US2470096A - Commutator - Google Patents

Description

May 17, 1949. M. Y. ECK 2,470,096

COKMUTATOR Filed Dec. 1.2, 1945 ONM IN VENT OR.

ATTORNEYS Patented May 17, 1949 COMMUTATOR Myron Y. Eck, Dayton, OhioA Application December 12, 1945, Serial No. 634,479

1s claims. (o1. 111-321) Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes without payment to me of any royalty thereon.

This invention relates to a means for suppressing the radio frequency interference generated by motors, generators, and similar electrical apparatus involving the use of commutators.

It is well known that the commutation of current through the armatures of motors and generatorsconstitutes a troublesome source of radio frequency interference. This is particularly true in the case of air-borne radio, radar, and television equipment. It has been found that unless some type of noise suppression equipment is utilized for reducing the'interference created by the motors and generators, the operation of air-borne receiving equipment is greatly interfered with. To date, the primary effort in suppressing such noise has been directed along the lines of complete shielding of the motor and generator leads, the application of pi filters to the leads of such motorsand generators and also to the use of capacitors placed across the brushes of the machines. However, each of these remedies is beset with certain difficulties which limit their usefulness. For example, in the shielding of the aircraft electrical system, extreme care must be taken to see that perfect contact is obtained between couplings and between the facing surfaces of covers and mounting iianges. In the case of filters, the size of the filters which must be used to effectively suppress the noise due to commutation is such that the filters often weigh as much or more than the motors or generators creating the disturbance. It has further been found that l,

the use of capacitors across the brushes of the machines is not very effective since they tend merely to shift the noise frequency. As the result of an effort to flnda more effective and more expedient solution to this problem, I have discovered that by connecting adjacent commutator bars through resistors of the proper value, the noise level due to commutation may be reduced by as much as40 to 1A in the higher radio fre quencies, say from 600 kilocycles up. This method of reducing radio frequency interference, however, will also be found to have a beneficial effect on radio frequencies below 600`ki1ocycles.

Accordingly, it is an object of my invention to provide an electrical connection between adiacent commutator bars of rotary electric machines, said connection being resistive in character, to thereby reduce the radio frequency interference generated by said machines.

Another object of my invention resides in the provision of a resistive electrical connection between adjacent commutator bars of electric motors and generators to thereby reduce the radio frequency interference created by such motors and generators.

An additional object of my invention resides in the provision of a one-piece commutator of molded construction having a body portion of moldable resistance material and commutator bars or segments of highly conductive material located within said body portion and isolated from one another by said resistance material.

It is a. further object of my invention to reduce the radio frequency interference resulting from the commutation of electric current through the armatures of electric motors and generators by substituting a special molded resistance material for'the mica insulation commonly used between adjacent commutator bars of such motors and generators.

Still a further object of my invention resides in the provision of a resistor in the form of a band or ring adapted to be placed over or pressed against the end of a conventional commutator so as to provide a resistance path between adjacent commutator bars.

Several specific embodiments of my invention are shown in the attached drawings for accomplishing the foregoing objects, it being understood, of course, that my invention is not limited to any particular one of the embodiments shown butrather by the scope of the claims appended hereto.

In the drawings:

Fig. 1 is a cross-sectional elevation of a commutator in which the customary mica insulating sheets between the commutator bars are replaced by sheets of resistance material of equivalent size and shape.

Fig. 2 is a cross-sectional elevation of the commutator of molded construction, the commutator bars being located within a molded body of resistance material and separated from one ing between adjacent bars.

n j 2,470,096 s.

another by a relatively thin wall of resistance material so as to provide a resistance path for the current between adjacent commutator bars.

Fig'. 3 is a side elevation of a commutator of conventional design, i. e., with mica insulating sheets between commutator bars, but having an annular ring of resistance material mounted thereon so as to contact each of the commutator bars and thereby provide a resistance path for the current between adjacent bars.

