US2388702A - Domestic appliance - Google Patents

Description

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W B dv 3% ATTORNEYS Nov. 13, 1945. e. c. PEARCE DOMESTIC APPLIANCE Filed Dec. 30, 1939 10 Sheets-Sheet l0 S R M N 5 W0 N b k A 9 m m B A a U M F 9 .m z r w w 0 4 2 llevll I: .l a M a m 2 a a w m w A wnfl v 3 n w A 1 O 2 5 Q 5555i d UNITED STATES PATENT OFFICE 2,888,702 Dosms'nc arrumcn George C. Pearce, Dayton, Ohio, assignor to General Motors Corporation, Dayton, Ohio, a corporation oi Delaware Application December 80, 1939, Serial No. 311,900

9Claims.

This invention relates to a domestic appliance and more particularly to heating arrangements in two-unit electric ovens and controls'therei'or.

It has been proposed to provide an oven switch mechanism capable of starting on either preheat circuit arrangement or bake circuit arrangement and provided with an automatic means for changing from the preheat to the bake arrangement when the oven reaches a certain temperature. Such a control has been provided with a single control knob. It has been found, however, that there is dimculty in making the user understand the necessary operation 01' such a knob in selecting preheat and baking circuit arrangements.

It is an object of my invention to provide a simple readily understood knob arrangement for an oven thermostat and switch providing an automatic change in circuit arrangements.

It is another object of my invention to provide a quiet dependable means for changing automatically from preheat circuit arrangement to bake circuit arrangement without detrimentally affecting the accuracy of operation oi the oven thermostat.

It is another object of my invention to provide electro-thermal means for controlling the change from preheat to bake circuit arrangement,

Another object of my invention is to provide accurate inexpensive control for controlling oven temperatures and for providing an automatic change from preheat circuit arrangement to bake circuit arrangement during the "ofi" cycle of the oven heating means.

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 form of the present invention is clearly shown.

In the drawings:

Fig. 1 is a sectional view through the entire mechanism taken along the line l-l of Fig. 7, showing the control knob in the "01? position with all parts at room temperature;

Fig. 2 is a view somewhat similar to Fig. 1 but showing only the thermostat proper in section with the temperature control knob set in a. baking temperature position and with the push button in setting position to initiate a preheat cycle, while the electro-thermal element has not been heated;

Fig. 3 is a view in elevation of the switch mechanism with the knob in broil position, the push button in setting position and the electro-thermal control element heated;

Fig. 4 is a fragmentary sectional view similar to the right portion or Fig. 1 showing the preheat switch and control mechanism set in preheat position with the push button released and the electro-thermal element cold;

Fig. 5 is a view similar to Fig. 4 with the pre-.

heat switch in preheat position, the push button released and the electro-thermal element heated and in a latching position;

Fig. 6 is a view similar to Figs. 4 and 5 showing the parts at the end of the preheat cycle with the electro-thermal element cool and with the preheat switch reset in bake position;

Fig. 7 is a right side view of the switch together with a diagrammatic representation of the oven and the electrical connecting circuits;

Fig. 8 is a sectional 8-8 of Fig, 1;

Fix. 9 is a sectional 9-9 of Fig. 1;

Fig. 10 is a sectional view 0! the thermostat proper taken along the line ill-l0 of Fig. 1;

Fig. 11 is a bottom sectional view taken along the line ii-il oi Fig. l with the knob in "o position;

Fig. 12 is a View similar to 3.1 with the knob in bake position; and

Fig. 13 is a simple wiring and electrical circuits.

Brief description Briefly, I have shown an automatic switch for a two-unit electric oven having a rotatable knob for setting the thermostat and an axially movable push button within the center of the knob for setting the control mechanism in preheat or broil circuit arrangement. The preheating is accomplished by pushing the push button, thereby setting a switch in preheat position which connects the upper heating unit of the oven to the source at maximum voltage. A bimetal element is placed in series with this switch and is heated as long as this switch is in preheat position. When the thermostat deenergizes all electric circuits supplying electric energy to the oven heating units, the bimetal element cools and engages a shoulder upon a link and upon further movement moves the preheat switch to bake position in which the upper heating unit is supplied with electric energy at less than maximum voltage.

