US3668371A

US3668371A - Circuit arrangement for accelerated continuous cleaning of self cleaning oven coatings

Info

Publication number: US3668371A
Application number: US153727A
Authority: US
Inventors: Millard E Fry; Robert D Bremer
Original assignee: General Motors Corp
Current assignee: Motors Liquidation Co
Priority date: 1971-06-16
Filing date: 1971-06-16
Publication date: 1972-06-06
Anticipated expiration: 1989-06-06

Abstract

A circuit arrangement for a continuously cleaning coated oven at an elevated temperature range above the normal operating range but not in excess of that allowed for non-locked oven operation so as to improve the thermal cleaning of the oven bottom wall coating. The arrangement includes a separate manually settable control switch having a Cook position for energizing the bake and broil elements in a conventional manner and a Clean position wherein the broil element is disconnected and the bake element is energized while maintaining the thermostatic condition for broil operation such that the oven will continuously self-clean by heating the oven bottom wall much hotter than the existing oven air temperature.

Description

United States Patent Fry et al.

[54] CIRCUIT ARRANGEMENT FOR ACCELERATED CONTINUOUS e CLEANING OF SELF CLEANING OVEN COATINGS [72] Inventors: Millard E. Fry; Robert D. Bremer, both of 1 Dayton, Ohio [73] Assignee: General Motors Corporation, Detroit,

Mich. 1

[22] Filed: June 16, 1971 [21] Appl.No.: 153,727

52 U.S. c1 ..219 413, 219/396, 219/397 511 1111. C1 ..F27d 11 00 [58] Field of Search ..2l9/396-398, 391,

[56] References Cited UNITED STATES PATENTS 3,036,192 5/1962 Fry ..219/39.1 3,121,158 2/1964 Hurko.. ...219/397 3,266,477 8/1966 Stiles ..126/19 1 yJune6, 1972 3,301,999 1/1967 Chisholm ..2 19/396 X 3,302,000 1/1967 Sherman... .....2l9/393 3,350,542 10/1967 Actman..;. ..2l9/4l2 3,342,976 9/1967 Kjellberg ..219/413 3,353,004 11/1967 Alexander .2 19/398 Primary ExaminerVolodymyr Y. Mayewsky Attorney-William S. Pettigrew [57] ABSTRACT A circuit arrangement for a continuously cleaning coated oven at an elevated temperature range above the normal operating range but not in excess of that allowed for nonlocked oven operation so as to improve the thermal cleaning of the oven bottom wall coating, The arrangement includes a separate manually settable control switch having a Cook position for energizing the bake and broil elements in a conventional manner and a Clean position wherein the broil element is disconnected and the bake element is energized while maintaining the thermostatic condition for broil operation such that the oven will continuously self-clean by heating the oven bottom wall much hotter than the existing oven air temperature.

3 Claims, 3 Drawing figures soiled oven bottom wall or liner should dividually controlled by The present invention relates to an improved control system for a low-temperature self-cleaning oven, and particularly to an accelerated continuously cleaning or low temperature thermal cleaning ceramic coated oven suited for domestic use in the kitchen. As discussed in an article in Appliance Magazine dated December 1970, pages 52-55, the development and advent of oven coatings which will continuously clean at normal oven operating temperatures has progressed to providing the range industry with a ceramic coating of versatile use at normal operating temperatures that will nearly eliminate the work of keeping the oven areas clean. The term low temperature thermal cleaning oven coating is defined to differentiate between an oven to whichv a continuous or thermal cleaning coating is applied to the oven walls requires the elevated temperature of 880 F. and higher to degrade oven wall soils. It has been found incontinuous cleaning ovens that an increase in normal oven operating temperatures from that of 350 to 450 or 550 F. is beneficial to the thermal cleaning process and especially the usually heavily be subjected to higher temperatures to promote the oxidation of the soil by the coating and thus the cleaning in this area. I

It is an object of the present invention to provide a continuous cleaning coated oven wherein elevated temperatures can be obtained in a conventional oven having an upper heating unit to supply heat for brolling operations and a lower heating unit to supply heat for baking operations by a circuit arrangement providing a cleaning operation that disconnects the broil unit and energizes the bake unit with the thermostat conditions for broil operation so that the oven bottom wall will be heated much hotter than the existing oven air temperature so as to increase the efficiency of the continuously cleaning coating on the bottom wall of the oven.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred embodiment of the present invention is clearly shown.

In the Drawings:

FIG. 1 is a front perspective view of aneye-level oven including the inner walls of the oven cavity coated with an oxidizing continuously cleaning coating;

FIG. 2 is a schematic wiring diagram of the control circuit for the oven:

FIG. 3 is a cycle chart showing the positioning of the various switch contacts in the diagram of FIG. 2.

