US3694717A

US3694717A - Starting and overload control device for electric motors

Info

Publication number: US3694717A
Application number: US192266A
Authority: US
Inventors: Robert F Prouty; James J Smith
Original assignee: Essex International Inc
Current assignee: Raytheon Technologies Corp
Priority date: 1971-10-26
Filing date: 1971-10-26
Publication date: 1972-09-26
Anticipated expiration: 1989-09-26
Also published as: CA930416A

Abstract

A starting and overload control device is provided whereby current is automatically supplied to both the starting and the main winding of an electric motor when the motor is first energized. Current to the starting winding is automatically terminated a predetermined time after the motor commences running. Also, the device automatically de-energizes the electric motor during overload conditions. The current control is accomplished by means of a bimetallic strip together with a heater operating in conjunction with a pair of leaf springs, all of which are mounted for cantilever movement.

Description

all.

United States Patent Prouty et a1.

[s41 STARTING AND OVERLOAD [451 Sept. 26', 1972 2,960,58 8 11/1960 Anderson et al ..337/l02 X CONTROL DEVICE FOR ELECTRIC 2,984,722 5/1961 Smith et a1 ..'.337/90 MOTORS v Primary Examiner-Bernard A. Gilheany [72] inventors: Robert F. Prouty; James J. Smith, Assistant Examiner p E Bell both of Loga po v Attorney-A. W. Molinare et al.

[73] Assignee: Essex International Inc., Fort ABSTRACT I Wayne, lnd. A starting and overload control device is provided [2.2] Flled' 1971 whereby current is automatically supplied to both the t [21] Appl. No.: 192,266 starting and the main winding of an electric motor when the motor is first energized. Current to the starting winding is automatically terminated a predeter- [52] US. Cl ..318/22l C, 318/472, 337/90, mined time after the motor commences running Also, 337/102 337/107 the device automatically de-energizes the electric 6 H0111 61/03 Hozk 17/08 motor during overload conditions. The current control [58] Field Of Search ..337/4l44, 90,. is accomplished by means of a bimetallic strip 8, 3374401318021 C, 221 together with a heater operating in conjunction with a 472 pair of leaf springs, all of which are mounted for cantilever movement. 1 R f C't d [56] erences e 5 Claims, 8 Drawing Figures UNITED STATES PATENTS 2,568,476 9/1951 Wierich et a1. ..,.3 3 7/9O X 1 /I7 64 38 so a 44 40 33b 46 a 66 ill! 45 "I I III 5 l /1 r" "-r I u 24 PATENTEDsznzs I972 SHEEI 1 OF 2 JAMES J. SMITH w U 0 MR WP NE T R E B O R 5 F m1; 2, ATToRri miminssrz mz 3.694.711 SHEET 2 0P2 INVENTORS ROBERT E. PR'OUTY JAMES J. SMITH FIG.8

' ATTORN STARTING AND OVERLOAD CONTROL DEVICE FOR ELECTRIC MOTORS BACKGROUND OF THE INVENTION The present invention is generally related to a device for controlling current supplied to the main and starting windings of an electric motor. In many electric motors for example those of the type that are generally used as compressors, the motor is started and stopped repeatedly. A starting winding is provided to generate the greater torque required during the starting operation and a main winding is provided for operating the motor after its synchronous speed has been reached. A variety of arrangements have been provided in .the prior art for accommplishing the function of first energizing both the starting and the main windings and later energizing only the main winding. Some of these devices in the prior art also provide an additional function of terminating the power supplied to the main winding under overload conditions when the current to the main winding exceeds some predetermined level. For example, US. Letters Patent No. 3,164,699, issued Jan. 5, 1965, Whitler et al. teaches such a device utilizing a conductive leaf spring and a pair of bimetal strips electrically connected between a power supply and the starting and main windings of the motor to be controlled.

It is also known in the prior art to provide a bimetal strip with a heater strip mounted thereon and electrically insulated therefrom for the purpose of operating a thermostat and a circuit-breaker. See for example US. Letters Patent No. 2,636,098 issued Apr. 21, 1953 to J .B. Cataldo.

