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

Abstract

A method is proposed 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 changing the wheel steering angle of at least one vehicle wheel (22, 24), the operating unit (14) being configured at least partially fail-operationally, and in at least one operating state in which a first error of the operating unit (14) is identified, the operating unit (14) changes the steering characteristics of the steering system (10) by intentionally modifying the steering feel by operation of the feedback actuator (18), in particular adapted to the first error.

Description

[Technical field]

[0001] Background technology The present invention relates to a method for operating a steering system of a vehicle, and further 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, 11, 12 and 13, advantageous configurations and developments of the invention being defined in the dependent claims. [Means for solving the problem]

[0006] Disclosure of the Invention A method is proposed for operating a steering system of a vehicle, in particular a motor vehicle, which steering system is configured as a steer-by-wire steering system and includes 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, the operating unit being configured at least partially fail-operational, and which changes the steering characteristic of the steering system in at least one operating state in which a first error of the operating unit is identified, in particular by a targeted correction of the steering feel by an operation of a feedback actuator adapted to the first error. The operating state in which the first error is identified thus corresponds in particular to an error operating state. Furthermore, the steering characteristic is changed by the modification of the steering feel, in particular in such a way that a feedback torque adapted to the first error is provided and / or achieved in this operating state, so that the driver can prepare and / or adjust to possible faults and / or possible failures of the feedback actuator, adapt his general driving strategy and / or drive or steer with caution. This arrangement can in particular improve the functioning scheme, 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 can provide a flexible, advantageously adaptive and / or variable way in which the steering characteristic can be adapted to the current operating conditions. Furthermore, advantageous maneuverability of the vehicle can be achieved and operational reliability can be increased.

[0007] The steering system is here configured as a steer-by-wire steering system, in which the driver target settings and / or in particular the driver's steering settings are preferably 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. 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 changing the wheel steering angle of the at least one vehicle wheel, and thereby 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 preferably 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, 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, 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 signals, forces and / or torques, 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, a feedback actuator is provided in this context in order to adapt the steering feel perceptible in particular via the steering wheel. To this end, the feedback actuator may comprise at least one further electric motor. "At least partially fail-operational" is to be understood as fail-operational or operationally reliable, in particular with respect to a first error. In particular, preferably by means of the feedback actuator, a feedback torque can in this case continue to be applied to the steering wheel after the first error, which feedback torque may be different from the feedback torque during normal operating conditions. A first error in this context therefore does not directly cause a fault and / or failure of the operating unit and / or the feedback actuator. However, in principle, a fault and / or failure of the operating unit and / or the feedback actuator can be caused in particular by a second error following the first error. "Faults and / or failures of the operating unit and / or feedback actuator" should be understood in particular to mean faults and / or failures of the operating unit and / or feedback actuator itself and / or of peripheral assemblies cooperating with the operating unit and / or feedback actuator, for example energy supplies, and failures of the operating unit and / or 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 regard to the torque variables at the vehicle wheels and steering wheel, a similar equivalence of variables between the vehicle wheels / steering wheel and the respective connected actuators applies.

[0008] Furthermore, the vehicle, preferably the steering system, comprises at least one computing unit, which is provided for implementing the method for the operation of the steering system. By "computing unit" is to be understood an electric and / or electronic unit having an information input, an information processing and an information output. Advantageously, the computing 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 computing unit in this case comprises at least one monitoring function for monitoring the operation of the operating unit and / or the feedback actuators. Furthermore, the computing unit is provided for monitoring and evaluating the operation of the operating unit and / or the feedback actuators by means of the monitoring function, in particular for identifying a first error of the operating unit. Furthermore, the calculation unit is provided for modifying the steering characteristic of the steering system in at least one operating state in which a first error of the operating unit is identified, and for this purpose for modifying the steering feel in a targeted manner, in particular by operation of a feedback actuator adapted to the first error. In this context, the calculation unit may in particular be provided for utilizing an error signal provided by the monitoring function for adapting the steering characteristic. 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 the form of a steering control device in particular. By "steering feel" in this context is to be understood in particular a haptic response, in particular in the form of a feedback torque, from the steering system to the driver, which is perceptible via the steering wheel. In particular, the feedback actuator is operated in such a way that in particular in a normal operating state without errors a normal steering feel is generated and provided to the steering wheel.Furthermore, the feedback actuator operates in such a way that a modified steering feel is generated and provided to the steering wheel, in particular in an operating state in which a first error is identified. Thus, a change from a normal steering feel to a modified steering feel is preferably made by adapting the feedback torque in order to modify the steering characteristics in this operating state. "Provided" is to be understood in particular as being specifically programmed, configured and / or equipped. An object being provided for a particular function is to be understood in particular as the object fulfilling and / or executing this particular function at least in an application state and / or an operating state.

