Rotor for axial flux motor

Abstract

Title of the invention: Rotor for axial flux motor The present invention relates to a rotor (4) for an axial flux motor (1) comprising a motor shaft element participating in defining an axis of rotation of the rotor (4), a magnetic element arranged around the motor shaft element, characterized in that the magnetic element is an annular bonded magnet (8) and in that the rotor (4) comprises an overmolded body (36) arranged at least between the bonded magnet (8) and the motor shaft element. Abstract figure: Figure 3

Description

Title of the invention: Rotor for axial flux motor

[0001] The present invention relates to the field of motor vehicles, and more particularly to the electrical machines equipping these motor vehicles.

[0002] Electric or hybrid motor vehicles use electrical machines, in particular electric motors with at least one stator and one rotor, which are often radial flux machines. In such machines, the rotor and the stator are coaxial and arranged around each other, such that windings embedded on one or the other of the rotor and the stator generate a magnetic flux in a radial direction relative to an axis of rotation of the electric machine.

[0003] In order to reduce the size of electrical machines in motor vehicles, it is known to use, instead of a radial flux machine, an axial flux machine which is more compact at least in a direction parallel to the axis of rotation of the electrical machine. In such a machine, the rotor and the stator are arranged successively next to each other along the axis of rotation of the electrical machine and the magnetic flux is then generated parallel to the axis of rotation of the electrical machine.

[0004] The rotor of an axial flux electrical machine, in the form of a disc, comprises at least one magnetic element. This magnetic element is for example obtained from a magnet powder, which is sintered to form an assembly subsequently cut into magnet segments with desired dimensions before being arranged within a rotor body previously produced, for example by molding a composite structure. In order to ensure mechanical strength of the assembly, in particular when the rotor is made to rotate at high speed, the rotor body conventionally has a yoke forming an outer circumference which makes the rotor massive, that is to say bulky. Furthermore, the manufacturing and assembly process involves steps of positioning the magnet segments one by one which are meticulous and numerous.This results in rotor manufacturing costs, resulting from a large amount of material to form the rotor body and tedious assembly operations. Finally, such a realization can involve difficulties in magnetizing the different magnets, when it is desired to modify the polarization from one magnet segment to another.

[0005] The present invention falls within this context by proposing a rotor for an axial flux electric machine whose manufacturing process is facilitated and for which the magnetization operations are simplified.

[0006] The main object of the present invention is thus a rotor for an axial flux motor comprising a motor shaft element participating in defining an axis of rotation of the rotor and a magnetic element arranged around the motor shaft element. According to the invention, the magnetic element is an annular bonded magnet and the rotor comprises an overmolded body disposed at least between the bonded magnet and the motor shaft element.

[0007] The rotor according to the invention is intended to be part of an axial flux motor, and in particular of an axial flux motor for an electric or hybrid motor vehicle.

[0008] The rotor comprises a drive shaft element, for example a transmission shaft or a hub, a center of which is inscribed in an axis of rotation of the rotor. The rotor also comprises a magnetic element, which is here a bonded magnet such as a bonded magnet made from a mixture of polymer and rare earth powder, for example neodymium, iron and / or boron. The bonded magnet is arranged so as to form an annular assembly, arranged radially around the drive shaft element. In addition to the bonded magnet, the rotor comprises an overmolded body which corresponds to a holding structure which has been overmolded onto the bonded magnet and onto the drive shaft element, in particular in order to hold the bonded magnet in position during rotation of the rotor. It is thus understood that the overmolded body is arranged at least partially covering the bonded magnet, as well as at least partially covering the drive shaft element.

[0009] The combination of the magnetic element and the body overmolded on this magnetic element gives the rotor a disc shape. It is thus possible to do without a conventional rotor body which notably has a yoke delimiting a thick outer edge of the rotor body. The use of a body overmolded around the bonded magnet makes it possible to reduce the weight of the rotor as well as to limit its manufacturing costs. Compared to the sintered magnets of the prior art, the bonded magnet according to the invention has improved mechanical strength and possible eddy current losses are limited.

