Axial flux rotor with magnets and a body made of composite material layers with fibers having different orientations

Abstract

The rotor (1) of an electromagnetic machine for axial flux has a body comprising an inner hub (2) concentric with a rotation axis (7). Branches (3) extend radially from the inner hub (2) relative to the rotation axis (7) towards a hoop (8) forming an outer circular edge of the rotor (1). In each space defined between two adjacent branches (3), a magnet structure (10) comprises a plurality of magnets (4). The body is constituted by several stacked composite material layers comprising fibers bonded by resin. For two adjacent and stacked layers, the fibers of each layer are oriented in different predetermined directions (F1, F2). In addition, a covering layer is located on each of the two opposite faces of the rotor body, consisting of several stacked composite material layers comprising fibers bonded by resin.

Description

Technical Field

[0001] The invention relates to a rotor for an electromagnetic motor or generator with axial flux, the rotor having a hub body and branches made of composite material layers with fibers having different orientations. The invention also relates to an electromagnetic motor or generator equipped with a rotor of this type. Background Art

[0002] The invention has advantageous but non-limiting application to electromagnetic motors that deliver high power at high speeds of rotation of the rotor, which is achieved by the specific characteristics of the rotor according to the invention. This type of motor can be used, for example, as an electromagnetic motor in a fully electric or hybrid motor vehicle.

[0003] Advantageously, but not limitingly, the electromagnetic motor or generator may comprise at least one rotor constituted by two stators, whereby these elements may be stacked on top of one another and separated by at least one air gap on a single shaft.

[0004] In high-speed applications, a rotating component (ie, rotor) with very high mechanical strength is required to improve the reliability of the system.

[0005] For electromagnetic machines with axial flux, the rotor comprises a body in the form of a disc-shaped support for the magnets, with two circular faces connected by a thickness, the disc being delimited between an outer edge formed by a band and an inner periphery delimiting a cavity for the rotating shaft.

[0006] The magnets are all held in the disc-shaped support by a holding device, with spaces being left between the magnets.

[0007] Electric motors with axial flux are often used as electric motors having a mass torque greater than that generated by electric motors with radial flux. They can therefore be used in low speed applications.

[0008] For high-speed applications, the design of the rotor in an electric motor with axial flux is more complicated, because the forces due to the centrifugal effect lead to relatively high mechanical stresses in the rotor. In addition, when the rotating parts are made of conductive materials, the losses caused by Foucault currents are dominant in both the magnets and the rotating parts.

[0009] For rotors that need to rotate at high speeds, the main disadvantage of electric motors at high speeds is the high probability that one or more magnets will detach from the rotor and at least part of the rotor will break apart. Therefore, the rotor of this type of electric motor must be able to withstand high speed rotation.

[0010] Prior art encourages those skilled in the art to strengthen the disk-shaped support of one or more magnets to resist centrifugal forces. This requires specific materials for the disk-shaped support and increasing its thickness to make the disk-shaped support more rigid.

[0011] This solution is not entirely satisfactory, since such an electric motor or generator equipped with a disk-shaped support is heavier and more expensive to manufacture.

[0012] One solution could be to create a grid structure of elongated single magnets in a fiber reinforced and resin structure to reduce Foucault currents, and use a body made of composite materials for a non-conductive rotor, ideally made of fiberglass, with straps placed on the periphery of the rotor to control the forces due to the centrifugal effect.

[0013] However, for applications where speeds become very high, mechanical stresses become such that it is necessary to reduce the mass of the magnets to achieve these rotational speeds. However, the torque that must be transmitted by the motor is proportional to the surface area of ​​the magnets that interact with the magnetic field generated by the stator. Therefore, a reduction in the magnetic surface area causes a reduction in the torque and, therefore, a reduction in the power of the machine. Summary of the invention

[0014] The problem to be solved by the present invention is to design a rotor for supporting a plurality of permanent magnets, the rotor being equipped with a strap for an electromagnetic machine with axial flux, which strap can, on the one hand, effectively retain the permanent magnets supported by the rotor, thereby preventing the magnets from detaching from the rotor, while effectively compensating for centrifugal forces, and, on the other hand, the strap has a mechanical strength such that the rotor can rotate at very high speeds.

