Electric motor having a rotatably mounted rotor

Abstract

The invention relates to an electric motor having a rotatably mounted rotor, wherein: the rotor has a rotor shaft, a permanent magnet ring, and a laminated rotor core mounted onto a rotor shaft; the laminated rotor core has a stack of first individual laminations, second individual laminations and third individual laminations; the laminated rotor core has, at its first axial end region, a partial core which is formed from first individual laminations and onto which a second individual lamination is adhesively bonded and / or placed, a third individual lamination being adhesively bonded and / or placed onto the side of the second individual lamination facing axially away from the first partial core; an additional second individual lamination is adhesively bonded and / or placed onto the side of the third individual lamination facing away from the second individual lamination; the second individual lamination has regions which are mutually spaced in the circumferential direction and of which the maximum outer radius is smaller than the maximum outer radius of the first and third individual laminations; and the permanent magnet ring is pushed onto the laminated rotor core.

Description

[0001] Electric motor having a rotatably mounted rotor

[0002] Description:

[0003] The invention relates to an electric motor having a rotatably mounted rotor.

[0004] It is generally known that an electric motor has a rotatably mounted rotor.

[0005] From US 2010 / 0 045 132 A1, the closest prior art is a rotor for an electric motor.

[0006] A rotor for a rotary electrical machine is known from JP 2012 - 249 389 A.

[0007] The invention is therefore based on the object of producing a rotor that rotates as evenly as possible, in particular without the need for balancing the rotor.

[0008] According to the invention, the object is achieved in the electric motor according to the features specified in claim 1.

[0009] Important features of the invention in the electric motor are that the electric motor has a rotatably mounted rotor, wherein the rotor has a rotor shaft, a permanent magnet ring and a rotor laminated core mounted on a rotor shaft, in particular wherein the rotor laminated core is connected to the rotor shaft in a rotationally fixed manner, wherein the rotor laminated core has a stack of first individual laminations, second individual laminations and third individual laminations, wherein the rotor laminated core has, at its first axial end region, a sub-package formed from first individual laminations, to which a second individual lamination is glued and / or applied, on the side of which sub-package facing away from the first sub-package a third individual lamination is glued and / or applied, wherein on the side of the third individual lamination facing away from the second individual lamination a further second individual lamination is glued and / or applied, wherein the second individual lamination is arranged in the circumferential direction, in particular three,has spaced-apart regions whose maximum outer radius is smaller than the maximum outer radius of the first and third individual laminations, wherein the permanent magnet ring is pushed onto the rotor lamination stack, in particular wherein the axis of rotation of the rotor shaft is aligned coaxially with the ring axis of the permanent magnet ring, in particular wherein the axial direction is aligned parallel to the axis of rotation of the rotor shaft and / or both the radial direction and the circumferential direction are related to the axis of rotation of the rotor shaft.

[0010] The advantage here is that the radially projecting regions of the third individual lamination act as a centering receptacle for the permanent magnet ring, wherein these regions are elastically deflected when the permanent magnet ring is pushed axially onto the rotor lamination stack and project into those free spaces which are caused by the reduction of the outer radius of the second individual lamination, in particular in those circumferential angular regions in which the radial projections of the third individual lamination are arranged.

[0011] This achieves a high-precision three-point bearing for the permanent magnet ring at the respective axial end area of ​​the rotor core.

[0012] An adhesive layer between the rotor lamination stack and the permanent magnet ring transfers torque from the permanent magnet ring to the rotor lamination stack during operation. The radially projecting areas contribute only slightly to this. During temperature changes, the rotor lamination stack, made of sheet steel, deforms more than the permanent magnet ring. In particular, the steel sheet expands radially when heated. The thermally induced deformations are absorbed and / or compensated for by the third individual sheet or the rotor lamination stack together with the adhesive layer arranged between the permanent magnet ring and the rotor lamination stack. Thus, the permanent magnet ring is not exposed to unacceptably high mechanical stresses. The permanent magnet ring is made of brittle material, in particular a powder alloy and / or a ceramic material.The adhesive layer also has a higher specific modulus of elasticity than the steel sheet and possibly even than the permanent magnet ring.

[0013] In an advantageous embodiment, the third individual lamination extends radially beyond the first individual lamination within the circumferential angular ranges covered by the regions. This is advantageous because, when the permanent magnet ring is pushed on, these regions come into contact with the permanent magnet ring and are elastically deformed by it, thus achieving precise alignment of the permanent magnet ring relative to the rotor core.

