Method for operating a steering system of a vehicle - Patents.com

Abstract

The invention is based on a method for operating a steering system (10) of a vehicle (12), in particular of a motor vehicle, the steering system (10) being configured as a steer-by-wire steering system and comprising an operating unit (14) with at least one steering wheel (16) and at least one feedback actuator (18) cooperating with the steering wheel (16), as well as at least one wheel steering angle adjuster (20) operatively connected to the operating unit (14) for varying the wheel steering angle of at least one vehicle wheel (22, 24), monitoring the operation of the feedback actuator (18) by means of a monitoring function (26) and varying the steering characteristics of the steering system (10) in at least one operating state in which a fault and / or failure of the feedback actuator (18) has been identified by means of the monitoring function (26). It is proposed to use a further monitoring function (28) to monitor the driver target setting (30) for the wheel steering angle regulator (20) and, if the dynamics of the driver target setting (30) in the operating state exceed a threshold value, to determine a compensation amount (31), particularly in the form of an offset, and to modify the driver target setting (30) with the compensation amount (31) in order to change the steering characteristic.

Description

[Technical field]

[0001] Background technology The invention is based on a method for operating a steering system of a vehicle as defined in the preamble of claim 1. Furthermore, the invention relates to a computing unit for implementing such a method, a steering system comprising such a computing unit and a vehicle comprising such a steering system. [Background technology]

[0002] From the prior art, vehicles are known with conventional steering systems, in which a steering wheel, for example in the form of a steering wheel, is mechanically fixedly connected via a steering column to a wheel steering angle regulator in the form of a steering gear. Furthermore, vehicles are known with steer-by-wire steering systems which can be operated without a direct mechanical connection between the steering wheel and the steered vehicle wheels, in which the driver target settings and / or steering settings are transmitted exclusively electrically. Such steer-by-wire steering systems typically comprise an operating unit with a steering wheel and a feedback actuator, and at least one wheel steering angle regulator which is mechanically separated from the operating unit, which may be configured, for example, as a central regulator or as an individual wheel regulator.

[0003] Furthermore, such steer-by-wire steering systems are essentially configured redundantly for reasons of operational reliability. With regard to the operating unit, it is possible, for example, to configure the operating unit in a fail-safe or fail-operational manner. Furthermore, it is also possible for the operating unit to be configured in a fail-operational manner with regard to the detection of the driver-target setting and in a fail-safe manner with regard to the feedback torque provided by the feedback actuator. In a corresponding configuration of the operating unit, in the event of a fault and / or failure of the feedback actuator, unintended steering movements can occur at the steering wheel due to the sudden disappearance of the feedback torque, which can be recognized by the steering system as a driver-target setting and / or steering setting and thus lead to undesired vehicle responses. Methods with which such error cases can be handled are described, for example, in DE 102016009684 A1 and DE 102018222442 A1. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] DE 102016009684 A1 [Patent Document 2] DE 102018222442 Summary of the Invention [Problem to be solved by the invention]

[0005] Starting from this, the object of the present invention is to provide a method which has improved properties, in particular with regard to its mode of operation. The above-mentioned object is achieved by the features of claims 1, 12, 13 and 14, advantageous configurations and developments of the invention being defined in the dependent claims. [Means for solving the problem]

[0006] Disclosure of the Invention The invention is based on a method for operating a steering system of a vehicle, in particular an automobile, wherein the steering system is configured as a steer-by-wire steering system and comprises an operating unit with at least one steering wheel and at least one feedback actuator cooperating with said steering wheel, as well as at least one wheel steering angle regulator operatively connected to the operating unit for changing the wheel steering angle of at least one vehicle wheel, monitoring the operation of the feedback actuator using a monitoring function, and changing the steering characteristics of the steering system in at least one operating state in which a fault and / or failure of the feedback actuator has been identified using the monitoring function.

