GB2423421A

GB2423421A - Armature construction and a method of manufacture therefor.

Info

Publication number: GB2423421A
Application number: GB0602899A
Authority: GB
Inventors: Gerhard Riepl
Original assignee: COMPACT CADDY Ltd
Current assignee: COMPACT CADDY Ltd
Priority date: 2005-02-15
Filing date: 2006-02-14
Publication date: 2006-08-23
Also published as: GB0602899D0; GB0503085D0

Abstract

An armature sector 100 is manufactured by forming an outer arc member 140 with a plurality of core segments 120 projecting from its inner surface 141 from a plurality of laminated layers of sheet metal. The outer arc member 140 is additionally provided with a series of grooves 142 in its inner surface, the grooves 142 provided between the projecting core segments 120. The core segments are each wound with Copper wire to provide coils 130. An inner arc member 110 is constructed from a laminate of sheet metal and is provided with a plurality of channels 111 in its outer surface, the channels 111 having a shape corresponding to the shape of the inner ends 122 of the projecting core segments 120. The inner ends 122 of the core segments 120 are then retained in the channels 111. The outer surface 143 of the outer arc member 140 is then machined removing material from its outer surface 143. When sufficient material is removed, the grooves 142 in the inner surface 141 of the outer arc member 140 extend through the whole of the member and the outer ends 121 of the individual core segments 120 are thus separated from one another by gaps 142.

Description

Electric Motor The present invention relates to electric motors and in

particular for armatures for electric motors.

In one known form of electric motor described in EP 0094978, there is provided two functional members, rotatable with respect to the each other, and having an air gap between two facing surfaces of the functional members. One of the functional members is provided with a multiplicity of permanent magnet poles of alternating polarity distributed in a ring arrangement on its side facing the air gap.

The other functional member is provided with a multiplicity of electromagnet poles distributed in a ring arrangement on its side facing the air gap, wherein the electromagnets are switchable such that by varying the polarity of the electromagnets, rotation of one of the functional members can be achieved. Typically in such designs, the functional members are coaxially mounted, and the member having the electromagnets is mounted within the member having the permanent magnets.

Typically in such motors, the member having the electromagnets comprises an armature comprising a ring portion having projecting from its outer surface a plurality of core segments upon which copper wire is wound, the coils of copper wire wound upon said core segments thus comprising the electromagnets.

For a given choice of magnets and sheet metal type the overall efficiency of this form of electric motor is dependent on: the resistance of the windings (i.e. amount of copper used: controllable by varying wire diameter, number of windings on the segment and width of the segment); and the air gap between the inner edge of the permanent magnet ring and the outer surface of the core segments. Additionally, to ensure smooth running, the gaps between the outer ends of the core segments should be minimised. This is achieved by having an outer end of the core segment that is wider than the portion of the core segment upon which the coil is wound.

Traditionally, such armatures are made by a method comprising the steps of: pressing an armature shape out of sheet metal; laminating a plurality of such sheet metal shapes to form an armature with the required thickness; and subsequently winding copper wire on to the cores from the outside. This method has a number of disadvantages including: the need to use large presses to make the armatures (very expensive tooling & machines not widely available); material waste (not only is a large amount removed to press the blank, but most of the metal left doesn't influence the way the motor functions); and difficulties with winding wire to form the coils.

Turning specifically to the difficulties of winding coils, as the wire has to fit through the gap between the outer ends of adjacent core segments, which for efficient motor performance is to be minimised, there is a restriction on the maximum wire diameter that can be used. As this is the case, the only means by which the amount of copper wire per coil may be increased is to wind over the segments twice (or more) using thinner wire, connecting the individual wires in parallel and/or to increase the length of the segments to allow more turns per coil. To enable the segment length to be increased, however requires that the outer diameter of the armature is larger as the gap between the winding on adjacent segments reduces towards the centre of the armature. A further problem is that the small amount of free space between the segments makes winding an intricate process that is very difficult, if not impossible, to automate.

It is therefore an object of the present invention to provide an electric motor and a method of manufacturing such a motor that overcomes or alleviates the above problems.

According to the present invention there is provided a method of manufacturing an armature or an armature sector for an electric motor comprising the following steps: forming an outer arc member having a plurality of core segments projecting from the inner surface of the arc member, providing a coil around each core segment; forming an inner arc member; affixing the ends of said projecting core segments to the outer surface of said inner arc member; machining the outer surface of the outer arc member to achieve a desired outer diameter; and forming gaps through the outer arc member such that the core segments are no longer connected to each other by said outer arc member.

This thus provides a method of manufacturing an armature that overcomes the limitations described above.

The method may be used to form a complete armature having outer and inner arc members with a 360 angular extent or may alternatively be used to form individual armature sectors, each having an angular extent of a fraction of 3 60 , individual annature sectors being connected to one another to form a complete armature. If the method is used to manufacture individual armature sectors, it preferably includes the further step of connecting the armature sectors together to form a complete armature. In a preferred implementation, each armature sector forming the complete armature has an equal angular extent. Typically, each annature sector may have an angular extent of 30 , 60 or 90 .

