Patent Publication Number: US-2023148781-A1

Title: Cooking device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a National Stage application of International Patent Application No. PCT/EP2020/060694, filed on Apr. 16, 2020, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a cooking device, in particular a steam oven, and a method for operating the cooking device. 
     BACKGROUND 
     The air within the cooking cavity of a cooking device, in particular a steam oven, is heated by means of heating elements. Typically, the cooking device comprises one or more fans, wherein each fan is enclosed by a ring heater to heat the air that is circulated by the fan. The heating elements and the fans are arranged in a heating cavity, e.g. at the back side of the cooking cavity. 
     The heat distribution in the cooking cavity of such a cooking device is more or less homogeneous. 
     SUMMARY 
     The problem to be solved by the present invention is therefore to provide a cooking device that creates different temperatures within the cooking cavity of a cooking device. 
     This problem is solved by the cooking device of claim  1 . 
     Hence, in a first aspect, the invention relates to a cooking device, in particular a steam oven, comprising at least the following elements:
         A cooking cavity: This is the cavity used for cooking the foodstuff.   A heating cavity: This is a cavity separate from the cooking cavity. It contains the heating unit as outlined below.   A wall arranged between the cooking cavity and the heating cavity: This wall mechanically separates the two cavities. Advantageously, the wall extends substantially vertically.   Ventilation openings arranged between the cooking cavity and the heating cavity to provide for an air exchange between the two cavities.   A heating unit: This heating unit is arranged in the heating cavity. It comprises a first and a second heating element and a fan. The fan is positioned and adapted to collect air from the cooking cavity and to convey the air, in two separate airflows, to interact with the first and second heating elements. (In this context, ‘interact’ is to be understood as the airflow entering into a heat exchange with the given heating element.) More specifically, the fan is positioned and adapted:
           a) to generate a first airflow interacting with the first heating element and being conveyed back into a first part of the cooking cavity and   b) to generate a second airflow interacting with the second heating element and being conveyed back into a second part of the cooking cavity.   
           A control unit: This control unit is adapted and structured to operate the first and second heating elements independently from each other, i.e. it can vary the average heating powers and/or temperatures of the two heating elements differently. For example, it may increase the power of one heating element while keeping the power of the other heating element constant or decreasing it, or vice versa.       

     This allows to feed two differently heated airflows back into the cooking cavity, which may e.g. be used to heat the foodstuff from two different sides, in particular from above and below. 
     For example, the first heating element may be operating while the second heating element is turned off, or vice versa. Both heating elements may advantageously be controlled independently of the fan. 
     Advantageously, the control unit may be adapted to operate the first and second heating elements at different average surface temperatures. In this context, “average” relates to an average over a time larger than the typical on-off-cycle of the heating elements when the average heating power is controlled by means of switching the heating elements on and off. In particular, ‘average’ refers to an average over a time period dt with dt being a value between 1 and 10 minutes, in particular between 2 and 6 minutes. 
     The first airflow passing the first heating element creates a first airflow circuit in the heating cavity and the cooking cavity and the second airflow passing the second heating element creates a second airflow circuit in the heating cavity and in the cooking cavity. 
     Due to the different controllability of the first and the second heating element, the first and the second airflow can be heated to different temperatures as they enter the cooking cavity. Therefore, the first and second parts of the cooking cavity can be maintained at different temperatures. Such different temperatures within the cooking cavity enable the optimization of various heating processes, e.g. for evaporating residual water that aggregates on the floor of the cooking cavity by adjusting the airflow such that it only heats up the floor section of the cooking cavity. A further example would be that, by adjusting the heating power of the respective airflow, the cooking device would apply a grilling function to the foodstuff within the cooking cavity. 
     In another advantageous embodiment, the first heating element is arranged above the fan and the second heating element is arranged below the fan. Advantageously, the second heating element below the fan might be heated to a higher temperature than the first heating element above the fan. 
