Method for operating a steer-by-wire steering system for a vehicle and steer-by-wire steering system

Abstract

A method for operating a steer-by-wire steering system (12) for a vehicle (10) and a steer-by-wire steering system (12) for a vehicle (10) are provided. The steer-by-wire steering system (12) has at least one steering wheel (28) and a road wheel actuator (14) with a control device (16). The road wheel actuator (14) is coupled to at least one steerable road wheel (20). A detected steering wheel angle of the steering wheel (28) is received by the control device (16). A target road wheel angle (48) of the steerable road wheel (20) is determined by the control device (16) based on the received steering wheel angle. The target road wheel angle (48) is limited by road wheel angle limits (50) that depend at least on the vehicle speed.A control signal is output by the control device (16) to an electric motor (22) of the road wheel actuator (14) or to an inverter coupled to the electric motor (22), based on the determined target road wheel angle (48). The control device (16) receives the vehicle speed. The road wheel angle limits (50) depend on the vehicle speed such that, for each vehicle speed, a change in the vehicle's lateral speed corresponding to a predetermined speed change limit can be achieved.

Description

The disclosure generally relates to a method for operating a steer-by-wire steering system for a vehicle and a steer-by-wire steering system. Steer-by-wire steering systems, hereinafter referred to as SBW steering systems, are a new vehicle steering technology. SBW steering systems eliminate the mechanical connection between the steering wheel and the steerable wheels. Two actuator subsystems work together to steer the vehicle: a steering wheel actuator with feedback, which generates feedback torque for the driver at the steering wheel (also called a feedback actuator (FBA)), and a road wheel actuator, which controls at least one, but typically several, steerable wheels of the vehicle into the desired position (also called a road wheel actuator (RWA)). In self-balancing (SBW) steering systems with yoke steering wheels or steering wheels that essentially have only one horizontal spoke (also called horn steering wheels or yoke steering wheels), hereinafter generally referred to as yoke steering wheels, it is desirable for increased comfort that the same hand position on the steering wheel can be maintained across the entire steering wheel travel, i.e., across all possible steering wheel angles. Therefore, it is known to reduce the steering wheel travel for yoke steering wheels compared to conventional steering wheels. The total steering wheel travel reflects the full range of steerable road wheel angles. This comfort feature eliminates the need to reposition your hands on the yoke steering wheel to cover the entire steerable road wheel angle range. Due to the mechanical decoupling of the steering wheel from the steerable road wheels, the SBW steering system can have a variable steering ratio, which describes the relationship between these parameters. Since the steering wheel travel is reduced in this configuration of yoke steering wheels compared to conventional steering wheels, the variable steering ratio can lead to steering behavior that is uncomfortable for the driver, for example, when high steering speeds are applied. DE 10 2007 000 650 B4 discloses a steering angle control device for a vehicle. A slip limitation control is implemented to adjust a longitudinal force applied to at least one of the wheels in order to limit wheel slip. A µ-split control is implemented as a slip limitation control. Steering angles are determined taking into account a percentage distribution of a stabilizing moment, i.e., a distribution rate. The distribution rate can be reduced with respect to a rear wheel in response to an increase in vehicle speed. US 11,873,042 B2 discloses a method for vehicle steering control in which a variable steering ratio and an additional superimposed angle are provided. The feedback torque actuator is controlled using a reference generator to ensure a target steering feel based on the torque. The target steering torque can be a function of the vehicle speed. DE 10 2014 017 127 A1 discloses a steer-by-wire steering system with an actuator mechanically decoupled from the steering wheel and a speed-dependent variable steering ratio. Steering stops limit the steering angle, while the actuator is simultaneously part of an active vehicle dynamics control system. The vehicle dynamics control system regulates the actuator based on a target / actual comparison of a vehicle dynamics parameter and can additionally include speed reduction devices and torque distribution. At high speeds, the controller can regulate the actuator up to full steering lock to stabilize oversteer. DE 10 2022 213 299 A1 discloses a steer-by-wire system with virtual translation in which a control unit generates a characteristic map for the actuator position as a function of steering angle and vehicle speed. The maximum wheel and steering angles are limited depending on the speed. The mapping can be described in sections by third-order polynomial functions. Parameters, e.g., turning points, and maximum angles are managed in tabular form and interpolated between support points. The system operates without mechanical coupling, adjusts the wheel position via an actuator motor, and limits the actuator travel / angles depending on the situation. JP 2014-133521 A describes a control logic for suppressing rack-end contacts at full lock by setting an upper limit for the command angle near the rack end and limiting the rate of change of the command angle when the driver cuts in. Near the upper limit, a limited output command is determined and used to control the steering motor accordingly, thereby preventing overshoot and noise. The system is designed for SBW architectures with mechanical decoupling and generates driving-condition-dependent haptic counterforces via a reaction force motor. DE 10 2019 215 549 A1 teaches the condition-dependent use of a conventional wheel steering angle control range in a first driving situation and the extension of this range in a second driving situation depending on an activation signal. Implementation is achieved via software / mechanical steering and end stops, a processing unit, and sensors. Activation / deactivation can be manual or automatic. The extension can take into account driving mode-specific load and occupant parameters and is reverted after a certain time or by deactivation to combine error-free operation with ease of use. DE 603 ​​07 756 T2 describes a steering control device that generates a virtual contact resistance force to limit the steering angle without physical stops and simultaneously prevent thermal stress on the motors. Dynamic thresholds for permissible steering ranges are adjusted depending on the speed; end-response forces and target currents are generated based on characteristic maps and by means of PID control. The system enables variable transmission characteristics. JP 2018-203182 A teaches a fault logic for left / right independently controlled SBW steering wheels that, in the event of a steering wheel defect, calculates a speed- and direction-dependent "Turning Limit Steering Angle" and sets this as the target angle for the intact wheel to prevent an unintended increase in the turning radius. The