GB1563543A - Brush holders for electric machines - Google Patents

Description

(54) IMPROVEMENTS IN BRUSH HOLDERS FOR ELECTRICAL MACHINES (71) We, ROBERT BOSCH GmbH., a German Company, of Postfach 50, 7 Stuttgart 1, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention concerns brush holders for electrical machines and in particular, a brush holder having brush guides for a carbon brush and a pressure spring.

In a conventional brush holder the centring arrangement for the pressure spring is shaped like a lid which is locked onto the brush guide behind tabs and which has an annular protrusion slightly projecting into the end of the spring, thus centring the spring in the brush guide.

One disadvantage relating to this type of brush holder is that the brush guide and centring device are designed in two parts.

Furthermore a one piece brush guide which is provided with a tab on the end near the spring which is bent over the brush guide opening, is usual. A spring centring device is not supplied in this instance because the carbon brush has a square cross-section and the corresponding brush guide serves simultaneously as a concentric spring guide.

It has also been proposed to design tabs which are diagonally bent over the spring end, at the spring end of a rectangular brush guide having lateral channels of arcuate section so as to centre the pressure spring.

However the disadvantage of such a brush holder is that the longitudinal slit for the braided brush lead wire extends from the commutator end of the brush guide so that when the carbon brushes become severely worn, the braided brush lead wire can come into contact with the commutator, thus leading to possible damage of the electric machine as a result of a short.

A feature of the present invention is that is provides a brush holder in which each brush guide is designed as one piece fitment and at a low cost and that it provides adequate guidance for a pressure spring of circular cross-section, whilst still affording guidance and support to the rectangular shape of the carbon brush. It is also designed to facilitate frequent and easy replacement of the carbon brush and accurate centring of the pressure spring.

According to the present invention a brush holder for an electrical machine, comprises a base plate, and at least two brush guides fixed to the base plate, each brush guide comprising a one-piece hollow body adapted to accommodate a carbon brush at its inner end and a pressure spring at its outer end, each brush guide body having a longitudinal slit along a first side extending from the outer end of that side but terminating short of the inner end thereof for receiving a brush connection wire, and further having a longitudinally extending profiled portion of arcuate cross section on a side opposite said first side corresponding to the exterior diameter of the coil spring to be accommodated therein, each brush guide also having four recessed lugs or tabs integral with the brush guide at its outer end for deformation inwardly to locate, centre and retain the spring after it and the brush have been inserted in the body.

In a preferred embodiment, the lugs or tabs which locate the coil spring are formed at the outer end of those sides of each brush guide which contain the longitudinal slit and the profiled portion of arcuate cross section.

The coil spring may be centred most accurately if each recess on the lugs or tabs has an edge which is inclined with respect to the longitudinal axis of the brush guide to act as a lead-in for locating and centring the spring.

The invention will now be further described by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a plan of part of a brush holder and brush guide; Fig. 2 shows the spring end of the brush guide of Fig. 1; Fig. 3 is a side view of the brush holder of Fig. 1; and Fig. 4 is a three dimensional view to a larger scale of a section of the spring end brush guide as shown in Fig. 2.

A brush holder according to the present invention has a base plate 1, of which only part is depicted in Fig. 1. Brush guides 2 are attached to the base plate 1 and one of these is illustrated on the base plate 1, being held thereon by a rivet 3 and by a lug on the plate in the region of the brush guide. In practice, two or more brush guides would be provided on each plate. The brush guide 2 is manufactured as a single element made from metal strip. It has a predominantly square body with end flanges 4 and 5 of the metal strip forming attachment collars overlapping one another and secured together by means of attachment rivet 3.

In the brush guide 2 a carbon brush 6 and its associated pressure loading spring 7 are accommodated. The pressure spring 7 urges the carbon brush 6 onto the curved surface of a commutator 8 in known manner. A braided brush wire lead 9 is attached to the carbon brush 6 and juts out from the body of the brush guide 2 through a longitudinal slit 10 in one side of the body. The braided brush wire lead shown is welded onto the base plate 1 since the carbon brush 6 illustrated serves as a negative pole of an electrical machine.

The longitudinal slit 10 extends from the open spring end of the brush guide 2. It terminates at a channel 11 of arcuate section extending outwardly from the body and which prevents the brush wire lead 9 from coming into contact with the commutator 8 when the carbon brush 6 becomes severely worn. The side opposite the longitudinal slit 10 of the brush guide 2 is profiled in such a way that it is of arcuate cross section and is adapted at 12 to the exterior curvature of the pressure spring 7 (see Figs. 2 and 4).

For retaining spring 7 within guide 2, slots 13 and 14 are formed in the side walls of the guide close to and parallel with the end face 15 of the body of the guide. Four lugs or tabs 16, 17, 18 and 19 resulting from the formation of the slots are then deformed inwardly of the hollow body to form retainers for the outer end convolution of the spring, and have angular cut-out sections on their inner corners to form co-operating locating faces 20 and 21 which engage, centre and hold the outer end of the spring as best shown in Fig. 4. To facilitate location and centring of the spring, faces 21 are conveniently inclined with respect to the longitudinal axis of the brush guide to afford a lead-in.

