EP1599930A2

EP1599930A2 - Rotary electric machine comprising a stator and two rotors

Info

Publication number: EP1599930A2
Application number: EP04717671A
Authority: EP
Inventors: Atef Abou Akar; Eric Coupart; Jacques Saint-Michel
Original assignee: Moteurs Leroy Somer SAS
Current assignee: Moteurs Leroy Somer SAS
Priority date: 2003-03-06
Filing date: 2004-03-05
Publication date: 2005-11-30
Also published as: US7250702B2; CN100559685C; WO2004082100A3; US20060175923A1; FR2852162B1; CN1757151A; WO2004082100A2; FR2852162A1; JP2006520178A

Abstract

The invention relates to an electric machine comprising a stator (10, 40) provided with a plurality of teeth (11, 41), each tooth supporting at lest one individual coil (13, 46, 47), an external rotor (30) which is radially arranged outside the stator and provided with constant magnets, an internal rotor (20) radially arranged inside the stator, provided with constant magnets and connected to the external rotor (30). At least one of the external (30) and internal (20) rotors is disposed in a flux concentration.

Description

The present invention relates to electrical machines and more particularly those comprising a stator, an outer rotor and an inner rotor integral with the outer rotor. A machine with two concentric rotors is described in international application WO 91/06147. The stator has teeth provided at their ends with pole shoes. The coils have heads on which a heat transfer fluid such as oil is sprayed in order to dissipate the heat from the coils. Such a machine is relatively complex to manufacture. The electric motor described in application WO 91/06147 also has a relatively large size in the axial direction, due in particular to the presence of the coil heads and the means for cooling them.

There is a need to benefit from a simplified construction machine and reliable operation without requiring cooling by spraying a heat transfer liquid on the coils.

There is also a need to have a machine with a relatively small footprint capable of operating with a high torque and / or a high speed.

The subject of the invention is, according to one of its aspects, an electric machine comprising: a stator comprising a plurality of teeth each supporting at least one individual coil, an external rotor disposed radially outside the stator and comprising magnets permanent, and - an inner rotor disposed radially inside the stator, comprising permanent magnets, and integral with the outer rotor.

Thanks to the use of individual coils associated with the stator teeth, rather than distributed coils, the construction of the machine is simplified and its reliability is increased. The presence of the exterior and interior rotors practically doubles the torque in the same volume, compared to a single rotor motor. Likewise, the stator is devoid of a fixed yoke which only serves electrically to re-engage the magnetic flux and which is a source of significant iron losses. Its elimination therefore entails the elimination of these losses and the considerable improvement in efficiency, in particular at high speed. Preferably, at least one of the outer rotor and the inner rotor is in flux concentration, and preferably the two rotors are in flux concentration, that is to say that two consecutive magnets of a rotor have faces of the same polarity arranged opposite a common adjacent pole piece, disposed between said magnets. This can reduce the amount of magnets used without degrading the performance of the machine. This can also allow the machine to operate at a high speed of rotation, the magnets of the inner rotor being able to be retained by the pole pieces, if necessary.

The two rotors have the same number of poles and the two rotors may or may not be offset angularly. In the embodiments where the rotors are angularly offset, when the number of phases m is even, the two rotors are advantageously offset by an angle substantially equal to π / S, for example to within 10%, where S = mp, S being the number of stator teeth, p being the number of pairs of poles of a rotor, and when m is odd, the two rotors are advantageously offset by an angle substantially equal to π / 2S, for example to within 10%.

The outer rotor may include pole pieces each having at least one recess on a radially outer side. This can make it possible to lighten the rotor without unduly reducing the efficiency of the machine, the magnetic flux lines being especially concentrated on the radially inner side of the pole pieces of the outer rotor. The pole pieces of the outer rotor can for example pass through a minimum of mid-length section in the circumferential direction.

The magnets of at least one of the inner rotor and the outer rotor may have a wedge shape when viewed along the axis of rotation of the machine, of width increasing in distance from the stator. Such a shape of the magnets can allow the pole pieces to hold at a high speed of rotation of the rotor, without it being necessary to glue the magnets for example. In a particular embodiment, the inner rotor comprises pole pieces linked to a machine shaft by complementarity of shapes. For example, the pole pieces of the inner rotor may have grooves and may be engaged by these grooves on ribs of the shaft. Such an arrangement can facilitate the construction of the rotor and in particular make it possible to avoid having to produce the pole pieces with openings making it possible to engage bars independent of the shaft of the machine, for example.

