Powder brake bearing of a steering system with improved nvh behavior

Abstract

The invention relates to a steering system for controlling a vehicle by means of a steer-by-wire concept, comprising an operating element, a steering shaft (3), an electric motor (6), and a continuously adjustable magnetorheological powder brake (5) which influences the rotation of the steering shaft (3) and which comprises two components that can be rotated relative to each other about an axis of rotation, a stator (8) with an associated coil (14) and, at a distance therefrom, a rotor (9) connected to the steering shaft (3), wherein at least one circumferential shear gap (16) at least partially filled with a magnetorheological medium is provided between the rotor (9) and the stator (8), the rotor (9) is rotatably mounted by means of at least one powder brake bearing (10) which is positioned separate from the steering shaft (3) and which is connected to the stator (8), and the steering shaft (3) is connected to the rotor (9) by means of a resilient coupling element (13).

Description

[0001] Powder brake bearing of a steering system with improved NVH behavior

[0002] The invention relates to a steering system for controlling a vehicle by means of a steer-by-wire concept with an associated magnetorheological powder brake, according to the features of the preamble of claim 1.

[0003] Various magnetorheological brakes are known from the prior art, in which, for example, a second rotating component is decelerated relative to a first component by activating the device. The coupling is achieved via a magnetorheological medium located between the two components, which is activated by a magnetic field.

[0004] A powder brake consists of a stator with an integrated coil and an opposing rotor. A magnetorheological medium, typically powder, is located in an air gap between the two non-contacting components. When current flows through the coil, this powder forms chain-like structures within the resulting magnetic field. These structures, now in contact with both components, create a frictional connection. The resulting braking effect is approximately proportional to the current flowing through the coil.

[0005] A steer-by-wire steering system for a motor vehicle with an electric motor and a magnetorheological brake is known from DE 10 221 241 A1. WO 2022 234 037 A1 discloses a magnetorheological brake designed for braking rotary motion, consisting of a shaft and a rotor rotatable about the shaft. The rotational motion of the rotor can be selectively braked by means of the magnetorheological brake, which includes a coil. For this purpose, a magnetorheological medium is introduced into a receptacle formed between the axle assembly and the rotor. This medium, in conjunction with a magnetic field from the electric coil, generates a braking torque that selectively reduces the rotational motion of the rotor. CN 218 761 045 U discloses a powder brake whose rotor is mounted in a support housing via two axially spaced bearings.The shaft bearings, positioned identically on one side of the rotor, are designed to protect the powder brake from external or internal (magnetic) forces and displacements. Due to this one-piece construction, the rotor is rigidly connected to the shaft.

[0006] WO 2022 / 170 050 A1 describes a steering force feedback actuator (FFA) of a steering system that incorporates a magnetorheological fluid brake (MRF brake) in conjunction with an electric motor. The rotor of the MRF brake is rigidly mounted on the brake shaft via two axially offset rolling bearings.

[0007] The invention is based on the objective of providing a functionally improved, magnetorheological powder brake bearing with optimized NVH (Noise, Vibration, Harshness) behavior compared to the prior art, wherein the design enables simplified manufacturing and assembly, in order to represent a reliable, cost-effectively realizable powder brake.

[0008] This problem is solved by the features of claim 1 and the method according to claim 10. Further preferred embodiments of the invention can be found in the dependent claims, the figures, and the accompanying description.

[0009] According to the invention, the rotor is rotatably mounted via at least one powder brake bearing positioned separately from the steering shaft and connected to the stator, and the rotor is connected to the steering shaft for drive via an elastic coupling element.

[0010] The invention ensures a stiffened mounting of the powder brake rotor while simultaneously decoupling it from the steering shaft. This concept avoids a rigid mounting of the shaft relative to the stator and thus, on the one hand, reduces vibrations, and on the other hand, the coupling element ensures a certain degree of elasticity due to tolerances, bearing assembly, and the connection with adjacent components, such as the electric motor.

[0011] The powder brake bearing is therefore exclusively designed for the rotor without a steering shaft, which advantageously provides axial and tilting rigidity to the rotor, thus preventing the steering shaft from influencing it. This design concept separates the bearing force path from the torque transmission path. Simultaneously, the bearing concept according to the invention ensures precise maintenance of the shear gap between the rotor and stator during operation, thereby preventing detrimental self-excitation caused by changes in the shear gap. Furthermore, this bearing enables reliable, smooth control of the powder brake at the end stop.

