GB2154375A

GB2154375A - Process for minimizing the operating noise of an electric motor having a commutator and motor implementing this process

Info

Publication number: GB2154375A
Application number: GB08432192A
Authority: GB
Inventors: Michael Bethry; Patrick Minois
Original assignee: ELECTRO MEC NIVERNAIS; Electromecanique du Nivernais Selni Ste
Current assignee: ELECTRO MEC NIVERNAIS; Electromecanique du Nivernais Selni Ste
Priority date: 1984-01-06
Filing date: 1984-12-20
Publication date: 1985-09-04
Also published as: FR2558012B1; DE8500060U1; IT1182338B; GB8432192D0; IT8552806V0; FR2558012A1; YU210184A; IT8567007A0; GB2154375B; IT8567007A1

Abstract

A process for reducing the operator noise of an electric motor utilises a motor having a commutator (12) working with brushes arranged to slide in slides (14) of a brush holder (10). The slide is made of elastic material and/or a material such as PTFE. This causes vibrations to be damped and the resonant frequencies of the assembly to be shifted to less troublesome values. <IMAGE>

Description

SPECIFICATION Process for minimizing the operating noise of an electric motor having a commutator and motor implementing this process The invention relates to a process for minimizing the operating noise of an electric motor having a commutator and to a motor implementing this process.

First we recall that the commutator of the rotor of an electric motor contains segments separated from each other distributed regularly around the axis of rotation of the motor, two diametrically opposed segments being connected to the ends of a same rotor armaturewinding turn or of a set of turns in parallel.

Two brushes also diametrically opposed, in fixed positions, unlike the commutator which rotates, are in friction contact with the segments of the commutator such as to sequentially supply an excitation current to the turns connected to the segments of the commutator or to sequentially short-circuit these turns.

Electric motors having commutators, in particular general purpose motors, are in general use for domestic or industrial applications.

The inventors have observed that the noise caused by the friction of the brushes on the commutator has a level that is often too high, particularly for domestic applications.

The invention remedies this disadvantage.

it results from noting that the noise resulting from the rotation of a motor having a commutator is due not only to the actual friction of the brushes on the segments but also to vibrations and other displacements caused by this friction. Thus the friction of the brush on the segments of the commutator causes vibrations by the shock of the brush against the sides of the metal slide in which it is mounted and these vibrations, noisy in themselves, cause vibrations in the frame, also metal, of the motor; these vibrations are also causes of noise. In addition the brush moves radially in its slide because of irregularities in the commutator and because of the return of the brush by a spring; the friction of the brush on the metal side of the slide is a source of noise.

The invention thus relates to a process for minimizing the operating noise of an electric motor having a commutator working in conjunction with brushes each of which slides in a slide of a brush-holder. It is characterized in that a slide is chosen made of an elastic material and/or a material having a low coefficient of friction such as polytetrafluoroethylene PTFE or similar.

With such a material the shocks of the brush against the side of the slide cause low, level noise. In addition this material damps the vibrations that are transmitted to the frame of the motor via the support. In addition, the resonant frequencies of the assembly are not the same as those obtained with a metal slide. Finally, the low friction of the brush against the sides of its slide is also a noise reducing factor.

According to another of its aspects, the invention relates to an electric motor having a commutator working in conjunction with brushes each of which slides in a slide of a brush-holder. It is characterized in that the slide is made of an elastic material having a low coefficient of friction such as the said polytetrafluoroethylene or similar.

In one embodiment, the slide is integral with the support. In a variant only the slide is made of an elastic material and/or material having a low coefficient of friction; this embodiment being less expensive in mat-erial than the previous one.

In order to further reduce the vibratory stresses acting on the brush and the parts connected to it, it is possible to call upon other arrangements that are known in themselves, such as the inclination of the brush relative to the radial direction.

Other characteristics and advantages of the invention will become apparent with the description of certain embodiments, this description being made with reference to the appended drawings in which: Figure 1 is an exploded view showing in perspective a part of the casing of an electric motor having a commutator with a brushholder and a brush, Figure 2 is a cross-sectional view of the brush-holder represented in Fig. 1, and Figure 3 is a side view of the motor represented in Fig. 1.

In the example the brush-holder 10 is mounted on an end plate of an electric motor having a commutator 1 2 (Figs. 1 and 3).

The bush-holder 10 is monoblock in the example, i.e. the support 1 3 and the slide 14 form one integral part manufactured by moulding in polytetrafluoroethylene (PTFE) such as that known under the trade name "TEFLON". As a variant, instead of PTFE one of its derivatives such as PFA or PFE is used.

Other plastic materials can also suit.

The slide 14 has a longitudinal axis 1 5 (Figs. 2 and 3) that is inclided at about 15 relative to a radial direction. This inclination is such that when moving along the axis 1 5 in the centripetal direction this direction corresponds to the rotation, represented by the arrow a in Fig. 3, of the motor about its axis 16. The brush is, for example, made of graphitic carbon.

