GB2060274A - Commutator device - Google Patents

Abstract

Each commutator piece in an electric motor comprises a commutator portion 2, and a terminal portion 3 integral therewith and bent at right angles thereto out of the surface thereof to define a supporting projection 8 at each side of the terminal portion extending therefrom in the direction away from the commutator portion. The commutator pieces are received on an insulating support with the terminal portions received in respective terminal grooves 6, 6' of the insulating support, the supporting projections received in an annular groove 9 on the insulating support, and the commutator portions arcuately bent about their length. The arrangement counters, for example, separation of distal ends of positions 2 and the support as discussed w.r.t. Fig. 1E (not shown). A gap between portion 3 and the washer or flange portion 5 (Fig. 7, not shown) tends to fill as washer 7 and the wall of groove 6 are softened during soldering of lead wires. <IMAGE>

Description

SPECIFICATION Commutator device This invention relates to commutator devices for electric motors.

Commutator devices for small electric motors have been proposed previously in the form of a plurality of commutator pieces mounted in position on an insulating support by means of an insulating washer. As we shall explain below with reference to Figs. 1A to E, we have found problems with this previously proposed arrangement. The present invention has arisen from our work seeking to avoid or mitigate these problems.

In accordance with the present invention, there is provided for an electric motor, a commutator device having a plurality of electrically conductive commutator pieces mounted in position on an insulating washer; each commutator piece comprising a commutator portion, and a terminal portion integral therewith and being bent at right angles thereto out of the surface thereof to define a supporting projection at each side of the terminal portion extending therefrom in the direction away from the commutator portion; and the commutator pieces being received on the insulating support with the terminal portions received in respective terminal grooves of the insulating support, the supporting projections received in an annular groove on the insulating support, and the commutator portions being arcuately bent about their length.

The invention also extends to the individual commutator pieces.

The invention is hereinafter more particularly described by way of example only with reference to the accompanying drawings, in which: Fig. 1 A shows a blank from which the commutator piece of a previously proposed commutator device may be formed; Fig. 1 B is a perspective view of the commutator piece formed from the blank of Fig. 1 A; Fig. 1 C is a perspective view of the insulating support of a previously proposed commutator device; Fig. 1 D is a perspective view similar to Fig. 1 C illustrating the fully assembled previously proposed commutator device; Fig. 1 E shows the previously proposed commutator device of Figs. 1A to 1 D in longitudinal section; Fig. 2A is a view generally similar to Fig. 1 A of a blank for forming a commutator piece for an embodiment of commutator device in accordance with the present invention;; Fig. 2B is a view generally similar to Fig. 1 B illustrating a commutator piece of a commutator device in accordance with the present invention; Fig. 3 is a perspective view generally similar to Fig. 1 C illustrating the insulating support of an embodiment of commutator device in accordance with the present invention; Fig. 4 is a front elevation of the insulating support of Fig. 3 as seen in the direction of the arrow a; Fig. 5 is a longitudinal section view of the insulating support of Figs. 3 and 4 as seen in the direction of the arrows b-b; Fig. 6 is a front elevation of a fully assembled commutator device in accordance with this invention; and Fig. 7 is a longitudinal sectional view of the commutator device of Fig. 6 taken along the line c-c' in Fig. 6.

The commutator piece 1 of the previously proposed commutator device of Figs. 1A to 1 E is produced by forming an electrically conductive metal strip, for example of copper, into blanks having a generally square spade shape (Fig. 1 A) similar to the shape of a Japanese battledore, and bending the blank along the dotted line shown in Figs. 1 A and 1 B to define a commutator portion 2 and a terminal portion 3 integral therewith. The commutator portion 2 is bent about its length into a circular-arc shape to complete the commutator piece 1 as shown in Fig. 1 B. The support 4 on which three such commutator pieces 1 are mounted is generally cylindrical as shown in Fig.

1 C, and is made of an insulating material, such as synthetic resin, with an integral flange portion 5 provided with terminal grooves 6, 6' and 6" (the latter not illustrated) for receiving the terminal portions 3. With three commutator pieces 1, 1' and 1" mounted on the insulating cylinder 4 with their terminal portions 3 received in the terminal grooves 6, 6' and 6", an insulating washer 7 (shown in Fig. 1 D) is fitted to the commutator portions 2 in order to hold the commutator pieces in position. Engagement of the terminal portions 3, 3' and 3n with the respective terminal grooves 6, 6' and 6" effectively prevents unwanted displacement circumferentially. It is difficult, however, to ensure that the commutator portions 2, 2' and 2" always remain in close contact with the insulating support cyclinder 4.The effect of tightening the insulating washer 7 is to hold the commutator piece in a so-called cantilevered state, as shown in Fig. 1 E. In this state, the distal end of the commutator portion 2 tends to separate from the insulating support cylinder 4, as shown by dotted lines in the figure. This would result in poor contact between the commutator portion and the brush during the rotation of the motor, leading to generation of sparks and electrical noise, deterioration of motor performance due to poor rectifying or shortening of the service life of the motor due to rapid wear of the brushes. To overcome this problem, various means have been proposed such as moulding the commutator pieces and the insulating cylinder into one piece or fixing the commutator pieces to the insulating cylinder using adhesive, but each of these involves increased manufactunng costs.

Reference numerals 1 to 7 in Figs. 2A to 7 correspond to the like numerals in Fig. 1.

