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

Abstract

The invention relates to a 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. For influencing the magnetic field, at least one intrinsically rigid actuator (8, 9, 12, 13) with location-dependent permeability is provided.

Description

[0001] Steering unit for a steer-by-wire steering system and method for producing a feedback actuator

[0002] The invention relates to a steering unit designed according to the preamble of claim 1, intended for use in a steer-by-wire steering system of a motor vehicle. Furthermore, the invention relates to a method for producing a feedback actuator for such a steering unit.

[0003] 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 has both electromagnetic and mechanical elements. Another component of the known steering unit operates as a purely passive device with spring force or pneumatically. This already provides a basic characteristic of the steering unit, whereby a counter-torque, which is applied to a steering shaft in the sense 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 necessary and, in extreme cases, can be perceived as a steering stop.Overall, the steering unit described in WO 2020 / 038522 A1 thus provides various means for generating feedback, which is generally to be generated artificially in a steer-by-wire steering system.

[0004] A steering unit for a steer-by-wire steering system, described in EP 1 409 326 B1 and also having the features according to the preamble of claim 1, operates to generate steering feedback with an electromagnetic brake comprising a stator and a rotatable disk made of a highly permeable material connected to a steering wheel. A number of energizable coils are associated with the stator. The device according to EP 1 409 326 B1 is said to be particularly suitable for use in a forklift truck. 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 that is intended to be suitable for use in both motor vehicles and entertainment devices.

[0006] Possible designs of other 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, such as thumb rollers in steering wheels.

[0007] The invention is based on the object of providing more advanced feedback options for a steer-by-wire steering system compared to the prior art, whereby a particularly favorable ratio between manufacturing expenditure and energy consumption during operation in a motor vehicle is sought.

[0008] This object is achieved according to the invention by a steering unit having the features of claim 1. The object is also achieved by a method designed according to claim 7 for producing a feedback actuator of 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.

[0009] The steering unit intended for use in a steer-by-wire steering system comprises a feedback actuator having at least one coil for generating a magnetic field. To influence the magnetic field generated by the coil, there is at least one rigid actuator element with location-dependent magnetic properties. In particular, the permeability within the respective actuator element can be location-dependent. Other magnetic properties that may vary from volume to volume within the actuator element include, for example, the saturation flux density, the coercive field strength, and the remanence.

[0010] The invention is based on the idea that in electrical machines, be they electric motors or electrically operated linear actuators, the magnetic flux is significantly influenced by the permeability of the materials used. To guide the magnetic flux specifically through certain parts of the motor or actuator while simultaneously preventing magnetic flux through other parts as much as possible, mechanically connected parts that differ significantly from one another in terms of their magnetic permeability can be installed.

[0011] The solution according to the application deliberately deviates from this approach by using at least one single-piece element, namely an actuator element, which has volume regions whose permeabilities differ significantly, instead of a plurality of parts with different permeabilities. Where permeability is mentioned in this text, the corresponding statements also apply, where applicable, to other magnetic properties. 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 has regions of different magnetic permeability and / or other material properties. For example, the actuator element has a flat basic shape, optionally with a three-dimensional character.In principle, the actuator element mentioned 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 can be realized that comprise at least one rotor element and at least one stator element, each with regions of different permeability, saturation flux density, and / or other location-dependent properties relevant to the operation of the feedback actuator.

[0012] This applies, for example, to embodiments of the steering actuator that comprise at least two stator-fixed, pot-shaped actuator elements and at least two rotor-fixed, likewise pot-shaped actuator elements, wherein the two rotor-fixed actuator elements are mechanically and magnetically connected to one another 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, likewise pot-shaped actuator elements, which are connected to one another at their bases.

[0013] In addition to connecting actuator elements at their bases, i.e., at disc- or annular-disk-shaped surfaces, connections can also be provided at other surfaces, particularly conical, spherically curved, or cylindrical, 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.