Fig. 4 is an end view of the commutator shown in Fig. 3.

Fig. 5 is a fragmentary view of an alternative form of'construction of the resistor ring.

Fig. 6 illustrates a modification of the device shown in Fig. 3 and 4, the ring of resistance material being placed against the end of the commutator.' instead of around its periphery.

' As shown'in Fig. 1 of the drawings, a commutator consisting of wedge-shaped copper bars or segments i0 separated by thin sheets or strips of resistance material i2 i secured in any desired manner to the motor shaft I4. As herein shown, the commutator is supported on the motor shaft I4 by means of a mounting bushing I6 which is insulated from the commutator proper by means of a thin cylinder of insulating material i8. The particular type of commutator construction utilized may be of any desired type, the significant feature being the substitution of strips of resistance material I2 for the customary mica insulation between' adjacent commutator bars III. The resistance material i 2 used in place of mica for separating the commutator bars may be -of a composition form similar to that used in making resistors of the so-called carbon type, i. e., 'a composition lconsisting of a conducting material-such as powdered carbon or graphite,l a filter consisting of an inertrmaterial such as talc or clay, and a synthetic resin bonding agent. If desired, a metal such as gold, silver, copper, etc., in either powdered or flake form may be used in place of the carbon or graphite as the conducting material in the composition. The material is molded into strips of suitable size and thickness for use in a commutator of the type shown in ing olf of the resistance u'sed than it is when the conventional mica insulated commutators are employed. In this connection it has been observed that the presence of the resistance material between the commu-- tator bars tends to shift the point of sparkless commutation back toward normal as a result of the reduced distortion of the magnetic field.

If desired, a commutator employing my invention may be made in accordance with Fig. 2 of the drawings in which the commutator bars 28 are of "circular cross-section and are cast or molded Within a body of resistance material 22 of the composition type so as to form a commutator of one piece or integral construction having a predetermined ohmic resistance between adjacent commutator bars. The resulting commutator body may then be mounted on the motor shaft i4 with an insulating bushing 24 interposed between the commutator vbody and the motor shaft. Besides being inexpensive to manufacture, this type of commutator has the added advantage of not requiring any undercutting of the material interposed between the commutator bars. This results from the fact that good brush lubrication will be provided by the composition type of resistance material which is used in place of the customary forms of insulating material. Furthermore, by using bars of circular crosssection in.v place of the more customary square or rectangular ones, the resistance between the brushes and the advancing commutator bars will be gradually and smoothly reduced as the brushes approach the bars. As shown in Fig. 2, bars 20' and 20" are approaching brushes 26 and 28 respectively, as the commutator rotates in the direction of the arrow 30. The tapered or wedgeshaped sections of resistance material 32 and 34 located under the forward tip of each of the brushes 26 and 28 will result in a gradual taperbetween the brushes and the approaching bars which finally reaches zero when actual contact between the brushes 26 and 28 and the bars 20' and 28", respectively-is accomplished. Thus, sparking at the brushes is practically eliminated and the creation ofelectrical transients as a result of the sudden shock- Fig. 1. The value of 'the resistance to be used between adjacent commutator bars will vary with different types and sizes of motors and is controlled primarily by the potential difference exist- This potential difference-inv turn depends, of course, upon the potential difference between adjacent brushes. It is necessary that the resistance between adjacent bars be high enough to prevent excessive current flow from one bar toanother as otherwise this shunting of current from one bar to the next would interfere with the proper operation of the motor or generator and cause excessive heating ofthe resistance'material and in turn the commutator. On the other hand, the resistance must be low enough to permit a small current to flow between the adjacent bars of the commutator so as to-realize the beneficial eiect of my invention in reducing the radio frequency interference due excitation of the armature windings is avoided.

