GB2180999A

GB2180999A - Brush gear for an electric motor

Info

Publication number: GB2180999A
Application number: GB08623195A
Authority: GB
Inventors: Takaichi Mabuchi
Original assignee: Mabuchi Motor Co Ltd
Current assignee: Mabuchi Motor Co Ltd
Priority date: 1985-09-26
Filing date: 1986-09-26
Publication date: 1987-04-08
Also published as: GB8623195D0; KR870005920U; KR900002355Y1; CN86106490A; JPS6257568U; GB2180999B

Abstract

A brush for an electric motor has a brush arm 2 which includes a brush contact portion 6 formed of a resilient material adapted for electrical contact with the commutator of an electric motor in a configuration in which the brush arm 2 is resiliently bent. The brush arm 2 also includes a terminal portion 3 which has a terminal lead portion 8 for electrical connection of the brush in an external electric circuit. A base portion b of the brush arm and the terminal portion are coupled together in overlapped relation. The brush arm is provided with slits 11 in the base portion whereby to extend the effective length 7 of the brush arm. The end portion of the base may be bent to allow slots 11 to be extended further towards the edge of the base (Fig. 6, 7). <IMAGE>

Description

SPECIFICATION Brush gearfor an electric motor Description This invention relates to brush gearforan electric motor. More specifically, it is concerned with an improved brush, with a motor case cover mounting the brush gear including the said brush, and with the motor as a whole.

It is a common practice in the design of so-called "miniature" electric motors, two provide the brush gear in the form of brushes which include thin metal brush arms which are resiliently bentto bring brushes proper into sliding contact with a commutator. For a stable arrangement, the brushes must maintain predetermined contact pressure and contact area and must faithfully follow the revolution of the commutator. In such arrangements, the brush arm will in each case have what may be defined as its "effective length", this being the length from the position where the brush makes contact with the commutator in practice to the fulcrum (that is: the fixed position from which the bending ofthe brush in use commences).

As we shall describe below, there are a numberof commonly encountered prior arrangements with different effective lengths for the brush arm. The prior arrangements sufferfrom a number of disadvantages, as we shall explain below, and the present invention has arisen out ofourworkseeking to provide improved brushes for electric motors in which the brush arm has a consistent effective length and can readily be produced with a consistent product quality without undue labour.

In accordance with the present invention, we provide a brushforan electric motor comprising: a brush arm including a brush properformed of a resilient material and adapted for electrical contact with the commutator of an electric motor in a configuration in which the brush arm is resiliently bent; and a terminal portion including a terminal lead portion adapted for electrical connection of said brush arm in an external electric circuit; a base portion of the brush arm and the terminal portion being coupled together in overlapped relation, and the brush arm being provided with slits in said base portion whereby to extend the effective length (as herein defined) ofthe brush arm.

The invention is hereinafter more particularly described by way of example only with reference to the accompanying drawings, in which Fig. 1 schematically illustrates at (A) (B) and (C) three alternative configurations for the brushes of miniature electric motors; Fig.P illustrates a first embodiment of brush constructed in accordance with the present invention, the brush being shown in end elevation at (A), in plan view at (B) and in end elevation but open condition at (C); Fig. 3 is a generally schematic view partly in elevation and partly in section of an embodiment of electric motor incorporating brush gear in accordance with the present invention; Fig. 4 is an internal end elevational view ofthe motor case cover ofthe motor of Fig. 3; Fig. 5 is a view generally similarto those of Fig. 1 for an embodiment of brush in accordance with the present invention incorporated in an electric motor; Fig. 6 illustrates an alternative embodiment of brush constructed in accordance with the present invention, the brush being shown in end elevation at (A) and in plan at (B); and Fig. 7 shows a plan view of a further modified embodiment of brush constructed in accordance with the present invention.

Referring first to the three conventional arrangements (A), (B) and (C) illustrated in Fig. 1,the brush gear generally indicated 1 comprises brushes consist- ing of a brush arm 2 and a brush base 3. A portion adjacent the distal end ofthe brush arm serves as the brush proper, or alternatively a separate brush proper is mounted onthe brush arm. In either case, the brush proper, indicated at6 in the diagrams makes contact with a commutator 4. The brush gear is suitably mounted from a motor case cover5 which serves as a brush holder.

The effective length 7 ofthe brush in the arrange- ment of Fig. 1(A) is shown. The arrangements (B) and (C) will also have effective brush arm lengths. In the arrangement of Fig. 1(A) the baseofthe brush arm is mounted in overlapped relation to a second member3 which may comprise part of a terminal portion for the brush, the terminal portion having a terminal lead portion which extends through an opening in the motor case cover to the exterior for connection in an electrical circuit.With this arrangement, however,the fulcrum forthe brush arm, which defines one end of the effective length will fall at the point a indicated in the figure, namely where the brush arm extends from the edge ofthe member 3. As will be appreciated, this results in a relatively short effective length for the brush arm making it difficult to maintain stable contact between the brush and the commutator under all the conditions likely to arise in use.

