Magnetorheological brake

Abstract

The invention relates to a magnetorheological brake (1) comprising: a stator (2), a rotor (3) which is arranged to rotate relative to the stator (2), a gap (4) between the rotor (3) and the stator (2), and a magnetorheological powder (5) located in the gap (4) between the rotor (3) and the stator (2), wherein at least one of the opposing surfaces (6, 7) of the rotor (3) and the stator (2) that define the gap (4) has a structure. Furthermore, the invention relates to a force feedback actuator, a steering device and a method for manufacturing a magnetorheological brake.

Description

[0001] The present invention relates to a magnetorheological brake, a force feedback actuator, a steering device and a method for manufacturing a magnetorheological brake. State of the art

[0002] Magnetorheological brakes are known today. These brakes feature a rotor that is designed to rotate around an axis. Opposite the rotor is a stator that remains stationary relative to the rotor. Between the rotor and stator is a circumferential gap containing a magnetorheological powder (hereinafter referred to as the powder). This powder is designed to change its shear or friction properties in the direction of rotation of the rotor when a suitable magnetic field is applied, thereby generating a braking effect on the rotor.

[0003] With such brakes, frictional vibrations, vibrations, and noise emissions can occur. These brakes can therefore exhibit poor noise, vibration, and harshness (NVH) characteristics. In haptic applications (human-machine interfaces such as steering, joysticks, or rotary knobs), this reduces comfort or is irritating. The reason for poor NVH characteristics can be that the area within the powder where shearing or friction occurs does not remain exclusively within the powder or is not initially located within the powder. It is possible that this area "migrates" towards the surface of the stator or rotor or initially establishes itself there during the braking process. Consequently, frictional vibrations occur due to a stick-slip effect between the powder and the respective surfaces.

[0004] Based on this, there is a need to improve such a magnetorheological brake.

[0005] Against this background, it is an object of the present invention to provide a magnetorheological brake which in particular has improved NVH behavior. Disclosure of the invention

[0006] These and other problems, which will be mentioned in the following description or which can be recognized by a person skilled in the art, are solved by the subject matter of the independent claims. Advantageous embodiments and further developments can be found in the dependent claims and the following description.

[0007] The magnetorheological brake according to the invention has: a stator a rotor that is arranged to rotate relative to the stator, a gap between the rotor and the stator, and a magnetorheological powder located in the gap between the rotor and the stator, wherein at least one of the opposing surfaces of the rotor and the stator, which define the gap, has a structure.

[0008] The rotor is designed to rotate around a rotational axis.

[0009] An axial direction can subsequently be a direction that is oriented parallel to the axis of rotation of the rotor.

[0010] A radial direction can subsequently be a direction that radiates from the axis of rotation of the rotor.

[0011] A circumferential direction can be a direction that runs along the circumference of the corresponding rotor surface or stator surface.

[0012] A direction of rotation can be a direction of rotation of the rotor around its axis of rotation.

[0013] The gap preferably extends in the direction of rotation or circumferential direction of the rotor around the rotor or within the stator, wherein the gap is radially limited by the surfaces of the rotor and the stator.

[0014] The stator can be designed for rotationally and axially fixed arrangement in a housing.

[0015] The rotor can be located inside the stator.

[0016] The surfaces of the rotor and the stator can also be referred to as rotor surface(s) and stator surface(s), respectively.

[0017] Preferably, the opposing surfaces of the rotor and the stator define the gap in the radial direction. They thus flank the gap in the circumferential direction or in the direction of rotation. That is, when the rotor rotates, the corresponding rotor surface moves relative to the stator surface, which is stationary opposite the rotor surface.

[0018] According to one embodiment, both opposing surfaces of the rotor and stator that define the gap have a structure. These structures on the rotor and stator surfaces can be manufactured in the same way and / or have the same shape, with particular reference to the following descriptions regarding the manufacturing and shape of the structure. Alternatively, both structures on the rotor and stator surfaces can be manufactured in different ways and / or have different shapes, with particular reference to the following descriptions regarding the manufacturing and shape of the structures.

[0019] According to one embodiment, the rotor surface can be an outer surface of a cylinder shell, while the stator surface can be an inner surface of a cylinder shell.

[0020] The structure can be created by post-processing the corresponding surfaces.