[0009] According to a particularly preferred configuration, it is proposed to operate the feedback actuator in this operating state, in particular for changing the steering characteristic, in such a way that the change from the normal steering feel to the modified steering feel is effected by means of a cross-fade, in particular by means of a moving average. For this purpose, a fading factor is advantageously defined, which initially has the value 0 and at the end of the cross-fade or fading phase has the value 1. In this case, the actual steering feel is obtained during the cross-fade or fading phase on the basis of the superposition of the normal steering feel with the modified steering feel and taking into account the fading factor. Preferably, the duration of the cross-fade can be further modified, in particular in relation to an additional amplification factor. Furthermore, the cross-fade is preferably effected on the basis of a torsion bar signal, particularly preferably on the basis of a torsion bar torque and / or a steering torque signal. In this case, the steering torque signal is equivalent to other variables, such as the motor torque of the feedback actuator and / or other operating signals of the operating unit. This makes it possible to achieve a particularly harmonious transition from the normal steering feel to the corrected steering feel, and also makes it possible to gradually adapt the driving and / or steering characteristics to a possible second error.

[0010] A particularly easy implementation of the cross-fading in terms of software technology can be achieved, in particular if an integrator is used for the cross-fading. In particular, the calculation unit may in this case include an integrator. Preferably, the integrator value of the integrator is in this context related to the torsion bar signal, preferably torsion bar torque signal and / or steering torque signal, the integrator value only becoming large when the torsion bar signal and / or steering torque signal exceed a predefined threshold value. Furthermore, the integrator is in this operating state correlated with the first error and is preferably activatable by an error signal provided by the monitoring function and / or is enableable by an enable signal. Preferably, the integrator is in this context activated only when a first error of the operating unit is identified. Thus, preferably, the integrator is deactivated in the normal operating state, which advantageously allows the resource demands to be reduced. Furthermore, the integrator may initially be blocked after activation, so that an additional enablement by an enable signal must be performed.

[0011] Basically, the duration of the cross-fade can be any value or a value related to the driving situation. However, it is preferably proposed that the duration of the cross-fade is at least 10 seconds, preferably at least 15 seconds, particularly preferably at least 25 seconds. This in particular allows a particularly flexible cross-fade to be achieved.

[0012] It is further proposed that the modified steering feel triggers a feedback to the driver that is at least temporarily located between a normal steering feel, in particular in normal operating conditions, and a passive steering feel without active feedback torque by the feedback actuator, i.e. preferably purely mechanical. In particular, the modified steering feel may in this case substantially deviate from the normal steering feel and may substantially deviate from the passive steering feel. This advantageously makes it possible to provide and / or achieve a steering characteristic that is adapted to the first error, by means of which the driver intuitively prepares for and / or adjusts to possible faults and / or possible failures of the feedback actuator.

[0013] It is further preferably proposed that the modified steering feel corresponds to, in particular resembles and / or has properties similar to, a passive steering feel. In addition, an optical or acoustic warning can be given as a consequence for the first error. This can achieve an advantageous warning and / or indicating effect.

[0014] According to a particularly preferred embodiment, it is proposed that the modified steering feel reproduces the inherent friction properties of the operating unit, in particular the properties of the mechanism of the operating unit, so that in particular a steering feel similar or similar to a passive steering feel can be reproduced or simulated.

