Method for fixing at least one magnet in a plastic carrier and rotor of an electric machine

Abstract

The invention relates to methods for fixing at least one magnet in a plastic carrier comprising the following steps: - providing a carrier body having a radially outer receiving space for the magnet, wherein the receiving space is open at its edges in an axial direction of the carrier body; - inserting the magnet into the receiving space; - placing a carrier cover axially onto the carrier body, wherein the carrier cover comes into contact with the carrier body at least at one or more predetermined connection points on a surface of the carrier body facing the carrier cover; - placing a sonotrode axially onto a contact surface of the carrier cover facing away from the connection points, wherein the sonotrode, in the placed state, has an initial axial distance to a region of the carrier cover covering the receiving space;- Welding of the carrier cover at the connection points with the carrier base body by supplying energy via the sonotrode, whereby the sonotrode together with the contact surface and the carrier base body are moved towards each other so that the initial distance in the axial direction is bridged.;

Description

The present invention relates to a method for fixing at least one magnet in a plastic carrier, in particular for the rotor of an electric machine, for example an electric motor, and to a rotor of an electric machine, in particular an electric motor.In electric machines, for example in electric motors, the rotor magnet or magnets must be suitably fixed in the magnet carrier, which is generally made of plastic. In principle, injection molding of the magnet or magnets is possible, which, however, is associated with high production costs and the risk of cracks forming. Particularly in the case of comparatively small quantities, overmolding is not considered for economic reasons. A further possibility of fixing is to glue the magnet or magnets in the plastic carrier. However, such an adhesion process is not sufficiently reliable.The object of the present invention is to specify a method for fixing at least one magnet in a plastic carrier, in particular a rotor of an electric machine, for example an electric motor, with which the fixing is achieved cost-effectively and reliably and the risk of cracking in the plastic carrier is reduced. Furthermore, a rotor of an electric machine with one or more appropriately fixed magnets is to be specified.The object according to the invention is achieved by a method comprising the steps of claim 1. Claim 15 specifies a rotor of an electric machine embodied according to the invention. Advantageous and particularly expedient embodiments of the invention are described in the dependent claims.The method according to the invention for fixing at least one magnet in a plastic carrier, for example a rotor of an electric machine, in particular an electric motor, has the following steps:providing a carrier base body which has a radially outer receiving space for the at least one magnet, wherein the receiving space is open at the edge in an axial direction and preferably also in the radial direction of the carrier base body;introducing the at least one magnet into the receiving space, for example by joining the carrier base body and the at least one magnet in the axial direction;placing a carrier cover in the axial direction onto the carrier base body, wherein the carrier cover comes into contact with the carrier base body at least at one or more predetermined connection points on a surface of the carrier base body facing the carrier cover;placing a sonotrode in the axial direction onto a contact surface of the carrier cover facing away from the connection points, wherein the sonotrode in the placed state has an initial distance in the axial direction from a region of the carrier cover covering the receiving space;welding the carrier cover at the connection points to the carrier base body by supplying energy by means of the sonotrode, wherein the sonotrode together with the contact surface and the carrier base body are moved towards one another, such that the initial distance in the axial direction is bridged.According to one embodiment of the invention, individual magnets are fixed to the plastic carrier, in particular at a distance from one another, for example one behind the other in the circumferential direction about the axial direction. According to an alternative embodiment, a single magnet is fixed to the plastic carrier, wherein the single magnet preferably has different poles. Finally, it is also possible to fix a magnet body with a plurality of magnets, in particular for forming a magnet with at least two poles, to the plastic carrier.Preferably, the initial distance in the axial direction between the sonotrode and the region of the carrier cover covering the receiving space is bridged at least partially by bending and / or deforming the region of the carrier cover covering the receiving space. In this case, the region deflects in particular elastically, advantageously with the application of a permanent prestress to the at least one magnet in the receiving space.The bending and / or deformation is preferably achieved in that, when the carrier cover is placed on the carrier base body in the axial direction or when the sonotrode and the carrier base body are moved towards one another, the carrier cover comes to bear against the at least one magnet in the axial direction.For example, the carrier cover has at least one projection in the region covering the receiving space, which projection