US2295409A - Commutator - Google Patents

Description

COMMUTAT OR Filed July 17, 1941 INVENTOR Edward J/(re/z, J7?

ATTORNEY Patented Sept. 8, 1942 UNITED STAT ES PATENT OFFICE COMMUTAIOR.

Edward}.- Kreh, Jig, Edgewood, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of" Pennsylvania Application July 17, 1941, Serial-N0. 402,724,

7 Claims.

consist of a large number of copper bars whichare separated by mica spacers and assembledinto a cylinder which is mounted on the-shaft of the machine. In the so-called V-ring construction,

the bars have U -grooves in their ends and are clamped between V-rings; under heavy pressure,

the V-rings being supported from the shaft of the machine. Whensuch acommutatonisin operation, its temperature rises and the parts tend to expand. The copper bars; however, have a higher coefficient of thermal expansionthan the V-rings and other supporting parts, whichare normally made of steel, and; thus thebars tend to expand more than the supporting elements between which they are clamped. This effect isaggravated by the fact that the bars reach higher temperatures than the supporting elements because of v the frictionof. the brushes which ride on the bars and theheating effect of thecurrents which flowin thebarsl porting and clamping elements-,- and stresses are setup which would tend to; cause buckling and distortion of the bars if no provision were made to permit this expansion. This greater expansion of th bars with respect to the supporting elements hasmade it necessary in medium andlarge sizecommutators to devise-constructions in which a certain. amount of flexibility or resilience is provided in the. clamping elements to permit them to yield or moveslightly as the bars expand and contract, and thus fol low up the expansion and construction of, the bars without releasing or substantially changing the clamping pressure on them.

One construction of this type which has been found satisfactory for some typesof machines is shown in the patent to G. W. Penney, No. 2,045,405, issued June 23, 1936, and assigned to Westinghouse Electric & Manufacturing Company. In the construction shown in this patent, the commutator bars are. clamped between V-rings which are mounted on a bushing-supported on the shaft. One of the rings is mounted on the bushing by means of a flexible, annular plate which permits it to yield and follow,

the expansion and contraction of the, bars, and

the V-rings are drawn together by means of through bolts extending in the annular space-- Thus the copper bars tend to expand more than the steel. sup-.

between the commutator bars and the bushing- These bolts serve to maintain the clamping pressure between the V.-rings, and are sufficiently resilient longitudinally to permit the slight movementof theflexibly, mounted V-ringwhich is necessary. to permit the expansion. of, the bars.

In. the ease of high speed commutators, such as are used on turbogenerator exciters, for example, the outside diameter of the commutator must be kept as small as possible in order to avoid excessive peripheral speeds, since such machines are usually driven at high speeds, such as. 3600 R. P. M. The shaft, diameter inmachines of this type is also relatively large, andv there. is, not sum.- cient'room to place the throughbolts and through bushing of the construction just described hetween the shaft and commutator bars without exceedin the permissible limit for the outside diameter of the commutator. For this reason, it. has been necessary in the past in machines of this. type to use the. shrink. ring type of. commutator in which the bars are held onto a sleeve on the shaft by meansof steel rings shrunk. in position over the bars, This type of construction is considerably more expensivethan the V- ring type, andthe present invention provides a construction by. which the V-ring type of coma mutator. can be used on high speedmachines,

The principal object of the invention, therefore, is to provide a commutator construction which is. especially suitable for high-speed.commutators of relatively small diameter.

A further object of the. inventionis, to. provide a commutator construction of. the. V-ringv type having suflicient flexibility to permit thermal expansion of the commutator bars, and. which requires aminimum of space sothat the out.-

side diameter of the commutator can be kept.

small.

Amore specific object of the invention. is to provide a v-ring commutatorconstruction in which sufficient, flexibility is provided to permit expansion of. the commutator bars, and which re quiresno through bolts or through bushing so that the space required is relatively small.

Another object of the invention is, to provide a V-ring type of commutatorconstruction inwhich one of the .V -rings is flexibly mounteddirectly on the shaft, and in which provision is made for assemblingthe commutator on the shaftvwithout permitting deflection of the flexible mounting during such assembly.

Other objects and advantages of the invention. will be. apparentfrom the following detailed de-,

scription, taken in connection with the accompanying drawing, in which- Figure 1 is a longitudinal sectional view of a commutator embodying the present invention and a portion of the machine with which it is used;

Fig. 2 is a partial transverse sectional view approximately on the line 11-11 of Fig. 1;

Fig. 3 is a partial transverse sectional view approximately on the line IIIIII of Fig. 1; and

Fig. 4 is a longitudinal sectional view similar to Fig. 1, showing a modified embodiment of the invention.

