US2520379A - Brush support - Google Patents

Description

Aug- 29, 1950 R. H. WARD 2,520,379

BRUSH SUPPORT Filed April 28, 1947 2 Sheets-Sheet l IN V EN TOR.

A TT ORNEYS.

Aug. 29, 1950 R. H. WARD 2,520,379

BRUSH SUPPORT Filed April 28, 1947 2 Sheets-Sheet 2 INVENTOR.

Patented Aug. 29, 1950 UNITED STATES PATENT OFFICE Superior `Carbon Products, Inc.,

Cleveland,

Ohio, a corporation of Ohio Application April 2S, 1947, Serial No. 744,390

(Cl. Til- 323) 6 Claims.

This invention relates to carbon brushes for electrical machines and more particularly to pressure compensating distributing means for and with carbon brushes of sectional construction whose sections may desirably have limited longitudinal movement relative to each other.

Sectional brushes in which the various sections are arranged in tandem relative to the rotational movement of a commutator possess a number of advantages. Among these may be mentioned the reduction in cross circuits between sections of short circuits in the contact portion of the brush and the more nearly constant and uniform contact with the commutator resulting from the ability of the various sections to conform to the contour and irregularities thereof.

Sectional brushes of the prior art have been urged to make contact with the commutator of an electrical machine by means of a single main spring which exerts a pressure thereupon, which pressure is transmitted to the individual sections by rigid means or a substantially rigid plate. In the alternative some sectional brushes have been forced into contact with the commutator by separate springs bearing separately upon the individual sections.

Sectional'brushes with separate spring mountings for each individual section have generally proved to be unsatisfactory, often .being more expensive and relatively complicated, and seldom being adapted for use or substitution in existing machines designed for one solid brush section with a single spring mounting. In order that each brush section having separate spring mountings shall carry its proper share of the current it is necessary to initially adjust each of the several springs to provide equal pressures. This initial adjustment may be soon lost in operation for the sections may well have different wear characteristics and/or be subjected to incidents of operation which lead to different rates of wear. Non-uniform wear as a consequence of these and other causes results in differences in exerted spring pressures and in consequent variation in current load with deleterious departures from designed performance and desired results. Another objection to separately sprung brush sections is their isolation Vfrom each other and independence from the movements of each other.

On the other hand sectional brushes of the prior art which are subjected to the direct or imperfectly balanced influence of a single heavy main spring, vthe pressure of which is transmitted to the sections by substantially rigid means are also objectionable. Such brushes fail to gain many of the potential advantages sought to be derived from sectional construction. The interplay between the movements of the separate sections is utilized only partially or not at all. The contact of the sections of such a brush with the surface of the commutator is inherently faulty inviting wide changes in contact pressure and resistance, uneven wear, electrical overload and attendant difficulties.

I provide a brush in which the sections are mechanically connected by a pressure compensating and equalizing device so that the pressure of a main spring is distributed beneficially to each of the sections and in which the brush sections maintain full and nearly perfect continuous contact with a commutator and substantially constant pressure thereupon. A substantially constant pressure of contact between each section and the commutator will minimize selective action of load current, provide uniform contact resistance and consequently improve commutation. Equal or substantially equal or desired distribution of current between the sections of my brush is one of its best advantages and an important object of my invention.

I also provide a gradual compensation for unequal wear by gradual unequal and self correcting lpressure distribution between sections. With such a design the sections carry their respective rated shares of current load and are each subjected to substantially constant pressure and/or constant pressure plus or minus a desirable increment of corrective or compensating pressure tending to re-establish equal pressures if the latter should tend to be departed from. Sparking and burning is reduced to a minimum.

The sections tend to wear evenly and are there# fore consumed at substantially equal rates. Maximum life is obtained from the whole brush by preventing disproportionate Wear of or burden upon one section to the exclusion of the other. Consequently waste is eliminated or reduced to a minimum.

A further advantage accruing to a brush of my design, coincident with longer brush life is the lengthened life of the commutator and also better maintenance of commutator surface. These two mutual effects, better brush performanoe and lengthened commutator life are complementary and are obtained with my brush. A brush whose sections are subjected to desirable and uniform unit pressures maintains surer contact with the commutator and by avoiding aszove ,m

f 3 high unit pressures and by eliminating sparking and burning keeps the commutator surface in good condition. Reciprocally, good surface condition of the commutator enables improved brush contact and operation to be more readily obtained and maintained.

