GB2085665A - Brush-holder for electrical machines - Google Patents

Abstract

The brush-holder has at least one pivotally mounted support arm (30) for a brush (31), which support arm is acted upon by a spring (35) for pressing the brush against a rotating counter-contact surface. The spring (35) is secured to the support arm (30) in the vicinity of the brush (31), as shown by a rivet (42), and its free end portion (44), extending beyond the fastening point, biases the brush to keep it in position. Consequently, the support arm may be rigidly formed. The brush-holder ensures reliable contacting between the brush and a rotating counter-contact surface even in the case of high mechanical stress. <IMAGE>

Description

SPECIFICATION Brush-holder for electrical machines The invention relates to a brush-holder for an electrical machine.

A brush-holder ofthis kind is already known (German Auslegeschrift No. 1,613,433) in which a moulded body of resilient plastics material serves as a support arm and has a recess in which the brush and a connection lead are clamped. Although this brush-holder is of simple construction, it can only withstand limited mechanical stress and is thus only suitable for machines of low output. The clamping connection of the brush in the support arm can become loose in the event of high mechanical stresses, whereupon satisfactory function of the brushholder may not be ensured.

In another known embodiment of a brush-holder (German Offenlegungsschrift 25 36 018), the support arm is in the form of a resilient element to which the brush is, for example, soldered or sintered. Although this results in a rigid connection between the brush and the support arm and also provides an inexpensive solution which is convenient with respect to assembly, the range of application of this solution is also limited owing to the fact that the support arm is not completely rigid transversely to the axis of the brush.

There is provided by the present invention a brush-holder for an electrical machine having at least one pivotally mounted support arm on which a brush is mounted, means for electrically connecting the brush to a contact secured relative to the frame, and a spring which acts upon the support arm for the purpose of pressing the brush against a rotating counter-contact surface; wherein the spring acting upon the support arm is secured to the support arm in the vicinity of the brush and a free end portion extending from the fastening point presses the brush against an axial shoulder on the support arm or against a retaining member secured to the support arm.

In contrast to the known brush holders, the brush holder in accordance with the present invention has the advantage that the support arm itself need not have any resilient properties and thus can be made as a dimensionally stable construction, so that a reliable and vibration-proof holder for the brush is provided by simple means and ensures reliable contact between the brush and the rotating counter-contact, even in the case of high mechanical stresses.

A particularly distortion-free ree holder and accurate guidance of the brush in the support arm result when the support arm is in the form of a rigid moulded body having a recess for receiving the brush, and the axial shoulder for supporting the brush is provided in the recess.

The axial shoulder in the excess can be a conically tapering portion of the recess, wherein additional frictional forces occur to hold the brush in the support arm.

The spring acting upon the support arm is preferably a leaf spring and its free end portion pressing against the brush can be reinforced by an additional spring which is secured to the support arm preferably together with the leaf spring.

Furthermore, the leaf spring acting upon the support arm can additionally serve as an electrical contacting element for the brush. If the brush is connected to a flexible connection lead, the latter can be soldered or welded advantageously to a metal fastening element for the spring, such as a hollow rivet, current being carried from this fastening element up to a contact, fixed relative to the frame, solely by the spring.

Three embodiments of the invention are illustrated in the accompanying drawings and will be further described in the following specification.

Figure 1 is a side elevation of the brush-holder in accordance with the first embodiment, and Figures 2 and 3 show the other two embodiments, in each case with reference to a section through the brush and the point at which it is secured to the support arm.

The brush-holder of Figure 1 has a main body 10 on which is formed a flange 11 which is provided with two bores 12 and 13 for securing the brushholder to the housing of a three-phase generator. A voltage regulator 17 for the three-phase generator is secured by rivets 15 and 16 to a second flange 14 which is formed at the top end ofthe main body 10 as seen in Figure 1. The voltage regulator 17 has two connection pins 18 and 19 which extend into a free space 20 which is delineated at the top by the voltage regulator 17, at the sides by two perpendicular walls 21 and 22, and at the bottom by a partition 23 of the main body 10.

A space 25 is formed in the main body 10 below the partition 23 and is defined by a perpendicular wall 26 and two side walls 27,28 of the main body 10. A pivot pin 29 is mounted in the two side walls 27, 28 and passes transversely through the space 25.

Two support arms 30 for respective brushes 31 are pivotally mounted on the pivot pin 29 and, in the drawing, are located in alignment in the direction of the pivot pin. Each support arm 30 is a rigid member which is moulded from plastics materiai and which has a hub portion 32 incorporating a bearing bore, and, at an obtuse angle thereto, the end portion 33 carrying the brush 31. The end portion 33 is provided with a longitudinal passage in which is guided a leaf spring 35 which, when the brush-holder is fitted, presses the brush 31 against a rotating countercontact surface 36 on the rotor shaft of the threephase generator.The central portion 38 of the leaf spring 35 is in the form of an open eye and is bent around the hub portion 32 of the support arm 30 so as to be spaced therefrom, and that end portion 39 of the leaf spring 35 which is remote from the brush 31 is secured to the main body 10 in the manner which will be further described below.

