Method for operating a steering system

Abstract

The invention relates to a method for operating a steering system (10a), wherein the steering system (10a) comprises at least one wheel steering angle adjuster (12a) with a rack (14a) for changing a wheel steering angle of at least one vehicle wheel (16a), wherein a first rack force signal (18a-c) is determined based on the dynamics of the rack (14a) and a first calculation algorithm is used in determining the first rack force signal (18a-c), and wherein an operating characteristic (20a-c) is determined as a function of the first rack force signal (18a-c), which is used in particular for controlling at least one steering function.It is proposed that, in order to monitor and / or verify the plausibility of the first rack force signal (18a-c) based on the dynamics of the rack (14a), at least a second rack force signal (22a-c) be determined, and that a second calculation algorithm with a lower complexity compared to the first calculation algorithm be used in determining the second rack force signal (22a-c).

Description

Prior ArtThe invention is based on a method for operating a steering system according to the preamble of claim 1.Various methods are known from the prior art, in which a rack force is determined and the determined rack force or an operating parameter derived therefrom is used to control a vehicle and / or steering function.For example, DE 10 2017 217 470 A1 discloses a method for operating a steering system, in which a rack force signal is determined on the basis of a movement of the rack and using a neural network and one or more steering functions, such as, for example, road feedback optimization, skew compensation, blockage detection, steering assistance dependent on the rack force and / or an adaptation of a steering feel, are carried out as a function of the rack force signal.Furthermore, DE 10 2011 052 881 A1 discloses a method for determining a rack force in a steering system, in which a first rack force signal is determined as a function of at least one force occurring in the steering system or at least one torque occurring in the steering system and a second rack force signal is determined as a function of at least one vehicle variable which characterizes a movement state of the vehicle, and wherein a resulting rack force is formed from the first rack force signal and the second rack force signal. In this context, an influence of the first rack force signal and / or the second rack force signal may be adjusted such that a desired steering feel is generated at a steering handle of the steering system.Furthermore, DE 10 2018 219 560 A1 discloses a method for operating a steering system, in which the rack force is calculated on the basis of a motion equation determined from a restoring force. The rack force can then be used, for example, to provide information about a roadway surface to a driver.Proceeding therefrom, the object of the invention is in particular to provide a method for operating a steering system having improved properties with regard to operational reliability. The object is achieved by the features of claims 1, 13 and 14, while advantageous embodiments and further developments of the invention can be found in the dependent claims.Disclosure of the InventionThe invention is based on a method, in particular a computer-implemented method, for operating a steering system, in particular during the operation of the steering system in a vehicle, wherein the steering system comprises at least one wheel steering angle actuator with a toothed rack for changing a wheel steering angle of at least one vehicle wheel, wherein a first toothed rack force signal is determined on the basis of a dynamics of the toothed rack and a first calculation algorithm, in particular with an increased complexity, is used in the determination of the first toothed rack force signal, and wherein an operating characteristic variable is determined on the basis of the first toothed rack force signal, which operating characteristic variable is used in particular for controlling at least one steering function. The steering function can correspond, for example, to road feedback optimization, skew compensation, blockage detection, steering assistance dependent on the steering rack force and / or an adaptation of a steering feel. Alternatively or additionally, however, the operating characteristic variable can also be used in a vehicle system that differs from the steering system, for example a brake system and / or a drive system, and can be used to control a corresponding vehicle function.It is proposed that at least one second rack force signal is determined for monitoring and / or plausibility checking the first rack force signal on the basis of the dynamics of the rack, and a second calculation algorithm with a lower complexity compared to the first calculation algorithm is used in the determination of the second rack force signal. The second rack force signal is thus used at least for monitoring and / or plausibility checking the first rack force signal. In addition, the second rack force signal can advantageously be taken into account in the determination of the operating parameter. The rack force signals define in particular an interaction or a interaction between the vehicle and a road surface or a subgrade. The more accurately the first rack force signal is calculated accordingly, the more realistic this interaction can be determined and can be taken into account in particular when executing steering functions. In contrast, for monitoring and / or plausibility checking the first rack force signal, a less precise rack force signal, and therefore the second rack force signal, may be sufficient to achieve a sufficiently high ASIL (Automotive Safety Integrity Level) evaluation. This configuration can increase operational reliability in particular. In addition, efficiency such as power efficiency, calculation efficiency, and / or cost efficiency may be improved.The steering system is in particular part of a vehicle, in particular of a motor vehicle, and is