Method for the operation of a vehicle's steering system

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 Art The present invention is based on a method for operating a steering system of a vehicle as described in the generic concept of claim 1. Furthermore, the present 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 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 steered vehicle wheels are known, where the driver's target setting and / or steering setting are transmitted exclusively electrically. Such a steer-by-wire steering system typically includes an operating unit comprising 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 project] [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, 12, 13 and 14, 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 The present invention relates to a method for operating 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 acting on the operating unit for changing the wheel steering angle of at least one vehicle wheel, wherein the operation of the feedback actuator is monitored using a monitoring function, and the steering characteristics of the steering system are changed in at least one operating state in which a fault and / or failure of the feedback actuator is identified using the monitoring function.

[0007] It is proposed to use further monitoring functions to monitor the driver target setting applied to the wheel steering angle adjuster by the driver, and, if the dynamics of the driver target setting in the operating state exceed a threshold, to determine a compensation amount, particularly in the form of an offset, and to modify the driver target setting using the compensation amount to change the steering characteristics. Thus, the operating state in which a fault and / or failure motion of the feedback actuator is identified using the monitoring function corresponds in particular to the driver operating state. Furthermore, the steering characteristics are modified by modifying the driver target setting, using the compensation amount, so that substantially unchanged steering behavior is provided and / or obtained, particularly in the operating state, especially when the feedback actuator transitions from an active state and / or a fully functional state to a passive state and / or a downgraded state, so that unintended steering movements by the driver due to a fault and / or failure of the feedback actuator do not lead to undesirable vehicle responses. This configuration allows for improvements in the functional operation, and advantageously, it can improve the controllability and / or steering capability 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 allows the steering characteristics to be flexibly adapted to current operating conditions. In addition, it can achieve advantageous vehicle operability and enhance operational reliability.

[0008] The steering system is configured here as a steer-by-wire steering system in which driver / target settings and / or steering settings 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. Preferably, the operating unit and the wheel steering angle adjuster are configured, in this specification, at least partially fail-operationally. A “wheel steering angle adjuster” should be understood as an actuator unit coupled to at least one vehicle wheel, which transmits driver / target settings and / or in particular the driver’s steering settings 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. To this end, the wheel steering angle adjuster may, advantageously, include 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, however, 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, particularly mechanically connected directly to the steering wheel, and provided for the purpose of detecting, particularly directly, signals, forces, and / or torque from the steering wheel, and / or transmitting, particularly directly, signals, forces, and / or torque from the steering wheel.Here, the feedback actuator is provided to provide at least active feedback torque in its normal operating state, thereby generating steering resistance and / or self-aligning torque in the steering wheel. Furthermore, the feedback actuator is provided in this context, in particular, to adapt a steering feel that is perceptible via the steering wheel. For this purpose, the feedback actuator may include at least one other electric motor. "Failure and / or failure of the feedback actuator" should be understood in particular as failure and / or failure of the feedback actuator itself, and / or failure of a peripheral assembly that works with the feedback actuator, such as the energy supply unit, and the resulting failure of the 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, such displacement 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 vehicle wheels and steering wheels, a similar equivalence of variables between the vehicle wheels / steering wheels and each connected actuator applies.

[0009] 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 a feedback actuator. Furthermore, the computing unit includes at least one additional monitoring function for monitoring, in particular, the driver target setting applied to the steering wheel by the driver, and in particular, the dynamics of the driver target setting. The computing unit is provided, in particular, for monitoring and evaluating the operation of the feedback actuator using the monitoring function. Furthermore, the calculation unit is provided, in particular, to monitor and evaluate the driver target setting applied by the driver to the wheel steering angle adjuster using additional monitoring functions. The calculation unit is also provided to modify the steering characteristics of the steering system in at least one operating state where a fault and / or failure of the feedback actuator is identified and the driver target setting dynamics exceed a threshold, and in addition, to correct the driver target setting using a compensation amount. In this context, the calculation unit is provided, in particular, to utilize error signals provided by monitoring functions and / or detection signals provided by additional monitoring functions for adapting 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 for the steering system, particularly in the form of a steering control device."Provided" should be understood, in particular, to be specifically programmed, configured, and / or installed. "Provided for a particular function" should be understood, in particular, to satisfy and / or perform that particular function, at least in its applied and / or operating state.

