GB2110883A - Brush holder - Google Patents

Abstract

A brush box comprising an insulating holder (1) with a conductor insert (4) for attachment to a brush (3) by a flexible conductor (11). The brush (3) is biased by a spring (13) within the holder or by coiled leaf springs outside the holder. <IMAGE>

Description

SPECIFICATION Brush holder This invention relates to brush boxes for hoiding brushes in electrical machinery.

Known means of holding brushes in electrical machinery comprises a metal box in which the brush may slide, a flexible connector between the brush box and the brush, and a biassing mechanism to urge the brush to project from the brush box and, in use, into contact with e.g. a commutator or slip ring.

When a brush is worn excessively it needs to be changed and this can be a difficult and time-consuming job in some electrical machinery, e.g. domestic appliances. Also a conducting brush box can be disadvantageous where space is restricted, as this can lead to short-circuiting.

This invention provides a brush box for use in electrical machinery comprising a brush holder of insulating material having a cavity for receiving an electrical brush, and a conductor insert having an electrical supply terminal portion, a leg to lie against a side of the brush holder cavity, and afoot to lie within the brush holder cavity and serve for attachment of a flexible conductor connection between the foot and the brush and, optionally, serve as an abutment for a biassing spring to toad the brush.

An advantage of such a brush box is that, having an insulating body, the risk of short-circuits is diminished.

Further advantages are that such a brush box is simple and cheap to manufacture, and can form part of a brush box assembly to be used as a cartridge, the entire brush box assembly being replaced when the brush has worn out.

The invention is illustrated by way of example with reference to the drawings Figs. 1 and 2.

Fig. lisa longitudinal section of a brush assembly and Fig. 2 is a longitudinal section of an alternative form of brush assembly.

A brush holder 1 of insulating material, e.g. glass filled or asbestos filled nylon has a cavity 2 to receive a brush 3. The brush 3 may be of graphite or any other suitable material or materials. A conductor insert 4 made of e.g. aluminium, brass tin, or coated steel, has an electrical supply terminal lug 5, a leg 6 lying along one side of the cavity 2, and a foot 7 lying across the cavity.

In the embodiment of Fig. 1 an extension 8 to the foot 7 is provided and lies along the side of the cavity opposite to the leg 6 so providing a stirrup shaped conductor within which the brush can slide. Such an extension can help to secure the conductor insert 4 in the cavity 2 by friction against the respective side wall but in the embodiment of Fig. 1 a bent-over tab 9 at the free end of the extension 8 is engaged with a recess 10 in the wall of the cavity 2.

The brush 3 is connected by a flexible conductor 11 to the foot 7 of the conductor insert 4. The attachment of the flexible conductor 11 to the foot 7 may be by e.g. soldering or riveting, and the attachment of the flexible conductor to the brush 3 may be by any of the known methods e.g. riveted, soldered, or a tamped metal powder connection.

Either the brush holder 1 and conductor insert 4 can be sold together for attachment to flexible conductor, biassing spring, and brush, or an assembled brush unit comprising all of these parts may be sold.

In Fig. 1 a compressive helical spring 13 is used to bias the brush 3 and holds the base of the brush 3 by frictional engagement with a reduced cross sectional portion 12.

In Fig. 2 an alternative arrangement for biassing the brush is shown comprising a "constant force spring" 14 which is effectively a pair of coiled leaf springs. Such an arrangement is well known in the manufacture of brush boxes as providing a relatively constant biassing force compared with helical springs. Other biassing means can easily be used with this invention.

Similarly alternative methods of securing the conductor insert in the holder may be envisaged, e.g. by screw attachment to the holder. The brush may be held in the holder of a brush assembly either by the strength of the flexible conductor or by other means such as by a tang at the mouth end of the conductor insert engaging a projection on the brush.

1. A brush box for use in electrical machinery and comprising a brush holder of insulating material having a cavity for receiving an electrical brush, and a conductor insert having an electrical supply ter minal portion, a leg to lie against a side of the brush holder cavity, and a foot to lie within the brush holder cavity and serve for attachment of a flexible conductor connection between the foot and the brush and, optionally, serve as an abutment for a biassing spring to load the brush.

2. A brush box as claimed in claim 1 wherein an extension to the foot of the conductor insert is provided to lie along that side of the brush holder cavity opposite to the side along which the conductor insert leg lies.

3. A brush box as claimed in claim 1 having a coiled leaf spring to urge the brush to project from the brush box.

4. A brush assembly comprising a brush box as claimed in claim 1, a brush, a flexible conductor connecting the brush and the foot of the conductor insert, and a biassing spring to urge the brush to project from the brush box.

