Abstract:
An oven for heating and frying food, particularly a rapid cook oven, includes walls and an openable oven door delimiting an oven space and heaters to heat food in the oven space. Such heaters including: microwave radiation devices, a frying plate having an undersurface, and heat circulating-air devices comprising a flow duct for removing circulating air from the oven space and leading it back into the oven space after cleaning, and a fan installed in the flow duct for creating a circulating-air flow in the said flow duct. The oven additionally includes structure delimiting a cooker space, thermal insulation between the oven space and the cooker space and a heater comprising a cooker situated in the cooker space.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. National Stage of International Patent Application No: PCT/FI2014/050842 filed Nov. 10, 2014, designating the United States and claiming benefit of Finland Patent Application No. 20136224 filed Dec. 5, 2013. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to an oven for heating and frying food, particularly a rapid cook oven, which includes an oven space, which is delimited by walls and an openable oven door leading to the oven space, as well as the following heating means for heating food in the oven space:
       microwave radiation devices,   a frying plate, and   heating circulating-air devices comprising a flow duct for removing circulating air from the oven space and leading it back into the oven space after cleaning, and a fan installed in the flow channel for creating a circulating-air flow in the flow duct.       
 
       BACKGROUND OF THE INVENTION 
       [0006]    The use of rapid cook ovens is intended to bring food portions to a serving temperature as quickly as possible, which generally means within 30-180 seconds of the order being placed. A second intention is the best possible quality of food portions. The very different behaviour of food when being heated makes achieving the goals challenging. The goals are best achieved using hybrid ovens using more than one heating technique. Most generally, the heat sources used nowadays in rapid cook ovens are microwave radiation devices and electrical resistances, which are arranged to heat air being circulated through the oven space. 
         [0007]    Hybrid ovens utilizing hot air and microwaves as heat sources are known from, for instance, the publications WO 95/09519 and WO 99/52328. Publication EP 1930660 A1, which discloses a circulating-air oven equipped with microwave heating, is also known from the prior art. 
         [0008]    Contamination is a problem in closed air-circulation ovens. Magnetrons in particular are sensitive to dirtying. Publication WO 98/54517 discloses an oven, in which there is closed air circulation and a catalyser for cleaning the air. 
         [0009]    Oil cookers are used particularly for the heating of potato chips. Such a solution is disclosed in, for instance, publication WO 98/54517. Known hybrid ovens do not have oil cookers. The main problem with oil cookers is dirtying of the oil. Publication WO 2008/144290 discloses an oil filtering technique. Further, the use of a cooker to heat frozen products creates a great deal of steam. A problem with ovens of the prior art is that several different devices are required to make a food portion, in which the components of the food portion are prepared at different temperatures and simultaneous preparation is difficult. 
       SUMMARY OF THE INVENTION 
       [0010]    The invention is intended to create an oven, particularly a rapid cook oven, intended to heat and fry food, which combines, in the same oven, at least a traditional oven, microwave heating, and a cooker, so that in the oven several components of a food portion can be prepared simultaneously at different temperatures. The method according to present invention is characterized by an oven for heating and frying food, particularly a rapid cook oven, comprising an oven space, which is delimited by walls and an openable oven door leading to the oven space, as well as following heating means for heating food in the oven space: microwave radiation devices, a frying plate having an undersurface and heating circulating-air devices comprising a flow duct for removing circulating air from the oven space and leading it back into the oven space after cleaning, and a fan installed in the flow duct for creating a circulating-air flow in the said flow duct, wherein the oven further comprising a structure delimiting a cooker space and the heating means further comprising a cooker situated in the said cooker space, and the said structure comprising thermal insulation between the oven space and the cooker space. 
         [0011]    This intention can be achieved by means of an oven, particularly a rapid cook oven, intended for heating and frying food, which includes an oven space, which is delimited by walls and an openable oven door leading to the oven space, as well as heating means for heating the foods in the oven space, being microwave radiation devices, a frying plate, and heating circulating-air devices, comprising a flow duct for removing circulating air from the oven space and leading it after cleaning back to the oven space, and a fan installed in the flow duct for creating a circulating air flow in the flow channel. The oven further includes a structure delimiting the cooker space and the heating devices further include a cooker located in the cooker space. The structure includes thermal insulation to prevent heat transfer between the oven space and the cooker space. The thermal insulation insulates the cooker from heat and thus prevents the higher temperature in the oven space from being transferred to the cooker and fatty steam burning onto the bottom of the frying plate. Thus, the temperature of the cooking liquid is prevented from becoming too high. 
         [0012]    By means of the oven according to the invention, a food portion can be prepared very rapidly, as the components required for the food portion can be placed simultaneously in the oven, in which each of the components can be prepared at the temperature required by the component, as the oven contains different temperature zones. 
         [0013]    The oven preferably further includes cleaning elements situated in the flow duct. With the aid of the cleaning elements, impurities contained in the circulating air can be effectively removed. 
