BACKGROUND OF THE INVENTION

Field of Invention This invention relates to a convection oven with an integral fan for improving the efficiency.

Description of the Prior Art It is known in the prior art to improve the cooking efficiency in ovens by reducing the uneven distribution of hot air and the temperature differences within the oven cooking cavity by means of a fan located within the oven cavity. Ovens employing this technique are commonly called convection ovens. It is much less well-known in the prior art to vary the direction of the air currents within the cooking cavity, in order to increase the even distribution of hot air. JP 9152131A2 "Convection oven" discusses a set of louvre panels with variable pitch, set into a wall of the oven cavity. Varying the pitch changes the direction of the hot airflow passing over the louvres into the oven cavity. The temperature differences within the oven cavity are said to be reduced by a more efficient circulation of the hot air. A similar mechanism is discussed in JP 2003185141 A2 "Heating cooker". The angle of a single louvre is adjusted to direct the flow of hot air from a fan either towards the upper or the lower part of an oven cavity. It is said that food items placed in the top or bottom of the cavity will be cooked more evenly.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an oven with an improved air distribution system, or one which will at least provide the public with a useful choice, hi a first aspect the present invention consists in an oven, comprising: an inner casing forming a cooking cavity, a heater for heating air in said oven, a fan located outside said cooking cavity, an air flow path leading air from said cooking cavity to said fan, and returning air to said cooking cavity from said fan, a fan cover or shroud, located in a panel of said inner casing, containing an arrangement of openings through which air can pass, said shroud rotating in use, and located in the path of air returning to said cooking cavity from said fan. To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred form of the present invention will now be described with reference to the accompanying drawings in which Figure Ia is a perspective view of an oven used with preferred embodiment of the current invention, showing the front of the oven with the door open, also showing the control panel, the oven cavity, the inner casing, the shroud and inner casing aperture. Figure Ib is a perspective view of an oven used with the alternative embodiment of the current invention, showing the front of the oven with the door open, also showing the control panel, the oven cavity, the inner casing, the shroud and inner casing aperture, and hidden detail of the gas burner. Figure 2a is a cutaway side view of the preferred embodiment, showing the oven casing and frame, the air flow path within the oven, the air heating element around the perimeter of the fan, the rotating shroud, and their respective motors. Figure 2b is a cutaway side view of the oven casing and frame in an alternative embodiment, showing the outer casing, the inner casing, the cooking cavity, the gas burner at the lower rear of the oven, the air flow path within the oven, the fan, the rotating shroud, and their respective motors. Figure 3a is a side view of the centrifugal fan and shroud assembly of the preferred embodiment, with two associated motors also shown, plus a simplified diagrammatical representation of the hot air flow through the centrifugal fan and shroud. Figure 3b is a side view of the centrifugal fan and shroud assembly of the alternative embodiment, with the two associated motors also shown, plus a simplified diagrammatical representation of the hot air flow through the radial fan and shroud Figure 4 is a detail diagram of the shroud, showing the preferred layout of the concentric hole rings and louvred pockets. Figure 5 is a detail diagram of the shroud, showing the airflow path for the preferred embodiment

