Rotor device and motor having the same

Abstract

The invention relates to a rotor arrangement (10) for a DC motor (100), comprising: a rotor shaft (14); a first layer formed on the rotor shaft (14) or an iron core (30) mounted on the rotor shaft (14); the invention relates to a rotor (1) comprising a first layer (22) and a second layer (22), the second layer (22) being formed on an outer surface (24) of the first layer and constituting a second magnetic layer (22), the second magnetic layer (22) having the shape of a cylindrical shell, the cylindrical shell of the second magnetic layer (22) having a thickness ((d2-d1) / 2) which is constant in the circumferential direction (P), measured in the radial direction from a longitudinal axis (Z) of the rotor shaft, and a length (L) measured in the axial direction parallel to the longitudinal axis (Z), wherein the ratio of the length (L) to the difference (d2-d1) between the outer diameter (d2) and the inner diameter (d1) of the second magnetic layer (22) is in the range between 4 and 15, including a boundary value.

Description

Technical Field

[0001] Various aspects relate to a rotor device for an electric motor having at least one permanent magnet, particularly a brushless DC motor, and such motors. Background Technology

[0002] As is well known, brushless direct-current motors (BLDC motors) can be used to drive moving parts in vehicles, such as sunroofs. These motors typically include a rotor equipped with permanent magnets and a stationary stator, which may have coils with iron cores that generate a magnetic field when current is applied in a controlled manner. BLDC motors can, for example, operate in three phases.

[0003] Current BLDC motor designs employ a rotor with concentrically arranged laminated steel plates on the shaft from the motor to the gearbox. In so-called SPM (surface permanent magnet) type motors, individual permanent magnets arranged in an alternating polarity orientation in the circumferential direction can be mounted on the outer surface of the relevant steel plate assembly.

[0004] Alternatively, in the IPM (internal permanent magnet) type, the permanent magnet can be mounted in a receiving section within a steel plate assembly. Typically, in both cases (SPM and IPM), magnetic adhesive is used to firmly secure the permanent magnet in place with a durable, high-strength connection. At least for SPM type motors, an additional rotor cover is provided to prevent the permanent magnet from detaching from the rotor due to centrifugal force at high speeds.

[0005] However, the aforementioned rotor design has some problems or drawbacks. On the one hand, it requires a large number of individual components, making the assembly process for the rotor unit very complex. This increases costs. Furthermore, due to the different material structures, at least when the motor is designed for high speeds, the rotor must be balanced, requiring additional assembly steps and, if necessary, additional counterweights.

[0006] Furthermore, in the aforementioned applications, the number of poles in the sintered magnets used in BLDC motors can hardly be increased due to limitations in aspect ratio (i.e., the ratio of height to width). Typically, the stator has 6 slots and 4 poles. However, to reduce, for example, the effect of cogging torque during operation, increasing the number of poles to 8 is highly desirable. Therefore, conventional structures may result in excessively low efficiency.

[0007] Finally, the issue of adverse noise must also be considered. As mentioned above, the additional number of components in the rotor can cause rotor imbalance, which, if not compensated for, can lead to increased noise.

[0008] Composite magnets or bonded magnets can provide a solution. The term "bonded" here does not refer to the "adhesive bonding" used in the aforementioned sintered magnets, but rather to magnets bonded with plastic, injection-molded, or die-cast. For example, such magnets can be made by embedding hard ferrite or rare-earth magnetic powder (generally, all sintered magnetic materials can be used in composite components (ferrite, NdFeB, SmCo, etc.)) into thermoplastic plastics (matrix materials: PA6, PA12, PPS, etc.).

[0009] Here, the proportion of magnetic powder determines the magnetic and mechanical properties. The proportion of magnetic powder can be, for example, between 84% and 94% (by weight). The bonded magnets offer a variety of possible magnetization shapes and geometries, especially complex shapes.