         [0014]    The oven preferably includes a limited flow connection between the cooker space and the oven space/flow duct permitting gases and vapours arising in the cooker to be removed to the oven space/flow duct and from there through the cleaning elements. With the aid of the flow connection, gases arising in the cooker can be directed to the flow duct, so that they cannot reach the oven space to disturb the heating of the components and to mix with them. In the flow connection, there is preferably a flow resistance, so that gases and vapours move mostly only due to excess pressure to the flow duct/oven space. 
         [0015]    The cleaning elements are preferably a catalyser and/or a grease filter. With their aid, the circulating air is cleaned of odours and grease, so that its circulation does not cause problems. 
         [0016]    The flow connection can be 0.5-4-mm, preferably 1-2-m wide. The flow connection will then be sufficiently narrow to prevent microwaves from progressing to the cooker space, and, on the other hand, sufficiently large to prevent sparking. 
         [0017]    The thermal insulation can be an air space and/or a thermal-insulation panel. By means of such a construction, the transfer of heat is cut off. 
         [0018]    Preferably, the construction is the frying plate arranged to delimit the said cooker space under the oven space. Situated underneath the frying plate, the cooker space is more effectively protected from the heat of the oven space and at the same time acts as a construction delimiting the oven space and the cooker space. The flow connection between the cooker space and the oven space will then function best. 
         [0019]    According to a second embodiment, there can be a separate wall between the oven space and the cooker space. The cooker space can then be elsewhere than underneath the oven space. 
         [0020]    The microwave-radiation devices preferably includes at least two magnetrons for creating temperature zones in the oven space. With the aid of at least two magnetrons, the microwave heating can be directed to the desired zone by using the magnetron that is located closest to the component to be heated. 
         [0021]    Preferably, the frying plate is divided into at least two parts, each part of which has independently operable secondary heating means. Thus, for its part, the frying plate can be used to form different temperature zones in the oven. 
         [0022]    The oven preferably includes at least two fans with motors and two secondary heating means for creating two different air circulations for the circulating-air heating. With the aid of two air circulations, it is also easier to achieve the desired heating temperatures of the components and the oven can be heated even more efficiently. The air circulation can then also be implemented without separate valves or other control means dividing the air circulation, which are needed to create two circulations with the aid of one fan. With the aid of the circulating-air means, the air in the oven can also be circulated through the catalyser, so that the oven can be implemented without a separate extractor hood. 
         [0023]    The frying plate is preferably inside the oven space. The fumes arising on the frying plate will then remain in the oven, just like the fumes created by using the other heating devices, so that the oven can be manufactured without a separate extractor hood to remove external fumes. In addition, the formation of the frying plate inside the oven will improve the total energy economy of the oven, as the heat of the other heating means can be utilized to preheat the frying plate, and vice versa. 
         [0024]    The cooker is preferably inside the oven, so that the steam rising from the cooker can be retained inside the oven and cleaned like the fumes arising on the frying plate. 
         [0025]    The cooker is preferably a fat cooker. By means of a fat cooker, a very great heating output is achieved, which in turn accelerates the cooking of the product being cooked. 
         [0026]    The inside of the frying plate preferably includes secondary heating means. The secondary heating means inside the frying plate are protected from splashes and, on the other hand, effectively conduct heat to the frying plate. 
         [0027]    The undersurface of the frying plate can include insulation to prevent the transfer of heat from the oven space to the cooker. The insulation attached to the undersurface of the frying plate prevents the medium in the cooker from coming into contact with the secondary heating means of the frying plate, thus preventing the creation of excess smoke. 
         [0028]    The secondary heating means are preferably electrical resistances. Electrical resistances are easy and cheap to implement and they can be used without separate ventilation built in connection with the oven. Further, electrical resistances are safer to use than, for example, heating means utilizing gas. 
         [0029]    According to a second embodiment, the heating means and the secondary heating means can include a gas burner for producing heat. The use of a gas burner does not affect the power consumption of the oven, so that the momentary power consumption of the oven remains smaller. In addition, a gas burner is extremely efficient, rapid to use, and burns gas very cleanly. 
         [0030]    The walls of the oven can include water channels running round the frying plate and a collection tank, to which the said water channels are led in order to recover liquid coming from food on the frying plate. The recovery of the liquid is important, so that the liquid will not, for example, run into the cooker when the oven door is opened. If the liquid to be used in the cooker is fat, liquid coming into contact with hot fat can cause violent foaming of the fat, or even an explosive fire. 
         [0031]    The oven door can include an airtight seal arranged to close both the oven space and the cooker simultaneously from in front when the oven door is closed. Fumes possibly arising in connection with the heating of components in the oven and water vapour arising in the cooker will then remain inside the oven. 
