Electric heating – Microwave heating – With diverse-type heating
Reexamination Certificate
2000-10-24
2002-04-23
Leung, Philip H. (Department: 3742)
Electric heating
Microwave heating
With diverse-type heating
C219S683000, C219S400000, C219S702000, C126S02100R
Reexamination Certificate
active
06376817
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a compact quick-cooking convection oven and more particularly to such an oven which is suitable for residential use that is, use in a home as opposed to a commercial establishment.
Compact quick-cooking convection ovens designed primarily for use in commercial establishments are described in U.S. Pat. Nos. 5,254,823; 5,434,390; 5,558,793; and 5,927,265 (hereinafter “the cited prior art ovens”), which patents are incorporated herein by reference. Such ovens have proven themselves to be satisfactory in use in a variety of commercial establishments. However, they are not uniquely adapted to meet the requirements for residential use where considerations of available voltage, size, warm-up time, operating and purchase costs, and the like may be quite different.
For example, an oven according to the cited patents, for use in a commercial establishment, may have cooking chamber dimensions of 5″ high by 18″ deep×18″ wide. By way of contrast, an oven suitable for residential use should preferably have cooking chamber dimensions about 12″ high×14″ deep×24″ wide. As another example, an oven situated in a commercial establishment will generally have available to it three phase 220-240 voltage. By way of contrast, in a residence in the U.S.A. the available power for an oven will generally be single phase 220-240 voltage. As a further example, an oven for use in a commercial establishment may have a substantial warm-up period (for example, thirty to sixty minutes) since the oven is only turned on once during the work day (typically well before any customers are allowed to enter the establishment) and then kept on throughout the work day. By way of contrast, an oven suitable for use in a residence should have a very brief warm-up time (typically less than 10 minutes), since it will probably be turned off between meals (that is, about three times a day), with a warm-up time being required after each turn-on. For the above-mentioned reasons and numerous others, a residential oven must adjust or compromise various features in order to achieve the same highly desirable rapid cook time as the commercial oven of the cited patents.
The cited prior art ovens feature opposed primary energy flows with flows of hot gas striking the upper surface of a food product within the cooking chamber and with microwave energy being launched upwardly from the floor of the oven into the lower surface of the food product. To provide bottom side convection heat transfer, the hot gas flow is pulled around the sides of the food product (from the upper surface thereof) and across the bottom of the surface of the food product by a low pressure gas return passage located directly below the food product. This produces a hot gas “shroud effect” about the food product. The desired hot gas flow beneath the lower surface of the food product is accomplished by using a food product-supporting, microwave-transparent, ceramic cooking platter which forces the gas flow along the lower surface of the food product (the food product being supported above the cooking platter by standoffs) before the gas flow can pass downwardly through the hole(s) of the cooking platter and exit downwardly from the cooking chamber.
The microwave energy is launched from below and enters the food product only after passing through the microwave-transparent cooking platter.
To generate the desired bottom launched microwave feed into the cooking chamber, a microwave launch cavity and wave guide feed are located below the cook chamber. The launch cavity is roughly 9 inches in diameter and 5 plus (1½ wavelengths desired) inches high, with a mode stirrer located near the top of the cavity. This cavity typically projects about 1 inch into the cooking chamber cavity. It is isolated from the cooking process by an environmental seal which is a 9 inch diameter microwave-transparent window (high temp) and a grease/water seal to prevent water from entering into the microwave launch area. This resonant cavity couples the microwave energy primarily directly to the food, with secondary cavity coupling. As a result, the volume associated with the microwave launching/feed kit is large and has the effect of limiting the overall product packaging (e.g., oven size) and configuration (reduced cooking chamber size given the launch cavity volume). It also negatively impacts the cooking chamber design because it limits cleaning of the chamber bottom. Given the large diameter can, the microwave feed, and the plug seal, the current microwave kit is complex and expensive to manufacture. It also requires a mechanically/motor driven mode stirrer (motor/gearbox, shaft, microwave seal, and stirrer blade) located in the launch cavity. In addition, the construction of the launch cavity, its ¼ wavelength matching feed section, and the plug seal (microwave transparent window and environmental seal) is expensive.
In the cited prior art ovens the platter channeled the hot gas flow below the food and had three primary functional requirements: (1) to support the food, (2) to stand the food off the platter upper surface and thereby create an gas flow path between the platter and the food, and (3) to be microwave transparent so that the electromagnetic microwave energy launched from below the food can pass through the food support (platter). These requirements lead to the use of a cast ceramic platter which has the desired microwave transparency properties and can be formed with a number of standoffs used to create flow channel(s) defined by the platter upper surface and the bottom surface of a food item or cooking dish. In addition, the ceramic plate is cast with several holes which permit the gas flow to exit the flow channels to the blower return. This sophisticated cast ceramic part is expensive, fragile, and difficult to clean.
Further, the platter is complicated and difficult to produce. For the platter to provide adequate heat transfer to the food, a substantial portion of the gas flow must be channeled between the food and platter. To achieve this, the platter must have a tight fit (small clearance) to the oven walls in order to prevent the gas flow from by-passing around the platter and flowing directly to the gas return passage. Minimizing flow by-pass between the platter and the door, coupled with the door features for controlling microwave leakage, has resulted in the oven door covering the cook zone, such cook zone being defined by the platter at the bottom, the cavity roof at the top, and the oven walls therebetween. In essence, a two cavity oven results: an upper chamber containing the cook zone, and a lower zone below the upper chamber containing the gas return space. Such a two cavity construction is more expensive to produce, given the presence of the lower chamber or return gas volume which is not required for standard ovens. This lower chamber also results in additional cleaning difficulties for the user or consumer as the platter must be removed and the lower chamber cleaned of food or grease that may spill passing through the holes in the platter, or be deposited by the gas carrying grease/food particles flowing through space below the upper chamber.
In the cited prior art ovens, both the convection heating subsystem and the microwave heating subsystem are electrically powered, with the majority of the power expended being allocated to the convection heating elements. The primary energy flows are as follows:
1. Convection Top: Hot gas flow heat transfer onto the upper surface of the food;
2. Microwave Top: Microwave energy input that passes through the cooking platter, but “misses” the food, reflects off the upper surfaces of the cooking chamber, and becomes absorbed by the food through the food upper or side surfaces;
3. Convection Bottom: Convection heat flow across the lower surface of the food; and
4. Microwave Bottom: Microwave energy input from the bottom of the cooking chamber, through the platter, through the bottom surface of the food pr
Gidner John David
McFadden David H.
Pool, III James K.
Winkelman Earl R.
Amster Rothstein & Ebenstein
Leung Philip H.
TurboChef Technologies, Inc.
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