The coils may be wound directly around the core segments or may be wound on supporting members, which are then mounted on said core segments. The coils are preferably comprised of copper wire.

A convenient method by which gaps can be formed through the outer arc member such that the core segments are now longer connected to each other by said outer arc member is by providing the outer arc member with a plurality of grooves on its inner surface, the grooves being provided between the projecting core segments.

In this way, when the outer surface of the outer arc member is sufficiently machined, the grooves extend through the full thickness of the outer arc member. Alternatively, the gaps can be formed by cutting through the outer arc member either before or after machining its outer surface.

The outer arc member, the inner arc member and the core segments are each preferably formed of laminated sheet metal. The individual sheet metal shapes are preferably formed by pressing.

Preferably, only one groove is provided on the inner surface of said outer arc member between each pair of projecting core segments. The grooves on said outer arc member may be provided midway between each projecting core segment or may be offset towards one core segment. The grooves may have any suitable profile, typically the groove profile would be substantially square or rectangular however other groove profiles including but not limited to U', V' and C' profiles can be used alternatively.

The outer arc member may be formed integrally with said core segments.

Alternatively, said core segments may be affixed to said outer arc member after formation. hi such embodiments the core segments can be affixed to the outer arc member by any suitable means including adhesive or the provision of cooperating formations on said core segments and the inner surface of said outer arc member.

The ends of the core segments may be affixed to the outer surface of the inner arc member by any suitable means including adhesive or the provision of cooperating formations on said core segments and the outer surface of said inner arc member.

According to a second aspect of the present invention there is provided an armature for an electric motor manufactured in accordance with the method of the first aspect of the present invention.

According to a third aspect of the present invention there is provided an electric motor comprising an armature according to the second aspect of the present invention.

According to a fourth aspect of the present invention there is provided an electric golf trolley comprising an electric motor according to the third aspect of the present invention.

In order that the invention is more clearly understood, it will now be described further herein, by way of example only and with reference to the following drawings in which: Figure 1 shows an armature sector of an armature for an electric motor according to the present invention; and Figure 2 shows an outer arc member, being an intermediate stage in the manufacture of the armature sector of figure 1; Figure 3 shows a single coil from the armature sector of figure 1; and Figure 4 shows a further intermediate stage in the manufacture of the annature sector of figure 1 wherein the coils of figure 3 are mounted on the outer arc member of figure 2 and said outer arc member is connected to an inner arc member.

Referring now to figure 1, an armature sector 100 of an armature for an electric motor comprises an inner arc member 110, having projecting therefrom core segments 120 upon each of which is wound a coil of copper wire 130 to form an electromagnet. In an electric motor, a plurality of such armature sectors 100, are arranged in a ring to comprise a complete armature or first functional member. A second functional member (not shown) is mounted coaxially with the first functional member and has a ring of permanent magnets of alternating polarity mounted on a surface facing the outer ends 121 of the core segments 120. By switching a current through the coils 130 in particular directions at particular times, the second functional member may be made to rotate relative to the first. The rotational motion may be used to power any suitable mechanical movement.

The armature sector 100 is manufactured by the following process. First an outer arc member 140 is formed, the outer arc member 140 being formed integrally with a plurality of core segments 120 projecting from its inner surface 141. The outer arc member 140 comprises a plurality of laminated layers of sheet metal, the layers being joined together by any suitable means. The outer arc member 140 is additionally provided with a series of grooves 142 in its inner surface. The grooves 142 extend radially outwards and are typically formed midway between the projecting core segments 120, but may alternatively be offset if desired.

In alternative embodiments, the core segments 120 may be formed separately to the outer arc member 140 and may then be affixed to the outer arc member 140 by adhesive or by suitable cooperating formations on the inner surface 141 of the arc member and the outer end 121 of the core segments 120.

In a preferred embodiment, copper wire is wound round a plurality of supporting members 150 to form coils 130. These coils 130 are then mounted on the core segments 120. This is facilitated by the fact that the supporting members 150 have an axial bore adapted to fit over the core segments 120. This allows the coils to be wound quickly, easily and accurately with cheap simple machinery. It is of course possible, if desired, to wind the coils 130 directly over the core segments 120.

This may be done when core segments 120 are projecting from the outer arc member 140.

The inner arc member 110 is constructed from a laminate of sheet metal. It is provided with a plurality of channels 111 in its outer surface, the channels 111 having a shape corresponding to the shape of the inner ends 122 of the projecting core segments 120. The inner ends 122 of the core segments 120 may thus be securely received and retained in the channels ill. The inner ends 122 may of course be affixed to the inner arc member 110 by any other suitable means including the use of adhesive or suitable fasteners, if required or desired.

