US2445021A

US2445021A - Thermostatic switch

Info

Publication number: US2445021A
Application number: US470445A
Authority: US
Inventors: Earl K Clark
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1942-12-29
Filing date: 1942-12-29
Publication date: 1948-07-13
Anticipated expiration: 1965-07-13

Description

y 13, 194& El. k. CLA K 2,445,021

THERMOSTATIC SWITCH Filed Dec. 29, 1942 3 Sheets-Sheet 1 wfiuzsszs; INVENTOR 1.. EHEL K CLHEK W?- BY 7? I A ORNEY y 1943' E. K. CLARK 2,445,021

THERIIOSTATIC SWITCH Filedbec. 29, 1942 3 Sheets-Sheet 2' WITNESSES: q 2 INVENTOR A ORNEY 3 Sheets-Sheet 3 E. K. CLARK THERMOSTATIC swncn July 13, 1948.

Filed Dec. 29, 1942 w m Wu 2 E 3 m M l1; I Y n m n. w mu 1 T lW W i WE m M Ma: y a W W I I i i i I I I I I i I I I i I I I I I I E I I. 5i

WITNESSES:

Patented July 13, 1948 THIBMOSTATIC SWITCH 12m x. ClarhMansileld, Ohio, lllllndl' to Westingholue Electric Corporation, East Pittsburgh, h, a corporation of Pennsylvania Application December 2a, 104:, Serial No. 410,445

5 Claims. (01. 200-139) This invention relates to heating apparatus, such as an oven in an electric range, and particularly to a temperature-control device therefor, and it has for an object to provide an improved device or the character set forth.

Present oven temperature controls usually com-prise a temperature-responsive element or medium which is located within the oven and provides the ioroe tor electing switching operations to cause enersization or deenergization of the oven heating elements in accordance with the temperature or heat demand of the oven. Such controls usually operate by opening the circuit when the temperature exceeds a given temperature to which the control has been adjusted, and by reclosing the circuit when the temperature has dropped to a somewhat lower value. Such a control usually comprises a snap-acting device in order to quickly open and close the switch contacts. Because of the force required to operate the snap-acting cans and also because of the heat lag between the oven temperature and the temperature-responsive medium or element, the temperature of the oven must drop a substantial amount before the contacts are reclosed. As n consequence, with most controls this type, heating elements are energized and deenergized for long periods and the oven temperature may fluctuate through a range oi about 30 F. or more.

accordance with my invention, 1 provide a switch having suiteble mechanism, such es s motor-driven com, for periodically moving one contect into end out of engagement with the other to provide intermittent energizatlon oi the heating element, the complete cycle including one "on period and one "0d" period, bein relatively short, for example, one'minute. The length oi the on period in relation to the length of the cycle is varied in response to the temperature or heat demand in the oven, preferably by moving vide a temperature control in which the iorce for etlecting necessary switching operations is not provided by the temperature-responsive medium or the oven thermostat.

It is another object or the invention to provide ill - moved up and down periodically toward and away an improved temperature control which maintains the temperature 01 the oven within a closer range of the desired temperature than is possible with known controls.

These and other objects are eflected by the invention as will be apparent from the following description and claims taken in connection with the accompanying drawings, forming a port oi. this application, in which:

Fig. l. is a perspective view of an electric cooking range in which the present invention is incorporated;

his. 2 is a front elevational view of a tempera.- ture-controlling device made in accordance with the present invention, with the cover removed and portions broken away;

Fig. 3 is a, vertical sectional view taken substentially on the line IH-III oi Fig. 2;

Fig. 4 is a, race view of a combined circuitselecting and temperature-controlling cam employed in the present device: and

Fig. 5 is e schematic wiring diagram of the circuits employed with the presentcontrcl device.

The range shown in Fig. l and generally indicssted it is of conventional construction and is shown merely to illustrate one adaptation of the temperature control of the present invention. As well understood, this range includes an oven compertment i i in which there are disposed on upp r heating element 92 which is used for broiling", and upper and lower heating elements 03 and M which may be connected in parallel and simultaneously energized to provide host for looking.