[0010] JP4701641B2 and US2018 / 109167A1 describe a rotor magnet (permanent magnet) consisting of a bonding layer. In its assembled state, the rotor magnet extends annularly around a rotor core fixed to a rotor shaft. A soft magnetic ferrite layer immediately adjacent to the rotor core has a generally wavy or sinusoidal thickness distribution in the circumferential direction. Subsequently, a thinner hard magnetic rare-earth layer is attached, its interior matching the wavy surface, and its exterior being cylindrical. The rare-earth layer forms eight thicker regions at the "troughs," which, upon magnetization, form eight magnetic poles.

[0011] Similarly, CN115036092A discloses a double-layer magnet structure in which the inner ring is made of a soft magnetic material and the outer ring is made of a hard magnetic material. Through appropriate external magnetization, eight magnetic poles are provided in segments, which are formed by trapezoids (instead of sinusoids as described above) protruding inward from the outer ring, thus making the outer ring thicker in these regions.

[0012] JP2013-198220A discloses an annular magnet for driving a rotor device of a magnetic storage hard disk, the annular magnet being composed of two cylindrical layers.

[0013] The concept of permanent magnets that extend continuously in a ring around the rotor shaft needs further refinement, especially in finding a balance between excessively high costs and the adverse effects of their special structure on magnetization in the assembled state. Summary of the Invention

[0014] The invention that meets this need relates to a rotor device for a DC motor, such as a rotor device for a vehicle roof drive, comprising a rotor shaft, a first layer formed on or mounted on an iron core on the rotor shaft, and a second layer, wherein the second layer is formed on the outer surface of the first layer and constitutes a second magnetic layer.

[0015] The second magnetic layer is cylindrical in shape, wherein the cylindrical shell of the second magnetic layer has a constant thickness in the circumferential direction, measured radially from the longitudinal axis of the rotor shaft, and a length measured axially parallel to the longitudinal axis. The ratio of this length to the difference (d2-d1) between the outer diameter d2 and the inner diameter d1 of the second magnetic layer has a value ranging from 4 to 15, including boundary values. Both diameters are measured perpendicular to the axis of the rotor shaft.

[0016] Therefore, the second magnetic layer extends continuously and uninterruptedly around the rotor shaft—it does not break down into individual magnets that need to be fixed separately. The formation of magnetic poles is achieved through magnetization, which depends on their position in the circumferential direction, inherent in conventional single magnets. Since the aspect ratio of a single magnet is not important in this case, there are no corresponding limitations, and it is entirely possible to form eight or more magnetic poles in the circumferential direction of the cylindrical outer shell of the second magnetic layer.

[0017] Furthermore, the second magnetic layer has a constant thickness in the circumferential direction. In existing technologies involving similar toroidal magnet structures, thickened portions are formed in the relevant magnetic layer at the locations where magnetic poles need to be formed. Conversely, this saves valuable rare-earth materials where thickening is not required (i.e., between magnetic poles). However, there is a drawback here: the corresponding mold and the magnetic field used for magnetization must be perfectly matched or aligned, as misalignment can have significant effects. Moreover, if the second magnetic layer has a figure-eight geometric symmetry, defects in the mold will be more pronounced in imbalances; this does not occur when forming a layer of constant thickness, as the formation of such a layer is inherently easy to control.

[0018] Furthermore, the study found that during operation, under drastically changing thermal conditions, the second magnetic layer is subjected to considerable stress, for example, due to the difference in thermal expansion between the first and second layers and between the rotor shaft with the iron core. A cylindrical shell-shaped layer of constant thickness helps improve durability and avoids "weak points" between the various thickened sections.

[0019] The current configuration of the rotor unit is based on the particular understanding that the length of the cylindrical shell of the second magnetic layer in the axial direction of the rotor shaft is related to the alternating magnetic field generated by the opposing stator. The longer the cylindrical shell of the second magnetic layer, the stronger the applied external magnetic field can be designed to generate torque. In contrast, the second magnetic layer has a certain thickness, which should be kept as small as possible for cost reasons. If the thickness is too thin, the generated magnetic field strength will be excessive. For this comparison, reference should be made to the family of hysteresis loops known in the art.

