US2658175A - Electrical apparatus - Google Patents

Description

Nov. 3, 1953 Filed Aug 5, 1952 2 Sheets-Sheet l zvz 34 4 4 4- l 52 57 Esq il gwd {48 I V O a I I I80 I E I INVENTOR. Harry H Clark.

Nov. 3, 1953 H. F. CLARK ELECTRICAL APPARATUS Filed Aug. 5, 1952 2 Sheets-Sheet 2 M 0 x mm INVENmIi; Harry F. C/qzk Z4 My Patented Nov. 3, 1953 2,658,175 ELECTRlCAL APPARATUS Harry F; Clark, Oakwood Ohio, assignor to General Motors Corporation, Dayton, Ohio, a corporation of Delaware Application Ailg'ust 5, 1952, Serial No. 302,777

Claims.

This invention relatesto an electrical apparatus and more particularlyto an electrothermal starting control for split phase electric motors.

Electrothermal starting controls for electric motors are a success. However, they have one particular disadvantage in comparison to electromagnetic s-tarting controls. Simple electromagnetic starting controls do not terminate the start ing period until the main winding current drops below a certain value. This provides a starting period which increases in length as the motor load increases and particularly the starting period increases in lengthas the motor accelerates more quickly. Electrothermal starting controls have provided a substantially uniform starting time regardless of the rate of motor acceleration and regardless of the load upon the motor. Consequently, the starting Period is made long enough for maximum loads and this is longer than necessary for lighter loads. The unnecessary prolonged Starting eriod for lighter loads causes an audible motor hum near the end of the starting period. g

It is an object of inventionto provide simple electrother'm starting control will quickly start a split p'hase electric motor at all times.

It is another objector a simple electroth'erlneil starting y will reduce the len gt of the sta period as the rate of motor acceleration inc :ases

It is another ohject of "m mention to rovide a simple electrothermal' star-ting control which will reset to the starting position during the off period but which is p i ideci with a simple resetting arrangement w will accomplish resetting at the start or each running periodif resetting to starting position does not takeplace before the starting attempt is made.

In the one form strated in which these objects are attain'e t" one is provided a simple cantilever bimetal switch carrying a contactwhich is connected in series'with the phase- Winding of the motor; 4 The end portion of this bimetal strip i s connected by a -s'ape'd toggle spring to a" hook-shaped cantilever compensating bimetal which compensates forthe effecto'f ain'- bient temperature on" the starting bimetalstrip. After this stripisi'hejated by the phase windin'g current to open the phase=winding circuit itis held in the runningflpos'ition' strip heater connected in seriesiwith the main winding circuit.

To increasejthe length of time that thestart ing. bimetal strip is ihth startingposition when motor acceleration isslow' and the load is heavy,

2 there is provided a second bimetal which has an arm normally in engagement with the starting bimetal strip. This second bimetal is made of more active bimetal material than the starting bimetal strip. This second bimetal is connected in series with the main winding and under heavy loads and heavy acceleration it will be heated to a higher temperature to oppose in greater amounts the movement of the starting bimetal strip from the starting position to the running position. The control normally returns to the starting position during the off cycle but if the motor is energized before resetting is accomplished, this second bimetal since it is made of more active bimetal than the starting bimetal switch will reset the starting bimetal strip immediately so that a successful start can be accomplished.

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

In the drawingsz' Figure 1 is a horizontal sectional view taken along the line l"-| of Figure 2 of a bimetal starting control embodying one form of my invention;

Figure 2 is a sectional View taken along the line 2- 2 of Figure 1';

Figure 3 is a sectional view taken along the line 3--3 of Figure 1;

Figure 4 is a sectional view taken along the line 4-4 of Figure 1;'

Figure 5 is a fragmentary sectional view similar to the upper'portion of Figure 1 showing the starting control in the running position; and

Figure 6 is a perspective view of the starting bimetal strip and its resetting control.

