Rotor for axial flux motor

Abstract

The present invention relates to a rotor (4) for an axial flux motor (1), comprising a drive shaft element which participates in defining an axis of rotation of the rotor (4) and a magnetic element arranged around the drive shaft element, characterized in that the magnetic element is an annular, bonded magnet (8) and the rotor (4) has a molded-on body (36) which is arranged at least between the bonded magnet (8) and the drive shaft element.

Description

The present invention relates to the field of motor vehicles and, more particularly, to electric machines with which these motor vehicles are equipped.Electric or hybrid vehicles use electric machines, in particular electric motors having at least one stator and one rotor, which are frequently radial flux machines. In such machines, the rotor and the stator are coaxial and are arranged around each other so that the windings mounted on the rotor or the stator generate a magnetic flux in a radial direction to the axis of rotation of the electric machine.In order to reduce the space requirement of electric machines in motor vehicles, it is known to use an axial flow machine instead of a radial flow machine, which axial flow machine is more compact at least in a direction parallel to the axis of rotation of the electric machine. In such a machine, the rotor and the stator are successively juxtaposed along the axis of rotation of the electric machine, and the magnetic flux is then generated parallel to the axis of rotation of the electric machine.The rotor of an electric axial flux machine in the form of a disk has at least one magnetic element. This magnetic element is made, for example, from a magnetic powder which is sintered into a unit which is then cut into magnet segments of the desired dimensions before it is placed in a rotor body which has been previously made, for example, by forming a composite structure. In order to ensure the mechanical strength of the assembly, particularly when the rotor is rotated at high speed, the rotor body conventionally has a yoke forming an outer periphery that makes the rotor solid, i.e., bulky. Moreover, the manufacturing and assembly process requires precise and numerous steps for positioning the individual magnet segments. This results in manufacturing costs of the rotor, which are a large amount of material for forming the rotor body and long assembly operations. Finally, such an arrangement may involve difficulties in magnetizing the various magnets if the polarization is to be changed from one magnet segment to another.The present invention is incorporated in this context by proposing a rotor for an axial-flow electric machine, the manufacturing method of which is facilitated and the magnetization operations are simplified.The main object of the present invention is thus a rotor for an axial flux motor having a drive shaft element involved in defining a rotor rotation axis and a magnetic element arranged around the drive shaft element. According to the invention, the magnetic member is an annular bonded magnet, and the rotor has a formed body disposed at least between the bonded magnet and the drive shaft member.The rotor according to the invention is provided to be part of an axial flux motor, in particular an axial flux motor for an electric or hybrid vehicle.The rotor comprises a drive shaft element, for example a transmission shaft or a hub, the center point of which lies in an axis of rotation of the rotor. The rotor also includes a magnetic element, which is a bonded magnet here, such as a bonded magnet made of a mixture of polymer and rare earth powder, e.g., neodymium, iron, and / or boron. The bonded magnet is arranged to form an annular unit disposed radially around the drive shaft member. In addition to the bonded magnet, the rotor includes an overmoulded body corresponding to a support structure overmoulded on the bonded magnet and the drive shaft member, in particular to hold the bonded magnet in position during rotation of the rotor. Thus, it is understood that the overmoulded body at least partially covers the bonded magnet and also at least partially covers the drive shaft element.The combination of the magnetic element and the body formed on this magnetic element gives the rotor a disk shape. As a result, it is possible to dispense with a conventional rotor body which has, in particular, a yoke which delimits a thick outer edge of the rotor body. The use of a body formed around the bonded magnet enables a reduction in the weight of the rotor and a limitation in its manufacturing cost. Compared with prior art sintered magnets, the bonded magnet of the present invention has improved mechanical strength and possible eddy current losses are limited.According