[0021] The structure can be tailored to the magnetorheological powder in such a way that the powder adheres to or is held on the rotor surface and / or the stator surface when the rotor rotates / moves relative to the stator. The adhesive or holding force on the powder particles at the respective surface(s) is greater than within the powder itself, i.e., between the powder particles. In other words, the structure is tailored to the magnetorheological powder such that the powder's adhesion to the rotor surface and / or the stator surface in the direction of rotation is stronger than any inherent adhesive or frictional force within the powder that counteracts shearing within the powder. This means that, by tailoring the structure to the powder, there is a location within the powder that is not in contact with the rotor or stator surface, where the adhesive or frictional force is lower.Frictional forces act, causing shearing to occur at this point and not on the rotor or stator surface. In other words, the structure is designed to fit the magnetorheological powder in such a way that shearing occurs within the powder itself when the rotor moves / rotates relative to the stator.

[0022] In particular, the structure on the powder can have the effect that surface friction between the powder and the surfaces of the rotor and stator is higher than internal / powder-internal friction.

[0023] In particular, the structure can be uneven.

[0024] The structure, particularly irregularities on the rotor and / or stator surfaces, reduces the number of frictional contacts, i.e., points of friction between the magnetorheological powder and the rotor and stator surfaces. This results in a shift of the friction point into the powder. In other words, the effective surface area of ​​the rotor or stator in contact with the powder at the lateral boundary of the gap is reduced, as the corresponding surface is interrupted, for example, by depressions in the structure, such as grooves.

[0025] The displacement of the friction points, particularly during the rotor's rotation, into the powder—that is, away from the rotor or stator surface—causes a stochastic shearing of the powder particles or particle chains within the powder. This means that the powder particles are now made of the same material sliding against each other. This reduces the stick-slip effect, which would occur much more readily with dissimilar materials at the friction point (powder-rotor surface or powder-stator surface).

[0026] Thus, the proposed invention reduces torque fluctuations and / or noise.

[0027] Furthermore, the structure, especially if it has irregularities, can be designed to suit the powder in such a way that turbulence occurs within the powder when the rotor rotates. This introduces greater dynamics into the powder, which promotes or intensifies the effect of friction or shear within the powder.

[0028] The advantage of the proposed solution lies particularly in the fact that – contrary to expectations – the stick-slip effect between the powder and the rotor surface and / or the stator surface can be reduced or eliminated if the rotor surface and / or the stator surface are textured (and thus, for example, made rougher) and not further smoothed (e.g., by appropriate coating or by mechanical processing such as polishing). The invention deliberately creates adhesion conditions for the powder on the relevant surface(s), so that a boundary layer of the powder forms on the rotor surface and / or the stator surface. The boundary layer on the rotor surface can rotate with the rotor. The boundary layer on the stator surface can adhere to it. This solution also has the advantage that a coating of the relevant surfaces is not necessary.Therefore, there is no risk that the stick-slip effect will increase again with the wear and tear of such a coating or the wear and tear of a correspondingly polished surface.

[0029] Such a magnetorheological brake can be implemented in a force-feedback actuator, such as the one described below. Alternatively, such a magnetorheological brake can also be used for a manually operated joystick or lever, or for a manually operated rotary knob or control.

[0030] According to one embodiment, the structure exhibits irregularities in the micrometer range. These irregularities can be, in particular, depressions and / or elevations on the stator surface and / or on the rotor surface. The radial extent of these irregularities can range from approximately 30 µm to approximately 100 µm, particularly from approximately 40 µm to approximately 90 µm, and further, particularly from approximately 50 µm to approximately 80 µm. These numerical values ​​can be used to tailor the design of the irregularities to the magnetorheological powder used and / or its particle sizes.

[0031] In general, the structure may exhibit irregularities whose depressions and / or elevations have a radial extent that is 3 to 20 times larger than the particle diameter of the magnetorheological powder.

[0032] According to one embodiment, the structure is either non-directional or directional. A non-directional or isotropic surface structure of the rotor and / or stator exhibits adhesive properties for the magnetorheological powder that are independent of both the circumferential and axial directions. This could, for example, be a structure corresponding to a uniform roughening of the surface. In the case of a directional or anisotropic surface structure of the rotor and / or stator, the structure exhibits properties that are direction-dependent. The direction can be the axial direction, the circumferential direction, or any other direction with axial and circumferential components within the gap.

