GB2187044A - Brush holder for electric motor - Google Patents

Abstract

The brush holder comprises an elongate plate (10) of resilient material having an aperture (13) for receiving a brush root (14), at least two gripping portions (16,17) bent out of the plane of the plate and disposed along opposite edges of the aperture, and at least one and preferably at least two transversely extending stiffeners (20,21) which are provided to increase the plate's resistance to distortion across the width of the plate. The stiffeners are preferably in the form of ribs or beads pressed from the plate, although they could be separate parts secured to the plate. <IMAGE>

Description

SPECIFICATION Brush holderforelectric motor This invention relates to a brush holder for an electric motor and particularly for small electric motors such as permanent magnet direct current micromotors.

It is well known, particularly in relation to p.m.d.c.

motors, to use brush holders which each comprise an elongate plate of resilient material provided with integral side walls and an aperture in the plate through which a root of a brush is inserted. The brush is retained in the aperture by gripping portions which are bent out of the plane of the plate and which bear against the brush root. It is common practiceto make the elongate plate from thin material to allow the plate to provide a spring action urging the brush against the commutator of the motor. However, when the root of the brush is inserted into the aperture in such a plate the plate is distorted out of its plane as the brush root spreads the gripping portions; also the side walls are forced outwardly. As the plate distorts in this mannerthe resulting pressure applied to the brush root by the gripping portions is diminished.

According to the present invention there is provided a brush holderforan electric motor, comprising an elongate plate of resilient material, an aperture in the plate for receiving a root portion of a brush, at least two opposed gripping portions bent out of the plane ofthe plate and disposed along the edge of the aperture, and at least one stiffener extending transversely of the plate and spaced from the aperture in the direction ofthe longitudinal extent of the plate.

Preferably, there are at least two stiffeners, one on either side ofthe aperture as considered in the direction ofthe longitudinal extent of the plate.

Advantageously, for ease of manufacture, the or each stiffener is in the form of a rib pressed from the plate. However, the or each stiffener could bea separate part secured to the plate.

The stiffener(s) will increase the plate's resistance to distortion across the width ofthe plate with the result that when a brush root is inserted into the aperture in the plate the plate will distort less and the gripping portions will therefore exert a greater gripping force, all other circumstances being equal, on the brush root.

The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which Figure t is a plan view of an end of a known brush holder, Figure2 is an end view of the brush holder of Figure 1 before insertion of a brush root, Figure 3 is a view similarto Figure 2 but after insertion of a brush root, Figure 4 is a plan view of one embodiment of a brush holder according to the present invention, Figure 5is an end view of the brush holder of Figure 4 before insertion of a brush root, and Figure6isaviewsimilarto Figure 4 after insertion of a brush root.

Referring firstly to Figures 1 to 3 of the drawings, the known brush holder shown therein is of a type commonly referred to as a brush leaf and comprises an elongate plate 10 of resilient electrically conductive material, e.g. beryllium copper, having integralsidewalls 11 and 12extending longitudinallyofthe plate and a rectangularaperture 13 in the plate for receiving a root 14 of a brush 15.

Gripping portions 16 and 17 are bentoutofthe plane ofthe plate and extend along opposite edges ofthe aperture 13.

As shown in Figure 3, when a root of a brush 15 having a lateral dimension greaterthanthe separation between the free longitudinal edges of the gripping portions 16 and 17 is inserted into the aperture 13,the plate distortswith the resultthatthe pressure applied bythegripping portions 16 and 17 on the brush root is not as great as it would otherwise have been.

Referring now to Figures 4 to 6 ofthe drawings,the elongate plate 10 has two elongate stiffening beads 20 and 21 pressed therefrom. The beads 20 and 21 extend transversely ofthe plate and are disposed one on eitherside ofthe aperture 13.

As shown in Figure 6, these beads 20 and 21 increase the resistance of the plate 10 to distortion, as considered intransverse section,with the result thatthe gripping portions maintain a better grip on the brush root.

As above described the plate has two beads 20 and 21. However,the plate may have only one such bead or even more than two. Instead of beads other appropriately shaped stiffeners could be provided and the stiffeners need not necessarily be pressed from the plate as they could be separate parts secured to the plate.

Moreover, although it is preferred that the brush holder has side walls these are not absolutely essential and in any event it is common practicefor the side walls notto extend along the full length of the plate.

1. A brush holder for an electric motor, comprising an elongate plate of resilient material, an aperture in the plate for receiving a root portion of a brush, at least two opposed gripping portions bent out ofthe plane of the plate and disposed along the edge ofthe aperture, and at least one stiffener extending transversely ofthe plate and spaced from the aperture in the direction ofthe longitudinal extent ofthe plate.

2. The brush holder of claim 1, wherein there are at least two stiffeners, one on either side of the aperture as considered in the direction ofthe longitudinal extentofthe plate.

3. The brush holderof claim 1 or claim 2, wherein the plate has integral sidewalls bent out of the plane of the plate and extending longitudinally of the plate overatleastthat region thereof adjacentto the aperture.

