The present invention describes a structure of a rotor for a variable reluctance electric machine and a method of manufacturing of such a structure.

We are dealing with variable reluctance, radial flux electric rotary machines. They comprise a stator and a rotor. The stator further comprises stator core and stator windings. The function of the stator is to generate a rotating magnetic field when AC currents flow through stator windings. The rotor typically rotates inside the stator, or outside the stator. The rotor has a high degree of magnetic anisotropy: it easily passes magnetic flux along low-reluctance axis (D) and it blocks the magnetic flux along high-reluctance axis (Q). Having that property, when exposed to magnetic field produced by the stator, the rotor has a tendency to align itself in such a way that low-reluctance axis (D) of the rotor provides passages for magnetic flux between active magnetic poles of the stator. Now, when the magnetic field of the stator rotates, so does the rotor and the machine in motor mode of operation can deliver mechanical torque. The quality of the variable reluctance electric rotary machine: in terms of efficiency and power factor depends on the level of anisotropy between low and high-reluctance magnetic axis.

The notion: variable reluctance electric rotary machine is used in broad sense in this disclosure: it extends to any electric rotary machine, where magnetic anisotropy of rotor is used. For example, there are induction machines, or permanent magnet machines, where the torque in some operating conditions is at least partially coming from variable reluctance. For the sake of this disclosure, we categorize all those machines as variable reluctance machines.

Very often rotors of variable reluctance electric machines comprise stack of laminations. Those laminations are typically made of a soft magnetic material and have circular shape. The soft magnetic material has low coercivity, so it can be easily magnetized. The laminations are stacked along axial direction of the motor - we consider transversally laminated structure. In order to achieve the desired anisotropy of magnetic properties of the rotor, the laminations contain a pattern of flux carrier stripes and flux barrier stripes. The flux barrier stripes are regions where soft magnetic material has been removed at some stage of production process, for example by punching, or cutting. Further the volume of flux barrier stripe can be either filled with some material, or with air, or other gas that fills the interior of the electric rotary machine, or vacuum, or in some types of electric machines, permanent magnets are inserted there. The flux barrier stripes are either from non magnetic material, or from a material whose effective magnetic permeability is lower than of flux carrier strips. Flux carrier stripes and flux barrier stripes are arranged in an alternating pattern.

In a typical state of the art lamination pattern, there exist ribs: narrow passages of soft magnetic material, whose function is to hold all flux carriers together and in that way provide mechanical retention for the rotor structure. This is especially important at high rotation speeds, where centrifugal forces tend to pull flux carrier strips apart. The width of ribs of soft magnetic material in the rotor pattern is a tradeoff between magnetic anisotropy and mechanical retention: wide passages provide improved retention at the cost of less anisotropy and narrow passages improve anisotropy, but worsen the retention.

The object of the present invention is to provide a rotor of a synchronous reluctance electric machine having high anisotropy of magnetic reluctance in different directions while at the same time guaranteeing high level of mechanical retention.

The solution is to use at least two patterns of laminations: A and B, where flux carriers stripes or flux barrier stripes between laminations of type A and type B overlap. Separation of flux carrier stripes provides high level of magnetic anisotropy, while overlapping or indirect overlapping secures mechanical retention.

BRIEF DESCRIPTION OF THE DRAWINGS

Further understanding of various aspects of the invention can be obtained by reference to the following detailed description in conjunction with the associated drawings, which are described briefly below.

Fig. 1 shows a typical state of the art lamination for a variable reluctance electric machine rotor.

Fig. 2 shows how laminations are stack together to form a rotor.

Fig. 3 shows exemplary embodiment of laminations of type A and B.

Fig. 4 shows laminations of type A and B overlapping.

Fig. 5 shows a stack of lamination of type A and B forming a rotor.

Fig. 6 shows a fragment of a cross section through laminations where rigid mechanical fixtures between laminations are used.

Fig. 7 presents top view of laminations of type A and B comprising holes in flux carrier stripes.

Fig. 8 presents a fragment of a cross section through laminations wherein a spacer layer is used.

DESCRIPTION

Most important notions used in claims are defined or explained here in the description. For others we refer to the common meaning used by professionals in the field of electric machines, that is reflected in the open literature.

