Annuls sector-shaped rotor segment, segmented rotor and electric machine

Abstract

The invention relates to an annulus sector-shaped rotor segment (1) for forming a segmented, permanent-magnet rotor (2) of an electric machine (3) comprising a plurality of magnet pockets (4) formed in the rotor segment (1) for receiving permanent magnets (5), the rotor segment (1) having, starting from its radially outer surface (24), a radially inwardly extending groove (10).

Description

[0001] Circular segment-shaped rotor segment, segmented rotor and electric machine

[0002] The present invention relates to a rotor segment in the shape of a circular ring for forming a segmented, permanently excited rotor of an electrical machine, comprising a plurality of magnetic pockets formed in the rotor segment for accommodating permanent magnets. The invention further relates to a segmented rotor and an electrical machine.

[0003] Segmented rotors are generally known from the prior art. For example, the published patent application DE 102009052 596 A1 describes a rotor for an electrical machine composed of individual segments. Each of these segments consists of a part that, when the rotor is assembled, is firmly connected to a corresponding part of the adjacent segment. This creates a separate, annular rotor structure that extends in the circumferential direction. Furthermore, each segment has a special opening designed to accommodate a permanent magnet.

[0004] Another segmented rotor is described in US2016094098A1. This rotor contains a core and permanent magnets. The core is constructed of ring-shaped bodies arranged in a stacking direction, consisting of segments. These segments are organized based on the number of magnetic poles formed by the magnets. The core has through-holes through which locating elements pass, stabilizing the structure. There are gaps between the core segments that are larger than the spaces between the through-holes and locating elements. Some ring-shaped bodies are circumferentially offset from others to optimize the magnetic properties.

[0005] Segmented rotors in electrical machines offer numerous advantages over traditional rotor designs, contributing to their increasing popularity and use. First, the segmented design allows for considerable flexibility and adaptability to various operating conditions, including thermal and mechanical stresses. The individual segments can operate independently and adapt more effectively to temperature fluctuations, reducing the risk of overheating and associated damage.

[0006] In terms of manufacturing, segmented rotors often prove to be more cost-effective, as the production of the individual segments is more efficient and can be more easily adapted to specific requirements. This also facilitates the use of different materials and manufacturing techniques.

[0007] The segmented design also allows for greater flexibility in rotor design. This opens up the possibility of optimally adapting the rotors to specific applications and requirements, which in turn can increase the efficiency and performance of the electric machines. Furthermore, by reducing mass inertia, better motor dynamics can be achieved, leading to improved acceleration and deceleration times.

[0008] The magnetic properties of segmented rotors can also be optimized, improving the overall performance and efficiency of the electric machine. The ability to manufacture each segment individually and precisely minimizes manufacturing errors and increases the overall quality and reliability of the motor.

[0009] However, by packaging a segmented rotor with cast aluminum, an unusual stress and stiffness distribution can develop in the laminated core during operation of the segmented rotor compared to solid sections. In particular, the contact points between two segmented laminations in a lamination layer are not able to transfer tensile stresses to one another. If a gap is assumed to avoid geometric overdetermination, neither tensile nor compressive forces can be transmitted at these joints. This can cause the individual segments to bend about an axis parallel to the rotor rotation axis. This can result in an expansion of the rotor and thus an undesirable change in the air gap, which is greater at these contact points than at comparable points within the segment. Secondly, the bending of the segment can cause high compressive stresses to arise at the stray webs near the air gap, which can also lead to buckling of these webs.This is also often undesirable.

[0010] The object of the invention is therefore to provide a rotor segment that avoids or at least mitigates the problems known from the prior art. Furthermore, the object of the invention is to realize an improved rotor and an optimized electric machine.

[0011] This object is achieved by a rotor segment in the form of a circular ring section for forming a segmented, permanently excited rotor of an electrical machine, comprising a plurality of magnetic pockets formed in the rotor segment for receiving permanent magnets, wherein the rotor segment has a groove extending radially inwardly from its radially outer lateral surface.

[0012] This provides the advantage that the groove prevents or at least reduces asymmetric air gap variations during rotation of the segmented rotor. The groove helps prevent compressive stress caused by bending in the flux stray webs adjacent to the air gap, which in rotors manufactured with a solid cutout are generally subjected to tensile or shear forces. The introduction of the groove, which can also be referred to as an outer diameter cutout, enables the two circumferential, radially extending sides of the rotor segment to deform away from and toward each other within a rotor segment.

