The rotor arrangement is thus of the kind known in practice that includes a stator, a rotor rotatably mounted in the stator, and two axially separated magnetic radial bearings which function in a lcnown manner to support the rotor from the stator for rotation in a contactless fashion. The magnetic bearings preferably have the nature of permanent magnets.

One problem with rotor arrangements of this kind is concerned with providing axial stabilisation of the rotor in the stator, owing to the fact that the magnetic bearing device causes axial instability of the rotor.

In the case of known technology, efforts are made to stabilise the rotor axially with the aid of electronically controlled electromagnets or with the aid of superconductive material.

Solutions of this nature are both complex and expensive.

Accordingly, one object of the present invention is to provide a rotor arrangement with which the rotor is stabilised axially with only slight or negligible friction, with the aid of structurally simple means and at relatively low cost.

This object is achieved by the present invention.

The invention is defined in the accompanying Claim 1.

In one particularly important aspect of the invention, the rotor is supported axially by a mechanical support located at least at one end of the rotor. In one practical embodiment of the invention, said end may consist of a spherical surface, or may carry a spherical element, such as a ball, and support against a preferably flat support surface that extends in a plane normal to the rotor axis.

Many embodiments include a mechanical rotor-support at each end of the rotor, wherein the supports are mutually separated by a distance that corresponds substantially to the axial length of the rotor.

According to further embodiments of the invention the support can be selectively adjusted axially, to support the rotor axially in a chosen axial position of the rotor.

In this regard, the support may be adjusted to a position in which the rotor is displaced from its axially unstable bearing-mounted position in a direction towards said support, which is displaced to the same extent and in the same direction. The rotor will then be held axially by oppositely acting forces from the magnetic bearings on the one hand and from the support on the other hand. This makes it unnecessary to support the other end of the rotor shaft axially, therewith enabling said end to be left free and used as a rotor input or output shaft. In the case of another embodiment the rotor can be carried in said arrangement at an angle in which the rotor is inclined to the horizontal plane, wherein the rotor may be displaced axially upwards from said unstable position so that the axial force component of the bearings will counteract the axially directed gravitational force component acting on the rotor. A mechanical axial support is provided at least at one end of the rotor in order to stabilise the rotor axially also in this embodiment.

In another embodiment, a magnet that attracts a rotor-mounted magnet is provided behind the axial support. The other end of the rotor may be free, with no axial support, whilst retaining the unstable state of equilibrium of the magnetic bearings.

When the ends of the rotor shaft are spherical, the spherical surfaces may conveniently have a common centre of curvature on the rotor shaft, for instance between the shaft ends, preferably at the centre-of-gravity point of the rotor. It is conceivable in this respect that the centre of curvature will lie at the midway point of the rotor. This will minimise the inconveniences that otherwise occur with tilting of the rotor shaft when it loses contact with a support surface. In one embodiment the ends of the rotor shaft may have radii whose sum exceeds the length of the rotor shaft. This will limit or restrict any obliqueness of the rotor shaft by interference in the supporting surface on said support, said surface normally being flat and normal to the stator axis.

The invention will now described by way of example and with reference to the accompanying drawings, in which Figure 1 is a schematic axially sectioned view of a rotor arrangement constructed in accordance with the present invention; Figure 2 is a schematic illustration of an axially displaceable rotor axial support; Figure 3 is a schematic illustration of an arrangement that includes only one mechanical axial support ; Figure 4 illustrates magnetic axial retention of the rotor shaft at an axial support; Figure 5 illustrates means for returning the rotor to a central position in the stator; Figure 6 illustrates a variant of the rotor return means shown in Fig. 5 ; and Figure 7 shows another embodiment of the rotor shaft.

Figure 1 illustrates a rotator 1 that is rotatable in a stator housing 2. The rotor is mounted on two radial permanent magnetic bearings 3 that are mutually spaced in an axial direction.

Each bearing includes a ring-shaped or annular permanent magnet 31, which is carried by the housing, and a permanent magnet 32 which is carried by the rotor 1 concentrically with its shaft 11. Each magnet 31, 32 has two magnetic poles that are separated in the axial direction of the rotor. In the case of the illustrated embodiment, the poles of the magnets 31,32 are positioned axially such as to repel each other radially.

Normally, it is endeavoured to hold the magnets in mutually similar axial positions, so as to prevent the bearings 3 from causing axial displacement of the rotor. However, the rotor 1 is unstable axially in this axial position.

In order to maintain the rotor in this unstable state, it is now proposed that the rotor is supported axially with the aid of a mechanical support. The embodiment shown in Fig. 1 includes a mechanical support 4 at each end 12 of the rotor 1.

