Magnetorheological brake

Abstract

The invention relates to a magnetorheological brake (1) which has a stator (2), a rotor (3), which is rotatably arranged relative to the stator (2), a gap (4) between the rotor (3) and the stator (2), which gap is delimited by a stator surface (2.1) and a rotor surface (3.1), and a magnetorheological powder (5), which has powder particles and which is located in the gap (4) between the rotor (3) and the stator (2), wherein the powder particles of the powder (5) have first powder particles (5.1) and second powder particles (5.2), and the first powder particles (5.1) have a grain size which lies below a first grain size limit value, and the second powder particles (5.2) have a grain size which lies above a second grain size limit value, and the first grain size limit value and the second grain size limit value are matched to one another such that, in the case of a magnetic field (6) passing through the gap (4), at least one contact force arises at a contact point (7) between two powder particles, which contact force is lower than at least one contact force between a powder particle and the stator surface (2.1) or a contact force between a powder particle and the rotor surface (3.1). The invention further relates to the use of a magnetorheological brake (1) for an operating element, to a force feedback actuator (8), to a steering device (12), and to a method.

Description

[0001] Magnetorheological brake

[0002] The present invention relates to a magnetorheological brake, a use of a magnetorheological brake, a force feedback actuator, a steering device and a method for manufacturing a magnetorheological brake.

[0003] State of the art

[0004] Magnetorheological brakes are known today. These brakes feature a rotor that is rotatable around an axis relative to a stator. A circumferential gap between the rotor and stator contains a magnetorheological powder (hereinafter referred to as 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 inducing a braking effect on the rotor. The shear or friction properties are essentially determined by chains of powder particles that are formed by the magnetic field generated through the gap, causing the powder particles to adhere to one another.

[0005] 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. This then results, for example, in an undesirable relative movement and thus frictional movement between the powder particles in direct contact with the respective surface and that surface.As a result, frictional vibrations can occur due to a stick-slip effect between the powder and the corresponding surfaces.

[0006] Based on this, there is a need to improve such a magnetorheological brake. Against this background, it is an object of the present invention to provide a magnetorheological brake which in particular exhibits improved NVH behavior.

[0007] Disclosure of the invention

[0008] 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, the following description, and the drawings.

[0009] The magnetorheological brake according to the invention comprises a stator and a rotor, the latter being rotatably arranged relative to the stator. Furthermore, the magnetorheological brake has a gap between the rotor and the stator, which is bounded by a stator surface and a rotor surface. The magnetorheological brake includes a magnetorheological powder, comprising powder particles, which is located in the gap between the rotor and the stator.

[0010] The powder particles are classified as first and second particles. The first particles have a grain size below a defined first grain size limit. The second particles have a grain size above a defined second grain size limit. The first and second grain size limits are coordinated such that, when a magnetic field passes through the gap, at least one contact force is generated at a contact point between two powder particles that is lower than at least one contact force between a powder particle and the stator surface or between a powder particle and the rotor surface.

[0011] If the contact force between the two powder particles is lower than the contact force between a powder particle and the stator surface and the contact force between a powder particle and the rotor surface, the friction point reliably forms in the powder.

[0012] The rotor is designed to rotate about an axis. Radially relative to the axis, the gap is bounded by the stator surface and the rotor surface. The rotor surface can be located radially inside, and the stator surface radially outside. This means that, in this case, the rotor is located within the stator, at least in the section of the rotor surface that defines the gap.

[0013] The particle sizes and particle size limits mentioned above can be understood as the mean diameter of each powder particle. For example, the mean diameter can be determined by considering a projection of a powder particle onto a plane, taking into account at least two straight lines extending from the edge of the projection that divide the projection into two halves of equal area and intersect. The mean diameter is then the average of the lengths of these lines. If the powder particles are spherical, the mean diameter can be determined as the diameter of the respective spherical shape.

[0014] When the rotor rotates, the rotor surface moves relative to the stator surface.

[0015] The brake is designed to generate the magnetic field that penetrates the gap. The brake can be designed to regulate the magnetic field. At a minimum, the brake can be designed to adjust the braking effect, to activate and deactivate the magnetic field. Preferably, the brake can be designed to adjust the braking effect by setting the magnetic field strength between at least two values.

[0016] The contact forces between the powder particles themselves and the contact forces between powder particles and the stator surface, or the contact forces between powder particles and the rotor surface, are essentially generated by the magnetic flux of the magnetic field that passes through the gap and thus also through the stator, the rotor and the powder particles.

[0017] The magnetic field and the resulting contact forces between the rotor surface, the powder particles, and the stator surface cause chains of powder particles to form between the rotor and stator surfaces. By appropriately selecting the particle sizes, specifically the first and second particle size limits of the powder particles, it is possible to form chains in which the contact forces between individual particles are lower than the contact forces between the powder particles of the corresponding chain and the rotor surface, and / or between the corresponding chain and the stator surface. These chains, which form essentially perpendicular to the gap between the rotor and stator surfaces, experience a transverse force due to the rotation of the rotor.If this transverse force exceeds a frictional force between two powder particles of the chain, which is formed by the contact force between these powder particles, these powder particles slide against each other and a friction point is formed at this point.

[0018] The advantage of the solution according to the invention lies particularly in the fact that the lower contact forces between the powder particles mean that the friction point does not form on the rotor surface and / or the stator surface, but instead between individual powder particles, i.e., within the powder itself. As a result, no relative movement occurs between powder particles in contact with the rotor surface and the rotor surface, and / or between powder particles in contact with the stator surface and the stator surface. The friction point for generating the braking effect of the magnetorheological brake can thus be reliably formed within the powder itself by appropriately shaping the powder.

[0019] The powder itself can contain powder particles of different sizes, which are distributed, particularly stochastically, in the gap or which are distributed, particularly stochastically, in the gap.

