US3821683A

US3821683A - Thermal switch

Info

Publication number: US3821683A
Application number: US00351848A
Authority: US
Inventors: T Bowling
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1973-04-17
Filing date: 1973-04-17
Publication date: 1974-06-28
Anticipated expiration: 1991-06-28
Also published as: CA1001696A

Abstract

A double-point, thermally-responsive, switch assembly for a self-cleaning electric baking oven fulfills several functions. The switch assembly includes a tube-rod type of differential thermal expansion thermostat which serves to translate a rise in temperature into rectilinear motion, which is translated through a ball and socket joint to a motion amplifier lever. The lever in turn effects the opening and closing of a pair of switches. One switch serves as an over-temperature limit protection for use during the normal baking cycle to effect cutting of power to the baking elements in the event of failure of the primary control system. A second switch is of the double-throw type which is used during the self-cleaning cycle. It serves first to close a first set of contacts to provide power for a cooling fan for keeping the outer wall temperatures of the oven within safe temperature limits. A second set of contacts, upon opening, removes power from a circuit which provides an electroresponsive means such that, when the temperature within the oven cavity is above a predetermined level, the oven door may not be opened. Means are provided for calibrating or adjusting the temperature at which each of the switches will be caused to be switched.

Description

United States Patent [1 owling [11] 3,821,683 5] June 28, 1974 1 THERMAL SWITCH [75] Inventor: Teamus Bowling, Fern Creek, Ky.

[73] Assignee: General Electric Company,

Louisville, Ky.

22 Filed: Apr. 17,1973 [21] App1.No.:3511,848

Primary Examiner-Harold Broome Attorney, Agent, or Firm-Richard L. Caslin; Francis H. Boos [5 7] ABSTRACT A double-point, thermally-responsive, switch assembly for a self-cleaning electric baking oven fulfills several functions. The switch assembly includes a tube-rod type of differential thermal expansion thermostat which serves to translate a rise in temperature into rectilinear motion, which is translated through a ball and socket joint to a motion amplifier lever. The lever in turn effects the opening and closing of a pair of switches. One switch serves as an, over-temperature limit protection for use during the normal baking cycle to effect cutting of power to the baking elements in the event of failure of the primary control system. A second switch is of the double-throw type which is used during the self-cleaning cycle. It serves first to close a first set of contacts to provide power for a cooling fan for keeping the outer wall temperatures of the oven within safe temperature limits. A second set of contacts, upon opening, removes power from a circuit which provides an electroresponsive means such that, when the temperature within the oven cavity is above a predetermined level, the oven door may not be opened. Means are provided for calibrating or adjusting the temperature at which each of the switches will be caused to be switched.

110 Claims, 5 Drawing Figures 3e 9 90 2e 8 12 L9 22 7 er a4. 80/ v14- THERMAL SWITCH BACKGROUND OF THE INVENTION The present invention relates to a thermallyresponsive switch assembly, and more particularly, to a double-point, thermally-responsive, safety control switch assembly for a self-cleaning electric oven to serve as a redundant switch to remove power from the oven heating units in case of a failure of the main oven control thermostat, and further to effect the operation of an indicator lamp and a cooling fan to maintain safe operating temperatures of the outer surfaces of the oven, and further to interrupt a door interlock circuit to prevent the opening of the oven door when the temperature within the oven is above a predetermined level.

This invention is related to the art of self-cleaning ovens which utilize a pyrolytic method of cleaning the interior walls of the oven cavity of food soil by raising the temperature of the walls into a heat-cleaning temperature range above about 750F. At this high temperature, the food soils are transformed into gaseous degradation products which are then oxidized and finally discharged from the oven cavity. The details of this method and of a preferred embodiment of an oven design in which it may be carried out are fully disclosed in US. Pat. No. 3,121,158 of Bohdan Hurko, which is assigned to the same assignee as the present invention.