architecture uses a host ECU sequence with setpoint setting and fault signals. If the actual angle exceeds the limit, target angles are limited, or, in the case of a double fault, a stop is triggered. DE 10 2019 214 225 A1 discloses a steer-by-wire system in which the entire steering movement range is mapped to a speed-dependent sub-range of the wheel steering angle control range in normal driving situations to achieve a constant and precise steering ratio. In exceptional situations, for example, over- or under-steering, the usable range is dynamically changed so that higher wheel steering angles can be accessed as needed. The mapping can switch between linear and non-linear behavior and can be parameterized using characteristic curve fields / polynomials, whereby the portion of the total range used in the first situation remains limited. DE 10 2021 200 370 A1 discloses a self-balancing (SBW) method and a control unit for steering in the low-speed range from standstill to parking / maneuvering, in which the instantaneous vehicle speed is detected and a speed-dependent limited maximum steering angle is determined from this. The actuator for adjusting the wheel steering angle is controlled depending on the steering angle request, taking this limited steering angle into account. DE 102 21 721 A1 teaches an electronic steering angle limiting function with a virtual stop that specifies the maximum permissible steering angle depending on boundary conditions such as speed, speed changes, load, and suspension travel. At low speeds, the maximum technically possible steering angle can be utilized, and at higher speeds, the possible steering angle can be reduced. The approach includes electronic control components for adjusting the steering angle implemented at the wheel and takes typical operating conditions into account. The task to be solved can be seen as providing an SBW steering system and a method for operating it, by means of which full steering control can be ensured even at high steering speeds. The problem is solved by the subject matter of the independent patent claims. Advantageous embodiments are specified in the dependent patent claims and the subsequent description, each of which, individually or in (sub-)combination, can represent aspects of the disclosure. According to one aspect, some embodiments of the disclosure relate to a method for operating a steer-by-wire steering system for a vehicle, hereinafter referred to as the SBW steering system. The SBW steering system comprises at least one steering wheel, a road wheel actuator (hereinafter referred to as the RWA), and a control device. The RWA is coupled to at least one steerable road wheel. The method comprises at least the following steps: - A detected steering wheel angle is received by the control device. - A target road wheel angle of the steerable road wheel is determined by the control device based on the received steering wheel angle. The target road wheel angle is limited by road wheel angle limits that depend at least on the vehicle speed. - A control signal is output by the control device to an electric motor of the RWA or an inverter coupled to the electric motor, based on the determined target road wheel angle. The control device receives the vehicle speed. The road wheel angle limits depend on the vehicle speed in such a way that, for every vehicle speed, a change in the vehicle's lateral speed corresponding to a predetermined speed change limit can be achieved. The method is based on the understanding that a vehicle's change in lateral velocity in a curve depends on its speed. As vehicle speed increases, a smaller wheel angle is required to achieve the maximum change in lateral velocity. Further steering beyond this point does not increase the change in lateral velocity any further. Because the system is dependent on vehicle speed, the wheel angle limits can be adjusted situationally. The SBW steering system thus ensures that the vehicle's lateral control is maximized at all vehicle speeds, and that this control is achieved even with steering wheels that have short steering throws, thanks to a comfortable steering feel. The mechanical decoupling of the steering wheel from the road wheels is used according to the invention to adjust the target road wheel angle, which depends on the steering input in the form of the steering wheel angle, according to the situation. For this purpose, road wheel angle limits are taken into account, which are determined by the vehicle speed. The road wheel angle limits are therefore variable depending on the vehicle speed. This limits the target road wheel angle in such a way that the maximum change in lateral speed can always be achieved, but the steerable road wheel is essentially only moved, i.e., rotated, up to the corresponding target road wheel angle. This allows for more flexible adjustment of the target road wheel angle via the vehicle speed and an optimal response to the respective steering wheel angle.As a result, optimized determination of the target road wheel angle is enabled, which is not limited by the need to always maintain the possibility of reaching the mechanical end stops of the steerable road wheel. This allows for an adapted relationship between the required target road wheel angle and the steering angle of the steering wheel, thereby optimizing the steering behavior of the SBW steering system, especially for steering wheels with short steering wheel travel. Consequently, the steering experience is more comfortable for the user than before. The road wheel angle limits represent control-engineered, vehicle speed-dependent limits for the target road wheel angle. These limits differ from maximum mechanical road wheel angle end stops, which mechanically limit the road wheel angle. Furthermore, the road wheel angle limits do not represent control-engineered end positions of the target road wheel angle intended to prevent contact with these mechanical end stops. Such end positions serve to protect the mechanical end stops, not to limit the target road wheel angle with respect to the vehicle's maximum lateral speed change. Rather, the road wheel angle limits represent situationally variable, determined, and considered limitations of the road wheel angle.In extreme cases, the road wheel angle limits can coincide with the control-engineered end positions of the road wheel angle, which are intended to prevent contact with the mechanical road wheel angle end stops. However, due to their dependence on vehicle speed, the road wheel angle limits differ from the corresponding end positions intended to protect the mechanical road wheel angle end stops. Optionally, the control device takes the vehicle speed into account when determining the target road wheel angle. The road wheel angle limits already depend on the vehicle speed. This means that, depending on the situation, vehicle speed-dependent limits are already considered for the target road wheel angle. Additionally, the target road wheel angle can also depend on the vehicle speed within the range of possible target road wheel angles defined by the road wheel angle limits. For example, the target road wheel angle can depend linearly on the vehicle speed at low vehicle speeds and exhibit an increasingly progressive dependency at higher vehicle speeds.This enables the SBW steering system to exhibit a steering behavior that, starting from the center of the steering wheel angle (i.e., the range of