The preheat switch is set in preheat position and the link properly set by the push button for broiling purposes as well as for preheat purposes.

view taken along the line view taken along the line diagram of the oven However, for broiling purposes the thermostat knob operates with the push button control to provide an opening of an additional switch providing ior'disconnecting the lower heating unit 2 aseanoa from the source of electric energy. The thermostat is provided with a novel lever arrangement,

temperature adjustment arrangement and a snap Construction of thermostat proper Referring now to the drawings there is shown a. thermostat frame member 28 made of heavy sheet steel formed into a channel shape. Extending between the edges of the flanges of the channel-shape frame member 28 is a sheet metal plate 22 and an insulating plate 24. These parts are held together by riveting or other suitable means, not shown. The plate 22 is provided with an aperture which receives the neck portion or a pancake-shaped diaphragm 28 which is fastened to the plate 22 by knurled nuts 28 threaded onto the neck portion of the diaphragm 28 and are located on either side of the plate member 22. A passage extends through the neck portion communicating with the interior of the diaphragm 28 and with the tubing 38 which connects with the thermostat bulb 32 located within or in heat exchange relation with the interior of the electric oven.

The pancake type diaphragm is provided with a button-shaped follower 84 which presses against the point 88 (see Fig. of the main lever 38. The main lever 88 is pivoted upon a conically pointed pin 48 which is riveted to an adjustable channel-shaped carrier plate 42 provided at one end with a sleeve 44 which is threaded onto the threaded portion 48 of a control shaft 48. This control shaft is rotatable mounted in a bearing member 58 which is threaded into a threaded aperture in the frame member 28. The control shaft 48 has fixed to it an L-shaped double ended arm 52, the straight end of which serves as a stop member in connection with the stop pin 54 extending from the frame member 28. The bent end of the arm 52 extends into a notch 54 within the control knob 58 which is made of insulating material. The turning of the knob 58 through the threaded engagement of the control shaft 48 with the threaded sleeve 44 moves the carriage member 42 toward or away from the button 34 of the diaphragm 28 in order to adjust the temperature at which the thermostat operates.

The extreme end of the primary lever 38 has a post 88 riveted to it. This post 8 8 is provided with a set-screw 82, locked by a lock-nut 84 and having a conical point which extends into a conical-shaped depression in a spring retainer 88.

provided at one end of the compression type toggle spring 68. The other end of the compression type toggle spring 68 is held within a recess of a block I8 of electrical insulating material. This block I8 is provided with inserted pins I2 and I4 which extend like arms from either side of the block 18. A flexible contact carrying strip 18 has its reduced portion wrapped around the extending portion of the pin 12 and another contact strip 18 on the other side also has a reduced portion wrapped around the extended portion of the pin 14. Each of these strips are formed of a flexible metal, such as spring bronze, and the strip 16 is provided with a slot 88 which receives at its extreme end the contact post 82 to which this end of the strip is firmly fastened. Likewise the strip 18 is provided with a slot 84 which has at its extreme end a contact post 88 to which that end of the strip is firmly fastened. The elongater slots in each of these strips are provided in order to provide more flexibility adjacent their anchoring portions. The strip I8 has a contact 88 riveted to it, while the strip 18 has a contact 88 riveted to it. These contacts engage the contact posts 82 and 84 respectively.. The anchoring posts 82 and 88 are fastened to the insulating sheet 24 and on the opposite side are provided with binding posts and screws 88 and 88.

