US3376444A - Carbon brush assembly - Google Patents

Description

April 1968 E. P. EATON, JR. ETAL 3,376,444

CARBON BRUSH ASSEMBLY Filed Sept. 15, 1965 2 Sheets-Sheet 2 Fm. 7 F7618 INVENTOR 648 14744; B 04 |//0 United States Patent 3,376,444 CARBON BRUSH ASSEMBLY Edgar P. Eaton, Jr., Morristown, N.J., and David Elow,

New Rochelle, N.Y., assignors to Carbone Corporation, Boonton, N.J., a corporation of New Jersey, and Consolidated Spring Corp., Brooklyn, N.Y., a corporation of New York Filed Sept. 13, 1965, Ser. No. 486,836 2 Claims. (Cl. 310-249) ABSTRACT OF THE DISCLOSURE A carbon brush assembly for electrical motors in which the end of the brush is formed with a cavity into which a portion of a helical electric contact spring is received. The end of the spring is shaped to conform to the shape of the cavity to provide good electrical contacts therebetween under all operating conditions.

This invention relates to a carbon brush assembly for small and medium power electric motors. It has particular reference to a low resistance coupling between a helical spring and a carbon block so that the usual flexible wire shunt is unnecessary.

The use of carbon brushes to form a sliding electrical connection is well known. They are used on commutators and slip rings attached'to a rotor in many types of electrical motors and converters. Since the commutator or slip ring rotates and cannot be perfectly round, the most suitable device for maintaining constant electrical contact is a spring of some type. Helical springs are universally used on small motors because they are compact and may be installed within a brush holder.

Springs are generally made of steel which is not a good conductor of electricity. If they are the only means for conveying the current from the brush to the outside circuit they are liable to overheat and lose their temper. For this reason, most of the brushes which carry currents of one ampere or more are now fitted with a flexible copper wire shunt which carries all of the current.

New types of springs have recently been introduced which have the required elasticity and, in addition, a low resistance. They are alloys of Phosphor bronze, beryllium copper, and other mixtures, one of which is commercially known as Cortem. Springs made of these materials can be used to furnish the resilient force needed by commutator brushes and to carry currents up to and including ten amperes. It has been found that in such applications, other problems are present, one of which is the necessity of making a good electrical contact between the end of the spring and the carbon brush. This problem is further complicated by the fact that when a helical spring is compressed, the turns expand slightly and if the turns are fitted around a cylindrical extension of the brush, compressing the spring causes a reduction of the contact force and probable arcing. The present invention solves this problem by placing the lower end of the helical spring within a cavity formed in the upper end of the brush. Then when the spring is compressed, the electrical contact is maintained.

As used throughout the specification and claims, the term cylindrical revolving conductor, refers to all classes of commutators and slip rings used on motor rotors. It also refers to revolving contact segments and rings which are used to make and break current to contact brushes.

An object of the present invention is to provide an improved carbon brush assembly which avoids one or more of the disadvantages and limitations of prior art assemblies.

3,376,444 Patented Apr. 2, 1968 Another object of the present invention is to provide a low resistance contact between a spring and a commutator brush for carrying current from a commutator to other parts of a motor or external circuit.

Another object of the present invention is to eliminate the flexible wire shunt on the smaller sizes of motors and in other applications where current does not exceed ten amperes.

A further object of the present invention is to reduce the cost of brush assemblies.

Still another object of the present invention is to simplify the operation of assembling the motor parts and to aid in repair work.

Another object of the present invention is to eliminate other types of brush parts that take up space and might be dangerous if contact is made with a commutator segment or a slip ring.

, A still further object of the present invention is to increase the sliding stability of the brush in its holder and provide extra wear by increasing the length of the brush faces in contact with the holder.

The invention comprises a carbon brush slidably mounted in a brush holder. The brush is formed with a cavity at one end for receiving one terminal of a helical spring; The helical spring has its other end abutting a cap on the holder and resiliently urges the brush against a revolving commutator or a sip ring. The brush cavity may be cylindrical or conical or a transverse slot.

The invention consists of the construction, combination and arrangement of parts, as herein illustrated, described and claimed.

In the accompanying drawings, forming a part hereof, is illustrated several forms of embodiment of the invention, in which drawings similar reference characters designate corresponding parts, and in which:

FIGURE 1 is a cross-sectional view, taken generally along a central plane, of a prior art brush holder showing the wire shunt.

FIGURE 2 is a cross-sectional View of the brush assembly shown in FIGURE 1 and is taken along 'line 2-2 of that figure.

FIGURE 3 is a cross-sectional view of one preferred form of the invention showing a carbon brush having a cylindrical cavity.

FIGURE 4 is a cross-sectional view of the brush assembly shown in FIGURE 3, and is taken along line 4-4 of that figure, looking in the direction of the arrows.

FIGURE 5 is a cross-sectional view of an alternate form of brush having a frusto-conical cavity for holding one end of the spring.

