Method for the operation of a vehicle's steering system

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 Art The present invention relates to a method for the operation of a steering system of a vehicle. Furthermore, the present invention relates to a computing unit for implementing such a method, a steering system provided with such a computing unit, and a vehicle provided with such a steering system.

Background Art

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

[0003] Furthermore, such steer-by-wire steering systems are inherently redundant for reasons of operational reliability. With respect to the operating unit, for example, it is possible to configure the operating unit to be fail-safe or fail-operational. In addition, the operating unit may be configured fail-operationally with respect to driver / target setting detection and fail-safe with respect to feedback torque provided by the feedback actuator. In a corresponding configuration of the operating unit, failure and / or malfunction of the feedback actuator may result in the sudden loss of feedback torque, causing unintended steering movements in the steering wheel. Such unintended steering movements may be interpreted by the steering system as driver / target setting and / or steering setting, leading to undesirable vehicle responses. Methods for handling such error cases are described, for example, in German Patent Application Publication No. 102016009684 and German Patent Application Publication No. 102018222442. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] German Patent Application Publication No. 102016009684 [Patent Document 2] German Patent Application Publication No. 102018222442 Specification [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Starting from this point, the object of the present invention is to provide a method having improved characteristics, particularly with respect to the functional mode. The above object is resolved by the features of claims 1, 11, 12 and 13, and advantageous configurations and variations of the present invention are described in the dependent claims. [Means for solving the problem]

[0006] Disclosure of the invention A method is proposed for the operation of a steering system of a vehicle, particularly an automobile, wherein the steering system is configured as a steer-by-wire steering system and includes an operating unit comprising at least one steering wheel and at least one feedback actuator cooperating with the steering wheel, and at least one wheel steering angle adjuster connected to the operating unit for changing the wheel steering angle of at least one vehicle wheel, wherein the operating unit is configured at least partially fail-operationally, and in at least one operating state in which a first error of the operating unit is identified, the steering characteristics of the steering system are changed, in particular by correcting the steering feel as intended by the operation of a feedback actuator adapted to the first error. Thus, the operating state in which the first error is identified corresponds in particular to an error operating state. Furthermore, the steering characteristics are modified, in particular, to provide and / or achieve a feedback torque adapted to the first error in this operating state, thereby allowing the driver to prepare for and / or adjust to possible failures and / or malfunctions of the feedback actuator, adapt their general driving strategy, and / or drive or steer cautiously. This configuration can improve the functional mode in particular, and advantageously, can improve the controllability and / or steerability of the vehicle in the event of an error or loss of active feedback torque from the feedback actuator. Furthermore, it can provide an advantageous adaptive and / or variable method that can flexibly adapt the steering characteristics to the current operating conditions. Furthermore, it can achieve advantageous operability of the vehicle and increase operational reliability.