     In another advantageous embodiment, the heating unit further comprises a second fan. In a mode of operation of the cooking device, the second fan collects air from the cooking cavity and conveys it towards the first and the second heating element. 
     In other advantageous embodiments, the heating unit may further comprise at least one second fan that collects air from the cooking cavity and conveys it toward the first and the second heating element. 
     In another advantageous embodiment, the heating unit comprises a first and a second subsection in the heating cavity. The first subsection comprises the first and the second heating element as well as the first fan. The second subsection comprises a third and a fourth heating element individually operatable at different temperatures and a second fan. In a mode of operation, the second fan collects air from the cooking cavity and conveys a third airflow towards the third heating element and a fourth airflow towards the fourth heating element. The third airflow is passed by into the first part of the cooking cavity, and the fourth airflow is passed back into the second part of the cooking cavity. 
     Advantageously, the control unit may be adapted to operate the third and fourth heating elements at different average surface temperatures. 
     In other embodiments, the cooking device may further comprise further subunits, each having further heating elements and a further fan. 
     In an advantageous embodiment, the control unit is adapted to control each heating element, e.g. the first, second, third and fourth heating element, independently from the first and/or second fan. Also, each of said heating elements might be controlled independently from the other heating elements. 
     In a further mode operation of the cooking device, the control unit may be adapted to control the first fan and the second fan individually. Therefore, only the first fan might be running and the second fan might be turned off or vice versa. 
     The rotation direction and/or the rotation speed of the first fan may be the same as or different from the rotation direction and/or rotation speed of the second fan. In particular, the control unit may be adapted to rotate the first and second fans with different speeds and/or with different directions. 
     Advantageously, in the intended operation of the cooking device, the rotation direction of the first fan is opposite to the rotation direction of the second fan. In other words, the control unit and/or fan drivers of the device is/are adapted to rotate the first and second fans in opposite directions. 
     Furthermore, an advantageous fan may comprise blades that extend from the rotation axis of the fan in a radial direction and end in blade tips. In operation, the tips of the blades rotate around the rotation axis. They form a substantially virtual rotation circle around the respective rotation axis. 
     In an advantageous embodiment, the rotation of the respective fan is adapted to convey the respective airflow to a specific sector of the cooking device. 
     Regarding the shape of the heating elements of the cooking device, in a further advantageous embodiment, at least one of the heating elements, in particular all of the heating elements, may comprise at least one curved portion that extends essentially along a sector section of the rotation circle described by the tips of the blades of the first fan. Advantageously, such a curved portion extends along a sector section of above 60°, very advantageously along a sector section of above 120°. 
     If the embodiment comprises a second fan, at least one of the heating elements may each further comprise at least a second curved portion that extends essentially along a second sector section of a rotation circle described by the tips of the blades of the second fan. In addition, the second curved portion advantageously extends along a sector section of above 60°, very advantageously along a sector section of above 120°. 
     In a further advantageous embodiment, the first and second curved portion may extend along sector sections with the same angle. 
     In another advantageous embodiment, the first sector section and the second sector section extend along different angles, advantageously wherein the angles differ by at 30°, in particular by at least 60°. 
     In an advantageous embodiment comprising a second subsection of the heating unit, the third and/or fourth heating element each can comprise at least one curved portion that extends essentially along a sector section of a rotation circle described by tips of blades of the second fan. Advantageously, the at least one curved portion of the third and/or fourth heating element extends along a sector section of above 60°, very advantageously along a sector section of above 120°. 
     Advantageously, the first, second, third and/or fourth heating element has the shape of a folded heating rod. Advantageously, such a folded heating element may be sectioned into three sections:
         A parallel section refers to a segment of the rod where a first and a second section of the folded rod are arranged essentially in parallel to each other.   A bent folding section connecting the first and the second section.   A connector section forming the beginning and the end of the rod. Advantageously, for easier mounting, the beginning and the end of the rod are close to each other, in particular closer than 10 cm.       