Referring now to the drawings and more particularly to Figures 1 and 5 there is shown an electric motor circuit including an electric motor 20 having a main or running winding 22 and a phase or starting winding 24. The common junction ofthe main and phase-windings is connected by a line switch 28 to the supply conductor 30. A capacitor 32' may be connected in series with the phase-winding 24 if desired but many starting controls will operate equally well Without this capacitor and it may be omitted where an ample starting torque can be obtained without its use;

Phase-winding control The phase-winding 24 and the capacitor 32 are connected by' the conductor ,34 to the L-shaped starting contact and terminal 36 the horizontal portion of which is beneath the base 38 and is connected thereto by the use of an upwardly extruded eyelet rivet which is internally threaded to receive a binding screw 39. The base 38 is made of a suitable mounted electrically insulated material and carries an integral U-shaped rib of the same material which supports the moving parts of the control. The base 38 may also be provided with additional stiffening ribs which are not shown.

Fastened to the rib :32 by the rivets 44 and 59 is a U-shaped bimetal member 55 having one leg 46 forming the starting cantilever bimetal strip portion having its high expansion side facing outwardly away from the center of the base 38. The high expansion side of the yoke portion of the U-shaped bimetal member 65 lies directly against the U'shaped rib Q2.

The movable end portion of the cantilever strip portion 66 carries a movable starting contact 41 shown in engagement with the L-shaped station ary contact 36. When the contacts 35 and 41 are closed, as shown in Figure l, the strip 46 is thereby connected in series with the phase-winding 24 and carries and is self-heated by the starting or phase-winding current. The outer face of the rib t2 carries a hook-shaped tempera ture compensating bimetal strip as also having its high expansion side iacin outwardly from the center of the base 38 and having its low expansion side lying against the outside oi the rib d2. It is fastened to the rib by two rivets ill. This compensating strip 48 has the same ehective length as the cantil ver strip portion id but is preferably much wider and somewhat thicker as shown in Figure 2.

The adjacent movable ends of the compensating strip at and the starting bimetal strip are connected by a thin C-shaped toggle leaf spring 5!). The end of this compensating bimetal strip 48 is notched while the adjacent end of the start" ing bimetal strip portion iii is provided with a small rectangular aperture 5! for receiving and holding the adjacent notched ends of the spring 5B. This forms the equivalent of a double toggle snap-acting arrangement since both the bimetal strip portions 46 and 38 are flexible. A setscrew 52 threads through the rib 4.2 and engages the base portion of the starting bimetal strip portion 46 to adjust its position.

In this form, the geometrical arrangement and the adjustment of the setscrew is such that when the starting bimetal strip portion it and its contact ll are in either the open or closed position the toggle spring 55! is at such an angle that when the strip 43 is cool it will move to or remain in the starting or closed position. Since the bimetal strip 45 is connected in series with the phasewinding 24 it will receive a flow of current as soon as the line switch 23 is closed. The cumulative heating efiect of this current through the starting bimetal strip portion 48 causes it to bow downwardly and move from the starting position, shown in Figure 1, to the running position shown in Figure 5 to open the phase-winding circuit. In this running position, its further movement is stopped by the island 58 formed as a part of the base 38. With this simple arrangement, the starting period is almost the same length at all times. This has made it necessary to adjust the setscrew 52 so that the starting time is sufficiently long to cause the motor to start properly under the most severe starting conditions which might be encountered. Therefore, when the starting conditions are normal, the phase-wind ing circuit has remained energized for a longer period than is necessary. The speed at which it is desired to deenergize the phase-winding is termed the balancing speed. For a motor having normal running speed of 1750 R. P. M., this balancing speed occurs at between about 1400 and 1600 R. P. M.

According to my invention in order to cause the bimetal strip portion 46 to move its contact 4'! from the starting position shown in Figure l to the running position shown in Figure 5 at the ideal time or at the balancing speed of the motor, I provide a reset bimetal member 5i having its lower end anchored in cantilever fashion to the L-shaped main winding terminal member 60. This terminal member 69 is connected by a binding screw 4%] threaded into the eyelet portion of the terminal 6% to the conductor 62 connecting with the second terminal of the main winding 22. The bimetal 5? has its upper portion I51 bent at right angles and provided with a U-shaped portion having an arm t3 extending toward and engaging the portion of the bimetal strip 46 on the opposite side from the contact 41. The arm 63 may be provided with a bent over tip I63. To prevent the transmission of the phase-winding current from the strip 48 to the bimetal 5! the strip i5 is provided with a localized coating MS of an electrical insulating material.

