Steering unit for a steer-by-wire steering system and method for manufacturing a feedback actuator

Abstract

Steering unit (1) for a steer-by-wire steering system, comprising a feedback actuator (2) which has at least one coil (5) for generating a magnetic field, wherein at least one rigid actuator element (8, 9, 12, 13) with location-dependent magnetic properties is provided for influencing the magnetic field, characterized in that at least one actuator element (12, 13) is designed as a rotor element, wherein at least one actuator element (8, 9) is designed as a stator element, characterized by at least two stator-fixed pot-shaped actuator elements (8, 9) and at least two rotor-fixed, also pot-shaped actuator elements (12, 13), wherein the two rotor-fixed actuator elements (12, 13) are mechanically and magnetically connected to each other and are arranged in an interior space (4) formed by the stator-fixed actuator elements (8, 9).

Description

[0001] The invention relates to a steering unit designed according to the preamble of claim 1 for use in a steer-by-wire steering system of a motor vehicle. The invention further relates to a method for manufacturing a feedback actuator for such a steering unit.

[0002] A steering unit of this type is known, for example, from WO 2020 / 038522 A1. The known steering unit comprises an electric motor and a brake separate from the electric motor, which incorporates both electromagnetic and mechanical elements. Another component of the known steering unit operates as a purely passive device using spring force or pneumatically. This already defines a basic characteristic of the steering unit, whereby a counter-torque, applied to a steering shaft in the form of a braking torque, depends on the angular position of the steering wheel. This basic characteristic can be refined by torques generated by the electric motor. Torque peaks can be generated by the separate brake if required and, in extreme cases, can be perceived as steering stop.Overall, the steering unit described in WO 2020 / 038522 A1 thus provides various means for generating feedback, which in a steer-by-wire steering system generally has to be artificially generated.

[0003] A steering unit for a steer-by-wire steering system, described in EP 1 409 326 B1 and also having the features of the preamble of claim 1, operates to generate steering feedback with an electromagnetic brake comprising a stator and a rotatable disc made of a highly permeable material connected to a steering wheel. The stator includes a number of currentable coils. The device according to EP 1 409 326 B1 is intended to be particularly suitable for use in a forklift truck.

[0004] Another steering resistance device is disclosed in DE 101 45 982 A1. Possible devices for generating a braking torque in this case include, among others, a fluid brake, a magnetic particle brake, an electric motor, a hysteresis brake, and a friction brake.

[0005] A steering feedback system that uses a magnetorheological fluid is disclosed, for example, in EP 1 211 159 A1. This is a steering force simulator intended for use in both motor vehicles and entertainment devices.

[0006] Possible designs for further magnetorheological braking devices are described in documents DE 10 2021 111 973 A1 and DE 10 2011 111 965 A1. These braking devices are designed for use in haptic control devices, for example, thumbwheels in steering wheels.

[0007] DE 10 2018 107 613 A1 discloses a reluctance motor comprising a rotor rotating about a longitudinal axis and a single stator. The rotor has teeth on a surface near the stator, while the stator has corresponding teeth on its surface near the rotor, the teeth of which extend in the direction of the longitudinal axis. The stator is designed to have at least two longitudinally arranged cavities for receiving a currentable ring coil, the windings of which are wound concentrically around the longitudinal axis. Furthermore, the stator is perforated on the side near the rotor to form an air gap, which is cylindrical in shape and concentric to the longitudinal axis, and has a constant height that is less than the extent of the ring coil in the direction of the longitudinal axis.

[0008] DE 602 25 461 T2 discloses a controllable brake comprising a rotor designed to have a working part on its circumference that extends parallel to a shaft on which the rotor is mounted. The brake also includes a shaft on which the rotor is mounted in such a way as to inhibit relative movement between the shaft and the rotor, and a housing with a first chamber that rotatably receives the rotor and contains a magnetic field generator. The magnetic field generator is arranged to generate a magnetic flux through a magnetically controllable material that is in contact with the working part of the rotor in the first chamber. The brake is further characterized by an active center-return device in the first chamber that causes the rotor to return to a relative center position.

[0009] The invention is based on the objective of providing more advanced possibilities for feedback in a steer-by-wire steering system compared to the prior art, whereby a particularly favorable ratio between manufacturing effort and energy requirements during operation in a motor vehicle is sought.

