US3590804A

US3590804A - Self cleaning gas fired oven

Info

Publication number: US3590804A
Application number: US796756A
Authority: US
Inventors: John A Welshofer; Earl T Rhinehart
Original assignee: Magic Chef Inc
Current assignee: Magic Chef Inc
Priority date: 1969-02-05
Filing date: 1969-02-05
Publication date: 1971-07-06
Anticipated expiration: 1988-07-06

Abstract

An oven cavity having an upper broil burner and a lower bake burner both of which are supplied with air from a motor driven blower and a centrifugal switch disables both burners when the blower stops. A first selector places both burners in operation for cleaning or conditions the apparatus for cooking and first thermostat cuts the broil burner out when cleaning temperature is approached. A second cooking selector and thermostat selects one of the burners for cooking operation. Hot gases from the oven are discharged into surrounding air after being diluted and cooled by air from the blower.

Description

United States Patent [72] inventors John A. Welshofer Cleveland; Earl T. Rhinehart, Apison, both of. Tenn. [21] Appl. No. 796,756 [22] Filed Feb. 5, 1969 [45] Patented July 6, 1971 [73] Assignee Magic Chef Inc.

Cleveland, Tenn.

[54] SELF CLEANING GAS FIRED OVEN 4 Claims, 9 Drawing Figs.

[52] U.S.Cl 126/21, 126/41 [51] int. Cl A2lb l/28, F24c 3/00 [50] FieldofSearch 126/21,2l A, 39, 39 C, 39 E, 39 G. 39 J, 41

[56] References Cited UNITED STATES PATENTS 3,033,463 5/1962 Doner et al. 126/39 J UX Primary ExaminerCharles J. Myhre Attorney-Bacon & Thomas ABSTRACT: An oven cavity having an upper broil burner and a lower bake burner both of which are supplied with air from a motor driven blower and a centrifugal switch disables both burners when the blower stops. A first selector places both burners in operation for cleaning or conditions the apparatus for cooking and first thermostat cuts the broil burner out when cleaning temperature is approached. A second cooking selector and thermostat selects one of the burners for cooking operation. Hot gases from the oven are discharged into surrounding air after being diluted and cooled by air from the blower.

JOHN A. WELSHOFER BY EARL T AH/NEHART ATTORNEYS PATENTFH m 6191i SHEEY 2 OF 6 IM'EM'ORS JoH/v H. WELSHOFER EARL 7. AH/NEHART ATTORNEYS PATENYHIJIIL 619?! 3,590,804

sum u [1F 6 M2 92 I26 CLEAN CONDITION g sacme SOLID 5T0 TIME 02m 95 IBRO/L All? 5w.

case memo. 25%

BY ERRL Z' RH/NEHART \d/ fl w/A7691 ATTORNEYS SELF CLEANING GAS FIRED OVEN CROSS REFERENCE TO RELATED APPLICATIONS The upper or broil burner shown in the present'application is the subject of a copending application filed by us on Dec. 2, 1968, Ser. No. 780,402, now U.S. Pat. No. 3,5] l,223. The pilot burners shown herein are fully described and claimed in the copending application of Earl T. Rhinehart, Ser. No. 770,77l, filed Oct. 25, 1968, now U.S. Pat. No. 3,510,240.

BACKGROUND OF THE INVENTION This invention relates to gas-fired ovens, and particularly to such ovens having features providing for pyrolytic self-cleaning thereof.

The technique of cleaning ovens by subjecting the same to high temperatures for a substantial period of time has recently been adopted. Heretofore such technique has been more or SUMMARY OF THE INVENTION The present invention solves the prior problems mentioned above by providing a source of slightly compressed fresh air to both the broil and brake burners and to the pilot burners therefor to ensure that all burners will ignite and operate under any and all oven conditions. A safety feature is provided whereby the burners are disabled in the event of failure of the blower to supply the required air to the burners. Compressed air is supplied not only to the main burners but also to the pilot burners to ensure reignition under all conditions that might exist in the oven. A further feature of the invention resides in the discharge of a stream of fresh air into the exhaust flue to thereby dilute and precool the hot gases discharging from the oven, particularly during a cleaning cycle. The self-cleaning oven employs both an upper broil burner and a lower brake burner, the broil burner being used during a self-cleaning cycle for a preheating step and is automatically turned off as the temperature approaches the desired temperature tobe maintained for self-cleaning. A further feature of the invention resides in sealing means between the oven door and the door opening so arranged and positioned to initially prevent deposit of cooking residue in the normally narrow channel opening between the door and door frame and further serving to insulate the outer surface of the door from the high oven temperature involved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational view, partly in section, of an FIG. 5 is an enlarged fragmentary vertical sectional view through a portion of the oven door seal;

