US1735579A - Short-circuiting device for motor commutators - Google Patents

Description

1929- I E; P. LARSH SHORT CIROUITING DEVICE FOR MOTOR COMMUTATORS Filed Jan. 17- 19,21

A TT ORNE Y.

Patented Nov. 12, 1929 UNITED STATES PATENT OFFICE.

I EVERETT P. L ARSH, OF DAYTON, OHIO, ASSIGNOB TO THE MASTER ELECTRIC COMPANY, F DAYTON, OHIO, A CORPORATION OF OHIO SHOBT-CIRCUITING DEVICE FOR MOTOR COMMUTATOBS Application filed January 17, 1921. Serial No. 437,906.

This invention relates to electric motors and more particularly to a short circuiting or operation changing device for alternating current motors of the repulsion-induction type, by which the motor is automatlcally changed from a repulsion starting condition to an induction running condition and'viceversa in accordance with Variations of speed.

The object of the invention is to simplify the structure as well as the means and mode of operation of such circuit changing devices wherebythey will not only be cheapened in construction, but will be more efficient in use, automatic in operation, uniform in action, automatically controlled, and unlikely to get out of repair.

A further object of the invention is to provideim roved means operated by centrifugal ten ency by which the commutator bars are automatically connected with a common electrical conductor which will promptly respond to variations of speed above and below a predetermined rate of rotation.

A further object of the invention is to provide a short circuiting or current changing device, which will have a wiping action insuring perfect electrical contact, in which this wiping action. will be further efi'ected under yielding pressure thereby obyiating any chatter or vibration and the incident arcing and burnin of the contactsurfaces.

A further ob ect of the invention is to provide means for controlling the movement of the short" circuiting or current changing members whereby their movement to effect the alternation of the. motor from repulsion to induction operation and vice-versa will be effected by a quick movement in either direction.

A further object of theinvention is to provide such a short circuiting or current changing device which will be compact, of few parts, and having no pivot joints, nor indirect movement, but in which the current controlling devices are directly operated by centrifugal tendency.

WVith the above primary and otherincidental objects in view as will more fully appear in the specification, theinvention consists of the features of construction, the parts and combinations thereof, and the mode of operation, or their equivalents, as hereinafter described and set forthin the claims.

Referring to the accompanying drawings, Fig. 1 is a sectional viewof a motor commutator and the short circuiting device forming the subject matter hereof applied thereto. Fig. 2 is an end elevation partly broken away of the short circuiting device and commutator. Fig. 3 is a perspective view. partly broken away of the assembled short circuiting device removed from the armatureshaft. Fig. 4 is a detail sectional view somewhat diagrammatic illustrating successive positions of the centrifugally operated short circuiting elements. Fig. 5 is a detail perspective view of one of the centrifugally oper-- ated contact slugs and a portion of the retaining and retracting ban fi,Figs. 6, 7 and 8 illustrate different modi engagement with the commutator. Fig. 9 is a further imodification thereof, wherein yielding spring means is em loyed. Figs-10 to 13 illustrate further modi cations. I

Like parts are indicated by similar characters of reference thruout the several views.

cations of the. means for deflecting the contact slug into The structure of the electric motor per se,

forms no part of the present invention, which pertains wholly to the short circuiting means for the commutator bars, by which the motor is caused to operate alternately as a repulsion motor and an induction motor.