[0014] In an advantageous embodiment, each individual lamination is adhesively bonded to its at least one adjacent individual lamination, in particular with an adhesive layer provided between adjacent individual laminations. This allows for precise manufacturing of the rotor lamination stack, as deforming welding is eliminated. Alternatively, punching and stacking is also possible. Centering can also be performed independently of the stacking process.

[0015] In an advantageous embodiment, the outer diameter of the first individual lamination, which is in particular a function of the circumferential angle, is equal to the outer diameter of the second individual lamination. It is advantageous in this case that the radially recessed regions of the second individual lamination on the outer circumference provide free space for the radially projecting and elastically deformed regions of the third individual lamination. In an advantageous embodiment, the outer radius of the first individual lamination, which is in particular a function of the circumferential angle, is independent of the circumferential angle, in particular with respect to the axis of rotation of the rotor shaft. It is advantageous in this case that the permanent magnet ring can be easily threaded onto the first sub-package made up of first individual laminations with its inner chamfer and then uses its chamfer to deform the radially projecting regions of the third individual lamination.

[0016] In an advantageous embodiment, the outer radius of the third individual lamination, which is maximum in particular as a function of the circumferential angle, has, in particular, three local maxima as a function of the circumferential angle, particularly relative to the axis of rotation of the rotor shaft as a function of the circumferential angle. It is advantageous that the permanent magnet ring is mounted on the rotor lamination stack by means of a three-point bearing. After the permanent magnet ring is pushed onto the rotor lamination stack, the adhesive layer hardens and thus forms a torque-transmitting connecting layer between the permanent magnet ring and the

[0017] The respective three-point bearing at each of the axial end areas of the rotor core serves to center and align the permanent magnet ring.

[0018] In an advantageous embodiment, the outer radius of the third individual lamination, which is particularly maximum as a function of the circumferential angle, in particular with respect to the axis of rotation of the rotor shaft, is a periodic function of the circumferential angle and, as a function of the circumferential angle, has, in particular, three local maxima as a function of the circumferential angle. It is advantageous that the permanent magnet ring is mounted on the rotor lamination stack by means of a three-point bearing. After the permanent magnet ring has been slid onto the rotor lamination stack, the adhesive layer hardens and thus creates a torque-transmitting connecting layer between the permanent magnet ring and the rotor lamination stack. The respective three-point bearing at each of the axial end regions of the rotor lamination stack serves to center and align the permanent magnet ring.

[0019] In an advantageous embodiment, the local maxima of the, in particular maximum, outer radius of the third individual lamination, in particular as a function of the circumferential angle, are arranged radially outside the first individual lamination, in particular - wherein as a function of the circumferential angle, the local minima of the, in particular maximum, outer radius of the third individual lamination have the same radial distance, in particular maximum radial distance, to the axis of rotation of the rotor shaft as the outer circumference of the first individual lamination - or wherein local minima of the, in particular maximum, outer radius of the third

[0020] Single sheet are arranged radially inside the first single sheet.

[0021] The advantage here is that the radially protruding areas can be deformed into the adjacent free spaces when the permanent magnet ring is pushed onto it.

[0022] In an advantageous embodiment, the circumferential angular range covered in the circumferential direction by the circumferentially spaced-apart regions of the second individual sheet, in particular three, whose maximum outer radius is smaller than the maximum outer radius of the first and third individual sheets, comprises the axial circumferential angular positions of the local maxima of the outer radius of the third individual sheet, in particular as a function of the maximum circumferential angle. It is advantageous in this case that the relative angular position of the second individual sheet can be adjusted to the third individual sheet.

[0023] In an advantageous embodiment, the permanent magnet ring is centered and / or aligned by means of the radially projecting regions, in particular relative to the rotor core and / or the rotor shaft. It is advantageous that the centering alignment of the permanent magnet ring can be achieved by means of the radially projecting regions of the third individual lamination before the adhesive layer hardens.

[0024] In an advantageous embodiment, the regions are deformed such that the region covered by the third individual lamination, including the regions in the axial direction, overlaps the region covered by a second individual lamination in the axial direction. This is advantageous because the radial reductions of the second individual lamination provide sufficient clearance for the deformed regions of the third individual lamination. Thus, the radially projecting regions of the third individual lamination are converted into axially projecting deformation regions when the permanent magnet ring is pushed on.