to an optional feature of the invention, the bonded magnet extends radially between an inner peripheral edge and an outer peripheral edge, the overmoulded body engaging the bonded magnet and the drive shaft member at least along the inner peripheral edge and being disposed around the outer peripheral edge.The bonded magnet is bounded radially, i.e. in a plane perpendicular to the axis of rotation of the rotor, by the inner circumferential edge and the outer circumferential edge. The inner peripheral edge is closer to the drive shaft member than the outer peripheral edge. The overmoulded body comprises a first part extending between the inner peripheral edge and the drive shaft member and a second part extending along the outer peripheral edge. These parts of the overmoulded body are both annular. Depending on the embodiment, the first part and the second part are separate from one another or are formed in one piece and have connecting legs which are arranged between segments of the bonded magnet.According to an optional feature of the invention, the rotor comprises at least one positioning device crossing the bonded magnet and the overmoulded body.The positioning device or adjusting device is used in a method for producing the rotor. It allows the correct positioning of the various rotor elements with respect to each other, for example within a mold into which the material used for the production of the overmoulded body is injected. The positioning device has dimensions which are matched to pins of the mold. Inside the overmoulded body, the positioning means corresponds to a portion which has not been overmoulded due to the pins of the mould. It should be noted that the position of this positioning device in the rotor depends on the embodiment of this rotor and in particular on the shape imparted to the bonded magnet, whether segmented or not.According to an optional feature of the invention, the positioning means is arranged on the inner peripheral edge of the bonded magnet.According to an optional feature of the invention, the positioning means is arranged on the outer peripheral edge of the bonded magnet.According to an optional feature of the invention, the bonded magnet is integrally formed.This is a first embodiment of the rotor, which is matched in particular to rotors with a reduced diameter.According to an optional feature of the invention, the bonded magnet comprises a plurality of angle segments fixedly connected to each other. In other words, a plurality of segments form the bonded ring-shaped magnet.This corresponds to a second embodiment in which the bonded magnet consists of several parts, here taking the form of angle segments, wherein the number of segments can vary from rotor to rotor depending on its dimensions or on the desired number of poles of the axial flux motor. Each angle segment is firmly connected to the two adjacent angle segments by the overmoulded body.According to an optional feature of the invention, the overmoulded body extends between the angle segments.The overmoulded body is inserted between the angle segments and overlaps them at least partially, whereby they can be firmly connected to one another. The overmoulded body thus has a function of holding the angle segments together.According to an optional feature of the invention, the positioning device is arranged between two adjacent angle segments.Alternatively, the positioning means is disposed within a given angular segment.According to an optional feature of the invention, the positioning device has at least one round hole and at least one elongated hole.The round hole and the elongated hole are either half holes or whole holes, i.e. holes whose cross-section defining the shape of the hole is closed. The round hole allows the bonded magnet in the injection mold to be centered with respect to the drive shaft member, while the other hole allows the position of the bonded magnet to be angularly adjusted due to its elongated shape. The bonded magnet has, for example, at least two holes per angular segment.The holes contribute to the holding function of the bonded magnet when the molded body is injected therein.According to an optional feature of the invention, the bonded magnet has a portion of reduced thickness extending from one of its peripheral edges, such thickness being measured along an axial direction of the rotor.The reduced thickness portion forms a step at the edge of the bonded magnet. Depending on the embodiment, it extends either starting from the inner circumferential edge, from the outer circumferential edge or from both circumferential edges. The reduced thickness portion facilitates the engagement of the over-molded body with the bonded magnet.According to an optional feature of