small steering wheel angles relative to the reference position of the center position (straight-ahead alignment)), transitions smoothly into the off-center range. Based on this method, it is no longer necessary to be able to reach the mechanical wheel angle end stops at every vehicle speed. Therefore, the entire mechanical wheel angle range no longer needs to be considered. Consequently, there is no longer a need to design the steering behavior of the SBW steering system to be very aggressive (progressive) in order to still ensure sufficient steering control within a relatively short steering wheel travel.This is made possible in particular because a relatively smaller road wheel angle is required as vehicle speed increases, which is taken into account by the dependence of the target road wheel angle on the vehicle speed. According to one aspect, the control device can take into account a variable steering ratio between the detected steering wheel angle and the target road wheel angle when determining the target road wheel angle. This variable steering ratio depends on the vehicle speed. This allows the steering behavior of the SBW steering system to be adapted as needed. This means that different steering inputs, in the form of different steering wheel angles, result in varying degrees of effect on the vehicle's lateral control via the steering of the steerable road wheel, provided the vehicle speed varies. Variable steering ratios are preferred at higher vehicle speeds, where they are less direct. Generally, at higher speeds, the driver responds with smaller steering inputs based on corresponding steering wheel angles. Variable steering ratios allow this to be taken into account. Nevertheless, the dependence of the target road wheel angle on the vehicle speed means that even steering inputs with high steering wheel speeds or relatively large steering wheel angles result in corresponding changes in the road wheel angle, ensuring the maximum change in the vehicle's lateral speed. Alternatively, instead of determining the target road wheel angle based on the received steering wheel angle, the control device can also determine a target rack travel or a target pinion angle. Both the target rack travel and the target pinion angle correspond to the target road wheel angle. The rack and pinion are coupled, at least indirectly, to the vehicle's steerable road wheel and the road wheel actuator, or to multiple road wheels, at least if a single RWA (steerable road wheel actuator) is provided for coupling to several steerable road wheels via a common rack. The target rack travel is limited by rack travel limits. The target pinion angle is limited by pinion angle limits. The rack travel limits and the pinion angle limits correspond to the road wheel angle limits and therefore depend on the vehicle speed.The control signal output by the control device can then alternatively depend on the determined target rack travel or the determined target pinion angle. Since the rack and pinion are at least indirectly coupled to the road wheel actuator and the steerable road wheel, the corresponding variables can be used for control as an alternative to the road wheel angle. Therefore, all explanations given regarding the target road wheel angle and the road wheel angle limits are correspondingly applicable to the target rack travel, the target pinion angle, the rack travel limits, and the pinion angle limits. In one embodiment, the velocity change limit can be 1.5 G, preferably 1.3 G, more preferably 1.2 G, and more preferably, in particular, 1 G. Here, G represents the mean change in the Earth's gravitational velocity of 9.81 m / s². These limits represent typical maximum lateral velocity changes of vehicles. Optionally, a tolerance road wheel angle range is taken into account for each vehicle speed for counter-steering and / or further steering using the steering wheel, for example if the vehicle is in an oversteering or understeering configuration. Preferably, the tolerance range for road wheel angles depends on the vehicle speed. Preferably, the tolerance range for the road wheel angle can be defined at the road wheel angle limit as a reference point. The tolerance range for the road wheel angle thus denotes an additional parameter range of the road wheel angle that can be achieved for the target road wheel angle. This means that the road wheel angle limit serves as a reference point around which corresponding tolerance ranges for road wheel angles are considered to allow for situational counter-steering or further steering adjustments. This ensures that the driver can apply a sufficient counter-steering or additional steering angle in under- or over-steering situations. In vehicles equipped with electronic stability control (ESC), the required counter-steering is significantly reduced or even eliminated, depending on the tuning, settings, and effectiveness of the steering system. To further assist the driver in oversteer situations, a handling controller can be used. This controller adds or subtracts a delta road wheel angle from the variable steering ratio to support the driver's counter-steering. Typically, the driver reacts too slowly and / or insufficiently in oversteer situations. A handling controller reacts more quickly and can thus further reduce the driver's counter-steering input. The handling controller requires additional rack travel, which is accounted for by the tolerance range of the road wheel angle. When the steering wheel is understeered, most drivers continue to steer even though the additional steering angle does not produce a stronger vehicle response. This is because the lateral force of the road wheel is already saturated, and therefore further steering input does not result in a greater change in lateral velocity. In other words, a tighter turn is not possible. Modern ESC functions detect understeer and typically assist the vehicle's steering response through speed reduction processes. These processes reduce the vehicle's speed and generate an additional moment around the vehicle's vertical axis, thereby achieving a tighter turning radius. The systems generally use the driver's additional steering angle as a measure of the process's strength. Therefore, an additional road wheel angle range is required, which is appropriately accounted for by the tolerance road wheel angle range. According to one embodiment, the target road wheel angle can therefore be defined by: - ​​a tolerance road wheel angle range during understeer situations, equivalent to a delta angle of the road wheel, - a tolerance road wheel angle range for countersteering in oversteer situations, equivalent to a delta angle of the road wheel, - a tolerance road wheel angle range for extended steering functions, such as a handling controller, or - combinations thereof. It should be noted that only one tolerance range (delta angle of the road wheel) of the tolerance ranges for understeer and oversteer situations needs to be considered. Specifically, the tolerance range with the larger absolute value is simply taken into account. Preferably, the tolerance range for the road wheel angle, measured from the support point defined by the road wheel angle limit, is ±20 mm or less of the road wheel angle in each direction, more preferably ±10 mm or less, more preferably ±5 mm or less, and more preferably ±3 mm or less. Alternatively, the tolerance range for the road wheel angle can also be a