US2316612A - Control device - Google Patents

Description

Patented Apr. 13, 1943 CONTROL DEVICE Heber L. NewelL-Stratford, Conn., assignor to General Electric Oom New York pany, a corporation of Application February 8l, 1940, Serial No. 317,850

8 Claims. (Cl. 200-138) My invention relates to a control device and more particularly to a control device for controlling the circuit of an electrical appliancein accordance with temperature changes of the appliance.

v it can readily carry the current of the electrical circuit which it is adapted to control; that it be in the form of a unitary assembly which can be separately rated and calibrated and then readily `applied to any particular appliance; that it be provided withsimple means for adjusting the calibration of the device Within given temperature limits after assembly; and that it be provided with means for preselecting within the given range the temperature to be maintained.

It is the primary object of my invention to provide a new and improvedvcontrol device having the above mentioned prerequisites.

It has been found that one of the principal factors which causes a non-uniform and unreliable operation of a temperature responsive con'- trol device over its operating range is the presence of stresses in the temperature responsive 4 element, usually a bimetal element, other than the stresses resulting froin temperature changes. These stresses'may be caused either by the manner in which the element is assembled and secured in its operative position or Iby the twisting andbinding of the element when it is moved in response to a temperature change.

It is a specific object of this invention to provide improved supporting means for the temperature responsive element, the supporting means being constructed and arranged to support the element loosely in its operative position so that substantially no stresses are set up in the blade during assembly thereof and so that binding or twisting of the element during operation of the device will be substantially eliminated.

In accordance with my invention I have provided a control device which is adapted to be constructed and assembled as a unit which can be readily mounted for use in the heating appIiance-the temperature of which is to be controlled. In one form thereof my improved control device comprises a supportin the form of a casing n which is mounted switch means comprising a. fixed contact and a movable contact, the latter being mounted on one end of a resillont arm. Loosely supported at its ends within the casing is a bimetallic temperature responsive clementwhich is positioned so that its movement in response to temperature changes will be transv mitted to the resilient arm to effect movement of the switch means to a different circuit controlling position. Adjustable stop means is provided to coact with the bimetal element between its supported ends in order to preselect within given limits the temperature at which the Ibimetallic element causes the switch means to be operated and additional means are provided for readily varying the calibration of the device so that the maximum and minimum temperature limits of the control may be adjusted after assembly. VvIn order to simplify the construction of my improved control device and to reduce manufacturing costs, the temperature responsive element and the contact arm are constructed and arranged so as to be at the same electrical potential and with such a construction only a relatively simple insulating member is required to insulate the adjusting means Afrom the contact arm and temperature responsive element assembly.

Additional objects and advantages of my invention will become apparent as the following description proceeds and the features of novelty which characterize my invention will be set forth in the claims appended to and forming a part of this speciiication.

For a more complete understanding of my invention, reference should be had to the accompanying drawing in which Fig. 1 is a sectional elevation of my improved temperature responsive control device; Fig. 2 is a plan view partly in section of the arrangement shown in Fig. 1; Fig. 3

is a view similar to Fig, 1 showing the elements of the control device in a diii'erent operative position; and Fig. 4 is a view taken on the line 4 4 of Fig. 1 and looking in the direction of the arrows.

In the drawing I have shown a form of my improved .control device which is particularly suitable for use as a temperature responsive control device for an electric roaster. It is to be understood, however, that my invention is not limited to a control device for such an application since the device is suitable and particularly adaptable for use in other types of heating devices such, for example, as electric ironers, water heaters, waille irons, and other such appliances.