The invention is shown in the drawing as applied to a commutator for a high speed dynamoelectric machine, such as a turbogenerator exciter, which has a shaft I on which are mounted the commutator 2 and armature 3. In the particular machine selected for the purpose of illustration, the central portion of the shaft, on

8 formed in its periphery, and the armature conductors 9 are placed in these slots in the usual manner.

The commutator 2 consists of a plurality of copper bars ll] of generally wedge-shaped crosssection, which are assembled to form a commutator cylinder, as shown in Fig. 3, the individual bars being separated by spacers ll of mica, or other suitable insulating material. Necks or risers 12 are provided at one end of the bars and the armature conductors 9 are connected to the necks. The commutator bars l0 have V-grooves formed in each end, and the commutator cylinder is clamped between V-rings l3 and M which engage in these V-grooves, and which are insulated from the bars ID by mica V-rings IS.

The rear V-ring I3 is intended to be mounted directly on the shaft I, and for this purpose it is provided with a mounting-portion l6, which is bored to fit on the shaft I with a press fit so that the portion I5 is adapted to be rigidly mounted on the shaft. The V-ring i3 is connected to its mounting portion l6 by a thin section I! which forms a flexible annular plate, thus permitting a certain amount of axial movement of the ring l3 without disturbing its rigid mounting on the shaft.

The V-rings l3 and M are connected by a tension member l8, which is preferably a hollow bushing extending between the V-rings, and having sufficient axial resilience to permit the slight axial movement of the V-ring [3. The internal diameter of the bushing I8 for most of its length is made large enough so that it fits over the shaft l with a small clearance, but at its end opposite to the V-ring l3, it has a portion 19 of reduced internal diameter which is adapted to fit on the shaft 1 with a press fit to secure the bushing [8 to the shaft. The bushing l8 may be attached to the V-ring l 3 in any suitable manner. As shown in the drawing, the V-ring is internally threaded at 20 and the bushing I8 has corresponding threads cut on it and is screwed into the V-ring l3 or otherwise made unitary therewith, in effect, by other suitable means. The \'-ring I4 is slidably mounted on mutator on the shaft occurs.

the opposite end of the bushing l8, and means are provided on the bushing for forcing the V- ring l4 against the commutator bars to apply clamping pressure between the V-rings. This clamping means preferably consists of a ringnut 2| which is threaded on the end of the bushing l8 and engages in an annular recess in the V-ring H.

In assembling the commutator, the bushing 18 is first attached to the V-ring [3 by means of the threads 20, or other suitable means, and the commutator bars I!) are then assembled between the V-rings. The bushing I8 is then rigidly held by a support (not shown) against its portion I9 and clamping pressure, which may be as high as 23 tons, or more, is applied to the V-ring It, so that the commutator bars are securely clamped between the two V-rings, the V-ring l4 sliding on the bushing portion l9 under the intense applied pressure. The retaining ring-nut 2| is then screwed tightly against V-ring M for maintaining the commutator bars under pressure after the assembling external clamping pressure is removed. Since the bushing 18 is rigidly secured to the ring [3, the bushing I8 will be in tension and will serve as a tension-member between the V-rings to maintain the desired clamping pressure on the commutator bars. After the commutator has been assembled and seasoned, it is placed on the shaft l of the machine by pressing it axially into position, the mounting-portion 16 of the V-ring l3 and the portion IQ of the bushing I8 securing the commutator to the shaft with a press fit. The press action between the shaft l and the bushing-pop tion l9 causes the bushing to expand and results in a press fit between the V-ring I4 and the bushing-portion l9, anchoring it thereto.

It has been found that, in the case of turbogenerator exciters, which are driven directly from the turbine which drives the generator, it is not necessary to key the commutator to the shaft, since there is no torsional vibration or pulsation in a turbine drive and no slippage 0f the com- For other applications in which torsional vibration or pulsating torques may be applied to the shaft I, it may be desirable to key the portion 19 of the bushing l8 to the shaft in order to prevent circumferential displacement of the commutator.

Since the commutator is assembled on the shaft by pressing it into position axially from the right-hand end of the shaft, as viewed in Fig. 1, it is apparent that the flexibl plate I! would be deflected by the axial pressure on the mounting-portion 16 of the V-ring l3 and would be collapsed against the body of the ring. In order to prevent this effect, a plurality of internally threaded holes 22 ar provided in the mounting-portion IS, the number and position of these holes corresponding to the number and position of the flutes 4 in the shaft l, or other suitable opening in the armature spider. Prior to assembling the commutator on th shaft, suitable set-screws 23 (Figs. 2 and 3) are inserted in the threaded holes 22 and tightened against the V-ring I 3 to maintain the flexible plate I! in its undeflected position while the commutator is being pressed on the shaft. After assembly of the commutator on the shaft, the set-screws can readily be removed since they are easily accessible through the flutes 4 of the shaft or spider, as clearly shown in Fig. 2.