         [0032]    The oven preferably includes separate and moveable baskets to be situated in the cooking tank for placing food in them to put them into and take them out of the tank, and a basket frame, in which the baskets are placed, which basket frame includes a mesh cover to keep the products under the surface of the cooking liquid. With the aid of the baskets, placing the components to be heated in the cooker can be done safely and quickly. When using the basket frame, the components to be heated cook on all sides and the heating can be performed entirely without a separate stage of turning the components, the components being completely surrounded by the cooking liquid. 
         [0033]    There is preferably a detachable protective cover in the cooker. With the aid of the use of the protective cover, the splashing of the cooker&#39;s cooking liquid out of the cooker can be prevented. In addition, the particularly dirtying parts of the cooker can be integrated in the detachable protective cover. At the same time, the protective cover advantageously prevents the baskets in the basket frame from rising out of the cooking liquid and prevents, for example, liquids that flow off the frying plate when the oven door is opened from entering the cooking liquid. Further, the protective cover also acts as a barrier to heat transfer. 
         [0034]    According to one embodiment, the oven includes means for lifting the baskets under electric control. The baskets can then be lifted automatically out of the cooking liquid when their components are cooked, without the user themself needing to open the oven door and lift the products. Thus, in the oven it is possible, for example, to continue heating the components on the frying plate, even though the components in the cooker are already cooked. Lifting of the baskets prevents the components burning due to overlong heating. 
         [0035]    According to one embodiment, in the cooker there is a closing element closing by positive operation with a feeding movement, which is arranged to close the cooker automatically when the oven door is closed. The positive operation can be implemented by using a shape-closing mechanism or by gravity. Positive control of the feed into the frying basket permits fat to be added safely, no matter whether it is in a solid or liquid form. Preferably, the closing element is arranged in the oven door to prevent the cooking liquid from splashing out of the cooker. Such a closing element is cheap to implement. 
         [0036]    According to a second embodiment, the cooker is constructed as a permanent part of the structure of the oven. The oven can then be implemented without separate rails and other parts for pulling the cooker out of the oven, which in turn reduces the manufacturing costs of the oven. 
         [0037]    The oven can include a steam recovery system for recovering steam. The recovery of steam, which would disturb the formation of different temperature zones, prevents the accumulation of steam in the oven space. 
         [0038]    The recovery system preferably includes a condenser. With the aid of the condenser, a large amount of steam can be condensed into water requiring a considerably smaller volume, which can be led, for example, to a drain or a collection tank. This is important, as hundreds of litres of steam arise in the oven, which would otherwise be released into the kitchen when the oven door is opened. 
         [0039]    According to one embodiment, the oven includes at least one cleaning element for collecting impurities from the circulating air. With the aid of the cleaning element the circulating air remains clean and does not contaminate the components of the food portion. 
         [0040]    The walls can be of thermal insulation, thus permitting controlled heat transfer from the oven space outwards. With the aid of the controlled heat transfer, heat is transferred out from the oven, making control of the temperature of the cooker easier. The thermal insulation can be, for example, wool or a thermally insulating mass. 
         [0041]    The oven preferably includes at least a grease filter and catalyser as cleaning elements. With their aid the circulating air remains effectively clean. 
         [0042]    The oven according to the invention is preferably equipped with control elements, with the aid of which the gases and vapours released from the cooker are directed to travel through the same cleaning elements as the vapours and gases released from frying. A filter and catalyser can act as the cleaning elements. 
         [0043]    The wall between the oven space and the flow channel can be perforated, which will prevent microwaves from progressing to the flow channel. The perforation also prevents the loss of power from the microwave-heating means to the external structures of the oven space. 
         [0044]    The grease filter can be situated in the flow channel, separate from the wall of the oven chamber. Situated in this way, the filter is easier to handle. The microwave loss is also considerably smaller and control of the blowing is better. The handling of the grease filter can be performed from outside the oven chamber, from the front wall. The use of tools also permits handling when hot. 
         [0045]    According to one embodiment, the roof of the oven space includes an upper baffle plate for guiding the circulating-air flow, above which upper baffle plate a resistance-element battery can be located, which can consist of three separate resistance elements, which can be controlled separately and which act on the different temperature zones of the oven space. With the aid of the resistance elements, the temperature of the air blown to a specific part of the oven space can be temporarily raised during the preparation of a recipe, without affecting the temperature of the whole oven space. 
         [0046]    The temperature of the catalyser can be monitored actively and, on the basis of the measurement results, the temperature of the air entering the catalysed can be corrected during the program. A rapidly reacting air-heating resistance is preferably situated in the flow channel immediately before the catalyser. The radiant heat of this heating resistance heats both the catalyser and the flowing air. 
         [0047]    In the rapid cook oven, the heating and frying of food is implemented partly with a known method with the aid of the microwave technique and circulating air heated by a thermal resistance. According to the invention, in the rapid cook oven, the cooker cooking liquid is also preferably heated with the aid of an electrical resistance. In the heating process, the heat of the oven space and the cooker are utilized for each other&#39;s benefit. The gases and vapours released from the cooker can be arranged to travel to the catalyser through the same cleaning elements as the vapours and gases released in frying. 
