GB2143682A - Improved disk commutator - Google Patents

Abstract

The invention relates to an improved disk commutator which comprises a metallic support 7 whose faces are insulated and on which a dish 1 is glued. This dish 1 comprises a ring 2 glued against the base 7d of the support, a central collar cooperating with a countersink 7b and a peripheral skirt 3 applied against the outer face 7c of the support. The dish comprises radial grooves 5, which determine plates 6 separated once a base of the ring is eliminated. The invention finds particular application to a disk commutator for an electric starter. <IMAGE>

Description

SPECIFICATION Improved disk commutator The present invention relates to an improved disk commutator.

It is known that a commutator of this type is usually constituted by a ring-shaped piece of copper on which is moulded a body of plastics material.

Moulding is generally also effected on a metal sleeve adapted to reinforce the bore in which the shaft of the machine will be force-fitted. After moulding, the plates are separated from one another by milling or turning the copper ring, this operation destroying radial beads connecting the plates together.

The plastics material constituting the body may also be moulded on a multiplicity of individual plates suitably maintained in the mould, but the complexity of the latter can readily be imagined if all the plates are to remain in position during moulding.

According to one or the other of the methods, the plates of the commutator are maintained in the plastics material by anchoring means, so that all the mechanical efforts absorbed by the plates and which are due either to the centrifugal force or to the thermal stresses generated by the welding of the conductors and by the functioning of the machine, are supported only by the plastics material of the body of the commutator. The plates often separate and this naturally leads to the commutator being put out of service. In an attempt to overcome these drawbacks, it has already been provided to reinforce the plastics body with a metallic piece, but this solution has not brought any noteworthy improvement and in addition seriously complicates moulding.

It may also be noted that the plates of the commutators supported by a thick insulant are heat-insulated so that the heat that they store is difficult to dissipate. Abnormal overheating therefore occurs in the known commutators, which, in certain cases, even deteriorates the plastics material.

Moreover, this insulant poses serious problems when the conductors are welded on the plates since in that case there are considerable risks of fusion of said insulant. The precautions necessary for heat protection of the latter involves considerably increased costs. Finally, there are problems of differential expansion between the plates and the insulant so that this factor may be detrimental, under severe conditions of use, to the longevity of the commutator.

The purpose of the improvements forming the subject matter of the present invention is to overcome these drawbacks and such improvements aim at allowing the plates of a disk commutator to withstand thermal shocks and the centrifugal force, whilst considerably improving their cooling.

A disk commutator according to the invention comprises a metal support rendered insulating on the surface and a multiplicity of plates each comprising an outer tab oriented perpendicularly to its trapezoidal partition and a lug parallel to the tab, the latter cooperating with the peripheral face of the support, whilst the lug is in abutment against the peripheral face of a countersink in the support, the various elements of each plate being adhered to the support by means of a heat-resistant glue.

The invention will be more readily understood on reading the following description with reference to the accompanying drawings, in which: Figure lisa partial view in perspective of the copper dish intended to form the active part of a disk commutator according to the invention.

Figure 2 is a section thereof along two radial grooves.

Figure 3 is a section showing the dish of Figure 1 mounted with respect to its metal support.

Figure 4 is a view similar to that of Figure 3, but showing the finished commutator.

Figure 5 is a partial view thereof in elevation.

Figure 6 is a view similar to that of Figure 1, but illustrating a variant.

Figure 7 is a view in perspective of one of the plates used with the support of Figure 3.

Figure 8 illustrates another embodiment of the support according to the invention.

Referring now to the drawings, the dish 1 partially illustrated in Figure 1 essentially comprises a ring 2 which is bordered by a skirt 3 on its outer periphery and by a collar 4 on its inner periphery. The skirt and the collar are oriented perpendicularly to the ring 2 and are of identical height. It will be noted that the dish 1 (Figure 1) comprises a multitude of grooves 5 oriented radially with a view to determining sectors 6 for reasons which will be explained hereinafter. It will be observed that the grooves 5 do not traverse the whole thickness of the ring 2, with the result that the latter comprises a solid base 2a illustrated in Figure 2.

The metallic support 7 adapted to receive the dish 1 is preferably made of an aluminium-based alloy, its faces being insulated by a varnish, anodization or any corresponding means. The support 7 presents in transverse section the form of a cone of which the central bore 7a which is adapted to be fitted on the shaft (not shown) of the armature, comprises a countersink 7b whose diameter corresponds, to within the clearance, to the outer diameter of the collar 4. The support 7 comprises a peripheral face 7c, perpendicular to its base 7d and whose diameter is, to within the clearance, equal to the inner diameter of the skirt 3 of the dish 1.

The latter may therefore be applied against the base 7d of the support 7, its central collarfitting in the countersink 7d, whilst its skirt is applied against the peripheral face 7c of the support.

