US2573968A - Centrifugal switch - Google Patents

Description

1951 K. M. HAMMELL ET AL 2,573,968

CENTRIFUGAL SWITCH Filed June 15, 1946 KEMPER M. HAMNELL BYROBERT P O'MALLEY Patented Nov. 6, 1951 CENTRIFUGAL SWITCH Kemper M. Hammell, Bloomington, and Robert P. OMalley, Farmer City, 111., assignors to Eureka Williams Corporation, Detroit, Mich., a corporation of Michigan Application June 15, 1946, Serial No. 676,885

1 Claim. 1

This invention relates to centrifugal switches v and has particular reference to a starting switch for single phase induction motors operative for opening the electrical circuit through the start ing windings when the speed of the motor is sufficiently high to produce the required torque when operating on the main or running windings.

While many switches of this type have heretofore been devised and used, the construction of such switches has been relatively expensive. This invention contemplates a switch of this type which is simple in construction and design and which is made from a relativelyfew simple parts. The switch is characterized by its simplicity of design, the relatively low cost of making the same and the dependability of operation thereof.

Principal objects of the invention, therefore, are to provide:

A new and improved centrifugal switch;

' A new and improved starting switch for electric motors useful for opening the circuit through the starting windings;

A centrifugal switch which is efficient in operation while simple in construction and hence relatively low in cost to make.

Other and further objects of the invention will be apparent from the following description and claims and will be understood by reference to the accompanying drawings, of which there is one sheet, which, by way of illustration, shows a preferred embodiment and the principles thereof and what we now consider to be the best mode in which We have contemplated applying those principles. Other embodiments of the invention embodying the same or equivalent principles may be used and structural changes may be made as desired by those skilled in the art without departing from the present invention and the purview of theappended claim. We also contemplate that of the several different features of our invention, certain ones thereof may be advantageously employed in some applications separate and apart from the remainder of the features.

In the drawings:

Fig. 1 is a fragmentary elevational view of an electric motor embodying the invention;

Fig. 2 is a sectional View taken along the line 2--2 of Fig. 1, looking in the direction of the arrows, and showing in elevation the plate assembly of the centrifugal switch contacts;

Fig. 3 is an enlarged sectional view of the switch with the weights thereof in their extended position;

Fig. 4 is a fragmentary sectional view of the 2 switch taken generally along the line 44 of Fig. 3, looking in the direction of the arrows; and

Fig. 5 is a side elevational view of part of the apparatus.

As illustrated in the embodiment of the invention selected for purposes of illustration, the centrifugal switch is designed to function as a starting switch for a single phase induction motor for opening the electrical circuit through the starting windings when the speed of the motor shaft is sufficiently high to obtain the required torque from the motor when running on the running windings.

As shown in Fig. 1, the switch may be arranged about the motor shaft l0 between a bearing [2 therefor and the armature IA. The switch in general comprises a contact assembly indicated generally at IS, a collar 18 which is mounted for slidable movement axially of the shaft ID, a spring 20 for biasing the collar 8 to one position and fiyweights 32 operative in response to centrifugal force for shifting the collar l 8 axially of the shaft against the force of the spring 20.

A U-shaped plate 24 having parallel arms 26 is arranged so that such arms are parallel to the shaft Ill and arranged on the opposite sides thereof, the plate being suitably secured to the armature M, for example, by means of screws 28. The shaft 10 extends through a central opening in the plate 24 and since the plate is secured to the armature 14, it will rotate with the shaft ID. The ends of the arms 26 are each provided with two tabs or projections 30, such tabs projecting toward each other.

Each arm 25 has pivotally associated. therewith an angularly shaped flyweight 32. Each of the flyweights 32 may be formed from plate or strip stock and as illustrated includes a central portion or long leg 34, a short leg 36, an arm 38 and a pair of tabs or projections 48. Each weight may be formed by suitable stamping operations from metal stock so thatparts thereof are integral. Each weight 32 is arranged to be disposed or nested within the arm 26 of the plate 24. The arms or fingers 38 engage in a seat 42 provided on the periphery of the collar IS. The spring 20 comprises a coil spring which is telescopically arranged relative to the hub of the collar 18 and confined between the collar l8 and the plate 24 so as to bias the collar l8 to the position as illustrated in Fig. 1, when the motor is at rest and during the operation thereof on the starting windings.

The tabs of the arms 26 and the weights 32 3 project in generally opposite directions and are interdigitated relative to each other so as to provide a pivotal mounting for the weights 32 on the arms 26 and so as to prevent lateral shiftretracted position as shown in Fig. 1 and their 1% extended position as shown in Fig. 3.

