WO2007110303A1

WO2007110303A1 - Improvement in an electric motor

Info

Publication number: WO2007110303A1
Application number: PCT/EP2007/052141
Authority: WO
Inventors: Sergio Bonacina; Elvio Tonus
Original assignee: Appliances Components Companies S.P.A.
Priority date: 2006-03-24
Filing date: 2007-03-07
Publication date: 2007-10-04
Also published as: ITPN20060010U1; EP2016665A1

Abstract

An electric motor comprises an outer frame, a stator stack accommodated within said outer frame, wherein said outer frame comprises at least a portion arranged to lie on a plane that is substantially orthogonal to the axis of the motor, and is configured into a shape that is symmetrical relative to a first plane extending through said axis of said motor and, preferably, is also symmetrical relative to a second plane lying orthogonally to said first axis and extending through said axis of said motor. Said outer frame is provided as a single-piece, unitary construction.

Description

IMPROVEMENT IN AN ELECTRIC MOTOR

DESCRIPTION

The present invention refers to an improved kind of electric motor, preferably of the type generally used as a drive means within household appliances, such as clothes washing machines, dishwashing machines and the like, and thus provided with corresponding operating capabilities.

Electric motors of the above-cited kind are generally known to be mass- produced in very large quantities on an industrial scale and therefore - considering also the quite extreme competitiveness requirements, which such products are generally required to comply with - they must ensure corresponding properties and capabilities of great flexibility in both their construction and their practical use, i.e. installation and assembly, in the various particular appliance types and models, in which they are due to operate.

Currently, however, such motors are manufactured using throughout traditional techniques and materials, which involve production costs to be sustained that are not liable to be curbed or reduced to any significant extent any further, if the same manufacturing techniques and construction materials are kept being used in a substantially unaltered manner.

Reference is hereby made in particular to the construction of electric motors, in which the stator winding is retained and supported by an outer structure, which is generally comprised of two frame halves, i.e. end- shields, which are provided individually, are usually configured in a cup- like or bowl-like shape, and are arranged relative to each other so as to contain and accommodate said stator winding therewithin; upon said stator winding having been fitted and assembled therebetween, said two frame halves are firmly coupled to each other by means of proper stay- bolts, or similar connecting and fastening means, so as to enable the construction of the motor to be completed.

Such two frame halves are then applied - with the aid of simple means generally known as such in the art - to appropriate support means, so that the motor can be installed in the intended site of use in a firm and stable manner.

Due to these motors being obviously rather heavy, and being further operated under use conditions that cause them to be exposed to rather significant vibratory stresses, these two frame halves are of course required to offer adequate, peculiar properties in terms of coupling strength, solidity and accuracy.

Such two frame halves must in fact act as a support - possibly by means of proper bearings - for the rotating shaft, which the related rotor of the motor is attached to, wherein anyone skilled in the art is fully aware of the fact that the coupling accuracy of the rotor - and, as a result, the corresponding accuracy and tightness in the dimensions and tolerances of the two frame halves - is of paramount importance in view of a correct and efficient operation of the motor.

For outer motor frames to be able to be provided, which are really capable of complying with these two basic requirements as noted above, a largely known method currently used in the art calls for such frames to be made of a metal material, in particular by means of some appropriate technique for forming a metal mass.

Typically, this method involves a die-casting technique for casting parts of an appropriate metal alloy. Since both the related technology and the materials used in the process are not only largely known as such in the art, but also of general use universally, any further detailed description thereof will be intentionally omitted here for reasons of brevity.

Anyhow, this technique, although quite easily implemented and reliable in its results, has a major drawback that is less and less acceptable in a highly competitive industrial environment, i.e. the high overall costs involved.

In view of reducing such costs, a solution has also been used in the art, in which such outer frames are produced by means of an injection- moulding process of a mass of a thermoplastic material. However, the process of injection moulding a mass of thermoplastic material is in turn largely known to give rise to cool-down shrinkage problems typically and usually occurring when moulded parts are ejected from the mould after injection.

Now, such shrinkage does of course not take place according to any symmetrical pattern all over the structure of the moulded part, particularly if such structure is itself inherently asymmetrical both dimensionally and geometrically.

As a result, after a shrinkage-connected problem has occurred, the original size tolerances and the coupling accuracy unavoidably undergo significant alterations that cannot be predicted to any acceptably accurate extent, thereby practically jeopardizing the possibility for the whole motor to be assembled in a correct, efficient manner.

It is therefore desirable, and is a main object of the present invention, actually, to provide an electric motor provided with at least an outer or enclosing frame that is particularly low-cost in both the materials and the production process used, and is further capable of being manufactured so as to fully do away with, or at least drastically reduce material shrinkage problems in the moulded parts and, ultimately, ensure that the original design dimensions and tolerances of the parts - as designed into, i.e. incorporated in the production means and tools, in particular injection moulds - are accurately maintained after production.

According to the present invention, these aims and advantages are reached in an electric motor provided with at least an outer frame incorporating the characteristics as set forth and recited in the appended claims.