N66 is a schematic diagram of the piping and conduits serving the oven; and

FIGS. 7, 8 and 9 are schematic circuit diagrams showing'the condition of the control circuits during baking, broiling, and cleaning cycles, respectively.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring first to FIGS. 1 through 6, numeral 2 indicates generally, by way of illustration, a gas range only schematically shown but which it is understood may include the usual top burners and other conventional features. The oven-defining portion of the range includes an outer metal shell 4, an inner metal shell 6 defining an'oven cavity 8, and thermoinsulation 10 between the

walls

4 and 6. The front wall of the oven cavity is provided with an oven door opening 12 and a swingable door 14 mounted on suitable hinges, not shown. In the upper portion of the oven cavity 8 is an upper or broiling burner 16, the details of which are more fully disclosed and claimed in the copending application Ser. No. 780,462, now US. Pat. No. 3,511,223 previously referred to. However, the broil burner comprises means providing an annular chamber I8 having a bottom wall comprising a perforated ring of metal and an inlet portion 22 (see FIG. 4) communicates with a conduit 24 for the admission of a gas and air mixture which is caused to burn at the perforated plate 20 and thus provide radiant heat for a broiling operation. lnwardly of the annular chamber 18 the upper burner'is provided with upper and

lower plates

26 and 28, each of which is provided witha central opening, 30 and 32, communicating with a horizontally extending flue duct 34. The opening 32 is substantially flush with the top wall of the oven cavity and spaced therebelow is a baffle plate 35 whereby vapors, odors and other gases in the oven are caused to flow around the periphery of the baffle plate 36 through the flame of the 'broil burner (when the latter is operating) to the flue duct The flue duct 34 communicates with an upright exhaust passage 37 having an upper discharge end 38 at the top of the range 2 and which extends downwardly past the open end of the flue duct 34 and terminates in an open lower end 40 outwardly of the oven cavity 8 but within a cabinet shell 42 of the range 2.

The inner shell 6 of the oven cavity is formed todefine a bottom well portion 44 in which a bake burner 46 and bake pilot burner 48 are located. A pilot burner 50 is also positioned adjacent the upper or broil burner 16. By way of example there is shown suitable adjustable shelf or platform 52 positioned over the bake burner 46 and which can be vertically positioned to rest on any of the ribs or supporting rails 54, as is more or less conventional.

Below the oven cavity 8 the range is provided with a compartment 56 in which the bake burner 46 is mounted to extend upwardly therefrom and loosely through an opening 58 in the bottom of the oven cavity, as clearly shown, particularly in FIG. 2.

The compartment 56 houses an electric motor 60 drivingly connected to a centrifugal blower 62 having a discharge and communicating with a plenum chamber 64. By referring to the sectional views of FIGS. 2 and3 and the schematic diagram of 1 FIG. 6, it can be seen that the'bake burner 46 comprises an inner tubular member 66 and an outer tubular member 68 spaced therefrom. Both the inner tubular member 66 and the annular space between it and'tubular member 68 communicate with the interior of the plenum chamber 64.

Also extending from and communicating with the plenum chamber is a conduit 70 directing air from the chamber 64 upwardly into the upright exhaust passage 36,'a conduit 72 directing air from the plenum chamber to the bake burner pilot 48, a conduit 74 directing air to the broil burner pilot 50 and a further conduit 76 directing air to the inlet conduit 24 of the upper or broil burner 16. The structure and operation of the pilot burners 48 and 50 are fully described in the copending application referred to and will not be further described here except to point out that the air suppliedthereto from the plenum chamber 64 ensures adequate fresh air for combustion under all conditions of operation.

A gas manifold 78 is located near the top of the range for connection to a gas supply pipe 80. From the manifold 78 a first conduit 82extends downwardly into the compartment 56 where it branches into a gas line 84 controlled by bake burner solenoid valve 86 to direct gas into the inner tubular member 66 of thebake burner. A second branch 88 is directed through the compartment 56, then upwardly through a broil burner solenoid valve 90 into a central portion of the inlet conduit 24 for the broil burner. Thus, when the solenoid valve 86 is energized and open, gas is supplied to the bake burner 46 and when the solenoid valve 90 is energized to open, it directs gas to the broil burner 16. Also conduits 91 and 93 direct gas from the manifold 78 to the bake burner pilot 48 and the broil burner pilot 50, respectively, with a solenoid valve 132 in the conduit 93.