[0007] The steering system is configured here as a steer-by-wire steering system in which the driver, target setting and / or in particular the driver's steering setting are advantageously transmitted to the vehicle wheels purely electrically. For this purpose, the steer-by-wire steering system includes an operating unit configured particularly redundantly and at least one wheel steering angle adjuster, mechanically separated from the operating unit and configured particularly redundantly. A "wheel steering angle adjuster" should be understood as an actuator unit coupled to at least one vehicle wheel, which transmits the driver, target setting and / or in particular the driver's steering setting to the vehicle wheel by a change in the wheel steering angle of at least one vehicle wheel, thereby advantageously being provided to control the orientation of at least one vehicle wheel and / or to influence the direction of travel of the vehicle. For this purpose, the wheel steering angle adjuster advantageously includes 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, which is actuated to this steering adjustment element. In this case, the wheel steering angle adjuster may be configured as a central adjuster and may correspond to at least two vehicle wheels, particularly steerable, and preferably configured as front wheels. Alternatively, the wheel steering angle adjuster may be configured as an individual wheel adjuster and may correspond to strictly one vehicle wheel, particularly steerable, and preferably configured as a front wheel. Furthermore, the “feedback actuator” should be understood in particular as an actuator unit distinct from the wheel steering angle adjuster, and particularly mechanically connected directly to the steering wheel, which is provided to detect, particularly directly, signals, forces and / or torque from the steering wheel and / or to the steering wheel. Here, the feedback actuator is provided to provide at least active feedback torque in normal operating conditions, thereby generating steering resistance and / or self-aligning torque in the steering wheel.Furthermore, a feedback actuator is provided in this context, particularly to adapt the steering feel perceptible via the steering wheel. For this purpose, the feedback actuator may include at least one other electric motor. "At least partially fail-operational" should be understood as being fail-operational, or reliable in operation, particularly with respect to the first error. Particularly preferably using a feedback actuator, in this case a feedback torque can continue to be applied to the steering wheel even after the first error, although this feedback torque may be different from the feedback torque under normal operating conditions. Thus, in this context, the first error does not directly cause failure and / or malfunction of the operating unit and / or feedback actuator. However, fundamentally, a second error, particularly following the first error, can cause failure and / or malfunction of the operating unit and / or feedback actuator. "Failure and / or failure of the operating unit and / or feedback actuator" should be understood to mean, in particular, failure and / or failure of the operating unit and / or feedback actuator itself, and / or failure of peripheral assemblies that work with the operating unit and / or feedback actuator, such as the energy supply unit, and the resulting failure of the operating unit and / or feedback actuator. Furthermore, the wheel steering angle is essentially equivalent to other variables between the steering actuator and the vehicle wheel, such as the displacement of the steering adjustment element and / or the displacement position and / or motor motion of the wheel steering angle adjuster. The same applies to the displacement of the steering wheel, which is equivalent to other variables between the steering wheel and the feedback actuator, such as the steering column angle and / or motor angle. With respect to torque variables in the vehicle wheel and steering wheel, a similar equivalence of variables between the vehicle wheel / steering wheel and each connected actuator applies.

[0008] Furthermore, the vehicle, preferably the steering system, includes at least one computing unit provided for carrying out a method for the operation of the steering system. “Computing unit” should be understood as an electrical and / or electronic unit having an information input unit, an information processing unit, and an information output unit. Advantageously, the computing unit further includes 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 control routine and / or closed-loop control routine, at least one computing routine, at least one calculation routine, at least one evaluation routine, and / or at least one adaptation routine. In particular, the computing unit includes at least one monitoring function for monitoring the operation of the operating unit and / or feedback actuator. Furthermore, the computing unit is provided for monitoring and evaluating the operation of the operating unit and / or feedback actuator by the monitoring function, particularly in order to identify a first error of the operating unit. Furthermore, a calculation unit is provided to modify the steering characteristics of the steering system in at least one operating state in which a first error of the operating unit is identified, thereby correcting the steering feel as intended, particularly by the operation of a feedback actuator adapted to the first error. In this context, the calculation unit may be provided, in particular, to utilize error signals provided by a monitoring function for the adaptation of the steering characteristics. Preferably, the calculation unit is incorporated here into a vehicle control device, such as a central vehicle control device, or, advantageously, a control device of the steering system, particularly in the form of a steering control device. In this context, “steering feel” should be understood, in particular, as a tactile response from the steering system to the driver, particularly in the form of feedback torque, which is perceptible via the steering wheel. In particular, the feedback actuator is operated so that a normal steering feel is generated and provided to the steering wheel, particularly in normal operating states without errors.Furthermore, the feedback actuator operates such that a modified steering feel is generated and provided to the steering wheel, particularly in operating conditions where a first error is identified. Therefore, in order to change the steering characteristics in this operating condition, a change is preferably made from a normal steering feel to a modified steering feel by adapting the feedback torque. "Provided" should be understood in particular as being specifically programmed, configured, and / or equipped. An object provided for a particular function should be understood in particular as the object fulfilling and / or performing this particular function, at least in the applied and / or operating conditions.

[0009] In a particularly preferred configuration, it is proposed that the feedback actuator be operated in this operating state, in particular to modify the steering characteristics, namely, that the change from a normal steering feel to a modified steering feel is performed using a crossfade, particularly using a moving average. For this purpose, advantageously, a fading coefficient is defined, which initially has a value of 0 and has a value of 1 at the end of the crossfade or fading phase. In this case, the actual steering feel is obtained during the crossfade or fading phase based on the superposition of the normal steering feel and the modified steering feel, and taking the fading coefficient into consideration. Preferably, the duration of the crossfade can be further modified, particularly in relation to an additional amplification factor. Furthermore, the crossfade is preferably based on a torsion bar signal, particularly preferably a torsion bar torque and / or 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 a normal steering feel to a modified steering feel. Furthermore, the driving characteristics and / or steering characteristics can be progressively adapted to possible second errors.

