Rotor assembly for an electric motor

Abstract

The invention relates to a rotor assembly (22) for an electric motor (20), having: a rotor shaft (24) orientated along an axial direction (A); at least two rotor cores (30) arranged coaxially and offset relative to one another along the rotor shaft (24), wherein the rotor cores (30) are each equipped with a number of rotor magnets (32) arranged tangentially distributed on the lateral surfaces of the rotor cores (30); two magnet positioning rings (42) for axial and radial form-fitting mounting of the rotor magnets (32) on the rotor cores (30), which are arranged on the opposite end faces of the respective outermost rotor cores (30); and a magnet fixing sleeve (28) placed on the rotor cores (30) for fixing the rotor magnets (32), wherein the rotor cores (30) are in direct contact with one another, wherein the rotor cores (30) have retaining contours (40) for tangentially retaining the rotor magnets (32), which project radially beyond the outer circumference of the respective rotor core (30), and wherein the retaining contours (40) of a rotor core (30) form an axial stop for the rotor magnets (32) of a neighbouring rotor core (30).

Description

[0001] Description

[0002] Rotor assembly for an electric motor

[0003] The invention relates to a rotor assembly for an electric motor, comprising a rotor shaft oriented along an axial direction and at least two rotor cores arranged coaxially and offset relative to one another along the rotor shaft. The invention further relates to a method for producing a rotor assembly and an electric motor having such a rotor assembly.

[0004] Today, motor vehicles typically feature power steering, which reduces the steering effort required to operate the steering wheel when stationary or at low vehicle speeds. The power steering assists the motor vehicle user during steering by supporting the steering effort applied by the vehicle user, for example, with a hydraulic system or an electric motor.

[0005] In an electric power steering system (EPS: Electric Power Steering, EPAS: Electric Power Assisted Steering), an electric motor mounted on the steering wheel mechanism (steering column, steering gear) supports and superimposes the vehicle user's steering movements with a generated auxiliary force. Brushless electric motors (brushless direct current motors, BLDC motors) are increasingly being used for such electric motor drives. These motors replace the wear-prone brushes of a rigid (mechanical) commutator with electronic commutation of the motor current.

[0006] Such a brushless electric motor, as a three-phase electric machine, essentially has a fixed (stationary) stator with an electric rotating field winding, which is supplied with a multi-phase three-phase current. The phases of the generated three-phase current and the associated rotating field are referred to as (motor) phases. In a figurative sense, this also includes the stator coils (phase winding) assigned to each such phase, along with the associated connecting lines (phase ends). The phases are interconnected, for example, at the star point of a star connection.

[0007] In the case of a brushless electric motor as a three-phase AC machine, the stator or its rotating field winding has three phases and thus at least three phase conductors or phase windings, which are each supplied with an electric current in a phase-shifted manner in order to generate a rotating magnetic field in which a rotor, usually provided with permanent magnets and also referred to as a rotor, rotates around its axis.

[0008] The rotor generally has a central rotor core, a particularly cylindrical, stamped-lamination core. The rotor core is, for example, securely joined to a rotor or motor shaft of the electric motor. In a surface permanent magnet rotor (SPM rotor), also known as a SPM rotor, the rotor magnets are attached or held to an outer periphery of a lateral surface of the rotor core. For this purpose, it is conceivable, for example, for the permanent magnets to be bonded to the lateral surface in a material-to-material manner, in particular by means of an adhesive or epoxy. Holding devices for the secure, non-material attachment and / or retention of the permanent magnets to the lateral surface are also conceivable.

[0009] The rotor, for example, is arranged in a toothed stator with a number of radially directed stator teeth and stator slots. The rotating field winding is applied particularly to the stator teeth. During operation of the electric motor, the magnetic resistance between the rotor and stator is varied by a change in the air gap when changing from stator tooth to stator slot relative to the permanent magnets, thereby influencing the force acting on the rotor. This causes a so-called cogging torque, which leads to fluctuating, unsteady motor operation and thus to noise.

[0010] To reduce the cogging torque of electric motors as permanently excited electrical machines, rotors are used, particularly in the case of long active parts, in which the rotor magnets are arranged offset to one another along the axial direction or the rotor shaft. This means that rotor magnets arranged axially one above the other or stacked are offset from one another in the tangential direction (circumferential direction / azimuthal direction). Such a cogging or offset arrangement of the rotor magnets has a beneficial effect on reducing the cogging torque and thus on reducing torque ripple of the electric motor. This subsequently has a beneficial effect on reducing the running noise of the electric motor.In other words, noise generation is reduced, which in turn improves the acoustic properties of the rotor and the electric motor, which is particularly desirable in its applications close to a vehicle interior.

[0011] To simplify rotor assembly, a so-called discrete set is possible, for example. In this case, a number of (individual) rotor packs equipped with rotor magnets are arranged coaxially along the rotor shaft and set relative to or against each other. This means that the rotor packs are each stacked with a tangential angular offset along the axial direction. In other words, the rotor packs equipped with rotor magnets are offset or rotated relative to each other in the tangential direction by a set angle. This means that a tangential set angle is realized from rotor pack to rotor pack along the axial direction or rotor shaft.