         [0048]    By means of the active control of the oven, it is possible to achieve different temperatures for varying durations of time in the different temperature zones of the oven space during the food-preparation process and, during the times between, to exploit the temperature differences of the zones for power saving. In the heating of the air of the oven, in connection with the upper baffle plate there are preferably three separate, rapidly heating and cooling heating elements, which can be operated together or separately. In this connection, the heating elements act as second heating means. Variation in temperature can be achieved primarily by means of a rapidly heating and cooling air-heating resistance in connection with the upper baffle plate as well as by means of a rapidly heating and cooling frying plate. The circulating air can first be heated to the base temperature of the oven space and then the second resistance package in the vicinity of the upper baffle plate can heat part of the air blown from the upper baffle plate to become hotter. The cooker and the frying plate can each have their own temperature. 
         [0049]    Each of the heating means can have its own temperature controller and measurement separately from the others. This can be implemented by means of software. The secondary heating means can be, for example, magnetrons and resistance packages. 
         [0050]    In one embodiment of the catalyser&#39;s air-heating resistance package, there is one resistance package, which can be switched on separately, for each separate circulating-air flow for each catalyser, each resistance package of which includes temperature measurement. In the heating of the circulating air, for each circulating-air flow there can be one resistance package, in which there is at least one resistance, in which there is temperature measurement. The resistance equipped with temperature measurement should always be switched on, if the resistance package of the circulating-air flow in question is switched on. Power can be lowered by leaving out one or more resistance being without air temperature measurement. In terms of the temperature controller of this resistance package, it is not important how many resistances are switched on in the resistance package. The temperature controller can only control the one in which there is temperature measurement. The other two resistance elements that can, if desired, be switched off are assumed to behave in the same way when switched on, because the heating load is similar for all the resistances of the resistance package. 
         [0051]    In one embodiment, the resistance packages are: 
         [0052]    an air-heating resistance package above the upper baffle plate, 
         [0053]    a resistance package of the frying plate, 
         [0054]    a resistance package of the cooker, 
         [0055]    as well as the air-heating resistance package of the catalyser referred to as an example. 
         [0056]    In addition, the resistances in the upper baffle plate, and, if necessary in the other resistance packages, can also be controlled separately under the control of the recipe, so that different temperatures are obtained for different temperature zones. Each magnetron used to produce microwaves can also have its own power controller separate from the others. By implementing the power control of the magnetrons separately, it is possible to produce a different microwave power for different places in the oven chamber. This can be implemented by means of software. 
         [0057]    By means of the oven according to the invention, considerable improvements over known ovens can be achieved. The quality of products can be ensured as the times of keeping them in the oven become more accurate. Thanks to the flow duct, the surface area of the grease filter can be larger than the surface area of a perforated plate and the shape can be different from the shape of the perforation. The flow resistance of the grease filter to the air is greater than that of a perforated plate. Therefore, by increasing the surface area of the grease filter a maximal air flow is obtained from the fan at the same power and the shape and location of the suction-air perforation are made favourable to the location of the suction-air flow. In addition, by means of this embodiment, the grease filter can be located at an easily accessible distance from the user. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0058]    In the following, the invention is described in greater detail with reference to the accompanying drawings, in which 
           [0059]      FIG. 1  shows a front view of one embodiment of the oven according to the invention, when the oven door is open, 
           [0060]      FIG. 2 a    shows a front view of one embodiment of the oven according to the invention, with the construction of the oven in cross-section, 
           [0061]      FIG. 2 b    shows the flow of steam in the embodiment of  FIG. 2   a,    
           [0062]      FIG. 3  shows the parts of the cooker separately, 
           [0063]      FIG. 4 a    shows a side cross-section of one embodiment of the oven according to the invention, with the detachable parts of the cooker outside the cooker, 
           [0064]      FIG. 4 b    shows a side cross-section of one embodiment of the oven according to the invention, with the cooker basket lifted out of the cooking liquid, 
           [0065]      FIG. 4 c    shows a side cross-section of one embodiment of the oven according to the invention, with the cooker basket lowered into the cooking liquid, 
           [0066]      FIG. 4 d    shows a side cross-section of the flow of gases in one embodiment of the oven according to the invention, with the oven door open, 
           [0067]      FIG. 5  shows an axonometric view of the construction of the oven, shown without the oven door and the external walls, 
           [0068]      FIG. 6  shows a side schematic diagram of the steam recovery system used in one embodiment of the oven, 
           [0069]      FIG. 7  shows an enlargement of detail A of  FIG. 2 . 
       
