Method for manufacturing a stator for an electric motor

Abstract

The invention relates to a method for manufacturing a stator for an electric motor comprising a yoke ring and a pole star ring with a plurality of stator teeth for arranging windings, preferably winding packages, wherein the pole star ring can be received in the yoke ring by inserting it into the yoke ring, with the stator teeth facing the yoke ring, and by expanding the pole star ring, the stator teeth are pressed against the yoke ring.Furthermore, the invention relates to such a stator for an electric motor comprising a yoke ring and a pole star ring that can be accommodated in the yoke ring and has a plurality of stator teeth for arranging windings and openings for arranging a rotor, wherein the stator teeth of the pole star ring are connected to one another via expandable connecting pieces that are plastically deformed in the assembled state.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a stator for an electric motor, comprising a yoke ring and a pole star ring having a plurality of stator teeth for arranging windings, preferably winding packages, the pole star ring being inserted into the yoke ring.Furthermore, the present invention relates to such a stator for an electric motor, comprising a yoke ring and a pole star ring that can be accommodated in the yoke ring and has a plurality of stator teeth for arranging windings and an opening for arranging a rotor. [Background technology]

[0002] A conventional electric motor has a stator forming the stationary motor component and a rotor forming the rotating motor component. In the case of an internal rotor, the stator typically comprises a stator yoke with stator teeth projecting radially inward. The stator teeth have pole pieces at their ends facing the rotor and are equipped with windings that generate an electromagnetic field during operation. To shape and amplify the electromagnetic field, the stator yoke with the stator teeth is typically made from a soft magnetic material, for example in the form of a laminated core.

[0003] When manufacturing a stator yoke, it is impossible to apply windings from the outside through a closed yoke ring, while the pole pieces make it difficult to access the stator teeth from the inside. Therefore, a one-piece stator yoke requires a complex winding process to provide the necessary windings on the stator teeth. Therefore, for the manufacture of stators for electric motors, it is known to use multi-part stator structures, with very different embodiments, such as stators composed of C-shaped segments, yoke rings for stators with individual stator teeth attached to the stator, or two-part stators with a pole star ring and a cylindrical yoke ring. These multi-part stator concepts allow for easy application of windings directly to the stator teeth.

[0004] Both the two-part stator pole star ring and the cylindrical yoke ring are typically made of multiple individual sheet metal elements arranged axially one above the other, which are assembled into a sheet metal stack by stamping, gluing, welding, baked enamel coating, or other lamination methods. For example, in U.S. Patent Application Publication No. 2002 / 0083572(A1), loosely packed stator sheets are aligned using an expanding mandrel and then secured in the motor housing by screws. The windings are wound around the freely accessible stator teeth of the pole star ring or pressed onto the stator teeth as a winding package. After the windings are attached to the externally accessible pole teeth, the pole star ring is joined by pressing or shrinking. Due to the press connection between the pole star ring and the yoke ring, manufacturing tolerances can result in air gaps between the stator teeth and the yoke ring, which leads to magnetic losses in the stator as well as deformation of the stator teeth and consequent rejection of the stator.

[0005] In two-piece stators known in the prior art, including a pole star ring and a yoke ring, the pole star ring is pressed axially into the yoke ring when the components are joined. Mechanical contact between the components during axial pressing can cause notches on the components and chips that adversely affect the operation of the electric motor. Furthermore, cracks can occur in the laminations of the pole star ring and the yoke ring, meaning that the laminations no longer lie flat against each other, leading to magnetic losses in the stator. Furthermore, precise contours and close tolerances of the pole star ring and the yoke ring are required during axial pressing to avoid air gaps between the stator teeth and the yoke ring or to ensure a consistent outer diameter of the yoke ring.