[0015] To this end, the invention relates to a rotor for an electromagnetic motor or generator, comprising: a body comprising an inner hub concentric with the central axis of rotation of the rotor; branches extending radially relative to the central axis of rotation starting from the inner hub towards a band forming a circular outer contour of the rotor; at least one magnet housed in each space defined between two adjacent branches, characterized in that:

[0016] - the body is constituted by a plurality of stacked layers of composite material comprising fibres bonded by a resin, the fibres of each layer being oriented in different predetermined directions for two stacked layers,

[0017] - A radial covering skin is located on each of the two opposite faces of the rotor body, the radial covering skin consisting of a plurality of stacked composite material layers comprising fibers bonded by resin.

[0018] The composite material according to the invention does not contain iron.

[0019] The construction of the rotor according to the invention is based on the discovery that the greatest stresses applied to the rotor at very high speeds occur at the level of the hub around the intermediate rotation axis of the rotor. It is therefore necessary to solidify this inner part of the rotor.

[0020] Applicants have found that stacking of composite material layers, each with a unique predetermined orientation direction, wherein each layer has a different orientation direction, strengthens the body and rotor. This is different from a single layer of composite material with fibers running in two different directions, which would be more difficult to manufacture because fibers in two different directions in the same layer may be displaced during injection of a binder (e.g., resin).

[0021] For applications where the line speed becomes very high, typically starting at 160 m / s or 180 m / s, the mechanical stresses become such that it is necessary to reduce the magnetic mass to achieve these rotational speeds. This has the major disadvantage that the torque that must be supplied by the motor is proportional to the surface area of ​​the magnets that interact with the magnetic field generated by the stator. Therefore, a reduction in the surface area of ​​the magnets results in a reduction in the torque and, therefore, a reduction in the machine power.

[0022] According to the invention, the body makes the hub and the branches in one piece. This increases the mechanical strength of the assembly and therefore of the rotor.

[0023] A covering skin or disc is located on each circular face of the rotor. The bands can be made of fiberglass, carbon or carbon fiber. The composite bands surround the large magnet or magnet structure circumferentially on the outer periphery of the rotor. If necessary, the bands also contribute to the radial retention of the magnets in addition to the retention provided by the outer layer of the composite coating.

[0024] The fibres of the composite material layers of the body are advantageously oriented perpendicularly to the fibres of adjacent stacked composite material layers.

[0025] Advantageously, the fibres of the composite material layers of the body are oriented with an offset of 30° to 45° relative to the fibres of adjacent stacked composite material layers.

[0026] Advantageously, the number of composite material layers of the body is determined based on the axial thickness of the magnet or magnet structure and the covering skin, the covering skin having a thickness between 0.3 mm and 2 mm.

[0027] Each branch advantageously has a width that decreases with distance from the inner hub, terminating in a tapered tip immediately adjacent the strap.The tapered tips of the branches may optionally be attached to the strap.

[0028] The applicant has taken into account the fact that in the case of an axial flux machine, the torque is proportional to the cube of the rotor radius. It is therefore better to increase the surface area of ​​the magnets on the periphery of the rotor than on the more internal parts of the rotor. The absence of magnets near the axis of rotation can therefore be easily offset by adding magnets on the periphery of the rotor, which can be achieved by the construction of branches whose width decreases with the distance from the center of the rotor until they are just conical tips with a width approaching zero.

[0029] It is therefore desirable to increase the surface area of ​​the cross section of the branches of the rotor at the level of their connection to the hub and to taper this section to increase the surface area of ​​the magnets in order to maintain a significant motor torque.

[0030] This has never been envisaged by the prior art, which only uses branches of constant thickness and hubs with a small radius to leave space for the magnets. Therefore, there is a strong bias towards reducing the magnet distribution on the rotor to increase the mechanical strength of the rotor, and the prior art tends to other solutions, such as the increase of branches and hubs in the axial direction, which will increase the weight of the rotor without a major beneficial effect on its strength.

[0031] The bases of two adjacent branches are advantageously separated by a middle portion of the inner hub having a concave shape rounded in the axial direction of the rotor, the inner hub having a radius equal to or less than one quarter of the radius of the rotor.

[0032] The curvature towards the inside of the intermediate portion between the branches makes it possible to reduce the mechanical stresses at the level of the thickest section of the branches supported on the outer periphery of the hub.

[0033] Each magnet or magnet structure advantageously has a width that increases with distance from the inner hub, terminating in a band around the rotor.