5. A brush box as described herein and with reference to the drawing.

The drawing(s) originally filed was/were informal and the print here reproduced is taken from a later filed formal copy.

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

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Brush holder This invention relates to brush boxes for hoiding brushes in electrical machinery. Known means of holding brushes in electrical machinery comprises a metal box in which the brush may slide, a flexible connector between the brush box and the brush, and a biassing mechanism to urge the brush to project from the brush box and, in use, into contact with e.g. a commutator or slip ring. When a brush is worn excessively it needs to be changed and this can be a difficult and time-consuming job in some electrical machinery, e.g. domestic appliances. Also a conducting brush box can be disadvantageous where space is restricted, as this can lead to short-circuiting. This invention provides a brush box for use in electrical machinery comprising a brush holder of insulating material having a cavity for receiving an electrical brush, and a conductor insert having an electrical supply terminal portion, a leg to lie against a side of the brush holder cavity, and afoot to lie within the brush holder cavity and serve for attachment of a flexible conductor connection between the foot and the brush and, optionally, serve as an abutment for a biassing spring to toad the brush. An advantage of such a brush box is that, having an insulating body, the risk of short-circuits is diminished. Further advantages are that such a brush box is simple and cheap to manufacture, and can form part of a brush box assembly to be used as a cartridge, the entire brush box assembly being replaced when the brush has worn out. The invention is illustrated by way of example with reference to the drawings Figs. 1 and 2. Fig. lisa longitudinal section of a brush assembly and Fig. 2 is a longitudinal section of an alternative form of brush assembly. A brush holder 1 of insulating material, e.g. glass filled or asbestos filled nylon has a cavity 2 to receive a brush 3. The brush 3 may be of graphite or any other suitable material or materials. A conductor insert 4 made of e.g. aluminium, brass tin, or coated steel, has an electrical supply terminal lug 5, a leg 6 lying along one side of the cavity 2, and a foot 7 lying across the cavity. In the embodiment of Fig. 1 an extension 8 to the foot 7 is provided and lies along the side of the cavity opposite to the leg 6 so providing a stirrup shaped conductor within which the brush can slide. Such an extension can help to secure the conductor insert 4 in the cavity 2 by friction against the respective side wall but in the embodiment of Fig. 1 a bent-over tab 9 at the free end of the extension 8 is engaged with a recess 10 in the wall of the cavity 2. The brush 3 is connected by a flexible conductor 11 to the foot 7 of the conductor insert 4. The attachment of the flexible conductor 11 to the foot 7 may be by e.g. soldering or riveting, and the attachment of the flexible conductor to the brush 3 may be by any of the known methods e.g. riveted, soldered, or a tamped metal powder connection. Either the brush holder 1 and conductor insert 4 can be sold together for attachment to flexible conductor, biassing spring, and brush, or an assembled brush unit comprising all of these parts may be sold. In Fig. 1 a compressive helical spring 13 is used to bias the brush 3 and holds the base of the brush 3 by frictional engagement with a reduced cross sectional portion 12. In Fig. 2 an alternative arrangement for biassing the brush is shown comprising a "constant force spring" 14 which is effectively a pair of coiled leaf springs. Such an arrangement is well known in the manufacture of brush boxes as providing a relatively constant biassing force compared with helical springs. Other biassing means can easily be used with this invention. Similarly alternative methods of securing the conductor insert in the holder may be envisaged, e.g. by screw attachment to the holder. The brush may be held in the holder of a brush assembly either by the strength of the flexible conductor or by other means such as by a tang at the mouth end of the conductor insert engaging a projection on the brush. CLAIMS

1. A brush box for use in electrical machinery and comprising a brush holder of insulating material having a cavity for receiving an electrical brush, and a conductor insert having an electrical supply ter minal portion, a leg to lie against a side of the brush holder cavity, and a foot to lie within the brush holder cavity and serve for attachment of a flexible conductor connection between the foot and the brush and, optionally, serve as an abutment for a biassing spring to load the brush.

2. A brush box as claimed in claim 1 wherein an extension to the foot of the conductor insert is provided to lie along that side of the brush holder cavity opposite to the side along which the conductor insert leg lies.

3. A brush box as claimed in claim 1 having a coiled leaf spring to urge the brush to project from the brush box.

4. A brush assembly comprising a brush box as claimed in claim 1, a brush, a flexible conductor connecting the brush and the foot of the conductor insert, and a biassing spring to urge the brush to project from the brush box.

5. A brush box as described herein and with reference to the drawing.

The drawing(s) originally filed was/were informal and the print here reproduced is taken from a later filed formal copy.