Segmented rotor for a slotless, electronically commutated electric motor and electric motor including such a rotor

Abstract

The present invention relates to a rotor for an electric motor with a slotless stator and an electronic commutator, the rotor having permanent magnet segments. According to the invention, the permanent magnet segments are spaced apart from one another at least over an axial region of the rotor along at least one cross-sectional plane, and the rotor has respective electrical insulation between the permanent magnet segments along at least one cross-sectional plane. A normal to each cross-sectional plane extends perpendicular to the axial direction of the rotor and perpendicular to the q-axis of the rotor if the rotor has one pole pair, or perpendicular to one of the q-axes of the rotor if the rotor has two or more pole pairs. A soft magnetic material is introduced between the permanent magnet segments along the cross-sectional plane and is electrically insulated by the electrical insulation of the permanent magnet segments.

Description

[Technical Field]

[0001] The invention relates to a rotor for an electric motor comprising a slotless stator and an electronic commutator according to the preamble of independent claim 1, and to an electric motor comprising such a rotor according to the preamble of claim 15.

[0002] The rotor according to the preamble of independent claim 1 comprises permanent magnet segments. [Background technology]

[0003] In electronically commutated electric motors, additional losses are induced in the electric motor by the pulse width modulation (PWM) of the power electronics. These losses are particularly high in low-inductance motors, such as electronically commutated electric motors with slotless stators. The main effect here is eddy currents in the rotor, and for a fixed intermediate circuit voltage, the additional losses are greatest at a duty cycle of 50%. There are already known solutions to this known problem, but they come with additional problems.

[0004] A well-known approach is the use of additional inductors in electronic devices, which can reduce current ripple and therefore losses. However, depending on the system, these additional inductors can be large, heavy, and expensive. In addition, these components introduce ohmic losses, making this approach less advantageous.

[0005] It is also known to select the winding voltage and / or intermediate circuit voltage so that the duty cycle is nearly 100%, thereby avoiding the problem of PWM-induced losses. However, without regulation of the intermediate circuit voltage, this is mainly possible only for motors operating at maximum speed. If operation takes place at different speeds, a complex and expensive control system is required to regulate the intermediate circuit voltage, which also affects the dynamics of the control system. In addition, this approach only partially solves the problem in the case of sinusoidal commutation, since the voltage has a sinusoidal curve and therefore the duty cycle varies continuously from 0 to the maximum value.

[0006] Another known approach is to axially segment the rotor into permanent magnet segments, where the rotor is segmented along a cross-sectional plane whose normal points in the axial direction of the rotor, and the individual permanent magnet segments are electrically insulated from each other.

[0007] However, to effectively suppress eddy currents, the axial thickness of the permanent magnet segment disk must be less than its diameter, so a large number of such permanent magnet segments is required, making this approach complex and expensive to manufacture. Summary of the Invention

[0008] It is therefore an object of the present invention to provide a rotor for an electric motor comprising a slotless stator and an electronic commutator, which reduces the additional losses induced by pulse width modulation (PWM) of the power electronics, thereby avoiding or at least mitigating the problems of the various known approaches described above.

[0009] This object is achieved by the features of independent claim 1. Thus, the object of the invention is achieved in that a rotor of the type under consideration comprises permanent magnet segments that are spaced apart from one another at least over an axial region of the rotor along at least one cross-sectional plane, the rotor having respective electrical insulation between the permanent magnet segments along the at least one cross-sectional plane, the normal of each cross-sectional plane extending perpendicular to the axial direction of the rotor and perpendicular to the q-axis of the rotor if the rotor has one pole pair, or perpendicular to one of the q-axes of the rotor if the rotor has more than one pole pair.

[0010] In this case, the extension of the cross-sectional plane in the axial direction is limited to an axial region of the rotor, which preferably comprises at least 90%, particularly preferably at least 95%, of the axial length of the rotor.

[0011] The solution according to the invention effectively prevents eddy currents in the rotor induced by PWM, requiring significantly fewer permanent magnet segments than known approaches with cross-sectional planes normal to the rotor axis.

