Method for controlling a magnetorheological brake, operating unit, computer program product and steer-by-wire system

Abstract

The invention relates to a method for controlling a magnetorheological brake (6) for an operating unit (1), in particular for influencing a driving direction of a motor vehicle (2) by a user, wherein the operating unit (1) has a rotatably mounted steering shaft (3), which is couplable to a steering means (4), and a magnetorheological brake (6), which is likewise torque-transmittingly connected to the steering shaft (3), and a control unit (7) for controlling the operating unit (1), comprising the steps of: ascertaining, by means of an inductance detection module (42), an actual parameter (41) representing the inductance (40) of the magnetorheological brake (6); feeding the actual parameter (41) into an averaging module (43) for determining an inductance mean value (44); using the inductance average (44) in a target current influencing module (45) for adapting a target current (46) for energising the magnetorheological brake (6) in order to provide a resistance torque (47) on the steering shaft (3).

Description

[0001] P241645

[0002] - 1 - Method for controlling a mechanical brake, control unit, computer program product and steer-by-wire system

[0003] The present invention relates to a method for controlling a magnetic steer brake for a control unit, in particular for influencing the driving direction of a motor vehicle by a user, wherein the control unit comprises a rotatably mounted steering shaft which can be coupled to a steering device, as well as a magnetic steer brake which is also connected to the steering shaft in a torque-transmitting manner, and a control unit for controlling the control unit. The invention further relates to a control unit, a computer program product, and a steer-by-wire system.

[0004] In steer-by-wire steering systems, magnetrheological or powder brakes are frequently used as part of feedback actuators. These brakes generate an adjustable braking torque that provides high-quality haptic feedback to the driver. By controlling an electromagnetic field, the viscosity or friction of a magnetizable powder within the braking system is regulated, allowing for stepless adjustment of the braking torque and ensuring a smooth steering feel without any annoying grinding or catching. However, a known and stable relationship between the control current and the frictional torque is necessary for precise and reproducible braking.

[0005] However, it has been shown that these magnetrheological brakes lose effectiveness during long-term use and under aging conditions. This weakening of the braking characteristic is caused by changes in the magnetic powder, which loses its originally intended physical properties over the course of its service life. In particular, powder aging and surface changes within the brake contribute to a progressive reduction in braking torque, which negatively affects haptic feedback and can ultimately impair the safety and accuracy of the steering system. Hardware-related measures, such as the use of different powder types or the application of special P241645

[0006] -2 - Surface treatments can only delay aging to a limited extent, but do not offer a long-term solution for the weakening of braking performance.

[0007] Current control concepts for steer-by-wire systems include mechanisms for fault monitoring and adjustment of the target braking torque based on driver and vehicle data, but they reach their limits when it comes to continuous recalibration. For example, patent DE102023112578 A1 from Inventus describes a fault monitoring device in which the control unit detects electrical and mechanical faults in the brake system and generates corresponding warnings. This approach relies on monitoring the braking torque using a torque sensor or an angle sensor. However, this requires a known and constant drive torque, which can only be guaranteed under certain driving conditions. A torque-based approach therefore proves insufficient, as calibration is only feasible in a few situations—for example, when the driver is not applying any steering torque and vehicle operation is not affected.This significantly limits the applicability of this continuous and adaptive recalibration.

[0008] Another approach to condition monitoring was described in the unpublished patent application DE102023113234.2 by SAG. This disclosure proposes measuring the current waveform in response to a voltage excitation to analyze the condition of the magnetic powder. The current response is intended to verify parameters such as the presence and distribution of the powder, as well as the brake's tightness. While this approach offers a diagnostic capability for detecting material and component defects, it is limited to verifying basic system integrity and is not suitable for continuous and precise calibration or compensation of braking performance during long-term operation.

[0009] In summary, the problem with the current state of the art remains that the aging of magnetic brakes in steer-by-wire systems leads to an undesirable weakening of the braking effect, which can only be inadequately compensated for by existing control concepts. P241645

[0010] - 3 - Torque-based approaches are only of limited practical application because they require a specific drive torque, while alternative testing methods are limited to diagnosing system faults and do not allow continuous calibration of braking performance.

[0011] It is therefore an object of the invention to provide a method for controlling a magnetic steer brake for a control unit, in particular for influencing the driving direction of a motor vehicle by a user, that avoids or at least reduces the problems known from the prior art. It is further an object of the invention to realize an optimized control unit, an optimized computer program product, and an improved steer-by-wire system.

[0012] This problem is solved by a method for controlling a magnetic rheostatic brake for an operating unit, in particular for influencing the driving direction of a motor vehicle by a user, wherein the operating unit comprises a rotatably mounted steering shaft which can be coupled to a steering device, as well as a magnetic rheostatic brake which is also connected to the steering shaft in a torque-transmitting manner, and a control unit for controlling the operating unit, comprising the steps of: determining an actual parameter representing the inductance of the magnetic rheostatic brake by means of an inductance sensing module; feeding the actual parameter into an averaging module to determine an inductance average value;

[0013] Use of the average inductance in a target current control module to adjust a target current for energizing the magnetrheological brake to provide a resistance torque on the steering shaft.

[0014] This method offers the advantage of enabling continuous and precise control of the magnetic brake even without steering movement, by regularly measuring and analyzing the inductance as a relevant parameter for the brake's aging condition. This allows the target current to be dynamically adjusted to the brake, ensuring consistent braking performance and a stable resistance torque at the steering shaft. Technically, this results in a long-term reliable and precise P241645

[0015] - 4 - Improved steering feel is achieved, which is particularly advantageous for safety-critical applications in steer-by-wire systems. Economically, this leads to an extended brake service life, as wear is compensated, and minimizes maintenance costs, as premature system failures are avoided through constant adjustment.

[0016] The invention thus enables, in particular, repeated calibration of the magnetic steer-by-wire brake in a steer-by-wire system by evaluating the inductance or changes in the inductance of the brake over time. This approach offers significant advantages with regard to positioning accuracy, the calibration process, and the system architecture.

[0017] Through continuous or periodic analysis and evaluation of the inductance and its age-related changes, the braking performance can be automatically adjusted to counteract the effects of aging. This means that the braking system can maintain the required braking effect and haptic feedback to the driver precisely and consistently throughout its entire service life. Adjusting based on inductance changes ensures that the system offers consistently high accuracy and operational reliability despite wear and aging of the magnetic powder, which is particularly important for safety-critical steer-by-wire steering systems.

[0018] The inductance evaluation method allows brake calibration to be performed without actively moving the steering wheel. This represents a significant advantage, as calibration can be carried out independently of the vehicle's operating phase and does not interfere with the driver. Unlike torque-based approaches, which are often only feasible at specific steering angles and in driverless states, inductance measurement enables calibration even when the vehicle is ready to drive.

[0019] This not only simplifies the calibration process, but also integrates it more efficiently and flexibly into vehicle use.

