Reversible mounting of a permanent magnet in an electrical machine

Abstract

Title of the invention: Reversible mounting of a permanent magnet in an electrical machine. The invention relates to an electrical machine with a permanent magnet rotor, the rotor (14) being able to rotate about an axis of rotation (16) relative to a stator of the electrical machine, the rotor (14) comprising a magnetic circuit (22) and at least one permanent magnet (20), the magnetic circuit (22) being configured to guide the magnetic flux generated by the permanent magnet (20), the permanent magnet (20) extending along the axis of rotation (16) and having a general radial cross-sectional shape adapted to generate the magnetic flux, the magnetic circuit (22) comprising a cavity (26) configured to contain the permanent magnet (20), the cavity (26) being in contact with the permanent magnet (20), wherein the permanent magnet (20) comprises at least one bore (32) extending parallel to the axis of rotation (16), in which the rotor (14) comprises as many stems (34) as bores (32),Each rod (34) is fitted into the corresponding bore (32) and fixed to the magnetic circuit (22). Figure for the abbreviation: Fig. 2,

Description

Title of the invention: Reversible mounting of a permanent magnet in an electrical machine

[0001] The invention relates to electrical machines used in very varied fields such as transport, industry, electrical generation, etc. More and more permanent magnet electrical machines are being implemented. These machines make it possible in particular to avoid the use of wound rotors requiring an electrical connection.

[0002] Permanent magnets are made of so-called hard ferromagnetic materials, i.e. those with a wide hysteresis cycle. In the middle of the 20th century, iron-nickel-aluminium alloys to which cobalt can be added contributed to the development of permanent magnets. More recently, the use of certain rare earths, particularly from the lanthanide family such as samarium, cerium and neodymium, has made it possible to significantly increase the demagnetization coercive fields of magnets. Today, neodymium-iron-boron (NdFeB) alloys are widely used.

[0003] In order to limit the use of natural resources, we seek to recycle as much complex equipment as possible at the end of its life. To do this, it is necessary to separate the different components of the equipment in order to treat these components separately, each through its own recycling channel.

[0004] The recycling of computer hard drives containing NdFeB magnets has been extensively studied. A hydrogen decrepitation technique leading to the fragmentation of the hard drives makes it possible to separate and recover the magnets in powder form.

[0005] Electric traction motors have recently made considerable progress, particularly in the automotive industry. The increase in the rotational speed of electrical machines used, particularly as motors in automobiles, poses problems of mechanical retention of the magnets in the rotors equipped with them. To ensure this mechanical retention, the surface mounting of the magnets is often replaced by a buried mounting inside stacks of sheets forming a magnetic circuit ensuring the guidance of the magnetic flux generated by the magnets. For the recycling of these new electric traction machines, the approach implemented for computer hard disks is not applicable due to the much greater mass of the order of several kg of NdFeB type magnets and due to the fixing of the magnets in the stacks of sheets by an adhesive attachment (using resins) and by a mechanical attachment (pins, punches).For these motors, the removal of the magnets. requires compensating for the adhesion and mechanical retention of the magnets inserted into the sheet metal packs. The magnets must therefore be extracted by mechanical means combined with heat treatments to reduce the adhesion of the resins. Heat treatments are restrictive because they are carried out on entire motors with the aim of degrading the glues used to fix the magnets and demagnetizing the magnets to reduce the magnetic forces that block the magnets or tend to agglomerate them. In certain electrical machines where the magnets are embedded, during manufacturing, within the internal sheets of the rotors, to extract the magnets, it is necessary to implement significant mechanical means such as ejectors driven by a hydraulic press. These mechanical means require significant investments that are difficult to support by recycling channels.Furthermore, this type of investment can only be profitable with standardization in the topology of electrical machines and the establishment of an upstream sector to increase volumes.

[0006] Furthermore, the mechanical forces implemented can impact the quality of the recovered magnets given the fragility of their materials.