[0012] The coupling element, exhibiting a defined elasticity, transmits a torque from the steering shaft to the rotor, while remaining flexible with respect to other forces such as tilting moments or axial forces. On the one hand, the coupling element couples the low-frequency torque, but on the other hand, it acts as an isolation mechanism for vibrations of both torsional, radial, and / or axial nature. The coupling element thus decouples and isolates the steering shaft and rotor from vibrations, preventing or significantly reducing the transmission of vibrations to the steering shaft.

[0013] The magnetorheological powder brake comprises a potted stator that surrounds a rotor at a distance, with these components being continuously rotatable relative to each other about a rotational axis. The powder brake requires no additional steering shaft bearings, thus protecting against preload that could adversely affect the rotational movement, generating noise and uneven torque. It also protects against over-constraints that can cause uneven drag torques, for example, in the bearings outside the powder brake. The invention's concept results in higher-frequency vibrations of the lighter rotor due to a stick-slip excitation, generating increased damping. This leads to improved NVH (Noise, Vibration, Harshness) performance, significantly reducing audible and / or perceptible vibrations.

[0014] Since in the powder brake according to the invention the rotor is mounted in or on the stator, and not on the steering shaft, with both axial and tilting rigidity, the rotor is not influenced by the steering shaft. The rigid mounting of the rotor relative to the stator, which is conducive to vibration avoidance, advantageously prevents changes in the shear gap and thus detrimental self-excitation.

[0015] Self-excitation is based on the effect that in a zone of smaller gap spacing, caused by radial displacement of the rotor due to insufficiently rigid bearings, the magnetic attraction and the local braking force increase significantly. During rotation, these zones migrate, generating a rotating orbital motion of the rotor associated with NVH (noise, vibration, and harshness), which derives its energy from the rotation itself. Therefore, this is not a resonance caused by excitation, but rather a self-excitation during rotation.

[0016] The design enables a reliable powder brake bearing, the manufacture of which is cost-effective. Axial sliding onto the steering shaft results in simple installation of the powder brake.

[0017] According to a preferred embodiment, the bearing in the powder brake is positioned centrally, in the middle of the rotor. For this purpose, an axially rigid and tilt-resistant rolling bearing with minimal play is used, for example, a standard bearing designed as a double-row angular contact ball bearing or as a four-point contact bearing. For effective sealing, including against the powder, the bearing is preferably sealed on both sides, for example, by means of separate seals attached to the stator or rotor by force and / or material bonding. According to a preferred embodiment, the bearing is preferably fixed on both sides by crimping embossed indentations instead of using retaining rings when installed.Local indentations or flanges formed as continuous shoulders can be produced, for example, by a forming assembly process involving axial riveting of the relatively soft rotor material in front of the bearing. This creates a connection free of axial, radial, and tilting play, thereby reducing bearing seat clearance. This assembly technique is advantageously applied to both the outer and inner rings of the rolling bearing. During riveting, a radial gap between the bearing and rotor fills under the riveting pressure, thus eliminating radial play in the bearing seat. Consequently, the local or circumferential plastic deformation of the soft rotor material and / or a bearing carrier made of, for example, aluminum, creates a low-clearance connection between the bearing and the adjacent components. The process can also be used with an additional soft intermediate or mounting ring.Additionally or alternatively, a sleeve made of aluminum, for example radially 1 mm thick and protruding on both sides, can be inserted between the powder brake bearing and the rotor. The protrusion can be plasticized and / or folded over using a stamping / crimping tool to achieve a radially and, through the crimping, also axially play-free bearing installation.

