GB2383125A

GB2383125A - An oven with microwave and resistance heating means.

Info

Publication number: GB2383125A
Application number: GB0129557A
Authority: GB
Inventors: Gavin John Coleman
Original assignee: Ceramaspeed Ltd
Current assignee: Ceramaspeed Ltd
Priority date: 2001-12-11
Filing date: 2001-12-11
Publication date: 2003-06-18
Anticipated expiration: 2021-12-11
Also published as: GB2383125B; GB0129557D0

Abstract

An oven comprises an oven cavity 17 with a main heating means (23 Fig1) and an auxiliary heating means 33. The main heating means may be a magnetron and the auxiliary heating means may be resistance element 33 and a fan 29 disposed in the base 3 of the cavity. A duct 31 guides the hot air to an aperture 35 in the oven cavity for heating the lower region of the food 27 placed on a supporting means, preferably a turntable 19 or a wire shelf. Preferably the aperture 35 is disposed in the cavity so that the hot air is directed between the base and the underside of the turntable. A vane arrangement 37 is disposed on the base for guiding the hot air. Preferably the vane is disposed so that it extends around the periphery of the turntable. The oven could be constructed so that the main heating source is any one of the heating means or that it is a grill element radiating heat downwardly towards the food.

Description

OVEN WITH AUXILIARY HEATING MEANS This invention relates to an oven with auxiliary heating means.

Ovens, such as microwave ovens and fan-assisted ovens, generally have one or more main heating means at the top or in an upper region of an oven cavity. Nevertheless, it is known to incorporate an auxiliary heating means in the region of the base of the oven cavity. Such an auxiliary heating means is generally employed because current rapidcook ovens, such as microwave ovens and top-grill ovens, cook the top and upper region of a food item placed in the oven cavity more effectively than the bottom or lower region thereof.

It has been proposed to arrange an auxiliary heating means beneath the lower wall of the oven cavity of a microwave oven, but such an arrangement has the disadvantage that it is necessary first to heat the base of the oven cavity and then to rely on conduction and convection from the base to the food item being cooked. In cases where the oven is provided with a turntable, the turntable forms a further barrier to the transfer of heat to the food item being cooked.

It has also been proposed to provide a secondary heating means within the oven cavity of a microwave oven. Such an

arrangement is known, for example, from US-A-3 172 987 and US-A-4 326 113. According to US-A-3 172 987 a sheathed resistance heating element is mounted slightly above the base of the oven cavity beneath a turntable. A similar arrangement is shown in US-A-4 326 113 except that the sheathed heating element substantially protrudes beyond the periphery of the turntable. The arrangement of a sheathed heating element within the oven cavity has the disadvantage that the heating element is relatively exposed and readily becomes soiled, while being relatively difficult to clean.

It has further been proposed in US-A-4 132 216 to provide a hot air oven for heating food-loaded cartridges which are arranged in an annular array on a turntable. Air is heated at the top of the oven cavity and blown by a propeller into the hollow core formed by the annular array, such that part of the air passes through holes in the cartridges and past food containers therein, while the remainder of the air passes through a flow passage beneath the cartridges and above the turntable. The arrangement of a heating element and a propeller within the oven cavity gives rise to the disadvantage that the internal components are difficult to clean, while the propeller is potentially dangerous and requires to be shielded from the user.

It is therefore an object of the present invention to provide an oven with auxiliary heating means which overcomes or ameliorates the above disadvantages.

According to the present invention there is provided an oven comprising an oven cavity, a main heating means for heating a food item placed in the oven cavity and auxiliary heating means arranged in the base of the cavity for heating a lower region of the food item, the auxiliary heating means including an aperture in the oven cavity for directing hot air towards the lower region of the food item.

The main heating means may comprise a resistance heating element and fan means for propelling air past the heating element and into the oven cavity. In such a case, the auxiliary heating means may include means for conveying a portion of the air heated by the resistance heating element of the main heating means to the aperture of the auxiliary heating means.

Alternatively or additionally, the main heating means may comprise a magnetron.

The main heating element may further comprise a grill element for directing radiation downwardly towards the food item.

The auxiliary heating means may comprise a resistance heating element and fan means for propelling air past the heating element and to the aperture.

The oven may include means for supporting the food item above the base of the oven cavity. The supporting means may comprise a turntable. The turntable may be formed with a recess in the lower surface thereof.

The aperture may be adapted to direct hot air between the supporting means and the base of the oven cavity.