comes to bear against the at least one magnet.In order to produce the initial distance provided according to the invention in the axial direction between the sonotrode and the region of the carrier cover covering the receiving space, the sonotrode can have a stepped working surface facing the carrier cover, comprising a protruding first surface region and a second surface region which is set back relative to the first surface region in the axial direction when the sonotrode is placed on the carrier cover in the mounted state, wherein the region of the carrier cover covering the receiving space is pressed against the second surface region during bending and / or deformation in the axial direction.Additionally or alternatively, the region of the carrier cover covering the receiving space can be set back in the axial direction with respect to the contact surface of the carrier cover.The one or more connection points at which the carrier cover is welded by means of the sonotrode or by means of the energy input through the sonotrode can preferably be tapered on its surface, so that at least one tip is formed. This allows simple and reliable welding.Particularly preferably, after bridging the initial distance between the sonotrode and the region of the carrier cover covering the receiving space, the region of the carrier cover covering the receiving space, in particular the at least one protrusion, is softened and plastically deformed by energy input by means of the sonotrode. This makes it possible to achieve a secure pressing of the at least one magnet in the axial direction against the carrier base body.Preferably, when the sonotrode is moved towards one another together with the contact surface and the carrier base body, the carrier cover is moved overall towards the carrier base body with the exception of the region covering the receiving space. This also includes the possibility of the active movement of the carrier base body onto the carrier cover.Preferably, the carrier cover and the carrier base body are guided against one another during the movement towards one another radially and in particular in the circumferential direction about the axial direction, for example by sliding surfaces which bear against one another accordingly. This ensures a desired mutual alignment of the carrier cover and carrier base body.According to one embodiment of the invention, the receiving space extends in the circumferential direction around the axial direction along the entire carrier base body and is in particular hollow cylindrical. Thus, for example, a hollow cylindrical magnet body, in which the at least one magnet is arranged or in which a plurality of magnets are arranged, can be introduced into the hollow cylindrical receiving space in the axial direction. Preferably, the magnetic body is held in the receiving space in a rotationally fixed manner about the axial direction after its introduction and fixing. Such a rotation prevention can be achieved, for example, by cooperating projections and recesses in the magnetic body and in the carrier base body.The carrier cover can preferably have a core region with which, when placed on the carrier base body, it dips into an, in particular cylindrical, opening in the carrier base body. The core region can abut radially on the inside on the carrier base body, in particular with individual radial projections and / or a press fit.A rotor according to the invention of an electric machine, in particular of an electric motor, has a plastic carrier and at least one magnet, wherein the at least one magnet has been fixed to the plastic carrier by a method according to the invention. This fixation according to the invention can preferably be detected by a prestress between the region of the carrier cover covering the receiving space and the magnet and, according to a preferred embodiment, by the welded state of the carrier cover at the one or more connection points of the carrier base body, optionally supplemented by the plastically deformed projections in the region of the carrier cover covering the receiving space, which projections bear against the at least one magnet.The invention is to be described below by way of example with reference to exemplary embodiments and the figures.The following are shown: FIG. 1 shows a rotor according to the invention in a three-dimensional plan view; FIG. 2 is an axial section through the rotor from FIG. 1 ; FIG. 3 shows the carrier base body and the carrier cover of the plastic carrier of the rotor from FIG. 1 in an exploded illustration; FIG. 4 shows the rotor during the fixing of the magnet according to the method according to the invention after the support cover has been placed on the support base body; FIG. 5 shows the rotor according to FIG. 4 at the end of the method according to the invention after the welding of the carrier cover to the carrier base body; FIG. 6 shows an alternative configuration of the sonotrode and the contact surface of the carrier cover in the method state analogous to FIG. 4 FIG. 7 shows the alternative configuration of the sonotrode and the contact surface of the carrier cover in the method state analogous to FIG. 5 ; FIG. 8 shows a particular bearing configuration of a rotor according to the invention with three bearing points; FIG. 9 shows the rotor from FIG. 8 in an exploded illustration.FIG. 1 shows a rotor 15 of an electric machine, for example an electric motor for an actuator, which rotor is produced by the method according to the invention. The rotor 15 has a plastic carrier 1 which carries a hollow cylindrical magnet 10. The magnet 10 is