[0007] . Finally, the presence of residual bonding resin on the surface of the magnets after ex traction, reduces the value of magnets because it constitutes a source of pollution during the magnet recycling stages. A magnet surfacing stage is therefore necessary at the end of extraction, but this operation is complicated if the magnets are damaged or fragmented. For all these technical reasons and the absence of binding regulations, the recycling of end-of-life magnets, particularly those from buried magnet motors, is not developed on a large scale despite the potential in terms of recovery of critical materials.

[0008] For this purpose, the subject of the invention is an electric machine with a permanent magnet rotor, the rotor being able to rotate around an axis of rotation relative to a stator of the electric machine, the rotor comprising a magnetic circuit and at least one permanent magnet, the magnetic circuit being configured to guide the magnetic flux generated by the permanent magnet, the permanent magnet extending along the axis of rotation and having a general radial section shape adapted to generate the magnetic flux, the magnetic circuit comprising a cavity configured to contain the permanent magnet, the cavity being in contact with the permanent magnet, wherein the permanent magnet comprises at least one bore extending parallel to the axis of rotation, in which the rotor comprises as many rods as bores, each rod being fitted into the corresponding bore and being fixed to the magnetic circuit.

[0009] Advantageously, each rod is fixed to the magnetic circuit by means of a first plate fixed to the magnetic circuit, plate in which the rod(s) are fixed at one of their ends.

[0010] Advantageously, the rotor comprises a second plate guiding the rod(s) at a second of their ends, the second plate being fixed to the magnetic circuit.

[0011] Advantageously, the rod(s) are fixed to the second plate.

[0012] Advantageously, the rotor comprises: - several stages of permanent magnets, - several stages of magnetic circuits each receiving a stage of permanent magnets, and the magnetic circuit stages are stacked along the rotation axis.

[0013] Advantageously, the rotor further comprises an intermediate plate arranged between each pair of consecutive stages of magnetic circuits, the intermediate plate(s) comprising as many holes as there are rods, the holes being crossed by the rods.

[0014] Advantageously, the rotor comprises, integral with the first plate or the second plate, as many stiffeners as there are permanent magnets per stage, the stiffener(s) being arranged opposite each permanent magnet of each stage and extending parallel to the axis of rotation, the stiffener(s) each being fitted in a groove of each magnetic circuit, the groove extending parallel to the axis of rotation.

[0015] Advantageously, the stiffener(s) are fixed to the two plates.

[0016] Advantageously, each stiffener comprises a protrusion arranged between each pair of consecutive stages of permanent magnets, each protrusion comprising as many bores as there are rods passing through the permanent magnets associated with the stiffener in question, each bore being adjusted to the rod passing through it.

[0017] Advantageously, each rod is configured to conduct a heat transfer fluid intended to cool the rotor.

[0018] The invention will be better understood and other advantages will appear on reading the detailed description of an embodiment given by way of example, a description illustrated by the attached drawing in which:

[0019] [Fig.l] schematically represents in perspective an electric machine according to the invention;

[0020] [Fig.2] represents in partial section the rotor of the electric machine represented in [Fig.l];

[0021] [Fig.3] represents in perspective two plates and rods of the rotor illustrated in [Fig.2];

[0022] [Fig.4] shows in exploded view the rotor illustrated in [Fig.2];

[0023] [Fig.5] partially illustrates a rotor variant of the electric machine shown in [Fig.l];

[0024] [Fig.6] illustrates an example of a means of connecting stiffeners and rods of the rotor of the variant of [Fig.5];

[0025] [Fig.7] represents in exploded perspective, the rotor of the variant of [Fig.5];

[0026] [Fig.8] schematically represents a rotor which can equip a machine electric according to the invention and equipped with a cooling circuit.

[0027] For the sake of clarity, the same elements will bear the same references in the different figures.

[0028] [Fig.l] shows in perspective an electrical machine 10 comprising a stator 12 and a rotor 14 which can rotate relative to the stator about an axis of rotation 16. In the example shown, the rotor 14 is an internal rotor and the stator 12 is external. It is also possible to implement the invention in an electrical machine with an external rotor and an internal stator.