[0020] Another advantage of the presented method is that neither additional sensors nor special hardware components are required to evaluate the inductance. P241645

[0021] - 5 - are required. The measurement and analysis are based on the electrical parameters already available, such as current and voltage, which are used to control the brake. This simplifies the system architecture, leading to a reduction in manufacturing costs and a decrease in space and energy requirements. Eliminating the need for additional sensors increases the reliability and lifespan of the system, as no further wear parts need to be added. Furthermore, this minimizes the demands on the control unit and allows for efficient data processing within the existing control loop.

[0022] First, the individual elements of the claimed subject matter of the invention are explained in the order in which they are mentioned in the claim set, and subsequently, particularly preferred embodiments of the subject matter of the invention are described.

[0023] Control unit

[0024] For the purposes of this patent application, a control unit is a device for controlling the driving direction of a motor vehicle by a user, and is used in particular in a steer-by-wire system. This control unit serves to translate the driver's steering movements into electronic signals, which are used to control the actual steering movements of the vehicle wheels. A key function of the control unit is to provide the driver with a realistic steering feel that comes as close as possible to that of a mechanical steering unit, in order to enable intuitive and safe vehicle control. To this end, the control unit is able to provide a variable resistance torque at the steering shaft, which generates haptic feedback and can be adapted to the driving situation.

[0025] The control unit advantageously features a rotatably mounted steering shaft coupled to a steering device, such as a steering wheel. To generate the desired resistance torque, the steering shaft is torque-transmittingly connected to a magnetic rudder brake, which allows the braking torque to be adjusted depending on the desired steering intensity and the brake's age. The control unit P241645 also includes...

[0026] - 6 -preferably a force feedback actuator, which is also connected to the steering shaft in a torque-transmitting manner and allows for sensitive control of the return and steering forces. The magnetrheological brake and the force feedback actuator are connected to a control unit that regulates the braking effect and the return torque depending on driving conditions and vehicle parameters. This control unit is further designed to continuously adjust the braking effect by dynamically adapting the target current to the magnetrheological brake, thereby compensating for aging effects.

[0027] steering shaft

[0028] For the purposes of this patent application, a steering shaft is a rotatably mounted shaft that establishes a mechanical connection between a steering device, such as a steering wheel, and a downstream device (e.g., a steering angle sensor) for controlling the direction of travel of a vehicle. The steering shaft transmits the torque applied by the user and the angle of rotation from the steering device to the control system, thereby precisely implementing the desired steering movement.

[0029] The steering shaft advantageously has a round cross-section, but can also have cross-sectional shapes other than circular, such as polygonal profiles, which particularly contribute to increased torsional rigidity and enable a positive-locking connection with other components. This variably designed cross-section offers flexibility in connecting to other mechanical components and contributes to the robust and reliable transmission of steering torque. The shaft can also be designed as a rotatable component, such as a disc or cup, with connecting elements.

[0030] Preferably, the steering shaft is connected to a magnetic ejector brake for torque transmission, allowing a variable braking effect to be applied to the steering shaft to ensure adjustable feedback to the driver and provide a realistic steering feel. Additionally, the steering shaft can be coupled to a force feedback actuator, which also transmits torque and generates P241645.

[0031] - 7 - enables dynamic steering resistance. This resistance is variably adjustable via the electronic control and provides the driver with situation-adapted haptic feedback.

[0032] Steering system

[0033] For the purposes of this patent application, a steering device is a mechanical, electrical, or electronic device operated by the user of a vehicle to effect or control a change in the direction of travel. The steering device serves as an interface between the driver and the vehicle's steering system and transmits the desired steering movement to the control unit, which electronically processes these movements via the steer-by-wire system and transmits them to the vehicle wheels.

[0034] The steering mechanism is preferably designed as a steering wheel, which is rotatably mounted and ergonomically designed to allow the user precise and controlled handling of the vehicle. Alternatively, the steering mechanism can also include other operating devices, such as a control lever or a joystick, which are controlled by rotary or tilting movements. This design provides the driver with comfortable and safe access to the vehicle's steering functions, while the desired steering movement is detected and haptic feedback is provided.

[0035] Mechanical rheological brake

[0036] For the purposes of this patent application, a magnetrheological brake is a braking system that operates by using a magnetrheological fluid or a magnetizable powder whose viscosity or

[0037] Friction properties vary depending on an applied magnetic field. The magnetrheological brake utilizes this property to generate a variable braking torque that acts directly on a steering shaft or similar rotating component, thus providing a precise, adjustable braking effect.

[0038] The function of the magnetrheological brake is therefore based on an electromagnetic control mechanism, in which a coil is located inside the P241645

[0039] - 8 - The brake generates a magnetic field. When current flows through the coil, a magnetic field is created that acts on the magnetrheological substance inside the brake. This magnetic field causes the particles in the magnetrheological fluid or powder to align into chain-like and adhesive structures, resulting in a significant increase in viscosity and enhanced braking effect. By varying the current, the intensity of the magnetic field, and thus the braking torque, can be continuously and real-time controlled.

[0040] Preferably, the magnetic brake assembly comprises a torque-transmitting connection to the steering shaft and a coil housed in a preferably ferromagnetic casing. The coil is advantageously mounted in a U-shaped coil carrier, which directs the magnetic field precisely to the braking area and ensures high efficiency in generating the braking torque. The coil carrier and the casing enclose a rotor, typically also made of ferromagnetic material, which is directly connected to the steering shaft and is braked by the magnetic field when the magnetrheological substance increases its viscosity.

[0041] The magnetrheological effect is particularly advantageous because it operates without mechanical actuators or force application, and the multitude of parallel particle chains enables a very uniform and long-lasting braking effect. The brake is controlled by an electronic control unit that regulates the current flow to the coil, thereby controlling the magnetic field and the resulting braking torque. By adapting the magnetic field to the vehicle's operating conditions, the system can maintain a consistent braking effect throughout its lifespan and adjust the braking force according to the aging of the magnetic powder, ensuring consistent performance and optimizing the driver's safety and steering feel.

[0042] control unit

[0043] For the purposes of this patent application, a control unit is a device or system component that has the function of controlling the magnetrheological brake by means of P241645

[0044] - 9 - Control of the current supply and adjustment of the control parameters to ensure a consistent and precise braking effect. The control unit preferably includes a control structure that uses the inductance of the brake as a key control parameter to dynamically compensate for aging effects and other changes in the system.

[0045] The control unit preferably comprises several modules, including an inductance sensing module, an averaging module, and a target current control module. The inductance sensing module is used to detect or estimate the current inductance of the brake. This inductance provides information about the condition of the magnetic particles and other wear parts within the brake that affect braking performance. The measured or estimated inductance is then fed into the averaging module, which calculates a smoothed average value from the collected inductance values. This average reduces short-term fluctuations and noise effects, thus creating a stable and reliable basis for the control system.The smoothed average inductance value is then fed into the target current control module, which uses this value to calculate the required target current for the brake and adjusts the actual current supply accordingly.