     Advantageously, the connector sections of the heating elements are connected to separate power drivers individually controllable be the control unit. 
     In a further advantageous embodiment, the first, second third and/or fourth heating element is arranged such that an end of the respective folding section or the connector section of the respective heating element forms an angle α relatively to a horizontal axis, wherein α≥60°. 
     The device may further comprise at least one deflector element arranged in the heating cavity. It is arranged between two of the heating elements and extends transversally to a tangential direction of the fan. In this context, a “tangential direction of the fan” is a direction that is tangential to a circle concentric to the fan&#39;s axis. Such a deflector elements obstructs air moving along the tangential direction from one heating element to the other, thereby reducing the heat exchange between the two heating elements. 
     In this case, at least one such deflector element might be arranged:
         between the connector section of the first heating element and the connector section of the second heating element, and/or   between the connector section of the first heating element and the folding section of the second heating element, and/or   between the folding section of the first heating element and the folding section of the second heating element.       

     If the device has third and fourth heating elements as mentioned, above, at least one such deflector element might also be arranged
         between the connector section of the third heating element and the connector section of the fourth heating element, and/or   between the connector section of the third heating element and the folding section of the fourth heating element, and/or   between the folding section of the third heating element and the folding section of the fourth heating element.       

     In particular, multiple deflector elements can be arranged at different locations of the heating cavity. 
     Advantageously, the cooking device comprises at least two deflector elements arranged in two of the above-mentioned arrangements, wherein every combination of arrangements may be possible. 
     The at least one deflector element may comprise a plate, in particular of metal, that is mounted between the respective heating elements. 
     In another advantageous embodiment, the curved section of the parallel section of the first heating element and a curved section of the parallel section of the second heating element form the smallest gap between the parallel section of the first heating element and the parallel section of the second heating element. This smallest gap is located between the first fan and the second fan. Advantageously, the curved section of the lower heating element is formed such that it crosses a plane defined by the rotation axes of the first fan and the second fan. 
     In at least one mode of operation of the device, the control unit may be adapted to maintain the temperature difference between the first airflow and the second airflow, as the airflows exit the heating cavity, at at least 20° C., in particular at at least 50° C., very particular at at least 100° C. This allows to maintain a substantial temperature gradient in the heating cavity. 
     The term airflow itself preferably refers to a respective volume of air that is circulating within the cooking cavity and the heating cavity, wherein the respective volume of air is heated by the respective heating element. 
     An advantageous embodiment of the present invention refers to a cooking device that is operated as a steam oven. In that case, the device comprises a steam generator, and the control unit is adapted to maintain a (relative) air humidity in the cooking cavity at at least 40%. In such an embodiment, all parts and processes are advantageously designed to be used in a highly humid environment. In particular, the fan, the first and second heating element, as well as any deflector, if present, may be of materials resistant against humidity, e.g. at least some of these parts may be formed (at least at their surfaces) from stainless steel. 
     In a further aspect, the ventilation openings comprise at least one entry opening at least a first exit opening and at least a second exit opening for leading are from the cooking cavity into the heating cavity and from the heating cavity into the cooking cavity, respectively. 
     The first fan may then be adapted:
         To convey air from the cooking cavity into the heating cavity through said entry opening.   To convey the first airflow from the heating cavity back into the cooking cavity through the first exit opening and to convey said second airflow from the heating cavity into the cooking cavity through the second exit opening.       

     Advantageously, the first exit opening(s) is/are located above the second exit opening(s), and/or the entry openings may be vertically located between the first and second exit openings. 
     A second aspect of the present invention refers to a method for operating such a device. The method comprises the step of operating the heating elements at different surface temperatures such that the first and second airflows have different temperatures when entering the cooking cavity from the heating cavity. 
     Advantageously, the heating elements are operated such that the temperature difference between the average surface temperatures of the first and second heating element is at least 20° C., in particular at least 50° C., very particular at least 100° C. 