Still in a particular embodiment, at least one of the rotors may include pole pieces disposed between the permanent magnets and each having, on their side facing the stator, a convex convex face towards the stator. Such a shape of the pole pieces can make it possible to minimize the difference Ld - Lq, therefore not to use the reluctance to generate the driving force, and to reduce the torque ripples.

In a particular embodiment, the stator comprising na _ents teeth, each rotor having n _pa ires pole pairs and the current being n _P h _ases phases, the number of ndents stator teeth may be selected so as to have the na relationship .nts ⁼ n _pa _ires * n _{prιa ses-} The respect of this relation can make it possible not to subject the stator to stresses tending to ovalize it.

In another particular embodiment, the stator can have 6n teeth and each of the rotors 6n ± 2 poles, n being greater than or equal to 2. This can make it possible to have a high winding factor, reflecting the efficiency of use of the windings. , and thus a higher efficiency and / or a smaller footprint of the machine.

In a particular embodiment, the stator teeth may each have a first free end situated opposite one of the rotors. The teeth can be fixed by a second end, opposite the first, on a non-magnetic support. The support may for example be made of non-magnetic steel or aluminum or also of an insulating material.

Such a configuration is particularly suitable when each tooth of the stator serves as a core for a winding by supporting a single individual coil. We talk about concentrated winding or in English "concentrated winding".

Alternatively, the stator teeth may each have two opposite free ends facing the inner and outer rotors, respectively. The teeth can be held for example substantially at mid-length by a non-magnetic support. This support can be generally tabular. Such an arrangement is particularly suitable when each of the stator teeth has two individual coils, which may not be electrically connected to each other, so as to have a stator comprising two independent electrical circuits, if necessary.

The stator may alternatively include a cylinder head made in one piece with the teeth. The cylinder head can be made of a magnetic material.

Preferably, the stator teeth are devoid of pole shoes, which allows the individual coils to be fixed by engaging them on the teeth, the coils being produced separately.

As a variant, the teeth of the stator may include pole shoes.

The stator teeth may have notches near their free end facing one of the rotors. The coils can be held on the teeth by non-magnetic wedges engaged in these notches.

The outer rotor can be surrounded by a casing, for example of non-magnetic steel or aluminum, which can be fixed on the shaft of the machine, which is for example of aluminum. For machines with a relatively large axial dimension, it may be desirable to split the structure in order to reduce the cantilever length of the stator and the rotors.

The stator can thus have a double structure, as can the inner rotor or the outer rotor. The machine can constitute a synchronous motor or a generator, or even both successively, and be used for example in an electric vehicle to drive the wheels and recover energy during braking.

The invention will be better understood on reading the detailed description which follows, of examples of non-limiting implementations thereof, and on examining the appended drawing, in which:

FIG. 1 is a schematic view in cross section of an example of a machine according to the invention, FIG. 2 is a partial and schematic view in axial section of the machine of FIG. 1,

- Figures 3 to 6 are partial views similar to Figure 1, of alternative embodiments of the invention, - Figure 7 is a schematic and partial cross-sectional view of an alternative embodiment of the stator, Figure 8 in isolation represents a support piece for the teeth of the stator of FIG. 7, FIG. 9 is a view similar to FIG. 7 of an alternative embodiment of the stator, FIG. 10 is an electrical diagram illustrating the possibility of having the stator two independent electrical circuits in order to easily constitute a neutral point, FIGS. 11 and 12 represent two examples of variant implementation of the invention, and - FIGS. 13 and 14 are views similar to FIG. 7 of alternative embodiments of the stator.

The electric machine 1 shown in Figures 1 and 2 comprises a stator 10, an inner rotor 20 and an outer rotor 30 integral with each other by means of a mechanical connection 2 between them. The stator 10 comprises a plurality of teeth 11 formed by a stack of magnetic sheets electrically insulated from each other, these teeth being fixed to a support piece 12 made of a non-magnetic material, for example a non-magnetic steel or aluminum, or in an insulating material.