[0020] Therefore, this invention aims to design the thickness of the second magnetic layer such that the direct correlation difference (d2-d1) between the outer diameter d2 and the inner diameter d1 of the second magnetic layer is proportional to the length, ensuring that the high-frequency alternating magnetic field does not cause excessive demagnetization of the magnetic material over time. According to internal research, a specified value range of 4 to 15 (inclusive) for this ratio (length divided by twice the thickness) has proven advantageous. If the ratio is greater than 15, the degree of demagnetization is excessive; while if it is less than 4, the cost of magnetic materials with the desired properties may be too high.

[0021] It should be noted that when considering the ratio of length to single thickness, a value between 8 and 30 is found to be most favorable.

[0022] According to a specific embodiment, the ratio of the length to the difference between the outer and inner diameters of the second magnetic layer is particularly preferred to be in the range of 6 to 10 (including boundary values), and more preferably 7 to 8 (including boundary values).

[0023] According to embodiments of the present invention, in the rotor device, the first and second magnetic layers are formed by plastic bonding using injection molding or die casting processes, respectively. As plastic bonding agents, without limiting their generality, one of the following groups is preferred: polyamide-6 (PA6), polyamide-12 (PA12), polyamide-66 (PA66), PBT, PET, PPS, or LCP. For plastic-bonded, primarily isotropic bonded magnets, at least in the case of the second magnetic layer, the shape of the magnetic layer also has relative flexibility, which can be ensured by mature injection molding or die casting processes. For many materials (e.g., NdFeB), no additional surface protection is required. The achievable magnetic flux density is relatively low, at least due to the presence of the plastic component, but this is compensated for by the correspondingly larger thickness of the second magnetic layer. The aforementioned plastic or resin materials have high temperature resistance and exhibit high durability under predetermined mechanical loads (high centrifugal force, high locking torque).

[0024] According to the extended scheme, the first layer is a first magnetic layer formed of a material having a first value for remanence, i.e., the magnetic flux density remaining after the magnetic field H of the outer magnetization layer is removed or turned off (for H=0, the remanence flux density B). R =μ0MR (vector symbols omitted), where M R (where μ represents magnetization and μ0 represents the magnetic field constant). The second magnetic layer is formed of a material having a second value for remanence, wherein the second value for remanence is greater than the first value. In particular, the material of the inner first magnetic layer can be a soft magnetic material, and the material of the outer second magnetic layer can be a hard magnetic material.

[0025] Therefore, the second magnetic layer has a very high remanent flux density after magnetization, and its coercivity is also very high due to the material properties, resulting in less slow demagnetization during operation. Furthermore, the second magnetic layer is positioned radially further outward, and thus can absorb greater torque during operation. The first magnetic layer allows for both inward (towards the rotor shaft) and outward-pointing magnetic fields, thereby supporting the function of the outer magnetic layer.

[0026] In a preferred embodiment, the first magnetic layer is also constructed in the shape of a cylindrical shell.

[0027] Alternatively, the first layer can also be a non-magnetic layer, preferably a thermoplastic manufactured by injection molding or die casting, but without magnetic materials. Preferably, the material is PA66. This has been found to be an economical alternative while still ensuring high torque and the thermal and mechanical durability of the external second magnetic layer.

[0028] According to another embodiment of the rotor device, the first magnetic layer may comprise a soft magnetic material in the form of a ferrite material. This is an inexpensive magnetic material that can adequately provide auxiliary functions.

[0029] The second magnetic layer can comprise hard magnetic materials in the form of rare-earth magnetic materials. These materials offer high magnetic energy density and coercivity, and especially high Curie temperatures, particularly in the case of samarium-containing materials. When used in conjunction with plastic-bonded injection molding or die casting, they are also particularly suitable for electric motors driving roof systems (with corresponding load and temperature requirements).