[0010] According to an optional feature of the invention, the bonded magnet extends radially between an inner peripheral edge and an outer peripheral edge, the overmolded body being arranged at least along the inner peripheral edge while being engaged on the bonded magnet and the motor shaft element, and around the outer peripheral edge.

[0011] The bonded magnet is delimited radially, i.e. in a plane perpendicular to the axis of rotation of the rotor, by the inner peripheral edge and the outer peripheral edge. The inner peripheral edge is closer to the motor shaft element than the outer peripheral edge. The overmolded body comprises a first part which extends between the inner peripheral edge and the motor shaft element, and a second part which extends along the outer peripheral edge. These parts of the overmolded body are both annular in shape. The first part and the second part are, depending on the embodiments, distinct from each other or in one piece by having connecting branches arranged between segments of bonded magnet.

[0012] According to an optional characteristic of the invention, the rotor has at least one positioning means passing through the bonded magnet and the overmolded body.

[0013] The positioning means, or indexing means, is used during a process for obtaining the rotor. It makes it possible to correctly position the different elements of the rotor relative to each other, for example within a mold into which the material used to produce the overmolded body is injected. The positioning means has dimensions adapted to pins of the mold. Within the overmolded body, the positioning means corresponds to a portion which has not been overmolded due to the presence of the pins of the mold. It should be noted that the position of this positioning means within the rotor depends on the embodiments of this rotor and in particular on the shape given to the linked magnet, segmented or not.

[0014] According to an optional characteristic of the invention, the positioning means is arranged on the internal peripheral edge of the linked magnet.

[0015] According to an optional characteristic of the invention, the positioning means is arranged on the external peripheral edge of the linked magnet.

[0016] According to an optional characteristic of the invention, the bonded magnet is made from a single piece.

[0017] This is a first embodiment of the rotor, which is particularly suitable for rotors of reduced diameter.

[0018] According to an optional characteristic of the invention, the linked magnet comprises a plurality of angular segments secured to each other.

[0019] This corresponds to a second embodiment in which the linked magnet is made in several parts, which here take the form of angular segments, the number of segments being able to vary from one rotor to another depending on the dimensions of the latter or even depending on a desired number of poles of the axial flux motor. Each angular segment is secured to the two angular segments which are adjoining it by the overmolded body.

[0020] According to an optional characteristic of the invention, the overmolded body extends between the angular segments.

[0021] The overmolded body is inserted between the angular segments and at least partially overlaps them, which allows them to be secured together. The overmolded body thus has a function of holding the angular segments together.

[0022] According to an optional characteristic of the invention, the positioning means is arranged between two neighboring angular segments.

[0023] Alternatively, the positioning means is arranged within a given angular segment.

[0024] According to an optional characteristic of the invention, the positioning means comprises at least one round hole and at least one oblong hole.

[0025] The round hole and the oblong hole are either half holes or full holes, that is, holes whose section defining the shape of the hole is closed. The round hole allows the centering of the bonded magnet in the injection mold relative to the motor shaft element, while the other hole allows angular adjustment of the position of the bonded magnet due to its oblong shape. The bonded magnet comprises, for example, at least two holes per angular segment.

[0026] The holes participate in the function of holding the bonded magnet when the overmolded body is injected into them.

[0027] According to an optional characteristic 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.

[0028] The portion of reduced thickness forms a step at the edge of the bonded magnet. It extends, depending on the embodiments, either from the internal peripheral edge, or from the external peripheral edge, or from both peripheral edges. The portion of reduced thickness facilitates the gripping of the overmolded body on the bonded magnet.

[0029] According to an optional characteristic of the invention, the bonded magnet has a central portion, between its internal peripheral edge and its external peripheral edge, the thickness of which is variable in at least one radial or orthoradial direction.

[0030] According to an optional characteristic of the invention, the central portion of the bonded magnet has a thickness which strictly increases from its internal peripheral edge to its external peripheral edge.

[0031] According to an optional characteristic of the invention, the central portion of the bonded magnet has, for a given radial dimension, a thickness of variable value around the periphery of the central portion.