[0014] Particularly in the case of multiple, mechanically and magnetically interconnected rotor-side actuator elements, shear gaps, for example, four or more shear gaps, are formed at various locations on the feedback actuator. Shear gap regions are generally 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 locations on the feedback actuator. With a mirror-symmetric design of two rotor-side actuator elements, at least one pair of the same shear gap diameter can exist.Alternatively, the shear gap diameter of a first rotor-side actuator element differs from the shear gap diameter of a second rotor-side actuator element, which can be expressed in pot shapes of different widths, which are described by the two actuator elements, each of which is assigned to the rotor. The same applies to pot-shaped stator-side actuator elements.

[0015] On both the stator and rotor sides, at least one actuator element having multiple regions of different permeability can describe a stepped pot shape, wherein individual, particularly cylindrical, regions of the actuator element in question can each define a shear gap and be separated by an intermediate region, particularly 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 gap. This applies, as does the explanations regarding 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 a rotor designed as an external rotor.

[0016] In various embodiments, the at least one actuator element, whose permeability is location-dependent, can be formed as a sheet metal part. A primary forming of the actuator element, for example, as a cast part or 3D-printed part, is also possible. Regardless of the method of manufacturing a blank from which the actuator element is to be manufactured, machining or post-processing is also possible.

[0017] Overall, the feedback actuator is designed, for example, as a powder brake. With regard to a possible design of a powder brake, reference is made to EP 0 458 465 B1, which relates to voltage control in conjunction with a magnetic braking system. Alternatively or in addition to a powder brake, an electric motor can be used, for example, as a 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 location dependence of the magnetic properties of the actuator element reduces magnetic shunts, i.e., field lines generated by coil current but bypassing the rotor without any useful effect.

[0018] The method according to the application for producing a feedback actuator of a steering unit for a steer-by-wire steering system comprises the following steps:

[0019] - Providing a plurality of actuator elements made of metal, in particular formed or rolled sheet steel, namely at least one stator element and at least one rotor element, each of these actuator elements being designed as a passive, non-energizable element,

[0020] - Provision of at least one energizable coil,

[0021] - heat treatment of at least one of the actuator elements such that areas of different magnetic permeability are established within the actuator element in question,

[0022] - Assembly of said actuator elements and the at least one coil, wherein a powder which can be influenced by the magnetic field of the coil is filled into an interior of the actuator formed between the stator- and rotor-side actuator elements, which powder develops a braking effect when the coil is energized during subsequent operation of the feedback actuator.

[0023] The location-dependent permeability of at least one actuator element can be generated, for example, by inductive heating, particularly as part of a hardening process. Targeted local heating by induction can be achieved by shaping and positioning the induction coil. In this case, the permeability in defined areas of the actuator element can be specifically reduced by heat treatment in the form of inductive hardening. The remaining areas of the actuator element thus become areas of relatively high magnetic permeability.

[0024] It is also possible to influence the permeability of the workpiece being processed, i.e., the metallic actuator element, through annealing. Annealing increases the permeability 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. Otherwise, annealing offers a way to optimize the permeability of the entire workpiece.

[0025] Heat treatment can be combined with gas treatment, particularly with carbon- and / or nitrogen-containing gases. Local masking can also be used to influence the magnetic properties near the surface through location-dependent diffusion. The 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.

[0026] The selection of machining parameters during the production of the actuator element always serves to optimize the magnetic flux within the finished feedback actuator, particularly by reducing unwanted secondary fluxes. This contributes significantly to a high achievable braking torque while maintaining moderate energy consumption.

[0027] Compared to non-stressed powder brakes, such as those used in feedback actuators, the minimization of the number of rotating and non-rotating parts, especially metal parts, represents an assembly-technical advantage. Not least due to the given geometric precision of the one-piece, rotor- or stator-fixed elements, which have a location-dependent magnetic permeability, gaps between rotating and non-rotating elements of precisely defined geometry can be produced even under the conditions of series production.

