US2573404A

US2573404A - Thermal control means for induction motors

Info

Publication number: US2573404A
Application number: US104652A
Authority: US
Inventors: Harry F Clark
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1948-07-20
Filing date: 1949-07-14
Publication date: 1951-10-30
Anticipated expiration: 1968-10-30
Also published as: GB673473A; US2593268A; FR60853E; GB673522A; DE870435C; FR985242A

Description

Oct. 30, 1951 H. F. CLARK 2,573,404

THERMAL CONTROL MEANS FOR INDUCTION MOTORS Filed July 14, 1949 2 SHEETSSHEET l I N VEN TOR.

3 BY Mwezerf. 62mm.

Oct. 30, 1951 CLARK 2,573,404

THERMAL CONTROL MEANS FOR INDUCTION MOTORS Filed July 14, 1949 2 SHEETS-SHEET 2 I 49 INVENTOR. E 63 .1 5 ##APff 64AM.

; I 38 l o @0 Patented Oct. 30, 1951 THERMAL CONTROL MEANS FOR INDUCTION MOTORS Harry F. Clark, Oakwood, Ohio, assignor to Genporation of Delaware eral Motors Corporation, Dayton, Ohio, a corl Application July 14, 1949, Serial N0. 104,652

This application is a continuation-in-part of my copending application S. N. 39,718 filed July 20, 1948, which in the first embodiment dis-- closes a bimetal starting and overload control in which a U-shaped bimetal has its two movable legs each provided with a'tog'gle spring connection with a compensating bimetal. Each leg is provided with a contact mechanism with one contact mechanism connected to the line to provide the overload control while the other contact mechanism is connected to the starting winding to provide the starting control. A movable heater means is connected in series with the running winding to control the heating of the starting bimetal leg during the running period to control its resetting at the end of the running period. This starting and overload bimetal control has been manufactured and successfully used in large quantities for 115 volt split phase refrigerator motors.

The control embodied in the present application incorporates the starting and overload bimetal control, the compensating bimetal and the toggle springs of this prior successful control. It differs from the control disclosed in the above application principally in that it provides an improved and more versatile heating system for the starting bimetal leg.

It is an object of my invention to provide an improved and even more simple and less expensive bimetal starting and overload control which can be readily adapted for use with all sizes and types of split phase motors in all the standard commercial voltages without any difiiculty or expensive change in design or manufacture.

It is another object of my invention to pro vide an inexpensive versatile form of bimetal starting and overload control in which the parts are of substantially the same size, shape and dimensions and can be made on the same machinery and assembled in the same way for all sizes and types of split phase motors in all the standard commercial voltages.

It is another object of my invention to provide a more simple and versatile heating arrangement for a bimetal starting control which can be used with a minimum of change for various types and sizes and voltages of split phase motors.

It is another object of my invention to provide a heating arrangement for a bimetal start ing control which is easier to manufactureand less critical in forming and setting.

Further objects and advantages of the pres- 15 Claims. (Cl. 318-221) ent invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred form of the present invention is clearly shown.

In the drawings:

Fig. 1 is a plan view of my improved starting and overload control, shown in the off posi tion, taken along the line ll of Fig. 2;

'Fig. 2 is a longitudinal vertical sectional view taken along the line 2-2 of Fig. 1;

Fig. 3 is a longitudinal vertical sectional view looking in the opposite direction, taken along the same line also designated 33 in Fig. 1;

Fig. 4 is a transverse vertical sectional view taken along the line'd'4 of Fig. 1;

Fig. 5 is a plan view of the control in the normay running position together with a wiring diagram;

Fig. 6 is a similar view showing the control in the positions assumed under heavy load during the running period;

Fig. 7 is a plan view of the U-shaped bimetal switch mechanism for controlling the heating of the auxiliary heating means; and

Fig. 8 is a view in elevation showing the compensating action of this U-shaped switch under high ambient temperatures.

