Rotors for electric motors

Abstract

The invention relates to a rotor (1) for an electric machine, comprising magnet pockets (20) and, inside the magnet pockets (20), permanent magnets (10), a first polymer composition comprising magnetic filler particles in a first region (22) and a second polymer composition comprising electrically conductive filler particles that do not induce eddy currents in a second region (24), as well as to a method for producing such a rotor (1) and a casting system for carrying out said method.

Description

Technical Field

[0001] The present invention relates to a rotor for an electric motor, comprising magnet pockets (Magnettasche, or magnet bags) and, within the magnet pockets, permanent magnets, a first polymer composition comprising magnetic filler particles in a first region and a second polymer composition comprising electrically conductive filler particles for avoiding the formation of eddy currents in a second region, as well as to a method for producing such a rotor. Background Art

[0002] A permanent magnet-excited electric motor is characterized by a stator carrying an electrical winding and a rotor rotatably mounted relative to the stator. The rotor carries a plurality of permanent magnets, the stator windings interacting with the magnetic fields of the permanent magnets during operation. A manufacturing challenge is the securing of the permanent magnets to the rotor base, also referred to as the lamination stack, the lamination pack, or simply the rotor laminations. The securing, typically achieved in, for example, tubular or strip-shaped pockets in the base, must be achieved with extreme precision in the tangential and radial directions to avoid rotor imbalance, which is particularly detrimental for high-speed machines. Imbalance is not only important during manufacturing, but also during operation and over the entire service life of the motor. Furthermore, economical production of the lamination stack and the permanent magnets is not possible without relatively large manufacturing tolerances.

[0003] The magnet fixation of embedded magnets has hitherto always been achieved by means of the same material, for example by means of adhesive bonding, mechanically by means of clamping webs, by means of adhesive tape, by means of an expandable coating or by means of transfer molding. Summary of the Invention

[0004] However, the methods for producing rotors and the corresponding rotors known from the prior art are not entirely satisfactory. Therefore, there is a need to provide a new method and a corresponding rotor that includes precisely oriented permanent magnets within the rotor pockets and has physical properties suitable for continuous operation.

[0005] According to the present invention, this technical problem is solved by a rotor for an electric machine, comprising a rotor lamination, wherein the rotor lamination comprises magnet pockets; permanent magnets, wherein the permanent magnets are fixed within the magnet pockets; wherein the magnet pockets have a first region and a second region and comprise a first polymer composition introduced into the first region by injection molding, and a second polymer composition introduced into the second region by injection molding; wherein the first polymer composition in the first region comprises magnetic filler particles, and the second polymer composition in the second region comprises electrically conductive filler particles. It is known to those skilled in the art that the electrically conductive particles are selected to have an appropriate size to avoid eddy currents.

[0006] To achieve precise, centered orientation of the magnets within the rotor's mounting pockets or magnet pockets, the present invention provides for the permanent magnets to be fixed using resin transfer molding, also known as injection molding. Injection molding achieves precise orientation of the permanent magnets within the magnet pockets. The inventive use of two different compositions—a first composition in the first region and a second composition in the second region—enables selective fixing of the permanent magnets and, moreover, optimal adjustment of the physical properties of the magnet mounting structure by selectively varying the polymer composition.

[0007] According to the invention, the polymer composition is introduced by means of injection molding, generally known as "resin transfer molding." Resin transfer molding is a method for producing molded parts from thermosetting plastics and elastomers, in which the molding compound is injected from a generally heated antechamber through a distribution channel into the mold cavity by means of a piston, where it hardens due to heat and pressure. Polymers, preferably formaldehyde resins and reactive resins, can be used as molding compounds.

[0008] The core of the rotor and method according to the present invention lies in the selective design of the magnet mounting structure for the embedded magnets. To functionalize the magnetically critical areas of the magnet mounting structure, a polymer composition, such as epoxy resin, is filled with magnetic particles. In the thermally critical areas, appropriately sized conductive particles are used, which have significantly better thermal conductivity than conventional, non-conductive particles, to more efficiently dissipate heat from the magnets. These areas filled with magnetic particles provide additional magnetic holding force and can be used for mechanical magnet mounting.

[0009] Most importantly, the use of two different compositions according to this embodiment, namely a first composition in the first region and a second composition in the second region, enables optimal adaptation (or adjustment) of the physical properties of the magnet fixing structure, in particular the heat emission, while achieving precise magnet positioning, wherein the first polymer composition in the first region has magnetic filler particles and the second polymer composition in the second region has conductive particles.

[0010] According to a preferred embodiment, a rotor is described, in which the first polymer composition does not contain any electrically conductive filler particles. According to a preferred embodiment, a rotor is described, in which the second polymer composition does not contain any magnetic filler particles.