[0010] This problem is solved according to the invention by a steering unit with the features of claim 1. Likewise, the problem is solved by a method designed according to claim 4 for manufacturing a feedback actuator for a steering unit for a steer-by-wire steering system. The embodiments and advantages of the invention explained below in connection with the manufacturing method also apply mutatis mutandis to the devices, i.e., the steering unit including the feedback actuator, and vice versa.

[0011] The steering unit intended for use in a steer-by-wire system comprises a feedback actuator, which includes at least one coil for generating a magnetic field. To influence the magnetic field generated by the coil, at least one rigid actuator element with spatially dependent magnetic properties is present. In particular, the permeability within the actuator element can be spatially dependent. Other magnetic properties that can vary from volume to volume within the actuator element include, for example, the saturation flux density, the coercive field strength, and the remanence.

[0012] The invention is based on the premise that in electrical machines, be they electric motors or electrically actuated linear actuators, the magnetic flux is significantly influenced by the permeability of the materials used. To selectively direct the magnetic flux through specific parts of the motor or actuator while simultaneously suppressing magnetic flux through other parts as much as possible, mechanically connected components with significantly different magnetic permeabilities can be used, for example.

[0013] The solution presented in the application deliberately departs from this approach by using, instead of multiple parts with differing permeabilities, at least one single-piece element, namely the actuator element, which has volume regions with significantly different permeabilities. Where permeability is mentioned in this text, the corresponding statements also apply, where applicable, to other magnetic properties.

[0014] For example, the permeability in a first volume region of the actuator element is at least twice, five times, or more than ten times higher than in a second volume region of the same actuator element. There are no fundamental restrictions regarding the basic shape of the actuator element, which may have regions of different magnetic permeability and / or other material properties. For example, the actuator element can have a planar shape, optionally with a three-dimensional form.

[0015] In principle, the actuator element in question can be a rotating element, i.e., a rotor element, or a non-rotating element, i.e., a stator element. In particular, configurations of the steering actuator are possible which include at least one rotor element and at least one stator element, each with areas of different permeability, saturation flux density, and / or other location-dependent properties relevant to the operation of the feedback actuator.

[0016] This applies, for example, to embodiments of the steering actuator which comprise at least two stator-fixed, pot-shaped actuator elements and at least two rotor-fixed, also pot-shaped actuator elements, wherein the two rotor-fixed actuator elements are mechanically and magnetically connected to each other and arranged in a cavity formed by the stator-fixed actuator elements. For example, the steering actuator comprises exactly two stator-fixed, pot-shaped actuator elements and exactly two rotor-fixed, also pot-shaped actuator elements, which are connected to each other at their bases.

[0017] In addition to connecting actuator elements at their bases, i.e., at disc- or ring-shaped surfaces, connections can also be provided at other surfaces, particularly conical, spherically curved, or cylindrical surfaces, to improve the magnetic flux. This applies, among other things, to cases where the feedback actuator is based on the principle of a powder brake.

[0018] Particularly in the case of multiple rotor-side actuator elements that are mechanically and magnetically interconnected, shear gaps, for example four or more shear gaps, are formed at various points in the feedback actuator. Generally, shear gap regions are areas where the flux lines around the stator coil lead into and out of the rotor. In this case, different shear gap diameters can be present at different points in the feedback actuator.

[0019] With a mirror-symmetrical design of two rotor-side actuator elements, at least one pair can have the same shear gap diameter. Alternatively, the shear gap diameter of a first rotor-side actuator element may differ from that of a second rotor-side actuator element, which can be expressed as cup shapes of different widths, described by the two actuator elements, each belonging to the rotor. The same applies to cup-shaped stator-side actuator elements.

[0020] On both the stator and rotor sides, at least one actuator element with several regions of differing permeability can describe a stepped pot shape, wherein individual, in particular cylindrical, regions of the actuator element each define a shear gap and can be separated by an intermediate region, in particular of a flat or conical shape. The magnetic properties of the intermediate region can differ from the magnetic properties of the regions bordering the shear gaps. This applies, as do the descriptions of simpler, non-stepped stator- and rotor-side geometric designs, both to embodiments in which the rotor is designed as an internal rotor and to embodiments with an external rotor.

[0021] In various embodiments, the at least one actuator element, whose permeability is location-dependent, can be designed as a sheet metal part. Alternatively, the actuator element can be manufactured using a forming process, for example, as a casting or 3D-printed part. Regardless of the method used to manufacture the raw part from which the actuator element is produced, machining or post-processing is possible.

