US3519797A - Oven control system - Google Patents

Description

July 7, 1970 B. I. KJELLBERG 3,519,

OVEN CONTROL SYSTEM Filed Nov. 27, 1968 POWER SUPPLY l a BAKE OFF CLEAN 26 27 l l l l 28 -50 HIGH DOOR TIMER LIMIT LATCH SOLENOIDDJ SWITCH SWITCH MICRO SWITCH l I I w 41 INVENTOR BURRE I. KJELLBERG I \jfiizma {4. g 44 FIG. 2

ATTORNEY United States Patent Ofiice 3,519,797. Patented July 7, 1970 3,519,797 OVEN CONTROL SYSTEM Burre I. Kjellberg, Ballwin, Mo., assignor t Dlatemp, Inc., St. Louis, Mo., a corporation of Missouri Filed Nov. 27, 1968, Ser. No. 779,530 Int. Cl. F2711 11/02; H051) 1/02 US. Cl. 219-413 2 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a domestic or household oven, and particularly to an oven having a hydraulic thermostatic control system which will operate over two distinct temperature ranges, the first being the normal cooking range of about 150 F. through 550 F., and the second being a heat cleaning temperature range having a fixed high limit setting between 850 F. and 1100 F. The present invention has extended the high limit setting some 150 F. beyond previous practice, with a consequent lowering of the time necessary for the cleaning cycle to accomplish its purposes.

The most common example of previous practice is exemplified by Pat. No. 3,121,158 by B. Hurko, issued on Feb. 11, 1964 and titled Household Cooking Ovens and Methods of Cleaning the Same. Other examples of relatively complicated elforts to obtain similar results are shown by the following patents: No. 3,027,444 by W. R. Weeks, issued on Mar. 27, 1962 and titled Hydraulic Thermostat Bulb Shielding Means; No. 3,293,410, by S. B. Welch, issued on Dec. 20, 1966 and titled Oven Thermostat with Anticipator Heater; and No. 3,293,411, by R. L. Dills, issued on Dec. 20, 1966, and titled Oven Temperature Control with Remote Sensor.

The principal object of my invention is to provide an oven control system which is reliable, which depends only on proven hydraulic elements and microswitches to regulate and control the baking cycles and the cleaning cycles of a household oven.

The number of constructions and methods used to solve these problems has been the results by many manufacturers attempting to stretch the temperature ranges over which organic fillers for hydraulic control systems will operate. As a consequence these control systems are expensive and unreliable. One object of my invention has been to reduce the cost of the control system to approximately one-third of the cost of those in present practice.

Under the practice of the Hurko Pat. No. 3,121,158 the upper temperature limit has been limited to about 950 F. By using suflicient insulation and an electric fan Hurko has built an oven which automatically cleans and which will never elevate the temperature of the outer casing above about 194 Fahrenheit. The purpose of limiting the temperature of the outercasing is to rule out the possibility of some heat injury to anyone who touched the outer surface of the oven after initiating the heating-cleaning cycle.

In general all the residues which collect in ovens as the results of spills, spattering and boil-overs, are either fatty acids, fats, proteins and carbohydrates. They are all organic compounds and upon the application of temperatures above 750 F., they will all degrade into elementary organic gases such as methane, ethane, carbon dioxide and water vapor together with a trace of free carbon which shows up as a little white or grey ash.

By increasing the amount of insulation slightly the temperature in the oven chamber can be raised above 1000 F. without making the outside of the oven dangerous to the operator. The precise control of temperatures in the range of 1000 to 1100 F. is most important as failure could result in injuries to the operator or in a household fire. Precise control is achieved by my invention.

I have shown a preferred embodiment of my invention in the drawings, however it will be understood that my invention is not limited to the particular structures depicted in the drawings and that it may be adapted for use in connection with the control of temperatures of other ovens which require regulation over large ranges.

In the drawings:

FIG. 1 is a schematic drawing of the oven control sys tem;

FIG. 2 is an enlarged side-elevational view of a portion of FIG. 1.

Referring now to FIG. 1, the numeral 10 is given to the selector switch. Selector switch 1 0 has three positions, OFF, BAKE, and CLEAN. In the OFF position, no power can flow from the power supply 11, through the oven heating elements, represented by the resistance element 12, which of course is contained in the oven chamber, provided with walls and a door for access in the conventional manner, but not depicted in the drawing.

