Patent Publication Number: US-6712063-B1

Title: Ovens with catalytic converters

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to ovens with catalytic converters for removing airborne grease particles. The invention relates to any type of oven, but is particularly applicable to microwave combination ovens. 
     It is known to use catalytic converters in ovens in order to flamelessly oxidise oxidisable components in the hot air from the cooking chamber. For example, a recycling oven using such a catalytic converter is described in International Patent Application Number PCT/US98/10736. In this oven hot air from the cooking chamber is passed through a catalytic converter before being returned to the cooking chamber. 
     One disadvantage of the arrangement described in international application number PCTIUS98/10736 is that daily cleaning is required for the ducting which directs hot air from the cooking chamber to the catalytic converter. A further disadvantage is that the air-flow within the cooking chamber is somewhat uneven. 
     The present invention seeks to overcome at least some of the disadvantages of the prior art. 
     SUMMARY OF THE INVENTION 
     According to the invention there is provided an oven comprising a number of chamber walls defining a cooking chamber, heating means for heating food within the cooking chamber, at least one opening in at least one of the chamber walls, fan means for driving air out of the cooking chamber through said opening, a grease filter attached substantially directly to the one of the chamber walls and a catalytic converter located downstream of said grease filter. 
     It will be appreciated that, because the grease filter is placed close to the cooking chamber, the labour involved in cleaning any ducting leading to the grease filter, required in the prior art, is avoided. 
     In different embodiments, the catalytic converter is located within 20, 10 or 5 centimeters of said opening. 
     The catalytic converter may be located substantially immediately adjacent the grease filter. 
     In a preferred embodiment there are no other components between the catalytic converter and the opening except the grease filter. 
     Conveniently, the air which is driven out of the cooking chamber is recirculated back into the cooking chamber after passing through the catalytic converter. 
     The oven may be a microwave combination oven. In such ovens heating of the food is achieved by a combination of microwave energy and electric heating elements. 
     There may be two such openings each provided with a catalytic converter having the features described above. 
     In this case, each opening may be provided with a separate fan. 
     The openings may be provided in opposite side walls of the oven. 
     An electric heating element may be provided to heat air in the cooking chamber. 
     The heating element may also be arranged to emit infrared radiation directly onto food within the cooking chamber. 
     In this case the electric heating element may be provided directly behind one of the chamber walls which is provided with perforations which allow the chamber wall both to transmit infrared radiation from the electric heating element and to reflect microwave radiation back into the cooking chamber. 
     The oven may further comprise a rotatably driven turntable for rotating food to be cooked within the cooking chamber. 
     The invention will now be more particularly described, by way of example only, with reference to the accompanying figures, which show two embodiments of microwave combination ovens constructed in accordance with the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a microwave combination oven provided with two air outlets; and 
     FIG. 2 shows a second embodiment in which the fans are located at the rear of the oven. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a cross-sectional view of a microwave combination oven  2  viewed in schematic form from above. The oven  2  comprises a cooking chamber  4  defined by two side walls  6  and  8 , a rear wall  10 , a front door  12 , a base  14 , and an upper wall (not shown) connected to the side walls  6  and  8  and the rear wall  10  above the base  14 . The front door  12  is hinged to the side wall  6  by hinges  16 , and can be opened to gain access to the cooking chamber  4 . 
     A rotating turntable  18  is mounted on the base  14  in known manner. Food within the cooking chamber  4  can be cooked by microwave energy provided by a microwave source (not shown) or by an electric heating element  20 , or by a combination of both in known manner. It is for this reason that such ovens are referred to as “combination” ovens. 
     In order to allow infrared radiation from the heating element  20  to fall directly on the food to be cooked, the rear wall  10  is provided with a plurality of perforations (not shown) and the heating element  20  is located directly behind the rear wall  10 . Furthermore, the inside surfaces of the walls of the cooking chamber  4  are formed from reflective stainless steel, which ensures that infrared radiation from the heating element  20  bounces around within the cooking chamber  4  in order to reach the food on the turntable  18  from substantially all directions. It will be appreciated that such infrared radiation is useful in browning the surface of the food to be cooked, if this is required. 
     The side walls  6  and  8  are provided with respective side openings  22  and  24 . Two fans  26  and  28  are provided for circulating air from within the cooking chamber  4 . The air is drawn out of the cooking chamber  4  through the two openings  22  and  24 , and re-enters the cooking chamber through the perforations formed in the rear wall  10 . Ducting  19  is provided to direct the air from the fans  26  and  28  to the rear wall  10 . The flow path of the air is illustrated by arrows  30  within the cooking chamber  4 , and by arrows  32  outside of the cooking chamber  4 . 
     The side openings  22  and  24  are provided with grease filters  34  and  36  attached to the side walls  6  and  8  respectively. These filters filter out large splatters of grease from food being cooked within the cooking chamber  4 . The grease filters  34  and  36  can be of any suitable type, including paper or electrostatic grease filters. The fact that grease filters  34  and  36  are attached to the side walls  6  and  8  avoids the need to clean any ducting between the side walls  6  and  8  and the grease filters  34  and  36 , as is necessary in the prior art mentioned above. 
     Catalytic converters  38  and  40  are attached directly to the grease filters  34  and  36  in order to flamelessly oxidise oxidisable components in the hot air which has passed through the grease filters  34  and  36 . This process also releases additional heat, which assists the cooking process. The catalytic converters  38  and  40  are formed from a metallic monolith containing the elements Iron, Chromium and Aluminium, onto which is deposited a catalytic coating containing Platinum together with one or more elements in the Lanthanide Series. 
     It will be appreciated that because the catalytic converters  38  and  40  are attached directly to the grease filters  34  and  36  there is no ducting leading to the catalytic converters  38  and  40  from the cooking chamber  4 , and the labour involved in cleaning such ducting is therefore avoided. There may of course be some ducting between the grease filters  34  and  36  and the catalytic converters  38  and  40 , but this should be kept to a minimum, and is ideally less than 20 cm. In this embodiment of the invention, the catalytic converters  38  and  40  are spaced approximately 2.5 cm from the openings  22  and  24 . 
     The fans  26  and  28  are connected directly behind tho catalytic converters  38  and  40 . 
     The cooking chamber  4  has a height of 31.5 cm, a depth of 33 cm, and a width of 33 cm. The side openings  22  and  24  are substantially circular, of diameter about 13 cm, and are formed by perforating the side walls  6  and  8  by circular holes of diameter 4.2 mm. A number of areas of similar perforations are also used in the rear wall  10 . These perforations allow the flow of air, while ensuring reflection of microwave radiation. 
     In the second embodiment shown in FIG. 2 like parts are given like reference numbers. The fans  26  and  28  are located towards the rear of the oven. The openings  22  and  24  are provided with triangular shaped grease filters  34  and  36  attached to the side walls  6  and  8  respectively. The catalytic converters  38  and  40  are attached directly to the grease filters  34  and  36 . This arrangement allows a more compact oven to be produced whilst ensuring that the ducting  19  remains free from any grease contamination. 
     It will also be appreciated that because there are two openings in the side walls of the cooking chamber  4 , each provided with a separate fan, the air-flow within the cooking chamber  4  is more even, and the food within the cooking chamber  4  cooks more evenly, than would be the case if only a single opening was provided. However, ovens having only a single opening are also included within the scope of the invention.