clamped in an axial direction 4 of the plastic carrier 1 between a carrier base body 2 and a carrier cover 5 of the plastic carrier 1.As can be seen in particular from FIG. 2, which shows an axial section along the axial direction 4 through the rotor 15 from FIG. 1, the carrier base body 2 has a radially outer receiving space 3, which is open at the edge not only radially outwards but also in the axial direction 4. The magnet 10 is inserted into this receiving space 3 in such a way that the magnet 10 encloses the carrier base body 2 concentrically with respect to the axial direction 4.The carrier base body 2 is pot-shaped at its axially outer end assigned to the carrier cover 5, and the carrier cover 5 is inserted with a core region 18 flush into the opening 19 of the carrier base body 2 and covers the hollow cylindrical axial extension of the carrier base body 2 with a substantially disk-shaped flange adjoining radially outwards, and the receiving space 3 with a region 7.With the disk-shaped flange, the carrier cover 5 is welded to the carrier base body 2 at a connection point 6 of the carrier base body 2. As can be seen from FIG. 3, in the exemplary embodiment shown, the connecting point 6 is circular and corresponds to a roof-shaped, pointed end region on the end face of the hollow-cylindrical axial extension of the pot-shaped axial end of the carrier base body 2.According to one embodiment of the invention, the hollow cylindrical axial extension for forming the pot-shaped region could also be configured segmented over the circumference around the axial direction 4 in order to reduce a press-in force for inserting the carrier cover 5. Additionally or alternatively, individual contact surfaces spaced apart from one another in the circumferential direction about the axial direction 4 could also be provided between the carrier base body 2 and the carrier cover 5.Referring again to FIG. 2, it can be seen that the magnet 10 is provided in or in the form of a hollow cylindrical magnet body 14, wherein the magnet 10 has at least two different poles arranged one behind the other in the circumferential direction about the axial direction 4. Alternatively, individual magnets 10 spaced apart from one another in the circumferential direction, in particular with polarity oriented differently from one another, could also be provided in the magnet body 14.The carrier cover 5 preferably, as can be seen in turn in particular from FIG. 3, in which the carrier cover 5 is shown with its surface placed on the carrier base body 2 in the assembled state upwards, i.e. directed away from the carrier base body 2, has a projection 9 which is likewise in the form of a circular ring here, with which the carrier cover 5 is braced in the axial direction 4 against the magnet 10 or the magnet body 14 when it has been fixed according to the invention. Instead of a single projection 9, a plurality of projections 9 spaced apart from one another in the circumferential direction about the axial direction 4 could also be provided.The core region 18 has radial projections 20 with which it bears radially on the inside in the carrier base body 2 in the state in which it is inserted into the carrier base body 2. For example, the core region 18 is inserted into the carrier base body 2 with a press fit. Such a press fit can be produced particularly easily with the radial projections 20. However, this is also possible without such radial projections 20.According to an embodiment which is not shown, the radial projections 20 can engage in corresponding pockets in the carrier base body 2 in the mounted state in order to produce a rotation prevention between the carrier cover 5 and the carrier base body 2. The anti-rotation means can, however, also be achieved by the press fit described.The projection 9 is likewise conically tapered in the axial direction 4 and has been softened and plastically deformed after the welding of the carrier cover 5 to the connection point 6 of the carrier base body 2, so that it bears on the magnet 10 or the magnet body 14 without play and reliably in the axial direction 4, see again FIG. 2.The region 7 of the carrier cover 5 covering the receiving space 3 in the axial direction 4 can be bent at least slightly rearward in the axial direction 4 compared to the remaining region, i.e. here the central region, i.e. in the direction away from the receiving space 3, and preferably bear against the magnet 10 or the magnet body 14 with an elastic prestress.As can be seen from FIG. 2 and also from FIG. 3, the carrier base body 2 has drivers 16 protruding in the axial direction 4 into the receiving space 3, which engage in diametrically opposed recesses 17 of the magnet 10 or magnet body 14 in the axial direction 4 in order to produce a positively rotationally fixed connection between the carrier base body 2 and the magnet 10 or the magnet body 14. The carrier cover 5 ensures with its clamping force exerted on the magnet 10 or the magnet body 14 in the axial direction 4 that the magnet body 14 is held securely with its recesses 17 on the drivers 16.These drivers 16 are optional, however. A frictional connection between the carrier base body 2 and the magnet 2 can additionally or alternatively establish a rotationally fixed connection between the carrier base body 2 and the magnet 2.The fixing of the magnet 10 to the plastic carrier 1 according to an exemplary embodiment of the method according to the invention is to be illustrated below with reference to FIGS. 4 and 5.FIG. 4 shows that the carrier base body 2 has been provided and the magnet 10, here in the form of