US2441192A

US2441192A - Thermostatic switch

Info

Publication number: US2441192A
Application number: US526601A
Authority: US
Inventors: Theodore E Graves
Original assignee: Wilcolator Co
Current assignee: Wilcolator Co
Priority date: 1944-03-15
Filing date: 1944-03-15
Publication date: 1948-05-11
Anticipated expiration: 1965-05-11
Also published as: GB608879A

Description

y T. E. GRAVES 2,441,192

'IIIHERNOS'IA'IIC SWITCH Filed March 15, 1944 4 Sheets-Sheet 1 1 a May 11, 1948. 'r. E. GRAVES THERMOSTATIC SWITCH Filed March 15, 1944 4 Sheets-Sheet 2 fl'h l, g I NVENTOR.

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ATTORNEY$ May 11, 1948. v. GRAgEs 2,441,192

THERMOSTATIC SWITCH Filed March 15, 1944 4 Sheets-Sheet 4 \Vg T/ 21 73,

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provided with means Patented May 11, 1948 v 2,441,192 THERMOSTATIC SWITCH Theodore E. Graves, West Orange, N. luassignor to The Wllcolator Company,

Elizabeth, N. 1., a

corporation of Delaware Application March 15, 1944, Serial No. 528,601 13 Claims. (Cl. 200-814) This invention relates to a snap-acting thermostat which may be used in various types of control apparatus, but which is particularly suited for controlling electrical heating circuits. The new snap-acting mechanism of the present invention includes a novel leaf-spring snap-acting device for making or breaking electrical circuits and for releasing a push-button switch.

The snap-acting device of this invention may be used for a variety of purposes in the control of electrical or gas heating apparatus. However, the improved snap-acting apparatus will be described and illustrated in connection with the control and operation of bake and broil" heating elements in the oven of an electric range. It is to be understood that the invention is not limited to the illustrated embodiment. v

Various types of control apparatus have been provided for the ovens of electric ranges where such ovens include an electric broiling unit and an electric baking unit, the controls being such as to provide a preheating period during which the baking and broiling circuits are connected in parallel for rapidly heating the oven to approximately the desired temperature. Such control apparatus have also been used in connection with selector switches and transfer switches to provide various heating conditions in the oven.

The improved apparatus of the present inventlon will be described in connection with its use of bake and broil circuits for preheating the oven, the automatic elimination of the broil circuit at a predetermined temperature, and the automatic subsequent use of the bake circuit to maintain a predetermined temperature.

An important feature of the present invention is the provision of a leaf-spring snap-acting device which has a sensitive snap but in which all parts may move freely without jamming at any temperature within the range of the thermostat and at the same time be effective without the use of loading springs. The device includes spring having three tongues, the outer two of which are pivoted in aligned knife-edge bearings under compression by placing a tension on the central tongue suflicient to substantially how the outer tongues. The free end of the central tongue is attached to the long end of a lever pivoted in such a way as to maintain a tension on the tongue and at the same time adapted to be actuated by a bellows responsive to the temperature changes in the oven. A movable block or insulating saddle provided with electrical contacts is attached to the top of the spring assembly and is adapted to be snapped into or out of contact with corresponding contact points mounted in the apparatus. A snap of the spring will occur when the free end of the lever attached to the middle tongue passes the dead center of the spring or the point where the spring is pivoted. The free end of the central tongue is preferably attached in spaced relation with respect to the actuating lever so that the pivot point of the spring is oilset with respect to the pivot point of the lever. This ofiset arrangement maintains the opposite end or the actuating lever against the bellows, thus providing the loading force usually found necessary in order to secure a sensitive return action of the bellows, as when the temperature of the oven is falling.