the invention, the bonded magnet has, between its inner peripheral edge and its outer peripheral edge, a central portion whose thickness is variable at least in a radial or orthoradial direction.According to an optional feature of the invention, the central portion of the bonded magnet has a thickness strictly increasing from its inner peripheral edge toward its outer peripheral edge.According to an optional feature of the invention, the central portion of the bonded magnet has a thickness varying over the circumference of the central portion for a given radial dimension.These thickness values are measured along the axial direction of the rotor. The central portion is to be seen between the inner peripheral edge and the outer peripheral edge and therefore does not include the reduced thickness portion which extends this central portion towards the interior of the rotor. In other words, the thickness of the bonded magnet increases steadily from the inner peripheral edge to the outer peripheral edge, except for the reduced thickness portion that may have a constant thickness. The thickness of the bonded magnet of variable value at the periphery of the central portion is considered by measuring the thickness of the bonded magnet at different points of a circle centered on the rotor axis and interposed between the inner peripheral edge and the outer peripheral edge in the axial direction of the rotor.Such thickness differences within the bonded magnet enable the torque ripple phenomenon to be limited.According to an optional feature of the invention, the positioning means is provided at the reduced thickness portion.According to an optional feature of the invention, the reduced thickness portion comprises at least one perforation.The perforation provided at the portion of reduced thickness, like other holes located at the edges of the angle elements of the bonded magnet, may in particular have the function of being filled with the material of the overmoulded body in order to increase and vary the contact areas between the bonded magnet and the overmoulded body and to ensure a transmission of force from one to the other instead of having the function of relative positioning of the various rotor components.According to an optional feature of the invention, the overmoulded body is made of plastic.The formed body is a non-magnetic structure. It is made, for example, of a thermoplastic, such as polyamide, having properties which facilitate its injection.The invention also relates to an axial flux motor comprising at least a stator and a rotor as mentioned above, the stator and the rotor being arranged one after the other along the axis of rotation of the rotor.The stator and the rotor are arranged one above the other along the rotor axis of rotation and both have a center point which lies in the rotor axis of rotation. Optionally, the drive shaft member includes apertures that help to ensure torque transfer and resist the forces exerted during high speed rotation of the rotor.According to an optional feature of the invention, the axial flux motor has a second stator, wherein the rotor is arranged between the two stators.The invention further relates to a method of manufacturing a rotor as mentioned above, comprising a step of positioning the bonded magnet in a mold and a step of forming the formed body on the bonded magnet.The positioning step corresponds to either injecting the bonded magnet into the mold or producing the bonded magnet remotely therefrom and then positioning it within the mold. In this positioning step, the bonded magnet is either a one-piece shape or the shape of angle segments. After the positioning step, the molded body is injected into the mold and at the same time covers the bonded magnet and the drive shaft element at least partially.According to an optional feature of the invention, the positioning step is carried out with the positioning device.Further features, details and advantages of the invention will become more apparent from reading the following description, on the one hand, and the embodiments, on the other hand, given by way of example and not limitation with reference to the accompanying drawings. Shown therein are: FIG. 1 schematically illustrates an axial-flow electric motor according to the invention in a non-limiting arrangement, including a first stator, a second stator and a rotor arranged between the first stator and the second stator; FIG. 2 schematically shows a first embodiment of the rotor from FIG. 1, wherein this rotor comprises a molded-on body and a magnetic element formed in one piece; FIG. 3 schematically shows a first variant of a second embodiment of the rotor from FIG. 1, wherein the magnetic element of the rotor consists of a plurality of