Rotor for electric machine, electric machine and method for producing such rotor

Abstract

The invention relates to a rotor (10) for an electric machine (12), an electric machine (12) and a method for producing such a rotor (10), comprising a base body (14), on a radially outer periphery (15) of which a plurality of rotor magnets (20) are arranged, the rotor magnets (20) being fastened to the base body (14) by means of a rotor sleeve (30) made of metal, wherein the rotor sleeve (30) has a delimited heat-treated region (32), which radially clamps the rotor sleeve (30) on the main body (14).

Description

Technical Field

[0001] The invention relates to a rotor for an electric machine as well as an electric machine and a method for producing such a rotor according to the independent claims. Background Art

[0002] DE 102007029719 A1 discloses a rotor for an electric machine in which "buried magnets" are arranged in radially outwardly closed magnet pockets of the rotor. The magnetic poles of the rotor are defined by the shape of radially outer tangential webs that radially outwardly close the magnet pockets. Therefore, in this embodiment, the precise tangential positioning of the magnets within the magnet pockets is relatively uncritical and has no significant effect on the rotor's braking torque.

[0003] CN 104659941 A discloses another rotor in which the magnets are positioned on the surface of the rotor base body by means of radial retaining tabs. A tape is then glued onto the magnets and pressed onto their curved circumferential surface. In this embodiment, the assembly process for securing the tape is very complex, as the gluing process quickly leads to contamination during assembly. This disadvantage is intended to be eliminated by the solution according to the present invention. Summary of the Invention

[0004] In contrast, the device and method according to the present invention, having the features of the independent claims, have the following advantages: after cooling of a restricted area of ​​the rotor sleeve, local heating of the restricted area generates inherent tensile stresses in the sleeve material, which lead to radial contraction of the rotor sleeve. Thus, after forming the heat-treated area, the rotor sleeve, which can previously be inserted onto the rotor magnet, in particular with a clearance fit, is pressed radially toward the rotor magnet. This has the advantage that the rotor sleeve can be inserted onto the rotor magnet without pressing, thus eliminating the need for an insertion phase at the axial ends of the rotor sleeve. By eliminating the insertion phase, the maximum outer diameter of the rotor sleeve can be reduced or post-processing of the insertion phase can be omitted. The restricted area of ​​the rotor sleeve is preferably heated so intensely that the rotor sleeve material melts, so that the shrinking process of the rotor sleeve, when the molten material solidifies again, reduces the inner diameter of the rotor sleeve so intensely that the rotor magnet is pressed against the base body and thus remains securely fixed during operation of the electric machine.

[0005] The measures listed in the dependent claims enable advantageous developments and improvements of the embodiments specified in the independent claims. To achieve the greatest possible reduction in the inner diameter of the rotor sleeve, the restricted heat-treated areas are formed as thermal gaps that extend in the axial direction parallel to the rotor axis. If these thermal gaps extend substantially over the entire axial length of the rotor sleeve, the inner diameter of the rotor sleeve decreases uniformly over its entire axial length, resulting in a uniform contact of the rotor sleeve against the surface of the rotor magnets.

[0006] In a preferred embodiment, the rotor magnets extend substantially over the entire axial extent of the rotor base body. Similarly, the rotor sleeve extends substantially over the entire axial length of the base body. In this embodiment, the axial heat gap is particularly advantageously formed between two adjacent rotor magnets in the circumferential direction, so that the rotor magnets are not damaged when the sleeve material is heated. Thus, the axial heat gap is formed radially directly above the base body or above radial webs molded onto the base body, without damaging the heating of the base body.

[0007] To precisely position the rotor magnets on the base body, radial retaining tabs are molded onto the last rotor magnet, on which the rotor magnet can be supported in the circumferential direction. It is particularly advantageous to also incorporate spring elements on the retaining tabs, which can compensate for manufacturing tolerances and temperature fluctuations. The radial retaining tabs and / or the spring elements can be particularly easily punched directly from the lamination stack as a single piece. The radial extent of the radial tabs is smaller than the maximum radial extent of the rotor magnets, so that the rotor sleeve rests securely in the radial direction against the outer surface of the rotor magnets as its diameter decreases.

