Steering system for a motor vehicle having a magnetorheological brake

Abstract

The invention relates to a steering system (10) for a motor vehicle having a magnetorheological brake (18). The steering system (10) has a steering shaft (11) which is mounted in a pull-out casing tube (12), at least one magnetorheological brake (18) being provided between the steering shaft (11) and the pull-out casing tube (12). The magnetorheological brake (18) has at least one rotor (13) and at least one stator (14), the rotor (13) being mounted on the steering shaft (11) for conjoint rotation therewith, and the stator (14) being fixed to at least one coil (15) in the pull-out casing tube (12) for conjoint rotation therewith.

Description

[0001] P241014 DE

[0002] - 1 -

[0003] Steering system for a motor vehicle with a mechanical brake

[0004] The invention relates to a steering system for a motor vehicle with a magnetorheological brake.

[0005] Magnetorheological brakes are known in the art and are used, for example, in steer-by-wire systems to simulate steering resistance for mechanical feedback. In a magnetorheological brake, two components rotating relative to each other—a stator with a coil and a rotor—are slowed down when the brake is activated. A magnetorheological medium is located in an annular gap between the stator and rotor. When current flows through the coil, this medium forms chain-like structures in the resulting magnetic field. This generates a braking force between the rotor and stator, which depends on the magnetic field generated by the coil in the annular gap. Such electrically controlled brakes are often also called powder brakes because of the magnetorheological medium.

[0006] For steering systems, especially steer-by-wire systems, sufficient braking torque or feedback torque from the magnetorheological brake is required to ensure adequate tactile feedback from the steering wheel. At the same time, the installation space for the steering system in a motor vehicle is severely limited.

[0007] The object of the invention is therefore to provide a steering system for a motor vehicle with a magnetorheological brake that allows for a small installation space and sufficient braking torque.

[0008] The invention solves the problem with the features of the independent claims.

[0009] A steering system for a motor vehicle with a magnetorheological brake is proposed, wherein the steering system has a steering shaft which is in a P241014 DE

[0010] - 2 - is mounted in the draw-out sleeve. At least one magnetorheological brake is arranged between the steering shaft and the draw-out sleeve, wherein the magnetorheological brake has at least one rotor and at least one stator, wherein the rotor is arranged on the steering shaft in a rotationally fixed manner, preferably with an interference fit, and wherein the stator with at least one coil is arranged in the draw-out sleeve in a rotationally fixed manner.

[0011] The proposed arrangement of the magnetorheological brake between the extension tube and the steering shaft prevents the magnetorheological brake from increasing the overall length of the steering system, particularly the steering column, thus enabling a smaller, and especially shorter, installation space for the steering system. The diameter of the annular gap(s) between the rotor and stator, as well as the diameter of the magnetorheological brake as a whole, inherently leads to a reduction in the achievable braking torque. However, this can be at least partially compensated for by magnetic assistance from the steering shaft and / or the extension tube. In advantageous embodiments, the cross-sectional area of ​​the rotor-back closure can be increased by more than 20% by the steering shaft, which is preferably designed as a hollow shaft. This has a quadratic effect on the magnetic forces in the annular gap of the magnetorheological brake.This can be achieved, for example, by a press-fit connection of the rotor of the at least one magnetorheological brake to the steering shaft. Simultaneously, the diameter of the coil or coils is also smaller with the proposed arrangement, so that their resistance per turn is correspondingly lower. Therefore, several coils can preferably be connected in series to achieve the required total resistance with regard to the heat generation to be avoided.

[0012] The steering shaft, as a hollow shaft, preferably forms an internal cable channel for a cable to an airbag or additional input device on a steering wheel or input device at the free end of the steering shaft. The steering shaft is further preferably made of a magnetizable material. Furthermore, the pull-out sleeve is preferred. P241014 DE

[0013] - 3 - magnetizable in three ways. The rotor and stator are preferably made of a soft magnetic material.