[0046] Preferably, the control unit regulates the target current via a proportional-integral controller (PI controller), which adjusts the current precisely and continuously. This PI controller adjusts the current level accordingly as soon as deviations between the actual and desired current are detected. The control unit varies the weighting factors of the PI controller, in particular the proportional (P) and integral (I) factors, based on the current inductance value. These control parameters are dynamically adjusted to the detected inductance to compensate for fluctuations in braking performance and brake response speed caused by aging effects and other influences. This ensures stable brake torque control and precise, reliable brake response under all operating conditions. P241645

[0047] - 10 - The control unit can also use feedforward parameters, which are likewise adapted to the determined inductance value, to keep the braking torque constant regardless of system-related changes. This ensures that the braking force and haptic feedback remain reliable and at a constant level even after extended periods of operation.

[0048] Inductance of the mechanical brake

[0049] For the purposes of this patent application, the inductance of the magnetrheological brake is the property of the brake coil to change its magnetic field "sluggishly" when the electric current changes. From an electrical perspective, the inductance describes the formation of a reverse voltage when the current changes, i.e., a time-dynamic behavior. This inductance is surprisingly directly related to the structure and composition of the magnetrheological powder as well as the geometric and material properties of the brake coil. In fact, the inductance changes with the aging of the magnetrheological powder, for example, through oxidation / oxide layer formation or structural changes within the powder, which affects the magnetic conductivity, particularly of the particle contacts essential for chain formation, and thus the overall behavior of the brake. The change in inductance exhibits the same progress as the (possibly)The progressive formation of an oxide layer (which is temperature-dependent) is therefore a suitable aging indicator for various brakes and different application environments. Inductance is preferably used as a key indicator of the brake's aging condition because it is a measurable and continuously monitored quantity that allows conclusions to be drawn about the stability and effectiveness of the generated braking torque. Dynamic adjustment of the control parameters based on the inductance ensures that the brake offers consistent braking behavior throughout its entire service life and that the haptic feedback to the user remains stable.

[0050] Actual parameters of the inductance

[0051] For the purposes of this patent application, an "actual parameter of inductance" is a value that represents the instantaneous inductance of the brake coil and reflects the current state of the magnetic material within the magnetrheological P241645

[0052] - 11 - Brake reflects. This actual parameter is preferably determined by measuring the characteristics of the brake's voltage-current curves and reflects changes in inductance caused by aging processes of the magnetic powder and mechanical influences. The actual inductance parameter enables the control unit to detect the wear state and material changes of the brake and react accordingly. Advantageously, this parameter is recorded continuously or at defined time intervals to ensure an accurate and up-to-date basis for adjusting the control parameters.

[0053]

[0054] For the purposes of this patent application, an inductance sensing module is a device for measuring and analyzing the inductance of a magnetic rheostatic brake, which serves as an indicator of the brake's aging state and is used to adjust the control parameters in the control system. The inductance sensing module preferably detects the inductance of the brake coil by analyzing the brake's electrical response to changes in the current or voltage supply. This measurement is preferably performed using a voltage-current step response, where the inductance is detected as a measurable voltage overshoot at a defined current step or as a phase shift between an alternating voltage and the resulting alternating current.

[0055] The inductance measurement module preferably comprises a sensor unit and a processing unit. The sensor unit preferably includes a voltage and current measuring device that enables precise measurement of the voltage applied to the brake coil and the current flowing through the coil. These measurements are forwarded to the processing unit, which evaluates the raw data and derives the current inductance value from it.

[0056] Advantageously, this analysis is performed by calculating the voltage overshoot or the phase angle, which enables an exact determination of the inductance even with short rise or fall times. Furthermore, the processing unit is advantageously configured to convert the measured inductance value into a form usable by the control system.

[0057] - 12 -transmits. The determined inductance value is processed in an averaging module for smoothing before being integrated into the control system.

[0058] By using the inductance sensing module, the condition of the magnetic powder and other components of the brake can be continuously monitored and analyzed.

[0059] Averaging module

[0060] For the purposes of this patent application, an averaging module is a device used to collect measured values ​​of a specific parameter, in this case the inductance of the magnetic diaphragmatic brake, over a defined period or over several operating phases and to process them into a smoothed average value. This average value represents a stable and long-term change in the parameter and serves as the basis for adjusting the system's operating parameters, in particular for controlling the target current.

[0061] The averaging module filters out fluctuations and noise effects from the measured values, which can arise from short-term operating conditions or external influences. By calculating an average over a large number of operating phases, advantageously 50,000 to 200,000 phases, or over a longer period, preferably between 0.5 and 5 years, a reliable and stabilized representation of the brake's aging condition is created. This smoothed representation provides a precise and robust basis for the subsequent adjustment of the target current values ​​and control parameters.

[0062] The averaging module advantageously includes a memory unit in which the recorded measurements, and especially the average value, are stored across the respective operating phase. This allows for "strong" averaging over multiple operating phases. This memory is read at the beginning of a new operating phase. This non-volatile (EEPROM) memory is written with a start value at least at the end of an operating phase or during initial commissioning.

[0063] For example, a calculation unit within the module can process the captured P241645

[0064] - 13 - The inductance values ​​are summed and the sum is divided by the number of measurements to calculate the average value. The calculation unit is connected to a control logic that forwards the average value to the setpoint current control and other control-relevant modules. This average value represents a long-term stable quantity that takes into account the aging and wear effects of the brake and allows for precise and timely adjustments to the control parameters.

[0065] Preferably, the averaging module is designed to use additional weighting parameters to vary the influence of individual measured values ​​on the average calculation, depending on the operating conditions. This weighting can be tailored to specific operating conditions, such as increased load or particular environmental factors, and contributes to the accuracy of the average. By continuously providing an updated and smoothed inductance value, the averaging module enables consistent and reliable adjustment of the control strategy throughout the brake's entire service life.

[0066] Average inductance

[0067] For the purposes of this patent application, an inductance mean value is a smoothed average value of the inductance of the magnetic brake, aggregated over a large number of operating phases and / or a period of time. This value is preferably obtained by continuously acquiring and averaging the inductance values ​​measured during operation, with extensive smoothing over several operating cycles and / or a period of time to compensate for short-term fluctuations and disturbances. This smoothing produces a reliable mean value that reflects the long-term trends in inductance change and can be used for long-term calibration and adjustment of the braking effect, ensuring that the brake delivers consistent performance regardless of age-related changes. It is also conceivable that change limits could be applied for this purpose, i.e., that an algorithm could limit the change in the mean value to, for example, 0.Limited to 1% per operating phase, or limited to a fixed change value per operating phase and rejecting any changes exceeding that value. P241645.