percentage of the road wheel angle limit, for example ±20%, more preferably ±10%, more preferably ±5%, and more preferably ±3%. In one embodiment, the control device can incorporate additional steering functions, such as a so-called micro-split control. Micro-split control refers to a control function in which a slip limitation control is applied to limit the slip of a road wheel. The slip limitation control is executed while the vehicle is driving on a road surface with different coefficients of friction for the road wheels on the right and left sides. In this case, the control device performs a steering angle control to adjust the wheel angle of the front road wheels on the left and right sides and / or the wheel angle of the rear road wheels on the left and right sides. The steering angle control limits the influence of yaw on the vehicle.The yaw moment is caused by a difference in longitudinal force between the wheels on the right and left sides of a given road surface. The control system then adjusts the steering angle of the wheels, depending on the vehicle side, to limit the yaw moment caused by the road surface. The control system can also provide a tolerance range for the wheel angle. In comparison with the tolerance road wheel angle ranges for understeer situations and oversteer situations, with regard to the further tolerance road wheel angle range for the µ-split control, only the single tolerance road wheel angle range with the largest absolute value needs to be taken into account by the control device, which simplifies the control. Considering a tolerance range for the road wheel angle can lead to the control device determining an adjusted target road wheel angle that exceeds an original road wheel angle limit (without a tolerance range), but lies within the tolerance range provided by the original road wheel angle limit. The achievable parameter space for the target road wheel angle is thus expanded by the tolerance range compared to the original road wheel angle limit. If the control device determines an adjusted target road wheel angle, the control signal output to the electric motor is, of course, also adjusted accordingly. Optionally, the ESC function can be configured to take into account that the counter-steering angle is artificially limited based on the road wheel angle limit and the tolerance range. In previous vehicles, driver inputs were used to assess the vehicle status and the driver's desired path. Since the driver inputs are artificially limited by this process, an adapted ESC function can be configured to respond to smaller and / or slower driver inputs while maintaining the same system output—that is, the same change in the road wheel angle of the steerable wheels. This allows the adapted ESC function to be aligned with the process, ensuring the familiar driver support provided by the ESC function. Preferably, the steering wheel travel from a center position is a predetermined steering wheel angle or less. The predetermined steering wheel angle can be, for example, ±220° from the center position, preferably ±200°, more preferably ±180°, and more preferably ±150° or less. While typical steering wheels can rotate more than one full revolution in any direction from the center position (straight-ahead position), steering wheels with particularly short steering wheel travel are also known. Therefore, the method is particularly well-suited for steering wheels with a relatively short steering wheel travel. The steering wheel travel refers to the maximum possible steering wheel travel between mechanical end stops of the steering wheel or between control-defined steering wheel travel limits, which are provided to protect the mechanical end stops of the steering wheel travel or to limit the steering wheel travel altogether.The steering wheel travel limits can be predefined, for example, by the steering assist system (SAS) applying a high counter-torque as soon as a steering angle of 180°, measured from the steering wheel's center position, is reached. Generally, the driver could then steer further with considerable force, but will usually refrain from doing so due to the high counter-torque. If the driver does continue steering, this can be compensated for by the SAS when returning to the neutral position. In one configuration, the steering wheel is a yoke steering wheel. Yoke steering wheels, in particular, have short steering throws. This design ensures that the driver does not have to reposition their hands while holding the steering wheel, even at large steering angles. This increases driver comfort while simultaneously ensuring optimized steering response from the SBW steering system. Preferably, the smoke and heat exhaust ventilation (SHEV) system, based on the control signal received from the control device, uses its electric motor to output a torque, thus rotating the steerable road wheel according to the target road wheel angle. Since the target road wheel angle is limited based on the road wheel angle limits with an optional tolerance range, the SHEV system's electric motor will not move the steerable road wheel into a position beyond these limits. This would have no effect on the vehicle's steerability anyway, as the road wheel angle limits reflect the configuration of the vehicle's maximum lateral velocity change as a function of its speed. According to a further aspect, the invention also relates to a computer program product comprising instructions that, when the computer program product is executed by a processor, cause the processor to execute at least part of the method described above, in particular the arithmetic and output steps. The advantages achieved by the method described herein are also achieved by the computer program product in a corresponding manner. According to an additional aspect, the invention also relates to a computer-readable storage medium comprising instructions that, when the computer program product is executed by a processor, cause the processor to execute at least part of the method described above, in particular the measurement, simulation, and calculation steps. The advantages achieved by the method described herein are also achieved correspondingly by the computer-readable storage medium. According to one aspect, some embodiments of the disclosure relate to a self-steering vehicle (SBW) steering system for a vehicle. The SBW steering system comprises at least one steering wheel, a smoke and heat exhaust ventilation (SHEV) system, and a control device. The SHEV system is coupled to at least one steerable road wheel. The control device is configured to: - receive a detected steering wheel angle; - determine a target road wheel angle of the steerable road wheel based on the received steering wheel angle. The target road wheel angle is limited by road wheel angle limits that depend at least on the vehicle speed; - output a control signal to an electric motor of the SHEV system or to an inverter coupled to the electric motor based on the determined target road wheel angle. The control device receives the vehicle speed. The road wheel angle limits depend on the vehicle speed in such a way that for every vehicle speed a change in vehicle lateral speed corresponding to a given speed change limit can be achieved. The advantages achieved through this method are also realized by the SBW steering system. In particular, the steering of the road wheel can be optimized even for short steering wheel