US2169989A - Refrigerating apparatus - Google Patents

Description

Aug. 15, 1939. G. c.- PEARCE REFRIGERATING APPARATUS 4 Sheets-Sheet 1 Filed Oct. 29, 1936 ZZZ VENTOR.

ATTORNEYS G. C. PEARCE REFRIGERATING APPARATUS Aug. 15, 1939.

Filed Oct. 29, 1936 4 Sheets-Sheet 2 6 %ENTOR. BY M 8% ATTORNEYS com fA/m 77/V6' sr/e/p 00594 TIA/G fire/P Patented Aug. 15, 1939 UNITED STATES PATENT OFFICE Application October 29, 1936, Serial No. 108,250

5 Claims.

This invention relates to refrigerating apparatus and more particularly to control means therefor. I

Household refrigerators are now very frequently made with the electric motor and compressor enclosed within a sealed casing. This makes it necessary that starting controls be mechanically independent of the motor but operated by conditions of the electric motor circuit.

Heretofore, such controls involved the use of relays. Such relays were relatively expensive and situated in the open air so that the contacts were subject to burning and oxidation.

It is an object of my invention to provide an improved form of electric motor control which is more simple, more dependable and has a longer life than the control means heretofore used.

It is among the objects of this invention to provide an improved control for the electric mo- 0 tor which drives the refrigerating system which is capable of automatically starting the motor when the current is turned on by the user and also'which is capable of restarting the system safely if the line current, or source of electrical 5 energy should be turned oil temporarily and then be turned on before the refrigerant pressure has equalized sufiiciently to permit the motor to start.

It is another object of my invention to provide an improved form of motor control system in which the contact mechanisms may be readily replaced by any inexperienced person without any danger of deranging the apparatus.

I I have discovered that by employing a vacuum tube and a bimetal control of the motor within 1 the vacuum tube, that the motor control is greatly simplified and improved.

It is another object of my invention to provide an improved temperature compensating control means within a vacuum tube, so that its opera- 9 tion will not be afiected by environment temperature within or without the tube.

It is another object of my invention to provide an improved electro-thermal' starting control system which is extremely simple-and inex- ,5 pensive, as well as being durable and reliable.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred form of ,o the present invention is clearly shown.

In the drawings: Fig. l is a vertical sectional view through a domestic electric refrigerator embodying my invention;

, Fig. 2 is a fragmentary sectional view of a portion of the machine compartment of the refrigerator shown in Fig. 1; I

Fig. 3 is a diagrammatic view of the refrigerating system including the motor control embodying my invention;

Fig. 4 is a wiring diagram for Fig. 3 with the addition of condensers for suppressing arcing of the contacts.

Fig. 5 is a wiring diagram somewhat similar to Fig. 4 in which the vacuum tube only contains one set of contacts;

Fig. 6 is a wiring diagram of a modified form of motor control system embodying a relay and a vacuum tube containing two sets of contacts;

Fig. 7 is a diagrammatic representation of a refrigerating system provided with a motor control embodying a modified form of my invention;

Fig. 8 is a sectional view of a vacuum tube containing one-set of thermally operated contacts;

Fig. 9 is a sectional view along the line 99 of Fig. 8; and

Fig. 10 is a sectional view of a vacuum tube containing two thermally operated contacts like that shown diagrammatically in- Flg. 3.

Briefly, in the drawings, I have shown a domestic electric refrigerator having an insulated sheet metal cabinet with an upper food storage compartment and a lower machine compartment containing a sealed motor-compressor unit. The operation of the motor-compressor unit is controlled by a switch means within the cabinet. For a starting control, the motor-compressor unit has a vacuum tube which contains thermally operable contact means which control the energization and deenergization of the starting winding. In one form, both the starting winding control means and the overload control means are placed within a sealed vacuum tube while in another form the starting winding con- .trol alone is placed in a sealed vacuum tube, while the overload device is placed outside the tube. In still another form, no such tubes are provided, but a snap acting means is used instead of the tubes. The thermal contact devices within the tubes are compensated for the effect of environment temperature so that the contacts will be operated substantially the same under all conditions. When the contacts are placed in a vacuum tube, the heat is more readily retained by the heaters and contacts and less heat and electric energy is required for the operation of the controls.

Referring now to the drawings, and more particularly to Figs. 1 and 2, there is shown a domestic electric refrigerator 20 having sheet metal outer walls 22 and sheet metal inner walls 24 enclosing a food compartment 26. Between the sheet metal inner walls and outer walls, insulating means 28 is provided.