[0006] German Patent Application Publication No. 10 2015 000 769 A1, for example, discloses a stator for an electric motor having a non-positive or frictional press connection between the stator teeth of the pole star ring and the yoke ring, in which the yoke ring is pressed axially onto the pole star ring and a material bond is formed via a microencapsulated adhesive. German Patent Application Publication No. 10 2016 201 967 A1 describes a tangential press connection between the stator teeth of the pole star ring and the yoke ring for reliable production of the stator, in which the stator teeth are formed with slit-like, resilient recesses and are inserted into axial grooves in the yoke ring, resulting in a press fit onto the yoke ring via tangential forces. Summary of the Invention

[0007] It is therefore an object of the present invention to provide an improved method for manufacturing a stator for an electric motor, which method simplifies the manufacture and assembly of the pole star rings and yoke rings, while reducing waste and ensuring a functionally reliable quality of the stator.

[0008] The object underlying the present invention is achieved by a method for manufacturing a stator for an electric motor, which provides a yoke ring and a pole star ring with a plurality of stator teeth for arranging windings, preferably winding packages. The pole star ring can be received in the yoke ring by inserting it into the yoke ring, with the stator teeth facing the yoke ring, and by expanding the pole star ring, the stator teeth are pressed onto the yoke ring. This method allows the pole star ring to be reliably and chip-freely positioned in the yoke ring. It may be advantageous to arrange the windings on the stator teeth before inserting the pole star ring, so that individual pre-manufactured winding packages can be pressed onto the stator teeth from the outside. To form the pole star ring, the individual stator teeth are connected to one another in the region of the inner pole pieces, for example by plastically deformable elements, preferably stretchable connecting pieces. When the pole star ring is inserted into the yoke ring, the stator teeth are positioned within the yoke ring with little or no mechanical stress, resulting in no notches, chips, or cracks in the stator teeth or the laminated core of the yoke ring. The ends of the stator teeth opposite the pole pieces face the inner circumferential surface of the yoke ring in the radial direction. Before expanding the pole star ring positioned therein, it is desirable to place the yoke ring within a thick-walled support ring so that the yoke ring is not stretched or deformed by the radial pressure during expansion. The radial force acting on the stator teeth presses the free ends of the stator teeth against the yoke ring, resulting in a press fit between the pole star ring and the yoke ring. The deformable elements between the stator teeth are stretched, elongated, or bent as the pole star ring is expanded.

[0009] In a preferred embodiment, the pole star ring has an opening with an inner diameter for locating the rotor, and expanding the pole star ring expands the inner diameter of the opening. This centrally located pole star ring opening allows for safe and easy application of radial force to expand the pole star ring, and the final inner diameter for locating the rotor in the fully assembled stator is only achieved after the pole star ring is expanded. For an error-free and efficient electric motor, a uniform distance is required between the stator teeth or pole pieces and the rotor, which is why all stator teeth are pressed as uniformly as possible onto the yoke ring.

[0010] In an advantageous variant of this method, one or more inwardly protruding connecting pieces are provided in the spaces between the individual stator teeth to form a pole star ring, and the connecting pieces are straightened by pressing the connecting pieces, thereby expanding the pole star ring. By applying force to the connecting pieces, the connecting pieces can be deformed and / or straightened. This enlarges the inner diameter of the openings in the pole star ring, thereby pressing the stator teeth against the yoke ring. The deformation can be performed plastically without heating, which reduces the complexity of the manufacturing process. Furthermore, the magnetic permeability of the connecting pieces is reduced, thereby reducing undesired magnetic flux crossing the connecting pieces.

[0011] In an advantageous embodiment, the yoke ring has a plurality of recesses on its inner circumferential surface for receiving the stator teeth of the pole star ring, into which the stator teeth are pressed when the pole star ring expands. This allows the ends of the stator teeth to be permanently fixed to the inner circumferential surface of the yoke ring by a tangential holding force. The recesses on the inner circumferential surface can be designed as axial grooves, and the deep radial grooves and the small residual gaps between the yoke ring and the stator teeth reduce the distribution of cogging torque between the individual teeth and the yoke ring. The provision of the recesses and the press-fit of the stator teeth into the recesses further allows for accurate positioning of the stator teeth within the stator, thus increasing the efficiency of the electric motor.