[0032] These thickness values ​​are measured along the axial direction of the rotor. The central portion must be considered between the inner peripheral edge and the outer peripheral edge, and therefore not include the portion of reduced thickness which extends this central portion towards the inside of the rotor. In other words, the thickness of the bonded magnet is always increasing from the inner peripheral edge to its outer peripheral edge, with the exception of the portion of reduced thickness which may have a constant thickness. The variable value thickness of the bonded magnet around the periphery of the central portion is observed by measuring, along the axial direction of the rotor, the thickness of the bonded magnet at different points of a circle centered on the axis of the rotor and included between the inner peripheral edge and the outer peripheral edge.

[0033] Such thickness variations within the bonded magnet make it possible to limit torque ripple phenomena.

[0034] According to an optional characteristic of the invention, the positioning means is carried by the portion of reduced thickness.

[0035] According to an optional characteristic of the invention, the portion of reduced thickness has at least one perforation.

[0036] The perforation carried by the portion of reduced thickness, like other holes arranged on the edges of the angular elements of the linked magnet, may in particular have the function of being filled by the material of the overmolded body, in order to increase and vary the contact surfaces between the linked magnet and the overmolded body and ensure transmission of forces from one to the other, rather than having the function of the relative positioning of the different components of the rotor.

[0037] According to an optional characteristic of the invention, the overmolded body is made of plastic.

[0038] The overmolded body is a non-magnetic structure. It is for example made of a thermoplastic such as polyamide, which has properties that facilitate its injection.

[0039] The invention further relates to an axial flux motor, comprising at least one stator and one rotor as mentioned previously, the stator and the rotor being arranged successively along the axis of rotation of the rotor.

[0040] The stator and the rotor are superimposed on each other along the axis of rotation of the rotor and they both have a center which is inscribed in the axis of rotation of the rotor. If necessary, the motor shaft element comprises orifices participating in ensuring the transmission of the torque as well as in resisting the forces exerted during the rotation at high speed of the rotor.

[0041] According to an optional characteristic of the invention, the axial flux motor comprises a second stator, the rotor being arranged between the two stators.

[0042] The invention further relates to a method for obtaining a rotor as mentioned previously, comprising a step of positioning the bonded magnet within a mold, and a step of overmolding the overmolded body onto the bonded magnet.

[0043] The positioning step corresponds either to the injection of the bonded magnet into the mold, or to the production of the bonded magnet remotely and then to its positioning within said mold. During this positioning step, the bonded magnet is either in a unitary form or in the form of angular segments. Following the positioning step, the overmolded body is injected into the mold, at least partially covering the bonded magnet and the motor shaft element.

[0044] According to an optional characteristic of the invention, the positioning step is carried out using the positioning means.

[0045] Other characteristics, details and advantages of the invention will emerge more clearly on reading the description which follows on the one hand, and examples of embodiment given for informational and non-limiting purposes with reference to the appended drawings on the other hand, in which:

[0046] [Fig-1] illustrates, schematically, an axial flux electric motor according to the invention, in a non-limiting arrangement comprising a first stator, a second stator and a rotor disposed between the first stator and the second stator;

[0047] [Fig.2] illustrates, schematically, a first embodiment of the rotor of [Fig.l], this rotor comprising an overmolded body and a magnetic element made from a single piece;

[0048] [Fig.3] illustrates, schematically, a first variant of a second embodiment of the rotor of [Fig.l], the magnetic element of the rotor being composed of several segments;

[0049] [Fig.4] illustrates, schematically, a second variant of the second embodiment of the rotor of [Fig.l], the magnetic element of the rotor being composed of several segments;

[0050] [Fig.5] illustrates, schematically, the magnetic element of the first variant embodiment of the second embodiment of [Fig.3], here without overmolded body;

[0051] [Fig.6] illustrates, schematically, the second variant embodiment of the second embodiment of [Fig.4], here without overmolded body;

[0052] [Fig.7] illustrates, schematically and in isolation, one of the segments of the first variant embodiment of figures 3 and 5;

[0053] [Fig.8] illustrates, schematically and in isolation, one of the segments of the second variant embodiment of figures 4 and 6.