Referring now to the drawings and in particular FIG. 1, there is shown for illustrative purposes an eye-level or mounted electric oven having a box-like configuration with an outer oven housing 12 and an inner cooking cavity or compartment l4 defined by frame opening 16 having a door, partially indicated at 17, hingedly mounted for closing the front opening 16 of the oven 10. The oven includes supporting racks 20 on the side walls of shelves (not shown) which in turn are utilized to supporting cooking utensils within the oven. For providing the necessary cooking operations a bake element 24 is positioned adjacent the bottom wall 26 of the ovenwhile a broil element 28 is supported near the top wall 29 of the oven.

To enhance the convenience and utility of the oven 10 a lamp housing 30 is positioned within the oven designed in a manner that the light will show downwardly into the oven. A conventional thermostat, shown schematically at 31 in FlG. 2, includes a temperature sensor in the form of an oven thermostat bulb 33 positioned near the top wall 29 adjacent the broil element 28. It is standard 33 adjacent the broil element 28 as the highest wattages normally developed by the heating elements are in the broil element. At the right of the oven is a front control panel 32 in which the upper and lower heating elements may be inan oven thermostat switch knob 34,

practice to locate the sensing bulb 22 thereof for supporting a plurality an oven timer 36 and the like which are standard in this art. it should be noted that coated oven liners may be slidably removed from the oven cavity 14 through the frame opening such as disclosed in US. Pat. No. 3,036,192 issued May 22, 1962 to M. E. Fry and assigned to the same assignee as the instant application.

In the preferred embodiment the exposed surfaces of the oven walls are coated with a self-cleaning ceramic coating having the characteristic of oxidizing oven food soils thereon in the temperature range between 400 and 600 Magazine article test results have shown that while thermal coatings do eliminate food soil at normal operating temperabeneficial to the cleaning process with the usually heavily soiled oven bottom wall requiring a temperature approaching 700 F. to clean this area.

The present invention is directed to the concept of accelerating the cleaning of the coating and particularly the of the standard baking element 24 of the oven. The hydraulic thennostat 31 controls the heating or cooling of the

oven elements

24 and 28 to maintain the temperature selected for all baking operations. Whenelement 24 produces no heat. For broiling, the broil element heats continuously except in unusual cases such as when the door is closed. In that case the thermostat sensing bulb, located adjacent the broil eleprevent the oven ambient temperature from exceeding the broil setting which is approximately 580 F. in the disclosed form.

As seen in FIG. 2 the thermostat 31 includes a pair of contacts, generally indicated at D, opened and closed by switches 38 and 40 closing fixed pairs of

contacts

50, 51 and 52, 53 respectively. The switches 38, 40 are cycled intermittently by and the sensing bulb 33 within the oven. The rate at which the contact Group D, indicated by contacts 38 and 40, are cycled is dependent upon the presetting of the standard oven temperature control knob 34, the preset temperature being sensed by the bulb 33 within the oven. vThus if the knob 34 is set for 325 F. the cycling contacts 38 and 40 will open and close to maintain the selected temperature (325 F.) within the oven.

The foregoing description has set forth only the conventional temperature response oven control thermostats which are well known in the art and such switch may,

for broil such that the oven bottom wall will be subjected to a high temperature in the range of 700 F. while the oven ambient temperature will not exceed 600 F.

Turning now to those components related to the oven cleaning cycle a selector switch assembly 60 is provided including a pair of heating element transfer (double pole-double throw) switches R and S which connect the broil heating element 28 for example,

and the bake heating element 24 in a particular manner to the source of power L,,' N and L2 depending upon whether a broil" or bake COOK operation or accelerated CLEAN operation is to be effected. More particularly and with the user settable knob 34 in the variable temperature bake position switch R on contact R, connects the broil element 28 through the oven thermostat contact C across L and N to ll8-volt power and switch S contact S thereby connecting the bake element 24 across line conductors L, and L to 236- volt power to provide heat energy for the baking function of the COOK operation thermally cycled at contact group D. As an example, 3,800 watts of heat energy may be provided during the bake function comprising 3,000 watts from'the bake element 24 and 800 from the broil element 28. 1

With the user settable knob 34 in the broil position (580 F.) the bake unit 24 is deenergized and switch R on contact R, connects the broil element 28 through the oven thermostat switch across L, and L to 236-volt power to provide heat energy for the-broiling function of the COOK operation which may be thermally cycled at D. Specifically, 3,200 watts of heat energy may be provided during the "broil". function, all from the broil element 28 since nected at contact For the CLEAN operation the selector switch assembly 60 is manually operated by a switch 48 on panel 32 to position the transfer switches R and S on contacts R and 8,, respectively. Thus, the broil element is disconnected while the bake element 24 is connected through the thermostat 31 across L,, L to 236-volt'powe'r cycled on both sides of the line by the thermal relay switches D.