Referring now to the drawings and more particularly to'Fig. 5', there is shown an electric motor circuit including an electric motor 20 hav-' ing main or running winding 22 and a phase or starting winding 24. The common junction of the main and

phase windings

22 and 24 is connected to the supply conductor 30. A starting capacitor 32 may beconnected in series with the phase winding 24 if desired and a running capacitor 33 may be connected between the phase. winding 24 and the conductor 62 if a motor hav.-' ing the characteristics of the capacitor start or capacitor start and run is desired. If not, the running capacitor 33 or both capacitors 32 and 33 may be omitted as illustrated in Fig. 6, since the connections are the same.

Phase winding control The phase winding24 and the capacitor 32 are connected by the conductor 34 to the L- shaped starting contact and terminal 36 (see Fig. 5), the horizontal portion of which is beneath the base 38 and is riveted thereto by the minal 36 extends upwardly through a slot in the,

base 38 and forms the-contact portion proper;

sion side facing outwardlyor from the center of H the base. The high expansion side oftheyols'e portion of the U-shaped bimetal member 85 lies directly against the rib 42.- The movable end portion of the cantilever strip portion 46 carries a movable starting contact 41 shown in engagement with the L-shaped starting contact 36, in Fig. 1 and shown in the open position in Fig. 5. In the open position, themovable end oftl'le strip portion 46 rests against the adjacent end of the island 68 integral with and projectingupwardly from the surface of the base 38. When the contae-ts-36-and-4T are-closed, as shown in Fig.- 1, the strip 46 is thereby cennectedin series with the phase winding 24 and conducts'andisself-heated by the starting or phase winding current; The outer face of the U-shaped rib 42 carries a hook- .shaped temperature compensating bimetal strip as willbe evident from thevertical sections shown Figs. 2 to 4 inclusive.

Theadjacent movable ends of the comperisating stripss' and the starting bimetal strip portion 46* are connected by a thin c -shaped toggle leaf spring as. The end of the compensatin'g bimetal strip 48 is notched while theadj'ac'ent end'of the startingbimetal strip portion 46 is provided with a small rectangular aperture 51'" for receiving and holding theadj'acent' notched end portions of the C shaped spring 58. This'forms. the equivalent of a double toggle snap-acting arrangement since both; the bimetal strippor'tions 46 and 48' are flexible; A set-screw 52 extends through the rib 4'2 and engages the'base. portion ofthe starting bimetaljstrip portion 45" to adjust its position. The" geometrical arrangement and the adjustment of the set-screw'j52 is such that when the starting bimetal strip po'rtion' 46. and its contact 41 are either the opener the closed position the togglespring 5D'is at such an angle that when the stri 46 is'co'ol it will move to or remain inthe closed position.

Ifhe eifect of the ambient temperature upon the starting bimetal strip portion 46' is" compensated for by the eifect of the ambient temperature upon thetemperature compensating bimetal strip 48 since both strip portions have their high expansion sides facing outwardly and therefore deflect in the same direction upon ambient temperature changes. Thus as the'ambin't temperature rises the startin'g bimetal strip portion will have an increasing tendency tomove away from the stati'onary contact 35 tending to reduce the contact pressure between the contacts 38 and 41. But as the ambient temperature rises, the compensating bimetal strip 48 wil1 deflect in the same general direction toward the stationary contact 36 to increase the angle of the toggle spring 50- to add to the original contact pressure an amount sufficient 4 to substantially compensate for the tendency of the starting bimetal strip portion 48 to reduce the contact pressure upon a rise in ambient temperature.

Where the load connected to the motor increases with the increase in ambient temperature'; the compensating bimetal strip 48"may be s'elected'to slightly over-compensatefor the efiect of ambient temperature to increase the starting time as the ambient temperature increases. If the lo ad-should decrease With the increase in ambient temperature then the compensating bimetal strip 48 may be selected to slightly undercompehsate for the effect of ambient temperature. The compensating bimetal strip 48 is proyid'ed' with a central embossed stiffening rib 4! to. regulate'its' deflection and its compensating action to substantially the amount desired. The central embossed rib 49! stiffens and reduces the deflection of the mid-portion of the compensating strip 48 to the amount desired toregulate its compensating eifect. The length of this embossedrib 491' may-be lengthened or shortened to secure the amount of stifines's and deflection desired.