An alternating current, repulsion-induction motor of the single phase type to which the present invention is particularly adapted is one which as the name indicates, starts as a repulsion motor and as the speed approaches its normal or maximum rate or rotation automatically changes its character,

and runs as an induction motor. Briefly described it consists of a field or stator of laminated toothed construction having a single wrnding thereon connected to the supply circult and a progressively wound armature or rotor with a commutator engaged by brushes during the starting or repulsion period to gether with speed controlled devices for short circuiting the armature windings thru the commutator after the armature has attained 7 adapted for a predetermined speed, which speed controlled means in some instances lifts the brushes from the commutator simultaneously with the short circuiting operation. There is no electrical connection between the stator and the rotor. The currents in the stator create an alternating flux which reacts on the rotor and induces its rotation. This type of motor, therefore, starts as a simple repulsion motor without compensating or auxiliary windings and operates as a repulsion motor until the rotor or armature approaches a synchronous speed .or one commensurate with the'windings, whereupon the speed controlled devices operate to automatically short circuit the armature winding thru the commutator. "Thus the motor is automatically transformed from a repulsion type into an induction motor having whatis essentially a squirrel cage rotor. It is the improvement of the speed operated governing onshort circuting device which forms the sub ect matter of the present invention. One of-the advantages of a machine of this type is that it 1s inherently a constant speed motor having a high starting torque with low current consum tion or minimum current'surge.

Tl ie typical repulsion motor without compensationves torque possible while the single phase induction rotor with the squirrel cage armature or its equivalent affords the most eflicient motor when running. Y

. A repulsion-induction type of motor combines these most desirable qualitiesm a sinle machine. As it possesses such high startmg torque characteristics it is well adapted for operating machinery which starts under full load, as pumps, air compressors, inding mills, etc. Requiring no starter t ey are automatic control, or distance operation. They start quickly and operate quietly and smoothly.

The above is ofit'ered merely to facilitate a thorough understanding of the purpose of the invention,,and-with no intent nor des rethat it shall in any way be construed as lim ting or restricting the application or scope of the invention. I

Inasmuch as the construction of the motor per se forms no part of this invention, it has not been illustrated. It is to be understood, however, that the short circuiting means forming the subject matter hereof is applicable to various styles of motors of the char-1 I acter heretofore indicated. Referring to the drawings, 1 is the armature shaft, on wh ch iscarried the usual commutator comprising the core '2 about the periphery of which are located a continuous succession ofcommutator bars 3, insulated from the core 2 and from each other by intervening bodies of insulating a the core 2., and are beveled or inclined on their the most efiicient startinginaterial 4.. The commutator bars 3 pro-- somewhat beyond the terminal face of' inner faces as at 5, thereby afiording a beveled The short circuiting means is embodied in a unitary structure capable of being assembled independent of the motor and applied thereto or removed therefrom without the necessity of disassemblingeither the motor or the short circuiting means. However, this short circuiting device may if desired be assembled directly upon the motor shaft.

The short circuiting device comprises a sleeve or hub 6, adapted to be secured upon the armature shaft 1, adjacent to the face of the commutator. This sleeve or hub 6, carries fixedly attached thereto, and immovable in relation'onevwitli the other, two spaced discs 7 and 8. The larger disc 8 is concave or cup shape affording an inwardly extending peripheral flange overhanging the sleeve or hub 6. These discs 7 and 8 may be secured to the sleeve or hub 6 in any'suitable manner.

The preferred mode of attachment is to form the hub or sleeve 6 with terminal shoulders or rabbts against which the respective discs 7 and.8 are assembled, andthe protruding .ends of the hub or sleeve 6 beyond such disc are then upset by spinning, stakin or other suitable operation. Intermediate t e respective discs 7 and 8 are assembled a plurality of radially disposed bifurcated slugs or con- .tact elements 9. These contact elements or slugs are somewhat wedge shaped or tapered as shown-in Figs. 2 and3, and are assembled side by each to form a continuous band about the hub 6, intermediate the discs 7 and 8. Extending about the assembled series of contact slugs or elements 9 and engaging in the external bifurcations 10 thereof is an endless elastic band 12. This band ma be of any suitable or desirable character, ut for convenience of manufacture and economy, a helical spring, the ends of which are joined to afford a continuous band of suitable diameter has been employed. In lieu of this type of elastic band, a coiled wirespring, the convolutions of which extend entirely around the assembly of slugs'or content elements may be employed, or several convolutions of a fiat spiral spring might be utilized.

