DE102024117178A1 - Rotor for an axial flux machine - Google Patents

Abstract

An axial flux machine (100) comprises a stator (105) and a rotor (110) which are rotatably mounted relative to each other about an axis of rotation (115). The rotor (110) comprises a rotor lamination (130) and several permanent magnets (135), wherein the rotor lamination (130) extends in a plane of rotation about the axis of rotation (115) and the permanent magnets (135) are axially attached to the rotor lamination (130). It is proposed that the rotor lamination (130) be manufactured by additive manufacturing and thereby metallurgically bonded to the permanent magnets (135).

Description

The present invention relates to an electric drive motor for a motor vehicle. In particular, the invention relates to an axial flux machine.

A motor vehicle can be powered by an electric drive machine. While the magnetic flux in a drive machine typically runs radially, in an axial flux machine, the magnetic elements are arranged such that the magnetic flux coupling the stator to the rotor runs axially. An axial flux machine can provide higher power or torque for the same installation space or mass and efficiency. It can also be more economical in terms of material usage; furthermore, it can free up space when positioning an axial flux machine as the drive motor in a motor vehicle.

In a known axial flux machine, permanent magnets are arranged in a ring around a rotating axis. In the axial direction, the permanent magnets are attached to a laminated core, which in turn is mounted axially to a rotor carrier. Connections are typically made using adhesive. However, the stiffness of the adhesive layer is temperature-dependent, which can cause changes in the axial gap between the permanent magnets and the coils on the stator of the axial flux machine. To minimize this gap, the adhesive joints must be applied very carefully and sealed to prevent the formation of dirt or air bubbles. Furthermore, the adhesive layer can create magnetic resistance to a magnetic field, potentially reducing the machine's efficiency.

One of the problems underlying the present invention is to provide an improved rotor for an axial flux machine, particularly for powering a motor vehicle. The invention solves this problem by means of the subject matter of the independent claims. The dependent claims describe preferred embodiments.

An axial flux machine comprises a stator and a rotor, which are rotatably mounted relative to each other about an axis of rotation. The rotor includes a rotor lamination and several permanent magnets, the rotor lamination extending in a plane of rotation about the axis of rotation, and the permanent magnets being axially attached to the rotor lamination. It is proposed that the rotor lamination be manufactured using additive manufacturing and thereby metallurgically bonded to the permanent magnet.

The material-bonded connection can be achieved without the use of an adhesive, allowing the arrangement of permanent magnets and rotor lamination to exhibit improved dimensional stability, particularly in the axial direction. Negative effects of adhesives, such as magnetic resistance or temperature-dependent mechanical expansion, can be avoided. The axial annular gap between the permanent magnets and electromagnets on the stator of the axial flux machine can be kept very small with improved dimensional stability. This enables the provision of an electric drive machine with a high power density.

Preferably, the rotor lamination is made of stainless steel. Such steel, which can also be referred to as stainless steel, typically has an austenitic microstructure, resulting in very low magnetic permeability. In practice, it can be assumed to be a non-magnetic material. The stainless steel can, in particular, be a material designated 1.4404, corresponding to AISI 316L. This material is widely used and its properties are well understood.

It is particularly preferred that the rotor lamination is produced directly on the permanent magnets using powder bed fusion.

A powdered material can be distributed in a layer of predetermined thickness on a base plate. The material can then be selectively melted briefly using a heat source. The heat source can comprise an electron beam, in which case it is referred to as electron beam melting (EBM). Alternatively, the heat source can comprise a light-emitting diode (LED), a process known as selective LED-based melting (SLEDM). In a preferred embodiment, the heat source comprises a laser. Various techniques can be performed with the laser, such as laser beam melting, direct metal printing (DMP), direct metal laser sintering (DMLS), or laser metal fusion (LMF).

In a particularly preferred embodiment, the rotor lamination is produced by laser powder bed fusion. The rotor lamination is preferably produced using a process known as laser powder bed fusion (PBF-LB/M). This process allows the Rotor laminations of sufficient size and accuracy can be produced. The process is also suitable for the mass production of rotor laminations.