4. The brush holder of anyone of the preceding claims, wherein the or each stiffener is in the form of a bead pressed from the plate.

5. A brush holder for an electric motor,

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Brush holderforelectric motor This invention relates to a brush holder for an electric motor and particularly for small electric motors such as permanent magnet direct current micromotors. It is well known, particularly in relation to p.m.d.c. motors, to use brush holders which each comprise an elongate plate of resilient material provided with integral side walls and an aperture in the plate through which a root of a brush is inserted. The brush is retained in the aperture by gripping portions which are bent out of the plane of the plate and which bear against the brush root. It is common practiceto make the elongate plate from thin material to allow the plate to provide a spring action urging the brush against the commutator of the motor. However, when the root of the brush is inserted into the aperture in such a plate the plate is distorted out of its plane as the brush root spreads the gripping portions; also the side walls are forced outwardly. As the plate distorts in this mannerthe resulting pressure applied to the brush root by the gripping portions is diminished. According to the present invention there is provided a brush holderforan electric motor, comprising an elongate plate of resilient material, an aperture in the plate for receiving a root portion of a brush, at least two opposed gripping portions bent out of the plane ofthe plate and disposed along the edge of the aperture, and at least one stiffener extending transversely of the plate and spaced from the aperture in the direction ofthe longitudinal extent of the plate. Preferably, there are at least two stiffeners, one on either side ofthe aperture as considered in the direction ofthe longitudinal extent of the plate. Advantageously, for ease of manufacture, the or each stiffener is in the form of a rib pressed from the plate. However, the or each stiffener could bea separate part secured to the plate. The stiffener(s) will increase the plate's resistance to distortion across the width ofthe plate with the result that when a brush root is inserted into the aperture in the plate the plate will distort less and the gripping portions will therefore exert a greater gripping force, all other circumstances being equal, on the brush root. The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which Figure t is a plan view of an end of a known brush holder, Figure2 is an end view of the brush holder of Figure 1 before insertion of a brush root, Figure 3 is a view similarto Figure 2 but after insertion of a brush root, Figure 4 is a plan view of one embodiment of a brush holder according to the present invention, Figure 5is an end view of the brush holder of Figure 4 before insertion of a brush root, and Figure6isaviewsimilarto Figure 4 after insertion of a brush root. Referring firstly to Figures 1 to 3 of the drawings, the known brush holder shown therein is of a type commonly referred to as a brush leaf and comprises an elongate plate 10 of resilient electrically conductive material, e.g. beryllium copper, having integralsidewalls 11 and 12extending longitudinallyofthe plate and a rectangularaperture 13 in the plate for receiving a root 14 of a brush 15. Gripping portions 16 and 17 are bentoutofthe plane ofthe plate and extend along opposite edges ofthe aperture 13. As shown in Figure 3, when a root of a brush 15 having a lateral dimension greaterthanthe separation between the free longitudinal edges of the gripping portions 16 and 17 is inserted into the aperture 13,the plate distortswith the resultthatthe pressure applied bythegripping portions 16 and 17 on the brush root is not as great as it would otherwise have been. Referring now to Figures 4 to 6 ofthe drawings,the elongate plate 10 has two elongate stiffening beads 20 and 21 pressed therefrom. The beads 20 and 21 extend transversely ofthe plate and are disposed one on eitherside ofthe aperture 13. As shown in Figure 6, these beads 20 and 21 increase the resistance of the plate 10 to distortion, as considered intransverse section,with the result thatthe gripping portions maintain a better grip on the brush root. As above described the plate has two beads 20 and 21. However,the plate may have only one such bead or even more than two. Instead of beads other appropriately shaped stiffeners could be provided and the stiffeners need not necessarily be pressed from the plate as they could be separate parts secured to the plate. Moreover, although it is preferred that the brush holder has side walls these are not absolutely essential and in any event it is common practicefor the side walls notto extend along the full length of the plate. CLAIMS

1. A brush holder for an electric motor, comprising an elongate plate of resilient material, an aperture in the plate for receiving a root portion of a brush, at least two opposed gripping portions bent out ofthe plane of the plate and disposed along the edge ofthe aperture, and at least one stiffener extending transversely ofthe plate and spaced from the aperture in the direction ofthe longitudinal extent ofthe plate.

2. The brush holder of claim 1, wherein there are at least two stiffeners, one on either side of the aperture as considered in the direction ofthe longitudinal extentofthe plate.

3. The brush holderof claim 1 or claim 2, wherein the plate has integral sidewalls bent out of the plane of the plate and extending longitudinally of the plate overatleastthat region thereof adjacentto the aperture.

4. The brush holder of anyone of the preceding claims, wherein the or each stiffener is in the form of a bead pressed from the plate.

5. A brush holder for an electric motor, substantially as hereinbefore described with reference to Figures 4-6 oftheaccompanying drawings.