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Patent Searching and Data


Title:
COMMUTATORS FOR ELECTRICAL MACHINES
Document Type and Number:
WIPO Patent Application WO/1991/006992
Kind Code:
A1
Abstract:
Conductive segments of a commutator of an electrical machine are made by spraying metal on to an insulating base to provide the material for the segments.

Inventors:
Copus
Arthur
Gordon
Application Number:
PCT/GB1990/001668
Publication Date:
May 16, 1991
Filing Date:
October 31, 1990
Export Citation:
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Assignee:
NELCO HOLDINGS LIMITED COPUS
Arthur
Gordon
International Classes:
H01R39/06; (IPC1-7): H01R39/06
Foreign References:
FR2373900A11978-07-07
GB2056788A1981-03-18
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Claims:
CLAIMS
1. A method of making conductive segments of a commutator of an electrical machine, comprising spraying metal on to an insulating base to provide a layer of material for the segments.
2. A method according to claim 1 further comprising shaping the surface of the layer of metal.
3. A process for fitting ends of armature conductors to a commutator, wherein in a first stage the ends of the conductors are fitted through channels in a base, and in a second stage the base and the ends of the conductors are sprayed with copper to provide the material for commutator segments and simultaneously to effect the connection between the conductors and the segments.
4. A process according to claim 3 wherein said conductors are wound on an armature leaving free ends which in said first stage are fitted through channels in said base, the ends of the conductors being trimmed to be substantially flush with the base.
5. A process according to claim 3 or claim 4 wherein a third stage comprises shaping the copper to form the commutator segments.
6. A process according to claim 5 wherein said third stage comprises shaping the copper by machining to size and removing rough edges, and separating the copper into segments by cutting slots in the copper between groups of conductors. SUBSTITUTE SHEET .
7. A process according to any of claims 3 to 6 wherein the base comprises a disc of insulating material.
8. An electrical commutator comprising a segmented layer of sprayed copper on an insulating former.
Description:
COMMUTATORS FOR ELECTRICAL MACHINES

This invention relates to commutators for electrical machines, and to manufacture of commutators.

An electrical machine of the type to which this invention relates typically comprises a rotating shaft carrying armature windings, with electrical connection to the armature windings being made through brushes contacting a segmented commutator that rotates with the shaft and to which the armature windings are connected. The preferred material for the commutator is copper, and the armature windings are usually connected to preformed segments of the commutator by brazing or welding.

The copper commutators required for such electrical machines are expensive to produce, not only because each one requires a large amount of copper which is a costly raw material, but also because the shaping of each commutator segment involves a complicated drawing process. Moreover, fitting of the armature windings into the commutator during construction of the machine is a slow process which usually has to be performed manually in order to obtain the necessary accuracy.

A commutator structure made from a printed circuit board is described in GB 2056788 for use in a micromotor. However, in this instance care is taken to have the winding contact zone separate from the brush track and the technique is not suitable for larger motors.

The present invention addresses, separately and together, the problem of commutator structure and armature winding contacts.

According to one aspect of the present invention the segments of a commutator of an electrical machine are made by spraying copper or other metal on to an insulating base to provide a layer of material for the segments. Such a technique avoids the use of preformed commutator segments and so provides a cheaper and/or quicker method of manufacture of the commutator.

A particular aspect of the invention is the simplification of attachment of the ends of the armature windings to respective armature segments. According to this aspect of the invention there is provided a process for fitting ends of armature conductors to a commutator wherein the commutator comprises a base of insulating material, and wherein in a first stage the conductors are fitted through channels in the base, and in a second stage the ends of the conductors are sprayed with copper to provide the material for the commutator segments and simultaneously to effect the connection between the conductors and the segments. The copper may then be shaped to form the commutator segments.

The invention will now be described by way of example with reference to the accompanying drawings, in which:

Figures 1A and IB show a first stage in the process according to the invention;

Figures 2A and 2B show a second stage; and

Figures 3A and 3B show a final stage in the process according to the invention.

The following description and the drawings all describe the process of the invention with reference to face-plate type commutators for use with brushes which bear in an axial

direction on the commutator segments. It is however to be understood that with only minor adaptation the method could also be applied to the more conventional barrel commutators with brushes that bear radially on commutator segments.