The reclosing control Since' thestarting bimetal strip portion 4a is biased to the closed or" starting position and moved to the open orrunning position by being self-heated by the phase winding current and since' 'the phase winding currentceases upon separation of the contacts 35', 41, some means is necessary to hold the strip portion 48 in the open or running position throughout the running period' of the motor to prevent reclosing of these

contacts

36, 4?. According to my invention I provide an electric heater 64 preferably inthe form of a' narrow ribbon of an electrical resistance heatingmatrial. One end of this heater G l is fastened to the bimetal strip portion 46 at the back of the starting contact 41 and extends therefrom toward the yoke or anchored portion of the U-shaped bimetal 65- in closely adjacent heat exchangerelationship with the starting bimetal strip portion 46. However, it is sufficiently separated from the bimetal strip portion 46; to allow free movement and bending of the starting bimetal strip portion Adjacent the yoke portion of the U-shaped bimetal 65, the heater 64 is bent sharply substan tially at right angles and its. end pgrtion 53 is fastened to the movable contact carrying leg 59 of a. U=shaped bimetal switch member 54. This the control with small highvoltage motors having a low current consumption.

With this type of bimetal and starting overload control the chief difficulty has been to' provide a control which will stay open during the entire running period under all conditions and reclose between thetime of the opening and the reclosing of the circuit either by anormal controlor by the overload protector. According to the present in vention to make it possible that sufiicient heat is supplied when the control is used with motors' having very low running current such as for example, 220 volt motors, the running winding cur.- rent is passed through the starting bimetal leg 46 to its connection with the heater 64 and thence through the heater 64 to the point at which it connects with the U-shaped bimetal strip 54. From this point the currentpasses through-the wide portion of the U-shaped bimetal strip 54 and through the terminal 66 and the conductor62 to the main or running winding 22. Thus the starting bimetal strip portion 46 is both self-heated and externally heated by the heater 64 through. the use of the running winding current. This provides sufiicient heat under light load conditions of low current consumption to keep the starting bimetal strip portion 46 in its open position during the running period.

However, if the main winding current would continue to flow through the starting bimetal 46 and the heater 64 under heavy load conditions so much heat would be stored up in the starting bimetal strip portion 46 and the heater 64 that the starting bimetal strip portion 46 would not return to the closed or starting position, shown in Fig. l, with sufficient rapidity when the circuit was opened by the normal control or the overload control. This rapid reclosing is desirable sothat if the opening of the motor circuit i of short duration the starting bimetal 46 will be in its starting position before the motor circuit can be reclosed.

According to my invention, to make this rapid reclosing possible under heavy load conditions, I provide the leg 59 with a switch contact I59. Upon the yoke portion of the U-shaped bimetal 65 I provide a contact I65 which is located soas to be in the path of the contact I59. upon the leg 59. The leg 59 of the U-shaped bimetal switch 54 extends in closely adjacent heat exchange relationship with the end portion 63 of the heater 64 which is parallel to the yoke portion of the U-shaped bimetal 65. Consequently this leg 59 is heated both by its connection with the heater.

64 and by reason of being located very close to a portion of the heater 64. arrangement, when the running winding current flowing through the starting bimetal 46 and the heater 64 becomes greatly more than sufficient. to keep the starting bimetalstrip portion 46 inthe open circuit position against the island 68, the leg 59 will curl downwardly to the position shown. in Fig. 6 to 'cause the main winding current to flow from the contact I65 to the contact I59 andv through the leg 59 andthe leg 51 of the U-shaped bimetal switch 54 to the main winding conductor 62. Thus when the switch contacts I59 and I65 are in the closed position, shown in Fig. 6, the main winding current does not pass through the starting bimetal strip portion 46 and the heater 64, but is shunted by the switch 54. Theswitch 54 will open and close the contacts I59 and'I65 to keep the starting bimetal strip portion, 46and.

the heater 64 from exceeding the maximum desirable temperature. In this way an effective means is provided for providing ample heating of the starting bimetal strip portion 46 without excessive heating for all split phase motor of varie ous types, sizes and voltages.