[0007] It is proposed to monitor, by means of a further monitoring function, in particular a driver-target setting for the wheel steering angle regulator applied by the driver to the steering wheel, and to determine a compensation amount, in particular in the form of an offset, in case the dynamics of the driver-target setting in the operating state exceed a threshold value, and to modify the driver-target setting by means of the compensation amount in order to modify the steering characteristic. The operating state in which a fault and / or a malfunction of the feedback actuator is identified by means of the monitoring function thus corresponds in particular to a driver operating state. Furthermore, the steering characteristic is modified by the modification of the driver-target setting and by means of the compensation amount, in particular in the operating state, in particular in the transition of the feedback actuator from an active and / or fully functional state to a passive and / or degraded state, such that a substantially unchanged steering behavior is provided and / or obtained, and in particular in such a way that unintended steering movements of the driver due to faults and / or malfunctions of the feedback actuator do not lead to undesired vehicle reactions. This configuration allows, in particular, to improve the functioning strategy, advantageously improving the controllability and / or steerability of the vehicle in the event of an error or loss of the active feedback torque of the feedback actuator. Furthermore, it is possible to provide a flexible, advantageously adaptive and / or variable, way of adapting the steering characteristic to the current operating conditions. Furthermore, advantageous maneuverability of the vehicle can be achieved and operational reliability can be increased.

[0008] The steering system is here configured as a steer-by-wire steering system, in which the driver target settings and / or steering settings are advantageously transmitted purely electrically to the vehicle wheels. For this purpose, the steer-by-wire steering system comprises an operating unit, in particular configured redundantly, and at least one wheel steering angle regulator, which is mechanically separated from the operating unit and in particular configured redundantly. Preferably, the operating unit and the wheel steering angle regulator are configured here at least partially fail-operationally. By "wheel steering angle regulator" is to be understood an actuator unit coupled to at least one vehicle wheel, which actuator unit is provided for transmitting the driver target settings and / or in particular the driver's steering settings to the vehicle wheels by a change in the wheel steering angle of the at least one vehicle wheel, and thereby advantageously for controlling the orientation of at least one of the vehicle wheels and / or for influencing the driving direction of the vehicle. For this purpose, the wheel steering angle regulator advantageously comprises at least one steering adjustment element, for example in the form of a rack, and at least one steering actuator, for example in the form of an electric motor, operatively connected to the steering adjustment element. In this case, the wheel steering angle regulator may be configured as a central regulator and may be associated with at least two vehicle wheels, in particular steerable and preferably configured as front wheels. Alternatively, however, the wheel steering angle regulator may be configured as an individual wheel regulator and may be associated with exactly one vehicle wheel, in particular steerable and preferably configured as a front wheel. Furthermore, a "feedback actuator" is to be understood as an actuator unit, in particular different from the wheel steering angle regulator, which is mechanically connected, in particular directly to the steering wheel, and which is provided for detecting signals, forces and / or torques, in particular directly from the steering wheel and / or for transmitting them, in particular directly to the steering wheel.Here, the feedback actuator is provided for providing at least an active feedback torque in normal operating conditions, thereby generating a steering resistance and / or a self-aligning torque at the steering wheel. Furthermore, the feedback actuator is provided in this context for adapting the steering feel, which is perceptible in particular via the steering wheel. For this purpose, the feedback actuator may comprise at least one further electric motor. By "faults and / or failures of the feedback actuator" is to be understood in particular faults and / or failures of the feedback actuator itself and / or of peripheral assemblies cooperating with the feedback actuator, for example energy supplies, and faults of the feedback actuator caused thereby. Furthermore, the wheel steering angle is essentially equivalent to other variables between the steering actuator and the vehicle wheels, such as, for example, the displacement of the steering adjustment element and / or the displacement position of the wheel steering angle regulator and / or the motor movement. The same applies for the displacement of the steering wheel, which is equivalent to other variables between the steering wheel and the feedback actuator, such as, for example, the steering column angle and / or the motor angle. With respect to torque variables at the vehicle wheels and steering wheel, similar equivalence of variables between the vehicle wheels / steering wheel and each connected actuator applies.