Another feature of the present invention is the provision of a novel snap-acting thermostatic control system which includes the snap-acting mechanism described above, associated with a leverage means for locking and releasing a preheat switch. An oven heating system arranged in accordance with this invention may comprise baking and broiling resistance heating elements in the oven with connections between them, a source of electrical supply including a push-button preheat switch for simultaneously operating the bake" and broil elements, a leverage means for locking the push-button switch in closed position and for releasing the push-button in such a way as to give a visible and audible signal at the end of the preheat. The leverage mechanism iunctions in cooperation with the bellows and the snap-acting mechanism to maintain the preheat conditions and to cut out the broil" element at a predetermined temperature. Thereafter, the temperature in the oven is maintained by the bake element under the control of the snap-acting thermostatic mechanism. The improved leverage means tor locking and releasing the push-button switch cooperates directly with the snap-acting mechanism without altering its sensitiveness. It comprises an adjustable lever pivoted between the push-button switch and the lower movable portion of the snap-acting mechanism.

A further feature of the present invention is the provision of a. novel arrangement or a. bellows mounted on a movable stem-bearing or axle centered in the stem or temperature setting screw of an oven regulator dial. The bellows is provided with a contraction limiting means and is mounted between the dial and the actuating lever, and there is direct and positive tension on the bellows from the snap-acting spring, thus avoiding the use of loading or bellows springs. Furthermore,

there are no sliding members to be operated by the bellows, and a very sensitive snap-acting movement is obtained with a minimum of moving parts and a maximum or free action.

The thermostat unit of the present invention is sensitive, compact, convenient to adJust, and lends itself to accurate and convenient mass production. Other important features, objects and advantages of the improved apparatus will be described in connection with the accompanying drawings, in which:

Fig. 1 is an enlarged vertical sectional view of the improved snap-acting thermostat control apparatus of the present invention.

Fig. 2 is a vertical sectional view of the apparatus shown in Fig. 1, taken on the line 2-4 of Fig. l.

Fig. 3 is a vertical sectional view of the apparatus taken on the line 33 of Fig. 1.

Fig. 4 is a broken horizontal sectional view of the dial construction shown in Fig. 1, taken on the line 44 of Fig. 1.

Fig. 5 is a front view of a portion of the apparatus shown in Fig. 1, taken on the line,5-5 of Fig. 1 with the dial removed.

Fig. 6 is an enlarged broken detailed view showing the structure of the eccentric button shown in Fig. 1. a

Fig. 7 is a front view of the improved snapacting spring removed from the remainder of the apparatus.

Fig. 8 is a front view of the dial and push-button mounting of the improved control apparatus adapted for use in connection with an electric oven.

Figs. 9, i0 and ii are wiring diagrams of the thermostatic control apparatus illustrating the various combinations of heating circuits which may be employed.

12 is a vertical sectional view showing the structural elements of the metal casing of Fig. i.

Fig. 13 is an elevational view showing the inside of the casing of Fig. 12.

Fig. 14 is a front view of the actuating lever for the snap-acting spring and bellows arrangement comprising a part oi. the apparatus shown in Fig. i.

Fig. 15 is a vertical central sectional view of the actuating lever shown in Fig. 14.

Referring to Figs. 1, 2 and 3 of the drawing, most of the elements of the improved apparatus passed through lows with respect to the threaded stem I4. The turning oi! the stem II (in making a temperature setting), or of the calibration screw I8 shifts the bellows in the housing Ill, and this the helical coil a flange i! The dial knob and 48 and a central B9. The snap-acting mechanism is mounted in a bracket member 35 attached to the lower inside aligned V-shapeci grooves 38 in which the lower ends of the

spring legs

47 and 48 rest. The ends of the

legs

47 and 48 are preferably knife-edged to provide a free pivot. The bracket 35 also includes two spaced outwardly tending arms tongue 49 to bow the

outer tongues

41 and 48 as shown in Fig. 1. The stress thus created holds the lever 42 and the spring 46 against their respective pivoting points, over-centered snap action. It will be noted, as

tongue 49 forces the knife edges 45 strongly against the pivots 4|. The upper end of the lever 42 is short compared to the lower end, and is provided with a recess 58 for receiving the point Of a sharpened pin or stud 59 attached to the end of the bellows IS. The snap-acting mechanism is mounted in the bracket 35 so that the central tongue 49 pulls on the button 50 in a line which is always to the right of the pivot bearings 4|.

This pull tends to swing the lever 42 in a counterclockwise direction on the pivot bearings 4| and therefore provides a substantial loading force against the bellows I and insures sensitive action of the bellows without the use of separate loading or bellows springs.