[0022] Overall, the feedback actuator is designed, for example, as a powder brake. Regarding a possible design of a powder brake, reference is made to EP 0 458 465 B1, which deals with voltage control in connection with a magnetic braking system. Alternatively or additionally to a powder brake, an electric motor can, for example, be used as the feedback actuator of the steering unit according to the application. In such a case, the electric motor can generate braking torques in generator mode. An active drive by the electric motor can also be provided, for example, to guide the steering wheel to its center position. In all cases, the spatial dependence of the magnetic properties of the actuator element reduces magnetic shunts, i.e., field lines that are generated by the coil current but bypass the rotor without having any useful effect.

[0023] The patented process for manufacturing a feedback actuator for a steering unit for a steer-by-wire steering system comprises the following steps: - Provision of several actuator elements made of metal, in particular formed or rolled sheet steel, namely at least one stator element and at least one rotor element, wherein each of these actuator elements is designed as a passive, non-energizable element, - Provision of at least one electrifiable coil, - Heat treatment of at least one of the actuator elements in such a way that areas of different magnetic permeability are created within the actuator element in question, - Assembly of the aforementioned actuator elements and the at least one coil, wherein a powder that can be influenced by the magnetic field of the coil is filled into an interior space of the actuator formed between the stator and rotor-side actuator elements, which exerts a braking effect in the subsequent operation of the feedback actuator when the coil is energized.

[0024] The varying permeability of at least one actuator element, depending on its location, can be achieved, for example, through inductive heating, particularly within the framework of a hardening process. Targeted local heating by induction can be achieved through shaping and positioning the induction coil. In this way, the permeability in defined areas of the actuator element can be selectively reduced by heat treatment in the form of inductive hardening. The remaining areas of the actuator element thus become regions of relatively high magnetic permeability.

[0025] It is also possible to influence the permeability of the workpiece being processed, i.e., the metallic actuator element, by annealing. Annealing increases the permeability that is reduced after heat treatment. Depending on the dimensions and shape of the workpiece, a locally varying permeability within the workpiece can be at least partially retained after annealing. Alternatively, annealing offers a way to optimize the permeability of the entire workpiece.

[0026] Heat treatment can be combined with gas treatment, particularly using carbon- and / or nitrogen-containing gases. Local masking can also be employed to influence the magnetic properties near the surface through location-dependent diffusion. Simultaneous influence on the mechanical properties is of secondary importance. The processes to which the actuator element is subjected to influence its magnetic properties—and thereby also other properties, including its hardness—can include rapid cooling processes.

[0027] The choice of machining parameters during the manufacturing of the actuator element serves in every case to optimize the magnetic flux within the finished feedback actuator, and in particular to reduce unwanted stray fluxes. This contributes significantly to a high achievable braking torque with simultaneously moderate energy consumption of the actuator.

[0028] Compared to unloaded powder brakes, such as those used in feedback actuators, minimizing the number of rotatable and non-rotatable parts, especially metal parts, offers an assembly advantage. This is further enhanced by the geometric precision of the one-piece, rotor- or stator-fixed elements, which exhibit a location-dependent magnetic permeability. This precision allows for the production of gaps between rotating and non-rotating elements of precisely defined geometry, even under mass production conditions.

[0029] An embodiment of the invention is explained in more detail below with reference to a drawing. The drawing shows: Fig. 1. Sectional view of a feedback actuator of a steering unit of a steer-by-wire steering system, Fig. 2 a stator element, manufactured as a sheet metal part and exhibiting areas of different magnetic permeability, arranged according to Fig. 1, Fig. 3 another stator element of the arrangement according to Fig. 1, Fig. 4 and Fig. 5 each a rotor element of the arrangement according to Fig. 1.

[0030] A steering unit designated by reference numeral 1 is intended for use in a steer-by-wire steering system (not shown) of a motor vehicle. The steering unit 1 includes a feedback actuator 2, which simulates the driving feel of a conventional steering system with a mechanical connection between the steering wheel and the steered wheels. The fundamental characteristic of a steer-by-wire steering system is the absence of a mechanical connection between the steering wheel and the wheels. For further information regarding steer-by-wire steering systems for passenger cars or other vehicles, such as construction machinery, reference is made to the prior art cited above.

