CA1312112C - Centrifugal starter switch apparatus - Google Patents

Abstract

CENTRIFUGAL STARTER SWITCH APPARATUS
Abstract Of The Present Invention A centrifugal actuator for an induction motor mounted on a motor shaft for operating a switch in the start winding circuit. A U-shaped base member is secured to the shaft with an elongated base extended diametrically of the shaft and with side members extending parallel to the shaft. A pair of oppositely disposed U-shaped weights are pivoted in hinges on the side members creating linkage and aligned pivot arms projecting around the hub body portion. The arms pivot on each other within confining walls of the hub. The weights under centrifugal force move the hub and actuate the switch. Springs on the opposite sides of the hub are secured to one end to the side members and at the other end to the hinges and extending diametrically over the body of the hub, said springs extended with movement of the weights to move toward the pivot point of the arms. The springs reset the actuator at a specified speed when the motor is de-energized. The plastic hub is subject to wear in use. Stop members located on the weights and/or bracket prevent the pivot point of the arms from moving past the linkage over center line.

Description

1 3 ~ 2 ~ ~ 2 CENTRIFUGAL STARTER SWITCH APPARATUS
Background Of l'he Present Invention The present invention relates to a centrifugal starter switch apparatus and particularly to a centrifugal actuator for switching high starting current motors and the like.
Integral horsepower motors often are constructed with a special start winding which is connec$ed in circuit during the initial starting of the motor to bring the motor up to speed. The start winding is preferably disconnected from the circuit as the motor approaches or reaches running speed. A
conventional switch mechanism or disconnecting of the start winding includes a switch unit mounted within the motor and a centrifugal actuator mounted on the shaft and rotating therewith to actuate the switch unit. The actuator holds the switch unit closed to provide current to the start winding. As the motor speed increases and approaches or reaches running speed, the centrifugal actuator moves a switch operator to open the switch unit and thereby disconnect the start winding from circuit.
The centrifugal actuator generally includes a spring loaded lever mechanism coupled to a pivoting bracket to establish a snap action movement of switch operator. A sliding hub or collar is coupled to and moved by the pivoting bracket between a stop position established by the spring and an axially offset position established by the centrifugal forces. The hub includes the switch operator for opening and closing the start switch unit and thereby the start winding circuit connection. Motors using such switch mechanisms are normally started and stopped many times over the life of the motor. The centrifugal switch actuator should have a corresponding life. If the

-2- 13~ 2 switch unit is not reset upon stopping, for example, the start winding is connected and at the next stop and start cycle the motor will not start and high current flows through the run winding. Destruction of the motor windings will occur unless personnel is present to immediately disconnect power from the motor. In any event, costly replacement of the centrifugal actuator would be required.
Larger induction motors are currently in demand in which starting currents of 110 amperes are required. The switch for switching such currents require special consideration to maintain a reliable life due to the increased forces and higher current ratings found in the larger motor applications. The actuator must include a positive snap action which insures movement from the start position to the run position without hesitation. This movement allows the contacts of the stationary switch to open cleanly with no restrikes, which particularly is important in the larger motor applications where more severe starting conditions and longer acceleration times are common place. Actuators without the positive snap action eature will have contact restrike due to the hesitation at switching speed during long acceleration times. Contact restrikes can result in capactior failure and contact welding. Further, a major problem encountered in the actuator for large motors is the increased wear due to higher centrifugal forces and impact forces. The higher forces are inherently necessary to provide the snap action, and are particularly severe due to the larger geometry.
A particularly satisfactory construction of an actuator is shown in U. S. Patent 4,386,290 which issued on May 31, 1983 to Monette. A hub slides on a shaft and and is coupled to actuate the shaft switch