[0020] The friction point in the powder can then form stochastically in the gap, depending on where the powder particles of the formed chains separate from each other.

[0021] The first powder particles can have a maximum particle size corresponding to that of the first particle size limit. The term "below the first particle size limit" should therefore be understood to mean that the first powder particles can also have, or can exclusively have, particle sizes corresponding to the first particle size limit. Mathematically, this is represented by a "<" expression.

[0022] The second set of powder particles can have a minimum particle size corresponding to that of the second particle size limit. The term "above the second particle size limit" is thus to be understood as meaning that the second set of powder particles can also have, or exclusively have, particle sizes corresponding to the second particle size limit. Mathematically, this is understood as a ">" expression. According to one embodiment, the first particle size limit is smaller than the second particle size limit. Therefore, the powder containing the first set of powder particles has small particles, as they are below and / or equal to the first particle size limit. Simultaneously, the powder containing the second set of powder particles has large particles, as they are above and / or equal to the second particle size limit.The varying sizes of the powder particles result in a magnetic flux that differs from contact point to contact point within a chain of powder particles. The first and second particle size limits are preferably matched such that the contact force between two small powder particles due to the magnetic flux at their contact point is lower than the contact force between the powder particles and the rotor and / or stator surface. This ensures that the probability of the chain breaking at a contact point between the corresponding powder particles is greater than the probability of a powder particle detaching from the stator and / or rotor surface. Consequently, the friction point forms within the powder, or at least away from the stator and / or rotor surface.

[0023] The small first powder particles are well suited for realizing this effect, since they become saturated with magnetic flux more quickly than the large second powder particles when the magnetic field is applied, so that the contact force between the small first powder particles cannot be increased to the same extent as between the large second powder particles.

[0024] According to one embodiment, the magnetorheological powder can also consist exclusively of powder particles whose particle size is below and / or equal to the first particle size limit and above and / or equal to the second particle size limit. In this case, the powder contains only the first and second powder particles. This increases the probability that chains of small and large powder particles will form, resulting in the required differential magnetic flux at the contact points within the chain.

[0025] According to one embodiment, the second particle size limit is at least 3 times, preferably 5 times, and particularly preferably 20 times, larger than the first particle size limit. It has been shown that magnetorheological brakes with a magnetorheological powder exhibiting this criterion show a stochastically reliable distribution of the friction point within the powder, i.e., a distance from the stator surface and / or the rotor surface, which is suitable, for example, for use with haptic control elements (e.g., joysticks, rotary knobs, force-feedback actuators, or steering devices). For example, the first particle size limit can be 1 pm, and the second particle size limit can thus be 20 pm. This means that the powder contains powder particles with a particle size of 1 pm or less and powder particles with a particle size of 20 pm or more.

[0026] According to further embodiments, the probability of the friction point forming can be increased further by increasing the factor. For example, the factor can be 30, 40, 50, 60, or 70.

[0027] According to one embodiment, the first particle size limit can be 1 pm. In this case, the first powder particles can have a particle size of 1 pm and / or less. The effect of friction point displacement into the powder can then be influenced by selecting the second particle size limit, for example, by choosing it according to the factors described above.

[0028] According to one embodiment, the second particle size limit can be 70 pm. In this case, the second powder particles can have a particle size of 70 pm and / or larger. The effect of friction point displacement into the powder can then be influenced by the choice of the first particle size limit, for example, by selecting it according to the factors described above.

[0029] According to one embodiment, the first particle size limit is 1 pm and the second particle size limit is 70 pm. In this case, the first powder particles can have a particle size of 1 pm and / or less. The second powder particles can have a particle size of 70 pm and / or more. With this choice of particle size limits, the particle sizes of the second powder particles are at least 70 times larger than those of the first powder particles. With this powder composition, an improvement in the reliable formation of the friction point within the powder has been observed, particularly for brake applications in haptic control elements (e.g., joysticks, rotary knobs, force feedback actuators, or steering devices). A powder with a combination of first and second particle size limits that are widely separated, e.g.,A particle size limit of 20 or more can be achieved by mixing different magnetorheological powders into a single powder. This makes it possible to adjust the particle size limits independently of the powder's manufacturing process. The powder described above, with a first particle size limit of 1 pm and a second particle size limit of 70 pm, can be produced in this way.

[0030] Magnetorheological powders with particle sizes of 1 pm and less, up to approximately 3 pm, can be produced by chemical processes such as precipitation processes, for example, the carbonyl iron process. This method allows for the production of comparatively small powder particles. Magnetorheological powders with particle sizes greater than 10 pm, particularly approximately 30 pm to 70 pm or more, can be produced, for example, by spraying processes in which the powder particles harden after being sprayed with a starting material. Both types of powder can be mixed and, if necessary, selectively treated, for example, by sieving, to produce the desired powder.

[0031] According to one embodiment, the powder particles, in particular the first powder particles, have a minimum particle size. This is primarily due to technical reasons. It can be 0.5 pm or 10% of the first particle size limit.

[0032] According to one embodiment, the minimum particle size of the powder particles, in particular the first powder particles, can also correspond to the first particle size limit. This means that in this case, the smallest powder particles in the powder are those that correspond to the first particle size limit. The powder then contains no smaller powder particles.

[0033] The technical lower limit for the minimum particle size of the powder particles essentially results from the necessary sealing of the gap, according to which the powder particles must have a minimum particle size in order not to overcome any sealing points.

[0034] According to one embodiment, the powder particles, particularly the secondary powder particles, have a maximum particle size. This is primarily determined by technical factors; for example, powder particles from spraying processes are larger than particles from chemical processes, such as precipitation processes, e.g., the carbonyl iron process. The maximum particle size can be 20 µm or 200% of the secondary particle size limit. According to one embodiment, the powder was treated such that powder particles larger than the maximum particle size were removed by a selective process, such as sieving, after the powder was produced, in order to ensure compliance with the maximum particle size.