Thermally-responsive or thermostatic switches are commonly used in domestic appliances such as baking ovens. Perhaps one of the most common types is the hydraulic thermostat which is essentially a hydraulicfilled bellows or diaphragm assembly that converts volumetric expansion or contraction thereof into rectilinear motion acting upon a switch mechanism. Others are of the differential thermal expansion type, and more particularly of the tube and rod thermostat type which control the movement of a lever in order to open and close separate switching elements. Such devices commonly use a lever with a fulcrum at one of its ends, the rod of the tube and rod thermostat applying pressure near this fulcrum point to effect movement in switching at the other end of the lever. Others couple the rod through a slip friction device to the lever. Still others use a tube-rod thermostat having its rod connected to a lever in tension, the lever having its fulcrum at one end and its switching contact at the other end. The prior art has also shown the use of ball and socket joints in compression to interconnect the rod of the tube-rod thermostat with the drive lever.

The present invention is concerned with the functions; firstly of insuring that during the baking operation, the over air temperature does not rise above the 600-650F range in the event of a failure of one of the temperature control elements; secondly of insuring that the housewife may not unlatch the oven door during a heat-cleaning operation unless the air temperature returns below approximately 550F; thirdly of insuring that the outside wall temperatures of the oven do not reach certain unsafe temperatures, and to effect this, at approximately 540F, a cooling fan is switched on to cause air to be circulated between the inner and outer walls of the oven.

The principal object of the present invention is to provide a double-point, thermally-responsive switch assembly which operates in conjunction with the oven heating means to back up the normal or primary oven thermostatic control system to prevent an overtemperature condition in the event of a control failure in the primary oven thermostat system.

It is a further object to provide a double-point, thermally-responsive switch assembly which has differential expansion thermostat which can translate a rise in temperature into rectilinear motion which will be translated to a motion amplifier lever and in turn to a pair of switches, one of which serves as a safety means to deactivate a load circuit during an over-temperature condition in the normal bake operation, and the other of which is a double function switch for use during the self-cleaning cycle first to activate a first control circuit and then to deactivate another control circuit when the temperature being monitored is above a predetermined level.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a multiple point, thermally-responsive switch assembly comprising a base, a housing attached to the base, and a plurality of switch means attached to the housing. Hingedly attached to the base is rigid, motion amplifier means which is adapted to operationally engage the switch means. Temperature responsive means is attached to the base, and has a driver which is operationally coupled with the amplifier means by a universal motion translator, the driver and the amplifier means being coupled in tension to effect opening and closing of the switch means upon the temperatureresponsive means being exposed to predetermined temperatures.

BRIEF DESCRIPTION OF THE DRAWING In the accompanying drawing:

FIG. l is an elevational view, broken away to reveal the various components of the switch assembly of the present invention, in one form thereof;

FIG. 2 is a rear elevational view of the housing of the switch assembly;

FIG. 3 is a view much like FIG. 1, however, taken along the lines 3-3 of FIG. 2 to further expose the operating components of the switch assembly;

FIG. 4 is an interior view taken generally along the lines l-4 of FIG. 1 to show the relation of the motionamplifier lever with the switches located within the housing; and

FIG. 5 is a schematic representation of a power and control circuit useful for a self-cleaning electric oven embodying the thermally-responsive switch assembly of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. I of the drawing, there is illustrated in accordance with the present invention, a doublepoint, thermally-responsive, control switch assembly as for use with a self-cleaning electric oven. A housing such as electrically insulating housing 12 of phenolic resin or the like is formed substantially in the shape of a hollow box. The housing 112 is furnished with a base or metallic cover 14 for substantially closing the housing and providing a mounting structure for certain components of the switch assembly. Cover plate 14 is held in place by a series of fastening screws (not shown) arranged in the holes as shown at 16 in FIG. 2.

Attached to the cover 14 is a temperature responsive means such as differential expansion tube-rod thermostat 20 intended to be exposed to the operating temperatures of the oven interior. Theremostat 20 comprises an outer tube 22 affixed to cover 14 at 24 by suitable means (such as welding). A driver, such as inner rod driver 26, is secured to the crimped free end 28 of outer tube 22 by suitable means (as by welding). Driver 26 is formed of a material such as Rodar or the like, having a coefficient of thermal expansion which is much lower than that of the material of outer tube 22. Tube 22 is formed of a material, such as lnconel or the like, having a coefficient of thermal expansion which is relatively high or large.