[0010] A particularly easy software-technical implementation of crossfading can be achieved, especially when an integrator is used for crossfading. In particular, the computing unit in this case may include an integrator. Preferably, the integrator value of the integrator is related in this context to the torsion bar signal, favorably torsion bar torque signal and / or steering torque signal, and the integrator value increases only when the torsion bar signal and / or steering torque signal exceed a predetermined threshold. Furthermore, in this operating state, the integrator correlates with a first error and is preferably activatable by an error signal provided by a monitoring function and / or activatable by an enable signal. Preferably, in this context, the integrator is activated only when a first error of the operating unit is identified. Therefore, preferably, the integrator is deactivated in normal operating states, thereby favorably reducing resource demands. Furthermore, since the integrator may be initially blocked after activation, additional enabling by an enable signal must be performed.

[0011] Basically, the crossfade duration can take any value or a value related to the driving conditions. However, it is preferably proposed that the crossfade duration be at least 10 seconds, preferably at least 15 seconds, and particularly preferably at least 25 seconds. This allows for a particularly flexible crossfade to be achieved.

[0012] Furthermore, it is proposed that the modified steering feel elicits feedback to the driver that is at least temporarily positioned between the normal steering feel in normal operating conditions and a passive steering feel without active feedback torque from the feedback actuator, i.e., preferably a purely mechanical characteristic. In particular, the modified steering feel in this case may be substantially deviated from the normal steering feel and substantially deviated from the passive steering feel. This can advantageously provide and / or achieve steering characteristics adapted to the first error, which the driver intuitively prepares for and / or adjusts for possible malfunctions and / or failures of the feedback actuator.

[0013] Preferably, the modified steering feel is proposed to correspond to, particularly similar to, a passive steering feel, and / or to have characteristics similar to a passive steering feel. Additionally, optical or audible warnings can be provided as a result of the first error. This can achieve advantageous warning and / or instructional effects.

[0014] In a particularly preferred configuration, it is proposed that the modified steering feel reproduces characteristics corresponding to the inherent friction characteristics of the operating unit, and especially characteristics corresponding to the mechanism of the operating unit. This makes it possible to reproduce or simulate a steering feel similar to or similar to a passive steering feel.

[0015] Furthermore, the modified steering feel can replicate 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 configuration of the present invention, it is proposed that the modified steering feel does not replicate the centering of the steering wheel. This allows the driver to intuitively be notified that the function of the steering system is limited, and to communicate that the driver should adapt their general driving strategy and / or drive or steer cautiously.

[0016] Furthermore, it is proposed that the maximum torque level of the modified steering feel exceeds the maximum torque level of the passive steering feel. Basically, the maximum torque level of the modified steering feel is also lower than the maximum torque level of the normal steering feel. However, the maximum torque level of the modified steering feel may, in relation to its corresponding application, exceed the maximum torque level of the normal steering feel, at least temporarily or under specific driving conditions. This can increase operational reliability in this operating state, in particular, compared to complete failure of the feedback actuator. Furthermore, improvements in driving comfort and / or steering comfort are achieved.

[0017] Furthermore, it is proposed that the modified steering feel can reproduce the nonlinear or linear damping characteristics of the control unit in particular, thereby improving safety and / or driving comfort and / or steering comfort. Preferably, the damping characteristics are adapted in relation to the steering speed of the steering wheel and / or the vehicle speed. Particularly advantageous is that, for example, the damping can be increased as the steering speed increases, such that damping only acts when the driver steers (excessively) quickly. However, alternatively, the damping characteristics can also reproduce the damping characteristics of the control unit in normal operating conditions, thereby increasing the similarity of the modified steering feel to the normal steering feel.

[0018] In this application, the methods for operating the steering system are not limited to the uses and embodiments described above. In particular, methods for operating the steering system to realize the functional schemes described herein may have a different number of individual elements, components, and units than those listed herein.

