WO1998010493A1

WO1998010493A1 - Commutator

Info

Publication number: WO1998010493A1
Application number: PCT/NO1997/000201
Authority: WO
Inventors: Svein Hestevik
Original assignee: Svein Hestevik
Priority date: 1996-09-03
Filing date: 1997-08-07
Publication date: 1998-03-12
Also published as: NO963687A; NO301915B1; NO963687D0; AU3870897A

Abstract

Commutator for electrical apparatus and equipment, in particular rotary electric machines, comprising a supporting member (45) and a number of electrically conductive segments (51-59) provided at a surface (45A) of the supporting member (45) and being electrically insulated from each other. At least said surface (45A) of the supporting member (45) consists substantially of aluminium. The surface (45A) is provided with a coating mainly of alumina (Al2O3) applied by thermal spraying of a powder material having alumina as a substantial ingredient. The electrically conductive segments (51-59) are applied on the alumina coating in the form of a copper layer.

Description

COMMUTATOR

This invention relates in general to the design of a commutator for rotary electric machines and other electrical apparatus and equipment units. As an alternative to rotating machines also linear electric motors in this connection can be provided with a commutator design according to the invention.

Electric machines being of interest in this connection can be both DC machines and AC machines. Moreover the prin- ciples and solutions to be explained in the following description, are essentially useful in motors as well as in generators. The new solution described for manufacturing a commutator, contributes to a high degree to more favourable cooling conditions for the commutator, which is very im- portant, in particular when there is the question of electric machines of higher or lower power rating.

Advantageously the commutator design can be incorporated in a total or combined machine structure as described in simultaneous patent application No. 96.3686. As an example of known techniques regarding commutators for electric machines, reference can be made to SE 356.642 and besides to Norwegian patent No. 169.570. Although this Norwegian patent specification does not mention anything about commutators for rotary electric machines, is relates to a method of applying an electrically conductive coating to a substrate. In one embodiment of the commutator according to the invention, the commutator segments are manufactured by means of a method corresponding substantially to what is described in the Norwegian patent specification. Stated more definitely the invention is directed to a commutator for rotary electric machines, comprising a supporting member and a number of electrically conductive segments provided at a surface of the supporting member and being electrically insulated from each other, whereby the novel and specific features essentially consist therein that at least said surface of the supporting member consists substantially of aluminium, that the surface is provided with a coating mainly of alumina (A1₂0₃) applied by thermal spraying of a powder material having alumina as a substan- tial ingredient, and that the electrically conductive segments are applied on the alumina coating in the form of a copper layer.

As already mentioned above the copper layer forming the segments, can be applied according to the above mentioned Norwegian patent specification, namely by thermal spraying of a copper powder. An alternative thereto can be to attach separate segments of copper foil material by means of adhesive techniques, which is fully possible with modern types of adhesives.

Compared to known designs the commutator according to the invention involves a number of advantages. In conventional electric machines the commutator as a rule is large and complicated. The individual commutator segments must be maintained in position and insulated from the machine structure or the supporting member. This is a manner of design requiring much space . Moreover the known types of segments will be somewhat elastic and can be deformed in the case of high rotational velocities. The segments in the commutator according to the invention can be made very thin, but anyhow can be very wear resistant. Furthermore, the coating of alumina can be very thin, which is advantageous for a good heat conduction, at the same time as sufficient electrical insulation is obtain- ed. With such an insulating coating and in particular in combination with thermally sprayed segments, unique properties are obtained in the various uses of the commutator. This in part is due to the spraying of the copper powder, which during the process will get a plasma form and be liquid, so that the conductive copper layer will have a particular structure. Thus, this form of copper layer is not suitable for usual etching, which in other uses can be regarded as a drawback, whereas in the uses contemplated here, this means an increased resistance against various stresses and strain. Moreover, it is obvious that this form of manufacturing commutator segments involves much freedom in configuring or shaping the segments.

Thus, commutators made according to the invention give a very good cooling of the segments, as these are heated because of the current flowing, and require little space at the same time as the mechanical stability also is very good. These advantages are obtained to a particularly high degree when the commutator is manufactured on the basis of the above mentioned Norwegian patent specification, that is primarily directed to a method of attaching electrical components to a substrate, such as a cooling flange.

