GB2096837A - Brushgear for electric motors - Google Patents

Abstract

A brush and brush holder assembly for an electric motor includes a brush holder 4 having longitudinally extending side walls 14, 16 for slidably receiving the brush 30, each of the side walls 14, 16 having an arcuate recess for receiving the brush spring 18 and elastomeric cushioning means 40, 42 in the arcuate recess in the brush receiving end of the holder for cushioning the brush against contact with the side walls of the holder. <IMAGE>

Description

SPECIFICATION Dampened printed circuit motor brushes The present invention relates to electric motors and, more particularly, to brush holders and brush holder assemblies for use in such motors.

Direct current, axial air-gap motors which employ disc armatures formed by printing or depositing metal windings, radially, at the opposite sides of an insulating disc or by laminating half turn metal stampings of the windings to the opposite sides of a prepreg disc and by fusing or welding the half turn ends from the opposite sides of the disc to each other at the inner diameter (I.D.) and the outer diameter (O.D.) of the armature, are light in weight, compact and have a wide variety of uses. In such motors, it is common practice to design and lay out the half turn printing or deposition or metal stamping so that the flat portion of the half turn conductors at one side of the armature might be utilized as the commutator.This area is usuaily located in the radial armature area adjacent the I.D. or hub of the armature. Using a portion of the conductor turns as the commutator in this fashion simplifies the manufacture of such armatures, reduces armature cost and weight. Such commutators do, however, cause such motors to be noisy.

Typical of these motors, a 14 cm printed circuit motor made of metal stampings has 141 conductors or windings per layer each of which, at one side of the armature adjacent the armature l.D. or hub, also acts as a commutator. These 141 conductor or commutator segments are separated from each other by a width of about half the width of the segment. A small separation or gap, merely for electrical isolation, is necessary for the motor function. Such large separation between the segments is a consequence of limitations in the stamping process. Such large separation can cause the brushes, however, as the armature and commutator segments rotate past the brushes at motor speeds, to chatter, rattle or vibrate in the brush holders causing noise.This noise has been found to persist despite special efforts and manufacturing procedures including diamond turning to eliminate it when conventional brush holders are used. However, brush holders constructed using the techniques described below have been found very effective in reducing this noise.

The brushes for such motors are generally rectangular and are generally mounted in metal holders usually of a size slightly larger than the brush so that the brush can slide freely into and out of the holder to accommodate both irregularities in the commutating surface and shortening of the brush with wear. The holder is provided with a spring which contacts the back of the brush and maintains the brush face in contact with the commutator as the armature rotates.

When a shunt electrical connection is provided to the brush as is generally done, the holder serves only as a mechanical guide and it is not required to serve as an electrical connection as well.

The present invention relates to a dampened brush assembly for use in electric motors, said assembly including a brush tube open at one end and having a brush longitudinally slidable therein, means in said tube for urging said brush outwardly of the open end of said brush tube and into engagement with a commutator passing in front of said brush tube open end and past said brush and cushioning means on the walls of said tube in the upstream and downstream directions of movement of said commutator past said tube and said brush for cushioning said brush against the side walls of said brush tube.

The inventors of the present invention have discovered that the chattering, rattling or vibration of the brushes in an electric motor, such as a radial air-gap or printed circuit motor, can be substantially reduced and, for practical purposes, substantially eliminated by isolating or damping the contact or impact between the brush and the brush holder as such brush is deflected in the holder by the passage of the commutator segments and segment gaps therebetween past the brushes. This is accomplished by providing a coating or insertion between the brush and brush tube of a cushioning material having a low rebound property, such as, for example, a butyl rubber.

The instant invention will be better understood from the following description, taken with the appended drawings, of a preferred embodiment of the invention.

Figure 1 is a view, partly in section and partly broken away, of a brush and brush housing assembly to which the invention is adapted.

Figure 2 is a view in section, taken at line 2-2 of Figure 1 of the brush and brush housing assembly of Figure 1.

Figure 3 is a plan view of a commutator segment, with brush in section thereon, taken at line 4--4 of Figure 1.

Figure 4 is a cross-section of the brush and brush housing assembly taken at line 4--4 of Figure 2.

Figure 5 is a cross-sectional view similar to Figure 4 but taken at line 5-5 of Figure 2.

The brush and brush housing assembly 2 includes a rectangular tube 4 having affixed and bonded to one end thereof cap 6, threaded at 8.