movements, ensuring comfortable steering behavior for the driver. This is made possible primarily by limiting the road wheel angle depending on the vehicle speed, thereby guaranteeing the maximum achievable lateral speed change in each situation, in accordance with a predefined speed change limit. In one embodiment, the SBW steering system includes at least one steering wheel sensor designed to detect the steering wheel angle. This allows the target road wheel angle to be precisely adjusted to the driver's steering input. Optionally, the SBW steering system includes at least one sensor configured to detect a measurement variable influenced by the RWA and transmit it to a steering wheel actuator (hereinafter referred to as FBA), and / or to the RWA, and / or the control device. The FBA is configured to apply a feedback torque to the steering wheel that depends on the detected measurement variable. This allows feedback torque to be provided to the driver at the steering wheel, giving them a situation-adapted feel for the vehicle's lateral control depending on the output of the RWA. The control device can adjust the steerable road wheel according to the target road wheel angle based on the measured value. The control device can be part of the RWA (Rail-Wave Exhaust System). The control device can also be part of the FBA (Full-Body Automation System). The control device can also be separate from the RWA and the FBA. The control device can also be part of another vehicle component, for example, a driving control device that performs further control functions. According to one aspect, some embodiments of the disclosure relate to a vehicle with an SBW steering system as previously described. The advantages achieved by the SBW steering system are correspondingly also achieved by the vehicle. The vehicle can be a land vehicle. The vehicle can have an internal combustion engine, it can be an electric vehicle, or it can be a hybrid vehicle. The invention, as well as further advantageous embodiments and developments thereof, are described and explained in more detail below with reference to the examples shown in the drawings. The drawings show: - Fig. 1 a vehicle with an SBW steering system according to the invention, - Fig. 2 a method according to the invention for operating an SBW steering system for a vehicle, and - Fig. 3 a schematic representation of a road wheel angle range in connection with the method according to the invention. All features mentioned below with reference to the exemplary embodiments and / or the accompanying figures can be combined alone or in any subcombination with features of the invention, including features of preferred embodiments. Fig. 1 shows a vehicle 10 with an SBW steering system 12 according to the invention. The SBW steering system 12 includes a smoke and heat exhaust ventilation (SHEV) 14 and a control device 16. The SBW steering system 12 also includes an air handling unit (AHU) 18. The AHU 18 and the SHEV 14 are coupled together. The control device 16 is shown separately from the smoke and heat exhaust ventilation (SHEV) 14. However, the control device 16 can generally also be part of the SHEV 14 or the ventilation unit 18, or be distributed as part of both the SHEV 14 and the ventilation unit 18. The RWA 14 is indirectly coupled to the steerable road wheels 20 of the vehicle 10. For this purpose, the RWA 14, according to the present embodiment, has an electric motor 22 which is coupled to a rack 24. The rack 24 is coupled to the steerable road wheels 20 of the vehicle 10. The displacement of the rack 24 with respect to a reference position, such as a neutral position (straight-ahead position), results in a change in the orientation of the steerable road wheels 20 about the steering axes of the respective road wheels 20. Alternatively, the RWA 14 can also be indirectly configured to rotate a single road wheel 20. If the vehicle 10 has several steerable road wheels 20, the SBW steering system 12 in this case has several partial RWAs 14 and / or several electric motors 22, each assigned to individual steerable road wheels 20, and which can individually influence the wheel angle of the individual steerable road wheels 20. The SBW steering system 12 has a sensor 26 designed to detect an operating parameter of the SBW steering system 12 influenced by the operation of the RWA 14, such as a road wheel angle of the steerable road wheels 20, a rack travel of the rack 24, or a pinion angle of a pinion coupled to the RWA 14 and the rack 24. Alternatively, the sensor 26 can also be configured as a torque sensor designed to detect the torque output by an electric motor 22 of the RWA 14 to a coupled component, such as the rack 24. Furthermore, the measured values ​​of the operating parameters thus detected are transmitted by the sensor 26 to the RWA 14 and / or the FBA 18. Of course, several sensor units can also form the sensor 26 together, thus enabling mutual plausibility checks and redundancy. The SBW steering system 12 also includes a steering wheel 28, to which the FBA 18 is coupled, at least indirectly, for example via a steering column. The FBA 18 is designed to exert a feedback torque on the steering wheel 28, thus providing the driver of the vehicle 10 with a feeling for the lateral control of the vehicle 10. The driver of vehicle 10 can execute 28 steering commands for vehicle 10 via the steering wheel. According to this embodiment, the steering wheel 28 is a yoke steering wheel. The steering wheel travel 30 of the steering wheel 28 is therefore shorter compared to that of a conventional steering wheel. In particular, according to this embodiment, the steering wheel 28 has a steering wheel travel 30 according to which, starting from the center position (straight ahead), the steering wheel 28 can be rotated a maximum of ± 180° based on control parameters. Other control-defined steering wheel travels can, of course, also be implemented. Thus, according to this embodiment, the steering wheel 28 can only be rotated by half a turn at a time from the center position. As a result, the driver of the vehicle 10 does not need to change their hand position when steering with the steering wheel 28. The driver does not have to reposition their grip. The steering wheel travel 30 is limited by mechanical steering wheel stops. In addition, the FBA 18 takes into account control-defined limit values ​​for the steering wheel travel 30 so that the steering wheel 28 is not moved by the driver of vehicle 10 in such a way that the mechanical steering wheel stops are stressed. Alternatively, the steering wheel stops can also allow a larger mechanical steering wheel travel, which is, however, limited by the control system, for example because the FBA 18 outputs high feedback torques for steering wheel angles greater than ± 180° starting from the center position. The SBW steering system 12 also includes at least one steering wheel sensor 32, which is configured to detect a steering wheel angle, i.e., a steering wheel position, of the steering wheel 28 relative to a reference position, for example, a center position (zero position). Consequently, the steering wheel sensor 32 can be used to detect steering inputs from the driver of the vehicle 10 based on the steering wheel 28. In this respect, a steering input defines a specific current steering wheel angle and steering wheel speed. A current steering command corresponds to a specific current target