    
    
       [0070]    In the figures, reference is made to the following reference numbers, which signify 
         [0000]    
       
         
               
               
             
           
               
                   
               
             
             
               
                 10 
                 oven 
               
               
                 11 
                 structure 
               
               
                 12 
                 oven space 
               
               
                 14 
                 oven-space walls 
               
               
                 15 
                 cooker space 
               
               
                 16 
                 oven door 
               
               
                 18 
                 microwave radiation 
               
               
                   
                 devices 
               
               
                 20 
                 frying plate 
               
               
                 22 
                 heating means 
               
               
                 24 
                 second heating means 
               
               
                 26 
                 cooker 
               
               
                 28 
                 cooking tank 
               
               
                 30 
                 thermal insulation 
               
               
                 32 
                 temperature zone 
               
               
                 33 
                 circulating-air means 
               
               
                 34 
                 fan 
               
               
                 35 
                 fan motor 
               
               
                 36 
                 electrical resistance 
               
               
                 37 
                 resistance 
               
               
                   
                 casting 
               
               
                 38 
                 magnetron 
               
               
                 40 
                 microwave seal 
               
               
                 41 
                 fat-cooker shut- 
               
               
                   
                 off element 
               
               
                 42 
                 water channels 
               
               
                 43 
                 slots 
               
               
                 44 
                 collector tank 
               
               
                 46 
                 seal 
               
               
                 48 
                 basket 
               
               
                 50 
                 basket frame 
               
               
                 52 
                 mesh cover 
               
               
                 54 
                 catalyser 
               
               
                 55 
                 flow connection 
               
               
                 56 
                 protective cover 
               
               
                 58 
                 upper baffle 
               
               
                   
                 plate 
               
               
                 60 
                 transverse duct 
               
               
                 62 
                 resistance element 
               
               
                 64 
                 exhaust connection 
               
               
                 66 
                 cleaning elements 
               
               
                 68 
                 resistance element 
               
               
                   
                 battery 
               
               
                 69 
                 grease filter 
               
               
                 70 
                 duct 
               
               
                 72 
                 condenser 
               
               
                 74 
                 outlet channel 
               
               
                 75 
                 basket lifting means 
               
               
                 76 
                 lifting arms 
               
               
                 77 
                 condenser duct opening 
               
               
                 78 
                 cooking-liquid surface 
               
               
                 80 
                 flow duct 
               
               
                 82 
                 ceiling 
               
               
                 83 
                 inlet connection 
               
               
                 84 
                 air-heating 
               
               
                   
                 resistances 
               
               
                 86 
                 cooker heating 
               
               
                   
                 resistances 
               
               
                 88 
                 wall insulation 
               
               
                 90 
                 cooking-liquid outlet 
               
               
                   
                 ducts 
               
               
                 91 
                 outlet valves 
               
               
                 92 
                 oven-door end of 
               
               
                   
                 cooker 
               
               
                 94 
                 front part of cooker 
               
               
                 96 
                 shaft 
               
               
                 98 
                 carrier rod 
               
               
                 100 
                 outer walls 
               
               
                 102 
                 level check opening 
               
               
                 104 
                 steam recovery system 
               
               
                 106 
                 cooling fan 
               
               
                 108 
                 magnetron 
               
               
                   
                 transformers and 
               
               
                   
                 capacitors 
               
               
                 110 
                 circuit-card 
               
               
                   
                 package 
               
               
                 112 
                 frying-plate 
               
               
                   
                 hinge mechanism 
               
               
                 114 
                 upper space 
               
               
                 116 
                 intermediate 
               
               
                   
                 ducts 
               
               
                 118 
                 air space 
               
               
                 120 
                 air space 
               
               
                   
               
             
          
         
       
     
