Abstract:
A convection cooking appliance includes an oven cavity surrounded by an air channel assembly. The appliance includes heating units and a microwave generator arranged in the air channel assembly. A blower assembly is provided to generate a recirculating flow of air through the air channel assembly and the oven cavity. A controller, responsive to operator inputs, as well as signals from both temperature and pressure sensors located in the air channel assembly, regulates the activation/deactivation state of each of the components. One of the heating units in the air channel assembly is preferably constituted by an open coil heating element which is de-activated when the pressure is sensed to be below a specified threshold.

Description:
[0001]    The present application constitutes a continuation-in-part of U.S. patent application Ser. No. 09/902,655 filed Jul. 12, 2001, pending, which is a continuation of U.S. patent application Ser. No. 09/650,417 filed Aug. 29, 2000, now U.S. Pat. No. 6,291,808, which claimed the benefit of U.S. Provisional Patent Application No. 60/153,224 filed Sep. 13, 1999. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention pertains to the art of cooking appliances and, more particularly, to a convection oven incorporating a pressure sensor in a recirculating air flow path for use in controlling at least one heating element of the cooking appliance.  
           [0004]    2. Discussion of the Prior Art  
           [0005]    It is known in the art of cooking appliances to utilize multiple heating elements within a single oven cavity for use in connection with baking, broiling and/or cleaning modes of operation. It has also been proposed in the art to incorporate a fan within the cooking appliance to enhance the flow of heated air through the oven cavity in order to provide for a more uniform temperature distribution and reduce required cooking times within the oven.  
           [0006]    Regardless of these known prior art arrangements, there exists a need for further enhancements in the control of the heated air flow for a convection oven. More specifically, since the heating element(s) is actually being cooled by the convection air flow, it is possible to operate the heating element(s) at a higher temperature, which can further reduce cooking times. However, if a higher operating temperature is established and the air flow was decreased, the result could be damage to the heating element(s). When electric heating elements are employed, a high resistance short to the chassis of the cooking appliance can also be created.  
           [0007]    Based on the above, there exists a need in the art of cooking appliances for a convection oven arrangement with enhanced control features which enables one or more electric heating elements to operate at relatively high temperatures when a flow of air is directed across the heating element(s), while automatically reducing an operating temperature of the heating element(s) when the flow is disrupted.  
         SUMMARY OF THE INVENTION  
         [0008]    In accordance with the invention, a convection cooking appliance is provided with at least one electric heating unit disposed outside an oven cavity of the cooking appliance. More particularly, the heating unit is disposed in a duct section of an air channel assembly which extends about and is in fluid communication with the oven cavity. A flow of air is directed through the channel assembly by a blower. In the most preferred form of the invention, a pressure sensor is employed to sense air pressure within the air channel assembly. The pressure sensor is linked to a controller for the heating unit in order to reduce or interrupt a current supply to the heating unit when the air pressure drops below a threshold value.  
           [0009]    In the most preferred embodiment of the invention, the heating unit is centered in the air flow stream and arranged continuous from side-to-side. The heating unit preferably defines a single coil extending in various rows, with each of the coil rows being arranged substantially perpendicular to the flow of air. With this configuration, the heating unit tends to interrupt any developing patterns of air flow other than a linear flow in a desired direction. Furthermore, the pressure sensor is preferably positioned so as to sense the pressure in the air channel assembly directly adjacent the heating unit. 
       
    
    
       [0010]    Additional objects, features and advantages of the present invention will become readily apparent from the following detailed description of a preferred embodiment thereof, when taken in conjunction with the drawings wherein like reference numerals refer to corresponding parts in the several views.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a perspective, partial sectional view of a convection cooking appliance constructed in accordance with the present invention;  
         [0012]    [0012]FIG. 2 is a cross-sectional side view of the cooking appliance of FIG. 1;  
         [0013]    [0013]FIG. 3 is a schematic side view, similar to that of FIG. 2, of the cooking appliance; and  
         [0014]    [0014]FIG. 4 is a block diagram illustrating a control arrangement used in the convection cooking appliance of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]    With initial reference to FIGS.  1 - 3 , a cooking appliance  1  is schematically shown in the form of a wall oven. Appliance  1  includes an oven cavity  5  generally defined by a bottom wall  8 , a top wall  9 , a rear wall  10  and a pair of side walls, one of which is indicated at  11 . Oven cavity  5  also has associated therewith an access opening  13  for food items to be placed into or withdrawn from cavity  5 . About access opening  13  is provided a frontal plate  16 . In a manner known in the art, frontal plate  16  is adapted to be mounted against a substantially vertical wall such as in the kitchen of a residential home, and would have a door (not shown) pivotally attached thereto for selectively sealing off access opening  13 .  
