GB2049306A

GB2049306A - Brush holding arrangement

Info

Publication number: GB2049306A
Application number: GB8015405A
Authority: GB
Original assignee: Mabuchi Motor Co Ltd
Current assignee: Mabuchi Motor Co Ltd
Priority date: 1979-05-10
Filing date: 1980-05-09
Publication date: 1980-12-17
Also published as: HK65185A; DE3017322A1; ES250592Y; JPS5845494Y2; JPS55162370U; BR8002854A; DE3017322C2; GB2049306B; ES250592U

Abstract

The brush-holder differs from that of GB 2 033 168 A in that the L-shaped gripping portions 4' are defined by cuts or incisions 10' (rather than by recesses) each having confronting faces that remain in frictional contact over the greater part of the length of the cut when the brush is inserted, thereby to resist longitudinal or twisting movement of the portions 4'. <IMAGE>

Description

SPECIFICATION Brush holding arrangement This invention is concerned with a brush holding arrangement for providing brush gear for an electric motor.

Various brush holding arrangements have been previously proposed for mounting brushes to provide brush gear for an electric motor. One such prior proposal, which we shall discuss in more detail below with reference to Figures 1 to 3 of the accompanying drawings, provides an elongate plate formed of resilient material and having a through aperture provided in the plate for reception of a root portion of a brush, the brush being retained in position by portions of the plate bent out of the plane thereof and bearing against the side surfaces of the root portion. Adequate pressure must be applied against the brush root portion if it is not to become detached since there has been a trend in recent years to forming the brush holding plate of relatively thinner material.The loss of mechanical strength cannot be overcome by increasing the width of the brush holding plate since, particularly in miniature electric motors, space is at a premium.

Our British Patent Application No 7935017 (Published Specification No 2033168) describes and claims an elongate plate formed of resilient material and on which a brush is adapted to be mounted to provide brush gear for an electric motor, the longitudinal marginal edges of the plate being bent out of the plane thereof, and a through aperture being provided in the plate for reception of a root portion of a brush, and portions of the plate which are generally L-shaped in section with one limb of the L lying generally in the plane of the plate and the other limb being bent out of the plane of the plate to one side thereof being formed along the edge of the aperture on opposite sides thereof so that when an appropriately dimensioned brush root portion is forced into said aperture from the other side of said plate the said other limb portions make planar contact with the sides of said root portion and the resultant elastic deformation of the plate supports the said root portion against retraction through the aperture.

The present invention provides an elongate plate formed of resilient material and on which a brush is adapted to be mounted to provide brush gear for an electric motor, the longitudinal marginal edges of the plate being bent out of the plane thereof, and a through aperture being provided in the plate for reception of a root portion of a brush, and portions of the plate which are generally L-shaped in section with one limb of the L lying generally in the plane of the plate and the other limb being bent out of the plane of the plate to one side thereof being formed along the edge of the aperture on opposide sides thereof, the said one limb of each L-shaped portion being separated from the remainder of the plate by incisions or cuts formed alongside the said one limb, whereby each said L-shaped portion is connected to the remainder of the plate only at its proximal end, the arrangement being such that when an appropriately dimensioned brush root portion is forced into said aperture from the other side of said plate the said other limb portions make planar contact with the sides of said root portion and the resultant elastic deformation of the plate supports the said root portion against retraction through the aperture.

The invention is hereinafter more particularly described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a previously proposed brush holding arrangement; Figure 2 is a sectional view taken in the plane of the lines A, A' in Figure 1; Figure 3 is a similar sectional view illustrating mounting of the brush on the plate; Figure 4 shows a plan view of a plate constructed according to the present invention; Figure 5 is a perspective view generally similar to Figure 1 illustrating a brush holding arrangement employing the plate of Figure 4; Figure 6 is a sectional view taken in the plane of the arrows B. B' shown in Figure 5, the view being generally similar to Figure 2; and Figure 7 is a view generally similar to Figure 3 but for the embodiment of Figures 4to 6.

Figures 1 to 3 shown one example of a previously proposed brush holding arrangement in which a brush 1, for example a carbon brush, with a root portion 2 is mounted on a brush holding plate 3 by means of portions 4 of the plate which are cut and bent out of the plane thereof at the edges of a through aperture 7 for receiving the root portion 2.

An end face 5 of the brush 1 is arranged to make electrical contact with a commutator portion of an electric motor (not shown), while surfaces 6 are arranged for engagement by the cut and bent portions 4 when the root portion 2 of the brushes is forced through aperture 7. The longitudinal marginal edges 8 of the plate 3 are bent out of the plane thereof for reinforcing the same. As will be clear from Figure 3, the root portion of the brush is forced between the cut and bent portions 4 and through aperture 7. The resiliency of the cut and bent portions 4 provides a force tending to restore the portions 4 to their original position. Thus, the brush 1 is resiliently supported on the plate 3, as shown in Figures 1 and 2, by the force exerted by the portions 4 on the surfaces 6.However, we have found that in brush holding arrangements of this type, damage may be caused to the brush root portion by virtue of the pressure exerted by the distal ends of portions 4 on the surfaces 6, the brush 1 being usually of a somewhat brittle material.