[0029] The stator 12 comprises a winding that can be supplied with multi-phase current, typically three-phase, and producing a rotating magnetic field at the supply frequency. The rotor 14 comprises one or more permanent magnets producing a rotating magnetic field with the magnetic field of the stator during rotation of the rotor 14 around its axis of rotation 16.

[0030] The electrical machine 10 can operate as a motor by transforming electrical energy into mechanical energy or as a generator by transforming mechanical energy into electrical energy.

[0031] [Fig.2] represents in partial section the rotor 14 of the electrical machine 10. The upper part of [Fig.2] represents the rotor 14 in a plane containing the axis of rotation 16 and the lower part of [Fig.2] represents the rotor 14 in a plane perpendicular to the axis of rotation 16.

[0032] The electrical machine 10 comprises a magnetic circuit 22 in which one or more permanent magnets 20 are arranged distributed radially around the axis 16. In the case of a plurality of permanent magnets 20 these are identical and three are shown in the upper part of [Fig. 2]. During operation of the electrical machine 10, the magnetic field generated by the different permanent magnets 20 clings to the rotating magnetic field generated at the stator 12. The magnetic circuit 22 channels the magnetic field generated by the permanent magnets 20.

[0033] The permanent magnets 20 may be arranged in notches of the magnetic circuit 22 and be flush with the outer surface of the rotor 14 opposite the stator. Alternatively, the permanent magnets 20 may be buried in the magnetic circuit 22. This arrangement makes it possible in particular to increase the rotation speed of the electrical machine 10 while avoiding the risk of the permanent magnets 20 becoming detached from the magnetic circuit 22. Between these two alternatives, it is also possible to provide 20 permanent magnets partly buried and partly flush.

[0034] The permanent magnets 20 shown in [Fig. 2] are not flush with the outer surface 24 of the rotor 14. They are identical and have a section of which a concave-shaped part opens in the direction of the stator 12, that is to say towards the top of [Fig. 2], this in order to create a concentration of magnetic flux and a higher induction in the air gap between the rotor 14 and the stator 12. The section of each permanent magnet 20 is constant over the major part of the length of the rotor 14 defined according to the axis of rotation 16.

[0035] For each permanent magnet 20, the magnetic circuit 22 comprises a cavity 26 configured to contain the permanent magnet 20 concerned. The cavity 26 is in contact with the permanent magnet 20. More precisely, the shape of the cavity 26 is complementary at least in part to the shape of the permanent magnet 20. As for the permanent magnet 20, the section of the cavity 26 perpendicular to the axis 16 is constant over the majority of the length of the magnetic circuit 22, a length defined according to the axis of rotation 16.

[0036] the magnetic circuit 22 may comprise one or more slots opening onto each cavity 26. In the example shown, for each cavity 26, the magnetic circuit 22 comprises two slots 28 and 30. In each of the slots 28 and 30, the outer surface of the permanent magnet 20 is at a distance from the magnetic circuit 22. The slots 28 form a barrier to the magnetic flux generated by the permanent magnet 20. In other words, the magnetic flux generated by the permanent magnet 20 tends to bypass the slots for the most part to concentrate in the magnetic circuit 22, the permeability of which is much greater than that of the vacuum or air contained in the slots 28 and 30.

[0037] The general shape of the permanent magnet 20 and that of the magnetic circuit 22 are defined in combination with the stator 12 to optimize the path of the magnetic fluxes in the electrical machine 10. The shape of the section of the permanent magnets 20 and the possible presence of the lights 28 and 30 are in particular adapted to this optimization.

[0038] The shape shown in [Fig.2] makes it possible to prevent the permanent magnets 20 from moving in their respective cavity around the axis 16. This immobilization of the permanent magnets 20, however, has limits. Indeed, during operation of the electrical machine, the rotation of the rotor 14 generates inertial forces which can be significant and which can therefore cause certain small movements of the permanent magnets 20 relative to their respective cavity. This is all the more troublesome as the concavity of the shape of the permanent magnet is small.

[0039] The invention makes it possible to improve the mechanical retention of the permanent magnets 20 in the magnetic circuit 22 regardless of the shape of the permanent magnets 20. The mechanical maintenance of the invention makes it possible to separate the permanent magnets 20 from the magnetic circuit 22, in particular in the event of repair and at the end of life of the electrical machine 10 in order to facilitate the recycling of the various components of the electrical machine 10.