[0008] Here, the cross section of the rotor magnet is particularly advantageously formed so that the radial circumferential surface is curved or circular. The radial inner surface of the magnet is preferably constructed as a straight, flat base surface, which is in full contact with the flat contact surface of the rotor base. The cross section of the rotor magnet transverse to the axial direction is advantageously constructed in the form of a "long loaf of bread", in which the curved radial outer surface is connected to the flat radial inner surface by means of two tangentially opposite side surfaces. These side surfaces preferably extend approximately perpendicular to the base surface, but as an alternative, they can also extend approximately in the radial direction to the base. The two opposite side surfaces of two adjacent magnets can be supported on the base in the tangential direction so that the rotor magnet is reliably positioned and fixed with respect to the tangential direction. The rotor sleeve is in contact with the central area of ​​the radial outer surface of the rotor magnet at least with respect to the circumferential direction so as to press the rotor magnet radially toward the contact surface.

[0009] The rotor sleeve can be manufactured particularly simply and cost-effectively using a deep-drawing method. For this purpose, a metal sheet is used, the material thickness of which is selected so that the desired radial shrinkage of the rotor sleeve occurs after cooling of the locally restricted, heat-treated area. The material of the rotor sleeve can also be selected accordingly to achieve a sufficient shrinkage of its inner diameter. For example, the rotor sleeve can be made of steel or aluminum, but in particular of a non-magnetic metal.

[0010] To save rotor weight and optimize magnetic flux, the rotor base advantageously has radial tabs that extend radially from the central hub to the outer yoke ring. This allows the hub to be plugged into, preferably pressed onto, the rotor shaft. A particularly flat contact surface for the rotor magnets is integrally formed on the outer circumference of the yoke ring. Radial retaining tabs are arranged tangentially to two adjacent rotor magnets, preferably in the circumferential region of the radial tabs.

[0011] The rotor according to the present invention is particularly suitable for use in electrically commutated EC motors, in which the rotor is designed as an internal rotor motor. Here, the rotor is arranged inside the stator, with the electronically commutated electrical windings arranged inside the stator housing. The rotor sleeve according to the present invention securely holds the rotor magnets in place on the rotor and prevents them from being thrown off.

[0012] To assemble the rotor according to the present invention, the rotor sleeve is inserted into the rotor in the cold state in the axial direction after the rotor magnets have been positioned on the rotor base. Subsequently, the material of the rotor sleeve is heated intensely in locally restricted areas using an external heat source so that, after cooling, the material of the rotor sleeve contracts in these areas. By appropriately arranging the locally restricted, heat-treated areas, inherent contraction stresses can be generated in these locally restricted areas during cooling, which press the rotor sleeve radially against the rotor magnets.

[0013] A particular advantage is that the laser beam can be used to heat and, in particular, melt the material in a confined area very precisely. The laser beam can be guided along the surface of the rotor sleeve with multiple degrees of freedom in order to form a correspondingly shaped, heat-treated area. The energy introduced and the focus of the laser beam can be adapted to the sleeve material or the material thickness of the rotor sleeve.

[0014] It is particularly advantageous to guide the laser beam in the axial direction, preferably over the entire axial length of the rotor sleeve, in order to form axial thermal gaps in the rotor sleeve. These thermal gaps are preferably formed between two rotor magnets with respect to the circumferential direction, with axial thermal gaps being formed between all rotor magnets, for example. In this case, inherent contraction stresses are generated, particularly in the tangential direction, between the rotor magnets. These inherent contraction stresses can cause the inner diameter of the rotor sleeve to contract more strongly at these locations than in the region of the rotor magnets' greatest radial extent.