Closure 10, having a screw driver slot 12 is threaded into threads 8 of cap 6. As best shown in Figure 1 and 5, the upstream and downstream sides of brush tube 4 in the direction of the arrow (Figure 1 ) of the movement of the commutator 20 are provided with arcuate walls 14 and 16 to accommodate brush spring 1 8. Commutator 20 is made up of segments separated by spacings 24.

As best shown in Figures 1, 2, 3 and 4, brush 30 is rectangular in cross-section, of a dimension slightly smaller than brush tube 4 and slides freely axially therein. At its end within tube 4, brush 30 is provided with boss 32 for receiving one end of compression spring 1 8. Shunt wire 36 of, e.g., stranded copper, is embedded at one of its ends in brush 30 in boss 32 and forms an electrical connection with the brush. At its opposite end shunt wire 36 is electrically connected to metal cap clip 38, having legs 38a and 38b extending downwardly into brush tube 4. The free end of compression spring 1 8 is seated in cap clip 38.

The brush and brush assembly described above is typical of the brush and brush assembly employed with axial air-gap printed circuit motors and the assemblies to which this invention is particularly adapted. In such typical assemblies, as the commutator 20 rotates past the end of brush 30, the brush is held in contact with commutator 20 by spring 18 in compression in brush tube 4. Thus, brush 30 slides in and out of tube 4 as irregularities, high spots, and the like, in commutator 20 pass under brush 30 but, for electrical purposes is, nevertheless, maintained in contact with commutator 20 and commutator segments 22.

As brush 30 passes from one commutator segment 22 to the next segment 22 across the spacing 24, brush 30 tends to be cocked and uncocked in brush tube 4, that is, brush 30 tends to be forced against the upstream or downstream side wall of tube 4 causing a chattering, rattling, vibration and noise at the brush. It is to the elimination of such chattering, rattling, vibration and noise that the present invention is directed.

In Figure 4, the commutator end of brush tube 4, at the upstream and downstream walls of the tube, is provided with a cushioning material of low rebound elastomeric material which cushions and dampens the cocking or contact of the brush with the upstream and downstream side walls of the brush housing but which, at the same time, does not interfere with the inward and outward movement of brush 30 in brush tube 4 or the maintenance of contact of the end of brush 30 with commutator 20 by compression spring 1 8.

In the preferred embodiment illustrated in Figure 4, the lower end of the arcuate walls 14 and 16 of brush tube 4 which, at the cap end of tube 4 accommodate compression spring 18, are provided with elastomeric cushioning means 40 and 42 which are relatively soft but not springy or of high rebound. Butyl rubber has been found to be particularly suited and is adhesively attached to the arcuate wall with a quick bonding cement, such as of the cyanoacrylate type or may be mechanically connected by providing suitable holes in the arcuate walls and projections into such holes by the butyl rubber members 40 and 42.

In their relaxed state, the cushioning members 40 and 42 should, of course, extend outwardly beyond the adjoining side walls of brush tube 4 but should not interfere with the inward and outward movement of brush 30 in brush tube 4.

When compressed, members 40 and 42 should cushion brush 30 and prevent brush 30 from contacting or be impacted onto the brush tube side wall.

While the utilization of members 40 and 42 in arcuate walls 14 and 1 6 is a convenient manner of carrying out the instant invention without alteration to the dimensions of the existing parts, it should be obvious to those skilled in the art that other cushioning arrangements might be employed. For example, by making the commutator end of brush tube slightly larger, the brush tube walls at the end of arcuate walls 14 and 1 6 might be coated with an elastomeric cushioning material having low rebound, such as butyl rubber. A sleeve of such material, rather than a coating, might also be employed.

The terms and expressions which have been employed throughout the specification are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention

Claims (5)

claimed. Claims

1. A dampened brush assembly for use in electric motors, said assembly including a brush tube open at one end and having a brush longitudinally slidable therein, means in said tube for urging said brush outwardly at the open end.

of said brush tube and into engagement with a commutator passing in front of said brush tube open end and past said brush, and cushioning means on the walls of said tube in the upstream and downstream directions of movement of said commutator past said tube and said brush for cushioning said brush against the side walls of said brush tube.

2. The dampened brush assembly as claimed in claim 1, in which the upstream and downstream walls of said brush tube include arcuate portions and said cushioning means is in said arcuate portions.

3. The dampened brush assembly as claimed in claim 1 or 2, in which said cushioning means is an elastomeric material.

4. The dampened brush assembly as claimed in claim 1 or 2, in which said cushioning means is of butyl rubber.

5. The dampened brush assembly as claimed in claim 1 or 2, in which said brush tube is rectangular.