[0012] In a variant of the method, an expansion tool, preferably with a wedge-shaped expansion element, is inserted into the pole star ring to expand it. Preferably, the expansion tool is inserted into the pole star ring after the pole star ring has been inserted into the yoke ring. Using a suitable expansion tool ensures uniform expansion of the pole star ring, thereby ensuring a good and uniform connection between the stator teeth and the yoke ring. In a practical design, the expansion tool is inserted axially into the rotor opening of the pole star ring, where it uniformly expands radially and applies a radial force to uniformly expand the pole star ring. The wedge-shaped expansion element can include a conical cone inserted into an expandable conical cylinder. The deeper the conical cone is inserted into the conical cylinder, the larger the circumference of the conical cylinder becomes, and the cylindrical outer surface of the conical cylinder presses against the pole star ring or the connecting piece of the pole star ring. The cylindrical profile distributes the contact force evenly throughout the axial length of the stator. The contact pressure is applied perpendicular to the axis of rotation of the motor or rotor.

[0013] In a particular variant, the spreading tool has a number of radially movable struts, preferably one strut for each stator tooth, which are pressed radially outward to spread the pole star ring. The radial force of the spreading tool is applied directly to each stator tooth via the struts pressing against the center of the stator tooth. A simultaneous and uniform radial force is applied to all stator teeth of the pole star ring, which results in a uniform contact pressure of all stator teeth against the yoke ring.

[0014] A variant of the alternative method provides that one or more inwardly protruding connecting pieces are provided in the spaces between the individual stator teeth to form the pole star ring, and the expansion tool has a plurality of radially movable struts, preferably one strut assigned to each space between the individual stator teeth, which are pressed radially outward to straighten the connecting pieces and thereby expand the pole star ring. One or more connecting pieces, preferably bent connecting pieces, can be provided in the spaces between the individual stator teeth, and the radially movable struts of the expansion tool abut substantially all of the connecting pieces in the spaces and press them outward. To expand the pole star ring, the struts of the expansion tool are positioned approximately centrally between the stator teeth, thereby allowing each connecting piece to be pressed as evenly as possible. Bending the connecting pieces and / or straightening pre-bent connecting pieces reduces the magnetic conductivity of the connecting piece material, because this material saturates more quickly after the bending process. A reduction in the magnetic conductivity of the connecting pieces of the individual stator teeth of the pole star ring is advantageous during operation of the electric motor, since the webs between the individual stator teeth form undesirable magnetic short circuits.

[0015] In an advantageous variant of the method, after the pole star rings have been expanded, the connecting pieces are removed by laser cutting or evaporation, in particular underwater, which prevents magnetic short circuits between the stator teeth and allows for higher torque. Due to their proximity to the winding package, the connecting pieces can only be removed to a limited extent by punching or mechanical cutting.

[0016] A useful design provides that the spreading tool has axially movable working wedges, the struts of which have wedge-shaped pressing surfaces. The conically expanding working wedges, which are axially movable towards the rotor opening, can exert a uniform radial force on the stator teeth or the connecting pieces of the pole star rings via the wedge-shaped pressing surfaces of the struts, so that the stator teeth are pressed uniformly outwards and against the yoke ring by the axially movable working wedges.