For ordinary cooking operations, which require various temperatures to be generated in the oven chamber by the power supply, which is conventional, by passing current through the heating element 12, an infinite or proportional control is desired. These temperature settings depend on the type of baking or broiling being accomplished, and range from to 550 Fahrenheit.

For baking purposes the selector switch 10 is turned from the OFF position to the BAKE position, shown by the dotted line 13. In the BAKE position power flows from the power supply 11, through the selector switch to, and through, the microswitch 14 and thence through the heater element 12, whence it returns in completing the circuit to the power supply 11.

Microswitch 14 has two lead connections 15 and 16. The on and off positions of the microswitch 14 are controlled by the lever 17. The lever 17 has an adjustable hingepoint 18, which can be raised or lowered in FIG. 1 by means of the temperature setting knob 19. The microswitch 14 is provided with a switch button 20, which disconnects the microswitch or connects it in series with the power supply, depending on the position of the switch button 20. At the further end of the lever 17 from the adjustable hinge point 18, is the diaphragm 21, the actuating element or motor element of the bake cycle.

Diaphragm 21 consists of a pair of nested corrugated expansible metal discs, well known in the art. Diaphragm 21 is provided with a stud 22 which is maintained in firm contact with the end of lever 17. The diaphragm 21 is connected by a capillary tube 23 to the hydraulic bulb 24. The diaphragm 21, the capillary tube 23 and the hydraulic bulb 24 are all filled with an expansible fluid. For my purposes I prefer to fill this circuit with mercury metal which remains fluid over the range and which may be maintained in close contact with a portion of the heater element 12.

The operation of this circuit is as follows. When the operator has turned the selector switch 10 to the BAKE position 13, the operator also sets the temperature setting knob 19 to the temperature desired for the bake cycle, thereby moving the adjustable hingepoint 18 either up or down from its previous position.

Meanwhile power in the form of an electrical current begins to flow from power supply 11, through the microswitch 14, and through the heater element 12. The heater element 12 begins to heat up and as it does it heats hydraulic bulb 24 and the fluid therein. The fluid expands as its temperature rises and so does the fluid in the capillary tube 23 and the diaphragm 21. As the fluid in the diaphragm 21 expands, the corrugated metal discs comprising the upper and lower surfaces move apart. The lower surface is fixed in position and therefore the motion is apparent at the upper surface, in turn, raising the stud 22 which is in contact with the free end of the lever 17. As the stud 22 rises, the free end of the lever 17 rises in FIG. 1, and this action raises the switch button 20 of the microswitch 14. When the desired temperature has been reached, which is the temperature established by the position of the adjustable hingepoint 18, the movement of the switch button disconnects the leads 15 and 16 of microswitch 14 from each other. The result that occurs is that no power flows through the microswitch to the heating element 12, which thereupon cools. The train of consequences is that the bulb 24 cools, the fluid therein cools and contracts as does the fluid in the capillary 23 and the diaphragm 21. The upper surface of the diaphragm 21 moves downward in FIG. 1, as does the stud 22 and the free end of the lever 17. Whereupon the switch button moves downward also to the point at which the leads 15 and 16 are again connected and power again flows through this circuit to raise the temperature of the heating element 12. Thus the cycling of the diaphragm 21 in expanding and contracting controls the cyclic flow of power to the heater element 12. When the BAKE cycle is finished the operator merely turns the selector switch 10 to the OFF position and may also turn the temperature setting knob 19 to its lowest or off position.

When after prolonged use or accidental spilling, the oven chamber becomes dirty and must be cleaned, the operator follows the ensuing procedure. First, the selector switch 10 is turned to the CLEAN position 25. In this mode of operation power passes from the power supply 11 through the selector switch 10 to the high limit switch 26, and to the door latch switch 27.

The high limit switch 26 has a fixed setting chosen by the manufacturer as being between 850 and ll Fahrenheit. In series with the high limit switch 26 is the timer 28, which has the purpose of maintaining the operation of the high temperature setting for a given length of time, whether it be for one or more hours as determined by the manufacturers requirements. Power flows in the CLEAN mode of operation from the high limit switch 26 through the timer 28 to the heater element 12, and the circuit is completed by a return connection wire, as before to the power supply.