[0013] This minimizes the pressure load in the adjacent scattering webs and eliminates the asymmetric air gap width change under speed.

[0014] The slot can fundamentally influence the magnetic flux between the two adjacent poles of the permanent magnet rotor. The radial inward extension of the slot must therefore be selected so that it does not influence the magnetic flux, or at least only to a reasonable extent.

[0015] Preferably, a rotor segment is formed from an electrical steel sheet, for example by stamping. Furthermore, it is preferred that a plurality of rotor segments are axially stacked and fixed, for example, by a potting compound, such as an aluminum casting, by welding, gluing, or the like.

[0016] It is fundamentally possible to arrange the permanent magnets in various arrangements within a rotor, and thus also within a rotor segment. Firstly, it is conceivable for at least some of the permanent magnets to be configured as surface-mounted permanent magnets. In this configuration, the magnets are attached directly to the surface of the rotor. This type of arrangement is simple, but it makes the magnets more susceptible to mechanical stress and thermal effects. Therefore, it may also be preferable to design the permanent magnets as embedded permanent magnets (also known as interior permanent magnets, IPM). The magnets are embedded in slots within the rotor, which enables better protection for the magnets, improved thermal properties, and more complex magnetic flux paths. The permanent magnets can also be placed in a V-shaped pattern or in an inclined arrangement within the rotor.This arrangement can help to improve the magnetic flux density and reduce the so-called “cogging torque”.

[0017] In a preferred embodiment of the invention, it can be provided that the rotor segment has a first group of magnetic pockets which are aligned in a V-shape with respect to one another, wherein the tip of the V-shaped magnetic pockets of the first group points radially inwards, and the rotor segment has a second group of magnetic pockets which are also aligned in a V-shape with respect to one another and the tip of the V-shaped magnetic pockets of the second group also points radially inwards, wherein the groove extends in the circumferential direction between the first group and the second group of V-shaped magnetic pockets. The V-shaped arrangement of the magnets can improve the magnetic flux density in the air gap between the rotor and stator. This can increase the efficiency of the machine because it enables a stronger magnetic coupling between the rotor and stator.A V-shaped arrangement of the magnets can also help reduce cogging torque, resulting in smoother running of the machine. Cogging torque refers to the jerky torque that can occur due to the interaction between the rotor magnets and the stator teeth.

[0018] According to an advantageous embodiment of the invention, the groove can have a substantially rectangular cross-sectional contour with a constant groove width. The advantage of this embodiment is that the rectangular shape is easy to manufacture and, for example, does not require complex punching tools. Furthermore, the rectangular shape has also proven particularly advantageous in terms of avoiding asymmetric air gap variations while minimizing magnetic flux interference.

[0019] According to a further preferred development of the invention, the groove can also be arranged circumferentially centrally between the first group and the second group of V-shaped magnetic pockets. This allows for a further improvement in avoiding asymmetric air gap variations while simultaneously optimizing the balancing properties of the rotor.

[0020] Furthermore, according to a likewise advantageous embodiment of the invention, it can be provided that the groove has a substantially circular cross-sectional contour at its radially inner end, the diameter of which is greater than the groove width. The advantageous effect of this embodiment is that an undesirable notch effect at the radially inner end of the groove can be counteracted by the circular cross-sectional contour. According to a further particularly preferred embodiment of the invention, this notch effect can be particularly effectively avoided by ensuring that the diameter of the circular cross-sectional contour is greater than 2 mm, preferably greater than 2.5 mm. Therefore, if bending of a rotor segment occurs with the groove under individual load cases, an excessive notch effect can be counteracted at this point by providing a radius that is also greater than the groove width of the groove itself.For the purpose of punchability, such a punched circle must have a minimum diameter of 02 mm, preferably 02.5 mm.

[0021] Furthermore, the invention can also be further developed such that the groove width is less than 2 mm, preferably less than 1.5 mm. Since the groove can affect the reluctance behavior of the electrical machine, it is advantageous to keep the groove width as small as possible along its radial extent. To ensure good punchability of the rotor segment, a groove width of less than 2 mm, preferably less than 1.5 mm, has proven particularly advantageous.