Pivotally or hingedly attached to cover 14 by hinge pin 32 is a rigid, motion-amplifier means such as metallic motion-amplifier lever 34. As is shown, driver 26 of thermostat 20 projects loosely through an opening in cover plate 14, and further, through an opening in motion-amplifier lever 34, and has been provided with threads 36 at its free end. Motion is transferred from the driver 26 to lever 34 through a universal motiontranslator such as ball and socket joint motiontranslator 40. This joint is formed of a recess or socket formed in lever 34 and is shown more clearly in FIG. 3 as at 42. The ball portion is formed on one side of a nut 44 which is threadedly engaged with rod driver 26. Compressive bias means, such as compression spring 48, is disposed between lever 34 and cover 14 for maintaining socket 42 of the lever in positive contact with motion translator ball 44. Spring 48 engages lever 34 at one end thereof adjacent motiontranslator 40 and is fixedly attached to cover 14 through holes provided therein.

Mounted within housing 12 are switch means, including a first switch 50 shown in FIG. 1. First switch 50 is of the normally-closed, single-pole, single-throw type, and further of the high-current type having a switchblade 51 adapted to flex only at the support or hinge point 52 to open a set of contacts 54, 54'. Compressive bias means, such as compression spring 56, is provided for maintaining

contact points

54, 54 in tightly closed engagement to prevent their destruction or welding together as by arcing or overheating. Referring to FIG. 3, a second switch 60 of the single-pole, double-throw, rocker-arm type is provided securedly attached within housing 12. Switch 60 has a rocker arm 61, first normally-

open contacts

62, 62 and second normallyclosed contacts 64, 64'. This switch 60 is also provided with compressive bias means, such as compression spring 66, for maintaining the normally-closed contacts in tightly closed engagement, and further, for maintaining in the open position the normally-open contacts.

Referring to FIG. 2, there is shown the rear side of housing 12 to reveal the external electrical connections or terminals of

switches

50 and 60.

Terminals

72 and 74 correspond to first switch 50, and extend into housing 112 to form part of the mounting means of first switch 50.

Terminals

76, 78 and 80 correspond to second switch 60 and pass through housing 12 to form the mounting means and part of the contact means of switch 60.

As shown in FIGS. 1 and 3, motion-amplifier lever 34 has a protrusion or abutment 84 formed of electrically insulating material, such as phenolic or the like. This abutment is securedly attached to the lever 34, and serves to operationally engage

switches

50 and 60 at suitable points on switch blade SI and rocker arm 61 respectively to effect switching in response to thermostat 20 being subjected to predetermined temperature levels. Another relationship may be seen of this engagement of abutment 84 with

switches

50 and 60 by referring to FIG. 4. As is shown, switches 50 and 60 are suitably located within housing 12 so as to be responsive to movement or contact by abutment 84 and thereby by lever 34. Switchblade 51 is suitably fastened to terminal 72 as by spot welding at 85 so as to be hinged that it may be flexed at hinge point 52 in response to engagement by abutment 84. This has been accomplished by providing rolled over edges on switch blade 51 for the whole length thereof except at the hinge point 52. By providing a rigid switch blade and allowing flexing only at the hinge point, and in conjunction with compressive spring 56 applying pressure against the switch blade 51 to maintain it in its normally closed position, the problem of change in calibration of opening temperature of contacts 54, 54' due to flexing, softening or work-hardening of the lever arm of switch blade 51 is essentially obviated. Contacts 54, 54' will maintain their relative positions during their lifetimes.

As can also be seen in FIG. 4, second switch 60 has a rocker arm 61 which is maintained in position by Center terminal 78. An elongated slot 86 in FIG. 3 (not readily visible) is provided in the inner portion of terminal 78 such that rocker arm 61 is free to move within the slot 86 (right to left in FIG. 3) subject to pressure from abutment 84. The initial effect then of increased pressure from abutment 84 is to cause normally-open contact 62, 62' to close, while at the same time allowing normally-closed contracts 64, 64' to remain closed. As the oven cavity temperature to which thermostat 20 is subjected is elevated, further pressure by abutment 84 will, after a dwell period ofa few degrees Farcnheit, force normally-closed contracts 64, 64' to open, while still maintaining the then closed

contacts

62, 62 in a closed position. It should be noticed that rocker arm 61 is always in electrical contact with terminal 78 mainly through the connections and structure of a dual, hairpin spring 66.

