Rotor for an electric machine

Abstract

Rotor (4) for a permanent-magnetically excited electrical machine, comprising a shaft (8), a rotor body (9) arranged on the shaft (8), and an integrally formed, multi-pole permanent magnet (10) arranged on the rotor body (9), wherein the rotor magnet (10) consists of a magnetically anisotropic permanent magnet material, wherein the rotor body (9) has a guide plate (11) on its circumference, which has a number of radially outwardly projecting projections (12) corresponding to the number of magnetic poles (16), wherein the projections (12) extend in the axial direction over the entire length of the rotor body (9), and wherein at least the guide plate (11) consists of a ferromagnetic material, wherein recesses (17) are provided radially inside the guide plates (11) of the rotor body (9) and are filled with non-magnetic material (23), characterized in that the non-magnetic material (23) simultaneously forms end plates (24) on the axial end faces of the rotor (4).

Description

[0001] The invention describes a rotor for a permanent magnet excited brushless electric machine, with a shaft, with a rotor body arranged on the shaft and with an integrally formed, multi-pole permanent magnet arranged on the rotor body.

[0002] Such one-piece multipole rotor magnets are, for example, injection-molded directly around a rotor body. The permanent magnet is then magnetized by applying an external magnetic field. One advantage of this is that even very small rotor diameters can be realized, since no individual magnets need to be mounted on or in the rotor body.

[0003] The rotor body is usually designed as a cylindrical sleeve that is arranged on the shaft.

[0004] In the state of the art, this rotor body is necessarily made of a non-magnetic, i.e. para- or diamagnetic material, for example aluminum, so that no short circuit of the magnetic field lines occurs inside the rotor body.

[0005] For injection-molded rotor magnets, for example, powdered magnetic material is mixed with plastic and then formed into a plastic-bonded permanent magnet by injection molding. Rare earth materials are typically used, which are comparatively expensive.

[0006] The use of magnetically anisotropic permanent magnets or magnetic materials is known. Magnetic anisotropy means that the permanent magnet material exhibits a preferred direction of magnetization. An anisotropic magnet can be created, for example, in an injection molding process by arranging magnets in the injection molding tool. The external magnetic field of the alignment magnets causes the magnetic material particles to align with this magnetic field. The resulting rotor magnet has a higher remanence in these predetermined preferred directions, allowing a higher magnetic flux density to be achieved through subsequent magnetization.

[0007] The smaller the particle size of the permanent magnet material powder, the greater the anisotropy that can be achieved.

[0008] The publication DE 10 2008 038 726 B3 describes a fastening of a rotor body to a shaft. The rotor body is stacked from individual sheets and has a polygonal central opening for inserting the shaft. At least one bending element is arranged on at least one polygonal side of the central opening. This element has linear contact with the shaft and is deflected by pressing the shaft into the central opening.

[0009] Document US 2006 / 0 113 857 A1 shows a ring magnet made of magnetically anisotropic magnetic material.

[0010] An object of the invention is to provide a rotor in which the rotor magnet can be manufactured with less magnetic material and yet with a comparable magnetic flux density.

[0011] The invention is defined in the independent claims. Advantageous embodiments are set forth in the subclaims.

[0012] According to a first aspect of the invention, a rotor is provided whose rotor body comprises a guide plate having a number of radially outwardly tapered projections corresponding to the number of magnetic poles. The projections extend axially over the entire length of the rotor body, and at least the guide plate is made of a ferromagnetic material. Recesses filled with non-magnetic material are provided within the guide plates of the rotor body. The non-magnetic material also forms end plates on the axial end faces of the rotor.

[0013] The radial thickness of the magnetic material is significantly thinner in the area of ​​the projections than in the area between the projections. This significantly reduces the amount of magnetic material required compared to a ring-shaped permanent magnet, resulting in correspondingly lower material costs.

[0014] The permanent magnet is preferably magnetically anisotropic. To impart a preferred magnetic direction, the injection molding tool has built-in permanent magnets that apply a magnetic field to the injection molding compound. This causes the isotropic permanent magnet material particles in the plastic melt to align according to this external magnetic field.