The U-shaped configuration of the switch 54 provides for temperature compensation as illustrated in Fig. 8. The effect of ambient temperature upon the contact carrying leg 59 willbe compensated for by the effect of ambient teme perature upon the anchored leg5'l. .That is,.thef

As the result of this.

raise the portion of the contact carrying leg 59 nearest the yoke of the U-shaped configuration so as to substantially compensate for the effect of ambient temperature.

The overload protector The main winding current together with the current flowing from the phase winding 24 through the starting contacts 36, 41 and the starting bimetal strip portion 46 will flow through the second leg 66 which forms the overload bimetal strip portion and the U-shaped bimetal member 65. The overload bimetal strip portion 66 carries a movable contact I6 which makes contact with the L-shaped stationary contact and terminal member I2 connecting through the main switch 28 with the other supply conductor I4. An overload compensating bimetal strip 76 having its high expansion side turned outwardly relative to the center of the base 38 like the overload bimetal strip portion 66 is fastened by rivets to the adjacent outer face of the U-shaped rib 42. His similar to the compensating strip 48 and has a similar central embossed stillening rib for stiffening and reducing the deflection of the midportion of the compensating strip to the amount desired to regulate its compensating effect. The length of the embossed rib may be lengthened or shortened to secure an amount of stiffness and deflection desired. The end portion of the compensating strip I6 is notched and a movable end portion of the overload bimetal strip portion 66 is provided with a rectangular aperture to receive the offset notched ends of the C-shaped toggle leaf spring I8 which may be identical to the toggle spring 56 but preferably has a greater spring force because of the greater width of the strip portion 66. The overload bimetal strip portion 66 is self-heated by the current flowing through the overload contacts In, 72 to the supply conductor 14.

When the strip portion 66 is self-heated sufficiently it will trip to the open position against the adjacent end of the island 68. The tripping point of the overload strip portion 66 is adjusted by bending the vertical portion of the terminal I2 toward or away from the strip portion 66 in order to reduce or increase the current value at which the overload portion 66 trips to the open position. The reclosing of the overload portion 66 is adjusted by the setscrew which threads through the U-shaped rib 42 and bears against the base of the overload bimetal strip portion 66 to adjust its position. The overload bimetal strip portion 66 is considerably wider than the starting bimetal strip portion 46 since it must be capable of carrying both the starting and main winding currents under the maximum starting and running load under which it is desired to operate the motor without tripping to the open position. Where the line current is low as in 230 volt motors, the width of the overload strip portion 66 may be reduced to increase the speed of tripping. As is evident from Fig. 2 the overload compensating bimetal strip portion I6 is considerably wider than the overload bimetal strip portion 66. The overload compensating bimetal 16!. preferably is slightly under-compensatedfor change in ambient temperature to, further come pensate for the reduced rateof heat dissipation of electric motors at higher. ambient. tempera? tures. The entire control is housed in a suitable case 356 which clampstightly over the; base; 3.8: completely enclosing the moving parts.

When the main switch 23.: is closed (see Figs.. 5. and 6), currentwill flow from the supply con-- ductor 36 through. the phase winding. 2-4.,3the.

capacitor 32, the conductor 34, the contacts 36,-;

47 and through the starting bimetal strip. portion 45. Current will also flow from the supply conductor 38 through the main winding 22, the conductor E2, the terminal 66 through the le 57' of. the U--shaped bimetal switch 54' to the portion 63 of the heater M. This main winding current will then now through the heater 64 to the starting bimetal strip portion 46 and this main Winding current will then how through the starting bimetal strip portion along with the starting or phase winding current and through the yoke portion of the overload bimetal-strip por-- tion 66 of the U-shaped bimetal member 65 and through the overload. contacts H3 and 12 and through the main, switch 23 to the supply conductor i4.