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unit. The centrifugal actuator includes a U-shaped mounting bracket fixed to the shaft with a pair of oppositely located and similarly mounted pivot levers coupled to position the hub on the shaft between the switch closing position and switch opening position.
The pivoted levers generally include pivot arms pivoted in suitable pivot bearing supports in the plastic hub. After a great number of cycles but well within the normal opera~ing life of the motor, the plastic bearing supports wear, changing the pivot movement of the levers. In moving to the switch open position, the levers may move beyond a normal tolerance range, resulting in the spring members moving over-center and positively holding the switch in the actuat.ed position. This can of course result in malfunction of the switching circuit, with possible destruction of the motor.
There is a demand and need for a modified centrifugal actuator which prevents such locking of the switch actuator and thereby the switch unit in the actuated position~
Summary Of Th_ Present Invention The present invention is particularly directed to a centrifugal switch actuator for a motor starter unit particularly adapted to actuators for large induction motors, and includes a simple mechanical structure which positively prevents the movement of the centrifugal weight member from a predetermined tolerance position and thereby significantly extends the effective operating life of the centrifugal actuator. Generally, in accordance with the teaching of the present invention, the switch actuator includes typical pivoted and spring-loaded actuating arm members which are moved between a spring loaded standby position and a pivoted actuated

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position. The switch actuator in accordance with this invention includes a mechanical stop unit located between the pivot arms a relatively fixed member of the switch mounting bracket. The stop unit is located with a space between the fixed member and the pivot arms under normal operation such that there is no effect under the normal switch operation. Wear within the pivot support unit of the switch actuator permits the switch pivoting bracket or arms to move toward the fixed member, and close the gap between the members.
After a predetermined wear, the stop unit will engage between ~he arms and the fixed member, preventing any further excessive movement of the switch operator to an over-center position of the spring members and positively holding the switch operator in position for subsequent operation. The simple mechanical stop thus maintains continued subsequent operation of the centrifugal actuator and significantly extends the useful life of the centrifugal actuator.
In a particularly practical construction~ the actuator includes a pair of U-shaped brackets or arms. The opposite ends of the U-shaped arms end in curved pivot arms~ The U-shaped arms project over the hub of the actuator, with the ends located in pivot slots or recesses on the opposite sides of the hub.
The curved end of the arm particularly bears on the opposed curved surface of the opposed arm. The hub is formed with relatively flat surfaces in the pivot slot area to provide a lateral bearing support for the pivot arms. The base of the arms include a pair of rearwardly extended pivot tabs which are pivotally mounted in the pivot slot which in turn are connected to the mounting hub. The arms include small laterally spaced projecting ~abs aligned with the mounting bracket and limiting outward pivoting of the arms, and ~hereby functioning to prevent the switch arms from moving sufficiently to move the bias spring over cent~r. Alternatively, stop tabs may be secured to ~he mounting bracket and extended toward the arms. Wear wi~hin the actuator may permit the arms to move into engagement with the limit tabs, into a locked actuated state.
The simple mechanical stop thus positively prevents excessive movement within the centrifugal actuator as will cause the switch mechanism to lock in the actuated position with possible start of the motor with only the run winding connected to the power supp ly .
The present invention thus provides a simple reliable and effective means to maintain and extend the operative life of a centrifugal switch actuator.
Brief Descrip~ion Of Drawin~s The drawings furnished herewith generally illustrate the best mode presently contemplated for the invention and are described hereinafter.
In the drawings:
Fig. 1 is a side elevational view of a centrifugal actutor constructed in accordance with the teaching of the present invention applied to a motor;
Fig. 2 is a view similar to Fig. 1 illustrating the running position of the centrifugal actuator with an associated centrifugal switch opening;
Fig. 3 is a pictorial view of the weight shown in Figs. 1 and 2;
Fig. 4 is a fragmentary sectional view taken generally on line 4-4 of FigO 2;
Fig. 4a is a simplified line or free body drawing of the pivot points and movement of the actuator shown in Figs. 1-4;