The support piece 12 is fixed, in the example described, to a frame 3 of the machine, as shown diagrammatically in FIG. 2.

In the example considered, the teeth 11 are fixed by their radially innermost end to the support piece 12, which has a generally tabular shape. The teeth 11 can be fixed by any means to the support piece 12, being for example welded thereto. Each tooth 11 carries an individual coil 13 which comprises one or more electrical conductors wound around the axis of the corresponding tooth. The coils 13 are connected to non-visible electrical conductors. A conventional device makes it possible, in the case where the machine is used as a motor, to generate a rotating magnetic field, and, in the case where the machine is used as a generator, to collect the induced current. The coils 13 can for example be connected to partially stripped cables, as described in patent application EP-A-1 251 623.

The teeth 11 are devoid, as can be seen, of pole shoes at their radially outer end, in order to allow the positioning of the coils 13 previously produced. The teeth 11 may have parallel or non-parallel lateral faces, in particular diverging faces away from the external rotor 30, in order for example to allow a certain jamming of the coils 13 on the teeth, as described in patent application EP-A-1 251 623 cited above.

The teeth may each have, in the vicinity of their free end, two small notches 14 intended to allow the fixing on the teeth of shims 15 for holding the coils. These shims 15 can be made of insulating material, for example plastic.

The inner rotor 20 includes a non-magnetic shaft 21, for example made of aluminum or an alloy of this metal, non-magnetic steel, or a composite material. The shaft 21 has ribs 22 used for the attachment of pole pieces

23 each consisting of a pack of identical superimposed magnetic sheets. The use of superimposed magnetic sheets makes it possible to reduce losses by induced currents. Each rib 22 has in cross section a general shape of T. The pole pieces 23 are not magnetically connected to each other, given the use of a non-magnetic material to make the tree.

In the example considered, the pole pieces 23 have a convex and convex face 24 in the direction of the stator 10.

Permanent magnets 25 are arranged radially between the pole pieces 23. Each magnet 25 has, when observed along the axis of rotation X of the machine, a slightly wedge-shaped shape, of width decreasing in the direction of the stator 10.

Each magnet 25 has transverse magnetization and can be in one piece or consist of several elementary magnets placed end to end. The magnetic poles of the same polarity of two adjacent magnets 25 are directed towards the pole piece 23 situated between these two magnets, as illustrated in FIG. 1. In the example shown, the magnets 25 extend over practically the entire radial dimension of the sides of the pole pieces 23 and in contact with them. The housings formed between the pole pieces 23, and in which the magnets 25 are placed, tend to widen under the effect of centrifugal force when the inner rotor 20 rotates at a speed greater than a predetermined speed, taking into account the elasticity of the materials used, this enlargement tending to decrease when the speed of rotation decreases. In general, the inner rotor 20 can be similar to the rotor described in patent application EP-A-1 249 919.

The outer rotor 30 comprises permanent magnets 31 placed between pole pieces 32, surrounded by a non-magnetic envelope 33, for example as described in patent application EP-A-1 251 023. The magnets 31 have in the example described a wedge shape when observed along the axis of rotation X of the machine, of width increasing away from the stator.

In the example considered, the poles of the two rotors are not angularly offset. Two consecutive magnets 25, 31 of the exterior 30 and interior 20 rotors have faces of the same polarity arranged opposite a common adjacent pole piece 23, 32, disposed between said magnets. Two pole pieces 23, 32 of each of the inner 20 and outer 30 rotors located on the same radius are of opposite N, S polarity.

In the example of FIGS. 1 and 2, the stator 10 has twelve teeth 11 and twelve coils 13, and each of the rotors has eight poles, but the numbers of teeth or of poles can be different without leaving the framework of the present invention.

Still in the example of these figures, the pole pieces 32 of the outer rotor 30 have radially inner 32a and outer 32b cylindrical faces. It is not beyond the scope of the present invention if the pole pieces have a different shape. The pole pieces of the outer rotor 30 may for example have a radially inner curved face, convex in the direction of the stator, as shown in FIG. 3. The outer rotor 30 may comprise pole pieces each comprising at least one recess on their radially outer side.