[0054] The features, variants and different embodiments of the invention may be combined with each other, in various combinations, provided that they are not incompatible or mutually exclusive. In particular, variants of the invention may be imagined comprising only a selection of features described below in isolation from the other features described, if this selection of features is sufficient to confer a technical advantage and / or to differentiate the invention from the prior art.

[0055] In the figures, the elements common to several figures retain the same reference.

[0056] In the detailed description which follows, the terms “longitudinal”, “transverse” and “vertical” specify the orientation of the rotor for an axial flux motor according to the invention, with the longitudinal axis corresponding to the axis of rotation of the axial flux motor, these terms referring to a reference L, V, T illustrated in the figures.

[0057] [Fig.l] thus illustrates, schematically, an axial flux motor 1 according to the invention, intended to equip an electric or hybrid motor vehicle. The axial flux motor 1 comprises a casing 2 which contains 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 so that the first stator 6A and the second stator 6B are arranged on either side of the rotor 4 in a longitudinal direction L in which an axis of rotation of the rotor 4 is inscribed. The rotor 4 and the stators 6 are respectively in the form of discs, a center of which is inscribed in the axis of rotation of the rotor 4.

[0058] A magnetic element of the rotor 4, which is a linked magnet 8, is arranged opposite a winding 10 of each of the stators 6, considering the longitudinal direction. The linked magnet 8 and the windings 10 are thus configured to allow the production of a magnetic field passing axially from the rotor to the stators.

[0059] The casing 2 is crossed, 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 level of the rotor 4, a hub 14 is interposed between the transmission shaft 12 and the rotor 4. The transmission shaft 12 like the hub 14 constitute motor shaft elements of the axial flux motor 1.

[0060] The rotor 4 according to the invention will now be described in detail in relation to FIGS. 2 to 8.

[0061] [Fig.2] illustrates a first embodiment of the rotor while a second embodiment of the rotor is shown in Figures 3 to 8. Figures 3, 5 and 7 detail a first variant of the second embodiment and Figures 4, 6 and 8 a second variant of this second embodiment. Unless otherwise stated, the characteristics described in relation to one of these embodiments or to one of these variants may apply, mutatis mutandis, to another embodiment or to another variant.

[0062] The rotor according to the invention comprises in particular a linked magnet 8 and an overmolded body 36.

[0063] The bonded magnet 8 of the rotor 4 is made of a material formed from a mixture of polymer and rare earths, for example an alloy of neodymium, iron and boron. The bonded magnet is obtained by injection into a mold, whether in the same mold as that into which the polymer is then injected or in a separate mold. The bonded magnet 8 is annular in shape and is arranged around the hub 14, at a non-zero distance therefrom.

[0064] The bonded magnet 8 is delimited radially, that is to say in a vertical-transverse plane perpendicular to the longitudinal direction L and to the axis of rotation of the rotor 4, by an internal peripheral edge 16 and an external peripheral edge 18. The internal peripheral edge 16 corresponds substantially to the smallest diameter of the bonded magnet 8 while the external peripheral edge 18 corresponds substantially to its largest diameter. Furthermore, the internal peripheral edge 16 is the portion of the bonded magnet 8 closest to the hub 14, forming the motor shaft element, the external peripheral edge 18 being the portion furthest from this hub 14.

[0065] The internal peripheral edge 16 and the peripheral edge 18 are joined to each other by a first face 20 and a second face 22 of the linked magnet 8. The first face 20 and the second face 22 are opposite in the longitudinal direction L. The first face 20 is for example opposite the first stator 6A and the second face 22 is opposite the second stator 6B.