As shown most clearly in FIG. 3, the blower motor 60 is provided with a centrifugal switch 92 sewing as a master switch to controloperation of the oven in a manner to be described later. Also, as best seen in FIG. 3, the conduit 76 leading from the plenum chamber 64 to the broil burner 16 is controlled by a shutter valve 94 operable by a solenoid 96. To open the valve 94 the solenoid 96 must be energized. Coupled to the shutter valve 94 is a microswitch 98 which closes a circuit when the shutter valve 94 is open and which opens that circuit when the shutter valve is closed. The purpose for this switch will be further described later.

Referring now particularly to FIG. 5, the oven door 14 also comprises an inner layer 100 of heat-conductive material, such as metal, an outer layer 102 of similar material and an interposed body of thermoinsulating material 104. The inner layer 100 is directed outwardly to define a peripheral edge portion 106 spaced from an adjacent portion of the outer layer 102, which latter is formed to define a boundary or trim edge for the oven door. The oven door opening 12 is bounded in part by an oblique surface portion 108 facing a concavity or channel 110 in the oven door edge. A sealing bead 112, of resilient heat-resisting material, is provided with a flange 114 extending between the portions 106 and 102 to thereby insulate the outer layer 102 from the high temperatures in the oven and the bead portion 112 provides a seal between the oven door and its opening 12 when the door is closed. It is to be particularly noted that the seal provided by the bead 112 is closely adjacent the inner edge of the door opening 12. In conventional oven door construction, resilient sealing means are usually provided to bear against the outer front face of the range cabinet, thus leaving an unobstructed but relatively narrow channel inwardly of the sealing means and communicating with the oven cavity so that deposits resulting from cooking can collect therein, rendering pyrolytic cleaning thereof quite difficult. That narrow channel or space is largely eliminated in the present construction and the surfaces adjacent the seal, on which matter can be accumulated, is fully exposed to the high cleaning temperature in the oven cavity and can be effectively cleaned by thermal operation during a normal cleaning cycle.

Refer now to FIGS. 7, 8 and 9 for a description of the various operations capable of being performed with the structure shown. It is to be understood that the electrical diagrams of these Figures are purely schematic and include only those components essential to the cycles to be described. Other circuit features which are more or less conventional in gas-fired ranges have been omitted. In FIG. 7, all of the components have been labeled and it is to be understood that corresponding components in FIGS. 8 and 9 represent those same elements.

In FIG. 7, numeral 116 represents a terminal block for connection to a source of electric power and comprises a terminal 118 and a ground terminal 120. The electrical controls include a first selectorswitch 122 in the from of a gang switch for conditioning the oven for a cleaning cycle or for cooking operations. A second selector switch 124 is manually set when the switch 122 is set for a cooking operation and this selector predetermines whether the broilburner or the bake burner will be placed in operation. The second selector 124 not only selects the burner to be operated but operates to set a thermostat to control operation of the selected burner during normal cooking operations. As shown in FIG. 7, the selector 122 has been set for a cooking operation and the selector 124 has been set to operate the bake burner. Obviously, as seen from the Figure, electric power is conducted from terminal 118 through a thermostatic switch 126 operable to control the baking temperature as preselectedby the selector 124. The circuit then continues through the centrifugal switch 92 and a flame detector switch 128, which is closed when the bake pilot 48 is burning. Current then is directed through a high-limit switch 130, which is thermostatically responsive to oven tern: perature to disable the system in the event oven temperature gets too high. From there current is directed to the second selector 124 and from the bake" terminal thereof through the bake burner solenoid valve 86, to open the same, then to ground. Thus, circuits are completed for effecting baking operation under the normal control of the thermostatic switch 126. However, ifthe blower motor 60 fails to operate, the centrifugal switch 92 will remain open and the entire system will be disabled. Likewise, failure of the bake pilot 48 or excessive temperature within the oven will also disable the entire system Otherwise, the baking operation proceeds in a conventional manner and may include any desired signal lights, timer, or the like. No circuit is shown for energizing the blower motor 60 but such a circuit could be provided by those skilled in the art in any desired manner. The blower may be caused to operate continuously while any burner is on, and to stop when the burner is off, or may be, and preferably is, caused to operate at all times when the oven is in operation.