[0030] The preferred material is a rare earth magnetic material, including materials from the group consisting of SmFeN, NdFeB or SmCo, which may contain other alloying additives that can particularly improve the temperature resistance of the relevant magnetic state.

[0031] A further improvement to the rotor assembly is that the first magnetic layer is formed directly on the rotor shaft, or directly on the iron core on the rotor shaft, wherein the iron core is made of laminated steel plates. This is a particularly practical structure.

[0032] According to a specific embodiment of the rotor device, the second magnetic layer has magnetization of at least eight magnetic poles along the circumferential direction. This configuration has proven to be very advantageous.

[0033] The invention also relates to an electric motor having a rotor assembly as described in the above embodiments. A corresponding stator assembly works in conjunction with the rotor assembly. In particular, the stator assembly can be configured with a basic structure surrounding the rotor assembly and a plurality of stator teeth for accommodating stator windings. If the rotor unit is equipped with eight magnetic poles, six slot segments can be formed between the stator teeth. According to the invention, an electric motor is provided with this structure, which can reduce noise based on a specific ratio between the slot segments and the magnetic poles.

[0034] The rotor shaft can rotate within two or more bearings housed in the motor housing. The rotor shaft can also be configured as a worm shaft in a section (e.g., the end region), which works in conjunction with a worm wheel in a worm gear drive to produce a suitable transmission ratio for a specific application.

[0035] The electric motor can be a brushless motor, preferably a BLDC motor used to drive the roof system of a vehicle (especially a motor vehicle). The roof system may include a sunroof, awning, sunshade, or similar device.

[0036] The present invention also includes a method for manufacturing a rotor device. The method includes: Provide rotor shaft; Provide a first mold that surrounds the rotor shaft; The first material is injected into a mold for injection molding or die casting to form a first layer in the shape of a cylindrical shell on the rotor shaft; Remove the first mold and provide a second mold that surrounds the rotor shaft; The second magnetic material is injected into the mold for injection molding or die casting to form a second magnetic layer in the shape of a columnar shell on the first layer; After injection molding or die casting is completed, the second magnetic layer is magnetized according to its position in the circumferential direction to form multiple magnetic poles.

[0037] In an extended version of this method, during the step of injection molding or die casting of the first material, a first magnetic material is used to form a first magnetic layer, wherein the material of the first magnetic layer has a first value for remanence, and the second material of the second magnetic layer has a second value for remanence, wherein the second value for remanence is greater than the first value. Furthermore, when the first magnetic material is injected or die-cast into the mold, the first magnetic layer is magnetized according to its position in the circumferential direction to support the formation of multiple magnetic poles in the second magnetic layer.

[0038] Magnetizing the first magnetic material during injection molding or die casting and then magnetizing the second magnetic material after injection molding or die casting has proven particularly advantageous. Magnetizing the first magnetic material or first magnetic layer during injection molding or die casting eliminates a separate process step, thus saving production time and costs; while magnetizing the second magnetic material only after the injection molding or die casting process is completed allows for high magnetic isotropy, resulting in a relatively high magnetic flux density, which is especially important in the case of the second magnetic material or second magnetic layer.

[0039] Other advantages, features, and details of various aspects can be obtained from the claims, the following description of preferred embodiments, and the accompanying drawings. In the drawings, the same reference numerals denote the same features and functions. Attached Figure Description

[0040] This is shown here: Figure 1 Parts of a rotor assembly according to a conventional example are shown in perspective, side view, and cross-sectional view (from right to left), including rotor sections and rotor shaft; Figure 2 A perspective sectional view shows a rotor device having a rotor section and a rotor shaft according to an embodiment of the present invention; Figure 3 A cross-sectional view shows a rotor device arranged in a stator according to an embodiment of the present invention, with magnetic flux density expressed in grayscale; Figure 4 According to one embodiment of the present invention, a curve showing the relationship between magnetic flux density and position angle in the circumferential direction on the surface of a rotor magnet is provided for three different ratios of the axial length of the rotor magnet to the thickness of the outer hard magnetic layer in the radial direction. Detailed Implementation

[0041] In the following description of preferred embodiments, it should be understood that this disclosure is not limited to the details of the structure and arrangement of the components described below and shown in the figures. All embodiments, including those not shown in the figures, can be practiced or implemented in various ways. Furthermore, it should be understood that the wording and terminology used herein are for descriptive purposes only and should not be construed as limiting by those skilled in the art. Additionally, in the following description, the same reference numerals in the figures denote the same or similar features or objects; therefore, in some cases, the same details will not be repeated in detail to maintain conciseness and clarity of description.