If desired, a conventional type of commutator provided with mica'insulating strips 43b 'between the commutator bars 38, as shown in Figs. 3 and 4, may be converted into a commutator incorporating the principles of my invention. This may begreadily accomplished by fastening a ring40 ture windings.

to the electrical disturbances resulting from commutation.

It has been found that the use of resistance material between commutator bars tends to reduce sparking at the brushes and also has a damping eifect on the transients created in the t armature windings during commutation. It appea-rs that the magnetic field of the motor or generator is less distorted when commutators constructed in accordance with my invention are of suitable resistance materialen the commutator so as to cause the intimate contact between each commutator bar 38 and the inner periphery of the ring 4 0. In this manner a resistance path is established between adjacent commutator bars so as` to enable a desired amount of current flow between adjacent arma- The ring 40 is preferably made in two halves which are placed on the commutator in the manner shown in the drawings and held securely in place by means of a clamping ring 42. A thin layer of insulating material 44 is preferably inserted between the ring 40 and the clamping ring 42 in' the manner shown in- Fig. 3.

The ring 40 may be molded or cast from a composition type of resistance material as shown in Fig. 3 and 4 or it may be constructed in the form ofa wire-wound resistor as shown in Fig. 5. As herein illustrated, the ring consists of a core 46 of any suitable insulating material about which a resistance wire 48 of"Nichrome," Manganin,"

etc., is served. The core material ll is preferably 'sumciently flexible to enable it to be bent into s.r circular shape after the wire is served thereabout so as to simplify the serving procedure. In the case ofthe wire-wound type of resistonthe ring is made in one piece instead of in halves as in the case of the composition type of resistor.

Fig. 6 shows an alternative type oi construction in which a ring of resistance material ill corresponding to the ring in Figs. 3 and 4 is pressed up against the end of a conventional type of commutator by means of a ilanged collar i! secured to the motor shaft Il by means of a set screw il. A thin disc of insulating material I6 is preferably placed between the collar 52 and the ring ll; Here again, as in the case of the construction shown in Figs. 3 and 4, the ring 50 may be molded or cast from a composition type of resistance material, though in one piece rather than in halves, or it may take the form of a wire-wound resistor as shown in Fig. 5.

While my invention has been designed primarily for use in connection with direct current motors and generators, it is to be realizedl that this principle may also be used in connection with alternating current motors of the universal type which make use of commutators for commutating the alternating current to the armature windings of the motor. The principles of my invention will be found useful wherever commutation of this character is utilized since the presence of the resistance material between the commutator segments or bars tends to reduce sparking at the brushes and also tends to reduce the transient currents arising within the windings of the machine as a result oi the commutation of current from one winding to another.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A commutator comprising a plurality of conducting bars arranged in spaced relationship with respect to one another, and means for electrically connecting each bar with an adjacent bar, said means comprising a molded high resistance element containing conductive material dispersed uniformly throughout insulating material, said element being in contact with each of said adjacent bars so as to provide a high resistance con-` ducting path between said bars ot substantially the same resistance at all normal operating temperatures of a motor or generator and of such a value as to suppress radio interference which would otherwise occur from commutation.

2. A commutator comprising a cylindrical core of insulating material, a plurality of conducting bars circumferentially spaced about the periphery of said core, and means for electrically connecting each of said bars with an adjacent bar, said means comprising a molded high resistance element containing conductive material dispersed uniformly throughout insulating material, said element being in contact with each of said adjacent bars so as to provide a high resistance conducting path therebetween of substantially the same resistance at all normal operating temperatures of said commutator andv being of a radiointerference-suppressing value.

3. A commutator comprising a plurality of conducting segments arranged in spaced relationship with respect to one another and sheets of high resistance material comprising conductive substances dispersed therein, said sheets being located between and in contact with adjacent segbetween, the enermax-sues e: said sheets being such that their resistance value will remain substantially the same overl the normal operating temperature range of a fmotor or generator.

4. A commutator comprising an annular series of conducting segments and sheets of high resistance material comprising dispersed conductive powdered materials interposed between and-in contact with adjacent segments so as to provide a conducting path therebetween.