     It is understood that the various embodiments, preferences, and method steps as disclosed in the specification may be combined at will, if not otherwise specified or explicitly excluded. Other advantageous embodiments are listed in the dependent claims as well as in the description below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood and objects other than those set forth above will become apparent from the following detailed description thereof. Such description refers to the annexed drawings, wherein: 
         FIG.  1   a    shows a perspective view of a cooking device according to a first embodiment of the present invention; 
         FIG.  1   b    shows a front view of the cooking device of  FIG.  1     a;    
         FIG.  1   c    shows a further embodiment according to the invention; 
         FIG.  1   d    shows a schematic sectional view along a vertical plane intersecting with the axis of the fan; 
         FIG.  1   e    shows a detail of  FIG.  1     d;    
         FIGS.  2   a  and  2   b    show each a front view of a cooking device according to two further embodiments; 
         FIG.  3    shows a front view of a cooking device according to a further embodiment; 
         FIG.  4    shows a front view of a cooking device according to another embodiment; and 
         FIG.  5    shows a schematic diagram of some of the components of an embodiment of the device. 
     
    
    
     Note: The wall separating the cooking cavity and the heating cavity is only shown in  FIGS.  1   d  and  1   e   . 
     DETAILED DESCRIPTION 
       FIG.  1   a    shows a schematic perspective view of a first embodiment of cooking device  100 . It comprises a cooking cavity  1  and a heating unit  2 . The heating unit  2  comprises a first  21  and a second  22  heating element capable to operate at different average surface temperatures and a fan  20 . 
     As shown in  FIG.  1   d   , the heating unit  2  is arranged in a heating cavity  25 . A wall  26  is arranged between the cooking cavity  1  and the heating cavity  25 . 
     In the shown embodiments, wall  26  extends vertically and forms a backside wall of the cooking cavity  1 , located opposite a user-facing opening  11  of the cooking cavity  1 . 
     Entry openings  27  as well as exit openings  28   a ,  28   b  are located between in wall  26  between the cooking cavity  1  and the heating cavity  25 . They form ventilation openings that allow the air to circulate between the two cavities  1  and  25 . 
     The cooking device  100  is configured in such a manner that, in the intended operation, the fan  20  collects air from the cooking cavity  1  and conveys a first airflow towards the first heating element  21  and a second airflow towards the second heating element  22 . The first airflow passing the first heating element  21  is conveyed back into a first part  12  of the cooking cavity  1 . The second airflow passes the second heating element  22  and is conveyed back into a second part  13  of the heating cavity. 
     The air enters the heating cavity  25  through the entry openings  27 . The first airflow leaves it through first exit opening  28   a , and the second airflow leaves it through second exit opening  28   b.    
     Advantageously, the first exit opening  28   a  is located in the upper half, in particular in the uppermost fourth, of the cooking cavity  1  while the second exit opening  28   b  is arranged in the lower half, in particular in the lowermost fourth, of the cooking cavity, which allows to generate a vertical temperature gradient in the cooking cavity  1  between its first part  12  and its second part  13 . 
     By arranging the exit openings  28   a ,  28   b  close to the top and bottom of cooking cavity  1 , the air tends to flow all the way to the user door  4  of cooking cavity  1 , where it is deflected and then returns along the top and bottom of the food to be prepared, which provides a more homogeneous temperature distribution along the depth (i.e. the direction perpendicular to user door  6 ) of cooking cavity  1 . 
     As illustrated in  FIG.  1   d   , the temperature difference between first part  12  and second part  13  becomes even more pronounced in the presence of a cooking tray  29  for the foodstuff  29   a  arranged between them. 
     Advantageously, fan  20  is a radial fan sucking in air along an axial direction and expulsing it radially, which allows to keep the heating cavity  25  small in axial direction of the fan  20 . 
       FIG.  1   b    shows a front view of the cooking device of  FIG.  1   a    with the details of the cooking device  100  and in particular of the heating unit  2 . 