[0034] The magnet structure advantageously comprises a plurality of single magnets, each of the plurality of single magnets having a polygonal shape, or each of the single magnets having an at least partially oval profile, the at least partially oval profile comprising a first portion forming the body of the single magnet, the first portion having a larger cross-section and extending over a width of the single magnet that is longer than at least one second longitudinal end portion of the associated first longitudinal end portion of the pointing magnet and decreasing as it approaches the first longitudinal end portion.

[0035] Each magnet structure is advantageously constituted by a plurality of single magnets connected together by fibre-reinforced insulating material, each single magnet having an elongated shape and extending in the axial direction of the rotor.

[0036] The above mainly applies to the use of covering skins. The large magnets used in rotors in the prior art dissipate a lot of heat. This heat dissipation makes it impossible to use axial retaining means in the form of covering skins or discs made of composite materials, and the heat dissipation may have an impact on the integrity of the coating, resulting in accelerated aging of the coating and the magnets.

[0037] Composite material covered discs are not often used in the prior art because they are not able to withstand the dissipation of the heat generated by the magnets.

[0038] Because the present invention preferably utilizes a large number of single magnets instead of the compact magnets of the prior art, there is less heat dissipation and the covering skins or disks can be used as axial retaining means, which advantageously replace the axial retaining means between the magnets and the rotor body, which in some cases requires modification of the magnets or their coatings to achieve additional fastening with the fastening means carried by the rotor.

[0039] A further synergy achieved by the invention is that the rotor can have a single magnet integrated into a magnet structure between each branch. Each three-dimensional magnet structure is composed of a plurality of single magnets.

[0040] This makes it possible to have a magnet structure with multiple single magnets. It has been determined that a structure with such multiple single magnets has a high level of insensitivity to space harmonics or currents generated by the stator windings. Therefore, the losses generated in the magnet structure are very low and the output (especially at high speeds) is very high. This type of magnet structure can form poles or can be a complete magnet.

[0041] One of the preferred measures of the present invention is to decompose the magnet structure, which may be a whole magnet or a magnetic pole as in the prior art, into a plurality of small or micro magnets. Large magnets are subject to losses caused by Foucault currents to a greater extent than their equivalents in small or micro magnets. Therefore, the use of small or micro magnets makes it possible to reduce these losses that impair the operation of the electromagnetic actuator.

[0042] It is known that in order to obtain a magnetic field of optimum strength, the ideal volume of a magnet should be close to the volume of a cube or cylinder whose length is equal to its diameter. It is also known that increasing the length of the magnet beyond this length will not achieve any increase in the magnetic field. However, the method adopted by the present invention in this preferred form goes against this generally accepted idea.

[0043] The length of the single magnet is significantly longer than the diameter or diagonal of its flat longitudinal surface, compared to what is recommended by prevailing current practice, essentially in response to the requirements for mechanical strength of the structure, which is the main object of the present invention.

[0044] Applicants have discovered that a plurality of single magnets in a magnet structure results in a magnet structure having much greater mechanical strength while maintaining magnetic properties nearly similar to those of a single magnet having a surface area equal to n times the base surface area of ​​n magnets when there are n single magnets.

[0045] The oval magnets may have facets. The single magnets thus obtained are "crystals" associated with each other, which are not connected over the entire surface of their facets or longitudinal faces, but resin and adhesive layers are used to construct a mesh network on the ends of the multi-faceted blocks with limited contact areas between the magnets.

[0046] Alternatively, for single magnets having a perfect oval shape with a rounded first portion, the contact between two adjacent single magnets is smaller and may be only a point contact and essentially corresponds to a small arc of a circle between the two single magnets. A recess may be hollowed out, the size of which is the arc of contact between the two adjacent single magnets, to receive an adhesive, advantageously in the form of a resin.

[0047] Advantageously, a plurality of single magnets of the magnet structure are connected together by a fiber-reinforced insulating material, each single magnet having an elongated shape and extending in a radial direction of the rotor.

[0048] Each magnet structure advantageously comprises at least one grid structure having cells, each cell defining a housing for a corresponding single magnet, each housing having internal dimensions just sufficient to allow the single magnet to be introduced into its interior while leaving a space between the housing and the single magnet to be filled with a fiber-reinforced resin, the grid structure being made of a fiber-reinforced insulating material.

[0049] The grid structure is held in place and may also be coated with a composite material layer. This type of grid structure makes it possible to hold a single magnet in place during manufacture of the magnet structure and has the advantage that it represents an additional stiffening element of the magnet structure, whereby the grid structure may also contain reinforcing fibers.