[0068] - 14 -

[0069]

[0070] For the purposes of this patent application, a target current control module is an electronic or software-based control unit used to adjust and fine-tune the target current for controlling a magnetic galvanic brake. The target current control module receives data representing the aging state and current operating parameters of the brake, in particular the average inductance value, which was previously determined by an averaging module. Using this information, the target current control module calculates the optimal target current required to generate a constant braking torque, compensating for changes caused by the aging process of the magnetic powder or other components.

[0071] Preferably, the target current control module comprises both a control and a feedforward component. The control component ensures the continuous adjustment of the target current by reacting to real-time data on the deviation between the target and actual current. It preferably uses a PI controller whose proportional (P) and integral (I) factors are influenced by the current inductance value, thus maintaining system stability even with changing inductance. The feedforward component, in turn, considers the long-term behavior of the inductance change and, by further adjusting the target current, ensures that the braking torque remains constant throughout the brake's service life. This is particularly advantageous because it achieves a smooth and precise braking effect without the need for frequent recalibration or manual adjustments.

[0072] The design of the target current control module preferably includes a processing unit that continuously evaluates the average inductance value and preferably dynamically adjusts the corresponding control parameters of the PI controller. Furthermore, the module can be equipped with a memory area in which data about the original inductance of the brake and the current adjustment of the target current are stored over time. This prevents the module from being P241645

[0073] - 15 -not only optimize the current operating condition, but also provide information about the aging of the brake via long-term diagnostics.

[0074] Target current

[0075] For the purposes of this patent application, a target current is the desired value for the current supplied to a magnetic rudder to generate a defined braking torque. This target current is the current specified by the control unit to achieve the desired resistance torque at the steering shaft, thus ensuring the haptic feedback and steering precision expected by the driver. Typically, the target current is converted into a pulse-width modulated signal, which drives several power switches (MOSFETs) in half-bridge or full-bridge configurations.

[0076] Advantageous embodiments of the invention

[0077] According to an advantageous embodiment of the invention, the adjustment of the target current can be performed dynamically in step c. This ensures that the target current automatically adapts to changing operating conditions and that the brake operates continuously at its optimal level. This results in higher system efficiency and accuracy, as the target current is always aligned with the current inductance and thus with the current state of the brake. Technically, this allows for an immediate response to aging or wear conditions without delay, which increases the operational reliability of the overall system.

[0078] According to a further preferred embodiment of the invention, the target current control module can also adjust the target current based on a divisor representing the ratio of the current to the original inductance. This allows the control system to react to changes in the brake's aging state without relying on more complex control algorithms. Calculating the divisor is simple and requires no additional sensors, keeping the system architecture straightforward while enabling efficient control.

[0079] Furthermore, according to an equally advantageous embodiment of the invention, it can be provided that the averaging module uses the inductance values ​​P241645

[0080] - 16 -smooths over a large number of operating phases, in particular strongly smooths, by averaging the measured values, which are aggregated over several operating phases and / or a period of time, in particular 50 to 200 phases or 10 to 500 km (which is still only about 1 / 1000 of the vehicle's service life), to reduce short-term fluctuations or noise effects. Technically, this ensures a stable and reliable average inductance value, which forms the basis for long-term adjustment of the target current. This achieves high long-term stability, resulting in smooth performance and fewer sudden adjustments, which improves both steering feel and control accuracy. Economically, this optimizes the service life of the brake, as the target current is increased smoothly and in accordance with the actual conditions, resulting in fewer failures and lower maintenance costs.

[0081] According to a further particularly preferred embodiment of the invention, the control unit for long-term diagnostics and maintenance can be configured to non-volatilely store the determined average inductance value and, preferably, other condition information to enable detailed monitoring of brake aging. This non-volatile storage of the average inductance value and other condition information allows for detailed monitoring of brake aging. Technically, this enables long-term analysis of brake performance and the diagnosis of deviations or unusual changes in condition. Advantageously, the system provides an overview of the wear status at any time, facilitating targeted maintenance planning and early detection of defects.Economically, this reduces both the costs of unplanned maintenance and the risk of sudden breakdowns, as the wear condition is always known and timely action can be taken.

[0082] Furthermore, the invention can also be further developed in such a way that the control unit adjusts the P and I factors of a PI controller based on the average inductance, in particular dynamically, in order to improve stability and control accuracy over the service life of the brake. This ensures that the brake control remains stable and precise, even when the P241645

[0083] - 17 - Inductance varies due to aging effects. Technically, this leads to improved control accuracy and a lower probability of control oscillations or instabilities, which increases the overall reliability of the system. Economically, this results in less stress on the brake and steering shaft, as the adjusted control parameters allow the system to operate more efficiently and minimize material wear.

[0084] In a preferred embodiment of the invention, the determination of the actual parameter can also be triggered by a first trigger signal. This reduces the effort required for continuous monitoring of the inductance, as the measurement is specifically limited to relevant operating conditions. Technically, this reduces the system load, since measurement cycles are selectively controlled and unnecessary measurements are avoided. Economically, this means higher energy efficiency and less computational effort, resulting in longer operating times and lower hardware requirements.

[0085] It can also be advantageous for the initial trigger signal to be activated by an operational event, such as the completion of a predefined operating phase of the control unit or the vehicle, or the reaching of a predefined vehicle mileage. This ensures that inductance measurements are only taken at relevant times, thus increasing the efficiency of diagnostics and monitoring. From a technical perspective, this is particularly beneficial because the system avoids unnecessary measurements and can focus on stable conditions. Economically, this targeted measurement strategy leads to reduced operating costs and a longer service life for the electronics, as there is less stress and wear caused by superfluous measurements.

[0086] Furthermore, it is advantageous if the first trigger signal is activated by a monitoring module configured to detect an evaluable operating situation of the control unit or the vehicle. This enables intelligent control where measurements are only taken when usable data can actually be generated. Technically, this ensures that the system only takes measurements when the conditions for this are met. P241645

[0087] - 18 - are optimal, which improves the measurement quality and reliability of the data.

[0088] Economically, this precise control reduces effort and increases the efficiency of data processing, contributing to a longer service life and lower maintenance costs.

[0089] For the manufacture and testing of a steering system, it is also advantageous if the trigger signal is generated by an external source, such as a service test device or an end-of-line test station. This allows the initial value for inductance averaging to be generated and stored. Likewise, the stored inductance average can be read out and subjected to testing.

[0090] It can also be advantageous to further develop the invention such that the control unit generates a second trigger signal when a predefined inductance change is exceeded, which in particular activates a warning and / or an emergency running function. This function offers the advantage that critical brake conditions can be detected quickly and signaled to the driver or the workshop. Technically, this is advantageous because it contributes to increased system safety and minimizes the probability of uncontrolled brake failure. Economically, this results in lower risks of consequential damage and safety incidents, which reduces overall operating costs.