The elastic band 12, of whatever character it may be, tends to contact the slugs or contact elements 9 into their innermost position.

5, formed bythe overhanging ends of the v The short circuiting commutator bars '3. unit is located upon the armature shaft 1 in juxtaposition to the face of the commutator core 2, with the inclined or beveled ends 5 of the bars overhanging the slugs or contact elements 9, from the inner side of the unit, while the shell or concave disc 8 over- 15 will engage the beveled face of the overhanging 1 by a clamp-nut 13, between which and the end of the sleeve or hub 6 is interposed a washer 14. The centrifugal tendency induced by the rotation of the shaft 1, and the series of contact slugs 9 carried thereby,

tends to move such slugs outwardly against the tension of the elastic contracting band 12. Whenever the centrifugal tendency is sufficient to overcome the tension of the band 12 the slugs 9 in their outward movement ends of the commutator bar 4, and upon increased centrifugal influence will tend to slide outward upon such inclined faces until they contact with the inner face of the concave disc or shell 8. It is to be noted that the shell or disc 8 is also provided with a beveled face 15. This bevel of the shell or disc 8 is, however, located somewhat more .remotely from. the center of rotation than the bevel 5 of the commutator bar. That is to say, the slugs will first en age the bevel 5 of the vcommutator bar an will thence travel along these inclined surfaces in a diagonal direction before engaging the beveled face 15 of the shell or disc 8, whereupon the slugs will wedge themselves in firm contact within the angle formed by the respective bevel faces 5 and 15, as shown by solid lines in Fi 4. Fig. 4 shows the successive steps in t e movement of the contact slugs under centrifugal tendency. Intheir normal osition when the rotor is at rest or before it has attained the predetermined operating speed, these contact slugs will be \held in a contracted position as shown by dotted lines, position I. However, as the rotor approaches the predetermined .speed at which the operation changes from repulsion to induction mode of operation, the slugs will move directl outward against the tension of the elastic band 12 until they contact the bevel 5 of the overhanglingl'com-- mutator bar as shown by dot andv as lines,

osition II. Further increase of speed inuces reater centrifugal influence, and the beveled face 5 of the commutator bars will have a camming action by which the slugs in their outward movement are deflected laterally, thus affordin I a wiping or rubbing contact between thes ugs' and the bevele face 5 of the commutatoiijbar, until the slugs, finallycome to'rest in enga ement with the retaining shell or disc 8. his wiping or rubbing action induced by the diagonal movement of the slugs u on the beveled face 5 from the position to the position III ,of 4 insures abrifiht clean contact sur M y insures perfect elec-' trical engagement. j

While the assembly of contact slugs 9 about the hub or sleeve 6 and intermediate the discs 7 and 8 will normally rotate in unison therewith independent of any driving engagement, and moreover, any independent rotation or slippage of the assembly of slugs in relation with the discs and hub would be immaterial, there have been shown in Figs. 2 and 3, driving vanes 16, projecting inwardly from the disc 7 intermediate the slugs 9. There may be'any number of these vanes provided as may be desired. In practice three or four of such vanes havebeen found amply sufficient. These vanes 16 in the illustrated construction comprise merely tongues or flaps of metal, stamped from the disc 7 at spaced intervals and protruding between successive slugs of the series, dividing the contact slugs into a plurality of groups and aflording a positive driving connection between the assembly of slugs and the carrier therefor. In lieu of this construction, the

hub or sleeve 6 may be slotted and driving vanes 17 may be inserted and secured within such radial slots shown in the detail view Fig. 10.

If so desired, the disc 7 may be entirely omitted, and the slugs may rest in direct contact with the terminal face of the commutation core 2.