[0012] This makes the rotor much easier and more cost effective to manufacture.

[0013] Advantageous embodiments of the invention are the subject matter of the dependent claims.

[0014] In a particularly preferred embodiment of the present invention, the electrical insulation is provided by an air gap, preferably a coating of insulating material such as a potting compound, a plastic film or platelet, paper, or preferably an electrically insulating adhesive. Effective electrical insulation effectively prevents induced eddy currents in the PWM. The electric motor can be designed as a multi-phase or single-phase electric motor and can rotate or vibrate during operation.

[0015] In a further preferred embodiment of the present invention, soft magnetic material is introduced between the permanent magnet segments along the cross-sectional plane, and this material is electrically insulated from the permanent magnet segments by electrical insulation. This increases the inductance in the direction of the q-axis, which can reduce the current ripple and therefore the induced eddy currents. The electrical insulation can be achieved even with a relatively low electrical resistance of a few ohms, for example, on the order of 1 to 10 ohms, because this already reduces the eddy currents.

[0016] Preferably, the soft magnetic material is designed as a laminate or laminated core, with the lamination direction extending parallel to the normal of the respective cross-sectional plane or in the axial direction of the rotor, which allows a high inductance to be produced simply and inexpensively.

[0017] In a preferred embodiment, the saturation magnetic field strength of the soft magnetic material is higher than the magnetic flux density of the rotor, and the soft magnetic material is preferably made of FeSi laminations, FeNi laminations, or soft magnetic composites, which can prevent saturation of the soft magnetic material and ensure the effect of preventing losses due to PWM-induced eddy currents.

[0018] According to a further particularly preferred embodiment, over at least 50% of the extent of a cross-sectional plane parallel to the q axis within the circumference of the rotor, the spacing between the permanent segments in the direction normal to the respective cross-sectional plane is less than 8%, preferably less than 5%, of the rotor diameter, which allows the permanent segments to be sufficiently large relative to the rotor diameter.

[0019] In a further preferred embodiment, the laminated core has a stacking direction parallel to the normal of each cross-sectional plane and fewer than 9, preferably fewer than 5, laminations. The direction in which the laminations are arranged or stacked on top of each other is called the stacking direction. The stacking direction is therefore perpendicular or orthogonal to the stacking plane.

[0020] In another preferred embodiment, the laminated core has a lamination direction in the axial direction of the rotor, and the extension of the laminated core in the direction normal to the respective cross-sectional plane increases at the rotor periphery. This allows more high-frequency magnetic fields to be directed into the laminated core, which has a positive effect on reducing losses due to PWM-induced eddy currents. In addition, the laminations are positioned in the rotor by a secure connection with the permanent magnet segments.

[0021] According to a further preferred embodiment, the rotor has only one pole pair and three or more, preferably three, permanent magnet segments, the cross-sectional plane preferably being arranged axisymmetrically with respect to the q-axis of the rotor. In the case of a rotor with only one pole pair, the use of three or more permanent magnet segments can further reduce losses due to PWM-induced eddy currents. In this case, three permanent magnet segments is usually sufficient.

[0022] According to another preferred embodiment, the rotor has two or more pole pairs, and the cross-sectional plane of the rotor extends along the q-axis of the rotor. When the rotor has two or more pole pairs, two or more q-axes are formed. The cross-sectional plane extending along each of these q-axes can effectively prevent PWM-reducing eddy currents around the entire rotor circumference.

[0023] In a further particularly preferred embodiment of the present invention, the permanent magnet segments are glued together while being electrically insulated. Segmentation makes the rotor structure weaker. However, by gluing, a sufficiently robust rotor can be produced.

[0024] According to a preferred embodiment of the present invention, a shaft stub is glued to the end face of the rotor. A continuous shaft is not practical, particularly in rotor embodiments with only one pole pair, since eddy currents may flow across the shaft. To prevent this, a shaft stub is used.

