US1779006A - Short circuiter - Google Patents

Description

E. PJLARSH 1,779,006

' 1 SHORT CIRCUITER 1 7 Filed July 28 192 Patented @et. 21,, 193% Paanr EVE-BET! P. LARSH, OF DAYTON, "OHIO, ASSIGNOR TO THE DIASTER ELECTRIC COMPANY, OF DAYTON, OHIO, A CORPORATION OF OHIQ SHORT CIRCUITER Application filed m 2a, 192;. Serial No. 728,661.

This invention relates to electric motors and more particularly to a short circuiting or operation changing device for alternating current motors of the repulsion induct-ion type,

5 by which the motor is automatically changed from a repulsion starting condition to an inductiongunning condition and vice versa in accordance with variations of speed.

The general subject matter hereof was origm inally contained in application Serial No. 528,223, filed January 10, 1922 (since matured into U. S. Patent No. 1,501,284, July 15, 1924), in which the construct-ions shown in Figs. 1 to 4 inclusive and Fig. 11 appeared .15 therein as Figs. 7, 8 and 9. and from which present claim 1 appearing therein as claim 10 was withdrawn upon' requirement for division.

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

A further object of the invention is to provide improved means operated by centrifugal tendency 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 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 the invention is to provide such a short circuiting or current chang-. ing 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.

With the above primary and other incidental objects in view as will more fully appear in the specification, the invention consists of the features of construction, the parts and combinations thereof, and the mode of operation or their equivalents as hereinafter described and set forth in the claims.

Referring to the accompanying drawings, Fig. 1 is a sectional view of a motor commutator and the short circuiting device form ing 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 detail sectional view of the contact members shown in Figs. 1 and 2. Fig. at is a similar enlarged detail view of a modification, embodying a different method of fulcrum mounting for the contact members. Fig. 5 is a similar enlarged detail view, showing a further modification of the mounting, wherein the rest or stop flange projects forwardly from the fulcrum abutment. 6 is a similar enlarged detail view showing further modification of the mounting and also an arcuate undercut contour for the commutator bars. Fig. 7 is an enlarged detail view of the construction shown in Fig. 6, to which is added an additional flange intermediate the contactmemher and the baseof the commutator, by which the short circuiter contact arms are confined, forming a unitary member, capable of disengagement from the motor, Without disassembly or loss of the parts. Fig. 8 illustrates a variation of the construction wherein the contact members are controlled against independent or premature movement, by a yieldable guard ring, which compels unison movement of the contact member's. Figs.

9 and 10i1lustrate the form of contact element and mounting shown in the preceeding figure, employing, however, an axially yield-- ing compression spring in lieu of the circumferential contractible hand. These constructions of Figs. 9 and 10 difier one from the other by subjecting such axially compressible spring to pressure in opposite directions, under the same centrifugal movement of the contact elements. Fig. 11 is a similar detail sectional view of a further modification, employing an intermediate contact, actuated by the movement of the centrifugally operated slugs or weights.

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

5 The structure of the electric motor per se,

forms no part of the present invention, which pertains wholly to the short eircuiting 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 re- [5 pulsion motor and as the speed approaches its normal or maximum rate of 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 winding thereon connected to the supply circuit and a pro-- gressively wound armature or rotor with a commutator engaged by brushes during the starting or repulsion period together with 2.1 speed controlled devices for short circuiting the armature windings through the commutator after the armature has attained 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 al-- ternating 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 operatesas a repulsion motor until the rotor or armature approaches a synchronous i 40 speed, whereupon the speed controlled devices operate to automatically short circuit the ar-' mature winding through the commutator. Thus the motor is automatically transformed from a .repulsion type into an induction motor having what is essentially a squirrel cage rotor. It is the improveinent of the speed operated governing or short circuiting device which forms the subject matter of the present invention. One of the advantages of 0 a machine of this type is that it is inherently a constant speed motor having a high starting torque with low current consumption or minimum current surge.