The base of the oven cavity may incorporate a vane arrangement for guiding the passage of hot air between the base and the supporting means. The vane arrangement may include a vane extending substantially around the periphery of the supporting means. The peripheral vane may be interrupted in the region of the aperture and may be provided with outwardly extending vane portions to guide air from the aperture to a location below the supporting means. Further vane portions may be provided within an area defined by the peripheral vane for guiding air beneath the supporting means.

For a better understanding of the present invention and to show more clearly how it may be carried into effect reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 is a plan view of an embodiment of a microwave oven incorporating an auxiliary heating means according to

the present invention, the top of the oven being omitted for clarity; Figure 2 is a front elevational view of the microwave oven shown in Figure 1, with the door of the oven removed for clarity; Figure 3 is a side elevational view showing, on a larger scale, details of part of the microwave oven shown in Figures 1 and 2; Figure 4 is a plan view of the base of the oven cavity together with the turntable and illustrating one embodiment of an air flow pattern beneath the turntable; Figure 5 is a partial cross-sectional view showing in more detail part of the turntable and a vane arrangement beneath the turntable; Figure 6 is a plan view of an embodiment of a fan-assisted oven incorporating an auxiliary heating means according to the present invention, the top of the oven being removed for clarity; and Figure 7 is a front elevational view of the fan-assisted oven of Figure 6 with the door removed for clarity.

The microwave oven shown in Figures 1 and 2 comprises a body having a top 1, a base 3, a back 5, side walls 7 and 9 and a door 11 provided with a handle 13 for opening and closing the door. A control panel 15 is provided for controlling operation of the oven. Provided within an oven cavity 17 is a turntable 19 which is rotatable in known manner when the oven is in operation. A plurality of feet 21 are provided beneath the oven body to support the oven on a suitable surface (not shown).

A magnetron, shown diagrammatically at 23, is provided in a chamber behind the control panel 15 and functions as a main heating means to supply microwaves in known manner into an upper region of the oven cavity 17 as indicated by arrows 25. The microwaves are very effective in heating the upper part of a food item 27, but are not as effective in heating the lower part of the food item.

The upper part of the food item 27 may additionally be heated with a grill heater (not shown) provided in the top 1 of the oven body and directed downwardly onto the upper part of the food item.

However, while the magnetron and a grill, if provided, effectively heat the upper part of the food item, the lower part of the food item is not effectively heated and this can lead either to the upper part of the food item being over-cooked or the lower part of the food item being under-

cooked. Either case is visually undesirable, while undercooking of the lower part of the food item can be hazardous to health.

According to the present invention there is provided in the lower region of the oven cavity an auxiliary heating means.

The auxiliary heating means is not required to provide heat to the entire oven cavity, only to the lower region of food item 27. Thus the heating capacity of the additional heating means can be relatively low.

The auxiliary heating means is shown diagrammatically in Figure 3 and comprises a fan 29 driven by an electric motor (not shown) which draws air as shown by the arrows into a duct 31 and propels the air past a resistance heating element 33 of known form which heats the air. The hot air then passes further along the duct 31 and enters the oven cavity 17 by way of an aperture 35 positioned substantially at the bottom of side wall 9 of the cavity adjacent the base 3 such that the hot air passes between the turntable 19 and the base 3 in order to heat the lower region of the food item (not shown in Figure 3) supported on the turntable 19.

As best shown in Figure 4, the flow path of hot air beneath the turntable 19 as indicated by arrows 39 is controlled by a vane arrangement 37. The vane arrangement comprises a substantially circular vane running beneath the periphery

of the turntable in order to reduce the escape of hot air from beneath the turntable until the air has given up its heat. The circular vane is interrupted in the region of the aperture 35 and is provided with outwardly extending vane portions to guide air from the aperture 35 beneath the turntable 19. The vane arrangement includes further vane portions beneath the turntable in order to guide the hot air to all regions of the underside of the turntable.

Clearly numerous alternative vane portions could be provided to fulfil a similar function.

The peripheral vane of the vane arrangement 37 is shown in more detail in Figure 5 and shows that the vane arrangement can be formed in the base by moulding or pressing, for example. Also shown in Figure 5 is a recess formed in the lower face of the turntable 19 in order to form with the vane arrangement 37 a chamber for the hot air beneath the turntable 19.

Clearly the auxiliary heating means can take other forms.

For example, hot air may be provided to the aperture 35 from a source of hot air to be directed primarily into an upper region of the oven chamber. Alternatively, a portion of unheated air to be circulated around the upper region of the oven cavity may be propelled past a suitable heater and provided to the aperture 35. Further, the fan and heater shown in Figure 3 can take alternative forms. What is

required is a means for providing a supply of hot air to the aperture 35.

