GB2101416A

GB2101416A - A D.C. rotating electric machine and a method of its manufacture

Info

Publication number: GB2101416A
Application number: GB08214754A
Authority: GB
Inventors: Karel Prochazka; Zybnek Slavik; Karel Skrdlant; Jiri Valka; Milan Drlik; Milan Mezirka
Original assignee: Z SILOPROUDE ELEKTROTECHNIKY K
Current assignee: Z SILOPROUDE ELEKTROTECHNIKY K
Priority date: 1981-05-22
Filing date: 1982-05-20
Publication date: 1983-01-12
Also published as: IT1151205B; DE3219276A1; IT8221424A0; CS224591B1

Abstract

The machine comprises a stator with a cage (7), of non-magnetic material supporting permanent magnets (3) in the shape of part- cylindrical shells, which bear on machine surfaces of bearing shields (5) of the machine and are encompassed and fixed by a shell (4) of the stator. The cage is composed of end rings connected by axial members and is made of non-magnetic material. A short-circuit around the windings of the rotor is produced if the cage is made of electrically conductive material. <IMAGE>

Description

SPECIFICATION A direct current rotating electric machine with excitation by permanent magnets, and a method of its manufacture The invention relates to a direct current rotating electric machine which is excited by permanent magnets in the shape of partcylindrical shells and with a stator of nonmagnetic material provided with a yoke of magnetically conductive material, particularly suitable for driving domestic appliances, and also a method of its manufacture.

Direct current machines acquired with the development of electronics an increasing importance as drive of different domestic appliances, particularly where their operation is controlled according to certain predetermined conditions as is the case, for instance, with automatic washing machines. For similar drives the designers attempt, in addition to meeting required parameters, to provide a very simple construction requiring minimum manufacturing costs. These conditions are well met by machines with permanent magnets. Their application results in the reduction of copper, of weight and of losses of the machine and thus in an improvement of the efficiency and in a reduction of the power supplied to the machine. So far permanent magnets are concerned ferrites in the shape of cylindrically bent segments are mostly used due to their substantially lower cost compared with other materials.One of the main problems in connection with the application of permanent magnets for electric machines, particularly for the mentioned purpose, is their fixing in the machine in order that these magnets would provide the required magnetic flux at optimum energetic utilization of the material and that no loosening of magnets would occur in the course of operation, or a reduction of their efficiency.

Neither mechanical clamps of different types nor glueing of magnets directly to the frame safeguard a sufficient mechanical rigidity of construction. By loosening of magnets the noise of the machine is increased and the magnitude of the magnetic flux is changed. A compact arrangement is obtained by casting in the permanent magnets into plastics material. This arrangement requires however a painstaking adjustment of the position of the magnets prior to casting, which is accomplished by the application of special fixtures, but even this does not guarantee a perfectly accurate geometry of the magnetic circuit due to the tolerances of the magnetic material. In all cases we have to consider the amount of required labour, which for mass production, is an important criterion when appreciating advantages of a new technical solution.

A direct current electric motor with permanent magnets is known, the shell of which is on its surface provided with openings for the insertion of permanent magnets, where additional magnetically conductive material is added outside the shell for closing the magnetic flux, which material simultaneously fastens the permanent magnets. The face parts of this tube-shaped shell form simultaneously bearing shields of the electric motor. The insertion of the rotor into this shell is rather difficult and the shell with the required bearing surfaces is not suitable for mass production as it is complicated.

It is an object of this invention to eliminate or at least to reduce these drawbacks of electric rotating machines. According to this invention the permanent magnets are situated in a supporting cage of non-magnetic material formed by two rings linked by axial members, the lateral faces of which determine the position of the permanent magnets, the external planar surfaces of the rings and their internal cylindrical surfaces forming bearing surfaces for offset parts of bearing shields, each offset part being in axial direction larger than the width of the associated ring and forming a bearing surface for the permanent magnets, the rings and the permanent magnets, being encompassed by a shell of the stator, made of magnetically conductive material.

The manufacturing method of a direct current electric rotating machine according to this invention consists in that after machining of the external planar surfaces and the internal cylindrical surfaces of the rings and after machining of the offset parts of the bearing shields coaxially with their hubs, the complete rotor is inserted into one shield with a rotor bearing, the supporting cage is fitted on the offset part of the bearing shield, into which the second rotor bearing is mounted, whereafter the permanent magnets are inserted into the supporting cage.

An advantage of the direct current electric rotating machine and of its manufacturing method according to this invention is a perfect coaxiality of mounting of the bearing shields with the hub of bearing shields, where the rotor bearing is supported, securing a perfect coaxiality of the rotor with the stator and thus also a uniform air gap below the poles as on the offset part of each bearing shield also permanent magnets are supported so that in the course of assembling no magnetic flux of the stator is acting on the rotor. It is equally possible to make replacements of permanent magnets in a simple way if the machine in the course of testing does not achieve prescribed parameters both due to influence of manufacturing allowances and due to insufficient magnetizing of permanent magnets. It is supposed that the permanent magnets are mounted already magnetized.

Another advantage of this solution according to this invention is the possibility of a reduction of the proper inductance of the rotor (particularly suitable for transistor regulators with high frequencies of around 20 KHz) and the improvements of commutation if the supporting cage is made of an electrically conductive material. The supporting cage acts in this case as a damping turn (a short circuit turn), eddy currents are induced in axial members of the supporting cage, acting against the cause of their origin, i.e. against the reaction of the rotor.

One embodiment of a direct current electric rotating machine according to this invention is shown in the accompanying diagrammatic drawing, wherein: Fig. 1 shows one half of an axial sectional view of the machine, Fig. 2 a radial cross-section of the machine shown in Fig. 1, Fig. 3 a part of an axial sectional view of the stator along an axial girder of the supporting cage, and Fig. 4 a cross-section of the stator along a plane indicated in Fig. 3 by A-A.