[0050] For example, it is known that a honeycomb grid structure can increase the strength of an element, in this case a magnet structure. The single magnets are inserted into a hexagonal housing that holds them in place. The walls of the housing act as electrical insulation, and the density of the housing in the magnet structure can be significantly increased. The honeycomb grid structure can be made of a fiber-reinforced insulating composite material.

[0051] Each magnet or magnet structure between two adjacent branches is advantageously embedded in at least one composite material layer, whereby the rotor is also coated in a composite material layer surrounding the embedded magnet structure in a body consisting of a plurality of composite material layers.

[0052] The composite material layers surrounding the rotor and constituting the hub and branches of the body are advantageously made of glass or carbon fibers cast in resin. These reinforcing fibers contribute to the strength of the magnet structure and in particular increase the bending stiffness and resistance to buckling.

[0053] The invention also relates to a method for producing a rotor of this type, the method comprising the following steps:

[0054] - casting a first layer of composite material comprising fibres bonded by a resin, the fibres of the first layer being oriented in a single predetermined direction,

[0055] - casting at least one second layer of composite material comprising fibers bonded by a resin, the fibers of the second layer being oriented in a predetermined direction different from that of the first layer,

[0056] - Harden the resin.

[0057] This method is easy to implement and it is easier to maintain the orientation of the fibers than if there were different orientations in each layer of the composite.

[0058] The width of each branch of the body of the hub at a point along its length extending radially from the outer periphery of the hub to the inner periphery of the strap is advantageously determined on the basis of an assessment of the permissible mechanical stresses that may be applied to the rotor, the maximum permissible rotational speed of the rotor and the mechanical strength of the material of the branch, the width of each branch being obtained by choosing for each branch a width at each point along its length that decreases with the distance from the hub, this reduction in width making it possible to achieve equal stresses in the interior of the branch.

[0059] Without any restrictions, the maximum stress exerted on the branch towards its end connected to the hub can be estimated at 120 MPa. The realization of this iso-stress makes it possible to minimize the width of the branch and therefore to use more efficiently the surface area of ​​the large magnet or magnet structure, therefore in the latter case more unitary magnets, which makes it possible to achieve greater torques and additionally compensate for the loss of magnet surface area towards the hub.

[0060] Finally, the invention relates to an electromagnetic motor or generator with axial flux, characterized in that it comprises at least one rotor of the type described above, the electromagnetic motor or generator comprising at least one stator carrying at least one coil, the electromagnetic motor or generator comprising one or more air gaps between at least one rotor and at least one stator. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Other features, objects and advantages of the invention will be explained in more detail below with reference to the accompanying drawings, which are provided by way of illustrative non-limiting examples and in which:

[0062] -Figure 1 is a schematic elevational view of a rotor for an electromagnetic machine with axial flux according to a first embodiment of the invention, the body comprising the hub and the branches of the rotor being made up of layers of composite material, each layer of composite material having an orientation of the fibers differing by 90° in two different layers,

[0063] - Figure 2 yes Figure 1 An enlarged schematic representation of a portion of a rotor is shown,

[0064] - Figure 3 is a schematic representation of a front view of a rotor for an electromagnetic machine with axial flux in a first embodiment of the invention, the body comprising the hub and the branches of the rotor being constituted by layers of composite material, each layer of composite material having an orientation of the fibers differing by 90° in two different layers,

[0065] - Figure 4 yes Figure 3 An enlarged schematic representation of a portion of a rotor is shown,

[0066] - Figure 5a , Figure 5b and Figure 5c It is a schematic representation. Figure 5a and Figure 5b corresponding to a corresponding embodiment of a single magnet having an oval shape, and Figure 5c Corresponding to a magnet structure including an oval-shaped single magnet, the oval-shaped single magnet is shown separated from the magnet structure. DETAILED DESCRIPTION

[0067] The accompanying drawings are provided by way of example, rather than by way of limitation of the present invention. They constitute schematic diagrams intended to aid understanding of the present invention and are not necessarily drawn to scale for practical applications. In particular, the sizes of the different parts do not represent actual conditions.

[0068] In the following, a single branch 3, a single base 3a and a single conical tip 3b of the branch 3 represent Figures 1 to 4 The same is true for a single magnet structure, designated 10, having an inner surface 10a and an outer surface 10b, a middle portion 9 between two branches for all middle portions, and a middle portion 9 for Figure 2 and Figure 4 The individual fibers in each composite layer are oriented either F1 or F2. Figures 1 to 4 In FIG. 1 , a single single magnet 4 is identified and represents all single magnets in the magnet structure 10 .