1312 a ~ 2 Fi~. 5 is a view similar to Fig. 2 illustrating an alternate embodiment of the invention;
and Fig. 6 is a view taken generally on line 6-6 of Fig. 5.
Description Of The Illustrated Embodiment Referring to the drawings and particularly to Figs. 1 and ~, a fragmentary end portion of an induction motor 1 is illustrated including an annular stator 2 mounted within an outer tubular frame, not shown. The s~a~or 2 includes a magne~ic stator core 4 secured to the frame, not shown~ A field winding 5 generally includes a run winding and an offset separate start winding which are interconnected to each other and to power supply as hereinafter described. Because such detail is well known, it is not specifically separately shown herein. In accordance with conventional practice, a rotor 6 having a rotor shaft 7 is rotatably mounted within the ~tator 3. The illustrated rotor 6, as widely used in an A.C.
induction motor, includes a cast squirrel-cage winding embedded within the rotor and thus located within the magnetic field of the field winding 5. The motor shaft 7 is supported within a cup~shaped end enclosure bell, not shown. The end bell defines an end chamber 10 within which a centrifugally actuated start switch assembly 11 is located. The start switch assembly 11 is electrically connected into circuit with the start winding of the field winding 5 for selected connection of the start winding into the circuit only during the starting of the motor and until such time as the rotor reaches or closely approaches normal operating speed.
The start winding is primarily connected into the circuit during the initial period ~o increase the starting torque for accelerating the motor to operating ~7~ ~ 3~

speed~ The centrifugally actuated start switch assembly 11 includes a start switch unit for apparatus 12 which is mounted on a suitable motor bracket 13 within the end chamber 10 immediately adjacent to the axial end of field winding 5. A centrifugal actuator 14 is located on the motor shaft 7 and in particular includes a hub 15 which is slidably mounted on the shaft 7. A pair of oppositely located centrifugal weights 16 having similar pivot arms 17 are pivotally coupled to the hub 15 and spring loaded~ as by coil springs 18 located to the opposite sides of the hub to a first position as shown in Fig. 1. The centrifugal weights 16 are pivotally mounted to a securement shaft bracket 19 which is firmly affixed to the rotor shaft 7. The bracke~ 19 is mounted to locate an annular operator of the hub 15 in engagement with the switch unit at rest (Fig. 1) and serves to hold the switch unit closed. The start winding is thereby connected into circuit during the initial starting period. At the desired or switching speed, the centrifugal weights 16 move outwardly, as shown in Fig. 2, with a snap action under the force of the rotational centrifugal forces and provide a corresponding retract movement vf the hub lS which snaps outwardly from the start-switch unit 12 to the position of Fig. 2. As a result, the start-switch unit 12 moves to an open circuit position, thereby disconnecting of the start winding from circuit.
The details of the stator, rotor and the like, as well as the centrifugal switch unit 12 may be of any known or other desired construction~ No further description of the detail of such components is therefore given other than as necessary to fully describe the present invention which is particularly directed to a unique centrifugally actuated switch unit ~ 3 ~

apparatus, a preferred embodiment o~ which is shown in the drawings and its mounting within the motor. The centrifugal switch unit is preferably constructed as disclosed in U.S. patent 4,419,550 which issued on December 6, 1983 to G. S. Monette or in the co-pending Canadian application Serial No. 570,913 entitled "Centrifugal Actuator For A.C. Induction Motor" which is filed herewith and which is assigned to the same assignee as this application.
The actuator 14 of the present invention includes limit or stop elements 21 located between the pivoting weights 16 and the hase 22 of bracket 19. The stop elements 21 positively limits the position of the pivot location of the weights 16, and thereby movement past over center position. This positively insures the reset of the weights 16 for proper subsequent start cycles.
More particularly, the hub 15 is a tubular member slidably mounted on shaft 7 and having a switch operator 24 secured to one end of hub 15. The hub 15 has pivot slots 23 on opposite sides of the hub within which the pivot ends 24 of the pivot arms 17 pivot.
As more fully shown in U.S. patent 4,419,550, the internal weights 16, which position switch hub 15 under centrifugal action, are pivotally mounted by a linkage to the bracket 19. The weights 16 are pivotally connected to hinges 25 by weight projections 26 which extend through slots in hinges 25. The hinges 25 in turn are also pivotally ~onnected to side members 27 of base bracket 19 by ears 28 which are lodged in slots 29 in side members 27. The pair of coil springs 18 are hooked at opposite sides to the hinges 25 and are hooked at the opposite end to side members 27 of the bracket 19 as at 27a. The springs 1~ operate to displace the actuator weights -16 to the rest position 1 3 ~