The differential of the toggle mechanism provided by the compression spring 88 and the flexible brass strips 18 and 18 are controlled by an adjusting screw I8! which limits the movement of the insulating block 18 and the contacts 88 and 88 away from the contact posts 92 and 84. This set-screw is provided with a lock-nut I83. The extreme end of the main lever is provided with a set-screw I85 which limits its range of movement in either direction. This set-screw is provided with a notch or grooved portion between which the extreme end of the main lever 38 moves. The set-screw is so adjusted that the main lever moves an equal distance upon either side of the center line of the toggle. The set-screw I88 is locked in this position by a lock-nut I88. The action of the toggle mechanism causes the lever 38 to snap from one extreme position to the other. In so doing, the other end of the toggle mechanism, where the contacts are located, also snaps from one extreme position to the other. This provides an excellent snap acting mechanism with a low differential and a relatively high contact pressure with high current-carrying capacity.

The main lever 38 is provided with an aperture which receives the set-screw IM and a second aperture which receives the threaded sleeve 44. A compression spring I81 extends between a washer I88 restingupon the sheet metal plate 22 and the insulating sheet 24 and extends into engagement with the main lever 38 to normally hold the main lever in contact with the button 34 and the conical pivot pin 48. The lower end of the main lever 38 is laterally held in position by a thin flexible connecting member III of spring bronze having arms riveted to the posts H3 provided upon a carriage plate member 42 and having another portion riveted to the lever 38 so as to provide a flexible anchorage for this end of the lever which will prevent any misalignment and provide a connection which cannot be disrupted by jarring or vibration.

A compression spring H5 is provided within a thimble I I! which is riveted within a recess in the frame member 28 and is held by a flange provided at its mouth. This compression spring [I5 bears against the carriage member 42 and serves to hold the shoulder of the shaft 48 against the adjacent end and the threaded bushing 58 during normal operating conditions. The spring Il5 has a force which exerts pressure above the resilient force of the diaphragm 28 but below stresses suflicient to permanently distort diaphragm 26. This arrangement allows the shaft 48 to move to the left away from the shoulder in the bushing 58 to allow for expansion of the diaphragm 28 when the knob 58 is set to temperatures below the existing temperature of the thermostat 32. For example, this commonly occurs when the oven has been heated to the desired temperature for the desired length of time and then the knob 56 is turned to the off" position or to a lower temperature setting. Thus under such conditions the diaphragm 28 remains expanded and this expansion is accompanied by assavoa Construction of preheat and broil control In order to provide a control which may be manually set to a preheat circuit arrangement change from preheat to baking arrangement as well as a broilin'g arrangement, I have provided an additional control mechanism operated by a push button and having a built-in connection with the thermostat for this purpose. The shaft 49 is hollow and through it passes a thin rod I2I. At the left end of the thin rod I2I there is provided a push button I29 located in the center of the knob 59 which is provided with a recess for receiving this knob. The shaft 49 is also provided with a recess which receives a, light compression type spring I25 which tends to push the push button outwardly. At the other end the shaft I25 there is provided a hexagonal guide member I21 which is fastened to the shaft by a set-screw.

Construction of the cam Surrounding this guide member I21 at the right end of the thin rod I2I is a cam member I29, formed of insulating material, which slidably receives the guide member I21 in a hexagonal recess and which is fixed to the rod I2] by the set-screw I9l. This cam member I29-is provided with an annular projection I99 at its outer end, a double second annular projection I35 at its mid-portion and a third annular projection I91 at its left end. This projection I91, as better shown in Figs. 11 and 12, is provided with a notch I 99 which is adapted to receive a cam I provided with an inclined lifting face which extends from the plate 22 of the thermostat. When the knob 59 is in the "off position, as in Figs. 1 and 11, the cam I is received within the notch I39. However. when the knob 59 is turned away from the "off position as in Fig. 12, then the cam I H will coact with the inclined surface of the notch and the adjacent face of the annular projection I91 to cam the cam member I29 to the right. The cam member I29 will always be moved at least this distance to the right whenever the knob 59 is turned away from the off position to any baking temperature position.