Tracing the circuit in detail the bake operation contacts A and C are closed positively while contacts D are cycling in accordance with the temperature within the oven as prescribed by the setting on knob or dial 34. As the cycle is inthe bake element 24 is discon- -itiated, the

heating elements

24 and 28 will be energized as follows: from L, through first circuit means including terminal 51 fixed contact 51, first cycling thermostat contact 38, fixed contact 50, terminal 50, line 54, to the junction 55 of the broil heating element 28 and the bake heating element 24.

From this point 55, the broil element 28 will be energized by way of line 56,-switch S through contact 5,, line 57, terminal 58, cam actuated switch blade 59 and movable'contact C to fixed contact 61 and terminal 62 to the neutral side line N, thus placing the'broil element 28 on ll8-volt operation. At the same time, the bake heating element 24 will be energized from the junction point 55, line 71, switch R, contact R,, line .72, terminal 73, switch blade 74, movable contact A, fixed contact 63, line 75, terminal 53, fixed contact 53', second thermostat cycling contact 40, fixed contact 52, terminal 52 to the other side of the line L thereby placing the bake element 24 on 236-volt operation. For the broil operation the cam operated movable contact B engages fixed contact 64 leading to junction 65 and placing the broil element 28 across the lines L,, L through cycling contacts D. The path of second circuit means for L includes terminal 52', fixed contact 52, second cycling thermostat contact 40, fixed contact 53, terminal 53, line 75 to junction 65 which connects first fixed bake contact 63 and fixed broil contact 64. The first fixed bake contact 63 is connected via first movable cam operated contact A, line 74, terminal 73 and line 72 to cook" contact R, of the transfer. switch while the fixed broil contact 64 is connected via movable contact 8, line 59, terminal 58 and line 57 to cook contact 8,. Third circuit means connect neutral line N to a second fixed bake contact 61 and thence via movable contact C, line 59, terminal 58 and line 57 to .cook" contact 8,.

As the CLEAN operation is initiated the heating element 24 will be energized as follows: from L, through terminal 51',

contacts

51, 38 and 50, terminal 50', line 54 to the junction point 55 of

theelernents

24 and 28. From this point 55, the

- bake element 24 will be energized by way of line 71, switch R contact R line 80, contact 8,, line57, terminal 58, line 59, movable contact B, fixed broil contact 64, junction 65, line 75, terminal 53', fixed contact 53, cycling thermostat contact 40, fixed contact 52 and terminal 52' to the other side of the line L thereby placing the bake element 24 on 236-volt operation. It will be noted that interconnected transfer switches R and S have a line 81 interconnecting the contact R, with the contact 8, while the line 80 interconnects the contact S, with the contact R The arrangement of the accelerated CLEAN position of the selector switch allows the broil element 28 to be disconnected and the bake element 24 to be energized with the thermostat conditioned for broil operation. Thus, the heat generated by the bake element 24 will act upon the bottom wall 26 of the oven to insure a thermal cleaning action on the coating. The oven chamber also has its side, top and back walls subjected to an elevated temperature between about 500 F. and about 600 F. which will allow accelerated cleaning of the coating thereon for improved soil removal.

A typical set of instructions for use with the instant invention would read as follows:

After heavy soilingrapid cleanup may be desired. A 5-hour cycle is recommended. This may be done at night.

ACCELERATED CLEANING 1. Move switch on console top to Clean. 2. Set stop time on timer.

3. Set cooking hours to 5.

4. Set oven thermostat to Broil.

AFTER CLEANING 1. Return thermostat to Off.

2. Return cooking hours to Manual.

3. Return switch on console top to Cook.

While the embodiment of the present invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted. I