[0015] The ferromagnetic guide plate acts as a magnetic flux concentrator, attracting the magnetic field lines of the alignment magnets. This results in a desired pre-alignment of the permanent magnet particles in the plastic mass. The permanent magnet thus acquires anisotropy, and due to the subsequent magnetization, it exhibits a higher remanence in this preferred direction.

[0016] Thus, despite a smaller amount of material, a magnetic flux density approximately equal to that of an anisotropic ring magnet can be achieved.

[0017] To further optimize this effect, the guide plate can be shaped so that the magnetic field lines of the alignment magnets are essentially perpendicular to the surface of the guide plate. This enhances the concentrating effect of the guide plate and optimizes the alignment of the magnetic material particles in the plastic melt during the injection molding process.

[0018] In order to achieve an optimal magnetic flux density in the rotor magnet, it is advantageous if both the magnetic pre-alignment and the magnetization are carried out in such a way that the magnetic pole transitions between the permanent magnet poles are essentially located in the area of ​​the projections.

[0019] Furthermore, in the area of ​​the permanent magnet poles, whose field lines emerge radially from the rotor, the guide plate has recesses, preferably located radially inward, filled with non-magnetic material. This non-magnetic material can be, for example, air or, preferably, a plastic material that does not contain permanent magnet particles and that is introduced into the recesses, for example, in a subsequent or preceding injection molding process.

[0020] A rotor magnet according to the invention can preferably be manufactured by injection molding. The permanent magnet consists of a plastic-bonded anisotropic permanent magnet material.

[0021] Any known permanent magnet material can be used for this purpose, in particular those magnet materials that contain rare earths, such as samarium-cobalt, neodymium-iron-boron or samarium-iron-nitrogen.

[0022] The rotor body can be constructed in a variety of ways, as long as the guide plate is made of a ferromagnetic material. For example, the rotor body can have a plastic core to which the guide plate is attached. Or the rotor body can be made in one piece with the guide plate from a ferromagnetic material.

[0023] It is particularly advantageous if the rotor body is stacked from individual rotor laminations. These rotor laminations can, for example, be manufactured in a single stamping process with the stator laminations of an electric motor. This eliminates the need for an additional manufacturing step and results in less waste.

[0024] A further aspect of the invention relates to an electric motor with a rotor according to the first aspect of the invention. This can be a preferably brushless, electronically commutated electric motor with a rotor according to the invention. Thus, a rotor according to the invention can be designed for an internal rotor or an external rotor. Likewise, the number of magnetic poles plays only a minor role. In principle, the invention can be used with just two magnetic poles. The rotor according to the invention is particularly advantageously used for rotor magnets with at least six magnetic poles.

[0025] The invention is explained in more detail below with reference to the accompanying drawings, the embodiments shown being in no way limiting.

[0026] It shows: Fig. 1 a longitudinal section through an electric motor according to the invention, Fig. 2 an oblique view of a rotor according to the invention with eight magnetic poles, Fig. 3 a cross-section of the rotor of the Fig. 2, Fig. 4 a longitudinal section of the rotor of the Fig. 2, Fig. 5 an oblique view of a rotor body stacked from individual rotor laminations for a six-pole magnet, Fig. 6 a possible design of a rotor lamination for the rotor body, Fig. 7 another farm of a rotor lamination for the rotor body, Fig. 8 a comparison of the magnet volume for different rotor body shapes, Fig. 9 a cross section of an injection molding tool for producing a rotor according to the invention and Fig. 10 the magnetic field line pattern in the tool of the Fig. 9.

[0027] The Fig. Figure 1 shows a motor according to the invention, designated overall by 1, which in this example is designed as an internal rotor. However, the invention can also be readily used for an external rotor. The motor 1 has a motor housing 2, a stator 3, and a rotor 4.

[0028] The stator 3 has a stator core 5, which is stacked in a known manner from individual stator laminations 6 and on which the stator windings 7 are arranged.

[0029] Regarding the exact structure of the motor housing 2, the stator 3 and possibly other components of the motor, reference is made to the published patent application DE 10 2008 053 ​​233 A1.