[0033] The directional structure can be formed by introducing and / or applying predetermined patterns. For example, the structure can be created on the rotor surface and / or the stator surface by post-processing the respective surface. Predefined patterns can, in particular, be grooves running transversely or obliquely to the circumferential direction. Such grooves can be arranged parallel to each other. Alternatively or additionally, the grooves can be intersecting. The angle between the intersecting grooves preferably opens in the circumferential direction. In particular, the intersecting grooves can be arranged at an angle of 100° to 150°, preferably 135°, to each other. Alternatively or additionally, the predetermined patterns can have ellipses, circles, or point-like depressions (e.g., craters). In addition to depressions, the predetermined patterns can also have corresponding raised areas.

[0034] According to one embodiment, the structure is produced or manufactured mechanically and / or thermally and / or chemically.

[0035] Mechanical production or manufacturing refers to the mechanical processing of the rotor and / or stator surfaces. This can be achieved, for example, by brushing or embossing. Brushes can be circular brushes capable of creating the ellipses or circles described above. Brushes can have appropriately hard and stiff bristles to create the desired structure. An erosive blasting process is also conceivable, in which an abrasive or blasting medium, contained within a fluid jet directed at the surface, acts upon it. Examples include shot peening and sandblasting. Furthermore, roughening the surface using a grinding process is another possible method.

[0036] Thermal generation or manufacturing refers specifically to the processing of the rotor and / or stator surface using a laser. This can be an erosive process. In particular, the structure can be created by melting and locally removing material from the corresponding surface through laser irradiation, thus forming a depression. The molten material can, for example, be deposited next to the depression, creating a raised area in the radial direction relative to the original surface level. This allows for the creation of a depression that extends from the top of the raised area to the bottom of the depression and is radially deeper than the initial depression formed by melting. For example, a line contour with a raised area width of 15 µm can be created in this way.The resulting depression can have a depth of 30 µm and the resulting elevation a height of 40 µm, both measured from the original surface level. This results in a total height of 70 µm from the bottom of the depression to the tip of the elevation in the radial direction.

[0037] In chemical production or manufacturing, an etching process may be used to adjust the roughness of the rotor surface and / or the stator surface.

[0038] It should be emphasized that the processes described above (mechanical, thermal, chemical) can be used individually or in combination to treat the respective surface. Furthermore, it is also possible to apply different processes belonging to the same category (mechanical, thermal, chemical) to one and the same surface. For example, mechanical brushing could be combined with an erosive blasting process. When combining the described processes, it is preferable to carry out individual processes sequentially. That is, a new process or treatment is only started after the completion of a preceding process or treatment.

[0039] The processes described above can be used to produce directional or non-directional structures. In particular, various predetermined patterns can be created. While roughening, blasting, and etching processes produce non-directional structures, other processes can create directional structures. This includes, for example, the laser treatment of the surface described above. With this method, grooves and other patterns, and thus directional structures, can be produced using the appropriate laser application. Embossing can produce a directional structure according to the embossing tool used, which is pressed into the surface. However, it is also conceivable to create a non-directional structure by embossing. If brushes are used, a non-directional pattern can be created by passing the brush over the surface a sufficient number of times. It is also conceivable to create a directional pattern, for example...when the brush is moved in only one direction to the corresponding surface (e.g., across or at an angle to the circumferential direction).

[0040] According to one embodiment, the surface of the rotor or stator has a roughened structure, or the surfaces of both the rotor and stator have a roughened structure. Manufacturing methods for such a roughened structure are described above. In one embodiment, the roughened structure is simply a roughened rotor or stator surface, without any other structural features. Alternatively, a structure can also have a roughening in addition to other structural elements (e.g., grooves), which is produced by a corresponding machining process (see above). The roughening generally leads to an increase in friction between the respective surface and the powder, thus facilitating the adhesion of the powder to the rotor or stator surface, allowing a corresponding powder boundary layer to form on this surface.According to one embodiment, the structure has a roughness value (specified as average roughness depth R). z ) which corresponds to a particle diameter three to twenty times that of the magnetorheological powder. In this way, a sufficient quantity of particles can be incorporated into the structure.