Referring now to FIGS. 2 and 3, calibration means are provided for adjusting the temperature at which switches 50 and 60 will be caused to be switched by motion-amplifier lever 34 and thereby by the thermostat 20. One such adjustment is the combination of the threaded end 36 of thermostat driver rod 26 and the ball nut 44 and socket motion-translator 40. An opening 90 is provided in the rear wall of housing 12 through which adjustment may be made of ball nut 44 so as to calibrate the point corresponding to the temperature at which it is desired that contacts 54, 54' of first switch 50 will be caused to be opened by abutment 84 of lever 34. Further, a set screw 92 is provided which is threadedly engaged with the inner end of terminal 80 of second switch 60 so as to form the contact 62. An opening 94 is provided in the rear wall of housing 12 such that set screw 92 may be adjusted externally, as by a screwdriver, to calibrate the point corresponding to the temperature to which thermostat 20 is subjected at which it is desired that normally-open contacts 62, 62' will become closed in response to contact by abutment 84.

Thermally-responsive switch assembly W has been primarily designed for use in a domestic or household baking oven of the self-cleaning type. Thermostat 20 has been designed to project within the cavity of the oven so as to be reponsive to operating temperatures therein. As shown in FIG. 1, mounting means 98 are provided for securing the switch assembly to a wall of the oven.

Preferably an opening is provided in the rear wall of the oven liner such that thermostat 20 may project through for a total distance of approximately 7 inches, flange 98 serving as part of the mounting means, coming to rest against the oven wall surface. Also included in the mounting means is a heat sealing gasket and a mounting washer (neither of which is shown) which will serve to compressibly hold flange 9S securely against the oven wall and which will be fastened thereto by suitable means (such as by screws, not shown).

The double-point, thermally-responsive switch assembly 10 is designed to be used as a control compo nent for a self-cleaning electric oven whose power and control circuits are illustrated in the schematic diagram of FIG. 5. The oven is furnished with an electrical service of 3-wire Edison source of power; nominally of 240 volts, single phase, 60 Hz., A.C. which is usually available in the average residence having adequate wiring. This voltage source is fed to the oven through a 3- wire cable having a pair of line wires L, and L with a voltage of 240 volts therebetween, and a grounded neutral conductor N, for supplying the electrical load of the oven. This electrical load is characterized by three heating elements; a baking element MN), 21 broiling element lltl2 and a mullion heater 104. The bake element 100 is usually located adjacent the bottom wall of the oven, the broil element 102 is usually located adjacent the top wall of the oven and the mullion heater 104 is usually wrapped around the outside of the oven liner adjacent to the front opening for replenishing the heat lost through and around the door opening during a high temperature, heat-cleaning or pyrolytic cycle. These heating elements W0, W2 and 1041 are arranged in circuits in combination with an oven selector switch 106 for setting up different combinations of heating elements at different voltages to obtain a variety of heating rates. A manually settable oven thermostat 1108 is also provided for controlling the temperature within the oven at preselected temperatures during baking operations and a maximum temperature during oven cleaning operations. Such an oven thermostat T08 is arranged serially with the heating elements lltlt), 102 and 1M for opening and closing the power circuit to the heating elements as a function of oven temperature with relation to the temperature predetermined or preset by the thermostat 108.

The oven selector switch 106 is provided with a series of line input terminals denoted as Ll, N, Lll, and L2, as well as a series of load terminals denoted as K, J, and P. This selector switch 106 is provided with a plurality of switch contacts 112 through 120. These switch contacts are labeled with the particular cooking or cleaning operation that is involved when such contacts are closed. For example, during a Baking or a Time Baking operation, contacts H2, H3, MS and 1119 are closed. During a Broiling operation, contacts 116 and ill! are closed. During a Cleaning cycle, contacts 113, llM, 1115, H6, H9 and 1120 are closed.

