GB2208974A

GB2208974A - Electric motor armature

Info

Publication number: GB2208974A
Application number: GB8719809A
Authority: GB
Inventors: Patrick Shui-Chung Wang; Roger Frederick Baines
Original assignee: Johnson Electric Industrial Manufactory Ltd
Current assignee: Johnson Electric Industrial Manufactory Ltd
Priority date: 1987-08-21
Filing date: 1987-08-21
Publication date: 1989-04-19
Also published as: GB8719809D0

Abstract

An armature in an electric motor comprises a stack (8) of steel laminations (9) carrying a wire winding (11). The stack (8) also comprises metal end laminations (10) having rounded edges (15) where the wire winding contacts the end laminations. The end laminations are provided with a coating or surface layer of metal oxide to form a high temperature insulating layer. Preferably the end laminations are formed of aluminium and anodised. The end laminations may be formed with integral flanges (13) which extend into winding tunnels (14) between arms of the stack. <IMAGE>

Description

ELECTRIC MOTOR ARMATURE The present invention relates to an electric motor, and in particular to an armature for such a motor.

Such armatures are made from a stack of steel laminations and wire is wound on arms of the armatures to form coils.

Various forms of insulation have been used to insulate the steel of the lamination stack from the winding wire.

It is known to pre-coat the stack of laminations with epoxy or paint or other such material. It is also known to place end laminations on the stack, made of fibre or other such insulating material. It is usual for the end laminations to have dimensions slightly larger than the inner steel laminations except for the outside diameter, so that the wire is supported out of contact with the steel. It is also known to provide flexible end laminations having sections which fold back into the winding tunnels formed between arms of the armature, for extra security in construction.

All of these known insulating arrangements are effective within limited temperature ranges. If these temperatures are exceeded then the insulators begin to decay or soften, sometimes even burning, and so the insulating properties are impaired.

Today many motors are being used in high temperature environments and many more are being asked to withstand stall conditions, when the shaft is held against turning although power is still applied to the motor, for long periods without damage or danger. New coatings for the winding wires, such as poly-amide-imide coatings, have increased the ability of the winding insulation to reach higher temperatures without degradation. This has placed the failure point now on the insulation between the laminations and the winding wires.

It is also known to insulate metal parts of an electric motor with oxide coatings. Such oxide coatings have a high electrical resistance and a high electrical breakdown temperature. However, it is difficult to get a good oxide coating on sharp edges, typically on edges having a radius of less than 0.5mum, and consequently, it is not good enough to just provide a metal oxide coating on a lamination stack as the lamination stack tends to have sharp edges in regions where the winding contacts the stack.

Accordingly, the present invention provides an electric motor comprising an armature having a steel lamination stack carrying a wire winding, the stack having end laminations which are formed from metal and which have rounded edges where the wire winding contacts the end laminations, the end laminations having a metal oxide coating or surface layer.

Thus, sharp edges are avoided in regions where the end laminations support the wire winding.

Preferably, the rounded edges of the end laminations have a radius greater than 0.5mm.

Preferably, the end laminations are dimensioned so that the wire winding is held spaced from the steel lamination stack.

Preferably, the end laminations are formed from metal sheet with integral flanges which extend into winding tunnels between arms of the stack, the end laminations having rounded edges where the flanges are bent out of the plane of the end laminations.

Alternatively, the end laminations may be die cast.

Preferably, the end laminations are of aluminium which has been anodised. The end laminations may, however, be of other metal, such as steel, which has, for example, a layer of aluminium deposited thereon and in this case the aluminium is anodised.

If desired the lamination stack per se also may have a metal oxide coating or surface layer which could be formed by depositing aluminium on the stack and anodising the aluminium.

The invention will be further described by way of example with reference to the accompanying drawings, in which, Figure 1 shows a small permanent magnet D.C. electric motor embodying a lamination stack of the invention; Figure 2 shows an embodiment of a lamination stack in accordance with the invention; Figure 3 shows an exploded view of the lamination stack of Figure 2, and Figure 4 shows an end lamination of the stack of Figures 2 and 3, on an enlarged scale.