[0025] In an advantageous embodiment, the third individual sheet has an outer web, an intermediate web, and an inner web in each of the circumferential angular regions covered by the regions in the circumferential direction, the outer web being arranged radially outside the intermediate web, the intermediate web being arranged radially outside the inner web, the intermediate web being radially spaced from the outer web and radially spaced from the inner web. It is advantageous in this case that the intermediate web is arranged radially between the two other webs and spaced from them. The two other webs are thus elastically deformable, particularly in the event of thermally induced geometric changes. The permanent magnet ring is thus protected from mechanical stresses. In particular, it can be manufactured from a ceramic material or another brittle material.

[0026] In an advantageous embodiment, the outer web, the intermediate web, and the inner web each extend in the circumferential direction. This advantageously means that the outer web and the inner web each exhibit increased elasticity due to the adjacent recess, thus compensating for thermally induced expansion without subjecting the permanent magnet ring to an unacceptably high load, which exhibits a lower thermally induced geometric change. In particular, the permanent magnet ring is preferably made of a powder alloy and / or a ceramic material.

[0027] In an advantageous embodiment, the outer web, the intermediate web, and the inner web are each spaced apart from one another by means of a respective recess, in particular a punched-out section, extending axially through the third individual sheet. Advantageously, the intermediate web is arranged radially between the other two webs and spaced from them. Thus, the other two webs are elastically deformable, particularly in the case of thermally induced geometric changes. The permanent magnet ring is thus protected from mechanical stresses. In particular, it can be manufactured from a ceramic material.

[0028] In an advantageous embodiment, the inner web rests against the rotor shaft. This is advantageous because, when sliding the rotor lamination stack onto the shaft, it can be centered and aligned at three circumferential points, thus enabling precise mounting of the rotor lamination stack on the rotor shaft.

[0029] In an advantageous embodiment, the outer web rests against the permanent magnet ring. This is advantageous because, when the permanent magnet ring is pushed onto the rotor core, it can be centered and aligned at three circumferential points, thus enabling precise mounting of the permanent magnet ring on the rotor core. In particular, thermally induced deformations can be accommodated by the elastically deformable outer web.

[0030] In an advantageous embodiment, the inner webs are spaced apart from one another in the circumferential direction, in particular so that the rotor shaft support on the inner circumference of the third individual lamination is designed with multiple, in particular at least three, interruptions. Advantageously, the interruptions allow thermally induced length changes of the inner webs to be accommodated by deformation of the inner webs.

[0031] In an advantageous embodiment, the third individual lamination has radial recesses in the circumferential direction between the inner webs, in particular so that the clear inner radius of the third individual lamination, in particular related to the axis of rotation of the rotor shaft, has a local maximum as a function of the circumferential angle. The advantage here is that the recesses create free spaces and thus the rotor lamination stack is accommodated at three circumferential points, in particular thus achieving stable alignment and centering. the permanent magnet ring has a chamfer running continuously in the circumferential direction on its front inner edge in the axial direction, in particular and a further chamfer running continuously in the circumferential direction on its rear inner edge in the axial direction, in particular wherein by means of the chamfer the radially protruding regions of the third individual lamination are formed into regions on the third individual lamination that protrude in the axial direction.The advantage here is that when the permanent magnet ring is pushed onto the rotor core, the deformation is carried out by means of the chamfer and requires only minimal force. Further advantages arise from the subclaims. The invention is not limited to the combination of features of the claims. Those skilled in the art will recognize further possible combinations of claims and / or individual claim features and / or features of the description and / or the figures, in particular from the task and / or the task posed by comparison with the prior art.

[0032] The invention will now be explained in more detail using schematic illustrations:

[0033] Figure 1 shows an oblique view of a rotor laminated core which can be plugged onto a rotor shaft 40 to form an electric motor according to the invention, the rotor laminated core comprising a stack of first individual laminations 1, second individual laminations 2 and at least one third individual lamination.

[0034] Figure 2 shows a top view of the second individual sheet 2.

[0035] Figure 3 shows a top view of the third individual sheet 3.

[0036] Figure 4 shows a transparent oblique view of the rotor.