[0009] Furthermore, the vehicle, preferably the steering system, comprises at least one calculation unit, which is provided for implementing the method for the operation of the steering system. By "calculation unit" it is to be understood an electric and / or electronic unit having an information input, an information processing and an information output. Advantageously, the calculation unit further comprises at least one processor, at least one operating memory, at least one input means and / or output means, at least one operating program, at least one open-loop and / or closed-loop control routine, at least one calculation routine, at least one calculation routine, at least one evaluation routine and / or at least one adaptation routine. In particular, the calculation unit comprises in this case at least one monitoring function for monitoring the operation of the feedback actuators. Furthermore, the calculation unit comprises at least one further monitoring function, in particular for monitoring the driver-target settings applied by the driver to the steering wheel, in particular for monitoring the dynamics of the driver-target settings. The calculation unit is in particular provided for monitoring and evaluating the operation of the feedback actuators by means of the monitoring function. Furthermore, the calculation unit is provided for monitoring and evaluating, in particular, the driver-target settings for the wheel steering angle regulator, which are applied by the driver to the steering wheel, by means of a further monitoring function. Furthermore, the calculation unit is provided for modifying the steering characteristics of the steering system in at least one operating state in which a fault and / or a failure of the feedback actuator is identified and the dynamics of the driver-target settings exceed a threshold value, and for correcting the driver-target settings by means of a compensation amount. In this connection, the calculation unit is provided in particular for utilizing error signals provided by the monitoring function and / or detection signals provided by the further monitoring function for adapting the steering characteristics. Advantageously, the calculation unit is here integrated in a control device of the vehicle, for example a central vehicle control device or in a control device of the steering system, advantageously in particular in the form of a steering control device."Provided" should be understood to mean, among other things, specifically programmed, configured and / or equipped. An object being provided for a particular function should be understood to mean, among other things, that this object fulfills and / or performs this particular function, at least in an application state and / or in an operational state.

[0010] Furthermore, it is proposed to take into account the current and / or impending driving situation when changing the steering characteristic, in particular when correcting the driver-target setting by means of a compensation amount, which allows, in particular, a situation-adapted change of the steering characteristic. In particular, the steering characteristic is changed in this case in relation to the current and / or impending driving situation. The current and / or impending driving situation is determined and / or predicted, for example, on the basis of at least one vehicle variable, for example the yaw rate, the steering wheel displacement and / or the steering movement. However, alternatively or additionally, the current and / or impending driving situation may also be derived from the route planning of a navigation system of the vehicle and / or from a corresponding sensor system of the vehicle, for example in the form of a camera system.

[0011] Advantageously, the operating state corresponds to cornering. Advantageously, the steering characteristic is changed here only if the wheel steering angle of the vehicle wheels is not equal to 0, preferably in particular if it has an absolute value of at least 0.1°. Particularly preferably, a change in the steering characteristic is therefore made when the vehicle is cornering, and not when the vehicle is driving straight ahead. This increases operational safety, in particular in dangerous driving situations. Furthermore, advantageously, a particularly efficient method is provided.

[0012] Furthermore, it is proposed that when changing the steering characteristic, in particular when correcting the driver-target setting by means of a compensation amount, the dynamics and / or the absolute value of the driver-target setting are taken into account, i.e. for example the maximum displacement of the steering wheel and / or the steering speed of the steering wheel. Preferably, the dynamics and / or the absolute value of the driver-target setting are determined by means of a further monitoring function. This makes it possible, in particular, to identify over-reactions of the driver when the active feedback torque of the feedback actuator disappears and in this connection to adapt the steering characteristic.

[0013] Furthermore, it is proposed to modify the driver's target setting by means of a compensation amount, so that the driver's target setting is reduced in the operating state in order to change the steering characteristic. Thus, in particular in the operating state, the driver's target setting, in particular modified by means of a compensation amount, which is transmitted to the wheel steering angle regulator instead of the driver's target setting and / or is used to control the wheel steering angle regulator in the operating state, is reduced in comparison with the driver's target setting, preferably by at least 10%, preferably by at least 20%, particularly preferably by at least 30%. Advantageously, the modified driver's target setting is here reduced by a maximum of 90%. This reduces the vehicle reaction and makes the situation more manageable for the driver.

[0014] Furthermore, it is proposed to add the driver's target setting and the compensation amount to one another in order to change the steering characteristic. In particular, this addition results in a driver's target setting which is modified in particular by means of the compensation amount. This allows the driver's target setting to be modified in a particularly easy manner, in particular by software techniques.

[0015] In a further embodiment, it is proposed to limit the maximum level of the compensation amount, in particular to allow for possible actual needs for stronger steering of the vehicle and to allow intentional oversteering of the changed steering characteristic, which can advantageously ensure, for example, that intentional steering movements can still be carried out during an avoidance maneuver.