segments; FIG. 4 schematically shows a second variant of the second embodiment of the rotor from FIG. 1, wherein the magnetic element of the rotor consists of a plurality of segments; FIG. 5 schematically shows the magnetic element of the first embodiment variant of the second embodiment from FIG. 3, here without the molded-on body; FIG. 6 schematically shows the second variant embodiment of the second embodiment from FIG. 4, here without the molded-on body; FIG. 7 shows schematically and in isolation one of the segments of the first variant embodiment from FIGS. 3 and 5 ; FIG. 8 is a schematic and isolated view of one of the segments of the second embodiment variant of FIGS. 4 and 6.The features, variants and different embodiments of the invention can be linked to one another in different combinations, provided they are not incompatible or mutually exclusive. In particular, variants of the invention are conceivable which comprise only a selection of the features described below, separately from the other features described, provided that this selection of features is sufficient to confer a technical advantage and / or to distinguish the invention from the prior art.In the figures, elements that share multiple figures retain the same reference number.In the following detailed description, the terms "longitudinal", "transverse" and "vertical" indicate the orientation of the rotor for an axial flux motor according to the invention, wherein the longitudinal axis corresponds to the axis of rotation of the axial flux motor and these terms refer to an axis cross L, V, T illustrated in the figures.FIG. 1 thus schematically shows an axial flow motor 1 according to the invention, which is provided for the equipment of an electric or hybrid vehicle. The axial flux motor 1 comprises a housing 2 which encloses a rotor 4 and at least one stator 6. As shown here, the axial flux motor 1 comprises a first stator 6A and a second stator 6B. The stators 6 and the rotor 4 are stacked such that the first stator 6A and the second stator 6B are disposed on one side and the other side of the rotor 4 in a longitudinal direction L in which a rotation axis of the rotor 4 is located. The rotor 4 and the stators 6 are each disc-shaped, with a center point lying in the axis of rotation of the rotor 4.A magnetic element of the rotor 4, which is a bonded magnet 8, is disposed opposite to a winding 10 of each stator 6 as viewed in the longitudinal direction. Thus, the bonded magnet 8 and the windings 10 are formed so that a magnetic field can be generated that runs axially from the rotor to the stators.The housing 2 is traversed in the longitudinal direction L by a transmission shaft 12 of the axial flux motor 1, which is parallel to the axis of rotation of the rotor 4. At the height of the rotor 4, a hub 14 is located between the transmission shaft 12 and the rotor 4; both the transmission shaft 12 and the hub 14 form drive shaft elements of the axial flux motor 1.The rotor 4 according to the invention will now be described in detail with reference to FIGS. 2 to 8.FIG. 2 shows a first embodiment of the rotor, while a second embodiment of the rotor is shown in FIGS. 3 to 8. FIGS. 3, 5 and 7 show a first variant of the second embodiment, and FIGS. 4, 6 and 8 show a second variant of this second embodiment. Unless otherwise stated, the features described for one of these embodiments or one of these variants correspondingly apply to another embodiment or another variant.The rotor according to the invention comprises in particular a bonded magnet 8 and a formed-on body 36.The bonded magnet 8 of the rotor 4 is made of a material made of a mixture of polymer and rare earth elements, for example, an alloy of neodymium, iron and boron. The bonded magnet is prepared by injection into a mold, either the same mold to which the polymer is subsequently injected or a separate mold. The bonded magnet 8 is annular and is disposed around the hub 14 and at a non-zero distance therefrom.The bonded magnet 8 is bounded radially, i.e. in a vertical-transverse plane perpendicular to the longitudinal direction L and to the axis of rotation of the rotor 4, by an inner circumferential edge 16 and an outer circumferential edge 18. The inner peripheral edge 16 substantially corresponds to the smallest diameter of the bonded magnet 8, while the outer peripheral edge 18 substantially corresponds to its largest diameter. Moreover, the inner peripheral edge 16 is the portion of the bonded magnet 8 closest to the hub 14 constituting the drive shaft member, while the outer peripheral edge 18 is the portion furthest from this hub 14.The inner peripheral edge 16 and the peripheral edge 18 are connected to each other by a first surface 20 and a second surface 22 of