A commutator piece 1 for a commutator device in accordance with this invention may be formed from a generally square spade shaped blank cut from an electrically conductive metal strip, such as copper, as shown in Fig. 2A. Projections 8 (for a purpose to be explained) are formed at each side of the terminal portion 3 by means of incisions.

The commutator portion 2 and the projections 8 are bent by a predetermined degree into a circular arc. The terminal portion 3 is bent along the dotted line shown in Fig. 2A to extend at right angles from the surface of the commutator portion. The resulting shape of the commutator piece 1 is shown in Fig. 28. The projections 8 extend away from the terminal portion in the direction away from the commutator portion 2.

The insulating support on which the commutator pieces 1 of Fig. 2B are mounted to form a commutator device in accordance with this invention is shown in Figs. 3 to 5. The embodiment ot support shown In Figs 3 to b comprises a cylinder portion 4 for accommodating three commutator pieces over the surface thereof.

The insulating cylinder 4 is made of an insulating material, such as synthetic resin, and is provided with an integral flange portion 5. On the flange portion 5, terminal grooves 6, 6' and 6" are provided for receiving the terminal portions 3 of the commutator pieces 1 and a segmented annular groove 9 is provided for receiving the supporting projections 8.

To mount the commutator pieces 1 of Fig. 28 on the insulating support of Fig. 3, three commutator pieces 1 are placed on the insulating cylinder 4 by engaging their terminal portions 3 and their supporting projections 8, the terminal grooves 6, 6' and 6" respectively and the respective segmented portions of annular groove 9. And then, the insulating washer 7 is fitted over the commutator portions 2, as described, referring to Fig. 1. No perspective view illustrating the external appearance of the resultant commutator device assembled in this way is shown because it is much like Fig. 1 D illustrating the previously proposed commutator device. However, a front view of the assembled commutator device is shown in Fig. 6 and a cross-sectional view taken on line c-c' in Fig. 6 is shown in Fig. 7.

As is evident from Figs. 3 to 7, a commutator piece 1 of the described embodiment of commutator device in accordance with this invention is held in place on the insulating support 4 both by tightening the insulating washer 7 over commutator portion 2 and by engagement of the supporting projections 8 with a segment of annular groove 9. This two-position support of the commutator pieces 1 does not tend to make the distal ends of the commutator portions 2 separate from the cylinder 4 and keeps the commutator portions 2 in close contact with the cylinder 4 over their entire surface. Furthermore, the engagement of the terminal portions 3 and the supporting projections 8 with respective terminal grooves 6 and with respective segments of the annular groove 9, respectively, serves to prevent the commutator pieces 1 from being moved in the circumferential direction of the cylinder 4.

Displacement of the commutator pieces in the axial direction is also prevented since the terminal portion 3 is held in place by the pushing force of the insulating washer 7.

ideally, the depth of the terminal groove 6 should be the same as the thickness of the terminal portion 3. In actual practice, however, the thickness of the terminal portion 3 may be changed for some reason or other. Allowing for this, the groove 6 may be formed slightly deeper than the thickness of the terminal portion 3, as shown in Fig. 7, causing a gap G to remain.

between the terminal portion 3 and the flange portion 5 or the insulating washer 7. Even in such a case, however, the commutator piece 1 is securely held on the insulating support 4 because the gap G tends to fill as the insulating washer 7 and the wall of the terminal groove 6 are softened by heat applied to the terminal portion 3 during soldering of a lead wire to the terminal portion 3.

Because the commutator pieces are firmly held in place and tend not to separate from the support generation of sparks and electrical noise between brushes and commutator pieces during the rotation of the motor is largely mitigated or prevented. Thus, a commutator device having improved rectifying performance in obtained. This leads to improved motor performance and prolonged motor life.

Claims (8)

1. For an electric motor, a commutator device having a plurality of electrically conductive commutator pieces mounted in position on an insulating washer; each commutator piece comprising a commutator portion, and a terminal portion integral therewith and being bent at right angles thereto out of the surface thereof to define a supporting projection at each side of the terminal portion extending therefrom in the direction away from the commutator portion; and the commutator pieces being received on the insulating support with the terminal portions received in respective terminal grooves of the insulating support, the supporting projections received in an annular groove on the insulating support, and the commutator portions being arcuately bent about their length.

2. A commutator device as claimed in Claim 1, wherein the insulating support is made of synthetic resin.

3. A commutator device as claimed in CLaims 1 or 2, wherein the insulating support comprises a cylindrical portion along which the commutator portions extend; and a flange portion having a surface perpendicular to the surface of the cylindrical portion, the terminal grooves being formed in the said perpendicular surface and extending radially of the axis of the cylindrical portion.

4. A commutator device according to Claim 3, wherein the annular groove is formed in said perpendicular surface adjacent its junction with the cylindrical surface such that the internal circumferential surface of the annular groove is flush with the cylindrical surface.

5. A commutator device according to any preceding Claim, wherein the said annular groove is segmented the respective segments thereof extending in the annular direction from one terminal groove to the next.

6. For an electric motor, a commutator device substantially as hereinbefore described with reference to and as shown in Figures 2B and 3 to 7.

7. A commutator piece for a commutator device of an electrical motor, the commutator piece being as defined in Claim 1.

8. For a commutator device of an electric motor, a commutator piece substantially as hereinbefore described with reference to and as shown in Figure 2B of the accompanying drawings.