The temperature control for the oven includes switch contests and other parts housed within a. casing to which may be disposed rearwardly of the beclssplasher as shown in Fig. l. The control also includes a temperature-responsive bulb ill located within the oven and a tube it extendinz; from the bulb to the housing it. It further includes e. control knob it which is disposed on the front of the backsplasher and mounted on a shaft 2i extending through the backsplasher. The knob is provided with indicie. designating an "of!" position, a plurality of baking positions having different temperature settings. and a broil position.

Referring now to Figs. 2 and 3, there are enclosed within the casing i6 two contacts 22 which are positioned by a thermostat in response to the oven temperature and two contacts 23 which are from the contacts 22. These two sets of contacts control both sides of the supply line to the heating element, but, so tar as the invention is conc rned, it will be sui'iicient to have one set of. concts controlling one side of the suppl line. The contacts 23 are carried by a pair of spring arms 24 mounted on brackets 25, and they are aligned with and adapted to engage the respon- ,aive contacts 22. Th contacts 23 are constantly oiled up and down, or toward and away from he contacts 22, by means of cams 26 mounted on it camshaft 21. The camshaft 21 is joumaied in the side walls of the housing, as shown in Fig. 2, and is driven, preferably at a speed of one R. P. M., by means of a motor 23 (Fig. The motor 23 is continuously energized as long as the control is in use. For example, it may be energized by a switch 23 which is closed in any suitable way, not shown, by the shaft 2| whenever the knob i9 is moved to any position other than the "off" position. It will be apparent that the motor 28 may drive similar cams in controls for other heating elements on the range, in which case it might also rotate at times when the knob i3 is in the off" position. The springs 24 are biased upwardly into engagement with the cams 24. The cams 26 may be of involute or any other suitable form and may have a throw of, for example, one-tenth of one inch.

The contacts 22 are mounted on the free ends of spring arms 3| fastened at their other ends to terminal brackets 32 mounted on the housing. The spring arms 3| are connected together by an insulating block or bridge 33, which may be suitably secured thereto as by riveting,

The contacts 22 are positioned by a thermostat responsive to oven temperature. .In the present embodiment, this thermostat is of the hydraulic type, including the thermostatic bulb H, the tube II, and a wafer 34 disposed within the housing, these parts being in communication and containing a medium which expands on increase in temperature. The wafer 34 is provided with a stud ll which is movable upwardly into engagement with the bridging piece 33 by the medium within the wafer upon increase in temperature,

The thermostat may be designed so as to move the contacts 22 a distance equal to the travel of the movable contacts 23, in this case inch, upon variation of temperature in the over of 50 F. In other words, assuming a temperature setting of 300 F., the contacts 22 may be positioned so that the contacts 23 will just touch them at the upper end of their travel when the temperature is 325 F. and will just remain in continuous engagement with the lower end of the travel when the temperature is 275 F.

The control further includes suitable mechasim controlled by the knob IQ for adjusting the setting to provide different baking temperatures. In the present embodiment, adjustment is effected by changing the vertical position of the wafer 34 in relation to the contacts 23.

The mechanism for eiiecting this adjustment includes an Lshaped plate member 35 pivoted on a rod 31 fixed in the walls of the housing. The wafer is mounted on the free end of the horizontal leg 38 of the plate 36. The plate 33 is angularly adjusted about the pivot rod 31 by a cam member 33 carried by the rotatable shaft 2 I. The upper end of the plate 36 carries an adjustable set screw 4| which is biased, by a compression spring 42 acting on the upper end of plate 35, into engagement with a cam surface 43 formed on the back of the cam member 39. The control may be calibrated by adjustment of the screw 4 l.

The cam surface 43 is shaped, as shown particularly in Figs. 3 and 4, so that as the k b 9 is rotated clockwise from its oil position, which corresponds to the low part 44 of the cam, the cam gradually moves the upper end of the plate toward the right, as viewed in Fig, 33, causing the wafer 34 to be lowered and consequently to bring the adjustable contacts 22 downwardly toward the movable contacts 23. Such downward movement raises the temperature setting since the contacts are engaged to energize the heating element until a higher temperature is reached, at which time the contacts begin to separate and to regulate.