Beneath the food compartment 26 is a sealed motor-compressor unit 30, the operation of which is controlled by a thermostat switch 32 above the cooling unit 34 in the food compartment 26. The cooling unit 34 cools the air within the food compartment and also freezes ice within the ice trays 36. The motor-compressor unit is connected with the evaporating means 34 and the condenser 38, located at the back of the cabinet, by return and supply refrigerant conduit means. The refrigerant is drawn from the evaporator, compressed within. the motor-compressor unit and forwarded to the condenser, where it is liquefied and thence forwarded under the control of a valve or elongated orifice to the evaporating means where it is evaporated to cool the air within the food compartment 26. Electric energy is supplied to the refrigerator through the electric conductor cord 40 which leads to the motor control means 42, which in turn is connected by electric conductor cords 44 and 46 with the switch 32 and the sealed motor-compressor unit 30.

Referring now more particularly to Figs. 3 and 4, one of the electric conductors 48 within the conductor cord 40, is connected to a connector 50 on the motor control unit 42 and this connector is thence connected by a conductor 52 within the conductor cord 44 which connects to the thermostatic switch means 32 found within the food compartment 26.

The switch means 32 is also connected by a conductor 54 within the cord 44 to a binding post or connector 56 on the motor control base 42.

The motor control base has a socket which receives a vacuum tube 58 having an ordinary radio tube type of base and connector which is plugged into the motor control base socket similarly to a radio tube in radio apparatus.

The connector 56 is connected through the base of the vacuum tube by a conductor 51 to a compensating bimetal strip 60-supported within the vacuum tube. This bimetal strip is anchored at one end to the base of the tube and at the outer end supports an electrical contact 62. This electric contact is normally kept in contact with another electrical contact 64 which is supported upon the end of a narrow operating bimetal strip 66, smaller in cross-sectional area, which is anchored opposite the bimetal strip 60 to the base of the tube. This anchored end of the operating bimetal strip 66 is connected to an electric heater 68 which in turn is connected to a second heater 10 located upon the opposite side of a shield I2 which separates the two heaters and prevents one of the heaters from influencing the bimetal strip controlled by the other.

This second heater I0 is connected through the base of the sealed tube by a conductor I4 to a connector 76 which in turn is connected by a conductor I8 to one end of the running winding 80 located within the sealed motor-compressor unit 30. The second heater I0 is also connected to the anchor end 'of another narrow operating bimetal strip 82 provided with a contact 84 at the opposite end which cooperates With an electrical contact 86 situated on the free end of another compensating bimetal strip 88 also anchored to the base. The anchor end of this bimetal strip 88 is connected by an electrical conductor 90 to a connector 92 upon the base of the motor control means which in turn is connected by an electrical conductor 94 to one end of the starting winding 96 within the sealed unit 30. The other ends of the starting and running winding are connected to a common conductor 98 which connects to a connector I02 which in turn is connected to a conductor I04 which extends through the electric conductor cord 40.

The compensating bimetal strips 60 and 88 compensate for the effect of environment temperature upon the operating bimetal strips 66 and 82 which are heated by the heaters 68 and I0. Thus, under substantially all environment temperatures, the switch contacts are opened and closed according to the effect of the heaters 68 and I0.

The bimetal strips are so calibrated that both sets of contacts are held closed when the electrical circuits are deenergized. the operating bimetal strip is made considerably narrower and smaller in cross-section than the compensating bimetal strip. It should be noted that the starting winding current passes through both bimetal strips of the starting winding control and the entire current through both bimetal strips of the overload control. This current, therefore, heats the operating bimetal strip much more than the compensating bimetal strip, and thus aids the heater to quickly open and hold open the contacts.

When the temperature of the evaporating means 34 rises indicating a demand for refrigeration, the thermostatic switch 32 closes, permitting energy to flow through the main and starting windings, as well as through the contacts and heater within the sealed vacuum tube. This In each case,

causes the rotor I06 to turn and operate the compressor I08 which is directly connected to the rotor. This compressor draws evaporated refrigerant from the cooling unit 34 and forwards the compressed refrigerant to the condenser, where the refrigerant is liquefied and forwarded through conduit means und-er the control of a suitable valve or elongated orifice to the evaporating means. During this time, the starting winding current is traversing the bimetal strips 82 and 88, and all the current is passing through the heater I0 so that the operating bimetal strip 82 will be heated by both currents. When suflicient current has passed through the circuits to cause the motor to approach full speed, the heater I0 will heat the operating bimetal strip 82 sufficiently to cause the contacts 84 and 86 to separate to deenergize the starting winding 96. Thereafter, during the remainder of the operating period, the sealed unit operates upon the running winding 80. The heating of the bimetals' is made easier and the heat is retained more readily because boththe heater and the bimetal are in a vacuum.

