​the feed passage 34. The heating element 24 is not heated in this area to prevent overheating of the connectors, undesirable heating of the walls of the cooking chamber, and correspondingly higher heat loss. Therefore, the second section 28 is located in the area of ​​the feed passage 34; more precisely, the first region 29 of the second section 28 is located at the feed passage, and the burn-in region 30 is located near the first section 26.

[0058] Adjacent to the second section 28 is the first section 26, which is actively heated by means of a resistance heater.

[0059] On the side of the heating tube 24 that is diametrically opposite to the feed passage 34 is a support member 36, which fixes the heating tube 24 to the side wall 16 of the cooking appliance 10.

[0060] In the area of ​​the feed passage 34, there is also a spray nozzle 38, through which water can be sprayed into the cooking chamber 12. Neither the support member 36 nor the spray nozzle 38 is directly heated; therefore, similar to the burn-off area 30, adhering impurities may deposit on the support member 36 and the spray nozzle 38.

[0061] Figure 3 A second example embodiment of a cooking appliance with two fan impellers 18 is shown, with two heating tubes 24 also arranged around the fan impellers 18. The heating tubes 24 extend from a feedthrough 34 and are secured to the corresponding sidewall 16 of the cooking appliance 10 by means of a support 36. Both heating tubes also have unheated second sections 28 in the region of the feedthrough 34, wherein a first region 29 is adjacent to the feedthrough, and a burn-in region 30 is adjacent to the first section 26, which is electrically heated by means of a resistance heater.

[0062] In this example embodiment of the cooking appliance 10, firmly adhered impurities also appear in the burnt area 30, the area of ​​the feed passage 34, the support member 36, and the spray nozzle 38.

[0063] Figure 4 A heating device 22 with a heat exchanger 40 is shown, which is installed in a gas-powered cooking appliance 10.

[0064] A gas burner 42 for actively heating the first section 26 is arranged in the heating device 22. In this heating device 22, a fuel-air mixture is supplied from a blower (not shown) to the gas burner 42 via a heating tube 24. The hot combustion gases generated during combustion then flow through the heating tube 24, which forms the second section 28. The gas burner 42 is supplied with the fuel-air mixture via a blower, which exits at the gas burner 42 and burns there. The exhaust gas generated in this way flows through the interior of the heating tube 24 and transfers heat to it. However, the heat transfer is not equally strong everywhere, because not all areas flow through at the same speed, and the exhaust gas temperature decreases towards the ends of the heating tube.

[0065] The heating tube 24 has a burn-off region 30 both upstream and downstream of the first section 26 with the gas burner 42. The burn-off region 30 is located on the heating tube 24 at the point where the heating tube 24 is introduced into the cooking chamber 12 or at the point where the heating tube 24 leaves the cooking chamber 12 again. The exact location of the burn-off region 30 depends on the flow velocity, exhaust gas temperature, and heat dissipation from the outside of the heating tube 24.

[0066] In an electric heating device, the temperature in the first section 26 is generally similar because the heating tube 24 is typically heated at roughly the same power density anywhere.

[0067] In the heat exchanger of the gas-powered cooking appliance 10, a much larger temperature difference is achieved, particularly due to the downward reduction in exhaust gas temperature. However, there are also regions with locally strong heat transfer (e.g., strong turbulence, bend flow, or similar flow effects) or locally weak heat transfer (e.g., dead zones), which can locally increase or decrease heat transfer. Depending on the heating tube layout and other boundary conditions, this may result in the formation of additional burn-off zones 30.

[0068] In order to remove firmly adhered impurities from the burn-on zone 30 in all the embodiments shown above, the heating device 22 operates at a certain power during a cleaning period of, for example, 15 minutes, such that a temperature of, for example, at least 400°C is established during a combustion period of, for example, at least 5 minutes due to heat transfer in the burn-on zone 30. Meanwhile, the temperature in the cooking chamber does not exceed 300°C.

[0069] Figure 5 Two curves are schematically shown, illustrating the temperature distribution along the heating element 24 during normal cooking (curve A) and during cleaning (curve B), respectively. The length of the heating element 24 is plotted on the x-axis, and the achieved temperature is plotted on the y-axis.

[0070] These two curves each represent snapshots because the distribution is not constant during the cooking or cleaning cycle. The decisive factor is that in cooking mode, the distribution generally conforms more closely to curve A for most of the time, while in cleaning mode, especially during the combustion phase, the distribution conforms more closely to curve B.

[0071] Below the graph, two additional schematic heating tubes 24 are shown, wherein the upper heating tube 24a and the marked sections and areas therein correspond to the heating tube 24 operating in normal operation, and the sections and areas of the lower heating tube 24b correspond to the heating tube 24 during the cleaning process.