[0010] Furthermore, it is proposed that when modifying steering characteristics, particularly when adjusting driver and target settings using compensation amounts, current and / or imminent driving conditions should be taken into consideration, thereby enabling modifications that are adapted to the specific circumstances of the steering characteristics. Specifically, the steering characteristics are modified in this case in relation to the current and / or imminent driving conditions. The current and / or imminent driving conditions are identified and / or predicted, for example, based on at least one vehicle variable, such as yaw rate, steering wheel displacement and / or steering motion. However, alternatively or additionally, the current and / or imminent driving conditions may be derived from the route planning of the vehicle's navigation system and / or from the vehicle's corresponding sensor system, for example, in the form of a camera system.

[0011] Advantageously, the operating state corresponds to cornering. Preferably, the steering characteristics are changed only when the wheel steering angle of the vehicle wheels is not equal to 0, and especially when its absolute value is at least 0.1°. Therefore, it is particularly preferable that the steering characteristics are changed when the vehicle is cornering, and not changed when the vehicle is driving straight. This enhances operational safety, especially in dangerous driving situations. Furthermore, advantageously, a particularly efficient method is provided.

[0012] Furthermore, when modifying steering characteristics, particularly when correcting driver / target settings using compensation amounts, it is proposed to consider the dynamics and / or absolute values ​​of the driver / target settings, 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 absolute values ​​of the driver / target settings are determined using additional monitoring functions. This allows for the identification of driver overreactions, particularly when the active feedback torque of the feedback actuator disappears, and in connection with this, the steering characteristics can be adapted.

[0013] Furthermore, in order to change the steering characteristics, it is proposed to modify the driver-target setting using a compensation amount so that the driver-target setting is reduced in the operating state. In particular, the driver-target setting modified using a compensation amount, which is transmitted to the wheel steering angle adjuster in place of the driver-target setting and / or used to drive and control the wheel steering angle adjuster in the operating state, is reduced compared to the driver-target setting, preferably by at least 10%, preferably at least 20%, and particularly preferably at least 30%. Advantageously, the modified driver-target setting is reduced here by up to 90%. This reduces vehicle response and makes the situation more manageable for the driver.

[0014] Furthermore, it is proposed to mutually sum the driver / target settings and the compensation amount in order to modify the steering characteristics. In particular, this summation allows for the driver / target settings to be modified using the compensation amount. This makes it particularly easy to modify the driver / target settings using software technology.

[0015] In further configurations, it is proposed to limit the maximum level of compensation to allow for the actual need for stronger steering of the vehicle and to enable intentional oversteering of the modified steering characteristics. This can, advantageously, ensure that intentional steering movements remain viable, for example, during evasive maneuvers.

[0016] Preferably, it is proposed to determine the compensation amount using a compensation function to which detection signals provided by at least the driver / target setting and / or further monitoring functions, and error signals provided by the monitoring functions, are supplied as input quantities. In particular, the calculation unit in this case may include the compensation function. Furthermore, the compensation function can be supplied with further vehicle variables such as vehicle speed, yaw rate and / or lateral acceleration. Preferably, when determining the compensation amount using the compensation function, a dynamic gradient limit is used, by which the increase in the driver / target setting is limited in relation to at least one driving characteristic quantity, here, the compensation amount is determined based on the difference between the driver / target setting with the gradient limited and the driver / target setting. In this context, the driving characteristic quantity particularly defines the conditions under which the corresponding gradient limit is made. Furthermore, a finite automaton or state machine may be used to determine the maximum gradient of the dynamic gradient limit. The reduction of the driver / target setting is preferably performed indefinitely. This configuration makes it possible to favorably modify the steering characteristics.