[0014] In preferred embodiments, the magnetorheological brake(s) have a length parallel to the steering shaft that is greater than its diameter. Exceeding the overall length of the magnetorheological brake(s) by their diameter is counterintuitive and not readily apparent, because magnetorheological brakes are typically designed to be short and have a relatively large diameter compared to their length. A long design exhibits magnetic bottlenecks, particularly at the inner and outer magnetic return paths, which dramatically reduce the achievable braking torque. Dividing the overall length into several magnetorheological brakes means that less magnetic flux needs to pass through the "magnetic bottlenecks" in the form of the inner rotor return path. As a result, the sum of the individual braking torques is greater than the braking torque of a single, undivided brake.

[0015] According to an advantageous further development, it is proposed that at least two magnetorheological brakes are arranged concentrically one behind the other between the steering shaft and the extension sleeve tube, each having a separate stator and at least one separate coil, wherein the at least two magnetorheological brakes have a common rotor or each a separate rotor.

[0016] Such an arrangement can also be described as a stacked arrangement. In this way, the achievable braking torque in the steering system can be doubled or tripled, for example, without increasing the installation space of the steering system. The braking torque of a single magnetorheological brake can be, for example, 4 Nm, so that by arranging several magnetorheological brakes, the achievable braking torque can be increased to, for example, 8 Nm, 12 Nm, 16 Nm, or 20 Nm. The proposed arrangement of at least two magnetorheological brakes enables a multi-coil arrangement, thereby achieving the required braking torque with a very small installation space. P241014 DE

[0017] - 4 - of the steering system. The braking torque of a single magnetorheological brake can therefore be designed to be smaller than the required braking torque of the steering system as a whole. The at least two magnetorheological brakes can therefore be constructed from identical parts or, in the case of a common rotor, have identical subassemblies.

[0018] In this context, a separate rotor or stator means that the rotor or stator is not physically bonded to another rotor or stator. Separate coils, in this context, have a gap between them that is not closed by windings. A common rotor, preferably continuous and forming the rotor for two or more magnetorheological brakes, can simplify assembly.

[0019] In an advantageous embodiment, the at least two magnetorheological brakes have a common sealing chamber for a magnetorheological medium, which is limited at both axial ends parallel to the steering shaft by a seal.

[0020] Therefore, when arranging multiple magnetorheological brakes, intermediate seals can be omitted, thus reducing the number of parts and the assembly effort. In alternative embodiments, intermediate seals can be provided between the magnetorheological brakes.

[0021] According to a further development, it is proposed that at least one magnetorheological brake has at least two annular gaps with different diameters. This allows for simplified mounting of a coil on the stator. It also facilitates the assembly of the stator and rotor.

[0022] Preferably, the stator of a magnetorheological brake has two coils spaced apart from each other parallel to the steering shaft. A further preferably an annular gap is provided between the rotor and stator of the magnetorheological brake (see P241014 DE).

[0023] - 5 - the two coils. By means of the spacing, it is possible to guide the magnetic flux between the coils. This is particularly advantageous with coils that are connected or energized in opposite directions. The two coils of the magnetorheological brake are preferably arranged symmetrically to a plane perpendicular to the steering shaft.

[0024] It is further proposed that the two coils are inserted into the stator from opposite sides and spaced apart by a portion of the stator. This allows for simple assembly of the two coils in the magnetorheological brake. Preferably, the magnetorheological brake has a one-piece stator and a retaining ring pressed onto the rotor. The pressed-on retaining ring allows the coils in the stator to be laterally enclosed by the rotor. Opposite the retaining ring, the rotor preferably has a collar. This allows, for example, a symmetrical rotor design with respect to the magnetic flux.

[0025] According to a further development, it is proposed that the magnetorheological brake(s) comprise at least two coils connected in opposite directions. In this context, "opposite directions" means that the magnetic flux around the two coils exhibits a region of similar polarity between them. This allows the magnetic flux in the annular gap between the two coils to be amplified.

[0026] Preferably, the at least two coils are connected in series, for example to reduce heating power. In alternative embodiments, at least two magnetorheological brakes are not connected in series and are connected to different output stages or control units.

