Improved Gas Oven Using Flame Switching

1. Field of the Invention

This invention most generally relates to a method and device for flame switching the flame from a single burner tube in order to associate the flame and the energy of the flame with different and distant energy using systems.

This invention more generally relates to gas stoves used either commercially and/or in the home having a bake oven which may be self-cleaning and may have broil capability. More particularly the invention relates to a new flame switchable gas burning device or assembly which may be placed at the top rear corner of the oven cavity. The functions of bake, broil and self-clean are accomplished with a single burner tube in which the flame is switched in order to operate in the broil or in the bake/self-clean mode. In the broil mode the radiant heat to the broiled products is indirect radiant heat in that the flame does not "see" the broiling products.

2. Description of the Prior Art

Common gas oven configurations can be divided into two approaches: "The single cavity for bake and broil, and an oven which features a large bake cavity and a smaller drawer for broiling. The single cavity designs use two separate burners to achieve bake and broil conditions whereas the two compartment approach shares a common burner.

To achieve bake conditions the single oven utilizes a gas burner subassembly located under the floor of the oven. The hot products of combustion flow through openings in the oven floor and heat the oven surfaces and interior space. This method of heating prevents the baked goods from looking directly at the burner. Broiling is accomplished by exposing the top surface of the food product directly to a highly radiant burner subassembly.

In a single oven approach, a separate broil burner is mounted at the top of the oven cavity looking directly down on the oven space. Typical broil burners are radiant screen or blue flame burner where the flame rolls over a metal spreader. With either approach, the burner looks directly at the food imparting a high radiant heat flux to the product. A single oven cavity approach is the typical configuration used for obtaining pyrolytic cleaning or self-cleaning oven performance. This cleaning process occurs when the soiled surfaces of the oven cavity reach temperatures in excess of 800.degree. F. which usually corresponds to oven air temperatures in the range of 875.degree. F. to 925.degree. F. Maintaining this high temperature condition for an extended period of time will result in the reduction of food soils to a powdery ash residue. This cleaning process is most effective except in the regions of the door gasket where the short conduction paths to the cooler door result in somewhat cooler surfaces with resulting reduction in cleaning performance.

This single cavity gas range is a relatively recent advancement in oven design. In the older design, the oven is configured with a large baking oven cavity and a lower smaller broiler cavity. A single burner is mounted between the two cavities and this burner looks directly into the broiler drawer for the desired radiant input to the food. During bake the hot gases produced by the single burner flow through the oven floor into the bake cavity. This oven design is not typically or readily adapted or adaptable for self-cleaning temperatures.

U.S. Pat. No. 3,973,551 to Caselini et at discloses an arrangement which is substantially different from the subject invention in that it uses a single bottom burner combined with a recirculating fan or blower for circulating hot air throughout the oven. While the specification indicated that the oven can direct substantial heat from the top area, it is not specifically seen to disclose a capacity for broiling in the conventional sense.

German AS No. 1 241 080 is of interest as regards the disclosed invention in that it illustrates the use of a single top burner and a recirculating fan for heating an enclosed oven cavity. However, hot gases are not circulated through the oven, but rather around the oven cavity. Thus, there is not observed a broiling capacity and the overall arrangement is substantially different from the subject invention.

U.S. Pat. No. 3,659,579 to Henderson et al shows an oven capable of baking and broiling, as well as self-cleaning. A single burner at the top of the oven is utilized as both a broiling and baking burner, with a recirculating fan arranged to move hot air and products of combustion throughout the oven space. It is to be noted that broth broiling and baking heat are supplied from the top of the oven, with the burner having a two-position configuration for broiling or baking. The overall arrangement of the burner and recirculating fan are seen to be considerably different from that used the the subject invention as disclosed herein by Applicant.

U.S. Pat. No. 3,437,085 to Perry shows a single top burner arrangement for an oven that can bake, broil or self-clean. However, there is not seen to be disclosed in this patent any arrangement comparable to the recirculating/diverting fan arrangement used in the subject invention.