[0019] Further advantages are described in the following drawings. The drawings illustrate embodiments of the present invention. [Brief explanation of the drawing]

[0020] [Figure 1a] A diagram schematically showing a vehicle equipped with a steering system configured as a steer-by-wire steering system. [Figure 1b] A diagram schematically showing a vehicle equipped with a steering system configured as a steer-by-wire steering system. [Figure 2] A diagram showing an exemplary graph of various signals for the operation of the steering system. [Figure 3] A diagram showing an exemplary flowchart including the main method steps of a method for the operation of the steering system.

Mode for Carrying Out the Invention

[0021] Description of Embodiment FIGS. 1a and 1b schematically show a vehicle 12 equipped with a plurality of vehicle wheels 22, 24 and a steering system 10, which is configured as a passenger car by way of example. The steering system 10 is operatively connected to the vehicle wheels 22, 24 and is provided to affect the driving direction of the vehicle 12. Further, the steering system 10 is configured here as a steer-by-wire steering system in which a driver's target setting or steering setting is electrically transmitted to the vehicle wheels 22, 24 in at least one operating state.

[0022] The steering system 10 has an operating unit 14 that can be operated in particular by the driver and / or occupants. The operating unit 14 includes, for example, a steering wheel 16 and a feedback actuator 18 that is mechanically coupled to the steering wheel 16. In this case, the feedback actuator 18 is provided to provide at least an active feedback torque in normal operating conditions, thereby generating a steering feel in particular in the form of steering resistance and / or self-aligning torque to the steering wheel 16. For this purpose, the feedback actuator 18 includes at least one electric motor (not shown) configured in particular as a permanently excited synchronous motor. Furthermore, the operating unit 14 is 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 include multiple electric motors.

[0023] Furthermore, the steering system 10 has a wheel steering angle adjuster 20, which is known in itself. The wheel steering angle adjuster 20 is configured to be 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 connected to at least two vehicle wheels 22,24, in particular the two front wheels, and is provided to convert driver / target setting or steering setting into steering motion of the vehicle wheels 22,24. For this purpose, the wheel steering angle adjuster 20 includes a steering adjustment element 36 configured, for example, as a rack, and a steering actuator 38 cooperating with this steering adjustment element 36. The steering actuator 38 includes, here in particular, at least one other electric motor (not shown) configured as a permanently excited synchronous motor, and is provided to drive and control the steerable vehicle wheels 22,24. Basically, the steering system may, of course, include multiple wheel steering angle adjusters, especially configured as individual wheel adjusters. Furthermore, the steering actuator may include multiple electric motors.

[0024] Furthermore, the vehicle 12 has a control device 40. In this case, the control device 40 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 further electrically connected to the operating unit 14. The control device 40 is provided to control at least the operation of the steering system 10. Here, the control device 40 is provided to drive and control the steering actuator 38 in relation to signals from the operating unit 14, for example, in relation to driver / target setting or steering setting and / or hand torque. The control device 40 may further be provided to drive and control the feedback actuator 18 in relation to signals from the wheel steering angle adjuster 20.

[0025] For this purpose, the control unit 40 includes a computing unit 34. The computing unit 34 includes, for example, at least one processor (not shown) in the form of a microprocessor and at least one operating memory (not shown). The computing unit 34 further includes at least one operating program stored in the operating memory, which includes at least one calculation routine, at least one calculation routine, at least one evaluation routine, and at least one adaptation routine. Furthermore, the computing unit 34 includes at least one monitoring function 26 in this case. However, the control unit may be fundamentally different from the steering control unit, and may be configured, for example, as individual central vehicle control units equipped with a central computing unit. Furthermore, it is conceivable to provide separate control units and / or computing units for the wheel steering angle adjusters and operating units, and to connect them to communicate with each other.

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

[0027] When the feedback actuator 18 malfunctions and / or fails, in certain circumstances and / or driving conditions, such as when cornering, the feedback actuator 18 transitions to a passive and / or downgraded state, which can cause unintended steering movements in the steering wheel 16 due to the sudden loss of feedback torque. Such unintended steering movements may be perceived by the steering system 10 as driver / target settings and / or steering settings, leading to undesirable vehicle responses. In this regard, it is assumed that the passive characteristics of the feedback actuator 18 with respect to torque feedback are sufficient to ensure the reliable operation of the vehicle 12, and that only the transition to the passive state may pose a controllability challenge. This is because, in the event of a corresponding malfunction and / or failure of the feedback actuator 18, the feedback torque typically decreases sharply. This is because the inherent passive friction in the steering system 10 is significantly smaller than the feedback torque under normal operating conditions. In particular, during cornering, a sudden reduction in feedback torque, and consequently a sudden reduction in counter torque at the steering wheel 16, can lead to serious safety issues. This is because, due to the driver's response time, they can only adjust their holding force with a time delay, resulting in steering the vehicle further into the curve than intended.