[0012] During rotor assembly, the set angle is generated mechanically, for example, during the shaft-tight joining of the rotor cores. The generated set angles are subject to a variety of assembly influences, such as grippers, belts, mechanical components, or measurement inaccuracies. Assembly inaccuracies often occur, leading to deviations from the desired set angles between the rotor cores. This adversely increases the cogging torque of the rotor or electric motor, resulting in increased noise during operation.

[0013] For multi-part, offset rotors, the use of an intermediate element (intermediate ring) is possible. This intermediate element is arranged between the rotor cores and axially supports the rotor magnets at the front between the rotor cores. This intermediate element is also intended to adjust the twist or offset angle between the rotor cores in a form-fitting manner. SPM rotor assemblies with such intermediate elements are known, for example, from DE 10 2017 223 622 A1 and EP 4 084 296 A1.

[0014] The invention is based on the object of providing a particularly suitable rotor assembly for an electric motor. In particular, a discretely offset rotor assembly with improved magnetic flux between the rotor cores is to be realized. The invention is further based on the object of providing a particularly suitable method for producing a rotor assembly and a particularly suitable electric motor.

[0015] With regard to the rotor assembly, the object is achieved according to the invention with the features of claim 1, with regard to the method with the features of claim 6, and with regard to the electric motor with the features of claim 10. Advantageous embodiments and further developments are the subject of the dependent claims (subclaims). The advantages and embodiments cited with regard to the rotor assembly are also transferable mutatis mutandis to the method and / or the electric motor, and vice versa.

[0016] The conjunction “and / or” is to be understood here and in the following in such a way that the features linked by this conjunction can be formed both together and as alternatives to one another.

[0017] The rotor assembly according to the invention is intended for, and is suitable and configured for, an electric motor, in particular for a power steering system of a motor vehicle. The rotor assembly comprises a rotor shaft and a rotor with two magnet positioning rings and a sleeve-like or cuff-like magnet fixing sleeve. The rotor is designed in several parts with at least two rotor cores (individual cores), with a number of rotor magnets arranged on each of the rotor cores. The rotor magnets are preferably permanent magnets.

[0018] "Axial" or an "axial direction" is understood here and below to mean, in particular, a direction parallel (coaxial) to the rotor shaft, i.e., perpendicular to the end faces of the rotor. Accordingly, "radial" or a "radial direction" is understood here and below to mean, in particular, a direction oriented perpendicular (transverse) to the rotor shaft along a radius of the rotor or rotor cores. "Tangential" or a "tangential direction" is understood here and below to mean, in particular, a direction along the circumference of the rotor or rotor cores (circumferential direction, azimuthal direction), i.e., a direction perpendicular to the axial direction and the radial direction.

[0019] The rotor, or each of the rotor cores, is joined to the rotor shaft, which is oriented along the axial direction, in a shaft-fixed manner. For this purpose, the rotor cores have, in particular, a central through-hole, by means of which the rotor cores are joined to the rotor shaft, preferably in a force-locking and / or form-locking manner—for example, by means of a press fit. The offset of the adjacent rotor cores is achieved, in particular, solely by the joining connection, in particular by the press fit, with the rotor shaft. In other words, the adjacent rotor cores are mounted on the rotor shaft with a defined offset angle, i.e., a tangential angular offset.

[0020] The term "positive connection" or "positive connection" between at least two interconnected parts is understood here and below to mean, in particular, that the interconnected parts are prevented from sliding against each other due to a frictional force acting between them. If the "connecting force" that causes this frictional force—that is, the force that presses the parts against each other—is missing, the positive connection cannot be maintained and can therefore be released.

[0021] A "positive connection" or a "positively locking retaining / connection" between at least two interconnected parts is understood here and below to mean, in particular, that the interconnected parts are held together at least in one direction by a direct interlocking of the contours of the parts themselves or by an indirect interlocking via an additional connecting part. The "blocking" of mutual movement in this direction is therefore due to the shape.

[0022] The rotor cores, in particular cylindrical ones, are preferably designed as stamped core stacks (rotor core stacks) with a number of rotor cores stacked or layered along the axial direction. The rotor cores are arranged coaxially with one another along the rotor shaft or are stacked and arranged offset from one another. The rotor cores thus form a core assembly.

[0023] The rotor cores are each equipped with a number of rotor magnets, which are arranged tangentially distributed on the respective outer lateral surfaces of the rotor cores. In particular, the rotor cores have a substantially equilateral polygonal or polygonal base surface, so that the lateral surface has a number of contact surfaces of equal area for the permanent magnets along the tangential or azimuthal direction, i.e., along the outer circumference. The rotor magnets are thus designed as surface magnets, with the rotor or rotor assembly being constructed using the SPM design. The rotor magnets have, for example, a rectangular or cuboid cross-sectional shape, preferably a loaf-shaped or bowl-shaped cross-section.

[0024] At each end of the rotor, i.e., at the end of the outermost rotor cores, a magnet positioning ring is provided as a retaining ring, which secures the rotor magnets against unwanted axial and radial slippage. The magnet positioning rings hold the rotor magnets firmly, particularly positively, to the outer surfaces of the rotor cores along the radial and tangential directions.