of Fig. 1 when rotation of the actuator ceases and also to preload the assembly.
The pivot slots 23 in hub 15 are formed by spaced abutment walls 31 and 32 which are preferably integrally molded with hub 15 adjacent the operator 24. The hub 15 is formed with a flat sur~ace between the walls 31 and 32. The walls 31 and 32 are generally curved walls formed by a plurality of flat, chordal surfaces.
The movement of the metal weights 16 from start to run creates sliding or rolling friction between the pivot ends 24 of weight arms 17 and the hub 15. T~e friction of members 24 causes erosion or wear to occur on the two abutment walls 31 and 32 of the hub 15. The progressive wear ultimately changes the weight/hub pivot location 35 of the weights 16 to the hub 15, as shown in Fig. 2. A hinge linkage pivot location 36 is established by the location of the weight projections 26 and the slots 26a in the hinges 25. This location 36 is normally to the motor side of the pivot location 35 and shown to the right thereof in Fig. 2. The reference to above and below herein refers to a vertically oriented motor with the switch apparatus at the upper end of the motor. The pivot location 35 is established to maintain a positive return force on the hinges and weights 16 so the -centrifugal actuator can return to the start position when the motor co~es to a stop. The positive return force is maintained if the weight/hub pivot location 35 is above, or to the left of, the linkage pivot location 36, as shown in Fig. 2 and in the simplified linkage drawing of Fig. 4a for the actuated switch position.
Fig. 4a illustrates the lower actuator portion of Fig.
2. The switch actuator 24, spring 17a and bracket 19 are shown in phantom. Worn abutments 31 and 32 on the ~31~

hub 15 would allow the weight/hub pivot location 35 to move in line with or below the linkage pivot location 36, which results in a zero or negative return force.
Thus, with the pivot locations in alignment, the system i5 in equilibrium with a zero return force. With the pivot location 35 moved past pivot location 36, the system is locked in the actuated state. The centrifugal actuator 14 wou~d then be pinned in the run position of Fig. 2 and could not close the switch unit 11. Once this failure occurs, the motor will not start on the naxt start cycle and the run winding may potentially burn out.
In a practical construction, the pivot locations 35 and 36 have a small separation in the original structures. The spacing is however larger than the space 37, and is shown substantially enlarged in Fig~ 4a for clarity of description. The stop elements 21 of the present invention, with the smaller spacing, prevent the weight/hub pivot location 35 from moving in line with/or below the linkage pivot location 36 when wear occurs to the abutments walls 31 and 32 of the switch hub 15. Therefore a positive return force is maintained.
More particularly in the embodiment of Figs.
1-3, the stop elements 21 are integral projection tabs on the back edge of the arms 17 of the U-shaped weight 16. In the collapsed position of the weights, the arms 17 are angled from the base 22 and the s~op tabs 21 are spaced from the bracket base 22. ~hen the weight 16 pivots outwardly, the arms 17 with the stop tabs 21 pivot toward the bracket base 22. The tabs 21 move to a position essentially parallel to the base 22. In the original structure, the tab 21 is spaced from the bracket base 22 as at 37. The weights 16 then move in the designed sequence.

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In starting the motor, the windings are energized with the switch 12 closed to supply current to the windings 5 including the start winding, not separately shown. The motor accelerates, and at the designed speed,the weights 16 snap outwardly, carrying the hub 15 toward the base 22 of bracket 19. The hub 15 and operator 24 moves axially away from the switch unit 12, which opens and disconnect the start winding.
As the wear continues and prior to movement to or below the pivot location 36, the tabs 21 move into engagement with the base 22 of bracket lg. The bracket base 22 thus forms a positive stop which prevents the arms 17, and particularly the weight/hub location 35 pivot of the arms, from moving to or past the linkage pivot location 36. The stop members thus serve to insure continued proper actuator functioning, with reset of the operator.
An alternate embodiment is shown in Figs. 5 and 6. The embodiments have the same components and operation. In Figs. 5 and 6 however, the stop limit includes block members 40 secured as by welding to the base 22 in alignment with the side arms 17 of the U-shaped weights 16. The block members 40 extend from the base toward the actuator arms 17.
The centrifugal actuator 14 of Figs. 5 and 6 functions in the sequence as the first embodiment. As the plastic hub 17 wears, the pivotal weight move inwardly. The arms 17 moves into engagement with the stop limit blocks 40 before the pivot point moves in line with or below the linkage location 36 to insure continued proper functioning of the actuator.
The use of the stop limit elements on the mounting bracket provides a convenient and effective structure for retrofitting existing centrifugal 13~2~2 actuators such as disclosed in the previously identified Monette patent.
The stop limit may of course use the combination of tabs on the arms and projections on the base, or any other similar position limit means ~o maintain the collapsing force of the springs 18.
The present invention thus provides a simple, but effective system for extending reliable operation of centrifugal actuators.