The fan-assisted oven shown in Figures 6 and 7 comprises a body having a top 51, a base 53, a back 55, side walls 57 and 59 and a door 61 provided with a handle 63 for opening and closing the door. A control panel 65 is provided for controlling operation of the oven. Provided within an oven cavity 67 is a turntable 19 which is rotatable in known manner when the oven is in operation.

A main resistance heating element 71 is provided behind the back 55 of the oven cavity and a fan 73 propels air past the heating element and distributes the hot air around the oven cavity for relatively even heating of the top and sides of a food item 75 to be heated. The fan will generally be provided with a protective cover, but such cover is omitted from Figure 7 for clarity. The hot air from the main heating element 71 is very effective at heating the upper part of the food item 75, but is not as effective at heating the lower part of the food item.

The upper part of food item 75 may additionally be heated with a grill heater 77 provided in the region of the top 51 of the oven body and directed downwardly onto the upper part of the food item.

However, while the hot air from the main heating element 71 and grill 77, if energised, effectively heat the upper part of the food item 75, the lower part of the food item is not effectively heated and this can lead either to the upper part of the food item being over-cooked or the lower part of the food item being under-cooked. This differential is exacerbated if the grill 77 is used in addition to the main heating element 71. Either case is visually undesirable, while under-cooking of the lower part of the food item can be hazardous to health.

According to the present invention there is provided in the lower region of the oven cavity an auxiliary heating means including an aperture 35 positioned substantially at the bottom of the back 55 of the oven cavity adjacent the base 53 such that hot air issuing from the aperture 35 passes between the turntable 19 and the base 3 in order to heat the lower region of the food item 75 supported on the turntable. The auxiliary heating means is not required to provide heat to the entire oven cavity, only to the lower region of food item 75. Thus the heating capacity of the additional heating means can be relatively low.

The auxiliary heating means can take essentially the same form as the auxiliary heating means shown in Figure 3 in which a fan 29 driven by an electric motor propels air past a resistance heating element and conveys the hot air to the aperture 35.

The vane arrangement shown particularly in Figures 4 and 5 may also be used, but has been omitted from Figures 6 and 7 for clarity.

Clearly the auxiliary heating means can take other forms.

In particular, a portion of the air heated by the main heating element 71 may be directed to the aperture 35.

Further, the fan and heater shown in Figure 3 can take alternative forms. What is required is a means for providing a supply of hot air to the aperture 35.

It should be noted the turntable 19 is not always required, particularly in relation to fan-assisted ovens. If the turntable is omitted an alternative means (not shown), such as a wire shelf, is provided to support the food item 27, 75 a short distance above the base of the oven cavity in order that the hot air can effectively heat the lower region of the food item.

Claims

CLAIMS 1. An oven comprising an oven cavity, a main heating means for heating a food item placed in the oven cavity and auxiliary heating means arranged in the base of the cavity for heating a lower region of the food item, the auxiliary heating means including an aperture in the oven cavity for directing hot air towards the lower region of the food item.
2. An oven as claimed in claim 1, wherein the main heating means comprises a resistance heating element and fan means for propelling air past the heating element and into the oven cavity.
3. An oven as claimed in claim 2, wherein the auxiliary heating means includes means for conveying a portion of the air heated by the resistance heating element of the main heating means to the aperture of the auxiliary heating means.
4. An oven as claimed in any preceding claim, wherein the main heating means comprises a magnetron.
5. An oven as claimed in claim 2,3 or 4, wherein the main heating element further comprises a grill element for directing radiation downwardly towards the food item.

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6. An oven as claimed in any preceding claim, wherein the auxiliary heating means comprises a resistance heating element and fan means for propelling air past the heating element and to the aperture.
7. An oven as claimed in any preceding claim and including means for supporting the food item above the base of the oven cavity.
8. An oven as claimed in claim 7, wherein the supporting means comprises a turntable.
9. An oven as claimed in claim 8, wherein the turntable is formed with a recess in the lower surface thereof.
10. An oven as claimed in claim 7,8 or 9, wherein the aperture is adapted to direct hot air between the supporting means and the base of the oven cavity.
11. An oven as claimed in any one of claims 7 to 10, wherein the base of the oven cavity incorporates a vane arrangement for guiding the passage of hot air between the base and the supporting means.
12. An oven as claimed in claim 11, wherein the vane arrangement includes a vane extending substantially around the periphery of the supporting means.

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13. An oven as claimed in claim 12, wherein the peripheral vane is interrupted in the region of the aperture and is provided with outwardly extending vane portions to guide air from the aperture to a location below the supporting means.
14 An oven as claimed in claim 12 or 13 and including further vane portions within an area defined by the peripheral vane for guiding air beneath the supporting means.
15. An oven substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.