[0041] According to one embodiment, the structure has recesses with a width approximately two to six times the diameter of the magnetorheological powder particles. This allows a sufficient number of powder particles to be accommodated in the recesses without being pulled or lifted out by shear forces from the powder in the gap (i.e., the powder particles not in the recesses). If the recess width is too large, these shear forces can act on the particles in the recesses, pulling or lifting them out. If the recess width is too small, powder particles can no longer be accommodated in the recesses, hindering the formation of the boundary layer on the respective surface(s).

[0042] Another aspect of the invention relates to a force feedback actuator, particularly for a vehicle steering system. The force feedback actuator comprises a drive unit and a magnetorheological brake as described above. The drive unit is preferably designed as an electric motor. Furthermore, the force feedback actuator has a mechanical interface, which is preferably rotatable. The force feedback actuator is designed to act on the mechanical interface by means of the magnetorheological brake, particularly via a connection between the rotor and the mechanical interface, and by means of the drive unit, in order to generate, for example, a counter-torque perceptible to a user.

[0043] Another aspect of the invention relates to a steering system for a vehicle. The steering system is specifically designed as a steer-by-wire system. The steering system comprises a steering element, e.g., a steering wheel, and a force-feedback actuator as described above, wherein the steering element is rotationally fixed to the mechanical interface. In this way, a counter-torque, perceptible to the driver at the steering element, can be applied to the steering element by the force-feedback actuator.

[0044] Another aspect of the invention relates to a method for manufacturing a magnetorheological brake, in particular a magnetorheological brake as described above. The method comprises the following steps: - Providing a rotor and a stator, - Creating a structure on at least one of the opposing surfaces of the rotor and stator that limits the gap.

[0045] According to one embodiment, a structure is created on both of the opposing surfaces of the rotor and the stator that define the gap.

[0046] The rotor and stator can then be assembled and the magnetorheological powder filled into the gap. The structure is created primarily by post-processing the corresponding surfaces of the rotor and stator.

[0047] Features described above in connection with the brake or the other items, and which relate in particular to one or more aspects of the manufacture of the rotor and stator or the corresponding structure, are also to be understood as features of the method disclosed herein and can be used to specify it. Detailed description based on drawings

[0048] Further aspects of the invention are explained below with reference to the accompanying drawings. These show: Fig. 1 a schematic section of a cross-sectional view of a magnetorheological brake, Fig. 2 a schematic partial view of the gap between rotor and stator, Fig. 3 a comparison of torque curves on a rotor of a magnetorheological brake, Fig. 4 microscopic images of the powder in the gap, Fig. 5 different predetermined patterns, Fig. 6. an effect of a line contour, and Fig. 7. An effect of a cross contour.

[0049] The drawings are purely schematic and serve only to illustrate the invention. The same elements are identified by the same reference numerals.

[0050] Fig. Figure 1 shows an example of a schematic section of a cross-sectional view of a magnetorheological brake.

[0051] A magnetorheological brake 1 is shown, comprising a stator 2 and a rotor 3, which is rotatably arranged relative to the stator 2. A gap 4 is formed between the stator 2 and the rotor 3, in which a magnetorheological powder (not shown) is contained. In the illustration shown, the rotor 2 is rotatably arranged about a horizontal axis A.

[0052] In the brake 1 shown, opposing surfaces 6, 7 of the rotor 3 and the stator 2, which radially define the gap 4 and flank it circumferentially, are designed to have a structure. This structure is designed to increase the friction between the powder in the gap 4 and the surfaces 6, 7, so that a boundary layer of powder forms on the surfaces 6, 7 and adheres to these surfaces.

[0053] In this way, shearing of the powder in the gap during rotation of the rotor 3 about axis A can occur within the powder itself and not between the powder and the surface 6 of the rotor 2 or the surface 7 of the stator 2. This reduces the NVH behavior and, in particular, the torque fluctuations acting on the rotor 2. The stick-slip behavior is especially improved because now identical materials slide against each other – the powder particles or particle chains formed within the powder – and the material of the stator 2 and rotor 3 is not involved in the friction or relative movement between the stator 2 or rotor 3 and the powder particles in contact with their surfaces 6 and 7.