A clip BI is riveted through the free end or body portion 80 of the spring 46, the rivet being applied through a hole 53. The clip extends through a positioning notch 62 and then substantially horizontally into a saddle 65 of electric insulating material, to which it is attached by a cotter pin 84. The saddle arrangement is substantially the same as that of Weddell, Patent .No. 2,197,230, and comprises separated

elongated sections

61 and 68, each of which carries a pair of vertically arranged movable contacts bridged by a conductor 10. These conductors are secured respectively to the sections of the insulating

material

61 and 58 by fastenings 1i.v Electric current is supplied to the apparatus through wires connected respectively to a pair of contacts 12 by binding posts and the saddle arrangement 65, together with the conductors 10. serve to bridge the contacts 12 with

contacts

13 and 14 mounted in the back cover I2 directly below the contacts 12. The movement of the saddle and movable contacts is restricted by spaced adjustable stop screws 84 which are engaged by projections 85 which preferably comprise an integral part of the insulating material of the saddle structure. The stop screws 84 may be operated from the front side of the metal case 1 and locked in place by means of lock nuts 86. The movement of the lower end of the lever 42 or of the tongue or leg 49 to the right between the pivot points of the bowed

legs

41 and 48 snaps the saddle mechanism against the

contacts

12, and 13 and 14, so as to supply current to the control and heating apparatus, while the movement of the lower end of the lever 42 to the left causes the saddle to snap to the left against the stop screws 84.

The bellows I5 is provided with an internal stop plug 80 which is adapted to engage a'rest block 8| upon the contraction of the bellows to a predetermined extent. This stop provides a convenient method for calibrating the apparatus and for preventing the closing of the contacts when the dial is set to off. The calibration is carried out by charging the bellows I5, capillary I6, and the bulb (not shown) so that the expanding end of the bellows does not move to unseat the stop 80 until an exact temperature such as 150 F. is reached at the bulb. A calibration mark is then placed on the dial for this point instead of for any lower temperature. Since the contraction of the bellows ceases when the bulb is at 150 F. because of the stop 80, the thermostat may then be accurately calibrated by beginning with this point on the dial. There is no movement of the bellows below the temperature of 150 F. and therefore when the dial is turned to off the bridging of the contacts 12 with the

contacts

13 and 14 will be broken and the contacts will remain open no matter how cold the bulb may become.

The importance of these features will be apparent when it is realized that in many cases it has been necessary to provide some form of mechanical lock to hold the contacts open in the of! position. Another advantage of this arrangement is that if fluid should be lost from the bulb or bellows, the contacts would still remain open in the off position of the dial. The calibration of the thermostat may be completed without removing or shifting the dial 3I, by merely setting the dial to the temperature of the bulb in the oven, and then. while holding the dial at this point, turning the calibration screw I8 to the right or to the left, until the thermostat snaps and opens the circuit.

Since the thermostatic control apparatus of the present invention is illustrated in connection with an oven provided with bake and broil resistance heating elements, and the temperature control is used primarily in baking, the contact 13 is connected to both the bake and broil" elements, while the contact 14 is connected to a transfer switch normally connected to the bake" heating element. The bake" and broil heating elements are normally used alternately; therefore, the transfer switch is provided with a connection to the "broil element. The pushbutton preheat" switch is arranged to supply current to the broil heating element independently of the transfer switch. A simplified arrangement of the transfer and push-button switches is shown in Figs. 9, 10 and 11, while the structure of the switches is shown in Figs. 1, 2 and 3, in which they are shown as mounted in a casing I00 of insulating material, attached to the lower part of the metal casing 1 by means of front screws IM and I02, set through lugs I03 and I04, and by side screws I01 and I08. The threaded holes for the screws are shown at I05, I08 and I08 in Figs. 12 and 13. The transfer switch is mounted in a recess IIO, back of a front cover III, and comprises a "broil" contact II5 on the head of a bolt H3, held in place by means of a nut H2. The bolt II3 provides connections to a lug II4 directly above the nut and to a bus bar IIGhaving a horizontal portion II1 (Fig. l) and a depending portion II8 to which is secured a contact I20 for the pushbutton switch. The terminal 14 is connected to the inlet of the transfer switch through a lug I2I (Fig. 2), mounted on a bolt I23, which also secures a bus bar I24 having a depending portion I25 and a contact I28 for the pushbutton switch. The bolt I23 also mounts a metal collar I21 and a long brass or copper spring conductor I28 having upper and lower contacts I29 and I30 arranged directly over contact II5. A nut I32 holds the bolt assembly in place and keeps the spring I28 in upward tension so that the contact I28 normally engages a contact I3l' mounted under a bus bar provided with a binding post I33 from which a wire leads to the bake resistance heating element. The spring conductor I28 may be depressed so that the movable contact I30 engages the contact II5 to supply current to the broil heating elementinstead of the "bake element, by rotating the dial 3I to broil" so that the dial finger 30 depresses a beveled slide bar I35 which rests on the spring conductor I28. In this position the finger or -blade 30 comes in contact with a stop 82 on the housing I0.