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS While the invention is susceptible to embodiment in different forms, two specific embodiments are shown in the drawings, and described in detail. The present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that as illustrated and described herein. The present invention consists of a fan with a rotating perforated and louvred faceplate cover or shroud, used in combination with, and integral to, a typical convection oven of either the gas or electric type. The fan is located between the oven outer casing and the oven inner casing. The oven inner casing is shaped to form a cooking cavity. The fan shroud is located in an aperture in the inner casing. The oven, fan and shroud combination provide an improved cooking efficiency over and above that previously known in the prior art, by distributing the hot air within the cooking cavity of the oven in a more even manner. With reference to Figures Ia, 2a, 3a and 5, a typical range (domestic gas stove/oven combination) 1 such as might be used with the current invention is shown. The shroud 3 is located in an aperture 103 in the rear wall of the inner casing 102, between a duct 101 and the cooking cavity 4. A fan 2 is located in the duct 101 directly behind the shroud 3. hi the preferred embodiment, the fan 2 is of the centrifugal type. The centrifugal fan 2 draws the air in through the holes 9 in the shroud 3, as shown by arrows 402 in Figure 2a, and then blows the air outward over a heating element 400, which is located around the perimeter of the centrifugal fan 2. A heating element cover 404 ensures that at least the majority of the heated air passing over the heating element 400 is directed back into the cooking cavity 4 through the louvred pockets 10, as shown by the arrows 401. In this embodiment, the air path leads in through the holes 9, over the element 400, and out through the pockets 10. As the shroud 3 is rotating, the direction of the hot airstream changes as it passes through the louvred pockets 10, giving a more even distribution of the hot air within the cooking cavity 4, and ensuring that hotspots do not develop (that is, areas within the cooking cavity 4 where the temperature differs enough from the temperature at another point so that any food within the cooking cavity 4 is in danger of being cooked unevenly). In an alternative embodiment, as shown with reference to Figures Ib, 2b and 3b, an air exit 104 is located at the lower front of the cooking cavity 4, allowing air to pass from the cooking cavity 4 into the duct 101. The duct 101 leads from the air exit 104 of the cooking cavity 4 back to the aperture 103, via the burner 8. The burner 8 is located in the duct 101, below the radial fan 403. In this embodiment, the air path leads from the cooking cavity 4, through the duct 101, to the fan 403 and then through the pockets 10 back to the cooking cavity 4. In this alternative embodiment, a stream of hot air 11 is generated by the electric heating element or gas burner 8. The hot air 11 rises by natural convection up that part of the duct 101 that passes between the rear wall of the inner casing 102 and the rear wall of the oven outer casing 5. The hot air 11 is sucked into the radial fan 403, and is then blown through the louvred pockets 10 and holes 9 of the rotating shroud 3 into the cooking cavity 4, the direction of the hot airstream being shown by arrows 12. As in the preferred embodiment already described, this results in a more even distribution of the hot air within the cooking cavity 4, and ensures that hotspots do not develop. The shroud 2 and fan 3 can be driven from a single common motor, with the shroud suitably geared to achieve the desired fan/shroud speed ratio. However, in the preferred embodiment, the shroud motor 7 and a separate fan motor 6 are located behind the fan 2. The typical rotation speed of the centrifugal fan 2 is in the region 0 - 4000 rpm, the speed being controlled by adjusting the power of motor 6, which is controlled via a circuit connecting the motor 6 to the oven control panel 13. The rotation speed of the shroud 3 is similarly controlled by controlling the speed of motor 7, and lies in the range 0 -20 rpm. In the alternative embodiment, the layout is similar, with radial fan 403 being substituted for centrifugal fan 2. The motors 6, 7 are connected to the shroud 3 and centrifugal fan 2 by any suitable connection means, such as nested drive shafts, these connection means being well known in the prior art. A connection mechanism such as this has the advantage of allowing the motors 6, 7 to be located remotely from the fan 2 and shroud 3. It has been found that having the fan 2 and the shroud 3 driven by separate motors 6, 7 as in the preferred embodiment offers at least the following advantages. As the shroud 3 is driven independently of the fan 2, the fan 2 and shroud 3 can be driven at different speeds and speed ratios as required. This offers users an advantage as different speed ratios can be used for different cooking conditions. Also, the shroud 3 can be kept stationary with just the fan 2 rotating if the item or items being cooked require this particular condition. This can be achieved by adjusting the outputs of the two motors independently, without the need for complex gearing to be used to provide the different speed ratios. A further advantage of using two motors is that the fan 2, shroud 3, and the fan and shroud motors 6 and 7 can be incorporated into the overall design and the layout of the range 1 in such a way that the least amount of space is occupied, and the motors 6 and 7 can be located remotely from the shroud 3 and fan 2. Also, the separate fan and shroud motors 6 and 7 can be positioned in relatively low temperature areas, away from the hot air stream, without the need to use complex gearing of the type that would be required if the fan 2 and shroud 3 were located remotely from their associated motors 6 and 7. The shroud 3 is formed from a flat circular metal plate of radius 300mm. The shroud can be made of any material that has good high temperature characteristics and which can be easily formed into the required shape. In the preferred embodiment, the shroud 3 is pressed steel plate. The plate has a central hole 301 through which a drive means 405 passes. Shroud 3 is attached to the drive means 405 by a nut/washer combination, tight fit, or similar. That part of the drive means 405 which protrudes into the cooking cavity 4 has a domed cover 14 fitted for cosmetic purposes, and to cover any sharp edges so that the cooking cavity 4 can be cleaned and maintained easily. Four concentric rings 302 of closely and evenly spaced small circular holes 9 are drilled, punched out or otherwise machined around central hole 301. In the preferred embodiment, the radius of the outermost one of the concentric rings 302 is 108mm. Between the outermost of the rings 302 and the rim of the shroud 3 are a series of louvred pockets 10. The louvred pockets 10 pass through the shroud 3, and are evenly spaced to form a generally circular pattern. In the preferred embodiment, the angle of the louvres is 45 degrees, and the pocket openings are 50 mm long, and 8 mm deep. The louvres deflect air passing through the shroud. hi the preferred embodiment, the louvred pockets 10 all open on the side of the shroud 3 which faces into the cooking cavity 4. The louvred pockets 10 are all aligned so that their openings are parallel. To help achieve an even circulation of air, half of the openings of the louvred pockets 10 face in one direction, and the other half face in the diametrically opposed direction, with those of said pocket openings which face in the same direction grouped together, so that it is possible to divide the shroud 3 into two semi-circular areas 302 and 303, with half the louvred pockets 10 in semi-circular area 302, facing away from the other half of the louvred pockets 10 in semi-circular area 303. The area of the shroud perforated by the holes 9 is balanced with the area of the shroud perforated by the louvred pockets 10, so the total area perforated by the holes 9 is substantially the same as that perforated by the louvred pockets 10. The pattern of holes 9 and pockets 10 described above has been found to give an extremely efficient distribution of hot air within the cooking cavity 4.