Referring to the drawing, it will be noted that my improved control device comprises a substantially rectangular-shaped frame or casing I 0 which in the preferred form of my invention is pressed from a single sheet of metal so as to4 have side walls II and a top wall I2. Provided within the frame and lying against the under side of the top wall I2 is a sheet of suitable insulating material I3, such as mica. Secured in the casing I0 `at one end thereof is a xed contact structure which comprises a contact button I4 made of some suitable precious material such as silver and welded or otherwise secured to -the the control device.

casing I the terminal plate I8 upon which is mounted a terminal screw I8a. A suitable in-` sulating washer I9 is provided between the top wall I2 of the casing and the base portion of the .terminal plate I8. Mounted in the end of the A casing opposite that to which the Xed contact structure is secured is a bracket 20 having a pair of horizontally extending ange portions 2| and 22 connected by a substantially vertical portion 23. The bracket is secured to the casing I0 by means of a rivet 24 which passes through openings provided in the ange portion 2I of the bracket and in the casing and is peened over at 25. Like the rivet IB, the rivet 24 is also arranged so as to secure to the casing I0 a second terminal plate 26 having a terminal screw 26a thereon' and a sheet of insulating material 21 is provided between the terminal plate and the top wall I2 of the casing. As shown in Fig. 1, each of the openings provided in the casing for receiving the rivets I6 and 24 has a diameter considerably larger .than the rivets in order to prevent grounding of the rivets on the casing and the openings provided in the mica strips I-3, I9

and 21 are arranged so as to center the rivets- AWith respect to the enlarged openings in the case. I Arranged to cooperate with the xed contact button I4 to form a switch means for performing circuit controlling'functions is a relatively movable contact button 28 made of a material similar to the contact button I4. The movable contact button 28 is rmly secured to the end of a -resilient contact arm 29 which in turn is secured at its opposite end by means of a pair of rivets 30 to the flange portion 22 of the bracket 20. The contact arm 29 is made from-a suitable thin resilient material which has been heat treated so as to have the proper resilient characteristics and then cut to the length required ior use in The contact pressure'between the xed and movable contact buttons I4 and 28 is controlled by the resilience and positioning of the contact arm 29. If it is desired to alter the amount of the contact pressure, it is merely necessary to bend the iange 22 of the bracket 20 upwardly or downwardly a slight amount during the assembly operation depending upon whether it is desired to increase or decrease the contact pressure.

From the description thus far, itis apparent that, when the contact arm is moved downwardly, the contact button 28 is moved away from the iXed contact button I4 thereby causing the control device to be moved to the open circuit position, and conversely, when the contact arm 29 is moved upwardly, the control device is in the closed circuit position. It is to be observed that the current controlled by the control device passes from the terminal member I8 through the rivet I6, the i'lxed contact button I4, the movable contact button 28 and into and through the contact arr'n 29 to the bracket 28 and thence to the second terminal member 26 through the rivet 24.

In order to increase the current carrying capacity of the control device. a thin sheet of low resistance material 3|, such as aluminum, is secured to the upper side of the contactarm 28 so as to lie under and in good electrical connection with the contact button 28 and also so as to of the bracket 20. ABy means 'of this low resistance path, the current will be shunted around the contact arm so that in operation very'little current will be carried by the arm thereby insuring that its elastic properties will be substantially unaffected by local heating currents during the operation of the control device.

As previously pointed out, the control device of my invention is adapted to be actuated in accordance with temperature changes so that the v heating circuit or circuit for controlling the heating circuit of an electrical appliance may be controlled thereby in accordance with changes in temperature of the appliance. In order to effect this operation of the control device, I have provided in accordance with my invention a temperature responsive member 32-which in the preferred form of my invention is a bimetallic element comprising two strips of metal having dislie between the contact arm and the flange 22 75 similarv temperature coeilicients of expansion, such as brass and steel, these two strips being i securely welded or brazed together over their entire length and width.