The set-screw 52 and the contact 36areso ad'- justed that the heat of the main winding-current. flowing through the heater 64 and both the main and phase winding current flowing through the starting bimetal 46 will causethestarting bimetal strip portion 46 to move from the position shown in Fig. l to the position shown in- Fig. 5 after a period of time which is sufficient to allow the motor to reach the proper switching speed Which is usually termed the balancing speed. The time of opening of the starting contacts 35, 4'! may be conveniently adjusted by bending the contact 35 toward or away from the contact 4'!"- to reduce or increase the starting time as desired. The opening or" the starting contact 41.. disconnects the starting conductor 34 and stops. the flow of the phase winding current through the start.

ing bimetal strip portion 46.

If the motor is of the capacitor start capacitorrun type, current will continue to flow through thephase winding 24 and the running capacitor Current will also continue to fioW from the.

33. supply conductor 36 through the main or'running winding 22 and the conductor 62 which will. be joined by any current flowing through the capacitor 33 and be conducted to the main winding terminal 69. From the main winding terminal 60 this current will fiOW through the U-shaped bimetal switch 54 and thence through the heater 64 and thence through the entire U-shaped bimetal member 65 from the contact 4'lto the contacts Hi from which point the current will flow through the terminal 12 and the main switch 28 to the supply conductor 14. Under lighter loads the switch contacts I59 and l65-will re main in the open position 'at all times. Under heavier loads these contacts will intermittently close and open to shunt the main winding current from flowing through the heater 6'4 and the starting bimetal strip portion 46 for brief intervals to limit the amount of heat stored in the starting bimetal strip 46 and the heater 64 so that.

rapid resetting of the starting bimetal 46 ispossible under all conditions. The greater the current flow and the greater the load the greater proportion of time the contacts I59 and leiwill be closed.

The control can be adapted to various sizes,-

8 types-and volta es of split.- phase: motors without. such a change inthe-dimensions andshapesyoif the-partsas, to. require new tools. and different; manufacturingprocedure for application to. mo.-. tors of pariouszsizes... Through the use of diner-.- ent' thicknesses; of bimetal and heater wire and through the use of different types of bimetalgand difierent. standard types and sizes of heater-rib Icon. it is.-.pos si.ble, to change the characteristics, of the control. to accommodate it to split pha e. motors: of the various types, sizes and voltages, without substantially increasing the manufactu-r. ing; cost andzplant and tool. investment;

While. the forrnofembodiment. of the -inven.-, tion as herein disclosed, constitutes apreierred fiorm it isto be understood that other; forms might be adopted, as may come within thescope of the claims Which-follow.

What is claimed is as follows: 1

1. A-control including a support, a bimetal, strip means supported upon said support,-a, con-.-: trol means connected to and operated by the. movement of a. portion of said strip means, said control; means having a portion connected to. said support, means including a heating circuit under the controlv of said control means for heating saidj strippmeans, a second heating means. located closelyadjacent to said strip means, a second; heating circuit. connected to said second heating. means for energizing said second heating. means. to. heat said strip means, and a current respone sive switch means having a thermal current sensi:-. tive actuating means connected in series. with said. second heating circuit and a normally open switch contact mechanism actuated thereby fen shunting said second heating means.

2.. A control including a support, a bimetal stripl means supported upon said support, a control means connected to and operated by the movement of aportion of said strip means, said con'-. trol means having a portion connected'to said support, means including a heating circuit under the control of said control means for heating said strip means, a second heating means located closely adjacent to said strip means, a second heating circuit connected to said second heating,

3. Acontrol including a support, a bimetal strip means provided with a first contact thereon, said. bimetal strip means being supported upon','said support, a second contact cooperating with said first contact, said second contact being connected to said support, means including a first electrical circuit portion connected in series with said strip means and the first and second contacts for heating said strip means to control the opening of said contacts,'an electric heating means hav-- ing one portion connected to said stripmeans: and extending therefrom in closely adjacentheat' exchange relationship along said strip means, a;

second electrical circuit means connected in series with said" strip means and said electric heating means for. energizing said heating means and for heating said strip means.