[0030] The rotor 4 has a shaft 8 on which a rotor body 9 and a one-piece multi-pole rotor magnet 10 are arranged. ( Fig. 2)

[0031] The rotor magnet 10 is a plastic-bonded permanent magnet that is injection-molded onto the rotor body 9. To achieve a high flux density, the rotor magnet 10 is magnetically anisotropic by applying an external magnetic field to the injection mold. The particles of the magnetic material in the plastic align along the external magnetic field. After the injection molding compound has cooled, the orientation of the permanent magnet particles is retained. The permanent magnet then exhibits a higher remanence in this preferred direction than in the other spatial directions. It can therefore be magnetized with a higher magnetic flux density in this preferred direction.

[0032] The permanent magnet poles are then imprinted by magnetization in a magnetizing device according to the anisotropic pre-alignment. Corresponding magnetizing devices are disclosed, for example, in patents DE 10 2004 018 963 B4 and AT 507 023 B1.

[0033] In the example shown, the rotor body 9 is stacked from individual rotor laminations 21. For this purpose, for example, those in the Fig. 6 and Fig. The star-shaped rotor laminations 21 shown in Figure 7 can be used. These rotor laminations 21 can preferably be punched from the same sheet metal at the same time as the stator laminations 6, in the rotor recess that is already present. This eliminates additional manufacturing effort and results in less waste.

[0034] The rotor laminations 21 are then stacked twisted against each other, as is usual with stators 3, in order to compensate for tolerances in the lamination material.

[0035] According to the invention, the rotor body 9 has a guide plate 11 on the circumference, which has a number of radially outwardly projecting, tapered projections 12 corresponding to the number of magnetic poles, wherein the projections 12 are extended in the axial direction over the entire length of the rotor body 9 ( Fig. 5). In the example, the cross-section of the rotor body 9 is approximately star-shaped ( Fig. 3), whereby the tips of the projections 12 are rounded.

[0036] This shape of the rotor body 9 reduces the volume of the molded-on rotor magnet 10 compared to a ring magnet, requiring less magnetic material in the injection molding process. This significantly reduces the manufacturing costs of the rotor magnet 10. Depending on the design of the rotor body 9, material savings of up to 30% can be achieved while maintaining the same magnetic flux density.

[0037] This is in Fig. 8 is shown schematically. Fig. Figure 8(a) shows a ring magnet according to the prior art. The Fig. In comparison, the rotor magnets 10 according to the invention shown in Figures 8(b) and (c) have only approximately 80% and 75% of the volume of magnetic material, respectively, which is achieved by the different shapes of the rotor bodies.

[0038] In order for the rotor magnet 10 to have a flux density comparable to that of a ring magnet despite the lower material requirements, according to the invention at least the guide plate 11 is made of a ferromagnetic material. The guide plate 11 is preferably shaped such that the magnetic field lines 13 ( Fig. 10) of an external magnet 14 for aligning the anisotropic magnetic material during the injection molding process are substantially perpendicular to the surface 15 of the guide plate 11.

[0039] The guide plate 11 acts as a field concentrator and is necessary to ensure that the field lines 13 of the external alignment magnetic field are closed without detours or attenuation. It is therefore absolutely essential that the guide plate 11 be made of a ferromagnetic material. This was previously completely impossible in the prior art, as otherwise the magnet would be short-circuited internally.

[0040] In order to prevent a magnetic short circuit to the shaft 8, recesses 17 filled with non-magnetic material are preferably located between adjacent projections 12 radially inside the guide plate 11.

[0041] The magnetic poles 16 are aligned such that the pole transitions 22 of the rotor magnet 10 are aligned as precisely as possible with the projections 12. It is important that both the anisotropic alignment during the injection molding process and the subsequent magnetization occur precisely according to this alignment. Inaccurate alignment of the magnetic poles 16 with the projections 12 results in a reduction in the magnetic flux density.

[0042] For alignment, the shaft 8, for example, has a flattening 20.

[0043] However, the guide plate 11 can also be formed separately and arranged on a rotor core. For example, it is conceivable for a guide plate made of ferromagnetic material to be arranged on a plastic core.

[0044] The rotor magnet 10 can then be molded onto the stacked rotor body 9 in an injection molding process. In a further injection molding process or in a two-component process, the recesses 17 in the rotor laminations can be filled with a non-magnetic material 23, for example, with a plastic without magnetic material, to increase the stability of the rotor 4, for example. End covers can also be molded from this plastic.