The reset bimetal is made of a more active bimetal material than the starting bimetal strip portion The reset bimetal 51 is connected in series with the main winding through the riveting of its base to the main winding terminal by the to the running position in Figure 5.

rivet 5-53. This bimetal 51 is used to prolong the starting period of the motor. It is arranged so that its high expansion side faces the center of the base Since the high expanding side of the bimetal 57 faces the center of the base 38 and the high side or" the bimetal strip portion 4% is away from the center of the base 38 the bimetals it and 57 when heated simultaneously will bow or deflect toward each other.

At the start 01'; the motor as long as the motor 20 is rotating at a low speed there will be a heavy flow of current thorugh the main winding 22 and through the main reset bimetal 51. When the motor accelerates rapidly under normal or light load, heavy current will quickly diminish and the heating effect upon the reset bimetal 51 will be small. Consequently, the reset bimetal 51 will generate a relatively low force opposing the movement of the starting bimetal strip portion 46 from the starting position shown in Figure l to the running position shown in Figure 5. This movement will therefore take place at the minimum time after the motor 20 is energized.

However, when the motor load is heavy, the motor will accelerate slowly and the heavy starting current will diminish slowly so that there will be much greater heating of the reset bimetal 51. Under these circumstances a much greater force will be generated more rapidly in the reset bimetal 5'! than in the starting bimetal strip portion 46. This will make it more difficult for the starting bimetal strip portion 46 to move from the starting position in Figure 1 Consequently, it will be necessary for the starting bimetal strip portion 45 to be heated for a longer time by the phase-winding current so that it attains a higher temperature to provide a greater force to overcome the greater opposing force provided by the reset bimetal 51 before the moveinentjto the running position can take place. In this way the reset bimeta1151 can prolong the starting (time.

Consequently, under .thisarrangement the adjusting screw '52 is adjusted so that under the minimum loafd'the starting bimetal strip portion 46 is opened'in a minimum length .of time such as 1% of a second which is adequate for Starting when the motor accelerates rapidly. This eliminates the motor hum which --is caused when the phase-winding is energized after the balancing speed of the motor is reached. When heavier loads are encountered and motor acceleration is slow, theireset bimetal .51 delays the movement of the starting bimetal strip portion 46 until the .main winding current falls off at the balancing speed. -;'Ihis prolongs the starting time. In this way I :have provided a simple arrangement whereby the starting :Deriod may .be .made variable :in accordance with the starting acceleration of'the-rmotor.

The "reclosin'g control Since the starting bimetal strip portion 46 is biased to the closed or starting position and is moved to the .open or running .position by being .self-heatedby the phase-winding current and since the phase-winding current ceases upon the separationof the contacts 36, 41, some means is-necessary to hold'the strip portion 46 in the open or running position throughout the remain- .dcr'of the running period-of the motor to prevent the reclosing of these contacts .36, 41. For this purpose there isprovided ,a ribbon type electric heaterfl having its lower-end riveted to the yoke portion of the .U-shaped bimetal member 65 at the base ofthe starting bimetal strip portion 46 by the rivet 44 previously mentioned. This heater -64 is connected in series with the main winding 22 by-any suitable arrangement. The heater 164 not-only supplies suflicient heat to the starting bimetal-strip portion 46 during the running period of the motor to keep the contact 41 in the runningposition after the end of the starting period, butit-also controls the resetting of the contact 47 to the starting position as shown inEigure :1.

When the flow of energy through the motor is discontinued by the use of the line switch 28, the heater 64- as wellas the bimetallic cool off and when they have become sufficiently e001 the to gle l-springafio will move the bimetal strip 46 and the contact-41 from the-running position shown in Fi ure 5 to the starting position shown in Figure 1. The heater 64 and the reset bimetal-5.! are conveniently combined in a reset control by connecting the upper end .of the heater -46 to the bent portion I51 of the reset bimetal ,5] at the point designated by the reference character 164. By so-doing the heater 64 and the bimetal -51 reconveniently connected in series with the main-winding-Zland at the same time the projection 63 maintains the upper portion of the heater 64 properly spaced from the starting bimetal strip 46 so that the desired limited amount of heat transfer between the heater 64 and thestrip portion .46 is provided.

The spacing of the heater 64 from the strip 45 insures that the heater :64 has a negligible effect upon the=bimeta1 strip portion 46 at the initial energizationeof themotor. The heater .64 slowly :heats the bimetal strip portion 46 so that its heating efiect-does not-become pronounced However, in a prolonged starting attempt it does bimetal '65.