5. The invention as dened in claim 4rv wherein said resistance material consists of a conducting material mixed with a conductive ller and a high resistance binder to form a solid body of resistance material.

6. A commutator comprising a generally cylindrical core of insulating material, a plurality of conducting bars circumferentially spaced about the periphery of said core, and a body of molded high resistance material disposed around and between said bars and around said core to form a commutator of unitary character wherein a high resistance conducting path is provided between neighboring commutator bars, over the i'ull area of their adjoining surfaces, the resistance value of said high resistance material being of great thermal stability and having radio interference suppressing properties when so used.

7. The invention as defined in claim ko wherein said bars are substantially circular in cross-section, but are slightly flattened at the commutator surface whereby together with the molded resistance material to form a smooth cylindrical commutator. a

8. A commutator comprising a plurality o! spaced conducting bars, insulating means for spacing adjacent bars and means for electrically connecting each bar with an adjacent bar, said means including molded resistance elements connected between adjacent bars, the resistance elements being adapted to allow a slight electrical iiow through their entire mass and to hold the flow stable under normal operating temperatures whereby to suppress radio interference.

9. In combination with a cylindrical commutator of conventional design having conducting segments and insulating sheets between adjacent segments, means for electrically connecting each commutator segment with an adjacent segment, said means including a resistor in the form of a ring, said resistor having molded high resistance portions engaging with each of said segments so as to provide a conducting path of high resistance and great thermal stability between segments, the combination having greater radio-interference suppressing qualities than an ordinary commutator.

l0. A commutator comprising conducting segments having outer peripheral brush engaging faces, sheet of insulating material between adjacent segments, and means for electrically connecting each segment with an adjacent segment, said means including a molded resistor in the form of a. ring mounted on said commutator, the inner peripheral surface of said ring engaging with the outer peripheral brush engaging faces of said conducting segments so as to provide a conducting path between segments, said path being of high resistance at all normal operating temperatures of an electric motor or generator and of such a value as to suppress radio interference due to commutation.

11. A segment separator for a commutator, said separator being a molded object adapted to ments so as to provide a conducting path there- 7l iit between the segments o! a cylindrical comamm of a composition incorporating a nonconductive' A,binder and an' electrically conductive powder .having lubricating properties for carbon brushes,

`the entire'seg'ment separatorbein'g adapted to pass only "a minute current i'rom segment to segment, but to pass the same value ot current at substantially all normal operating temperatures of an electric motor so that radio interference due to rough commutation will be materially reduced.

12. A commutator comprising a molded core of a dielectric composition of sumciently high resistance to prevent short circuits between bars embedded therein but suiiiciently conductive to allow minute current leakage from bar to bar. the composition of said core comprising a distributed finely divided conductive substance and a synthetic resinous binder therefor, slots of substantially circular cross section in the periphery of said core for the reception of substantially circular cross section conductive bars and substantially circular cross section bars mounted in said slots whereby to be partially encircled by the material of saidvcore. A 'l 13. A commutator comprising a substantially cylindrical assembly o! metallic-segments and high resistance separators for said segments. said commutator having an outer shoulder, a ring mounted on said shoulder, said ring being molded of plastic materialhaving a slightfbut stable leakage of current i'rom segment to segment when said ring is in close contact -with the outer curfaces of said segments at said shoulder. t

` MYRON Y. ECX.

nEFEnENcEs orrnn The following references are of record in tho file of this patent:

UNITED STATES PATENTS Number Name Date 465,970 Edison Deo. 29, 1891 773,881 Milch Nov. 1, 1904 780,046 Lamme Jan. 17, 1905 882.682 Heyland Mar. 24', 1908 1,511,316 Bastian Oct. 14, 1924 FOREIGN PATENTS Number Country Date 156,910 y(.rermany Jan. 3, 1904

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