In addition to the comments above, it should be further noted that while both Henderson and Perry offer broiling and baking, they differ significantly from Applicant's Invention in that both use forced air (pressurized) burners and Henderson must use a manually operated damper to move between broil and bake as compared to flame switching and Perry uses two gas lines, three burner to move between broil and bake modes.

It would be advantageous to provide a gas fired oven having one burner which would operate in the broil, bake and self-clean mode and which would use one burner device and one oven cavity which would be used for both broiling and baking. It would also be advantageous if the oven did not require the use of complicated controls and devices in order to effect acceptable broiling and baking and where the emission standards and performance standards are met and/or exceeded using simple devices and simple controls.

The present invention in it's most simple form or embodiment is directed to a single tube burner device for use as a broiler in a gas stove having an oven cavity. The gas burner device is comprised of a burner tube having a plurality of flame holes so situated on the burner tube so that a flame will develop in a direction toward the oven front. Because of the combination of a flame spreader plate and a shield plate positioned relative to each other and relative to the burner tube so as to define a broil flame channel and because of fresh air which is directed onto the burner tube through an upper and a lower gap the flame will develop onto or attach to the upper surface of the shield plate and be below the downward facing surface of the spreader or within the broil flame channel defined by such two surfaces. The shield plate is heated and radiates heat to the product which is to be broiled. The broil flame channel height diminishes going from the burner tube toward the front or forward facing channel opening. The channel further slopes upward from the burner tube toward the front-facing broil channel opening to substantially compensate for the natural buoyancy of the broil flame.

By including a means for creating a low pressure zone above and rearward of the burner tube of the above described broiler device, the device becomes a flame switchable gas burning device. The flame which is established as a broil flame and which is established within the broil flame channel will, when a low pressure zone is created above the burner tube, shorten and bend and develop into the low pressure zone which physically may be a draw vent. The flame is shortened and is used to heat the air which is circulated through the low pressure zone and back into the oven cavity. Such heat is convection heat and is useful for baking products within the oven cavity. Without the low pressure zone, which typically may be created by a hot air pump or blower, the flame is a broil flame which provides heat for radiant heating. Turning on the hot air pump and thereby creating the low pressure zone causes the flame to switch and become a source of convection heat for baking and for oven self-cleaning.

This invention is also directed to a method of flame switching in order to associate a flame and the energy of the flame with different and distinct energy using systems. The flame is caused to be established in a first direction to being established in a second direction, that is the flame is switched, by the method of establishing a flame in the first direction, providing a source of fresh air directed toward the source portion of the flame and creating a low pressure zone or a negative pressure field in a region proximate to the source portion of the flame and directed in the second direction thereby causing the flame to switch and be established in the second direction. Again, by providing a low pressure region or i.e., a negative pressure zone or region in addition to the other elements such as the fresh air etc., the flame is caused to switch from being established in a first direction to being established in a second direction. In effect, the flame is bent into the low pressure zone and thus switches from providing heat or energy to a first energy using system associated with the first direction to providing heat to a second energy using system associated with the second direction. Such a feature provides a convenient and simple method for using a single burner in multiple functions. It should be understood that it is possible to switch the flame so that it can be used for more than two isolated and separate functions.

It is a primary object of the present invention to provide a method of flame switching in order to use a single source of flame as a heat or energy source for a plurality of functions.

It is another object of the invention to provide a method for broiling, baking and self-cleaning in an oven cavity of a gas stove.

A further object of the present invention is to provide an improved gas stove which has better broiling, baking and self-cleaning characteristics than currently available gas stoves and which meet or exceed the established ANSl Z-21.1 emission standards and has a temperature profile which meets or exceeds all ANSl gas oven design requirements.

It is a still further object of the invention to provide a flame switchable gas burning device which is attachable within an oven cavity of a gas stove which device makes the oven a broil or a bake/self-clean oven simply by causing, by the creation of a low pressure zone, the flame emanating from the flame ports of the burner tube to switch from being established in the broil flame channel when there is now low pressure zone, to being established in the direction of the low pressure zone within, typically, a draw vent located to the rear of and above the flame ports.