[0027] Furthermore, an electric motor is preferably arranged in the extension tube, which is connected to the steering shaft and configured to rotate the steering shaft relative to the extension tube. The electric motor can be used to... P241014 DE

[0028] - 6 - In addition to the magnetorheological brake(s), feedback is provided to a steering operator. The proposed arrangement of the electric motor allows the installation space of the steering system to be kept small, while in addition to the pure braking torque of the magnetorheological brake, an actuating torque can be applied to the steering shaft. The steering shaft therefore does not need to extend from the extension tube opposite the input device or the steering wheel. In possible embodiments, a gearbox is provided on the electric motor. In alternative embodiments, the electric motor is located outside the extension tube, thereby increasing the required installation space accordingly.

[0029] The extension tube is preferably guided in an extension support, which receives the torque from the extension tube and is designed to transfer it into the vehicle structure, thus enabling axial adjustment of the steering shaft's position. This allows, for example, longitudinal adjustment of a steering wheel mounted at the free end of the steering shaft. The steering system can further include, for example, return springs and / or sensors. In advantageous embodiments, the proposed arrangement of the magnetorheological brake and preferably also an electronic motor within the extension tube eliminates the need to extend the concealed end of the extension tube into the extension support.

[0030] According to a further development, it is proposed that the at least one magnetorheological brake has at least one permanent magnet for a basic braking torque. A magnetorheological braking torque is generated in the magnetorheological brake by means of the permanent magnet, which acts without current being energized to the coil(s). This allows, for example, a currentless basic braking torque of 0.1 to 0.5 Nm to be generated as a constant emergency running characteristic. Furthermore, in preferred embodiments, a magnetic field can be generated by energizing the coil(s) in the direction of the current. With a magnetic field in the same direction, this field produces a braking effect that is additive to the braking effect of the permanent magnet, or with an oppositely oriented field, it cancels out the braking effect of the permanent magnet. P241014 DE

[0031] - 7 -

[0032] The invention is explained below with reference to preferred embodiments and the accompanying figures.

[0033] Fig. 1 shows a steering system with a magnetorheological brake between the steering shaft and the extension tube;

[0034] Fig. 2 shows a steering system with two oppositely connected coils and a schematic representation of the magnetic flux;

[0035] Fig. 3 shows a steering system with a magnetorheological brake and an electric motor between the steering shaft and the extension tube;

[0036] Fig. 4 shows a steering system with two magnetorheological brakes with identical parts;

[0037] Fig. 5 shows a steering system with three magnetorheological brakes; and

[0038] Fig. 6 shows a steering system with a magnetorheological brake with a

[0039] Permanent magnets

[0040] Figure 1 shows an embodiment of a steering system 10 for a motor vehicle. The steering system 10 has a steering shaft 11, at the free end of which, for example, a steering wheel or other input device can be attached. The steering shaft 11 is rotatably mounted in an extendable outer tube 12 by means of a steering shaft bearing 21, see also Figure 3. A magnetorheological brake 18 is arranged in the extendable outer tube 12. The magnetorheological brake 18 has a rotor 13, which is pressed onto the steering shaft 11, which is designed as a hollow shaft, and a stator 14, which is mounted in the extendable outer tube 12. The stator 14 has two coils 15, each of which is inserted into the stator 14 from one axial side and is held at a distance from each other by a radially inwardly extending section of the stator 14.The rotor 13 encloses a coil 15, in this embodiment the left coil 15, axially with a collar 24, and the other coil 15 with a locking ring 19, which is pressed onto the rotor 13. In this advantageous- P241014 DE.

[0041] - 8 - In the exemplary embodiment, the magnetorheological brake 18 therefore has a symmetrical double coil structure.

[0042] The coils 15 can be supplied with electric current via a cable guide 25 to activate the magnetorheological brake 18. In advantageous embodiments, the coils 15 preferably have a center radius of 20 mm and, for example, 180 to 250 turns. The resistance of a coil is, in advantageous embodiments, 4 to 6 ohms.

[0043] The steering shaft 11, as a hollow shaft, preferably serves for cable routing inside it to a steering device or a steering wheel, which can be attached to the free end of the steering shaft 11.