6 have an effect'u'pon the reset bimetal5l 'andth'e starting bimetal :strip "portion l 46 and assists the bimetal strip portion 146 in acquiring suflicient powerto-fina'lly overcomethe force'of the reset bimetal 51 to terminate the starting period.

As its name implies, the reset bimetal-51 has asecond function. litheidleperiodof themotor 20 is not su'flici'ently long for the startingbimetal strip portion 46 :to .cool off andreturnfrom the running position shown in Figure-5 'to'the starting position .shown in 'Figure' 1, the motor 2 0wil1 not start and a heavy 'current'will flow through the main winding :circuit from the supply conductor 35 through the line switch 28 and the main winding 22 the conductor 62, the main winding terminal '60, the reset bimetal 6-1, the heater 64, to the other side 'ofthe line.

This current will 'be so heavy that the reset bimetal 5'! will almost-instantly deflect upwardly and move the starting bimetal strip portion 46 from the positionsh'own in Figure 5 to the position shown in Figure 1. This will connect the phase-Winding 24 into the circuit so that a rotating field is provided for starting the motor 2c. Because of the use of a very active bimetal material for the reset bimetal 51, this action takes place so rapidly that no noticeable motor hum occurs. The reset bimetal '51 and the heater 64 therefore provide a resetting control which is very simple and inexpensive in construction and which assures quiet dependable starting which keeps the main winding energizedfor the time required to get the best starting effort out of the motor.

The compensating bimetal 48 is -provided with a stiffening rib 49l which controls itsmovement under changes in ambient temperature. The longer the rib 491 the less movement of the compensating bimeta1 48 under a selected change in temperature. Ambient temperature afiects both the starting bimetal "46 and the reset bimetal 5? since these two bimetals are exposed-at all times and the compensating bimetal-'48 is called upon for a lesser compensating action. Therefore, the rib -49lis'made longer =toreduce the compensating action of the compensating bimetal-48 to the amount required.

The overload protector The main winding current is conducted through the resettingrbimetal 5'! and the-electric heater'ee to the yoke .portion of the U-shaped The phase wi-miing current is also conducted by the starting bimetal strip portion to the yoke portion of the U-shaped bimetal member 55. The lower portion'of this U-shaped bimetal member is provided with acantilever overload bimetal strip portion 66. This portion 66 carries a movable contact it which normally makes contact with theL-shaped stationary contact and terminal member "[2 connecting with the second supply conductor 33.

A hook-shaped overload compensating bimetal strip ifi is fastened byrivets to the adjacent outer face ofthe rib '42. This overload compensating bimetal strip 16 andithew'overload bimetal strip portion 66 both have their high expansion sides turned outwardly relative to the center of the base 38. The end portion of the overload compensating bimetal strip 16 is-notched. The movable end portion of the over-load bimetalstrip portion 66 is provided witha rectangular aper- *ture.

This rectangular aperture and the notch in the strip 16'receive the off-set-notched ends of the G-shaped toggle leaf spring 18. The overload bimetal strip portion 66 is self-heated by the current flowing from the yoke portion of the 'U-shaped bimetal member 65 through the overload contacts Hi, 12 to the second supply conductor 13.

When the strip portion 66 is self-heated sufficiently it will trip to the open position into contact with the adjacent part of the island 68. The tripping point of the overload strip portion 66 is adjusted by bending the vertical contact portion of the terminal l2 toward or away from the strip portion 66 in order to reduce or increase the current value to which the overload portion 66 trips to the open position. The reclosing of the overload por ion 66 is adjusted by the setscrew 80 which bears against the base of the overload bimetal strip portion 66 to adjust its position. To assure the reclosing of the bimetal strip portion 66 in the event that the screw 88 is not properly adjusted, I connect a small ceramic heater 1G5 across the terminal '52 and one of the rivets H6 which fastens the compensating bimetal 16 to the U-shaped rib 52. As a consequence, when the overload contact it moves to the open position, there will be a small current fiow through the heater IE6 and through the U-shaped bimetal member 65 and the reset control to the main winding. This current will be so small it will have substantially no effect upon the remainder of the circuit but due to its high resistance substantially all the heat will be generated in the ceramic heater I66. This ceramic heater GEES will apply sufficient heat to the overload bimetal 16 that it will deflect upwardly after a period of time and insure the reclosing of the bimetal at. To prevent vibration from changing the adjust ments of the setscrews 30 and 52, there is pro vided a U-shaped wire spring I36 extending between the screws 52 and 80 so as to apply sufficient friction upon them to prevent movement under such conditions.