[0031] In this case, the feedback actuator 2 comprises a powder brake 3, although a powder, which is contained in an interior space designated 4 of the powder brake 3 and is influenced by a magnetic field, is not shown. A coil 5 is provided for generating the magnetic field. The coil 5 is held in a stator 7. The stator 7 comprises two stator elements 8, 9, which will be discussed in more detail later. A stator ring designated 6 is located, viewed radially, at the same height as the coil 6 and abuts an end face of the coil 5 in the axial direction.

[0032] A shaft 11 is mounted in the stator 7 by means of a rolling bearing 10, in this embodiment a ball bearing. The shaft 11 is rigidly coupled to the steering wheel of the steer-by-wire steering system. Two rotor elements 12, 13 are attached to the shaft 11, belonging to a rotor designated 14. The rotor elements 12, 13 are located entirely within the interior 4. Two sealing elements 15, 16 are provided for the dynamic sealing of the interior 4, with sealing element 15 contacting the stator element 9 and sealing element 16 contacting a housing ring 17. The housing ring 17 is attached to the inside of the stator element 8 by means of fastening elements 18, namely rivets. Further fastening elements 43, which in this embodiment are also rivets, connect the rotor elements 12, 13 to each other.

[0033] The two stator elements 8, 9 and the two rotor elements 12, 13 are collectively referred to as actuator elements 8, 9, 12, 13. The coil 5 serves to generate a magnetic field that penetrates gaps Sp formed between the stator 7 and the rotor 14, in which a powder, for example in the form of iron filings, is located. In this case, the gaps Sp are formed between sections of the inner circumferential surface of the stator element 9 and cylindrical outer circumferential surfaces of the rotor elements 12, 13. Each of the actuator elements 8, 9, 12, 13, which are sheet metal parts, is essentially cup-shaped. The stator element 8 has approximately the same wall thickness as each of the two rotor elements 12, 13. The stator element 9, on the other hand, has a significantly thinner wall. The four actuator elements 8, 9, 12, 13 can be manufactured from sheet metal using forming processes.

[0034] Regarding the shape of the stator element 8, reference is made to the Fig. 1 and Fig. 3. The stator element 8 is also referred to as the outer stator element. An outer cylindrical section of the stator element 8, designated 19, simultaneously forms the outer circumferential surface of the in Fig. Figure 1 shows a section of the steering unit 1. In the axial direction, the outer cylindrical section 19 extends over most of the length of the feedback actuator 2, measured in the same direction. An outer annular section 20 of the stator element 8 adjoins one of the end faces of the outer cylindrical section 19. The radial width of the outer annular section 20, together with the wall thickness of the stator element 9, denoted by d9, determines the value denoted by H. 37designated height of the at least approximately rotationally symmetric interior space 4, to be measured in the radial direction, to be measured at one of its two end faces, whereby any rounding at the edge of the outer ring-shaped section 20 is disregarded.

[0035] Adjoining the inner edge of the outer annular disc-shaped section 20 is a central cylindrical section 21 of the stator element 8, which is significantly shorter than the outer cylindrical section 19. Adjoining the central cylindrical section 21 is a transition section 22 with a conical, slightly convex base shape. The inner edge of the transition section 22 seamlessly transitions into an inner annular disc-shaped section 23. The fastening elements 18 are held in the inner annular disc-shaped section 23. The inner edge of the inner annular disc-shaped section 23 transitions into an inner cylindrical section 24, the width (i.e., axial extent) of which is greater than the axial extent of the central cylindrical section 21, but less than the width of the outer cylindrical section 19 of the stator element 8.The rolling bearing 10 is inserted between the inner circumferential surface of the inner cylindrical section 24 and the shaft 11, with its outer ring, designated 25, being supported in the axial direction on the housing ring 17.

[0036] Overall, the stator element 8, which can be connected to housing components of the steering unit 1 (not shown) or can itself be designed as a housing, exhibits high mechanical stability. The wall thickness of the stator element 8, measured at the outer cylindrical section 19, is designated d8 and, in the exemplary embodiment, is more than twice, namely approximately three times, the wall thickness d9 of the stator element 9. Apart from the comparatively thin-walled inner cylindrical section 24, the wall thickness d8 of the stator element 8 is essentially uniform.