road wheel angle according to which the steerable road wheels 20 are to be aligned. Since the road wheels 20 are at least indirectly coupled to the steerable road wheels 20 via the rack 24 and a pinion in the power transmission path of the RWA 14, a steering command is equivalent to a target rack travel of the rack 24 and a target pinion angle of the pinion, so that a desired orientation of the road wheels 20 is achieved. Changing the steering wheel position dynamically modifies the current steering input from the user, which in turn leads to a dynamic change in the target road wheel angle. The dependence of the target road wheel angle on the current steering input, in the form of the current steering wheel angle, is taken into account by the control device 16 within the framework of a steering ratio. The steering ratio thus describes how the target road wheel angle dynamically varies depending on the steering wheel angle. In general, the steering ratio is variable. This means that, especially for small steering wheel angles relative to the reference position (center position), the target road wheel angle can depend linearly on the steering wheel angle. For larger steering wheel angles, a transition to a non-linear relationship is taken into account. According to this embodiment, the steering wheel sensor 32 is integrated into the FBA 18. In other embodiments, however, the steering wheel sensor 32 can be separate from the FBA 18. The steering wheel sensor 32 is configured to transmit the detected steering wheel angle to the RWA 14 and / or to the FBA 18. The control device 16 includes a processor. The control device 16 is configured to receive the steering wheel angle from the steering wheel sensor 32. Based on the received steering angle requirements, the control device 16 can determine the corresponding current target road wheel angle and other variables or properties of the SBW steering system 12. The control device 16 is also configured to output corresponding control signals to the electric motor 22 of the smoke and heat exhaust ventilation system (SHEVS) 14 or to a converter coupled to it. To execute the corresponding control routines, the control device 16 can take into account further parameters of the vehicle 10, such as the vehicle speed. To detect the vehicle speed, the vehicle 10 according to this embodiment has a speed sensor 34 which is configured to detect the vehicle speed and transmit it to the RWA 14 and / or the FBA 18. Alternatively, the control device 16, the RWA 14, and / or the FBA 18 can also receive the vehicle speed from another vehicle component, for example a driving control device or a control device that performs other control functions. Based on the control signal, the electric motor 22 of the RWA 14 provides an output torque to align the steerable road wheels 20 accordingly. The output torque from the electric motor 22 of the RWA 14 is exerted on the rack 24, thus indirectly varying the alignment of the steerable road wheels 20. The sensor 26 detects a property influenced by the RWA 14, such as the road wheel angle of the steerable road wheels 20, a displacement of the rack 24 or a pinion angle of a pinion, and transmits the detected measurement to the RWA 14 and the FBA 18. The FBA 18 determines a corresponding feedback torque, which is output to the steering wheel 28. The SBW steering system 12 can of course also have several similar and generally identical functional components, for example several steering wheel sensors 32, thereby ensuring redundancy. According to this embodiment, the vehicle 10 comprises a higher-level driving control device 36. The higher-level driving control device 36 is configured to perform autonomous or semi-autonomous driving functionalities. For example, the higher-level driving control device 36 can autonomously influence the lateral control of the vehicle 10. For this purpose, the higher-level driving control device 36 can, for example, specify a steering wheel angle, which is subsequently adjusted accordingly by the FBA 18 of the SBW steering system 12. The steering wheel angle is detected by the steering wheel sensor 32 and transmitted to the RWA 14, or it is transmitted directly to the RWA 14 by the higher-level driving control device 36. Here, the SBW steering system 12 is shown as a front axle steering system. The vehicle 10 and the SBW steering system 12 can optionally also have additional steerable road wheels 20, for example rear wheels, which are coupled with an additional common RWA 14. The steerable road wheels 20 can be moved between mechanical road wheel angle end stops 38 by the RWA 14. To prevent stress on the mechanical road wheel angle end stops 38, the RWA 14 takes into account control-defined end positions of the road wheel angle. Fig. 2 shows a method according to the invention for operating an SBW steering system 12 for a vehicle 10. Optional steps are shown in dashed lines. In optional step S2, the control device 16 receives a vehicle speed from the vehicle 10. For example, the vehicle speed of the vehicle 10 can be detected by the speed sensor 34 and transmitted to the control device 16. In the subsequent step S4, the control device 16 receives a detected steering wheel angle from the steering wheel 28. The steering wheel angle of the steering wheel 28 is detected by the steering wheel sensor 32 and transmitted to the control device 16. According to this embodiment, the steering wheel 28 is a yoke steering wheel whose steering travel is limited to one full rotation. Starting from a center position (straight-ahead position), the yoke steering wheel can be rotated ±180°. In the subsequent step S6 of the procedure, the control device 16 determines a target road wheel angle for the steerable road wheels 20 based on the received steering wheel angle. The target road wheel angle is limited by road wheel angle thresholds that depend at least on the vehicle speed of the vehicle 10. This means that the control device 16 applies a transmission ratio between the steering wheel angle and the target road wheel angle to determine the target road wheel angle of the steerable road wheels 20. Step S6 can be further developed in various ways through the optional steps S8, S10 and S14. Optionally, step S8 can be included, in which the control device 16 takes into account a variable steering ratio between the detected steering wheel angle and the target road wheel angle. This allows, for example, a linear dependence of the target road wheel angle on the detected steering wheel angle for small steering wheel angles starting from the reference position of the steering wheel's center position 28. For relatively larger steering wheel angles starting from the reference position, the target road wheel angle can then depend non-linearly on the detected steering wheel angle. This allows for both direct and / or progressive steering behavior for different ranges of the detected steering wheel angle. According to optional step S10, the control device 16 incorporates a variable steering ratio that depends on the vehicle speed. While the road wheel angle limits are already dependent on the vehicle speed 10, the speed-dependent variable steering ratio allows for the consideration of dynamic relationships between the target road wheel angle and the detected steering wheel angle. This means, for example, that for the same relative angular offset of the detected steering wheel angle from the reference