[0044] Furthermore, a seal 16 and an associated sealing plate 26, preferably made of stainless steel, are provided on each of the axial sides, enclosing a sealing chamber 20 for a magnetorheological medium of the magnetorheological brake 18. The magnetorheological brake 18 has three annular gaps 17 between the rotor 13 and the stator 14. The braking torque of the magnetorheological brake 18 acts in the annular gaps 17 between the rotor 13 and the stator 14, transmitting a steering torque from the rotor 13 to the steering shaft 11 and from the stator 14 to the extension sleeve 12.

[0045] Figure 2 shows a detailed view of the magnetorheological brake 18 of the steering system 10, in which the two coils 15 of the magnetorheological brake 18 are connected in opposite directions and, in this advantageous embodiment, in series. This is illustrated by the magnetic flux lines. Accordingly, the flux lines run parallel in the annular gap 17 between the two coils 15, which are separated by a section of the stator 14. Figure 2 also illustrates that the magnetic flux overcomes the "magnetic bottleneck" near the inner diameter of the rotor 13 by traversing, i.e., using, some of the field lines on the magnetizable steering shaft 11.

[0046] Figure 3 shows another embodiment of a steering system 10 which has the same magnetorheological brake 18 as the embodiment of P241014 DE

[0047] - 9 -

[0048] Figures 1 and 2. In addition to the steering shaft bearings 21, the embodiment shown in Figure 3 has an end stop 22 and an electric motor 23. The electric motor 23 can be controlled additionally or alternatively to the magnetorheological brake 18.

[0049] Figure 4 shows another embodiment of a steering system 10, which also has a steering shaft 11 rotatably mounted in an extension tube 12. In this advantageous embodiment, the steering system 10 has two magnetorheological brakes 18 arranged one behind the other on the steering shaft 11, so that both magnetorheological brakes 18 are arranged coaxially with the steering shaft 11. Each of the two magnetorheological brakes 18 has a separate, i.e., independent, rotor 13 and stator 14. The magnetorheological brakes 18 are arranged axially adjacent to one another between the steering shaft 11 and the extension tube 12. The two magnetorheological brakes 18 are axially delimited by the seals 16 and sealing plates 26, whereby in this advantageous embodiment no intermediate seal is provided between the magnetorheological brakes 18.The two seals 16 thus seal a sealing chamber 20 for the magnetorheological medium or powder, which extends over both magnetorheological brakes 18 and the corresponding annular gaps 17. In this advantageous embodiment, the coils 15 are connected in series. In this advantageous embodiment, the two magnetorheological brakes 18 have some identical parts or, as shown, even completely identical parts.

[0050] The magnetorheological brakes 18 are, in this illustration, slid onto the steering shaft 11 from the right for mounting the steering system 10, with the rotors 13 advantageously pressed onto the steering shaft 11. The stators 14 are secured in the extension sleeve 12 by sliding it onto the stator sleeve by means of a positive locking mechanism, so that an electrically controlled braking torque can be generated between the steering shaft 11 and the extension sleeve 12.

[0051] Figure 5 shows a further advantageous embodiment of a steering system 10, which, unlike the embodiment of Figure 4, has three magnetorheological brakes 18 arranged one behind the other. Accordingly, the achievable P241014 DE

[0052] - 10 -

[0053] The braking torque of the embodiment shown in Figure 5 is 50% greater than the achievable braking torque of the embodiment shown in Figure 4. The stacked arrangement of several magnetorheological brakes 18 within the extension tube 12 enables a sufficiently high braking torque despite the radius of the annular gap 17 for generating the braking torque being limited by the extension tube 12.

[0054] The embodiments shown in Figures 4 and 5 can, analogously to the embodiment shown in Figure 3, additionally include an electric motor 23 and / or an end stop 22 to limit the rotation range of the steering shaft 11. In further embodiments with at least two magnetorheological brakes 18 between the steering shaft 11 and the extension tube 12, arranged concentrically to the steering shaft 11 one behind the other, the at least two magnetorheological brakes 18 can have a common rotor 13.

