US2565120A - Commutator - Google Patents

Description

Aug. 21, 1951 L, R ER Em 2,565,120

COMMUTATOR Filed Sept. 20, 1949 %&

Horry D.Else.

ATTOR EY INVENTORS Leroy CCorter 0nd Patented Aug. 21, 1951 Leroy 0. Carter and Harry D. Else, Lima, Ohio, assignors to Westinghouse Electric Corporation,

. East Pittsburgh, Pa.,

. Vania a corporation of Pennsyl- Applica'tion September 20, 1949, Serial No. 116,766

The present invention relates to commutators for dynamo-electric machines, and more particularly to a high-speed commutator of relatively large diameter. s

Commutators which operate at relatively high speeds, such as 10,000 to "12,000 R. P". Ma, for example, are subjected to very high centrifugal forces, especially if the diameter is relatively large, and the commutator barsmust be adequately supported to withstand these forces, and the resulting stresses, so as to prevent deformation or relative movement of the-bars; One conventional solution of this problem is touse shrink rings placed over the peripheral surface of the commutator to support the bars between their ends. The use of such shrink rings, however, necessarily lengthens the commutator, and also requires the brushes to be placed in two or more groups on opposite sides of the rings, which introduces a difficult problem in the design of the brushholders.

This conventional shrink ring construction is not suitable for the commutators of machines such as aircraft generators, because of thenec essary lengthening of the commutator, with a corresponding increase in the length of the machine, which is undesirable, and in many cases not permissible. Furthermore, it "is desirable in aircraft generators to be able to remove the brush rigging as a unit axially of the machine 2 Claims. (01. 171--32V1) means are removed to the ends of the commutator, where-they do not interfere with the brushes, and do not require any undesirable lengthening of the commutator.

A more specific object of the invention is to 1 provide a high-speed commutator in which the V-grooves of the bars, and the V-rings which clamp the bars into the commutator cylinder, are moved axially inward toward the centers of the bars, so as to support the bars near the center of the commutator, and in which banding means are provided on the extending end portions of the bars to support the bars at the ends, the banding means being placed beyond the working surface of the commutator, sothat no increase in length of the machine in which the commutator is used is required.

Other objects and advantages of the invention will be apparent from the following detailed description, taken in connection with the accompanying drawing, in which;

when disassembly becomes necessary for maintenance purposes, and this, of course, would 'be impossible with a shrink ring of the usualtype extending radially above the surface of the commutator, with brushes on both sides of the ring. The use of handing wire around the center of the commutator, instead of a solid ring', is also undesirable, because it also would result in lengthening the commutator, and would require the brushes to be disposed in two groups on opposite sides of the wire. be a difficult problem in securing the banding wire in place, since the commutators of aircraft generators frequently run hot enough to soften or even melt solder. It will be apparent, therefore, that the design of a high-speed commutator for aircraft generators, and similar applications, presents a difficult problem, since the conventional type of construction cannot be used.

The principal object of the present invention is There would also 1 parent that its usefulness is not necessarilyre stricted to this particular application, and it is suitable for any type of machine in which high speeds are necessary. Fig. 1 shows atypical direct-current aircraft generator embodying the commutator of the present invention. The machine shown in this figure has a frame I on which pole pieces 2 are mounted, with field windings 3 carried on the pole pieces. The frame 1 is closed at one end by an end bracket 4 of any suitable construction, and at the other end 'by an-end bracket 5, which extends over the commutator 6. The machine has ashaft I supported on bearings in the endbrackets, and an armature 8 of any usual construction is mounted on the to provide a high-speed commutator construction in which the commutator bars are adequately supported against centrifugal forces without requiring any lengthening of the working surface of the commutator or any radial obstructions.

.Another object of the invention is to provide a high-speed commutator in which banding means are used to support the commutator bars against centrifugal forces, but in which the banding shaft 1 and has a winding of any suitable type connected to the commutator 6. Brushholders 9, carrying brushes which engage the commutator, are supported on 'a rocker ring I0 which is secured to the end bracket '5. An air shield 'Il may be secured to the outside of the bracket 5 in order to direct a blast of cooling air through the machine.

It will be apparent from Fig. 1 that if a shrink ring were applied .over the center of the commutator 6 in the conventional way, the brushes would have to be disposed in two groups, on opposite sides of the ring, and .that the commutator would have to .be .lengthened by (an amount at least equal to the width of the ring, resulting in a corresponding increase in the length of the machine itself, which is undesirable and frequently not permissible in aircraft generators. It will also be apparent that the presence of such a ring, extending radially beyond the commutator surface, would make it impossible to withdraw the rocker ring In and brushholders 9 axially from the machine as a unit, which is desirable when disassembling machines of this type. In accordance with the present invention, however, a commutator construction has been provided which utilizes banding means to support the commutator bars, but which avoids the difficulties involved in the use of. shrink rings, or other banding means, at the center of the commutator.