[0091] According to a further preferred embodiment of the invention, the averaging module can be provided with additional parameters for determining the average inductance value, in particular for weighting. This allows the smoothing and averaging of the inductance values ​​to be even more precisely tailored to specific operating conditions. Technically, this leads to an improved adaptation of the target current values ​​to the actual ambient conditions, which optimizes the accuracy of the brake control. Economically, this flexibility enables targeted adaptation of the system to various requirements, which increases efficiency and reduces energy consumption. P241645

[0092] - 19 - The invention can also advantageously be implemented in such a way that the control unit further comprises a force-feedback actuator which is connected to the steering shaft in a torque-transmitting manner, wherein a signal representing an actual braking voltage is provided to the inductance sensing module for determining the inductance. Technically, this enables a combination of magnetrheological braking and force feedback, which creates a realistic and responsive steering feel for the driver.

[0093] Economically, this offers the possibility of providing more complex steering functions without additional systems, which reduces construction costs and the complexity of the overall system.

[0094] Furthermore, it is advantageous to send a target braking torque to the target current control module and use it to determine the target current. Technically, this leads to a precise match between the target torque and the actual braking torque, enabling accurate steering control. Economically, this reduces energy consumption, as the system only supplies the exact current required, resulting in less wear and tear and lower operating costs.

[0095] It can also be provided that the setpoint current control module includes characteristic curve interpolation and / or multiplication by the inductance ratio (actual parameter / original inductance). This combination of features offers the advantage that the setpoint current control module incorporates both characteristic curve interpolation and multiplication by the ratio of the actual inductance to the original inductance. The multiplication is particularly advantageous when applied to the result of the interpolation, which is equivalent to a corrective increase in the current depending on the inductance loss. This enables dynamic adaptation to aging effects, ensuring constant braking performance. Technically, this ensures long-term stable control without performance loss, which is crucial for the system's longevity and reliability.Economically, this results in a reduction in maintenance costs and an extension of the brake's service life. P241645.

[0096] - 20 - In summary, the invention relates to a method for calibrating and adjusting the braking characteristic in magnetrheological brakes used in steer-by-wire systems. These brakes contain magnetizable powder whose inductance and magnetic resistance change over time due to aging processes. These changes negatively affect braking performance, as the braking characteristic weakens over time and the required braking effect can no longer be reliably generated.

[0097] Tests conducted by the applicant have shown that the change in the braking characteristic is primarily caused by the aging of the powder. A change in the powder was able to restore the original braking performance, indicating the crucial role of the powder in maintaining the stability of the braking characteristic.

[0098] The aging of the powder leads to a change in inductance and magnetic resistance, which significantly affects the overall inductance and resistance of the brake, thereby reducing the braking effect.

[0099] This aging effect is compensated for in particular by determining the current state of the powder in the magnetic diaphragm brake through an analysis of its inductance and short-term response behavior. The short-term response behavior is preferably measured using a voltage-current step response or a similar method that accurately captures the brake's inductance. Since aging effects are typically a slow and continuous process, the determined inductance value is heavily smoothed or averaged over many operating phases. This reduces the impact of short-term fluctuations or measurement noise and provides a stable average value that reliably represents the actual aging state of the brake.

[0100] Based on this smoothed average inductance value, the brake control is adjusted to maintain the desired braking effect even with changing powder conditions. Specifically, the target current for controlling the brake is increased to compensate for the loss of braking force due to aging. This adjustment typically results in a current increase of approximately 10-30% over the entire service life to maintain a constant P241645

[0101] - 21 - To ensure braking torque. This dynamic current adjustment keeps the braking effect stable throughout the entire service life of the brake, which improves safety and steering feel in the vehicle.

[0102] Optionally, the determined aging status can also be stored in the control unit and used for various purposes. For example, the status can be communicated to the driver or workshop to indicate brake wear. Furthermore, the control unit can activate a warning or emergency running mode if the condition changes too drastically to ensure the functionality of the steer-by-wire system.

[0103] Overall, the method offers an efficient and reliable approach for detecting and compensating for aging effects in magnetrheological brakes, thereby maintaining stable braking performance and extending the brake's service life. Adjusting the brake control based on inductance analysis ensures that the brake delivers a consistent and precise braking torque even after numerous operating cycles, without requiring any mechanical or hardware modifications.

[0104] The object of the invention is further achieved by an operating unit for influencing the driving direction of a motor vehicle by a user, comprising a rotatably mounted steering shaft which can be coupled to a steering device, as well as a force-feedback actuator which is connected to the steering shaft in a torque-transmitting manner, and a magnetrheological brake which is also connected to the steering shaft in a torque-transmitting manner, and a control unit for controlling the operating unit, wherein the control unit is configured to determine an actual parameter representing the inductance of the magnetrheological brake by means of an inductance detection module, and to feed the actual parameter into an averaging module for determining an average inductance value.and for the use of the average inductance in a setpoint current control module to adjust a setpoint current for energizing the magnetrheological brake to provide a resistance torque on the steering shaft. P241645

[0105] - 22 -

[0106] This control unit, through the torque-transmitting connection of the force-feedback actuator and magnetrheological brake to the steering shaft, offers the advantage of providing a realistic steering feel and precise haptic feedback to the driver. The integration of the control unit with an inductance sensing module and averaging module allows for continuous adjustment of the braking effect via the target current, resulting in a stable resistance torque and thus a consistent driving experience. Technically, this improves steering precision, and the control unit automatically adapts to the aging of the brake, ensuring a consistent braking torque throughout the brake's entire service life. Economically, this results in reduced maintenance and repair costs, as the braking performance is continuously adjusted to wear, achieving a longer service life without any loss of performance.

[0107] The problem of the invention can also be solved by a computer program product stored on a machine-readable medium, or a computer data signal embodied by an electromagnetic wave, with computer program code suitable for carrying out a method according to any one of claims 1-14, thereby enabling the implementation of the method on various hardware platforms. The software solution allows for flexible and cost-effective adaptation and updating of the control system without the need for hardware modifications. This offers the advantage of simple maintenance and the possibility of optimization through software updates. Technically, this enables easy integration into existing systems, and economically, the flexibility leads to better adaptation to future requirements, which extends the service life and application possibilities of the control system and reduces operating costs.

[0108] Finally, it is also possible to solve the problem of the invention by means of a steer-by-wire system for a motor vehicle comprising an operating unit according to claim 15 and / or a control unit configured to execute a method according to any one of the preceding claims 1-14. By integrating an operating unit with a control unit in a steer-by-wire system for motor vehicles, the P241645

[0109] - 23 - The invention is advantageously applied to safety-critical steering systems. The structure of this system enables precise control of the steering movement by providing a resistance torque at the steering shaft, which improves haptic feedback for the driver and makes the driving experience safer and more controlled. Technically, the control unit enables continuous adjustment of the brake, adapting to the aging state of the brake and thus guaranteeing constant braking performance. Economically, the steer-by-wire system offers long-term advantages by reducing mechanical wear parts and the associated maintenance costs, while simultaneously increasing the functional safety and reliability of the steering system throughout its entire life cycle.