[0069] All statements made with respect to one of these individually identified elements apply to all similar elements that are not individually identified.

[0070] Referring to all the accompanying drawings, and in particular to Figures 1 to 4 , which respectively show enlarged views of the rotor 1 and a part of the rotor 1 according to the invention, the rotor 1 having two branches 3, between which is inserted a magnet structure 10 consisting of a plurality of single magnets 4 of polygonal shape.

[0071] This embodiment is not restrictive, and a single large magnet can be inserted between the two branches 3, whereby the single large magnet cannot be confused with the single magnets 4 of the magnet structure 10 visible and recognizable in Figure 2 and Figure 4 .

[0072] This type of rotor can advantageously be used in an electromagnetic motor or generator with axial flux. The rotor 1, which is advantageously circular, has a body including an inner hub 2 concentric with the central axis of rotation 7 of the rotor 1 or the longitudinal intermediate axis of the rotor 1. The branches 3 in the rotor 1 extend radially from the inner hub 2 towards the straps 8 forming the circular outer contour of the rotor 1 with respect to the central axis of rotation 7.

[0073] The hub 2 and the branches 3 are a single piece and form the rotor body 2, 3. At least one magnet (i.e., a large magnet or a magnet structure 10 including a plurality of small single magnets 4) is received in each space defined between two adjacent branches 3.

[0074] According to the invention, the body 2, 3 is constituted by a plurality of stacked composite material layers, the composite material layers comprising fibers joined by resin, and the fibers of each layer being oriented in predetermined directions F1, F2, and for two stacked layers, the predetermined directions are different.

[0075] Cover plates or surfaces are located on each of the two opposite faces of the body 2, 3 of the rotor. The cover plates or surfaces are not shown in the figures because they radially cover the circular surface of the rotor 1, and the body 2, 3 is constituted by a plurality of stacked composite material layers, the composite material layers comprising fibers joined by resin. Cover surfaces or plates not shown in the figures can be located on each circular face of the rotor 1 to prevent the axial movement of the magnet structure 10 or the large magnet between the two branches 3.

[0076] Taking into account all these features together, the body 2, 3 of the rotor 1 is significantly strengthened.

[0077] Several embodiments of the composite material layers can be envisaged. Non-limiting examples will now be described below.

[0078] As Figure 1 and Figure 2 show, the fibers of the composite material layers of the body 2, 3 can be oriented perpendicular to the fibers of adjacent stacked composite material layers, Figure 2 and the directions F1 and F2 shown are perpendicular.

[0079] like Figure 3 and Figure 4 As shown, the fibers of the composite material layers of the bodies 2 , 3 are oriented with an offset of 30° to 45°, 30° in these figures, relative to the fibers of the adjacently stacked composite material layers.

[0080] There may be more than two stacked composite material layers. The number of composite material layers of the body 2, 3 is determined based on the axial thickness of the magnet or magnet structure 10, and the cover skin has a thickness between 0.3 mm and 2 mm.

[0081] like Figure 1 and Figure 3 As best shown in , each branch 3 may have a width that decreases with distance from the inner hub 2 and terminates in a tapered tip 3 b proximate to the strap 8 .

[0082] Each large magnet or magnet structure 10 may have a width 1 a that increases with distance from the inner hub 2 and terminates in a band 8 surrounding the rotor 1 .

[0083] A loss of space for the magnets is created on the peripheral end portion of the rotor 1 as a result of increasing the width of the branch 3 towards its end or base portion 3 a facing the hub 2 and, if appropriate, also as a result of increasing the radius of the hub 2 .

[0084] The arrangement of orienting each large magnet or magnet structure 10 having a maximum width 1a towards the outer periphery of the rotor 1 makes it possible to increase the portion of magnets located on the periphery of the rotor 1 and thus increase the total magnetized surface area.

[0085] Still specifically referring to Figure 1 and Figure 3 , the conical tip 3 b of each branch 3 may be at least two to four times narrower than the base 3 a of the branch 3 connected to the inner hub 2 .

[0086] The bases 3a of two adjacent branches 3 may be separated by a middle portion 9 of the internal hub 2. This middle portion 9 may have a concave shape that is rounded towards the axis of the rotor 1. The internal hub 2 may have a radius that is equal to at least one quarter of the radius of the rotor 1, which in practice results in a hub 2 that is larger than the hub 2 of the prior art. The radius of the rotor is equal to the radius of the branch 3 plus the thickness of the strap 8.