In order to insure uniformity of action of the bimetallic member 32, I havein accordance with my invention provided a novel arrangement ior supporting the element 32 in its operative position so that a simple straight section of bimetal can be employed without requiring any preforming or stamping and, in addition, I have provided a supporting arrangement which requires no welding or riveting of the bimetal which usually causes internal stresses to be set up within the bimetal blade which aiect its operation. As shown in Figs. 1 and 4, the bimetallic element 32 is adapted to lie between the contact arm 29`and the top wall of the casing Ill and is arranged to extend in substantially the same direction as the contact arm 29 and in substantially parallel relation therewith. 'As shown, the bimetallic element is loosely supported at each end. 'I'he supporting means for one end comprises a slot 33 which is provided in the vertical wall 23 of the bracket 20. 'Ihe support for the opposite end of the bimetal element 32 comprises a metallic stud 34 which is riveted to the contact arm 29 near the contact carrying end thereof and is provided with a shank 36 which is adapted to extend `through an opening 31 provided in the end of the bimetallic element 32. The diameter of the open- \ing 31 in the -bimetal element is made substantially larger than the diameter of the shank 36 so that a loose connection will be formed between the bimetal element and the stud 34.' A head 38 is provided at the end of the shank 36 so as' to prevent the bimetal blade from being accidentally removed from the stud.

It will be observed that by means of this mounting arrangement, the bimetallic element 32 is loosely mounted in position so that at normal temperatures there are no stresses set up in the element. ,Of course; the combination of the slot supporting means at one end and the pin and opening supporting means at the opposite end provides some lateral restrain on the bimetal element, particularly when the entire assembly is moved or shaken. However, this restraint merely serves to constrain the elements so thatl it will be maintained in its operative position in the control device. For all practical purposes and in so far as the thermal characte..stics of the bimetal element are concerned, it maybe said that the bimetal element oats in the control device. This floating feature is, as previous- 1yl explained,v very important in that it insures uniformity and reliability of operation of the .bimetal element over the range of adjustments thereof and eliminates initial stresses in the blade and also stresses arising from bending or twisting of the blade during operation of the control device.

The bimetallic element is mounted in the oontrol device so that the metal having the higher coeilicient of expansion is on top as viewed in Fig. 1. Thus upon an increase in temperature, the bimetal will tend to bow upwardly in the center which bowing produces a downward deflection of the ends. transmitted throughthe stud 34 to the contact arm 29 causing an opening of the contacts at some predetermined temperature. It is to be observed that both the bimetal element and the contact carrying arm 29 are at substantially the same potential. This factor simplifies the problem of insulation within the casing I and also the problem of insulation of the temperature adjusting means to be described below with respect to the bimetal element and the contact arm.

In order to control the temperature at which the control device operates, I have provided an adjusting screw 39 having a rounded end 40 which is adapted to engage a suitable ceramic insulating bushing 4 l iwhich issupported in an opening provided in the bimetallic element 32 intermediate its ends. The bushing 4| is molded from some suitable ceramic material and serves not only as the surface against which the end of the adjusting screw 39 abuts but it also serves to insulate electrically the bimetal element and the adjusting screw. The adjusting screw is threadedly supported in a threaded bushlng42 which in turn is' threadedly supported in a threaded collar 43 secured to the top wall of the casing I0. The bushing 42 is provided at the upper end with a knurled portion 44 onto which is pressed an operating shaft 45 which is provided with a slot 46 Aex- This latter motion will be tending along its length. The threads on the collar 43 and the bushing 42 are arranged so that rotation of the shaft counterclockwise as viewed in Fig. l causes the rounded end of the adjusting screw to move downwardly with respect to the bimetal blade whereas movement of the shaft adapted `to engage the longitudinal slot 4S provided in the shaft so that rotation of the disk wit-h reference to the shaft will be prevented. Directly opposite the inwardly extending abutment 49 is'an outwardly extending abutment 49. This abutment is adapted to engage 'a tongue 50 pressed out of a bracket 5| which is welded or otherwise suitably secured to one of the longitudinal side walls of the casing Hl. The tongue 50 in cooperation with the abutment 49 provided on the dis'k 41 function as stops to limit the rotation of shaft 45 so that the total rotation thereof is less than 360 degrees. In order to provide frictional restraint on the shaft 45 so that it is maintained in any of its adjusted positions.