The door latch switch circuit has novel and inherent safety features which render it absolutely foolproof. The door latch switch 27 operates a solenoid 28, which is conventional in nature, having a return spring, energizing coil and bolt. The novelty lies in the opposite wiring of the high limit switch and the door latch switch.

In their normal condition, the high limit switch 26 is operated with normally closed contact made; Whereas the door latch switch 27 is operated with normally open contact made. For this purpose I supply the dual switching lever 29, which has what amounts to two free ends, 30 and 31, shown in greater detail in FIG. 2.

The high limit switch 26 and the door latch switch 27 are mounted together in a case. At the bottom of the switches is the pivot or fulcrum 33 mounted midway along the length of the dual switching lever 29. The left end of the dual switching lever 29 is positioned between the stud 34 on the high limit hydraulic diaphragm 35, and the switch button 36 on the high limit switch 26. The

right end of the dual switching lever 29 is provided with an integral mounting ring 37. A hole has been bored and threaded through both the end 31 of the dual switching lever 29 and through the mounting ring 37. An adjusting screw 38, provided with a screwdriver slot 39, is mounted in the threads in the end 31 of the dual switching lever 29 and the threads of the mounting ring 37. The upper end of said adjusting screw 38 is positioned in bearing contact against the switch button 40 of the door latch switch 27.

The lower end of the adjusting screw 38 projects downward along the central axis of the return spring 41, which at its upper end is positioned around the mounting ring 37 and at its lower end around the access hole 42 which provides access for calibration purposes to the screwdriver slot 39 of the adjusting screw 38.

In the CLEAN position the power flow through the high limit switch 26 and thence through the timer 28, causes the heater element 12 to heat up again. This heats the hydraulic bulb 43 and the fluid within. I prefer in this connection to use either mercury or an alloy of sodium and potassium, both of which are serviceable over the temperature ranges required. However other fills such as these may be used, so long as they are liquid at room temperature. The principal limitation on the choice of the filling liquid is the boiling point and the proper liquid is chosen to reach the temperature required.

As the filling liquid heats up the liquid in the capillary 44 and the hydraulic diaphragm 35 heats up. The rise in temperature causes the upper surface of the diaphragm 35 to move upward in the figures, and stud 34 bears against the free end of dual switching lever 29, causing that free end 30 to press upward against the switch button 36 of the high limit switch. As the temperature reaches the fixed setting desired the upward movement of the switch button 36 finally disconnects the power supply 11 from the heater element 12. As soon as this happens the heater element 12 cools and the process reverses, until the switch button 36 again connects the power supply to the heater element 12. Thus the temperature remains relatively constant, cycling with small deviations from the fixed temperature setting for the CLEAN cycle.

The fixed temperature setting for the CLEAN cycle is accurately established upon calibration, by moving the diaphragm up or down. The diaphragm 35 can be raised or lowered simply by turning the positioning screw 45, which is threadably mounted on the case 32. Lowering the diaphragm 35 away from the high limit switch 26 has the effect of raising the high limit temperature setting, since it means that more expansion of the fluid within the diaphragm 35 is required to actuate the switch button.

Since the dual switching lever 29 bears against the pivot or fulcrum 33, the movement of the free end 31 of lever 29 is opposite to the movement of the free end 30 thereof. This action produces an inherent safety feature.

There is great danger in ovens operating above 600 Fahrenheit. If an operator were to accidentally open one, an extremely bad burn can be sustained as well as the possibility of causing a fire among nearby articles. As the temperature inside approaches and passes 1000 Fahrenheit, this danger becomes significantly greater. For this purpose I have designed this oven control system so that the oven door cannot be opened at above 600 Fahrenheit. When the selector switch is first turned to the CLEAN position 25, power from the power supply 11 flows through the door latch switch 27 to the solenoid 28 and the latch bolt moves, locking the oven chamber door. The operator cannot get the oven chamber open while the selector switch 10 is in the CLEAN position, because the door latch switch has moved the latch bolt through the operation of the solenoid. The temperature in the oven chamber rises because power is also flowing to the heater element 12 through the timer. As seen before, the fluid in the diaphragm bulb 43 heats up and the diaphragm 35 expands, which results in raising the left free end 30 of the dual switching lever 29.