[0045] A possible method for producing a rotor 4 according to the invention includes, for example, the following steps: First, the rotor body 9, consisting of individual rotor laminations 21, is pressed onto a shaft 8. The individual rotor laminations 21 are rotated relative to one another to compensate for magnetic and geometric manufacturing and sheet metal tolerances.

[0046] The rotor body 9 is then inserted into an injection molding tool 18 and aligned according to the projections 12 relative to the alignment permanent magnets 14 arranged in the injection molding tool. Subsequently, the injection molding is carried out using a plastic-bonded magnetic material while subjected to the magnetic field 13 generated by the alignment magnets 14. The permanent magnet material particles in the plastic injection molding compound align themselves according to the external magnetic field 13.

[0047] Optionally, a non-magnetic sleeve, for example made of stainless steel, can be pushed onto the outer circumference of the rotor magnet as mechanical protection.

[0048] Also optionally, in a further injection molding process, non-magnetic material 23, in particular plastic without permanent magnet material, can be injected into any recesses 17 present in the rotor laminations 21. At the same time, end plates 24 can be molded onto the end faces of the rotor body 9.

[0049] Finally, the permanent magnet is magnetized in a magnetizing device.

[0050] However, a rotor magnet according to the invention can also be produced by other methods, for example by sintering, which is why the method described is not intended to be restrictive in any way.

[0051] A corresponding injection molding tool 18 is shown as an example in the Fig. 9. The tool 18 has a receptacle in the center for the rotor body 9 to be overmolded. The tool 18 contains an alignment permanent magnet 14 for each future rotor magnet pole to align the permanent magnet particles distributed in the plastic compound. In the example, the alignment magnets 14 are approximately trapezoidal in shape and magnetized tangentially according to the arrows to essentially achieve a Halbach field.

[0052] As in Fig. As can be seen in Figure 10, the field lines 13 of the alignment magnets 14 extend in the magnetic material in such a way that they are each essentially perpendicular to the surface 15 of the guide plate 11, thereby ensuring optimal alignment of the permanent magnet particles in the plastic melt. As already described above, this ensures an optimal anisotropic magnetic formation of the rotor magnet 10. Reference symbol 1 engine 2 engine housings 3 Stator 4 Rotor 5 Stator core 6 Stator sheet 7 Stator winding 8 Wave 9 Rotor body 10 rotor magnet 11 Baffle 12 lead 13 Magnetic field line 14 Alignment magnet 15 Surface guide plate 16 magnetic pole 17 Recess 18 injection molding tool 20 Flattening 21 Rotor sheet 22 Pole transition 23 non-magnetic material 24 end plates

Claims

[1] Rotor (4) for a permanent magnet excited electrical machine, with a shaft (8), with a rotor body (9) arranged on the shaft (8) and with an integrally formed, multi-pole permanent magnet (10) which is arranged on the rotor body (9), wherein the rotor magnet (10) consists of a magnetically anisotropic permanent magnet material, wherein the rotor body (9) has a guide plate (11) on the circumference, which has a number of radially outwardly projecting projections (12) corresponding to the number of magnetic poles (16), wherein the projections (12) are extended in the axial direction over the entire length of the rotor body (9) and that at least the guide plate (11) consists of a ferromagnetic material, wherein recesses (17) are provided radially inside the guide plates (11) of the rotor body (9) and are filled with non-magnetic material (23), characterized bythat the non-magnetic material (23) simultaneously forms end plates (24) on the axial end faces of the rotor (4). [2] Rotor (4) according to claim 1, wherein the guide plate (11) is shaped such that the magnetic field lines (13) of an external alignment magnet (14) for aligning the anisotropic magnetic material are substantially perpendicular to the surface (15) of the guide plate (11). [3] Rotor (4) according to claim 1 or 2, wherein the pole transitions (22) of adjacent rotor magnetic poles (16) are each arranged in the region of the projections (12). [4] Rotor (4) according to one of claims 1 to 3, wherein the rotor magnet (10) is made of a plastic-bonded permanent magnet material in an injection molding process. [5] Rotor (4) according to one of claims 1 to 4, wherein the rotor body (9) is stacked from individual rotor laminations (21). [6] Electric motor (1) with a rotor (4) according to one of claims 1 to 5.

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