The arrangements shown at (B) and (C) represent two modified arrangements which seekto increase the effective length by bending the brush arm, in arrangement (B) effectively th rough a right-angle and in (C) effectively through 1800.

In both these arrangements, however, the bending ofthe brush arm itself requires process steps which are labour intensive. The bending steps also lead to uneven accuracy in the resulting components due to bending and cracks and other defects due to the Bauschinger effect associated with a rigid material. As a result, consistent product quality cannot be maintained to the standard we would wish.

Where appropriate, like reference numerals to those employed in Fig. 1 are employed for like parts in the embodiments of brush constructed in accordance with the present invention and which will now be described in detail below.

The brush of Fig. 2 has a brush arm 2 carrying a base portion 2a mounted in overlapped relation with a terminal portion 3. The terminal portion 3 includes a terminal lead portion 8which is adapted for electrical connection of the brush in an external electric circuit.

Connecting means9 hold the brush arm and terminal portion together. A region 6 adjacentthe distal end of the brush arm services as a brush proper being adapted for contact with a commutator as shown in Figs. 4and 5. The brush arm may optionally be provided with a brush arm damper 10 for damping unwanted vibrations which may arise as the com mutator rotates in use ofthe motor.

As will be seen from Fig. 2, the brush base portion is generally rectangular in configuration with the brush arm which is also generally rectangular extending in one direction therefrom. The brush arm is provided with a plurality of slots therein open at the distal end of the brush and thereby defining a plurality offingers.

The brush base portion is provided with slits 11 which in the arrangement illustrated are continuous with the side edges ofthe brush arm.

Figs. 3 to 5 showthe brush of Fig. 2 mounted as brush gear in an electric motor. As can be seen, the terminal lead portions 8 extend through openings 12 in a motor case cover5which serves also as a holder forthe brush gear. A rotorshaft 13 is mounted in bearings 14 in the motorcase cover and in the motor case 16 and a rotor 5 is mounted on the shafttogether with the commutator4. Mounted interiorly of the motor case 16 is a permanent magnet shown stippled in cross-section.The motor case coverS is suitably made of synthetic resin and the brush gear may be a force fit thereto.

With the configuration illustrated in Fig. 2, the brush will have an effective fulcrum in the region ofthe root 6 of the slits 11 leading to an increased effective length 7 forthe brush arm as best shown in Fig. 5.

Fig. 6 shows a modified arrangement. The edge of the brush base portion opposite the direction in which the brush arm extends is bent at 2b out ofthe plane of the brush base portion. This bent portion has two advantages. Firstly, the reinfornement it confers on the brush base portion assists in preventing the brush arm from being twisted or bent in use. Secondly, and as shown in Fig. 7 which is a modification ofthe Fig. 6 arrangement, the effective length 7 can be yetfurther increased to the absolute maximum, since the slits 11 can be extended to the absolute maximum,that isto terminate adjacent the bent edge so as to extend effectively right across the brush base portion. Adjustment ofthe height ofthe bent edge enables the spring forces in the brush arm to be adjusted.

Claims

1. Abrushforan electricmotorcomprising: a brush arm including a brush properformed of a resilient material and adapted for electrical contact with the commutator of an electric motor in a configuration in which the brush arm is resiliently bent; and aterminal portion including a terminal lead portion adapted for electrical connection of said brush in an external electric circuit; a base portion ofthe brush arm andtheterminal portion being coupled together in overlapped relation, and the brush arm being provided with slits in said base portion whereby to extend the effective length (as herein defined) of the brush arm.

2. A brush according to Claim 1, wherein the brush extends from the said base portion in one direction, the edge of the base portion on the side opposite the said one direction being bent out of the plane of the base portion to provide reinforcement therefor.

3. A brush according to Claim 2,wherein the said slits extend across said base portion to terminate closely adjacentthe said bent edge.

4. A brush according to any preceding claim wherein the said base portion is generally rectangular in shape, the brush proper has a generally rectangular shape overall but is divided by lengthwise slits into a plurality offingers, the said lengthwise slits being open at the distal end ofthe brush properand terminating adjacent the overlap between the base portion and the terminal portion, and the slits in the brush base are continuous with the side edges ofthe brush proper.

5. Foran electric motor, a brush substantially as hereinbefore described with reference to and as shown in Figs. 2 to 7 ofthe accompanying drawings.

6. Brush gearforan electric motor, comprising a motor case cover adapted to serve as a holder for brush gearforthe motor, and two brushes constructed in accordance with any of the preceding claims mounted in said brush holder with the respec tive terminal lead portions extending through terminal lead apertures in said motor case coverfor electrical connection in an external electric circuit.

7. A motor case cover substantially as hereinbe- fore described with reference to and as shown in Figs.

2 to 7 of the accompanying drawings.

8. An electric motor having a motor case mounting one or more permanent magnetstherewithin and adapted to serve as the statorforthe motor; a rotor shaft mounting a rotor and commutator; and a motor casecoveraccording to Claims 6 or7 closing one axial end ofthe motor case, and with the brushes proper thereof resiliently bent into sliding contact with the commutator.