Electric heating – Microwave heating – With diverse-type heating
Reexamination Certificate
2001-07-06
2002-06-04
Leung, Philip H. (Department: 3742)
Electric heating
Microwave heating
With diverse-type heating
C219S400000, C219S685000, C219S748000, C219S762000, C219S757000, C126S02100R
Reexamination Certificate
active
06399930
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a combination convection/microwave oven and, in particular, to a convection/microwave oven that is capable of cooking food products by convection energy alone or by a combination of convection and microwave energy.
It is customary in the food service industry to use convection ovens to cook food items, such as bakery products, meat products, vegetable products and the like. It is also customary to use standard cooking utensils, such as an one-half size standard restaurant pan.
Ovens that use both microwave energy and thermal energy transferred by convection are described in U.S. Pat. Nos. 4,358,653, 4,392,038 and 4,430,541. For example, U.S. Pat. No. 4,430,541 discloses an oven having a source of microwave energy disposed in a bottom of the oven's cooking chamber and a blower arranged in a side wall to produce a heated airflow. A food product in a container is situated above the microwave source and in the path of the heated airflow. In ovens of this type, the container is positioned in the microwave energy pattern so that substantially all of the microwave energy is incident on the bottom of the container.
A combination oven in which the effect of reflected microwave energy is diminished is described in U.S Pat. No. 4,410,779. The oven has a microwave coupler that produces a heating pattern in which the major portion of microwave energy impinges directly on a food body and is substantially absorbed thereby, before reflection from the oven walls. For the circumstance where there is no food body, the food body is small or the food body is positioned on a metal dish, the reflected radiation has a substantial phase cancellation in the coupler and is re-reflected back into the cooking chamber. To further reduce the effect of reflected microwave energy, the oven walls are constructed of a material that partially absorbs the microwave energy so as to prevent the build up of high intensity field patterns in the oven.
Another combination oven is described in U.S. Pat. No. 4,691,088. This oven uses a pair of stacked trays with microwave energy being introduced to the cooking cavity via the bottom thereof. Power transfer in the oven is automatically responsive to the dielectric load of the food. A forced hot air system blows hot air into the cavity so as to impinge upon the food from above. This oven has a singular purpose to cook food solely by a combination of microwave energy assisted by forced hot air or convection. It has no capability to operate solely in a convection mode. In addition, this oven situates the lower tray at distances from the bottom of the cavity that result in extremely poor transfer of microwave energy to food on the tray. In addition, this oven is incapable of cooking food items without the use of a specially designed rack and tray.
Microwave energy can thaw and cook food products rapidly, but it generally does not provide surface finishing, browning, or other characteristics provided by cooking in an oven environment. Accordingly, microwave ovens with added thermal convection energy have become popular in the restaurant industry. When prior art combination convection/microwave ovens have been used to cook frozen food products, such as biscuits, pies and other bakery goods, dark spots and other non-uniformities often form on the food product. Food products with dark spots are unsightly and, therefore, unpalatable to customers.
The dark spots are formed due to non-uniform energy transfer to and within the food product during the cooking process. The temperature of a frozen food product, for example, can be non-uniform due to conditions existing in the freezer, to non-uniformity of the food product itself, to the package that contains the food product and/or to conditions that occur in the oven. When thawing and/or cooking a frozen food product in prior art ovens, the bottom of the product is warmed by the direct impingement of the microwave energy. However, the top and sides of the food product are being warmed by the heated airflow. The frozen food product cools the heated airflow so as to affect the cooking or thawing temperature of the top and sides. This effect is known as the chill factor as it is similar to the wind chill factor produced by wind on a cold day. As the food product continues to thaw and then to cook, the sides and top remain cooler than the bottom and, thus, enhance the formation of the dark spots or other indications of non-uniform cooking.
Additionally, prior art combination convection/microwave ovens require the use of microwave transparent cooking containers, such as those made with ceramic or glass. This reduces the flexibility of means of thermal transfer and may affect the characteristics of the cooked products.
Thus, there is a need for a combination convection/microwave oven that can rapidly thaw, cook and/or brown food products with increased uniformity of interior and exterior properties.
There is also a need for a combination convection/microwave oven that is capable of cooking food products situated on a microwave reflective dish or pan.
There is also a need for a combination oven that can operate solely in a convection mode or in a combined convection and microwave mode.
SUMMARY OF THE INVENTION
A combination oven of the present is operable in a normal cook mode to cook food in a normal cook time and in a fast cook mode to cook food in a faster time. When in the normal cook mode, the oven uses only convection heat. When in the fast cook mode, the oven uses both convection heat and microwave heat.
According to one aspect of the invention, the convection heat is a heated airflow that is circulated through a cooking chamber that is in fluid communication with a plenum. The heated airflow is formed as a laminar pattern that has a first laminar air stream above the rack and a second laminar air stream below the rack. At least one of the laminar air streams has a pair of loops that share a common path toward an egress port area. The laminar air streams are created by spaced apart ingress port areas for each laminar air stream and a common egress port area.
According to another aspect of the invention, the microwave energy is introduced through a bottom of a cooking chamber. A rack is disposed in the near field of the microwave energy at a height above the cooking chamber bottom such that a random wave guide is formed between the chamber bottom and the bottom of a microwave reflective pan. The random wave guide directs the microwave energy via a spacing around the pan into a region above the rack where it is reflected by the chamber walls and top to impinge upon a food product in the pan from its sides and top. The chamber walls, top and bottom are highly microwave reflective. The height is preferably in a range of about 2.0 inches to about 3.25 inches.
According to yet another aspect of the invention, a stirrer distributes the microwave energy uniformly in cooking chamber to avoid hot spots forming on the food products.
The oven of the invention is extremely flexible as the pan may be a one-half size standard restaurant pan. On the other hand, the food may be placed directly on the rack or in a microwave transparent container and still be cooked by microwave energy and convection heat in a fast cook mode.
According to the method of the invention, the microwave energy is directed between the chamber bottom and the bottom of the reflective pan and through a spacing about the pan to a region above the pan. Hot air is circulated above and below the pan. According to another aspect of the method of the invention, microwave energy is introduced into the cooking chamber and hot air is circulated through the cooking chamber in a laminar airflow pattern. The laminar airflow has one laminar air stream above the level and second laminar air stream below the level.
REFERENCES:
patent: 3569656 (1971-03-01), White et al.
patent: 4283614 (1981-08-01), Tanaka et al.
patent: 4332992 (1982-06-01), Larsen et al.
patent: 4335290 (1982-06-01), Teich
patent: 4358653 (1982-11-01), Weiss
patent: 4
Day William
Harter David
Molloy Paul
Leung Philip H.
Ohlandt Greeley Ruggiero & Perle LLP
The Garland Group
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