[0035] According to one embodiment, the maximum particle size of the powder particles, in particular the second powder particle, can also correspond to the second particle size limit. This means that in this case, the largest powder particles in the powder are those that correspond to the second particle size limit. The powder then contains no larger powder particles.

[0036] The technical upper limit for the maximum particle size of the powder is essentially determined by the required flowability of the powder in the gap. If the powder particles, especially the secondary powder particles, are too large, they can tilt against each other, which can generate an undesirable additional moment on the rotor, thus worsening the NVH (noise, vibration, and harshness) performance.

[0037] According to one embodiment, the first powder particles make up 30-70% of the powder.

[0038] According to one embodiment, the second powder particles comprise 30-70% of the powder.

[0039] According to one embodiment, the first powder particles comprise 30-70% of the powder and the second powder particles comprise 70-30% of the powder.

[0040] According to one embodiment, the ratio of the number of first powder particles of the powder to the number of second powder particles of the powder is 1:2 to 2:1.

[0041] By selecting these proportions and / or the ratio of the number of first powder particles to the number of second powder particles, the powder's flowability during gap filling is improved, as described below. Furthermore, rotation of the rotor enhances the mixing of the powder particles within the gap. This ensures that powder particles of different grain sizes, particularly the first and second powder particles, are stochastically distributed within the gap. Consequently, contact points are created within the powder, the contact force of which allows the contact to break down due to the rotor's rotation.

[0042] According to one embodiment, the powder particles include third powder particles with one or more particle sizes that lie between the first and second particle size limits. This means that the powder can also contain particles with an intermediate particle size, i.e., a particle size between the first and second particle size limits. Especially when the powder contains these third powder particles, thorough mixing of the powder and thus a stochastic formation of the friction point within the powder is more likely, because the third powder particles, due to their particle size, can mix with the first and second powder particles, thus preventing, for example, clumping, i.e., a local accumulation of exclusively first powder particles.Such clumping counteracts the formation of friction points within the powder, because the resulting clump of small first powder particles can behave like a single large second powder particle. The magnetic flux between the clump then generates contact forces at the interface between the clump and a second large powder particle, forces equivalent to those between two second large powder particles. In this case, no contact point would form at this location where the contact force is sufficiently low for the resulting chain to break apart when the rotor rotates.

[0043] According to one embodiment, the third powder particles comprise 20-50% of the powder to improve mixing during rotor rotation. The proportions of the first and second powder particles are then reduced accordingly. For example, an equal distribution of first, second, and third powder particles is conceivable, each comprising one-third of the total powder. With a 20% proportion of the third powder particles, the first powder particles could, for instance, constitute a proportion of 20% to 60%, and the second powder particles a corresponding proportion of 60% to 20%. With a 50% proportion of the third powder particles, the first powder particles could, for example, constitute a proportion of 10% to 40%, and the second powder particles a corresponding proportion of 40% to 10%.

[0044] According to one embodiment, the ratio of the sum of the number of first powder particles of the powder and the number of second powder particles of the powder to the number of third powder particles of the powder is 1:1 to 2:1 in order to improve mixing when the rotor is rotated.

[0045] Another aspect of the invention relates to the use of a magnetorheological brake as described above for a control element. The control element can have a haptic interface designed for manual operation by a user. The interface is mechanically connected to the rotor of the magnetorheological brake, so that a braking effect on the rotor can also act on the interface and, in particular, can act haptically on the control element. For example, such a control element, especially the haptic interface, can be designed as a pivoting or rotatable element, wherein a rotary or pivoting movement applied by a user acts on the rotor of the magnetorheological brake and sets it in rotation.The brake can exert a braking effect on the rotor, whereby the braking effect, and thus the haptic feedback experienced by the user at the interface or control element, can be adjusted by appropriately setting and / or changing the magnetic field. Using such a brake for a control element allows for the desired braking effect to be set, and this can also be adapted to user requirements or design-specific needs by modifying the brake's control mechanism accordingly. The control element can be designed, in particular, as a joystick, rotary knob, or as a control element for a vehicle's steering system.

[0046] 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, a magnetorheological brake as described above, and a mechanical interface. The mechanical interface is designed for connection to an input element, thereby connecting the brake rotor and the drive unit to the input element. The mechanical interface can be configured as a rotatable shaft. The connection between the mechanical interface and the input element, the brake rotor, and / or the drive unit can be torque-transmitting.

[0047] The drive unit can be configured to apply a drive torque to the mechanical interface. In particular, the drive unit can be configured to apply the drive torque to the mechanical interface in a first or second direction of rotation, depending on the requirements. The drive unit can be designed as an electric drive motor configured to apply the drive torque to the mechanical interface.

[0048] The magnetorheological brake is designed to apply a corresponding braking torque to the mechanical interface. In this way, both a drive torque from the drive unit and a braking torque from the brake can be applied to the mechanical interface, which the user can feel haptically at the mechanical interface or at a connected control element. This makes it possible to represent a desired behavior of the force feedback actuator at the mechanical interface and thus perceptibly to the user.

[0049] Another aspect of the invention relates to a steering device for a vehicle. The steering device comprises an input element designed as a steering element and a force feedback actuator as described above. The input element is coupled to the mechanical interface. The input element can be designed as a steering wheel. In this way, it is possible to provide a user, in this case a vehicle driver, with haptic feedback on the steering element.

[0050] According to one embodiment, the steering system can be designed as a steer-by-wire system. In this configuration, the mechanical interface is not connected to the steered wheels of the vehicle. Haptic feedback about the current driving state of the steered wheels, for example, through a return torque at the input element, is not possible here due to the lack of a mechanical connection between the wheels and the input element. This can then be achieved by the integrated force-feedback actuator. In this way, eliminating the mechanical connection to the wheels results in a space saving.