The legs 34- and 36 of the weights form a mass which operates in response to centrifugal force during the rotation of the shaft II! .to shift the weights from the position illustrated in "Fig.

1 to that illustrated in Fig. 3. As the arms 38 of the weights engage the seats-42 on the collar, the centrifugal force will have 'to be sufiicient before the weights are moved to their extended position to collapse the, spring 2! When the speed of the shaft H; is sufficiently high to obtain the required torque from the running windings of the "motor, the centrifugal force of the flyweights-32 will move the same to their extended position, thereby shifting the collar l8 soas to open the electric circuit through the starting windings. Obviously, the speed at which the weights 32 will be moved to their extended position will be dependent upon the mass of the weights 32, the speed of the shaft 10, the force of "the spring 28 and the friction in the system. All of this may be readily de-' termined so as to obtain the shifting 'of the collar I8 to open the switch controlling the starting windings at the desired speed of the motor.

It is likewise evident that when the speed of the motor shaft is reduced below the throw out speed of the weights 32, the'spring will be operative to shift the weights to their retracted position as shown in Fig. l and to close the switch controlling the starting windings. However, as is well known, the speed at which the weights will be returned to their retracted position will be somewhat less than the speed at which the weights will be moved to their extended position due to the different 'eifective distances which the mass of the weights 32 are in their extended and retracted positions from the center-of rotation. Tabs 48 struck out of the plate 24 are arranged toengage the weights 32 so as to form a stop to determine their retracted position while the arms'25 form a stop for determining the extended position of the Weights 32.

The contact assembly 15 includes a plate 'of insulating material 50 suitably secured to the end bell of the motor in the position'indicated. in Fig. 1. A flexible ring 52 is secured to the plate by means of rivets 54 and includes an 'arm 55 carrying'a switch contact 58 and an embossing or rivet head 60 with which the collar [8 is engageable. A contact 62 iscarriedby a rigid arm 54 mounted on the plate 50 by means of rivets 65. The contacts 58 and BZ'are included in the-circuit of the starting windings and when engaged close such circuit.

Thearm "66 carried by the plate .50 forms a stop for limiting the movement of the contact 58 away'from the contact 62. When the ring 52 is notsubjected to the action of the spring 23, the contacts 58 and 62 will beseparated as the ring '52 is constructed and arranged sothat when relieved of the load of the collar -|8 and the spring 20, it will position the contact 58 away from the contact 6 2.

The tabs 48 due to their engagement with the fiyweights 32 and the engagement between the arms 38 thereof and the collar l3 will limit the axial movement of the collar is in response to :the spring 23. -The electrical circuit for the starting windings is suitably connected to the ring 52 and to the arm 54. The resiliency of .'the arm 56 and the ring 52 will to a large extent .relieve the contacts 58 and 62 of any material load of'the spring 20.

While 'we have illustrated and described a .preferred embodiment of our invention, it is understood that-this is capable of modification, and We, therefore, do not wish to be limited to the precise details set forth, but desire to avail ourselves of such changes and alterations as fall withinthe purview of the following claim.

We claim:

A centrifugal switch for an electric motor comprising a U-shaped plate adapted to ice-mounted on the shaft of said motor with the parallel'arms of said plate arranged parallel to and spaced from said shaft and on opposite sides of said shaft, the end of each arm being provided with spaced integral tabs projecting therefrom and toward said shaft, a flyweight for each arm comprising an angular plate member having a central portion disposed between one of said arms and said shaft, said central portion having spaced integral tabs projecting from one end thereof and away from said shaft, said arms being provided with a straight edge between said first named tabs, said tabs on said weight and said central portion defining an angle therebetween slightly greater than the corner formed by said angle being adapted to engage said straight edge so as to provide a pivotal mounting for said weight upon said edge of said arm, a collar'slidable on said shaft, each of said weights having an arm projecting from the pivoted end thereof toward said shaft and en-- gageable with a portion of said collar, a spring associated with said collar and said shaft for moving said collar along said shaft into a first position away from said U-shaped plate and for pivoting said flyweights into a first'position with said central portions disposed angularly with respect to said parallel arms, said weights under the influence of centrifugal force pivoting on said pivotal mounting into a second position with said central portions resting against said parallel arms, said latter movement of said weights into said second position moving said collar along said shaft into a second position against the force of said spring, and a pair of switch contacts, one of said contacts being resiliently mounted and arranged to be engaged by said collar upon movement of said collar into one of its positions.

KEMPER M. ROBERT P. OMALLEY.

REFERENGES (JITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Conley Dec. '26, .1939

Images