The axial flux machine can further comprise a magnet carrier that supports the permanent magnets against one another. The magnet carrier can include several elements, each located between adjacent permanent magnets around the circumference of the axis of rotation. The magnet carrier can be manufactured conventionally from a predetermined material. In one embodiment, this is the same material as that of the rotor lamination. The magnet carrier can help to fix the permanent magnets against each other and against the rotor lamination. Furthermore, the magnet carrier, together with the permanent magnets, can define a flat surface in the axial direction onto which the rotor lamination can be deposited in the manner described herein. An arrangement of the permanent magnets and the magnet carrier can have a uniform axial thickness.

Preferably, the rotor further comprises a flux ring that extends radially outside the permanent magnets around the axis of rotation. It is preferred that the rotor lamination is metallurgically bonded to the flux ring during its additive manufacturing process.

The rotor lamination, permanent magnets, flux ring, and, if applicable, the magnet carrier can thus form a separately manageable unit. This unit can be easily attached with the required precision to another element of the rotor, in particular to a rotor carrier. The flux ring material can also include stainless steel, especially the same material used for the rotor lamination and/or the magnet carrier.

According to a further aspect of the present invention, a motor vehicle comprises an axial flux machine as described herein. The motor vehicle can, for example, be a motorcycle or a passenger car. The axial flux machine can have a high power density (in kW/kg) and be very compact. In one embodiment, the axial flux machine is configured to directly drive a wheel of the motor vehicle. This can, in particular, be a hub motor that is integrated with a wheel of the motor vehicle.

According to yet another aspect of the present invention, a method for manufacturing a rotor for an axial flux machine, in particular for use as a drive machine of a motor vehicle, comprises the following steps: arranging permanent magnets along a circumference around an axis of rotation of the rotor; applying a layer of a powdered material to an axial side of the permanent magnets; and melting the powdered material so that the material forms a rotor lamination which is bonded to the permanent magnets in the axial direction.

The method can be used to manufacture a rotor or an axial flux machine described herein. Features or advantages of the rotor or the axial flux machine can be transferred to the method, and vice versa.

It is particularly preferred that elements of a magnet carrier are arranged between adjacent permanent magnets such that their surfaces lie in a plane with the axial surfaces of the permanent magnets. The powdered material can be applied to the surfaces and melted there. In this way, the rotor lamination can be made more flat.

The permanent magnets, and optionally the magnet carrier and/or flux ring, can be placed in a mold before the powdered material is applied, so that their surfaces are flush with a surface of the mold. No bond is formed between the rotor lamination and the mold during manufacturing. After the rotor lamination is complete, all components can be removed from the mold, and the mold can be reused to produce another rotor assembly.

To achieve a particularly strong bond between the rotor lamination and a permanent magnet, the powdered material can be melted in the area where the permanent magnet abuts an element of the magnet carrier before being melted in an axial region of the permanent magnet. This allows a thermally and mechanically robust bond to be created at the interface between the permanent magnet and the magnet carrier, which can then be continued or extended along the axial surface of the permanent magnet.

The powdered material can only be melted in a predetermined area that is moved across the surface. This area can be relatively small, with a diameter of less than approximately 1 mm. It is preferred that the movement within the area of a permanent magnet follows a predetermined pattern, which can be meandering. Various meandering patterns are conceivable. bar. In another embodiment, the pattern can also cover the surface of the permanent magnet in the manner of a spiral.

In one embodiment, the pattern extends across a surface of the permanent magnet from the outer boundary region to an inner axial region. For example, the pattern can initially circumferentially traverse the permanent magnet along the boundary region. After this first circumference, a further circumference can be made offset further inward on the permanent magnet, so that the subsequent circumference has essentially the same shape but a shorter length. Further circumferences can be carried out in this manner until the entire surface of the permanent magnet has been melted. After this process, another layer of powdered material can be applied and melted in a similar manner.