[0018] A preferred embodiment comprises a one-piece, rotationally symmetrical rotor made of soft pure iron. Alternatively, a rotor comprising two or more components can be used, the individual parts of which are joined together to form a single, fatigue-resistant unit. The material preferably used is soft pure iron with a low carbon content and minimal alloying elements, as well as good magnetic properties, particularly with high susceptibility or saturation flux density. Due to the soft rotor material, the bearing seat and other structural elements are machined or manufactured to the tolerances required for interference fits using suitable machining processes, preferably turning or milling processes or a rolling technique.According to a further embodiment, the braking torque is transmitted to the steering shaft via a coupling element located axially next to the bearing, which is elastic and damping due to its shape and / or material. This resilient coupling element compensates for axial, radial, and angular misalignments of the steering shaft relative to the rotor. This eliminates the need for adjustments based on assembly tolerances of the steering shaft and components located on the steering shaft, such as the electric motor and its bearings. Simultaneously, shaft stress caused by over-constraint of the bearings is avoided.

[0019] For elastic rotor coupling, a preferred embodiment uses a coupling element, resilient due to its shape and / or material, designed as a thin, elastic steel disc with semicircular recesses on the outer surface. Alternatively, a wire element, a curved spring, or a coil spring made of spring steel can be used as the coupling element. In each case, the coupling element is preferably connected to the rotor on the outer surface via a flange plate and engages positively in notches on the shaft on the inner surface. Advantageously, several spring coils are arranged in parallel, resulting in high stiffness and, through varying coil configurations, a backlash-free connection. Furthermore, an elastomer coupling in a star geometry can be used as the coupling element, positioned between tooth-like zones of the rotor and steering shaft and / or intermediate components.A window damper comprising two parallel discs is also suitable as a coupling element, with a helical compression spring being inserted in each of the windows of the discs.

[0020] Another embodiment of the powder brake bearing provides that, regardless of the design and material used, the coupling element exhibits an elasticity of 3–50 Nm / °. Advantageously, the torsionally flexible coupling element allows for the measurement of changes in the steering angle when the powder brake is activated and the brake rotor is stationary. According to a further embodiment of the powder brake, the stator includes a single coil and two circumferential shear gaps, offset both axially and radially, which are at least partially filled with a magnetorheological medium. Alternatively, if required, a powder brake can be used in which the stator is assigned several coils and / or shear gaps, whereby the shear gaps can also be designed as disc gaps instead of cylinder-shell gaps. The powder brake bearing includes at least one seal to limit and simultaneously effectively seal the shear gaps and consequently the powder chamber.Preferably, two seals are provided, placed on either side of the rotor and radially outside the powder brake bearing.

[0021] According to a preferred embodiment, the powder brake bearing is integrated into a steer-by-wire (SbW) steering system that includes a continuously variable magnetorheological brake (MRF brake). The steering system further comprises a telescopic steering shaft with an end-mounted control element, a control unit, at least one angle sensor in conjunction with an end stop, and an electric motor. The powder brake and the electric motor are mounted separately on the steering shaft. The angle sensor, positioned at the end of the steering column (also called the steering shaft), can be used by the control unit to commutation the electric motor. In this steering system, a steering input detected by manually turning the control element is electronically transmitted to a vehicle actuator, also called a road wheel actuator (RWA), which adjusts the steering angle of the steerable wheels accordingly.

[0022] The invention further relates to a method for a steer-by-wire steering system of a vehicle, in which the rotation of the steering shaft can be influenced by a powder brake as described above. According to the method, an end-stop release is provided for the end-stop range of the steering shaft, whereby the powder brake releases as soon as a reduced rotation angle is detected. A threshold value of 0.1° to 1° is preferably provided for the angle reduction. The invention is explained in more detail below with reference to various exemplary embodiments. The figures show the following in detail:

[0023] Fig. 1 shows a section of a steering system with magnetorheological powder brake and electric motor in a perspective view; and

[0024] Fig. 2 shows a first embodiment of a magnetorheological powder brake in half-section; and

[0025] Fig. 3 shows a second embodiment of a magnetorheological powder brake in half-section; and

[0026] Fig. 4 shows a first embodiment of a flexible shaft connection of the rotor to the steering shaft in a 3D view; and

[0027] Fig. 5 shows a second embodiment of a flexible shaft connection of the rotor to the steering shaft in a 3D view; and

[0028] Fig. 6 shows a third embodiment of a flexible shaft connection of the rotor to the steering shaft in a 3D view; and

[0029] Fig. 7 shows a graphical representation of the controllability advantage that an elastic rotor coupling makes possible.