The Baking circuit has the bake element lltlt) operating at full wattage across lines L1 and L2 at 240 volts through first switch 50 and its

switch contacts

54, 54 to the line terminal Lll through switch contacts U2, M3 to load terminal K and through the bake element 100. During the Baking cycle, the other two

heating elements

102 and 104 are also energized. They are in a series circuit connected back to first switch 5% through contacts 54 and 541 by means of oven selector switch lltlo, terminal Lll through oven switch contacts 118, 119 to load terminal P, and then through the mullion heater MM and the broil element W2.

In the Broiling circuit only the broil element W2 is energized and it is across lines Ll and L2 through first switch 50 contacts 54 and 54' to oven selector switch terminal Ll through switch contacts 117 and 116 to load terminal I and then through the broil element 102.

Should there be a component failure during an operation of Baking, Time Baking or Broiling and should the oven temperature rise above the preset tempera ture of the oven thermostat 10S and reach an oven temperature of say 600 to 650F, then first switch 50 of double-point, thermally-responsive switch ll) would be operated by thermostat 20 to open the circuits through switch contacts 54, 54', thereby de-energizing the heating elements and preventing a runaway temperature condition. Thus, first switch 50 of the thermal switch assembly It serves as an over-temperature limit control when the oven is in any normal cooking operation. In the event of a malfunction of the primary temperature control, any hazard due to overheating of the oven during the Baking, Broiling and Time Baking mode of operation is eliminated.

Second switch 60 of the thermally-responsive switch assembly 10 is arranged to be in an operating circuit only during the heat-cleaning mode of operation. During the cleaning operation, the three

heating elements

100, 102 and 104 are connected in parallel at half voltage across line L2 and neutral conductor N in order to obtain a heating rate somewhat lower than the heating rate of the normal baking operation. At temperatures belowabout 540F, the

switch contacts

64, 64 of second switch 60 are in their normally-closed state to allow actuation of door interlock solenoid 122. At temperatures above 540F,

contacts

62, 62 are closed to provide the power for cooling fan 11241 which causes air to be circulated between the oven liner wall and the outer oven wall and the outer oven walls so as to keep these outer walls cooled. After a temperature dwell of approximately 10F, or somewhere near 550F, normally-closed contacts 64, 64' of second switch 60 are opened cutting power from door interlock solenoid 122, thus preventing the electrical circuit for the door latch from being actuated.

Contacts

62, 62 remain closed until the interior temperature of the oven drops below 540F. For a more thorough discussion of the oven door latching environment in which the present invention is used, reference is made to US. Pat. No. 3,484,858 Jordan et al, assigned to the same assignee as the present invention.

In order to set up the heat-cleaning circuit there are several preliminary operations that must be performed first. It is imperative that the oven door first be closed and then locked before the heat-cleaning cycle is initiated, and also that the door remain closed and incapable of being operated or opened while the oven temperatures are above normal cooking temperatures. A door latch mechanism is actuated by a door lock lever (not shown) and is provided with an automatic latching means in the form of a spring-biased, pivoted hook member 125 which latches the door latching mechanism in both its open and closed positions. In other words, the latching means must be disengaged before the oven door lock lever may be shifted. This is accomplished by connecting a solenoid 122 across line L1 and neutral conductor N through second switch 60

contacts

64, 64 and then to a momentary latch-release switch 126 and then through the solenoid 122 to switch contacts 136 and 137 of the selector switch 106. Thus, at temperatures below the operating temperature of second switch 60, that is below 540F, it is possible to switch the oven door lock lever by closing the momentary latch releasing switch 126, thereby energizing solenoid 122 which picks up the automatic locking device and releases the door latch mechanism. However, at temperatures above normal cooking temperatures, that is, above 550F, contacts 64, 64- of second switch 60 will be opened thereby disabling the solenoid circuit and preventing access to the oven during the heatcleaning cycle. It is not felt necessary to go into any further detail of the power and control circuit since the present invention is centered around the double-point, thermally'responsive switch assembly 10 rather than in the overall circuit and oven combination in which it has been used.

Modifications of this invention will occur to those skilled in this art, therefore, it is to be understood that this invention is not limited to the particular embodiments disclosed but that it is intended to cover all modifications which are within the true spirit and scope of this invention as claimed.