[0028] An embodiment of the invention is explained in more detail below with reference to a drawing. In the drawings:

[0029] Fig. 1 shows a detail of a feedback actuator of a steering unit of a steer-by-wire steering system in a sectional view,

[0030] Fig. 2 shows a stator element of the arrangement according to Fig. 1, manufactured as a sheet metal part, having regions of different magnetic permeability,

[0031] Fig. 3 shows a further stator element of the arrangement according to Fig. 1,

[0032] Fig. 4 and 5 each show a rotor element of the arrangement according to Fig. 1.

[0033] A steering unit, designated overall by reference numeral 1, is intended for use in a steer-by-wire steering system (not shown in detail) of a motor vehicle. The steering unit 1 comprises 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. A fundamental characteristic of a steer-by-wire steering system is the absence of a mechanical connection between the steering wheel and the wheels. Furthermore, with regard to steer-by-wire steering systems for cars or other vehicles, such as construction machinery, reference is made to the prior art cited above.

[0034] In the present case, the feedback actuator 2 comprises a powder brake 3, although a powder that can be influenced by a magnetic field and is contained in an interior space of the powder brake 3, designated 4, is not shown. A coil 5 is provided to generate 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 below. A stator ring, designated 6, is located, viewed in the radial direction, at the same height as the coil 6 and adjoins an end face of the coil 5 in the axial direction.

[0035] 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 firmly coupled to the steering wheel of the steer-by-wire steering system. Two rotor elements 12, 13 are fastened to the shaft 11 and are assigned to a rotor designated overall by 14. The rotor elements 12, 13 are located entirely within the interior space 4. Two sealing elements 15, 16 are provided for dynamic sealing of the interior space 4, with the sealing element 15 contacting the stator element 9 and the sealing element 16 contacting a housing ring 17. The housing ring 17 is fastened to the inside of the stator element 8 by means of fastening elements 18, namely rivets. Further fastening elements 43, which are also rivets in the exemplary embodiment, connect the rotor elements 12, 13 to one another.

[0036] 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 has the task of generating a magnetic field which penetrates gaps Sp formed between the stator 7 and the rotor 14, in which gaps a powder, for example in the form of iron filings, is located. In the present 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 pot-shaped. The stator element 8 has approximately the same wall thickness as each of the two rotor elements 12, 13. The stator element 9, in contrast, has considerably thinner walls. The four actuator elements 8, 9, 12, and 13 can be manufactured from sheet metal using forming processes. Regarding the shape of the stator element 8, please refer to Fig.1 and 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 section of the steering unit 1 shown in Fig. 1. In the axial direction, the outer cylindrical section 19 extends over most of the extent of the feedback actuator 2, measured in the same direction. An outer annular disk-shaped section 20 of the stator element 8 adjoins one of the end faces of the outer cylindrical section 19.The width of the outer annular disc-shaped section 20, which is to be measured in the radial direction, together with the wall thickness of the stator element 9, designated by dg, determines the height, designated by H37, of the at least approximately rotationally symmetrical interior space 4, which is to be measured in the radial direction, to be measured on one of its two end faces, whereby any roundings on the edge of the outer annular disc-shaped section 20 are disregarded.

[0037] Adjoining the inner edge of the outer annular disk-shaped section 20 is a central cylindrical section 21 of the stator element 8, which is considerably shorter than the outer cylindrical section 19. Adjoining the central cylindrical section 21, in turn, is a transition section 22 with a conical, slightly convex basic shape. The inner edge of the transition section 22 merges seamlessly into an inner annular disk-shaped section 23. The fastening elements 18 are held in the inner annular disk-shaped section 23. The inner edge of the inner annular disk-shaped section 23 merges 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.

[0038] Overall, the stator element 8, which can be connected to housing components of the steering unit 1 (not shown) or can be designed as a housing itself, exhibits high mechanical stability. The wall thickness of the stator element 8, measured at the outer cylindrical section 19, is designated ds and, in the exemplary embodiment, is more than twice, namely approximately three times, the wall thickness dg of the stator element 9. Apart from the comparatively thin-walled inner cylindrical section 24, the wall thickness ds of the stator element 8 is essentially uniform.