Under ordinary conditions of usage, the yielding resistance of the elastic band 12 may be relied upon to afford definition to the movements of the contact slugs. The slugs will not tend to move until the centrifu al influence due to increased speed is su cient to overcome the tension of the band 12. The

' initial outward movement of the slugs against the tension of the band materially increases their tendency to move further under centrifugal influence thru the fact that with each degree of movement their distance from the center of rotation is increased, and hence the centrifugal influence accelerated. This in itself is suflicient to induce. a quick movement into and out of'operative position. However to afford further definition to this movement, the contact slugs .9 may be caused to tilt or incline within the carrier toward the commutator and thus have a frictional bearingupon the face of the commutator core- 2 or upon'the' int posed retaining disc 7 as the case may be, w ich must be overcome in addition to the retractive influence of the elastic band 12. To this end, the hub or sleeve 6 thereby afiordingla frictional contact or bearing. In Fig. 7, t ehub' or sleeve 6 is inclined in the opposite direction to form aperipheral may be tapered or inclined .as shown inFigs.

' groove 18, in which engages a projecting finger or corner 19 of the slug to forma fulcrum u on which the retractive band 12 tends to ti t the slug 9 inwardly. The peripheral groove 18 is of such extent that the fulcrum point will be guided outwardly by thecam action of the groove, as the slug is retracted under the influence of the band 12. At the same time the outer or bifurcated end of the slug will be tilted toward the commutator. In Fig. 8 the inner edge of the slug and the hub or sleeve have both been inclined in the same direction, so that the retractive'action of the elastic 'band 12 tends to slide the slug 9 downthe inclined or tapered face of the hub or sleeve 6 into frictional contact with the face of the commutator. In Fig. 9 a spring disc or series of spring fingers 20 secured to 'the inner face of the shell or disc 8 serve to yieldingly press the slugs toward the commutator. In these constructions the centrifugal influence must first overcome the frictional engagement of the slug with the disc 7 or the face of the commutator, tending to straighten the slug upward before it begins its outward travel against the tension of the elastic band 12. It will be understood that the disc 7 may be employed or omitted as is found most desirable or convenientl However, by employing 'the disc 7 the short circuiting mechanism may be independently assembled, and interchangeably employed upon different motors, or shipped to distant points for substitution.

wherein in lieu of the driving vanes 16 or 17, certain contact slugs at spaced intervals of the character described possessingthe particular features of advantage before enumerated as desirable, but which obviously is susceptible of modification in its form, proportions, detail construction and arrangement of parts without departing from the principle.

involved or sacrificing any of its advantages. While in order to comply with the statute the invention has been described in language more or less specific as to structuralfeat'ures,

- it is to be understood that the invention-is not limited to the specific details shown, but

that the means and construction herein -disclosed comprise but one of several modes of. putting the invention into effect and the in- W vention is therefore claimed in any of "its forms or modifications Within the legitimate and valid scope of the appended claims. y

In Fig. 13 there is shown a modification Having thus described my invention, I claim: 1

1. In a short circuiting means for. commutators, a commutator having a peripherally arranged series of commutator bars, a series of independent bifurcated contact slugs arranged in a concentric circular series in proximity to the lateral face of the commutator and slidable radially thereon into e'ngagement with the commutator bars, and an elastic band engaging in the bifurcations of the slugs against the tension of whioh'the series of'slugs is expanded by centrifugal influence and means engaged by the slugs durmg their radial movement for laterally deflecting the slugs to insure lateral'wiping contact with the commutator bars.

2. In a short circuiting device for commut-ators, a circular series of independent polygonal slugs having registering-notches forming a peripheral groove in the assembled circular series of slugs, an elastic retaining band engaged in said 'groove, said circular series of slugs being concentrically disposed in juxtaposition to the lateral face of the commutator and radially expansible under centrifugal influence and a cam face in the path of radial movement of the slugs engaged thereby as they approach the limits of their radial movement by which they are laterally urged to insure a wiping electrical engagement with the commutator bars.