The push-button mechanism of the prehea switch, is mounted between the spaced contacts I20 and I28, and comprises a cylindrical metal stem I40 having an end portion I40 of slightly reduced diameter and an elongated portion I48 with a threaded end to which is secured a pushbutton I43 of insulating material. This button is mounted directly below the dial 3I and is normally held in extended position by a main compression spring I45 which is mounted around a reduced section I within a cylindrical opening I44. The push-button assembly also includes a sleeve I49 of insulating material mounted against all of insulating material, and

' the latter. When the dial the larger section of the stem I, a sleeve "I of reduced diameter provided with a flange I55, :3. metal contact bar I52 adapted to bridge the contacts I25 and I26, and mounted over the sleeve section I5I against the flange I50. The bar I52 engages a shoulder of the casing I and limits the outward movement of the button 3. The contacts I20 and I26, together with the contact bar I52 and other parts of the apparatus, are mounted in a rectangular cavity N of the casing I00. A spring I 53 is mounted over the sleeve section I5I in a space Ml between the contact bar i52 and the end of the button section I. This spring keeps the contact bar against the contacts I20 and I26, when the push-button I43 is pushed in.

One of the important features of the present invention is the provision of means for holding the push-button in place to bridge the contacts I20 and I26, and at the same time provide means automatically operable by the snap-acting mechanism or bellows for opening the push-button and switch, and releasing the push-button at the end of the preheat period, in such a manner as to give an audible and visible signal. The novel means for cooperating with the snap-acting mechanism in this way may be referred to as a trigger or releasable latch comprising a. friction pawl I55 having the flat construction and shape shown in Figs. 1 and 3. The pawl I55 is pivoted in a slot cut in a horizontal section of a bracket I54. The lower end of the pawl is provided with a slot I56 which extends over an adjusting screw I51 between the head of the screw and a spring I58, adapted to urge the pawl I55 toward the head of the screw. A spring may be placed on stem I40 instead of on screw I51. The pawl lever I55 extends above its fulcrum point in the bracket I54 and slightly to the right of the button 55. Opposite the button 50 the pawl I55 is provided with an adjustable screw I58 which is provided with a lock nut IBII. The button 50 bears against the screw I59 under the conditions shown in Fig. l, and its movement to the right is limited so that the pin 59 may, under certain conditions, move away from the lever 42. The portion I45 01 the push-button stem I40 extends through a hole I52 drilled at right angles to the metal in the lower portion of the pawl I55. The hole is a sufficiently close fit for the stem section I40 so that while the stem may be pushed freely through the hole into a depression IBI, if the pawl is rocked counter-clockwise on its pivot, it will on the other hand bite into and pinch the stem upon any slight movement in the opposite direction, thus holding the stem securely at approximately its innermost position. The bridging contact bar I52 will, therefore, be held firmly against the con I tacts I20 and I26 under I53.