The present invention is directed towards improvements in bimetal protective control devices for singlephase induction motors. Accordingly, it is an object of the present invention to provide a new and improved starting and overload control device for such motors. It is also an object. of the present invention to provide such a device, compact in size and economical to produce.

It is further an object of this invention to produce such a device which will be utilizable with inexpensive electric motors and which will be responsive to low currents and yet able to carry high currents without fusing. It is also an object of the present invention to provide a device which may be operated by a single bimetal strip which moves to a first position for terminating current to the starting winding after the motor is energized and which moves to a second position for terminating all current to the motor under overload conditions when current to the main winding exceeds a predetermined level.

SUMMARY OF THE INVENTION The present invention is generally related to a starting and overload control device for single-phase induction motors. In a preferred embodiment, the device of this invention is connectable between the motor to be controlled and a power supply. The device includes a bimetal strip and heater adjacent thereto, a firstelectrically conductive leaf spring adjacent to and extending in the same direction as the bimetal strip, and a second electrically conductive leaf spring adjacent and extending in the same direction as the first leaf spring. The bimetal strip and leaf springs are mounted in a housing for cantilever movement with the heater and bimetal strip in series between a supply terminal and an electric contact on the end of the bimetal strip. The first leaf spring is in series between the main winding of the motor and a pair of contacts connected to the moving end of the spring, and the second leaf spring is connected in series between the starting winding and an direction away from the first and second leaf springs causing the de-energization of the starting winding. If the current exceeds a predetermined level, the bimetallic strip moves further, separating its contact from the first leaf spring contact causing de-energization of the main winding as well.

In the preferred embodiment, the heater is formed of an electrically conducting elongated strip adapted to be folded about the bimetal strip so as to provide the maximum sensitivity for the bimetal strip in response to the current supplied to the motor.

BRIEF DESCRIPTION OF THE DRAWINGS There follows a brief description of the drawings showing a preferred embodiment of this invention wherein like numerals refer to like elements and wherein:

FIG. 1 is a perspective view of the control device of this invention;

FIG. 2 is a side elevational view of the control device of this invention with a portion of the cover thereof removed;

FIGS. 3-6 are schematic views of the operative portions of the present invention in various operational modes;

FIG. 7 is an enlarged side cross-sectional view of the device shown in FIG. 2, taken substantially along the lines 7-7; and

FIG. 8 is an overhead view of the heater of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 1 Referring generally to FIGS. 1 & 2, a control device 10 is shown. The device 10 includes a housing having a base member 12 and cover member 14. The

members

12 and 14 may be formed of a durable plastic or other strong electrically insulating material. A pair of

male input terminals

16 and 17 are provided to be connected to a standard A.C. outlet or other power supply (not shown). When the control device 10 is used in conjunction with a single phase induction motor, it is desirable to have three power supply terminals. Accordingly, a first power supply terminal 18, a second terminal 20 and a third terminal 22 are provided and connected to the member 12. Input terminal 16 is electrically connected to third output terminal 22.

Referring to FIG. 3, the

input terminals

16 and 17 of the present device may be connected to a standard altemating current power source 30. Terminal 16 is connected to a node 32 shared by a main winding 34 and a starting winding 36 of a motor 37 to be controlled. The input terminal 17 is electrically connected to a heater strip 38 which is folded about and in series with a bimetal strip 40 as will be more fully described. The bimetal strip 40 and its accommpanying heater 38 are in series between the supply terminal 17 and an electrical contact member 42 connected to the end of the bimetal strip 40. The bimetal strip 40 is mounted so that heat from the heater 38 will cause the strip 40 to move upwardly away from

springs

44 and 50, as will be described.

A first leaf spring 44 is mounted for cantilever movement on the mounting bushing 24 below the heater 38 and bimetal strip 40 and is connected in series between the main winding 34 and a pair of electrically connected

contact members

46 and 48. Both the upper contact member 46 and the lower contact member 48 are connected to the moving end of the first leaf spring 44.