         [0016]    Extending generally along top, bottom and rear portions of cavity  5  is an air channel assembly  26  defined by ducting that leads into and out of cavity  5 . More specifically, air channel assembly  26  includes a lower air return section  29 , an upper air delivery section  30  and a rear air transfer section  31 . Lower air return section  29  is open into cavity  5  through a substantially central return air outlet  33  formed in bottom  8 . In the most preferred form of the invention, return air outlet  33  is constituted by a generally circular insert provided with various spaced holes (not shown). In a similar manner, upper air delivery section  30  includes a discharge or delivery inlet  35  formed in top wall  9 . Although only partially shown in FIG. 1, inlet  35  is also preferably constituted by a generally circular-shaped insert which is attached to the remainder of upper air delivery section  30  and which is provided with a plurality of holes  37 .  
         [0017]    As will become more fully evident below, the particular construction of cooking appliance  1  can significantly vary in accordance with the present invention. More specifically, it is only important in accordance with the present invention that cooking appliance  1  include an air channel assembly, such as that discussed above with reference to assembly  26 , as well as a blower assembly, such as that generally indicated at  40 , for use in generating a circulating flow of air through oven cavity  5 . Although not considered a part of the present invention, a preferred construction for oven cavity  5  and air channel assembly  26  can be found in pending U.S. patent application Ser. No. 09/649,957 entitled “OVEN CAVITY CONSTRUCTION” filed Sep. 13, 1999 which is hereby incorporated by reference.  
         [0018]    In the preferred embodiment shown, cooking appliance  1  constitutes an electric appliance and, more specifically, a combination convection, microwave and radiant cooking device. As shown in this figure, cooking appliance  1  is provided with an annular filter basket  46 , having a multitude of circumferentially spaced holes  47 , which is positioned within lower air return section  29  and through which the air flowing from cavity  5  through return air outlet  33  is directed. Arranged below filter basket  46  is a microwave generator unit  48  incorporating a magnetron and mode stirrer (both not specifically shown).  
         [0019]    Encircling at least a portion of filter basket  46  is a first electric heating element  52 . Heating unit  52  is shown as constituted by a sheathed electric resistance heating element having upper and lower interconnected legs  53  and  54 . First electric heating unit  52  is preferably provided to heat return air flowing from oven cavity  5 , through outlet  33  and filter basket  56  prior to the air reaching a catalyst indicated at  57 . In a manner known in the art, catalyst  57  functions to eliminate smoke and the like from the air stream. As shown, catalyst  57  extends partially within a rotatable blower element  60  which forms part of blower assembly  40 . Although blower element  60  can take various forms while performing the desired air flow generating function, blower element  60  preferably constitutes a centrifugal unit arranged at the juncture of lower air return section  29  and rear air transfer section  31 . In general, blower element  60  is secured to a shaft member  62  that is rotatably mounted through a bearing assembly  64 . Shaft member  62  also has attached thereto, for non-relative rotation, a sheave  66  which is adapted to receive a belt (not shown) for use in rotating blower element  60  through shaft member  62  in combination with an electric motor (also not shown). As illustrated, sheave  66  is preferably arranged within a housing extension  68  which projects from rear air transfer section  31 .  
         [0020]    Preferably mounted in upper air delivery section  30  adjacent rear transfer section  31  is a second electric heating element arrangement  70  that is preferably constituted by a bank of open heating coils. Most preferably, second heating unit  70  is defined by a single open electric coil arranged in multiple rows, with each row running back and forth across essentially the entire width of upper air delivery section  30  so as to be substantially perpendicular to the direction of flow through upper air delivery section  30 . In any event, second heating unit  70  functions to further heat the air flowing through channel assembly  26  prior to the air reaching discharge inlet  35  as will be more fully discussed below.  
         [0021]    Also shown in this figure is a third electric heating unit  72  which, in a manner similar to first electric heating unit  52 , is preferably constituted by a sheathed, resistance-type heating element. Third electric heating unit  72  preferably extends adjacent top wall  9  and constitutes an additional heat source for cavity  5  of cooking appliance  1 . The particular manner in which first, second and third electric heating units  52 ,  70  and  72  are utilized during operation of cooking appliance  1  for a cleaning mode of operation is detailed in U.S. patent application Ser. No. 09/650,416 filed Sep. 13, 1999 entitled “SELF-CLEANING SYSTEM FOR A COOKING APPLIANCE” which is hereby incorporated by reference.  