[0039] The interior space 4, the shape of which is already 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 bear against a shaft shoulder 26, which in this case represents an integral component of the shaft 11, but could also be a separate part, for example, pressed onto the shaft 11.

[0040] The thin-walled stator element 9, fundamentally comparable to the stator element 8, is a complexly shaped part with a pot-like basic shape. 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 disk-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.

[0041] In the axial direction, the outer cylindrical section 27 of the stator element 9 is more extensive than the central cylindrical section 21 of the stator element 8. An outer annular disk-shaped section 28 and a central cylindrical section 29 of the stator element 9 adjoin the outer cylindrical section 27. The sections 29, 28 form an annular step in which the coil 5 is arranged. The entire outer cylindrical section 27, as well as the area of ​​the central cylindrical section 29 not surrounded by the coil 5, has a higher magnetic permeability than the rest of the stator element 9. Together with the design of the rotor elements 12, 13, the stator element 8, and the stator ring 6, which will be explained in more detail below, the location-dependent permeability of the stator element 9 contributes significantly to avoiding undesired secondary flows within the powder brake 3.

[0042] On the end face of the powder brake 3 opposite the outer annular disc-shaped section 20, on the left side in the arrangement according to Fig. 1, the central cylindrical section 29 is adjoined by 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 basic 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.

[0043] The interior space 4 can be roughly divided into a disc space 35, which functions as a powder space and in which both rotor elements 12, 13 are located adjacent to one another, 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, arranged radially further outward than the annular space 36, relative to the center axis of the shaft 11. The aforementioned height H37 represents the height, i.e., radial extent, of the annular space 37 and is greater than the height designated H36 of the annular space 36 located on the left in the arrangement according to Fig. 1.

[0044] The merging sub-chambers 35, 36, 37 of the interior space 4 describe a modified Y-shape overall. 38, 39 designate annular disk-shaped sections of the rotor elements 12, 13 within the disk space 35. The annular disk-shaped sections 38, 39 are also referred to as the bases of the rotor elements 12, 13. The fastening elements 43 are also located in the disk space 35. The annular disk-shaped section 38 of the rotor element 12 merges at its outer edge into a cylindrical section 40, which is arranged in the annular space 36. The annular space 36 is bounded radially outwardly by the central cylindrical section 29 of the stator element 9 and radially inwardly by the inner cylindrical section 31 of the same stator element 9. The outer edge of the annular disc-shaped section 39 of the rotor element 13 is adjoined by a transition section 41 which, like the transition section 22, is curved.The transition section 41, in turn, merges into a cylindrical section 42 of the rotor element 13, which is more extensive in both the radial and axial directions than the rotor element 12. The cylindrical section 42 is located within the annular space 37 and is arranged outside the cylindrical section 40 without any radial overlap. The annular space 37 is bounded radially outwardly by the outer cylindrical section 27 of the stator element 9 and radially inwardly by the central cylindrical section 21 of the stator element 8.

[0045] Just like the stator element 9, the rotor elements 12, 13 have regions of increased permeability. In the case of the rotor element 12, these are the cylindrical section 40 and, to some extent, the annular disk-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 some extent, the annular disk-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.

[0046] The spatial dependence of the magnetic permeability is achieved without designing any of the components 8, 9, 12, 13 in multiple parts. Rather, by inductive hardening those areas of the elements 8, 9, 12, 13 that are intended to conduct magnetic flux to the least possible extent, a relatively high magnetic flux is achieved in the remaining areas of the corresponding elements 8, 9, 12, 13. In Fig. 1, the magnetic flux generated by the coil 5 is shown ideally, with areas of relatively high permeability also marked. In fact, secondary fluxes not shown in Fig. 1, which do not contribute to the effect of the powder brake 3, occur only to a small extent at most.