[0030] Figure 1 shows a section of a steer-by-wire steering system 1 of a vehicle, in which there is no direct connection between a control element, in particular a steering wheel (not shown), and the steered vehicle wheels (not shown). The steering angle of the control element is determined by means of an angle sensor 2 and transmitted by wire to an associated actuator and / or steering mechanism for adjusting the steering wheels. The control element is connected at its end to a telescopic steering shaft 3, which, in a known design, is adjustable in both length and angle. The steering shaft 3 is operatively connected to an electric motor 4, also called a feedback motor, and a magnetorheological powder brake 5, also called a force-feedback brake (MRP). The electric motor 4 is rotatably mounted on the steering shaft 3 by means of two motor bearings 6, 7 arranged on either side of the electric motor 4.

[0031] The magnetorheological powder brake 5 comprises a potted stator 8, which surrounds a rotor 9 at a distance from each other. These components are rotatable relative to each other and continuously about an axis of rotation. The rotor 9 is mounted on an axially projecting hub 11 within an annular cavity 12 of the stator 8 via a powder brake bearing 10. Furthermore, the rotor 9 is connected to the steering shaft 3 by means of an elastic coupling element 13. A coil 14 associated with the stator 8 engages with play in a receptacle 15 of the rotor 9, forming shear gaps 16, 17 offset in two planes between the stator 8 and rotor 9.

[0032] Fig. 2 shows the powder brake 5 in half-section and illustrates further details. The powder brake bearing 10, guided on the hub 11 of the stator 8, is held on both sides externally by local or circumferential, shoulder-forming indentations 18 of the rotor 9, also called crimping. On the inside, the rolling bearing of the powder brake bearing 10 is supported on one side by a side wall 20 of the stator 8 and fixed in position on the other side by indentations 19 of the hub 11. To seal the shear gaps 16, 17 of the powder brake 5, a seal 22 is provided on both sides of the rotor 9, positioned in side walls 20, 21 of the stator 8, the sealing lips of which are supported laterally on the rotor 9.The rotor 9 forms two radially offset steps laterally relative to the central receptacle 15 for the coil 14. These steps, together with a corresponding inner contour of the stator 8, define the shear gaps 16, 17 filled with a magnetorheological medium, preferably in powder form. Figure 3 shows a half-section of the powder brake 25, illustrating in particular the construction and arrangement of the coupling element 23 inserted between the steering shaft 3 and the rotor 29, as well as the powder brake bearing 30, which is centrally positioned on the rotor 29 and includes a rolling bearing. For torque transmission, the elastic coupling element 23 is positively and / or materially bonded to the steering shaft 3 and the rotor 29. Torque-transmitting contour elements of the steering shaft 3 and / or the rotor 29 may, for example, include a flange with holes, screws, or rivets. The coupling element 23 is capable of preventing axial and / or radial displacements orTo compensate for angular misalignments of the steering shaft 3 without affecting the function of the rotor 29 and the size of the shear gaps 26, 27. In contrast to the powder brake 5, the powder brake 25 shown in Fig. 3 includes a rotor 29 with a raised stage, which allows the accommodation of a large coil 34 associated with the stator 28.

[0033] Figures 4 to 6 show three variants of elastic coupling elements in conjunction with the steering shaft 3 and the rotor 9. Figure 4 shows a coupling element 13 made of spring steel, which is permanently fixed in position on the inside of the steering shaft 3 and on the outside of the rotor 9. Figure 5 shows a coupling element 23 made of elastomer, which engages, for example, between toothed-flank-shaped zones of the rotor 9 and the steering shaft 3. A coupling element 23 designed as a wire element, in particular as a curved spring, is shown in Figure 6, which comprises several parallel windings to achieve higher stiffness. For backlash-free connection, the coupling element 33 can be fixed to the rotor 9 on the outside via a retaining plate. On the inside, the coupling element 33 engages positively in notches of the steering shaft 3.