[0051] However, it is also conceivable that the steering system is designed for mechanical coupling with the steered wheels of a vehicle. In this case, it is possible to supplement the haptic feedback, which is perceptible via the mechanical coupling with the steered wheels, with the drive torque of the drive unit and / or the braking torque of the magnetorheological brake, in order to adjust a desired steering feel.

[0052] Another aspect of the invention relates to a method. The method comprises the steps of providing a stator, providing a rotor rotatably arranged relative to the stator, and filling a gap located between the rotor and the stator, and bounded by a stator surface and a rotor surface, with a magnetorheological powder as described above.

[0053] According to one embodiment, a method is provided in which the gap is filled with the powder, which comprises powder particles, wherein the powder particles of the powder comprise first powder particles and second powder particles, and the first powder particles have a particle size that is below a first particle size limit, and the second powder particles have a particle size that is above a second particle size limit, and the first particle size limit and the second particle size limit are matched to each other such that, in the case of a magnetic field passing through the gap, at least one contact force is generated at a contact point between two powder particles which is less than at least one contact force between a powder particle and the stator surface or one contact force between a powder particle and the rotor surface.

[0054] The brake, in particular the rotor and stator, can be designed as described above.

[0055] Selecting powder particles of different grain sizes, as described above, has a positive effect on filling the gap, as the powder's flowability is improved by using particles of varying sizes. This reduces the likelihood of individual powder particles sticking together or becoming stuck, which could ultimately clog a filling tool such as a funnel. In particular, if the second grain size limit is larger, preferably by a factor of 3 to 20, and especially preferably by a factor of 3 to 5, than the first grain size limit, the powder particles' flowability is ensured.

[0056] According to one embodiment, the method is a method for manufacturing a magnetorheological brake, in that the provision of the stator and the provision of the rotor involve newly manufactured components.

[0057] According to one embodiment, the method is a method for retrofitting or improving an existing magnetorheological brake, in that the provision of the stator and the provision of the rotor involve components that were already installed in a magnetorheological brake. The method can then include a further step preceding the filling of the gap, in which magnetorheological powder that is not configured as described above is first removed, particularly from the gap. In this way, the NVH behavior of an existing magnetorheological brake can be improved by replacing the existing powder with a powder as described above.

[0058] A significant advantage of the invention, considering all aspects described above, is that a substantial improvement in the brake's NVH (noise, vibration, and harshness) behavior can be achieved simply by selecting the appropriate powder configuration. This means that no structural modifications to the brake are necessary to achieve this effect. The invention, particularly the replacement of the magnetorheological powder, thus represents a cost-effective measure for improving NVH performance.

[0059] Detailed description based on drawing

[0060] Further measures improving or clarifying the invention are described in more detail below, together with a description of an embodiment of the invention, with reference to the figures. The figures show:

[0061] Fig. 1 is a schematic sectional view of a magnetorheological brake according to an embodiment of the invention,

[0062] Fig. 2 shows a section of a microscope image of a magnetorheological powder used,

[0063] Fig. 3 shows a schematic representation of a single chain of powder particles in the gap, penetrated by a magnetic field.

[0064] Fig. 4 shows a schematic representation of the magnetic field passing through several powder particles in the gap,

[0065] Fig. 5 shows a progression of contact forces of individual powder particles in a chain,

[0066] Fig. 6 shows two torque curves of a brake with different powder configurations.

[0067] Fig. 7 shows a schematic representation of the distribution of different particle sizes for three different compositions of the powder according to three embodiments of the invention.

[0068] Fig. 8 shows a schematic representation of a force feedback actuator, and

[0069] Fig. 9 shows a schematic representation of a steering device for a vehicle. The figures are purely schematic and serve only to illustrate the invention. The same elements are labelled with the same reference numerals.

[0070] Fig. 1 shows a schematic and exemplary sectional view of a magnetorheological brake 1. A horizontal axis A, about which a rotor 3 is rotatably mounted, extends around this axis. A stator 2 is provided in the radial direction R, i.e., extending upwards from axis A in the drawing. The rotor 3 is rotatably mounted relative to the stator 2 about axis A. In the illustrated embodiment, both rotor 3 and stator 2 are essentially rotationally symmetrical about axis A. Therefore, for clarity, the rotor 3 and stator 2 are shown only above axis A, and only the portion of the stator 2 facing the rotor 3 is shown. Other parts of the brake 1 are also omitted for clarity.

[0071] The brake 1 further comprises a gap 4, which is provided between the stator 2 and the rotor 3. The gap 4 is bounded in the radial direction R by a rotor surface 3.1 and a stator surface 2.1. The rotor surface 3.1 and the stator surface 2.1 face each other. In the brake 1 shown, the rotor surface 3.1 is arranged radially on the inside, while the stator surface 2.1 is arranged radially on the outside. The gap 4 thus extends rotationally symmetrically about the axis A.

[0072] A magnetorheological powder 5 is provided in the gap 4. The brake 1 is designed to generate a magnetic field (not shown) that penetrates the gap 4. The magnetic flux, which also penetrates the powder particles of the powder 5, causes contact forces to form at the contact points of individual powder particles, causing the powder particles to adhere to one another. In this way, chains of powder particles form in the powder 5 between the stator surface 2.1 and the rotor surface 3.1, with the chains also forming contact forces with the stator surface 2.1 and the rotor surface 3.1 due to the magnetic flux.