       DETAILED DESCRIPTION OF THE INVENTION 
       [0071]      FIGS. 1-7  show one embodiment of the oven  10  according to the invention. In all embodiments, the oven  10  includes an oven space  12 , which is delimited by walls  14  and an openable oven door  16  leading to the oven space  12 . In addition, the oven  10  includes microwave radiation devices  18  as heating means  22 , heating circulating-air means  33 , and a cooker  26 . The heating circulating-air means comprise a flow duct for removing the circulating air from the oven space and leading it to the oven space and a fan installed in the flow duct for creating a circulating-air flow in the flow duct. The oven  10  further includes a structure  11  delimiting the cooker space  15 , in which the cooker  26  is situated, and the structure  11  includes thermal insulation  30  between the oven space  12  and the cooker space  15  for preventing heat transfer. In addition, the oven  10  preferably includes cleaning elements  66  situated in the flow duct  80  and a limited flow connection  55  between the cooker space  15  and the oven space/flow duct  80 , permitting the removal of gases arising in the cooker  26  from the cooker  26  to the oven space/flow duct  80  with the aid of excess pressure. In the embodiments of  FIGS. 1-7 , the frying plate  20  delimits the oven space and the cooker space from each other, at the same time acting as a base for food to be fried. However, it should be understood that the cooker can also be located to the side of or above the oven space, if the structure  11  is, for example, a partition or some other delimiting structure. 
         [0072]    Differing from  FIG. 1 , the oven according to the invention can also include two cookers side by side, of which one is preferably a fat cooker. The other cooker can also be a fat cooker or, for example, a cooker, in the cooking tank of which water is used as the cooking liquid. In the oven according to the invention, the heating of components of food portions can be performed at least by cooking with the cooker, frying on the frying plate with the aid of circulating air, and/or heating with the aid of microwaves. Preferably, there is also the alternative of frying on the frying plate with the aid of the frying plate&#39;s own secondary heating means. In addition to these, it is also possible to steam in the oven with the aid of steam obtained from the cooker. The oven  10  preferably also includes second heating means  24 , in which case heat is produced for the primary heating means. In this connection, reference to heating means is more specifically to the different methods of heating, which includes the previously mentioned microwave heating, frying heating, circulating-air heating, and cooking heating. On the other hand, reference to secondary heating means refers, for example in the case of circulating-air heating, to an electrical resistance, which produces heat for the circulating-air means. 
         [0073]    In  FIG. 1 , the oven door  16  is tilted to the open position. The cooker  26 , which contains the cooking tank  28 , is integrated inside the oven  10 . In the embodiment of the cooker  26  depicted in  FIG. 1 , there are two moveable baskets, in which the food to be fried, such as potato chips, are placed. According to  FIG. 2   a,  heating resistances  86 , by means of which the cooking liquid is heated to the desired temperature, are situated in the bottom of the cooker  26 . 
         [0074]    According to  FIG. 1 , the oven door  16  preferably includes a microwave seal  40  for preventing the travel of microwaves, arranged to close the oven space  12  when the oven door  16  is closed. The microwave seal  40  is preferably a thin steel plate bent into shape, to be placed in the centre of the oven door  16 , which corresponds in shape to the cross-sectional shape of the opening of the cooker  26 . In the surface of the steel plate, there are preferably slots  43  according to  FIG. 1 , which act as an obstacle to the progress of microwaves, but at the same time allow gases from the cooker space  15  into the oven space  12 . The construction of the microwave seal can also be some other construction that is generally known to function. The oven door preferably also includes a cooker shut-off element  41  located beneath the microwave seal  40 , which consists of as many parts as there are baskets in the cooker. The shut-off element  41  corresponds in shape to the cross-section of the opening of the cooker  26 . A seal  46 , which is airtight and electrically conductive preferably runs round this microwave seal  40  and the cooker shut-off element  41 . The seal is intended to make the oven door airtight and, at the same time, to prevent the microwaves from getting out of the oven by grounding the microwaves. This seal can be a seal like the seals of the prior art used to seal known oven doors, for example, an electrically conductive rubber-silicon seal. 
         [0075]      FIGS. 2 a   - 3  show the construction of the cooker  26  in greater detail. The cooker  26  preferably includes a cooking tank  28 , heating resistances  86 , at least one basket  48 , and cooking liquid in the cooking tank  28 , which is shown in  FIGS. 4 d    and  7 . The cooker  26  together with the cooking tank  28  can be pulled out of the oven  10  on guides. A detachable protective cover  56 , which is a particularly dirtying component, is preferably attached to the cooker  26 . Thanks to the protective-cover solution, the particularly dirtying components can be detached and washed by machine washing or some other powerful washing methods, without having to be careful with the heating resistances and similar sensitive components. 
         [0076]    When using the cooker  26 , the components of the food portion to be cooked, for example, potato chips, are placed in the basket  48 , which can be, according to  FIG. 3 , a basket open on top, or a basket with a cover, in which the components are inside the basket. According to  FIGS. 4 a   - 4   c,  the cooking tank  28  of the cooker  26  is preferably open on the front side  94  above the surface of the cooking liquid  78  of  FIG. 4 d    at the end  92  nearest the oven door  16 , so that the basket  48  can be pushed into the cooker  26  underneath the frying plate  20 . According to  FIGS. 4 a   - 4   c,  the cooking tank  28  of the bottom of the cooker  26  can include basket lifting means  75 , with the aid of which the basket  48  is lifted out of and lowered into the cooking liquid in the cooking tank. The lifting means  75  preferably include lifting arms  76 , which are pivoted on transverse shafts to the sides of the cooker  26 . Continuations of the shafts are arranged in connection with the oven door, so that the opening of the oven door at the same time rotates the shafts in such a way that the lifting arms  76  rotate from the horizontal position according to  FIG. 4 a    to the vertical position according to  FIG. 4   b.  At the ends of the lifting arms  76  are carrier rods  98 , on the top of which the basket  48  is supported when it is in the cooker  26 , according to  FIG. 4   b.  When the oven door is closed, the lifting arms  76  again rotate to the horizontal position, when the basket is lowered into the cooking liquid. The components being cooked in the open basket can float on the surface of the frying liquid, but, in the case of a closed basket, the construction of the basket keeps the components entirely submerged in the cooking liquid. 