[0011] Most importantly, according to this embodiment, the use of two different compositions, a first composition in the first region and a second composition in the second region, allows for optimal adaptation of the physical properties of the magnet mounting structure, particularly heat dissipation, while simultaneously achieving precise magnet positioning. The first polymer composition in the first region contains magnetic filler particles and no conductive filler particles, while the second polymer composition contains conductive filler particles and no magnetic filler particles. By separating regions containing only conductive filler particles or only magnetic filler particles, heat dissipation and magnetic transfer can be optimized.

[0012] According to a preferred embodiment, a rotor is described, wherein the first polymer composition comprises a first polymer and the second polymer composition comprises a second polymer.

[0013] In general, by using a first polymer composition comprising a first polymer and using a second polymer composition comprising a second polymer, the polymer compositions are prevented from mixing with each other.

[0014] Preferably, a rotor is described in which the demulsibility of the first polymer composition, in particular but not exclusively the density and / or viscosity and / or hydrophilicity and / or hydrophobicity, differs from the demulsibility, density and / or viscosity and / or hydrophilicity and / or hydrophobicity of the second polymer composition. In the context of the present application, a difference in demulsibility is understood to mean the property that the polymer compositions do not mix with one another in the liquid state during transfer molding.

[0015] In this context, it is preferred that the polymers, or polymer compositions containing these polymers, differ from one another in their type, in particular in their physicochemical properties, such as hydrophilicity and / or hydrophobicity, so that the polymer compositions do not mix with one another in the liquid state during transfer molding. Therefore, according to a further preferred embodiment, the first polymer is a substantially hydrophilic polymer, while the second polymer is a substantially hydrophobic polymer. This makes it possible, in particular, to carry out a method in which the first and second polymer compositions are injected simultaneously into the magnet pockets, since the different physicochemical properties prevent mixing of the first and second compositions during rotor production.

[0016] On the other hand, the demulsification of the composition or the avoidance of mixing can also be achieved in the following manner, that is, the density and / or viscosity of the first polymer composition is different from the density and / or viscosity of the second polymer composition. On the one hand, by changing the first polymer of the first polymer composition relative to the second polymer composition, the density and / or viscosity of the first polymer composition can be changed relative to the density and / or viscosity of the second polymer composition. Another possibility is to change the concentration of the filler particles and the type and amount of the additive. In general, by the density or viscosity of the first polymer composition that is significantly different from the second polymer composition, the polymer compositions are prevented from mixing with each other. This can especially be performed in the following method, in which the first polymer composition and the second polymer composition are injected into the magnet pocket at the same time.

[0017] According to a further aspect of the present invention, a casting system for producing a rotor according to the invention is described, wherein the casting system has a first channel, through which a first polymer composition is introduced into a first region of the magnet pockets, and a second channel, through which a second polymer composition is introduced into a second region of the magnet pockets.

[0018] According to a preferred embodiment, a rotor is described in which the first region is arranged laterally of the magnet pockets. The lateral sides of the magnet pockets are defined as regions adjoining the long sides of the magnets, which are designed as thin strips. Since magnetic transfer is desired, the use of magnetic filler particles is preferred.

[0019] According to a preferred embodiment, a rotor is described in which the second region is arranged on the top side of the magnet pockets. The top side of the magnet pockets describes the region adjoining the short sides of the magnets, which are designed as thin strips. Electrical steel sheets obstruct the magnetic flux toward the stator toward the iron edges, i.e., the top sides of the magnet pockets, and between the magnets. Therefore, as little electrical steel sheet as possible is used at these locations. Therefore, no additional magnetic filler particles are used, with electrically conductive fillers being advantageous because they can dissipate heat.

[0020] According to another aspect of the present invention, a method for manufacturing a rotor is described, wherein the method comprises the steps of:

[0021] - providing a rotor for an electric machine, the rotor comprising a rotor lamination, wherein the rotor lamination comprises magnet pockets;

[0022] -Placing the permanent magnet into the magnet pocket, wherein the method further comprises the steps of:

[0023] - placing a first polymer composition into a first region of the magnet pocket by means of injection molding;

[0024] - introducing a second polymer composition into the second region of the magnet pocket by means of injection molding.

[0025] In the production process, preferably in a first step, a matrix with electrically conductive particles is injected around the magnets in the magnet pockets. Parallel thereto or in a second step, a matrix with magnetic particles is injected into the associated regions.

[0026] The different embodiments of the invention mentioned in this application can advantageously be combined with one another unless otherwise stated separately. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be described below with reference to the accompanying drawings.