These and further objects of the present invention will become apparant to those skilled in the art after a study of the present disclosure of the invention.

FIG. 1 is a schematic representation of the invention operating in the broil mode;

FIG. 2 is a schematic representation of the invention operating in the bake mode.

FIG. 3 is a perspective view of a gas stove utilizing the flame switchable gas burning device illustrating the air flow and the flame configuration when the stove is operated in the broil mode;

FIG. 4 is a perspective view of a gas stove utilizing the flame switchable gas burning device illustrating the air flow and the flame configuration when the stove is operated in the bake/self-clean mode;

FIG. 5 is a side sectional view of an oven having the flame switchable gas burning device mounted within the oven and illustrating the draw vent, recirculation air duct, recirculation air distribution plenum, fresh air vent and the upper and lower gaps formed by the burner tube and the edges of the fresh air vent and also illustrating an example or possible geometry of the broil flame channel;

FIG. 6 is an exploded perspective view of the flame switchable gas burning device illustrating the fresh air vent, the draw vent, the burner tube and a means for creating a broil flame channel;

FIG. 7 is a schematic pictorial illustrating a cross section of the flame switchable gas burning device having a broil flame; and

FIG. 8 is a schematic pictorial illustrating a cross section of the flame switchable gas burning device having a bake flame.

The following is a description of the preferred embodiment of the invention. While the flame switchable character of the device, the method for switching the flame and the flame attachment to a surface of a shield plate is the fundamental nature of the invention, for the purpose of illustration, the method and device of the instant invention will be described primarily with regard to how the device and method is used within a gas stove and particularly within an oven cavity of a typical consumer type of gas stove appliance. It is understood that the flame switchable gas burning device as illustrated and described herein may have different dimensions and variations of the illustrated basic geometry.

Refer now to FIGS. 1, 2, 3, 4, 7 and 8 which illustrate, in several ways, the basic operation of the invention in the broil mode and the bake/self-clean mode. FIGS. 1, 3 and 7 illustrate that when the blower 40 is in the off or broil position, such that no recirculation air 32 is flowing or such that no low pressure zone 30 is created in the proximity of the burner tube 10, the broil flame 14 from the burner tube flame ports 12 will follow the upper surface 56 of the broil flame channel shield plate 54 toward the broil flame channel opening 62. The shield plate 54 is consequently heated and such heat is radiated from the downward facing surface 58 of the shield plate 54 thereby broiling the product within the oven cavity 8 by indirect radiant heat. FIGS. 2, 4 and 8 illustrate that when the blower 40 is turned on i.e., a low pressure zone 30 is created above and to the rear of the burner tube 10 the broil flame 14 will shorten and will bend into the draw vent 34 wherein the low pressure zone 30 is established. The flame switches from a broil flame 14 to a bake flame 16 as a consequence, in part, of the low pressure zone 30 and the increase flow of fresh air 22 which is directed across the burner tube 10 by the fresh air vent 20 through an upper gap 26 and a lower gap 28 defined to be proximate to the burner tube 10. Incorporating a recirculating air duct 36 which is connected to the draw vent 34 and the input side of the blower assembly 38 and a recirculating air plenum 44 which is in air communication via a recirculating air duct 42 with the output side of the blower assembly 38 causes the flow of heated recirculation air 32 through the oven cavity 8. The plenum 44 is typically located on or in the bottom surface of the oven cavity 8 and is configured to evenly distribute the heated recirculation air 32 throughout the oven cavity 8. In both the broil and bake/self-clean modes an amount of exhaust air 72 exhaust from the oven cavity 8. The amount which exhausts is adequate to balance the flow of fresh air 22 into the system. In the broil mode, the amount of fresh air 22 is less than when the device 5 is operating in the bake/self-clean mode. It should be pointed out that the amount of air which is exhausted and thus the amount of fresh air 22 that is brought into the system is less than in conventional prior art ovens. In part because the fresh air 22 is delivered by the fresh air vent 20 via the upper and the lower gaps 26 and 28 directly to the broil flame 14 and to the bake flame 16 and the flame ports 12 in the broil and the bake/self-clean modes, complete combustion of the flame is effected even though the recirculated air 32 is low in oxygen. It should be further noted that as a result of, in part, the directing of the fresh air 22 directly to the burner tube 10 and the flames 14 and 16 and flame ports 12, the oven cavity 8 heat up time and efficiency, in all the modes of operation, is improved.

