Patent Publication Number: US-8525080-B2

Title: Oven, especially domestic oven and method for operating such an oven

Description:
The invention relates to an oven, especially to a domestic oven, with a cooking cavity, wherein means are arranged for supplying hot air to the cavity. Furthermore, the invention relates to a method for operating such an oven. 
     Ovens of this kind are well known in the art and useful for an effective cooking using hot air. Pre-known hot air systems for domestic ovens work normally with a heating element and a fan wheel that blows air from the environment onto the heating element to heat the air and heat with the hot air the food in the oven. 
     Some recipes that have a high mass and water content require a high heat transfer to the food especially in the beginning of the cooking or baking process in order to e.g. seal the surface of the food or to dry out the surface of the food fast enough. 
     Other recipes need a lower heat transfer to prevent the burning of the food. A generally higher heating power leads also to a higher energy consumption because not every kind of food can absorb the same heat quantity. 
     Pre-known hot air ovens have deficiencies to adapt the cooking parameters in an optimized way when hot air is applied for the cooking process. 
     Therefore, it is an object of the invention to provide an oven, especially a domestic oven, which uses hot air for cooking purposes and which is able to better optimize the supply of hot air to the food in the cooking cavity. It should become possible to run a cooking process in the oven with optimized parameters with respect to the supply of heated air into the cavity. 
     Furthermore, a method for operating such an oven is to be proposed which achieves better cooking results. 
     The solution of this object according to the invention relating to an oven is characterized in that the means for supplying hot air to the cavity comprise at least two heating elements, wherein air is ventilated along or through the heating elements by at least one fan. 
     Preferably, the at least two heating elements are arranged along one common flow path which leads to the cavity. It is also possible, that the at least two heating elements are arranged along at least two flow paths which lead to the cavity. In the latter case each heating element can have its own flow path, which leads to the cavity. By this arrangement it is possible that one of the flow paths discharges in an upper region of the cavity to heat up specifically that region of it. Furthermore, it becomes possible that one of the flow paths discharges in a lower region of the cavity to specifically load heat in that region of it. 
     According to one embodiment of the invention all heating elements have the same heating power. A typical value for the power is 1.500 W. It is also possible that at least two heating elements have different heating powers. Normally, the power of such a heating element is between 1.000 W and 2.000 W. 
     A preferred embodiment is characterized in that a circular heating element is arranged around the fan. 
     A cheap realization of the invention is possible when the heating elements are designed to have a switch on position and a switch off position only. 
     To deal with the different recipes according to the invention an oven can be equipped with a hot air system with (at least) two heating elements which can be switched on an off and can be combined to have the optimal power adapted to the recipe. 
     The method for operating an oven, especially a domestic oven, is characterized in that air is ventilated through at least one flow path which leads to the cavity, wherein the air is heated up during its passage of the at least one flow path by means of at least two heating elements and wherein air is ventilated along or through the at least two heating elements by at least one fan. 
     Preferably, the air is heated up by passing the at least two heating elements, which are arranged along one common flow path which leads to the cavity. Alternatively, the air is heated up by passing the at least two heating elements, which are arranged along two separate flow paths which lead to the cavity. 
     The hot air can preferably be discharged in an upper or in a lower region of the cavity. 
     With the suggested equipment and method according to the invention a hot air system is supplied by which different heating powers can be realized depending on the requirements of the recipe. 
     In principle the adaptation of the heating power could also be realized with only one heating element, which could e.g. have a heating power of 3.000 W and which is switched on and off in certain intervals. But by this way a larger variation of the oven temperature is created in a kind like a saw-tooth-profile. This would lead to a more uneven heat distribution and to a worse cooking or baking performance. 
     By the proposal according to the invention a better uniformity of the heating situation is achieved. The more heating elements are used the more even the temperature profile gets. Accordingly, the more even the browning of the food gets. 
     The adjustable heating power can be used to create special heating modes for the oven, for example one for heavy loads, one for fast cooking or baking and one for very slow heating up. 
     Depending on the position of the heating elements relative to the direction of the air flow a higher heat transfer can be forced in a certain area only by using the hot air system. 
     Consequently, the overlapping of heating power of at least two heating elements can be effective to adjust the average heating power. 
    