[0028] Figure 1 shows a rotor for an electric machine according to one embodiment; and

[0029] Figure 2 The rotor is shown in another view. DETAILED DESCRIPTION

[0030] Figure 1 A rotor 1 for an electric machine is shown, comprising a rotor lamination 10, wherein the rotor lamination 10 includes magnet pockets 20. Permanent magnets are positioned within the magnet pockets 20. The magnet pockets 20 have a first region 22 and a second region 24. A first polymer composition is introduced into the first region 22 by injection molding. Simultaneously or subsequently, a second polymer composition is introduced into the second region 24 by injection molding. The first polymer composition in the first region 22 contains magnetic filler particles. The second polymer composition in the second region 24 contains electrically conductive filler particles.

[0031] The core of the rotor and method according to the present invention lies in the selective design of the magnet-fixing structure of the embedded magnets. To functionalize the magnetically critical region 22 of the magnet-fixing structure, a polymer composition, such as epoxy resin, is filled with magnetic particles. Conductive particles, which have significantly better thermal conductivity than conventional, non-conductive particles, are used in the thermally critical region 24 to more efficiently dissipate heat from the magnets. Regions 22 filled with magnetic particles provide additional magnetic holding force and can also be used for mechanical magnet fixing.

[0032] First regions 22 are arranged on the lateral sides of the magnet pockets. Second regions 24 are arranged on the top sides of the magnet pockets. Second regions 24 can have various shapes, as can be seen in the figures. Towards the iron edges, i.e., the top sides 24 of the magnet pockets 20 and between the magnets 30, the electrical steel sheet obstructs the magnetic flux toward the stator. Therefore, minimal electrical steel sheet is used in these locations. Therefore, no additional magnetic filler particles are used, although electrically conductive filler particles are advantageous because they are thermally conductive.

[0033] Figure 2 Another view shows the rotor. There are a plurality of magnet pockets 20. Permanent magnets 30 are fixed inside the magnet pockets 20. Each magnet pocket 20 has a first region 22 and a second region 24. A first polymer composition is introduced into the first region 22 by injection molding. Simultaneously or subsequently, a second polymer composition is introduced into the second region 24 by injection molding. The first polymer composition in the first region 22 contains magnetic filler particles, as already described. Figure 1 The second polymer composition in the second region 24 has conductive filler particles, as already described for Figure 1 As described.

[0034] List of Reference Numerals

[0035] 1 rotor

[0036] 10 rotor laminations

[0037] 20 magnet pockets

[0038] 22 First Area

[0039] 24 Second Area

[0040] 30 permanent magnets

Claims

1. A rotor (1) for an electric motor, comprising A rotor lamination (10), wherein The rotor lamination (10) includes a magnet pocket (20), and the magnet pocket (20) has a first region (22) and a second region (24); A permanent magnet (30) is positioned inside the magnet pocket (20); a first polymer composition having magnetic filler particles, which is introduced into the first region (22) by injection molding; and a second polymer composition having electrically conductive filler particles, which is introduced into the second region (24) by injection molding; Wherein, the first polymer composition is different from the second polymer composition.

2. The rotor (1) according to claim 1, wherein The first polymer composition having magnetic filler particles in the first region (22) does not have conductive filler particles.

3. The rotor (1) according to claim 1, wherein The second polymer composition having conductive filler particles in the second region (24) does not have magnetic filler particles.

4. The rotor (1) according to claim 1, wherein: The first polymer composition comprises a first polymer and the second polymer composition comprises a second polymer.

5. The rotor (1) according to any one of claims 1 to 3, wherein: The demulsibility of the first polymer composition is different from the demulsibility of the second polymer composition.

6. The rotor (1) according to claim 5, wherein The demulsibility properties are density and / or viscosity and / or hydrophilicity and / or hydrophobicity.

7. The rotor (1) according to any one of the preceding claims 1 to 3, wherein: The first region (22) is arranged on a lateral side of the magnet pocket.

8. The rotor (1) according to any one of the preceding claims 1 to 3, wherein The second region (24) is arranged on the top end side of the magnet pocket.

9. A method for manufacturing a rotor according to any one of claims 1 to 8, comprising the steps of: - A rotor (1) for an electric machine is provided, the rotor comprising a rotor lamination (10), wherein: The rotor lamination (10) includes a magnet pocket (20); - placing the permanent magnet (30) into the magnet pocket (20), characterized in that the method further comprises the steps of: - placing a first polymer composition into the first region (22) of the magnet pocket (20) by means of injection molding, wherein the first polymer composition comprises magnetic filler particles; - placing a second polymer composition into the second region (24) of the magnet pocket (20) by means of injection molding, wherein the second polymer composition comprises electrically conductive filler particles; - wherein the first polymer composition is different from the second polymer composition.

10. An injection molding-gating system for carrying out the method according to claim 9, wherein: The pouring system A first channel is provided through which a first polymer composition can be introduced into a first region (22) of the magnet pocket (20) and A second channel is provided through which a second polymer composition can be introduced into a second region (24) of the magnet pocket (20).

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