Circular segment-shaped rotor segment, segmented rotor and electric machine

Abstract

A circular segment-shaped rotor segment (1) for forming a segmented, permanent excitation 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), wherein the rotor segment (1) has a radially inwardly extending groove (10) starting from its radially outer surface (24), characterized in that the groove (10) has a substantially circular cross-sectional contour (11) at its radially inner end, the diameter (12) of which is larger than a groove width (13) of the groove (10).

Description

[0001] The present invention relates to an annular segment-shaped rotor for forming a segmented, permanent magnet rotor of an electric machine, comprising a plurality of magnet pockets formed in the rotor segment for receiving permanent magnets. The invention further relates to a segmented rotor and an electric machine.

[0002] Segmented rotors are generally known from the prior art. For example, German patent application DE 102009052 596 A1 describes a rotor for an electric machine composed of individual segments. Each of these segments consists of a part which, when the rotor is assembled, is firmly connected to a corresponding part of the adjacent segment. This creates an independent, ring-shaped structure of the rotor that extends circumferentially. Furthermore, each segment has a special opening designed to receive a permanent magnet.

[0003] Another segmented rotor is described in US2016094098A1. This rotor contains a core and permanent magnets. The core is composed of ring-shaped bodies arranged in a stacking direction, each 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 fixing elements pass, stabilizing the structure. There are gaps between the core segments that are larger than the spaces between the through-holes and fixing elements. Some ring-shaped bodies are offset circumferentially compared to others to optimize the magnetic properties.

[0004] Segmented rotors in electric 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, thereby reducing the risk of overheating and associated damage.

[0005] In terms of manufacturing, segmented rotors often prove to be more cost-effective, as the production of individual segments can be made more efficient and more easily adapted to specific requirements. This also facilitates the use of different materials and manufacturing techniques.

[0006] 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 increases the efficiency and performance of the electric machines. Furthermore, reducing inertia results in improved motor dynamics, leading to faster acceleration and braking times.

[0007] 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 defects and increases the overall quality and reliability of the motor.

[0008] However, by laminating a segmented rotor with cast aluminum, an unusual stress and stiffness distribution can develop within the laminated core during operation, compared to solid sections. In particular, the contact points between two segmented sheets within a single sheet layer are unable to transmit tensile stresses. Assuming a gap to prevent geometric overdetermination, neither tensile nor compressive forces can be transmitted at these joints. This can cause the individual segments to bend around an axis parallel to the rotor's axis of rotation.

[0009] This can lead to two things: firstly, a widening of the rotor, and consequently 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 at the scattering webs near the air gap can generate high compressive stresses, which can also lead to buckling of these webs. This, too, is generally undesirable.

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

[0011] This problem is solved by an annular segment-shaped rotor segment for forming a segmented, permanent excited rotor of an electric machine comprising a plurality of magnet pockets formed in the rotor segment for receiving permanent magnets, wherein the rotor segment has a groove extending radially inwards from its radially outer surface.

[0012] This offers the advantage that the groove prevents or at least reduces asymmetrical air gap variations during rotation of the segmented rotor. The groove helps avoid the pressure stress caused by bending in the flux gap webs adjacent to the air gap, which in solid-cut rotors are generally subjected to tensile or shear forces. The introduction of the groove, which can also be described as an outer diameter cutout, allows the two circumferential, radially extending sides of the rotor segment to deform away from and towards each other. This minimizes the pressure stress in the adjacent flux gap webs and eliminates the asymmetrical change in air gap width during rotation.

[0013] The groove can, in principle, influence the magnetic flux between the two adjacent poles of the permanent magnet rotor. Therefore, the radial extent of the groove towards the inside must be chosen so that it does not influence the magnetic flux, or at least only to an acceptable extent.

[0014] 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 on top of each other and fixed, for example by a potting compound such as an aluminum casting, by welding, bonding, or similar methods.

[0015] It is generally possible to arrange the permanent magnets in various configurations within a rotor, and thus also within a rotor segment. One option is to configure at least some of the permanent magnets as surface-mounted magnets. In this configuration, the magnets are attached directly to the rotor surface. 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 implement the permanent magnets as embedded permanent magnets (also known as interior permanent magnets, IPMs). Here, the magnets are embedded in slots within the rotor, which allows for better protection of 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 angled arrangement within the rotor.This arrangement can help to improve the magnetic flux density and reduce the so-called "cogging torque".