[0047] steering unit

[0048] Feedback actuator

[0049] Powder brake

[0050] Interior of the powder brake

[0051] Sink

[0052] Stator ring

[0053] stator

[0054] Stator element

[0055] Stator element

[0056] Rolling bearings

[0057] Wave

[0058] Rotor element

[0059] Rotor element

[0060] rotor

[0061] Sealing element

[0062] Sealing element

[0063] Case ring

[0064] Fastening element between the stator element 8 and the stator ring 17 outer cylindrical section of the stator element 8 outer annular disc-shaped section of the stator element 8 middle cylindrical section of the stator element 8

[0065] Transition section inner annular disc-shaped section inner cylindrical section

[0066] outer ring

[0067] Shaft shoulder outer cylindrical section of the stator element 9 outer annular disc-shaped section of the stator element 9 middle cylindrical section of the stator element 9 middle annular disc-shaped section of the stator element 9 inner cylindrical section of the stator element 9 32 middle annular disc-shaped section of the stator element 9

[0068] 33 Transition section

[0069] 34 inner annular disc-shaped section of the stator element 9

[0070] 35 Target room, powder room

[0071] 36 first annular space

[0072] 37 second annular space

[0073] 38 annular disc-shaped section of the rotor element 12

[0074] 39 annular disc-shaped section of the rotor element 13

[0075] 40 cylindrical section of the rotor element 12

[0076] 41 Transition section

[0077] 42 cylindrical section of the rotor element 13

[0078] 43 Fastening element between the rotor elements 12, 13 ds Wall thickness of the stator element 8 dg Wall thickness of the stator element 9

[0079] H36 Height of the annular space 36

[0080] H37 Height of the annular space 37

[0081] Sp gap

Claims

Patent 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, characterized in that at least one inherently rigid actuator element (8, 9, 12, 13) with location-dependent magnetic properties is provided for influencing the magnetic field.

2. Steering unit (1) according to claim 1, characterized in that at least one actuator element (12, 13) is designed as a rotor element.

3. Steering unit (1) according to claim 1 or 2, characterized in that at least one actuator element (8, 9) is designed as a stator element.

4. Steering unit (1) according to claims 2 and 3, characterized by at least two stator-fixed pot-shaped actuator elements (8, 9) and at least two rotor-fixed, likewise pot-shaped actuator elements (12, 13), wherein the two rotor-fixed actuator elements (12, 13) are mechanically and magnetically connected to one another and are arranged in an interior space (4) formed by the stator-fixed actuator elements (8, 9).

5. Steering unit (1) according to one of claims 1 to 4, characterized in that the actuator element (8, 9, 12, 13) is designed as a sheet metal part.

6. Steering unit (1) according to one of claims 1 to 5, characterized in that the feedback actuator (2) is designed as a powder brake.

7. Method for producing a feedback actuator (2) of a steering unit (1) for a steer-by-wire steering system, comprising the following steps: - providing a plurality of actuator elements (8, 9, 12, 13) each 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 regions of different magnetic permeability are established within this actuator element (8, 9, 12, 13), - Assembling all actuator elements (8, 9, 12, 13) and the coil (5), wherein a A powder which can be influenced by the magnetic field of the coil (5) is filled into the space formed by the actuator elements (8, 9, 12, 13).

8. The method according to claim 7, characterized in that the location-dependent different permeability of the actuator elements (8, 9, 12, 13) is generated by local inductive hardening.

9. A method according to claim 7 or 8, characterized in that the permeability is influenced by annealing.

10. Method according to one of claims 7 to 9, characterized in that during the assembly of the coil (5) and actuator elements (8, 9, 12, 13) a gap-shaped space is formed which is to be filled with the powder and which is delimited on both sides, that is to say on the rotor and stator sides, by surface sections (40, 42, 27, 29) of the rotor- and stator-side actuator elements (8, 9, 12, 13) which have an increased magnetic permeability compared to other surface sections of the respective elements (8, 9, 12, 13).

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