3. In a short circuiting device for commu tators, a disc fixedly mounted in paralled spaced relation with the commutator, converging spaced flanges upon the commutator and disc respectively, the inner circum- I ference of the disc flange being of greater diameter than that of the commutator flange,

and a series of centrifugally actuated weights loosely interposed between the commutator and disc adapted to initially engage the.

commutator, flange under the influence of centrifugal force and slide thence upon the inclined flange of the commutator into engagement with the disc flange.

' 4. In a construction of the character described, a commutator, a disc fixedly mounted-in parallel spaced relation with the commutator, one of said members'havinga flange inclined to the axis of rotation and extendin toward the other member, a series of centri gally actuated weights looselyin- :terposedv between the commutator and disc and radially movable under centrifugal influence and adapted to engage the inclined flange as they ap roach the limit of their radial movement t ereby being laterally deflected into wedgingengagem'ent with the other member.

'5. In a constructibn of the character described, a commutator having aperipherally disposed series of commutator bars, a

' disc fixedl mounted in parallel spaced relation with t e commutator, a series of o'entrifugally actuated weights loosely interposed between the disc and commutator, an elastic band against the tension of which the weights are radially movable under centrifugal influence into electrical engagement with the commutator bars, 'said commutator bars being beveled for laterally deflecting the weights by their engagement therewith during their radial movement.

6. In aunitary short circuiting device for commutators, a spool like carrierv comprising a hub sleeve and parallel spaced discs secure thereto, a series of contact slugs interposed between the discs, and vanes carried by said spool separating the series of slugs into groups and affording positive driving connection therefor, said spool carrying the contact slugs being immovably mountable in juxtaposition to the lateral face of a commutator the bars of which are engaged by the slugs when distended by centrifugal 1n fluence.

7. In a short circuiting device for commutators, a circular series of independent contact slugs concentrically arranged 1n juxtaposition to the lateral face of the commutator and controlled by centrifugal mfluence, means for effecting a tilting movement of the slugs as they approach the limit of their retractive movement, and a gulde member frictionally engaged by the tilted slugs to afford temporary resistance to their radial movement under centrifugal influence-1 8. In a short circuiting device. for commu tators, a commutator having a eripherally disposed series of commutator ars, a.d1sc located in parallel spaced relation with the lateral face of the commutator, a circular series of independent contact slugs concentricall arranged relative thereto and confined etween said disc and the lateral face of the commutator and controlled by centrifugal influence, yielding retracting means for said slugs, and a fulcrum seat for the slugs at-the inner limit of the1r movement laterally ofiset relative to the plane of mflu-, ence of the retracting means whereby the slugswill be laterally tilted when 1n the1r retracted positions.

9. In a short circuiting devlce for commutators, a circular series of independent contact slugs concentrically arran ed in jux taposition to the lateral face of t e commu tator and capable of both radial and lateral shifting movement, said slugs being movable radially into engagement with the commutator bars by centrifugal influence, a guide jfor vsaid'slug's, and means for deflecting the slu s laterally into frictional contact wlth then: guide to afford a supplemental frictional resistance. to their radlal movement under centrifugal influence.

- 10; In a short circuiting device for commutators a disc fixedly mounted in parallel spaced relation with the. commutator, contact the serles of contact member 1s expanded into h and engaged thereby in their radial movement under centrifu a1 influence, said slugs being deflected lateraflly thru a slidin movement until arrested b said disc Eetween which and the beveled ars the slugs have a wedging engagement."

11. In a short circuiting device for electric motors, a commutator includin a series of commutator bars to be electrica ly intercon nected, a disc located in parallel spaced relation with the commutator, an annular series of centrifugally actuated contact members confined intermediate the disc and the lateral face of said commutator, an annular contractile band aginst the tension of which the contact members are radiallymovable, under centrifugal influence, and means for effecting a tilting movement of the contact members laterally toward the commutator incident to their radial movement.