[0016] Preferably, it is further proposed to determine the compensation amount using a compensation function to which at least the detection signal provided by the driver target setting and / or the further monitoring function and the error signal provided by the monitoring function are supplied as input quantities. In particular, the calculation unit may in this case include the compensation function. Furthermore, the compensation function may be supplied with further vehicle variables, such as, for example, the vehicle speed, the yaw rate and / or the lateral acceleration. Preferably, in addition, a dynamic gradient limitation is used when determining the compensation amount using the compensation function, by means of which the increase of the driver target setting is limited in relation to at least one driving characteristic variable, whereby the compensation amount is determined advantageously on the basis of the difference between the gradient-limited driver target setting and the driver target setting. In this connection, the driving characteristic variable in particular specifies the conditions under which the corresponding gradient limitation is performed. Furthermore, a finite automaton or a state machine may be used to determine the maximum gradient of the dynamic gradient limitation. The reduction of the driver target setting is preferably performed indefinitely. This configuration makes it possible to advantageously change the steering characteristic.

[0017] A particularly high level of operational safety can be achieved if dynamic gradient limitation is performed in conjunction with the current driving situation and / or if the current driving situation is taken into account when gradient limitation is performed. Preferably, in this context, at least the presence or absence of a curved road is taken into account. Furthermore, the vehicle speed can advantageously be taken into account.

[0018] It is further proposed to take into account the steering direction and / or steering movement as a function of the driver's target settings as driving characteristic variables and / or to take into account the direction of the curve if the operating state corresponds to cornering. For example, in this context, a distinction can be made between left and right turns and / or between constant cornering and cornering with active steering movements. In the presence of constant cornering, for example, only a minimum gradient is used in the dynamic gradient limitation, whereas an additional gradient amplification can be performed in the case of active steering movements by the driver. Particularly advantageously, in this context, when cornering, the dynamic gradient limitation is only activated if the driver has not returned the steering wheel to the centering or zero position. This makes it possible to achieve, in particular, a gradient limitation that is adapted to the situation.

[0019] According to a preferred configuration, it is further proposed that the change of the steering characteristic in the operating state is first maintained over a first time interval and then gradually reduced over a predefined second time interval, in particular in the form of a predefined duration. The first time interval here can in particular be a predefined duration or can correspond to a predefined driving situation, for example until the next straight run or until the next turn. This makes it possible in particular to improve the transition from the steering characteristic in a normal operating state without an error to the steering characteristic in an error operating state.

[0020] In a further configuration, it is further proposed to take the vehicle speed into account when changing the steering characteristic, in particular when correcting the driver-target setting by means of a compensation quantity. In particular, the vehicle speed is taken into account here at least when determining the dynamic gradient limit. This allows a particularly flexible adaptation of the steering characteristic to the current operating conditions.

[0021] In this application, the method for the operation of the steering system should not be limited to the above-mentioned applications and embodiments, in particular, the method for the operation of the steering system may have a different number of individual elements, components and units than those listed herein to achieve the functional scheme described herein.

[0022] Further advantages are explained in the following description of the drawings, in which exemplary embodiments of the invention are shown. [Brief description of the drawings]

[0023] [Figure 1a] FIG. 1 is a simplified diagram illustrating a vehicle equipped with a steering system configured as a steer-by-wire steering system. [Figure 1b] FIG. 1 is a simplified diagram illustrating a vehicle equipped with a steering system configured as a steer-by-wire steering system. [Diagram 2] FIG. 2 illustrates an example graph of various signals for the operation of the steering system. [Diagram 3] FIG. 2 shows an exemplary flow chart including the main method steps of a method for operation of a steering system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Description of the embodiment 1a and 1b show in a simplified manner a vehicle 12, exemplarily configured as a passenger car, with a number of vehicle wheels 22, 24 and a steering system 10. The steering system 10 is operatively connected to the vehicle wheels 22, 24 and is provided for influencing the driving direction of the vehicle 12. Furthermore, the steering system 10 is configured here as a steer-by-wire steering system, in which driver target settings 30 or steering settings are electrically transmitted to the vehicle wheels 22, 24 in at least one operating state.

[0025] The steering system 10 comprises an operating unit 14, which can be operated in particular by the driver and / or passengers. The operating unit 14 comprises a steering wheel 16, for example in the form of a steering wheel, and a feedback actuator 18, which is in particular mechanically coupled to the steering wheel 16. In this case, the feedback actuator 18 is provided for providing at least an active feedback torque in normal operating conditions, thereby generating a steering resistance and / or a self-aligning torque to the steering wheel 16. For this purpose, the feedback actuator 18 comprises at least one electric motor (not shown), which is in particular configured as a permanently excited synchronous motor. Furthermore, the operating unit 14 is configured here in a fail-operational manner with respect to the detection of the driver target settings 30, in particular with respect to the steering wheel 16, and in a fail-safe manner with respect to the feedback torque provided by the feedback actuator 18. Alternatively, the steering wheel may be configured as a joystick, a steering lever and / or a steering ball or similar. Furthermore, the feedback actuator may comprise a plurality of electric motors. Furthermore, the operating unit can essentially be designed in a fail-safe or fail-operational manner.