Claims (13)

THE EMBODIMENTS OF THE INVENTION TO WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A centrifugal actuator, comprising an operating member, a shaft mounting member, weight elements, a pivot unit pivotally mounting said weight elements to the mounting member and said operating member, said weight elements being movable between a first position and a second position in response to rotation of said shaft mounting member, said operator member being moved by said weight elements, spring means secured to the mounting member and coupled to said weight elements and stressed in response to a selected rotational speed of said mounting member and establishing a return force on said weight elements, said pivot unit being subject to wear and creating a wear related movement of said weight elements and said operator members from said second position, and stop limit means on said mounting member and said weight elements, said stop limit means being constructed and arranged with a gap within the limit means with the weight elements moved between said first position and said second position, said stop limit means being constructed and arranged to close said gap and being engaged in response to selected wear-related movement of the weight elements and thereby limiting said wear-related movement of said weight elements and maintaining said return force with wear of said weight elements and operator member.

2. The centrifugal actuator of claim 1 wherein said weight elements include a pair of U-shaped members having side pivot arms having pivot ends including curved pivot edges, said operator member having confirming pivot walls and having said pivot ends mounted within said pivot walls in opposed abutting pivot engagement with said pivot walls to form said pivot unit, said pivot walls confining said pivot ends and the movement of said weight elements to said first and second positions, said pivot ends and said pivot walls being subject to said wear as the result of the pivoting of said pivot ends and permitting movement beyond said second position to close said gap.

3. The centrifugal actuator of claim 2 wherein said pivot arms have an angular offset outer portion with said pivot ends extended parallel to the arms.

4. The actuator of claim 3 wherein said pivot edges are circular and smooth.

5. A centrifugal actuator comprising a shaft mounted hub having flat bearing surfaces on opposite sides of the hub and moving on the shaft, said hub being formed of a solid plastic, axially spaced bearing wall integrally molded to the bearing surfaces in the hub and forming bearing slots, a first U-shaped pivot weight, a second U-shaped pivot weight, each of said weights having side bearing arms having curved bearing edges, said weights telescoped over said hub with the bearing edges in abutting engagement within said bearing slots to form a pivot support, a mounting bracket, a hinge means having a first pivot connection to the bracket and a second pivot connection to said weights, the location of the pivot connection of said weights to said hinge means being spaced from said pivot support location, said weights pivoting in said bearing slots and establishing a first movement of said hub on the shaft in response to shaft rotation, coil spring units connected between the bracket and said hinge means urging the weights to a standby position within said first movement of the weights, said first movement of the weights and hub being extended along said path in response to repeated wear related movement of the weights and hub toward a position wherein said springs fail to urge the weights to said standby position, and a mechanical stop means located in the extended path of said weights and hub and in spaced relation to the first named path of said hub and weights and operable to limit the movement of said pivot support location toward the hinge connections of said hinge means to maintain the return action of said coil springs.

6. The actuator of claim 5 wherein said stop means including projecting tab on each of said side bearing arms operable to engage said bracket and limiting the movement of the bearing edges of said bearing arms.