[0022] In a likewise preferred embodiment of the invention, it can also be provided that the groove has a shoulder at its radially outer end that is set back radially inward relative to the radially outer circumferential surface. This makes it possible to provide a geometry close to the air gap as part of the outer contour punch, so that the punching overlap area and thus the burr are not positioned at the air gap. Since the punching overlap area and thus the burr are not positioned at the air gap, the formation of a metallic burr that could impair the air gap is avoided. The specific geometry also enables a more homogeneous magnetic field distribution in the air gap, since disruptive irregularities in the rotor surface that could influence the magnetic field are avoided.

[0023] The object of the invention is further achieved by a segmented, permanently excited rotor of an electrical machine comprising a plurality of rotor segments in the form of an annular segment according to one of claims 1-8.

[0024] Particularly preferably, the rotor is configured as a permanently excited rotor for a synchronous machine.

[0025] According to a further preferred embodiment of the

[0026] The subject matter of the invention can be provided with the rotor segments being fixed by means of an aluminum casting. In this case, the rotor, particularly designed for a permanent-magnet synchronous machine, has its rotor segments held together by a separate material, such as aluminum, with the force transmission between segment layers being achieved via transverse forces in the additional material. The aluminum then preferably primarily serves the function of mechanically connecting the rotor segments to one another, but not necessarily of fixing the entire rotor segment set to other components.

[0027] Finally, the object of the invention can also be achieved by an electric machine, in particular for a drive train of a motor vehicle, comprising a stator and a segmented, permanently excited rotor according to one of claims 9-10.

[0028] The invention will be explained in more detail below with reference to figures without limiting the general inventive concept.

[0029] It shows:

[0030] Figure 1 is a cross-sectional view of a segmented, permanent magnet rotor,

[0031] Figure 2 shows a first embodiment of a rotor segment in a cross-sectional view and in an enlarged detail of the groove area,

[0032] Figure 3 shows a second embodiment of a rotor segment in a cross-sectional view and in an enlarged detail of the groove area,

[0033] Figure 4 shows a third embodiment of a rotor segment in a cross-sectional view and in an enlarged detail of the groove area, Figure 5 shows a motor vehicle with an electric drive train in a schematic representation.

[0034] Figure 1 shows a segmented, permanently excited rotor 2 of an electric machine 3 comprising a plurality of rotor segments 1 in the shape of an annular segment. The rotor 2 consists of a total of four identical rotor segments 1, which are arranged circumferentially adjacent to one another to form a closed annulus. The rotor segments 1 are connected in a rotationally fixed manner to the rotor shaft 21. To absorb transverse forces, aluminum cutouts 22 are provided in the rotor segments 1, through which cast aluminum passes, thus securing the rotor segments to one another.

[0035] A rotor segment 1 in the shape of a circular ring comprises a plurality of magnetic pockets 4 formed in the rotor segment 1 for accommodating permanent magnets 5. The rotor segment 1 has a first group 6 of magnetic pockets 4 which are aligned in a V-shape with respect to one another, with the tip 8 of the V-shaped magnetic pockets 4 of the first group 6 pointing radially inward. Furthermore, the rotor segment 1 has a second group 7 of magnetic pockets 4 which are also aligned in a V-shape with respect to one another, and the tip 9 of the V-shaped magnetic pockets 4 of the second group 7 also pointing radially inward. In the section between the magnetic pockets 4 of a group 6, 7, which widens radially outwards due to the V-shaped alignment, a further magnetic pocket 19 for a permanent magnet 20 is provided for each group 6, 7. These permanent magnets 20 are occasionally also referred to as T-magnets or tangential magnets.

[0036] At the radially inwardly directed ends of the magnetic pockets 4, a drop-like stray flux barrier 23 is formed in the cross-sectional contour.

[0037] The rotor segment 1 further comprises, starting from its radially outer surface 24, a groove 10 extending radially inward in the circumferential direction between the first group 6 and the second group 7 of V-shaped magnetic pockets 4. The groove 10 has a substantially rectangular cross-sectional contour 18 with a constant groove width 13, which can also be clearly seen from the detailed view in Figure 2. Figure 2 also clearly shows that the groove 10 runs centrally in the circumferential direction between the first group 6 and the second group 7 of V-shaped magnetic pockets 4.