Construction of switch for disconnecting lower unit Spaced from the insulating'sheet 24 of the thermostat is a platform I43 of insulating material which is supported by the two contact posts 92 and 94 as well as an additional post I45 located at the other end of platform I49. The platform I43 is spaced from the insulating sheet 24 by collars upon the three posts. The insulating platform I43 on its right face is provided with a square copper or brass conductor plate I41 which surrounds the post 92 and a conductor plate I49 which surrounds the post 94. These plates are also riveted to the platform I43. The conductor plate I49 has an extension provided with a binding screw I59. The plate I41 is provided with a post II to which is connected one end of a spring brass strip I55 while the plate I 49 is provided with a post I59 to which is connected one end of a. spring brass strip I51. As is better shown in Fig. 9 the other ends of the spring brass strips I55 and I51 are joined by a connecting insulating member I59 having a semiand. which will thereafter provide an automatic a toggle action for the free 3 recess provided with a tongue III. A toggle spring I99 is hooked to a connector riveted to theinsulating member I59 in order to provide end of the brass strips I55 and I51. At its other end the toggle spring I59 is anchored to an adjusting screw I95 which may be turnedto move the anchored end of toggle spring I99 to the left or the right as desired. r

The free end of each of the strips I55 and I51 is provided with a switch contact, these contacts being designated by reference characters I91 and I99\re spectively. A cooperating contact I99 is formed on the inner end of a copper or brass plate I1I which is riveted to insulating platform I49 and is provided with a terminal binding screw I19. A cooperating contact I19 is formed at the end of the post which is mounted upon the inner end of a copper and brass plate I15 also riveted to the platform I49 and provided with a terminal binding screw I11. The cam member I29 is provided with a projection I19 which is adapted to register with the tongue I9I when the knob 55 is turned to the broil position so that when the push button I29 is depressed, contacts I91 and I59 will be separated from the contacts I99 and I19 to deenergize the lower oven heating unit.

The preheat termination control To the right of the platform I49 and spaced therefrom is a second insulating platform I9I. This platform is also supported by spacing collars mounted upon contact posts 92 and 94 as well as the supporting post I45. As is better shown in Fig. 8 copper or brass plate I99 is riveted to platform I9I and connects to the contact post 92 and at its other en is provided with a post I 95. A copper or brass strip member I91 is also riveted to the center portion of platform I9I and is provided with a terminal binding screw I99. This strip I91 is provided with posts IN and I99 which support a thin bronze strip I95.

a an I and is provided at opposite ends with suitable anchoring holes for the hooked ends of the twin tension springs I91 and I99 which cause the blade portion of member I95 to move with a, snap action. The free end of the member I95 is provided with a large contact 292 upon its right face and a smaller contact 294 upon its left face. The small contact 294v is adapted to engage contact post 299 provided upon the terminal strip 299 which is riveted to the platform I9I and, as viewed in Fig. 8, extends to the right side of the platform where it is provided with a terminal binding screw 2I9. The large contact 292 is paper 229, is a single bimetal member 222 of the same material as the bimetal member 2 I9 so that it will compensate for changes in ambient temperature. This member or strip 222 is provided with an opening at one end which receives the latch member 224, formed of insulating material. This latch member 224 is pressed toward the cam member I9I by a watch spring 229 anchored to the upper end of the post 2I9 and having a hooked end portion engaging the latch member 224. The latch member 224 is pivotally connect- 4 ed by a pin 228 to the flanged end portion the The electrical connections between the control and the oven In Fig. '7 there is shown diagrammatically an electric oven 248 provided with an upper heating unit 242, primarily for broiling purposes, and a lower heating unit 244 primarily for baking purposes. The thermostat and control as well as the oven is supplied with electrical energ from a three-wire source designated A, O and B. Normall the neutral or middle conductor is designated as 0, while the conductors A and B are designated as the live or outside conductors. With this system there is ordinarily provided a potential of 230 volts across the conductors A and B and 115 volts across either 0-3 or OA. This is commonly known as the three-wire Edison System.