[0025] A magnet fixing sleeve is placed or pressed onto the rotor cores or core assembly to secure the rotor magnets. The magnet fixing sleeve is designed, for example, as a tubular, hollow cylindrical, sleeve-shaped, or cuff-shaped (cover or retaining) casing. The magnet fixing sleeve can be designed as a deep-drawn (stainless) steel or aluminum part.

[0026] The magnet fixing sleeve acts as a magnet cover and is placed axially onto the stack assembly, and thus onto the rotor magnets. The fitting is achieved in particular by means of an axial press fit, whereby it is possible, for example, for only the rotor magnets to be in mechanical (touch) contact with the magnet fixing sleeve. In other words, the press fit for fastening the magnet fixing sleeve is achieved in particular solely by means of rotor magnets. This means that the outer circumference of the rotor magnets is larger than the outer circumference of the rotor stacks and / or the magnet positioning rings, so that the rotor magnets are joined to the magnet fixing sleeve, for example, radially at an apex. This advantageously and simply reduces the mechanical demands regarding the stability and strength of the magnet positioning rings.In particular, this makes it possible to produce the magnetic positioning rings as cost-effective plastic injection-molded parts.

[0027] The magnet fixing sleeve has a certain oversize along the axial direction with regard to the axial height of the stack assembly. This means that the magnet fixing sleeve has two end-face collar areas (end faces), which are bent (crimped) radially inward in a process step following the press fit. This means that the magnet fixing sleeve, when assembled, positively engages or encloses the stack assembly - and thus the rotor. The rotor stacks have holding contours for the tangential holding of the rotor magnets, which protrude radially from the outer circumference of the respective rotor stack. The holding contours are thus arranged as radial separating webs between the tangentially distributed rotor magnets, whereby the outer circumference of the holding contours is preferably smaller than the outer circumference of the rotor magnets.The rotor cores thus have radially projecting projections on the surface between the magnetic poles, between which the rotor magnets are positioned tangentially. The retaining contours limit any tangential misalignment of the rotor magnets.

[0028] According to the invention, the rotor cores are arranged directly adjacent to one another. The end faces of adjacent rotor cores therefore touch each other. The retaining contours of one rotor core form an axial stop for the rotor magnets of an adjacent rotor core. The offset or staggered arrangement of the rotor cores results in an axial boundary between the rotor cores when viewed from the end face along the axial direction due to the radially protruding retaining contours below them. Thus, the rotor magnets of one rotor core are supported axially on the retaining contours of the adjacent rotor core.Due to the offset, direct and immediate arrangement and the retaining contours, unlike the prior art, an intermediate element (intermediate ring) arranged between the rotor cores for offsetting the rotor cores is eliminated, meaning that the magnetic flux between the rotor cores is not interrupted by an air gap (or an intermediate element). This creates a particularly suitable rotor assembly for an electric motor.

[0029] For the axial fixation of the rotor magnets, it is therefore particularly provided that the rotor magnets are axially enclosed between a retaining contour of an adjacent rotor core and one of the end-face magnet positioning rings. In rotors or rotor assemblies with more than two rotor cores, in which several rotor cores are arranged successively or in cascade, the rotor magnets of the core-inside rotor cores are axially enclosed between the retaining contours of the adjacent rotor cores. In particular, an axial positive fit is thus realized between the retaining contours or the retaining contours and a magnet positioning ring. This significantly simplifies the assembly of rotors with axially stacked and (discretely) offset rotor cores. This enables particularly simple and cost-effective assembly of the rotor assembly.

[0030] The rotor magnets are thus held tangentially by the retaining contours of the associated rotor core and, at least on one end face, axially by the retaining contours of an adjacent rotor core, and optionally, axially and radially by a magnet positioning ring, with the magnet fixing sleeve securing the rotor magnets in a form-fitting and / or force-fitting manner, particularly in the radial direction. As a result, the rotor magnets are arranged stably and reliably on the rotor cores. In particular, the rotor magnets are held or fastened to the casing or contact surfaces of the rotor cores without any material bond. This ensures that the rotor magnets are aligned and held tangentially, radially, and axially within the rotor core assembly without any material bond.

[0031] Preferably, the angle of inclination is dimensioned such that the retaining contours of adjacent rotor cores are arranged in the axial direction with as little overlap or overlap as possible. This ensures a particularly large axial contact surface of the retaining contours for the rotor magnets of the adjacent rotor core.

[0032] The term "material bond" or a "material connection" between at least two interconnected parts is understood here and below in particular to mean that the interconnected parts are held together at their contact surfaces by material union or cross-linking, for example due to atomic or molecular bonding forces, optionally under the action of an additive. Accordingly, "material bond-free" refers to a holding or fastening of the parts in the absence or the lack of such a "material bond" or a "material connection". In a suitable further development, the holding contours are trapezoidal or dovetail-shaped in cross-section. The side walls of the holding contours are each oriented in particular along the radial direction. Preferably, the holding contours only realize a positive connection in the tangential direction for the rotor magnets of the associated rotor core.This enables a simple and cost-effective assembly of the rotor cores or the laminated core stacks. Furthermore, it enables particularly easy and collision-free insertion or fitting of the rotor magnets.