Generally, several layers of the powdered material are applied and melted successively. It is preferred that the rotor is cooled to a predetermined temperature before each layer is melted. In particular, it is possible to wait between melting one layer and applying or melting the next until the molten material or the rotor has cooled sufficiently to eliminate thermal stress. This allows for improved dimensional accuracy and stress-free manufacturing of the rotor.

• 1 eine schematische Darstellung eines beispielhaften Rotors für eine Axialflussmaschine;
• 2 einen Rotor für eine Axialflussmaschine;
• 3 Schritte eines Herstellungsverfahrens für einen Rotor für eine Axialflussmaschine;
• 4 eine schematische Darstellung einer Herstellungsvorrichtung für ein Rotorblech mittels additiver Fertigung; und
• 5 ein beispielhaftes Muster eines erwärmten Bereichs bei einer additiven Fertigung

illustriert.The invention will now be described in more detail with reference to the attached drawings, in which:

• 1 a schematic representation of an exemplary rotor for an axial flux machine;
• 2 a rotor for an axial flux machine;
• 3 Steps of a manufacturing process for a rotor for an axial flux machine;
• 4 a schematic representation of a manufacturing device for a rotor lamination using additive manufacturing; and
• 5 An exemplary pattern of a heated area in additive manufacturing

illustrated.

An axial flux machine 100 can be used, in particular, as a drive motor for a motor vehicle. The axial flux machine 100 comprises a stator 105 (not shown) and a rotor 110, an exemplary variant of which is shown in 1 The rotor 110 is mounted so as to be rotatable about an axis of rotation 115 relative to the stator 105.

The rotor 110 comprises a rotor carrier 120, to which an arrangement 125 is attached, which may include a rotor sheet 130, a number of permanent magnets 135, a magnet carrier 140 and a flux ring 145.

The permanent magnets 135 are arranged regularly around a circumference around the axis of rotation 115. A line connecting the north and south poles of a permanent magnet 135 runs essentially parallel to the axis of rotation 115. The magnet support 140 can support the permanent magnets 135 circumferentially. For this purpose, the magnet support 140 is subdivided into individual elements, with each element positioned between two adjacent permanent magnets 135. Additionally, a radial outer and/or radial inner enclosure can be provided to secure the permanent magnets 135 radially. The magnet support 140 and the permanent magnets 135 typically have the same thickness along the axis of rotation 115, so that together they essentially form a disk in the shape of an annulus with a constant axial height.

The permanent magnets 135 and, if applicable, the magnet carrier 140 can be attached to the rotor lamination 130 using an adhesive. The rotor lamination 130 can be attached to the rotor carrier 120 using a further layer of adhesive. The flux ring 145 can also be glued to the rotor carrier 120 or to another element of the rotor 110.

An alternative technique is presented below that allows the assembly 125 to be manufactured with materially bonded elements without the use of an adhesive. This enables the production of a dimensionally accurate assembly 125, allowing the manufacture of an axial flux machine 100 with a precise axial air gap between the rotor 110 and the stator 105. In this way, an axial flux machine 100 can be provided that delivers high power. In one embodiment, this power can be several hundred kW, for example, approximately 500 kW.

2 Figure 1 shows a schematic representation of a rotor 110 of an axial flux machine 100. The upper section shows a view along the axis of rotation 115, and the lower section shows a symbolic longitudinal section through the axis of rotation 115. The depicted part of the rotor 110 corresponds to the arrangement 125 of a rotor 110 according to [reference missing]. 1 .

In the longitudinal section, contact surfaces 205 between permanent magnets 135 and the rotor lamination 130 are highlighted by means of dashed lines. To achieve a precise, durable, and temperature-stable connection between the permanent magnets 135 and the rotor lamination 130, it is proposed that the rotor lamination 130 be manufactured directly on the permanent magnets 135 using additive manufacturing methods. Specifically, the rotor lamination 130 should be produced by melting a powdered material, whereby the material can reach a temperature sufficient to establish a metallurgical bond with the permanent magnet 135.