[0016] In a preferred embodiment of the invention, the rotor segment may have a first group of magnet pockets arranged in a V-shape relative to each other, with the apex of the V-shaped magnet pockets of the first group pointing radially inwards, and a second group of magnet pockets also arranged in a V-shape relative to each other, with the apex of the V-shaped magnet pockets of the second group also pointing radially inwards, the groove extending circumferentially between the first and second groups of V-shaped magnet pockets. The V-shaped arrangement of the magnets improves the magnetic flux density in the air gap between the rotor and stator. This can increase the efficiency of the machine by enabling stronger magnetic coupling between the rotor and stator.A V-shaped arrangement of the magnets can also help reduce cogging torque, resulting in smoother machine operation. Cogging torque refers to the jerky torque that can arise from the interaction between the rotor magnets and the stator teeth.

[0017] 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 complexly shaped stamping tools. Furthermore, the rectangular shape has also proven to be particularly advantageous with regard to avoiding asymmetrical air gap variations while minimizing magnetic flux interference.

[0018] According to a further preferred embodiment of the invention, the groove can also be arranged to run centrally in the circumferential direction between the first and second groups of V-shaped magnet pockets. This allows for a further improvement in avoiding asymmetrical air gap variations while simultaneously optimizing the rotor's balancing properties.

[0019] Furthermore, according to another advantageous embodiment of the invention, the groove can have a substantially circular cross-sectional contour at its radially inner end, the diameter of which is larger 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, a particularly effective avoidance of this notch effect can be achieved by having a diameter of the circular cross-sectional contour greater than 2 mm, preferably greater than 2.5 mm. Thus, if bending of a rotor segment occurs in certain load cases, even with the groove, an excessive notch effect at this point can be counteracted by providing a radius that is also larger than the groove width itself.For the purpose of punchability, a minimum diameter of Ø2 mm, preferably Ø2.5 mm, should be provided for such a punched circle.

[0020] 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 electric machine, it is advantageous to keep the groove width as small as possible along its radial extent. For the purpose of maintaining good stampability of the rotor segment, a groove width of less than 2 mm, preferably less than 1.5 mm, has proven particularly advantageous.

[0021] In a further preferred embodiment of the invention, the groove may also have a shoulder at its radially outer end that is set back radially inwards relative to the radially outer surface. This allows for a geometry close to the air gap to be provided as part of the outer contour punch, so that the punched overlap area, and thus the burr, is not positioned at the air gap. Since the punched overlap area, and thus the burr, is not positioned at the air gap, the formation of a metallic burr that could impair the air gap is avoided. Furthermore, the specific geometry enables a more homogeneous magnetic field distribution in the air gap, as disruptive irregularities in the rotor surface that could influence the magnetic field are avoided.

[0022] The object of the invention is further solved by a segmented, permanent excitation rotor of an electric machine comprising a plurality of circular segment-shaped rotor segments according to one of claims 1-8.

[0023] The rotor is particularly preferably configured as a permanent magnet rotor for a synchronous machine.

[0024] According to a further preferred embodiment of the invention, the rotor segments of the rotor can be fixed by means of an aluminum casting. In this case, the rotor, particularly one 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 the segment layers being achieved via transverse forces in the additional material. The aluminum preferably serves primarily to mechanically connect the rotor segments to one another, but not necessarily to fix the sum of the rotor segments to other components.

[0025] Finally, the problem of the invention can also be solved by an electric machine, in particular for a drive train of a motor vehicle, comprising a stator and a segmented, permanent excitation rotor according to one of claims 9-10.

[0026] The invention will now be explained in more detail with reference to figures, without limiting the general concept of the invention.

[0027] It shows: Fig. 1 A cross-sectional view of a segmented, permanent magnet rotor, Fig. 2 a first embodiment of a rotor segment in a cross-sectional view and in a close-up of the groove area, Fig. 3 a second embodiment of a rotor segment in a cross-sectional view and in a close-up of the groove area, Fig. 4 a third embodiment of a rotor segment in a cross-sectional view and in a close-up of the groove area, Fig. 5 A motor vehicle with an electric powertrain in a schematic representation.