[0037] The interior space 4, the shape of which is partially defined by the stator element 8 and the housing ring 17, is closed by the stator element 9 and the shaft 11 with the two sealing elements 15, 16 held on the shaft 11. The sealing elements 15, 16 abut a shaft shoulder 26, which in this case is an integral part of the shaft 11, but could also be a separate part, for example, pressed onto the shaft 11.

[0038] The thin-walled stator element 9, essentially comparable to the stator element 8, is a complexly shaped part with a pot-like base. An outer cylindrical section of the stator element 9, designated 27, contacts the inner circumferential surface of the outer cylindrical section 19 of the stator element 8 and simultaneously abuts the outer annular disc-shaped section 20 of the relatively thick-walled stator element 8. In particular, the thin-walled stator element 9 can be pressed into the thick-walled stator element 8.

[0039] In the axial direction, the outer cylindrical section 27 of the stator element 9 is more extended than the middle cylindrical section 21 of the stator element 8. An outer annular section 28 and a middle cylindrical section 29 of the stator element 9 adjoin the outer cylindrical section 27. Sections 29 and 28 form a ring-shaped step in which the coil 5 is arranged. The entire outer cylindrical section 27, as well as that part of the middle cylindrical section 29 not surrounded by the coil 5, exhibits a higher magnetic permeability compared to the rest of the stator element 9. Together with the design of the rotor elements 12 and 13, the stator element 8, and the stator ring 6, which will be explained in more detail below, the spatial dependence of the permeability of the stator element 9 contributes significantly to preventing unwanted stray fluxes within the powder brake 3.

[0040] On the end face of the powder brake 3 opposite the outer ring-shaped section 20, in the arrangement according to Fig. On the left side, a central cylindrical section 29 is connected to a central annular-disc-shaped section 30, an inner cylindrical section 31, a central annular-disc-shaped section 32, a transition section 33 with a conical base shape, and an inner annular-disc-shaped section 34. The sealing lip of the sealing element 15 contacts the inside of the inner annular-disc-shaped section 34.

[0041] The interior space 4 can be roughly divided into a disk space 35, which serves as a powder chamber and in which both rotor elements 12 and 13 are located adjacent to each other; a first annular space 36, into which the rotor element 12 engages; and a second annular space 37, which is partially filled by the second rotor element 13. The annular space 37 is, on average, radially further outward than the annular space 36, relative to the central axis of the shaft 11. The previously mentioned height H 37 represents the height, i.e. radial extent, of the annular space 37 and is greater than that with H 36 designated height of the arrangement according to Fig. 1 of the annular space located on the left 36.

[0042] The interconnected sub-spaces 35, 36, 37 of the interior space 4 together describe a modified Y-shape. The annular disk-shaped sections 38 and 39 of the rotor elements 12 and 13 within the disk space 35 are designated as such. These annular disk-shaped sections 38 and 39 are also referred to as the bases of the rotor elements 12 and 13. The fastening elements 43 are also located within the disk space 35. The annular disk-shaped section 38 of the rotor element 12 transitions at its outer edge into a cylindrical section 40, which is located within the annular space 36. The annular space 36 is bounded radially outward by the central cylindrical section 29 of the stator element 9 and radially inward by the inner cylindrical section 31 of the same stator element 9.

[0043] A transition section 41, which is curved like the transition section 22, adjoins the outer edge of the annular disk-shaped section 39 of the rotor element 13. The transition section 41, in turn, transitions into a cylindrical section 42 of the rotor element 13, which is more extended in both the radial and axial directions compared to the rotor element 12. The cylindrical section 42 is located within the annular space 37 and is arranged radially outside the cylindrical section 40 without overlap. The annular space 37 is bounded radially outwards by the outer cylindrical section 27 of the stator element 9 and radially inwards by the central cylindrical section 21 of the stator element 8.

[0044] Like the stator element 9, the rotor elements 12 and 13 exhibit regions of increased permeability. In the case of rotor element 12, these are the cylindrical section 40 and, to a lesser extent, the annular-shaped section 38. In the case of the second rotor element 13, the regions of increased permeability are the cylindrical section 42, the transition section 41, and, to a lesser extent, the annular-shaped section 39. To optimize the magnetic flux, the outer cylindrical section 19 of the stator element 8 is also designed as a region of increased magnetic permeability.