[0034] Figure 7 shows, in a diagram, a control advantage in the soft end-stop phase made possible by the elastic coupling of the rotor 9, 29 to the steering shaft 3 within the powder brake 5, 25. In the diagram, the ordinate represents the steering angle L and the abscissa the time axis T. The curve in the diagram illustrates how the steering angle changes over time during the end stop. After the powder brake is activated, for example, after reaching the limit angle, it is active in section A (brake rotor angle). In this phase, the rotor movement is interrupted, but a slight rotation of the steering shaft (3) is possible due to the coupling elasticity. Section B, shown with a dashed line and running parallel to section A, corresponds to a steering shaft angle detected by the sensor at the shaft end. A counter-movement of the control element by the driver causes a small change in the steering angle signal.Due to the torsional stiffness of the coupling element (13, 23, 33), the signal is small but measurable. As a result, the control system detects the change in steering angle, releases the powder brake (5, 25), and allows the driver to reverse further, a return from the soft end stop, as illustrated by a downhill curve section C.

[0035] List of reference signs

[0036] Steering system

[0037] Angle sensor

[0038] steering shaft

[0039] electric motor

[0040] Powder brake

[0041] engine mounts

[0042] engine mounts

[0043] stator

[0044] rotor

[0045] Powder brake bearings

[0046] hub

[0047] cavity

[0048] Coupling element

[0049] Sink

[0050] Recording

[0051] Shear gap

[0052] Shear gap

[0053] embossing

[0054] embossing

[0055] side wall

[0056] side wall

[0057] seal

[0058] Coupling element

[0059] Powder brake

[0060] Shear gap

[0061] Shear gap

[0062] stator

[0063] rotor

[0064] Powder brake bearings

[0065] Coupling element

[0066] Coil A Curve section

[0067] B Curve section

[0068] C Curve section

[0069] L steering angle

[0070] T Time axis

Claims

Patent claims 1. Steering system (1) for steering a vehicle, by means of a steer-by-wire concept, comprising a control element, a steering shaft (3), an electric motor (6) and a continuously adjustable magnetorheological powder brake (5, 25) influencing the rotation of the steering shaft (3), which comprises two components rotatable relative to each other about an axis of rotation, a stator (8, 28) with associated coil (14) and, spaced apart therefrom, a rotor (9, 29) connected to the steering shaft (3), wherein at least one rotating shear gap (16, 17) at least partially filled with a magnetorheological medium is provided between the rotor (9, 29) and the stator (8, 28), characterized in that the rotor (9, 29) is rotatably mounted via at least one powder brake bearing (10, 30) positioned separately from the steering shaft (3) and connected to the stator (8, 28), and the rotor (9, 29) is connected to the steering shaft (3) via an elastic coupling element (13, 23, 33).

2. Steering system (1 ) according to claim 1 , characterized in that the powder brake bearing (10, 30) is placed centrally, in the middle of the rotor (9, 29).

3. Steering system (1 ) according to one of the preceding claims, characterized in that the powder brake bearing (10, 30) is fixed in position in the installed state by embossings (18, 19) produced at least on one side by riveting.

4. Steering system (1) according to one of the preceding claims, characterized in that the powder brake bearing (10, 30) includes a four-point bearing or a double angular contact bearing as a rolling bearing.

5. Steering system (1) according to one of the preceding claims, characterized in that an axially laterally associated with the powder brake bearing (10, 30) elastic coupling element (13, 23, 33) transmits a braking torque to the steering shaft (3).

6. Steering system (1 ) according to claim 5, characterized in that a steel disc, a spring element or an elastomer coupling element is used as the elastic coupling element (13, 23, 33).

7. Steering system (1 ) according to one of the preceding claims, characterized in that the coupling element (13, 23, 33) has an elasticity of 3-50 Nm / ° regardless of the design and the material used.

8. Steering system (1 ) according to one of the preceding claims, characterized in that the powder brake (5, 25) radially outside the powder brake bearing (10, 30) includes at least one seal (22) limiting the shear gap (16, 17) and / or a powder space.

9. Steering system (1 ) according to one of the preceding claims, characterized in that the powder brake bearing (10, 30) is integrated in a force feedback brake (MRP) of a steering system (1 ) designed as a steer-by-wire.

10. Method for steering a motor vehicle by means of a steer-by-wire steering system in which the rotation of a steering shaft (3) can be influenced via a powder brake (5, 25), characterized in that the powder brake (5, 25) can be released in an end-stop area of ​​the steering shaft (3) as soon as a reduced rotation angle is detected.

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