When the pawl lever is rocked or rotated in a counter-clockwise direction on its fulcrum point, it will release the stem of the push-button which immediately snaps to the left, in Fig. 1, breaking the broil circuit, and returning the push-button I43 to its outward tension of the spring 011" position to any desired baking temperature position. the threaded stem II moves to the left in the threaded member II, and permits the belposition with a visible move- I lows I5 to move to the left in Fig. 1. At the same time, the lower end of lever 42 moves to the right, the spring 45 snaps to close the current supply contacts, the button 50 contacts the screw I55 to push the pawl lever I55 in a clockwise direction. so that when the push-button H3 is pushed in to initiate a preheating operation, it is held in. place by the pawl lever I 55. The oven now is operating under preheat conditions with the circuits connected in parallel in the manner shown in Fig. 10.

Now, as the temperature of the oven approaches the desired point, the bellows I5 gradually expands and moves the lower end or the lever 42 to the left. The adjusting screw I59 on the upper end of the pawl lever I55 follows this movement because of the urging of the spring I55 at the opposite end of the pawl lever. By the time the button 50 moves a predetermined distance from the point where the spring 45 snaps and opens the current supply contacts, the pawl lever has rotated to an angle where it suddenly releases the push-button stem IIII. When the straight section of lever I55, which includes the hole I 52, approaches nearer to an angle of to the stem I 40', it begins to lose its grip, as will be apparent from the description and showing. The head of the adjusting screw I51 stops the further movement of the pawl lever I55 so that the screw I59 disengages the button 50 as the lower end 01' lever 42 continues to move to the left, to th snap position and beyond. The lower portion oi the snap-acting mechanism, therefore, is free to move back and forth through the snapping position of the thermostat independent of and without interference by pressure from the pawl lever I 55. The adjusting screws I51 and I5! at the opposite about 25f F. below the temperature setting for the oven. The at this point avoids overshooting the temperature for which the oven is set. The desired adjustment may be secured by moving the screw I55 until the trigger lever I55 releases the push- After the push-button I" has been released in the manner described above, and the desired preheat temperatureis reached in the oven, the snap-acting spring tacts, and thereafter the oven is maintained at the desired baking temperature by element under control of preheat circuit may be used at any time when the "bake circuit is on, to speed up the heating operation by merely pushing in the button I" desired temperature.

From the foregoing description, it will be apparent that in the heating system of this invention, the improved thermostatic controller mechcally controlling the oven temperature and for changing the heating connections after a presponse to a rise in heating cycle so as to continue the operation with only the "bake" heating element. The improved apparatus is of simple construction, easy to adjust and operate, and does not require the use of loading spri gs and hand-locking mechanism such as are commonly employed in the art.

Having described the invention in its preferred form, what is claimed as new is:

l. A temperature control apparatus including a main switch, a thermostat responsive to changes in temperature for opening and closing the main switch, a handle for adjusting said thermostat to difierent temperature settings, a second switch connected into an outlet of said main switch and normally biased to open position, manually operable means for closing said second switch, a latch mechanism for holding said manually operable means in its switch closing position and for thereby holding said second switch in closed position, and means operable by said thermostat in response to a rise in the temperature to a predetermined temperature set by said handle for releasing said latch mechanism and thereby permitting said second switch to open at said predetermined temperature.

2. A control apparatus as defined by claim 1, in which the manually operable means includes a stem and the latch mechanism includes a means for gripping said stem.

3. A temperature control apparatus including a main switch, a thermostat responsive to changes in temperature for opening and closing the main switch, a handle for adjusting said thermostat to different temperature settings, a-second switch connected into an outlet of said main switch and normally biased to open position, push button means operable for manually closing said second switch, leverage means adapted to engage the push button means for holding said second switch in closed position when the push button is pushed in, said leverage means being arranged in operative relation to said thermostat so that said push button is released by the thermostat in retemperature to a predetermined temperature with respect to the temperature set by said handle.

4. A control apparatus as defined by claim 3 in which the push button means includes a stem and the leverage means includes means for gripping the stem.