[0028] Therefore, in order to avoid such a serious safety situation, a method for the operation of the steering system 10 is proposed below. Here, a computing unit 34 is provided in particular to carry out this method, and for this purpose has a computer program that includes corresponding program code means. However, alternatively, a computing unit associated with the operating unit of the control device that carries out this method may also be provided.

[0029] According to the present 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 characteristics of the steering system 10 are changed by correcting the steering feel as intended through the operation of the feedback actuator 18 adapted to the first error. Thus, here, the feedback torque provided by the feedback actuator 18 is modified in order to achieve a change in steering characteristics and thereby achieve feedback adapted to the first error. However, the operating unit 14 may also include means for modifying the steering feel that are different from those of the feedback actuator 18. In this case, the steering characteristics are changed by providing and / or modifying the steering feel so that steering characteristics adapted to the first error are achieved in this operating state. The objective here is for the driver to prepare for and / or adjust for possible failures and / or malfunctions of the feedback actuator 18, so that the driver can adapt their general driving strategy and / or drive or steer cautiously.

[0030] Here, the feedback actuator 18 is operated to change the steering feel from the normal steering feel 28 to the modified steering feel 30, which in turn produces feedback to the driver, which lies between the normal steering feel 28 in normal operating conditions and a passive steering feel without active feedback torque from the feedback actuator 18, i.e., purely mechanical characteristics (see also Figure 2 in particular). The normal steering feel 28 is characterized in particular by resetting to the straight position, centering or steady torque formation, and prominent damping characteristics known to the self. In contrast, the characteristics of the passive steering feel are, in particular, an extremely low torque level which may be considered essentially identical to that of a passive steering feel, steering torque in the form of friction torque, i.e., torque opposing the driver's direction of motion, no centering, stationary steering wheel at the point where the steering wheel is released, and very slight damping based solely on mechanical characteristics.

[0031] Here, the modified steering feel 30 has characteristics similar to and / or equivalent to a 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, thereby the steering wheel 16 comes to rest at the point where it is released. This allows the driver to intuitively be notified that the function of the steering system 10, or more precisely, the function of the operating unit 14, is limited, and further communicates that the driver should adapt their general driving strategy and / or drive or steer carefully. In addition, the potential complete failure of the feedback actuator 18 can be mitigated by adapting the feedback torque or steering feel.

[0032] However, at the same time, the maximum torque level of the modified steering feel 30 exceeds that of the passive steering feel, thereby improving operational reliability in this operating state, particularly compared to a complete failure of the feedback actuator 18, and improving driving comfort and / or steering comfort. In this regard, the modified steering feel 30 can further reproduce the nonlinear or linear damping characteristics of the operating unit 14, and the damping characteristics can further be adapted in relation to the steering speed of the steering wheel 16 and / or the vehicle speed. 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 using a crossfade and a moving average. For this purpose, a fading coefficient is defined, which initially has a value of 0 and has a value of 1 at the end of the crossfade or fading phase. In this case, the actual steering feel is obtained during the crossfade or fading phase based on the superposition of the normal steering feel 28 and the modified steering feel 30, and taking the fading coefficient into consideration. Moreover, the duration of the crossfade can be changed in particular in relation to an additional amplification factor, thereby advantageously allowing the crossfade from the normal steering feel 28 to the modified steering feel 30 to be more or less rapid depending on the situation. In this case, the duration of the crossfade is advantageously at least 25 seconds. The objective here is to slowly change the characteristics or steering feel of the steering system 10 from normal tactile feedback to passive or purely mechanical tactile feedback, thereby allowing the driver to prepare for possible malfunctions and / or failures of the feedback actuator 18.