[0025] In a further preferred embodiment of the present invention, the rotor is surrounded by a non-conductive capsule, preferably a carbon fiber tube or ceramic sleeve, or an outer synthetic resin laminate. This further improves robustness. Carbon fiber tubes have the added advantage that carbon fiber has a similar coefficient of expansion to magnetic materials, making the rotor robust against temperature changes. The carbon fiber tube can also be impregnated with epoxy resin and cured or baked. This increases the rotor's strength, and the coating also serves as insulation.

[0026] In another preferred embodiment, the axial region where the permanent magnet segments are spaced apart constitutes only a partial region of the rotor's total axial length, and the permanent magnet segments are designed so that they are not segmented at the axial ends of the rotor, preferably at ends that comprise less than 10%, particularly preferably less than 5%, of the rotor's axial length. This can reduce the fragility of the rotor while still reducing PWM-induced eddy currents. An embodiment with such ends is particularly preferred for rotors with only one pole pair.

[0027] In another preferred embodiment, the rotor is designed as a four-pole Halbach rotor with eight permanent magnet segments that are electrically insulated from one another in cross-sectional planes along the q-axis, and these cross-sectional planes are provided with soft magnetic laminations that are electrically insulated from the permanent magnet segments.

[0028] The invention further relates to an electric motor having a slotless stator and an electronic commutator, the electric motor comprising a rotor according to at least one of the embodiments described above. [Brief explanation of the drawings]

[0029] In the following, non-limiting embodiments of the invention will be explained in more detail with reference to the drawings, given by way of example.

[0030] [Figure 1]1 is a cross-sectional view of an embodiment of a rotor according to the present invention comprising a pole pair, a cross-sectional plane, and a laminated core with a lamination direction parallel to the normal of the cross-sectional plane. [Figure 2] 2 is a cross-sectional view of a second embodiment of a rotor according to the present invention, comprising a pole pair, a cross-sectional plane, and a laminated core with lamination direction in the axial direction of the rotor. [Figure 3] 3 is a cross-sectional view of a third embodiment of a rotor according to the present invention, comprising a pole pair, two cross-sectional planes, and two laminated cores with lamination directions parallel to the normal of the cross-sectional planes. FIG. [Figure 4] 4 shows an axial cross-sectional view of the third embodiment shown in FIG. 3. [Figure 5] 10 is a cross-sectional view of a fourth embodiment of a rotor according to the present invention, comprising two pole pairs, two cross-sectional planes and four laminated cores with lamination directions parallel to the normal of the cross-sectional planes. FIG. [Figure 6] 10 is a cross-sectional view of a fifth embodiment of a rotor according to the present invention, comprising two pole pairs, two cross-sectional planes and a laminated core with lamination direction in the axial direction of the rotor. FIG. [Figure 7] 10 is a schematic cross-sectional view of a fifth embodiment of a rotor according to the invention, which is designed as a four-pole Halbach rotor. DETAILED DESCRIPTION OF THE INVENTION

[0031] In the following drawings, identical parts are provided with the same reference numerals. If a figure contains a reference numeral that is not explicitly discussed in the description of the corresponding figure, reference is made to the description of the preceding or following figure. The figures show only cross-sectional views of embodiments of a rotor according to the invention. Other components of the electric motor, which are also claimed, are not shown in the figures. For the components of the electric motor according to the invention, reference is made to the general description.