[0073] In the illustrated embodiment, the powder particles of powder 5 comprise first powder particles and second powder particles, wherein the first powder particles have a particle size below a first particle size limit, and the second powder particles have a particle size above a second particle size limit. The first and second particle size limits are matched such that, when a magnetic field generated by the brake passes through the gap 4, at least one contact force is generated at a contact point between two powder particles that is less than at least one contact force between a powder particle and the stator surface 2.1 or one contact force between a powder particle and the rotor surface 3.1. In this way, it can be achieved that the formed chain breaks at the contact point formed by these two powder particles when the rotor 3 rotates.These two powder particles separate from each other here. In contrast, the powder particles in contact with the stator surface 2.1 or the rotor surface 3.1 adhere more strongly to the stator surface 2.1 or the rotor surface 3.1, respectively, and the probability of these particles detaching from the stator surface 2.1 or the rotor surface 3.1 is lower compared to the probability of the two powder particles separating. Thus, the friction point that forms when the rotor 3 rotates about axis A can be reliably formed stochastically for the respective application within the powder 5 and not between powder 5 and stator surface 2.1 or between powder 5 and rotor surface 3.1. This improves the NVH behavior of the brake 1.

[0074] Fig. 2 shows a section of a microscopic image of a magnetorheological powder used.

[0075] The powder 5 shown can be used in the gap 4 of the brake 1, as shown in Fig. 1.

[0076] The depicted powder 5 comprises first powder particles 5.1, which have a particle size below a first particle size limit. The depicted powder 5 comprises second powder particles 5.2, which have a particle size above a second particle size limit. For illustrative purposes, one first powder particle 5.1 and one second powder particle 5.2 are each labeled with a reference numeral.

[0077] Furthermore, the powder 5 here contains third powder particles 5.3, whose particle size lies between the first and second particle size limits. Although the third powder particles 5.3, due to their comparatively smaller difference in particle size, result in a contact force with a first powder particle 5.1 or with a second powder particle 5.2 that is greater than the contact force that would develop between first powder particles 5.1, the third powder particles 5.3 nevertheless lead to an improved or more reliable formation of the friction point within the powder 5, as they ensure better mixing of the powder particles in general, thus preventing clumping, i.e., a local accumulation of exclusively first powder particles 5.1. Such clumping counteracts the formation of the friction point within the powder 5, because the resulting clump of small first powder particles 5.1...1 may behave like a single large second powder particle 5.2, such that the magnetic flux between the clump causes contact forces at the contact point between the clump and a second large powder particle 5.2 that correspond to those between two second large powder particles 5.2. In this case, no contact point would form at this location where the contact force is sufficiently low for the formed chain to detach here when the rotor rotates.

[0078] In the illustration shown, the first powder particle 5.1 has a particle size of 3 pm, the second powder particle 5.2 has a particle size of 60 pm, and the third powder particle 5.3 has a particle size of 50 pm. The powder shown is configured such that the first particle size limit is 3 pm and the second particle size limit is 60 pm. This corresponds to a factor of 20 between the two particle size limits.

[0079] Fig. 3 shows a schematic representation of a single chain of powder particles in the gap, penetrated by a magnetic field.

[0080] The gap 4 can correspond to the gap 4 shown in Fig. 1.

[0081] The illustration shows, on the left, a section of a rotor 3 with a rotor surface 3.1 facing to the right. Opposite the rotor 3, on the right, is a section of a stator 2 with a stator surface 2.1 facing to the left. The radial direction R points to the right, so that the rotor surface 3.1 defines the inner radial boundary of the gap 4, and the stator surface 2.1 defines the outer radial boundary of the gap 4. The rotor 3 is rotatable relative to the stator 2 about an axis (not shown) oriented perpendicular to the plane of the drawing. Rotation of the rotor 3 results in movement of the rotor surface 3.1 in the direction of movement B shown. For the sake of clarity, the curvature of the rotor surface 3.1 and the stator surface 2.1 has been omitted.

[0082] The gap 4 is penetrated by a magnetic field 6 from the brake 1, the course of individual magnetic field lines 6.1 being shown, with only two magnetic field lines 6.1 being marked with reference symbols for clarity. The magnetic field 6 also penetrates the stator 2 and the rotor 3 in addition to the gap 4.

[0083] A chain of differently sized powder particles of the magnetorheological powder located in gap 4 is shown. The chain extends radially in the direction R from the rotor surface 3.1 to the stator surface 2.1 along the horizontal black line in gap 4. The chain includes, in particular, first powder particles 5.1, whose particle size is below a first particle size limit, and second powder particles 5.2, whose particle size is above a second particle size limit. Additionally, this chain also includes third powder particles 5.3, whose particle sizes lie between the first and second particle size limits.

[0084] For the sake of clarity, only a single chain of powder particles is shown here; further powder particles filling gap 4 are not shown. The powder particles of the chain touch at contact points 7, of which only two contact points 7 are labeled with reference symbols for clarity.

[0085] Below the diagram of gap 4 is a graph showing the magnetic flux density within the depicted chain of powder particles between rotor surface 3.1 and stator surface 2.1. The position along the chain between rotor surface 3.1 and stator surface 2.1 is plotted from left to right. The magnetic flux density is plotted upwards. Due to the different particle sizes of the powder particles, the magnetic flux density of the magnetic field varies considerably along the chain. It can be observed that a higher magnetic flux density develops in the smaller powder particles, for example, in the first powder particles 5.1, than in the larger powder particles, for example, in the second powder particles 5.2. The small first powder particles 5.1 therefore reach saturation with the magnetic flux relatively early.The flux density reaches a maximum value at the contact points 7 of the individual powder particles and then decreases again within a powder particle.

[0086] Due to the higher saturation of the smaller first powder particles 5.1, the formation of a contact force at their contact points 7 induced by the magnetic field 6 is limited compared to the larger second powder particles 5.2. Therefore, the formed chain has contact points 7 with varying contact forces, so that individual powder particles of the chain can break up or detach due to movement of the rotor surface 3.1 in the direction of motion B at points with comparatively low contact forces. Subsequently, a friction point forms within the powder in the gap 4 at this point. The more of these contact points 7 that can be detached by the rotor movement are present, the more reliably the friction point forms within the powder and the better the NVH behavior of the brake can be designed.