[0054] Fig. Figure 2 shows an example of a schematic partial view of the gap between rotor and stator.

[0055] A section of a stator 2 is shown, which is arranged opposite a rotor 3. The surfaces 6, 7 of rotor 3 and stator 2, which are opposite each other here and flank the gap 4, have a structure in the form of depressions. When the rotor 3 rotates about an axis (not shown), surface 6 moves past surface 7 in the direction of rotation R.

[0056] In slot 4, magnetorheological powder 5 is provided, the particles of which are represented here by a multitude of circles. The recesses of the structure on surfaces 6, 7 are sized to accommodate a specific number of particles. These particles are then located in the recesses, which in this example extend transversely to the direction of rotation R (i.e., perpendicular to the plane of the drawing). Due to the partitions of stator and rotor material, which delimit the recesses to the left and right in the drawing, the powder particles in the recesses cannot be displaced by shear forces relative to stator 2 and rotor 3. The recesses thus act as pockets that hold the powder particles relative to stator 2 and rotor 3.

[0057] Furthermore, it becomes clear that the recesses in the structure, which are filled with the powder particles, lead to a reduction in the friction points between powder 5 and the respective surfaces 6, 7, since only those areas of surfaces 6, 7 come into contact with the powder 5 where material from stator 2 and rotor 3 extends to the gap 4. Two of these areas are circled as examples.

[0058] At the same time, these areas surrounded by circles lead to an increase in turbulence in the powder 5 and thus to increased dynamics in the powder 5, which shifts the friction point or the point where shearing occurs in the powder 5 away from the surfaces 6, 7 and more towards the center of the gap 4.

[0059] Fig. Figure 3 shows an example comparison of torque curves on a rotor of a magnetorheological brake.

[0060] The torque profiles on the rotor over time are compared between a state-of-the-art magnetorheological brake (top, i.e., without a structure on the stator and rotor surfaces) and an otherwise identical magnetorheological brake in which a structure was created on the stator and rotor surfaces by roughening through shot peening (bottom). This is therefore an undirected structure.

[0061] The scale of both graphs is the same, therefore the moment curves are comparable. Looking at the amplitude of the vibration in the depicted curves, a reduction in amplitude from 355 mNm to 275 mNm, and thus a reduction of 23%, can be observed. This corresponds to a significant improvement in NVH behavior.

[0062] Fig. Figure 4 shows exemplary microscopic images of the powder in the gap at the in Fig. 3 embodiments shown.

[0063] The image above shows the situation according to the state of the art, i.e., without any structure on the respective surfaces of rotor 3 and stator 2. Stator 2 is shown on the left, and rotor 3 on the right. Both flank a gap 4, which is filled with magnetorheological powder 5. Here, friction or shearing of the powder particles or powder chains relative to the surfaces of rotor 3 and stator 2 takes place. In the circled area, a slanted arrangement of the particle chains within the powder 5 is clearly visible. This means that the particle chains remain intact here and do not shear against each other or detach from one another, since the friction or adhesion between the particles is higher than the friction between the powder particles and the respective surfaces of rotor 3 or stator 2. Thus, a friction point forms there, i.e., on the surfaces of rotor 3 and stator 2. The friction point between stator 2 or rotor 3 and powder 5 leads to the [missing information - likely a specific phenomenon or phenomenon]. Fig. 3 unwanted moment vibrations due to stick-slip effects at the friction points.

[0064] The image below shows, under a microscope, the effect of surface roughening by shot peening. No particle chains are visible in the circled area. Instead, a homogeneous pattern of powder particles is seen. This is because the roughening has increased the static friction between powder 5 and rotor 3 or stator 2, exceeding the frictional forces within powder 5. Consequently, the point of friction shifts into the circled area, i.e., into powder 5. The friction between the powder particles is significantly more uniform, resulting in a reduction of the amplitude in Fig. 3 below results.

[0065] Fig. Figure 5 shows examples of different predetermined patterns for generating a structure.

[0066] Shown are different predetermined patterns 10, 20, 30, 40, 50, which are depicted on a corresponding surface 6, 7 for illustrative purposes. The circumferential direction or the direction of rotation is a perpendicular direction here.

[0067] Pattern 10 has parallel grooves that run perpendicular to the direction of rotation.