[0017] In particular, a high level of operational safety can be obtained when dynamic gradient limiting is performed in relation to the current driving conditions, and / or when the current driving conditions are taken into consideration when gradient limiting is performed. Preferably, in this regard, at least whether or not there is curved driving is taken into consideration. Furthermore, advantageously, vehicle speed may be taken into consideration.

[0018] Furthermore, it is proposed that steering direction and / or steering motion correlated with the driver and target setting be considered as driving characteristics, and / or, if the operating state corresponds to cornering, the curve direction be considered. For example, in this regard, left curves and right curves may be distinguished, and / or constant cornering and cornering with active steering motion may be distinguished. When constant cornering exists, in the dynamic gradient limit, for example, only the minimum gradient is used, and in contrast, if the driver actively steers, an additional amplification of the gradient may occur. Particularly advantageous in this regard, the dynamic gradient limit is activated only when the driver has not returned the steering wheel to the centering position or zero position during cornering. This makes it possible to achieve a gradient limit that is adapted to the situation.

[0019] In a preferred configuration, it is further proposed that the change in steering characteristics in the operating state be first maintained over a first time interval, and then reduced in an adjustable manner over a predetermined second time interval, particularly in the form of a predetermined period. The first time interval may, in particular, be a predetermined period, or it may correspond to a predetermined driving condition, for example, until the next straight drive or until the next curve change. This makes it possible to improve the transition from steering characteristics in a normal operating state without errors to steering characteristics in an error operating state.

[0020] In further configurations, it is proposed to consider vehicle speed when modifying steering characteristics, particularly when adjusting driver and target settings using compensation amounts. Specifically, vehicle speed is considered, at least when determining dynamic gradient limits. This allows for particularly flexible adaptation of steering characteristics to current operating conditions.

[0021] In the present application, the method for the operation of the steering system should not be limited to the above-described uses and embodiments. In particular, the method for the operation of the steering system for realizing the functional modes described in this specification may have a different number of individual elements, components, and units from the numbers listed in this specification.

[0022] Further advantages are described in the following description of the drawings. The drawings show embodiments of the invention.

Brief Description of the Drawings

[0023] [Figure 1a] It is a diagram schematically showing a vehicle equipped with a steering system configured as a steer-by-wire steering system. [Figure 1b] It is a diagram schematically showing a vehicle equipped with a steering system configured as a steer-by-wire steering system. [Figure 2] It is a diagram showing an exemplary graph of various signals for the operation of the steering system. [Figure 3] It is a diagram showing an exemplary flowchart including the main method steps of the method for the operation of the steering system.

Modes for Carrying Out the Invention

[0024] Description of Embodiments FIGS. 1a and 1b schematically show a vehicle 12 equipped with a plurality of vehicle wheels 22, 24 and a steering system 10, configured exemplary as a passenger car. 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 30 or a steering setting is electrically transmitted to the vehicle wheels 22, 24 in at least one operating state.

[0025] 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 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 fail-operationally with respect to the detection of the driver and target setting 30, and in particular with respect to the steering wheel 16, and fail-safe with respect to the feedback torque provided by the feedback actuator 18. Alternatively, the steering wheel may be configured as a joystick, steering lever and / or steering ball or similar. Furthermore, the feedback actuator may include multiple electric motors. Furthermore, the operating unit may be configured to be either fail-safe or fail-operational.

[0026] 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 30 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.

[0027] 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 the driver / target setting 30. 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.

[0028] 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 in this case includes at least one monitoring function 26, at least one further monitoring function 28, and at least one compensation function 33. 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 with a central computing unit. Furthermore, separate control units and / or computing units may be provided for the wheel steering angle adjusters and operating units, and these may be interconnected to communicate with each other.

[0029] 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 known on its own for detecting at least one vehicle variable, such as yaw rate, an external sensor system known on its own for detecting at least one vehicle variable, such as a camera system, and / or a known navigation system.