[0038] As shown in Figure 3, the groove 10 can have at its radially inner end a substantially circular cross-sectional contour 11, the diameter 12 of which is greater than the groove width 13 of the groove 10. The diameter 12 of the circular cross-sectional contour 11 is greater than 2 mm, preferably greater than 2.5 mm, the groove width 13 of the groove 10 then being less than 2 mm, preferably less than 1.5 mm.

[0039] What can be seen from Figure 4 is that the groove 10 can also have, at its radially outer end, a shoulder 14 which is set back radially inwards relative to the radially outer circumferential surface 24.

[0040] Finally, Figure 5 shows an electric machine 3 in a drive train 15 of a motor vehicle 16, comprising a stator 17 and a segmented, permanently excited rotor 2, as is known from Figures 1-4.

[0041] The invention is not limited to the embodiments illustrated in the figures. The above description is therefore not to be considered restrictive, but rather explanatory. The following claims are to be understood as meaning that a stated feature is present in at least one embodiment of the invention. This does not exclude the presence of further features. Where the claims and the above description define 'first' and 'second' features, this designation serves to distinguish between two similar features without establishing a priority. List of reference symbols

[0042] 1 rotor segment

[0043] 2 rotors

[0044] 3 electric machine

[0045] 4 magnetic pockets

[0046] 5 permanent magnets

[0047] 6 first group

[0048] 7 second group

[0049] 8 lace

[0050] 9 top

[0051] 10 grooves

[0052] 11 Cross-sectional contour

[0053] 12 diameters

[0054] 13 Groove width

[0055] 14 paragraph

[0056] 15 Powertrain

[0057] 16 motor vehicle

[0058] 17 Stator

[0059] 18 Cross-sectional contour

[0060] 19 magnetic pocket

[0061] 20 permanent magnets

[0062] 21 Rotor shaft

[0063] 22 aluminum cutouts

[0064] 23 Flux leakage barrier

[0065] 24 lateral surface

Claims

Claims 1. A rotor segment (1) in the form of a circular ring section for forming a segmented, permanently excited rotor (2) of an electrical machine (3), comprising a plurality of magnetic pockets (4) formed in the rotor segment (1) for receiving permanent magnets (5), characterized in that the rotor segment (1) has a groove (10) extending radially inwards starting from its radially outer circumferential surface (24).

2. Rotor segment (1) according to claim 1, characterized in that the rotor segment (1) has a first group (6) of magnetic pockets (4) which are aligned in a V-shape with respect to one another, the tip (8) of the V-shaped magnetic pockets (4) of the first group (6) pointing radially inwards, and the rotor segment (1) has a second group (7) of magnetic pockets (4) which are also aligned in a V-shape with respect to one another and the tip (9) of the V-shaped magnetic pockets (4) of the second group (7) also pointing radially inwards, the groove (10) extending in the circumferential direction between the first group (6) and the second group (7) of V-shaped magnetic pockets (4).

3. Rotor segment (1) according to claim 1 or 2, characterized in that the groove (10) has a substantially rectangular cross-sectional contour (18) with a constant groove width (13).

4. Rotor segment (1) according to one of the preceding claims 2 or 3, characterized in that the groove (10) runs circumferentially centrally between the first group (6) and the second group (7) of V-shaped magnetic pockets (4).

5. Rotor segment (1) according to one of the preceding claims, characterized in that the groove (10) has at its radially inner end a substantially circular cross-sectional contour (11), the diameter (12) of which is greater than the groove width (13) of the groove (10).

6. Rotor segment (1) according to claim 5, characterized in that the diameter (12) of the circular cross-sectional contour (11) is greater than 2 mm, preferably greater than 2.5 mm.

7. Rotor segment (1) according to one of claims 3-6, characterized in that the groove width (13) of the groove (10) is less than 2 mm, preferably less than 1.5 mm.

8. Rotor segment (1) according to one of the preceding claims, characterized in that the groove (10) has at its radially outer end a shoulder (14) which is set back radially inwards with respect to the radially outer circumferential surface (24).

9. Segmented, permanently excited rotor (2) of an electrical machine (3) comprising a plurality of rotor segments (1) in the form of an annular segment according to one of claims 1-8.

10. Rotor (2) according to claim 9, characterized in that the rotor segments (1) of the rotor (2) are fixed by means of an aluminum casting.

11. An electrical machine (3), in particular for a drive train (15) of a motor vehicle (16), comprising a stator (17) and a segmented, permanently excited rotor (2) according to one of claims 9-10.

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