[0033] In one conceivable embodiment, the rotor assembly, or rotor or rotor stack assembly, comprises exactly two rotor stacks. This ensures a particularly compact rotor assembly.

[0034] In an advantageous embodiment, the retaining contours extend essentially over the entire axial height of the respective rotor core. In particular, the retaining contours extend essentially uninterrupted, thus realizing a stable and large-area tangential mounting for the rotor magnets of the respective rotor core. When the rotor cores are designed as stamped laminated cores, this means that essentially all rotor laminations are provided with the retaining contours, and that the retaining contours are arranged axially aligned and stacked one above the other. This improves the stability of the retaining contours in the axial direction, thus realizing a particularly stable axial stop or axial contact surface for the rotor magnets of the adjacent rotor core.

[0035] An additional or further aspect of the invention provides that the magnet positioning rings have axially upstanding retaining webs in the direction of the rotor cores, which, in the joined state, each radially abut a free end of a retaining contour in sections, and which each tangentially overlap two adjacent rotor magnets in sections in the radial direction. The retaining webs thus realize the radial form-fit of the magnet positioning rings for the rotor magnets. The arrangement of the retaining contour and retaining webs is essentially T-shaped, with the retaining contour forming the vertical T-leg and the retaining web forming the horizontal T-leg.

[0036] The method according to the invention is intended for the production of a rotor assembly described above, and is suitable and designed for this purpose. According to the method, a rotor shaft, at least two rotor cores, a number of rotor magnets, two magnet positioning rings, and a magnet fixing sleeve are provided. The rotor cores each have retaining contours for tangentially holding the rotor magnets, which protrude radially beyond the outer circumference of the respective rotor core.

[0037] According to the method, a first rotor core is joined to the rotor shaft in a first process step. In particular, the first rotor core is pressed axially onto the rotor shaft in a form-fitting and / or force-fitting manner using a press fit.

[0038] Subsequently, in a second process step, one of the magnet positioning rings is arranged or placed on the front side of the first rotor package.

[0039] In a third process step, the first rotor stack is equipped with a number of rotor magnets. For this purpose, the rotor magnets are inserted tangentially and positively into the magnet receptacles formed between the retaining contours. The rotor magnets are secured against axial and radial slippage by the magnet positioning ring.

[0040] After the first rotor core has been assembled, the second rotor core is joined to the rotor shaft in a fourth process step. In particular, the second rotor core is pressed axially onto the rotor shaft using a press fit, either positively or non-positively. The second rotor core is applied or pulled onto the rotor shaft at a tangential angle to the first rotor core, so that the second rotor core is arranged offset or offset relative to the first rotor core. The second rotor core is joined to the rotor shaft in such a way that the first and second rotor cores are in direct or immediate axial contact with one another at the end faces.

[0041] In particular, in the fourth process step, the defined twist or set angle is adjusted directly during the process, for example, using a servo axis, ensuring particularly high angular accuracy between the rotor cores. The higher angular accuracy of the tangential set angle between the rotor cores results in a particularly low cogging torque of the rotor or rotor assembly. In particular, this reduces torque ripple during rotor operation, which has a beneficial effect on the acoustic properties of the rotor or an electric motor equipped with it.

[0042] In a fifth process step, the second rotor core is equipped with a number of rotor magnets. The rotor magnets are inserted or placed into the magnet receptacles formed between the retaining contours of the second rotor core and axially delimited by the retaining contours of the adjacent rotor core, so that the rotor magnets are seated tangentially between the retaining contours of the second rotor core and are axially supported on the retaining contours of the adjacent rotor core.

[0043] For a rotor or stack assembly with multiple rotor stacks, i.e., more than two, the fourth and fifth process steps are repeated for each additional rotor stack. In a subsequent sixth process step, the other magnet positioning ring is arranged or placed on the axially outermost second rotor stack, so that the rotor magnets of this rotor stack are held axially and radially in a form-fitting manner by the magnet positioning ring.

[0044] In a final, seventh process step, the magnet fixing sleeve is placed or pulled onto the assembled rotor cores. This provides a particularly suitable method for manufacturing a rotor assembly. In an advantageous embodiment, the magnet fixing sleeve is pressed axially onto the rotor cores and rotor magnets. In particular, this creates a press-fit connection between the magnet fixing sleeve and the rotor magnets.

[0045] In a suitable refinement, the rotor magnets are held radially by a funnel when a rotor stack is assembled. The funnel thus ensures that the rotor magnets do not accidentally slide radially out of the magnet holders. Instead of a funnel, a (retaining) ring, for example, is also conceivable.

[0046] In the third process step, the rotor magnets are secured at a lower end by the magnet positioning ring against axial and radial slipping out, with the funnel securing the rotor magnets, in particular, at an upper end, i.e., at a front side opposite the magnet positioning ring. In the fifth process step, the funnel secures the rotor magnets, in particular, at a lower end, with the upper end being held by the second magnet positioning ring in the sixth process step.