[0017] The present invention also relates to a stator for an electric motor, comprising a yoke ring, preferably a cylindrical yoke ring, a pole star ring that can be accommodated in the yoke ring and has a plurality of stator teeth and rotor openings, and windings, preferably winding packages, arranged on the stator teeth. According to the invention, the stator teeth of the pole star ring are connected to one another via extendable connecting pieces that are plastically deformed in the assembled state compared to the original state of the stator, so that the stator teeth are pressed against the yoke ring compared to the original state. In its initial or pre-assembled state, the stator is not assembled in separate parts that are not attached to one another. This allows for precise alignment and reliable positioning of the stator teeth on the yoke ring, so that the stator teeth and / or pole pieces have the same radius and / or the same inner distance from the rotor axis, thereby ensuring a uniform air gap for the rotor as much as possible in the electric motor. This not only improves the efficiency of the electric motor through precise positioning of the stator teeth within the yoke ring, but also reduces the possibility of manufacturing waste and electric motor defects by avoiding chipping, deformation, and cracking of the laminated iron core during stator manufacturing. Expandable connecting pieces, particularly plastically deformable connecting pieces, between the individual stator teeth of the pole star ring, whose deformation is not reversible or not fully reversible after the application of radial force, allow for quick and easy positioning of the pole star ring within the yoke ring before the radial force is applied, and for uniform expansion of the pole star ring and pressing of the stator teeth against the yoke ring upon application of the radial force. This enables safe, rapid, and therefore cost-effective manufacture of stators with a permanent press fit of the stator teeth against the inner peripheral surface of the yoke ring. The connecting pieces also allow for magnetic shorting between the stator teeth, which can reduce existing torque ripple depending on the wiring, pole pairs, and number of teeth of the electric motor.

[0018] To ensure good magnetic conductivity of the stator, the pole star ring may be designed as a stack of stator lamellas, with each stator lamella being designed as a lamella ring that extends across all stator teeth of the pole star ring and forms a flexible connecting piece between the stator teeth. This not only ensures good magnetic conductivity of the stator teeth, but also allows for easy formation of the flexible connecting pieces. The stator lamellas may be formed as blanks or stamped lamella rings and may be joined to form a lamella stack by stamping, gluing, welding, bonding, etc. At least three stator lamellas of the pole star ring may be formed as lamella rings, preferably evenly distributed across the thickness of the lamella stack. For example, every fifth, tenth, or twentieth stator lamella of the lamella stack may be designed as a lamella ring to enable a corresponding functionally reliable design of the pole star ring. Alternatively, all stator lamellas of the lamella stack can be designed with thin connecting pieces which, after spreading the pole star rings and pressing the stator teeth against the yoke ring, form a closure of the stator in the direction of the rotor opening and allow all winding cavities between the closed pole star rings and the yoke ring to be cast without the need for additional internal sealing.

[0019] Advantageously, the stretchable connecting pieces can be designed as bent connecting pieces, preferably bent radially, which makes it possible to simply provide both sufficient stretchability for expanding the pole star ring and plastic deformation for ensuring sufficient stability of the pole star ring when it is inserted into the yoke ring, so that after expansion the stator teeth can be pressed against the yoke ring. Typically, the bent connecting pieces between the stator teeth are positioned at the inner ends of the stator teeth and / or pole pieces and have outwardly curved bends.

[0020] In an alternative embodiment, the expandable connecting pieces can be designed as radially bent, curved connecting pieces that protrude into the central opening of the pole star ring, particularly in the pre-assembled state. Curved inward means curved toward the center of the stator or pole star ring. The center of the stator is on the rotation axis of the motor or rotor. These inwardly curved connecting pieces are directly stretched or straightened by the support posts of the expansion tool during expansion, which significantly reduces the magnetic conductivity of the connecting pieces. The connecting pieces have a certain degree of rigidity. When pressed against the stator teeth, the connecting pieces are stretched. As soon as the pressure on the stator teeth is reduced, the connecting pieces partially return to their original shape. When the support posts of the expansion tool press against the connecting pieces, the contact pressure directly deforms the connecting pieces. This reduces the springback of the material or connecting pieces after the expansion tool is removed. This more precisely defines the radius inside the stator around which the motor rotor rotates. By pressing the connecting piece, it is bent into place and therefore to the predetermined inner diameter of the opening, which corresponds to the inner diameter of the stator. The small tolerance of the inner diameter allows a larger rotor to be inserted into the stator, which allows for a smaller air gap between the stator and rotor and therefore a higher torque to be achieved.