[0066] The bonded magnet 8 is a unitary element in the first embodiment of [Fig. 2], that is to say that it is made in one piece. On the contrary, for the second embodiment of Figures 3 to 8, the bonded magnet 8 comprises a plurality of angular segments 24. An angular segment 24 corresponding to the first variant of Figures 3 and 5 is shown in isolation in [Fig. 7], and an angular segment 24 corresponding to the second variant of Figures 4 and 6 is shown in isolation in [Fig. 8]. These angular segments 24 extend from the inner peripheral edge 16 to the outer peripheral edge 18. Due to the annular shape of the bonded magnet 8, the angular segments 24 have a dimension measured along the inner peripheral edge 16 that is smaller than a dimension measured along the outer peripheral edge 18.

[0067] In Figures 5 and 7 representing 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 to a reduction in a thickness of the angular segment 24 of the bonded magnet 8 measured along the longitudinal direction L. In other words, the grooves 26 constitute hollows arranged radially in at least one of the faces 20, 22 of the bonded magnet 8, here both in the first face 20 and in the second face 22.

[0068] The groove 26 of a given angular segment 24 is arranged substantially in the middle of this angular segment 24. In other words, each angular segment comprises a first side 28 facing an adjoining first angular segment 24 and a second side 30 facing an adjoining second angular segment 24, this groove 26 being substantially equidistant from the first side 28 and the second side 30. The first side 28 and the second side 30 correspond to walls of the angular segment 24 which connect on the one hand the internal peripheral edge 16 and the external peripheral edge 18, and on the other hand the first face 20 and the second face 22. The sides 28, 30 delimit the angular segment 24 in a plane perpendicular to the first face 20 and to the second face 22 of the linked magnet 8.

[0069] In Figures 6 and 8, the angular segments 24 of the bonded magnet 8 according to the second embodiment variant are devoid of such radial grooves 26 extending from the inner peripheral edge 16 to the outer peripheral edge 18. This results in a smaller angular dimension and therefore a number of angular elements necessary to form the periphery of the bonded magnet in the second embodiment variant which is more important than the number of angular elements required in the first embodiment variant.

[0070] Thus, as shown in the first variant of Figures 3 and 5, the linked magnet 8 comprises ten angular segments 24 whose dimensions are identical, while for the second variant of Figures 4 and 6 the linked magnet 8 is composed of twenty angular segments 24 with identical dimensions.

[0071] In [Fig.2], the unitary bonded magnet 8 according to the first embodiment is smooth, that is to say that its first face 20 and its second face 22 are substantially flat, but one could however envisage a unitary bonded magnet 8 provided with grooves 26 as described above.

[0072] The bonded magnet 8 has through holes 32 at its grooves 26. As is particularly visible in [Fig.7], these through holes 32 are of increasing size from the inner peripheral edge 16 to the outer peripheral edge 18. Each groove 26 here has at least one round hole 32A and one oblong hole 32B. The round hole 32A is arranged in the vicinity of the inner peripheral edge 16 and the oblong hole 32B is arranged in the vicinity of the outer peripheral edge 18, without however this arrangement being limiting of the invention.

[0073] Each of the first side 28 and the second side 30 further has a half hole 32, so that when the angular segments 24 are placed side by side to give its annular shape to the linked magnet 8, the half holes 32 of two adjoining angular segments form a substantially complete hole 32.

[0074] All or part of the holes are intended to be filled with polymer material forming the overmolded body, which has the effect of increasing the contact surface between the bonded magnet and the overmolded body, and of ensuring that these contact surfaces are oriented in different directions to ensure that the forces and rotational torques are properly transmitted when the rotor is stressed. Polymer material is here arranged between two adjoining angular elements, which has the effect of ensuring good orthoradial force transmission.

[0075] In this context, it is advantageous that the through holes 32 are of increasing size from the inner peripheral edge 16 to the outer peripheral edge 18 since this makes it possible to ensure a greater quantity of polymer material interposed between the adjoining angular segments at a distance from the hub, where more stresses due to centrifugal force are exerted during rotation of the axial flux motor.