[0032] FIG. 1 is a cross-sectional view of a first embodiment of a rotor 1 according to the present invention in an axial region 8 of the rotor 1, which is divided into multiple permanent magnet segments 2. In this case, the rotor 1 has two permanent magnet segments 2 in the axial region 8, whose magnetization directions are indicated by thick black arrows and form a single-pole pair magnetic field. The magnetization direction is also indicated by the d-axis 5 of the rotor 1. The two permanent magnet segments 2 are spaced apart along a cross-sectional plane 3. In this case, the cross-sectional plane 3 has a normal 10 aligned perpendicular to the axial direction of the rotor 1 and perpendicular to the q-axis 6 of the rotor 1. A soft magnetic material in the form of a laminated core 4 is introduced between the two permanent magnet segments 2 along the cross-sectional plane 3. In this embodiment, the laminated core 4 has a lamination direction parallel to the normal 10 of the cross-sectional plane 3 and includes eight laminations. Alternatively, fewer laminations, e.g., fewer than five laminations, can be preferably used. The two permanent magnet segments 2 and the laminated core 4 are electrically insulated from each other by electrical insulation. The electrical insulation between the permanent magnet segments 2 along the cross-sectional plane 3 is particularly strong in electronically commutated electric motors with slotless stators, preventing PWM-induced eddy currents that can adversely affect the operation of such electric motors. The laminated core 4 also increases the inductance in the q-axis 6, which reduces current ripple and, as a result, can additionally reduce eddy currents. The electric motor can be a multi-phase electric motor.

[0033] 2 shows a cross-section in the axial region 8 of a second embodiment of a rotor 1 according to the invention. The essential difference with respect to the first exemplary embodiment is that the laminated core 4 has a lamination direction in the axial direction of the rotor 1 and the extension of the laminated core 4 increases towards the outer periphery of the rotor 1 in the direction of the normal 10 to the cross-sectional plane 3. This allows, on the one hand, more high-frequency magnetic fields to be conducted to the axial laminated core 4, and, on the other hand, the laminations of the laminated core 4 are positioned with a positive fit relative to the permanent magnet segments 2. It is also important for this exemplary embodiment that the laminated core 4 is electrically insulated from the permanent magnet segments 2 by electrical insulation.

[0034] 3 is a cross-sectional view in an axial region 8 of a third exemplary embodiment of a rotor 1 according to the present invention. The rotor 1 has three permanent magnet segments 2, all of which have the same magnetization direction and thus form a single-pole pair magnetic field. The permanent magnet segments 2 are spaced apart from one another along two cross-sectional planes 3, each of which has a normal 10 oriented perpendicular to the axial direction of the rotor 1 and perpendicular to the q-axis 6 of the rotor 1. In this case, the cross-sectional planes 3 are arranged axisymmetrically in the rotor with respect to the q-axis 6. Laminated cores 4 are inserted between the permanent magnet segments 2 along the cross-sectional planes 3, and the laminated cores 4 are electrically insulated from each adjacent permanent magnet segment 2 by electrical insulation.

[0035] FIG. 4 is an axial cross-sectional view of the rotor 1, with a cross-section at the axial region 8, similar to the third exemplary embodiment shown in FIG. 3 . The rotor 1 is segmented in the axial region 8 and has three permanent magnet segments 2 separated by two cross-sectional planes. However, this segmentation does not exist throughout the entire axial length of the rotor 1. Therefore, the embodiment of FIG. 4 has an end 9 at one axial end where the permanent magnet segments 2 are not separated from each other. At the end 9, the permanent magnets can be formed integrally, thereby increasing the robustness of the rotor 1. Because the axial region 8, which is segmented into multiple permanent magnet segments 2, includes a majority of the axial length, preferably at least 90% of the axial length, PWM-induced eddy currents can still be sufficiently reduced. Shaft stubs are attached to each axial end of the rotor 1 shown in FIG. 4 and, together with the segmented permanent magnets, form the shaft 7 of the rotor 1.