The heater 68 is calibrated so that under safe motor currents, the contacts 62 and 64 will remain closed. However, when an unsafe amount of current begins to pass through the heater 68, the bimetal 66 will be heated sufliciently to cause the contacts 62 and 64 to be separated to deenergize 'the entire system.

The wiring diagram in Fig. 4 illustrates the wiring system shown in Fig. 3 in a very simple manner. However, in addition to the wiring shown in Fig. 3, Fig. 4 shows a condenser IIO connected to the conductor 94 on one side and to the conductor 54 on the other side, in order to suppress any arcing at the contacts 84 and 86, while a second condenser H2 is connected to theconductors 54 and 18 to suppress arcing at the contacts 62 and 64. These condensers, need be used ordinarily only under severe conditions,

but their use at any time is desirable from the electrical standpoint.

The construction of the vacuum tube is shown in Fig. 10 as one example of the structure. In Fig. 10 there is provided a sealed glass vacuum tube I 20. similar to that which has been used for radio tubes. Glass is preferred on account of the fact that it enables the contacts to be readily viewed, but if desired, a metal tube may be used in place of the glass tube. This glass tube and bulb has a glass base I22 within it which is sealed to the bulb at their lower edges as shown at I24. The base has a glass tube I26 connecting to the interior of the bulb so that the bulb may be evacuated after the base and the bulb are joined. Ordinarily, no gases are introduced, but some inert gas may be introduced if desired. After the bulb is evacuated, this tube I26 is sealed as shown. An ordinary radio tube base I28 is sealed and cemented to the lower end of the bulb by a cementing and sealing material I30. The base is provided with four prongs or electrical plug connectors I32 which are received within suitable sockets in the motor control base 42, Fig.

3. Three of these prongs are connected by the conductors 51, 14 and .80 to the thermally operated contact means which is supported by the base.

a pin which "forms the upper end of the conductor 51 and the heater 68 which is formed of a loop-of resistance wire supports the lower end of the bimetal 66 and is itself supported by a long pin I34 which is fused into the base I22. The shield- 12 is supported by another pin fused into the base,,while the heater 10 is supported by another long pin I36. The heater 10.which is also formed of a loop of resistance wire also supports the lower end of the operating bimetal 82, while the compensating bimetal 88 is supported by the upper end of the conductor 80. The lower 3 end of the long pin I36 acts as a conductor connectlng the one end of the heater with the conductor 14.

In Fig. I have shown a modified form of wiring diagram in which I50 indicates the running winding, I52 indicates the starting winding and I54 indicates the sealed vacuum tube. The

starting and running windings I52 and I50 are connected by a common conductor I56 to one side of the supply line. The running winding I50 is connected through a. connection I 58 to a heater I60 within the sealed vacuum tube which in turn is connected to another connector I62 to a current overload device I64 {shown diagrammatically. This current overload device I64 is in turn connected to a thermostatic switch means I66 similar to the switch means 32 of Figs. 1 to 4 also shown diagrammatically. This switch means I66 is in turn connected to theother side 01' the supply line by the conductor I68.

The starting winding is connected through the connector I to a compensating-bimetal strip I12 anchored to the base of the sealed vacuum tube I54. The free end of this bimetal strip has a contact which cooperates with a contact upon the free end of the operating bimetal ship I 14 which has its anchored end connected to the electrical conductor connected between the heater I60 and the running winding I50. In order to suppress arcing at the contacts, a condenser I16 may be connected between the starting and running winding circuits as shown if desired. However, under ordinary conditions, such a. condenser may be omitted.

Thebimetal 60 is supported at its lower end by In operation, the contacts supported by the bimetals I12 and I14 remain in closed position when the circuit is deenergized. However, when the switch I66 is closed, current flows through both the running and the starting windings, thus causing the heater I60 to heat the bimetal I14. When suflicient heat has been applied to the bimetal I14, the bimetal I14 curlsin such a direction to separate the starting winding contacts to deenergize the starting winding. By this time, under normal conditions, the motor has reached suilicient speed to operate solely upon the running winding.

