GB2052320A - Providing an electrical contact surface on a stack of insulated laminations - Google Patents

Abstract

An electric motor has an impregnated stack of stator laminations 3 with contact surfaces 31, 32 at its axial ends, and bearing plates connected to the contact surfaces 31, 32 of the stack of stator laminations 3. In order to achieve a good electrical contact between the stack of stator laminations 3 and the bearing plates and, circumstances permitting, a simultaneously perpendicular and plane parallel positioning of the bearing plates without splinter-producing retreatment of the stack of stator laminations, the contact surfaces (31, 32) are provided with a plurality of depressions impressed into the stack of laminations (3). Depressions in the form of truncated pyramids are preferably impressed by means of a "rough planing process". The invention can be used to particular advantage in small motors with an insulated stack of stator laminations and a single protective conductor connection at the bearing plate. <IMAGE>

Description

SPECIFICATION Providing an electrical contact surface on a stack of insulated laminations This invention relates to providing an electrical contact surface of insulated laminations. It is concerned, particularly but not exclusively, with an electric motor having an impregnated stack of insulated stator laminations, and bearing plates which are secured to axial ends of the stack of stator laminations.

The laminations sandwiched in a stack of stator laminations are usually provided with an insulating coating, which is formed, for example, while the electrically conductive laminations are glowing, before or after stamping, by an oxidising gaseous atmosphere. A known procedure for preliminary strengthening of the stack of laminations, before clamping it between two bearing plates, is to rivet the layered stack of stator laminations, and/or to steep it in an impregnating liquid which will cement the stator laminations to one another after curing.If the bearing plates are mounted upon a stack of laminations which has been insulated and/or impregnated in this way and has not received any further treatment, there is a disadvantage in that, among other things, a high electrical transfer resistance exists between the stack of stator laminations on the one hand and the adjoining bearing plates on the other.

If motors of such a kind are to be provided, in accordance with appropriate regulations, with a so-called protective conductor connection, e.g. for an earth conductor, it is necessary to attach separate protective conductor connection terminals both to the two bearing plates and to the stack of stator laminations, because of the high transfer resistance between the bearing plate and the stack of stator laminations.

Attempts have already been made to remove the insulative coating in the area of the contact surfaces bya brushing process, in orderto reduce the transfer resistance between the stack of stator laminations and the bearing plate. However, a subsequent accurate positioning of the bearing plates on the stack of laminations cannot be guaranteed by this process in every case. Screwing in of a centering shoulder has produced, in addition to accurate positioning of the bearing plates on the stack of laminations, a good electrical contact. However, finishing of this kind has been expensive, with a particularly excessive labour cost component.

The present invention aims, particularly but not exclusively, to reduce considerably the cost of a protective conductor connection in an electric motor, while keeping manufacture and assembly simple, and affording accurate positioning of bearer plates.

According to the present invention, there is provided a method of providing an electrically conductive contact surface on an end face of a stack of electrically conductive laminations having an electrically insulative coating, the method comprising the step of impressing said end face to form a plurality of depressions thereon, thereby breaking said coating around.the depressions.

It has been shown, surprisingly, that as a result of the impressing process, in the area of the webs remaining between the depressions, and in the area of the transition to the impressed depressions, a bright metallic contact surface of the end lamination of the stack of laminations can be formed, free from insulation.

In a preferred embodiment of the invention, where two bearing plates are secured to contact faces of a stack of stator laminations, we have found it possible to achive such a good electrical contact from the stator to the bearing plates that a single protective conductor connection terminal, advantageously attached to only one bearing plate, is quite sufficient to provide a good electrically conductive connection from the stack of stator laminations (which is not provided with a separate connection terminal), and the other bearing plate, to the protective conductor connection.

In one advantageous embodiment of the invention the contact surface is provided with a plurality of punctiform depressions in a waffle-like pattern; depressions in the form of truncated pyramids have proved to provide a good erosion of impregnation and insulation, and to require a low-cost stamping tool. On the trapezoid upper surfaces of the truncated pyramid, and particularly in the transition from the base surface of the pyramid to the remaining upper surface of the end lamination, a particularly good erosion of impregnation is produced, as is a bright metallic contact surface between the stack of laminations and an adjoining plate.

If a stamp die in a stamping or pressing device is adjusted in such a way that two contact surfaces are advantageously formed simultaneously to achieve a positioning of two bearing plates on a stack of stator laminations perpendicular and/or mutually plane parallel to a motor axis, a stator assembly, accurate in form and dimension, except for axially concentric centering of the bearing plates, can be prepared in the non-cutting operation of eroding the insulation and/or steeped impregnation. The axial concentric alignment of the bearing plates on the stack of stator laminations can be achieved during assembly most simply by means of spigots cast axially onto the bearing plates, which spigots engage corresponding holes stamped into the laminations of the stack of stator laminations.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will be made, by way of example, to the accompanying diagrammatic drawing, in which; Figure 1 is a side view of an assembled motor, in partial cross-section; Figure 2 is a partial top view of a bearing plate with a protective conductor connection terminal; Figure 3 is a top view of the stack of stator laminations, with the impressed contact surfaces for the bearing plates; and Figure 4 is a side view of the stack of stator laminations as shown in Figure 3.