the magnet body 14, has been introduced into the receiving space 3. This is done by fitting the magnet 10 over the carrier base body 2 in the axial direction 4.The carrier cover 5 was then placed onto the carrier base body 2 in the axial direction 4, so that it comes to rest against the carrier base body 2 at the connection point 6. This is illustrated in FIG. 4. As explained, in particular a press fit can be produced between the core region 18 and the carrier base body 2.Subsequently, a sonotrode 11 is placed in the axial direction 4 on the contact surface 8 of the carrier cover 5 facing away from the connection point 6. The sonotrode 11 has a stepped working surface 13 such that it initially comes to bear with the contact surface 8 by way of the step projecting in the axial direction 4 in the direction of the carrier cover 5, wherein the step set back for this purpose in the axial direction 4 has an initial distance 12 in the axial direction 4 from the region 7 of the carrier cover 5 or from the contact surface 8. The initially abutting surface region of the working surface 13 of the sonotrode 11 is referred to as the first surface region 13.1, and the region arranged at the initial distance 12 from the carrier cover 5 is referred to as the second surface region 13.2.If the sonotrode 11 is now energized and as a result introduces energy into the carrier cover 5 via the first surface region 13.1, the carrier cover 5 is welded at the connection point 6, which is directly opposite the first surface region 13.1 of the working surface 13 of the sonotrode 11 in the axial direction 4. In this case, the carrier cover 5 moves in the direction of the carrier base body 2, wherein its central region, i.e. the core region 18, dips further into the carrier base body 2. During this movement, the carrier cover 5 moves as a whole until the projection 9 abuts the magnet 10 or the magnet body 14. If the carrier cover 5 is now moved further in the direction of the carrier base body 2, the region 7 deflects away from the magnetic body 14 in the axial direction 4 until it comes to rest against the second surface region 13.2 of the working surface 13 of the sonotrode 11. In the resting state, energy is introduced into the region 7 with the sonotrode 11, so that the projection 9 is softened and plastically deforms on the magnet body 14 or the magnet 10. The sonotrode 11 can be switched off after a defined welding path has been reached.A tension force in the axial direction 4 between the region 7 and the magnet 10 or the magnet body 14 can be maintained if desired.Thus, the method for fixing the magnet 10 is completed.In Figures 6 and 7 an alternative embodiment is shown which operates according to the same principle. In this case, the first surface region 13.1 and the second surface region 13.2 of the working surface 13 of the sonotrode 11 are positioned within a common radial plane, and the region 7 of the carrier cover 5 directly opposite the second surface region 13.2 in the axial direction 4 and covering the receiving space 3 is offset back in the direction of the receiving space 3 with respect to the section of the carrier cover 5 with the contact surface 8 opposite the first surface region 13.1. This also achieves an initial distance 12 when the sonotrode 11 is placed on the contact surface 8 between the second surface region 13.2 and the region 7.The embodiments according to FIGS. 4 and 5, and also 6 and 7 can be combined, i.e. the stepped sonotrode 11 can be placed on a stepped surface of the carrier cover 5 in order to make the steps smaller in each case or to achieve a greater initial distance 12.FIG. 8 shows an axial section of a rotor 15 designed according to the invention with three bearing points 21, 22, 23. FIG. 9 shows the rotor 15 in an exploded view. The other components are provided with the same reference numerals as in the previous figures.The first bearing point 21 is located in the region of a first axial end of the rotor 15, which is formed by the axial end of the carrier base body 2 facing away from the carrier cover 5 and, for example, as shown in the figures, has an output pinion, for example, if it is the rotor 15 of an electric motor. The second bearing point 22 is located in the region of the second axial end of the rotor 15 and is formed by the carrier cover 5. The third bearing point 23 is located axially between the first bearing point 21 and the second bearing point 22 and has a contact body 25 which is radially prestressed by a leaf spring 24.All bearing points 21, 22, 23 are provided within an axial bore 26 which extends along the axial direction 4 through the entire rotor 15, that is to say the carrier base body 2 and the carrier cover 5 axially adjoining the latter. The bearing points 21, 22, 23 each form radially outer bearing surfaces for a shaft or axle (not shown) inserted through the axial bore 26, the first and second bearing points 21, 22 are correspondingly supported by a radially inner surface of the carrier base body 2 or of the carrier cover 5, and the third bearing point 23 is supported by a radially inwardly directed surface of the contact body 25 which is supported elastically resilient radially outwards against a radially inner surface of the carrier base body 2 via the leaf spring 24.List of reference characters1 Plastic carrier 2 Carrier base body 3 Receiving space 4 Axial direction 5 Carrier cover 6 Connecting point 7 Region 8 Contact surface 9 Projection 10 Magnet 11 Sonotrode 12 Distance 13 Working surface 13.1 First surface region 13.2 Second surface region 14 Magnetic body 15 Rotor 16 Driver 17 Recess 18 Core region 19 Opening 20 Radial projection 21 First bearing point 22 Second bearing point 23 Third bearing point 24 Leaf spring 25 Contact body 26 Axial bore