[0021] Preferably, the connecting pieces have breaking notches. In particular, the breaking notches may be punched. Due to tensile or bending stresses during the spreading movement, the connecting pieces may break during the spreading movement. For this purpose, the radial spreading movement of the spreading tool can be increased. The breaking of the connecting pieces prevents a magnetic connection or a magnetic short circuit between the stator teeth and increases the achievable torque.

[0022] A useful embodiment provides that the yoke ring has a plurality of recesses distributed on its inner circumferential surface for receiving the radial ends of the stator teeth. The provision of substantially uniformly distributed recesses allows for uniform placement and more accurate positioning of the stator teeth during stator manufacturing. In particular, these recesses distributed on the inner circumferential surface of the yoke ring can be designed as axially extending grooves. The yoke ring is preferably cylindrical. The lateral edges of the grooves allow for more accurate positioning of the stator teeth and at the same time allow for a tangential press fit between the groove edges and the radial ends of the stator teeth, the effect of which improves with the groove depth. The radial ends of the stator teeth may be rectangular in shape so that the tangential press fit securely holds them in the grooves and thus securely connects them to the yoke ring. The press fit at the axially extending groove edges not only allows for the introduction of tangential forces into the stator teeth but also allows for accurate alignment of the stator teeth in the rotor axial direction. In this design, the extendable connecting pieces are used only to position the stator teeth relative to the yoke ring when the pole star ring is inserted and expanded. Once the stator teeth are securely pressed into the grooves on the inner surface of the yoke ring, the stator teeth are securely positioned within the grooves and connected to the yoke ring by a tangential press fit. The extendable connecting pieces between the individual stator teeth can be removed after the pole star ring is expanded. This advantageous design eliminates magnetic short circuits between the stator teeth, thereby enabling higher torque. Removal of the connecting pieces can be preferably achieved by cutting or vaporizing with a laser beam underwater. Due to their proximity to the winding package, removal of the connecting pieces is only possible to a limited extent by punching or mechanical cutting. [Brief explanation of the drawings]

[0023] 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. [Figure 1] FIG. 1 is a perspective view of a pole star ring for a stator according to the present invention; [Figure 2]FIG. 2 is a perspective view of the pole star ring and several individual winding packages of FIG. 1. [Figure 3] FIG. 3 is a perspective view of the pole star ring of FIGS. 1 and 2 with a winding package pressed into it. [Figure 4] FIG. 4 is a perspective view of the pole star ring and yoke ring with the winding package of FIG. 3 inserted therein. [Figure 5] FIG. 5 is a perspective view of the yoke ring of FIG. 4 with a pole star ring inserted. [Figure 6] 6 is a perspective view of a stator according to the invention with the yoke ring of FIGS. 4 and 5 and the expanded and pressed-in pole star ring of FIG. 3. FIG. [Figure 6a] 7 is an enlarged partial cross-sectional view of the stator of FIG. 6, showing the expansion tool diagrammatically. [Figure 7] 7 is a cross-sectional view of the stator of FIG. 6 without the winding package and with the expansion tool shown diagrammatically. [Figure 7a] FIG. 8 is a cross-sectional view of the stator of FIG. 7 without the winding package and without the expansion tool. [Figure 8] FIG. 7 is a perspective cross-sectional view through the stator of FIG. 6, with the expansion tool housed within the stator. [Figure 8a] FIG. 9 is a cross-sectional view of the stator and expansion tool of FIG. 8. [Figure 9] 10 is an enlarged partial cross-sectional view of a further embodiment of a stator according to the invention with an expansion tool shown diagrammatically. DETAILED DESCRIPTION OF THE INVENTION