[0040] For this purpose, each permanent magnet 20 comprises at least one bore 32 extending parallel to the axis of rotation 16. The bore 32 passes right through the permanent magnet 20. In the example shown, each permanent magnet 20 comprises two bores 32. A larger number of bores 32 is of course possible.

[0041] Cooperating with each bore 32, the rotor 14 comprises a rod 34 fitted into each bore 32. In other words, the rotor 14 comprises as many rods 34 as there are bores 32. In practice, the permanent magnets 20 may comprise other bores in which rods would not be inserted. These other bores could make it possible to insert, when dismantling the motor, rods which would supplement those already in place to facilitate the extraction of the magnets. These additional rods can then have a role of mechanical reinforcement or even allow the heating of the magnets in order to allow their demagnetization. These other bores may have other functions than the mechanical maintenance of the permanent magnet concerned, in particular a magnetic function. Other bores may also be provided in the event of standardization of the permanent magnets 20 for other types of electrical machines.For the purposes of the invention, only the bores 32 into which rods 34 are inserted are considered.

[0042] To ensure the immobilization of the permanent magnets 20 relative to the magnetic circuit 22, the rods 34 are fixed to the magnetic circuit 22. The fixing of the rods 34 can be done in different ways, for example by directly fixing a curved part of them to the magnetic circuit 22. Alternatively, as shown in [Fig. 2], the rotor 14 comprises a plate 36 fixed to the magnetic circuit 22 and to the rods 34 at one of their ends 38. The plate 36 extends mainly in a plane perpendicular to the axis of rotation 16. The plate 36 can be an integral part of the magnetic circuit 22. It is possible to make the plate 36 in a diamagnetic or paramagnetic material unlike the magnetic circuit 22 made of ferromagnetic material. The rods 34 and the plate 36 mainly have a function of mechanically holding the permanent magnets 20.As a first approach, it is preferable that the plates 36 are magnetically insulating to limit magnetic leaks at the axial ends of the rotor 14.

[0043] The fixing of the rods 34 to the magnetic circuit 22 is advantageously removable, in order to facilitate the detachment of the permanent magnets 20 from the magnetic circuit 22. The plate 36 can for example be fixed to the magnetic circuit 22 by removable elements such as screws or rivets which can be eliminated during the operation of detaching the permanent magnets 20. The fixing of the rods 34 on the plate 36 can also be removable. For example, the end 38 of each rod 36 can be threaded in order to be screwed into a tapping of the plate 36. Any other means of fixing the rods 34 on the plate 38 is possible, for example by riveting or welding.

[0044] [Fig. 3] shows in perspective the rods 36 fixed to the plate 34 as well as a second plate 40 making it possible to improve the stability of the mechanical holding of the permanent magnets 20 in the rotor 14. In order not to overload the figure, the magnetic circuit 22 and the permanent magnets 20 are not shown in [Fig. 3]. More precisely, the plate 40 guides the rods 34 at a second from their ends 42. The plate 40 is also fixed to the magnetic circuit 22 for example in the same way as the plate 36. The plate 40 may comprise holes 44 in each of which a rod 34 can slide. This sliding makes it possible, for the installation of the plate 40, to avoid a chain of dimensions that is too tight in the assembly of the rotor 14.

[0045] In addition to the sliding, the rods 34 can be fixed to the plate 40. The fixing can be adjustable, in particular as a function of dispersions in the length of the magnetic circuit 22, length defined along the axis 14. It is for example possible to provide a thread at the end 42 of each rod, this thread sliding in each smooth bore 44 of the plate 40, a nut screwed onto each thread locking the position of the plate 40 by tightening it against the magnetic circuit 22.