[0076] In the second variant of the second embodiment illustrated in figures 4, 6 and 8, the bonded magnet 8 has a portion of reduced thickness 34 at at least one of its peripheral edges 16, 18. Here, the bonded magnet 8 has such a portion of reduced thickness 34 for each of its peripheral edges 16, 18, with a first portion of reduced thickness 34A along the inner peripheral edge 16 and a second portion of reduced thickness 34B along the outer peripheral edge 18. The portion of reduced thickness 34 extends substantially equidistant from the first face 20 and the second face 22, as is particularly visible in [Fig.8].

[0077] The first portion of reduced thickness 34A has a through hole 32, here a round hole 32A, which is formed in a projecting zone of the first portion of reduced thickness 34A so as to form a hole whose section is closed. The second portion of reduced thickness 34B has a through hole 32, here an oblong hole 32B, which is formed on the edge of the second portion of reduced thickness so as to form an open hole. However, without departing from the scope of the invention, embodiments could be envisaged in which the first portion of reduced thickness 34A would carry the oblong hole 32B and the second portion of reduced thickness 34B would have a round hole 32A, and in which it is the first portion of reduced thickness 34A which would carry an open hole, or half-hole.

[0078] It is notable that these holes also make it possible to increase the contact surface between the polymer material and the bonded magnet and make this contact surface less smooth and uniform in order to increase the capacity for transmitting the forces of the magnet bonded to the overmolded body.

[0079] As mentioned previously, the rotor 4 according to the invention comprises an overmolded body 36. This overmolded body 36 is made of thermoplastic polymer, in particular polyamide, and it is obtained by an operation of overmolding the polymer onto the bonded magnet present in an injection mold of the rotor.

[0080] The overmolded body 36 is arranged at least between the linked magnet 8 and one of the motor shaft elements, here between the linked magnet 8 and the hub 14. The overmolded body 36 more precisely comprises a first part 38 arranged along the inner peripheral edge 16, between this inner peripheral edge 16 and the motor shaft element, and a second part 40 arranged along the outer peripheral edge 18. The first part 38 extends radially from the hub 14 to the inner peripheral edge 16, engaging these two elements, while the second part 40 surrounds the outer peripheral edge 18. Where appropriate, the overmolded body 36 is engaged on the portion of reduced thickness 34 and covers it both at the level of the first face 20 and the second face 22.

[0081] In the first embodiment of [Fig.2], that is to say for a unitary bonded magnet 8, that is to say made in one piece, and without grooves 26, the first part 38 and the second part 40 are distinct and physically separated from each other by the bonded magnet 8. On the contrary, in the embodiments for which the bonded magnet 8 is composed of a plurality of angular segments 24, the first part 38 and the second part 40 of the overmolded body 36 are connected to each other by branches 42 of this overmolded body 36. In other words, a branch 42 of the overmolded body 36 extends between two adjoining angular segments 24. Similarly, in the embodiments for which the linked magnet 8 comprises grooves 26, the first part 38 and the second part 40 are connected to each other by at least one branch 42, that is to say that a branch 42 of the overmolded body 36 extends within a groove 26. Where appropriate, branches 42 may extend on the one hand in the grooves 26 and on the other hand between two adjoining angular segments 24.

[0082] As is illustrated in particular in Figures 5 and 6, the hub 14 is equipped with at least one orifice 43, here with a plurality of orifices 43. Each orifice 43 passes through the hub 14 from one side to the other in the longitudinal direction L. The overmolded body 36 extends through these orifices 43.

[0083] The rotor 4 has at least one positioning means 44 passing through both the linked magnet 8 and the overmolded body 36. The positioning means 44 comprises for example one of the through holes 32 mentioned previously in relation to the linked magnet 8, as well as an opening 46 formed in the overmolded body 36 opposite said through hole 32. The overmolded body 36 extends within the through holes 32 which do not participate in forming a positioning means 44.

[0084] As illustrated in the first embodiment of [Fig.2], the rotor 4 equipped with a unitary linked magnet 8 comprises two positioning means 44 arranged on either side of the hub 14, here diametrically opposed. Each positioning means 44 here comprises one of the through holes 32 arranged on the first portion of reduced thickness 34, that is to say at the internal peripheral edge, and an opening 46 passing through the overmolded body 36 opposite said through hole 32. Although this is not shown here, the through holes 32 participating in the positioning means 44 of the rotor 4 could alternatively be arranged on the second portion of reduced thickness 34B, that is to say at the external peripheral edge 18.