45 clockwise causes the rounded end of the adjustserves to support the hairpin spring and provide the stop 59 but, in addition, it serves as the means for mounting the control device in an appliance, such as an electric roaster, and a pair of openings is provided in the wall 54 of the bracket for receiving screws for securing the control device to the side wall of an appliance such as an electric roaster.

In order to enclose the operative elements of thel control device, a cover 59 is secured to the casing I9 by means of rivets 51. The cover 55 is made from some good conducting material, such as aluminum, and is provided with a vertically extending ilange portion or duck bill 59 which is adapted to lie adjacent the surface of the appliance the temperature of which is to be controlled so as to conduct heat readily to the control device. In a roaster, for example, the duck bill 58 is adapted to lie between the bottom surface of the roaster and the bottom heating units therefor. It is to be understood. of course, that any other suitable cover might be employed for the control device.

As previously described, the adjusting screw 39 is threadedly mounted within the bushing 42 and, by adjusting this screw with reference to the bushing, the temperature limits of the control device may be adjusted. In accordance with one phase of my invention, the temperature limits or the temperature range through which the control device operates vary from a manually settable off position at room temperature to a predetermined high temperature setting. Thus, in calibrating the device. the adjusting screw is set so that when the shaft 45 has been rotated counterclockwise, as viewed in Fig. 1, until the abutment 49 engages the stop 59, the rounded end 40 of the adjusting screw will have engaged the insulating button 4l and caused the bimetal element and contact arm assembly to be moved downwardly to cause the movable contact 28 to move out of engagement with the fixed contact i4. The adjusting screw 39 is positioned so that this manual opening of the control device takes place during approximately the last 20 degrees of movement of the shaft 45 in the counterclockwise direction. With the `adjusting screw thus positioned, the high temperature limit o.- the control device is also determined for in rotating the shaft in a clockwise direction until the abutment 49 again engages the stop 50, the end 40 of the adjusting screw will have been moved away from the insulating button 4I a predetermined amount. l

While this adjustment is the preferred adjustment for my improved control device, it will be understood that by means of the line adjustment obtainable withfthe screw 39 and the rough adjustment obtainable by means of the threaded relation between the sleeve 42 and the bushing V 43 when the collar 4l is raised on the shaft 45 so that the abutment 49 does not engage the stop 50, any other temperature limits may be selected for the control device.

vIt is to be observed that by means of a separate mounting .of the adjusting screw 39, the

position of the adjusting screw may be varied a small amount after the device has been assembled and is checked for calibration so that the device will function at the desired high temperature limit. This adjustmenaof course, does not destroy the adjustment for an off position at normal or room temperatures but merely causes this oil' position to be obtained either earlier or later than that previously set depending upon whether the adjusting screw is moved inwardly or outwardly to thereby engage the insulating button 4I sooner or later when the shaft l5 is rotated in a counterclockwise direction into engagement with the stop Eli.

In considering the operation of my improved control device, reference will be had to Figs. 1 and 3. Fig. l shows the operative position of the component elements of the-control device when the shaft 45 has been rotated in the counterclockwise direction until the abutment 49 engages the stop 50. In this position, the contacts are open as shown. Fig. 3 represents the position of the component elements when the shaft 45 has been rotated the full distance in the clockwise direction so that the abutment 49 engages the stop 50. This represents the maximum temperature setting for the control device. Assuming that the control device is set to maintain the maximum temperature for which it is calibrated, that is, assuming that the elements are in the position shown in Fig. 3, the electrical circuit controlled by the device will be energized and the temperature of the appliance heated by this electrical circuit will begin to rise. Heat will be conducted through the duck bill 58 to the control device and the bimetal element will start to bow upwardly. As long as the temperature of the device being controlled is below the predetermined maximum temperature, the bowing of the bimetallic element will be unimpeded and, because of the iioating arrangement by which it is supported, no binding of the element will occur during this bowing operation. When the device being c'ontrolled approaches the temperature at which the control device is set to operate, the bimetallic element will have bowed suillciently far so as to cause the insulating button 4i to move up into engagement with the rounded end 40 of the adjusting screw which acts as a stop. The adjusting screw thereafter impedes further bowing of the temperature responsive element in response to increase in temperature and an additional temperature rise causes the right-hand end of the bimetal element (as viewed in Fig. 1) to deiiect downwardly 'about the point of contact between the insulating button 6l and the end of the adjusting screw 40 as a pivot point. This downward deflection of the right-hand end of the bimetal is transmitted through the stud 34 to the contact arm 29.