[0036] FIG. 5 is a cross-sectional view of a further embodiment of a rotor 1 according to the present invention, which is a two-pole rotor. The rotor 1 has four permanent magnet segments 2, which are magnetized according to the thick black arrows. The permanent magnet segments 2 are spaced apart along two cross-sectional planes 3, and the normals 10.1 to the cross-sectional planes 3 are aligned perpendicular to the axial direction of the rotor 1 and perpendicular to the possible q-axes 6.1 and 6.2 of the rotor 1. The laminations are arranged along the q-axes 6, 6.1, and 6.2, which means that the q-axes 6, 6.1, and 6.2 lie within the lamination plane. The d-axes 5 are electrically perpendicular to the q-axes 6, 6.1, and 6.2, respectively. In the case of a single-pole motor, the d-axis 5 is electrically and mechanically or geometrically perpendicular to the q-axis 6 in each case and is therefore parallel to the normal 10. In the case of a multi-pole rotor, there are multiple d-axes 5 and q-axes 6.1 and 6.2, corresponding to the number of pole pairs. In this case, the d-axis 5 and the q-axis 6.1, 6.2 are electrically perpendicular to each other at an angle of 90°. The mechanical angle between the d-axis 5 and the q-axis 6.1, 6.2 corresponds to half of 360° divided by the number of poles. For a rotor 1 with two pole pairs, the mechanical angle between the d-axis 5 and the q-axis 6.1, 6.2 is 360° / 2 / 4 = 45°. For a rotor 1 with three pole pairs, the mechanical angle between the d-axis 5 and the q-axis 6.1, 6.2 is 360° / 2 / 6 = 30°. Along the cross-sectional plane 3, a soft magnetic material in the form of a laminated core 4 is introduced, with its lamination direction parallel to the normal to the cross-sectional plane. The laminated core 4 and the permanent magnet segments 2 are insulated from each other by electrical insulation. The rotor 1 shaft is not provided between the laminated cores 4 at the center of the rotor 1. In an alternative embodiment, a shaft made of a non-conductive material may be disposed.

[0037] FIG. 6 also shows a cross-sectional view of a further exemplary embodiment of a rotor 1 according to the present invention, designed as a two-pole rotor 1. In contrast to the exemplary embodiment shown in FIG. 5, this embodiment has a laminated core 4 with a lamination direction in the axial direction of the rotor 1, which is inserted along the cross-sectional plane 3 between the permanent magnet segments 2. The extension of the laminated core 4 in the direction of the normal 10 to the cross-sectional plane 3 increases at the rotor's outer periphery, so that, on the one hand, more high-frequency magnetic fields can be directed toward the axially laminated core 4, and the laminations of the laminated core 4 are positioned relative to each other and to the permanent magnet segments 2. In the exemplary embodiment shown in FIG. 6, the shaft 7 of the rotor 1 is guided through the axially laminated core 4. In this embodiment, the shaft 7 has a diameter greater than the minimum distance between the permanent magnet segments 2 along the cross-sectional plane 3. In this case, the magnetic field is guided around the shaft 7.

[0038] 7 is a cross-sectional view through a further exemplary embodiment of a rotor 1 according to the present invention, which is a two-pole Halbach rotor 1 formed from eight permanent magnet segments 2 with magnetization directions marked as black arrows. These permanent magnet segments 2 are also spaced apart from one another along two cross-sectional planes 3 by electrical insulation, the normals 10.1, 10.2 of which are aligned perpendicular to the axial direction of the rotor 1 and to the respective q-axes 6.1, 6.2 of the rotor 1. Soft magnetic material in the form of laminated cores 4 can also be introduced along these cross-sectional planes 3, which are in turn insulated from the permanent magnet segments 2 by electrical insulation.

[0039] In any case, with respect to the exemplary embodiments described above, electrical insulation can be produced by, among other things, an air gap, an insulating material, a coating such as a plastic film or platelet, paper, or an electrically insulating adhesive. The illustrated rotor can be coated with a carbon fiber tube and laminated with a synthetic resin, or coated with a ceramic sleeve, so as to increase the robustness of the rotor 1. In this case, it is important that this type of encapsulation is not electrically conductive, since this would negate the effect of the segmentation. [Explanation of symbols]

[0040] 1 rotor 2 permanent magnet segments 3 Section plane 4 Laminated Core 5d axis 6, 6.1, 6.2 q-axis 7 shaft 8 Axial area 9 End 10, 10.1, 10.2 Normal