By way of example, FIG. 3 shows an external rotor comprising recesses 34 between each of the pole pieces 32 and the non-magnetic envelope 33. In this example, the pole pieces 32 of the outside rotor 30 each pass through a minimum. mid-length in the circumferential direction.

Of course, the outer rotor 30 could also not have recesses 34 and the pole pieces 32 of the convex convex faces 32a in the direction of the stator, without departing from the scope of the present invention. In the examples of Figures 1 to 3, the permanent magnets 25 and 31 of the inner 20 and outer 30 rotors are generally trapezoidal. It is not beyond the scope of the present invention when the shape of the magnets is different.

By way of example, there is partially shown in FIG. 4 a machine comprising permanent magnets, of generally parallelepiped shape. It is not beyond the scope of the present invention when the magnets of only one of the two rotors are trapezoidal and the magnets of the other rotor are parallelepiped. The pole pieces 23 of the inner rotor 20 can then include recesses 26 allowing the magnets to be retained between two successive pole pieces.

The inner rotor 20 which has just been described with reference to Figures 1 to 3 comprises pole pieces 23 fixed by complementary shapes on ribs 22 of the shaft 21. It is not beyond the scope of the present invention when the pieces poles 23 are fixed in another way to the shaft 21.

The pole pieces 23 shown in FIG. 4 are fixed by bars 27 passing through the pole pieces and connected at each of their ends to holding flanges, not shown. The shaft 21 is in this example of generally cylindrical shape.

In the examples which have just been described, the poles of the inner and outer rotors are not angularly offset.

It is not beyond the scope of the present invention when the poles of the two rotors are angularly offset, as shown by way of example in FIG. 5. In this figure, the poles are offset by an angle α which may have been deliberately exaggerated for the sake of clarity of the drawing. When the number of phases m is even, the two rotors can be offset by an angle α substantially equal to π / S, where S = mp, S being the number of teeth of the stator, P being the number of pairs of poles d 'a rotor, and when m is odd, the two rotors can be offset by an angle α substantially equal to π / 2S. Such an offset makes it possible to reduce, or even eliminate, the torque pulsations.

In the examples which have just been described, the number of teeth n _teeth of the stator is equal to 12, the number of poles of each of the rotors is equal to 8, the number of pairs of poles n _pa i _res being equal to 4 , the number of phases being equal to 3, thus verifying the relation n _den ts = n _pha ses * n _P ai _re s. It is not beyond the scope of the present invention when the number of stator teeth or the number of poles of each of the rotors is different.

By way of example, FIG. 6 shows a machine comprising twelve teeth and ten poles at each of the rotors. The stator thus has 6n teeth and each of the rotors 6n ± 2 poles, n being equal to 2 in this example, but it is not beyond the scope of the present invention when n is greater than 2.

In the examples which have just been described, each of the stator teeth carries a single individual coil, but it is not beyond the scope of the present invention when each of the stator teeth carries more than one, and in particular two, individual coils . By way of example, there is shown in FIG. 7, schematically and partially, a stator 40 comprising teeth 41 held substantially at mid-length of their radial edges 42 by a support 43 non-magnetic or made of insulating material or even the combination of both, of closed ring shape on one or both sides. As a variant, the support 43 can be magnetic. The teeth 41 have free ends 44 and 45 respectively facing the inner rotor 20 and the outer rotor 30, each devoid of pole shoes.

Coils 46 and 47 are respectively placed on either side of the support 43 on each tooth 41 to create a magnetic field rotating respectively in the interior and exterior rotors or to recover the current induced by the interior and exterior rotors. In the example of FIG. 7, the edges 42 of each tooth 41 are parallel but the teeth 41 could, if necessary, have edges 42 which are not parallel, the teeth 41 widening for example in the direction of the support 43 so that the coils 46 and 47 can be engaged on the teeth 41 with a certain clamping effect. The teeth 41 could also have at each of their free ends 44, 45 two small notches intended to allow the fixing on the teeth of shims for holding the coils on the teeth, in a similar manner to what has been described with reference to FIGS. 1 and 2.

In what has just been described, the teeth are devoid of pole shoes, but it is not going beyond the ambit of the invention if the teeth comprise pole shoes 70 allowing, for example, the fixing of support wedges 71 coils, as shown schematically in Figure 13.