A further consideration in the life of carbon brushes and in the life of a commutator is the ability of the pressure transmitting means to yield quickly to the independent movement of the sections whenever the surface of the commutator imposes or requires such movement. To fail to yield thus subjects the sections to abnormally high, if but momentary, pressures and results in an increased rate of commutator wear and brush consumption. An important factor governing this ability of the brush sections to yield quickly and at least partially relieve these sudden pressures is the inertia of the various parts including the main spring and pressure distributing means.

v Where, as in the sectional brushes of the prior art, reliance is placed on the main spring and a heavy substantially rigid pressure plate to absorb the sudden longitudinal movements or tend 'ency 0f movement of the sections, the sections have a tendency to wear unevenly and the electrical performance of the brush is also impaired. Consider the Veffect in such a case of a surface irregularity or bump on the commutator suddenly raising the leading section of the brush. Due to the inertia of the main spring and plate a heavy pressure is exerted on the leading section while the pressure on the trailing section falls substantially to zero. As a consequence the leading section carries most of the current. 'I'his heavy pressure is relieved only partially by the time the leading section begins its return movement. However, the main spring again by reason of its inertia tends to be equally slow in returning and is still in partially lifted position when the same bump encounters the trailing section of the brush and lifts that also. The trailing section therefore meets with some or much pressure relief due to the inertia of the main spring and its correspondingly slow return. At this time the pressure on the leading section momentarily falls to Zero. Thus there tends to be wide and rapid changes in the unit pressure between the sections and the commutator and the trailing sectiontends to be subjected in the aggregate to less pressure than the leading section with undesirable results as to both sections and to the brush as a whole.

. It is an object of my invention to solve the problems and secure the advantages above discussed. It is more specifically an object of my invention to provide a sectional brush which maintains a substantially constant evenly cushioned and self-compensating contact with a ccmmutator or the like whereby said brush possesses improved electrical characteristics with each of the sections being subjected in the aggregate to uniform pressures and each of the sections carrying substantially at all times its rated current load, and with malfunctions of operation such as sparking and burning reduced to a minimum. It is an object of my invention to provide a pressure distributing means for a sectional carbon brush whose parts are small in mass and consequently possess low inertias whereby to respond easily and rapidly to the independent movements f said sections. It is a further object to provide a sectional carbon brush of a construction which will absorb and Vsubstantially cancel out deleterious vibrations which would tend periodically to throw the brush free of a commutator and otherwise interfere with the eiicient operation of the brush. It is a further object to provide a brush having sections mounted for individual longitudinal movement whereby said sections will freely and independently accommodate themselves to the surface irregularities of a commutator and thus maintain improved electrical contact therewith.

Another object is to provide a sectional brush havingr a pressure distributing device adapted to maintain substantially equal pressure on each of the sections, and which will have its own tendency to repair departures from equal distribution without first requiring wide differences in pressure between sections to initiate a corrective influence. Another object is to provide a sectional carbon brush whose sections are mechanically linked by a pressure distributing member whereby the brush may be conveniently handled as a unit and which is adapted for use withrsubstantially standard brush holders and springs without alteration or special fittings. Another object is to provide an inexpensive sectional brush and pressure distributor having a long and efficient life and substantially continuous satisfactory performance.

These and other objects and advantages will appear more fully in the following description and drawings wherein, Figure l is a perspective view showing the individual sections of my brush, embodying my invention, the sections being shown in assembled position but without the connecting and pressure distributing means employed therewith. Figure 2 is a longitudinal sectional view of my fully assembled brush and pressure distributing and compensating member in operative position, together with a section of a commutator. Figure 3 is a View similar to that of the upper part of Figure 2 showing a condition with one of the sections standing higher than the other. Figure 4 is a fragmental View similar to Figure 3 showing an instantaneous condition resulting from the response of the brush to the rapid upward thrust of a single section. Figure 5 is a perspective view showing the pressure distributing device of Figure 2, the device being turned upside down so that details of construction will be clearly revealed. Figure 6 is a sectional View similar to Figure 2 of a modified form of my invention.