FIG. 8 shows the condition of the circuits when the first selector switch 122 is set for a cooking operation and the second selective switch 124 is set to select the broil burner for operation. With the circuits in this condition current is again conducted through the switch 122, cooking thermostat 126, centrifugal switch 92, bake burner flame switch 128 and highlimit switch 130 to the second selector 124, which directs current through the broil terminal to the control elements for the broil burner. Thus current is conducted through the solenoid 96 which controls shutter valve 94 to provide air from the plenum chamber 64 to the broil burner 16. When the shutter valve 94 is open, switch 98 is closed, as shown in FIG. 8. Current is also conducted through the solenoid controlling valve 132, controlling a supply of gas fuel to the broil pilot burner 50, and through the pilot burner flame detecting switch 134. Initially, there is no flame at the broil pilot burner 50 and switch 134 will then be conditioned to direct current through a transformer 136 to energize glow coil 138 to ignite the gas flowing through pilot valve 132, and thus place the broil pilot in operation. The flame detector switch 134 then detects that pilot flame and completes a circuit through the broil burner gas valve to supply gas to the broil burner which is then ignited. Broiling then continues in a conventional manner, under the control of oven thermostat 126 and broiler highlimit thermostat in the usual manner and until completed. Here again, failure of the blower motor 62 will open centrifugal switch 92 to disable the broil burner and failure of the bake pilot flame detector switch 128 will also disable the broil burner. Failure of the solenoid 96 or failure of the shutter 94 to open will result in broil burner air switch 98 remaining open with the resultant shutting down of the broil burner.

FIG. 9 illustrates the condition of the circuits during a hightemperature cleaning operation. Before proceeding with a description of this operation, it is to be pointed out that the oven door 14 can be opened and closed at will during a normal broiling or baking operation but a locking latch (not shown) is provided so as to ensure that the oven door is closed and locked before a cleaning cycle can be initiated. In FIG. 9, switch 140 is closed only when the oven door is closed and locked in its closed position. Further circuits and controls, not shown, are provided for operating a solenoid (not shown) which is arranged to permit locking or unlocking of the oven door. That solenoid is normally controlled by a manual button (not shown) which must be depressed to actuate the solenoid before the oven door can be manually locked and must again be depressed before the oven door can be manually unlocked. That pushbutton is normally in series with a thermostat switch exposed to oven temperature so that the oven door can be unlocked and opened at oven temperatures up to about 575- I 600 F. but cannot be unlocked or open at temperatures from about 600 to about 900 F., which is the temperature range for self-cleaning operation. As will be apparent from FIG. 9, the oven door must be closed and locked to close the master switch 140. In FIG. 9, the first selector 122 is shown set to condition the apparatus for cleaning. It is immaterial at this time where the selector 124 is set and for convenience it is shown in an intermediate position. Numeral 142 indicates a cleaning cycle timer which is set and starts to operate when a cleaning cycle commences and causes the cleaning to continue through a predetermined period of time. With the controls set as illustrated in FIG. 9, current is conducted from terminal 118 through the oven door lock switch 140 and a further thermostatic switch 144 set to disable the system at a temperature above about 900 F. in the oven cavity. From there current is directed through the centrifugal switch 92, bake pilot flame switch 128, and through the timer 142. From the timer 142 current is directed through both

terminals

146 and 148. From terminal 146 current flows through the manual reset broil burner thermostat control switch 150, which when opened disables the broil burner. From thermostat 150 current goes through coil 152 of relay switch 154 to close normally open contacts 156 and to open normally closed contacts 158. Closing of contacts 156, which are held closedby coil 152, directs current to the broil burner controls, already described. From terminal 148 of timer 142 current is conducted to the solid-state delay device 160 and then through the bake burner solenoid valve 86 to open the same. The delay device 160 will close in 3 to 8 minutes after power has been supplied. Thus, both the bake and broil burners are placed in operation. The manual reset broil burner thermostat switch 150 is normally set to open at a temperature at about or slightly lower than the desired cleaning temperature at which thermostat switch 144 is set. Thus, both burners operate until the temperature in the oven cavity is brought up to substantially the temperature desired for a cleaning cycle and the broil burner is then cut off and stays off for the remainder of the clean cycle, the baking burner serving to maintain the desired cleaning temperature. The opening of switch 150 deenergizes coil 152 and contacts 158 are again closed by bypass delay device 160, permitting off-on cycling of the bake burner without time delays. The cleaning cycle continues until the timer 142 operates to open the circuits through

contacts

146 and 148 and shut the burners off. When the cleaning cycle has been completed and the oven cooled sufficiently to open the oven door, the thermostat switch 150 is reclosed mechanically (by means not shown) by the oven door latch mechanism as the door is unlatched. This makes the system ready for the next cleaning cycle.