[0026] Furthermore, the steering system 10 comprises a wheel steering angle adjuster 20, which is known per se. The wheel steering angle adjuster 20 is configured mechanically separated from the operating unit 14. The wheel steering angle adjuster 20 is connected to the operating unit 14 purely electrically. Furthermore, the wheel steering angle adjuster 20 is configured, for example, as a central adjuster. The wheel steering angle adjuster 20 is operatively connected to at least two vehicle wheels 22, 24, in particular the two front wheels, and is provided for converting the driver-target settings 30 into a steering movement of the vehicle wheels 22, 24. For this purpose, the wheel steering angle adjuster 20 comprises a steering adjustment element 36, which is configured, for example, as a rack, and a steering actuator 38 which cooperates with the steering adjustment element 36. The steering actuator 38 comprises here at least one further electric motor (not shown), which is configured, in particular, as a permanently excited synchronous motor, and is provided for driving and controlling the steerable vehicle wheels 22, 24. In principle, the steering system may of course include a number of wheel steering angle regulators, in particular configured as individual wheel regulators. Furthermore, the steering actuator may include a number of electric motors.

[0027] Furthermore, the vehicle 12 has a control device 40, which in this case is configured as a steering control device and is therefore part of the steering system 10. The control device 40 is electrically connected to the wheel steering angle regulator 20. The control device 40 is furthermore electrically connected to the operating unit 14. The control device 40 is provided for controlling at least the operation of the steering system 10. The control device 40 is here provided for controlling the steering actuator 38 in conjunction with a signal of the operating unit 14, for example in conjunction with a driver target setting 30. The control device 40 may furthermore be provided for controlling the feedback actuator 18 in conjunction with a signal of the wheel steering angle regulator 20.

[0028] For this purpose, the control device 40 comprises a calculation unit 34. The calculation unit 34 comprises at least one processor (not shown), for example in the form of a microprocessor, and at least one operating memory (not shown). The calculation unit 34 further comprises at least one operating program stored in the operating memory, which operating program comprises at least one calculation routine, at least one calculation routine, at least one evaluation routine and at least one adaptation routine. Furthermore, the calculation unit 34 comprises in this case at least one monitoring function 26, at least one further monitoring function 28 and at least one compensation function 33. In principle, however, the control device can also be different from the steering control device and can be configured, for example, as an individual central vehicle control device with a central calculation unit. Furthermore, it is conceivable to provide separate control devices and / or calculation units for the wheel steering angle regulator and the operating unit, which are communicatively connected to each other.

[0029] Furthermore, the vehicle 12 and / or the steering system 10 may include further components and / or assemblies not shown, for example an internal vehicle sensor system known per se for detecting at least one vehicle variable, e.g. yaw rate, an external sensor system known per se, e.g. in the form of a camera system, and / or a known navigation system.

[0030] In case of a fault and / or failure of the feedback actuator 18, unintended steering movements may occur at the steering wheel 16 due to the sudden disappearance of the feedback torque when the feedback actuator 18 transitions from an active and / or fully functional state to a passive and / or degraded state under certain circumstances, e.g. when driving around curves, and / or in certain driving situations, which may be interpreted by the steering system 10 as a driver target and / or steering setting, causing undesired vehicle responses. In this context, it is assumed that the passive properties of the feedback actuator 18 with respect to the torque feedback are sufficient to ensure reliable operation of the vehicle 12, and only the transition from the active to the passive case may be a challenge in terms of controllability. The reason for this is that in case of a corresponding fault and / or failure of the feedback actuator 18, the feedback torque is abruptly reduced, since the inherent passive friction in the steering system 10 is much smaller than the feedback torque in normal operating conditions. Particularly when driving around curves, a sudden reduction in the feedback torque and thus in the counter torque at the steering wheel 16 can lead to critical situations in terms of safety, since due to his reaction time the driver can only re-adjust his holding force with a time delay, which results in steering further into the curve than intended.