The outer surface 143 of the outer arc member 140 is then machined. This removes material from the outer surface 143. When sufficient material is removed from the outer surface 143, the grooves 142 in the inner surface 141 of the outer arc member 140 extend through the whole of the member arid the outer ends 121 of the individual core segments 120 are thus separated from one another by gaps 142, the gaps being provided by the grooves 142. In an alternative method, the grooves may be omittcd and the gaps provided by making cuts through the outer arc member 140 either before or after machining.

This method of manufacture allows greater flexibility in varying the air gap between the inner edge of the permanent magnet ring and the outer end 121 of the core segments 120 forming the outer edge of the electromagnet ring in electric motors of this type. This is because by varying the amount of material removed from the outer surface 143 of the outer arc member 140 it is possible to vary the position of the outer edge of the electromagnet ring in addition to the position of the inner edge of the permanent magnet ring.

In order to ensure even machining, the armature sectors 100 are connected together to form a complete armature before machining. Conveniently, the complete armature may then be mounted on a lathe for machining to an accurate and controllable outer diameter.

In the above embodiments, the coils 130 are formed by winding or fitting the coils 130 from the inner end of the core segments 120. As such, there is no constraint on the maximum wire diameter used in the coils 130 resulting from the need to thread the wire between the outer ends 121 of the core segments 120. As this is the case, the gap 142 (groove width) between the outer ends 121 of the core segments 120 can be chosen independently of the wire diameter to ensure smooth running. This has the additional advantage that there is greater flexibility in the choice of wire diameter and number of windings that can be used.

A further advantage comes with manufacturing the armature from a number of armature sectors 100 rather than as a single piece. This is because all the armature sectors 100 are much smaller than a complete armature. As such, each sheet metal layer can be pressed from a sheet of metal of a similar size to the armature sector 100 rather than a sheet of metal a similar size to the complete armature. The layers can thus be pressed by smaller and cheaper presses. Additionally, far less waste is generated when pressing the layers.

It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiments which are described by way of

example only.

Claims

Claims 1. A method of manufacturing an armature or an armature sector for

an electric motor comprising the following steps: forming an outer arc member having a plurality of core segments projecting from the inner surface of the arc member, providing a coil around each core segment; forming an inner arc member; affixing the ends of said projecting core segments to the outer surface of said inner arc member; machining the outer surface of the outer arc member to achieve a desired outer diameter; and forming gaps through the outer arc member such that the core segments are no longer connected to each other by said outer arc member.
2. A method as claimed in claim 1 wherein the coils are wound directly around the core segments.
3. A method as claimed in claim I wherein the coils are wound on supporting members, which are then mounted on said core segments.
4. A method as claimed in any preceding claim wherein the coils are comprised of copper wire.
5. A method as claimed in any preceding claim wherein the gaps are formed by cuffing through the outer arc member either before or after machining its outer surface.
6. A method as claimed in any one of claims 1 to 4 wherein gaps are formed through the outer arc member by providing the outer arc member with a plurality of grooves on its inner surface, the grooves being provided between -li- the projecting core segments such that when the outer surface of the outer arc member is sufficiently machined, the grooves extend through the full thickness of the outer arc member.
7. A method as claimed in claim 6 wherein only one groove is provided on the inner surface of said outer arc member between each pair of projecting core segments.
8. A method as claimed in claim 6 or claim 7 wherein the grooves on said outer arc member are provided midway between each projecting core segment.
9. A method as claimed in claim 6 or claim 7 wherein the grooves on said outer arc member are offset towards one core segment.
10. A method as claimed in any one of claims 6 to 9 wherein the groove profile is substantially square or rectangular.
11. A method as claimed in any preceding claim wherein the method is used to form a complete armature having outer and inner arc members with a 360 angular extent.
12. A method as claimed in any one of claims 1 to 10 wherein the method is used to form individual armature sectors each having an angular extent of a fraction of 3 60 , said individual armature sectors being connected to one another to form a complete armature.
13. A method as claimed in claim 12 wherein the method includes the further step of connecting the armature sectors together to form a complete armature.

- 12 -
14. A method as claimed in claim 12 or claim 13 wherein each armature sector has an angular extent of 30 , 600 or 90 .
15. A method as claimed in any one of claims 12 to 14 wherein each armature sector forming the complete armature has an equal angular extent.
16. A method as claimed in any preceding claim wherein the outer arc member, the inner arc member and the core segments are each formed of laminated sheet metal.
17. A method as claimed in claim 16 wherein the individual sheet metal shapes are formed by pressing.
18. A method as claimed in any preceding claim wherein the outer arc member is formed integrally with said core segments.
19. A method as claimed in any one of claims I to 18 wherein said core segments are affixed to said outer arc member after formation.
20. A method as claimed in claim 19 wherein the core segments can be affixed to the outer arc member by adhesive or the provision of cooperating formations on said core segments and the inner surface of said outer arc member.
21. An armature for an electric motor manufactured in accordance with the method any one of claims 1 to 20.
22. An electric motor comprising an armature as claimed in claim 21.
23. An electric golf trolley comprising an electric motor as claimed in claim 22.