What is claimed is: t

l. A continuously cleaning oven comprising an outer oven housing enclosing walls defining a bake and broil compartment, said compartment having a bottom wall, opposite side walls, a door for closing said compartment,a rear wall and a top wall, a thermal cleaning coating on the exposed surface of at least said bottom wall, and having the characteristic of oxidizing oven food soils thereon in the oven temperature range of between 400 and 600 jacent the bottom wall and a broiling element supported adjacent the top wall of the compartment, control means for said bake and broil elements settable in a cook position to control said elements to efiect a cooking operation including a bake operation and a broil operation and user settable in a clean position to control said elements to effect an accelerated thermal cleaning operation, said control means including a circuit connecting said bake and broil heating elements to a source of electrical power, an oven temperature thermostat connected in said circuit and presettable throughout an oven temperature range in said cook position for controlling the energization of said bake and broil elements in a cycling mode during said bake operation, and presettable in a fixed broil setting in said cook" position for controlling the energization of said broil element for normally continuous operation during said broil operation but adapted to cycle said broil element at an oven temperature in excess of substantially 600 F., said thermostat including a sensor supported adjacent said top wall for sensing oven temperature thereat, said circuit includinga double pole-double throw transfer switch interconnected in series electrical circuit between said thermostat and said elements for connecting said elements in said cook" position for said cooking operation, and said transfer switch operative for connecting said elements in said clean position such that when said thermostat is set in said broil" setting said circuit provides full wattage to said bake element and no wattage to said broil element whereby said bottom wall is heated to an accelerated F., a baking element'supported adcleaning temperature by said bake element while said thermostat functions to cycle said bake element to prevent the oven temperature at said sensor from exceeding substantially 600 F. during the accelerated thermal cleaning operation.

- .2. A continuously-cleaning oven as recited in claim 1 wherein the thermostat sensor is in the formof an hydraulic diaphragm bulb.

3. A continuously cleaning oven comprising an outer oven housing enclosing walls defining a bake and broil compartment, said compartment having a bottom' wall, opposite side walls, a door for closing said'compartment, a rear wall and a top wall, a thermal cleaning coating having the characteristic of oxidizing oven food soils thereon in the oven temperature range of between 400 and 600 F. on the exposed surface of at least said bottom wall, a baking element supported adjacent the bottom wall and a broiling element supported adjacent the top wall of the compartment, control means for said baking and broiling elements settable in a cook position to control said elements to effect a cooking operation including a bake operation and a broil operation and user settable in a clean position to control said elements to effect an accelerated thermal cleaning operation, said control means including a circuit connecting said bake and broil heating elements to a source of electrical power, an oven temperature thermostat having first and second cycling contacts connected in said circuit and presettable throughout an oven temperature range in said cook" position for controlling the energization of said bake and broil elements in a cycling mode during said bake operation and presettable in a fixed broil setting in said cook position for controlling the energization of said broil element for normally continuous operation during said broil operation but adapted to cycle said broil element at an oven temperature in excess of substantially 600 F., said thermostat including an hydraulic sensing bulb supported adjacent said top wall for sensing oven temperature thereat, said control circuit including first and second line conductors and a neutral conductor connected to said source of power; said oven temperature thermostat having first and second cycling switches controlled by said bulb and operative with said cycling contacts so as to be responsive to temperatures in said oven compartment; said control means including a pair of interconnected transfer switches in the form of a double pole-double throw switch, first circuit means connecting said first line conductor and said first thermostat cycling contact to a junction of said broil heating element and said bake heating element, said broil heating element having its other side connected to one switch of said pair of interconnected transfer switches, said bake heating element having its other side connected to the other switch of said pair of interconnected transfer switches, second circuit means connecting said second line conductor and said second thermostat cycling switch to a junction of a first fixed thermostat bake contact-and a fixed broil contact, said first fixed bake contact connected via a first movable bake contact to one cook" contact of said transfer switch, said fixed broil contact connected via a double throw movable contact to the other cook contact of said transfer switch, third circuit means connecting said neutral conductor to a second fixed bake contact; said second bake contact connected via said double throw movable contact to said other cook contact of said transfer switch, said one cook" contact electrically connected to an opposite clean contact of said transfer switch; said other cook contact electrically connected to an opposite clean contact of said transfer switch thereby connecting said heating elements in a cook" circuit to provide alternatively full cycling power to said broil element or cycling power to said bake element and said broil element, said interconnected transfer switches operative for connecting said elements in a clean circuit such that when said thermostat is set in said broil setting said circuit provides full wattage to said bake element and no wattage to said broil element whereby said oven bottom wall is heated to an accelerated cleaning temperature while said thermostat functions to cycle said bake element to prevent the oven temperature at said sensor from exceeding substantially 600 F. during the accelerated thermal cleaning operation.

