Electric heating – Microwave heating – With diverse-type heating
Reexamination Certificate
2003-01-27
2004-04-20
Leung, Philip H. (Department: 3742)
Electric heating
Microwave heating
With diverse-type heating
C219S400000, C219S757000, C126S02100R
Reexamination Certificate
active
06723970
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to the art of cooking appliances and, more particularly, a cooking appliance including a forced-air convection system having a partitioned duct assembly adapted to mix a plurality of air flows within the appliance.
2. Discussion of the Prior Art
In general, cooking appliances that perform a cooking process using a forced air convection air flow are known. Typically, forced air convection systems direct a heated air flow into an oven cavity. In operation, the heated air flow circulates about the oven cavity and impinges upon the food item to perform the cooking process. Of the many design considerations that must be accounted for when designing forced air systems, ventilation is perhaps the most important.
There are two key factors to be considered in the design of an oven ventilation system. The first is the volumetric flow rate of a re-circulating air flow. If the air flow rate is too high, cooking performance is compromised and, in addition, the time required to pre-heat the oven is increased. The higher the flow rate, the more difficult it is to transfer thermal energy into the air flow to raise the temperature of the convection air stream. Accordingly, the prior art is replete with examples of forced air convection ovens requiring secondary heating systems. Additional heating elements are often placed either below or in a bottom portion of the oven cavity to serve as an additional heat source for raising the temperature of convection air streams to the appropriate level.
The second key factor in the design of a ventilation system is the conditioning of the exhaust air flow temperature. If the exhaust air flow is too hot, then ventilation components must be designed to prevent high temperatures from transferring to surrounding cabinetry or to other areas of the appliance or the kitchen. Also, an exhaust air flow that is maintained at too high a temperature will lower the efficiency of the oven by carrying off a portion of the heat required for cooking. Therefore, heat exiting the oven in the exhaust must be replaced in order to maintain an uniform cooking environment.
Alternatively, too low an exhaust air flow, and deposits begin to form on the surfaces of the ventilation system. During cooking, food byproducts in the form of fats, grease and the like enter the forced air flow. These byproducts can accumulate on the surfaces of the ventilation system and, in the presence of a low exhaust air flow, develop into smoke which could ultimately enter into kitchen areas. Accordingly, the ventilation system must be designed to reduce the amount of food byproducts entering the air flow such that the remainder can be easily carried from the system.
The prior art includes several examples of ventilation systems which attempt to mitigate the problems associated with the accumulation of food byproducts. In general, manufacturers have designed systems that maintain the byproducts solely within the cooking chamber. In this fashion, grease build-up in the ventilation system is minimized. However, these designs require shorter intervals between cleaning operations in order to maintain the thermal efficiency of the oven. Other designs require the incorporation of a catalyst material which serves to enhance the combustion of the byproducts. While the use of a catalyst can be effective, it adds to the overall cost of the appliance.
Accordingly, there exists a need in the art for a cooking appliance including a forced air convection venting system that will enable a more efficient thermal transfer between heating components and the air flow.
Particularly, there exist a need for a ventilation system that can reduce the air flow rate and, in addition, condition the temperature of the exhaust air flow.
SUMMARY OF THE INVENTION
The present invention is directed to a cooking appliance including an oven cavity and a forced air convection system having a convection fan, a heating element and a duct assembly. Specifically, the duct assembly includes an oven air inlet portion and an incoming air inlet portion. The oven air inlet portion is partitioned into first and second compartments adapted to receive both an incoming and oven air flows.
In accordance with a preferred form of the invention, the cooking appliance performs a convective cooking process through operation of the fan assembly at a convection fan speed. In this manner, oven and incoming air flows are combined in the first compartment prior to being passed into the forced air convection system and over the heating element to establish a heated, convective air flow. At this point, the heated air flow is introduced into the oven cavity. Similarly, the oven and incoming air flows are combined in the second compartment to form a tempered exhaust air flow which is subsequently carried from the cooking appliance through associated exhaust ducting.
In a preferred form of the invention, the first compartment is constituted by ⅔ the overall cross-sectional area of the duct assembly and the second compartment by the remaining one third. In this manner, a controlled, mixed product of the oven and incoming air flows moderates the temperature of the incoming air while, at the same time, maximizing the volume of air passing over the heating element. With this arrangement, the presence of smoke and smoke generating byproducts are substantially eliminated from the oven air flow without the need for a catalyst.
In further accordance with the preferred embodiment, the cooking appliance of the present invention includes a convection baking function. Specifically, in a bake mode, the convection fan is operated at less than half the normal convection cooking speed to enhance the overall thermal conductivity between the heating element and the recirculating air flow. Most preferably, the convection fan is operated at approximately one-quarter the convection fan speed such that a uniform heating environment is established within the oven cavity. In this manner, a food item can undergo a baking process without being exposed to the higher speed air typically associated with convection cooking. This arrangement eliminates the requirement for an additional baking element, typically arranged either on or below a lower portion of the oven cavity.
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patent: 4802459 (1989-02-01), McFadden et al.
patent: 5406932 (1995-04-01), Joseph et al.
patent: 5674425 (1997-10-01), Hong
patent: 5918589 (1999-07-01), Valle et al.
patent: 6344637 (2002-02-01), Lee et al.
Diederiks & Whitelaw PLC
Leung Philip H.
Maytag Corporation
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