As shown in detail in Fig. 2, the new commutator comprises a plurality of commutator bars or segments l2, which are disposed in a cylinder in'the usual manner and insulated from each other by means of mica segments or other suitable means. Each of the bars I2 has a neck or near the center of the commutator, and the exriser l3 near one end for connection to the leads from the armature winding, and has opposed V-grooves I l on the lower side of the bar. It will be seen from Fig- 2 that the V-grooves M of the commutator bars are spaced a substantial distance from the ends 01 the bar towards the center of the bar, so that the ends of the bar extend axially beyond the V-grooves. Thus, as compared to the conventional design of commutator bars, the V-grooves have been moved inward toward the center a substantial distance. Each of the bars [2 is provided at the end adjacent the neck l3 with an end portion l5 which extends axially beyond the neck I3 and which has an upper edge or surface below that of the main or body portion of the bar 12. Similarly, the other end of the bar has an extending end portion IS with an upper edge which is below the edge of the main portion of the bar. Thus the end portions I5 and I6 of the bars l2, when assembled in the complete commutator, form cylindrical surfaces of reduced diameter, as compared to the diameter of the central cylindrical surface formed by the main part of the bars, which constitutes the working surface of the commutator engaged by the brushes.

The commutator is supported on a sleeve or bushing H, which may be mounted on the shaft 1 by spiders of any suitable type, or in any other desired manner. A V-ring [8, which has a snug sliding fit on the bushing l1, engages a shoulder adjacent one end of the bushing, and a second V-ring I9 is threaded on the other end of the bushing H. The V-rin-gs l8 and I9 engage in the v-grooves M to clamp the commutator bars l2 together in a commutator cylinder, the bars being insulated from the rings l8 and I9 by mica ,V- rings 20.

The overhanging ends of the bars I2, which extend beyond the V-grooves, are supported against centrifugal forces, by banding means applied to the end portions [5 and [6 of the bars l2. In the preferred embodiment of the invention shown in the drawing, the banding means at each end of the commutator consists of two tapered rings 2! and 22. The inner ring 2| is axially split at one point, as indicated at 23, and is tapered so that its largest diameter is towards the center of the commutator. The ring 2| is insulated from the commutator by a band or bands of insulating material 24, such as mica' tape, and an insulating ring 25. After the split tending ends are supported by the banding means 2| and 22. Thus, adequate support is obtained without requiring any banding means, or other supporting means, on the working surface of the commutator, and thus lengthening of the working surface of the commutator is avoided. The extending end portions iii of the commutator bars do not require any lengthening of the machine itself since they merely occupy space which is already available in the machine. Thus, the end portions It at one end extend under the leads 26 from the armature winding, in space which is normally unoccupied, and the end portions [6 at the opposite end extend under the rocker ring H] where ample space is available. No lengthening of the machine is required, therefore, and no division of the brushes into separated groups is necessary, so that brushholders of usual design can be used. Since there are no substantial radial obstructions, the brush rigging can be removedvaxially from the machine as a unit without difficulty.

It will be understood that any suitable type of banding means can be applied to the end portions 15 and I6 of the commutator bars. The particular double ring arrangement shown is desirable because it is readily applied, and the wedging effect obtained by the oppositely tapered rings makes it possible to tighten the inner ring 2I' against the bars during and after seasoning of the commutator. It is to be understood, however, that any other suitable banding means might be utilized, such as banding wire wound around the end portions [5 and it and soldered in place, or a single solid ring at each end heated and shrunk onto the commutator.

It should now be apparent that a commutator construction has been provided which is particularly suitable for high-speed commutators where high centrifugal forces are encountered.- A particular embodiment of the invention has been shown and described for the purpose of illustra tion, but it will be obvious that various changes and modifications may be made within the scope electric machine, said commutator comprising a bushing, a plurality of commutator bars disposed in a cylinder about said bushing, each of said commutator bars having opposed V-grooves in its inner side, said V-grooves being spaced a substantial distance from the ends of the bar toward the center thereof, V-rin-gs supported on the bushing and engaging in said V-grooves to clamp the bars into a commutator cylinder, the commutator bars having end portions extending axially beyond the V-rings, said end portions forming cylindrical surfaces of reduced diam eter, and banding means engaging said end por- 5 tions at each end of the commutator, said banding means tightly engaging the end portions to support them radially against centrifugal force, the banding means being held in place solely by engagement with the commutator bars.

2. A high-speed commutator for a dynamoelectric machine, said commutator comprising a bushing, a plurality of commutator bars disposed in a cylinder about said bushing, each of said commutator bars having opposed V-grooves in its inner side, said V-grooves being spaced a substantial distance from the ends of the bar toward the center thereof, V-rings supported on the bushing and engaging in said V-grooves to clamp the bars into a commutator cylinder, the commutator bars having end portions extending axially beyond the V-rings, said end portions forming cylindrical surfaces of reduced diameter, and banding means engaging said end portions at each end of the commutator, the banding means at each end comprising an axially split, tapered ring engaging the commutator bars,

and a solid, oppositely tapered ring engaging the first-mentioned ring and clamping the banding means tightly against the commutator bars to support them radially against centrifugal force, the banding means being held in place solely by engagement with the commutator bars.

LEROY C. CARTER. HARRY D. ELSE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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