the bonded magnet 8. The first surface 20 and the second surface 22 are opposite to each other in the longitudinal direction L. For example, the first surface 20 faces the first stator 6A and the second surface 22 faces the second stator 6B.The bonded magnet 8 is a one-piece element in the first embodiment of FIG. 2, i.e. it is formed in one piece. In contrast, in the second embodiment of FIGS. 3 to 8, the bonded magnet 8 has a plurality of angle segments 24. An angle segment 24 corresponding to the first variant of FIGS. 3 and 5 is shown isolated in FIG. 7, and an angle segment 24 corresponding to the second variant of FIGS. 4 and 6 is shown isolated in FIG. 8. These angle segments 24 extend from the inner circumferential edge 16 to the outer circumferential edge 18. Due to the ring shape of the bonded magnet 8, the angle segments 24 have a dimension measured along the inner circumferential edge 16 that is smaller than a dimension measured along the outer circumferential edge 18.In Figs. 5 and 7, which illustrate the first variant of the second embodiment, each angular segment 24 of the bonded magnet 8 is provided with a groove 26 extending radially from the inner peripheral edge 16 to the outer peripheral edge 18. Each groove 26 thus corresponds, measured along the longitudinal direction L, to a reduction in the thickness of the angular segment 24 of the bonded magnet 8. in other words, the grooves 26 form depressions which are formed radially in at least one of the surfaces 20, 22 of the bonded magnet 8, here both in the first surface 20 and in the second surface 22.The groove 26 of a particular angle segment 24 is located substantially in the middle of this angle segment 24. in other words, each angle segment has a first side 28 opposite an adjacent first angle segment 24 and a second side 30 opposite an adjacent second angle segment 24, this groove 26 being substantially the same distance from the first side 28 and from the second side 30. The first side 28 and the second side 30 correspond to walls of the angle segment 24 that connect, on the one hand, the inner peripheral edge 16 and the outer peripheral edge 18 and, on the other hand, the first surface 20 and the second surface 22. The sides 28, 30 delimit the angle segment 24 in a plane lying perpendicular to the first surface 20 and to the second surface 22 of the bonded magnet 8.In FIGS. 6 and 8, the angle segments 24 of the bonded magnet 8 according to the second embodiment do not have such radial grooves 26 that extend from the inner circumferential edge 16 to the outer circumferential edge 18. This results in a smaller angular dimension and thus a larger number of angle elements required for forming the circumference of the bonded magnet in the second embodiment variant than the number of angle elements required in the first embodiment variant.Thus, the bonded magnet 8 shown in the first variant of FIGS. 3 and 5 comprises ten angle segments 24 with identical dimensions, while the bonded magnet 8 in the second variant of FIGS. 4 and 6 consists of twenty angle segments 24 with identical dimensions.In Fig. 2, the one-piece bonded magnet 8 according to the first embodiment is smooth, i.e. its first surface 20 and its second surface 22 are substantially planar, but a one-piece bonded magnet 8 provided with the above-described grooves 26 would also be conceivable.The bonded magnet 8 has through holes 32 at its grooves 26. As can be seen particularly clearly in FIG. 7, the size of these through-holes 32 increases starting from the inner circumferential edge 16 to the outer circumferential edge 18. Each groove 26 here has at least one round hole 32A and one slot 32B. The round hole 32A is disposed near the inner peripheral edge 16 and the long hole 32B is disposed near the outer peripheral edge 18, but this arrangement does not limit the invention.Both the first side 28 and the second side 30 also have a hole half 32 such that when the angle segments 24 are arranged side by side to give the bonded magnet 8 its ring shape, the hole halves 32 of two adjacent angle segments form a substantially complete hole 32.The holes are all or partly intended to be filled with polymer material forming the overmoulded body, thus enlarging the contact area between the bonded magnet and the overmoulded body and ensuring that these contact areas are oriented in different directions to ensure correct transmission of the forces and torques under load of the rotor. In this case, polymer material is arranged between two angle elements adjoining one another, as a result of which good orthoradial force transmission is ensured.In this connection, it is advantageous if the size of the through holes 32 increases from the inner circumferential edge 16 to the outer