The figures show a dishwasher pump motor.

Bearing plates 1,2 abut contact surfaces 31, 32 on the axial ends of a stack of stator laminations 3. The bearing plates, 1, 2 overlap the coil ends 8 of the stator winding inserted in the stack of stator laminations 3, and contain roller bearings 6,7 in bearing bores, in which roller bearings a rotor shaft 5, carrying a stack of rotor laminations 4 with a squirrel cage, is rotatably fixed. Rivet heads, with the help of which the stack of stator laminations 3 is prestrengthened after stacking, are designated by the reference number 37. In order to strengthen the stack of stator iaminations 3 further, the latter is subsequently impregnated by being steeped in a polyester resin, which after curing, cements the laminations of the stack of stator laminations 3 together, and povides additional strengthening.

As can be seen particularly in Figure 3, the contact surfaces 31, 32 are formed with impressed depressions, and extend only partially over the end faces of the stack of stator laminations 3. The bearing plates 1,2 abut the stack of laminations only in these areas.

Recesses in the contact surfaces of the bearing plates 1, 2 are provided in the area of rivets 10, the heads 37 of which project axially over the stack of stator laminations 3. Centering holes 35,36 or 33,34 which are impressed into the laminations of the stack of stator laminations 3, serve for the axiallyconcentric alignment of the bearing plates 1,2.

During assembly of the stack of stator lamination 3, spigots cast in the bearing plates 1,2 engage in the centering holes 35,36 or 33, 34, and thus align the bearing plates with the motor shaft. The centering holes are impressed in one stamping operation together with winding slots 12, and after stacking of the stack of stator laminations 3 with subsequent strengthening riveting, a winding may be centered in the stator bore by means of the centered punched out slots 12.

The radial notches 38,39 visible in Figure 3 in the area of the contact surfaces 31,32, serve to accommodate bolts 9 (Figure 1) with the help of which the two bearing plats 1, 2 are secured in their aligned position on the stack of stator laminations 3. As a result of the radial indentation of the holes 38,39, a bulging distortion of the bearing plates 1,2 as the bolts 9 are tightened is largely avoided.

As a result of stamping the axial end faces of the stack of laminations 3 to form the depressions, the impregnation and insulation of the respective end laminations at the border areas between the depressions and the remaining intermediate webs in the area of the contact surfaces 31, 32 is eroded in such a way that a bright metallic contact surface is produced, between the respective end lamination of the stack of stator laminations 3 and the adjoining bearing plate 1 or 2.Through the corresponding alignment of the stamp die and of the stack of stator laminations 3 mounted in the stamping device, on the one hand the contact surface 31 or 32 at eached axial end lies at a right angle to the axis of the motor shaft, and on the other hand, simultaneously the contact surface 31 at one axial end is impressed plane-parallel to and at a constant distance a from the contact surface 31 a at the other axial end.

In Figure 4, the small compression volume of bulging on the upper and lower borderlines in the area of the contact surface 31 or 31 a is recognisable, and the axially constant distance a is marked. Thus it can be seen that, simultaneously with the erosion of the insulation or impregnation in the area of the contact surfaces 31,32, an angular dispostion and plane parallelism of the bearer plate supports can be achieved, and with it an improved mechanical motor construction with precise rotor centering and precise air gap dimensioning.

As can be seen from the partial cross-section according to Figure 2, a protective conductor connection terminal 11 is attached to the inner side of one bearing plate 1 facing the stack of stator laminations 3, which terminal, because of the good electrical contact between the bearer plate 1 or 2 andthe stack of stator laminations 3, which is achieved quite simply, suffices as the only connection for the protective conductor of the entire motor.

The depressions may advantageously be impressed in the stack of laminations by a "rough planing" process.

The invention is particularly applicable to small motors.

Claims (11)

1. A method of providing an electrically conductive contact surface on an end face of a stack of electrically conductive laminations, having an electrically insulative coating, the method comprising the step of impressing said end face to form a plurality of depressions thereon, thereby breaking said coating around the depressions.

2. A method according to Claim 1, wherein said depressions are punctiform depressions, in a wafflelike pattern.

3. A method according to Claim 1 or 2, wherein said depressions are in the form of truncated pyramids.

4. A method according to Claim 1,2 or 3, wherein said contact surfaces extend only partially over said end faces.

5. A method according to any preceding claim, wherein substantially parallel electrically conductive contact surfaces are formed simultaneously at oppqsite end faces of said stack.

6. A method according to any preceding claim, including the stpes of securing an electrically conductive plate to said stack, in electrical contact with said surface or a respective one of said surfaces, and securing a single terminal for a protective conductor to either said plate or said stack.

7. A method according to any preceding claim, wherein the laminations of the stack are riveted together, and/or cemented together by a cured impregnating material.

8. A method according to any preceding claim, wherein said stack is a stack of laminations for the stator of an electric motor.

9. A method according to Claim 5,6 and 8, wherein a respective said plate is secured to each of said surfaces, and serves as a bearing plate for the motor, and said depressions are formed substantially parallel to the stator axis.

10. A method of providing an electrically conductive contact surface on a stack of laminations, the method being substantially as hereinbefore described with reference to the accompanying drawing.

11. An electric motor having a stack of laminations produced by a method according to any preceding claim.