position (straight ahead), different steering behaviors are considered for different vehicle speeds. If the vehicle 10 is traveling at high speeds, the driver typically makes only minor steering inputs based on small steering wheel angles measured from the straight-ahead reference position (straight ahead).At low vehicle speeds, for example during parking maneuvers, a different steering behavior can be ensured. This provides a variable steering ratio that takes the vehicle speed into account depending on the driving situation. In particular, the optional step S10 allows the control device 16 to take into account a variable steering ratio which is less direct at higher vehicle speeds, thus resulting in smaller target road wheel angles for the same detected steering wheel angles compared to lower vehicle speeds. In accordance with step S12, the road wheel angle limits are determined by the control device 16 such that a vehicle lateral velocity change of 1 G is achievable. This ensures that the control device 16 maximizes the steerability of the vehicle 10 with respect to lateral control at all vehicle speeds. Based on the steering ratio, the road wheel angle limits correspond to a specific steering wheel angle of the steering wheel 28. Without the corresponding limitation provided by the road wheel angle limits, the driver of the vehicle 10 could turn the steering wheel 28 to larger road wheel angles. This would actually correspond to larger target road wheel angles. However, with increasing vehicle speed, a smaller road wheel angle is required to achieve the maximum lateral velocity change of the vehicle 10.Even further turning of the steering wheel 28 beyond the corresponding steering wheel angle does not increase the lateral velocity change of the vehicle 10 any further. It follows that the target road wheel angle can be limited by corresponding road wheel angle limits, which on the one hand depend on the vehicle speed and on the other hand are dimensioned such that the maximum vehicle lateral velocity change is ensured. Optionally, step S14 can also be considered by having the control device 16 take into account a tolerance range for the road wheel angle limits. This tolerance range allows for the creation of a tolerance zone for driving-related events such as oversteer, understeer, and / or a µ-split steering function of the control device 16. To accommodate this tolerance range, the control device 16 can include a handling controller that executes the corresponding steering functions. Since the tolerance range is defined based on the road wheel angle limit, the target road wheel angle can then also assume values ​​beyond the road wheel angle limit. As a result of the optional steps S8, S10 and S14, the target road wheel angle depends on: - a tolerance road wheel angle range for understeer situations, equivalent to a delta angle of the road wheels 20, - a tolerance road wheel angle range for countersteering in oversteer situations, equivalent to a delta angle of the road wheels 20, - a tolerance road wheel angle range for extended steering functions, such as a µ-split control, which provides slip limitation control for different road wheels 20 to compensate for different coefficients of friction, for example by means of a handling controller, or - combinations thereof. Following step S6, the procedure includes step S16, in which the control device 16 determines a control signal for the electric motor 22 of the smoke and heat exhaust ventilation system (SHEVS) 14 based on the determined (or adjusted based on the tolerance range of the road wheel angle) target road wheel angle and outputs it to the electric motor 22 of the SHEVS 14. The control signal specifies the target road wheel angle to be achieved for the steerable road wheels 20. In the optional subsequent step S18, the road wheels 20 (generally at least one road wheel 20) are controlled by the RWA 14 and its electric motor 22 based on the received control signal so that the road wheels 20 assume an orientation that corresponds to a target road wheel angle of the steerable road wheels 20, which is equal to the target road wheel angle. For this purpose, the RWA 14 can, for example, have a control loop with feedback that takes into account the measured value acquired by the sensor 26. Fig. 3 shows a schematic representation of a road wheel angle range 40 of steerable road wheels 20 in connection with the method according to the invention. The steerable road wheels 20 are generally movable along the road wheel angle range 40 between the mechanical road wheel angle end stops 38. According to this embodiment, the control device 16 takes into account control-engineered end positions 42 that prevent the steerable road wheels 20 from reaching the mechanical road wheel angle end stops 38 at all. This protects the mechanical road wheel angle end stops 38. The reference position 44 for the road wheel angle range 40, corresponding to a straight-ahead orientation, is designated. The reference position 46 is a current road wheel angle of the steerable road wheels 20. A steering input from the driver of vehicle 10, based on a corresponding steering wheel angle, is detected by the steering wheel sensor 32. Based on the detected steering wheel angle and taking into account the vehicle speed of vehicle 10, the control device 16 determines the target road wheel angle 48. The target road wheel angle 48 is limited by a road wheel angle limit value 50, which depends on the vehicle speed of vehicle 10. The road wheel angle limit value 50 indicates the target road wheel angle 48 at which the maximum change in the vehicle's lateral velocity is reached. Further rotation of the steerable road wheels 20 beyond the road wheel angle limit value 50 has no effect due to the vehicle speed and is therefore prevented. With regard to the road wheel angle limit value 50, the control device 16 takes into account a tolerance road wheel angle range 52 in order to be able to consider an additional parameter range for special steering situations based on the road wheel angle limit value 50. The tolerance range for the road wheel angle 52 is determined with regard to possible oversteering situations, understeering situations, the road wheel angle of the steerable road wheels 20, which corresponds to a maximum vehicle lateral velocity change of 1 G, and additional steering functions of the SBW steering system 12. The individual sub-factors can, in principle, lead to different tolerance ranges for the road wheel angle 52. However, only the tolerance range for the road wheel angle 52 with the largest absolute value needs to be considered, as it encompasses the other tolerance ranges for the road wheel angle 52. A maximum value of the target road wheel angle 48 is therefore limited by the road wheel angle limit value 50 and the additional tolerance road wheel angle range 52. Based on the target road wheel angle 48, the control device 16 then determines a corresponding control signal, which is output to the electric motor 22 of the RWA 14. Although the disclosure has been presented and described in relation to one or more embodiments, the person skilled in the art will be able to make equivalent changes and modifications after reading and understanding this description and the accompanying drawings. QUOTES INCLUDED IN THE DESCRIPTION This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited Patent Literature DE 10 2007 000 650 B4