circumferential edge 18, since it is thereby possible to ensure that at the location where more loads are exerted due to the centrifugal force during the rotation of the axial flow motor, a larger amount of inserted polymer material is present between the adjacent angle segments at a distance from the hub.In the second variant of the second embodiment, shown in FIGS. 4, 6 and 8, the bonded magnet 8 has, on at least one of its peripheral edges 16, 18, a portion of reduced thickness 34. Here, the bonded magnet 8 has such a reduced thickness portion 34 at each of its peripheral edges 16, 18, with a first reduced thickness portion 34A along the inner peripheral edge 16 and a second reduced thickness portion 34B along the outer peripheral edge 18.The first reduced thickness portion 34A has a through hole 32, here a round hole 32A, which is formed in a protruding region of the first reduced thickness portion 34A so as to form a closed cross-sectional hole. The second reduced thickness portion 34B has a through hole 32, here an elongated hole 32B, which is formed at the edge of the second reduced thickness portion so as to form an open hole. Without departing from the scope of the invention, embodiments could be contemplated wherein the first reduced thickness portion 34A includes the elongated hole 32B and the second reduced thickness portion 34B includes a round hole 32A, and wherein the first reduced thickness portion 34A is the one having an open hole or a half hole.It should be noted that here too, these holes increase the contact area between the polymer material and the bonded magnet and make this contact area less smooth and uniform, so that the force transmission capacity from the bonded magnet to the molded body is increased.As mentioned above, the rotor 4 according to the invention has a formed-on body 36. This overmoulded body 36 is made of a thermoplastic polymer, in particular polyamide, and is made by overmoulding the bonded magnet present in a rotor injection mould with the polymer.The overmoulded body 36 is arranged at least between the bonded magnet 8 and one of the drive shaft elements, here between the bonded magnet 8 and the hub 14. More precisely, the overmoulded body 36 comprises a first part 38 arranged along the inner peripheral edge 16 between this inner peripheral edge 16 and the drive shaft element, and a second part 40 arranged along the outer peripheral edge 18. The first portion 38 extends radially from the hub 14 to the inner peripheral edge 16 and engages these two members while the second portion 40 surrounds the outer peripheral edge 18. Optionally, the over-molded body 36 engages and covers the reduced thickness portion 34 at both the first surface 20 and the second surface 22.In the first embodiment of FIG. 2, i.e. in the case of a bonded magnet 8 which is in one piece, i.e. in one piece and is embodied without grooves 26, the first part 38 and the second part 40 are separate parts and are physically separated from one another by the bonded magnet 8. In contrast, in embodiments where the bonded magnet 8 is comprised of a plurality of angle segments 24, the first portion 38 and the second portion 40 of the over-molded body 36 are interconnected by legs 42 of that over-molded body 36. In other words, a leg 42 of the over-molded body 36 extends between two adjacent angle segments 24. Similarly, in embodiments where the bonded magnet 8 has grooves 26, the first portion 38 and the second portion 40 are interconnected by at least one leg 42, i.e., a leg 42 of the over-molded body 36 extends within a groove 26.As is shown in particular in FIGS. 5 and 6, the hub 14 is provided with at least one opening 43, in this case with a plurality of openings 43. Each opening 43 passes completely through the hub 14 in the longitudinal direction L. The overmoulded body 36 extends through these openings 43.The rotor 4 has at least one positioning device 44 which traverses both the bonded magnet 8 and the formed-on body 36. The positioning means 44 has, for example, one of the through-holes 32 mentioned above in connection with the bonded magnet 8, and an opening 46 formed in the molded body 36 opposite to the through-hole 32. The overmoulded body 36 extends within the through holes 32 which do not contribute to the formation of a positioning device 44.As shown in the first embodiment of Fig. 2, the rotor 4 equipped with a one-piece bonded magnet 8 comprises two positioning means 44 arranged on one side and on the other side of the hub 14, here diametrically opposed. Each positioning device 44 here comprises one of the through-holes 32 arranged on the first portion of reduced thickness 34, i.e. at the level of the inner peripheral edge, and an opening 46 passing through the overmoulded