Abstract:
The invention concerns an oven wherein a globally parallelepiped muffle chamber ( 1 ) contains a centrifugal convection turbine ( 9 ) driven by a motor ( 10 ) and arranged adjacent to the centre of the rear peripheral wall ( 7 ). Annular electrical resistors ( 12, 13 ) are placed at the periphery of the turbine, the assembly being surrounded by a mechanical protection grid ( 22 ). The convection turbine ( 9 ) and the heating means ( 12, 13 ) are placed in the muffle chamber ( 1 ) communicating directly with the cooking volume ( 81 ), without separating wall countering the air flow. The oven is thus provided both with self-cleaning effect and a better cooking heat distribution in the oven.

Description:
TECHNICAL FIELD OF THE INVENTION  
         [0001]    The present invention relates to ovens for cooking food, and more particularly convection ovens used in institutional kitchens.  
           [0002]    Convection ovens for cooking food generally comprise a metal muffle surrounding an interior muffle cavity, with a lower wall forming a floor, an upper wall forming a ceiling, and four vertical peripheral walls. At least one of the peripheral walls is provided with an access door for introducing food to be cooked into the interior cavity of the muffle and extracting it therefrom.  
           [0003]    In the interior space of the oven, i.e. in the interior cavity of the muffle, convection of air is achieved by a convection turbine that is driven in rotation by a motor and is generally disposed in the vicinity of one of the peripheral walls that has no access door. The turbine is mounted to rotate about a rotation axis perpendicular to the peripheral wall.  
           [0004]    The document U.S. Pat. No. 4,369,760 A, for example, describes a portable fan for circulating air in an oven into which it is inserted. The fan, placed near the posterior wall of the oven, discharges air axially toward the front in the direction of the food to be cooked. There is no heating element placed in the flow of air, with the result that heat exchange is unsatisfactory. Also, the blades of the fan are not protected effectively.  
           [0005]    Heating means can advantageously be placed in the flow of air, upstream or downstream of the turbine, and can be adapted to heat the air that is propelled into the muffle by the turbine, encouraging the cooking of the food.  
           [0006]    In most prior art ovens, such as those described in the document U.S. Pat. No. 6,114,664 A, the interior cavity of the muffle is divided into two compartments: a cooking compartment, accessible via the door, and conformed to receive the food to be cooked, and a heating compartment, containing the convection turbine and the heating means such as resistive electrical heating elements or gas burners. The cooking compartment is always isolated from the heating compartment by a box or by a separating wall that is generally perpendicular to the rotation axis of the turbine and comprises a few holes through which air can pass. The separating wall has a double effect of channeling the flow of air propelled by the turbine, and protecting the heating compartment from splashed grease and other materials from the food being cooked. In fact, in prior art ovens, a constant concern is preventing splashes from food being cooked soiling the members inside the heating compartment, namely the turbine, the heating means and sensors used to control these elements.  
           [0007]    Despite the presence of the separating wall, manual cleaning operations are periodically required to guarantee that the oven is clean. Cleaning cannot be automated in the prior art oven structures, and necessitates demounting and remounting the separating wall.  
           [0008]    Another problem that is encountered in gas ovens of this kind for cooking food is the difficulty of ensuring regular cooking of all the food in the oven, regardless of its position within the cooking compartment. It is found in fact that the cooking of the food can vary significantly as a function of the position of the food in the cooking compartment. Some areas of the cooking compartment can overheat the food, while other areas achieve insufficient heating. Also, the evenness of cooking is modified as a function of the type of food to be cooked, and as a function of the quantities of food introduced into the cooking compartment.  
         SUMMARY OF THE INVENTION  
         [0009]    One object of the present invention is namely to avoid the drawbacks of prior art structures of convection ovens for cooking food, with the aim of assisting cleaning or selfcleaning of the oven and achieving more even cooking.  
           [0010]    The invention stems from the surprising observation that eliminating the separation wall between the cooking compartment and the heating compartment, combined with a turbine rotation direction aspirating air axially to discharge it in the vicinity of the peripheral walls, achieves at one and the same time an effect of selfcleaning of the oven and more even cooking.  