Fig. 1 presents a typical lamination (1) used in state of art. It comprises plurality of flux carrier stripes (2) and plurality of flux barrier stripes (3) forming an alternating pattern along a radial direction. In this particular example the rotor has four magnetic poles. The pattern of flux carrier stripes (2) and flux barrier stripes (3) is formed in such a way, that the magnetic reluctance along Q axis is significantly different than the magnetic reluctance along D axis, what results in the desired magnetic anisotropy of the rotor. In order to provide necessary mechanical retention, in state of the art solution, ribs (4) of lamination material are used. Those ribs (4) provide mechanical connection between different flux carrier stripes (2) The central structure (8) is a flux carrier that mechanically connects to opening for a shaft (5).

Fig. 2 presents how laminations (1) are stacked together to form a rotor of a variable reluctance electric rotary machine.

Fig. 3 presents an exemplary embodiment of lamination type A (1 A) and type B (1 B) - top view. Both of them comprise flux carrier strips (2) and flux barrier strips (3). In this particular example the rotor has four magnetic poles, and although the four-pole rotor is a typical case, this invention is not limited to that particular number of magnetic poles. It can contain also a different number of poles: two, six, etc.. The pattern of flux carrier stripes (2) and flux barrier stripes (3) is formed in such a way, that the magnetic reluctance along Q axis is significantly different than the magnetic reluctance along D axis, what results in the desired magnetic anisotropy of the rotor. For both lamination types A and B, each flux barrier stripe (3) separates the lamination (1 A) or (1 B) into two different parts. For example if we take one particular flux barrier stripe (31), after cutting it out from the lamination material, there are two different flux carrier stripes (21) and (22), where it is not possible to draw a continuous line from one of them (21) to another one (22) without crossing the geometric boundary of the magnetic material of the lamination. In general, two flux carrier stripes (21) and (22) are separated from one another if and only if any continuous line between the two flux carrier stripes has to cross the material boundary. On Fig. 1 , all pairs of flux carrier strips are not separated, while on Fig. 3, any pair of flux carrier strips is separated. Since all of flux barrier stripes (3) on both lamination patterns A and B are separated, there are no ribs (4) present on the lamination pattern.

Fig. 4 presents laminations of type A and type B overlapping when both laminations are stacked together to form the rotor of the variable reluctance electric rotary machine - top view. There exist flux carrier overlap (6) between flux carrier strips (2) from lamination type A and flux carrier strips (2) from lamination type B. Many flux carrier strips (2) from lamination type A overlap with two different flux carrier strips (2) from lamination type B: for example flux carrier stripe (22) overlaps with strip carrier (23) and also stripe (22) overlaps with central structure (8). Similarly, many flux barrier strips (3) from lamination type A overlap with two different flux barrier strips (3) from lamination type B. Now let's introduce the notion of indirect overlap: we say that two flux carrier stripes (21) and (22) overlap indirectly if and only if they overlap, or there exist a third flux carrier stripe (23), such that the first flux carrier stripe (21) overlaps with the third one (23) and the third one (23) overlaps indirectly with the second one (22). This is a recursive definition. In other words, it means that two flux carrier stripes (21) and (22) overlap indirectly, if they overlap, or if there exist an ordered set of carrier stripes (23), (24), .... such that (21) overlaps with (23), and (23) overlaps with (24) and so on until the last element of the set overlaps with (22). The regions of overlap between (21) and (23) can be different than the regions of overlap between (23) and (22). The notion of indirect overlap is relevant for mechanical retention: in case flux barriers are filled with air and at least some flux carrier stripes are separated from the central structure, after stack of laminations is formed, all flux carrier stripes that are separated from central structure must indirectly overlap with central structure in order to guarantee mechanical retention of the complete structure.

Fig. 5 presents how laminations of type A and B are stacked together to form the rotor of the variable reluctance electric rotary machine. In this particular embodiment, the particular order is: ABAB..., but this invention covers all possibilities, as there might be a different orders of lamination stacking, for example: AABBAABB, AABAAB, .... Also, there might be more than two pattern types: A, B, C and different permutations, or variations can also be arranged in a particular order, say AABCCAABCC etc.

