Method for producing an encased rotor of a permanent magnet

The method serves for manufacturing a canned rotor of a permanent magnet motor. Firstly a shaft (2) provided with a rotor core [rotor laminated sheet package] (3) together with a pre-blank (11) forming the later magnet and a [sheet] metal casing (6) surrounding the pre-blank is applied with play into a pressing tool (12). The pre-blank (11) is then deformed by way of end-face pressure impingement such that it then bears with a non-positive fit and over the whole surface on the rotor core [rotor laminated sheet package] (3) and on the [sheet] metal casing (6), wherein the casing (6) is widened radially until its bearing on the pressing tool (12) by way of the radially widening pre-blank (11). After this the magnetisation and hardening is effected, whereupon the free spaces remaining between the [sheet] metal casing (6) and lid (2) are closed by two annular lids, which are tightly connected to the [sheet] metal casing (6) and the shaft (2) with a material fit.

The invention relates to a method for manufacturing a canned rotor of a permanent magnet motor.

With rotors of permanent magnet motors, permanent magnets are either to be arranged directly on the motor shaft or on a rotor iron part seated on the rotor shaft, for example a rotor core [laminated sheet package]. With this it may be the case of individual magnets to be distributed uniformly over the periphery of one or more annular magnets which are suitably polarised. Since the torques occurring on the motor shaft are produced via the magnetic flux between the stator and the rotor and thus also via the permanent magnets located therein, the magnets are to be fastened in a suitably stable manner. For this there are mechanical solutions such as for example are known from the U.S. Pat. Nos. 4,855,630 and 5,140,210 or 5,627,423. Such mechanical fastenings are not only expensive in manufacture but they furthermore tend to be unbalanced which must be compensated as the case may be.

Such mechanical fastenings are furthermore often not practical if the rotor needs to be completely canned, as is usually the case with wet-running motors. In particular with the magnets used today which are based on neodynium at all events one must prevent these from coming into contact with water. Here plastic encasings are usually not sufficient since as a rule they are not diffusion-proof.

From the U.S. Pat. No. 5,495,658 there is known a method with which the magnet is formed and sintered in the later rotor casing and only after this is the shaft inserted. The dimensional accuracy in particular on the rotor casing is supposed to be particularly favorable due to this. The manufacturing method described in this document is however not so suitable for the large-scale manufacture of canned rotors. On the one hand the fastening of the shaft represents a problem and on the other hand high tension stresses are introduced into the magnet on account of the pressing-in, which should be avoided after its hardening. Furthermore, this manufacturing method is not suitable for rotors provided with a rotor core comprising a rotors laminated sheet package, since the connection between the rotor core (rotor laminated sheet package) and the magnet may not be controlled or is only very difficult to control, and in any case the rotor core (rotor laminated sheet package) on the peripheral side needs to be machined with material removal.

Against this background it is the object of the invention to provide a method for manufacturing a canned rotor of a permanent magnet motor with which such rotors may be inexpensively manufactured in large scale manufacture, in particular industrial scale manufacture, in particular whilst avoiding the previously mentioned disadvantages.

SUMMARY OF THE INVENTION

According to the invention this object is achieved by providing a method for manufacturing a canned rotor of a permanent magnet motor, in particular a wet-running motor, with the following method steps to be carried out after one another: a shaft, where appropriate provided with a rotor iron part together with a pre-blank surrounding this and forming a later magnet and with a (sheet) metal casing surrounding the pre-blank is applied into a pressing tool; the pre-blank is deformed by end-face pressure impingement such that it bears with a non-positive fit on the inside on the shaft or the rotor iron part which is present as the case may be, and on the outside on the (sheet) metal casing, wherein the casing is widened radially by the radially widening pre-blank, until its bearing on the pressing tool; the (sheet) metal casing before or after the magnetisation and hardening of the blank is closed at the end face by two annular lids which are tightly connected to the (sheet) metal casing and the shaft or to the rotor iron part.

Advantageous embodiments and further formations of the method as well as the construction of such a rotor are defined in the dependent claims, the subsequent description and the drawings.

In one embodiment, the method according to the invention is formed as follows:

First, a shaft or as the case may be a shaft already provided with a rotor iron part with a pre-blank which as the case may be is of several parts and which forms the later magnet, and with a cylindrical sheet metal section which forms the later sheet metal casing is applied into a pressing tool. The components at the same time have an adequate play to one another so that they may be joined into one another practically without any force effort. The pre-blank in one or more pressing procedures is then deformed by end-face impingement with pressure to an extent such that it bears with a non-positive fit on the inside on the shaft (if the magnet is directly seated on the shaft) or on the rotor iron part and on the outside on the metal casing.