The support 43 is shown diagrammatically in FIG. 8. Of generally annular shape, it has openings 48 intended to receive the teeth 41. These can be fixed by any means to the support 43, for example by force, by welding or again by gluing.

It is not beyond the scope of the present invention when the stator is produced differently.

The stator can for example comprise coils 46, 47 placed on a yoke 73 produced integrally with the teeth 41, for example in a magnetic material, as illustrated diagrammatically in FIG. 14. The stator of Figure 14 can be achieved by molding for example, or by stacking sheets. The stator can still be produced differently.

For example, there is shown in Figure 9 a stator having teeth 41 having in the middle of their edges 42 notches 50 adapted to receive ends 52 of elements 53 connecting the teeth together.

Each of the elements 53 has a generally curved shape, being provided at its ends with reliefs intended to cooperate with the notches 50 to securely hold two successive teeth 41. The elements 53 can be non-magnetic or, alternatively, magnetic. The coils carried by the same tooth can be electrically connected to each other, but it is not beyond the scope of the present invention when the two coils of the same tooth are not electrically connected to each other.

In this case, as shown in FIG. 10, the internal and external coils of the stator can form two independent three-phase electric circuits 61 and

62 connected, at the output of the machine 1, to respective rectifier circuits 63, 64 then to raising or lowering choppers 65, 66, with the constitution of a neutral point

67.

The two electrical circuits 61 and 62 may or may not have a common neutral point 69 shown in dotted lines, which may or may not be connected to the neutral point 67 of the two step-up or step-down choppers 65 and 66.

FIGS. 11 and 12 show other possible configurations. In particular, as illustrated in FIG. 11, the internal rotor 20 can be connected to the external rotor 30 by a mechanical connection 2 'which extends radially between two parts 10a and 10b of the stator 10, the latter having a double structure.

Each part 10a or 10b has teeth each carrying one or two individual coils like what has been described above and the inner and outer rotors each have a double structure also, with respective first parts 20a and 30a intended to cooperate with the part 10a of the stator and of the respective second parts 20b and 30b intended to cooperate with the part 10b of the stator.

In the alternative embodiment of FIG. 12, the stator 10 also has a double structure with two parts 10a and 10b, as do the inner and outer rotors. The parts 10a and 10b of the stator are connected to the frame 3 by means of a mechanical connection 70 connecting to the opposite ends of the parts 10a and 10b of the stator. The part 20a of the inner rotor is connected, by a mechanical connection 2 "similar to that shown in FIG. 2, to the part 30a of the outer rotor and it is the same for the other part 20b of the inner rotor, which is connected by a mechanical connection 2 "to the other part 30b of the outer rotor 30.

In the examples of FIGS. 11 and 12, the stator and the interior and exterior rotors are generally symmetrical with respect to a median plane M perpendicular to the axis of rotation X, but this is not compulsory and it is possible without going out of the framework of the present invention to realize double structures with asymmetrical parts. Of course, the invention is not limited to the examples which have just been described. One can in particular combine together the characteristics of the various embodiments described.

Throughout the description, including the claims, the expression “comprising a” should be understood as being synonymous with “comprising at least one”, unless otherwise specified.

Claims

1. Electric machine comprising:

- a stator (10; 40) comprising a plurality of teeth (11; 41) each supporting at least one individual coil (13; 46; 47),

- an outer rotor (30) disposed radially outside the stator and comprising permanent magnets,

- an inner rotor (20) disposed radially inside the stator, comprising permanent magnets, and integral with the outer rotor (30), at least one of the outer rotor (30) and the inner rotor (20) being flux concentration.

2. Machine according to the preceding claim, characterized in that the teeth (11; 41) of the stator (10; 40) are devoid of pole shoes.

3. Machine according to any one of the preceding claims, characterized in that two magnets (25; 31) consecutive of at least one of the outer rotor (30) and the inner rotor (20) have faces of the same polarity arranged opposite a common pole piece (23; 32), disposed between said magnets.

4. Machine according to any one of the preceding claims, characterized in that the two rotors (20; 30) have the same number of poles

(25; 31).

5. Machine according to the preceding claim, characterized in that the poles (25; 31) of the two rotors (20; 30) are not angularly offset.