What is claimed is:

l. A multiple point, thermally-responsive switch assembly comprising:

a base;

a housing attached to said base;

a plurality of switch means attached to said housing;

rigid, motion-amplifier'means hingedly attached to said base, said amplifier means operationally engaging said switch means;

temperature responsive means attached to said base,

said temperature responsive means having a driver; and

a universal motion translator operatively coupled in tension said driver and said amplifier means to further effect opening and closing of said temperature responsive means being exposed to predetermined temperatures.

2. The invention of claim 1 wherein the temperature responsive means is a thermostat of the differential expansion type having an outer tube secured to the base and an inner driver secured to the tube at the free end thereof, the driver being formed of a material having a much lower coefficient of thermal expansion than that of the outer tube material.

3. The invention of claim 1 wherein the rigid amplifier means is a lever for transferring motion from said driver to said switch means to effect opening and closing thereof.

4. The invention of claim 1 wherein the universal motion translator is a ball and socket joint.

' 5. A double-point, thermally-responsive switch assembly comprising:

a base;

a housing attached to said base;

a pair of switch means attached to said housing;

a rigid, motion-amplifier lever hingedly attached to said base, the amplifier lever operationally engaging said switch means;

a differential expansion thermostat having an outer tube secured to said base and an inner rod driver secured to the tube at the free end thereof;

a motion translator of the ball and socket type ope ratively coupled in tension said lever with said driver for effecting the opening and closing of said switch upon said thermostat being exposed to predetermined temperatures;

bias means for compressively maintaining said lever in positive contact with said motion translator ball;

and calibration means located in said housing individually adjusting the temperature at which each of said switch means will be caused to be switched by said lever and, thereby, by said thermostat.

6. The invention of claim 5 wherein a first of said switch means is of the normally-closed, single-pole, single-throw type, and a second of said switch means is of the single-pole, double-throw type, adapted first to close a set of normally-open contacts at a calibratable predetermined temperature, then, after a short temperature dwell, to open a set of normally-closed contacts while still holding closed the normally-open contacts.

7. The invention of claim 5 wherein the calibration means is a threaded adjustment at the free end of the driver combined with a nut forming a part of the ball and socket motion translator, and a set screw adjustment for biasing the contacts of one of said switch means.

8. The invention of claim 5 wherein the thermostat driver is formed of a material having a much lower coefficient of thermal expansion than that of the material of the outer tube.

9. A double-point, thermally-responsive, control switch assembly for a self-cleaning electric oven com prising:

an electrically-insulating housing;

a metallic cover for said housing;

a first switch of the normally-closed, single-pole, single-throw type, the switch being secured within said housing;

a second switch of the single-pole, double-throw, rocker-arm type, the switch being secured within said housing and having first, normally-open contacts and second, normally-closed contacts;

a rigid, metal, motion-amplifier lever hingedly at tached at a point off-center thereof to said cover, the lever having an abutment of insulating material located at a free end of the lever further from the hinge point thereof and adapted to operationally engage said first and second switches;

a differential expansion thermostat having an elongated outer tube secured to said base and an inner, rod driver secured to the tube at the free end thereof, the driver being formed of a material having a much lower coefficient of thermal expansion than that of the material of the outer tube, the ther- 9 mostat being adapted to project within the oven to switched by said lever and thereby, by said thermosense the temperature therewithin; stat, including a threaded adjustment at the free a ball and socket joint motion translator operationd f aid d iv ombined with a nut forming a y Coupled in tension Said lever at a free end part of said ball and socket motion translator, and

nearer the hinge point thereof with the free end of 5 said driver for effecting the opening of said first Swtch .upon the thermostat being exposed 10. The invention of claim 9 wherein said first switch determined elevated temperatures, and closing of the normally-open contacts of said second switch, is of the high. Switchblade type adaptd to and after a short temperature dwell, the opening of 0 only at the h point the contacts i fm the normally-closed contacts of said second switch further havmg f P blas means for mamtammg while holding closed the normally-open contacts; the 9 Pomts P Y' engagement, and compressive bi means disposed between Said lever wherein said second switch has compressive bias means and said cover for maintaining said lever in positive for maintaining Said, normally-Closed Contacts in tight" contact with said motion translator ball; and ly-closed ng g and for maintaining p the calibration means for adjusting the temperature at normally-open contacts.