body 36 opposite the through-hole 32. Although not shown here, the through holes 32 involved in the positioning means 44 of the rotor 4 could alternatively be arranged on the second portion of reduced thickness 34B, i.e. at the level of the outer peripheral edge 18.In embodiments in which the one-piece bonded magnet 8 has grooves 26, the rotor 4 could otherwise have two positioning devices 44 each arranged on a groove 26. For example, a first positioning device 44 would have, on the one hand, one of the through holes 32 mounted in a given groove 26 as close as possible to the outer peripheral edge 18 and, on the other hand, an opening 46 formed opposite it in the overmoulded body 36, and a second positioning device 44 would have, on the one hand, one of the through holes 32 mounted in a groove 26 radially opposite the given groove 26 with respect to the axis of rotation of the rotor 4, this through hole 32 being arranged as close as possible to the outer peripheral edge 18 and, on the other hand, an opening 46 formed opposite it in the overmoulded body 36.In the second embodiment, i.e. if a plurality of angle segments 24 forming the bonded magnet 8 are present, the rotor 4 has at least two positioning devices 44 per angle segment 24.In the first variant of the second embodiment, shown in FIGS. 3, 5 and 7, the rotor 4 comprises in its entirety twenty positioning devices 44. each angular segment 24 comprises in particular two positioning devices 44 arranged in its groove 26. Thus, for each angular segment 24, there are a first positioning device 44 comprising, on the one hand, a through hole 32 arranged in a specific groove 26 in the vicinity of the inner peripheral edge 16 and, on the other hand, an opening 46 formed opposite it in the overmoulded body 36, and a second positioning device 44 comprising, on the one hand, a through hole 32 arranged in one and the same groove 26 in the vicinity of the outer peripheral edge 18 and, on the other hand, an opening 46 provided opposite it in the overmoulded body 36.In the second variant of the second embodiment, shown in FIGS. 4, 6 and 8, the rotor 4 comprises a total of forty positioning means 44, i.e. two for each of the angle segments 24. more precisely, each angle segment 24 comprises a first positioning means 44 consisting, on the one hand, of the through hole 32 arranged on the first reduced thickness portion 34A, i.e. on the inner peripheral edge 16, and, on the other hand, of the corresponding opening 46 formed in the overmoulded body 36, and a second positioning means 44 consisting, on the one hand, of the through hole 32 arranged on the second reduced thickness portion 34B, i.e. on the outer peripheral edge 18, and, on the other hand, of the corresponding opening 46 formed in the overmoulded body 36.In other words, at least two positioning devices per one-piece element of the bonded magnet result. In these at least two positioning devices, there are, in particular, a positioning device having a round through hole 32 which ensures a first fixed positioning point, and a positioning device having an elongate through hole which ensures a second positioning point which permits position adaptation.It will be appreciated that each aperture 46 formed in the overmoulded body has a respective through hole 32 formed in the bonded magnet and that each aperture 46 results either from the presence of a pin inserted into the respective through hole 32 to hold the bonded magnet in position upon injection of polymer into the mould to effect overmoulding of the overmoulded body around the magnet or from the presence of a bolt for closing the mould.A method for manufacturing the rotor 4 according to the present invention will now be described in detail. This manufacturing method includes a placing step in which a drive shaft member of the rotor 4, e.g., the hub 14, is placed in a rotor injection mold. The position of the hub 14 forms a position reference system for the later positioning of the bonded magnet, which position reference system can be ensured by a pin associated with the mold.The manufacturing method also includes a positioning step of positioning the bonded magnet 8 within the rotor injection mold. In this positioning step, the bonded magnet 8, as the case may be, is either injected directly into the injection mould of the rotor, which is then used to inject the polymer to be formed, or it is produced at another manufacturing station, in particular by injection into another mould, and then arranged in a fixed form in the rotor injection mould. It will be appreciated that in the case where the bonded magnet 8 is injected directly into the rotor mould, one or more inserts are provided to simulate the presence of the polymer, this insert being removed