A permanent magnet 135 preferably comprises an alloy with a rare-earth element, in particular neodymium. The melting of the powder is further preferably carried out only very briefly and limited to a small local area, so that the magnetic properties of the permanent magnet 135 can remain essentially unchanged during the production of the rotor lamination 130. Optionally, a corresponding connection can also be made between the rotor lamination 130 and the flux ring 145 during the production of the rotor lamination 130. In a further embodiment, a corresponding connection can also be made between the rotor lamination 130 and the magnet carrier 140.

3 shows steps of a manufacturing process 300 for a rotor 110 of the type of 2 for an axial flux machine 100. From top to bottom, steps 305, 310 and 315 are shown. For each step 305 to 315, a longitudinal section is shown in the left area and a cross-section with respect to the axis of rotation 115 is shown in the right area.

In a first step 305, a build platform 320 is provided, which has predetermined, radially symmetrical recesses 325. The build platform 320 can be made of a material that is resistant to welding with steel, for example, a ceramic.

In a second step 310, the permanent magnets 135, the magnet carrier 140, and optionally the flux ring 145 are inserted into the recesses 325. The permanent magnets 135 are arranged at regular intervals around a circumference centered on the axis of rotation 115. An element of the magnet carrier 140 can be positioned between adjacent permanent magnets 135. Elements of the magnet carrier 140 can be connected to each other by means of a radially inner and/or a radially outer ring. In this case, the magnet carrier 140 can also abut the permanent magnets 135 radially on the inside or outside.

It can be seen that the axial surfaces of the permanent magnets 135, the magnet carrier 140 and the optional flux ring 145 lie in a plane that preferably is flush with the upper surface of the build platform 320.

In a third step 315, the rotor lamination 130 can be deposited on this surface using additive manufacturing methods. For this purpose, a layer of a powdered material can be applied to the surface before the layer is heated in predetermined sections using a heat source. In this way, a large number of layers can be deposited successively, which together form the rotor lamination 130.

The rotor lamination 130 may already be welded to the permanent magnets 135, the magnet carrier 140 and/or the flux ring 145 due to its thermal manufacturing process. However, no metallurgical bond is established with respect to the assembly platform 320.

4 shows a schematic representation of a manufacturing device 400 for a rotor lamination 130 of a rotor 110 for an axial flux machine 100 according to 2 or 3 .

The manufacturing device 400 comprises an energy source 405, preferably a laser. The laser can be directed into a predetermined melting area 415 on a build platform 320 by means of a mirror 410. A camera 420 is provided to detect the actual position of the melting area 415 and to control the laser 405 or the mirror 410 accordingly.

On the build platform 320, a powdered material 425 is applied in a layer of a predetermined thickness. By controlling the mirror 410 and optionally by moving the build platform 320 relative to the energy source 405 or the mirror 410, the melting zone 415 can be moved across the powdered material 425 on the build platform 320 in a predetermined pattern. In the melting zone 415, the powdered material 425 melts briefly due to the application of heat and solidifies again when the zone 415 is moved further. During this process, the material 425 is temporarily in a liquid phase, in which a metallurgical bond can be formed with an adjacent element. Such an element can, in particular, comprise a permanent magnet 135, a magnet carrier 140, or a flux ring 145, which are located in 4 not shown. In this way, the rotor lamination 130 can be manufactured precisely according to predetermined specifications and immediately early on, they are bonded to one of the other elements mentioned.

5 Figure 500 shows an exemplary pattern of the movement of a heated melting area 415 during additive manufacturing. The illustration follows a perspective parallel to the axis of rotation 115 on a permanent magnet 135, which is surrounded by a magnet carrier 140. The shape of the permanent magnet 135 is to be understood as symbolic.

Pattern 500 begins in the lower right area of the illustration, where the permanent magnet 135 abuts the magnet carrier 140 in the plane of rotation with respect to the axis of rotation 115. Pattern 500 initially follows the boundary between the permanent magnet 135 and the magnet carrier 140 until it has essentially completed one revolution around the permanent magnet 135. Pattern 500 then completes another revolution, oriented to the previously completed revolution and maintaining a predetermined lateral distance from it.