[0047] In a suitable embodiment, the funnel is removed when the magnetic fixation sleeve is applied. Preferably, the funnel is moved away essentially at the same time as the magnetic fixation sleeve is pulled on. This ensures collision-free application of the magnetic fixation sleeve.

[0048] In a preferred application, the rotor assembly described above is part of an electric motor. The electric motor according to the invention is particularly suitable and configured for a power steering system of a motor vehicle. The electric motor has a stator and a rotor shaft rotatably mounted relative to the stator, on which rotor shaft the rotor cores of the rotor are fixedly supported. The rotor cores of the rotor are arranged offset relative to one another along the rotor shaft. The electric motor is particularly preferably designed as a brushless electric motor in the manner of an internal rotor. In an application for a power steering system, the electric motor is arranged in the region of a driver's cab, wherein the rotor according to the invention ensures particularly smooth motor operation because particularly high angular accuracy of the offset of the rotor cores is ensured.This reduces the noise generated by the electric motor in a more advantageous and easier way, which has a positive impact on the user comfort of the vehicle.

[0049] An embodiment of the invention is explained in more detail below with reference to a drawing. In the drawings:

[0050] Fig. 1 shows a schematic representation of an electric motor power steering system of a motor vehicle,

[0051] Fig. 2 shows a perspective view of a rotor assembly of the power steering, Fig. 3 shows a perspective view of a rotor of the rotor assembly, Fig. 4 shows a perspective view of a rotor package of the rotor,

[0052] Fig. 5 shows a perspective view of a magnet positioning ring of the rotor, Fig. 6 shows a section of the rotor in the area of ​​the magnet positioning ring in plan view,

[0053] Fig. 7 shows a central region of the rotor in perspective, and Fig. 8 shows the rotor assembly in perspective sectional view.

[0054] Corresponding parts and sizes are always provided with the same reference symbols in all figures.

[0055] Fig. 1 shows in a schematic and simplified manner a motor vehicle 2 with a steering wheel 4 and with a steering gear 6 coupled thereto for moving wheels of the motor vehicle 2 (not shown in detail). To reduce the required steering force, an electric motor power steering 8 is provided between the steering wheel 4 and the steering gear 6.

[0056] The power steering system 8 is mechanically coupled, on the one hand, to a steering column 10 coupled to the steering wheel 4 and, on the other hand, to a steering gear 6. The power steering system 8 has two rotation sensors 12, 14 and a torsion bar 16 arranged between the rotation sensors 12 and 14. The rotation sensors 12, 14 are signal-coupled to a controller 18. The controller 18 also transmits signals to an electric motor 20, which is drive-coupled to the steering gear 6.

[0057] When a vehicle user turns the steering wheel 4 using a steering force, the steering column 10 is turned or rotated accordingly. This deflects the torsion bar 16, which is detected by the rotation sensors 12 and 14. The rotation sensors 12 and 14 send corresponding measurement signals to the controller 18, which controls and / or regulates the electric motor 20 depending on the measurement signals. During operation, the electric motor 20 generates a rectified auxiliary force to support the steering force and move the steering gear 6.

[0058] The structure of a rotor assembly 22 of the electric motor 20 is explained in more detail below with reference to Fig. 2 to Fig. 8.

[0059] The rotor assembly 22 has a central rotor shaft 24 and a rotor 26 and a sleeve-like or cuff-like magnet fixing sleeve 28.

[0060] The rotor 26, shown individually in Fig. 3, is designed in this embodiment as a two-part assembly with two offset rotor cores (individual cores) 30, with a number of permanent-magnet rotor magnets 32 arranged on each of the rotor cores 30. The rotor magnets 32 are provided with reference numerals in the figures merely as examples.

[0061] The rotor 26, designed as an SPM rotor, or each of the (SPM) rotor packs 30, is joined to the rotor shaft 24, which is oriented along an axial direction A. For this purpose, the rotor packs 30, shown individually in Fig. 4, have a central through-opening 34, by means of which the rotor packs 30 are non-positively and / or positively joined to the rotor shaft 24 by means of a press fit. The setting of the adjacent rotor packs 30 is realized solely by the joining connection, in particular by the press fit, with the rotor shaft 24. In other words, the adjacent rotor packs 30 are mounted on the rotor shaft 24 with a defined setting angle, i.e., a tangential angular offset.

[0062] The approximately cylindrical rotor cores 30 are formed, for example, as stamped laminated cores (rotor cores) with a number of rotor laminations stacked or layered along the axial direction A. In the embodiment shown, the rotor cores 30 have a substantially equilateral octagonal base surface. The base surface is therefore, for example, an octagon, so that the outer surface has eight contact surfaces 36 of equal area for the rotor magnets 32 along a tangential or azimuthal direction T. Each rotor core 30 is thus equipped with eight rotor magnets 32. The rotor magnets 32 have a loaf-shaped cross-section (see, for example, Fig. 6), with the flat contact surface being placed on the contact surfaces 36 so that the curved surface protrudes outwards.