At this time the oven temperature is still highly elevated and a cooling cycle commences. As long as the oven temperature remains above about 575600 F., the oven door cannot be opened and that condition continues until the oven temperature is reduced to a value where the previously referred to thermostat again places the oven door unlocking pushbutton in circuit.

As previously described, conduit 70 from plenum chamber 64 extends upwardly to the upright flue passage 36. During any cooking or cleaning cycle, including the cooling-down period, fresh cooling air is caused to jet upwardly in the passage 36 to dilute and cool exhaust gases issuing from flue conduit 34. Obviously, discharge of exhaust gases into a room during the high temperature cleaning cycle will be highly undesirable and impractical. As previously noted, the upright exfrom the lower chamber 56 to one side of exhaust assa e 36 and then extends horizontally therein, as shown in FIG. and

is provided with upwardly directed openings 162 serving to direct jets of air upwardly in the passage 36. While it has been indicated that operation of the blower 62 may take place at any desired times, it is preferred that the blower operation continue throughout the cooling-down period following a cleaning cycle. The cleaning cycle timer 142 can be made to return to the off position as soon as burner operation is terminated or could be set to return to off position only after completion of the cooling-down period. This would be particularly desirable if the blower 62 were connected to operate only when the circuits are conditioned for operation of either of the burners. Clearly, however, the timer must return to the off position after complete cool down.

We claim:

1. A self-cleaning gas-fired oven comprising: means defining an oven cavity; a broil burner at the top of said cavity; a bake burner at the bottom of said cavity; first selectively operable means for placing both burners in operation simultaneously for self-cleaning of said oven; air supply means for supplying both said burners with fresh combustion air under pressure; an exhaust flue for discharging hot gases from said oven cavity into ambient air adjacent said cavity; and means directing a flow of air from said air supply means into and along said flue toward a discharge end thereof for cooling and diluting said hot gases.

2. A self-cleaning oven as defined in claim 1 wherein said exhaust flue comprises an upright passageway portion exteriorly of said oven cavity with its discharge end uppermost and a passageway directing said hot gases from said cavity to an intermediate portion of said upright passageway; the lower end of said upright passageway being open whereby to admit ambient air thereto for further cooling and dilution of said hot gases.

3. A self-cleaning oven comprising: means defining an oven cavity; a broil burner at the top of said cavity; a bake burner at the bottom of said cavity; first selectively operable means for placing both burners in operation simultaneously for selfcleaning of said oven; air supply means for supplying both said burners with fresh combustion air under pressure; second selectively operable mean for placing only said broil burner or said bake burner in operation and including first thermostatic control means for controlling the operation of the selected burner; second thermostatic control means, energized by said first selectively operable means when actuated to place both said burners in operation, for disabling said broil burner at a temperature less than that for self-cleaning of said oven.

4. A self-cleaning oven comprising: means defining an oven cavity; a broil burner at the top of said cavity; a bake burner at the bottom of said cavity; first selectively operable means for placing both burners in operation simultaneously for selfcleaning of said oven; air supply means for supplying both said burners with fresh combustion air under pressure; and means responsive to operation of said first selectively operable means for delaying initial operation of said bake burner for a predetermined time interval after initial operation of said broil burner.

Claims

3. A self-cleaning oven comprising: means defining an oven cavity; a broil burner at the top of said cavity; a bake burner at the bottom of said cavity; first selectively operable means for placing both burners in operation simultaneously for self-cleaning of said oven; air supply means for supplying both said burners with fresh combustion air under pressure; second selectively operable mean for placing only said broil burner or said bake burner in operation and including first thermostatic control means for controlling the operation of the selected burner; second thermostatic control means, energized by said first selectively operable means when actuated to place both said burners in operation, for disabling said broil burner at a temperature less than that for self-cleaning of said oven.

4. A self-cleaning oven comprising: means defining an oven cavity; a broil burner at the top of said cavity; a bake burner at the bottom of said cavity; first selectively operable means for placing both burners in operation simultaneously for self-cleaning of said oven; air supply means for supplying both said burners with fresh combustion air under pressure; and means responsive to operation of said first selectively operable means for delaying initial operation of said bake burner for a predetermined time interval after initial operation of said broil burner.