[0087] The hub 2 and the branches 3 may be made of glass or carbon fibers cast in resin. Strong plastic fibers may also be used to increase the strength of the rotor 1, and in particular the bending strength and resistance to buckling.

[0088] As mentioned above, for solidification of the rotor 1, the hub 2 and the branches 3 are a single piece forming a composite body having fibers with different orientations F1, F2 according to the composite layers that comprise them. The branches 3 may optionally be connected to the straps 8 by their tapered ends 3b.

[0089] Special reference Figure 1 , Figure 3 and Figure 5a to Figure 5c Each magnet structure 10 may be composed of a plurality of single magnets 4 joined together by fiber-reinforced insulating material, each single magnet 4 having an elongated shape and extending in the axial direction of the rotor 1. Only one of the single magnets 4 is identified in the figure, and the single magnet 4 should not be confused with the magnet structure 10 or a large magnet not shown in the figure.

[0090] It follows that each magnet structure 10 can be three-dimensional and consist of a plurality of single magnets 4 .

[0091] exist Figures 1 to 4 In the embodiment, each of the plurality of single magnets 4 is in a polygonal shape.

[0092] exist Figure 5a , Figure 5b and Figure 5c In the embodiment, each single magnet 4 can at least partially have an oval profile, which includes a first portion 4a forming the body of the single magnet 4, the first portion 4a having a larger cross-section and extending over a longer length of the single magnet 4 than at least one second longitudinal end portion 4b pointing to the associated first longitudinal end portion of the single magnet 4, the cross-section of the second longitudinal end portion 4b decreasing as it approaches the first longitudinal end portion.

[0093] exist Figure 5a In the embodiment, the single magnet 4 has an almost perfect oval shape with a first portion 4a and two rounded second ends 4b having a convex shape. Figure 5c It can be seen in FIG. 1 that the contact between two adjacent oval single magnets 4 is basically point contact, or extends along a limited arc.

[0094] In this case, the single magnet 4 may have an at least partially oval outer contour, wherein a first portion 4a forming the body of the single magnet 4 has a larger cross section and extends over a longer length of the single magnet 4 than at least one second portion 4b.

[0095] exist Figure 5b In the embodiment, the single magnet 4 may have at least one second portion 4b as an extension of the first portion 4a at at least one longitudinal end of the single magnet 4. There may be two second portions 4b, wherein the second portions 4b are at one longitudinal end of the single magnet 4, respectively.

[0096] One or more second portions 4b may be directed towards an associated longitudinal end of the magnet, having a smaller cross-section close to the longitudinal end.

[0097] like Figure 5b As shown, one or more second longitudinal end portions 4b may be concave or may have a convex shape. One or more second longitudinal end portions 4b may terminate at their associated longitudinal ends in an intermediate facet 11 forming a longitudinal end. Figure 5b In the case of an oval shape, the intermediate facets 11 forming the longitudinal ends are concave and are only optional.

[0098] In this Figure 5b In one embodiment, one or more second longitudinal ends 4b may include a transverse facet inclined toward the longitudinal axis of the single magnet 4, which is close to the associated longitudinal end of the single magnet 4.

[0099] like Figure 5c As shown, in the magnet structure 10, the single magnets 4 are directly adjacent to each other and partially in contact. The single magnets 4 are bonded together by deposition of an adhesive. A plurality of single magnets 4 create a grid structure of magnets, and no retaining elements are interposed between each other except for the adhesive, and the single magnets 4 are in direct contact between adjacent magnets. The first portion 4a and the second portion 4b for the single magnets are also provided in the grid structure. Figure 5c Shown in.

[0100] exist Figure 2 and Figure 4 In FIG. 5A , the single magnets 4 can be adhesively connected to each other without a grid structure between them. The same is true for FIG. 5C . The adhesive can be a composite material layer or an adhesive resin, advantageously a thermosetting or thermoplastic.

[0101] Each large magnet or magnet structure 10 between two adjacent branches 3 may also be embedded in a composite material layer. The rotor may also be entirely coated in a composite material layer.

[0102] Thus, there can be at least a first layer of stacked layers of composite material surrounding a single magnet 4, at least a second layer of stacked layers of composite material for individually surrounding the magnet structure 10, and at least a third layer of stacked layers of composite material for coating the rotor 1, it being known that the body 2, 3 comprising the hub 2 and branches of the rotor is also made of stacked layers of composite material having fibers of different orientations depending on the layer.