[0072] The temperatures set on the two heating elements 24a and 24b can be basically divided into three zones:

[0073] A region of the heating elements 24a and 24b has a temperature within a temperature range T1, which substantially corresponds to the temperature in the cooking chamber. This portion is the first region 29 of the second segment 28 of the heating elements 24a and 24b.

[0074] The adjacent region is the sintering region 30, which has a temperature within the temperature range T2. For clarity, the temperature range T2 is shown in shaded lines and represents the critical or intermediate temperature range in which strong adhesion of impurities occurs.

[0075] The first section 26, which is adjacent to the second section 28, has a temperature higher than the temperature range T2 and therefore within the temperature range T3, in which the thermal oxidative decomposition of impurities occurs.

[0076] When comparing the two curves A and B, as well as the heating elements 24a and 24b shown below, it can be noted that the temperature at the first segment 26 during the cleaning process (curve B) is significantly higher than the temperature during the cooking process (curve A).

[0077] This causes the burn-on region 30 on the heating tube 24b to spatially shift further toward the first region 29 compared to the heating tube 24a. The burn-on region 30 is positioned further to the left on the heating tube 24b than on the heating tube 24a. Therefore, the actual burn-on region 30 on the heating tube 24b has a temperature within the temperature range T3, and thus thermal oxidation occurs there.

[0078] Meanwhile, the same temperature exists in the first region 29 of the second section 28 on the two heating tubes 24a and 24b. Therefore, the cooking chamber temperature is as high during the cleaning process (curve B) as it is during normal operation (curve A).

[0079] By raising the temperature in the original burnt zone 30 for a sufficiently long period of time, such as more than 15 minutes of cleaning time, thermal oxidation occurs on the impurities adhering there, causing them to detach. The required cleaning time depends on the cooking system used and the amount and intensity of the adhering impurities.

[0080] Figure 6 Temperature curves in the burn-in zone 30 of the heating element 24 are shown, and the temperature curves during the normal cooking process (curve A) are compared with the temperature curves in the burn-in zone 30 during the cleaning process (curve B).

[0081] At the start of the cooking process (curve A), cooking chamber 12 is still cold when the temperature is below the desired temperature. Therefore, heating device 22 is initially continuously activated and heats very intensely. This causes the burnt-on area to heat, initially within temperature range T1, and then within temperature range T2. Temperature range T2 is also briefly exceeded, causing the burnt-on area 30 to briefly have a temperature within temperature range T3. However, a temperature peak within temperature range T3 does not necessarily occur in every cooking process. Depending on the cooking process, there are also processes where the peak is only within range T2. T1 alone is also possible, but then no firm adhesion occurs.

[0082] Once the desired temperature in cooking chamber 12 is reached, heating element 22 switches to cyclic operation. Control unit 32 controls heating element 22 to keep the cooking chamber temperature as close as possible to the desired temperature. When the desired temperature is first reached, heating element 22 is deactivated, causing the temperature in heating element 24 to drop. Similarly, the cooking chamber temperature drops after a short delay, so that when a lower threshold of the cooking chamber temperature is reached, heating element 22 is reactivated. The temperature of heating element 24 rises again. This results in repeated small heating peaks.

[0083] As long as the desired temperature of the cooking chamber 12 is not changed by, for example, the user, the cyclic operation continues, because maintaining the desired temperature in the cooking chamber 12 generally does not require the heating device 22 to operate continuously at maximum heating power.

[0084] When the desired temperature of cooking chamber 12 is first reached, the heating element 24 experiences a peak temperature in the adhesion zone 30 (the first peak on the far left of curve A). Then, depending on the cooking process, the temperature level drops more or less rapidly until it stabilizes at an approximately constant level. The temperature level at which the heating element 24 stabilizes is precisely within the critical temperature range T2, within which increased impurity adhesion occurs. In principle, it is also conceivable that the temperature does not remain consistently within temperature range T2, but rather briefly falls below or exceeds temperature range T2. Even so, strong adhesion is possible. The decisive factor is that the curve remains within temperature range T2 for a relatively long time, and only rarely, and especially never, enters temperature range T3 for an extended period.

[0085] The reason for the gradual decrease in temperature after the first peak is that even when the cooking chamber temperature has reached the desired temperature, the temperature in the heating element 24 continues to rise slightly due to the inertia of the cooking appliance until the entire cooking appliance is heated through.

[0086] Curve B shows an idealized curve of the temperature distribution of the heating element 24 in which the heating device 22 is permanently activated. For example, the heat load in the cooking chamber 12 may have been increased by, for example, placing a container of water in the cooking chamber 12. This requires a constant high power from the heating device 22 to achieve the same (high) desired temperature in the cooking chamber 12.

[0087] Due to the high load in the cooking chamber 12, the temperature of the heating element 24 initially rises slowly, but then exceeds the highest temperature of curve A (the first peak), and after reaching the desired temperature in the cooking chamber 12, the temperature of the heating element 24 remains at approximately the highest temperature within its temperature range T3 because the heating device 22 is permanently activated.