The typical repulsion motor without com"- pensation gives the most eflicient starting torque possible while the single phase induction rotor with the squirrel cage armature or its equivalent affords, the most eflicient motor when running. A repulsion induction type of motor com- 4-. binds these most desirable qualities in a single machine. As it possesses such high starting torque characteristics, it is well adapted for operating machinery which starts under full load, as pumps, air compressors, and grinding however, that the short circuiting means forming the subject matter hereof is applicable tovarious styles of motors of the character heretofore indicated. Referring to the drawings, 1 is the armatureshaft, on which is carried the usual commutator comprising the core 2, about the periphery of which are located a continuous succession of commutator bars 3, insulated from the core 2 and from each other by intervening bodies of insulating material 4. The commutator bars 3 project somewhat beyond the terminal face of the core 2. The overhanging portions of the commutator bars 3 ma v'be variously shaped, either of rectangular form as shown in Figs. 5, 8 and 10, or beveled'as shown in Figs. 1, 3, i and 9, or such overhanging portion may be undercut in arcuate contour. as shown in Figs. 6 and 7.

The short eircuit-ing mechanism comprises an annular series of contact slugs 0r oscillatory arms 5, arranged approximately in parallel relation with the axis of rotation and with each other, and in proximity to the lateral face of the commutator. The inner ends of these oscillatory contact arms orslugs 5 extend within the recess formed by the projecting or overhanging ends of the commutator bars 3, with which the contact members make engagement upon outward or distended movement thereof. The contact members 5 are fulcrumed or otherwise mounted for oscillatory movement in a suitable mounting. provided with a rest or stop flange limiting the retraction of such contact arms ,or slugs. The annular series of contact arms or slugs so mounted for oscillatory movement outwardly under'centrifugal influence is peripherally engaged by a surrounding contractile band 6, preferably, tho not necessarily in the form of an endless helical spring. This endless helical-spring-or contractile band 6 is common to all of the slugs or contact arms 5 of the annular series, and yieldingly resists outward swinging motion under centrifugal influence. Such c ontractible band or spring is loosely seated upon the exterior margins of the succession of contact slugs or arms 5.

The outer margin of these contact arms is tendency of the surrounding band or spring the commutator face, so that the contractile preferably inclined slightly inwardly toward ITO spaced away from the fulcrum or pivotal] connection of such contact elements. However, as these contact members are oscillated outwardly under centrifugal mfluence, the

, inclination of the outer margins or faces of the contact elements is changed and as such elements approach the outer limit of their oscillatory movement, there is a tendency for til? such contractile band in seeking a point of minimum diameter to shift away from the commutator and toward the pivotal or fulcrum connection of the contact elements, therefore, somewhat decreasingits yielding resistance to their movement. Upon the decrease of speed and the concurrent retraction of the series of contact elements 5, the change in the marginal line of the contact elements tends to divert the contractile band 6 inwardly toward the commutator, and away from the pivotal or fulcrum point of such member. Thus when the contact elements are retracted as shown in the drawings, the contractile band is located a greater distance from the pivotal or fulcrum point of such members,

and hence affords greater resistance to their expansive or outward swinging motion. It thus requires a greater initial'eftort to overcome the initial resistance of the annular contractible spring band 6. However, as the contact members move outwardly toward engaging positions. with the commutatorbar, the shifting motion of the contractile band due to the changing inclination of their peripheral margin graduallydecreases the resistance of the spring, causing the contact members to move more quickly and more firmly into contact with the commutator bars. Conversely the movement of the spring away from the fulcrum point and toward its original position adjacent to the contact ends of the elements up on decrease of speed accelerates the retraction of such elements. This retractile orshifting movement of the spring gives definition to the movement of the contact elements afiording a quick acting or snapping operation of the short circuiter. It resists the initial movement, but the movement once initiated, the contact elements are permitted to move quickly into their operative engagement with the bars due to the shifting movement ofthe contractile band.

The difference in the forms of the several devices is primarily in their mounting, altho other slight differences are to be noted. In Figs. 1 and 3, the contact elements or oscillatory arms are shown provided upon their gamer sides with notches 7, which engage over the marginal edge of a fulcrum disc 8. The disc'8 is of ofiset annular form, to aflord a shoulder or shelf 9, upon which the contact elements 5 rest when in their retracted position under the contractible influence of the exteriorly disposed annular band 6. This supporting and fulcrum disc 8 is carried by a suitable collar 10 removaL-ly engageable upon the armature shaft in proximity to the commutator. To retain the contact elements 5 in engagement with the peripheral edge of the fulcrum disc 8 against displacement therefrom, while permitting their inwardly and outwardly swinging movement, the mounting also includes a concave disc 11, which overhangs the pivotal ends of the contact elements or arms 5.