12. In a short circuiting device for electric motors, a commutator includin a series of commutator bars to be electrica ly interconnected, a disc located in parallel spaced relaradial and lateral tion with the'commutator, an annular series of centrifugally actuated contact members confined between the disc and the lateral face of said commutator, an annular contractile band concentrically arran ed exteriorly of said contact members, an camming means by which the contact members are laterally deflected in engagement'with the commutator bars in addition to their radial movement.

13. In a short circuiting device for commutators, a series of commutator bars to .be interconnected, a disc mounted in fixed relation with the commutator, an annular series of independent centrifugally actuated contact elements mounted in juxtaposition to the disc, an annular contractile hand against the tension of which the series of contact member is expanded into enga ement'with the con tact ars by centrifuga influence and interengaging means between certain individual contact members and the disc permitting relative radial movement, but limiting relative circumferential movement of the contact members and disc.

14; In .ashortcircuiting device for commutators, a series of commutator bars to be interconnected, a disc mounted in fixed spaced relation with the commutator, an annular series of independent centrifugally actuated contact. elements interposed between the'commutator and disc, an annular contractile band against the tension of which enga ement with the contact bars by centrifugal influence, and means for preventing circumferntial movement of the contact members in relation with the disc but permitting relative movement thereof in" a radial direction.

15. In a short circuiting device 'for motors,

' the combination with a circular series of comlocated in the path of radial movement of said contact members in spaced relation with the commutator bars, and engaged by the contact members at the limit of their radial movement, while maintaining their engagement with said bars. v

16. The -combination with a circular series of commutator bars having a beveled interior surface, a series of centrifugally controlled contact members and yielding restraining means common to the contact members against the tension of which the said members are movable radially into engagement with the beveled interior surface and a limiting stop in spaced relation with the commutator bars engaged by said contact members by further movement and in continued outwardly inclined direction under "centrifugal influence while in sliding engagement with the beveled interior surface of the commutator bars to interconnect the bars one with another.

17 In a short circuiter for commutators, a disc fixedly mounted in spaced parallel relation with the commutator, the adjacent faces of the disc and commutatorbeing convergent one towardthe other, a short circuiter for the commutator bars comprising an. annular series of centrifugally actuated weights confined for radial movement between the disc and commutator, and an annular contractile band exteriorly surrounding the weights against the tension of which the weights are rad'ally movable under centrifugal influence to expand the band, the radial expansion of said short circuiter serving to electrically interconnect the disc and commutator bars to connect the bars electrically one to another.

18. In a short circuiter for. commutators, a disc mounted in fixed parallel spaced relation with-the commutator the adjacent faces ofthe disc and commutator converging one toward the other, an annular ex ansible and contractible short circuitin .devmeincluding a series of weights confined for radial movement intermediate the disc and commutator and an elastic contractile band circumferentially surrounding the series of weights, said short circuiting device being radially expansible by centrifugal influence into wedging engagement with the adjacent converging faces of the commutator and disc. 19. In a short circuiting mechanism for single-phase, alternating current motors and in combination with the armature and commutator thereof, cooperating weight and spring elements operable'radially relative to the armature shaft one of which is electrically conductive and adapted to be moved slidably in a radial direction into wiping contact with the lateral'face of the commutator to effect short circuiting of the armature, and means whereby said contact is made with increasing pressure as the weights move outwardly.

20. In short-circuiting mechanism for single-phase, alternating current motors and in combination with the armature and. commutator thereof, a plurality of radial centri fugal elements arranged in substantially equal groups circumferentially of the armature shaft and retained axially thereon-by a disc having a series of radial slots, certain of said elements being operable in said slots and acting to retain the elements of each group as to lateral displacement thereof, and a spring element arranged circumferentially and operable radially with the centrifugal elements.