[0087] Fig. 4 shows a schematic representation of the magnetic field passing through several powder particles in the gap.

[0088] The chain of powder particles, already discussed above in connection with Fig. 3, extends in the gap 4 in the radial direction R from the rotor surface 3.1 to the stator surface 2.1 along the horizontal black line. In contrast to the representation in Fig. 3, further powder particles, also located in the gap 4, have been added here. It can be seen that the magnetic field lines 6.1 of the magnetic field 6 pass through different powder particles. This results in contact points 7 with different magnetic flux densities and thus also with different contact forces, which can cause a stochastic breaking of the formed chains, so that the friction point within the powder 5 develops.

[0089] The schematic representation of the powder 5 in the gap 4 further shows that the chains are not necessarily formed in the radial direction R. Rather, a different formation of the chains at an angle to the radial direction R is possible.

[0090] Fig. 5 shows a progression of contact forces of individual powder particles in a chain.

[0091] A schematic diagram shows the distribution of contact forces at individual contact points along a chain containing different powder particles, specifically small first powder particles and large second powder particles, as described above. The chain extends from the rotor surface to the stator surface. This could be, in particular, the rotor surfaces 3.1 and stator surfaces 2.1 shown in Fig. 1 or Fig. 3, respectively, within the resulting gap 4. The individual contact points are numbered from 1 to 15. It can be seen that some contact points exhibit comparatively low contact forces. These are, in particular, contact points 1, 8, 10-12, and 14. Chain breakage at these contact points is therefore more likely than breakage at contact points with higher contact forces, such as contact point 9, but also contact points 2-7, 13, or 15.

[0092] This schematic example therefore shows that random chain breakage is possible due to the different grain sizes used, so that the friction point can be shifted into the powder.

[0093] Fig. 6 shows two torque curves of a brake with different powder configurations.

[0094] The torque curves correspond to a braking torque of the brake 1, as shown, for example, in Fig. 1, where a constant and identical magnetic field was applied in both cases, passing through the gap 4. The braking torque is plotted against time and acts on the rotor 3.

[0095] The first powder configuration results in the braking torque curve shown in the dashed line. A magnetorheological powder was used, containing powder particles with grain sizes between 5 pm and 10 pm. No special particle size matching was performed with this powder, and in particular, no selection of first powder particles with a grain size below a first grain size limit or of second powder particles with a grain size above a second grain size limit was made. The powder used thus represents the state of the art. It can be seen that the generated braking torque fluctuates considerably between a maximum value of 6.8 Nm and a minimum value of 5.8 Nm. This is an undesirable characteristic of brake 1, as the torque fluctuations are particularly detrimental to the NVH (noise, vibration, and harshness) performance in haptic applications for which brake 1 is used.

[0096] In contrast, the NVH behavior can be improved with a magnetorheological powder whose powder particles have first and second powder particles, wherein the first powder particles have a grain size below a first grain size limit, and the second powder particles have a grain size above a second grain size limit, and the first and second grain size limits are matched such that, in a magnetic field passing through the gap 4, at least one contact force is generated at a contact point between two powder particles which is less than at least one contact force between a powder particle and the stator surface 2.1 and / or one contact force between a powder particle and the rotor surface 3.1.

[0097] Such a magnetorheological powder results in the torque profile shown in the diagram with the solid line. A powder with particle sizes ranging from 1 pm to 70 pm was used. It is evident that the torque fluctuation has decreased significantly. The braking torque now only fluctuates between a maximum value of 6.7 Nm and a minimum value of approximately 6.25 Nm. This more than halves the amplitude of the torque fluctuation and correspondingly improves the NVH (noise, vibration, and harshness) behavior of brake 1.

[0098] This suggests, in particular, that a magnetorheological brake already designed according to the state of the art can be significantly improved in its NVH behavior by replacing the magnetorheological powder with a magnetorheological powder as described above.

[0099] Fig. 7 shows a schematic representation of the distribution of different particle sizes for three different compositions of the powder according to three embodiments of the invention.

[0100] The horizontal axis represents the particle size, and the vertical axis represents the corresponding proportion of particle size to the respective powder composition. The individual distribution curves are not drawn to scale, so a comparison of individual sections at the same positions on the vertical axis is not possible. This figure is intended only to schematically illustrate embodiments of the invention.

[0101] As a reference, a particle size distribution 50 of a typical powder, corresponding to the prior art, is shown. The particle size distribution 50 has the form of a bell curve, which is essentially axially symmetrical around a maximum distribution value 50.3 of the most frequently occurring particle size. The maximum particle sizes 50.2 and the minimum particle sizes 50.1 of the powder are in a 2:1 ratio to each other. This means that the largest powder particles are twice as large as the smallest powder particles. The powder does not have a specific particle size distribution as defined by the invention. The particle size distribution 51, shown with a solid line according to an embodiment of the invention, shows two bell curves with the maximum distribution values ​​51.1 and 51.2 of the most frequently occurring particle sizes, with the bell curve containing the maximum distribution value 51.1 being the most frequently occurring.Figure 1 describes the distribution of first powder particles that lie below a first particle size limit of 60, and the bell curve with the maximum distribution value of 51. Figure 2 describes the distribution of second powder particles that lie above a second particle size limit of 70. It can be seen that between the particle size limits of 60 and 70, the particle size distribution 51 is zero. This means that such a powder can consist exclusively of first powder particles, which are small (i.e., below the first particle size limit of 60), and second powder particles, which are large (i.e., above the second particle size limit of 70).

[0102] Compared to particle size distribution 50, it becomes clear that particle size distribution 51 is significantly broader. The ratio of the maximum particle size 51.4 of the powder to the minimum particle size 51.3 of the powder can be at least 5:1, and in particular 20:1. This means that the largest powder particles are five times, and in particular twenty times, larger than the smallest powder particles.

