GB2164502A

GB2164502A - Rotary electric machine

Info

Publication number: GB2164502A
Application number: GB08519736A
Authority: GB
Inventors: Takaichi Mabuchi
Original assignee: Mabuchi Motor Co Ltd
Current assignee: Mabuchi Motor Co Ltd
Priority date: 1984-08-06
Filing date: 1985-08-06
Publication date: 1986-03-19
Also published as: HK34791A; GB2164502B; GB8519736D0

Abstract

A rotary electric machine has a housing provided with an end closure 3 on which the brush gear for the rotary electric machine is mounted. The brush gear comprises two arm guides 14 mounted interiorly of the end closure. Brush arms 16 are coupled at their proximal ends to respective arm guides and have brush means 20 at their distal ends. An arc-shaped leaf spring 22 has its means 21 on the brush arms and ends engaged with spring receiving serves to bias the brush means into engagement with commutator or like pick-up means mounted for rotation with the rotor of the rotary electric machine. <IMAGE>

Description

SPECIFICATION Rotary electric machine Description This invention relates to rotary electric machines.

We have encountered problems in the provision of brush gear for rotary electric machines, and in particular for so-called "miniature" rotary electric machines such as miniature motors with a relative high output. It has previously been suggested, for example, to provide brushes and an associated spring incorporated in a cylindrical brush holder, the resiliency of the spring serving to bias the brushes into contact with a commutator or like pick-up means mounted for rotation with the rotor. We have found, however, that in brush gear of this general construction the biasing force on the brushes tends to vary with wear. Moreover, the construction tends to be relatively complicated.In another previously suggested arrangement, brushes are mounted on brush arms which are made of a resilient material and auxiliary brush arms reinforce the otherwise insufficient bias provided by the brush arms. We have also found that in this construction the biasing forces tend to vary with wear of the brushes. Moreover, the construction is again relatively complicated, and the brushes are not readily replaceable.

The present invention has arisen from our work seeking to overcome these drawbacks.

In accordance with the present invention, we provide a rotary electric machine having a housing provided with an end closure therefor on which brush gear for the said rotary electric machine is mounted, the brush gear comprising two arm guides mounted interiorly of the said end closure, brush arms coupled at their proximal ends to respective arm guides and having brush means at their distal ends, and an arc-shaped leaf spring, the ends of which are engaged with spring receiving means on the brush arms, serving to bias the said brush means into engagement with commutator or like pick-up means mounted for rotation with the rotor of the rotary electric machine.

The invention is hereinafter more particularly described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a somewhat schematic elevational view of the brush gear of a rotary electric machine constructed in accordance with the present invention as seen in the axial direction of the machine looking in the direction of the end closure thereof; Figure 2 is an elevational view of the end closure (shown in phantom lines) and the brush gear of Fig. 1 as seen from the right in Fig. 1; Figure 3 is a cross-sectional view through a brush arm guide of the brush gear of Figs. 1 and 2, to an enlarged scale; Figure 4 is a perspective view of a rotary electric machine in accordance with the present invention; Figure 5 is a longitudinal sectional view through the rotary electric machine of Fig. 4;; Figure 6 is an axial end elevational view of the rotary electric machine of Figs. 4 and 5 as seen from the left thereof; Figure 7 is a similar axial view as seen from the right in Figs. 4 and 5; Figure 8 is a side elevational view of the rotary electric machine of Figs. 4 and 5 as seen from the bottom in the said Figs. looking upward; and Figure 9 is an enlarged cross-sectional view through a preferred brush arm guide.

The embodiment of rotary electric machine shown in the accompanying drawings by way of example is a so-called "miniature" electric motor having a housing comprising a generally cylindrical motor case 1 and respective axial end closures 2 and 3 coupled together by means of fastening screws 4. As shown in Fig. 6, end closure 2 is provided with slotted holes 5 in which the fastening screws are received, the arrangement being such that the mounting position of end closure 3 (and thus also of the brush gear, described below, mounted thereon) relative to the remainder of the rotary electric machine can be adjusted over an arc. These slotted holes 5, together with vent holes 6 (Fig. 6) serve as cooling vent holes for the rotary electric machine.

Respective bearings 7 mounted in end closures 2 and 3 support a rotor 8 by means of its shaft 9. A commutator or like pick-up means co-operating with the brush gear of the rotary electric machine is provided at 10. End closure 3 has vent slots 11 as necessary for dissipating heat. As will be apparent from Fig.

4, a substantial part of the end closure 3 is cut away on one side (the bottom half in Fig.

4) with the exception of a portion 3a (see Figs. 4 and 5) on which the brush gear, generally indicated 12, is mounted. The stator is provided by the cylindrical motor case 1 interiorly of which are mounted permanent magnets 13 (though at 90 degrees from the position shown in Fig. 5).

Referring particularly to Figs. 1 to 3 and Fig.

5, the brush gear 12 includes two brush arm guides 14 each in the form of a generally cylindrical post made of a metallic material.

End closure 3 is made of an insulating material, such as a synthetic resin, and the arm guides 14 are fixedly mounted thereto via washers 15 by staking. Brush arms 16 are formed of metallic strip stock and have proximal end portions 1 6a which extend partway cricumferentially about the associated post 14.