Reference is made to the following application and patent owned by the same assignee: S. N. 599,791 filed June 16, 1945, Harry F: Clark, applicant, Pat. 2,618,721 granted November 18, 1952.

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 as may come within the scope of the claims which follow.

What is claimed is as follows:

1. A control including a bimetal strip means, a control means connected to and operated by the movement a portion of said bimetal strip means, means including a first heating circuit under the control of said control means for heating said bimetal strip means, a resetting control including a bimetal support extending near to and generally parallel to said strip means and having its high expanding side away from said bimetal strip means to cause it to bow toward the strip means when heated, said resetting con trol also including an electric heater supported by said bimetal support alongside and adjacent to said strip means, a second heating circuit portion connected to said electric heater and said support in parallel circuit relationship with the first heating circuit to normally energize said heater to heat said strip means and for heating said bimetal support abnormally during abnormally high current flow to cause said support to bow toward the strip means, said support being provided with a resetting, extension for engaging and moving said strip means under abnormally high current conditions.

2. A control including a bimetal strip means, a control means connected to and operated by the movement of said strip means from a first position to a second position and return, a snap acting means cooperating with said strip means to provide a limited force to hold the strip means and the control means in said first position,-

means including a first heating circuit under control of said control means for heating said strip means sufficiently to cause its bimetal action to overcome the restraining force of the snap acting means to move the strip means and the control means from the first position to the second position, a resetting control including a bimetal support located in opposite relationship to the strip means so that they deflect toward each other if heated simultaneously, said bimetal support having an extension for engaging and moving said strip means and said control means from the second position to the first position, said resetting control also including an electric heater supported in heating relationship to said bimetal strip means and a second heating circuit portion connected to energize said heater and said bimetal support for heating said bimetal strip means to hold said strip means in the second position during normal current flow in said second heating circuit portion and for heating said bimetal support during abnormally high current flow in said second circuit portion to insure resetting of said bimetal strip means and said control means to the first position.

3. A control including a bimetal strip means, a control means connected to and operated by the movement of said strip means from a first position to a second position and return, a snap acting cooperating with said strip means to provide a limited force to hold the strip means and the control means in said first position, means including a first heating circuit under control or said control means for heating said strip means sufficiently to cause its bimetal action to overcome the restraining force of the snap acting means to move the strip means and the control means from the first position to the second position, a resetting control including a bimetal support located in opposite relationship to the strip means so that they deflect toward each other if heated simultaneously, said bimetal support having an extension for engaging and moving said strip means and said control means from the second position to the first position, said resetting control also including an electric heater supported in heating relationship to said bimetal strip means and a second heating circuit portion connected in series with said heater and said bi metal support for heating said bimetal strip means to hold said strip means in the second position during normal current flow in said second heating circuit portion and for heating said bimetal support during abnormally high current flow in said second circuit portion to insure resetting of said bimetal strip means and said con trol means to the first position. a

4. A control including a bimetal strip means, a control means connected to and operated by the movement of said strip means from a first position to a second position and return, a snap acting means cooperating with said strip means to provide a limited force to hold the strip means and the control means in said first position, means including a first heating circuit under control of said control means for heating said strip means sufficiently to cause its bimetal action to overcome the restraining force of the snap .9. acting means to move the strip means and the control means from the first position to the sec-- ond position, a resetting control including a bimetal support located in opposite relationship to the strip means so that they deflect toward each other if heated simultaneously, said resetting control also including an electric heater supported. by said bimetal support alongside said strip means for heating the strip means to hold the strip means and the control means in the second position, said bimetal support having an extension extending into engagement with said strip means for maintaining said heater properly spaced from said strip means and for moving said strip means and control means from the second position to the first position, and a second heating circuit portion connected to energize said heater and said bimetal support for heating said bimetal strip means to hold said strip means in the second position during normal current flow in said second heating circuit portion and for heating said bimetal support during abnormally high current flow in said second circuit portion to insure resetting of said bimetal strip means and said control means to the first position.