[0045] The spatial dependence of the magnetic permeability is achieved without making any of the components 8, 9, 12, 13 multi-part. Rather, a relatively high magnetic flux is achieved in the remaining areas of the corresponding elements 8, 9, 12, 13 by inductively hardening those areas that are intended to conduct the least possible magnetic flux. Fig. Figure 1 shows an idealized representation of the magnetic flux generated by coil 5, with areas of relatively high permeability also marked. In reality, in Fig. 1. Unvisualized tributaries that do not contribute to the effect of the powder brake 3, at most to a small extent. Reference symbol list 1 steering unit 2 Feedback actuator 3 Powder brake 4 Interior of the powder brake 5 coil 6 Stator ring 7 Stator 8 Stator element 9 Stator element 10 rolling bearings 11th wave 12 Rotor element 13 Rotor element 14 Rotor 15 sealing element 16 Sealing element 17 Housing ring 18 Fastening element between the stator element 8 and the stator ring 17 19 outer cylindrical section of the stator element 8 20 outer annular disc-shaped section of the stator element 8 21 middle cylindrical section of the stator element 8 22 Transition section 23 inner ring-shaped section 24 inner cylindrical section 25 outer ring 26 wave shoulder 27 outer cylindrical section of the stator element 9 28 outer annular disc-shaped section of the stator element 9 29 middle cylindrical section of the stator element 9 30 middle annular disk-shaped section of the stator element 9 31 inner cylindrical section of the stator element 9 32 middle annular disk-shaped section of the stator element 9 33 Transition section 34 inner annular disk-shaped section of the stator element 9 35 Disc room, powder room 36 first annular space 37 second annular space 38 ring-shaped section of the rotor element 12 39 ring-shaped section of the rotor element 13 40 cylindrical section of the rotor element 12 41 Transition section 42 cylindrical section of the rotor element 13 43 Fastening element between the rotor elements 12, 13 d8 Wall thickness of the stator element 8 d9 Wall thickness of the stator element 9 H 36 Height of the annular space 36 H 37 Height of the annular space 37 Sp gap

Claims

[1] Steering unit (1) for a steer-by-wire steering system, comprising a feedback actuator (2) which has at least one coil (5) for generating a magnetic field, wherein at least one rigid actuator element (8, 9, 12, 13) with location-dependent magnetic properties is provided for influencing the magnetic field, characterized by , that at least one actuator element (12, 13) is designed as a rotor element, wherein at least one actuator element (8, 9) is designed as a stator element, characterized by at least two stator-fixed pot-shaped actuator elements (8, 9) and at least two rotor-fixed, also pot-shaped actuator elements (12, 13), wherein the two rotor-fixed actuator elements (12, 13) are mechanically and magnetically connected to each other and are arranged in an interior space (4) formed by the stator-fixed actuator elements (8, 9). [2] Steering unit (1) according to claim 1, characterized by, that the actuator element (8, 9, 12, 13) is designed as a sheet metal part. [3] Steering unit (1) according to one of claims 1 or 2, characterized by , that the feedback actuator (2) is designed as a powder brake. [4] Method for manufacturing a feedback actuator (2) of a steering unit (1) for a steer-by-wire steering system, comprising the following steps: - Provision of several actuator elements (8, 9, 12, 13) made of metal, namely at least one stator element (8, 9) and at least one rotor element (12, 13), - Provision of at least one energizable coil (5), - Heat treatment of at least one of the actuator elements (8, 9, 12, 13) such that areas of different magnetic permeability are established within this actuator element (8, 9, 12, 13), - Assembly of all actuator elements (8, 9, 12, 13) and the coil (5), wherein a powder that can be influenced by the magnetic field of the coil (5) is filled into a space formed between the stator- and rotor-side actuator elements (8, 9, 12, 13), characterized by , that when the coil (5) and actuator elements (8, 9, 12, 13) are assembled, a slit-shaped space is formed which is to be filled with the powder, which is bounded on both sides, i.e. rotor-side and stator-side, by surface sections (40, 42, 27, 29) of the rotor-side and stator-side actuator elements (8, 9, 12, 13) respectively, which have an increased magnetic permeability compared to other surface sections of the respective elements (8, 9, 12, 13). [5] Method according to claim 4, characterized by , that the location-dependent different permeability of the actuator elements (8, 9, 12, 13) is generated by local inductive hardening. [6] Method according to claim 4 or 5, characterized bythat permeability is affected by annealing.

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