[0015] Furthermore, the modified steering feel can reproduce the centering of the steering wheel, thereby increasing the similarity of the modified steering feel to the normal steering feel. However, according to a preferred embodiment of the invention, it is proposed that the modified steering feel does not reproduce the centering of the steering wheel. This can intuitively inform the driver that the functioning mode of the steering system is limited and can convey that the driver should adapt his general driving strategy and / or drive or steer with caution.

[0016] It is further proposed that the maximum torque level of the modified steering feel is greater than the maximum torque level of the passive steering feel. In principle, the maximum torque level of the modified steering feel is further less than the maximum torque level of the normal steering feel. However, the maximum torque level of the modified steering feel may also be greater than the maximum torque level of the normal steering feel in connection with the corresponding application, at least temporarily or in certain driving situations. This allows an increased operational reliability in this operating state, in particular compared to a complete failure of the feedback actuator. Furthermore, an improvement in driving comfort and / or steering comfort is achieved.

[0017] It is further proposed that the modified steering feel reproduces the non-linear or linear damping characteristic, in particular of the operating unit, so that safety and / or driving comfort and / or steering comfort can be increased. In this case, the damping characteristic is preferably adapted as a function of the steering speed of the steering wheel and / or the vehicle speed. It is particularly advantageous, for example, to increase the damping as the steering speed increases, so that the damping only comes into effect when the driver steers (too quickly). However, as an alternative, the damping characteristic can also reproduce the damping characteristic of the operating unit in normal operating conditions, so that the similarity of the modified steering feel to the normal steering feel can be increased.

[0018] 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.

[0019] 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]

[0020] [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

[0021] 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 or steering settings are electrically transmitted to the vehicle wheels 22, 24 in at least one operating state.

[0022] 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 sensation, in particular in the form of a steering resistance and / or a self-aligning torque on the steering wheel 16. For this purpose, the feedback actuator 18 comprises at least one electric motor (not shown), in particular configured as a permanently excited synchronous motor. Furthermore, the operating unit 14 is here configured to operate fail-operationally, i.e. reliably, with respect to a first error. 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 number of electric motors.

[0023] The steering system 10 further 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's desired settings or steering settings 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 comprise a number of wheel steering angle regulators, in particular configured as individual wheel regulators. Furthermore, the steering actuator may comprise a number of electric motors.

[0024] 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 adjuster 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 driving the steering actuator 38 in conjunction with a signal of the operating unit 14, for example in conjunction with a driver target setting or steering setting and / or a hand torque. The control device 40 may furthermore be provided for driving the feedback actuator 18 in conjunction with a signal of the wheel steering angle adjuster 20.

[0025] 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 in this case comprises at least one monitoring function 26. 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.

[0026] Additionally, the vehicle 12 and / or steering system 10 may include additional components and / or assemblies not shown, such as an internal vehicle sensor system for detecting at least one vehicle variable, such as yaw rate, an external sensor system, such as in the form of a camera system, and / or a known navigation system.

[0027] 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 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 nature of the feedback actuator 18 with respect to the torque feedback is sufficient to operate the vehicle 12 reliably, and only the transition 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 usually 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 adjust his holding force with a time delay, which results in steering further into the curve than intended.

[0028] 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.

[0029] According to the invention, the operation of the operating unit 14 and / or the feedback actuator 18 is monitored by the monitoring function 26 and in at least one operating state in which a first error of the operating unit 14 is identified, the steering characteristic of the steering system 10 is changed by a deliberate modification of the steering feel by an operation of the feedback actuator 18 adapted to the first error. Here, therefore, the feedback torque provided by the feedback actuator 18 is modified in order to achieve a change in the steering characteristic and thus a feedback adapted to the first error. Basically, however, the operating unit 14 may also comprise means for the modification of the steering feel, different from the feedback actuator 18. In this case, the steering characteristic is modified by providing a steering characteristic adapted to the first error in this operating state and / or by modifying the steering feel so as to achieve it. The aim here is to prepare and / or adjust the driver to possible faults and / or possible failures of the feedback actuator 18, so that he can adapt his general driving strategy and / or drive or steer with caution.