[0037] As shown in the figures, the electric motor has the rotatably mounted rotor, for the production of which the rotor laminated core is placed on the rotor shaft 40 and then a permanent magnet ring, not shown in the figures, is placed on the rotor laminated core.

[0038] The rotor lamination stack comprises a stack of individual laminations (1, 2, 3) that are adhesively bonded to one another. For this purpose, each individual lamination (1, 2, 3) is coated with adhesive, in particular a bonding varnish, and the stack is then formed so that the entire stack is adhesively bonded.

[0039] The stack has at its respective axial end a first partial stack of first individual sheets 1, which are shown together as an entire part in Figure 1 and are designated only by the reference number 1. At least one second individual sheet 2 is glued to this first individual sheet 1, to which a third individual sheet 3 is applied on the side facing away from the first individual sheet 1, to which a second individual sheet 2 is in turn applied, to which a partial stack of first individual sheets 1 is then applied on the side facing away from the third individual sheet 3, which partial stack is shown together as an entire part in Figure 1 and is designated only by the reference number 1. The permanent magnet ring 41 is hollow and has a chamfer on its end face, radially inwardly arranged, circumferentially extending edge, in particular an annular edge.This chamfer is conical in shape and facilitates the placement of the permanent magnet ring 41 onto the stack.

[0040] The axial direction is aligned parallel to the rotor shaft's rotational axis. The circumferential and radial directions are also aligned relative to the rotor shaft's rotational axis.

[0041] The first individual sheets 1 have a surface area of ​​a circular cylinder as their outer circumference.

[0042] The second individual sheet 2 has first, radially raised regions 21 on the second individual sheet 2, which are spaced apart from one another in the circumferential direction and each cover first circumferential angular ranges, in which the outer radius is equal to the outer radius of the circular cylinder, wherein this outer radius is larger than in second, radially recessed regions 22, which each cover second circumferential angular ranges and which are each arranged in the circumferential direction between the first regions 21. The outer radius of these second regions 22 is smaller than the outer radius in the first regions 21. In the circumferential direction, a respective first circumferential angular range adjoins a respective second circumferential angular range.

[0043] The maximum outer diameter of the second single sheet 2 is equal to the maximum outer diameter of the first single sheet 1.

[0044] The third individual sheet 3 has, on its radial outer circumference, three radially projecting regions 30 which are spaced apart from one another in the circumferential direction and which, in particular, exceed the maximum outer diameters of the first and second individual sheets (1, 2). To facilitate elastic deformation of the radially projecting regions 30 of the third individual sheet 3, kidney-shaped recesses 32 and further kidney-shaped recesses 33 are provided radially within these regions 30 in the individual sheet 3. Thus, a radially inner inner web 35, an intermediate web 34, which is formed between the two recesses 32 and 35, and an outer web 31 are formed. The outer web 31 has the radially outward-facing elevation 30. The recess 32 is arranged radially outside the recess 33 and causes the improved elastic deformation of the outer web 31. Likewise, the recess 33 causes an easier elastic deformation of the inner web 35.

[0045] Since the first individual laminations 1 have an outer radius that is independent of the circumferential direction, in particular a constant outer radius, in particular a circular outer circumference, and the clear inner radius of the permanent magnet ring 41 is larger than the outer radius of the first individual lamination 1, the permanent magnet ring 41 can initially be pushed force-free onto the first partial package formed from first individual laminations 1 during the manufacture of the rotor.

[0046] The permanent magnet ring 41 can also be pushed over the second individual sheet 2 essentially without force, since this second individual sheet 2 does not have a larger outer radius than the first individual sheet 1.

[0047] However, as soon as the permanent magnet ring 41 abuts the, in particular three, radially projecting regions 30 of the third individual sheet 3 and elastically deforms them, a corresponding force is required. The deformed regions of the third individual sheet 3 are deflected into the free space provided by the second, radially recessed regions 22.

[0048] Elastically prestressed, the radially raised areas 21 then press against the inside of the permanent magnet ring 41 and thus form a three-point bearing of the permanent magnet ring 41 at the axial position of the second individual sheet 2.

[0049] On the side of the second individual lamination 2 facing away from the third individual lamination 3, which is arranged on the side of the third individual lamination 3 facing away from the partial package of first individual laminations 1, a partial package of first individual laminations 1 is arranged, which is thus arranged between the first axial end region of the rotor lamination stack and the second axial end region of the rotor lamination stack.