[0034] Furthermore, an integrator 32 is used for crossfading. Under normal operating conditions, the integrator 32 is 0 and / or inactive, and is activated only in this operating condition by an error signal provided by the monitoring function 26. Thus, the integrator 32 is activated only when a first error in the operating unit 14 is identified. In this context, the integrator value of the integrator 32 is related to the torsion bar signal or torsion bar torque and / or steering torque signal, and the integrator value increases only when the torsion bar signal or torsion bar torque and / or steering torque signal exceeds a predetermined threshold.

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

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

[0037] Based on Figure 2 and especially curve 52, a slow or gradual change in steering feel or feedback moment from the normal steering feel 28 to the modified steering feel 30 can be identified. A first error occurs at 4 seconds. Based on this, the feedback actuator 18 is operated to make a gradual change to the modified steering feel 30. In the illustrated case, the modified steering feel 30 consists exemplary of frictional characteristics alone. The torque level is also extremely low, which means that the change in 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 can easily control the driving situation. This is because the torque situation changes only slightly, and there is no large excess torque accompanied by obvious steering motion in the event of a second error or failure of the feedback actuator 18. At 37 seconds, the corresponding second error occurs exemplary. In this case, the passive steering feel, which is not explicitly illustrated, has a value of 0.4 Nm, for example, while the modified steering feel 30 has a value of 0.75 Nm. That is, in this case, only a minimal change occurs when transitioning 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, a value of 4.6 Nm is obtained, for example, and therefore, a significantly large torque fluctuation occurs when the feedback actuator 18 fails.

[0038] Finally, Figure 3 shows an illustrative flowchart that includes the main method steps for the operation of the steering system 10.

[0039] Step 60 of the method corresponds to a normal operating state without any errors. In this 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 step 62 of the method, the monitoring function 26 is used to identify the first error in the operating unit 14.

[0041] In the subsequent step 64, the steering characteristics of the steering system 10 are modified, in particular, by the operation of the feedback actuator 18, which has been adapted to the first error, thereby correcting the steering feel as intended. To this end, the feedback torque provided by the feedback actuator 18 is modified so that a gradual transition occurs from the normal steering feel 28 to the modified steering feel 30.

[0042] The illustrative flowchart in Figure 3 merely illustrates the method for the operation of the steering system 10. In particular, it is possible to modify individual method steps or add additional method steps. In this regard, for example, changes to the modified steering feel 30 can be made using appropriate crossfades, particularly using moving averages.

Claims

1. A method for operating the steering system (10) of a vehicle (12), The steering system (10) is configured as a steer-by-wire steering system and includes an operating unit (14) equipped with 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) connected to the operating unit (14) for changing the wheel steering angle of at least one vehicle wheel (22, 24). The aforementioned operating unit (14) is configured to be at least partially fail-operational, In at least one operating state in which a first error of the operating unit (14) is identified, the steering characteristics of the steering system (10) are changed by correcting the steering feel as intended through the operation of the feedback actuator (18). A method for operating the feedback actuator (18) such that, in the operating state, the change to the modified steering feel (30) is performed using a crossfade.

2. The method according to claim 1, wherein an integrator (32) is used for the crossfade, and the integrator (32) is activated in the operating state by an error signal correlated with the first error.

3. The method according to claim 1 or 2, wherein the duration of the crossfade is at least 10 seconds.

4. The method according to claim 1, wherein the modified steering feel (30) produces feedback to the driver that is at least temporarily positioned between the normal steering feel (28) and the steering feel due solely to mechanical characteristics.

5. The method according to claim 1, wherein the modified steering feel (30) has characteristics equivalent to a steering feel based solely on mechanical characteristics.

6. 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).

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

8. The method according to claim 1, wherein the maximum torque level of the modified steering feel (30) exceeds the maximum torque level of the steering feel due to mechanical characteristics alone.

9. The modified steering feel (30) reproduces the damping characteristics, The method according to claim 1, wherein the damping characteristics are adapted in relation to the steering speed of the steering handle (16) and / or the vehicle speed.

10. A computing unit (34) for carrying out the method according to claim 1.

11. A steering system (10), An operating unit (14) including at least one steering wheel (16) and at least one feedback actuator (18) cooperating with the steering wheel (16), A wheel steering angle adjuster (20) is connected to the operating unit (14) for controlling the wheel steering angle of at least one vehicle wheel (22, 24), The calculation unit (34) according to claim 10, A steering system (10) equipped with the following:

12. Vehicle (12), A vehicle (12) equipped with the steering system (10) according to claim 11.

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