[0103] The particle size distribution 52, shown with a dashed line according to one embodiment of the invention, shows three connected bell curves with the maximum distribution values ​​52.1, 52.2, and 52.3 of the most frequently occurring particle sizes. The bell curve with the maximum distribution value 52.1 describes the distribution of first powder particles that are below the first particle size limit 60, and the bell curve with the maximum distribution value 52.2 describes the distribution of second powder particles that are above the second particle size limit 70. It can be seen that the third bell curve with the maximum distribution value 52.3 lies between the particle size limits 60 and 70. This means that such a powder contains, in addition to the first powder particles, which are small (i.e., below the first particle size limit 60), and second powder particles, which are large (i.e., above the second particle size limit 70).The second particle size limit is 70, and the third powder particles may have a particle size between the particle size limits of 60 and 70.

[0104] Compared to particle size distribution 51, it becomes clear that there is a continuous distribution of particle sizes between the maximum particle size 52.5 and the minimum particle size 52.4. The ratio of the maximum particle size 52.5 to the minimum particle size 52.4 of the powder can be at least 5:1, and in particular 20:1. This means that the largest powder particles are five times, and in particular twenty times, larger than the smallest powder particles.

[0105] The particle size limits 60, 70 can in particular have a ratio of 3:1.

[0106] The particle size distribution 53, shown with a dashed line according to one embodiment of the invention, exhibits a continuous distribution curve. In contrast to the particle size distributions 51 and 52, this curve shows a curve where the edges on the left and right slope down relatively sharply. This means that this particle size distribution 53 has a maximum particle size 53.2 and a minimum particle size 53.1, which were produced by selective processes such as sieving and / or mixing desired powder particles of corresponding particle sizes.

[0107] In the example shown here, the grain size distribution 53 is narrower than the grain size distributions 51, 52, i.e., the ratio of the maximum grain size 53.2 to the minimum grain size 53.1 may be less than 5:1, e.g. 4:1 or 3:1 (not shown).

[0108] It is nevertheless evident that here too, there are first powder particles that fall below the first particle size limit of 60, and second powder particles that fall above the second particle size limit of 70. That is, here too, there is a proportion of first, i.e., smaller, powder particles and a proportion of second, i.e., larger, powder particles. It can be seen that this particle size distribution 53 has a comparatively large number of third powder particles whose particle size lies between the first particle size limit of 60 and the second particle size limit of 70, since the particle size distribution 53 reaches its maximum here and forms a convex shape with the horizontal axis.

[0109] The powder, corresponding to particle size distribution 51, exhibits a sharp and distinct separation between first and second powder particles, as no third powder particles are present. This ensures that corresponding differences in magnetic flux develop between the powder particles.

[0110] In comparison, the powders corresponding to particle size distributions 52 and 53 also contain third powder particles whose particle sizes lie between those of the first and second powder particles. This leads to better mixing of the powder particles and reduces or eliminates the tendency of the powder, especially the first powder particles, to clump.

[0111] Unlike powders with particle size distributions 51 and 52, powder with particle size distribution 53 exhibits a sharp boundary between the smallest and largest powder particles, as indicated by the minimum particle size 53.1 and the maximum particle size 53.2. This has the advantage that no other powder particles are present in this powder. The particle sizes of the powder can thus be tailored to specific requirements or the desired effect. Furthermore, such boundaries are conceivable for any particle size distribution, and particularly for particle size distributions 51 and 52. It is also conceivable that the powder could have only such a minimum or maximum particle size. A minimum particle size could, for example, be chosen to prevent excessively small powder particles that would cause problems with the brake seal.This prevents issues that would lead to powder leakage from the brake gap. In particular, the sealing of the brake gap can be designed to be less complex. For example, a maximum particle size can be selected to prevent the powder particles from becoming wedged together due to differing particle sizes. This applies to both the operation of the brake, i.e., the powder in the brake gap, and the filling process, where the powder is poured into the gap and should ideally be free-flowing.

[0112] The powder configurations corresponding to the particle size distributions 51, 52 and 53 can be used in particular in the brake 1, as shown in Fig. 1.

[0113] Fig. 8 shows a schematic representation of a force feedback actuator, according to a further aspect of the invention.

[0114] The force feedback actuator 8 shown has a magnetorheological brake 1, which can be designed like the brake 1 from Fig. 1. The force feedback actuator 8 also has a drive unit 9. The drive unit 9 can be designed as an electric motor or include an electric motor.

[0115] The force feedback actuator 8 has a mechanical interface 10 that extends vertically in the drawing and is designed as a shaft. The shaft is rotatable about the vertically extending axis A and is oriented coaxially to the axis A. The mechanical interface 10 is designed to be connected to an input element. This could be, for example, a joystick, a rotary knob, or a steering element such as a steering wheel. The input element can be connected to the mechanical interface 10, for example, at its upper free end.

[0116] Brake 1 and drive unit 9 are connected to the mechanical interface 10.

[0117] For example, the mechanical interface 10 may extend through the rotor 3 of the brake 1, so that the rotor 3 can apply a braking torque generated by the brake 1 to the mechanical interface 10. The drive unit 9 is configured to apply a drive torque to the mechanical interface 10. The drive unit 9 may preferably be configured to apply the drive torque to the mechanical interface 10 in both directions of rotation.

[0118] to raise 10.

[0119] By appropriately controlling the brake 1 and the drive unit 9, e.g. by a control unit (not shown) of the force feedback actuator 8, haptic feedback can be generated which is perceptible to a user at the mechanical interface 10 or at an input element coupled to it in a torque-transmitting manner.

[0120] Fig. 9 shows a schematic representation of a steering device for a vehicle, according to a further aspect of the invention.