[0031] In order to avoid such safety-critical situations, a method for operating the steering system 10 is therefore proposed below, in which in particular a calculation unit 34 is provided for carrying out the method and for this purpose has in particular a computer program with corresponding program code means, but alternatively a calculation unit associated with an operating unit of the control device which carries out the method can also be provided.

[0032] According to the invention, the operation of the feedback actuator 18 is monitored by means of a monitoring function 26 and a driver target setting 30 for the wheel steering angle regulator 20 is monitored by means of a further monitoring function 28. Furthermore, faults and / or failures of the feedback actuator 18 are identified by means of the monitoring function 26 and a compensation quantity 31 for changing the steering characteristic of the steering system 10 is determined in at least one operating state in which the dynamics of the driver target setting 30 determined by means of the further monitoring function 28 exceed a threshold value. The steering characteristic of the steering system 10 is then changed in that the driver target setting 30 is corrected by means of the compensation quantity 31, which here corresponds in particular to an offset. In this case, the steering characteristic is changed by the correction of the driver target setting 30 by means of the compensation quantity 31 as follows: That is to say, in the operating state, in particular when the feedback actuator 18 passes from an active and / or fully functional state to a passive and / or degraded state, a substantially unchanged steering behavior is provided and / or obtained, and unintended steering movements of the driver due to faults and / or failures of the feedback actuator 18 are modified in such a way that they do not lead to undesired vehicle reactions. In this case, the modification of the steering characteristic is first maintained for a first time interval, for example until the next straight run or until the next turn, and then is adaptively reduced for a predefined second time interval or for a predefined time period. The adaptive reduction can be carried out in this context, for example, in a manner similar to that described in DE 10 2021 213 389 A1.

[0033] According to the method of the invention, the current and / or impending driving situation is further taken into account and the steering characteristic is changed in relation to the current and / or impending driving situation, whereby a corresponding change of the steering characteristic is preferably made only when driving around a curve or if an impending curve of the vehicle 12 is identified, so that the operating state corresponds to driving around a curve, whereby the steering characteristic is changed only if the wheel steering angle of the vehicle wheels 22, 24 is not equal to 0.

[0034] Furthermore, when changing the steering characteristic, in particular when correcting the driver target setting 30 using the compensation amount 31, the dynamics and / or absolute value of the driver target setting 30 for the wheel steering angle regulator 20, i.e., for example, the maximum displacement of the steering wheel 16 and / or the steering speed of the steering wheel 16, are taken into account.

[0035] Furthermore, the driver target setting 30 is modified by means of the compensation amount 31, in such a way that the modified driver target setting 32, which is transmitted to the wheel steering angle regulator 20 instead of the driver target setting 30 in the operating state and / or which is used to drive and control the wheel steering angle regulator 20 in the operating state, is in particular reduced compared to the driver target setting 30 (see also in particular FIG. 2). A reduction of the driver target setting 30 is in particular meaningful if, based on the current and / or impending driving situation and / or based on the dynamics and / or absolute value of the driver target setting 30, it has been determined that the driver steers further into the curve than intended. In this case, a reduction of the driver target setting 30 reduces the vehicle reaction and makes the situation more manageable for the driver. Essentially, the controllability is improved by a reduction of the driver target setting 30, since the loss of the driver's steering precision due to the lack of feedback torque can be at least partially compensated for by a reduction in the vehicle reaction.

[0036] In particular, the driver target setting 30 and the compensation amount 31 are added together in this case to obtain a corrected driver target setting 32 for the wheel steering angle regulator 20. In this connection, the following relationship holds: angRW mod =angRW driver +angRW comp

[0037] Here, angRW mod represents the modified driver-goal setting 32, and angRW driver represents the driver target setting 30, and angRW comp represents the compensation amount 31.