which each of said switches will be caused to be a set-screw adjustment for biasing said normallyopen contacts of said second switch.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 a 821 a 683 Dated June 28 1974 mus Bowlin Inventor(s) 7 Tea g It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 7, line 51, after "tension" insert between Column 8, line 13, "coupled" should read coupling Column 9,

line 4, "coupled" should read coupling Signed and sealed this 24th day of September 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents FORM PO-105O (10-69) uscoMM-Dc Q0376-p59 a U5. GOVERNMENT PRINTING OFFICE: I969 o-aes-zzu,

IINITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 a 821 a 683 Dated June 28 a 1974 T mus Bowlin Inventor(s) ea g It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

(SEAL) Attest:

MCCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents

Claims

1. A multiple point, thermally-responsive switch assembly comprising: a base; a housing attached to said base; a plurality of switch means attached to said housing; rigid, motion-amplifier means hingedly attached to said base, said amplifier means operationally engaging said switch means; temperature responsive means attached to said base, said temperature responsive means having a driver; and a universal motion translator operatively coupled in tension said driver and said amplifier means to further effect opening and closing of said temperature responsive means being exposed to predetermined temperatures.

5. A double-point, thermally-responsive switch assembly comprising: a base; a housing attached to said base; a pair of switch means attached to said housing; a rigid, motion-amplifier lever hingedly attached to said base, the amplifier lever operationally engaging said switch means; a differential expansion thermostat having an outer tube secured to said base and an inner rod driver secured to the tube at the free end thereof; a motion translator of the ball and socket type operatively coupled in tension said lever with said driver for effecting the opening and closing of said switch upon said thermostat being exposed to predetermined temperatures; bias means for compressively maintaining said lever in positive contact with said motion translator ball; and calibration means located in said housing individually adjusting the temperature at which each of said switch means will be caused to be switched by said lever and, thereby, by said thermostat.

9. A double-point, thermally-responsive, control switch assembly for a self-cleaning electric oven comprising: an electrically-insulating housing; a metallic cover for said housing; a first switch of the normally-closed, single-pole, single-throw type, the switch being secured within said housing; a second switch of the single-pole, double-throw, rocker-arm type, the switch being secured within said housing and having first, normally-open contacts and second, normally-closed contacts; a rigid, metal, motion-amplifier lever hingedly attached at a point off-center thereof to said cover, the lever having an abutment of insulating material located at a free end of the lever further from the hinge point thereof and adapted to operationally engage said first and second switches; a differential expansion thermostat having an elongated outer tube secured to said base and an inner, rod driver secured to the tube at the free end thereof, the driver being formed of a material having a much lower coefficient of thermal expansion than that of the material of the outer tube, the thermostat being adapted to project within the oven to sense the temperature therewithin; a ball and socket joint motion translator operationally coupled in tension said lever at a free end nearer the hinge point thereof with the free end of said driver for effecting the opening of said first switch upon the thermostat being exposed to predetermined elevated temperatures, and closing of the normally-open contacts of said second switch, and after a short temperature dwell, the opening of the normally-closed contacts of said second switch while holding closed the normally-open contacts; compressive bias means disposed between said lever and said cover for maintaining said lever in positive contact with said motion translator ball; and calibration means for adjusting the temperature at which each of said switches will be caused to be switched by said lever and thereby, by said thermostat, including a threaded adjustment at the free end of said driver combined with a nut forming a part of said ball and socket motion translator, and a set-screw adjustment for biasing said normally-open contacts of said second switch.

10. The invention of claim 9 wherein said first switch is of the high current, switch-blade type adapted to flex only at the hinge point to open the contacts, said switch further having compressive bias means for maintaining the contact points in tightly-closed engagement, and wherein said second switch has compressive bias means for maintaining said normally-closed contacts in tightly-closed engagement and for maintaining open the normally-open contacts.