[0121] As part of the steering system 12, the force feedback actuator 8 shown above in Fig. 8 is shown here, which is enclosed by a dashed box. For its description, please refer to the description of Fig. 8.

[0122] The mechanical interface 10 is used here as a torque-transmitting input element.

[0123] 11 is coupled, which here is designed as a steering element, e.g. as a steering wheel. A user can thus receive haptic feedback directly via the steering element, which is applied to the mechanical interface 10 in the form of a braking torque from the brake 1 and / or in the form of a drive torque from the drive unit 9 of the force feedback actuator 8.

[0124] The steering device 12 shown can be designed as a steer-by-wire steering device.

[0125] In this embodiment of the steering device 12, the mechanical interface 10 is not connected to or designed for such a connection with the steered wheels of a vehicle. Haptic feedback regarding the current driving state of the steered wheels, e.g., through a restoring torque at the input element 11, is not possible here due to the lack of a mechanical connection between the wheels and the steering element. This can instead be achieved by the integrated force feedback actuator 8, by controlling the drive unit 9 and / or the brake 1 accordingly, e.g., by a control unit (not shown) of the force feedback actuator 8. In this way, eliminating the mechanical connection to the wheels results in a space-saving advantage for the steering device 12 and / or the vehicle. However, it is also conceivable that the steering device 12 could be designed for mechanical coupling with the steered wheels of a vehicle.In this case, it is possible to supplement the haptic feedback, which is perceptible via the mechanical coupling with the steered wheels, by the drive torque of the drive unit 9 and / or by the braking torque of the magnetorheological brake 1, by controlling the drive unit 9 and / or the brake 1, e.g. by a control unit (not shown) of the Force-.

[0126] Feedback actuator 8 can be controlled accordingly in order to adjust the desired steering feel.

[0127] Reference symbol list

[0128] 1 (magnetorheological) brake

[0129] 2 Stator

[0130] 2.1 Stator surface

[0131] 3 Rotor

[0132] 3.1 Rotor surface

[0133] 4 columns

[0134] 5 (magnetorheological) powder

[0135] 5.1 First powder particles

[0136] 5.2 second powder particles

[0137] 5.3 third powder particles

[0138] 6 Magnetic field

[0139] 6.1 Magnetic field line

[0140] 7 Contact point

[0141] 8 Force feedback actuator

[0142] 9 Drive unit

[0143] 10 mechanical interface

[0144] 11 Input element

[0145] 12 Steering device

[0146] 50 grain size distribution

[0147] 50.1 Minimum grain size

[0148] 50.2 Maximum grain size

[0149] 50.3 Maximum distribution value

[0150] 51 Grain size distribution

[0151] 51.1 Maximum distribution value

[0152] 51.2 Maximum distribution value

[0153] 51.3 Minimum grain size

[0154] 51.4 Maximum grain size

[0155] 52 Grain size distribution

[0156] 52.1 Maximum distribution value

[0157] 52.2 Maximum distribution value

[0158] 52.3 Maximum distribution value

[0159] 52.4 Minimum grain size

[0160] 52.5 Maximum grain size

[0161] 53 Grain size distribution

[0162] 53.1 Minimum grain size 53.2 Maximum grain size

[0163] 60 first grain size limit

[0164] 70 second grain size limit

[0165] Axis A B Direction of movement

[0166] R Radial direction

Claims

Claims 1. Magnetorheological brake (1) comprising: a stator (2), a rotor (3) rotatably arranged relative to the stator (2), a gap (4) between the rotor (3) and the stator (2) bounded by a stator surface (2.1) and a rotor surface (3.1), and a magnetorheological powder (5) comprising powder particles and located in the gap (4) between the rotor (3) and the stator (2), wherein the powder particles of the powder (5) comprise first powder particles (5.1) and second powder particles (5.2), and the first powder particles (5.1) have a particle size below a first particle size limit, and the second powder particles (5.2) have a particle size that is above a second particle size limit and the first particle size limit and the second particle size limit are coordinated such that, in the case of a magnetic field (6) passing through the gap (4), at least one contact force is generated at a contact point (7) between two powder particles which is less than at least one contact force between a powder particle and the stator surface (2.1) or one contact force between a powder particle and the rotor surface (3.1).

2. Brake (1) according to claim 1, wherein the first particle size limit is smaller than the second particle size limit.

3. Brake (1) according to one of the preceding claims, wherein the first particle size limit is 1 pm and / or wherein the second particle size limit is 70 pm.

4. Brake (1) according to one of the preceding claims, wherein the first powder particles (5.1) comprise 30-70% of the powder (5) and / or wherein the second powder particles (5.2) comprise 30-70% of the powder (5).

5. Brake (1) according to one of the preceding claims, wherein the powder particles of the powder (5) comprise third powder particles (5.3) having one or more particle sizes that lie between the first particle size limit and the second particle size limit.

6. Brake (1) according to claim 5, wherein the third powder particles (5.3) constitute 20-50% of the powder (5).

7. Use of a magnetorheological brake (1) according to any one of claims 1 to 6 for a control element.

8. Force feedback actuator (8), in particular for a steering device of a vehicle, comprising: a drive unit (9), a magnetorheological brake (1) according to one of claims 1 to 6, and a mechanical interface (10) designed for connection with an input element (11), whereby the rotor (3) of the brake (1) and the drive unit (9) can be connected to the input element (11).

9. Steering device (12) for a vehicle, comprising: an input element (11) designed as a steering element, and a force feedback actuator (8) according to claim 8, wherein the input element (11) is coupled to the mechanical interface (10).

10. The procedure comprises the following steps: Providing a stator (2), Providing a rotor (3) rotatably arranged relative to the stator (2), filling a gap (4) located between the rotor (3) and the stator (2) and bounded by a stator surface (2.1) and a rotor surface (3.1), with a magnetorheological powder (5) according to any one of claims 1 to 6.

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