[0038] In order to determine the compensation quantity 31, a compensation function 33 is further used in this case. The driver target setting 30 and the error signal provided by the monitoring function 26 are supplied to the compensation function 33 as input quantities. Preferably, in this context, the absolute value is first formed by multiplying the driver target setting 30 by its sign. Therefore, only an excessively rapid rise of the driver target setting 30 in a certain direction, in particular in the positive direction, is relevant for determining the compensation quantity 31. Furthermore, a dynamic gradient limitation is used, with which it is possible to limit the rise of the driver target setting 30, if necessary, in connection with at least one driving characteristic variable and to determine a gradient-limited driver target setting. In this context, the driving characteristic variable in particular specifies the conditions under which a corresponding gradient limitation takes place. Furthermore, a finite automaton or a state machine can be used to determine the maximum gradient of the dynamic gradient limitation. Typically, the gradient is selected here such that the corrected driver target setting 32 in the operating state is reduced compared to the driver target setting 30. In contrast, the reduction of the driver target setting 30 is carried out without limitation. Here, the difference formation between the gradient-limited driver target setting and the driver target setting 30 results in an offset, which is finally further multiplied with the sign of the driver target setting 30 to obtain the compensation quantity 31. This ensures that the driver target setting 30 is always reduced in the operating state. Furthermore, the maximum level of the compensation quantity 31 can be further limited in order to allow for a possible actual need for stronger steering of the vehicle 12.

[0039] The dynamic gradient limitation is furthermore carried out in relation to the current driving situation. In this context, at least whether a curve is present or not is taken into account. Furthermore, the vehicle speed can be taken into account. Furthermore, as driving characteristic variables, the steering direction, steering movements and / or curve direction are taken into account, which are correlated with the driver-target settings 30. In this context, for example, a distinction is made between left and right turns, as well as between constant curves and curves with active steering movements. In the presence of constant curves, for example, only a minimum gradient is used, whereas in the case of active steering movements by the driver, an additional amplification of the gradient can be carried out, in particular by means of an amplification factor, so that the desired steering can be ensured. The amplification factor can be selected, for example, in relation to the vehicle speed, in which case the increase is smaller the higher the vehicle speed. Furthermore, in this case, activation of the gradient limitation only takes place when the driver has not returned the steering wheel to the centering or zero position when curves are being driven. For this purpose, for example, a further threshold value for the steering speed can be defined, which makes it possible to reliably identify that the driver has returned the steering to the centering or zero position. The steering movement to the centering or zero position can essentially be set as an end condition for the compensation function 33, for which the vehicle speed should additionally be below a limit value.

[0040] FIG. 2 shows an example graph of various signals for operation of the steering system 10.

[0041] The vertical axis 42 is the magnitude axis. The horizontal axis 44 shows the time (in seconds). The curve 46 shows the virtual course of the displacement of the steering wheel 16, here in particular in the form of an actual steering wheel angle, without a change in the steering characteristic by means of a modification of the driver-target setting 30. The curve 48 shows the course of the displacement of the steering wheel 16, here in particular in the form of an actual steering wheel angle, with a change in the steering characteristic by means of a modification of the driver-target setting 30. The curve 50 shows the course of the wheel steering angle of the driver-target setting 30 or of the vehicle wheels 22, 24, without a change in the steering characteristic by means of a modification of the driver-target setting 30. The curve 52 shows the course of the modified driver-target setting 32 or of the wheel steering angle of the vehicle wheels 22, 24, with a change in the steering characteristic by means of a modification of the driver-target setting 30. Furthermore, the curve 54 shows the course of the compensation quantity 31.

[0042] It can be seen from Fig. 2 that the driver first steers into the curve and then drives at a constant radius until the feedback actuator 18 fails at 10 seconds. The curves 50 and 52 clearly show the reduced wheel steering angles of the vehicle wheels 22, 24 and the associated reduced vehicle reaction obtained by the method according to the invention. Furthermore, based on the curves 46 and 48 it can be seen that a tilted position of the steering wheel 16 can occur due to the correction of the driver target settings 30 by means of the compensation amount 31. However, this immediately disappears again due to the reduced change in the steering characteristic while adjusting.

[0043] Finally, in FIG. 3, an exemplary flow chart including major method steps of a method for operation of the steering system 10 is shown.

[0044] Method step 60 corresponds in particular to a normal operating state without any errors, where the driver's target settings 30 are transmitted to the wheel steering angle regulator 20, whereby the wheel steering angle regulator 20 is actuated by the driver's target settings 30. Furthermore, the behavior of the feedback actuator 18 is monitored by means of a monitoring function 26 and the driver's target settings 30 for the wheel steering angle regulator 20 are monitored by means of a further monitoring function 28.

[0045] In method step 62, a fault and / or failure of the feedback actuator 18 is identified using the monitoring function 26. Furthermore, a further monitoring function 28 is used to identify that the dynamics of the driver target setting 30 exceed a threshold value.