The brush 31 has an annular shoulder 40 and is inserted into a correspondingly shaped recess 41 in the end portion 33 of the support arm 30. The parts are so dimensioned, and their tolerances are such, that the brush is slightly oversize and is seated in the recess 41 in a p(ay-free manner. If required, the brush can be additionally retained in the support arm 30 by adhesive. The spring 35 is secured to the support arm by a hollow metal rivet 42 in which a flexible connection lead 43 for the brush 31 is soldered. That free end portion 44 of the leaf spring 35 which extends beyond the hollow rivet 42 is bent in a S-shaped manner and its apex or crest presses against the inserted brush 31, whereby an additional retaining force is exerted on the brush 31.

That end portion 39 of the lead spring 35 which is remote from the brush 31 is connected to a contact element secured to the main body 10. The leaf spring 35 of the support arm 30 visible in the drawing is connected to an angled contact bracket 46 which is connected to the housing of the voltage regulator 17 by a metal rivet 16 and, by way of the said housing, to components in the voltage regulator. The leaf spring 35 of the second one (not visible in Fig. 1) of the support arms 30 is connected to a contact plate 47 which, on the one hand, forms a soldering tongue 48 for connection of an electrical lead and, on the other hand, has an extension 49 which is welded to the connection pin 19 of the voltage regulator 17.

The other connection pin 18 of the voltage regulator 17 is welded to a contact plate 50 which projects through the perpendicular wall 21 of the main body 10 and which has an extension 51 which rests on the flange 11 and extends into the region of the bore 12 and is connected to earth when the brush-holder is fitted.

In the arrangement which has been described, the brush 31 is retained in the support arm 30 by simple means in a reliable and vibration-free manner, so that reliable contacting is ensured between the brush 31 and the rotating counter-contact surface 36 even under high mechanical stress and at high rotational speeds. Current is fed to the brush 31 solely by the leaf spring 35 between the hollow rivet 42 on the support arm 30 and the fixed contact mounted on the main body 10.

In the embodiment of Figure 2, a brush 54 has a conical head 55 which is seated in a play-free manner in a complementary recess 56 in a support arm 57. A leaf spring 59 is secured to the support arm 57 by means of a rivet 60 and the free end portion 58 of the spring 59 acts upon the brush 54. The free end portion 58 of the leaf spring 59 is reinforced by a second leef spring 61 which, together with the leaf spring 59, is secured to the support arm 57 by the rivet 60. The electrical connection of the brush 54 is effected solely by the leaf spring 59, so that separate additional means are not required for this purpose.

As a result of conicity of the head 55 of the brush 54 and ofthe corresponding portion ofthe recess 56 in the support arm 57, additional frictional forces occur forthe purpose of retaining the brush 54 in the support arm 57.

In the embodiment of Figure 3, a brush 64 is secured to a support arm 65, in the form of an inherently stable plastics part, by an additional sheet metal member 66 which, together with a leaf spring 67, is secured to the support arm 65 by means of a rivet 68.

The top of the brush 64 has an annular shoulder 69 whose bottom annular surface rests partially on a free end portion 70 of the leaf spring 67 extended beyond the rivet 68, and partially on an angled end portion 71 of the sheet meta! member 66. The sheet metal member 66 is of slightly resilient construction and is provided with a concave portion 71 which presses resiliently against the top end face of the annular shoulder 69 of the brush 64. In this manner, the brush 64 is retained in the sheet metal member 66 in a vibration-free manner, the leaf spring 67 in this case also serving as a contacting element for the brush 64 in addition to its holding function.

Claims (10)

1. A brush-holderforan electrical machine having at least one pivotally mounted support arm on which a brush is mounted, means for electrically connecting the brush to a contact secured relative to the frame, and a spring which acts upon the support arm for the purpose of pressing the brush against a rotating counter-contact surface; wherein, the spring acting upon the support arm is secured to the support arm in the vicinity of the brush and a free end portion extending from the fastening point presses the brush against an axial shoulder on the support arm or against a retaining member secured to the support arm.

2. A brush-holder as claimed in claim 1, wherein the support arm is a rigid moulded body having a recess for receiving the brush, and the axial shoulder for supporting the brush is provided in the recess.

3. A brush-holder as claimed in claims 1 and 2, wherein the axial shoulder is formed by a conically tapering portion of the recess in the support arm.

4. A brush-holder as claimed in any of the preceding claims, wherein the spring is a leaf spring.

5. A brush-holder as claimed in claim 1,wherein a sheet metal member is provided at the free end portion of the support arm, to serve as a retaining memberforthe brush, and the brush is provided with an annular shoulder which is clamped in the sheet metal member.

6. A brush-holder as claimed in claim 4, wherein the free end portion of a leaf spring also fastened to the arm is arranged to act on the brush annular shoulder to assist in retaining the shoulder in the retaining member.

7. A brush-holder as claimed in claim 6, wherein the leaf spring and the sheet metal member are commonly secured to the support arm by a fastening element.

8. A brush-holder as claimed in one ofthe preceding claims 1 to 4, wherein the spring which pres seethe brush against the rotating counter-contact surface is secured to the support arm by a hollow metal rivet in the bore of which is soldered a flexible lead for the brush.

9. A brush-holder as claimed in one ofthe preceding claims, wherein the spring acting upon the support arm is that used with the releasing member of claimS, serves as a contacting elementforthe brush.

10. A brush-holder substantially as hereinbefore described with reference to Figure 1,2 or 3 of the accompanying drawings.