Each support 4 has facing its respective end a flat support surface that extends in a plane normal to the rotor shaft 11. Each end 12 of the rotor has a spherical surface 13 that contacts the support surface 40 of the support 4 at the end 12 of the shaft. The spherical surfaces 13 may have a common centre of curvature on the shaft 11, preferably at the centre-of gravity of the rotor, for instance at the axial midway point of the rotor.

It will be seen in Fig. 2 that the support 4 is carried on a threaded shaft 41 whose threads 42 engage a threaded opening 22 in the stator housing, and that the threaded shaft carries a lock nut 43 that can support against the wall of the stator housing so as to lock the support shaft firmly against rotation about its long axis. It will also be seen that the support shaft is fitted with a turning knob or the like 44.

Shown in Fig. 3 is an embodiment that requires only one support 4. Fig. 3 thus shows rotor 1 displaced from its unstable position to the right of the figure, so that the repulsive forces acting between the magnets 31, 32 in respective bearings 3 will displace the rotor 1 to the right in Fig. 3, said displacement force being taken up by the support 4. In this case there is no need to support the end 17 of the rotor shaft, therewith enabling said end 17 to be left free and connected to a co-axial input or output shaft for example.

Figure 4 illustrates an embodiment in which a first magnet 51 is located in the proximity of the supportive surface of the support 4, and in which a second magnet 52 is located at the end of the shaft 11 resting against the support 4. The magnets 51,52 are disposed to attract each other so as to keep this end of the shaft in contact with the adjacent support 4. The magnets are suitably rotational-symmetrical about the rotational axis of the shaft 11 and the stator axis respectively.

In another embodiment, the magnet 52 is omitted and the magnet 51 acts directly on the magnet 32.

It will be obvious to the person skilled in this art that a typical electric motor can be constructed by a suitable arrangement of the rotor and stator. It will also be obvious to the skilled person in this art that the rotor and the stator can co-act to form some form of working machine. For instance, the arrangement can be used as a fan or blower, a vacuum cleaner motor, a power storage system, a high-speed centrifuge, a turbine generator, and so on.

Minimum friction, minimum wear, minimum noise generation, no maintenance, are among those advantages afforded by the present invention. Further advantages include an effective speed range, stabilisation in the absence of power supply, low costs, and simple stabilisation (no complex control system required) Should the arrangement shown in Fig. 1 tilt so that the rotor shaft is inclined to the horizontal, the force at which the rotor abuts the lower support 4 can be lightened by displacing the supports 4 axially upwards, so that at least some of the effect of gravity axially on the rotor can be taken up magnetically as a result of the mutual axial displacement of the magnets 31, 32 in respective bearings.

Those ends of the rotor shaft that shall support against the support 4 may be given a convex rotational-symmetrical arcuate or curved shape, by working a respective end of the shaft itself, or may be manufactured separately and fitted to the rotor shaft per se. For example, the convex end of the rotor shaft may be formed by a ball mounted centrally on the actual end of the rotor shaft.

In the case of those embodiments of the arrangement in which both ends of the rotor shaft co-act with a respective support 4, it may be suitable to ensure that both shaft ends are in abutment with respective supports 4 at the same time with a small abutment force, at least when the rotor shall rotate at high speeds.

The embodiment shown in Fig. 5 the rotor includes an electrically conductive plate or disc 37. The plate is centred on the rotor and placed in the proximity of a stator-carried permanent magnet 31, which in this case is also used for the magnetic radial bearing of the rotor. The plate extends in a plane normal to the rotor axis or shaft. If the rotor 1 should be

displaced from its central position in the stator, the magnetic field from the magnet 31 will generate electric currents in the plate 37, these currents creating, in turn, forces that strive to return the plate 37 to its central position in the stator and which thus counteract any radial movement of the rotor.

As shown in Fig. 6, the outer edge of the plate 37 may be bent so as to extend inwards over the peripheral surface of the magnet 31 when said surface is exposed. The plate 37 is preferably rotational-symmetrical in relation to and parallel with adjacent surfaces of the magnet 31.

The plate 37 may, of course, co-act with a separate magnet whose sole purpose is to centre the plate 37/the rotor 1.

As will be understood, several pairs of plates 37 and magnets 31 may be disposed along the rotor, preferably equidistantly from respective radial bearings of the rotor.

Figure 7 shows an embodiment in which the rotor shaft 11 is divided perpendicular to the rotor axis. The embodiment includes a springy circular plate or disc 38 which is fitted between and joined to the resultant parts of said shaft, so as to provide axial resilience between the end 12 of the rotor and the main part of the rotor and therewith limit the load acting on the contact surfaces between the rotor end 12 and the support 4, for instance when adjusting said surfaces into abutment with each other. Alternatively, this resilience can be achieved by embodying a corresponding spring means in the structure carrying the support 4. In one embodiment (not shown) the curved or arcuate surface 13 may be formed by a ball which is carried directly by a spring that corresponds mechanically, for instance, to the plate 38 and which, in turn, carries the end of the rotor shaft.