provided for providing a steering functionality. The steering system is preferably designed as a steer-by-wire steering system, in which a steering specification of a driver is preferably transmitted purely electrically to the vehicle wheels. A "wheel steering angle actuator" is to be understood in this context as an actuating unit operatively connected to at least one vehicle wheel, which is provided to transmit a steering specification to the vehicle wheel by changing a wheel steering angle of the vehicle wheel and thereby advantageously control at least one orientation of the vehicle wheel and / or influence a direction of travel of the vehicle. For this purpose, the wheel steering angle actuator comprises at least one toothed rack and in particular at least one steering actuator operatively connected to the toothed rack, for example in the form of an electric motor. The wheel steering angle actuator can be designed in particular as an individual wheel actuator and be assigned exactly to one, in particular steerable, vehicle wheel or can be designed as a central actuator and be assigned at least two, in particular steerable, vehicle wheels. The wheel steering angle actuator can furthermore be assigned to a vehicle axle designed as a rear axle or advantageously to a vehicle axle of the vehicle designed as a front axle. The term "the second calculation algorithm has a lower complexity compared to the first calculation algorithm" is to be understood in particular to mean that the second calculation algorithm presupposes and / or processes a lower number of input variables and / or variables and / or requires a lower computing power, in particular compared to the first calculation algorithm. For example, the first calculation algorithm can use dynamics or preferably a movement of the rack to calculate the first rack force signal and take into account at least one further vehicle characteristic variable, such as a vehicle speed, and / or at least one further steering characteristic variable, such as in particular a transmission and / or motor behavior of the steering actuator and / or friction effects in the wheel steering angle actuator and / or inertia effects in the wheel steering angle actuator. The second calculation algorithm can likewise use dynamics or preferably a movement of the rack for calculating the second rack force signal, but, when calculating the second rack force signal, at least one of the aforementioned further vehicle characteristics and / or further steering characteristics is dispensed with or the further vehicle characteristics and / or the further steering characteristics are determined by means of a simplified model and / or a simplified algorithm. Furthermore, the first calculation algorithm and the second calculation algorithm could also use different steering models or vehicle models, such as a single-lane model, a two-lane model and / or a kinematic model, for calculating the corresponding rack force signal.In addition, the vehicle may include a computing unit which is provided to carry out the method for operating the steering system. A "computing unit" is to be understood in particular as an electrical and / or electronic unit which has an information input, an information processing and an information output. The computing unit advantageously further comprises at least one processor, at least one memory, at least one input and / or output means, at least one operating program, at least one control routine, at least one calculation routine, at least one evaluation routine and / or at least one determination routine. In particular, the computing unit is provided to ascertain the first rack force signal on the basis of a dynamics of the rack and to use the first calculation algorithm in the ascertainment of the first rack force signal. In addition, the computing unit is provided in particular to ascertain the operating parameter as a function of the first rack force signal. In addition, the arithmetic unit is advantageously provided for monitoring and / or plausibility checking the first rack force signal. In this context, the computing unit is provided, in particular, to ascertain the second rack force signal on the basis of the dynamics of the rack and to use the second computation algorithm, which is different from the first computation algorithm, in particular, when ascertaining the second rack force signal. Furthermore, the computing unit can be provided to ascertain a dynamic or a movement of the rack, for example on the basis of a detection signal of a rack position sensor and / or on the basis of a movement of the steering actuator. Furthermore, the computing unit can be provided to use the operating parameter for controlling at least one steering function. The computing unit is preferably integrated into a control device of the vehicle, for example a central vehicle control device or a control device of the steering system. "Provided" is to be understood in particular as being specially programmed, designed and / or equipped. The fact that an object is provided for a specific function is to be understood in particular to mean that the object fulfills and / or executes this specific function in at least one application state and / or operating state.It is furthermore proposed that the steering system comprises an operating unit which is mechanically separate from the at least one wheel steering angle actuator and has a steering handle, for example in the form of a steering wheel, and also has a feedback actuator which interacts with the steering handle, and the operating parameter is used at least for actuating the feedback actuator and therefore in particular for generating a steering feel. In this case, the steering function accordingly corresponds in particular to a feedback torque provided by the feedback actuator for acting on the steering handle or a steering feel on the steering handle generated thereby. The feedback actuator is preferably controlled in the manner of a controller. In this way, in particular a particularly advantageous steering feel, in particular in a