[0030] Here, on the other hand, the feedback actuator 18 is operated in such a way that a change from the normal steering feel 28 to a modified steering feel 30 occurs, which causes a feedback to the driver, which lies between the normal steering feel 28 in the normal operating state and a passive steering feel without active feedback torque by the feedback actuator 18, i.e. purely mechanical (see also in particular FIG. 2). The normal steering feel 28 is characterized in particular by a reset to a straight ahead position, a centering or a constant torque build-up, and a pronounced damping characteristic known per se. On the other hand, the passive steering feel is characterized in particular by a very low torque level, which may essentially be identical to the passive steering feel, a steering torque in the form of a friction torque, i.e. a torque opposing the driver's movement direction, no centering, a standstill of the steering wheel at the point where the steering wheel is released, and a very slight damping due to mechanical characteristics only.

[0031] Here, the modified steering feel 30 has characteristics similar to and / or quasi-passive steering feel. For this purpose, the modified steering feel 30 reproduces characteristics corresponding to the inherent friction characteristics of the operating unit 14 and does not include centering, so that the steering wheel 16 comes to rest at the point where the steering wheel 16 is released. This makes it possible to intuitively inform the driver that the functioning of the steering system 10, or more precisely, the functioning of the operating unit 14, is limited and to communicate that the driver should adapt his general driving strategy and / or drive or steer with caution. Furthermore, a potential complete failure of the feedback actuator 18 can be mitigated by adapting the feedback torque or steering feel.

[0032] At the same time, however, the maximum torque level of the modified steering feel 30 exceeds that of the passive steering feel, which allows the operating reliability in this operating state to be increased, in particular compared to a complete failure of the feedback actuator 18, and the driving and / or steering comfort to be improved. In this connection, the modified steering feel 30 can furthermore reproduce the non-linear or linear damping characteristic of the operating unit 14, which can furthermore be adapted as a function of the steering speed of the steering wheel 16 and / or the vehicle speed. Here, preferably, the damping is increased as the steering speed increases.

[0033] Furthermore, the change from the normal steering feel 28 to the modified steering feel 30 is performed by means of a cross-fade and by means of a moving average. For this purpose, a fading factor is defined, which initially has the value 0 and at the end of the cross-fade or fading phase has the value 1. The actual steering feel is then obtained during the cross-fade or fading phase on the basis of the superposition of the normal steering feel 28 with the modified steering feel 30 and taking the fading factor into account. Furthermore, the duration of the cross-fade can be changed, in particular in relation to an additional amplification factor, so that advantageously, depending on the situation, a more or less rapid cross-fade from the normal steering feel 28 to the modified steering feel 30 can be performed. The duration of the cross-fade is in this case advantageously at least 25 seconds. The objective here is to gradually change the characteristic or steering feel of the steering system 10 from normal haptic feedback towards passive or purely mechanical haptic feedback, thereby preparing the driver for possible failure and / or possible failure of the feedback actuator 18.

[0034] Furthermore, an integrator 32 is used for the cross-fading, which in normal operating conditions is zero and / or deactivated and is only activated in this operating condition by the error signal provided by the monitoring function 26. The integrator 32 is therefore only activated when a first error of the operating unit 14 is identified. The integrator value of the integrator 32 is in this connection related to the torsion bar signal or the torsion bar torque and / or the steering torque signal, the integrator value only becoming large when the torsion bar signal or the torsion bar torque and / or the steering torque signal exceed a predefined threshold value.

[0035] FIG. 2 shows an example graph of various signals for operation of the steering system 10.

[0036] The vertical axis 42 is the magnitude axis. The horizontal axis 44 indicates the time (in seconds). Curve 46 shows the course of the displacement of the steering wheel 16, here in particular in the form of the actual steering wheel angle. Curve 48 shows the course of the normal steering feel 28. Curve 50 shows the course of the corrected steering feel 30. Curve 52 shows an exemplary course of the feedback torque actually provided by the feedback actuator 18.