[0046] In the subsequent method step 64, a compensation quantity 31 is determined, the driver target setting 30 is corrected using the compensation quantity 31, and a corrected driver target setting 32 is determined, thereby changing the steering characteristic of the steering system 10. The corrected driver target setting 32 is then transmitted, in particular instead of the driver target setting 30, to the wheel steering angle regulator 20, whereby the wheel steering angle regulator 20 is activated using the corrected driver target setting 32.

[0047] The exemplary flow chart of FIG. 3 is merely an exemplary illustration of a method for the operation of the steering system 10. In particular, it is also possible to modify individual method steps or to add additional method steps. In this context, it is conceivable, for example, to take into account the current driving situation. Furthermore, the compensation quantity 31 can be determined using a compensation function 33 to which the driver-target setting 30 and the error signal provided by the monitoring function 26 are supplied as input quantities, and when determining the compensation quantity 31, a dynamic gradient limit is used, by means of which the increase of the driver-target setting 30 is limited in relation to at least one driving characteristic quantity.

Claims

1. A method for operating a steering system (10) of a vehicle (12), in particular an automobile, comprising: The steering system (10) is configured as a steer-by-wire steering system and includes an operating unit (14) having at least one steering wheel (16) and at least one feedback actuator (18) cooperating with the steering wheel (16), and at least one wheel steering angle adjuster (20) operatively connected to the operating unit (14) for varying a wheel steering angle of at least one vehicle wheel (22, 24), 1. A method of monitoring operation of the feedback actuator (18) using a monitoring function (26) and modifying steering characteristics of the steering system (10) in at least one operating condition in which a fault and / or failure of the feedback actuator (18) is identified using the monitoring function (26), comprising: The method further comprises monitoring a driver target setting (30) for the wheel steering angle regulator (20) using a further monitoring function (28), determining a compensation amount (31), particularly in the form of an offset, if the dynamics of the driver target setting (30) in the operating state exceed a threshold value, and correcting the driver target setting (30) using the compensation amount (31) in order to change the steering characteristic.

2. 2. The method according to claim 1, further comprising taking into account the current and / or impending driving situation when changing the steering characteristic.

3. 3. The method according to claim 1 or 2, characterized in that the steering characteristic is changed only if the operating state corresponds to cornering and the wheel steering angle of the vehicle wheels (22, 24) is not equal to 0.

4. 4. The method according to claim 1, further comprising taking into account the dynamics and / or absolute value of the driver-target settings (30) when changing the steering characteristic.

5. 5. The method according to claim 1, further comprising modifying the driver target setting (30) using the compensation amount (31) so that the driver target setting (30) is reduced in the operating state in order to change the steering characteristic.

6. 6. The method according to claim 1, further comprising adding together the driver-target setting (30) and the compensation amount (31) to change the steering characteristic.

7. The method according to any one of the preceding claims, further comprising limiting a maximum level of the compensation amount (31).

8. determining said compensation quantity (31) using a compensation function (33) to which the error signals provided by said driver / target setting (30) and said monitoring function (26) are supplied as input quantities, 8. The method according to claim 1, further comprising the step of: determining the compensation amount (31) using a dynamic gradient limitation, by means of which an increase in the driver-target setting (30) is limited in relation to at least one driving characteristic variable.

9. The method of claim 8 , wherein the dynamic gradient limiting is performed in relation to current driving conditions.

10. 10. The method according to claim 8 or 9, further comprising taking into account a steering direction and / or a steering movement that are correlated with the driver-target settings (30) as driving characteristic variables and / or taking into account a curve direction if the operating state corresponds to curve driving.

11. 11. A method according to any one of claims 1 to 10, wherein the modification of the steering characteristic in the operating state is first maintained for a first time interval and then tapered off in a controlled manner for a second predetermined time interval.

12. A computing unit (34) for carrying out the method according to any one of claims 1 to 11.

13. A steering system (10), in particular a steer-by-wire steering system, comprising: an operating unit (14) including at least one steering wheel (16) and at least one feedback actuator (18) cooperating with said steering wheel (16); at least one wheel steering angle adjuster (20) operatively connected to said operating unit (14) for controlling the wheel steering angle of at least one vehicle wheel (22, 24); A calculation unit (34) according to claim 12, A steering system (10) comprising:

14. A vehicle (12), in particular a motor vehicle, comprising: A vehicle (12) comprising a steering system (10) according to claim 13.

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