While the construction as shown in Figs. 1 i

and 3 discloses the contact arms or elements 5 as being rounded on their inner end for engagement with internally beveled faces of the commutator bars 3, it is to be understood that these contact arms 5 may be formed with flat contact faces to agree when in out ward position with the interior faces of the rectangular ends of the overhanging bars 3, as shown in Figs. 8 and 10. The construction and operation being identical and the only variation being that of the contact surfaces upon the swinging arms 5 and the overhanging bars 3, which are clearly shown in Figs. 8 and 10, it is not thought essential to increase the number of views to show such variations of the construction disclosed in Figs. 1 and 3.

In Fig. l, the mounting is varied from that previously described by providing within a disc 12, an annular semi-circular groove or with a second disc 14 of smaller diameter than the disc 12, which forms the support or rest, limiting the retractiv'e movement of the contact elements 5 under the influence ofthe externally disposed spring 6. Furthermore the spring 6 is shown seated in a shallow notch in the outer margin of the contact element or arm 5, which tends to restrain the shifting movement of the contractile band heretofore described, by which its influence is diminished as the contact arms swing outwardly. This seating notch may be made of greater or less depth, thereby retaining the retractile band at its point of greatest ef-' ficiency, and maximum influence for longer or shorter periods of time, thus delaying the operative movement of the contact element's, until a maximum predetermined speed has been acquired. The contact arms 5 may or may not be provided with a retaining ring 12' extending thru perforations in the arms at-approximately their center of oscillation. Such ring is a convenience in retaining the assembly of contact elements intheir annular form, but is not an essential feature. The pperation, function and result of the construction shown in Fig. 4 is substantially thesame as that shown in Figs. 1 and 3, except that the contact. elements of Figs. 1 to 3 is fulcrumed within the notch 7 upon the peripheral margin of the disc 8, whereas in Fig. 4 the rounded edge of such contact members have rotating seats within the annular grooved depressions in the disc 12.

In Fig. 5 the construction is much the same as that previously described. The contact element 5 is capable of oscillatory movement within the mounting or support, against the tension of .the circumferentially disposed contractile band 6.. The band 6 as in the construction shown in Figs. 1 to 3 is capable of shifting movement toward and from the center of oscillation, thereby varying its-resistance as the contact elements are oscillated under centrifugal influence. In this figure, the contact element is shown as making flat butt contact with the interior face of the overhanging portion of the commutator bars 3. The mounting or support for the contact elements'is quite similar to Fig. 4 in that it employs a disc 15, quite similar in its form and function to the disc 12. This disc 15 is formed with the same annular grooved depression 13, to form the abutment seat for the oscillating contact arms 5. In lieu of the separate disc or support 14, as show 1 in Fig. 4, the construction illustrated in Fig. 5 employs a projecting flange 16 closely adjacent to the supporting and abutment disc 15. In fact the disc '16 and disc '15 are preferably, tho not necessarilyintegrally united by welding, or otherwise to form a single mounting member, in which the rounded head of the pivotal portions of the contact elements 5 are loosely clasped against withdrawal. Thus the annular assembly of contact elements are retained in their assembled form as a unitary structure. It will be noted in Fig. 5 that the arcuate flanges of the discs 15 and 16 together extend slightly more than half way around the circular head of the contact elements. These discs 15 and 16 are carried upon a sleeve or mounting ring 10 as before referred to.

Theconstruction shown in Fig. 6 is in some respects a composite of the two mounting discs, 11 and 8 shown in Fig. 3. The disc 17 illustrated in Fig. 6 is laterally oifset at 18 to form the shoulder or annular ledge upon which the contact elements'5 rest when in their innermost position. The outer margin of this offset portion 18 of the disc 17 is reversely bent to form an annular grooved socket or recess 19 in which the rounded head- 20 of the contact elements 5 are seated for rocking movement.