[0015] In these installation methods, it is particularly advantageous to construct the rotor sleeve without an introduction phase because the rotor sleeve can be inserted onto the radially outer surface of the rotor magnet with clearance. Since the introduction phase is omitted, the rotor has a smaller outer diameter after installation, or material processing during the introduction phase can be omitted after the rotor sleeve is inserted. Unlike the conventional shrinkage and extrusion of the sleeve, circumferential stress can be generated later after insertion, so that on the one hand, the rotor sleeve can be inserted onto the rotor magnet with clearance and then a sufficient radial pressing force can be generated on the rotor magnet by partial melting of the rotor sleeve. The size of the radial pressing force for the rotor sleeve can be influenced by the number of thermal gaps and the surface extension. Since the rotor magnet is preferably magnetized in the radial direction beforehand, it is held on the contact surface of the rotor base by magnetic force when the rotor sleeve is inserted. Since the material of the rotor sleeve is melted by means of a laser beam, the magnetic properties of the rotor magnet are not impaired.

[0016] In an alternative embodiment, locally limited areas of the rotor sleeve can be heated inductively, whereby, for example, multiple limited heat-treated areas can be produced simultaneously on the rotor sleeve. The induction heating power can be adjusted to such a high level that the corresponding material of the rotor sleeve melts. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description.

[0018] in:

[0019] Figure 1 A sectional view of a first embodiment of a rotor according to the invention is shown in longitudinal section;

[0020] Figure 2 Shown in accordance with Figure 1 a side view of an embodiment of ; and

[0021] Figure 3 Another embodiment of a rotor in an electric machine is shown in cross section. DETAILED DESCRIPTION

[0022] exist Figure 1 , the rotor 10 of the electric machine 12 is shown, which has a base body 14, on the outer periphery 15 of which a contact surface 16 is molded. On the contact surface 16, a rotor magnet 20 is arranged, which preferably extends over the entire axial length 13 of the base body 14. The rotor magnet 20 is designed in an arc shape along the circumferential direction 9 and has an inner base surface 26 and a radial outer surface 24. A rotor sleeve 30 rests on the radial outer surface 24 and serves as a throw-off protection for the rotor magnet 20. The rotor sleeve 30 is manufactured, for example, from sheet metal, in particular by means of a deep drawing method. For assembly, the rotor sleeve 30 is first inserted into the radial outer surface 24 of the rotor magnet 20 in the axial direction 8 with clearance. Thereafter, the locally restricted areas 32 are heat treated in such a way that they shrink after cooling and develop inherent tensile stresses. As a result, the inner diameter 29 of the rotor sleeve 30 is reduced, so that the rotor sleeve 30 is pressed in the radial direction 7 against the radial outer surface 24 of the rotor magnet 20. As a result, the rotor magnet 20 is pressed radially at its base surface 26 against the contact surface 16 of the base body 14. As a result, the rotor magnet 20 can be securely fixed to the base body 14 without the rotor sleeve 30 having to be inserted onto the rotor magnet 20 by means of a press fit. Figure 1 In the embodiment, a laser beam 40 is used as a heat source 42 for heat treatment of the restricted area 32, by means of which the locally restricted area 32 is preferably melted. If the laser beam 40 is directed onto the rotor sleeve 30 from the outside, a so-called thermal gap 34 is formed on the rotor sleeve, which preferably extends in the axial direction 8 of the rotor sleeve 30.

[0023] In the case of distribution over the circumference, a plurality of thermal gaps 34 are formed as limited heat-treated areas 32, such as in Figure 2 . Preferably, the thermal gaps 34 extend over the entire axial length 31 of the rotor sleeve 30 . The number of thermal gaps 34 can influence the radial pressing force with which the rotor sleeve 30 is pressed against the rotor magnets 20 . For example, a thermal gap 34 can be formed between two rotor magnets 20 in each case with respect to the circumferential direction 9 . This prevents the magnetic material of the rotor magnets 20 from being damaged during the heat treatment of the rotor sleeve 30 .