[0063] To reduce the mass moment of inertia of the rotor 26, the rotor cores 30 each have eight recesses 38 penetrating the respective laminated core. The recesses 38 are distributed uniformly around the respective central through-opening 34 along the tangential direction T. The recesses 38 have an approximately drop-shaped or diamond-shaped cross-sectional shape, with the respective tip oriented toward a center line of the respective contact surface for the rotor magnets 32. The recesses 38 are provided with reference numerals in the figures merely as examples.

[0064] The rotor cores 30 have radially projecting retaining contours 40 on the outer circumference for tangentially holding the rotor magnets 32. The retaining contours 40 are thus arranged as radial separating webs between the tangentially distributed rotor magnets 32. The retaining contours 40 thus limit the contact surfaces 36 and reduce tangential misalignment of the rotor magnets 32.

[0065] As can be seen, for example, in Fig. 6, the retaining contours 40 have a trapezoidal or dovetail-shaped cross-sectional shape. The retaining contours 40 extend essentially over the entire axial height of the respective rotor core 30. Two retaining contours 40 adjacent in the tangential direction T, together with the contact surface 36 arranged therebetween, thus form an approximately trough-shaped magnet receptacle for the respective rotor magnet 32. The loaf-shaped rotor magnets 32 are positively seated in the magnet receptacle. The retaining contours 40 preferably only realize a tangential positive connection for the rotor magnets 32.

[0066] As can be clearly seen from Fig. 3, two magnet positioning rings 42 are provided for axially and, in particular, radially securing the rotor magnets 32. These rings, in the joined or assembled state, are placed on the outer end faces of the adjacent rotor cores 30. At the mutually facing end faces, the rotor cores 30 are in direct axial contact with one another.

[0067] The magnet positioning rings 42 shown individually in Fig. 5 each have a circular ring-shaped ring body 44. As can be seen comparatively clearly in Fig. 6, the ring body 44 projects radially beyond the respective rotor core 30. In other words, the ring body 44 of the magnet positioning rings 42 projects upwards from the rotor cores 30 along a radial direction R. The ring body 44 has a radial width that is slightly smaller than the combined radial dimension of the rotor core 30 and the rotor magnets 32. Thus, the ring body 44 does not project beyond the rotor magnets 32 arranged on the lateral surface of the rotor cores 30 along the radial direction R. In particular, the vertices or vertex regions of the loaf-shaped rotor magnets 32 form the radially outermost points of the rotor 26.

[0068] The annular body 44 has a central circular opening for the passage of the rotor shaft 24. The circular opening has an eight-pointed star shape as its inner contour, whereby eight radially inwardly projecting tooth extensions 46 are exposed on the radial inside of the annular body 44. On the flat side facing the rotor cores 30, the annular body 44 has eight retaining webs 48 and eight retaining extensions 50, which are formed axially upwardly on the annular body 44. The retaining extensions 50 and retaining webs 48 are formed integrally, i.e., one-piece or monolithic, onto the annular body 44. The retaining webs 48 and retaining extensions 50 are provided with reference numerals in the figures merely as examples.

[0069] The retaining projections 50 are each formed on the radially inner tooth tips of the tooth projections 46. In the assembled state, the pin-, cylinder-, or bolt-shaped retaining projections 50 of the magnet positioning ring 42 engage in the recesses 38 of the respective facing rotor core 30. The teardrop or diamond shape of the recesses 38 acts like a centering aid when joining the magnet positioning ring 42 to the rotor cores 30. This means that the magnet positioning ring 42 engages axially, at least in sections, into the respectively assigned rotor core 30 by means of the retaining projections 50.

[0070] The retaining webs 48 are arranged tangentially distributed on the outer edge or outer circumference of the annular body 44. The retaining webs 48 are arranged tangentially offset from the retaining extensions 50, so that the retaining webs 48 are positioned radially outwardly of the retaining contours 40 of the rotor core 30. In the joined state, the tangential retaining webs 48 each bear radially in sections against a free end of a retaining contour 40. The retaining webs 48, which are approximately trapezoidal in cross-section, thus form an approximately T-shape with the retaining contours 40 for radially retaining the rotor magnets 32, with the radial retaining contour 40 forming the vertical T-leg and the tangential retaining web 48 forming the horizontal T-leg. As can be seen in particular in Fig. 6, the holding webs 48 partially overlap the rotor magnets 32 arranged adjacent to the holding web 48 in the radial direction.

[0071] As can be seen comparatively clearly in the top view of Fig. 6, the holding extensions 48 rest against the radially outer contour of the loaf-shaped rotor magnets 32 in such a way that the rotor magnets 32 are at least partially and radially enclosed in these contact areas. This means that the rotor magnets 32 are held in a form-fitting manner along the tangential direction T by means of the holding contours 40 and in a form-fitting manner along the radial direction R by means of the holding webs 48, wherein the annular body 44 realizes an axial limitation to the rotor core end face. The annular body 44 of the magnet positioning ring 42 is radially clamped to the rotor core 30 in a force-fitting and / or form-fitting manner by the holding extensions 50 engaging in the recesses 38 and the holding webs 48 resting on the free ends of the holding contours 40.