Inasmuch as the overhanging portions of the commutator bars 3 are shown in Fig. 6 as shaped to agree therewith. Such variations have been shown in Figs. 3 and 4, 5, 8 and 10. In lieu of mounting the disc 7 in a sleeve or collar 10, it may be clamped against the lateral face of the commutator b a clamp nut 21, as shown in Fig. 6. Fig.- differs from Fig. 6 only in the addition of a retaining disc 22, projecting intermediate the assemblyof oscillatory contact arms 5 and the face of the commutator, to "prevent the displacement or disengagement of the contact elements 5 from the supporting disc 17 when the latter is disconnected from the motor. The disc 22 is preferably formed integral with the disc 17, or attached thereto by welding or riveting. In both Figs. 6 and 7 the contact arms are capable of radial oscillation under centrifugal influenceagainst the yielding resistance of the surrounding band 6.

It sometimes occurs that one of the contact elements being loosely supported between the neighboring contact element is inclined to move outwardly under centrifugal influence in advance of the remainder of the assembly. The contractile band 6 being flexible will 10- cally yield to permit such premature oscillation of a small group of such contact elements,- either together or singly. While such premature oscillation is not a serious defect, since it occurs only momentarily in advance of the general extension of the remaining slugs of the series, into short circuiting engagement with the commutator bars, it is nevertheless from an engineering stand-point, more desirable to have the contact elements all move in unison. To this end, in Fig. 8 there is shown the construction illustrated in Fig. 5 and heretofore described, to which is added an inflexible conical or tapered collar 24, exteriorly surrounding the oscillating contact arms 5 27 so that such marginal flange 27 overhangsthe tapered conical collar 24. In lieu of locating the, surrounding contractile spring 6 directly engagement with thecontact elements 5, such contracting spring 6 is located in the convergent space between the tapered collar 24 and the peripherally projecting portions of the disc 15. The contractile .tendency of the band 6 within the convergent space intermediate'the tapered collar 24 and the peripheral portion of the disc 15 tends to shift such tapered collar 24 laterally toward the commutator. and hence causes pressure upon the projection 25 or the side of the indentation 26. This lateral pressure ofthe collar 24 tends to oscillate such contact elesion the premature movement of the contact elements is prevented. The pressure of the contact elements 5 upon the tapered collar 24 necessary to expand the contractile band 6 requires the operation of all or substantially all of the annular series of contact arms.

' The premature movement of the contact arms or small groups of arms will be insuficient to effect the distension of the band 6 and hence such arms having premature tendency to oscillate will be retarded until the prior assembly of contact elements is influenced by centrifugal tendency suificient to overcome the tension of the spring and move into contact with the commutator bars as a unit.

While the constructions heretofore described employing the contractile band 6 circumferentially surrounding the assembly of contact elements is the preferred construction,- to meet certain other conditions of use, wherein the presence of an exteriorly arranged spring member might prove objectionable, two alternative forms of yielding resistance to the oscillation of the contact armsare shown in Figs. 9 and 10. In Fig. 9 the mounting of the elements is quite similar to that shown in Fig. 3. The contact element 5 shown in Fig. 9 is provided .with the same fulcrum notch 7 in its inner margin engaging over the margins of the fulcrum disc 8. The disc 8 is ofiset at 9 as before describedto form a rest or support for the contact elements when retracted. However, in lieu of fixedly mounting the disc 11 which overhangs the pivotal ends of the contact elements as shown in Fig. 3 the corresponding disc 28 in Fig. 9 is provided with a projecting sleeve or hub 29, having sliding engagement upon the motor shaft. Inside the hub 29 and engaging the terminal flange 30 thereof at one end and abutting at its opposite end upon a ring or collar 31 secured upon the motor shaft is ahelical spring 32. The contact element 5, however, instead of beingprovided with concentric heads, are provided with eccentric Tugs or noses 33, which as the contact arm 3 moves outwardly, bears against the interior face of the reciprocatory disc 28 pressing such disc'outwardly against the tension of the spring 32. Upon reduction of speed the expansion of the spring 32 placed under tension by the outward swinging movement of the contact elements 5 urges the reciprocatory disc 28 toward the commutator as the speed decreases. The pressure of such disc 28 against the eccentric nose or lug 33 of the contact element 5 tends to oscillate such elements inwardly to their retracted positions at rest upon the ledge or shoulder 9 of the fulcrum disc 8. Thus the action,

function and result of the contact elements shown in Fig. 9 is the same as that previously described, but their movements are under the control of a helical compression spring 32 enclosed within the annular series of contact elements.

