GB2028005A

GB2028005A - Brush holding assemblies for electrical machines

Info

Publication number: GB2028005A
Application number: GB7927323A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1978-08-05
Filing date: 1979-08-06
Publication date: 1980-02-27
Also published as: FR2432793B1; GB2028005B; JPS5523899U; IT7922284V0; JPS6233498Y2; DE7823480U1; FR2432793A1

Abstract

A brush holding assembly for an electrical machine is pre-assembled as a structural unit. A plate (1) of insulating synthetic material supports two pairs of metal brush holders (7), the holders (7) being radially displaceably inserted into recesses (5, 6, Figure 3 not shown) in the plate (1) and being held in position on the plate by brush pressure springs (16). Holders (19, Figure 3 and 26) are also moulded on the plate for a live bus (20) connected to the positive brushes, and for the tails (14) of the brushes; and terminals (29) are provided on the plate, in the region of mounting holes (33, Figure 4 not shown), for the tails of the negative brushes. <IMAGE>

Description

SPECIFICATION Brush holding assemblies for electrical machines The invention relates to a brush holding assembly comprising at least two pairs of brush holders mounted on a support plate.

Such an assembly is known wherein the support plate is made from electrically conductive material and the brush holders fixed thereon formed from insulating synthetic material. However, it has proved disadvantageous that the rough operating conditions in motor vehicles and the penetration of moisture into the synthetic brush holders result in disintegration of the synthetic material of the, generally sintered, brushes. Furthermore, the synthetic material brush holders increasingly fail to meet thermal requirements.

It is also known practice in a brush holding assembly to use an insulated support ring on which the metal brush holders are guided in a longtudinal slot and are fixed by means of screws. The positive brushes are connected by means of an insulated connection cable whose ends are provided with terminal parts and are screwed onto the respective brush holders The brush pressure springs take the form of helical springs and act by way of an associated pivotable lever upon the brushes which are merely guided on the brush holder. Because such brush holding assemblies have so many individual parts, they are not suitable for economical automatic mass production. Also, these known brush holding assemblies do not guarantee adequately shake-free guidance of the brushes.

The present invention resides in a brush holding assembly comprising an insulating support plate which is made of synthetic material and on which are disposed at least two pairs of metallic brush holders which receive brushes, and a live bus which is connected two of the brushes, recesses being formed in the support plate and the brush holders being inserted radially displaceably in said recesses and held in position on the support plate by pressure springs which bias the brushes, holders for the live bus and for tails of the brushes being moulded on the support plate and terminal parts for the tails of the other two brushes being disposed in the region of mounting holes of the support plate and the brush holding assembly being constructed as a unit which may be completely pre-assembled on the support plate.

This construction has the advantage that it is automatically pre-assembled as a structural unit on a support plate made from synthetic material. The support plate is so formed that all components may be disposed on it in a detachable yet shake-free manner by plugging or insertion without special fastening components, thus making it economicai for mass production. Another advantage is that the brushes are guided over their entire length in metallic brush holders which are held by the brushpressure springs in position on the support plate.

The live bus, which is integrated in the brush holding assembly and is made from inexpensive non-insulated material, is of particular advantage. Provided with a flat connecting region for another electrical conductor, it does not have to be insulated.

The invention is further described, by way of example, with reference to the drawings, in which: Figure 1 shows a part of a starter motor with its brush holding assembly shown in cross-section along the line I-I of Figure 2, Figure2 is a section along the line ll-ll of Figure 1, Figure 3 is a view of the brush holding assembly in the direction of the arrow III of Figure land Figure 4 is a section of the bearing plate along the line IV-IV of Figure 3.

The brush holding assembly has a support plate 1 which is moulded from insulating synthetic material.

The support plate 1 has a central bore 2 through which a commutator 3 of a starter motor 4 for an internal combustion engine projects. Recesses 5 and 6, each pair for accommodating a brush holder 7, are formed in the bearing plate 1. Associated Indentations 9 and 10 join up with the recesses 5 and 6 respectively on the underside 8 of the support plate 1.