The brush holder can be readily mass produced at a reasonable cost with the brush guides 2 designed in one part, because brush guides of this type can be manufactured automatically with dependable finish. The shape of the brush guide guarantees a safe brush wire lead guide together with a vibration proof, concentric spring guide and spring support whereby, when replacing the carbon brushes, the pressure spring can be introduced simply from the outer end, be compressed and the retaining lugs or tabs bent inwardly to hold it and the brush in place. This process can be repeated several times.

WHAT WE CLAIM IS: 1. A brush holder for an electrical machine, comprising a base plate, and at least two brush guides fixed to the base plate, each brush guide comprising a one-piece hollow body adapted to accommodate a carbon brush at its inner end and a pressure spring at its outer end, each brush guide body having a longitudinal slit along a first side extending from the outer end of that side but terminating short of the inner end thereof for receiving a brush connection wire, and further having a longitudinally extending profiled portion of arcuate cross section on a side opposite said first side corresponding to the exterior diameter of the coil spring to be accommodated therein, each brush guide also having four recessed lugs or tabs integral with the brush guide at its outer end for deformation inwardly to locate.

centre and retain the spring after it and the brush have been inserted in the body.

2. A brush holder as claimed in claim 1, in which the lugs or tabs are formed at the outer end of those sides of each brush guide which contain the longitudinal slit and the profiled portion of arcuate cross section.

3. A brush holder as claimed in claim 1 or 2 in which each recess on the lugs or tabs has an edge which is inclined to the longitudinal axis of the brush guide to act as a lead-in for locating and centring the spring.

4. A brush holder for an electrical machine constructed and arranged substantially as hereinbefore particularly described with reference to and as illustrated in the accompanying drawings.

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

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. A brush holder according to the present invention has a base plate 1, of which only part is depicted in Fig. 1. Brush guides 2 are attached to the base plate 1 and one of these is illustrated on the base plate 1, being held thereon by a rivet 3 and by a lug on the plate in the region of the brush guide. In practice, two or more brush guides would be provided on each plate. The brush guide 2 is manufactured as a single element made from metal strip. It has a predominantly square body with end flanges 4 and 5 of the metal strip forming attachment collars overlapping one another and secured together by means of attachment rivet 3. In the brush guide 2 a carbon brush 6 and its associated pressure loading spring 7 are accommodated. The pressure spring 7 urges the carbon brush 6 onto the curved surface of a commutator 8 in known manner. A braided brush wire lead 9 is attached to the carbon brush 6 and juts out from the body of the brush guide 2 through a longitudinal slit 10 in one side of the body. The braided brush wire lead shown is welded onto the base plate 1 since the carbon brush 6 illustrated serves as a negative pole of an electrical machine. The longitudinal slit 10 extends from the open spring end of the brush guide 2. It terminates at a channel 11 of arcuate section extending outwardly from the body and which prevents the brush wire lead 9 from coming into contact with the commutator 8 when the carbon brush 6 becomes severely worn. The side opposite the longitudinal slit 10 of the brush guide 2 is profiled in such a way that it is of arcuate cross section and is adapted at 12 to the exterior curvature of the pressure spring 7 (see Figs. 2 and 4). For retaining spring 7 within guide 2, slots 13 and 14 are formed in the side walls of the guide close to and parallel with the end face 15 of the body of the guide. Four lugs or tabs 16, 17, 18 and 19 resulting from the formation of the slots are then deformed inwardly of the hollow body to form retainers for the outer end convolution of the spring, and have angular cut-out sections on their inner corners to form co-operating locating faces 20 and 21 which engage, centre and hold the outer end of the spring as best shown in Fig. 4. To facilitate location and centring of the spring, faces 21 are conveniently inclined with respect to the longitudinal axis of the brush guide to afford a lead-in. The brush holder can be readily mass produced at a reasonable cost with the brush guides 2 designed in one part, because brush guides of this type can be manufactured automatically with dependable finish. The shape of the brush guide guarantees a safe brush wire lead guide together with a vibration proof, concentric spring guide and spring support whereby, when replacing the carbon brushes, the pressure spring can be introduced simply from the outer end, be compressed and the retaining lugs or tabs bent inwardly to hold it and the brush in place. This process can be repeated several times. WHAT WE CLAIM IS:

1. A brush holder for an electrical machine, comprising a base plate, and at least two brush guides fixed to the base plate, each brush guide comprising a one-piece hollow body adapted to accommodate a carbon brush at its inner end and a pressure spring at its outer end, each brush guide body having a longitudinal slit along a first side extending from the outer end of that side but terminating short of the inner end thereof for receiving a brush connection wire, and further having a longitudinally extending profiled portion of arcuate cross section on a side opposite said first side corresponding to the exterior diameter of the coil spring to be accommodated therein, each brush guide also having four recessed lugs or tabs integral with the brush guide at its outer end for deformation inwardly to locate.

centre and retain the spring after it and the brush have been inserted in the body.

2. A brush holder as claimed in claim 1, in which the lugs or tabs are formed at the outer end of those sides of each brush guide which contain the longitudinal slit and the profiled portion of arcuate cross section.

3. A brush holder as claimed in claim 1 or 2 in which each recess on the lugs or tabs has an edge which is inclined to the longitudinal axis of the brush guide to act as a lead-in for locating and centring the spring.

4. A brush holder for an electrical machine constructed and arranged substantially as hereinbefore particularly described with reference to and as illustrated in the accompanying drawings.