In Figs. 8 and 9, the construction of the vacuum tube I54 is illustrated. In these figures, there is shown for the purposes of illustration, a sealed glass bulb I18 provided with a glass base I80 upon which the contacts are supported and an external base I82 which is cemented to the lower portion of the glass bulb and provided with prong or plug type radio connectors, I58, I62 and I10. In this sealed bulb, the heater I60 is formed in the form of a depending loop supported at its upper end upon pins extending into the base I80. At the lower end, this heater supports the lower end of the narrow operating bimetal I14 while the wider compensating bimetal I12 is supported by a U-shaped bracket I84 which is fastened to short pins extending into the base I00. It is clearly shown in Fig. 8 that the operating bimetal strip I14 is narrower than the compensating bimetal strip I12. Since the starting winding current passes through both bimetals, the operating bimetal will be heated by this current a greater amount than the compensating bimetal, thus aiding the heater in' opening and holding open the contacts. This construction is simple and satisfactory.

In Fig. 6, a wiring diagram of a modified form 01' motor control is shown. In this system, there is provided a running winding 202, a starting winding 204, a relay coil 206 in series with the running winding for operating the relay contact mechanism 288 in series with the starting winding 204. One end of the running winding and one end of the starting winding are connected to a common conductor 2I0 which connects to one side of the electrical supply line. The other end of the relay coil 206 and the starting winding contacts are also connected together and connect to a connector 2I2 of a sealed vacuum tube 2I4.

Within the sealed vacuum tube 2 I4 is a heater 2I6 for heating an operat ng bimetal 2I8 carrying at its free end a contact cooperating with a contact supported upon the free end of a compensating bimetal 220. This compensating bimetal 220 has a larger cross-sectional area than the operating bimetal 2 I8. The compensating bimetal 220 has its anchor end connected to a connector 222 which in turn is connected by an electrical conductor to a point in the running winding support between the relay coil 206 and the running winding 202. The contacts supported by the bimetals 2 I8 and 220 are normally open when the circuit is deenergized. Connected in series with the heater 2I6, is a second heater 224 which serves as a thermal overload heater. This thermal over load heater operates the operating bimetal 226 which at its free end carries a contact cooperating with a contact upon the free end of a compensating bimetal 228 of larger cross-sectional area, which in turn is connected to a connector 230 of the sealed tube. 2. The contacts carried by the bimetals 226 and 228 are normally closed and do This connector 230 is connected to the thermostat switch 232 which in turn is connected by a conductor 234 to the other side of the electrical supply line. If desired, a condenser 236 may be connected across the terminals of the connectors 212 and 230, while a second condenser 238 may be connected across the terminals of the connectors 212 and 222. These condensers may be of small capacity and may be used for suppressing the arc across the contacts within the sealed tube. These condensers, however, may be omitted if desired.

When the switch 232 closes, current will flow through the conductor 210, the running winding 202, the relay coil 206 through the heaters 216, 224, the bimetals226 and 228, the switch 232 and the conductor 234 to the other side of the electrical supply line. This fiow of current will be suflicient to close the starting relay contacts 208 which in turn will cause current also to flow through the starting winding 204 in parallel with the running winding. When sufficient current has passed through the heater 252 and the operating bimetal 218, the operating bimetal 218 will be heated sumciently to cause the closing of the contacts which the bimetal 218 and the bimetal 220 support. This deenergizes the relay coil 208 to cause the opening of the starting winding contacts, thereby deenergizing the starting winding. By this time the motor will have attained sufficient speed to run solely upon the running winding. Should any overload current occur, the heater 224 will heat the operating bimetal 226 sufliciently to cause the separation of its contact from the contact carried by the'bimetal 228 to deenergize the system.

I find by providing the control contacts within a sealed vacuum tube, that not only will the life of the contact and the contact mechanisms be increased, but also more simple control systems may be used. Also theheat produced by the heaters is more readily retained so that less heat and therefore less current is required to hold the contacts open. The sealing of the contacts protects them from oxidation as well as from any sort of foreign matter. Should there be any inflammable vapors present, they will not be ignited because they" are excluded from the presence of the contacts by the sealed vacuum tube.