[0085] For embodiments in which the unitary bonded magnet 8 has grooves 26, the rotor 4 could otherwise comprise two positioning means 44 each arranged on a groove 26. For example, a first positioning means 44 would comprise on the one hand one of the through holes 32 arranged on a given groove 26 closest to the outer peripheral edge 18 and on the other hand an opening 46 arranged opposite it within the overmolded body 36, and a second positioning means 44 would comprise on the one hand one of the through holes 32 arranged on a groove 26 radially opposite the given groove 26 relative to the axis of rotation of the rotor 4, this through hole 32 being arranged closest to the outer peripheral edge 18, and on the other hand an opening 46 arranged opposite it within the overmolded body 36.

[0086] For the second embodiment, that is to say in the presence of a plurality of angular segments 24 forming the linked magnet 8, the rotor 4 has at least two positioning means 44 per angular segment 24.

[0087] In the first variant of the second embodiment shown in Figures 3, 5 and 7, the rotor 4 in its entirety comprises twenty positioning means 44. Each angular segment 24 more particularly comprises two positioning means 44 arranged in its groove 26. There is thus, for each angular segment 24, a first positioning means 44 involving on the one hand a through hole 32 arranged in a given groove 26 in the vicinity of the internal peripheral edge 16 and on the other hand an opening 46 arranged opposite it in the overmolded body 36, as well as a second positioning means 44 involving on the one hand a through hole 32 arranged in the same groove 26 in the vicinity of the external peripheral edge 18 and on the other hand an opening 46 arranged opposite it in the overmolded body 36.

[0088] In the second variant of the second embodiment illustrated in Figures 4, 6 and 8, the rotor 4 comprises in all forty positioning means 44, that is to say two for each of the angular segments 24. More precisely, each angular segment 24 comprises a first positioning means 44 composed on the one hand of the through hole 32 arranged on the first portion of reduced thickness 34A, therefore on the internal peripheral edge 16, and on the other hand the corresponding opening 46 formed in the overmolded body 36, as well as a second positioning means 44 composed on the one hand of the through hole 32 arranged on the second portion of reduced thickness 34B, in other words on the external peripheral edge 18, and on the other hand the corresponding opening 46 formed in the overmolded body 36.

[0089] In other words, it results that there are at least two positioning means per unit element of linked magnet. In these at least two positioning means, there are in particular a positioning means with a through hole 32 of round shape which ensures a first fixed positioning point and a positioning means with a through hole of oblong shape which ensures a second positioning point allowing an adjustment of the position.

[0090] It is understood that each opening 46 provided in the overmolded body has a corresponding through hole 32 provided in the bonded magnet and that each opening 46 results either from the presence of a pin engaged in the corresponding through hole 32 to hold the bonded magnet in position in the mold during the injection of polymer to carry out the overmolding of the overmolded body around the bonded magnet, or from the presence of a mold closing pad.

[0091] A method for obtaining the rotor 4 according to the invention will now be detailed. This method of obtaining comprises a placement step during which an element of the rotor motor shaft 4, for example the hub 14, is placed within a rotor injection mold. The position of the hub 14 forms a position reference for the subsequent positioning of the linked magnet and this position reference can be ensured by means of a pin associated with the mold.

[0092] The production method also comprises a positioning step during which the bonded magnet 8 is arranged within the injection mold of the rotor. During this positioning step, the bonded magnet 8 is, depending on the embodiments, either injected directly into the injection mold of the rotor which will then be used to inject the polymer to be overmolded, or produced at another manufacturing station, in particular by injection into another mold, then arranged in solid form within the injection mold of the rotor. It is understood that in the case where the bonded magnet 8 is injected directly into the injection mold of the rotor, one or more drawers are provided to simulate the presence of the polymer, this drawer then being removed when it is a question of injecting the polymer.