           [0011]    Accordingly, to achieve the above and other objects, the invention proposes a convection oven for cooking food, comprising:  
           [0012]    a muffle with a generally parallelepipedal interior cavity delimited by a lower floor wall, an upper ceiling wall and four peripheral walls, at least one of the peripheral walls being provided with an access door for entry of food to be cooked into the interior cavity of the muffle and its exit therefrom,  
           [0013]    a centrifugal convection turbine, driven in rotation by a motor, disposed in the interior cavity of the muffle in the vicinity of the center of an adjacent peripheral wall with no access door, mounted to rotate about a rotation axis perpendicular to the adjacent peripheral wall, and adapted to aspirate air axially toward the center of the adjacent peripheral wall and to discharge it radially toward the edges of the adjacent peripheral wall,  
           [0014]    heating means placed in the flow of air upstream or downstream of the convection turbine, and adapted to heat the air that is propelled into the muffle by the convection turbine to cook the food,  
           [0015]    a cooking volume, reserved in the interior cavity of the muffle to receive food to be cooked;  
           [0016]    according to the invention, the convection turbine and the heating means are placed in the interior cavity of the muffle in direct communication with the cooking volume, with no separation wall opposing the circulation of air, with a mechanical protection grid conformed and interposed between the convection turbine and the cooking volume to prevent the contact of a user&#39;s hand with the blades of the rotating convection turbine.  
           [0017]    It is found in particular that relatively cool air is aspirated from an enlarged axial aspiration area occupied by the food to be cooked, and that the warm air discharged is confined to the vicinity of the peripheral walls, away from the food to be cooked. This results in improved heat exchange between the heating means and the air, and more even heating of the peripheral walls. Direct contact between the air that is too hot and the food is prevented.  
           [0018]    In a first embodiment, constituting an electric oven, the heating means comprise annular resistive electrical heating elements placed at the periphery of the convection turbine.  
           [0019]    In another embodiment, constituting a gas oven, heating means comprise a gas burner placed axially in the aspiration inlet of the convection turbine, or placed radially at the periphery of the convection turbine.  
           [0020]    The convection turbine can advantageously be a generally cylindrical structure, with a posterior flange carrying a plurality of short blades at the front and distributed around its periphery.  
           [0021]    The diameter of the convection turbine can advantageously be greater than one third of the greater dimension of the adjacent peripheral wall.  
           [0022]    Surprisingly, the inventors have found that more even cooking is still obtained, in the absence of any separation wall, if the turbine is driven in rotation in the reverse direction, i.e. in the direction in which the inclination of the blades would tend to push the air toward the axis of the turbine. Clearly upon reverse rotation a turbine with short blades still pushes air centrifugally, but to a reduced degree.  
           [0023]    Thanks to the structure according to the invention, the speed of the turbine can be varied over a relatively wide speed range, for example from 700 to 1300 revolutions per minute, without overheating the heating elements such as resistive electrical heating elements, thanks to improved heat exchange with the air. This means that the convection can be modulated as a function of the nature of the food to be cooked, to improve the quality thereof.  
           [0024]    Good circulation of air in the oven can be obtained by providing a removable shelf support frame, that can be passed through the door of the oven, and that consists of uprights connected by crossmembers to form an open parallelepipedal structure allowing free circulation of air and carrying lateral slideways perpendicular to the door to receive slidingly and support horizontal shelves on which food to be cooked can be placed.  
           [0025]    The oven is very easy to clean, and it is found that food sprayed from the food to be cooked does not remain on the turbine or the heating means, and is evacuated immediately by the flow of air toward the lower floor wall. This results in selfcleaning of the oven.  
           [0026]    Cleaning can be further improved by providing a cleaning device that sprays water into the muffle. To this end, a cup can be used and placed adjacent the center of the upper wall of the muffle and central water supply means to produce a flow of water toward the periphery of the cup and parallel to the upper wall.  