4. A control including a support, a bimetal strip means-provided with a first contact thereon, said bimetalistrip means being Supported upon said pp rt, a second contact cooperating with said first contact, said second contact being connected to said support, means including a first electrical circuit portion connected in series with said strip means and the first and second contacts for heating said strip means to control the opening of said contacts, an electric heating means having one portion connected to said strip means and extending therefrom in closely adjacent heat exchange relationship along said strip means, a second electrical circuit means connected in series with said strip means and said electric heating means for energizing said heating means and for heating said strip means, and a temperature responsive control means connected to said second electrical circuit means for controlling said heating means.

5. A control including a support, a bimetal strip means having a support portion supported upon said support and a movable portion provided with a first switch contact, said second contact being connected to said support, a second switch contact cooperating with said first contact, a first electrical circuit means connected in series circuit with said strip means and said contacts, an electric heating means having a portion connected to said movable portion of said strip means and extending from the place of connection in closely adjacent heat exchange relationship along said strip means, a second electric circuit means connected in series circuit with said heating means, a second bimetal strip means having a portion connected to said heating means and extending in closely adjacent heat exchange relationship along said heating means, said second strip means having a movable portion and a third switch contact upon said movable portion for controlling the heating of said heating means.

6. A control includin a support, a bimetal strip means having a support portion supported upon said support and a movable portion provided with a first switch contact, a second switch contact cooperating with said first contact, said second switch contact being connected to said support, a first electrical circuit means connected in series circuit with said strip means and said contacts, an electric heating means havin a portion connected to said movable portion of said strip means and extending from the place of connection in closely adjacent heat exchange relationship along said strip means, a second electric circuit means connected in series circuit with said heating means, a second bimetal strip means having a temperature compensating portion and an operating portion extending in closely adjacent heat exchange relationship to said heating means and provided with switch means connected to said second circuit means for controlling the heating of said heating means.

'7. A control including a support, a bimetal strip means havin a support portion supported upon said support and a movable portion provided with a first switch contact, a second switch contact cooperating with said first contact, said second switch contact being connected to said support, a first electrical circuit means connected in series circuit with said strip means and said contact, an electric heating means havin a portion connected to said movable portion of said strip means and extending from the place of connection in closely adjacent heat exchange relationship along said strip means, a second electric circuit means connected in series circuit with said heating means, a second bimetal strip means having a temperature compensating portion and an operating portion extending in closely adjacent heat exchange relationship to said heating means and provided with a third switch contact, and a fourth switch contact cooperating with said third switch contact and connected to said second circuit means for controlling the heating of said heating means.

8. A control including a support, a bimetal strip means havin a support portion supported upon said support and a movable portion provided with a first switch contact, a second switch contact connected to said support cooperating with said first contact, a first electrical circuit means connected in series circuit with said strip means and said contacts, an electric heating means having a portion connected to said movable portion of said trip means and extending from the place of connection in closely adjacent heat exchange relationship along said strip means toward said support portion, a U-shaped bimetal strip means having an anchored leg at one side of said support portion and a movable leg substantially aligned with but normally spaced from said support portion, said heating means having a portion extending in closely adjacent heat exchange relationship along said movable leg and being connected to the movable leg adjacent to the yoke portion of said U-shaped bimetal strip means, a

I second electric circuit portion connected in series circuit relationship with said heating means, said movable leg being provided with circuit controlling means for controlling the heating of said heating means.

9. A control including a support, a bimetal strip mean provided with a first contact thereon, said strip means being supported upon said support, a second contact connected to said support cooperating with said first contact, means including a first electrical circuit portion connected in series with said strip means and the first and second contacts for heating said strip means to control the opening of said contacts, an electric heating means having one portion connected to said strip means and extending therefrom in closely adjacent heat exchange relationship along said strip means, a second electrical circuit means connected in series with said strip means and said electric heating means for energizing said heating means and for heating said strip means, and a current responsive control means connected to said second electrical circuit means for controlling said heating means.

i 10. A control for an electric motor having main and phase windings including a support, a bimetal strip means supported by said support and a switch means controlled by the movement of the strip means from the starting position to the running position, said switch means and said strip means being connected in series with the phase winding to control its energization, a heating means located closely alongside of and in intimate heat exchange relation with said strip means and connected in series with said main winding for keeping the switch means and the strip means in the running position during the running period, a second separate independent bimetal strip means, and a second switch means operated by said second strip means electrically connected in shunt circuit arrangement with said heating means for regulating the heating rate of said heating means to limit the heat applied to said first strip means.