[0030] When the feedback actuator 18 malfunctions and / or fails, under certain circumstances and / or driving conditions, such as when cornering, the feedback actuator 18 transitions from an active and / or fully functional state to a passive and / or downgraded state. This sudden loss of feedback torque may cause unintended steering movements in the steering wheel 16, which may be perceived by the steering system 10 as driver / target settings and / or steering settings, resulting in 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 from the active to the passive state may pose a controllability challenge. This is because the feedback torque decreases sharply upon the corresponding malfunction and / or failure of the feedback actuator 18, since 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.

[0031] 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.

[0032] According to the present invention, the operation of the feedback actuator 18 is monitored using a monitoring function 26, and the driver / target setting 30 for the wheel steering angle adjuster 20 is monitored using a further monitoring function 28. Furthermore, the monitoring function 26 is used to identify faults and / or failures of the feedback actuator 18, and the further monitoring function 28 is used to determine a compensation amount 31 for changing the steering characteristics of the steering system 10 in at least one operating state in which the dynamics of the driver / target setting 30 determined exceed a threshold. The steering characteristics of the steering system 10 are then changed by modifying the driver / target setting 30 using a compensation amount 31, which in this case corresponds in particular to an offset. In this case, the steering characteristics are changed by the modification of the driver / target setting 30 using the compensation amount 31 as follows: In other words, in the operating state, particularly when the feedback actuator 18 transitions from an active state and / or a fully functional state to a passive state and / or a downgraded state, substantially unchanged steering behavior is provided and / or obtained, and unintended steering movements due to faults and / or failures of the feedback actuator 18 are modified so as not to lead to undesirable vehicle responses. In this case, the modification of the steering characteristics is first maintained over a first time interval, for example, until the next straight drive or the next curve change, and then gradually reduced over a predetermined second time interval or a predetermined period. This gradual reduction can be carried out in this context, for example, in the same manner as described in German Patent Application Publication No. 102021213389.

[0033] According to the method of the present invention, the current driving conditions and / or imminent driving conditions are further taken into consideration, and the steering characteristics are modified in relation to the current driving conditions and / or imminent driving conditions. Here, preferably, the corresponding modification of the steering characteristics is made only when the vehicle is cornering or when imminent cornering of the vehicle 12 is identified. As a result, the operating state corresponds to cornering, where the steering characteristics are modified only when the wheel steering angles of the vehicle wheels 22, 24 are not equal to 0.

[0034] Furthermore, when modifying the steering characteristics, particularly when correcting the driver / target setting 30 using the compensation amount 31, the dynamics and / or absolute value of the driver / target setting 30 with respect to the wheel steering angle adjuster 20, i.e., the maximum displacement of the steering wheel 16 and / or the steering speed of the steering wheel 16, are taken into consideration.

[0035] Furthermore, the driver-target setting 30 is modified using a compensation amount 31 such that a modified driver-target setting 32, which is transmitted to the wheel steering angle adjuster 20 in place of the driver-target setting 30 in the operating state, and / or used to drive and control the wheel steering angle adjuster 20 in the operating state, is reduced in particular compared to the driver-target setting 30 (see also Figure 2). The reduction of the driver-target setting 30 is particularly meaningful when it is identified that the driver is steering more towards the curve than intended, based on the current and / or imminent driving conditions, and / or based on the dynamics and / or absolute value of the driver-target setting 30. In this case, the reduction of the driver-target setting 30 reduces the vehicle response, making the situation more manageable for the driver. Basically, the loss of driver steering precision due to insufficient feedback torque can be compensated at least in part by a reduction in vehicle response, so controllability is improved by reducing the driver-target setting 30.

[0036] Specifically, in order to determine the corrected driver / target setting 32 for the wheel steering angle adjuster 20, the driver / target setting 30 and the compensation amount 31 are added together in this case. In this context, the following relationship holds: angRW mod =angRW driver +angRW comp

[0037] Here, angRW mod This represents the revised driver target setting 32, angRW driver This represents the driver / target setting 30, angRW comp This represents a compensation amount of 31.