[0046] [Fig. 4] shows an exploded view of a rotor 50 of an electrical machine according to the invention. To facilitate and standardize the manufacture of the permanent magnets 20, it may be preferable for it to have a length, defined along the axis of rotation 16, shorter than that of the rotor 50. For this purpose, the rotor 50 comprises several permanent magnet stages 20 stacked. Three stages 52, 54 and 56 of permanent magnets 20 stacked along the axis of rotation 16 are shown in [Fig. 4]. Each stage 52 of permanent magnets 20 is inserted into a stage of magnetic circuits 22, respectively 58, 60 and 62 as previously described with the aid of [Fig. 2]. In practice, the invention can be implemented regardless of the number of stages.

[0047] Advantageously, the electrical machine 50 further comprises an intermediate plate arranged between each pair of consecutive stages of magnetic circuits. In the example shown, an intermediate plate 64 separates the stages 58 and 60 and an intermediate plate 66 separates the stages 60 and 62. The intermediate plates 64 and 66 are similar to the plate 40. The intermediate plates 64 and 66 comprise as many holes 68 as rods 34. The holes 68 are crossed by the rods 34. The intermediate plates make it possible to stiffen a substructure of the rotor constituted by the permanent magnets 20 and the rods 34 inserted in the bores 32 of the permanent magnets 20. The intermediate plates make it possible to reduce the diameter of the rods 34 and corresponding bores 32 for the same rigidity of the substructures. The reduction in diameter of the bores 32 makes it possible to increase the volume of material of the permanent magnets 20.

[0048] [Fig. 5] partially represents a variant of rotor 70 which can be implemented in an electrical machine according to the invention. On the left part of [Fig. 5], appear the three stages 52, 54 and 56 of permanent magnets 20, as well as the plate 40 represented in a plane containing the axis of rotation 16. The right part of [Fig. 5] represents the same components of rotor 70 in projection in a plane perpendicular to the axis 16. In order not to overload the figure, the three stages of magnetic circuits, 58, 60 and 62 as well as the rods 34 are not represented. Alternatively, the plate 40 can be replaced by the plate 36. In the example shown, each stage 52, 54 and 56 comprises six permanent magnets 20. As mentioned above, the invention can be implemented regardless of the number of permanent magnets 20 per stage. However, each stage 52, 54 and 56 comprises the same number of permanent magnets 20.

[0049] In order to improve the stiffness of the rod / magnet substructure of the rotor 70, the latter may comprise, integral with the plate 40, as many stiffeners 72 as there are permanent magnets 20 per stage, in this case six stiffeners 72. The stiffeners 72 are arranged opposite each permanent magnet 20 of each stage and extend parallel to the axis of rotation 16. The stiffeners 72 are each fitted into a groove 74 of each magnetic circuit. The groove 74 extends parallel to the axis of rotation 16.

[0050] Still to improve the stiffness of the rotor 70, the stiffeners 72 can be fixed to the plate 36, not shown in [Fig.5]. As for the rods 34 which can be fixed to the plate 40, the stiffeners 72 can be threaded at their end 74 passing through smooth holes in the plate 36 and nuts assembled on the threaded ends 74 can ensure the fixing of the entire rotor 70.

[0051] To further improve the stiffness of the rod / magnet substructure of the rotor 70, it is possible to connect the stiffeners 72 and the rods 34. [Fig. 6] illustrates an example of a means of connecting the stiffeners 72 and the rods 34. [Fig. 6] represents in perspective the plate 36 and the stiffeners 72 equipped with these means. More precisely, each stiffener 72 comprises a protrusion 76 arranged between each pair of consecutive stages of permanent magnets 20. Each protrusion 76 comprises as many bores 78 as rods 34 passing through the permanent magnets 20 associated with the stiffener 72 in question. Each bore 78 is adjusted to the rod 34 which passes through it. In this way the magnets are extracted from the rotor and remain in place in the structure stiffened by the stiffeners 72

[0052] [Fig.7] shows in exploded perspective, the rotor 70 with here the three stages 52, 54, 56 of permanent magnets 20, the three stages 58, 60, 62 of magnetic circuits each receiving one of the stages of permanent magnets 20, the rods 34 and the plate 36 to which the rods 34 are fixed as well as the stiffeners 72 and the plate 40 to which the stiffeners 72 are fixed.