         [0022]    As represented in FIG. 4, each of blower assembly  40 , microwave generator  48  and first, second and third electric heating units  52 ,  70  and  72  are linked to an appliance controller or CPU  73  and regulated based on established operator settings input at  74 , as well as signals received from a temperature sensor  75  and a pressure sensor  76 . The present invention is particularly directed to the manner in which cooking appliance  1  can be effectively operated, while assuring that one or more of heating units  52 ,  70  and  72  do not get overloaded due to a lack of air flow within air channel assembly  26 .  
         [0023]    First of all, a user of cooking appliance  1  can select, through operator input controls  74 , a convection cooking mode wherein heating element  52  is initially activated, along with blower assembly  40  and heating unit  70 , to direct a flow of recirculating air through oven cavity  5 . With this arrangement, heated air will be caused to flow within air channel assembly  26  and through holes  37  in order to impinge on food items to be cooked within oven cavity  5 . During operation, blower assembly  40  can produce a certain degree of turbulence which is considered detrimental to the uniform and consistent flow of air through channel assembly  26 . However, as indicated above, heating unit  70  is preferably constituted by various rows of open coils, with six rows of coils being shown in the preferred embodiment depicted in the drawings. Since the coils are open and arranged perpendicular to the flow of air, any turbulence developed by the operation of blower assembly  40  is transformed into a linear or laminar flow which enhances a smooth and continuous flow through oven cavity  5  for uniform heating.  
         [0024]    During a convection cooking mode of operation, heating unit  70  can be cycled on and off by controller  73  in dependence on the temperature of the air as signaled by sensor  75 , and the operation of heating unit  70  can be disrupted based on a pressure measured by pressure sensor  76  in air channel assembly  26  as will be discussed more fully below. Within the spirit of the invention, heating unit  70  can also be variably controlled, such as by establishing low, medium or high wattage settings. Although not shown, heating unit  70  is preferably, electrically linked to controller  73  through the use of a triac. Regardless of the particular operating status of heating unit  70 , blower assembly  40  and heating unit  52  are operated continuously throughout the convection cooking mode in accordance with the most preferred embodiment of the invention. The user of cooking appliance  1  can also select a microwave cooking mode wherein controller  73  activates generator  48 . Again, heating unit  52  is preferably, continuously operated whenever cooking appliance  1  is operational. Furthermore, in a cleaning mode, each of heating units  52 ,  70  and  72  are controlled for effective preheating and high temperature operation as referenced above.  
         [0025]    As clearly shown in the drawings, pressure sensor  76  is preferably mounted directly adjacent heating unit  70  and includes a sensing tube  80  having a first end portion  84 , which is arranged outside of air channel assembly  26 , an intermediate portion  88 , which is secured to and extends through a cover  90  for heating unit  70  by means of a mounting plate  92 , and a second end portion  95  which preferably angles down and towards a central zone of air channel assembly  26 . First end portion connected to a switch (not shown) which, in turn, is linked to controller  73 . On the other hand, second end portion  95  has a open end  98  exposed to within air channel assembly  26 .  
         [0026]    With this arrangement, pressure sensor  76  is used to sense the air pressure within air channel assembly  26 . As shown, pressure sensor  76  is located downstream of blower assembly  40  and, most preferably, directly adjacent heating unit  70 . In accordance with the most preferred form of the invention, when pressure sensor  76  senses that the air pressure in this portion of air channel assembly  26  falls below a specified threshold and signals the same to CPU  73 , CPU  73  functions to interrupt the flow of current to upper heating unit  70 . Preferably, heating unit  70  will not be energized when the air pressure is below the specified threshold. In this manner, heating unit  70  will be protected from damage and any potential high resistance short will be avoided when certain undesirable circumstances exists. Particularly, heating unit  70  will be interrupted if blower assembly  40  stops running, whether through a fault or controlled operation, the drive belt to blower  40  fails, or the bearings associated with blower  40  seize up. Therefore, the incorporation of pressure sensor  76  functions as a redundant safety circuit for the overall cooking appliance  1 .  
         [0027]    Although described with respect to a preferred embodiment of the invention, it should be recognized that various changes and/or modifications can be made to the invention without departing from the spirit thereof. For example, although the invention has been described as having pressure sensor  76  linked to heating unit  70  through CPU  73 , a pressure sensor  76  could be linked through a suitable switch to directly interrupt power to heating unit  70  when the pressure threshold requirement is met. In addition, it should be realized that signals from pressure sensor  76  can also be used in controlling the operation of heating unit  52  and/or  72  as well. Furthermore, it is contemplated that pressure sensor  76  can be relocated, preferably still within air channel assembly  26 , in accordance with the invention. In any event, the invention is only intended to be limited by the scope of the following claims.