[0103] As not shown in the drawings but used as a reference to similar elements already identified in the drawings, each magnet structure 10 may include at least one grid structure having grid cells, each grid cell defining a housing for a corresponding single magnet 4. Each housing may have an internal dimension just sufficient to allow a single magnet 4 to be introduced into its interior while leaving a space between the housing and the single magnet 4 filled with fiber-reinforced resin, the grid cells being made of fiber-reinforced insulating material.

[0104] The band 8 can be made of glass fiber or carbon or carbon fiber. The composite band 8 circumferentially surrounds the magnet structure 10 or the large magnet on the outer periphery of the rotor 1. If necessary, the band 8 also contributes to the radial retention of the magnet structure 10 or the large magnet in addition to the retention guaranteed by the outer layer of the composite coating. The conical tip 5d of the branch 3 can optionally be connected to the band 8.

[0105] The invention relates to a method for manufacturing a rotor 1 having the following steps for manufacturing a body 2 , 3 of a rotor 1 comprising a hub 2 and branches 3 .

[0106] The first step is to cast a first layer of composite material comprising fibres bonded by resin, the fibres of the first layer being oriented in a first predetermined direction F1.

[0107] The second step is to cast at least one second layer of composite material comprising fibers bonded by resin, the fibers of the second layer being oriented in a second predetermined direction F2 different from the first predetermined direction F1 of the first layer.

[0108] The third step is to harden the resin.

[0109] The bodies 2 , 3 are then ready for forming the skeleton of the rotor 1 .

[0110] Advantageously, the invention also relates to a method for manufacturing a rotor 1 of this type, in which the width l of each branch 3 along its length at a point extending radially from the outer periphery of the hub 2 to the inner periphery of the strap 8 at a known distance from the central rotation axis 7 of the rotor 1 is determined based on an assessment of the permissible mechanical stresses that can be applied to the rotor 1, the maximum permissible rotation speed of the rotor 1 and the mechanical strength of the branch material.

[0111] The width of each branch 3 decreases with increasing distance from the hub 2 by choosing for each branch 3 a width at each point along its length which makes it possible to obtain equal stresses in the interior of the branch 3 .

[0112] Figure 1 and 3 It is shown that the width of the branches 3 decreases with increasing radius and therefore with increasing distance from the central axis 7 of the rotor 1 .

[0113] Advantageously, the width of each branch at a point extending radially along its length is given by the following equation:

[0114]

[0115] Wherein K is a constant that varies according to the thickness of the strap and represents the mechanical strength of the material of the branch, ρ is the density of the magnet structure, σm is the allowable mechanical stress that may be applied to the rotor 1 and therefore to the branch, θ is the aperture angle of each magnet structure, and W is the allowable maximum rotation speed of the rotor 1.

[0116] Finally, the invention relates to an electromagnetic motor or generator with axial flux, comprising at least one rotor 1 as described above, comprising at least one stator carrying at least one coil, comprising one or more air gaps between at least one rotor 1 and at least one stator.

[0117] The electromagnetic motor or generator may preferably comprise at least one rotor 1 associated with two stators.

Claims

1. A rotor (1) for an electric motor or generator, the rotor (1) comprising: a body (2, 3) comprising an inner hub (2) concentric with a central rotation axis (7) of the rotor (1), branches (3) extending radially from the inner hub (2) relative to the central rotation axis (7) towards a band (8) forming a circular outer contour of the rotor (1); at least one magnet structure (10) having a plurality of single magnets (4), the at least one magnet structure (10) being accommodated in each space defined between two adjacent branches (3), the body (2, 3) consisting of a plurality of layers of composite material containing fibers bonded by resin, characterized in that the layers are stacked and the fibers of each layer are oriented in different predetermined directions (F1, F2) for two stacked layers, a radial covering skin layer being located on each of two opposite faces of the body (2, 3) of the rotor and consisting of a plurality of stacked layers of composite material containing fibers bonded by resin, in, The inner hub (2) has a middle portion (9) between two adjacent branches (3), and the middle portion (9) is bent toward the inside.

2. The rotor (1) according to claim 1, in, The fibers of the composite material layers of the body (2, 3) are oriented perpendicularly to the fibers of adjacently stacked composite material layers.

3. The rotor (1) according to claim 1, in, The fibers of the composite material layers of the body (2, 3) are oriented with an offset of 30° to 45° relative to the fibers of adjacently stacked composite material layers.