Features and advantages of the present invention will anyway be more readily understood from the description that is given below by way of non- limiting example with reference to the accompanying drawings, in which:

- Figure 1 is a perspective view of an electric motor according to the present invention;

- Figure 2 is a planar view of a face of an outer frame according to a first embodiment of the present invention, as represented in a plane extending orthogonally to the axis of the motor;

Figure 3 is a planar view of a second, improved embodiment of a face or end-shield of an outer frame according to the present invention, as represented in a plane extending orthogonally to the axis of the motor; - Figure 4 is a perspective view of an outer frame of a motor according to the present invention, as viewed from an outside position very close to an end portion of the motor, but rather away from the axis thereof.

With reference to Figures 1 and 2, in an electric motor according to the present invention there is provided an outer frame 1 adapted to - at least partly - accommodate and support the related stator 2; this frame may integrally include a plurality of support means 3 adapted to enable the motor to stably and firmly engage the support or resting members thereof, or such support means may be provided in the form of separate devices that are applied to said frame after the latter has been produced, i.e. moulded.

The motor frame 1 is configured in a cup-like or bowl-like shape and comprises a portion 4, which has an approximately planar shape - except for some strengthening ribs 5 provided thereon - or has anyway an extension that prevailingly develops along a plane, and which is arranged orthogonally to the axis X of the motor. In other words, this portion 4 practically forms the bottom wall of the cup-like or bowl-like shape taken by such frame.

Since a basic aim to be reached is the ability of producing such frame economically, i.e. in as low a cost as possible, while avoiding asymmetrical shrinkage occurrences, the solution being proposed to this purpose lies in producing said frame 1 using well-known injection-moulding or similar processes for moulding thermoplastic engineering materials, thereby obtaining economically sustainable, adequately low-cost motor frames, as desired.

In order to avoid the problem of asymmetrical shrinkages taking place after moulding, the present invention teaches to provide the structure of said frame with such contours and shape as to be fully symmetrical relative to a plane h passing through the axis X of the motor; in this way, the shrinkages, which the material and, hence, the moulding will unavoidably be subject to, are practically caused to act in a correspondingly symmetrical manner, so that the geometries and dimensions of the whole frame, and particularly the central portion thereof bearing the motor shaft and/ or the stator, will remain substantially constant.

This practically turns out as being tantamount to reaching the desired aim of substantially maintaining dimensions, geometry and positioning of said frame, in particular in the central portion thereof, accurately unvaried.

With reference to Figure 3, an advantageous improvement can be obtained by improving the symmetry properties of said motor frame; in this connection, in fact, the latter is further designed so as to be symmetrical relative to a second plane k, which is logically inclined relative to said first plane h, but still passing through the axis X of the motor.

Also filly apparent is at this point the fact that this procedure can be repeated in connection with further planes of symmetry.

It has however been noticed that it is by no means absolutely necessary for a motor frame to be so designed as to feature a certain number of planes of symmetry, since if only second plane of symmetry k is adopted and - by the way - said second plane of symmetry k is itself orthogonal to said first plane of symmetry h, a fully satisfactory final result is obtained, which cannot be improved to any significant extent through the adoption of further planes of symmetry, actually.

From a number of experimental applications of the present invention it has moreover been found that a further beneficial effect can be seen to collaterally derive therefrom: it has in fact been noticed that the drastic reduction in or - in the best cases - the avoidance of asymmetrical material shrinkage problems in the moulded part forming the frame enables moulds to be designed and used featuring multiple moulding cavities or impressions, typically in the number of 4 or more, instead of a significantly lower number of moulding cavities, i.e. 1 or 2 at the most, as allowed for by currently available moulding techniques applied to forming motor frames that are not provided, i.e. are not designed in accordance with the present invention, for the above-noted material shrinkage problems to be effectively avoided.

Now, all those skilled in the art will be capable to readily appreciate that this opportunity is such as to really enable the productivity of the whole moulding process to be improved to a significant extent, thereby further increasing the overall competitiveness of the final products in a marked manner.

This description is concluded by putting again the stress on the fact - although this does not really seem to be necessary as far as those skilled in the art are concerned - that the whole motor frame made in accordance with the present invention must of course be configured and formed in a symmetrical manner, wherein this requirement shall not be understood as solely applying to the head portion, i.e. end-shield of the frame shown in the various Figures, but also to the remaining portion thereof, i.e. the portion comprising the cylindrical side portion thereof, which cannot obviously be illustrated in its entirety in the form of a three-dimensional graphical representation.

Claims

1. Electric motor comprising:

- an outer frame (1),

- a stator stack (2) accommodated within said outer frame, - possibly one or more support means (3) applied to the outside of said frame, wherein said outer frame comprises at least a portion (4) arranged to lie on a plane that is substantially orthogonal to the axis (X) of the motor, characterized in that said frame is configured into a shape that is symmetrical relative to a first plane (h) extending through said axis (X) of said motor.

2. Electric motor according to claim 1 , characterized in that said frame is configured into a shape that is symmetrical relative to a second plane (k) that is inclined relative to said first axis (h) and extends through said axis (X) of said motor.

3. Electric motor according to claim 2, characterized in that said second plane (k) is orthogonal to said first axis (h).

4. Electric motor according to any of the preceding claims, characterized in that said portion (4) is formed integrally in a single- piece unitary construction.

5. Electric motor according to any of the preceding claims, characterized in that said portion (4) is formed by a process of injection moulding a thermoplastic material.