5. In a temperature control apparatus including a mounting and a rotatable dial thereon, an expansible and contractible bellows responsive to temperature changes set in said mounting with one end firmly engaging said dial, a, lever having one end engagin the end of the bellows opposite the dial. said lever being pivoted in the mounting by means of a pivot closely adjacent to the bellows and thereby providing a short lever section engaging the bellows and a relatively long lever section extending beyond the pivot, a snapacting spring pivoted in the mounting on the opposite side of said lever from said bellows in laterally spaced relation to the pivot of the lever and having a tension member attached to the long end of the lever by a spacing attachment, a control means operable by said snap-acting spring, said dial, said bellows, said lever and said spring being mounted directly in series and arranged so that the tension of the spring maintains the short end of the lever in sensitive firm engagement with the bellows in any operative position of the of a separate loading means for the bellows.

temperature with respect to the lever, thereby avoiding the use 6. In a temperature control apparatus as defined by claim 5, a second control means in the mounting normally biased to inoperative position, a manually operable member. for moving said second control means to operative position, a latch for holding said manually operable member in position to retain said second control means in operative position, the expansion of said latch.

7. In a temperature control apparatus as defined by claim 5 in which said snap-acting spring includes a pair of spaced compression spring legs upon which the spring is pivoted and a tension leg mounted between said legs and attached to the spacing attachment on the lever.

8. In a temperature control apparatus including a mounting and a rotatable dial thereon, an expansible and contractible bellows responsive to temperature changes set in said mounting with one end firmly engaging said dial, a lever having one end engaging the end of the bellows opposite the dial, said lever being pivoted in the mounting by means of a pivot closely adjacent to the bellows and thereby providing a short lever section engaging the bellows and a relatively long lever section extending beyond the pivot, a snap-acting spring pivoted in the mounting on the opposite side 01' said lever from said bellows in laterally spaced relation to the pivot of the lever and having a tension member attached to the long end of the lever by a spacing attachment, 2. control means operable directly by said snap-acting spring, a second control means normally biased to inoperative position, a manual push button means including a stem for moving the second control means to operative position, lever having an aperture on one side of its pivot point through which the stem extends, the end portion of the pivoted lever on the other side of the pivot point being provided with an adiustable means in operative engagement with the first mentioned lever.

9. In a device for controlling electric heatin circuits including a main switch for connecting and disconnecting a heating circuit with a current source, a thermostat responsive to changes in temperature for opening and closing the main switch and a handle for adjusting said thermostat to different temperature settings, a lever actuated by the thermostat for opening and closing the main switch, a second switch connected into an outlet of the main switch and normally biased to open position, av manual push means including a stem for moving the second switch to closed position, a stem holding means adapted to engage the stem when the push means is pushed in and to retain it in the pushed in position thereby to hold the second switch in closed position, and means actuated by the movement it the lever in response to a. temperature rise for releasing the stem holding means to thereby open the second switch.

bellows for releasing said 10. In a device as defined by claim 9 in which said stem holding means includes a pivoted lever having an aperture through which the stem extends and by which it is adapted to be engaged and held by the pivoted lever.

11. In a device as defined by claim 9 in which the stem holding means includes a pivoted lever having an aperture through which the stem extends, one end of the pivoted lever being in operative engagement with the first mentioned lever.

12. In a device as defined by claim 9 in which the stem holding means includes a pivoted lever and means responsive to' a pivoted 11 having an aperture on one side of its pivot point and through which the stem extends, the pivoted lever on the other side of its pivot point being provided with an adjustment means in operative engagement with the first mentioned lever.

13. In a temperature controi apparatus as defined by claim 5 in which'said spacing attachment is adjustable and comprises an eccentric device for increasing or for decreasing the tension on said tension member.

THEODORE ELIOT GRAVES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Number Powers July 25, 1922 Number Name Date wombl Feb. 8, 1927 ODowd Sept. 20, 1927 Loranger et a1 June 12, 1928 Henning Oct. 13, 1931 Johnson Sept. 19, 1933 Strong Apr. 3, 1934 Werring Nov. 16, 1937 Dasher May 31, 1938 Neweil June 27, 1939 Riche Nov. 21, 1939 Parkhurst Dec. 17, 194i) Rowe Oct. 28, 1941 Dubilier June 30, 1942 Burch July 14, 1942 Pearce Feb. 9, 1943 Gender Oct. 12, 1943 Pearce Nov. 13, 1945