In Figures 4to 7, which illustrate a brush holding arrangement embodying the present invention, it will be seen that brush holding plate 3' (made of an electrically conductive, resilient material, as before) has portions 4' cut along incisions 10' and bent out of the plane of the plate along 9' into a generally L-shaped section. The incisions 10' at both sides of the L-shaped portions 4' do not involve removal of material but result in the said portions being connected to the remainder of the plate only at their proximal ends. One limb 11' of the L of each portion 4' is bent out of the plane of the plate to the same side as the bent marginal edges 8' and serves as a brush contact portion; and the other limb 12' forms a base for its L-shaped portion 4' lying in the plane of the plate.

The provision of incisions or cuts 10' at both sides of the L-shaped portions 4' permits these portions to be resiliently bent more freely, the elastic deformation extending into and being accomodated by the bent marginal edge regions 8' provided along both sides of the plate 3'. To mount the brush 1, its root portion 2 is forced into the through aperture 7 in the direction shown by an arrow in Figure 7. This causes expansion or spreading apart of the brush contact portions 11 ' of the L-shaped portions 4', inducing elastic deformation of the marginal edge regions 8' as shown at 13' in Figures 5 and 6. By this means, the brush 1 is inserted into aperture 7 with its surfaces 6 and upstanding limbs 11 of the L-shaped portions 4' kept essentially in contact with each other.The fully mounted configuration is shown in Figures 5 and 6 from which it will be apparent that the marginal edge regions 8' are elastically deformed by expansion outward as the brush 1 enters aperture 7. Thus, the brush 1 is held in position by resiliency inter alia of the edge regions 8'. As shown, the incisions or cuts 10' extend to the foot of the marginal edge regions 8'. The chosen length 1 of the incision 10' as determined by (i) the thickness t of the material of the plate, and (ii) the height of the bent marginal edge edge regions 8', to achieve the desired resilience to be caused by deformation of the edge regions 8'.

The length of the incision 10' may not be such as to extend to the foot of the edge regions 8' in some cases, or may be so long as to encroach upon the edge region 8' in other cases, depending on the aforementioned factors (i) and (ii). In extreme cases the mere provision of incisions and bending to achieve the L-shaped configuration of cut and bent portions 4' may be sufficient to cause deformation in the marginal edge regions 8'. In all cases elastic deformation of the marginal edge regions 8' as shown by elastically deformed regions 13' contributes to the force holding the brush 1 in position.

As explained above, the provisions of cuts or incisions 10' alongside the L-shaped portions 4' enables these portions to flex to some extent substantially as a whole, the elastic deformation being largely taken up in the marginal edge portions 8'. The plate 3' is, however, formed of relatively thin material and there might therefore be a tendency for the L-shaped portions to be displaced sideways thereof (i.e, longitudinally of the plate) or to twist.

This tendency is largely overcome by providing mere cuts or incisions 10' without significant removal of material alongside the portions 4' since the side edges of the base portions 12' of the L-shaped .portions 4' over at least the greater part of their lengths from the respective proximal ends of the portions 4' remain in frictional contact with or at least alongside the remainder of the plate across the cuts or incisions, even when the plate is elastically deformed by mounting a brush, as shown in Figure 6.

Claims

1. An elongate plate formed of resilient material and on which a brush is adapted to be mounted to provide brush gearfor an electric motor, the longitudinal marginal edges of the plate being bent out of the plane thereof, and a through aperture being provided in the plate for reception of a root portion of a brush, and portions of the plate which are generally L-shaped in section with one limb of the L lying generally in the plane of the plate and the other limb being bent out of the plane of the plate to one side thereof being formed along the edge of the aperture on opposite sides thereof, the said one limb of each L-shaped portion being separated from the remainder of the plate by incisions or cuts formed alongside the said one limb, whereby each said L-shaped portion is connected to the remainder of the plate only at its proximal end, the arrangement being such that when an appropriately dimensioned brush root portion is forced into said aperture from the other side of said plate the said other limb portions make planar contact with the sides of said root portion and the resultant elastic deformation of the plate supports the said root portion against retraction through the aperture.

2. A plate according to Claim 1, wherein the longitudinal marginal edges of the plate are bent out of the plane thereof to said one side.

3. A plate according to Claim 1 or Claim 2, wherein the said L-shaped portions are formed along the said edge of the aperture adjacent the marginal edges of the plate.

4. A plate according to Claim 3, wherein the length of each said cut or incision is selected to provide the desired resilient force on the brush root portion, and preferably extends to the foot of the adjacent marginal edge portion of the plate.

5. Substantially as hereinbefore described with reference to Figures 4 to 7 of the accompanying drawings, an elongate plate formed of resilient material and on which a brush is adapted to be mounted to provide brush gear for an electric motor.