steering system designed as a steer-by-wire steering system, can be provided. Furthermore, even without a torque sensor, a safety concept with a sufficiently high ASIL evaluation can be achieved, in particular in the case that the behavior of the rack force is caused by the road geometry.In addition, it is proposed that the first rack force signal and / or the second rack force signal is / are calculated on the basis of a movement equation of the rack. Thus, the first rack force signal and / or the second rack force signal are preferably calculated based on the equation of motion of the rack. In this way, in particular an advantageously simple and / or efficient calculation of the rack force can be achieved.According to one embodiment, it is proposed that a tolerance range for the first rack force signal is determined by means of the second rack force signal and, in the case that the first rack force signal lies outside the tolerance range for the first rack force signal, the first rack force signal is limited to the second rack force signal and / or by means of the second rack force signal. In the latter case, the first rack force signal can be limited, for example, to the tolerance range determined by the second rack force signal. In particular, in the case that the first rack force signal lies within the limits of the tolerance range for the first rack force signal, the operating parameter is determined directly from the first rack force signal. In principle, in this case, the first rack force signal can also be used as an operating parameter, in particular for controlling the at least one steering function and preferably for controlling the feedback actuator. This can improve operational reliability. In particular, the limitation ensures that, in the case that the operating parameter is used for controlling the feedback actuator, no excessively large torque is permitted in the direction of an end stop of the operating unit, which torque could lead to safety-critical situations, in particular when driving without hands on the steering handle. In particular in the case of cornering, with a corresponding configuration of a front axle of the vehicle, a steering force in the direction of a neutral or straight-ahead position can be achieved, wherein the steering force is correlated with the second rack force signal and this can therefore be used to limit the first rack force signal.It is further proposed that a time duration of the first rack force signal outside the tolerance range for the first rack force signal and / or a distance of the first rack force signal from the limit values of the tolerance range for the first rack force signal is determined, and in the case that the time duration exceeds a time limit value and / or the distance exceeds a distance limit value, a system reaction is initiated. As a system reaction, for example, the tolerance range determined by the second rack force signal can be reduced to such an extent that the first rack force signal is directly limited to the second rack force signal. Alternatively or additionally, the system reaction can comprise, for example, generating a notification message and / or degradation of the vehicle and / or of the steering system, for example, switching off and / or reducing the feedback torque in the case of generating a steering feel. In this way, in particular robustness and / or operational reliability can be further increased.According to an alternative embodiment, it is proposed that a first torque signal is determined on the basis of the first rack force signal and a second torque signal is determined on the basis of the second rack force signal, wherein the first torque signal is used to determine the operating parameter, and wherein a tolerance range for the first torque signal is determined by means of the second torque signal, and in the case that the first torque signal lies outside the tolerance range for the first torque signal, the first torque signal is limited to the second torque signal and / or by means of the second torque signal. In the latter case, the first torque signal can be limited, for example, to the tolerance range determined by the second torque signal. In particular, in this case, the first torque signal can be used for controlling the steering function and in particular for controlling the feedback actuator. This also allows operational reliability to be improved. The limitation ensures, in particular, that in the case that the operating parameter is used for controlling the feedback actuator, an excessively large torque is not permitted in the direction of an end stop of the operating unit.In addition, it is also proposed in this case that a time duration of the first torque signal outside the tolerance range for the first torque signal and / or a distance of the first torque signal from the limit values of the tolerance range for the first torque signal is determined, and in the case that the time duration exceeds a time limit value and / or the distance exceeds a distance limit value, a system reaction is initiated. As a system reaction, for example, the tolerance range determined by the second torque signal can be reduced to such an extent that the first torque signal is directly limited to the second torque signal. Alternatively or additionally, however, the system reaction can also correspond to the aforementioned system reaction. In this way, in particular robustness and / or operational reliability can be further increased.According to a further embodiment, it is proposed that a first partial signal, in particular a first rack force partial signal, is determined by means of the first calculation algorithm, and a second partial signal, in particular a second rack force partial signal, is determined, in particular by means of a third calculation algorithm, wherein the first rack force signal is determined from the first partial signal and the second partial signal. The second partial signal can be calculated, for example, as a function of a deflection of the steering handle and a vehicle speed. For this purpose, for