[0050] Since a second individual lamination 2 is also arranged at the other axial end region of the rotor lamination stack between the sub-package of further first individual laminations 1 and the third individual lamination 3 arranged there, the attached permanent magnet ring 41 is also received at the other axial end region by means of a three-point bearing.

[0051] This makes centering the permanent magnet ring 41 very simple and precise. Balancing the rotor and / or readjusting the permanent magnet ring 41 is not necessary.

[0052] The circumferential angle range covered by the recess 32 preferably comprises the circumferential angle range covered by the outer web 31. The radial width of the outer web 31 is predetermined by the recess 32. Preferably, the radial width of the outer web 31 is independent of the circumferential angle.

[0053] The radial width of the recess 32 is preferably also independent of the circumferential angle, in particular at least in the circumferential angle range covered by the outer web 31.

[0054] The rotor lamination stack is also received on the rotor shaft 40 at three inner circumferential regions, in particular receiving regions. For this purpose, the inner circumference of each individual lamination (1, 2, 3) has three circular receiving regions spaced apart from one another in the circumferential direction, the center of which is located on the rotational axis of the rotor shaft.

[0055] Thus, the rotor shaft 40 is received at the receiving areas 36 of the radial inner circumference of the individual laminations (1, 2, 3) and lies in contact with these receiving areas 36, in particular in a flat manner.

[0056] Radial recesses 37 are arranged in the circumferential direction between the receiving areas 36, at which the minimum inner radius is larger than in the receiving areas 36.

[0057] Since the inner webs 35 are elastically deformable due to the radially adjacent respective kidney-shaped recesses 33 and are therefore pressed against the rotor shaft in an elastically prestressed manner, a precise alignment of the rotor shaft relative to the rotor laminated core is achieved.

[0058] In the receiving areas 36, the minimum inner radius is independent of the circumferential angle. Starting from one of the receiving areas 36, the minimum inner radius increases strictly monotonically in the circumferential direction in the area of ​​the radial recess 37 up to a local maximum and then decreases strictly monotonically until it reaches the next receiving area 36. In further embodiments according to the invention, the respective receiving area 36 has a local minimum of the minimum inner radius of the individual lamination (1, 2, 3). Thus, these minima bear against the rotor shaft 40 with a high spring force. Due to the recesses 33, the inner web 35 is deflectable and presses against the rotor shaft 40 with the spring force.

[0059] List of reference symbols

[0060] 1 first single sheet

[0061] 2 second single sheet

[0062] 3 third single sheet

[0063] 21 first, radially raised areas

[0064] 22 second, radially recessed areas

[0065] 30 radially outstanding area

[0066] 31 outer bridge

[0067] 32 recess

[0068] 33 Recess

[0069] 34 intermediate bridge

[0070] 35 inner web

[0071] 36 Recording area

[0072] 37 radial retraction

[0073] 40 Rotor shaft

[0074] 41 Permanent magnet ring

Claims

Patent claims:

1. An electric motor comprising a rotatably mounted rotor, the rotor having a rotor shaft, a permanent magnet ring, and a rotor lamination stack mounted on a rotor shaft, in particular the rotor lamination stack being connected to the rotor shaft in a rotationally fixed manner, characterized in that the rotor lamination stack comprises a stack of first individual laminations, second individual laminations, and third individual laminations, the rotor lamination stack having, at its first axial end region, a sub-package formed from first individual laminations, to which a second individual lamination is glued and / or applied, on the side of which sub-package facing away from the first sub-package, a third individual lamination is glued and / or applied, and on the side of the third individual lamination facing away from the second individual lamination, a further second individual lamination is glued and / or applied, the second individual lamination having, in particular, three regions (22) spaced apart from one another in the circumferential direction,whose maximum outer radius is smaller than the maximum outer radius of the first and third individual laminations, wherein the permanent magnet ring is pushed onto the rotor lamination stack and adhesively bonded to the rotor lamination stack, in particular wherein the rotational axis of the rotor shaft is aligned coaxially with the ring axis of the permanent magnet ring, in particular wherein the axial direction is aligned parallel to the axis of rotation of the rotor shaft and / or both the radial direction and the circumferential direction are related to the axis of rotation of the rotor shaft.

2. Electric motor according to claim 1, characterized in that the third individual sheet projects radially beyond the first individual sheet within the circumferential angle ranges covered by the regions (22).