21. In short-curcuiting inechanism for single-phase, alternating current motors and in combinnation with the armature and the commutator thereof, a plurality of radial centrifugal elements arranged circumferentially of the armature shaft and retained axially thereon by a disc supported on the armature shaft and havinga series of radial slots,

certain of said elements being operable in said slots and acting to retain the elements of each group as to lateral displacement thereof, and a spring element against the yielding resistance of which the centrifugal elements are radially movable into engagement with the commutator segments, said elements being sub ected to resistance by said disc at an angle to their said radial movement whereby.

pressure is provided for establishing wipin contact between said centrifugal elements an the commutator segments.

22. In short-circuiting mechanism for singlehase, alternating current motors and in com ination with the armature and the commutator thereof, a plurality of radial, wedgeshaped centrifugal elements arranged in groups circumferentially of the armature shaft and retained axially thereon by a disc mounted on said shaft and, having a series of radial slots, other radially disposed 'elements interposed between'the groups of the wedge-shaped elements and enga ed in said slots to retain the elements of eac group as to lateral displacement thereof, and a spring element arranged circumferentially and operable radially with the centrifugal elements against the yielding resistance of which the centrifugal elements are movable for establishing contact between said centrifugal 'elements and .the'commutator segments;

23. In a short circuiter for electric motors and the like, the combination with an armature and commutator, of a series of centrifu- 24. In a short circuiter for electric motorse and the like, the combination with an armature and a commutator, of a plurality of cen trifugally actuated weights located at spaced intervals about the armature shaft and movable substantially radially relative thereto, an annularjhelical spring band exteriorly surrounding the weights and yieldingly resisting their outward movement, and a slotted guide disc located contiguous to said weights within the slots of which the weights project and defining the paths of movement of said weights to effect the short circuiting of the armature windings.

25. In a. short circulting device for electricmotors and the like, the combination with an armature and a commutator, of a series of centrifugally actuated weights disposed in different radial positions about the armature shaft and movable substantially radially relative thereto, a spring tension member circumferentially surrounding the weights against the tension of which the weights are movable to effect the short circuiting of the armature windings, and guide means for said weights directing their movement toward and from the armature shaft. 26. In a short circuiting device for electric motors and the like, the combination with an armature and a commutator, of a series of centrifugally actuatedweights disposed in different radial positions about'the armature shaft and movable substantially radially relative thereto, an annular helical spring band exteriorly surrounding the weights, and a disc with which the weights have engagement at spaced intervalsto insure unison rotation with thearmature and to guide said weights in'their to and fro movement relative to the armature shaft to effect the short circuiting of the armature windings.

27. In a short circuiting deviceior electric motors and the like, the combination with an armature and commutator, of a series of weights arranged circumferentially and operable radially relative to the armatureshaft and an annular helical spring band exterior- 1y surrounding the weights against the yielding resistance of which the weights are movable into and out of contact with the commutator segments and a deflecting surface engaged by the weights as they approach the outward limit of their radial movement whereby said contact is effected with increasing lateral pressure as the weights move outwardly.

28. A short circuiter for electric motors, the combination with a commutator, a plurality of weight elements arranged circumferentially of the commutator shaft and movable in radial directions under centrifugal influence into short circuiting engagement with said commutator, said weights having therein registering marginal indentations forming a seat for a retractile spring and a helical spring, the ends of which are interconnected into an annular band having seating engagement in the registering indentations of the weight elements against the yielding resistance of which the weight elements move under centrifugal influence to effect short circuiting of the commutator.

29. A short circuiting device for electric motors including in combination with a cominutator an annular-series of contact 'members subject to centrifugal influence and movable thereby in radial directions into short circuiting contact engagement with the commutator, said contacts being notched in their outer edges to form a seat fora retractile spring'and a helical spring having its ends interconnected into annular formation seated in the registering notches and yieldingly resisting the movement of the contact members into engagement with the commutator under centrifugal influence.

In testimony whereof, I have hereunto set my hand this 15th day of January, 1921.

E. P. LARSH.

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