Four metal brush holders 7 of substant ally rectan gularcross-section have on a narrow side two bent-out tabs 11 and 12 which have an end bent approximately parallel to the narrow side of the brush holder 7. On a broad side of each brush holder 7 is a slot 13 which is open towards the commutator 3 and out of which a tail 14 of a carbon brush 15 is guided. The entire length of the brush 15 is guided in the brush holder 7. One end face of the brush 15 is pressed against the commutator 3 while its other end face lies adjacent to one end of a compression spring 16 which is likewise housed in the brush holder 7. In addition, the brush holder 7 is provided at its end remote from the commutator 3 with two guide lugs 17 and 18.The guide lugs 17 and 18 are adapted to the circular periphery of the helical compression spring 16 with the result that the compression spring 16 is centered on the rectangular brush 15. The ends of the guide lugs 17 and 18 are bent over the end of the compression spring 16 which projects out of the brush holder 7. The tabs 11 and 12 of each brush holder 7 project through the recesses 5 and 6 of the support plate 1. The compression spring 16 holds the brush holder 7 on the suport plate 1 in that it urges the brush holder 7 radially away from the commutator 3 until the bent ends of the tabs 11 and 12, which project through the recesses 5 and 6, engage in the indentations 9 and 10 on the underside 8 of the support plate 1.

Two forklike holders 19 are formed on the underside 8 of the support plate 1 in the region of two adjacent-lying pairs of recesses 5, 6. A live bus 20 made from non-insulating material is bent into a substantially U-shape. It is locked into the holders 19. The ends of the live bus 20 are flattened and are located in lateral notches 21 and 22 on two opposite sides of the support plate 1. The back of the U-shaped live bus 20 projects laterally beyond the support plate 1 and has a flat connecting region 23.

In the illustrated embodiment, the live bus 20 is made from inexpensive wire having a round crosssection. It may, however, have a different crosssection.

On the side 24 of the support plate 1 which carries the brush holders 7, there are formed projecting crosspieces 25 for lateral guidance of the brush holders 7 and fourforklike holders 26. The latter are located near the side of each brush holder 7 which is provided with the slot 13 for the tail 14 of the brush 15. The associated tails 14 of the brushes 15 are clamped into the holders 25. The ends of the tails of the two oppositely lying positive brushes 15 project into the notches 21 and 22 and are fixed there by means of resistance welds on the ends of the live bus 20. The ends of the tails of the two negative brushes 15 are fixed by means of resistance welds on two associated terminals parts 27 and 28. The terminal parts 28 and 27 are U-shaped and are provided with tags 29 which are bent perpendicularly from their backs the associated tail 14 is welded onto the tag 29.A hole 30 in one limb each of the terminal parts 27 and 28 is aligned with a threaded bore 31 in the other limb of the terminal parts 27 and 28. It is the limb towards which the tag 29 is bent that is provided with the threaded bore 31. The support plate 1 is provided, at least on its underside 8, with ribs 32 which act as assembly aids for the terminal parts 27 and 28. Between the ribs 32 there is a mounting hole 33 for each of the terminal parts 27 and 28 in the support plate 1. The terminal parts 27 and 28 are placed laterally on the support plate 1 in such a manner that the hole 30 and the threaded bore 31 align with the mounting hole 33.

The brush holding assembly thus formed is automatically pre-assembled and forms a complete unit with all the brushes already connected. The unit need only be connected to a current terminal 34 of the excitation winding of the starter motor 4. For this purpose, the current terminal 34 is fixed on the connecting region 23 of the live bus 20 by means of resistance welding. A covering cap 35 is placed over the unit and is screwed by means of screws 36 on the terminal parts 27 and 28 on the support plate 1. The covering cap 35 is fixed on the housing of the starter motor 4.

Claims

1. A brush holding assembly for an electrical machine, comprising an insulating support plate which is made of synthetic material and on which are disposed at least two pairs of metallic brush holders which receive brushes, and a live bus which is connected two of brushes, recesses being formed in the support plate and the brush holders being inserted radially displaceably in said recesses and held in position on the support plate by pressure springs which bias the brushes, holders for the live bus and for tails of the brushes being moulded on the support plate and terminal parts for the tails of the other two brushes being disposed in the region of mounting holes of the support plate, and the brush holding assembly being constructed as a unit which may be completely pre-assembled on the support plate.

2. A brush holding assembly as claimed in claim 1, in which indentations are formed on the underside of the support plate remote from the brush holders and adjoin the recesses and in which ends of fastening tabs of the brush holders engage in there indentations.

3. A brush holding assembly as claimed in claim 1 or 2, in which the pressure springs of the brushes are helical compression springs.

4. A brush holding assembly as claimed in claim 1, in which the live bus has a flat connecting region to which another electrical conductor is attached.

5. A brush holding assembly as claimed in any of claims 1 to 4, in which the live bus is made from non-insuiated material.

6. A brush holding assembly substantially as herein described with reference to and as illustrated in the accompanying drawings.