FIGS. 3 and 4 illustrate in perspective views the flame configuration and path and the air flow through the oven cavity 8 when the device 5 is mounted in or attached to the upper rear region of the oven cavity 8 of a gas stove. FIG. 3 illustrated the operation in the broil mode and FIG. 4 illustrates the bake/self-clean mode respectively.

The present invention is illustrated in FIG. 5 as an improved gas stove having a gas fired oven 70 which can perform bake, broil and self-clean operations. This oven design 70 utilizes a single burner tube 10 located at the top of the oven cavity 8. The flame switchable gas burning device 5 is configured so as to create a low radiant flame or bake flame 16 required for baking and for self-clean and a high radiant flame 14 necessary for broiling. In the instant invention, the partially premixed atmospheric tube burner 10 which is located parallel to the back wall of the oven fires towards the center of the oven cavity 8. The flame created is either directed towards the center of the oven cavity 8 for broiling, or is turned or pulled into a draw vent 34 to create the low radiant flame or bake flame 16 needed for the bake/self-clean mode. The flame bending or flame switching into the draw vent 34 is accomplished by the use of a hot gas recirculation blower 40 which supplies the suction necessary for flame switching. Suction of the flame and its products of combustion into the draw vent 34 are channeled to the suction or input side of the blower assembly 38 by means of a hot gas or draw duct 36 which runs outside and parallel to the back wall of the oven cavity 8. Oven air is also drawn into the draw vent 34 and subsequently into the draw duct 36 and is also mixed with the products of combustion. The output of the blower assembly 38 is directed via a recirculation air duct 42 to a recirculation air distribution plenum 44 which is located within and along the bottom of the oven cavity 8. This method of recirculating oven air and hot combustion products to the bottom of the oven cavity 8 creates a force convection flow through the oven cavity 8 and it introduces the heat input to the cavity 8 in such a manner that it can rise and flow past the bake products in a manner that produces uniform product cooking. A negative pressure or a low pressure field 30 is created and must be controlled such that the flame is not pulled off the burner tube 10, and so that the flame is bent in such a manner that it does contact a surface before combustion is essentially complete and that the low pressure field 30 is uniform over the length of the burner tube 10 to ensure that all flames are directed into the draw vent 34. The draw vent baffle plate 31, illustrated in FIG. 6, may be used for and operates to equalize the blower suction across the length of draw vent 34. Successful flame bending is accomplished by providing sufficient space between the burner tube 10 relative to the draw vent 34 so that the flame can complete combustion before it enters the recirculation air duct 36. The bake flame 16 must enter the draw vent 34 without impinging upon any obstruction and be short enough so that it does not impinging upon any part of the draw vent 34 or upon any part of the draw duct 36. There must also be provided enough unobstructed space in front of the burner flame ports 12 to allow the flame to bend without impinging on any part of the device 5.