    
     
       In the drawings embodiments of the invention are depicted. 
         FIG. 1  shows schematically a first embodiment of a domestic oven from the side, 
         FIG. 2  shows a second embodiment of the invention in the illustration according to  FIG. 1 , 
         FIG. 3  shows the switching situation over the time of two heating elements of the oven according to a first method of operation and 
         FIG. 4  shows an alternative switching situation in the depiction of  FIG. 3 . 
     
    
    
       FIG. 1  shows a first embodiment of a domestic oven  1 . It has a cooking cavity  2  which can be opened by a door  9  to put food into the cavity  2  and to take cooked food out of it. The oven  1  is equipped with means  3 ,  4 ,  5 ,  6  for supplying hot air into the cavity  2  for cooking or baking the food in the cavity  2 . 
     This means according the embodiment of  FIG. 1  comprise two heating elements  3  and  4  which are inserted into a flow path  7  which connects the environment E with the cavity  2 . 
     It should be mentioned that also a circuit air flow can take place from the cavity  2  in the flow path  7  and back to the cavity  2 . 
     The air is ventilated by a fan  5 . The air heated by the heating elements  3  and  4  is loaded into the cavity  2  in a bottom region of it. 
     In the embodiment according  FIG. 2  there are arranged two separate hot air supplies: Hot air is loaded into the cavity  2  in an upper region of the cavity  2  by means of a first heating element  3  which is arranged in a first flow path  7 , in which also a first fan  5  is integrated. Furthermore, additional hot air is loaded into a lower region of the cavity  2  by means of a second heating element  4  which is arranged in a second flow path  8 , in which a second fan  6  is integrated. 
     By controlling the switching of the heating elements  3 ,  4  and the fans  5 ,  6  respectively the input of heating power into the cavity  2  can be effectively regulated. A not depicted control unit switches the heating element and fans respectively as illustrated in two examples in  FIGS. 3 and 4 . 
     In  FIG. 3  a principle of switching the heating elements is shown. The figure shows a heating cycle which can be defined as a certain time interval. 
       FIG. 3  shows the switching situation of a first heating element H 1  (e.g. the heating element  3  in  FIGS. 1 and 2 ) and a second heating element H 2  (e.g. the heating element  4  in  FIGS. 1 and 2 ). The heating elements H 1  and H 2  can be switches on or off only. The respective switching position is depicted over the time t during the cooking process. 
     It can be seen that a certain overlapping phase Ov takes place when both heating elements H 1  and H 2  are switched on. Reference is made to the sum S in the upper diagram. 
     In  FIG. 4  an alternative switching situation is depicted. Here the heating element H 2  is switched on continuously. For a certain time, the first heating element H 1  is switched on additionally. So also here an overlapping phase Ov takes place in which the heating power into the cavity is specifically high. 
     The power can be adapted by adjusting the length of the overlapping interval Ov shown in  FIGS. 3 and 4 , i.e. the phase in which both heating elements H 1 , H 2  are switched on. 
     By the described method, the minimum power per cycle is the power of one heating element. In the embodiment each heating element has a heating power of 1.500 W, which is the minimum heating power. The maximum power is that of both heating elements, i.e. 3.000 W. 
     The maximal and minimal power possible can be adjusted by the powers of the heating elements H 1 , H 2  which are equal in the embodiments. It is also possible that the heating powers of the two (or more) heating elements are not equal. I.e. the heating power of the heating elements must not necessarily be equal. 
     To use more heating elements it must be ensured that the same amount of air is flowing past each element, otherwise the heat distribution gets uneven in the cavity, too. This problem can be solved for example by having two circular heating elements around one fan. 
     But also a geometry where the heater sit in different positions regarding the air flow is possible for example to achieve a higher heat transfer in a certain area of the oven cavity. There could be for example two fan wheels with a heating element around each that are placed one in the upper part and one in the lower part of the cavity (see  FIG. 2 ). 
     With a heater switching as shown in  FIG. 4  a higher heat transfer can be obtained in one half of the cavity. 
     REFERENCE NUMERALS 
     
         
           1  Oven (domestic oven) 
           2  Cooking cavity 
           3 ,  4   
           5 ,  6  Means for supplying hot air 
           3  Heating element 
           4  Heating element 
           5  Fan 
           6  Fan 
           7  Flow path 
           8  Flow path 
           9  Door 
         E Environment 
         Ov Overlapping phase 
         S Sum of heating powers 
         H 1  Heating element  1   
         H 2  Heating element  2   
         t Time