Claims

1. A continuously cleaning oven comprising an outer oven housing enclosing walls defining a bake and broil compartment, said compartment having a bottom wall, opposite side walls, a door for closing said compartment, a rear wall and a top wall, a thermal cleaning coating on the exposed surface of at least said bottom wall, and having the characteristic of oxidizing oven food soils thereon in the oven temperature range of between 400* and 600* F., a baking element supported adjacent the bottom wall and a broiling element supported adjacent the top wall of the compartment, control means for said bake and broil elements settable in a ''''cook'''' position to control said elements to effect a cooking operation including a bake operation and a broil operation and user settable in a ''''clean'''' position to control said elements to effect an accelerated thermal cleaning operation, said control means including a circuit connecting said bake and broil heating elements to a source of electrical power, an oven temperature thermostat connected in said circuit and presettable throughout an oven temperature range in said ''''cook'''' position for controlling the energization of said bake and broil elements in a cycling mode during said bake operation, and presettable in a fixed ''''broil'''' setting in said ''''cook'''' position for controlling the energization of said broil element for normally continuous operation during said broil operation but adapted to cycle said broil element at an oven temperature in excess of substantially 600* F., said thermostat including a sensor supported adjacent said top wall for sensing oven temperature thereat, said circuit including a double pole-double throw transfer switch interconnected in series electrical circuit between said thermostat and said elements for connecting said elements in said ''''cook'''' position for said cooking operation, and said transfer switch operative for connecting said elements in said ''''clean'''' position such that when said thermostat is set in said ''''broil'''' setting said circuit provides full wattage to said bake element and no wattage to said broil element whereby said bottom wall is heated to an accelerated cleaning temperature by said bake element while said thermostat functions to cycle said bake element to prevent the oven temperature at said sensor from exceeding substantially 600* F. during the accelerated thermal cleaning operation.

2. A continuously-cleaning oven as recited in claim 1 wherein the thermostat sensor is in the form of an hydraulic diaphragm bulb.

3. A continuously cleaning oven comprising an outer oven housing enclosing walls defining a bake and broil compartment, said compartment having a bottom wall, opposite side walls, a door for closing said compartment, a rear wall and a top wall, a thermal cleaning coating having the characteristic of oxidizing oven food soils thereon in the oven temperature range of between 400* and 600* F. on the exposed surface of at least said bottom wall, a baking element supported adjacent the bottom wall and a broiling element supported adjacent the top wall of the compartment, control means for said baking and broiling elements settable in a ''''cook'''' position to control said elements to effect a cooking operation including a bake operation and a broil operation and user settable in a ''''clean'''' position to control said elements to effect an accelerated thermal cleaning operation, said control means including a circuit connecting said bake and broil heating elements to a source of electrical power, an oven temperature thermostat having first and second cycling contacts connected in said circuit and presettable throughout an oven temperature range in said ''''cook'''' position for controlling the energization of said bake and broil elements in a cycling mode during said bake operation and presettable in a fixed ''''broil'''' setting in said ''''cook'''' position for controlling the energization of said broil element for normally continuous operation during said broil operation but adapted to cycle said broil element at an oven temperature in excess of substantially 600* F., said thermostat including an hydraulic sensing bulb supported adjacent said top wall for sensing oven temperature thereat, said control circuit including first and second line conductors and a neutral conductor connected to said source of power; said oven temperature thermostat having first and second cycling switches controlled by said bulb and operative with said cycling contacts so as to be responsive to temperatures in said oven compartment; said control means including a pair of interconnected transfer switches in the form of a double pole-double throw switch, first circuit means connecting said first line conductor and said first thermostat cycling contact to a junction of said broil heating element and said bake heating element, said broil heating element having its other side connected to one switch of said pair of interconnected transfer switches, said bake heating element having its other side connected to the other switch of said pair of interconnected transfer switches, second circuit means connecting said second line conductor and said second thermostat cycling switch to a junction of a first fixed thermostat bake contact and a fixed broil contact, said first fixed bake contact connected via a first movable bake contact to one ''''cook'''' contact of said transfer switch, said fixed broil contact connected via a double throw movable contact to the other ''''cook'''' contact of said transfer switch, third circuit means connecting said neutral conductor to a second fixed bake contact; said second bake contact connected via said double throw movable contact to said other ''''cook'''' contact of said transfer switch, said one ''''cook'''' contact electrically connected to an opposite ''''clean'''' contact of said transfer switch; said other ''''cook'''' contact electrically connected to an opposite ''''clean'''' contact of said transfer switch thereby connecting said heating elements in a ''''cook'''' circuit to provide alternatively full cycling power to said broil element or cycling power to said bake element and said broil element, said interconnected transfer switches operative for connecting said elements in a ''''clean'''' circuit such that when said thermostat is set in said ''''broil'''' setting said circuit provides full wattage to said bake element and no wattage to said broil element whereby said oven bottom wall is heated to an accelerated cleaning temperature while said thermostat functions to cycle said bake element to prevent the oven temperature at said sensor from exceeding substantially 600* F. during the accelerated thermal cleaning operation.