[0028] In the Fig. Figure 1 shows a segmented, permanent magnet rotor 2 of an electric machine 3 comprising a plurality of annular segment-shaped rotor segments 1. The rotor 2 consists of a total of four identical rotor segments 1, which are arranged circumferentially to form a closed annulus. The rotor segments 1 are rotationally fixed to the rotor shaft 21. To absorb lateral forces, aluminum cutouts 22 are provided in the rotor segments 1, which are penetrated by aluminum castings and thus fix the rotor segments relative to one another.

[0029] An annular rotor segment 1 comprises a plurality of magnet pockets 4 formed within the rotor segment 1 for receiving permanent magnets 5. The rotor segment 1 has a first group 6 of magnet pockets 4, which are oriented in a V-shape relative to each other, with the apex 8 of the V-shaped magnet pockets 4 of the first group 6 pointing radially inwards. Furthermore, the rotor segment 1 has a second group 7 of magnet pockets 4, which are also oriented in a V-shape relative to each other, and with the apex 9 of the V-shaped magnet pockets 4 of the second group 7 also pointing radially inwards. In the region defined by the V-shaped orientation, which widens radially outwards between the magnet pockets 4 of a group 6, 7, a further magnet pocket 19 for a permanent magnet 20 is provided for each group 6, 7. These permanent magnets 20 are sometimes also referred to as T-magnets or tangential magnets.

[0030] At the radially inwardly directed ends of the magnet pockets 4, a droplet-shaped stray flux barrier 23 is formed in the cross-sectional contour.

[0031] The rotor segment 1 further has a groove 10 extending radially inwards from its radially outer surface 24 in the circumferential direction between the first group 6 and the second group 7 of V-shaped magnetic pockets 4.

[0032] The groove 10 has an essentially rectangular cross-sectional contour 18 with a constant groove width 13, which can also be clearly seen in the detailed view in the Fig. 2 can be understood. Fig. 2 can also be clearly seen that the groove 10 runs in the circumferential direction centrally between the first group 6 and the second group 7 of V-shaped aligned magnetic pockets 4.

[0033] As in the Fig. As shown in Figure 3, the groove 10 can have a substantially circular cross-sectional contour 11 at its radially inner end, the diameter 12 of which is larger than the groove width 13 of the groove 10. The diameter 12 of the circular cross-sectional contour 11 is larger than 2 mm, preferably larger than 2.5 mm, wherein the groove width 13 of the groove 10 is then less than 2 mm, preferably less than 1.5 mm.

[0034] What the Fig. As can be seen from 4, the groove 10 can also have a shoulder 14 at its radially outer end which is set back radially inwards from the radially outer surface 24.

[0035] Finally, the Fig. 5 an electric machine 3 in a drive train 15 of a motor vehicle 16, comprising a stator 17 and a segmented, permanent magnet rotor 2, as derived from the Fig. 1-4 is known.

[0036] The invention is not limited to the embodiments illustrated in the figures. The foregoing description is therefore not to be considered limiting, but rather explanatory. The following claims are to be understood as meaning that a named feature is present in at least one embodiment of the invention. This does not preclude the presence of further features. Insofar as the claims and the foregoing description define 'first' and 'second' features, this designation serves to distinguish between two similar features without establishing any hierarchy. Reference symbol list 1 rotor segment 2 Rotor 3 electric machine 4 magnetic pockets 5 permanent magnets 6 first group 7 second group 8 top 9 top 10 Nut 11 Cross-sectional contour 12 diameter 13 groove width Paragraph 14 15 Powertrain 16 motor vehicle 17 Stator 18 Cross-sectional contour 19 magnetic pockets 20 permanent magnets 21 Rotor shaft 22 aluminum cutouts 23 Stray flow barrier 24 Surface area QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 102009052 596 A1

[0002] US 2016094098A1

[0003]

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 by that the rotor segment (1) has a groove (10) extending radially inwards from its radially outer surface (24). [2] Rotor segment (1) according to claim 1, characterized bythat the rotor segment (1) has a first group (6) of magnetic pockets (4) which are aligned in a V-shape relative 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 relative 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 by 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 bythat the groove (10) runs in the circumferential direction 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 by that the groove (10) has at its radially inner end a substantially circular cross-sectional contour (11) whose diameter (12) is greater than the groove width (13) of the groove (10). [6] Rotor segment (1) according to claim 5, characterized by 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 by 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 bythat the groove (10) has at its radially outer end a shoulder (14) which is set back radially inwards relative 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 by that the rotor segments (1) of the rotor (2) are fixed by means of an aluminum casting. [11] Electric 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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