[0038] To determine the compensation amount 31, a compensation function 33 is used in this case. The compensation function 33 is supplied with error signals provided by the driver / target setting 30 and the monitoring function 26 as input quantities. Preferably, in this context, the absolute value is first formed by multiplying the driver / target setting 30 by its sign. Therefore, to determine the compensation amount 31, only an excessively rapid rise in the driver / target setting 30 in a certain direction, particularly in the positive direction, is relevant. Furthermore, a dynamic gradient limit is used, and this gradient limit can be used to limit the rise of the driver / target setting 30 as needed in relation to at least one driving characteristic, thereby determining a driver / target setting with a limited gradient. In this context, the driving characteristic particularly specifies the conditions under which the corresponding gradient limit is applied. Furthermore, a finite automaton or state machine may be used to determine the maximum gradient of the dynamic gradient limit. Typically, here the gradient is selected such that the modified 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 performed without restriction. Here, an offset is created by the formation of a difference between the driver target setting with a restricted gradient and the driver target setting 30, and this offset is ultimately multiplied by the sign of the driver target setting 30 in order to determine the compensation amount 31. This ensures that the driver target setting 30 is always reduced in the operating state. Furthermore, the maximum level of the compensation amount 31 can be further restricted to allow for any actual need for stronger steering of the vehicle 12.

[0039] Dynamic gradient limiting is further performed in relation to the current driving conditions. In this regard, at least whether or not curve driving is present is considered. Furthermore, vehicle speed may be considered. Furthermore, steering direction, steering motion, and / or curve direction, which correlate with the driver and target setting 30, are considered as driving characteristics. In this regard, for example, left curves and right curves are distinguished, and alongside this, constant curve driving and curve driving with active steering motion are distinguished. If constant curve driving is present, for example, only the minimum gradient is used, and in contrast, if the driver actively steers, additional amplification of the gradient can be performed, particularly using an amplification coefficient, thereby ensuring the desired steering. The amplification coefficient can be selected, for example, in relation to the vehicle speed, in which case the increase decreases as the vehicle speed increases. Furthermore, in this case, gradient limiting is activated only when the driver has not returned the steering to the centering position or zero position during curve driving. For this purpose, for example, an additional threshold for steering speed can be defined to reliably identify that the driver has returned the steering wheel to the centering position or the zero position. The steering movement to the centering position or the zero position may essentially be set as the termination condition for the compensation function 33, for which it is desirable that the vehicle speed is additionally below a limit value.

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

[0041] The vertical axis 42 represents the magnitude axis. The horizontal axis 44 shows time [in seconds]. Curve 46 shows the virtual transition of the displacement of the steering wheel 16, which in this case is the actual form of the steering wheel angle, without any change in steering characteristics using the driver / target setting 30 modification. Curve 48 shows the transition of the displacement of the steering wheel 16, which in this case is the actual form of the steering wheel angle, with the change in steering characteristics using the driver / target setting 30 modification. Curve 50 shows the transition of the wheel steering angle of the driver / target setting 30 or vehicle wheels 22,24, without any change in steering characteristics using the driver / target setting 30 modification. Curve 52 shows the transition of the wheel steering angle of the modified driver / target setting 32 or vehicle wheels 22,24, with the change in steering characteristics due to the modification of the driver / target setting 30. Furthermore, curve 54 shows the transition of the compensation amount 31.

[0042] Figure 2 shows that the driver first steers into a curve and then drives at a constant radius until the feedback actuator 18 fails at 10 seconds. Curves 50 and 52 clearly illustrate the reduced wheel steering angle of the vehicle wheels 22 and 24, and the associated reduced vehicle response, obtained by the method according to the present invention. Furthermore, based on curves 46 and 48, it can be seen that a tilted position of the steering wheel 16 may occur based on the modification of the driver target setting 30 using the compensation amount 31. However, this is immediately resolved again by reducing the change in steering characteristics through adjustment.