[0110] The invention will now be explained in more detail with reference to figures, without limiting the general concept of the invention.

[0111] It shows:

[0112] Figure 1 shows a motor vehicle with a steer-by-wire system in a schematic block diagram.

[0113] Figure 2 shows a first embodiment of an operating unit in a schematic axial section view,

[0114] Figure 3 shows a detailed view of the control unit in a schematic axial section representation of two states.

[0115] Figure 4 shows a block diagram of the control unit,

[0116] Figure 5 shows the time course of the current and voltage at the brake in a schematic diagram representation.

[0117] Figure 6 shows a current-braking torque diagram (top) and a time course of the brake inductance in a diagrammatic representation (bottom), P241645

[0118] - 24 - Figure 7 Time course of the measured current and voltage at the brake in a diagram representation,

[0119] Figure 8 shows a circuit diagram of an averaging module.

[0120] Figure 9 shows a circuit diagram of a controller stabilization using the average inductance.

[0121] Figure 1 shows a control unit 1 for influencing the driving direction of a motor vehicle 2 by a user. The control unit 1 is integrated into a steer-by-wire system 20, so that a steering movement of the steering device 4 is electrically transmitted from the control unit 1 to a road wheel actuator 33, which then adjusts the corresponding steering angle at the vehicle wheels of the vehicle axle.

[0122] As can be clearly seen in Figure 2, the control unit 1 has a rotatably mounted steering shaft 3 (which can also be designed as a hollow shaft or external rotor), which can be coupled to the steering device 4, as well as a force feedback actuator 5, which is also connected to the steering shaft 3 in a torque-transmitting manner. Furthermore, the control unit 1 has a magnetic brake 6, which is also connected to the steering shaft 3 in a torque-transmitting manner. In this embodiment, the force feedback actuator 5, the magnetic brake 6, and the steering device 4 are connected directly (without a gearbox).

[0123] Furthermore, the operating unit 1 has a control unit 7 for controlling the operating unit 1, the function of which will be explained in detail below.

[0124] The magnetrheological brake 6 has an electromagnet with a current-energizing excitation coil 14, the field lines 30 of which run through the stator 16 and the rotor 15 connected to the steering shaft 3. P241645

[0125] - 25 - The ring-shaped excitation coil 14 is received in a coil carrier 18 with a U-shaped cross-section, which is closed radially on the outside by the coil closure 17. Radially on the inside, the coil carrier 18 is closed by the coil closure 19. The coil carrier 18 and the coil closure 17 are made of a ferromagnetic material. The excitation coil 14, the coil carrier 18, and the coil closure 17 form the stator 16 of the brake 6. The stator 16 is supported on the rotatable brake shaft 23, which is part of the rotor 15, via the bearing shields 21, 22 and the rolling bearings 24, 25. The rotor 15 is sealed against the bearing shields 21, 22 by the seals 26, 27.

[0126] The magnetrheological brake 6 contains magnetizable particles in a carrier fluid. These particles behave differently depending on the control state of the brake 6, as illustrated in Figure 3. In the de-energized state, i.e., without current flowing to the excitation coil 14, the magnetrheological particles are largely unstructured and distributed throughout the fluid (de-energized state, left). When current is applied to the excitation coil 14 (energized state, right), a magnetic field is generated that attracts the particles and forms them into stable chains along the field lines. This chain formation creates a magnetic bridge within the brake 6 and increases the inductance of the excitation coil 14. Simultaneously, the adhesion of the chains to the walls of the brake 6 generates a frictional torque, which is used to selectively generate a resistive torque that can be directly transmitted to the steering shaft 3.

[0127] In endurance tests, it was found that the aging of the magnetic diaphragmatic brake 6 causes a progressive lowering of the braking torque characteristic, as shown in the upper diagram of Figure 6. This aging effect manifests itself as a gradual flattening and compression of the braking torque characteristic over time, as opposed to a simple shift or other change in the shape of the characteristic. This compression results in the brake 6 exhibiting a progressively lower braking torque for the same control current over its service life.

[0128] The progression of this settling can be mathematically represented as a function of the service life. The braking torque M(l, service life) is then given by the P241645

[0129] - 26 - Formula M(l, runtime) = Mnew(l) * f(runtime) is expressed, where the factor f(runtime) is 1 at the beginning of the service life and gradually decreases over time. This reduction of f(runtime) correlates with a decrease in the inductance 40 of the brake 6 or a corresponding measured quantity indicating the inductance 40, such as the amplitude or area of ​​the voltage overshoot. This means that the aging effect can also be directly observed and quantified based on the change in inductance 40.

[0130] To account for these aging effects and compensate for the decreasing braking effect, a correction factor can be implemented in the control system. One possibility, for example, is to use an odometer factor f(runtime), which considers the state of aging depending on the operating time or vehicle mileage, but this is imprecise. Alternatively, the inductance (L) itself can be used as a direct indicator of aging. In this case, the current inductance 40 of the brake 6 is stored and evaluated in the control unit 7 using a function or table g(inductance L). This function provides a targeted adjustment of the current required for a desired braking torque.

[0131] By using the inductance 40 as an aging indicator, a continuous adjustment of the target current 46 is enabled to compensate for the aging effect, thus ensuring a constant braking effect over the entire service life of the brake 6. This method therefore allows the aging state to be precisely determined and the braking performance of the magnetrheological brake 6 to be sustainably stabilized without the need for mechanical adjustments or hardware updates.

[0132] The procedure is explained in more detail below.

[0133] During a current step change, where the current supply is abruptly altered, a characteristic voltage waveform appears in which the total inductance of the system can be measured by a voltage overshoot. This can be seen in Figure 5 and Figure 7. The voltage waveform reaches P241645 in three phases.

[0134] - 27 -steady-state values: the initial value (point a), the overshoot (point b), and the final value (point c). The steady-state voltage values ​​at points (a) and (c) are determined by the ohmic resistance of the excitation coil 14, while the voltage overshoot at point (b) is influenced by the total inductance of the system. The value of the voltage overshoot—that is, the difference between point (b) and point (c)—can be measured with particular precision and provides an accurate reference for the inductance of the brake 6.

[0135] The magnitude of the voltage overshoot varies depending on the aging state and the type of powder in the brake 6 and can decrease by 10 to 25% by the end of the brake 6's service life. With decreasing inductance 40, the voltage overshoot becomes increasingly shorter and sharper. This measurement allows for a precise assessment of the inductance 40 and thus monitoring of the powder's aging. This change in the overshoot with each current step change allows the condition of the magnetrheological brake 6 to be monitored throughout its entire service life and used to adjust the target current 46, ensuring consistent and reliable braking performance.