     The fan  20  comprises blades that extend, from a rotational axis A of the fan  20  (cf.  FIG.  1   d   ), along radial direction and end in tips  201  of the fan  20 . 
     The first  21  and the second  22  heating element each has the shape of a folded heating rod. Each respective folded rod has a parallel section “a” where a first section of the rod is formed essentially in parallel to a second section of the rod. In addition, each respective folded rod has a folding section “b”, which refers to the bent portion of the rod between the first and the second section. Furthermore, a connector section “c” of each of the respective rods is referring to the two portions at the beginning and at the end of the rod, which are mounted close to each other. The connector section c of the first  21  and the second  22  heating elements are controllable independently from each other. 
     The first  21  as well as the second  22  heating element both comprise a curved portion  210 . The curved portion  210  of each heating element  21 ,  22  extends within the parallel section of each respective rod. The curved portion  210  extends essentially along a sector section of a rotation circle described by the tips  201  of blades of the fan  20  of the heating unit  2 . The heating elements  21 ,  22  each extend essentially along a sector section of above 60°. 
     A first deflector element  5  is arranged between the folding section b of the first heating element  21  and the connector section c of the second heating element  22 . A second deflector element  5  is arranged between the connector section c of the first heating element  21  and the folding section b of the second heating element  22 . 
     In an advantageous mode of operation of the cooking device, the temperature difference between the first airflow and the second airflow is at least 20° C., advantageously at least 50° C., very advantageously at least 100° C. 
     The cooking device  100  is advantageously a steam oven, wherein in the intended operation, the humidity of the air is at least 40%. 
       FIG.  1   c    shows a further embodiment. The embodiment is similar to the embodiment shown in  FIG.  1   b   , except that in  FIG.  1   b    the second heating element  22  and the first heating element  21  are arranged such that the folding section b of the first heating element  21  and the connector section c of the second heating element are arranged next to each other and the folding section b of the second heating element  22  and the connector section c of the first heating element are arranged next to each other. In  FIG.  1   c   , in contrast, the folding sections b of the first  21  and the second  22  heating element are arranged next to each other and the respective connector elements c of the two heating elements  21 ,  22  are arranged next to each other. 
       FIG.  1   d    shows another advantageous design element of the present device that can be used in any of its embodiments. As can be seen, the heating elements  21 ,  22  are formed by pipes. At least in one plane extending through the axis A of rotation of fan  20 , in particular in the vertical plane which corresponds to what is shown in  FIG.  1   d   , the plane intersects, on each side of the axis A, at least two pipes. In the embodiment of  FIG.  1   d   , two pipe intersections  61   a ,  61   b  are located above axis A and two pipe intersections  61   c ,  61   d  below axis A. 
     As can best be seen from  FIG.  1   e   , in said plane, the two closest pipe intersections  61   a ,  61   b  are mutually offset along the axial as well as the radial direction of fan  20 . This is in contrast to the classic design where the two pipe intersections  61   a ,  61   b  are both at the same radial distance from axis A, and it allows to maintain a larger shortest distance D (i.e. a larger gap) between the two pipes and reduces the resistance experienced by the radial airflow  62  from fan  20  as it passes the pipes. 
     As can be seen in  FIG.  1   e   , the direction of the shortest distance D between the pipe intersections  61   a ,  61   b  and the direction of fan axis A (the horizontal direction in  FIG.  1   e   ) are arranged at a mutual an angle α. Advantageously, this angle α is between 30 and 60°. 
     Hence, in more general terms, the heating elements  21 ,  22  are advantageously formed by pipes. In at least one plane extending through the axis A of rotation of fan  20 , the closest pipe intersections  61   a ,  62   b  of the pipes with the plane have a direction of closest distance D that is under an angle α to the axis A of fan  20 . The angle α is between 20° and 70°, in particular between 30° and 60°. If the angle is smaller than this range, the distance D decreases and the friction of the airflow increases. Also, the friction becomes very sensitive to any misalignment of the pipes, thereby tending to make the airflow inhomogeneous. If the angle is too large, the heating elements require too much space in radial direction or one pipe starts to shadow the other pipe, thereby affecting the heat transfer from the heating elements to the air. 