A second leaf spring 50 is mounted for cantilever movement on the bushing 24 below the first leaf spring 44 and is in series connection between the starting winding 36 and a contact member 52 connected to the end of the second leaf spring 50. A stop member shown generally as an adjustable screw 54 is positioned in the arc of travel of the first leaf spring 44. A lip 56 extends outwardly from the first leaf spring 44 and is adapted to Contact the stop member or screw 54 when the first leaf spring 44 moves sufficiently upwards.

A double faced magnet 62 is connected to the moving end of the first leaf spring 44 and positioned so as to cooperate with an upper magnetically permeable armature 64 connected to the moving end of the bimetallic strip 40 and so as to cooperate with a lower magnetically permeable armature 66 connected to the moving end of the second leaf spring 50. In the START mode, before sufficient current is supplied to the heater 38 to cause the bimetallic strip 40 to move upwardly, the circuit is made between

contacts

42, 46, 48 and 52. After sufficient current is'supplied to the heater 38 to heat the bimetallic strip 40, the strip 40 moves upwardly. The second and lower leaf spring 50 is defined having a sharp bend 68 in a direction away from the bimetal strip 40 and first leaf spring 44 so as to resist upward movement.

Sequence Of Operation The device shown in FIG. 3 is in the START mode with current being freely conducted from the input terminal 17 through the heater 38 and bimetal strip 40 to the

contact members

42 and 46. The current is then conducted from contact member 46 to the main winding 34 and from the contact member 48 to the contact member 52, through the second leaf spring 50 to the starting winding 36. Accordingly, both the starting winding 36 and main winding 34 are energized.

Referring to FIG. 4, the device 10 is in the RUN mode. The heater 38 has supplied sufficient heat to the bimetal strip 40 to cause an upward movement of the bimetal strip 40. As has been explained, the second leaf spring 50 is adapted to provide more resistance to upward movement i.e.,' movement toward the bimetal strip 40, than is the first leaf spring 44. Accordingly, as

shown in FIG. 4, the second leaf spring separates from electrical contact with the contact member 48 of the first leaf spring 44 at a predetermined position prior to separation of the first leaf spring from bimetal strip 40. The starting winding 36 is then deenergized and the main winding 34 remains energized by the flow of current from the bimetal strip 38 to the first leaf spring 44 and ultimately to the main winding When excessive current is supplied, e.g., in the case where the motor 37 is overloaded, more heat is supplied from the heater 38 to the bimetal strip 40 causing an additional upward movement of the bimetal strip 40 and the first leaf spring 44 as shown in FIG. 5.

After the lip 56 of the first leaf spring 44 contacts the stop screw 54, further upward movement of the leaf spring 44 is prevented and when the bimetal strip 38 continues its

upward movement contacts

42 and 46 are separated with a snap action. Referring to FIG. 6, when

contacts

42 and 46 are separated, no. power is supplied from the power source 30 to either the main winding 34 or the starting winding 36 and the device 10 is in the STOP mode. The separation of

contacts

42 and 46 also terminates the flow of current to the heater 38, allowing the bimetal strip 40 to cool. After cooling, the strip 40 returns to the position shown in FIG. 3, and power may once again be supplied to the motor 37 to commence operation thereof.

When

contacts

42 and 46 are separated, the first leaf spring 44, because it is biased towards the second leaf spring 50, moves downwardly to a position where

contacts

48 and 52 touch. In this manner, current may be simultaneously conducted to both the main and start

windings

34 and 36 when the bimetal strip 40 cools sufficiently to allow

contacts

42 and 46 to touch. This feature is to be distinguished from prior art devices which may tend to get out of sequence. Where this occurs, and the main winding is energized first, the motor may continue to cycle on main winding locked rotor.