In the following description the invention will be explained more closely with reference to the drawings, wherein:

Fig. 1 in axial section shows a design of a DC machine (axial machine) , where a commutator based on the invention can be incorporated, Fig. 2 shows the arrangement of segments in a commutator according to the invention, for an electric machine, Fig. 3 in cross section shows the supporting member for the commutator in Fig. 2, and Fig. 4 in enlarged cross section shows an edge portion of the supporting member in Fig. 3, for illustrating details of the segment structure. The machine shown in Fig. 1 comprises a stator housing 2 with bearings for an axle 1 supporting a rotor or armature. Carried by a central part of the rotor there is shown an iron core 10 with a winding 11, whereby the winding arrangement comprises a r? ber of separate coils. The coils 11 are wound around iron cores 10.

In the stator 2 there are mounted permanent magnets as shown at 3A and 3B in Fig. 1, i.e. at either side of the armature iron core 10, whereby intermediate air gaps are denoted 6A and 6B, respectively, in Fig. 1. The magnetizing direction of the two permanent magnets is indicated with arrows therein. In a more or less conventional way there can be provided an iron circuit for closing the magnetic field through the stator.

The commutator structure in the machine design according to Fig. 1 is shown generally at 15, whereby a brush member 5 is adapted to cooperate with the commutator in a conventional manner. The actual commutator will now be discussed with reference to the remaining figures of drawings.

Figs. 2, 3 and 4 show a main or supporting member 45 having a surface 45A that is provided with a relatively high number of commutator segments as shown at 51-59 in Fig. 2 and with an enlarged detail illustration comprising the segment 51 in Fig. 4. Supporting member 45 corresponds to part 15 in Fig. l. According to the invention the supporting member 45 is made of aluminium or in the alternative only the surface 45A consists of aluminium. While there is shown here a commutator with the segments lying in a plane on a circular disc, it is of course possible to provide the segments on an external or internal cylinder surface, as is previously known. Other geometrical shapes in several modi- fications will be possible, depending on the type of machine, apparatus or equipment into which the commutator structure shall be incorporated.

The aluminium substrate or surface 45A is well suited for applying an insulating layer of alumina. This according to the invention is applied advantageously by thermal spraying of a powder material having alumina as a substantial ingredient. In actual practice this applying step can take place very favourably by means of method steps corresponding to what is described in the aforementioned Norwegian patent No. 169.570. This results in a ceramic and electrically insulating layer, which however, in the present context has a desired and sufficient heat conducting capacity. The heat conductivity depends on the thickness of the layer, and in the commutator design in question here, it is convenient with a coating or layer having a thickness in the order of magnitude of 0,3 mm. In Fig. 4 the insulating coating of alumina is shown at 50, and as shown at 50A this coating can have a gradually decreasing thickness towards the perimeter or edge of the supporting member 45. Then on top of coating 50 copper segments 51 are applied as shown in Fig. 4. The radially outer edge 51A of each segment 51 preferably is located a short distance radially inside edge portion 50A, among other things for the purpose of obtaining a secure electric insulation. The required copper segments 51 are then applied onto coating 50. This can take place by gluing of copper foil, but according to the invention it is preferred to employ a spraying method substantially as described in the afore- mentioned Norwegian patent specification. This involves thermally spraying of copper powder so as to form the copper segments. As regards details of the manufacturing steps corresponding to the description in the aforementioned Norwegian patent specification, reference is here just made thereto.

According to the invention the copper segments as sprayed can favourably have a thickness of about 0,3 mm, but also larger thicknesses, e.g. up to about 1 mm can be desirable in certain cases. As to the alumina coating concerned, this can as such in machines for low voltages, have lesser thickness than 0,3 mm as mentioned above, e.g. 0,2 mm. Another dimension of significance in the commutator structure, is the gap or space between adjacent segments. With the particular applying method by thermal spraying, these gaps can be made conveniently narrow.

Claims

C l a i m s

1. Commutator for electrical apparatus and equipment, in particular rotary electric machines, comprising a supporting member (45) and a number of electrically conductive segments (51-59) provided at a surface (45A) of the supporting member (45) and being electrically insulated from each other, c h a r a c t e r i z e d in that at least said surface (45A) of the supporting member (45) consists substantially of aluminium, the surface (45A) is provided with a coating (50) mainly of alumina (A1₂0₃) applied by thermal spraying of a powder material having alumina as a substantial ingredient, and the electrically conductive segments (51-59) are applied on the alumina coating (50) in the form of a copper layer (51) .

2. Commutator according to claim 1, c h a r a c t e r i z e d in that the copper layer (51) is formed by thermal spraying of copper powder.

3. Commutator according to claim 1, c h a r a c t e r i z e d in that the copper layer (51) is formed by a copper foil attached by means of an adhesive.

4. Commutator according to claim 1 or 3 , c h a r a c t e r i z e d in that the copper layer (51) is terminated (51A) radially outwards at a distance from the edge of the supporting member (45) .