FIGURE 6 is a cross-sectional View of another alternate form of brush also having a frusto-conical cavity with the cone reversed.

FIGURE 7 illustrates another form of the invention in which the cavity is ring-shaped.

FIGURE 8 illustrates another form of the invention employing a dovetail slot in the top of the brush.

FIGURE 9 is a view similar to FIGURE 3 in which the cavity is internally threaded to anchor the spring.

FIGURE 10 is a view similar to FIGURE 5 in which the cavity is internally threaded.

FIGURE 11 is a cross-sectional view taken on line 11-11, in FIGURE 8.

Referring to FIGURES 1 and 2, a prior art brush assembly is shown for comparison. A hollow, generally rectangular brush holder 10 is formed with a brush receiving central portion 11. A brush 12A is slidably carried within the holder 10 and rides upon a commutator 13. The upper end of brush 12A is formed with a cylindrical stub 14 which helps to position the lower end of a helical spring 15. The upper end of spring 15 may be supported by a washer 16 although there are other structures which 3 may be used for this purpose. The washer 16 is held against a cap 17 which closes the upper end of the brush holder 10 and is secured to it by screw threads.

The electrical junction-s between the spring ends and the brush and cap are not sufficient to provide a good low resistance path. Also, if the spring is of steel it cannot pass currents greater than one-quarter amperes with any efficiency. For this reason, a flexible copper wire shunt 18 is connected between the upper end 14 of the brush 12A and washer 16 to carry all of the current. This type of construction is costly but necessary when steel springs are used.

One form of the present invention is shown in FIG- URES 3 and 4. In this form, the top of the brush 12B contains a cavity 21, instead of having a stub and the exterior flat faces of the brush which make sliding contact with the inside surfaces 11 of holder 10 have a greater bearing length and are lesssubject to binding due to tilting particularly as the brush. gets smaller. The lower end of spring 15 is compactly wound in a small helix which is tightly fitted into cavity 21. The upper end of the spring 15 bears against the bottom Olf cap 17A, which urges it against the brush 1213. This type of connection at the brush end is well suited to a spring under compressive tension because, as is well known, the coils of a helical spring expand when the spring is compressed. When cap 17A is screwed into place the lower end of the spring tends to expand and press tightly on the inner surfaces of the cavity 21, thereby providing good electrical connections. If the spring is made of beryllium copper or some of the other alloys, such as Cortem, the flexible shunt 18, shown in FIGURES 1 and 2, is not needed.

The brush 12D, shown in FIGURE 6, is still another alternate form of the invention where the cavity is frustoconical but having its lower diameter smaller than the opening. As before, the lower end 200 of spring 15 is formed to fit snugly into the cavity.

As a further embodiment of the present invention, the brush 12E shown in FIGURE 7, may be formed with a ring shaped cavity 22 to receive the end of the spring 15. The outside diameter of the core 23 within the ring should be of a size which will provide a firm engagement with the spring 15 and good electrical wiping contact.

tail slot 24 across the top of the brush 12F to receive the 'slid into the groove laterally:

spring 15. In this form of the invention the spring may be In FIGURES 9 and 10, the cavities 25, 26, are similar to those shown in FIGURES 3 and 5 except they are internally threaded as indicated at 27, 28, to receive the spring 15. The threads have a pitch and depth to accommodate the spring size and helix.

While this brush assembly has been designed primarily for small motors using cylindrical shaped commutators or slip rings, it is obvious that they may be used in any brush assembly which makes sliding contact with a moving conductive surface.

Having thus fully described the invention, What is claimed as new and desired to be secured by Letters Patent of the United States, is:

1. A carbon brush assembly for electrical motors which include a cylindrical revolving axially aligned conductor comprising, a carbon brush rod having a substantially constant cross sectional shape, a brush holder having a hollow portion for slidably retaining the brush, said brush being formed with a cylindrical cavity at one end, a helical spring for resiliently holding the other end of the brush against said revolving conductor, one end of said spring having a helical end portion of reduced diameter and a shape similar to the brushcavity which end is positioned in said brush cavity for making electrical contact with the sides of the cavity, and a conductive cap secured to said holder for making an electrical connection to the other end of the spring.

2. A carbon brush assembly as claimed in claim 1 wherein the cavity is ring shaped in cross section.

References Cited UNITED STATES PATENTS 626,708 6/ 1899 Lundell 310 -249 XR 1,743,682 l/1930 Oswald 310-248 XR 2,199,532 5/1940 Weeks 310-249 2,615,939 10/ 1952 Mitchell 310249 XR FOREIGN PATENTS 1,039,415 8/ 1966 Great Britain.

651,170 10/ 1937 Germany.

The embodiment shown in FIGURE 8 employs a dove- 45 MILTON HIRSHFIELD Primary Examiner D. F. DUGGAN, G. NUNEZ, Assistant Examiners.

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