[0055] Figure 6 shows a further embodiment of a steering system 10 for a motor vehicle, wherein the steering system 10 has a steering shaft 11 which is mounted in an extendable outer tube 12. The magnetorheological brake 18 is arranged between the steering shaft 11 and the extendable outer tube 12, the magnetorheological brake 18 comprising a rotor 13 and a stator 14. The rotor 13 is rotationally fixed to the steering shaft 11, and the stator 14 with a coil 15 is rotationally fixed within the extendable outer tube 12. The magnetorheological brake 18 has a permanent magnet 27, which in this advantageous embodiment is arranged in or on the stator 14. The permanent magnet 27 generates a basic braking torque in the magnetorheological brake 18, which acts without energizing the coil 15. The basic braking torque, for example, is in the range of 0.1 to 0.5 Nm.The permanent magnet 27 of the magnetorheological brake 18 enables constant emergency running behavior with the basic braking torque. Depending on the current applied to the coil 15, a braking torque can be generated by the coil 15, which acts in addition to the basic braking torque, or the basic braking torque can be canceled out by the coil 15. The magnetorheological brake 18 with a permanent magnet 27 can be combined with the other embodiments shown. P241014 DE.

[0056] - 11 -

[0057] List of reference signs

[0058] 10 Steering system

[0059] 11 Steering shaft

[0060] 12 Extraction sleeve tube

[0061] 13 Rotor

[0062] 14 Stator

[0063] 15 coils

[0064] 16 Seal

[0065] 17 Annular gap

[0066] 18 Magnetorheological brake

[0067] 19 Locking ring

[0068] 20 Sealing chamber

[0069] 21 Steering shaft bearings

[0070] 22 End stop

[0071] 23 electric motor

[0072] 24 collars

[0073] 25 Cable routing

[0074] 26 Sealing plate

[0075] 27 Permanent magnet

Claims

P241014 DE - 12 - Patent claims 1. Steering system (10) for a motor vehicle with a magnetorheological brake (18), wherein the steering system (10) has a steering shaft (11) which is mounted in an extendable outer tube (12), wherein at least one magnetorheological brake (18) is arranged between the steering shaft (11) and the extendable outer tube (12), wherein the magnetorheological brake (18) has at least one rotor (13) and at least one stator (14), wherein the rotor (13) is arranged non-rotatably on the steering shaft (11), and wherein the stator (14) with at least one coil (15) is arranged non-rotatably in the extendable outer tube (12).

2. Steering system (10) according to claim 1 , characterized in that the magnetorheological brake (18) or the magnetorheological brakes (18) have a length parallel to the steering shaft (11) which is greater than its diameter.

3. Steering system (10) according to one of the preceding claims, characterized in that at least two magnetorheological brakes (18) are arranged concentrically to the steering shaft (11) and the extension sleeve tube (12) one behind the other, each having a separate stator (13) and at least one separate coil (15), wherein the at least two magnetorheological brakes (12) have a common rotor (13) or each a separate rotor (13).

4. Steering system (10) according to claim 3, characterized in that the at least two magnetorheological brakes (18) have a common sealing chamber (20) for a magnetorheological medium, which is parallel to the steering shaft (11) at both axial ends by each of ei- P241014 DE - 13 - a seal (16) is limited.

5. Steering system (10) according to one of the preceding claims, characterized in that the at least one magnetorheological brake (18) has at least two annular gaps (17) with different diameters.

6. Steering system (10) according to one of the preceding claims, characterized in that the stator (14) of a magnetorheological brake (18) has two coils (15) spaced apart parallel to the steering shaft (11).

7. Steering system (10) according to claim 6, characterized in that the two coils (15) are inserted into the stator (14) from opposite sides and are spaced apart from each other by a part of one stator (14), wherein the magnetorheological brake (18) has a one-piece stator (14) and a locking ring (19) pressed onto the rotor (13).

8. Steering system (10) according to one of the preceding claims, characterized in that the magnetorheological brake (18) or the magnetorheological brakes (18) have a total of at least two coils (15) which are connected in opposite directions.

9. Steering system (10) according to one of the preceding claims, characterized in that an electric motor (23) is arranged in the extension sleeve tube (12), which is connected to the steering shaft (11) and is configured to rotate the steering shaft (11) relative to the extension sleeve tube (12).

10. Steering system (10) according to one of the preceding claims, characterized in that the at least one magnetorheological brake P241014 DE - 14 - (18) has at least one permanent magnet (27) for a basic braking torque.

Images