[0136] Figure 7 shows a measurement result from a comprehensive analysis of the magnetrheological brake 6, illustrating the change in the step response when comparing measurements before and after a 300,000 km endurance run. During the investigation, the target current 46 was increased from 0 to 520 mA at time 8.00 seconds. The actual current waveform showed a delay of approximately 50 ms before reaching the target current 46. Because the signal was recorded at a high frequency of 1 kHz, the current waveform is relatively smooth, allowing for precise tracking of the current profile.

[0137] At the beginning of the current surge, the voltage on the right-hand scale rises from 0 V to 3.6 V and exhibits an overshoot caused by the inductance 40 and the dynamic characteristics of the brake 6. Measurements showed that the voltage overshoot was larger and slightly delayed before the continuous run, while it was smaller and less pronounced after the continuous run. This difference in overshoot behavior is shown on P241645.

[0138] - 28 -a decrease in the inductance 40 of the brake 6, which occurs during the service life due to aging and wear of the brake powder.

[0139] The voltage waveforms were recorded at a lower sampling rate of 0.01 s, resulting in a slightly stepped representation. Despite this limited sampling rate, the effect of the inductance change is clearly visible and is consistent in other measurements as well.

[0140] The measurements demonstrate that the aging effect is particularly noticeable during large current surges, as the overshoot is more pronounced and less masked by noise components. The effect is also evident during current regressions, confirming a consistent change in inductance in both directions and thus indicating a sustained decline in magnetic properties over the device's lifetime.

[0141] These findings provide valuable data for the long-term analysis and monitoring of brake 6 and confirm that continuous adjustment of the control to the aging state of brake 6 is necessary to ensure a constant braking effect.

[0142] Figure 4 shows a control unit 7 which, through the effect described above, uses the inductance 40 of the brake to regulate the target current 46. With reference to Figure 4, a method for controlling a magnetic rheostatic brake 6 for an operating unit 1, in particular for influencing the driving direction of a motor vehicle 2 by a user, is now explained, wherein the operating unit 1 has a rotatably mounted steering shaft 3, which can be coupled to a steering device 4, as well as a magnetic rheostatic brake 6, which is also connected to the steering shaft 3 in a torque-transmitting manner, and a control unit 7 for controlling the operating unit 1.

[0143] The process includes the following steps:

[0144] First, an actual parameter 41 representing the inductance 40 of the magnetrheological brake 6 is determined using a P241645

[0145] - 29 - Inductance sensing module 42. Subsequently, the actual parameter 41 is fed into an averaging module 43 to determine an average inductance value 44. Then, the average inductance value 44 is used in a target current control module 45 to adjust a target current 46 for energizing the magnetrheological brake 6 to provide a resistance torque 47 at the steering shaft 3.

[0146] Preferably, the adjustment of the target current 46 is carried out dynamically.

[0147] Figure 4 also clearly shows that the set current influence module 45 adjusts the set current 46 based on a divisor that represents the ratio of the current to the original inductance.

[0148] The averaging module 43 can smooth the inductance values ​​over a large number of operating phases, in particular smooth them significantly, by averaging the measured values ​​that are aggregated over several operating phases and / or a period of time, especially 50 to 200 phases, in order to reduce short-term fluctuations or noise effects. For long-term diagnostics and maintenance, the control unit 7 can non-volatilely store the determined average inductance value 44 and preferably other condition information to enable detailed monitoring of the aging of the brake 6.

[0149] The determination of the actual parameter 11 can be triggered by a first trigger signal 48, which is activated, for example, by an operational event, such as the completion of a predefined operating phase of the control unit 1 or the vehicle 2, or the reaching of a predefined vehicle mileage. It is also possible for the first trigger signal 48 to be activated by a monitoring module configured to detect an evaluable operating situation of the control unit 1 or the vehicle 2.

[0150] Figure 4 also shows that the control unit 7 generates a second trigger signal 49 when a predefined inductance change is exceeded, which in particular activates a warning and / or an emergency running function. P241645

[0151] - 30 -

[0152] Additional parameters 52 can also be provided to the averaging module 43 for determining the inductance mean 44, in particular for weighting.

[0153] The control unit 1 further includes a force feedback actuator 5, which is connected to the steering shaft 3 in a torque-transmitting manner, wherein a signal 51 representing an actual braking voltage 50 is provided to the inductance detection module 42 to determine the inductance 40.

[0154] A target braking torque 53 is sent to the target current control module 45 and used to determine the target current 46.

[0155] The target current influence module 45 includes a characteristic curve interpolation, and / or a multiplication with the inductance ratio actual parameter 41 / original inductance.

[0156] Figure 8 shows a possible embodiment of the averaging module 43. The upper dashed box symbolizes the averaging step, which contributes to the long-term stability and accuracy of the inductance measurement.

[0157] Furthermore, the use of a weighted learning factor is evident, which ensures that measurements obtained in dynamic situations with high current or voltage changes receive a higher weighting than measurements from steady-state phases. In steady-state situations, the current-voltage relationship is primarily influenced by the ohmic resistance, not by the inductance. This weighted approach ensures that the inductance measurement reliably reflects the actual magnetic response of the system by effectively filtering out irrelevant measurements from uniform operating phases.

[0158] Furthermore, the weighting factor allows for a discriminatory selection of current and voltage jumps: for example, it can selectively select only P241645

[0159] - 31 -Consider upward jumps or jumps within certain amplitude ranges to further increase the relevance of the data for inductance measurement. This selective weighting improves the accuracy of the system by excluding non-representative measurements.

[0160] The section labelled "formula block" serves to continuously calculate a new estimation result for the inductance 40 and is therefore a possible implementation option of the procedure step for determining inductance.

[0161] Mathematically, this process is based on solving the differential equation for the parameter L, resulting in the following formula:

[0162]

[0163] This equation ensures that the inductance L is calculated exactly from the measured values ​​of the voltage u(t), the current i(t), the ohmic resistance (R), and the rate of change of the current di(t) / dt. By continuously applying this formula, the current inductance value is accurately estimated and stabilized over time by the weighted average.

[0164] Figure 9 shows a method for controlling the actuation of a magnetic rheological brake 6, which in particular ensures the stability and precision of the brake control over the entire lifetime of the system by adjusting the control parameters of a current controller.

[0165] The control is achieved by a dynamic control system that includes both a feedforward control and a current controller. The current controller adjusts the current supplied to the brake coil 6 and compensates for deviations between the actual current and the target current. The current controller is designed as a PI controller (proportional-integral controller), which performs the control correction based on a proportional and an integral component. This control structure enables precise and dynamic P241645

[0166] - 32 - Adjustment of the power supply, which ensures stable braking and consistent haptic feedback.

[0167] For the stability and effectiveness of the control system, it is crucial that the weighting factors of the PI controller, namely the proportional factor (P-factor) and the integral factor (I-factor), are correctly selected. However, the weighting of these parameters is highly dependent on the inductance 40 of the brake coil, which can change over the operating period due to aging processes of the magnetic powder and other components. With a lower inductance, the brake coil reacts faster, which means that the I-factor must be reduced to avoid control oscillations and instabilities.