Claims

1. A rotor (1) for an electric motor, comprising a slotless stator and an electronic commutator, the rotor (1) having permanent magnet segments (2) spaced apart from one another at least over an axial region (8) of the rotor (1) along at least one cross-sectional plane (3), the rotor (1) having respective electrical insulation between the permanent magnet segments (2) along the at least one cross-sectional plane (3), and a normal (10, 10.1, 10.2) of each of the cross-sectional planes (3) being , extending perpendicular to the axial direction of the rotor (1) and perpendicular to the q-axis (6) of the rotor (1) if the rotor (1) has one pole pair, and perpendicular to one of the q-axes (6.1, 6.2) of the rotor (1) if the rotor (1) has two or more pole pairs, wherein soft magnetic material is introduced between the permanent magnet segments (2) along the cross-sectional plane (3), the material being electrically insulated by the electrical insulation of the permanent magnet segments (2).

2. 2. A rotor (1) according to claim 1, characterized in that the electrical insulation is made by an air gap, preferably a potting compound, an insulating material such as a plastic film or platelet, paper, or a coating such as a preferably electrically insulating adhesive.

3. 3. A rotor (1) according to claim 1 or 2, characterized in that the soft magnetic material is designed as a laminated or laminated core (4), the lamination direction extending parallel to the normal (10, 10.1, 10.2) of the respective cross-sectional plane (3) or in the axial direction of the rotor (1).

4. The rotor (1) according to any one of claims 1 to 3, characterized in that the saturation magnetic field strength of the soft magnetic material is higher than the magnetic flux density of the rotor (1), and the soft magnetic material is preferably made of FeSi laminations, FeNi laminations, or a soft magnetic composite material.

5. A rotor (1) according to any one of claims 1 to 4, characterized in that over at least 50% of the extent of the cross-sectional planes (3) parallel to the q-axis (6, 6.1, 6.2) within the circumference of the rotor (1), the spacing between the permanent segments (2) in the direction of the normal (10, 10.1, 10.2) to the respective cross-sectional planes (3) is less than 8%, preferably less than 5% of the rotor diameter.

6. A rotor (1) according to any one of claims 1 to 5, characterized in that the laminated core (4) has the lamination direction parallel to the normal (10, 10.1, 10.2) of the respective cross-sectional plane (3) and has less than 9, preferably less than 5 laminations.

7. 6. The rotor (1) according to claim 1, wherein the laminated core (4) has the lamination direction in the axial direction of the rotor (1), and the extension of the laminated core (4) increases in the direction of the normal (10, 10.1, 10.2) of the respective cross-sectional plane (3) on the outer periphery of the rotor (1).

8. A rotor (1) according to any one of claims 1 to 7, characterized in that the rotor (1) has only one pole pair and three or more, preferably three, permanent magnet segments (2), the cross-sectional plane (3) being preferably arranged axisymmetrically with respect to the q-axis (6) of the rotor (1).

9. A rotor (1) according to any one of claims 1 to 7, characterized in that the rotor (1) has two or more pole pairs and the cross-sectional plane (3) of the rotor (1) extends along the q-axis (6) of the rotor (1).

10. A rotor (1) according to any one of claims 1 to 9, characterized in that the permanent magnet segments (2) are glued together in an electrically insulated manner.

11. A rotor (1) according to any one of claims 1 to 10, characterized in that a shaft stub is glued to an end face of the rotor (1).

12. A rotor (1) according to any one of claims 1 to 11, characterized in that the rotor (1) is surrounded by a non-conductive capsule, preferably a carbon fibre tube or a ceramic sleeve, or a synthetic resin laminate on the outer surface.

13. A rotor (1) according to any one of claims 1 to 12, characterized in that the axial region (8) in which the permanent magnet segments (2) are spaced apart from one another constitutes only a partial region of the entire axial length of the rotor (1), and the permanent magnet segments (2) at the axial ends of the rotor (1) are designed not to be segmented in end regions (9), which preferably amount to less than 10%, particularly preferably less than 5%, of the axial length of the rotor (1).

14. An electric motor with a slotless stator and an electronic commutator, characterized in that it comprises a rotor (1) according to any one of claims 1 to 13.

Images