[0024] exist Figure 3, a cross-section of an electric machine 12 is shown as another exemplary embodiment. The rotor 10 is arranged within the stator 11, preferably having an electrically commutated winding that interacts with the rotor magnets 20 of the rotor 10. The rotor body 14 here comprises a hub 54, which is arranged on a rotor shaft 57. Radial webs 56 extend radially outward from the hub 54 to a yoke ring 55, which is closed in the circumferential direction 9. Recesses 52 are formed between the radial webs 56, which reduce the weight of the rotor 10. The base body 14 can, for example, consist of individual laminations stacked axially and connected to one another, in particular by means of stacking 51. On the outer circumference 15 of the yoke ring 55, the contact surface 16 for the rotor magnets 20 is designed as a flat surface in the circumferential direction 9. The rotor magnets 20 rest on this flat contact surface 16 with their flat base surface 26. The rotor magnets 20 here preferably have a "loaf-shaped" cross-section 23, wherein side surfaces 25 are respectively formed between the curved radial outer surface 24 and the flat inner base surface 26. Along the circumferential direction 9, radial retaining webs 22 are formed on the base body 14 between the rotor magnets 20. These radial retaining webs 22 serve to correctly position the rotor magnets 20 and can optionally also be constructed as spring elements 21, which fix the rotor magnets 20 along the circumferential direction 9 between the retaining webs 22. The rotor magnets 20 are preferably magnetized along the radial direction 7, wherein adjacent rotor magnets 20 then form opposite poles. In this case, the yoke ring 55 serves as a yoke between two adjacent rotor magnets 20. In Figure 3In the embodiment in FIG, the curvature of the radial outer surface 24 of the rotor magnet 20 differs from a circular ring around the center point 50 of the rotor 10. The radial extent of the radial retaining webs 22 is smaller than the radial extent of the side surfaces 25 of the rotor magnet 20. If, after axial insertion of the rotor sleeve 30, restricted heat-treated regions 32 are now formed tangentially between the rotor magnets 20, these regions generate inherent compressive stresses that press the rotor sleeve 30 in the radial direction 7 toward the rotor magnets 20. In this case, the rotor sleeve 30 rests radially against the rotor magnet 20 in the region of the curved radial outer surface 24. In the tangential peripheral region between two adjacent rotor magnets 20, the restricted heat-treated region 32 of the rotor sleeve 30 is at a radial distance from the radial retaining webs 22. Due to the inherent shrinkage stresses of the heat-treated region 32, the rotor sleeve 30 adheres radially to the surface of the rotor 10, so that, in particular, the rotor sleeve 30, after its heat treatment, deviates from a precisely circular shape about the center point 50. The limited heat-treated region 32 is preferably designed here as an axial heat gap 34, which extends in the axial direction 8 along the side surfaces 25 of the rotor magnets 20. The material of the rotor sleeve 30 is preferably non-magnetically conductive so that the magnetic field lines of the rotor poles extend radially outward from the rotor magnets 20 toward the stator 11. An air gap is formed between the outer circumference of the rotor sleeve 30 and the stator 11 so that the rotor 10 can rotate unimpeded within the stator 11. Axial heat gaps 34 are preferably formed between all rotor magnets 20, wherein the rotor 10 has, for example, six, ten, twelve, or eighteen rotor magnets 20, which extend substantially over the entire axial extent 13 of the base body 14. The electric machine 12 is designed, for example, as an electrically commutated EC motor, wherein the output element is arranged on the rotor shaft 57. The rotor magnets 20 are securely held on the base body 14 by the rotor sleeve 30, even if the rotor magnets 20 are damaged during operation.

[0025] It should be noted that with respect to the exemplary embodiments shown in the drawings and in the description, a wide variety of possible combinations of the individual features are possible. Thus, for example, the specific design and arrangement of the contact surface 16 and the rotor magnet 20 can be varied. For example, the rotor magnet 20 can also be disc-shaped or square-shaped instead of having a loaf-shaped cross section. Similarly, the specific design and number of radial retaining tabs 22 can be adapted to the requirements of the electric motor 12. The deformability of the rotor sleeve 30, and thus the resulting contact pressure, can be adjusted by the material used and its wall thickness, as well as by the number and extent of the limited heat-treated regions 32. As an alternative heat source 42, the heat-treated regions 32 can also be produced by induction heating, in which case multiple thermal gaps 34 can be simultaneously formed. The present invention is particularly suitable for use in EC motors designed as internal rotors, in particular for the rotational drive of components or for adjusting components in motor vehicles, but is not limited to such applications.