As previously described, the contact arm is made from resilient material and is inclined upwardly so that a predetermined amount of contact pressure will exist between the xed and movable contacts. The initial downward deflection of the right-hand end of the temperature responsive element is resisted or opposed by the upward component of force exerted by the resilient contact arm. However, when the temperature of the device being controlled attains the .predetermined maximum temperature for which the control devicev is set to operate, the

v,is manifested ilrst by an upward deflection of the right-hand of .the element. When the 75 temperature is decreased to the point that the right-hand end has deflected upwardly so that its downward component is less than the upward component of the contact arm, then the contacts will close and the heating circuit will be again energized so as to raise the temperature of the appliance. When the predetermined desired temperature is again reached, the control device will function as previously described.

It is to be observed that during this entire operation the bimetallic element is relatively free tomove with reference to its supporting means and therefore binding or twisting, which would materially affect the uniformity of operation ofl the control device, is eliminated. Of course, it will be understood that any temperature setting between the oi position at room temperature and the maximum temperature may be selected by suitably positioning the shaft 4E and that the control device will function in the manner described for any of these intermediate settings.

When it is desired to deenergize the appliance completely, that is, to assume manual control thereof, it is necessary only to rotate the shaft 45 in the counterclockwise direction, as viewed in Fig. 2, until the abutment 49 engages the stop Sli. Under these circumstances the rounded end le of the adjusting screw will be moved down against the insulating button 4I and will have caused the contact arm to be moved downwardly so that the contact 2B is moved away from the contact I4, as previously described. With the adjusting screw thus in engagement with the insulating button 4i, the control device cannot reclose at any normal temperature, such as room temperature, but it is positively held in the open circuit position.

While I have shownv a particular embodiment of my invention, it is to be understood, of course.

that I do not wish to be hunted thereto since many modifications may be made, and I, therefore, contemplate by the appended claims to cover all such modii'lcations as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A control device for controlling an electrical circuit in accordance with temperature changes comprising a support, switch means mounted on said support, a bracket having a slot therein mounted on said support at a point remote from said switch means, a resilient arm having one end secured to said bracket and itsv ance with temperature changes.

2. In a control device for controlling an 'electric circuit in accordance with temperature changes, a casing having a top wall, a stationary contact secured to said top wall, a bracket havling a slot therein secured to said top wall at a point remote'from. said stationary contact, a resilient armxed at one end to said bracket and having its opposite end free to move, a movable contact mounted on said free end of said arm and adapted to engagesaid xed contact, a stud mounted onsaid arm intermediate 'its ends, and a temperature responsive element having one end loosely supported by said stud and its opposite end extending through said slot in said bracket so as to be loosely supported by said bracket, said bimetallic element being constructed and arranged to cause said arm to be moved in accordance with temperature changes.

3. In a control device for controlling an elec-` spaced' relation to the xed end of said arm and having its opposite end loosely supported on said stud so that movement of said end in response to temperature changes will cause movement of said arm, and means for preventing said bimetallic element from being accidentally moved oi said stud.