[0043] Finally, Figure 3 shows an illustrative flowchart that includes the main method steps for the operation of the steering system 10.

[0044] Step 60 of the method corresponds to a normal operating state without any errors. In this case, the driver / target setting 30 is transmitted to the wheel steering angle adjuster 20, thereby driving and controlling the wheel steering angle adjuster 20 according to the driver / target setting 30. Furthermore, the operation of the feedback actuator 18 is monitored using the monitoring function 26, and the driver / target setting 30 with respect to the wheel steering angle adjuster 20 is monitored using a further monitoring function 28.

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

[0046] In the subsequent step 64, a compensation amount 31 is determined, the driver / target setting 30 is modified using the compensation amount 31, and the modified driver / target setting 32 is determined, thereby changing the steering characteristics of the steering system 10. Subsequently, the modified driver / target setting 32 is transmitted to the wheel steering angle adjuster 20, in particular, instead of the driver / target setting 30, thereby driving and controlling the wheel steering angle adjuster 20 using the modified driver / target setting 32.

[0047] 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, the current driving conditions may be taken into consideration. Furthermore, the compensation amount 31 can be determined using a compensation function 33 to which error signals provided by the driver / target setting 30 and the monitoring function 26 are supplied as input quantities. When determining the compensation amount 31, a dynamic gradient limit is used, and this dynamic gradient limit is used to limit the increase of the driver / target setting 30 in relation to at least one driving characteristic quantity.

Claims

1. A method for the operation of a vehicle (12), particularly an automobile steering system (10), 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). A method for monitoring the operation of the feedback actuator (18) using a monitoring function (26), and changing 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) is identified using the monitoring function (26), Further monitoring functions (28) are used to monitor the driver / target setting (30) for the wheel steering angle adjuster (20), and if the dynamics of the driver / target setting (30) exceed a threshold in the operating state, a compensation amount (31) in particular of the form of offset is determined, and the driver / target setting (30) is modified using the compensation amount (31) in order to change the steering characteristics. A method for considering the current driving conditions and / or imminent driving conditions when changing the steering characteristics.

2. The method according to claim 1, wherein the steering characteristics are changed only when the operating state corresponds to cornering and the wheel steering angle of the vehicle wheels (22, 24) is not equal to 0.

3. The method according to claim 1, wherein the dynamics and / or absolute values ​​of the driver and target setting (30) are taken into consideration when the steering characteristics are changed.

4. The method according to claim 1, wherein, in order to change the steering characteristics, the driver / target setting (30) is modified using the compensation amount (31) so that the driver / target setting (30) is reduced in the operating state.

5. The method according to claim 1, wherein the driver / target setting (30) and the compensation amount (31) are added together in order to change the steering characteristics.

6. The method according to claim 1, which limits the maximum level of the compensation amount (31).

7. The compensation amount (31) is determined using the compensation function (33) to which the error signals provided by the driver / target setting (30) and the monitoring function (26) are supplied as input amounts. The method according to claim 1, wherein when determining the compensation amount (31), a dynamic gradient limit is used, and the increase in the driver target setting (30) is limited by the dynamic gradient limit in relation to at least one driving characteristic quantity.

8. The method according to claim 7, wherein the dynamic gradient limit is performed in relation to the current driving conditions.

9. The method according to claim 7, wherein the steering direction and / or steering motion correlated with the driver / target setting (30) are considered as driving characteristic quantities, and / or the curve direction is considered when the operating state corresponds to curve driving.

10. The method according to claim 1, wherein the change in steering characteristics in the operating state is first maintained over a first time interval, and then reduced over a predetermined second time interval while being adjusted.

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

12. A steering system (10), in particular a steer-by-wire steering system, 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 11, A steering system (10) equipped with the following:

13. Vehicles (12), especially automobiles, A vehicle (12) equipped with the steering system (10) according to claim 12.

Images