         [0077]    According to one embodiment, the cooker can include a separate basket frame  50  according to  FIGS. 3 and 4   a,  in which the open baskets  48  are placed. The basket frame  50  can have a closed mesh cover  52 , which prevents the food portion components being cooked from floating when the basket  48  is completely submerged in the cooking liquid. By means of such a system, it is possible to avoid the need for turning the components being cooked, the components being entirely submerged. The basket frame can be a metal construction, which forms a frame, inside which the basket is placed. When using the basket frame, the baskets are submerged in the cooking liquid along with the basket frame. 
         [0078]    The cooker can include lifting means for lifting the baskets by electric control. When the basket is lifted above the surface of the cooking liquid, the components in the basket can be steamed by steaming with the cooking liquid, preferably water, in the cooking tank of the cooker. The lifting means preferably include a lifting spring, which is tensioned when the oven door is closed. The spring can be released in a controlled manner with the aid of an electrically controlled solenoid, in which case the basket can also be lifted out of the cooking liquid when the oven door is closed. When the desired cooking time has been reached, the solenoid opens the locking of the spring, when the spring rotates the lifting arms of the lifting means so that the basket rises out of the cooking liquid. According to  FIGS. 4 a   - 4   d,  the frying plate  20  of the oven  10  is preferably detachable, so that it can be removed for cleaning the oven. Alternatively, the frying plate can only be tiltable around the hinge mechanism  112  shown in  FIG. 4   d.    
         [0079]    Outside the oven space, a vertical flow duct  80 , which forms a connection from the sides of the frying plate  20  to the top of the oven space  12  according to  FIG. 2   a,  is preferably arranged on at least one of its sides. The flow ducts  80  are preferably formed between the oven&#39;s wall insulation  88  and the walls  14  of the oven space  12 . The circulating air is blown downwards from the inlet connection  83  of the ceiling  82  of the oven space  12  and sucked from near the frying plate  20 , into the flow duct  80  from the exhaust connection  64  in the walls  14  above the frying plate  20 . There is preferably suction perforation as protection of the exhaust connection  64 , which also prevents the microwaves from progressing outside the oven space. The exhaust connections  64  can be situated, for example, 0.5 mm above the surface of the frying plate in the walls  14 . The ceiling  82  is preferably a perforated metal plate, which permits the air to circulate, but prevents the microwaves from progressing outside the oven space. Above the oven space  12  there is preferably at least one fan  34 , with the aid of which a flow of circulating air is created. There is preferably one fan  34  for each flow duct  80 , so that the same fan  34  both sucks and blows. In air circulation implemented using one fan and motor, it is necessary to use, in addition, the aid of airflow control valves or other control elements, by means of which the airflow is divided in the desired ratio to the different air circulations. 
         [0080]    According to  FIGS. 1 and 2   a,  at the exhaust connection  64  of the walls  14  of the oven  10  places are formed in the walls  14  for cleaning elements  66 . The gases and vapours released from the heating of food-portion components in the oven are guided to travel through the cleaning elements  66 . The cleaning elements are a catalyser  54  and a grease filter  69 , to which grease in the air and steam adheres. Of these, the catalyser is the more important. From the grease filter  69  air is sucked in the flow duct  80  upwards to the fan  34 , which blows the air to the catalyser  54  through rapidly reacting air-heating resistances  84 . The air-heating resistances  84  heat the circulating air to become sufficiently hot (usually at least 230° C.), so that the fine particles and other impurities in the air burn when the air travels through the catalyser. Both the grease filter  69  and the catalyser  54  are situated in the flow duct  80  in such a way that all the circulating air flows through them. The grease filter is preferably a panel-type filter, which can be pulled out when the oven door is open, so that its cleaning and changing is extremely simple. In the oven, there are preferably two flow ducts  80  symmetrically on each side of the oven space  12 . Here the frying plate  20  prevents passage of the circulating air to the cooker  26 , but the flow connections  55  preferably at the sides of the frying plate  20  permit the passage of gases and smoke in the cooker space to the exhaust connections  64 . 
         [0081]    According to  FIG. 2   a,  in the oven there are preferably two flow ducts  80 , which are separate from each other over the entire distance, so that separate circulating-air flows are guided to the temperature zones  32  on the left and right sides of the oven  10 . Once the airflow has travelled through each part of the catalyser  54 , the circulating air preferably meets a resistance-element battery  68  consisting of at least two resistance elements  62 , which in this connection can be second heating means  24  for heating the circulating air. The resistance battery can also be implemented using one resistance element. Each resistance element  62  is directed to heat a specific part of the circulating air flow. The resistance elements  62  of the resistance-element battery  68  can be preferably controlled independently of each other, so that the circulating air led through them receives an individual temperature when passing through each resistance element  62 . For its part, this permits the creation of temperature zones  32  with different temperatures in the oven space  12  using the circulating air flows of different temperatures. The heated air flow that has travelled through the resistance elements  62  then travels through the upper baffle plate  58  forming the ceiling  82  of the oven  10 , which guides the airflow so that temperature zones  32  with at least two different temperatures are formed in the oven space  12 . 
         [0082]    According to  FIG. 2   b,  the evaporating moisture and frying smoke in the cooker  26  move, thanks to the excess pressure forming in the cooker space  15 , preferably through the flow connections  55  in the sides of the frying plate  20  from the cooker space  15  to the oven space  12 , where they travel from the exhaust connections  64  in the sides of the frying plate  20  to the flow duct  80  and through it to the fan  34 . The fan  34  blows the circulating air through the air-heating resistances  84  to the catalyser  54  and from there on to the second heating means  24 . After this, the circulating air travels through the inlet connections  83  of the ceiling  82  back to the oven space  12 . 