[0042] Figure 1An example of a conventional rotor assembly 50 for a brushless DC motor is shown. The rotor shaft 14 has an iron core 54 on which a total of four spaced-apart magnets 56 are bonded in grooves on the outer surface of the iron core, wherein the magnets are sintered magnets. In this embodiment, the magnets 56 are formed by magnetic north poles (N) and magnetic south poles (S), but are not shown in the figure for simplicity. Thus, in the arrangement of the four magnets 56 shown, a total of eight magnetic poles are provided. The eight magnetic poles (N, S) are alternately oriented to obtain the desired magnetic field. To prevent the magnets 56 from detaching under the typically high speeds and associated high centrifugal forces of a BLDC motor, a support 58 is externally provided on the rotor assembly, extending circumferentially and at least partially covering and holding the magnets 56 in place.

[0043] Figure 2 An embodiment of the rotor device 10 according to the present invention is shown schematically. The perspective view shows a cross-section perpendicular to the longitudinal axis Z of the rotor shaft of the rotor device 10 at the end side. A first magnetic layer 20 is formed directly on the rotor shaft 14 by injection molding or die casting. This first magnetic layer has an outer surface 26 having a radius constant relative to the longitudinal axis Z in the circumferential direction P. The outer surface 24 of the first magnetic layer has an outer diameter d1. The rotor shaft 14 itself is cylindrically constructed, therefore the first magnetic layer 20 generally has the shape of a cylindrical shell.

[0044] Along the longitudinal axis Z, the first magnetic layer 20 has a length L. For manufacturing, a mold is provided through which the rotor shaft 14 extends. The corresponding mold can be positioned within a magnetizing device (not shown) through which a suitable multipole magnetic field is constructed, passing through the mold. Simultaneously, a mixture of thermoelastic and / or thermoplastic resin with ferrite powder is injected into the mold (injection molding or die casting). During this process, the ferrite particles are neatly arranged in the magnetic field, thereby retaining residual magnetization after cooling or hardening. The advantage is that the magnetic material can be directly injection molded onto the rotor shaft 14. No subsequent assembly is required.

[0045] A second magnetic layer is constructed on the first magnetic layer 20 or its outer surface 24. The second magnetic layer also has a cylindrical outer surface 28 with a radius that remains constant relative to the longitudinal axis Z in the circumferential direction P. The outer surface 28 of the second magnetic layer has a constant outer diameter d2. The inner diameter d1 of the second magnetic layer 22 corresponds to the outer diameter of the first magnetic layer 20. With this structure, the second magnetic layer 22 has an overall cylindrical shell shape similar to the first magnetic layer 20, but is thinner (thickness is (d2–d1) / 2).

[0046] Along the vertical axis Z, the second magnetic layer 22 has the same length L as the first magnetic layer 20. In principle, their lengths can also be different. However, the length L of the second magnetic layer 22 is important for the following discussion.

[0047] To fabricate the second magnetic layer 22, a mold is again provided through which the rotor shaft 14 and the first magnetic layer 20 formed thereon extend. A mixture of thermoelastic and / or thermoplastic resin with metal powder composed of rare-earth magnetic materials is injected into the mold (injection molding or die casting). SmFeN particle (samarium iron nitride) alloys are preferred here. This material has high demagnetization resistance and is therefore particularly suitable. Another option is a SmFeN / ferrite hybrid magnet or a SmFeN / NdFeB hybrid magnet, the latter having particularly excellent properties in terms of energy density and coercivity. Mixtures of thermoelastic and / or thermoplastic resin with NdFeB or SmCo particle metal powder are also particularly suitable.