To make a commutator according to the invention, the base 7d, and the face 7c and the countersink 7b of the support are coated with heat-resistant glue, then the dish 1 is applied to said support so as to be fixed thereto.

The assembly obtained is then placed in an installation for welding the conductors coming from the armature on the skirt 3.

The grooves 5 determine sectors 6 provided at their two ends with tabs forming part of the skirt 3 and the collar 4 respectively. Under these conditions, to separate the sectors 6 from one another, it suffices to remove the base 2a by appropriate machining. An assembly of plates 8 isolated from one another and glued to the support 7 is thus obtained.

Prior to such machining, one or more conductors 9 coming from the armature (Figure 4) are associated with each of the outer tabs 8a of the plates 8 forming part of the skirt 3, such welding being effected by means of an electrode which is applied against the outer tab of each sector. Said tab is perfectly maintained by the peripheral face 7c of the support 7, so that the dish 1 is not deformed by the welds in question. Once the welds are effected, the abovementioned machining is carried out in order to remove the base 2a.

it will be observed that the shape of the support 7 enables the conductors to pass along the concave truncated face 7e without the latter being in contact therewith in order to avoid damaging them.

It will be noted that the support 7 may comprise coaxial incisions (not shown) made in its base 7d, with a view to receiving secondary collars borne by the ring 2 of the dish 1 and concentric to collar 4.

According to another embodiment, the dish might bear on its useful face 7d radial beads la (Figure 6) in which the grooves 5 would be extended so as to project from the useful face of the dish. By turning or milling the beads, the plates 8 would thus be separated with a minimum loss of copper.

According to a variant embodiment, the plates 8 may be made independently as illustrated in Figure 7, each plate comprising, as forth preceding variant, a trapezoidal partition 8a, an outer tab 8b adapted to cooperate with the peripheral face 7c of the support 7 and a central lug 8c abutting against the peripheral face of the countersink7b. To maintain the plates side by side on the base 7d of the support with view to gluing them on the base without their touching, it is provided to arrange on the base 7d of the support 7 radial beads 7f of height less than the thickness of the partition 8a of each plate 8 so that they are recessed with respect to the front face of the commutator, i.e. to the plane containing the front faces of all the plates.

A disk commutator has thus been made whose active part, i.e. the plates, are perfectly well anchored with respect to their support, particularly due to the presence of the tabs 8b said tabs positively retaining the plates with respect to the countersink of the support 7 when they are subjected to centrifugal force. Moreover, as the support 7 is made of metal, it allows easy dissipation of the calories accumulated in the individual plates during operation of the electric machine. This support may moveover comprise fins for increasing the coefficient of dissipation of the calories.

In addition, there is no need to provide any supplementary insert for good holding of the commutator on the shaft of the machine, since the support 7 is provided to be matallic and it is particularly adapted to absorb the efforts of fit.

Finally, it will be noted that the thickness of copper, i.e. that of the plates, is selected solely with a view to the electrical function and it is not determined by the mechanical anchoring devices as is necessary in the known commutators.

It must, moreover, be understood that the foregoing description has been given only by way of example and that it in no way limits the domain of the invention which would not be exceeded by replacing the details of execution described by any other equivalents.

Claims (9)

1. A disk commutator for rotating electric machine, wherein it comprises a metal support rendered insulating on the surface and a multiplicity of plates each comprising an outer tab oriented perpendicularly to its trapezoidal partition and a lug parallel to the tab, the latter cooperating with the peripheral face of the support, whilst the lug is in abutment against the peripheral face of a countersink in the support, the various elements of each plate being glued to the support by means of a heat-resistant glue.

2. A disk commutator as claimed in claim 1, wherein each plate is obtained from a dish divided by radial grooves into sectors which are separated from one another after its assembly to the support and welding of the conductors of the armature to said sectors.

3. A disk commutator as claimed in claim 2, wherein the grooves determine a base which is eliminated in order to constitute the plates.

4. A disk commutator as claimed in claim 2, wherein the grooves project beyond the useful face of the dish in radial beads which are planed in order to separate the plates.

5. A disk commutator as claimed in claim 2, wherein the support is in the form of a conical washer comprising a cylindrical peripheral face connected by a concave truncated wall to a boss in which the central hole of the support is made.

6. A disk commutator as claimed in claim 5, wherein the height of the tabs of each plate is equal to that of the cylindrical peripheral face of the support.

7. A disk commutator as claimed in claim 2, wherein the support comprises cooling fins.

8. A disk commutator as claimed in claim 2, wherein the dish comprises secondary collars concentric to the first collar and which engage in incisions made in the support coaxially to the countersink.

9. A disk commutator for rotating electric machine substantially as described hereinbefore and illustrated in the accompanying drawings.