11. A control for an electric motor having main and phase windings including a support, a bimetal strip means supported by said support amen;

and a. switch .means controlled Joy. thev movement of .the striplmeans from v.the starting position .to the running position,saidlswitch. means and said stripmeans being connected .in series with the phasewinding to control. itsrenergization, a heating ,means located closely alongside of and in intimate heat exchange relationiwith said :strip means-land connected in series with said main winding 'for keeping theswitch means and the strip means in the running position during the running period, ;a second separate independent bimetal str-ipameans, and a second switch means operated (by said :second strip means having its temperature responsive actuating element connected in series circuit arrangement with said heating. means.eand;having:normally open switch contact 'means connected in shunt circuit arrangementwith :said heating means for shunting said heating :means in response to a predetermined heating eirect-of the main winding-current -to limit the temperature attained by .said

heating means.

. 12.:A control including a support, a .bimetal strip :means having .a'support portion supported upon saidsupport and azmovableportion, acontrol means having a qaort-ioni-connected to said movable portion=-and a portionconnected to said support, a first electrical-circuit means connected in series circuit relation with said strip means, an electric heating means extending closely alongside a;partof the-mova'ble portion of .the bimetal strip means in 'intimateheat exchange relation therewith, a second electric circuit means :connected in series :circuit relation with said heating -means, zandta normally open -tem-- perature responsive switch 'means connected in said second circuit means 'inshunt .circuitrelationship with said electric heating means.

13. vA :control including -.a support, a bimetal strip means supported .in a cantilever arrangement "upon said support to provide the strip means with .a support portion and "a movable portiomca switch 'means connected to and operated by the movable portion ofisai'd'bimetal strip means, 'a ifirst electrical circuit :means connected in series with said stripmea'ns and said switch means, an electrical heating *means extending closelyalongside of and in intimate heat exchangetrelation with a part 'of *thefmovable'portion of said bimetalstripmeans and having one terminal electrically connected to said 'movable portion and a second terminaL'a-nd a second electrical circuit means connectedt'o saidsecond ter minal.

level control including a.. support, a bimetal stripmeans supported in a .cantileverarrang'ement upon said support to provide the strip means with a support portionanda movable portion, a switch means connected to and.operated by the movable portion of said bimetaLstrip means, a first electrical circuit means connected in series with said strip means and saidswitch means, an electrical heating means extending closely alongside of and in intimate heat exchange relation with apart ofthe movablemor tion of said bimetal strip means and ha'vingone terminal electrically connected -to said movableportion and a second terminal, and .a second electrical circuit means connected .tosaidsecond terminal, and a supply conductor .for the (fir-st and second circuit means connected tothesup port portion-0f said bimetal stripsmeans.

15. A control for an electric motor :having main and phase windings including .a support, a bimetal strip means supported :ina cantilever arrangement upon said support to provide the strip means with a support portion and a-movable portion, a switch means connected to and operated by the movable portion of said strip means, said switch means-and said strip means being connected in series with said-phase winding to controlits energization,.an-electrical'heatin'g-means extending closely alongside-of :andin intimate heat exchange relation with r2, =part of the movable portion of said bimetal strip means and having one terminal electrically-connected to said movable ortion and a second terminal, said second terminal being connected to .said main winding, and "a supply conductor'for both windings electrically connected to the support portion'of said bimetal strip'means.

HARRY F. CLARK.

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

UNITED STATES PATENTS Number Name Date 1,783,520 Pearce Dec. 2, 1930 1,830,578 Vaughan Nov. 3, 1931 2,158,288 Kuhn May 16, 1939 2,304,018 'Raney Dec. 1, 1942 2,379,602 Stickle July 3, 1945 2,417,912 Clark Mar. '25, 1947 2,447,488 Clark Aug. '24, 1948 2,463,935 Fish Mar. -8, 1949 2,483,515 Alexander Oct. 4, 1949