[0093] When the bonded magnet 8 is arranged in the mold in solid form, the positioning step involves the through holes 32 of the bonded magnet 8. The latter is thus correctly positioned within the mold by sliding pins of the mold through these through holes 32. The cooperation of the through holes 32 and the pins makes it possible to position the bonded magnet 8 relative to the motor shaft element, where appropriate the hub 14, which is already placed in the mold. For example, in the presence of a round hole 32A and an oblong hole 32B, one of these two through holes 32 makes it possible to center the bonded magnet 8 and the other allows for adjustment of the positioning.

[0094] Once the motor shaft element and the bonded magnet 8 are suitably arranged within the mold, the production method comprises an overmolding step during which the overmolded body 36 is overmolded in the mold so as to connect the motor shaft element and the bonded magnet. The polymer material chosen to form the overmolded body 36 then penetrates into the orifices of the hub 14 as well as into all the through holes 32 of the bonded magnet 8 which are not crossed by pins of the mold, and it forms the first part at the internal peripheral edge 16 and the second part at the external peripheral edge 18. When the bonded magnet 8 has portions of reduced thickness 34, the polymer material of the overmolded body covers them.Similarly, for the embodiments in which the bonded magnet 8 has grooves 26, the polymer material of the overmolded body fills them, and if the bonded magnet 8 comprises angular segments 24 it is inserted between these angular segments 24 to form the branches 42 participating in securing the adjoining angular segments.

[0095] The present invention thus provides a rotor for an axial flux electric machine comprising a bonded magnet and an overmolded body, the use of such an overmolded body fa- encouraging a process for obtaining the rotor.

[0096] The present invention cannot, however, be limited to the means and configurations described and illustrated here and it also extends to any equivalent means and configuration as well as to any technically operative combination of such means.

Claims

Claims

1. Rotor (4) for axial flux motor (1) comprising a motor shaft element participating in defining an axis of rotation of the rotor (4), a magnetic element arranged around the motor shaft element, characterized in that the magnetic element is an annular bonded magnet (8) and in that the rotor (4) comprises an overmolded body (36) arranged at least between the bonded magnet (8) and the motor shaft element.

2. Rotor (4) according to the preceding claim, in which the bonded magnet (8) extends radially between an inner peripheral edge (16) and an outer peripheral edge (18), the overmolded body (36) being arranged at least within the inner peripheral edge (16), engaged on the bonded magnet (8) and the motor shaft element, and around the outer peripheral edge (18).

3. Rotor (4) according to any one of the preceding claims, having at least one positioning means (44) passing through the bonded magnet (8) and the overmolded body (36).

4. Rotor (4) according to the preceding claim in combination with claim 2, wherein the positioning means (44) is arranged on the inner (16) or outer (18) peripheral edge of the bonded magnet (8).

5. Rotor (4) according to any one of the preceding claims, in which the bonded magnet (8) is made in one piece.

6. Rotor (4) according to any one of claims 1 to 5, in which the linked magnet (8) comprises a plurality of angular segments (24) secured to each other.

7. Rotor (4) according to the preceding claim, in which the overmolded body (36) extends between the angular segments (24).

8. Rotor (4) according to the preceding claim in combination with claim 3, wherein the positioning means (44) is arranged between two neighboring angular segments (24).

9. A rotor (4) according to any preceding claim in combination with claim 2, wherein the bonded magnet (8) has 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).

10. Rotor (4) according to any one of the preceding claims in combination with claim 2, in which the bonded magnet (8) has a central portion, between its internal peripheral edge (16) and its external peripheral edge (18), the thickness of which is variable according to at least one radial or orthoradial direction.

11. Rotor (4) according to any one of the preceding claims, in which the overmolded body (36) is made of plastic.

12. An axial flux motor (1), comprising at least one stator (6, 6A, 6B) and a rotor (4) according to any one of the preceding claims, the stator (6, 6A, 6B) and the rotor (4) being arranged successively along the axis of rotation of the rotor (4).

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