[0037] Based on FIG. 2 and especially on the curve 52, a slow or gradual change of the steering feel or feedback moment from the normal steering feel 28 to the modified steering feel 30 can be identified. At the time 4 seconds, a first error occurs. On this basis, the feedback actuator 18 is actuated so that a gradual change to the modified steering feel 30 occurs. In the illustrated case, the modified steering feel 30 consists, by way of example, only of friction characteristics. Furthermore, the torque level is very low, so that the change in the feedback torque to the driver in the event of a possible second error or failure of the feedback actuator 18 is also small, and the driver easily controls the driving situation, since the torque situation changes only slightly and there is no large excess torque with a clear steering movement in the event of a second error or failure of the feedback actuator 18. At the time 37 seconds, by way of example, a corresponding second error occurs. In this case, the passive steering feel, not explicitly shown, has a value of 0.4 Nm by way of example, whereas the modified steering feel 30 has a value of 0.75 Nm, i.e. in this case only minimal changes occur when passing from the modified steering feel 30 to the passive steering feel. In contrast, observing the difference between the normal steering feel 28 and the passive steering feel results in a value of 4.6 Nm by way of example, thus resulting in significantly larger torque fluctuations in the event of a failure of the feedback actuator 18.

[0038] Finally, in FIG. 3, an exemplary flow chart including major method steps of a method for operation of the steering system 10 is shown.

[0039] Method step 60 corresponds to a normal operating state, in particular without errors, in which case the steering feel corresponds to the normal steering feel 28. Furthermore, the operation of the operating unit 14 and / or the feedback actuator 18 is monitored by the monitoring function 26.

[0040] In method step 62, a first error in the operating unit 14 is identified by means of the monitoring function 26.

[0041] In the subsequent method step 64, the steering characteristic of the steering system 10 is altered, in particular by a targeted modification of the steering feel by an action of the feedback actuator 18 adapted to the first error. For this purpose, the feedback torque provided by the feedback actuator 18 is altered in such a way that a gradual transition from the normal steering feel 28 to the modified steering feel 30 occurs.

[0042] 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 carry out the modifications to the modified steering feel 30 with a corresponding cross-fading, in particular by using a moving average.

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), The operating unit (14) is configured at least partially for fail-operation; A method for changing the steering characteristics of the steering system (10) in at least one operating state in which a first error of the operating unit (14) is identified, by intentionally modifying the steering feel by operation of the feedback actuator (18), in particular adapted to the first error.

2. 2. The method according to claim 1, further comprising operating the feedback actuator (18) in such a way that in the operating state, a change to the modified steering feel (30) is made by means of a cross-fade, in particular by means of a moving average.

3. 3. The method of claim 2, further comprising using an integrator (32) for said cross-fading, said integrator (32) being activated in said operating state by an error signal that is correlated with said first error.

4. The method of claim 2 or 3, wherein the duration of the crossfade is at least 10 seconds.

5. 5. The method of claim 1, wherein the modified steering feel (30) causes a feedback to the driver that is at least temporarily between a normal steering feel (28) and a passive steering feel without an active feedback torque from the feedback actuator (18).

6. 6. The method of claim 1, wherein the modified steering feel (30) has characteristics corresponding to a passive steering feel without active feedback torque from the feedback actuator (18).

7. 7. The method according to claim 1, wherein the modified steering feel (30) reproduces characteristics corresponding to the inherent friction characteristics of the operating unit (14).

8. 8. The method according to claim 1, wherein the modified steering feel (30) does not replicate the centering of the steering wheel (16).

9. 9. The method according to claim 1, wherein a maximum torque level of the modified steering feel (30) exceeds a maximum torque level of a passive steering feel without active feedback torque by the feedback actuator.

10. The modified steering feel (30) reproduces the damping characteristics, 10. A method according to any one of the preceding claims, comprising adapting the damping characteristic in relation to the steering speed of the steering wheel (16) and / or the vehicle speed.

11. A computing unit (34) for carrying out the method according to any one of claims 1 to 10.

12. 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 11; A steering system (10) comprising:

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

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