[0005] US 11,873,042 B2

[0006] DE 10 2014 017 127 A1

[0007] DE 10 2022 213 299 A1

[0008] JP 2014-2014 DE

[3021] ADE 10 2019 215 549 A1

[0010] DE 603 ​​07 756 T2

[0011] JP 2018-203182 A

[0012] DE 10 2019 214 225 A1

[0013] DE 10 20 2012 2014 DE 10 2010 102 21 721 A1

[0015]

Claims

Method for operating a steer-by-wire steering system (12) for a vehicle (10), wherein the steer-by-wire steering system (12) comprises at least a steering wheel (28), a road wheel actuator (14), and a control device (16), wherein the road wheel actuator (14) is coupled to at least one steerable road wheel (20), and wherein the method comprises at least the following steps: - receiving a detected steering wheel angle of the steering wheel (28) by the control device (16), - determining a target road wheel angle (48) of the steerable road wheel (20) by the control device (16) based on the received steering wheel angle, wherein the target road wheel angle (48) is limited by road wheel angle limits (50) that depend at least on the vehicle speed.and- outputting a control signal to an electric motor (22) of the road wheel actuator (14) or an inverter coupled to the electric motor (22) based on the determined target road wheel angle (48) by the control device (16), wherein the control device (16) receives the vehicle speed, and wherein the road wheel angle limits (50) depend on the vehicle speed such that for each vehicle speed a change in vehicle lateral speed corresponding to a predetermined speed change limit can be achieved, ., Method according to claim 1, characterized in that the control device (16) takes into account the vehicle speed of the vehicle (10) when determining the target road wheel angle (48). Method according to claim 1 or 2, characterized in that the control device (16) takes into account a variable steering ratio between the detected steering wheel angle of the steering wheel (28) and the target road wheel angle (48) when determining the target road wheel angle (48), and wherein the variable steering ratio depends on the vehicle speed. Method according to claim 3, characterized in that the variable steering ratio is less direct at higher vehicle speeds. Method according to one of the preceding claims, characterized in that the control device determines a target rack travel of a rack (24) corresponding to the target road wheel angle (48), which is coupled to several steerable road wheels (20), and wherein the target rack travel is limited by means of rack travel limits which correspond to the road wheel angle limits (50). Method according to one of the preceding claims, characterized in that the target road wheel angle (48) depends on the vehicle speed in such a way that for each vehicle speed a tolerance road wheel angle range (52) is taken into account for counter-steering and / or further steering by means of the steering wheel (28). Method according to claim 6, characterized in that the tolerance road wheel angle range (52) is dimensioned as a support point at the road wheel angle limit value (50). Method according to claim 7, characterized in that the tolerance road wheel angle range (52) measured from the support point defined by the road wheel angle limit value (50) is ±20 mm or less of the road wheel angle in each direction, or measured at the road wheel angle limit value (50) is ±20%. Method according to one of claims 6 to 8, characterized in that for understeer and oversteer situations only the larger of the tolerance road wheel angle ranges (52) is taken into account by the control device (16). Method according to one of the preceding claims, characterized in that a steering wheel travel of the steering wheel (28) starting from a central position is at least a predetermined steering wheel angle or less. Method according to one of the preceding claims, characterized in that a steering wheel movement (30) of the steering wheel (28) starting from a central position has a predetermined steering wheel angle of ±220° or less. Method according to one of the preceding claims, characterized in that the road wheel angle limits (50) represent control-engineered vehicle speed-dependent limits of the target road wheel angle (48), wherein the road wheel angle limits (50) are different from maximum mechanical road wheel angle end stops (38) that mechanically limit the road wheel angle. A steer-by-wire steering system (12) for a vehicle (10), wherein the steer-by-wire steering system (12) comprises at least one steering wheel (28), a road wheel actuator (14), and a control device (16), wherein the road wheel actuator (14) is coupled to at least one steerable road wheel (20), and wherein the control device (16) is configured to: - receive a detected steering wheel angle of the steering wheel (28), - determine a target road wheel angle (48) of the steerable road wheel (20) based on the received steering wheel angle, wherein the target road wheel angle (48) is limited by road wheel angle limits (50) that depend at least on the vehicle speed, and - output a control signal to an electric motor (22) of the road wheel actuator (14) or an inverter coupled to the electric motor (22) based on the determined target road wheel angle (48), wherein the control device (16) receives the vehicle speed,and wherein the road wheel angle limits (50) depend on the vehicle speed in such a way that for each vehicle speed a change in vehicle lateral speed corresponding to a specified speed change limit can be achieved. Steer-by-wire steering system (12) for a vehicle (10) according to claim 13, characterized in that the steer-by-wire steering system (12) has at least one steering wheel sensor (32) which is configured to detect a steering wheel angle of the steering wheel (28). Steer-by-wire steering system (12) for a vehicle (10) according to claim 13 or 14, characterized in that the steer-by-wire steering system (12) has at least one sensor (26) which is configured to detect a measured quantity influenced by the road wheel actuator (14) and to transmit it to the steering wheel actuator (18), and wherein the steering wheel actuator (18) is configured to apply a feedback torque to the steering wheel (28) which depends on the detected measured quantity.

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