[0024] FIG. 1 shows a perspective view of a pole star ring 1, which together with a yoke ring 2 and a winding package 3 form a stator 4 according to the invention. In the illustrated embodiment, the star-shaped pole star ring 1 is manufactured as a laminated core consisting of several stator laminations stacked axially one above the other and joined together, for example by stamping, to form a central cylindrical opening 5. When the stator 4 is assembled, the rotor of an electric motor is received in the opening 5 and can rotate axially. The star-shaped pole star ring 1 has several stator teeth 6 extending radially outward, which form pole pieces 7 located radially inward of the cylindrical opening 5 and which, in the assembled state, face the rotor of the electric motor. To position the stator teeth 6 within the pole star ring 1 and form a closed ring of the pole star ring 1 around the opening 5, the stator teeth 6 are connected to one another via extendable connecting pieces 8 in the region of the pole pieces 7. 1, the connecting pieces 8 are designed as radially outwardly bent webs formed by the individual stator lamellas of the pole star ring 1, which is designed as a laminated core. In the illustrated embodiment, only individual lamellas are provided with a connecting piece 8, for example every 5th, 10th or 20th lamella. The connecting pieces 8 are generally distributed evenly across the thickness of the stator tooth 8 in the axial direction.

[0025] 2 and 3, the individual pre-fabricated winding packages 3 are pressed onto the radially outwardly projecting stator teeth 6, with each stator tooth 6 being provided with a winding package 3 (see FIG. 2). As can be seen in the perspective view of the pole star ring 1 in FIG. 3, the winding packages 3 are pressed completely onto the stator teeth 6 up to the pole pieces 7, so that the radially outwardly projecting ends 9 of the stator teeth 6 protrude slightly beyond the winding packages 3.

[0026] The perspective view in FIG. 4 shows the pole star ring 1 with the winding package 3 pressed onto the stator teeth 6, as well as the yoke ring 2 in the assembled position. The yoke ring 2 has recesses 10 on its inner periphery for positioning the stator teeth 6, which in this embodiment are designed as axially extending grooves 19. In the assembled position shown here, each radially protruding end 9 of the stator teeth 6 is aligned with an axially extending groove 19 on the inner periphery of the yoke ring 2. Like the pole star ring 1, the yoke ring 2 can also be manufactured as a laminated core made of layered stator laminations. As can be seen in FIG. 5, during assembly, the yoke ring 2 is pressed axially onto the pole star ring 1, and the protruding ends 6 of the stator teeth 6 are simply guided through the grooves 19 on the inner periphery of the yoke ring 2, resulting in no chips or notches on the grooves 19 and the protruding ends 9. A gap 11 is left between the protruding end 9 and the groove bottom 20 of the groove 19 .

[0027] After positioning the pole star ring 1 in the yoke ring 2, a radially acting force is applied through the openings 5 ​​to each stator tooth 6 and / or each pole piece 7 of the stator tooth 6, so that the protruding ends 9 of the stator teeth 6 are pressed into the recesses 10. As can be seen in Figure 6, the protruding ends 9 of the stator teeth 6 rest on the bottoms 20 of the grooves 19, so that the initially present gaps 11 are substantially filled by the protruding ends 9.

[0028] When the pole star ring 1 is expanded radially and the protruding ends 9 are pressed into the recesses 10 of the yoke ring 2, the openings 5 ​​are expanded and the spacing between the individual stator teeth 6 increases. Due to the increased spacing between the stator teeth 6, the expandable connecting pieces 8 between the stator teeth 6 are stretched as the pole star ring 1 is expanded radially, thereby flattening the bending of the connecting pieces 8. Since in this embodiment the connecting pieces 8 are formed by the stator laminations of the laminated core of the pole star ring 1, most of the expansion of the connecting pieces 8 occurs as plastic deformation. This can also be seen in the enlarged partial cross-sectional view of Figure 6a, which shows the expanded pole star ring 1 and the stator teeth 6 pressed into the grooves 19 of the yoke ring 2. A radial force is applied to the stator teeth 6 by means of an expansion tool 12, shown here only diagrammatically, which presses the protruding ends 9 of the stator teeth 6 firmly into the grooves 19 of the yoke ring 2, in which case the bending of the connecting pieces 8 is flattened to compensate for the large distance between the stator teeth 6.