example, a meshing model and / or a characteristic map can be used. As a result, the first rack force signal can be optimized in particular and advantageously adapted to the specific steering function.Alternatively, it is proposed that a base signal, in particular a rack force base signal, is determined by means of the first calculation algorithm and the base signal is modified by means of at least one modification characteristic variable, in particular one correlated with the steering function, wherein the first rack force signal is determined from the base signal modified, in particular with the modification characteristic variable. The modification characteristic variable can be correlated here, for example, with a steering characteristic or a steering behavior about a neutral or straight-ahead position, in particular in the case where the steering function corresponds to the feedback torque provided by the feedback actuator or serves for adapting the steering feel at the steering handle. In particular, a variability can be increased as a result. In addition, the first rack force signal can be optimized and advantageously adapted to the specific steering function.In principle, a base signal, in particular a rack force base signal, could also be determined from the aforementioned first subsignal and the aforementioned second subsignal, which base signal is then modified with a modification characteristic variable, in particular correlated with the steering function, and is used to determine the first rack force signal. In this case, too, the first rack force signal can be optimized and advantageously adapted to the specific steering function.A particularly high level of operational reliability can be achieved in particular if at least one third rack force signal is determined for monitoring and / or plausibility checking of the first rack force signal. The third rack force signal is thus used at least for monitoring and / or plausibility checking the first rack force signal. In addition, the third rack force signal can advantageously be taken into account in the determination of the operating parameter. In particular, a fourth calculation algorithm can be used in the determination of the third rack force signal. Particularly advantageously, the third rack force signal can be calculated as a function of a deflection of the steering handle and a vehicle speed. For this purpose, for example, a meshing model and / or a characteristic map can be used. In addition, the fourth calculation algorithm can correspond in this case in particular to the third calculation algorithm.It is furthermore proposed that a further tolerance range for the first rack force signal is determined by means of the third rack force signal and, in the case that the first rack force signal lies outside the further tolerance range for the first rack force signal, the first rack force signal is limited to the second rack force signal and / or by means of the second rack force signal. In the latter case, the first rack force signal can be limited, for example, to the tolerance range determined by the second rack force signal. In principle, however, even in the case that the first rack force signal lies outside the further tolerance range for the first rack force signal, the first rack force signal could be limited to the third rack force signal and / or by means of the third rack force signal. In particular, the first rack force signal can thus be monitored by means of two tolerance ranges, wherein, for example, in a first step a check is made as to whether the first rack force signal lies within the limits of the tolerance range for the first rack force signal and in a second step a check is made as to whether the first rack force signal lies within the limits of the further tolerance range for the first rack force signal. Alternatively, the tolerance range for the first rack force signal, which tolerance range is determined in particular by means of the second rack force signal, and the further tolerance range for the first rack force signal, which tolerance range is determined in particular by means of the third rack force signal, can also be combined to form a common tolerance range for the first rack force signal. In this case, the first rack force signal is limited in the case that the first rack force signal lies outside the common tolerance range for the first rack force signal. This can further improve operational reliability.In addition, it is also proposed in this case that a time duration of the first rack force signal outside the further tolerance range for the first rack force signal and / or a distance of the first rack force signal from the limit values of the further tolerance range for the first rack force signal is determined, and in the case that the time duration exceeds a further time limit value and / or the distance exceeds a further distance limit value, a system reaction is initiated. The system reaction can correspond to the aforementioned system reaction. When using a common tolerance range for the first rack force signal, in this case a time duration of the first rack force signal outside the common tolerance range for the first rack force signal and / or a distance of the first rack force signal from the limit values of the common tolerance range for the first rack force signal can also be determined, and in the case that the time duration exceeds a common time limit value and / or the distance exceeds a common distance limit value, a system reaction can be initiated. In this way, in particular robustness and / or operational reliability can be further increased.The method of operating the steering system and the vehicle herein are not intended to be limited to the application and embodiment described above. In particular, the method for operating the steering system and the vehicle for fulfilling a mode of operation described herein can have a number that differs from a number of individual elements, components and units mentioned herein.DRAWINGSFurther advantages are evident from the following description of the drawings. Several exemplary embodiments of the invention are shown in the drawings.The following are shown: FIGS. 1 a- b show a vehicle with a steering system designed as a steer-by-wire steering system in a simplified illustration, FIG. 2 shows a signal flow diagram for ascertaining an operating characteristic variable, which is used in particular for controlling at least one steering function, FIG. 3 shows an exemplary flow diagram with main method steps of a method for operating the steering system, FIG. 4 shows a further signal flow diagram for determining an operating parameter according to a further exemplary embodiment of the invention, and FIG. 5 shows a further signal flow diagram for determining an operating parameter according to a further exemplary embodiment of the invention.DESCRIPTION OF THE EMBODIMENTSFIGS. 