     Advantageously, this condition is fulfilled for the vertical plane extending through the axis A of fan  20 . 
     In another advantageous embodiment, the above condition is fulfilled for a plurality of different planes, in particular for all planes within an azimuthal angular range of at least 45°. In this context, the azimuthal angle is the angle between two directions extending perpendicularly through axis A of fan  20 . 
       FIG.  2   a    shows another advantageous embodiment where, in addition to the embodiment as shown in  FIGS.  1   a  and  1   b   , the heating unit  2  of the cooking device  100  comprises a first fan  20  and a second fan  30 . The cooking device  100  is configured in such a manner that, in the intended operation, the second fan  30  collects air from the cooking cavity  1  and conveys it towards the first  21  and the second  22  heating element. 
     In preferred operation of the cooking device  100 , the rotation direction of the fan  20  is opposite to the rotation direction of the second fan  30 , which improves the symmetry of the temperature distribution in the cooking cavity  1 . 
     In another advantageous mode of operation of the cooking device  100 , the rotation direction of the first fan  20  may be the same as the rotation direction of the second fan  30 . 
     The first fan  20  and the second fan  30  each comprise blades that extend from the rotational axis A of the respective fan  20 ,  30  in radial direction and end in tips  201 ,  301  of the respective fan  20 ,  30 . 
     The first  21  and the second  22  heating element again each have the shape of a folded heating rod. Each respective folded rod has a parallel section “a” where a first section of the rod is formed essentially in parallel to a second section of the rod. In addition, each respective folded rod has a folding section “b” which refers to the bent portion of the rod between the first and the second section. Furthermore, a connector section “c” of each of the respective rods is referring to the two portions at the beginning and at the end of the rod, which are mounted close to each other. The connector section c of the first  21  and the second  22  heating elements are controllable independently from each other. 
     The first  21  and the second  22  heating element each comprise a first curved portion  210  that extends essentially along a sector section of a rotation circle described by the tips  201  of blades of the first fan  20 . The first  21  and the second  22  heating element further comprise each a second curved portion  211  that extends essentially along a second sector section of a second rotational circle described by tips  301  of blades of the second fan  30 . The curved portion  201  of each of the heating elements  21 ,  22  may extend along a sector section of more than 120°. The second curved portion  211  of each of the heating elements  21 ,  22  may extend along a sector section of more than 120°. 
     A first deflector element  5  is arranged between the folding section b of the first heating element  21  and the folding section b of the second heating element  22 . A second deflector element  5  is arranged between the connector section c of the first heating element  21  and the connector section b of the second heating element  22 . 
     The parallel section “a” of the first heating element  21  between the folding section b and the connector section c has a curved section d, which is curved in a way to form the smallest gap ds to the parallel section a to the respective curved section d of the parallel section a of the second heating element  22 . 
     In an intended operation of an advantageous cooking device, the temperature difference between the first airflow and the second airflow is at least 20° C., advantageously at least 50° C., very advantageously at least 100° C. 
     The cooking device  100  might advantageously be a steam oven, wherein in the intended operation, the humidity of the air is at least 40%. 
       FIG.  2   b    shows presently preferred embodiment to  FIG.  2   a   . The embodiment in  FIG.  2   b    differs from the embodiment in  FIG.  2   a    in that the curved section d of the lower heating element, which is the second heating element  22  in this embodiment, is curved such that it crosses a plane  220  defined by the rotation axes of the first fan and the second fan (i.e. both rotational axes lie in said plane  220 ). 