7. A centrifugal actuator for a motor having a shaft and having a shaft mounting bracket including a plate member extended normal to a mounting opening adapted to be fixed on the motor shaft, a sliding collar member having a mounting opening for slidably mounting of the collar on the motor shaft, a pair of opposed pivot weights, each of said weights having a substantially U-shaped configuration including a base and a pair of side pivot arms, said side pivot arms having curved ends to define pivot surfaces, said pivot weights being telescoped over said collar with said side pivot arms projected over said collar and terminating essentially centrally of the collar, said weights being mounted in opposed aligned relation with the curved ends of the pivot arms in abutting bearing engagement, spring loaded hinge means interconnecting said pivot weights to said mounting bracket and including means whereby said pivot weights respond to centrifugal forces created by rotation of said mounting bracket to pivot said pivot weights outwardly and moving said collar with respect to the mounting bracket as the result of said pivoting in said collar, pivot limit means interposed between said pivot weights and said bracket, and spaced from said pivot weights during said movement of said weights, repeated pivoting of said weights causing wear within said pivot surfaces tending to move said pivot weights in a path to a locked position in response to centrifugal forces, said limit means located in said path and limiting the movement of said weights in the presence of wear of the pivot surfaces and preventing movement of said weights to the locked position.

8. The apparatus of claim 7 wherein said limit means is an offset limit surface projecting from one of said bracket or said weights toward the other of said bracket and said weights.

9. A centrifugal actuator comprising a hub having switch actuating means at one end of the hub for engaging a switch having contacts movable between a first circuit position and a second circuit position, said hub having a body portion connected to the hub and extending from the switch actuating means and disposed to be assembled on a shaft of an electric motor for rotation by the shaft, a U-shaped base member of magnetic material assembled over the body portion opposite the switch means and comprising an elongated base extended diametrically of the shaft and located adjacent to the motor and side members connected to the base which combine with the base to block the flow of magnetic flux from the windings of the motor to the internal parts of the centrifugal actuator, a pair of oppositely disposed U-shaped weights having aligned arms projecting from a base portion around the hub body portion and pivoting on each other within confining walls of the hub and pivoting in a first pivot plane to a position under centrifugal force to move the hub and thereby the contacts of the switch from said first circuit position to said second circuit position, a pivot linkage pivotally connecting said weights to said base member and having a second pivot location located to one side of said first pivot location, springs on the opposite sides of the hub secured to one end to the side members and at the other end to the linkage and extending diametrically over the body of the hub, said springs extended with said weights to move said hub and pivot arms toward said pivot plane with the pivot arms spaced from the pivot plane whereby said springs are operable to return the actuator to said rest position when the motor shaft is no longer rotating, said confining walls of said plastic hub being subjected to wear under repeated cycling of the weight arms and said first pivot location moving toward said second pivot location with said wear, and spaced stop members located between said weights and said base member and spaced to prevent engagement with the hub moved from the rest position and engaged under selected wear of the confining walls prior to wear permitting said pivot arms to move into said pivot plane.

10. The centrifugal actuator of claim 9 wherein said linkage includes pivot hinges connecting the weights to the side members, said springs being connected to said hinges, said confining walls having oppositely disposed abutments which have a knife edge at the abutting end, ends of the weight arms rotating around the knife edges of the abutments to move the weights inwardly or outwardly under centrifugal forces.

11. The centrifugal actuator of claim 9 wherein said stop members are secured to and extend from said arms toward said base.

12. The centrifugal actuator of claim 9 wherein said stop members are secured to and extend from said base toward said arms.

13. A centrifugal switch actuator, comprising a bracket means for securement to a rotatable motor shaft, a pair of oppositely disposed weight arm units pivotally interconnected to said mounting bracket means and including opposed pivot arms, a collar, said pivot arms having a pivot connection to said collar and said collar moved by the pivoting of the arms on said bracket means, an over-center linkage means coupled to said arm units and having a spring coupled to said linkage means biasing said weight arm units to a first rest position, said weight arm units moving from said first rest position to a second actuated position in response to centrifugal forces associated with rotation of said shaft and said arms pivoting within said collar and moving axially of the shaft and axially toward the over-center position of said spring and linkage means, said pivoting of said arms creating wear within said collar whereby said arms and collar move further toward the over-center position with operation of the actuator, stop means limiting the position of said weights between said rest position established by said linkage means and said actuated position established by said centrifugal forces, said pivot location of said arms shifting with respect to said linkage means in the actuated position in the presence of wear within the pivot connection, and mechanical limit means located between said bracket means and said weight arm units and being spaced therefrom in the absence of selected wear in the pivot member to positively limit the movement of said arms whereby said pivot point does not move in line with or past said over-center position of said linkage means in response to said pivot members.