[0029] The press-fit between the stator teeth 6 and the yoke ring 2 is essentially created by tangential forces between the side walls of the grooves 19 and the protruding ends 9 of the stator teeth 6. Due to the permanent press-fit connection between the stator teeth 6 and the yoke ring 2, after the pole star ring 1 has been expanded, the connections between the individual stator teeth 6 via the connecting pieces 8 are no longer necessary, and therefore the connecting pieces 8 can also be removed after the expansion process. Furthermore, due to the uniform expansion process and the uniform pressing of the stator teeth 6 onto the yoke ring 2, all stator teeth 6 are pressed outward by the expansion tool 12 essentially uniformly and to the same extent, so that the pole pieces 7 of the stator teeth 6 are all at the same distance from the axial axis. This can be particularly seen in the cross-sectional views of the stator 4 without the winding packages 3 in FIGS. 7 and 7a.

[0030] FIG. 8 shows a perspective cross-sectional view of the expansion tool 12 with the stator 4 arranged inside. The expansion tool 12 has a thick-walled support ring 13 against which the yoke ring 2 abuts during the expansion and pressing process, preventing the yoke ring 2 from being expanded or bent. The cross-sectional view also shows the structure of the pole star ring 1, which consists of a laminated core of stator teeth 6 and / or stator laminations. The expansion tool 12 has an axially movable operating wedge 14, which is moved axially by a centrally located threaded bolt 16 against the preload force of a spring 15. The conically tapered flanks of the operating wedge 14 act on a number of radially movable struts 17, which are held on the operating wedge 14 via elastic rings 18 (see also FIG. 8a). The force applied axially via the actuating wedge 14 is converted into a radial force via the inclined inner flanks of the struts 17, which acts uniformly on the straight outer flanks of the struts 17 against the stator teeth 6, forcing the stator teeth 6 into the recesses 10 in the yoke ring 2.

[0031] A further embodiment of a stator 4 according to the invention and a corresponding manufacturing method are shown in FIG. 9, which shows an enlarged, partial cross-section of the stator 4 and a diagrammatically illustrated expansion tool 12. The pole star ring 1 of this stator 4 according to the invention has a plurality of stator teeth 6 with inner pole pieces 7 and protruding ends 9. The pole star ring 1 is arranged in a yoke ring 2, and each stator tooth 6 of the pole star ring 1 is provided with a winding package 3 previously fitted onto it from the outside. To form the pole star ring 1, each stator tooth 6 has a plastically deformable connecting piece 8 at the edge of the pole piece 7, the bent part of which projects inward relative to the pole piece 7 into the opening 5 of the pole star ring 1. In this variant, the expansion tool 12 generates a radial force acting on the connecting pieces 8 between the individual stator teeth 6, straightening the connecting pieces 8 and expanding the pole star ring 1. This causes the protruding ends 9 of the stator teeth 6 to be pressed against the inner circumferential surface of the yoke ring 2, thereby creating a permanent press fit of the pole star ring 1 or the stator teeth 6 in the yoke ring 2. By bending the connecting pieces 8, the magnetic conductivity of the connecting pieces 8 is reduced, thereby reducing undesirable magnetic short circuits between the individual stator teeth 6. In this embodiment too, the inner circumferential surface of the cylindrical yoke ring 2 can be provided with axially extending recesses 10 or grooves 19 in order to accurately position the stator teeth 6. [Explanation of symbols]

[0032] 1 pole star ring 2 yoke ring 3-winding package 4 Stator 5 Opening 6 stator teeth 7 pole piece 8 Connection piece 9 Protruding end 10 recess 11 Gap 12 Expand Tool 13 Support ring 14 Actuating Wedge 15 Spring 16 Threaded Bolt 17 Posts 18 Elastic Ring 19 Groove 20 Groove bottom

Claims

1. providing a yoke ring (2) and a pole star ring (1) having a plurality of stator teeth (6) for arranging windings, preferably winding packages (3), said pole star ring (1) being capable of being housed in said yoke ring (2); Inserting the pole star ring (1) into the yoke ring (2) so that the stator teeth (6) face the yoke ring (2); and spreading said pole star ring (1) so that said stator teeth (6) are pressed against said yoke ring (2).