At the same time the dimensioning of the pre-blank and metal casing is configured such that the casing during the pressing procedure may radially widen up to its bearing on the pressing tool. After this deformation procedure the metal casing is closed at both end faces by a lid. The lids on the inner side are sealingly connected to the shaft or to the rotor iron part and on the outer side to the metal casing. The magnetisation and hardening of the blank is effected after the pressing procedure.

Rotor iron part in the context of the present invention is to be understood as any component between the shaft and the magnet conducting the magnetic flux. Such a component may typically be formed by a rotor core (rotor laminated sheet package) or also a ferrite sintered body.

The method according to the invention not only creates an intimate non-positive union between the blank or the magnet, the (sheet) metal casing and the rotor iron part or shaft, but furthermore in practically one working procedure ensures a high radial dimensional accuracy of the rotor. A further considerable advantage of the method according to the invention in particular lies in the fact that with a rotor equipped with a rotor core (rotor laminated sheet package), the rotor core (rotor laminated sheet package) on the outer periphery does not need to be machined separately since the pre-blank bears flushly onto the outer side of the rotor core (rotor laminated sheet package) by way of the pressing procedure. A further considerable advantage of the method according to the invention lies in the fact that one does not need to use any adhesive for fastening the magnet, which loses its strength properties in particular at high operating temperatures. Furthermore with regard to manufacturing technology it is advantageous that in spite of using a sintered pre-blank one may do away with the critical handling with powder. The pre-blank constructed as a sintered body may be manufactured separately without interfering with the remaining manufacturing and assembly process.

The pre-blank may be of several parts, for example, in the form of ring segments or rings or ring segments bearing on one another in an axial manner. The pre-blank preferably consists of two rings bearing axially on one another which are impinged by pressure from both axial sides simultaneously or also after one another. On account of the introduction of pressing force on both sides and due to the fact that one applies two rings bearing axially on one another one may very easily control the flow procedure of the material. One ensures a uniform material flow over the whole axial length of the pre-blank.

In order to completely encapsulate the rotor, i.e. in a fluid-tight manner, it is useful to form the lids by sheet metal shape parts which at their inner side are connected to the shaft and at their outer side to the metal casing. According to the design of the rotor iron part it may be sufficient on the shaft side to weld the (sheet) metal casing to the rotor iron part instead of to the shaft in order to achieve a sealed encapsulation. For welding the (sheet) metal casing to the lids it is useful on the one hand to design the lid cup-shaped and on the other hand to let the (sheet) metal casing of the motor to project beyond the blank, seen in the axial direction, that is, the later magnets. Then specifically the lid edge may be welded to the (sheet) metal casing in a region which is distanced so far from the blank or magnet that a noticeable heat effect, in particular a heat effect compromising the magnet is avoided. The welding procedure may thus also be effected after the magnetisation. Furthermore it is possible in this manner to carry out the welding of the casing and lid from the outside of the casing, in that one welds through the casing for example by way of a laser.

Usefully the pressing tool, casing and pre-blank are dimensioned such that the casing with the pressing procedure is plastically deformed beyond its elasticity limit. By way of this deformation of the casing a calibration of the rotor may be simultaneously effected so that for this one requires no separate working procedure.

The magnetisation and hardening of the blank may in principle be effected at any time after the reshaping (deformation) procedure. If a hardening is effected by an external heat effect, the magnetisation and subsequent hardening is advantageously effected before the connection of the (sheet) metal casing to the lids, since due to the heat effect with the hardening procedure, residual moisture or gases which may be present are removed.

According to the construction type and the material used, as the case may be one may however do away with a hardening by way of an external heat effect. The hardening is then effected during operation of the motor, for example during a trial run specially conditioned for this, but also during normal operation. As the case may be one may also completely do away with a hardening of the magnet since this is mechanically rigidly tensioned between the (sheet) metal casing and the shaft or sheet metal casing and rotor iron part, and otherwise is not subjected to any mechanical loading.

The invention is hereinafter described in more detail by way of one embodiment example shown in the drawing. There are shown in

FIG. 1, lateral view of a rotor manufactured according to the invention;

FIG. 2, an end view in the direction of the arrow II inFIG. 1;

FIG. 3, a longitudinal section through the rotor according toFIG. 1;

FIG. 5, the detail V inFIG. 3in an enlarged representation; and

FIGS. 6A–6Fillustrate the manufacturing process in four part steps by way of schematic longitudinal section representations.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

The rotor1shown individually by way ofFIGS. 1 to 6Fconsists of a shaft2on which the rotor core rotor laminated sheet package3is fastened. The rotor core3comprises a rotor laminated sheet package on a peripheral side3a(FIG. 6A) is surrounded by a blank4which consists of two rings5which abut one another at the end face and are flush with one another and which forms the magnet of the rotor. The rotor core3is not machined on the peripheral side and the blank4connects to this unmachined outer periphery of the rotor core3over the whole surface in a flush manner and is connected to this with a non-positive fit.