After a number of revolutions, the melting area 415 of the pattern 500 reaches a point that is at its maximum distance from the lateral boundaries of the permanent magnet 135. This location is in 5 The transition from pattern 500 with a solid line to a dashed line is shown. After reaching this point, pattern 500 can be continued by extending the melting area 415 in the opposite direction of rotation, so that the melting area 415 is always located between two adjacent cycles. A cycle can be considered a weld, so that the welds of the first part can be laterally welded together by the second part of pattern 500. Pattern 500 ends when the melting area 415 reaches the point where pattern 500 began.

It should be noted that the illustrated pattern 500 is representative of different patterns that create a metallurgical connection between the permanent magnet 135 and an externally adjacent element 140, which is then continued inwards via the axial end face of the permanent magnet 135.

Reference sign

100

Axial flux machine

105

stator

110

rotor

115

axis of rotation

120

Rotor carrier

125

arrangement

130

Rotor plate

135

Permanent magnet

140

Magnetic carrier

145

River ring

205

Site area

300

Proceedings

305

first step

310

second step

315

third step

320

Construction platform

325

Exclusion

400

Manufacturing device

405

Energy source (laser)

410

Mirror

415

Melting area

420

camera

425

powdered material

500

Pattern

Claims (13)

An axial flux machine (100) comprising: - a stator (105) and a rotor (110) which are rotatably mounted relative to each other about an axis of rotation (115); - wherein the rotor (110) comprises a rotor lamination (130) and several permanent magnets (135); - wherein the rotor lamination (130) extends in a plane of rotation about the axis of rotation (115); - wherein the permanent magnets (135) are axially attached to the rotor lamination (130); - wherein the rotor lamination (130) is manufactured by additive manufacturing and is metallurgically bonded to the permanent magnets (135). Axial flux engine (100) according to Claim 1 , wherein the rotor sheet (130) is made of stainless steel. Axial flux engine (100) according to Claim 1 or 2 , wherein the rotor sheet (130) is manufactured by powder bed fusion directly on the permanent magnets (135). Axial flux engine (100) according to Claim 3 , wherein the rotor sheet (130) is manufactured by powder bed fusion of metal using a laser beam. Axial flux machine (100) according to one of the preceding claims, further comprising a magnet carrier (140) which supports the permanent magnets (135) against each other. Axial flux machine (100) according to one of the preceding claims, wherein the rotor (110) further comprises a flux ring (145) which extends radially outside the permanent magnets (135) on a circumference around the axis of rotation (115); wherein the rotor lamination (130) is materially bonded to the flux ring (145) as part of its additive manufacturing. Motor vehicle comprising an axial flux machine (100) according to one of the preceding claims. Method (300) for manufacturing a rotor (110) for an axial flux machine (100); the method comprising the following steps: - Arranging (310) permanent magnets (135) along a circumference around an axis of rotation (115) of the rotor (110); - Applying (315) a layer of a powdered material (425) to an axial side of the permanent magnets (135); and - Melting (315) the powdered material (425) so that the material (425) forms a rotor lamination (130) which is bonded to the permanent magnets (135) in the axial direction. Procedure (300) according to Claim 8 , wherein elements of a magnet carrier (140) are arranged between adjacent permanent magnets (135) such that their surfaces lie in a plane with axial surfaces of the permanent magnets (135); wherein the powdered material (425) is applied to the surfaces and melted there. Procedure (300) according to Claim 9 , wherein the powdered material is melted in an area where a permanent magnet (135) is adjacent to an element of the magnet support (140) before the material is melted in an axial area of the permanent magnet (135). Procedure (300) according to one of the Claims 8 until 10 , wherein the powdered material (425) is melted only in a predetermined melting area (415) which is moved over the surface; wherein the movement in the area of a permanent magnet (135) follows a predetermined pattern (500) which has the form of a meander. Procedure (300) according to Claim 10 and 11 , wherein the pattern (500) extends over an area of the permanent magnet (135) from the outer boundary region to an inner axial region. Procedure (300) according to one of the Claims 8 until 12 , wherein several layers of the powdered material (425) are applied and melted successively; wherein the rotor (110) is cooled to a predetermined temperature before melting a layer.