US1568682A - Commutation - Google Patents

Description

Jan. 5 ,1926. v

. F. s. MARCELLUS COMMUTATION Filed Oct. 9, 1923 Inventor i Fredrick 5. Marcellus, y h W His Attorney.

Patented Jan. 5, 1926.

- UNITED STATES FREDRICK S. MARCELLUS, OF AMSTERDAM, NEW YORK, ASSIGNOR 'IO TRIO COMPANY, A CORPORATION OF NEW YORK.

1,568,682 PATENT OFFICE.

OOMMUTATION.

Application filed October 9, 1923. Serial No. 667,575.

and in particular for dynamo electric machines of the instrument class where variation in voltage at the commutator brushes is decidedly objectionable.

The well known commutation arrange ment where brushes rub against the commutator is in general unsatisfactory for instrument purposes not only because of the appreciable drop in voltage between the brushes and the commutator but particularly because of the variations in this socalled contact voltage under different conditions. If, in the common arrangement, the brush pressure is increased until the contact voltage is constant and of an infinitesimal value under all conditions as is essential for instrument purposes the friction be comes excessive and the wear on the commutator and brushes necessitates their frequent adjustment and replacement. Jodifications of the well known commutation arrangement have been proposed and used to a limited extent in instrument work .where the yoltage of the commutated circuit is substantially constant and of a high value as compared to the contact voltage ,and where the commutated current and speed of rotation of the commutator does not vary appreciably. The commutating type instrument has advantages which would make its use more general if the commutation difliculties could be eliminated or materially diminished.

It is a primary object of my invention to provide a commutating device in which the objections above referred to are substantially eliminated. Another object of my invention is to provide a commutating device where the contact pressure is automatically varied in proportion to the speed of rotation of the commutator. ther advantages of my invention will appear as the description proceeds.

In carrying my invention into effect I cut grooves in the commutator transversely of the commutator bars preferably in the form of a worm and provide brushes therefor out to fit the grooves in the commutator preferably in the form of worm pinions meshing with the worm cut in the commutator. These brushes are split and the parts thereof are resiliently caused to bear against opposite sides of the commutator grooves whereby greatly increased contact area be tween commutator and the brushes is made available and whereby the brush pressure and the friction incident thereto is materially reduced. The contact thus provided is largely longitudinal instead of radial and when the arrangement is in the form of a worm screw the work done by the screw increases with the speed of rotation of the commutator so that the contact pressure is proportional to the speed of rotation whereby the minimum contact pressure necessary for good commutation may be automatically maintained at all speeds. In such an arrangement the direction of rotation may be reversed without allecting the brush adjustment to the slightest extent.

The features of my invention which I believe to be novel and patentable will be pointed out in the claims appended hereto. For a better understanding of my invention reference is made to the following description taken in connection with the accompanying drawings, Fig. l of which represents my invention applied to an electric tachometer; Fig. 2 shows an end View of the commutator and brush rigging of Fig. 1 and also illustrates how the pinion brush may be utilized to operate a register; Fig. 3 is a detailed sectional view of a preferred form of brush pinion; Fig. 4 is a section taken on line 44 of Fig. 8; and Fig. 5 is a modification of my invention particularly designed for high current machines.

Referring to the drawings, and more in particular to Fig. 1, I have illustrated an electric tachometer connected to measure the I speed of a shaft 10. The stationary field member 11 of the tachometer is represented as a permanent magnet, between the poles of which a direct current armature 12 rotates. The commutator 13 of the armature 12 is represented as having at segments and electrically it is similar to the usual commutator. lts surface instead of being smooth has a worm thread cut therein. The commutator may be made up and assembled GENERAL ELEC- in the-usual way, and the wormcut therein after: assembling. 'Fhe brushes 14 comprise worm pinions accurately cut to mesh with the/worm on. the commutator and" su tably resistance. as compared: toathefcarbon brush:

usually used. The carbon brush or its equivalent is; desirable in the usual commutation arrangement because 0t its: wearing and lubricating properties-. In==my present arrangement thevbrush pressure may be reduced' to a very lowval ueso that a metal pinion-brush-may'beused, and" when it is considered that metal such as pure copper has several hundred times the conductivity of pure carbon the great advantage of my invention as regards voltage drop in the brushes themselves becomes evident;

pinion brushes 14 are-- mounted on suitable; shaftslh which are'pivotally'h'eld stationary frames 16 constituting the brush holders which ot course are insulated from and supported-by a stationary portion of the machine as is usual; The brush holders are connected by wires 17 with voltmeter 18 cal-ibrated 'inspeed units.

In an electric tachometer where friction is oh no particular importance, I mayw provide spring conducting clips or brushes 19 between the brushholder- 16 and the hub 20 of the pinion 14. ThlSflS l'lOt essential, however, since there isample contactingsurface between the bearing'ofshaft 15 and; the metallic brush holders 161' Ifdesired-an oil wick 2 1' maybe-provided to lubricate the worm gear or the commutz tor and brush rigging may be enclosed in a suitable chamber and" allowed to run in oil if desired.

To improve the. brush. contact I' have found it advantageous to split the pinions 1 1 in half, asrepre'sented in Fig. 3 andprovide a coiled spring 22 under tension betweenthe halves of the pinion tending to rotate one-halt of the pinion with respect to the other half. A suitable cavity is provided about the shaft 15.to accommodate the spring the ends otwhich are secured'to the-two halves of the pinion by bent-over portions 23 which fit into corresponding recesses; Before the'pinion is-placed in mesh with the worm the two halves of the pinion are rotated with respect-to each other to give the spring the desired tension. hen the pinion is in place, the spring tends to unwind and in doing so, acorresponding tooth in the two halves'of the worm pinion bear firmly against the opposite walls oi" the commutator groove with which it is in mesh and makes a good contact even though there should I happen to be considerable acceleration and deceleration of the commutator and even though the grooves may happen to be worn somewhat wider: than the teeth of? the pinion. This arrangement autom ati cally compensates for any wear which may ake-v p ae n ake q n a ju me ofthebrushes. unnecessary. It will be noted however, that the contact pressure is adjustableaby adjusting the tension of the spring 22 rather than pressing the brushes radially againsti the commutator as is usually the case.

With the arrangement; described, it will be evident that when the commutator speed is very low, the work done by the worm in driving the pinions; will-beaminimum yet a liberal andexcellent metal to-qnetal contact between-the voltmeter 18'and the coils of the armature 12 will be maintained. As the speed increases, the work done in turning the inionswill increase and conseuently the contact pressure will increase. This work is very small in any case although it conditions make it desirable the amount of work done by the worm may be increased by increasing the pitch of the worm or increasing the tension of -the spring clips 19. The increase in contact pressure with speed may be thus adjusted so that any tendency to produce a poor contact by vibration at high speed or an increase in contact voltage due to an increase of the current at high speed is automaticallycompensated t'or. I- have found that with this arrangement'on an electric tachometer, accurate results at all speeds are obtained. The pointer of the voltmeter does not fluctuate at very low speeds or at very high speeds as is the case with the usual form ot'electric tachometer,but gives a true, steady deflection at all speeds so-that the actual speed of the shaft 10 may be observed over the entire deflection range of the voltmeter.

The friction ofthis type of commutation arrangement is considerably less than the usual arrangement tor equal conditions of speed and'the value of currentcommutators. There .is no chance for poor contact due to the brushes sticking. Dirt particles do not affect the commutation. to the same extent as. in the usualarrangements The contacting surfaces are kept bright and polished due to the continuous rotation ofthe parts and the contacting surface of the brushes is continually changing, thus evenly distributingitlie wear and'assuring long life. The heat radiating capacity of both the commutator andthe brushes is materially increased over the usual arrangement, which is a decidedadvantage where large currents are to be commutatedfi Sparkingdue to brush vibration is entirely eliminated.