The conductor A is connected to the binding screw 96 while the conductor B is connected 'to the binding screw 98; These screws form part of the binding post and connect to the thermostat contact. The upper heating unit 242 is connected by the conductor 246 to the binding screw I89 and also by the conductor 248 to the binding screw I58 formed on the end of the brass or copper plate I49 which connects to the contact post 94. The lower oven heating unit 244 is connected by the conductor 258 to the binding screw I13, and by the conductor 252 to the binding screw I11. The binding screw 2I8 is connected by the conductor 254 to an external resistance 256 which in turn is connected to the neutral supply conductor O.

Operation in bake position When the oven has not been used and all the parts are room temperature they will be in the position shown in Fig. l as long as the knob 58 is in the oil position. In order to start the baking operation without preheating, the control knob 56 is merely turned to the temperature desired. This will cause movement of the threaded sleeve 44 and the carriage member 42 away from the button 34 of the diaphragm 26, and under this condition the compression spring I81 will move the main lever 38 rapidly to its extreme left position with a snap action as limited by the stop screw I85. The set-screw 62 will thus be moved across the center line of the toggle mechanism formed by the compression spring 68 and the spring bronze strips 18 and 18 to snap the thermostat contacts 88 and 98 to closed position. When the oven comes up to temperature, the thermostat bulb 32 will be heated suflicientl to expand the diaphragm 28 to cause the button 34 to bear against the point 36 of the main lever 38 so as to pivot the main lever 38 about its fulcrum point 48 to return the thermostat toggle mechanism with a snap action to the position shown in Fig. 1. Thus for baking without preheating the thermostat will cycle between the positions shown in Figs. 1 and 2 in order to maintain the oven at the proper temperature.

Current flow in bake positioncurrent flows through the conductor 252 to the binding screw ll'l, through the conductor strip I15 to the contact I18 which is in contact with the contact I69. From the contact I69, the current flows through the strip I51 to the plate I49 and thence through the contact post 94 to the contact 98 from which the current flows through the strip 18 to the anchoring post 86 which is provided with a contact screw 98 to which the conductor B is connected.

Current also flows from the plate I49 through the conductor 248 to the upper heating unit 242 from which current flows to the conductor 246 to the binding screw I89 which is formed on the end of the conductor. strip I81. From the conductor strip I 81 the current flows through the posts I 9| and I93 to the bronze strip member I35 which in the baking circuit has its lower contact 284 in contact with the contact post 286, provided upon the end of the conductor strip 288 having a binding screw 2I8 which connects to the conductor 252 and to the external resistance 258 which in turn connects to the neutral conductor 0. Thus as is more clearly shown in the wiring diagram, Fig. 13, the lower oven heating unit is connected across the supply conductors A-B while the upper heating unit is connected in series with the external resistance 256 across the conductors OB. Thus the lower oven heating unit is supplied with 230 volts while the upper heating unit is supplied with volts diminished by the voltage expended in the external resistance 256.

Operation of preheat-bake arrangement When it is desired to bring the oven more quick- 1 v to a desired temperature, the knob 56 is turned to the baking temperature desired and in addition the push button I23 is depressed as shown in I Fig. 2. This causes the shoulder I36 of the projection I35 of the cam I29 to engage the projection 232 of the latch member 224 in order to pivot the latch member 224 in a counter-clockwise direction about its pin 228 so that the shoulder 238 of the latch member 224 will pass through the opening in the compensating bimetal member 222. This movement of the latch member 224 will also move the bronze strip with a snap action produced by the toggle springs I91 and I99 to lift the contact 284 away from its contact post 286 and to cause the upper contact 282 to make con- I Current flow in preheat arrangement In this position of the control mechanism, the