Claims

Method for fixing at least one magnet (10) in a plastic carrier (1), having the following steps: - providing a carrier base body (2) which has a radially outer receiving space (3) for the at least one magnet (10), wherein the receiving space (3) is open at the edge in an axial direction (4) of the carrier base body (2); - introducing the at least one magnet (10) into the receiving space (3); - placing a carrier cover (5) in the axial direction (4) on the carrier base body (2), wherein the carrier cover (5) comes to bear against the carrier base body (2) at least at one or more predetermined connection points (6) on a surface of the carrier base body (2) facing the carrier cover (5); - placing a sonotrode (11) in the axial direction (4) on a contact surface (8) of the carrier cover (5) facing away from the connection points (6), wherein the sonotrode (11) in the placed state has an initial distance (12) in the axial direction (4) from a region (7) of the carrier cover (5) covering the receiving space (3); - welding the carrier cover (5) at the connection points (6) to the carrier base body (2) by supplying energy by means of the sonotrode (11), wherein the sonotrode (11) together with the contact surface (8) and the carrier base body (2) are moved towards one another, such that the initial distance (12) in the axial direction (4) is bridged.Method according to Claim 1, characterized in that the initial distance (12) is bridged at least partially by bending, in particular elastic bending, and / or deformation of the region (7) of the carrier cover (5) covering the receiving space (3).Method according to Claim 2, characterized in that, when the carrier cover (5) is placed on the carrier base body (2) in the axial direction (4) or when the sonotrode (11) and the carrier base body (2) are moved towards one another, the carrier cover (5) comes to bear against the at least one magnet (10) in the axial direction (4).Method according to claim 3, characterised in that the carrier cover (5) has, in the region covering the receiving space (3), at least one projection (9) which comes to bear against the at least one magnet (10).Method according to one of Claims 2 to 4, characterized in that the sonotrode (11) has a stepped working surface (13) facing the carrier cover (5), comprising a projecting first surface region (13.1) and a second surface region (13.2) which is set back relative to the first surface region (13.1) in the axial direction (4) when the sonotrode (11) is placed on, wherein the region (7) of the carrier cover (5) covering the receiving space (3) is pressed against the second surface region (13.2) during bending and / or deformation in the axial direction (4).Method according to one of Claims 2 to 5, characterized in that the region (7) of the carrier cover (5) covering the receiving space (3) is set back in the axial direction (4) with respect to the contact surface (8).Method according to one of claims 1 to 6, characterised in that the one or more connection points (6) is / are tapered on their surface.Method according to one of Claims 2 to 7, characterized in that, after bridging the initial spacing (12), the region (7) of the carrier cover (8) covering the receiving space (3), in particular its at least one projection (9), is softened and plastically deformed by energy input by means of the sonotrode (11).Method according to one of Claims 2 to 8, characterized in that, when the sonotrode (11) is moved towards one another together with the contact surface (8) and the carrier base body (2), the carrier cover (5) is moved overall towards the carrier base body (2), with the exception of the region (7) covering the receiving space (3).Method according to claim 9, characterised in that the carrier cover (5) and the carrier base body (2) are guided towards one another during the movement towards one another radially and in particular in the circumferential direction about the axial direction (4).Method according to one of Claims 1 to 10, characterized in that the receiving space (3) extends in the circumferential direction around the axial direction (4) along the entire carrier base body (2) and is in particular hollow-cylindrical.Method according to claim 11, characterised in that the at least one or more magnets (10) is / are arranged in a cylindrical magnet body (14) which is introduced into the hollow cylindrical receiving space (3).Method according to claim 12, characterised in that the magnetic body (14) is held in the receiving space (3) in a rotationally secure manner about the axial direction (4).Method according to one of Claims 1 to 13, characterized in that the carrier cover (5) has a core region (18), with which, when it is placed on the carrier base body (2), it dips into an opening (19) in the carrier base body (2), wherein the core region (18) bears radially on the inside against the carrier base body (2), in particular with individual radial projections (20) and / or a press fit.Rotor (15) of an electric machine, in particular of an electric motor, having a plastic carrier (1) and at least one magnet (10), wherein the at least one magnet (10) has been fixed to the plastic carrier (1) by a method according to one of Claims 1 to 14.Rotor (15) according to Claim 15, characterized in that the region (7) of the carrier cover (5) covering the receiving space (3) is braced against the at least one magnet (10).

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