[0088] If the heating power of the heating device 22 is always at its maximum value, the temperature of the heating tube 24 can be permanently maintained above the temperature range T2, and the burn-off area 30 can be cleaned by thermal oxidation.

[0089] The curve shown here represents the highest possible temperature during cleaning. Cleaning can also be effective if heating device 22 is not permanently active, i.e., if heating device 22 is switched to cyclic mode, but the on-time is significantly longer than normal operation (higher average power). The decisive factor is that the temperature is maintained within the temperature range T3 for a longer period of time, even in cyclic operation. In this hotter cyclic operation, individual heating phases are longer and heating pauses are shorter compared to normal operation.

[0090] It's even meaningful to set the temperature as close as possible to the temperature range T2. Ideally, this would result in a smaller heat load or less cooling of the cooking chamber, which is generally easier to achieve. Additionally, the lower temperature load on some components avoids an unnecessary reduction in their lifespan.

[0091] Alternatively, or in addition to increasing the heat load in the cooking chamber 12, the cooking chamber door of the cooking appliance 10 can be opened to allow heat introduced into the cooking chamber 12 to be released into the environment. The cooking chamber ventilation system can also be turned on to allow cool air to flow into the cooking chamber, and the cooking chamber can be actively cooled by a water source such as steam from a steam generator and / or water from spray nozzles. Furthermore, it is recommended to utilize the maximum possible temperature of the cooking chamber, such that the heating device 22 is always set to strive for the maximum permissible cooking chamber temperature.

[0092] Additionally, the speed of the fan impeller 18 can be reduced. In addition to a lower fan impeller speed and a higher cooking chamber temperature, cooling can be reduced by limiting the reverse operation of the fan impeller 18 to a rotation direction that generates a higher temperature at the point to be cleaned.

[0093] The highest possible temperature at the heating element 24 is achieved when the heat load corresponds exactly to the maximum power of the heating device 22. The heat load is the heat-consuming device that generates the heat. By controlling the heating device 22, the heat generated at the heating element 24 is on average only as much as the heat consumed by the consuming device; otherwise, the cooking chamber temperature would, in most cases, rise significantly above the maximum cooking chamber temperature. When the cooking chamber 12 is empty, initially only the air and components of the cooking appliance 10 need to be heated. Once the cooking appliance 10 is heated, only the energy required to cover the heat loss of the cooking appliance 10 needs to be supplied, thus requiring very little power on average. By increasing the heat load, the cooking appliance 10 must be supplied with significantly more heat on a permanent basis. The type of consuming device is independent of the required heating power. For open cooking chamber ventilation systems, fresh, cold air must be additionally heated. When using a water container, the water must also be heated and may need to evaporate later. When the cooking chamber door is open, air exchanges with the cold ambient air, so the incoming cold air must also be heated.

[0094] If the heat load is below the maximum heating power, then cooking appliance 10 enters the above reference. Figure 6 The described cycle operation. If the load is even higher, the heating power is insufficient to reach the desired temperature of cooking chamber 12. This increases heat dissipation, and the temperature of heating element 24 remains low even though the heating unit is permanently activated.

[0095] In addition to generating a permanently high heat load, the desired temperature in the heating zone 30 can also be achieved by alternately heating and cooling the cooking chamber 12.

[0096] This is Figure 7 As shown in the figure, curve A again shows the temperature distribution at the burn-off zone 30 during normal operation, and curve B shows the possible cyclic operation of the cleaning process.

[0097] During the cleaning process, after heating and when the desired temperature in the cooking chamber 12 is reached, there is a heating pause and therefore a longer cooling period for the cooking chamber 12. This also causes the temperature of the heating element 24 to drop more sharply (curve B) compared to the temperature during normal operation (curve A). Subsequently, when reheating to the desired temperature of the cooking chamber 12 in curve B, the heating device 22 must reheat for a longer period of time, resulting in a higher heating peak compared to the heating peak that occurs during normal operation.

[0098] The sum of the peak values ​​allows for a sufficiently long time to reach the temperature required for the thermal oxidative decomposition of impurities in the burnt zone 30. This method is particularly suitable when the heat load cannot be permanently introduced into the cooking chamber 12. However, this results in a longer cleaning time.

[0099] Figure 8An overview of the cleaning method according to the present invention is shown.

[0100] In the first step S1, select the cleaning program.

[0101] In the second step S2, the heating device is then turned on, so that the first section 26 of the heating tube 24 is heated.