The monoblock brush-holder 10 includes a fixing plate 1 9 of elongated shape with, at each of its ends, circular projections 20 and 21 surrounding holes 22 through which can be passed means of fixing, such as screws 23 (Fig. 3), to the end plate 11. The latter has corresponding holes 24 opening on a flat surface 25 in a plane perpendicular to a radial direction. At the centre of the flat surface 25 opens another hole 26 emerges having a rectangular cross-section forming a housing for the lower part 27 of the support 13, i.e.

the part 27 of the support 1 3 that is below the plate 19.

This lower part 27 includes two lateral sides 28 and 29 perpendicular to the plate 19, a bottom 30 inclined at 15 relative to the plate 19, and the slide or housing 14 for the brush 1 8 that is also inclined at 15 relative to a direction perpendicular to the plane of the plate 1 9 in a direction such that, near this plate 19, the slide 14 is close to the lateral side 29 and distant from side 28. The bottom 30 is thus parallel to the end 1 7 of the brush 1 8. This bottom 30 is of course open to allow the brush 18 to pass through.

The cross-section of the internal part of the slide 14 is generally rectangular corresponding to the cross-section of the brush 18 with, however, in the middle of its long sides, grooves 31 and 32 in the shape of a sector of the same cylinder with axis 1 5. These slots or grooves form the housing for a spring 33 applied against the outer end 34 of the brush 1 8 in order to apply its inner end 17 against the commutator 12.

The upper surface 35 of the slide 14 has a groove 36 with edges parallel to the small sides of the rectangle formed in cross-section by the internal part of the slide. This groove 36 forms a housing for a plate 37 forming a stop for the upper end of the spring 33. This plate 37 is maintained in the groove by closing down a tab 38 formed by moulding with the rest of the brush-holder 10 and hinged to an upper edge of the latter. The hinge 39 is preferably formed by a simple thinning of this tab 38 at its join with the rest of the slide. Application against the upper surface 35 is obtained for example by means of screws opposite the hinge 39.

The part of the slide 14 above the plate 1 9 has, like that part below the plate, a general parallelepipedal shape.

To make the assembly strong, triangular flanges 40 and 41 connect a long side of the plate 19 to an edge of the slide t4.

In one embodiment, on the outer surface of the tab 38 is inscribed an arrow which, when the said tab is closed down, represents the required direction of rotation of the motor.

If the direction of rotation of the motor is changed, the brush-holder is turned through 180 so that the inclination relative to the radial direction still has the same direction relative to the direction of rotation of the motor.

In a way that is known in itself, the inclination of the brush relative to the radial direction applies the brush against a lateral side of the slide. The vibrations are thus attenuated.

However, this attenuation is, as has been noted, insufficient to reduce the noise to an acceptable level for certain applications. That is why, in accordance with the invention, the material of the slide is PTFE which is elastic, damps the vibrations and reduces the proportion of the latter that are transmitted to the end plate 11. The low friction of the graphitic carbon brush 1 8 against the PTFE, PFA or PFE side is also a noise-reducing factor. The monobloc embodiment of the brush-holder can also contribute to a reduction in sound level.

The invention includes not only a motor having a commutator but also the brushholder described above.

Claims

1. Process for minimizing the operating noise of an electric motor having a commuta- tor working in conjunction with brushes eachz of which slides in a slide of a brush-holder,X characterized in that a slide is chosen made of an elastic material and/or a material having a low coefficient of friction such as polytetrafluoroethylene (PTFE) or similar.

2. Electric motor having a commutator working in conjunction with brushes each of which slides in a slide of a brush-holder, characterized in that the slide is made of an elastic material having a low coefficient of friction such as polytetrafluoroethylene (PTFE) or similar.

3. Motor according to Claim 2, characterized in that the slide is integral with the rest of the brush-holder.

4. Electric motor according to-Claim 3, characterized in that the brush-holder is monoblock, the slide forming an integral part with a support, this brush-holder being for example produced by moulding.

5. Motor according to any of Claims 2 to 4, characterized in that the brush is inclined relative to a radial direction.

6. Motor according to any of Claims 2 to 5, characterized in that the brush-holder includes a plate for fixing against a flat surface on the motor casing.

7. Motor according to Claim 5, characterized in that the configuration of the brush is such that it can be turned round in order to maintain its direction of inclination when the direction of rotation (a) of the motor is changed.

8. Motor according to any of Claims 2 to 7, characterized in that it includes a tab at the top of the slide for maintaining a support spring applying the brush against the commutator and having on its outer surface a means of marking the direction of rotation of the motor.

9. Motor according to Claim 8, characterized in that the plate (18) is integral with the slide (14). its hinge (39) on the slide being formed by a thinning.

1 0. An electric motor substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.