Fig. 6 presents a fragment of a cross section - side view - through laminations wherein rigid mechanical fixtures between laminations are used. At the place of flux carrier overlap (6), or flux barrier overlap (7), a rigid mechanical fixture (92) or (93) can be used in order to immobilize the two parts that overlap versus one another. In this particular embodiment the rigid mechanical fixture is an inter-lamination adhesive material that cause overlapping structures to stick together. In general, the rigid mechanical fixture between flux carrier stripes (92) or flux barrier stripes (93) can be of different form: it could be an extra hole penetrated by a bolt, or a rivet, it could be welding, or it could be a bump, or any other mechanical solution that guarantees that when the rotor is formed from lamination stack, the parts joined by the rigid mechanical fixture will not move versus one another.

Fig. 7 presents top view of laminations of type A and B comprising holes in flux carrier stripes (2) on lamination type A (36A) and on lamination type B (36B). Since corresponding holes on lamination of type A and B overlap, a rigid mechanical fixture (92) can be inserted. The rigid mechanical fixture is in this case a rod, that when inserted in holes will immobilize flux carrier stripes (2) of lamination type A versus flux carrier stripes (2) of lamination type B, providing in that way sufficient mechanical retention. After the insertion, all rigid mechanical fixtures (92) are oriented parallel to the axis of rotation of the rotor. In order to avoid a situation where holes (36A, 36B) would pose an obstacle for magnetic flux, at least some of rigid mechanical fixtures (92) can be made of a magnetic material, for example silicon steel.

Fig. 8 presents a fragment of a cross section - side view - through laminations wherein a spacer layer (35) is used. The spacer layer is a lamination inserted between lamination of type A (1 A) and lamination of type B (1 B). The spacer layer increases the vertical distance between flux carrier stripes from lamination type A and B, where those flux carrier stripes overlap. Spacer layer is made from a non-magnetic material. The purpose of the spacer layer is to keep high reluctance along high reluctance axis Q by avoiding magnetic flux to "jump" between flux carrier stripes on lamination of type A and B. Such "jumps" of magnetic flux would be possible, where flux carrier stripes overlap (6) and the thickness of the spacer layer (35) determines the permanence.

Also shown on Fig. 8 are elements that can be inserted in the stack of laminations, such as: a shaft (55) inserted in the central hole (5), rigid mechanical fixtures (92) inserted in holes in a flux carrier strip on lamination of type A and B (36A), (36B), and bars (37) inserted in flux barrier stripes (3), where flux barrier stripes from laminations of type A and B overlap (7). Rigid mechanical fixtures (92) and bars (37) might provide sufficient mechanical retention by immobilizing all flux carrier stripes (2) in the entire rotor to the shaft. Some rigid mechanical fixtures (92) might provide additional functions: for example, they can pass magnetic flux to avoid that holes (36A), (36B) would form an obstacle for the magnetic flux. For that purpose, those rigid mechanical structures might be made from a magnetic material, like silicon steel.

Bars (7) might also be used for purposes other than mechanical retention: for example, they can be permanent magnets forcing some magnetic fields in the rotor structure even without electric currents in stator windings. For that purpose, those bars (7) might be made from a hard magnetic material of high coercivity. Alternatively, bars (7) might be made from a material of high electric conductivity, like aluminum or copper. LIST OF REFERENCE NUMERALS

1 Lamination

1A Lamination of type A

1 B Lamination of type B

2 Flux carrier stipe

21 A particular flux carrier stripe on lamination type A

22 A particular flux carrier stripe on lamination type A

23 A particular flux carrier stripe on lamination type B

3 Flux barrier stripe

31 A particular flux barrier stripe on lamination type A

35 Spacer layer

36A Hole in a flux carrier strip on lamination of type A 36B Hole in a flux carrier strip on lamination of type B 37 Bar

4 Rib

5 Opening for a shaft

55 Shaft

6 Flux carrier overlap

7 Flux barrier overlap

8 Central structure

92 Rigid mechanical fixture between flux carrier stripes

93 Rigid mechanical fixture between flux barrier stripes D Low reluctance axis

Q High reluctance axis