A preferred form of my invention is exemplified in a brush comprising two sections and equipped with a pressure distributing device adapted to maintain substantially Vequal and/or desirable compensating pressures on the sections. Thus a carbon brush I3 comprising sections ll and l2 is mounted within a brush holder i3 and is urged to make contact with the commutator I of an electrical machine by the pressure, downwardly as viewed, of a main spring i5. The sections lil and Il are disposed in tandem relative to the direction of rotation of the commutator I4, section Il being referred to as the leading section and section I2 being referred to as thetrailing section. Appropriate electrical leads L are secured to each of the two sections as shown in Figure 1 in a manner well known in the art.

The pressure of the main brush spring I5 is transmitted to said sections by the pressure equalizing and transmitting device 20 interposed between the main spring and the brush sections comprising a generally tubular sleeve 2l carrying a leafv spring 22, see also Fig. 5, which coop- :acciones crates with brackets and I1 xedly Asecured to sections II and I2 respectively. The brackets portions are seated in appropriate recesses ,I9

.in the leading and trailing faces of sections II and I2 respectively. The clips preferably are xedly secured to their respective sections by rivets I3.

vExtending,substantiallyparallel to and spaced from the top faces of the sections and engage- .able with the device 26 are the substantially horizontal leg portions Ita and I'Ia of brackets l5 and Il respectively. When the sections are assembled the horizontal leg portions extend toward each other in substantially the same plane ybut their ends are spaced apart so that the sections may move freely vertically with respect to each other without locking or binding of the brackets.

The device 2t comprises a generally tubular sleeve 2| adapted to fit over, engage and be supported by brackets I f5 and Il and is preferably C-shaped in section with inwardly extending underlips 23. When assembled on said brackets, Figs. 2, 3 and 4, the lip portions 23 extend laterally beneath the legs iia and Ila and the leaf spring 22 bears upon the top surfaces of the legs, tending to hold the legs in yieldable ycontact with the lips and holding the device and sections II and l2 in, yielding and detachably assembled relation. The leaf spring 22 is ,preferably xedly secured to the sleeve by a centrally located rivet 25 wherewith the right and left, as viewed, halves of the spring tend to act independently of each other except as the stress in one half is transmitted to the other by tipping or canting the sleeve. Preferably the spring 22 is light in weight being just strong enough to transmit the necessary or den sired brush pressure onto the commutator. Preferably, though not necessarily, the legs IBa and I'Ia of the brackets are provided with shallow lateral grooves 24 which provide seats for reentrantly curved tips 25 of the leaf spring and which thus locate the spring on the brackets and yieldably lock the sections II and I2 together in assembled relation.

To assemble the brush, the sleeve 2| is slipped over the legs of the brackets I8 and I'I, the lip portions 23 extending laterally beneath the brackets, the spring 22 being slightly compressed and bearing upon the upper faces of the legs of the brackets. The sections are then inserted into the brush holder. The main brush spring I5 then bears preferably upon the exact middle of the top face 27 of the sleeve as at X and the pressure thereof is transmitted substantially equally to the sections by the leaf spring 22 and the respective brackets. I thus provide a sectional brush which may be used with a standard brush holder and a single main brush spring with at least the same convenience obtaining with unitary brushes.