Claims

1. A rotor (10) for an electric machine (12), comprising a base body (14), on the radially outer circumference (15) of which a plurality of rotor magnets (20) are arranged, wherein the rotor magnets (20) are fixed to the base body (14) by means of a rotor sleeve (30) made of metal, wherein the rotor sleeve (30) has a limited heat-treated area (32) which radially clamps the rotor sleeve (30) to the base body (14).

2. The rotor (10) according to claim 1, characterized in that The heat-treated region (32) is designed as an axial heat gap (34), which extends in particular over the entire axial length (31) of the rotor sleeve (30).

3. The rotor (10) according to claim 1 or 2, characterized in that The rotor magnets (20) extend substantially over the entire axial length (13) of the base body (14), and the axial thermal gap (34) is arranged between two adjacent rotor magnets (20) along the circumferential direction (9).

4. The rotor (10) according to any one of the preceding claims, characterized in that Radial retaining webs (22) for the rotor magnets (20) are formed on the base body (14) along the circumferential direction (9) between the flat contact surfaces (16) for the rotor magnets (20), and the retaining webs in particular respectively abut tangentially against opposite side faces (25) of two adjacent rotor magnets (20).

5. The rotor (10) according to any one of the preceding claims, characterized in that The rotor magnets (20) have a "loaf-shaped" cross section (23) and respectively bear flatly against the contact surface (16) with their base surfaces (26), and the radial outer surface (24) is curved, the arc-shaped section (36) of the rotor sleeve (30) bears radially against the radial outer surface, and the rotor magnets (20) are pressed radially against the contact surface (16).

6. A rotor (10) according to any one of the preceding claims, characterised in that The rotor sleeve (30) is produced as an uninterrupted ring in the circumferential direction (9) and is produced in particular by means of deep drawing.

7. A rotor (10) according to any one of the preceding claims, characterised in that The base body (14) has a central hub (54) and a surrounding yoke ring (55), wherein the central hub is pressed onto the rotor shaft (57) and contact surfaces (16) for the rotor magnets (20) are molded on the outer side of the yoke ring, wherein radial webs (56) extend in particular between the hub (54) and the yoke ring (55).

8. An electric machine (12) having a rotor (10) according to any one of the preceding claims, which is rotatably arranged within a stator (11) having electronically commutated windings.

9. A method for producing a rotor (10) for an electric machine (12), preferably according to any one of the preceding claims, characterized by the following steps: - axially inserting the rotor sleeve (30) onto the rotor magnet (20); - local heating of the rotor sleeve (30) in order to form a restricted heat-treated area (32); - Cooling the rotor sleeve (30), wherein the heat-treated region (32) generates inherent shrinkage stresses that press the rotor magnets (20) in the radial direction (8) toward the contact surface (16).

10. The method according to claim 9, characterized in that The heat-treated region (32) is heated, in particular locally melted, by means of a laser beam (40).

11. The method according to claim 9 or 10, characterized in that The laser beam (40) is guided radially from the outside along the axial extension (31) of the rotor sleeve (30) in order to form an axial thermal gap (34).

12. The method according to claims 9 to 11, characterized in that The rotor sleeve (30) is plugged onto the rotor magnet (20) with a clearance fit without an introduction phase, and a press fit is formed between the rotor sleeve (30) and the rotor magnet (20) only after local heating of the heat-treated region of the rotor sleeve (30).

13. The method according to claim 9 or 12, characterized in that A restricted heat-treated area (32), in particular a plurality of axial heat seams (34) are heated simultaneously by means of induction heating.

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