With some shaft and armature core designs, however, it might not be possible to locate the holes 22 in such a position that the set-screws placed in them would be accessible after'th commutator is placed on the shaft. In such cases, the holes 22 may be omitted and the construction shown in Fig. 4' may be employed. In this embodiment of the invention, the construction of the commutator is the same as that previously described, except that a plurality of struts or pressure-bars 24 are placed in longitudinal grooves cut in the internal surface of the bushing I 8; The lengths of these struts 24' are such that they normally engage the mounting-portion 16 of the V-ring I3. The bushing l8 isstill free to stretch under increased load due tozcopper-expansion, since it is. attached to the struts only at the end [9. The struts prevent deflec tion of the flexible plate I! during the pressed.- fit assembly of the commutator on the shaft.

The effect of the construction described herein will be readily apparent. When the commutator is in operation and the copper bars I become heated, they tend to expand more than the steel supporting members, and theflexible plate I! of the rear V-ring I3- permit this ring to move axially suflioiently to allow the expansion of. the bars. The bushing or tension member Iilis made of sufliciently thin cross-section, so as to have enough axial resilience to permit this movement of the ring l3 to take place, and: thus the ring is permitted to move a smallamount back and forth and follow the expansion and contraction of the commutator bars l0 without releasing or materially changing the clamping pressure on them. Since one of the V-rings is mounted directly on the shaft, no through bushing i required for the commutator, and no through bolts are necessary since the tension member l8 performs the function for which such bolts, have been used in prior constructions. Thus, the radial space required between the shaft and the bars for the supporting and clamping elements of the commutator is reduced to a minimum, making possible the use of V-ring type commutators on high speed machines in which the outside diameter of the commutator must be kept small. The use of the bushing. I8 is also advantageous in that it avoids the concentrations of stress which occurred around the heads of the previously used bolts and thus effects a uniform distribution of stress around the circumference of the V-rings. It will be apparent, therefore, that the new construction offers many advantages in that it is very compact and occupies a minimum of space, so that the relatively inexpensive V-ring type of construction can be used for high speed commutators, and also that it has sufficient flexibility to permit expansion of the copper bars, thus allowing the commutator to adjust itself to any thermal condition.

It is to be understood that the invention is capable of various modifications and embodiments, and is not restricted to the particular constructional forms shown in the drawing for purposes of illustration. The invention is not restricted, therefore, to the specific details of construction shown and described, but in its broadest aspect it includes all equivalent modifications and embodiments which com within the scope of the appended claims.

I claim as my invention:

1. A commutator stucture for mounting on the shaft of a dynamo-electric machine, comprising a plurality of commutator bars disposed to form a commutator cylinder and having V-grooves in their ends, oppositely disposed V-rings engaging in the V-grooves of. said. commutator cylinder,- one of said V-rings having. a mounting-portion adaptedtobemounted. directly on the shaft and having a. flexible portion which permits it. to move axially as the commutator bars, expand and contract under the influence of temperature changes, a cylindrical. tension-member extending between the V'-rings inside the commutator cylinder, means for removably but rigidly connecting one end of said tension-member to said flexibly mounted V-ring, the other end: of said tension-member being mounted on the shaft, the second V'-ring being supported by said tensionmember, and means on said tension-member for holding the second V-ring against the commutator bars whereby said commutator bars are maintained clamped between the V-rings.

2. A commutator structure for mounting on the shaft of a dynamo-electric machine, comprising a plurality of commutator bars disposed to form a commutator cylinder and having V- grooves in their ends, oppositely disposed V-rings engaging in the V-grooves of said commutator cylinder, one of said V-rings having a main. V- ring body-portion engaging the V-groove at its endof thecommutator, and also having amounting-portion mounted directly: on the shaft, and still further having a flexibleportion joining said main body-portion and said mounting-portion whereby to permit said main. body-portion to move axially as thecommutator bars expandand contract under the influence of temperature changes, a tension-member extending between the V-rings inside the commutator cylinder, one end of said tension-member being rigidly connected to the main body-portion of said. flexibly mounted V -ring, and its other, end being. mounted on the shaft, said tension-member encircling the shaft and having suflicient axial resilience to allow said movement of the flexibly mounted V-ringr, the second V-ring being-supported on said tension member, and means on the tension-member for holding the second V-ring against the commutetor bars whereby said commutator bars are maintained clamped between the V-rings..