3. Electric motor according to one of the preceding claims, characterized in that the respective individual sheet is adhesively connected to its at least one nearest adjacent individual sheet, in particular wherein an adhesive layer is provided between each of the nearest adjacent individual sheets.

4. Electric motor according to one of the preceding claims, characterized in that the maximum outer diameter of the first individual sheet, in particular as a function of the circumferential angle, is equal to the maximum outer diameter of the second individual sheet.

5. Electric motor according to one of the preceding claims, characterized in that the maximum outer radius of the first individual sheet, in particular as a function of the circumferential angle, in particular relative to the axis of rotation of the rotor shaft, is independent of the circumferential angle.

6. Electric motor according to one of the preceding claims, characterized in that the outer radius of the third individual lamination, in particular as a function of the circumferential angle, maximum, in particular with respect to the axis of rotation of the rotor shaft as a function of the circumferential angle, has in particular three local maxima as a function of the circumferential angle and / or that the outer radius of the third individual lamination, in particular as a function of the circumferential angle, maximum, in particular with respect to the axis of rotation of the rotor shaft, as a function of the circumferential angle, is a periodic function of the circumferential angle and as a function of the circumferential angle has in particular three local maxima as a function of the circumferential angle.

7. Electric motor according to one of the preceding claims, characterized in that the local maxima of the, in particular maximum, outer radius of the third individual sheet are arranged radially outside the first individual sheet, in particular as a function of the circumferential angle, - wherein, as a function of the circumferential angle, the local minima of the, in particular maximum, outer radius of the third individual lamination have the same radial distance, in particular maximum radial distance, from the axis of rotation of the rotor shaft as the outer circumference of the first individual lamination or wherein local minima of the, in particular maximum, outer radius of the third individual lamination are arranged radially inside the first individual lamination.

8. Electric motor according to one of the preceding claims, characterized in that the circumferential angular range covered in the circumferential direction by the circumferentially spaced-apart regions (22) of the second individual sheet, in particular three, whose maximum outer radius is smaller than the maximum outer radius of the first and third individual sheet, comprises the axial circumferential angular positions of the local maxima of the outer radius of the third individual sheet, in particular as a function of the circumferential angle maximum.

9. Electric motor according to one of the preceding claims, characterized in that the permanent magnet ring is centered and / or aligned by means of the radially projecting regions (22), in particular relative to the rotor core and / or the rotor shaft.

10. Electric motor according to one of the preceding claims, characterized in that the regions (22) are deformed such that the region covered in the axial direction by the third individual sheet together with the regions (22) overlaps with the region covered in the axial direction by a second individual sheet.

11. Electric motor according to one of the preceding claims, characterized in that the third individual sheet has in each of the circumferential angular regions covered by the regions (22) in the circumferential direction an outer web, an intermediate web and an inner web, wherein the outer web is arranged radially outside the intermediate web, wherein the intermediate web is arranged radially outside the inner web, wherein the intermediate web is radially spaced from the outer web and radially spaced from the inner web.

12. Electric motor according to one of the preceding claims, characterized in that the outer web, the intermediate web and the inner web each extend in the circumferential direction and / or that the outer web, the intermediate web and the inner web are each spaced apart from one another by means of a respective recess, in particular a punched-out portion, extending in the axial direction through the third individual sheet.

13. Electric motor according to one of the preceding claims, characterized in that the inner web rests on the rotor shaft and / or that the outer web rests on the permanent magnet ring.

14. Electric motor according to one of the preceding claims, characterized in that the inner webs are spaced apart from one another in the circumferential direction, in particular so that the receptacle of the rotor shaft on the inner circumference of the third individual sheet is interrupted several times, in particular at least three times.

15. Electric motor according to one of the preceding claims, characterized in that the third individual lamination has radial recesses in the circumferential direction between the inner webs, in particular so that the clear inner radius of the third individual lamination, in particular related to the axis of rotation of the rotor shaft, has a local maximum as a function of the circumferential angle.

16. Electric motor according to one of the preceding claims, characterized in that the permanent magnet ring has a chamfer running continuously in the circumferential direction on its front inner edge in the axial direction, in particular and has a further chamfer running continuously in the circumferential direction on its rear inner edge in the axial direction, in particular wherein by means of the chamfer the radially projecting regions of the third individual sheet are formed into regions projecting in the axial direction on the third individual sheet.

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