, Fig. 10 difiers from Fig. 9 only in the fact that itis fulcrumed upon a lug or projection 34 seated within the inturned flange of a supporting disc 35, stationarily mounted upon the motor shaft. The contact arm 5 in this construction is provided with an inwardly extending lug or shoulder 36, which engages a sliding collar 37, movable toward the commutator against the tension of an interposed spring 38. As the speed of thecrotor diminshes, thereaction of the spring 38 pressing the collar 37 outwardly against the lug 36, oscillates the contact elements 5 inwardly until arrested by engagement upon the peripheral margin of the collar 37 The construction shown in Fig. 11 differs from those previously described thru the fact that the slugs or centrifugally controlled members do not directly engage the commutator bars, but in lieu thereof, the centrifugally cont-rolled slugs 5 are enclosed or housed within a peripherally flanged or cup disc 39, the marginal flange of which is slotted to form a succession of tongues or yielding fingers 40, overhanging the peripheral faces of the assembly of slugs. The slugs in their outward movement against the resistance of the elastic band 6 engage the flexible overhanging fingers or tongues 39, flexing such fingers outwardly into wiping engagement with the metal faces of the commutator bar. To insure a'clean wiping contact, the extremities of the flexible fingers or contact slugs 39 are preferably bent outwardly and backwardly to afiord bearing surfaces or contact shoes of greater extent. The slugs are retained within the overhanging fingers or contact tongues, intermediate the supporting disc, and the core of the commutator. Tf a unitary structure is desired, capable of being removed from and applied to motors, as a unit, the disc may be mounted upon a collar or hub 41, which carries at the inner side of the series of slugs a second disc or ring 42 to retain the slugs or centrifugally controlled members when the unit is removed from the motor.

From the above description it will be apparent that there is thus provided a device of the character described possessing the 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 rinciple involved or sacrificing any of its a vantages.

While in order to comply with the statutes the invention has been described in language more or less specific as to structural features,

it is to be understood-that the invention is not limited to the specific details shown, but that the means and construction herein disclosed comprises the preferred form of several modes of putting the invention into eflect,

and the invention is,therefore, claimed in any of itsforms or modifications within the legit-- imate and valid scope of the appended claims.

Having thus described my invention, I claim:

1. In a short circuiting device for commutators, .a series of oscillatory slugs located in concentric spaced relation with the lateral face of the commutator, a fulcrum bearing for the slugs of the series, an annular helical spring band surrounding the-series of slugs against the tension of which the slugs are oscillated outwardly into contact with the commutator bars. 7

2. In a short circuiter for motors, a commutator having overhanging commutator ba rs, an annular series of oscillatory contact arms arranged interiorly of the overhanging bars of the commutator and extending therebeyond with which the arms engage when distended, a mounting for said oscillatory contact arms located in fixed spaced relation beyond the end ofthe commutator and on which the contact arms are fulcrumed for to and fro oscillatory movement in radial directions relative to the'axis of rotation 'of the commutator, and a helical spring, the ends of which are interconnected into annular form, exteriorly engaging the arms intermediate their fulcrums and their points of engagement with the overhanging commutator bars against the tension of which the arms are distended by centrifugal influence into contact engagement with the over hanging portions of the bars to electrically interconnect the bars one with another.

3. In a short circuiter for motors, a series of oscillatory arms arranged in annular series in proximity to the lateral face Jf the motor commutator and subject to oscillation by centrifugal influence radially in relation with the axis ofmotation of the commutator,

a fulcrum mounting for the armslocated in fixed spaced relation with the commutator, and a helical spring having its end-s interconnected to form an annular elastic band, exteriorly surrounding the annular series of oscillatory arms against the tension of which said arms are oscillated by centrifugal influence to eifect the interconnection of the commutator bars one with another.