At the same time the right free end 31 of the dual switching lever 29 lowers. This lowering continues, against the pressure of the return spring 41 until the low setting point is reached. The low setting point is approximately 600 Fahrenheit. This point is established by turning the adjusting screw 38 by means of a screwdriver in the screwdriver slot 39. Raising the adjusting screw 38 raises the low setting.

When the right free end 31 of the dual switching lever reaches the low setting point, the door latch switch deenergizes because the door latch switch 27 has reached normally open contact. This means that above 600 Fahrenheit, the electrical system condition has no effect on the door latch. It must remain locked.

This is most important for the following reason that previous locking mechanisms for cleaning control systerns could fail on power failure. Thus under the previous systems power failures could unlock the door. If the door can be unlocked and opened at such elevated temperatures a very dangerous condition exists.

With my system, when the oven has cooled below the CLEAN cycle temperature, the door latch switch 27 reverses or transfers, allowing the housewife to open the oven chamber door. Then the BAKE cycle is available simply by changing the selector switch 10 to BAKE position 13.

It will also be noted that the additional safety advantage accrues from the following. Once the CLEAN cycle is initiated, the accidental return of the selector switch 10 to OFF or even to BAKE has no effect. This is due to the fact that the change of the selector switch 10 which cuts off the power to the solenoid 28 is ineffective to change the position of the door latch. The power to the solenoid is off and cutting the power ofi at the selector switch 10 will have no effect.

The position of the dual switching lever 29, and in particular, the position of the freely moving ends 30 and 31, is what determines the ability to open the oven door, and these positions are controlled by the temperature in the oven chamber as detected by the diaphragm bulb 43.

It is to be understood that many changes, modifications, and variations may be made in the details of the construction and the filling fluids and arrangements of parts within the scope of the appended claims without departing from the spirit of the invention.

I claim:

1. In an oven control system for an oven having a chamber, a heating element disposed within said chamber, an electrical power supply to power said heating element, an oven door on said chamber and a door latch to lock said oven door,

a first hydraulic diaphragm bulb for controlling the baking temperature of said chamber by controlling the power input from said power supply to said heating element, said diaphragm bulb being located adjacent to said heating element and being filled with liquid mercury to sense by contact conduction the heat output of said heating element,

a microswitch in series connection with and controlling the flow of power from said power supply,

a lever having an adjustable hingepoint to establish the temperature setting at which said microswitch is actuated,

an expansible diaphragm in series with said first hydraulic diaphragm bulb and expansible to actuate said microswtich through movement of said lever,

a second hydraulic bulb for controlling the cleaning temperature of said chamber by controlling the power input from said power supply to said heating element, said second diaphragm bulb being located adjacent to said heating element and being filed with liquid mercury to sense by contact conduction the heat output of said heating element,

a second microswitch in series connection with and controlling the flow of power from said power supply during the cleaning cycle for said chamber, said second microswitch having normally closed contact made,

a timer in series connection with said second microswitch to regulate the length of time of maintaining the cleaning temperature,

a solenoid to control the movement of said door latch,

a third microswitch wired in opposition to said second microswitch so that the normally open contact is made, both said second and third microswitches mounted together, and both provided with switch buttons,

a fulcrum mounted between the switch button on said second microswitch and the switch button on said third microswitch,

a dual switching lever mounted against said fulcrum and having two free ends, one to actuate the switch button on said second microswitch, and the other to actuate the switch button on said third microswitch, and

an expansible diaphragm in series with said second hydraulic bulb and expansible to control the movement of both ends of said dual switching lever.

2. The device described in claim 1 and further characterized by a selector switch to select the baking cycle or the cleaning cycle by actuating power flow to either the first microswitch or to the second and third microswitches.

References Cited UNITED STATES PATENTS 2,428,642 10/1947 Weeks 2l9513 X 2,611,850 9/1952 Walton 2195l1 3,032,636 5/1962 Schauer 219412 3,342,976 9/1967 Kjellberg 219-413 3,356,832 12/1967 Kjellberg 219413 VOLODYMYR Y. MAYEWSKY, Primary Examiner US. Cl. X.R. 219-5 13

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