[0048] In this case, the required magnetization can only be performed after cooling or hardening. The advantage is that the magnetic material can be directly injection molded onto the outer surface 24 of the first magnetic layer 20, eliminating the need for subsequent bonding.

[0049] Figure 3 The image shows a cross-section of a brushless motor 100, which has... Figure 2 The image shows the rotor assembly and the stator assembly 40 surrounding the rotor assembly. The grayscale image illustrates the simulation results of the magnetic flux density during motor operation. Reference numeral 26 indicates two of the total eight magnetic poles set during the magnetization process described above. These eight magnetic poles, formed in the second magnetic layer, are opposite to the six slots or stator teeth 44 of the stator assembly 40. The stator assembly 40 has an external basic structure 42 from which the six stator teeth 44 extend inward to the longitudinal axis Z of the rotor shaft 14. Each stator tooth 44 has a stator head 46, the head face of which forms a slot with the outer surface 28 of the second magnetic layer 22.

[0050] As described above, the second magnetic layer 22 has an outer diameter d2 relative to the outer surface 28 and an inner diameter d1 relative to the inner adjacent outer surface 24 of the first magnetic layer 20. The inner diameter d1 of the second magnetic layer 22 is the same as the outer diameter d1 of the first magnetic layer 20 because they coincide. In this case, the thickness of the second magnetic layer 22 in the circumferential direction P is a constant (d2-d1) / 2.

[0051] In this embodiment, the length L of the second magnetic layer 22 along the longitudinal axis is specifically 22 mm, and the difference d2-d1 between the outer diameter d and the inner diameter d1 of the second magnetic layer is 3 mm. For geometric reasons, this difference is equivalent to twice the thickness of the second magnetic layer 22. In this case, the ratio σ between the length L and the difference d2-d1 is... m Approximately 7.3. It has been found that when the value is less than σ... m When σ = 4, the cost of manufacturing the second magnetic layer for mass production is too high (mainly due to the material cost of rare earth materials) compared to the improvement in motor life due to remanent magnetization. Furthermore, it was found that when the value is greater than σ...m At a density of 15, due to the small layer thickness, the demagnetization is too great compared to the energy density of the active magnetic field, while the cost of using rare earth materials is negligible.

[0052] Figure 4 The graphs show the magnetic flux density B, determined based on the outer perimeter (angle ɸ) of the second magnetic layer 22, after magnetization for three different cases. Figure 4 In particular, for the ideal case σ m =L / (d2-d1)=7.3 (see the curve marked by arrow B), for the lower boundary σ of the interval found here m =4 (see the curve marked by arrow A) and the upper boundary σ m =15 (see the curve marked by arrow C), plotting the relationship between the magnetic flux density B before the motor starts running and the angular position ɸ of the circumferential direction P in magnetic layer 22. It can be seen that for the upper boundary σ... m =15, meaning the second magnetic layer is relatively thin compared to its length, with only a small amount of magnetic flux density B available. During operation, due to the continuous repetition of the hysteresis loop, the magnetic flux density is higher than σ. m The value of 7.3 decreases even faster. From the upper boundary, it is approximately σ. m Starting at 15, the thickness of the second magnetic layer will increase costs, and under the current circumstances, these costs cannot be compensated by technological advantages.