4. In a short circuiter for motors, a series of oscillatory arms each comprising a body having substantially circular heads at its opposite extremities, and -medially contracted intermediate thecircular head, said arms being arranged in annular series in proximity to the lateral face of the motor commutator and subject to oscillation bycentrifugal influence radially 'in relation with the axis of rotation of the commutator, a fulcrum mounting for the arms located in fixed spaced relation with the commutator, and an elastic band exteriorly surrounding said arms at a substantially mid-length point against the yielding resistance of which the arms are swingingly adjustable under centrifugal influence to elfect the electrical, interconnection of the commutator bars one with another. 7

5. In ashort c1rcu1t1ng devlce for motors, a serles of oscillatory arms arranged in annular series in proximity to the lateral faceof the motor commutator and subject to oscillation by centrifugal influence radially in relation with the axisof rotation of the com-. mutator, a fulcrum mounting, for the arms located in fixed spaced relation with the commutator, a stop member fixedly l'ocatedinteriorly of the annular series of oscillatory arms limiting their approach toward the axis of oscillation, and an annular elastic band exteriorly surrounding the annular series of arms against the yielding resistance of which the arms are movable away from the stop member under centrifugal influence to effect electrical interconnection of the commutator bars one with another. 6. In a short circuiter for motors, an annular series of oscillatory arms arranged in parallel relation in proximity to the face of the motor commutator and radially movable of which the arms are capable of radial swinging movement about the abutting engagement with said disc, 7 I

7. In a short circuiting device for commutators, a series of oscillatory contact members located in concentric spaced relation with the bars of the motor commutator, a mounting for said contact members including a stationary flange overhanging the outer ends of said contact members and upon which said members abut during their swinging movement, said mounting also including a second stationary flange located interiorly of the annular series of contact members upon which the contact members rest when retracted, and an elastic contractile band exteriorly surrounding the series of contact members against the tension of which said members are moved into short circuiting engagement with the commutator bars-by centrifugal influence. j w

8. In a short circuiting device for commutators, a series of oscillatory contact members located in concentric spaced relation with the bars of the motor commutator, a mounting I tension of whihh the dumbbell shaped eletill maaooe for said contact members including ,a flange overhanging the outer ends of said contact members and upon which said members abut during their swinging movement, said mounting also including a second flange stationarily located interiorly of the annular series of contact members upon which the contact members rest when retracted, and a spring against the tension of which said members are movable under centrifugal influence into short circuiting engagement with the commutator bars.

9. In a short circuiting device for commutators, an annular series of oscillatory contact members located in juxtaposition to the commutator bars and engageable therewith upon outward oscillatory movement under centrifugal influence. a fulcrum mount-ing for said contact members, and a radially eX- pansible and contractible spring ring against the yielding tension of which the contact members are movable into engagement with the commutator bars.

10. In a short circuiting device for commutators, an annular series of oscillatory contact members located in juxtaposition to the commutator bars and engageable therewith upon outward oscillatory movement under centrifugal influence, a fulcrum mounting for said contact members, and an annular helical spring having peripheral engagement with each of the contact elements of the series against the yielding resistance of which the contact members are movable into short circuiting engagement with the commutator.

11.-As an article of manufacture, a short circuiting element for motor commutators comprising a substantially dumbbell shaped element, having arcuate endsand marginal indentations, between such arcuate ends.

12. A short circuiter for motor commutators including an annular series of substantially symmetrical dumbbell shaped contact elements having arcuate ends, and marginal indentations intermediate said arcuate ends, a mounting for said elements and yielding spring resistance means, against theyielding ments are movable into short circuiting engagement with the commutator bars.

13. In an apparatus of the character described, a rotatable shaft, contacts arranged about said shaft, a pair-of plates secured to the shaft and having their peripheral edges formed to provide an annular supporting channel, of substantially circular cross section,contact members supported in said channel for movement into engagement with said contacts, and means tending to holdsaid contact members out of engagement with said contacts.

14:. In an apparatus of the character described, a rotatableshaft, cont-acts arranged about said shaft, a pair of plates secured to the shaft and having their peripheral edges formed to provide an annular supportingchannelhaving an annular slot at one side thereof, contact members pivotally supported at one end in said channel and adapted to move outwardly into engagement with; said contacts, one edge of said annular, slot being adapted to stop the inward movement of the contact members, and means tending to hold the contact members in engagement with said edge.