In my vacuum tubes, I have provided not only operating bimetal members, but also compensatlng bimetal members which compensate for the effect of environment temperatures upon the operating bimetal members. This is particularly important where two heaters are provided so that the effect of one heater will not impair the proper operation of the contacts and bimetal members controlled bythe other heater. It is, of course, also of advantage in a single contact vacuum tube since environment temperature will not affect its time of operation. The operating bimetal members'are made smaller in cross-section than the compensating bimetal members. Since current traverses both these members the operating bimetal will be heated thereby more than the compensating bimetal. The sealed vacuum tubes are relatively inexpensive and if they should become inoperative for any reason whatsoever, they may be as readily replaced as a radio tube. Since radios are so widely distributed, it seems that anyone should be able to replace such a tube without difficulty.

' While I prefer'to operate the contacts and their heaters in a vacuum, it is possible to operate these in air under ordinary conditions if desired. For example, in Fig. '7, I have shown a refrigeratingsystem with thermally operated control means which are not enclosed within a sealed vacuum 'tube but are provided with a permanent magnet controlled snap action to preserve the contacts. In Fig. 7, the refrigerating system includes a compressor 310, a condenser 311, an evaporator 312. The compressor discharges the compressed refrigerant to the condenser 311 which in turn discharges liquefied refrigerant through the expansion device 313 to the evaporator 312 where the refrigerant is evaporated and returns through the line 314 to the compressor 310. The expansion device 313 may be of any suitable character, but preferably is of the elongated orifice type which maintains a fixed and continuously open orifice, so calibrated as to length and cross-sectional areaythat it maintains the evaporator 312 at the proper tem-,

perature to-maintain the object being cooled at a substantially constant temperature notwithstanding variations in the surroundingatmosphere. In such a system, the elongated orifice in the expander 313 permits a continuous passage of refrigerant therethrough, and should the compressor 310 stop temporarily, this flow through the orifice continues and in a relatively short time equalizes the pressures throughout the refrigerating system, so that if the compressor should be restarted after such a short time, it starts with substantially no load.

Under ordinary conditions, such a system is stopped only for the purpose of defrosting the evaporator 3B2 and this defrosting operation is performed only once or twice a. month and is not of the type of stopping operation which is intended to maintain temperature conditions in.

the object being cooled. On the contrary, sucha stopping operation generally permits the object being cooled to warm above the desired temperature, but the operation is performed because of the large accumulation of frost on the evaporator and because of its undesirable inconvenience. After such a stopping operation and because of its long duration, the compressor starts under no load characteristics and hence the compressor need not be provided with unloading mechanism, other than the expander 313 itself. The motor 315 for driving the compressor may be of the split phase type which is provided with a starting winding 316 and a running winding 311, and, as is usual with this type of motor the starting torque is small. Such a motor-compressor unit is capable of starting only if the entire refrigeration system has become substantially equalized as to pressure throughout, or if the unit is provided with an automatic unloader for removing the pressure differential load during the starting period. In this particular system, no unloader need be used, as it is possible to permit the system to equalize by a sufliciently long pe- 'riod ofidleness during the infrequent stops which may be necessary.

The control for the motor includes starting contacts 318 for controlling the flow of electric current to the starting winding and running contacts 313 for controlling the flow of electric current to the running windings. A starting control 320 is provided for the contacts 318 and a running control 321 is provided for the contacts 310. The control 320 includes a thermostat in the form of a bimetallic strip 322 heated by a resistance 323 in an electric circuit between the source of electrical energy 324 and the motor 315 which passes through the resistance 323. The bimetallic strip 322 opens the contacts 318 by moving the rod 3l8a carrying the movable contact upwardly against the magnet resistance 325 by a snap action in the well-known manner. The running control 32l includes a thermostat in the form of a bimetallic strip 326 heated by a resistance 32'! through which an electric circuit passes from the source of electrical energy 324 to the motor 3l5. The strip 326 opens the contacts 3l9 by moving the rod 3l3a carrying the movable contact upwardly by a snap action against the magnet resistance 328.

The construction and calibration is such thatthe thermostat 320 opens the contacts 3l8 after the motor 3| has attained its running speed and maintains the contacts open so long as the motor continues to operate normally. The control 32! is constructed and calibrated so that the contacts 3l3 remain closed so long as the motor runs normally but will open if the motor should I 320 is constructed so that it heats quickly and Opens the contacts 3l8 before the contacts 3l9 can be opened and is of such construction that the contacts 3l8 are opened after a predetermined period of time sufiicient to normally permit the motor 3l5 to attain its running speed.