with the current to the I 246 which in turn free end of the bronze strip I95 by same voltage, 230 volts, order to provide more four times its heat output provided in the baking circuit arrangement. Thus, the current for the upper oven heating unit flows from the supply conductor A through the binding post as, through the thermostat contacts 88 and 92 along lower oven heating unit. The current then flows through the binding post 22 to the contact strip III thence through the post Ill to the U-shaped bimetal member 2I8, thence the current passes through the U-shaped bimetal member 2I8 to the opposite post 2| which is provided with the overhanging contact support 2 for supporting the contact 2I2 which is now in engagement with the contact 202 upon the'iree end or the bronze strip lit. The current then passes throughthe bronze strip I II to the conductor strip III which is provided with binding screw Ill connecting it with the conductor connects to the upper oven heating unit 242 which is also connected to the conductor 248 connecting to the .binding screw Ill upon the copper or brass conductor plate I49 which connects to the conductor post 84 making contact with thermostat contact 80 for connection through the bronze strip I8 and through the anchoring post as and the binding screw 88 to the conductor 80.

Operation the bimetal as the oven comes up to the desired temperature the thermostat contacts 88 and 90 will be open thus stopping the flow of current through the bimetal member 2Il. This will cause the bimetal member 2Il to gradually move the compensating strip downwardly to the position shown in Fig. 6 carrying with it the latch member 224 and the reason 01' the engagement of the shoulder 230 with the lower surface of the free end of the compensating strip 222 around the aperture provided for receiving the latch member 224. From this point on, the control will always be connected in bake circuit arrangement until the control is reset.

Operation for broiling For broiling, only the upper oven heating unit 242 is used at 230 volts. In order to broil, the knob 58 is turned to its highest temperature position with thearm 52 against the stop screw 54 as shown in Fig. 3. This brings the projection I19 upon the cam I29 into alignment with the projection I8I upon the I59. After this, the push button I23 is depressed as shown in Fig. 3 in order to separate the contacts I81 and I69 from the contact I68 and I'll! to deenergize the lower oven heating unit. This movement of the cam member I will also move insulating connection ton and cam then released. This allows only the upper oven heating unit 242 to be supplied at 230 volts through the same circuit described for preheating. At this high temperature setting of the thermostat and with only the upper oven heating unit being employed, the thermostat contacts 24 and 90 will remain closed throughout the broiling period because of. insuiilcient oven temperature to open the contacts. When the knob 56 is turned to the "03 down oil the cam I4I into the notch I88 provided for this purpose so that the projection I" will return the contacts I" and I into engagement with the contact posts I and I10 to reconnect the lower oven I32, upon the cam member I28, will always be in the position to engage the projection 232 or the latch member 224 whenever the latch member 224 is set to the position shown in Figs. 4 and 5 inorder to return the latch member 224 and the strip I85 to the position shown in Figs. 1 and. 6 where the contact 204 is again in contact with the post 208. With this mechanism there is no load placed upon the thermostat mechanism for automatically accomplishing the change from preheat circuit arrangement to bake circuit arrangement. The broiling circuit arrangement is accomplished by the push button I22 rather than the tempera ture control knob 56. The Operation of both the thermostat and the preheat, bake control are very quiet. The control has a long life and is free from connections which involve much wear.

While the form or embodiment of the invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all the claims which follow.

What is claimed is as follows:

1. An electric heating means for heating a zone to be heated, means for connecting said heating selectivehr into a baking circuit arrangement for baking purposes and a preheat circuit for quick preheating, thermal means eiiective only when cooling for changing the connecting means to change the preheat circuit arrangement to the bake circuit arrangement, and means for heating the thermal means when the heating means is connected in preheat circuit arrangement, and thermostatic switch means responsive to temperatures of said zone for controlling the connection of the heating means for the zone and the means for heating the thermal means to a source 01' power.

2. An electric oven comprising upper and lower heating means, means for supplying electric enlower heating means and a comparatively small heat output from the upper heating means for returning said normal purposes, electrothermal means for increasing the heat output of the upper heating means for a limited period and thereafter upper heating means to the small heat output, and means responsive to oven temperatures for controlling the connection of the upper and lower heating means and the electrothermal means to a source of power.