15. In an apparatus of thecharacter described, the combination in a unitary structure of a support adapted to be secured to a shaft, and a plurality of contact, ;members pivotally supported at the periphery of said support and extending laterally therefrom in overhanging relation thereto, said support comprising a pair of plates disposed adjacent to one another at their hub portions and having their outer marginal portions flared outwardly to provide supporting and stop ping means for said contact members.

16. In an apparatus of the characterdescribed, a rotatable shaft, contacts arranged about said shaft, a pair of plates secured to the shaft and having their peripheral edges formed to provide an annular supporting channel, contact members supported in said channel for movement into engagement with said contacts, and means tending to hold said contact members out of engagement with said contacts.

17 In apparatus of the character described,

a rotatable shaft, contacts arranged about said shaft, a pair of plates secured to the shaft and having their peripheral edges spaced one from the other to afford an intermediate recess to receive the ends of a series of contact members, movable contact members held in said recess by the peripheral margin of one plate overhanging said contactmembers and the peripheral margin of theother plate engaging beneath said contact members said contact members being movable into engagement with said contacts and yielding means exteriorly disposed relative to said series of contact members tending to hold said contact members out of-engagement with said contacts. v f I 18. In an apparatus of the character described, a rotatable shaft, contacts arranged about said shaft, a pair of plates carried by the shaft, an annular series of movable contact members for movement into engagement with said contacts, the peripheral margin of one of the plates overhanging the series of movable contact members to retain said members in their assembled relation, the peripheral margin of the other of the plates extending interiorly of the series of movable contact members and forming a limiting stop for scribed, arotatabl shaft, contacts arranged plate.

about said shaft, a pair of platesintercom:

with said contacts, one of the plates being.

adapted to stop the inward movement of the contact members, and means tending to hold the contact members in engagement wlth said 20. In an apparatus of the character ddscribed, the combination in. a unitary structure, of a support adapted to be secured to a shaft, and a plurality of'contact members pivotally supported at the periphery of said support and extending laterally therefrom in overhanging relation thereto, said support comprising a pair of plates. interconnected one to the other at their hub portions and having their Eiuter margins spaced one from the other to provide supporting and stopping means for said contact' members.

21. In a short circuiting device for com-- mutators, a serles of contacts to be engaged;

a circular series of independent oscillatory contact slugs concentrically arranged in juxtaposition to the lateral face of the commutator and movable radially into engage ment with the commutator bars by centrifugal influence, said slugs being indented on their inner edges, a supporting disc, the periphery of which is. straddled by the indented slugs, and a contractile band against the tension of which the series of slugs is capable of outward swinging movement into engagement with said contacts.

22. In a short circuiting device for commutators, a disc mounted in a parallel plane spaced from the lateral face of the commutator, a series of oscillatory contact slugs arranged in a concentric series about said disc with their inner edges resting upon the periphery of the disc, and an elastic band surrounding the slugs, against the tension of which the slugs are movable into engagement with the commutator bars by centrifugal influence.

23. Ina short circuiting device for commutators, a series of oscillatory contact slugs having indentations in'their opposite edges, a disc positioned in spaced relation with the lateral face of the commutator over the periphery of which the indentations in the inner edges of the slugs engage, and an elastic band engaging in the indentations in the outer edges of the slugs against the tension of which the series ofslugs is movable into engagement with the commutator bars under centrifugal influence.

24. In a short circuiting device for commutators, a circular series of oppositely in= dented oscillatory contact slugs a supporting disc therefor engaging within the indentations at one side of the slugs, and an elastic band engaging in the indentations in the opposite side of the slugs against the tension of which the series of slugs is expansible into contact with the'commutator bars under centrifugal influence.

25. In a short circuiting device for com mutators, a circular series of centrifugally actuated oscillatory contact slugs having indentations in their inner edges, expansible into contact with the commutator bars under centrifugal influence, and a supporting disc about the periphery of which the slugs are arranged with the periphery of the disc normally engaging within said. indentations.

In testimony whereof,'I have hereunto set hand this25th day of July A. D. 1924.

EVERETT P. LARSH.

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