[0053] Figure Labels 10. Rotor assembly 14 Rotor shaft 20 First Magnetoid Layer 22 Second Magnetic Layer 24 Outer surface (first magnetic layer) 26 poles, magnetic poles 28. Outer surface 40 Stator Assembly 42 Basic Structure 44 stator teeth 46 Stator Head 48 Stator windings 50 Rotor Unit (Conventional Type) 54 Iron Core 56 Sintered Magnets 58 brackets 100 electric motor

Claims

1. A rotor assembly (10) for a DC motor (100), comprising: Rotor shaft (14); The first layer is constructed on the rotor shaft (14) or on an iron core mounted on the rotor shaft (14); The second layer is constructed on the outer surface (24) of the first layer, wherein the second layer is a second magnetic layer (22). The second magnetic layer (22) has the shape of a cylindrical shell, wherein the cylindrical shell of the second magnetic layer (22) has a thickness ((d2-d1) / 2) that is constant in the circumferential direction (P) and measured radially from the longitudinal axis (Z) of the rotor shaft, and a length (L) that is measured axially parallel to the longitudinal axis (Z). The ratio of the length (L) to the difference (d2-d1) between the outer diameter (d2) and the inner diameter (d1) of the second magnetic layer (22) is the following value, which is in the range of 4 to 15, including boundary values.

2. The rotor device (10) according to claim 1, wherein The first layer and the second magnetic layer (22) are constructed by injection molding or die casting processes, respectively, using plastic adhesives.

3. The rotor device (10) according to claim 1 or 2, wherein The first layer is a first magnetic layer (20), which is formed of a material having a first value for remanence. The second magnetic layer (22) is formed of a material having a second value for remanence, wherein, The second value used for residual magnetism is greater than the first value.

4. The rotor device (10) according to claim 1 or 2, wherein The first layer is a non-magnetic layer, preferably a thermoplastic plastic.

5. The rotor device (10) according to any one of claims 1 to 4, wherein The ratio of the length (L) to the difference (d2-d1) is in the range of 6 to 10, including boundary values.

6. The rotor device (10) according to any one of claims 1 to 5, wherein The ratio of the length (L) to the difference (d2-d1) is in the range of 7 to 8, including boundary values.

7. The rotor device (10) according to claims 1 to 6, wherein The first layer also has the shape of a columnar shell.

8. The rotor device (10) according to claim 3 or 5 to 7 (wherever claim 3 is cited), wherein The first magnetic layer (20) comprises a soft magnetic material, preferably a ferrite material.

9. The claim 1 to 8, wherein The second magnetic layer (22) comprises a hard magnetic material, preferably a rare earth magnetic material.

10. The rotor device (10) according to claim 9, wherein The rare earth magnetic material is one of the following: SmFeN, NdFeB, or SmCo, wherein... Alloy additives are included.

11. The rotor device (10) according to any one of claims 1 to 10, wherein The first layer is constructed directly on the rotor shaft (14), or directly on the iron core (30) mounted on the rotor shaft (14), wherein, The core (30) is made of laminated steel plate.

12. The rotor device (10) according to any one of claims 1 to 11. The second magnetic layer (22) has at least eight magnetic poles (26) magnetized in the circumferential direction (P).

13. An electric motor (100), comprising: The rotor device (10) according to any of the preceding claims; as well as Stator assembly (40).

14. The electric motor (100) according to claim 13, wherein The motor (100) is a brushless motor, preferably a brushless DC motor for driving the roof system.

15. A method for manufacturing a rotor assembly, comprising: Provide rotor shaft; Provide a first mold that surrounds the rotor shaft; The first material is injected or die-cast into the mold to form a first layer in the shape of a cylindrical shell on the rotor shaft; Remove the first mold and provide a second mold that surrounds the rotor shaft; The second magnetic material is injected or die-cast into the mold to form a second magnetic layer in the shape of a columnar shell on the first layer; After injection molding or die casting is completed, the second magnetic layer is magnetized according to its position in the circumferential direction to form multiple magnetic poles.

16. The method of claim 15, wherein In the step of injection molding or die casting the first material, a first magnetic material is used to construct the first magnetic layer, wherein... The material of the first magnetic layer has a first value for remanence, and the second material of the second magnetic layer has a second value for remanence, wherein the second value for remanence is greater than the first value; When the first magnetic material is injected or die-cast into the mold, the first magnetic layer is magnetized according to its position in the circumferential direction to support the construction of multiple magnetic poles in the second magnetic layer.

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