[0053] [Fig. 8] schematically represents one of the rotors 14 or 70 equipped with a cooling circuit for evacuating heat that may be produced in the rotor during operation of the electrical machine. Each rod 34 is configured to conduct a heat transfer fluid intended to cool the rotor. For this purpose, the rods 34 may be hollow and thus form a channel in which a heat transfer fluid circulates. Outside the rods, the heat transfer fluid circulates in an exchanger 80 that may be a radiator for cooling the heat transfer fluid by convection in the ambient air. The circulation of the heat transfer fluid may be carried out by means of a circulation pump 82. It is possible to circulate the heat transfer fluid in a single-phase or two-phase loop, the rods then forming an evaporator and the exchanger a condenser.It is possible to do without the circulation pump 82 by providing natural conduction as achieved in a heat pipe.

Claims

Claims

1. An electric machine with a permanent magnet rotor, the rotor (14; 70) being rotatable about an axis of rotation (16) relative to a stator (12) of the electric machine (10), the rotor (14; 70) comprising a magnetic circuit (22) and at least one permanent magnet (20), the magnetic circuit (22) being configured to guide the magnetic flux generated by the permanent magnet (20), the permanent magnet (20) extending along the axis of rotation (16) and having a general radial cross-sectional shape suitable for generating the magnetic flux, the magnetic circuit (22) comprising a cavity (26) configured to contain the permanent magnet (20), the cavity (26) being in contact with the permanent magnet (20), in which the permanent magnet (20) comprises at least one bore (32) extending parallel to the axis of rotation (16), in which the rotor (14 ;70) comprises as many rods (34) as bores (32), each rod (34) being fitted into the corresponding bore (32) and being fixed to the magnetic circuit (22).;

2. Electrical machine according to claim 1 in which each rod (34) is fixed to the magnetic circuit (22) by means of a first plate (36) fixed to the magnetic circuit (22), plate (36) in which the rod(s) (34) are fixed at one of their ends (38).

3. An electrical machine according to claim 2, wherein the rotor (14; 70) comprises a second plate (40) guiding the rod(s) (34) at a second of their ends (42), the second plate (40) being fixed to the magnetic circuit (22).

4. An electrical machine according to claim 3, wherein the rod(s) (34) are fixed to the second plate (40).

5. Electrical machine according to one of claims 3 or 4, in which the rotor (14; 70) comprises: - several stages of permanent magnets (52, 54, 56), - several stages of magnetic circuits (58, 60, 62) each receiving a stage of permanent magnets (52, 54, 56), in which the stages of magnetic circuits (58, 60, 62) are stacked along the axis of rotation (16).

6. An electrical machine according to claim 5, wherein the rotor (14; 70) further comprises an intermediate plate (64, 66) disposed between each pair of consecutive stages of magnetic circuits (58, 60, 62), the intermediate plate(s) (64, 66) comprising as many holes (68) as rods (34), the holes (68) being crossed by the rods (34).

7. An electrical machine according to one of claims 5 or 6, wherein the rotor (70) comprises, integral with the first plate (36) or the second plate (40), as many stiffeners (72) as there are permanent magnets (20) per stage (52, 54, 56), the stiffener(s) (72) being arranged opposite each permanent magnet (70) of each stage (52, 54, 56) and extending parallel to the axis of rotation (16), the stiffener(s) (72) each being fitted into a groove (74) of each magnetic circuit (58, 60, 62), the groove (74) extending parallel to the axis of rotation (16).

8. An electrical machine according to claim 7, wherein the stiffener(s) (72) are attached to both plates (34, 40).

9. An electrical machine according to claim 7, wherein each stiffener (72) comprises a protrusion (76) arranged between each pair of consecutive stages (52, 54, 56) of permanent magnets (20), each protrusion (76) comprising as many bores (78) as rods (34) passing through the permanent magnets (20) associated with the stiffener (72) in question, each bore (78) being fitted to the rod (34) passing through it.

10. Electrical machine according to one of the preceding claims in which each rod (34) is configured to conduct a heat transfer fluid intended to cool the rotor (14; 70).

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