The blank4on its outer periphery is surrounded by an essentially cylindrical metal casing6which bears over the whole outer circumference of the blank4on this and is connected to this with a non-positive fit.

The region between the shaft2and the metal casing6(FIG. 6Ais closed off by two lids7which in each case immersed into the space formed between the metal casing6and the shaft2and are formed by sheet metal shape parts. The lids7comprise an edge8(FIG. 5) and edge9(FIG. 4) extending inwards and outwards respectively via which they are welded to the part of the metal casing6or the shaft2extending beyond the blank4. The detail IV which is enlarged inFIG. 4, clearly shows the outer edge9which bears within the metal casing6and is welded to this over the circumference. The metal casing6projects axially over the edge9.

The detail V (FIG. 3), which is enlarged inFIG. 5, shows the welding of the inner edge8to the shaft2, and specifically via a fillet weld lying at the end face on the inner edge8between the shaft2and the lid7. The lids7furthermore comprise eight dome-shaped impressions10(FIG. 2) which serve for stabilizing and for preventing oscillations.

The previously described rotor1is hermetically sealed with respect to the rotor core3and the blank4which forms the magnet, by way of the metal casing6and the lid7as well as the shaft2and is envisaged for application in the can of a wet-running motor. At the same time, the shaft2at both sides of the rotor core3on the other side of the lids7carries axial bearings. The long, free shaft end2a(FIG. 3) for example carries an impeller of a circulation pump.

The manufacture of the previously described rotor is effected as shown by way ofFIGS. 6A–6Fand described hereinafter.

In a first step, the shaft2with the rotor core3fastened thereon, the cylindrical metal casing6and a pre-blank11is applied into a pressing tool12. The pre-blank11consists of two equally large rings12aand12b(FIG. 6A) bearing flush on one another, of a presintered magnetisable material based on neodynium. The presintering is effected such that one achieves a retention of the pre-blank11, that is, of the two rings and a sufficient shape stability, but that despite this a further deformability may be achieved, that is, a hardening is not yet effected. The components are matched to one another such that they lie in one another with play, wherein the pre-blank11in its axial length projects beyond the rotor core3at both sides.

Within the pressing tool, which is constructed of several parts and here is not shown in detail, the components are fixed in the position shown inFIG. 6B. With this, the metal casing6lies with play within the pressing tool12. In a step shown inFIG. 6C, there is then effected the actual pressing procedure, and specifically simultaneously from above and below. The punches mustering the pressing force are indicated at13. The pressing force direction is deduced from the arrows shown inFIG. 6B. The punches13are traversed so far that the pre-blank11at the end face occludes flushly with the rotor core3and thus forms the blank4, as is described and shown by way ofFIG. 6C. The dimensioning of the volumes of the pre-blank11, the free space formed between the rotor core3and the metal casing6as well as the diameter of the metal casing6are selected such that if the pre-blank11has been reshaped into the blank4pressed inFIG. 6c, this not only bears over the whole surface and with a non-positive fit on the outer periphery of the rotor core3and on the inner periphery of the metal casing6, but that furthermore the metal casing has been radially plastically deformed up to its bearing on the pressing tool due to the reshaping pressure, and thus has been calibrated.

After removing the pressing tool12which for this purpose is designed of several parts, not only is there formed a rigid connection between the shaft2, rotor core3, blank4and metal casing6, but the metal casing is furthermore already calibrated, that is, is brought to its exact radial dimension. In this shape (illustrated inFIG. 6D), the rotor is already completely stable, and it may be magnetised and also hardened, whereupon then subsequently the lid7is added and is welded externally by way of lasers. The magnetisation and hardening may be effected before as well as after the complete encapsulation.

With the previously described embodiment example, the blank4formed from the pre-blank11consists of two rings, by which means one is to achieve a more uniform material flow with the pressing procedure. To support this, two punches13from above and below are provided for mustering the pressure forces. It is to be understood that the blank or the pre-blank may also be basically formed as one piece or may consist of several segments.

The following table lists various part numbers and corresponding parts:1—rotor2—shaft3—rotor core4—blank5—rings6—metal casing7—lids8—inner edge9—outer edge10—embossing11—pre-blank12—pressing tool13—punch

While the method herein described, and the form of apparatus for carrying this method into effect, constitute preferred embodiments of this invention, it is to be understood that the invention is not limited to this precise method and form of apparatus, and that changes may be made in either without departing from the scope of the invention, which is defined in the appended claims.