           [0027]    Thanks to the absence of any separating wall, the cleaning device has an immediate cleaning action at one and the same time on the cooking compartment and on the turbine and the heating means. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]    Other objects, features and advantages of the present invention will emerge from the following description of particular embodiments, which description is given with reference to the accompanying drawings, in which:  
         [0029]    [0029]FIG. 1 is a perspective view of a first embodiment of an oven according to the invention, heated electrically  
         [0030]    [0030]FIG. 2 is a front view of the FIG. 1 oven;  
         [0031]    [0031]FIG. 3 is a right-hand side view of the FIG. 1 oven, in section taken along the line A-A;  
         [0032]    [0032]FIG. 4 is a perspective view of a second embodiment of an oven according to the invention, heated by gas  
         [0033]    [0033]FIG. 5 is a front view of the FIG. 1 oven; and  
         [0034]    [0034]FIG. 6 is a left-hand side view of the FIG. 1 oven, in section taken along the line B-B. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]    In both embodiments, as depicted in the figures, a convection oven according to the invention comprises a muffle  1  having an interior cavity  8  of generally parallelepipedal shape delimited by a bottom floor wall  2 , a top ceiling wall  3 , two opposite lateral peripheral walls  4  and  5 , an anterior peripheral wall  6  and a posterior peripheral wall  7 .  
         [0036]    In both the embodiments depicted, the anterior peripheral wall  6  is fitted with an access door for introducing food to be cooked into the interior cavity  8  of the muffle and extracting it therefrom.  
         [0037]    The interior faces of the walls of the muffle are generally smooth, to prevent sticking and retention of food particles liable to be separated from food to be cooked.  
         [0038]    A convection turbine  9  is driven in rotation by a motor  10  supplied with power by an external electrical power supply. The convection turbine  9  is of the centrifugal action type, aspirating air axially via its center and discharging air radially via its periphery. To this end it comprises inclined blades, in the usual manner known in the art. The convection turbine  9  is disposed in the vicinity of the center of a peripheral wall with no access door. In the embodiment shown, the convection turbine  9  is disposed in the vicinity of the center of the posterior peripheral wall  7  of the muffle.  
         [0039]    Alternatively, in an embodiment that is not depicted in the figures, an oven can have two opposite doors respectively formed in the anterior peripheral wall  6  and in the posterior peripheral wall  7 , with the turbine placed in the vicinity of one of the opposite lateral peripheral walls  4  and  5  of the oven.  
         [0040]    The convection turbine  9  is mounted to rotate about a rotation axis  11  perpendicular to the posterior peripheral wall  7  to which it is adjacent.  
         [0041]    Accordingly, the convection turbine  9  aspirates air axially toward the center of the posterior peripheral wall  7  and discharges air radially toward the edges of the posterior peripheral wall  7 .  
         [0042]    Heating means are placed in the flow of air upstream or downstream of the turbine, and are adapted to heat the air that is propelled into the muffle by the convection turbine  9 .  
         [0043]    In the embodiment depicted in FIGS.  1  to  3 , the heating means comprise annular resistive electrical heating elements  12  and  13 , placed at the periphery of the convection turbine  9 , and supplied with power by an external electrical power supply to which they are connected by power supply conductors  15 . The annular resistive electrical heating elements  12  and  13  are therefore placed in the flow of air downstream of the convection turbine  9 .  
         [0044]    In the embodiment depicted in FIGS.  4  to  6 , the heating means comprise a gas burner  14  placed axially in the aspiration inlet of the convection turbine  9 . The other components from the embodiment shown in FIGS.  1  to  3  are depicted again, and identified by the same reference numbers. The gas burner  14  is directed toward the posterior wall  7  of the oven, i.e. toward the center of the turbine  9 . It is supplied via a supply pipe  16 . A pipe  17  for evacuating burned gases passes through its central portion.  
         [0045]    Means for receiving the food to be cooked are also provided inside the muffle  1 . In the embodiments depicted in the figures, a cooking volume  81  is reserved inside the interior cavity  8  of the muffle to receive food to be cooked, and a removable simple frame is provided to support shelves, adapted to enter the muffle through the door provided in the anterior peripheral wall  6 . The shelf support frame comprises uprights connected by top crossmembers to constitute an open and generally parallelepipedal structure allowing free circulation of air inside the oven. The shelf support frame structure carries lateral slideways, for example in the form of U-shaped profiles, perpendicular to the anterior peripheral wall  6 , and conformed to receive sliding fashion and to support the lateral edges of horizontal shelves on which food to be cooked can be placed.  