A manual control for stopping and starting the system may be provided and this may include a snap acting lever mechanism 330 adapted to en gage the hook 33l which is an extension of the contact rod 2l9a which controls the opening and closing of the contacts 3I9. The rod 3I9a may have a sliding engagement with the strip 326 with a stop 333 attached to the rod 319a in such a manner that the rod 3l9a may be moved upwardly without disturbing bimetal 326. Thus, the manual control 330 may be operated to open the contacts 3I9 by moving hook 331 and therefore the rod 3| 9a. upwardlywithout disturbing the bimetal 326, and if the manual control 330 is placed in the closed position, it permits the rod 3|9a to move downwardly and be actuated by the bimetal 326 acting through the stop 333 independently of the manual control.

Under ordinary operation, the manual control 330 is moved to releasenthe ro d 3l9a downwardly to close the contacts 3!!! and this initiates a starting cycle in which electric current flows through both windings M6 and 3H and both resistances 323 and 321. After a length of time suflicient to permit the motor to start, the contacts 3l8 are fail to start because the pressure differential in running thermostat 32] will become overheated and the contacts 3|9 will be opened. When these contacts are open, the flow of current through the resistances 323 and 32'|.stops and permits the thermostats 320 and 32! to cool, thus reclosing the contacts 3l8 and 3|9. When these contacts are reclosed, a starting cycle is initiated which if successful will permit the motor 3l5 to run as long as desired, but if unsuccessful, will reinitiate another overload and restarting cycle until such time as compressor is unloaded sufiicicntly to permit the motor M5 to start.

While the form of embodiment of the invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

l. A motor control system including an electric motor having a phase and a main winding, a sealed receptacle having the oxygen removed therefrom, starting contact mechanism located within the sealed receptacle for controlling the connections of the phase winding,thermal operating means located within said sealed receptacle for controlling the starting contact mechanism, overload mechanism located within said' sealed receptacl for controlling the energization of the phase and main windings, and means within said sealed receptacle for preventing the thermal operating means from having its operation directly influenced by the presence of the overload mechanism in 'the sealed receptacle.

2. A motor control system including an electric motor having a phase and a main winding, a sealed receptacle having the oxygen removed therefrom, starting contact mechanism located Within the sealed receptacle for controlling the connections of the phase winding, thermal operating means located within said sealed receptacle for controlling the starting contact mechanism, overload mechanism located within said sealed receptacle for controlling the energization of the phase and main windings, and a shield within said sealed receptacle located between said overload mechanism and said thermal operating means for preventing the direct transmission of radiant energy from the thermal operating means to the overload mechanism.

3. A motor control system including an elec-.

tric motor having a phase and a main winding, a sealed receptacle having the oxygen removed therefrom, starting contact mecl-anism located within the sealed receptacle for controlling the connections of the phase winding, thermal operating means located within said sealed receptacle for controlling the starting contact mechanism, overload mechanism located within said sealed receptacle for controlling the energization of the phase and main windings, and a shield within said sealed receptacle located between said overload mechanism and said thermal operating means for preventing the direct transmission of radiant energy from the thermal operating means to the overload mechanism, and compensating means within said sealed receptacle for both the thermal operating means and the overload mechanism for compensating for the effect of the temperature conditions existing within the sealed receptacle upon the thermal operating means and the overload mechanism.

4. A motor control system including an electric motor having a phase and a main winding, a. sealed receptacle having oxygen removed therefrom, starting contact mechanism located within the sealed receptacle for controlling the connections of the phase winding, a bimetal operating means for said starting contact mechanism, electric heating means within said sealed receptacle for heating said bimetal operating means to operate the contact mechanism, overload contactmeans for compensating for the effect of the temperature conditions within the sealed receptacle upon the bimetal operating means.

5. A motor control system including an electric motor having a phase and a main winding, a sealed receptacle having oxygen removed therefrom, starting contact mechanism located within the sealed receptacle for controlling the connections of the phase winding, a bimetal operating means for said starting contact mechanism, electric heating means within said sealed receptacle for heating said bimetal operating means to operate the contact mechanism, overload contact mechanism located Within said sealed receptacle for deenergizing the motor, an overload bimetal operating means within said sealed receptacle for operating said overload contact mechanism, an overload electric heating means within said sealed receptacle for heating said overload bimetal operating means, bimetal temperature compensating means for each of said bimetal operating means for compensating for the effect of the temperature conditions within the sealed receptacle upon the bimetal operating means, and a shield located between said two electric heating means for confining their radiant energy to their respective bimetal means.

GEORGE C. PEARCE.

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