[0168] Therefore, the determined or estimated inductance 40 of the brake 6 is used as a control parameter to dynamically adjust the P and I factors of the PI controller. The inductance 40 of the brake 6 is measured regularly and serves as an indicator of the brake 6's aging condition. By continuously adjusting the control parameters to the current inductance value, the current controller can operate stably, regardless of how much the inductance 40 varies over time. This ensures that the braking effect remains consistent and the system stability is maintained even with progressive aging.

[0169] In addition to the P and I factors, the feedforward parameters of brake 6 can also be adjusted to the determined inductance value. This further improves control accuracy and reduces the need for manual calibrations or maintenance.

[0170] The invention is not limited to the embodiments shown in the figures. The foregoing description is therefore not to be regarded as limiting, but as explanatory. The following claims are to be understood as meaning that a named feature is present in at least one embodiment of the invention. This does not preclude the presence of further features. Insofar as the claims and the foregoing description are 'first' and P241645

[0171] - 33 - Defining a 'second' characteristic, this designation serves to distinguish between two similar characteristics without establishing a hierarchy. P241645

[0172] - 34 - List of reference symbols

[0173] 1 control unit

[0174] 2 motor vehicles

[0175] 3 Steering shaft

[0176] 4 Steering devices

[0177] 5 Force feedback actuator

[0178] 6 Brake

[0179] 7 Control unit

[0180] 9 Program

[0181] 21 Steer-by-Wire system

[0182] 30 field lines

[0183] 33 RWA

[0184] 40 inductance

[0185] 41 Current Parameters

[0186] 42 Inductance measurement module

[0187] 43 Averaging Module

[0188] 44 Inductance average

[0189] 45 Target current control module

[0190] 46 Target current

[0191] 47 Section modulus

[0192] 48 Trigger signal

[0193] 49 Trigger signal

[0194] 50 Actual braking voltage

[0195] 51 Signal

[0196] 52 parameters

[0197] 53 Target braking torque

Claims

P241645 - 35 - Claims 1. Method for controlling a magnetic rheostatic brake (6) for an operating unit (1), in particular for influencing the direction of travel of a motor vehicle (2) by a user, wherein the operating unit (1) comprises a rotatably mounted steering shaft (3) which can be coupled to a steering device (4), as well as a magnetic rheostatic brake (6) which is also connected to the steering shaft (3) in a torque-transmitting manner, and a control unit (7) for controlling the operating unit (1), comprising the steps: a) Determination of an actual parameter (41) representing the inductance (40) of the magnetrheological brake (6) using an inductance measurement module (42), b) Input of the actual parameter (41) into an averaging module (43) to determine an inductance mean (44), c) Use of the average inductance (44) in a set current control module (45) to adjust a set current (46) to energize the magnetrheological brake (6) to provide a resistance torque (47) on the steering shaft (3).

2. Method according to claim 1 , characterized by the fact that in step c) the adjustment of the target current (46) is carried out dynamically.

3. Method according to claim 1 or 2, characterized by the fact that The set current control module (45) adjusts the set current (46) based on a divisor that represents the ratio of the current to the original inductance. P241645 - 36 - 4. Method according to any of the preceding claims, characterized by the fact that The averaging module (43) smooths the inductance values ​​over a large number of operating phases, in particular strongly smooths them, by averaging the measured values ​​which are aggregated over several operating phases and / or a period of time, in particular 50 to 200 phases, in order to reduce short-term fluctuations or noise effects.

5. Method according to any of the preceding claims, characterized by the fact that The control unit (7) stores the determined average inductance value (44) and preferably other status information non-volatilely for long-term diagnostics and maintenance, and reads out the stored value at the beginning of an operating phase.

6. Method according to any of the preceding claims, characterized by the fact that the control unit (7) adjusts the P and I factors of a PI controller based on the average inductance (44) in order to improve, in particular, the stability and control accuracy over the lifetime of the brake (6).

7. Method according to any of the preceding claims, characterized by the fact that The determination of the actual parameter (41) is triggered by a first trigger signal (48).

8. Method according to claim 7, characterized by the fact that P241645 - 37 - the first trigger signal (48) is activated by an operating event, such as in particular the completion of a predefined operating phase of the control unit (1) or the motor vehicle (2) or the reaching of a predefined vehicle mileage.

9. Method according to claim 7 or 8, characterized by the fact that the first trigger signal (48) is activated by an observation module that is set up to detect an evaluable operating situation of the control unit (1) or the motor vehicle (2).

10. Method according to any of the preceding claims, characterized by the fact that The control unit (7) generates a second trigger signal (49) when a predefined inductance change is exceeded, which in particular activates a warning and / or an emergency running function.

11. Method according to any of the preceding claims, characterized by the fact that The averaging module (43) is provided with additional parameters (52) for determining the inductance mean (44), in particular for weighting.

12. Method according to any of the preceding claims, characterized by the fact that the control unit (1) further comprises a force feedback actuator (5) which is connected to the steering shaft (3) in a torque-transmitting manner, wherein a signal (51) representing an actual brake voltage (50) is provided to the inductance detection module (42) to determine the inductance (40). P241645 - 38 - 13. Method according to any of the preceding claims, characterized by the fact that a target braking torque (53) is sent to the target current control module (45) and used to determine the target current (46).

14. Method according to any of the preceding claims, characterized by the fact that the target current control module (45) includes a characteristic curve interpolation, and / or a multiplication with the inductance ratio actual parameter (41) / original inductance.

15. Control unit (1) for influencing the direction of travel of a motor vehicle (2) by a user, comprising • a rotatably mounted steering shaft (3) which can be coupled to a steering device (4), as well as • a force feedback actuator (5) which is connected to the steering shaft (3) in a torque-transmitting manner, and • a magnetic rheumatic brake (6) which is also connected to the steering shaft (3) in a torque-transmitting manner, and • a control unit (7) for controlling the operating unit (1 ), characterized by the fact that the control unit (7) is set up, P241645 - 39 - • to determine an actual parameter (41) representing the inductance (40) of the magnetrheological brake (6) using an inductance sensing module (42), and • for feeding the actual parameter (41) into an averaging module (43) for determining an inductance mean value (44), and • for the use of the average inductance (44) in a target current control module (45) for adjusting a target current (46) for energizing the magnetrheological brake (6) for providing a resistance torque (47) on the steering shaft (3).

16. Computer program product stored on a machine-readable medium, or computer data signal embodied by an electromagnetic wave, comprising a computer program code suitable for performing a method according to any one of claims 1-14.

17. Steer-by-wire system (21) for a motor vehicle (2) comprising an operating unit (1) according to claim 15 and / or a control unit (7) configured to execute a method according to any one of the preceding claims 1-14.

Images