The direct current electric rotating machine according to this invention comprises a rotor 1 mounted in a stator which consists of a supporting cage 2 with permanent magnets 3 in the form of part-cylindrical shells, a stator shell 4 and bearing shields 5. Collecting means 6 are provided in one of the bearing shields 5. The supporting cage 2 and the bearing shields 5 are made of magnetically non-conductive material, the shell 4 is of a magnetically conductive material. The supporting cage 2 comprises two end rings 7 interconnected by axial elongate members 8 which determine the position of the permanent magnets 3, i.e. their distribution along the circumference of the stator. The external planar surface 9 and the internal cylindrical surface 10 of each end ring 7 form bearing surfaces for the offset part 11 of the associated bearing shield 5.Each offset part 11 is in the axial direction larger than the width of the associated ring 7 so that after mounting of the bearing shields 5 on the supporting cage 2 the, offset parts 11 of the bearing shields 5 form bearing surfaces for the permanent magnets 3. The offset part 11 is machined simultaneously with the hub 1 2 of the bearing shields 5 where the bearing 13 of the rotor 1 is arranged in assembled state. In this way perfect coaxiality of both surfaces is secured and thus also the coaxiality of the rotor 1 with the main poles, formed by the permanent magnets 3.

That secures a uniform air gap between the rotor 1 and the stator, reflected advantageously in parameters of the machine. The thickness of the rings 7 of the supporting cage 2, measured in the radial direction of the machine, corresponds to the thickness of the permanent magnets 3, so that the shell 4 of the stator, bearing on the external cylindrical surface 14 of the rings 7 of the supporting cage 2, firmly encompasses the permanent magnets 3 and forms the yoke of the stator. The shell 4 of the stator can have the shape of a tube slipped on to the assembled stator. Due to manufacturing allowances of the permanent magnets 3 it is advantageous if the cylindrical shell 4 of the stator is interruped by at least one axial slot 1 5.After the shell 4 of the stator has been slipped on to the stator, or after location of its individual parts, it is possible to draw it sufficiently tightly against the stator. It is however always necessary to situate the axial slot 1 5 of the shell 4 of the stator at the axis of the main pole, as otherwise the magnetic circuit of the stator would be interrupted. The bearing shields 5 are fixed to the supporting cage 2 either by means of bolts passing through the machine at the axial members 8 or by glueing, possibly also by means of the shell 4 of the stator, which is, for instance by radially arranged screws, connected to the bearing shields 5. It is advantageous to manufacture the supporting cage 2 and the bearing shields 5 by the method of accurate casting, requiring minimum machining.

The manufacture of the machine according to this invention can proceed so that only individual parts of the stator, manufactured by the method of accurate casting are machined, namely the external planar surface 9 and the internal cylindrical surface 10 of the supporting cage 2, and also the offset part 11 of the bearing shield 5 coaxially with the hub 12. The supporting cage 2 is thereafter inserted into one of the bearing shields 5 with an inserted bearing 13 for the rotor 1 and the second bearing shield 5 is mounted to the supporting cage 2. All operations are facilitated because the permanent magnets 3, the attractive forces of which would particularly interfere with the mounting of the rotor are not yet at their place. The permanent magnets 3 are inserted into the already assembled stator to the bearing surfaces formed by the extending offset part 11 of the bearing shields 5 and by lateral faces of the axial members 8 of the supporting cage 2, whereafter the shell 4 of the stator is fixed. The permanent magnets 3 are inserted into the supporting cage 2 advantageously already magnetized. The magnetization is accomplished in a special fixture. A possible replacement of the permanent magnets 3 after the operating parameters have been tested can be accomplished by the removal of the shell 4 of the stator only, without elaborately disassembling the whole machine.

Claims

1. A direct current electric rotating machine which has a stator and a rotor mounted in bearings, and which is excited by permanent magnets in the shape of part-cylindrical shells, the machine comprising a supporting cage made of non-magnetic material and formed by two spaced apart rings interconnected by axial elongate members, the permanent magnets being located in the cage such that lateral faces of the elongate members determine their position, the machine further comprising bearing shields having offset parts, the outer planar surfaces and internal cylindrical surfaces of the rings forming bearing surfaces for the offset parts, the offset parts being in the axial direction larger than the width of the rings and forming bearing surfaces for the permanent magnets, the rings and the permanent magnets being encompassed by a shell which forms part of the stator and is made of a magnetically conductive material.

2. A machine according to Claim 1, wherein the stator shell is interrupted by at least one axial slot.

3. A machine according to Claim 1 or 2 wherein the supporting cage is made of an electrically conductive material and forms a short circuit turn around the winding of the rotor.

4. A machine according to Claim 1 or 2 wherein the supporting cage and the bearing shields are made of plastics.

5. A direct current electric rotating machine constructed, arranged and adapted to operate substantially as herein described with reference to, and as shown in, the accompanying drawing.

6. A method of manufacture of a direct current electric rotating machine according to any one of Claims 1 to 5, wherein the outer planar surface and the internal cylindrical surface of each ring are machined and the offset part of each bearing shield is machined coaxially with a hub of the bearing shield, and the complete rotor is mounted into one bearing shield comprising a rotor bearing, the supporting cage is fitted on the offset part of said one bearing shield, and a second rotor bearing is mounted, together with a second bearing shield, to the supporting cage, the permanent magnets are inserted into the supporting cage on the offset parts of the bearing shields, whereafter the stator shell is mounted on the external cylindrical surfaces of the rings and is fastened in position.

7. A method of manufacture of a direct current electric rotating machine substantially as herein described with reference to the accompanying drawings.