The control further includes a, switch which serves as a selector switch whereby either the broiling element l2 or baking elements l3 and I may be energized, and which also serves as a line switch to disconnect both elements in the oil position of the knob l9. This switch includes conductor springs 45 whose upper ends are disposed between contacts 46 connected to the baking elements and contacts 41 connected to the broil element, and are provided with double contacts 43. The conductor Springs 45 are provided with oilset portions 43 adapted to ride on the peripheral cam surface 5| of the cam. As shown particularly in Figs. 2 and 4, the peripheral cam surface 5! is formed with diametrically opposed laterally offset recesses 52 which position the springs 45 to move the contacts 48 into engagement with the contacts 41 of the broiling element when the knob is in the broil position. Flat spots 53 position the contacts 48 in the intermediate position when the knob is in the on position, and the remainder of the peripheral cam surface 5| maintain the contacts 48 in engagement with the contacts 48 of the baking elements.

The electric circuit may be traced as follows: From supply conductors L1 and L2, the two sides of the electric supply line extend through the brackets 32, the spring arms 3i, the

contacts

22 and 23, the arms 24, the brackets 25, conductor straps 55, the conductor springs 45, the contacts 48, and then either through the contacts 46 to the opposite terminals of the baking elements i3 and I4 to complete the circuit thereto or through the contacts 41 to the terminals of the broiling element to complete the circuit thereto.

Operation The primary characteristic of the operation of the present switch is that the circuit is made and broken periodically, the cycle of operation being preferably of the order to one minute, and the rate of heat delivery to the oven is varied by varying the 1ength of the on period in relation to the length of the cycle. While this is an on and off control, the cycle is sufficiently short so that the effect is substantially the same as varying continuous wattage input. The input is varied from zero to full wattage through a temperature range of, for example, 50 F.

Assume, for example, that the oven is at room temperature and that it is desired to begin baking operation. The knob is positioned at the desired temperature setting, which will be assumed to be 300 F. for the purpose of an example, and which will adjust the control to vary the length of engagement to the contacts upon variation in temperature between, for example, 275 F. and 325 F. The adjustment of the knob moves the contacts 22 below the limit of travel of the contacts 23 so that the contacts are maintained in continuous engagement. Accordingly, the baking elements remain continuously energized to raise the temperature of the oven as quickly as possible until the temperature reaches 275 R, the lower limit of the regulating range. As the temperature rises above 275 F., the contacts I! are moved upwardly by the expanding wafer 34 into the travel of the contacts 13, so that during the lower portion of the travel the contacts 23 disengage the contacts 22 and periodically open the circuit. The average wattage input to the oven is thus gradually decreased as the temperature within the oven rises. As the heat input to the oven is decreased to the value at which it just balances the heat losses therefrom, there will be no further increase in temperature and an equilibrium point is reached. The temperature will now remain substantially constant. This equilibrium point may be, for example, 300 F., the midpoint of the regulating range. providing onehalf maximum wattage input to oil'set a 50% heat loss from the oven. Should there be an increase in heat load, as occasioned by the opening of the oven door, the oven temperature would decrease, lowering the contacts 22 to provide greater length of engagement with the contacts 23. The heat input is thus increased to raise the temperature until the equilibrium point temperature is restored.

Assume now that the knob I9 is adjusted to a lower temperature setting, say 250 F. This movement places a lower portion of the cam surface '48 in contact with the set screw ll, so that the wafer It is raised and, because of the excess temperature of 300 F. in the oven, raises the contacts 22 above and clear of the path of travel of contacts 23 to effect complete deenergization of the baking elements. As the oven temperature drops down to the new regulating range, the wafer I contracts and moves the contacts 22 into the pathof travel of the contacts 23, at first providing very short "on periods. The on" periods gradually increase until the heat input equals the heat losses from the oven, at which time there will be no further change in temperature and no change in heat input.