[0102] In the third step S3, the heating device 22 operates at a certain power for, for example, a cleaning time of 15 minutes, so that due to heat transfer in the burnt zone 30, a temperature of at least 400°C is established within a combustion time of at least 5 minutes, causing impurities adhering to the burnt zone 30 to detach. Simultaneously, the maximum permissible cooking chamber temperature does not exceed, for example, 300°C. In step S2, the power of the heating device 22 may be temporarily reduced, causing one or more heating pauses, wherein after each heating pause, the power of the heating device 22 is increased again and a heating peak occurs.

[0103] In parallel with or after heating the cooking chamber 12 with the heating device 22, the cooking chamber 12 may be actively cooled in an additional step S4, for example, by directing steam from the steam generator into the cooking chamber 12, and / or by introducing water from the spray nozzles 38 into the cooking chamber 12, and / or by activating the cooking chamber ventilation system. Alternatively, this process may be performed with the cooking chamber door open, and / or the heat load in the cooking chamber 12 may be increased, and / or the speed of the rotating fan impeller 18 in the cooking chamber 12 may be reduced.

[0104] In a further step S5, the cooking chamber 12 is rinsed with a cleaning solution such as alkali or acid.

[0105] The cleaning method can be performed as a standalone cleaning procedure, or it can be combined with an existing cleaning procedure for the cooking appliance 10, such as one used to clean the cooking chamber 12 with chemical cleaners.

Claims

1. A method for cleaning a cooking appliance (10), said cooking appliance (10) comprising a cooking chamber (12) and a heating device (22) having a heating element (24), wherein, The heating element (24) has a first section (26) that can be actively heated and a second section (28) that is not actively heated adjacent to the first section (26), wherein, during normal operation of the cooking appliance (10), impurities are deposited and burned onto the burning area (30) in the second section (28), wherein the method includes the following steps: a) Select a cleaning program; b) Turn on the heating device (22) so that the first section (26) of the heating tube (24) is heated; c) During the cleaning period, the heating device (22) is operated at a power such that, through heat transfer in the burn-on zone (30), a temperature is reached that causes impurities adhering to the burn-on zone (30) to detach during a combustion period of at least 1 minute and preferably at least 5 minutes, while preventing the temperature in the cooking chamber (12) from exceeding the maximum permissible cooking chamber temperature.

2. The method according to claim 1, characterized in that, In step c), a temperature of at least 400°C is achieved in the sintering region (30).

3. The method according to claim 1, characterized in that, Step c) is followed by step d), in which the cooking chamber (10) is rinsed with a cleaning solution.

4. The method according to claim 1, characterized in that, The heating device (22) operates at maximum power in step c), wherein, in particular, the cleaning duration is at least 15 minutes.

5. The method according to claim 1, characterized in that, In step c), the temperature in the cooking chamber (12) is at most 300°C, and the temperature in the first section (26) of the heating tube (24) is between 500°C and 850°C.

6. The method according to claim 1, characterized in that, The heating device (22) is an electric heater or a heat exchanger (40). In the electric heater, the first section (26) is actively heated and the second section (28) is not actively heated but is indirectly heated by heat transfer. In the heat exchanger (40), the first section (26) is actively heated via a burner, particularly a gas burner (42), and the second section (28), located downstream of the first section (26), is not actively heated but is indirectly heated by heat flow.

7. The method according to claim 1, characterized in that, During the cleaning process, the cooking chamber (12) is actively cooled in particular by directing steam from the steam generator into the cooking chamber (12) in a further step and / or introducing water from the nozzle into the cooking chamber (12) and / or turning on the cooking chamber ventilation system.

8. The method according to claim 1, characterized in that, During the cleaning process, the cooking chamber door of the cooking appliance (10) is opened, and / or the heat load in the cooking chamber (12) is increased, and / or in a further step the speed of the rotating fan impeller (18) in the cooking chamber (12) is reduced, and / or the reverse operation of the fan impeller (18) is restricted.

9. The method according to claim 1, characterized in that, In step c), the power of the heating device (22) is temporarily reduced to cause a heating pause, and after the heating pause, the power of the heating device (22) is increased again to cause a heating peak.

10. The method according to claim 1, characterized in that, The first section (26) of the heating tube (24) is heated to the extent that impurities located on the support (36) of the heating tube (24) and / or on the spray nozzle (38) and / or on other components in the cooking chamber (12) are removed.

11. The method according to claim 1, characterized in that, The method is a standalone cleaning procedure and / or a combination of a cleaning procedure for the cooking appliance (10), which uses chemical cleaners to clean the cooking chamber.

12. A cooking appliance (10) comprising a cooking chamber (12) and a heating device (22) having at least one heating tube (24), said heating tube (24) having an actively heatable first section (26) and a non-actively heatable second section (28) adjacent to the first section (26), and said heating tube (24) having a burn-off region (30) on which burn-off impurities can be deposited, wherein, The cooking appliance (10) has a control unit (32) configured and set to operate the cooking appliance (10) and the heating device (22) such that the cooking appliance (10) and the heating device (22) perform the method according to claim 1.

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