       FIG.  3    shows another advantageous embodiment where the heating unit comprises a first and a second subsection  2   a ,  2   b . The first subsection  2   a  comprises the first and second heating elements  21 ,  22  and the first fan  20 . The second heating subsection  2   b  comprises a third  41  and a fourth  42  heating element capable to operate at different average surface temperatures and a second fan  40 . Second fan  40  is advantageously a radial fan, too. 
     The cooking device  100  may be configured in such a manner that, in at least one mode of operation, the second fan  40  collects air from the cooking cavity  1  and conveys a third airflow towards the third heating element  41  and a fourth airflow towards the fourth heating element  42 . The third airflow passing the third heating element  32  creates a third airflow circuit and the fourth airflow passing the fourth heating element  42  creates a fourth airflow circuit. The third airflow enters the cooking cavity in its first part  12  and the fourth airflow enters the cooking cavity in its second part  13 . 
     Again, in an advantageous mode of operation, the rotation direction and/or rotating speed of the first fan  20  can be opposite to or different from the rotation direction and/or rotating speed of the second fan  40 . 
     In another advantageous mode of operation, a rotation direction and/or rotating speed of the first fan  20  can have the same direction and/or speed as the second fan  40 . 
     The first fan  20  and the second fan  40  each comprise blades that extend from the rotational axis A of the respective fan  20 ,  40  in radial direction and end in tips  201 ,  401  of the respective fan  20 ,  40 . 
     Again, the first  21 , second  22 , third  41  and fourth  42  heating element each may have the shape of a folded heating rod. Each respective folded rod has a parallel section “a” where a first section of the rod is parallel to a second section of the rod. Each heating element  41 ,  42  has a folding section “b” which refers to the bent portion of the rod between the first and the second section. Furthermore, a connector section “c” of each of the respective rods is formed by the two portions at the start and at the end of the rod, which are mounted close to each other. The connector section of the first  21 , the second  22 , the third  41 , and the fourth  42  heating element are controllable independently from each other. 
     The first  21  and the second  22  heating element each comprise a curved portion  210  that extends essentially along a sector section of a rotation circle described by the tips  201  of blades of the fan  20 . 
     The third  41  and the fourth  42  heating element each comprise a curved portion  410  that extends essentially along a sector section of a rotation circle described by the tips  401  of blades of the fan  40 . 
     The curved portion  201  of each of the heating elements  21 ,  22 ,  41 ,  42  extends essentially along a sector section of more than 60°. 
     A first deflector element  5  is arranged between the connector section c of the first heating element  21  and the connector section c of the second heating element  22 . A second deflector element  5  is arranged between the connector section c of the third heating element  41  and the connector section c of the fourth heating element  42 . 
     In an advantageous operation of the cooking device, the temperature difference between the first airflow and the second airflow, as they enter the cooking cavity  1 , is again at least 20° C., advantageously at least 50° C., very advantageously at least 100° C. The temperature difference between the third airflow and the fourth airflow, as they enter the cooking cavity  1 , is at least 20° C., advantageously at least 50° C., very advantageously at least 100° C. 
     The cooking device  100  might advantageously be a steam oven, wherein in the intended operation, the humidity of the air is at least 40%. 
       FIG.  4    shows another advantageous embodiment of the device, again with a first fan  20  and a second fan  40 . The first heating element  21  extends above the two fans  20 ,  40  and the second heating element  22  extends below the two fans  20 ,  40 . 
     The fans  20 ,  40  are advantageously rotating in opposing directions. 
     The first and second heating elements may be symmetric to each other, which allows to use the same type of heating rod for both of them. 
     The first and second heating elements may be curved and shaped as those if the embodiment of  FIG.  2     a.    
     Advantageously, the connector section of the first heating element  21  is adjacent to the folding section of the second heating element  22  and the folding section of the first heating element  21  is adjacent to the connector section of the second heating element  22 . 
     Notes 
       FIG.  5    shows a block diagram of some components of a cooking device  100 . 