6. Machine according to claim 4, characterized in that the poles (25; 31) of the two rotors (20; 30) are angularly offset.

7. Machine according to the preceding claim, characterized in that when the number of phases m is even, the two rotors (20; 30) are offset by an angle substantially equal to π / S where S = mp, S being the number of teeth (11; 41) of the stator (10; 40), p being the number of pairs of poles of a rotor, and when m is odd, the two rotors (20; 30) are offset by an angle α substantially equal to π / 2S.

8. Machine according to any one of the preceding claims, characterized in that the external rotor (30) comprises pole pieces (32) each comprising at least one recess (34) on a radially external side.

9. Machine according to the preceding claim, characterized in that the pole pieces (32) of the outer rotor (30) each pass through a minimum of mid-length section in the circumferential direction.

10. Machine according to any one of the preceding claims, characterized in that the magnets (25; 31) of at least one of the inner rotor (20) and the outer rotor (30) have a wedge shape when observed along the axis of rotation of the machine, increasing in width away from the stator.

11. Machine according to any one of the preceding claims, characterized in that the inner rotor (20) comprises pole pieces (25) linked to a shaft (21) of the machine by complementarities of shapes.

12. Machine according to the preceding claim, characterized in that the pole pieces (25) of the inner rotor (20) have grooves and are engaged by these grooves on ribs (22) of the shaft (21).

13. Machine according to any one of the preceding claims, characterized in that at least one of the rotors (20; 30) comprises pole pieces (23; 32) disposed between the permanent magnets (25; 31) and having , on their side facing the stator, each one face (24) convexly convex towards the stator.

14. Machine according to any one of the preceding claims, the stator comprising n _ents teeth (11; 41), each of the rotors n _pa i _re s pairs of poles (25; 31) and the current being at n _pna _{s s} phases , characterized in that the number of teeth (11) ndents of the stator (10; 40) is chosen so as to have the relation ndents ⁼ npaires * phases-

15. Machine according to any one of claims 1 to 13, characterized in that the stator (10) has 6n teeth (11; 41) and each of the rotors (20; 30) 6n ± 2 poles (25; 31) , n being greater than or equal to 2.

16. Machine according to any one of the preceding claims, characterized in that the teeth (11) of the stator (10) each have a first free end situated opposite one of the rotors (20; 30).

17. Machine according to the preceding claim, characterized in that the teeth (11) are fixed by a second end, opposite the first, on a non-magnetic support (12).

18. Machine according to the preceding claim, characterized in that each tooth (11) of the stator (10) supports a single individual coil (13).

19. Machine according to any one of claims 1 to 15, characterized in that the teeth (41) of the stator (40) each have two opposite free ends (44; 45) facing the inner and outer rotors respectively.

20. Machine according to the preceding claim, characterized in that the teeth (41) are held substantially at mid-length by a non-magnetic support (43;

53).

21. Machine according to one of the two preceding claims, characterized in that each of the teeth (41) of the stator (40) comprises two individual coils (46; 47).

22. Machine according to the preceding claim, characterized in that the two coils (46; 47) carried by the same tooth (41) are not electrically connected to each other.

23. Machine according to any one of claims 1 to 15, characterized in that the stator comprises a cylinder head (73) formed integrally with the teeth (41).

24. Machine according to the preceding claim, characterized in that the yoke (73) is made of a magnetic material.

25. Machine according to any one of the preceding claims, characterized in that the teeth (11; 41) have notches (14) near their free end facing one of the rotors (20, 30).

26. Machine according to claim 1, characterized in that the stator teeth have pole shoes (70).

27. Machine according to any one of the preceding claims, characterized in that it has a double structure (10a, 10b; 20a, 20b; 30a, 30b).

28. Machine according to any one of the preceding claims, characterized in that it constitutes a synchronous motor.

29. Machine according to any one of the preceding claims, characterized in that it constitutes a generator.

30. Electric machine comprising: a stator (10; 40) comprising a plurality of teeth (11; 41) devoid of pole shoes and each supporting at least one individual coil (13; 46; 47), an external rotor (30) arranged radially outside the stator and comprising permanent magnets, an inner rotor (20) disposed radially inside the stator, comprising permanent magnets, and integral with the outer rotor (30).