2. 2. The method according to claim 1, wherein the pole star ring (1) has an opening (5) with an inner diameter for placing a rotor, and by expanding the pole star ring (1), the inner diameter of the opening (5) is enlarged.

3. 3. The method according to claim 1, wherein the pole star ring (1) is formed by providing one or more inwardly projecting connecting pieces (8) in the spaces between the individual stator teeth (6), and the pole star ring is expanded onto the connecting pieces (8) by pressing.

4. 4. The method according to claim 1, wherein the yoke ring (2) has a plurality of recesses (10) on its inner circumferential surface for accommodating the stator teeth (6) of the pole star ring (1), and when the pole star ring (1) is expanded, the stator teeth (6) are pressed into the recesses (10).

5. 5. The method according to claim 1, wherein an expansion tool (12), preferably having wedge-shaped expansion elements (14), is introduced into the polar star ring (1) to expand the polar star ring (1).

6. the expansion tool (12) has a plurality of radially movable struts (17), preferably one strut (17) assigned to each stator tooth (6); 6. A method according to claim 5, wherein the struts (17) are pushed radially outwards to spread the pole star rings (1).

7. the spaces between the individual stator teeth (6) are provided with one or more inwardly projecting connecting pieces (8) to form the pole star ring (1), the expansion tool (12) having a plurality of radially movable struts (17), preferably one strut (17) assigned to each space between the individual stator teeth (6); 6. A method according to claim 5, wherein the struts (17) are pressed radially outwards to straighten the connecting pieces (8) and thereby open the pole star ring (1).

8. 8. A method according to claim 7, wherein the connecting pieces (8) are removed after the pole star ring (1) has been unfolded by cutting or vaporizing with a laser beam, in particular in water.

9. A stator (4) for an electric motor, comprising a yoke ring (2), preferably a cylindrical yoke ring (2), a pole star ring (1) that can be accommodated in the yoke ring (2) and has a plurality of stator teeth (6) and an opening (5) for arranging a rotor, and windings, preferably winding packages (3), arranged on the stator teeth, the stator comprising: The stator (4), characterized in that the stator teeth (6) of the pole star ring (1) are connected to one another via expandable connecting pieces (8), the connecting pieces (8) being plastically deformed in the assembled state compared to the original state of the stator (4), and the stator teeth (6) are pressed against the yoke ring (2) compared to the original state.

10. 10. A stator (4) for an electric motor according to claim 9, characterized in that the pole star ring (1) is designed as a stack of stator lamellas, the individual stator lamellas being designed as lamella rings that extend over all stator teeth (6) of the pole star ring (1) and form the expandable connecting pieces (8) between the stator teeth (6).

11. 11. A stator (4) for an electric motor according to claim 10, characterized in that at least three stator laminations are formed as lamination rings, said lamination rings being preferably evenly distributed over the thickness of the lamination stack.

12. A stator (4) for an electric motor according to any one of claims 8 to 11, characterized in that the extendable connecting pieces (8) are preferably designed as radially bent bending connecting pieces (8).

13. 13. A stator (4) for an electric motor according to claim 12, characterized in that the extendable connecting pieces (8) are designed as connecting pieces (8) that are bent radially and curved towards the openings (5), and that in a pre-assembled state the connecting pieces (8) protrude in particular into the openings (5) of the pole star ring (1).

14. A stator (4) for an electric motor according to any one of claims 12 to 13, characterized in that the connecting piece (8) has a breaking notch.

15. 15. A stator (4) for an electric motor according to any one of claims 9 to 14, characterized in that the yoke ring (2) has a plurality of recesses (10) distributed on its inner circumferential surface for receiving the radial ends (9) of the stator teeth (6).

16. 16. A stator (4) for an electric motor according to claim 15, characterized in that the recesses (10) distributed on the inner circumferential surface of the yoke ring (2) are designed as axially extending grooves (19).

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