when the polymer is to be injected.When the bonded magnet 8 is fixed in shape in the mold, the through holes 32 of the bonded magnet 8 are used in the positioning step. This is correctly positioned within the mould by sliding pins of the mould through these through holes 32. The cooperation of the through holes 32 and the pins allows positioning of the bonded magnet 8 with respect to the drive shaft member, optionally the hub 14, already in the mold. For example, in the presence of a round hole 32A and an elongated hole 32B, one of these two through holes 32 allows the bonded magnet 8 to be centered and the other allows the positioning to be adjusted.Once the drive shaft member and the bonded magnet 8 are properly disposed in the mold, the manufacturing method includes a forming step of forming the formed body 36 in the mold to connect the drive shaft member and the bonded magnet. The polymer material chosen to form the overmoulded body 36 then penetrates the openings of the hub 14 and all the through-holes 32 of the bonded magnet 8 which are not penetrated by shaped pins, and forms the first part at the inner peripheral edge 16 and the second part at the outer peripheral edge 18. Likewise, in embodiments where the bonded magnet 8 has grooves 26, they are filled with the polymeric material of the overmoulded body, and when the bonded magnet 8 comprises angle segments 24, it fits between these angle segments 24 to form the legs 42 involved in the attachment of the adjacent angle segments.The present invention thus proposes a rotor for an axial flow electric machine having a bonded magnet and a formed body, and the use of such a formed body simplifies a method of manufacturing the rotor.However, the present invention is not limited to the devices and embodiments described and illustrated herein, and extends to all equivalent devices and embodiments, as well as to any technically operable combination of such devices.

Claims

A rotor (4) for an axial flux motor (1) comprising a drive shaft element involved in defining a rotational axis of the rotor (4) and a magnetic element arranged around the drive shaft element, characterized in that the magnetic element is an annular bonded magnet (8), and the rotor (4) comprises a formed body (36) corresponding to a supporting structure formed on the bonded magnet (8) and on the drive shaft element and arranged at least between the bonded magnet (8) and the drive shaft element.The rotor (4) according to the preceding claim, wherein the bonded magnet (8) extends radially between an inner peripheral edge (16) and an outer peripheral edge (18), wherein the overmoulded body (36) is engaged with the bonded magnet (8) and the drive shaft element at least inside the inner peripheral edge (16) and is arranged around the outer peripheral edge (18).Rotor (4) according to any one of the preceding claims, comprising at least one positioning device (44) passing through the bonded magnet (8) and the overmoulded body (36).Rotor (4) according to the preceding claim in combination with claim 2, in which the positioning device (44) is arranged on the inner circumferential edge (16) or on the outer circumferential edge (18) of the bonded magnet (8).Rotor (4) according to one of the preceding claims, in which the bonded magnet (8) is formed in one piece.Rotor (4) according to any one of claims 1 to 5, wherein the bonded magnet (8) comprises a plurality of angle segments (24) which are secured to one another.Rotor (4) according to the preceding claim, in which the overmoulded body (36) extends between the angular segments (24).Rotor (4) according to the preceding claim in combination with claim 3, in which the positioning device (44) is arranged between two adjacent angle segments (24).Rotor (4) according to any one of the preceding claims taken in combination with claim 2, wherein the bonded magnet (8) comprises a portion of reduced thickness (34, 34A, 34B) extending from one of its peripheral edges (16, 18), such thickness being measured along an axial direction of the rotor (4).Rotor (4) according to any one of the preceding claims, taken in combination with claim 2, wherein the bonded magnet (8) has a central portion between its inner peripheral edge (16) and its outer peripheral edge (18), the thickness of which is variable at least in a radial or orthoradial direction.Rotor (4) according to one of the preceding claims, in which the overmoulded body (36) is made of plastic.Axial flux motor (1) comprising at least one stator (6, 6A, 6B) and a rotor (4) according to any of the preceding claims, wherein the stator (6, 6A, 6B) and the rotor (4) are arranged one after the other along the axis of rotation of the rotor (4).

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