Figure 1A shows a partial sectional view of an electric machine. Armature laminations 1 are wound with armature conductors 2. These armature conductors may be round wire, rectangular or stranded, but in the illustrated embodiment they are shown as round wire conductors. In a first stage of the method according to the invention, free ends 3 of the armature conductors pass through slots or holes 4 in an insulating former or plate 5 which forms the base shape for the commutator. The commutator rotates on motor axis 6, and the insulating plate is therefore, for a face-plate type commutator, preferably disc-shaped with a substantially circular periphery.

Figure IB shows an end view of a small section of the insulating plate viewed from point X in Figure 1A during the first stage of the process. The free ends 3 of the armature conductors, having passed through the slots or holes 4 in the insulating disc 5, protrude a little way beyond the holes 4.

Figure 2A illustrates a second stage in the construction of the commutator contacts. The free ends 3 of the armature conductors are first trimmed, if necessary, so that they do not protrude much beyond the face 7 of the insulating plate. A coating 8 of copper or other metal is then sprayed on to the face of the insulating plate in a layer which completely covers the face of the plate in the region of the conductors, as shown in Figure 2B. A surface treatment, such as sand blasting, may be used to aid keying. The copper is spray-coated on to the face of the plate in a layer

having a depth sufficient to cover the ends of the conductors with some excess, and to allow the surface of the copper to be machined in the final stage of the process. Typically the sprayed copper layer will have a depth of 2mm, which is machined down to about 1.5mm.

The final stage, which involves shaping the layer of copper, is shown in Figures 3A and 3B. The sprayed copper coating is machined to size, and the rough edges at the inner and outer periphery of the spray-coated area on the disc are removed. The copper layer is then separated into wedge-shaped commutator segments 9, as shown in Figure 3B, by cutting slots 10 in the copper layer between each group of conductors, such that each group of conductors is electrically isolated from the others.

The face-plate commutator, comprising a segmented layer of sprayed copper on an insulating former, is now ready for use. The brushes of the electrical machine are able to form electrical contact with the smooth copper surface 11 of each of the segments 9 of the commutator, as in any conventional solid copper commutator. However, in the present invention, a substantial proportion of the commutator is made of an insulating material, such as a rigid plastic which is both cheaper than copper, and lighter giving a lighter load for the rotor assembly. The commutator base is also more easily formed into the required shape than is machining a copper block, and the subsequent copper deposition process enables easier segment production than separate machining of segments and subsequent assembly. It will be realised that the commutator may be formed as a single, integral structure, thereby eliminating both assembly and alignment problems. The ends of the armature windings are also firmly embedded in the copper layer giving good electrical and

mechanical contact, and again simplifying or removing assembly and alignment problems.

The copper swarf which is produced by the machining in the final stage of the process may be collected and recycled for future use in the copper spraying stage. The process is therefore very economical in its use of copper in comparison to ordinary methods of construction of commutators.

In the above description it has been assumed that the ends of the wires will protrude beyond the disc, and in general this is preferred. However, it may not be necessary, the spraying process being capable of forming an adequate bond with just the ends of the copper wires, as for example would be the case if the wire ends were flush with the disc or even slightly recessed within it.

After assembly of an armature it is usual for it to be coated or impregnated with a polyester varnish which provides both additional insulation and mechanical bonding. Usually this coating is applied (for example by dipping) at the end of assembly of the armature and commutator, the brush tracks requiring protection during dipping or subsequent cleaning.

In the present invention the polyester dipping (or other equivalent process) can conveniently take place after the armature has been wound and the ends passed through the apertures in the insulating commutator disc. The polyester thus helps to form a mechanical bond between the wires and the disc. The ends of the wires and the disc may then be machined both providing polyester free wire surface for electrical contact and a rough surface to aid keying of the sprayed copper.

SUBSTITUTE SHEET

In this machining it is convenient for the wires and disc surface to be flush: mechanical bonding between the disc and wires being aided by polyester varnish that has travelled down the wires and bore of the apertures in addition to keying with the sprayed copper.