Construction Of The Preferred Embodiment Of This Invention Referring now to the control device 10 shown in FIGS. 7 and 8, construction of the device 10 and heater 38 may be seen in greater detail. Within the base 12 is affixed the mounting bushing 24. The heater member 38 and bimetal strip 40 about which the heater 38 is folded are mounted for cantilever movement on the mounting bushing 24. The upper member 38A of the heater 38 is in electrical connection with the input terminal 17 which is also mounted on the bushing 24.

The heater 38 is an elongated symmetrical metal strip of electrically conducting material which will generate heat when current flows therethrough. A rectangular aperture 70 is defined on the center thereof. The heater 38 includes a first or upper arm 38A and a second or lower arm 383. Slots 72 are defined on the ends of the arms 38A and 38B respectively. These slots 72 are adapted to receive the bushing 24 therethrough where the heater 38 is folded in half about the bimetal strip 40. The aperature 70 is adapted to receive the bimetal strip 40. An insulating sleeve 74 surrounds the exposed portion of the bimetal strip 40 to electrically insulate it from the heater 38.

This upper arm 38A is separated from the bimetallic strip 40 by an insulating washer 60. The lower arm 38B of the heater 38 is in electrical connection with the mounted end of the bimetallic strip 40 so that when current is conducted to the device from the terminal 17, it must pass through the upper and lower arms 38A and 38B of the heater 38 before being conducted to the bimetallic strip 40.

The particular construction of this heater 38 is of special advantage because it maintains a substantial portion of the heater 38 in close physical relation to each side, of the bimetallic strip 40 in order to facilitate the transmission of heat from the heater 38 to the bimetal strip 40 for the purpose of increasing sensitivity of the strip 40. Also, this particular construction of the heater 38 provides for easy and economic construction and assembly of the control device since the heater need be merely foldedabout the bimetal strip 40. The device 10 also has the advantage of a snap action sequence of operation. In other words, when the bimetal strip 40 is urged upwardly to the position where the second leaf spring 50 releases, the force of spring 50 has increased to a level where it is slightly greater than the magnetic force between the armature 66 and magnet 62, tending to hold the ends of the first and second leaf springs together. When the

contacts

48 and 52 are slightly separated, the magnetic force between armature 66 and magnet 62 drops rapidly, and the second leaf spring 50 snaps away from the first leaf spring 44 without chattering of the

contacts

48 and 52 which might otherwise occur. This same snap action occurs when the

contacts

42 and 46 of the bimetal strip 40 and first leaf spring 44 separate. The positive release between the

contacts

42 and 46 is effectuated by the action of the stop screw 54 against the lip 56 of the first leaf spring 44. As has been explained, release of these

contacts

42 and 46 is followed by the making of a circuit between

contacts

48 and 52 which also is accomplished by a snap action. This snap action connection is produced by the spring force of the first leaf spring 44 which is biased toward the second leaf spring 50 and by g the magnetic attraction between the magnet 62 and armature 66.

While in the foregoing, there has been described a preferred embodiment of the present invention, it is to be understood that this embodiment is merely illustrative of the principles of this invention and that other embodiments may be made without departing from the true spirit and scope of this invention.

What is claimed is:

l. A starting and overload protection device for an electric motor connectable between said motor and a power supply said motor having a starting winding and a main winding for operating said motor, comprising, in combination:

mounting means;

a bimetal strip mounted on said mounting means on one end thereof for cantilever movement having an electrical contact and a magnetically permeable armature connected to the other end thereof;

a heater mounted on said bimetal strip, said heater and said strip being in series between a first supply terminal and said contact connected to said bimetal strip;

a first electrically conducting leaf spring mounted at one end for cantilever movement on said mounting means adjacent said bimetal strip having a double faced magnet and a pair of electrical contacts connected to the moving end thereof and positioned such that said magnet may attract said armature of said bimetallic strip so as to make a circuit between the electrical contact of said bimetal strip and one said contacts of said first leaf spring, said first leaf spring being in series between said pair of contacts and said main winding; and