[0068] Pattern 20 features elliptical grooves arranged one above the other.

[0069] Pattern 30 has two groups of parallel grooves arranged perpendicular to the direction of rotation and to each other (cross contour).

[0070] Pattern 40 has dot-shaped depressions.

[0071] Pattern 50 has parallel grooves arranged perpendicular to the direction of rotation.

[0072] The Fig. 6 and Fig. Figure 7 shows an example of the effect of a line contour (pattern 10 in Fig. 6) and a cross contour (pattern 30 in Fig. 7) at an angle of 135°. Both structures were created using a laser, as described above.

[0073] The two images above each show an enlarged view of the created structure at its highest point (left) and lowest point (right). Below is a snapshot of column 4 containing powder 5.

[0074] In both cases, it can be seen that the created structure causes a shift of the friction point into the powder 5 (circled area in the lower illustration).

[0075] The dimensions of the structure in Fig. The distance between the depressions is 40 µm from the original surface level to the top of the elevation and 30 µm from the original surface level to the bottom of the depression. The wall between the depressions is 15 µm wide. The width of the depressions is 50 µm at the top and 30 µm at the bottom.

[0076] The dimensions of the structure in Fig. The distance from the original surface level to the top of the raised area is 40 µm, and the distance from the original surface level to the bottom of the depression is 25 µm. The total depth at an intersection point is 140 µm. The wall between the depressions has a thickness of 80 µm. The width of the depressions is 50 µm at the top and 80 µm at the bottom.

[0077] The above described Fig. 1 and Fig. Figure 2 shows embodiments in which both the surface 6 of the rotor 3 and the surface 7 of the stator 2 have a structure. However, this should not be understood as limiting the invention. Instead, embodiments are also conceivable in which only one of the surfaces 6, 7 is provided with a structure. This can be advantageous, for example, if only one of the surfaces 6, 7, without a structure, would tend to result in friction, i.e., relative movement between powder 5 and the corresponding surface 6, 7. Thus, in such cases, it may be sufficient to provide only one of the surfaces 6, 7 with a structure to improve the NVH behavior. Fig.Figures 3 to 7 show the effects when both the rotor 3 and the stator 2 are provided with a corresponding structure. Further embodiments are also conceivable in which only the rotor surface or only the stator surface has a corresponding structure. Reference symbol list 1. Brake / magnetorheological brake 2 Stator 3 Rotor 4 columns 5 powders / magnetorheological powder 6 Surface 7 Surface 8 predetermined patterns Axis R direction of rotation

Claims

[1] Magnetorheological brake (1) comprising: a stator (2), a rotor (3) which is arranged to rotate relative to the stator (2), a gap (4) between the rotor (3) and the stator (2), and a magnetorheological powder (5) located in the gap (4) between the rotor (3) and the stator (2), wherein at least one of the opposing surfaces (6, 7) of the rotor (3) and the stator (2) that define the gap (4) has a structure. [2] Brake (1) according to claim 1, wherein the structure has irregularities in the µm range. [3] Brake (1) according to any of the preceding claims, wherein the structure is non-directional or directional. [4] Brake (1) according to claim 3, wherein the directed structure is formed by introducing / applying predetermined patterns. [5] Brake (1) according to one of the preceding claims, wherein the structure is produced / manufactured mechanically and / or thermally and / or chemically. [6] Brake (1) according to one of the preceding claims, wherein the surfaces of the rotor (3) and / or the stator (2) have a roughened structure. [7] Brake (1) according to one of the preceding claims, wherein the structure has recesses having a width that corresponds to approximately two to six times the particle diameter of the magnetorheological powder (5). [8] Force feedback actuator for a steering system of a vehicle, comprising: a drive unit, a magnetorheological brake (1) according to any one of claims 1 to 7, and a mechanical interface. [9] Steering device for a vehicle comprising: a steering element, and a force feedback actuator according to claim 8, the steering element is coupled to the mechanical interface in a rotationally fixed manner. [10] Method for manufacturing a magnetorheological brake, in particular a magnetorheological brake (1) according to any one of claims 1 to 7, comprising the following steps: Providing a rotor (3) and a stator (2), Creating a structure on at least one of opposing surfaces (6, 7) of the rotor (3) and the stator (2) that defines the gap (4).

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