[0072] The rotor cores 30 are arranged directly adjacent to one another on the rotor shaft 24. The end faces of the adjacent rotor cores 30 thus have mechanical contact. Due to the offset or staggered arrangement of the rotor cores 30, when viewed from the end face along the axial direction A, an axial boundary is created between the rotor cores 30 by the radially protruding retaining contours 40 located underneath. As shown, for example, in Fig. 7, the retaining contours 40 of one rotor core 30 thus form an axial stop for the rotor magnets 32 of the other rotor core 30, and vice versa.

[0073] The magnet fixing sleeve 28 for fixing the rotor magnets 32 is placed or pressed onto the rotor cores 30 or the core assembly—as can be seen, for example, in Fig. 8. The magnet fixing sleeve 28 is designed as a tubular, hollow cylindrical, sleeve-shaped, or cuff-shaped (covering or holding) casing. The magnet fixing sleeve 28 can be designed as a deep-drawn (stainless) steel or aluminum part.

[0074] The magnet fixing sleeve 28 acts as a magnet cover and is axially mounted on the rotor 26, and thus on the rotor magnets 32. The mounting is achieved in particular by means of an axial press fit, with preferably only the rotor magnets 32 being in mechanical (touch) contact with the magnet fixing sleeve 28.

[0075] The magnet fixing sleeve 28 has a certain oversize along the axial direction A with respect to the axial height of the package assembly. This means that the magnet fixing sleeve 28 has two end-face collar regions (end faces) 52. The collar regions 52 are bent (crimped) radially inward after the press-fit of the magnet fixing sleeve 28, and thus the

[0076] Magnetic fixing sleeve 28 is axially positively secured to the rotor 26.

[0077] The rotor magnets 32 of the rotor assembly 22 are thus held in a form-fitting manner tangentially by the retaining contours 40 of the associated rotor core 30 and axially on one end face by the retaining contours 40 of the adjacent rotor core 30, as well as axially and radially on the other end face by a magnet positioning ring 42. The magnet fixing sleeve 28 is mounted on the assembled rotor 26, by means of which the rotor magnets 32 are fixed in a form-fitting and / or force-fitting manner, particularly in the radial direction. As a result, the rotor magnets 32 are held stably and reliably, as well as without material contact, to the rotor cores 30.

[0078] A method for manufacturing the rotor assembly 22 is explained in more detail below. According to the method, the rotor shaft 24, the two rotor cores 30, sixteen (16) rotor magnets 32, two magnet positioning rings 42, and a magnet fixing sleeve 28 are provided.

[0079] In a first method step, a first rotor core 30 is joined to the rotor shaft 24. In particular, the first rotor core 30 is pressed axially onto the rotor shaft 24 by means of the through-opening 34 in a form-fitting and / or force-fitting manner.

[0080] Subsequently, in a second method step, one of the magnet positioning rings 42 is arranged or placed on the outer end face of the first rotor core 30.

[0081] In a third method step, the first rotor core 30 is equipped with eight rotor magnets 32. For this purpose, the rotor magnets 32 are inserted tangentially and positively into the magnet receptacles formed between the holding contours 40. The rotor magnets 32 are secured against axial and radial slipping out by the magnet positioning ring 42. Preferably, the rotor magnets 32 are secured against axial and radial slipping out at a lower end by the magnet positioning ring 42, with a funnel holding the rotor magnets 32, in particular at an upper end, i.e., on an end face opposite the magnet positioning ring 42, or securing them against slipping out.

[0082] After the first rotor core 30 has been fitted, the second rotor core 30 is joined to the rotor shaft 24 in a fourth process step. In particular, the second rotor core 30 is pressed axially onto the rotor shaft 24 by means of the through-opening 34 using a press fit in a form-fitting and / or force-fitting manner. The second rotor core 30 is applied or pulled onto the rotor shaft 24 rotated tangentially to the first rotor core 30 by a set angle, so that the second rotor core 30 is arranged set or rotated relative to the first rotor core 30. The second rotor core 30 is joined to the rotor shaft 24 in such a way that the rotor cores 30 are in direct or immediate axial contact with one another at their end faces. The defined twist or set angle is preferably set directly in the process using a servo axis, so that particularly high angular accuracy between the rotor cores 30 is ensured.

[0083] In a fifth method step, the second rotor stack 30 is equipped with eight rotor magnets 32. The rotor magnets 32 are inserted or placed into the magnet receptacles formed between the retaining contours 40 of the second rotor stack 30 and axially delimited by the retaining contours 40 of the first rotor stack 30, so that the rotor magnets 32 are seated tangentially between the retaining contours 40 of the second rotor stack 30 and are axially supported on the retaining contours 40 of the respective first rotor stack 30. For the fifth method step, the funnel is moved toward the second rotor stack 30 so that the funnel secures the rotor magnets 32 of the second rotor stack 30, particularly at a lower end.

[0084] In a subsequent sixth method step, the other magnet positioning ring 42 is arranged or placed on the second rotor core 30, so that the rotor magnets 32 of this rotor core 30, particularly at an upper end, are held axially and radially in a form-fitting manner by the magnet positioning ring 42. In a final seventh method step, the magnet fixing sleeve 28 is pressed onto the loaded rotor cores 30, and the collar regions 52 are bent radially inward. Preferably, the funnel is moved away or removed essentially simultaneously with the pulling on of the magnet fixing sleeve 28.