3. A commutator structure for mounting on. the shaft of a dynamo-electric machine comprising av plurality of commutator bars disposed to form a commutator cylinder and having V-grooves in their ends, a V-ring engaging in the V-groove at one end of the commutator cylinder, means for flexibly mounting said V-ring directly on the shaft to permit it to move axially as the commutator bars expand and contract under the influence of temperature changes, a bushing fitting over the shaft inside the commutator cylinder, one end of said bushing being attached to said V-ring and the other end of the bushing being rigidly mounted on the shaft, a second V- ring supported on the bushing at its end opposite to said first mentioned V-ring and engaging in the V-groove of the commutator cylinder at that end, and means on the bushing for holding said second V-ring against the commutator bars whereby said commutator bars are maintained clamped between the V-rings.

4. A commutator structure for mounting on the shaft of a dynamo-electric machine comprising a plurality of commutator bars disposed to form a commutator cylinder and having V- grooves in their ends, a V-ring engaging in the V-groove at one end of the commutator cylinder, means for flexibly mounting said V-ring directly on the shaft to permit it to move axially as the commutator bars expand and contract under the influence of temperature changes, a bushinglfit ting over the shaft inside the commutator cylinder, one end of said bushing being attached to said V-ring and the other end of the bushing being rigidly mounted on the shaft, said bushing having a small clearance from the shaft and having sufficient axial resilience to permit said movement of the V-ring, a second V-ring supported on the bushing at its end opposite to said first mentioned V-ring and engaging in the V- groove of the commutator cylinder at that end, and means on the bushing for holding said second V-ring against the commutator bars whereby said commutator bars are maintained clamped between the V-rings.

5. A commutator structure for mounting on the shaft of a dynamo-electric machine compris ing a plurality of commutator bars disposed to form a commutator cylinder and having V- grooves in their ends, a v-ring engaging in the V-groove at one end of the commutator cylinder, a flexible annular plate mounted directly on the shaft and carrying said V-ring to permit axial movement of the V-ring as the commutator bars expand and contract under the influence of temperature changes, a bushing fitting over the shaft inside the commutator cylinder, one end of said bushing being attached to said V-ring and the other end of the bushing being rigidly mounted on the shaft, said bushing having a small clearl ance from the shaft and having sufficient axial resilience to permit said movement of the vring, a second V-ring supported on thebushing at its end opposite to said first mentioned V-ring and engaging in the V-groove of the commutator cylinder at that end, and means on the bushing for holding said second V-ring against the commutator bars whereby said commutator bars are maintained clamped between the V- rings.

6. A commutator structure for mounting on the shaft of a dynamo-electric machine comprising a plurality of commutator bars disposed to form a commutator cylinder and having V- grooves in their ends, a V-ring engaging in the V-groove at one end of the commutator cylinder, a flexible annular plate mounted directly on the shaft and carrying said V-ring to permit axial movement of the Vering as the commutator bars expand and contract under the influence of temperature changes, a bushing fitting over the shaft inside the commutator cylinder, one end of said bushing being attached to said V-ring and the other end of the bushing being rigidly mounted on the shaft, said bushing having a small clearance from the shaft and having sufficient axial resilience to permit said movement of the V-ring, a second V-ring supported on the bushing at its end opposite to said first mentioned V-ring and engaging in the V-groove of the commutator cylinder at that end, means on the bushing for holding said second V-ring against the commutator bars whereby said commutator bars are maintained clamped between the V-rings, and means effective during assembly of the commutator on the shaft of the machine for preventing movement of said flexible plate.

7. A commutator structure for mounting on the shaft of a dynamo-electric machine comprising a plurality of commutator bars disposed to form a commutator cylinder and having V- grooves in their ends, a V-ring engaging in the V-groove at one end of the commutator cylinder, a flexible annular plate mounted directly on the shaft and carrying said V-ring to permit axial movement of the V-ring as the commutator bars expand and contract under the influence of temperature changes, a bushing fitting over the shaft inside the commutator cylinder, one end of said bushing being attached to said V-ring and the other end of the bushing being rigidly mounted on the shaft, said bushing having a small clearance from the shaft and having suflicient axial resilience to permit said movement of the V-ring, a second V-ring supported on the bushing at its end opposite to said first mentioned V-ring and engaging in the V-groove of the commutator cylinder at that end, and means on the bushing for holding said second v-ring against the commutator bars to clamp them between the V- rings, said flexible plate having a plurality of threaded holes therein for the reception of screws during assembly of the commutator on the shaft of the machine to prevent movement of the flexible plate during such assembly.

EDWARD J. KREI-I, JR.

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