The brush arm 16 has an edge portion 16b in electrical contact with a plate 17 which is arranged to serve as the terminal for connecting the rotary electric machine in an external electric current, the brush arm being clamped in place on the arm guide 14 by means of the said terminal plate 17, a fixing plate 18 made of an insulating material and a screw 19. The proximal end portion of the brush arm 16 is strengthened by means of a rib 16c. Longitudinal marginal edge portions 16d of the brush arm are bent out of the plane of the strip stock from which it is formed.

Brushes 20 proper are mounted at the distal ends of the brush arms 16 and spring receptacles 21 made of an insulating material are provided at a point intermediate the ends of the brush arms. As best shown in Fig. 1, an arc-shaped metallic leaf spring has its ends received in the respective spring receptacles 21 whereby to bias the brushes 20 into contact with a co-operating commutator 10 or the like. It will be appreciated that, with the construction shown, as the brushes 20 wear, the displacement of the brush arms at the position of engagement with the spring 22 is substantially less than the displacement of the brush arms at the distal ends thereof where the brushes 20 are mounted.Consequently, the biasing force resulting from resiliency of the spring will remain substantially the same as the brushes wear, and the rotating moment about the post 14 will remain substantially the same. Thus, the pushing force exerted by a brush on the commutator will remain essen tialiy constant as the brushes wear.

Because the two spring receptacles 21 are each made of insulating material, should either of the brush arms 16 mistakenly make electrical contact with the metallic leaf spring 22, insulation will be maintained by the spring receptacle assocated with the other brush arm, so avoiding a short-circuit between the two brush arms.

To replace the brushes 20, the ends of the leaf spring 22 are disengaged from the spring receptacles 21. The brush arms can then readily be removed from the arm guides 14 by loosening the respective fastening screws 19 and sliding the brush arm sideways. The brush 20 can then be replaced by a new brush 20 on the brush arm so removed; or, alternatively, a replacement pre-assembled brush/brush arm unit can be substituted.

Because the brush gear 12 is mounted on the lower inner surface of the closure 3, the brushes 20 rotate with the closure 3. Consequently, the relative positions of the brushes 20 with respect to the magnets 13 can be adjusted by selecting the position of the screws 4 in the slotted holes 5, so adjusting the angular position of the closure 3 relative to the cylindrical motor case 1. The position of the brushes 20 for optimum commutation can thus be readily chosen.

Referring now to Fig. 9 which shows an alternative embodiment, it will be seen that the post 14 is provided with circumferential ridges 1 4a on its outer surface. These ensure good electrical contact with the proximal end of the brush arm 16.

Although the description hereinabove has been primarily concerned with rotary electric machines in the form of a motor having a commutator 10, it should be understood that the invention applies equally well to direct current generators and other direct current machines, and also to slip-ring type motors, and to generators and other alternating current machines. In alternating current machines, adjustment of the commutating position will, of course, be unnecessary.

We have found that with the embodiments described above, the essentially constant biasing force on the brushes, independently of the state of wear of the brushes has the effect of stabilising the electrical performance of a motor. The construction of the brush gear is relatively simple, thereby facilitating manufacture and assembly. Brushes can readily be replaced with new brushes.

The provision of vent holes on the respective end closures efficiently dissipate heat generated in the rotor windings and by sliding contact between the commutator and the brushes. The commutating position can readily be adjusted for optimum results without removing components of the motor. We have found that the provision of the circumferential ridges 1 4a improves electrical contact between the brush arms and the associated arm guides, and hence with the terminals.

Claims

1. A rotary electric machine having a housing provided with an end closure therefor on which brush gear for the said rotary electric machine is mounted, the brush gear comprising two arm guides mounted interiorly of the said end closure, brush arms coupled at their proximal ends to respective arm guides and having brush means at their distal ends, and an arc-shaped leaf spring, the ends of which are engaged with spring receiving means on the brush arms, serving to bias the said brush means into engagement with commutator or like pick-up means mounted for rotation with the rotor of the rotary electric machine.

2. A rotary electric machine according to Claim 1, wherein the spring receiving means comprise spring receptacles made of an insulating material and mounted on the brush arm, which brush arm is made of metal, at a point intermediate its ends, and wherein the said leaf spring is made of metal.

3. A rotary electric machine according to Claim 1 or Claim 2, wherein each said arm guide comprises a post, the proximal end of the associated brush arm extending partway circumferentially of said post and being clamped axially thereto by co-operating screw means and a plate adapted to serve as an electric terminal for connection of the rotary electric machine in an external circuit.

4. A rotary electric machine according to Claim 3, wherein each said post is formed of electrically conductive material and is provided with at least one circumferential ridge thereon, the proximal end portion of the brush arm being in electrical contact with said post at least through said ridge(s).

5. A rotary electric machine according to any preceding claim, wherein each brush arm is formed of strip stock with longitudinal marginal edge portions thereof bent out of the plane of the said strip stock.

6. A rotary electric machine substantially as hereinbefore described with reference to and as shown in the accompanying drawings.