         [0083]      FIG. 4 d    shows the flow routes of vapours and smoke arising in the cooker space  15  and oven space  12 , when the oven door  16  is open. According to  FIG. 4   d,  the smoke and vapours travel through the exhaust connections  64  to the flow ducts  80 , in which the vacuum created by the fans  34  suck them through the fans  34  to the catalyser  54 . The catalyser  54 , the air-heating means  84  for it, and the second heating means of the circulating air means are all preferably in the upper space  114 , in which excess pressure is created with the aid of the fan  34 . A condenser duct opening  77  is located in the upper space  114 , from where the recovery-system  104  duct  70  starts, through which the vapours are led to the condenser  72 . With the aid of such an arrangement, the exhaust connections  64  suck the vapour and smoke so effectively to the catalyser and condenser that the passage of the vapours and smoke outside the oven is prevented almost completely. 
         [0084]    According to  FIGS. 2 a    and  5 , the active frying plate  20  is preferably located above the cooker  26 . Between the frying plate  20  and the cooker  26  there can be thermal insulation  30 , which prevents the transfer of heat from the oven space  12  to the cooker space  15 . Beneath the frying plate  20  there can be an air space as thermal insulation or preferably an encased thermal-insulation board. It is also possible to use a separate cooled air flow. Preferably the electrical resistance  36  of the frying plate  20  is situated inside the frying plate  20  above the thermal insulation  30  and a light-construction rapidly-reacting frying surface is attached on top of the electrical resistance  36 . The frying surface can be, for example, an aluminium-alloy casting, or of some other metal suitable for the purpose. The degree of filling of the cooking tank of the cooker can be checked from a check opening  102  and when the cooking tank is full the used cooking liquid can be removed from the cooking tank through cooking-liquid outlet ducts  90 , using outlet valves  91 . The filling of the cooking tank can, in turn, be performed by way of the oven door. 
         [0085]    For microwave heating, the oven includes at least one magnetron  38  according to  FIG. 5 , which creates microwaves in the oven space. The number of magnetrons used in the oven preferably corresponds to the number of temperature zones to be arranged in the oven space. With the aid of microwave heating, it is advantageously possible to defreeze food-portion components very rapidly, which would otherwise be impossible using circulating air or the frying plate. Microwave heating cannot be restricted particularly to a specific temperature zone, but instead when microwave heating is being used all the components on the frying plate in the oven space receive some kind of heating effect. The operation of the magnetrons is, however, controlled in such a way that, when it is desired to heat a specific temperature zone in the oven space, precisely the magnetron nearest to this temperature zone is used, when the effect of the microwaves transmitted by the magnetron will be greatest on the food-portion component in this temperature zone. 
         [0086]    Although the second heating means in  FIGS. 1-7  are formed with the aid of electrical resistances, it should be understood that induction or gas heating, for example, can also be used as the heating means in the oven according to the invention. In an induction-heated oven, an electrical field, which makes the thermal surface of the frying plate become hot, can be induced in the frying plate with the aid of a varying magnetic field. Gas heating can be used in place of electrical resistances for heating the circulating air, in which case gas is burned with the aid of a burner to create heat. 
         [0087]    In the oven according to the invention, each of the components of a food portion on the frying plate can be heated using one or more manners of heating, i.e. microwaves, circulating air, or by using the frying plate, simultaneously or periodically. In other words, for example mashed potato can be heated using one temperature zone, for example, using simultaneously microwaves, circulating air, and the frying plate at a temperature of 220° C., while at the same time a steak is being fried in the adjacent temperature zone using only circulating air and the frying plate at a temperature of 340° C. Usually, the temperatures used in the oven are in the range 200-350° C., but in the case of certain products the temperature can be lower or higher than the aforementioned range, in which case the temperatures can vary in the range 100-500° C. 
         [0088]      FIG. 6  shows a schematic diagram of the steam recovery system  104  preferably used in the oven according to the invention. The recovery system can include a duct  70  leading from the oven space  12 , which is led to a condenser  72  that is preferably higher than the oven space  12  in the oven  10 . The water in the components evaporates to become water vapour as a result of the heating of the components performed on the frying plate  20  and in the cooker  26 . Water vapour and smoke are sucked into the flow duct  80  of the circulating-air means and blown with the aid of the fan  34  through the catalyser to the upper space  114 . Finally, the water vapour ends up through the duct  70  from the upper space  114  at the condenser  72 , where it is condensed into water against the cold condenser surfaces. An outlet channel  74  is formed from the condenser  72  downwards, along which the water can be led to the collection tank  44 , which can be easily emptied.  FIG. 6  does not show the flow duct and other parts belonging to the circulating-air means, with the aid of which the circulating air and along with it also the water vapour and smoke are transferred from the oven space to the upper space. 
         [0089]    According to  FIG. 7 , water channels  42 , the purpose of which is to collect the liquid coming from the food-portion components heating on the frying plate  20 , are formed in the walls of the oven space to run round the frying plate. The water channels  42  preferably run round the frying plate  20  and a collector line leaves the water channels, to collect the liquid. The liquid can be led, for example, to the same collector tank  44  of  FIG. 6 , in which the liquid coming from the condenser  72  is collected. According to  FIG. 7 , there can be a separate intermediate duct  116  between the grease filter  69  and the wall  14  of the oven, which forms a separate air duct. According to  FIG. 7 , the thermal insulation between the oven space  12  and the cooker space  15  is also formed, in addition to the thermal insulation  30 , of air spaces  118  and  120 , as well as a protective cover  56 . Together, these form effective insulation. 
         [0090]    As something that does not belong to the invention, it can be stated that the oven can also be implemented without a cooker, in which case the oven includes only microwave means, circulating-air means, and a frying plate as heating means, of which at least one heating means is arranged to create at least two different temperature zones in the oven space. By means of such an oven, a possibility is achieved, compared to ovens of the prior art, to prepare several different components simultaneously in the oven, each component being at its specific heating temperature. The components to be cooked would then be prepared in a separate cooker. Further, as an idea separate from the invention, the oven can, in applicable parts and with a new configuration, also be applied without air circulation, implemented with the aid of a hood. The use of the hood then replaces the use of the cleaning element and the catalyser.