4. A control device for controlling an electrical circuit in accordance with temperature changes comprising a support, a bracket having a slot therein mounted on said support, a resilient arm mounted on said bracket, switch means associated with said support on said arm and adapted to be actuated in accordance with movement of said arm, a bimetallic element having an opening in one end and having its opposite end extending through said slot in-said bracket so as to be loosely supported by said bracket rin spaced relation to said arm, means for loosely supporting said end of said bimetal having said opening therein on said arm. and for transmitting movement of said end of said bimetal to said arm, said means comprising a stud mounted on said arm and having a portion of reduced diameter adapted to be in'- serted in said opening in said bimetal element, and a head formed on said portion of reduced diameter to prevent said bimetal element being accidentally removed therefrom after it has been assembled thereon.

5. In a control device for controlling an electrical circuit'in accordance with temperature changes, a casing having a to'p wall, a stationary contactsecured to said'top wall, a bracket -having a slot therein secured to said top wall at a point remote from said stationary contact, a resilient arm xed at one end to said bracket and having its opposite end free ,to move, a movable contact on said free end of saidjarm and adapted to engage said iixed contact, a stud mounted on said arm, and a temperature responsive element lying between said top wall of said casing and said arm in spaced relation to said arm, said element having one end loosely supported by said stud and its opposite end extending through said slot in said bracket so as to be loosely supported by said bracket, and

means for causing said end of saidbimetal ele-A ment which is mounted on said stud to deect downwardly at a predetermined temperature an amount suillcient to cause said arm to move said movable contact away from said fixed contact.

6. A control device for controlling an electrical circuit in accordance with temperature changes comprising a casing, a bracket mounted on said casing and having a slot therein, a resilient arm secured at one end to said bracket and having its opposite end free to move, switch means associated with said casing and said arm and adapted to be moved to different circuit controlling positions in accordance with movement of said arm, a bimetallic element having one .end extending through said slot in said bracket so as to be loosely supported thereby and having its opposite end loosely associated with said arm near the free end thereof so as to cause movementof said arm in accordance with temperature changes, an insulating member mountedv on said bimetallic element intermediate its ends, an adjusting screw mounted on said casing and having an end adapted to be engaged by said insulating member to control the temperature at which said bimetallic element causes said arm to move said switch means to a different circuit controlling position.

7. In a control device for controlling an electric circuit in accordance with temperature changes, a casing, a bracket mounted in said casing and having a slot therein, a resilient arm mounted on said bracket, contact means associated with said casing and said arm and adapted .to be actuated by movement of said arm so as to perform a circuit controlling function, a bimetallic element spaced from said arm and having one end extending into said slot so as to be loosely supported by said bracket, a stud mounted on said arm adjacent the free end thereof and constructed and arranged to engage loosely the opposite end of said bimetal element and to support it in spaced relation with respect to said arm, an insulating member mounted on said bimetallicelement intermediate its ends, an adjusting screw having a rounded end adapted to be engaged by said insulating member, and means for varying the position of said end of said adjusting screw relative to said insulating member to regulate the temperature setting of the control device, said last mentioned means being movable between two limiting positions one of which corresponds to aipredetermined high temperature and the other of which corre- -sponds to a manually settable oil position at room temperature.

8. A control device for controlling an electrical circuit in accordance with temperature changes comprising a switch, a movable arm for actuating said switch, a bimetallic element, supports adjacent the ends of said element, said supports being constructed and arranged to loosely engage and support said element to permit an unrestricted bowing action of said element in accordance with temperature changes thereof, one of said supports being iixed and the other movably mounted and operatively connected to said arm, a stop arranged to engage said element between said supports to limit ther-bowing action of said element beyond an amount corresponding to a predetermined temperature thereof whereby force is then-transmitted through the support connected to said arm to cause movement of said arm and actuationof said switch, and means for varying the position of said stop relative to said element to permit adjustment of said predetermined temperature.

HEBER L. NEWELL.

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