4. A rotor (1) according to any one of claims 1 to 3, in, The number of composite material layers of the body (2, 3) is determined based on the axial thickness of the magnet structure (10), and the cover layer has a thickness between 0.3 mm and 2 mm.

5. A rotor (1) according to any one of claims 1 to 3, in, Each branch (3) has a width that decreases with increasing distance from the internal hub (2) and terminates in a tapered tip (3b) abutting against the strap (8).

6. A rotor (1) according to any one of claims 1 to 3, in, The bases (3a) of two adjacent branches (3) are separated by a middle portion (9) of the inner hub (2), the middle portion (9) having a concave shape rounded towards the axis of the rotor (1), the inner hub (2) having a radius equal to at least one quarter of the radius of the rotor (1).

7. A rotor (1) according to any one of claims 1 to 3, in, Each magnet structure (10) has a width that increases with distance from the inner hub (2), terminating in the band (8) surrounding the rotor (1).

8. A rotor (1) according to any one of claims 1 to 3, in, Each of the plurality of single magnets (4) of the magnet structure (10) is polygonal in shape, or each single magnet (4) at least partially has an oval profile, the oval profile including a first portion forming the body of the single magnet (4), the first portion having a larger cross-section than other portions of the single magnet (4) and extending over a longer length of at least one second longitudinal end portion of the single magnet (4) than an associated first longitudinal end portion pointing toward the single magnet (4), the cross-section of the at least one second longitudinal end portion decreasing as the at least one second longitudinal end portion approaches the first longitudinal end portion.

9. A rotor (1) according to any one of claims 1 to 3, in, The plurality of single magnets (4) of the magnet structure (10) are connected together by fiber-reinforced insulating material, and each single magnet (4) has an elongated shape extending in the radial direction of the rotor (1).

10. A rotor (1) according to any one of claims 1 to 3, in, Each magnet structure (10) comprises at least one grid structure having grid cells, each of the grid cells defining a shell for a corresponding single magnet (4), each shell having an internal dimension just sufficient to leave a space filled with fiber-reinforced resin between the shell and the single magnet (4) after the single magnet (4) is introduced into the interior thereof, the grid cells being made of fiber-reinforced insulating material.

11. A rotor (1) according to any one of claims 1 to 3, in, Each magnet structure (10) between two adjacent branches (3) is embedded in at least one composite material layer, the rotor (1) is also coated in at least one composite material layer surrounding the embedded magnet structure, and the body (2, 3) is composed of multiple composite material layers.

12. A rotor (1) according to any one of claims 1 to 3, in, The composite material layers of the hub (2) and the branches surrounding the rotor and constituting the body (2, 3) are made of glass or carbon fibers cast in resin.

13. A method for manufacturing a rotor (1), the rotor (1) comprising a body (2, 3) consisting of a plurality of composite material layers comprising fibers bonded by resin, the method comprising the step of casting a first layer of composite material, the fibers of the first layer being oriented in a first predetermined direction (F1), the method being characterized by: the step of casting at least a second layer of composite material stacked on the first layer of composite material, the fibers of the second layer being oriented in a second predetermined direction (F2) different from the first predetermined direction (F1) of the first layer; and hardening the resin.

14. A method for manufacturing a rotor (1) according to any one of claims 1 to 3, in, The body (2, 3) comprises an inner hub (2) concentric with the central rotation axis (7) of the rotor (1), branches (3) radially extending from the inner hub (2) relative to the central rotation axis (7) towards a band (8) forming a circular outer contour of the rotor (1), the width of each branch (3) of the body (2, 3) of the hub (2) at a point along the length of each branch (3) extending radially from the outer periphery of the hub (2) to the inner periphery of the band (8) being determined based on the allowable mechanical stress that can be applied to the rotor (1), the allowable maximum rotation speed of the rotor (1) and the mechanical strength of the material of the branch (3), the width of each branch (3) being reduced as the distance from the hub (2) increases by selecting the width at each point along the length of each branch (3) for each branch (3), the width ensuring equal stress in the interior of the branch (3).

15. An electromagnetic motor or generator having an axial flux, It is characterized in that The electromagnetic motor or generator comprises at least one rotor (1) according to any one of claims 1 to 12, the electromagnetic motor or generator comprises at least one stator carrying at least one coil, the electromagnetic motor or generator comprises one or more air gaps between the at least one rotor (1) and the at least one stator.

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