To begin a broiling operation, the knob 99 is turned to the broil position in which the contacts 40 are brought into engagement with the contacts 41 leading to the broiling element 62. Also, the set'screw 49 engages a portion of the cam surface it, which portion may be flat or inclined, and is designated 51 and is relatively high to provide a relatively high temperature adjustment of the thermostat. The high part ill of the cam surface it adjusts the temperature control to a temperature which is higher than any temperature normally encountered in the oven during broiling operation but which, nevertheless, is within the range of safe operation of the oven. During the brciling operation, the oven door is left in slightly open position to provide the desired ventilation. This ventilation prevents the oven attaining the temperature at which the control is set, so that the

contacts

22 and 23 remain in engagement to provide continuous energize.- tion of the broiling element. However, should the door be closed, the temperature control will.

when the set temperature is reached, control the energization of the heating element in the same manner as described above. In other words, the temperature control is not intended to come into play normally during broiling. but it does serve as a temperature-limiting control to prevent any excessive temperature within the oven.

While the invention has been shown in but one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of tit 6 variou changes and modifications without departing from the spirit thereof, and it is desired, therefore, that only such limitations shall be placed thereupon as are specifically set forth in the appended claims.

What is claimed is:

1. A temperature-responsive control for an electric heating element comprising a movable contact-carrying arm, an adjustable contact-carrying member, cooperating movable and adjustable contacts carried by said arm and said member, respectively, said movable contact-carrying arm being biased in the direction to move the movable contact toward the adjustable contact, a rotating cam engaging said movable contactcarrying arm in the direction to move the movable contact away from the adjustable contact and operating to cyclically move said movable contact into and out of engagement with said ad- Justable contact, temperature-responsive means acting on said adjustable contact-carrying memher to move the adjustable contact away from the movable contact in response to increase in temperature and toward the same in response to decrease in temperature, and manually-adjustable means for varying the position or said adjustabie contact-carrying member in relation to temperature of said temperature-responsive means.

2. A temperature-responsive control for an electric heating element, said control comprising a pair of contact-carrying spring arms and a pair of cooperating contacts carried thereby, each of said spring arms being biased in the direction to move the contact carried thereby toward the cooperating contact, a movable supporting member, temperature-responsive means including a part mounted on said supporting member and adapted to position one of said spring arms, a rotating cam adapted to engage the other spring arm in the direction to move the contact carried thereby away from the other contact, means for rotating said cam, and means for adjusting the position of said supporting member, thereby adjusting the temperature setting of the control.

3. A control as set forth in claim 2 wherein the part of the temperature-responsive means mounted on the supporting member is an expansible chamber and wherein said temperatureresponsive means further comprises another chamber, a connection between the two chambers, and a thermal liquid within the chambers and the connection.

An electrical control device comprising first and second contact-carrying arms, first and second cooperating contacts carried by said arms, respectively, said first arm being biased in the direction to move said first contact toward said second contact, a rotating cam adapted to engage said first arm in the direction to move said first contact away from said second contact and callsbetween the two chambers and a thermal liquid filling the chambers and the connection, and

means including and controlled by a manuallyactuated member for varying the relation between the position or said second arm and the temperature of said temperature-responsive means.

5. A temperature-responsive control comprising a movableand an adjustable contact-carrying arm, cooperating movable and adjustable contacts carried by said movable and adjustable arms, respectively, each of said arms being biased in the direction to move the contact carried thereby toward the cooperating contact, a rotating cam engaging said movable contact-carrying arm in the direction to move the movable contact away from the adjustable contact and operating to cyclically move said movable contact into and out of engagement with said adjustable'contact, temperature-responsive means actuating said adjustable arm in the direction to move the adjustable contact away from the movable contact in response to increase in temperature and permitting opposite movement thereof in response to decrease in temperature, and manually-adjustable means tor varying the position of said adjustable arm in relation to temperature of said temperature-responsive means.

EARLK.CLARK.

REFERENCES 01'!!!) The following references are of record in the 10 tile of this patent:

UNITED STATES PATENTS OTHER REFERENCES C. 0. Falrchild, Throttling Electric Heat, "Instruments," December 1937, pages 305 and 300.