It will also be observed, Figs. 2, 3 and 4, that the curved end of the spring I5 affords a rolling rather than a true pivoted or whife-tree contact with the top surface 2l of the sleeve 20. Thus as mentioned initial contact between the spring I5 and the sleeve preferably takes place along the line X transversely of the sleeve in the middle thereof when the sections are new and properly proportioned. If, however, one of the sections tendsto wear whereby to stand lower '6 than the other, .as `section I2 is `shown with exaggeration lower than .I.I in Fig. 3, or if inoperation vrthe upward movement of section II relative to section .I2 is comparatively slow whereby to tip thefsleeve Ibodily rather than merely ilex the right, as viewed, half of the spring as suggested in Fig, 4, then the sleeve will roll under the lower curved surfaceof the endof the spring I5 shifting the line of contact rightwardly, as viewed, from X to Y, thereby tending to stress Vthe right half of the spring 22 ,more Vthan the left half Vand placing a greater pressure on the section II than on Vthe section I2 for the period of time that the section II stands higher than the section I2. The rolling action between the sleeve Vand the spring I5 is accompanied and facilitated by limited ipivotal movement of the points of contact A `and B between the ends of the spring .and the indentures v24 in the legs of the brackets IS and I`I During the time the condition illustrated in Fig. 3 persists, whether the same be measured in seconds or hours, the leg I 5a will tend to be spaced away from the lip 23 substantially in proportion to the overstress in the right half of the spring 22 while the leg I la will have contact with the lip evidencing in part the understress of the left half of the spring 22; the gross pressure on the brush as a whole, assuming the condition of Figure 3 to be substantially free from inertia effects, corresponding to the pressure exerted by the spring I5. In the condition shown in Fig. 3 the inner end of the leg Ila is just about to contact the lip 23 so that further tipping of the sleeve 2l will begin to flex the left half of the spring 22 whereby to limit the extent of the compensating unbalance and thereby prevent undesirably wide differences in pressure ybeing exerted upon the different sections of the brush. It will be understood that substantially the same kind but oppositely disposed effects will transpire if and whenever the section I2 stands higher than the section II under the conditions above discussed. rihus the tendency of the device V2G to exert unequal pressures under the above conditions effects the compensations through which equality or distribution of pressure is restored, if lost, and /or maintained without substantial or deleterious departure from desirable equality at substantially all times. While l prefer the initial conn tact between the rounded end of the spring and the top of the sleeve to be in the exact middle of the latter it will be appreciated as a ,pracical matter that such geometrical exactitude is not essential to the benelcent operation and reu sults of my invention since the form and tendencies above described will persist regardless of the exactitude of the initial relation of the parts and bring about the desired balance and distribution of forces since any unbalance will initiate its own correction as above described.

In contrast with the condition and operation illustrated in Figure 3, when the surface of the commutator changes sharply or locally as due to surface irregularities brush accommodates itself in a different manner as illustrated in ure Li. Such surface irregularities may i.- nose sharp sudden longitudinal thrusts upon the `bi ash sections. It is with regard to ability to yield quickly and easily to sudden upv/ard thrusts of an individual section as shown in Figure ff, that my brush possesses other advantages. if, for example, the leading section I I should encounter a bump on the commutator it would be raised suddenly upward against the leaf spring 2I. The

mass 'of the leaf' spring is relatively small and its inertia' is correspondingly small. It is free therefore to respond quickly to the upward thrust of section Il, the result being to flex the right half of the leaf spring momentarily. The pivotal movement of the sleeve and the yielding of the main spring l takes place relatively more slowly due to the inertia of the greater masses that are involved and these movements therefore lag behind the response of the leaf spring. Indeed the section may be subjected to such a quick shock that the response of the sleeve and main spring takes place only partially or substantially not at all. 'Ihat is to say, the duration of the upward thrust of the section Il as occasioned by a bump o-r irregularity on the commutator in some instances may be so short as to result only in an unbalanced flexing of the leafy spring, the thrust terminating before the sleeve and main spring have had time to respond substantially. My invention thus enables quick small upward movements of the individual sections to take place locally and independently within the system, reducing localized excess pressure and wear. When section l l is raised upwardly under such a sharp thrust, section l2 remains in contact with the commutator under substantially normal bearing pressure. On the other hand since the low inertia of spring 2l enables a quick response to the upward movement of section Il, the pressure on section ll is relieved quickly. Although for the duration of the thrust the pressure on section ll is somewhat greater than normal it is less so than would be the case where a heavier spring or mass had to be flexed or moved. In addition, the characteristic of the leaf spring desirably is such that its exerted pressure does not increase inordinately as it is flexed. The spring 2l may be embodied in multi-leaf form if the period of vibration of a particular brush and commutator developed a periodic vibration in the spring that might impair the mode of operation desired for the best performance of my invention.