5. A control for an electric motor having main and phase-windings including a bimetal strip means and a switch means connected in series with said phase-winding for controlling the energization of the phase-winding, said switch means being connected to and operated by said strip means from a first position to a second position and return in response to changes in temperature of said strip means, a snap acting means cooperating with said strip means to provide a limited force to hold the strip means and switch means in the first position, a resetting control including a bimetal support located in opposite relationship to the strip means so that they defiect toward each other if heated simultaneously, said bimetal support having an extension for engaging and moving said strip means and said switch means for the second position to the first position, said resetting control also including an electric heater supported in heating relationship to said bimetal strip means, said bimetal support and said heater being connected in series with said main winding so that the heater is energized during the running period to heat and hold the bimetal strip means and the switch means in the second position during the running period and so that the high starting current will heat the bimetal support to cause it to deflect for resetting the strip means and the switch means at the start of each running period.

6. A control for an electric motor having main and phase-windings including a bimetal strip means and a switch means connected in series with said phase-winding for controlling the energization of the phase-winding, said switch means being connected to and operated by said strip means from a first position to a second position and return in response to changes in temperature of said strip means, a snap acting means cooperating with said strip means to provide a limited force to hold the strip means and switch means in the first position, a resetting control including a bimetal support located in opposite relationship to the strip means so that they deflect toward each other if heated simultaneously, said resetting control also including an electric heater supported by said bimetal support alongside said strip means for heating the strip means to hold the strip means and the switch means in the second position, said bimetal 10 support having an extension extending into engagement with said strip means for maintaining said heater properly spaced from said strip means and for moving said strip means and switch means from the second position to the first position, said bimetal support and said heater being connected in series with said main Winding, so that the heater is energized during the running period to heat and hold the bimetal strip means and the switch means in the second position during the running period and so that the high starting current will heat the bimetal support to cause it to deflect for resetting the strip means and the switch means at the start of each running period.

'7. A control for an electric motor having main and phase-windings including a bimetal strip means and a switch means connected in series with said phase-winding, a snap acting means cooperating with said strip means to provide a limited force to hold the strip means and the switch means in the starting position, said switch means being connected to and operated by said strip means when heated by the phase-winding current from the starting position to the running position, an electric heater energized coincidentally to the energization of said main winding and located in heating relationship to said strip means for holding the strip means and the switch means in the running position during the running period of the motor, and electrically operated means connected in series with said main winding having opposing means engaging said strip means when in starting position for retarding the movement of the strip means to the running position in accordance with the main winding current.

8. A control for an electric motor having main and phase-windings including a bimetal strip means and a switch means connected in series with said phase-winding, a snap acting means cooperating with said strip means to provide a limited force to hold the strip means and the switch means in the starting position, said switch means being connected to and operated by said strip means when heated by the phase-winding current from the starting position to the running position, an electric heater energized coincidentally to the energization of said main winding and located in heating relationship to said strip means for holding the strip means and the switch means in the running position during the running period of the motor, a bimetal opposing means having an extension extending into engagement with said strip means and having its high expansion side located so that as it is heated it will oppose with increasing force the movement of the strip means and the switch means from the starting position to the running position, said bimetal opposing means being connected in series with the main winding to increase the length of the starting period as long as the heavy main winding current continues.

9. A control for an electric motor having main and phase-windings including a bimetal strip means and a switch means connected in series with said phase-winding, a snap acting means cooperating with said strip means to provide a limited force to hold the strip means and the switch means in the starting position, said switch means being connected to and operated by said strip means when heated by the phase-winding current from the starting position to the running position, and electrically operated means connected in series with said main winding having opposing means engaging said strip means when in starting position for retarding the movement of the strip means to the running position in accordance with the main winding current.

10. A control for an electric motor having main and phase-windings including an electrothermal means and a switch means connected in series with the phase-winding, said switch means being connected to and operated by said electrothermal means when heated by the phase-winding current from the starting position to the running position, an electric heater energized coincidentally to the energization of said main winding and located in heating relationship to said electrothermal means for holding said electrothermal means and the switch means in the running position during the running period of the motor, and electrically operated means connected in series with said main winding having opposing means operating upon said switch means for retarding the movement of said switch means to the running position in accordance with the main winding current.

HARRY F. CLARK.

No references cited.

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