3. An electric oven comprising upper and lower heating means, means for supplying electric energy so as to obtain a high heat output from the lower heating means, and a comparatively small heat output from the upper heating means for normal baking purposes, means for increasing the heat output of the upper heating means, electro-thermal means for returning the upper position the cam member I20 rides heating unit while the shoulder coming within the scope of heating means to the small heat output, and means responsive to oven temperatures for controlling the connection oi the upper and lower heating means and the electro-thermal means to a source of power.

4. An electric heating means for heating a zone tr be heated, thermostatic switch means for controlling the connection of the heating means to a power source to regulate the temperatures of said zone as desired, means for connecting said heating means selectively into a baking circuit arrangement and into a preheat circuit arrangement, means including a thermal device operated by current flowing in the preheat arrangement for preparing for a change from preheat circuit arrangement to bake circuit arrangement, said thermal device including means effective upon its reduction in temperature'in response to opening of said thermostatic switch means for accomplishing a change from preheat to bake circuit arrangement.

5. An electric heating means for heating a zone to be heated, thermostatic switch means for controlling the connection of the heating means to a power source to regulate the temperatures of said zone as desired, means for connecting said heating means selectively into a baking circuit arrangement and into a preheat circuit arrangement, a movable device, a latching means for latching the movable device to said connecting means when the movable device is operated in one direction, manually operable means for moving the connecting means from the baking circuit arrangement to the preheat circuit arrangement, current operated means operated by the current flowing in the preheat arrangement for moving said movable device in said one direction to provide for the latching of the latch means, said movable device being provided with means for moving it in the opposite direction upon deenergization of said current operated means by the thermostatic switch means for moving the connecting means from the preheat circuit arrangement to the baking circuit arrangement.

6. An electric heating means for heating a zone to be heated, thermostatic switch means for controlling the connection of the heating means to a power source to regulate the temperatures of said zone as desired, means for connecting said heating means selectively into a baking circuit arrangement and into a preheat circuit arrangement, manually operable means for moving means to a power source to regulate the temperatures of the zone as desired, thermally operable connecting means having bake and preheat alternative positions for connecting said heating means selectively into a bake circuit arrangement and into a preheat circuit arrangement, said connecting means including thermaloperating means and means dependent upon said switch means for heating said thermal operating means when positioned Lin the preheat position tor the preheat circuit arrangement and f r discontinuing the heating when positioned n the bake position for the bake circuit arrangement, said thermal operating means including means effective upon its cooling for moving the connecting means from the preheat to the bake position.

8. An electric heating means for heating a zone to be heated, a power source, a doublethrow switch means having one position for connecting one portion of the heating means in parallel circuit arrangement with a second portion of the heating means to the power supply at full voltage and a second position connecting said one portion to the power source at reduced voltage with the second portion remaining connected to the power source at. full voltage, said switch means having means for holding itself in either position, a thermal operating means operably connected to said switch means, a small heating means for heating said thermal operating means when said double-throw switch means is in said one position, a thermostatic switch means for controlling the connection of the heating means to the power source to regulate the temperatures of said zone as desired and for deenergizing said small heating means when said zone reaches the desired temperautre, said thermal operating means including means eflective upon its reduction in temperature in response to the deenergisaid connecting means into the preheat circuit arrangement, and a thermal device rendered effective in response to the opening of said thermostatic switch means for causing the movement of said connecting means from the preheat to the baking circuit arrangement.

7. An electric heating means for heating a zone to be heated, a thermostatic switch means for controlling the connection of the heating zation of the second heating means for moving said double-throw switch means from said one position to said second position.

9. An electric heating means for heating a zone to be heated, thermostatic switch means cior controlling the connection of the heating means to a power source to regulate the temperatures of said zone as desired, means for connecting said heating means selectively into a baking circuit arrangement and into a preheat circuit arrangement, manually operable means for moving said connecting means into the preheat circuit arrangement, and means including an electrical circuit portion controlled by said thermostatic switch means and a, current conducting electro-thermal device connected in said circuit portion and rendered efiective in response to the opening of said thermostatic switch means for causing the movement of the connecting means from the preheat circuit arrangement to the baking circuit arrangement.

GEORGE c. PEARCE.

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