         [0046]    The convection turbine  9  and the heating means  12 ,  13  or  14  are placed in the muffle  1  in direct communication with the cooking volume  81 , with no separating wall opposing the flow of air. There is merely provided a mechanical protection grid  22 , which is conformed and interposed between the cooking volume  81  and the combination of the convection turbine  9  and the heating means  12 ,  13  or  14 , to prevent mechanical contact of a user&#39;s hand with the blades of the rotating turbine or with the heating means. The mechanical protection grid  22  is of closed and enveloping cylindrical shape, with a cylindrical peripheral portion  23  and a plane front portion  24 . The mechanical protection grid  22  has mesh size that is sufficiently large not to impede the flow of air toward or away from the convection turbine  9  and sufficiently small for a user&#39;s fingers not to pass through them. The mesh size can for example be chosen from a range of values from approximately 2×2 mm to 8×8 mm. A mesh of approximately 4×4 mm can advantageously be chosen.  
         [0047]    In the embodiment shown in FIGS.  4  to  6 , using a gas burner  14 , the central region of the front portion  24  of the mechanical protection grid  22  carries a filter  29  or a grid of finer mesh, encouraging a regular flow of air around the gas burner  14  to stabilize the flame.  
         [0048]    Clearly, in the oven structure as defined above, the air discharged radially by the convection turbine  9  is guided only by the peripheral walls of the muffle  1 , and is distributed more freely throughout the cooking volume  81 . This achieves more even cooking.  
         [0049]    Simultaneously, there is nothing to oppose the free movement of splashed food particles that come from the food to be cooked in the cooking volume  81  and that can propagate into the whole of the interior cavity  8  of the muffle  1 , and especially toward the convection turbine  9  and the heating means  12 ,  13  and  14 . However, the free flow of air produces an effect of self-cleaning of the oven, and the particles do not remain in the area occupied by the convection turbine  9  and the heating means  12 ,  13  and  14 .  
         [0050]    To assure good convection of air, a convection turbine  9  with a generally cylindrical structure can advantageously be used, with a posterior flange  25  in the shape of a disc carrying a plurality of short blades  26  at the front and distributed around its periphery. The diameter D of the convection turbine  9  is preferably more than one third of the larger dimension (width or height) of the adjacent posterior peripheral wall  7 .  
         [0051]    In the embodiment depicted, the convection turbine  9  has at least twelve blades  26  at the front that have a radial dimension less than one tenth of its diameter D.  
         [0052]    Improved cooking can be achieved by causing the convection turbine to rotate in the reverse direction, thereby reducing the centrifugal thrust that the convection turbine  9  exerts on the air. The reverse direction is defined relative to the orientation of the blades  26 : in FIGS. 2 and 5, it can be seen that the blades  26  are inclined to the left relative to their corresponding radial direction C; by virtue of this orientation, the blades are efficient at pushing the air centrifugally when the turbine turns clockwise; in this case the reverse direction is the counterclockwise direction.  
         [0053]    The embodiments depicted further comprise a cleaning device  27  that sprays water into the muffle  1 .  
         [0054]    The cleaning device  27  can comprise a horizontal cup adjacent the center of the upper ceiling wall  3 , with central water supply means to produce a flow of water toward the periphery of the cup parallel to the upper ceiling wall  3 . The water is sprayed radially at the periphery of the cup, preferably when the oven is still relatively warm, and the water then flows over all of the peripheral walls of the oven as well as over the convection turbine  9  and the heating means.  
         [0055]    The particular structure of the oven according to the invention also enables correct operation as a combination oven, i.e. with steam in the cooking enclosure generated by an integrated steam generator.  
         [0056]    The present invention is not limited to the embodiments that have been described explicitly, but includes variants and generalizations thereof within the scope of the following claims.