[0085] The claimed invention is not limited to the exemplary embodiments described above. Rather, other variants of the invention can also be derived therefrom by those skilled in the art within the scope of the disclosed claims without departing from the subject matter of the claimed invention. In particular, all individual features described in connection with the various exemplary embodiments can also be combined in other ways within the scope of the disclosed claims without departing from the subject matter of the claimed invention.

[0086] List of reference symbols

[0087] 2 motor vehicles

[0088] 4 steering wheel

[0089] 6 steering gear

[0090] 8 Power steering

[0091] 10 Steering column

[0092] 12 rotation sensor

[0093] 14 rotation sensor

[0094] 16 Torsion bar

[0095] 18 controllers

[0096] 20 electric motor

[0097] 22 Rotor assembly

[0098] 24 Rotor shaft

[0099] 26 Rotor

[0100] 28 Magnetic fixing sleeve

[0101] 30 rotor pack

[0102] 32 rotor magnet

[0103] 34 Through opening

[0104] 36 contact surface

[0105] 38 recess

[0106] 40 Holding contour

[0107] 42 Magnetic positioning ring

[0108] 44 ring bodies

[0109] 46 Dental process

[0110] 48 Stop bridge

[0111] 50 Retaining process

[0112] 52 collar area

[0113] A axial direction

[0114] R Radial direction

[0115] T Tangential direction

Claims

Claims 1. Rotor assembly (22) for an electric motor (20), comprising - a rotor shaft (24) directed along an axial direction (A), - at least two rotor packs (30) which are arranged coaxially and offset from one another along the rotor shaft (24), wherein the rotor packs (30) are each equipped with a number of rotor magnets (32) which are arranged tangentially distributed on the lateral surfaces of the rotor packs (30), - two magnet positioning rings (42) for axially and radially positively holding the rotor magnets (32) on the rotor packs (30), which are arranged on the opposite end faces of the respective outermost rotor packs (30), and - a magnet fixing sleeve (28) placed on the rotor packs (30) for fixing the rotor magnets (32), - wherein the rotor packs (30) lie directly against one another, - wherein the rotor packs (30) have holding contours (40) for tangentially holding the rotor magnets (32), which project radially beyond the outer circumference of the respective rotor pack (30), and - wherein the holding contours (40) of a rotor core (30) form an axial stop for the rotor magnets (32) of an adjacently arranged rotor core (30).

2. Rotor assembly (22) according to claim 1, characterized in that the holding contours (40) are trapezoidal or dovetail-shaped in cross section.

3. Rotor assembly (22) according to claim 1 or 2, characterized in that the rotor assembly (22) has exactly two rotor packs (30).

4. Rotor assembly (22) according to one of claims 1 to 3, characterized in that the holding contours (40) extend substantially over the entire axial height of the respective rotor core (30).

5. Rotor assembly (22) according to one of claims 1 to 4, characterized in that the magnet positioning rings (42) have axially upstanding retaining webs (48), which each radially abut a free end of a holding contour (40) in sections, and which each tangentially overlap two adjacently arranged rotor magnets (32) in the radial direction in sections.

6. A method for producing a rotor assembly (22) according to one of claims 1 to 5, - wherein a rotor shaft (24), at least two rotor cores (30), a number of rotor magnets (32), two magnet positioning rings (42), and a magnet fixing sleeve (28) are provided, wherein the rotor cores (30) have holding contours (40) for tangentially holding the rotor magnets (32), which protrude radially from the outer circumference of the respective rotor core (30), - wherein a first rotor package (30) is joined to the rotor shaft (24), - wherein one of the magnet positioning rings (42) is arranged on the first rotor package (30), - wherein the first rotor package (30) is equipped with the rotor magnets (32) in such a way that the rotor magnets (32) are seated tangentially between the holding contours (40), - wherein at least one second rotor stack (30) is joined to the rotor shaft (24) by a predetermined angle of rotation, so that the rotor stacks (30) directly abut one another at the end faces, - wherein the second rotor package (30) is equipped with the rotor magnets (32) in such a way that the rotor magnets (32) are arranged tangentially between the retaining contours (40) and are supported axially on the retaining contours (40) of the adjacent rotor package (30), - wherein the other magnet positioning ring (42) is arranged on the axially outermost second rotor package (30), and - wherein the magnet fixing sleeve (28) is placed on the rotor packs (30) and rotor magnets (32).

7. Method according to claim 6, characterized in that the magnet fixing sleeve (28) is pressed onto the rotor cores (30) and rotor magnets (32).

8. Method according to claim 6 or 7, characterized in that the rotor magnets (32) are held radially by a funnel when a rotor package (30) is loaded.

9. Method according to claim 8, characterized in that the funnel is removed when the magnetic fixing sleeve (28) is fitted.

10. Electric motor (20), in particular for a power steering system (8), comprising a stator and a rotor assembly (22) rotatably mounted relative thereto according to one of claims 1 to 5.

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