The drawing and mixing of oven air or recirculation air 32 with the products of combustion in the recirculation air duct system 34, 36, 38, 40, 42, and 44 produces the oven recirculation and it reduces the temperature of air flowing through the duct system. Typical recirculation flows reduce recirculation air temperatures in the duct system to temperatures less than about 800.degree. F. depending upon the setting of the oven bake temperature. These surprisingly low temperatures, even when the stove is operating in the self-clean mode make possible the use of standard oven materials such as e.g. aluminized steel. Since the stove during the bake mode has recirculated through the oven cavity 8 recirculation air 32 which contains the products of combustion and a resulting lower than normal concentration (21% by volume) of oxygen past the flame, the fresh air 22 required for secondary combustion must be delivered to the region of the burner flame ports 12. The addition of the fresh air 22 at this location ensures that the flame sees the desired level of oxygen to complete combustion, and it allows the oven cavity 8 to operate at excess air or fresh air 22 (sometimes referred to as wash through air) levels that promote efficiency of oven heating. In order to operate a prior art oven in a recirculation mode, excessive amounts of secondary or fresh air would be required in order to obtain the needed oxygen level for proper combustion of the gas at the burner ports. This large flow of air through the prior art oven results in a very inefficient oven requiring excess gas input for normal heat up times.

To deliver fresh secondary air i.e., fresh air 22 to the flame ports area, a fresh air vent 20 approximately equal in length to the burner tube length is located relative to the burner tube 10 and the flame ports 12 so that there is provided an upper and a lower gap 26 and 28 respectively which gaps 26 and 28 direct fresh air 22 to the flame ports 12. Also a fresh air duct 24 is created outside of the back wall of the oven cavity 8 which is in air communication with the fresh air vent 20 and ambient air. The action of drawing air up the duct 24 is created by the venting of exhaust air 72 from the oven cavity 8 by means of the exhaust vent 74 typically located on the top wall of the oven cavity 8 and forward of the front-facing broil flame channel opening 62. Air flow out of the oven cavity 8 creates an oven condition which in turn draws air into the oven maintaining a mass flow balance through the oven cavity 8. The recirculation blower 40 assists in the fresh air injection via the gaps 26 and 28 but the blower 40 does not have to operate when the improved oven 70 is operating in the broil mode. Adequate fresh air is vented to the flame ports 12 so that the broil flame 14 is lengthened but completes combustion as it travels toward the front of the oven cavity 8. The broil flame 14 extends from the burner tube flame ports 12 substantially to the broil flame channel opening 62 and is attached to the shield plate 54 and within the broil flame channel 50 because of the fresh air injection and because of the relationship of the shield plate 54 to the burner tube 10 and to the spreader plate 52.

When the improved gas stove 70 is operated in the broil mode the blower 40 is not operating and no recirculation air 32 flows. Consequently less fresh air 22 is directed to the flame ports 12 and the flame thus directs itself toward the front of the oven cavity 8 within the broil flame channel 50 and essentially on the upward facing surface 56 of the shield plate 54. Because of the lesser amount of oxygen rich air i.e. fresh air 22 at the flame ports 12 the flame must burn longer in order to complete combustion and therefore the broil flame 14 extends forward seeking the oxygen needed. Combustion will be complete about when the leading edge of the broil flame 18 reaches the front-facing broil flame channel opening 62. The shield plate 54 is evenly heated and this heated surface looks down onto the food to provide the necessary radiant heat flux for broiling. In FIG. 6 there is shown a radiant heat equalizing plate 59 which may be used to further "even-out" the distribution of radiant heat flux. The broil flame 14 attachment to the upward facing surface 56 of the shield plate 54 requires that the shield plate 54 slope upward and forward toward the front the oven cavity 8 and that a spreader plate 52 be located above the shield plate 54 to further confine the broil flame 14 and that a sufficient sized front-facing broil flame channel opening 62 exist so as to allow the broil flame 14 to "roll up" the shield plate surface 56 and toward the exhaust vent 74. The broil flame 14 is contained substantially between the spreader plate 52 and the shield plate 54.

In another embodiment of the invention incorporates a right and a left broil flame channel enclosure panels 64 and 66 respectively. With reference to FIG. 6, it is noted that these panels can be adapted as needed by placing apertures 63 therein to more evenly distribute the broil flame 14 over the shield plate surface 56.

It is thought that the flame switchable gas burning device of the present invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the form, construction and arrangement of the parts thereof without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely a preferred or exemplary embodiment thereof.