For electric meter 'workwhere a substantially constant voltage circuitis to be commutated and where themeter speed-doesnot vary materially andis of constant direction, the pitch of the worm gear may be reduced to zero and the spring clips 19 may be eliminated to decrease the friction to a negligible value. It will be an advantage, however, to retain the worm screw feature of the brushes since then 1 may operate the meter register from one of the pinions 14-, I have illustrated in Fig. 2 at 24:. The er:- tension 25 of shaft 15 between the brush holder and register will preferably be made of insulating material. On the tachometer the register may be calibrated to give the number of rotations of the shai't 1.0. The Worm screw feature is also advantageous ior meter work since it will tend to maize the brush friction loss more nearly proprn'tional to the other losses which increase with the load, giving a better load curve for the instrument.

lln Fig. 1, l have represented an electric circuit 26 containing a shunt 2 The shunt leads may be connected to the brushes the commutator machine by means of the switch 28 and the shaft 10 disconnected, thus representing the application of my invention to an ampere hour meter.

1 do not wish to limit my invention to electric meter work nor to the particular modification shown and described as it will be evident that the advantages of high conductivity of the brushes, a good contact under all conditions of speed and direction of rotation, the liberal heat radiating surface of the brushes and nmutator 211K the long wearing features of my improved type of commutation device will be advantageous in large dynamo electric machines such as power motors and generators.

In Fig. 5 I have illustrated a modification of my invention particularly applicable to machines of the la t mentioned class where large currents are to be couuuutated. The commutator 5'30 is grooved but instead oi: using a worm thread, thrust collars l-lil merely wave back and forth slightly in order to give the brush constructed in the term of a rack, a slight reciprocating motion. If this modification is used with a machine having the usual end play, the reciprocating motion will exist without the necessity of having the thrust collars 31 wave back and forth. The rack 32 may be split lengthwise and provided with a spring 33 between the sections analogous to the spring 22 of Fig. l, tending to move one section lengthwise with respect to the adjacent section to ass ire contact on both sides of the thrust collars and the rack teeth under all conditions. A suitable stationary guide and support 3% is provided through which the brush rack 32 may slide and the outer end of the rack may be extended to accommodate current leads preferably one for each section of the rack. In this modification, the contacting surface is materially increased over the usual carbon brush contact for the same width of brush. The advantageous features of metal to metal contact, the increased heat radiating surface, the automatic brush adjustment for wear, the inere? cl contact pressure with speed and the reversibility of the direction of rotation of the commutator without changing the adjustment or the brushes, are retained and I intend to cover such modification in certain of the claims appended hereto.

iVha-t I claim as new and desire to secure by Letters Patent of the United States, is:

l. A commutating arrangement for dynamo electric machines comprising a circumteren'cially grooved commutator and brushes bearing thereon cut to iitsaid grooves, said brushes having relatively movable sections litting into the same groove and resilient means for causing said sections to press against opposite sides of said groove.

A dynamo electric machine of the commutator type, means mechanically driven from said machine by a worm and pinion gearing, said worm constituting a commutator for said machine and said pinion constituting a brush for such commutator.

8. A brush for a commutator type dynamo electric machine comprising a pinion gear split at right angles to its axis and provided with resilient means tending to rotate the sections of said pinion with re spectto each other about said axis.

at. A brush tor a commutator type dynamo electric machine comprising a pinion gear split at right angles to its axis and provided with adjustable means tending to rotate the sections of said pinions with respect to each other about said axis.

5. A commutating device comprising a grooved commutator, rotatably mounted brushes meshing with the commutator groove and resilient means for producing lateral as distinguished from radial contact between said brushes and groove.

In witness whereof, I have hereunto set my hand this 8th day of October, 1923.

FRIEDRICH S. MARCELLUSZ

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