A modification of my invention, illustrated in Figure 6, contemplates the aflixation of a light leaf spring il by a rivet #il or by other means secured to the main brush spring I5. Preferably the leaf spring is firmly fixed to the main spring although it is within my invention to permit some play in the fastening so that limited pivotal movement between the leaf spring and the main spring may be possible. With such spring means the brackets may be dispensed with and the leaf spring preferably bears directly on the upper faces of the brush sections.

In operation of the device of Figure 6 the leaf spring et will flex -unsymmetrically in quick response to sharp upward thrusts of the respective sections and so cushion the lagging response of the main spring. When a slow response is required as when the change of commutator surface is gradual or one section tends to wear more rapidly than the other the leaf spring lil will transmit more pressure to the high section, as to section il of Fig. 3, and less to the low section wherewith to tend to bring about or reestablish a condition of balanced pressure as between the two sections.

In both forms of my invention, and especially in the preferred form, I have the advantage of relatively light independent spring support for each of the brush sections without, however, having the disadvantages of. complete independence,- but rather with the advantage of interaction between the'sections under those conditions where the transmission of action and reaction between the sections is desirable. My invention while permitting desirable independent movement of each of the brush sections also provides automati-c compensation wherewith to repair any tendency toward uneven wear or unequal or undesirable pressure distribution between brush sections. I also preserve the advantage of a single spring control and adjustment of the gross pressure exerted upon the 'brush as a whole While avoidingY the disadvantages of faulty pressureI distribution inherent in the application of pressure from a single spring as by rigid means to the different brush sections.

While I have illustrated and described certain preferred forms of my invention, changes and improvements will occur to those skilled in the art without departing from the spirit and teachings hereof and I do not care to be limited to the preferred Iform of my invention or any forms herein specifically illustrated or in any manner other than by the claims appended hereto.

I claim:

1. A sectional brush and pressure distributing assembly comprising a pair of brush sections adapted to have sliding contact with a commutator or the like in tandem, I -shaped brackets secured to the top portions of said sections with the transverse legs of the bracket spaced from the ends of each sections, a sleeve-like member having top, side and bottom walls, a leaf spring having its mid-portion secured to the mid-portion of the top wall of said sleeve member and having its ends disposed adjacent the ends of the bottom wall of said sleeve member and yieldingly movable away from said bottom wall, the legs of said brackets entering the ends of said sleeve member between the ends of said spring and the said bottom wall when said sections are disposed in operative relation to each other, said sections being retained in operative relation by the grip on said legs. between said spring and the said bottom wall of said sleeve member.

2. Pressure distributing means for a sectional brush both sections of which have oppositely disposed brackets wth legs spaced from the ends of the sections and approaching each other, a sleeve receiving the legs of said brackets when the sections are assembled and resilient means disposed within said sleeve and urging the legs of said brackets into contact with a wall of the sleeve wherewith to resiliently resist relative angular displacement between the legs of said bracket and the sleeve.

3, A tandem multiple brush assembly comprising a pair of brushes, a bracket attached to each brush having a leg overlying and spaced from the end of each brush, a sleeve receiving said legs in its opposite ends respectively and a spring disposed in said sleeve and bearing on said legs.

4. The assembly of claim 3 in which said legs contact the lower wall of said sleeve and said spring contacts the upper wall thereof and said legs are limited in their freedom of angular movement relative to said sleeve by contact therewith in one angular relation thereto.

5. The assembly of claim 3 in which the ends of said spring and said legs respectively are curved and notched for resilient locking engagement to releasably secure said assembly together.

6. A brush holder for a sectional brush in which the brush sections are arranged in tandem relative to a moving conductor comprising ybracket legs secured to the brush sections and extending upwardly therefrom, sleeve means connecting the brush sections and adapted to transmit the pressure of a main spring to said brush sections, and parts connected to said legs and disposed at an angle thereto and lying Within said sleeve in yielding relation thereto.

RICHARD H. WARD.

REFERENCES CITED Number Number 10 UNITED STATES PATENTS Name Date Van Depoele Feb. 25, 1890 Reist Sept. 7, 1897 FOREIGN PATENTS Country Date Austrial Sept. 25, 1933 Germany May 30, 1931

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