a second electrically conducting leaf spring mounted at one end thereof for cantilever movement on said mounting means and positioned adjacent said first leaf spring and second leaf spring being disposed away from said first leaf spring so as to oppose movement of said second leaf spring toward first leaf spring and having a magnetically permeable armature and an electrical contact connected to the movable end thereof and positioned such that said magnet may attract said second leaf spring armature to place the other of first leaf spring contacts into electrically conducting relationship with said contact of said second leaf spring, said second leaf spring being in series between the second leaf spring contact and said starting winding said bimetal strip being mounted such that when power is transmitted to said supply terminals, said bimetal strip moves in a direction away from said first and second leaf springs causing the termination of current to said second leaf spring and therefore to said starting winding after said bimetal strip passes a first predetermined position and causing the termination of current to said first leaf spring and therefore to said main winding after said strip passes a second position.

2. The device as set forth in claim I wherein said heater comprises an elongated metallic strip extending on both sides of said bimetal strip and electrically insulated therefrom along a substantial portion thereof such that heat generated from said heater may be readily transmitted to both sides of bimetal strip.

3. The combination as set forth in claim 1 wherein said heater comprises a symmetrically formed elongated strip having an aperature defined about in the center thereof and first and second slots defined on the ends thereof, said strip adapted to be folded about said bimetal strip with the aperature receiving the bimetal strip therethrough and the slots adapted to receive the mounting means, and including means for electrically insulating said heater from said bimetal strip along a substantial portion thereof.

4. The combination as set forth in claim 1 including stop means positioned in the path of motion of said first leaf spring to prevent said first leaf spring from moving past a predetermined point such that the contacts of said bimetal strip and said first leaf spring may be separated with a snapaction when said bimetal strip passes a predetermined position.

5. The combination as set forth in claim 1 wherein said first leaf spring is biased toward said second leaf spring such that when the contacts of said first leaf spring and said bimetal strip are separated, said first leaf spring moves toward said second leaf spring to place the contacts of said first and second leaf springs in electrically conducting relationship.

Claims

1. A starting and overload protection device for an electric motor connectable between said motor and a power supply said motor having a starting winding and a main winding for operating said motor, comprising, in combination: mounting means; a bimetal strip mounted on said mounting means on one end thereof for cantilever movement having an electrical contact and a magnetically permeable armature connected to the other end thereof; a heater mounted on said bimetal strip, said heater and said strip being in series between a first supply terminal and said contact connected to said bimetal strip; a first electrically conducting leaf spring mounted at one end for cantilever movement on said mounting means adjacent said bimetal strip having a double faced magnet and a pair of electrical contacts connected to the moving end thereof and positioned such that said magnet may attract said armature of said bimetallic strip so as to make a circuit between the electrical contact of said bimetal strip and one said contacts of said first leaf spring, said first leaf spring being in series between said pair of contacts and said main winding; and a second electrically conducting leaf spring mounted at one end thereof for cantilever movement on said mounting means and positioned adjacent said first leaf spring and second leaf spring being disposed away from said first leaf spring so as to oppose movement of said second leaf spring toward first leaf spring and having a magnetically permeable armature and an electrical contact connected to the movable end thereof and positioned such that said magnet may attract said second leaf spring armature to place the other of first leaf spring contacts into electrically conducting relationship with said contact of said second leaf spring, said second leaf spring being in series between the second leaf spring contact and said starting winding said bimetal strip being mounted such that when power is transmitted to said supply terminals, said bimetal strip moves in a direction away from said first and second leaf springs causing the termination of current to said second leaf spring and therefore to said starting winding after said bimetal strip passes a first predetermined position and causing the termination of current to said first leaf spring and therefore to said main winding after said strip passes a second position.

2. The device as set forth in claim 1 wherein said heater comprises an elongated metallic strip extending on both sides of said bimetal strip and electrically insulated therefrom along a substantial portion thereof such that heat generated from said heater may be readily transmitted to both sides of bimetal strip.

4. The combination as set forth in claim 1 including stop means positioned in the path of motion oF said first leaf spring to prevent said first leaf spring from moving past a predetermined point such that the contacts of said bimetal strip and said first leaf spring may be separated with a snap action when said bimetal strip passes a predetermined position.