     In particular, and in all embodiments, the cooking device comprises a control unit  110 , which may e.g. be a microprocessor system including memory and program instructions. It may be implemented as a single unit or comprise several subunits. Control unit  110  is adapted to control the components of the device and to carry out the steps for operating it automatically. 
     The device may further comprise a series of power drivers  111 - 114 , advantageously with at least one power driver for each heating element, with each power driver  111 - 114  powering one heating element. The control unit may be adapted to control the power drivers independently and individually in order to power the heating elements  21 ,  22 ,  41 ,  42  independently and individually at different, and advantageously differently varying, power levels. For example, the power drivers  111 - 114  may comprise relays for switching the heating elements on or off at short cycles (e.g. a few ten seconds) in order to control their average heating power. Alternatively, semiconductor switches may be used, 
     The device may further comprise at least one fan driver  115 ,  116  for operating the fan(s)  20 ,  30 ,  40  of the heating unit. Again, there may be one fan driver  115 ,  116  per fan, and the control unit  110  may be adapted to control the fan drivers  115 ,  116  and therefore the fans independently and individually. 
     As shown in in  FIG.  5   , the device may further comprise at least one temperature sensor  117  for measuring a temperature within cooking cavity  1  and/or heating cavity  25 . In this case, control unit  110  may be adapted to control the temperature measured by the temperature sensor  117  in a closed loop, adapting it to a desired temperature. 
     Advantageously, there is only one such temperature sensor  117 , which may e.g. be arranged in heating cavity  1  (i.e. it is located to measure a signal indicative of the temperature in heating cavity  1 ) in order to measure (and regulate in a closed loop) the temperature at a given point in heating cavity  1 . In this case, and in at least one mode of operation, control unit  110  may be adapted to maintain different temperatures in the first and second part  12  and  13  of the cooking cavity  1  by keeping the temperatures of the first and second heating elements  21 ,  22  (and, where available, of the third and fourth heating elements  41 ,  42 ) at different average surface temperatures. Advantageously, these average temperatures differ by at least 20° C., in particular by at least 50° C. 
     In one embodiment, temperature sensor  117  may comprise two redundant temperature measuring units for safety reasons. These two measuring units are, however, located to measure the temperature at substantially the same position of cooking cavity  1  and are therefore considered to be a single temperature sensor. 
     If the device is a steam oven, it may further comprise a steam generator  118  as it is known to the skilled person. Control unit  110  may be adapted to cause the steam generator  118  to generate steam to be fed to the cooking cavity  1 . 
     As shown in the embodiments of  FIGS.  2   a   ,  3 , and  4 , if there are a first and a second fan  20 ,  40 , there are advantageously at least two deflector elements  5 , with the two fans  20 ,  40  being arranged between them. The deflector elements  5  interrupt the vertical air flows to the left and right of the two fans  20 ,  40 . 
     The two fans are advantageously rotating in opposite directions. In this case, there may advantageously be no deflector element between the two fans  20 ,  40 . 
     Further, if there are at least two fans  20 ,  40 , the axes of the two fans are advantageously arranged horizontally, and the fans are arranged horizontally side by side as shown in all the embodiments having two fans. 
     The mode where the two heating elements  21 ,  22  (and  41 ,  42 , where available) are operated at different average surface temperatures may be only one of several operating modes. In another operating mode, the control unit may be adapted to operate the two heating elements  21 ,  22  (and  41 ,  42 , where available) at the same average surface temperatures in order to generate a homogeneous temperature distribution within the cooking cavity  1 . 
     Even though only shown in  FIGS.  1   d  and  1   e   , advantageously all embodiments comprise a heating cavity  25  separated by a wall  26  from the cooking cavity  1 . 
     In the example of  FIG.  1   d   , there are several entry openings  27 , but there may be only a single entry opening, which may be protected by a grid. 
     Similarly, while  FIG.  1   d    only shows one first and one second exit opening  28   a ,  28   b , there may be several first exit openings  28   a  and/or several second exit openings  28   b.    
     While there are shown and described presently preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.