In the drawings, Figure 1 shows a fractional horsepower permanent magnet DC (PMDC) motor 1 which is exemplified by the applicants Pt;DC motor marketed under catalogue number HC610G. Such a motor comprises an outer steel cylindrical casing 2 having a plastics end cap 3. The configuration of the internals of the motor are well known and, briefly, comprise a pair of permanent magnets, forming a stator, held in the casing 2 against the cylindrical inner wall; a rotor assembly comprising a shaft 4 supporting an armature and commutator and journalled in bearings 5 in the end cap 3 and in the opposite end of the casing 2 (not shown); and brush gear supported by the end cap 3 and bearing on the commutator. Tabs 6 providing electrical connection to the brushes of the brush gear and vent holes 7 provide for cooling of the motor.

Figure 2 shows a lamination stack 8 which is mounted fast on shaft 4 to form an armature of the rotor assembly of motor 1. Stack 8 comprises a stack of thin steel laminations 9 which are pressed fitted on the shaft to form a coherent assembly. Stack 8 also comprises end laminations 10. Wire is wound on the arms of the stack, as is known in the art, to form coils 11 which are fed via the brush gear and commutator to drive the motor.

The end laminations 10 have mushroom-shaped arms 12 to correspond with the shape of the arms of the inner laminations 9 of the stack 8 and are formed, by pressing, from thin metal sheet with integral flanges 13 which extend a short distance into winding tunnels 14 between the arms of the stack 8. The arms 12 therefore overlap the arms of the inner laminations 9 except at the outer circumference of the armature and at the tips of the heads of the mushroom-shaped arms and support the winding coils 11 away from the arms of the inner steel laminations 9.

The end laminations 10 are formed with rounded edges, typically having a radius greater than 0.5mm, where the flanges 13 are bent out of the plane of the end laminations 10 so as not to create difficulties in providing a good oxide layer on these edges 15.

The end laminations 10 are preferably of aluminium which is anodised after forming the flanges to provide a surface layer of aluminium oxide, about 30 microns deep. The oxide layer forms a tough layer of insulation between the winding coils 11 and the end laminations and as aforesaid the end laminations 10 support the winding coils 11 away from the inner steel laminations 9.

If desired, the stack of inner steel laminations 9 could also have a metal oxide coating or surface layer. In this case the stack of inner steel laminations could be assembled on the shaft and then coated with a layer of aluminium by vacuum deposition. The aluminium is then anodised to form a surface layer of aluminium oxide, whereafter the end laminations 10 are mounted on the anodised stack 8 and the stack is wound to form an armature. During vacuum deposition and anodising the exposed shaft 4 is protected, for example, with plastics sleeves.

The end laminations, instead of being formed from thin metal sheet, could be die cast, preferably in aluminium and then anodised. By die casting the end laminations the edges of the laminations are naturally rounded (typically having a radius greater than 0.5mm) as a result of the die casting process.

If the end laminations are die cast, the flanges 13 may be omitted, although, if the flanges are omitted it is preferable that the die cast end laminations are dimensioned to overlap slightly the surface of an adjacent lamination, except at the outer diameter, so that the wire winding is held spaced from inner laminations. If the end laminations are die cast, one end lamination could be provided with a central cylindrical extension which extends away from the lamination stack along a shaft supporting the stack to provide a base of an assembled commutator.

The above embodiment is given by way of example only and various modifications will be apparent to persons skilled in the art without departing from the scope of the invention as defined in the accompanying claims.

Claims

1. An electric motor comprising an armature having a steel lamination stack carrying a wire winding, the stack having end laminations which are formed from metal and which have rounded edges where the wire winding contacts the end laminations, the end laminations having a metal oxide coating or surface layer.

2. An electric motor as claimed in claim 1, wherein the end laminations are dimensioned so that the wire winding is held spaced from the steel lamination stack.

3. An electric motor as claimed in claim l or claim 2, wherein the end laminations are formed from metal sheet with integral flanges which extend into winding tunnels between arms of the stack, the end laminations having rounded edges where the flanges are bent out of the plane of the end laminations.

4. An electric motor as claimed in claim 1 or claim 2, wherein the end laminations are die cast.

5. An electric motor as claimed in any one of claims 1 to 4, wherein the end laminations are of aluminium which has been anodised.

6. An electric motor as claimed in any one of claims l to 4, wherein the end laminations have a layer of aluminium deposited thereon and the aluminium is anodised.

7. An electric motor as claimed in any one of claims 1 to 6, wherein the lamination stack per se also has a metal oxide coating or surface layer.

8. An electric motor as claimed in claim 7, wherein the stack has a layer of aluminium deposited thereon and the aluminium is anodised.

9. An electric motor substantially as hereinbefore described with reference to the accompanying drawings.