1 aand 1 b show a vehicle 42 awhich is embodied as a passenger motor vehicle by way of example and has a plurality of vehicle wheels 16 aand a steering system 10 ain a simplified illustration. The steering system 10 acomprises an operative connection with the vehicle wheels 16 aand is provided for influencing a direction of travel of the vehicle 42 a. Furthermore, the steering system 10 ais in the present case designed as a steer-by-wire steering system, in which a steering specification is electrically forwarded to the vehicle wheels 16 ain at least one operating state.The steering system 10 acomprises an operating unit 24 a, which can be actuated in particular by a driver and / or occupant. The operating unit 24 aincludes a steering handle 26 a, for example in the form of a steering wheel, and a feedback actuator 28 acoupled mechanically to the steering handle 26 a. The feedback actuator 28 ais provided for providing a feedback torque and thereby for generating a steering resistance and / or a restoring torque to the steering handle 26 a. Accordingly, the feedback actuator 28a for generating a steering feel is provided on the steering handle 26a. Alternatively, a steering handle could also be designed as a joystick, as a steering lever and / or as a steering ball or the like.Furthermore, the steering system 10 aincludes a wheel steering angle actuator 12 a. The wheel steering angle actuator 12 ais formed mechanically separately from the operating unit 24 a. The wheel steering angle actuator 12 ais connected purely electrically to the operating unit 24 a. Furthermore, the wheel steering angle actuator 12 ais designed as a central actuator. The wheel steering angle actuator 12 acomprises an operative connection with at least two of the vehicle wheels 16 a, in particular two front wheels, and is provided for converting the steering specification into a steering movement of the vehicle wheels 16 a. For this purpose, the wheel steering angle actuator 12 aincludes a toothed rack 14 aand a steering actuator 44 acooperating with the toothed rack 14 a, in particular in the form of an electric motor. In principle, a steering system could also comprise a plurality of wheel steering angle actuators, in particular designed as individual wheel actuators. Furthermore, a steering actuator could be designed, for example, as a linear drive and / or comprise a plurality of electric motors.In addition, the vehicle 42 aincludes a control device 46 a. In the present case, the control device 46 ais designed as a steering control device and consequently part of the steering system 10 a. The control device 46a has an electrical connection to the wheel steering angle actuator 12a. The control device 46 afurther has an electrical connection to the operating unit 24 a. The control device 46 ais provided at least for controlling an operation of the steering system 10 a. For this purpose, the control device 46 aincludes a computing unit 40 a. The computing unit 40 aincludes at least one processor (not shown), for example in the form of a microprocessor, and at least one operating memory (not shown). In addition, the computing unit 40 aincludes at least one operating program stored in the operating memory with at least one control routine, at least one calculation routine, at least one evaluation routine and / or at least one determination routine. In principle, however, a control device could also be different from a steering control device and be designed, for example, as a single central vehicle control device with a central processing unit. It is also conceivable to provide separate control units and / or arithmetic units for a wheel steering angle actuator and for an operating unit and to connect these to one another in a communicating manner.In order to improve operational safety, a method for operating the steering system 10 ais proposed below. In the present case, the computing unit 40 ais in particular provided to execute the method and for this purpose has in particular a computer program with corresponding program code means. In principle, however, another computing unit, for example a central vehicle control device, could also be provided for carrying out the method.The description relates below to FIG. 2, in which an exemplary signal flow diagram is shown.In the present case, a dynamic, advantageously a movement, of the toothed rack 14 ais determined and a first toothed rack force signal 18 ais determined on the basis of the dynamic of the toothed rack 14 aby means of a first calculation block 48 a. The first calculation block 48 acomprises a first calculation algorithm which is used to determine the first rack force signal 18 a. For example, the first calculation algorithm can use an equation of motion of the rack 14 ato calculate the first rack force signal 18 aand take into account at least one further steering characteristic variable, such as a gear and / or motor behavior of the steering actuator 44 aand / or friction effects in the wheel steering angle actuator 12 aand / or inertia effects in the wheel steering angle actuator 12 a. The more accurately the first rack force signal 18 ais calculated in this case, the more realistic this interaction can be determined between the vehicle 42 aand a vehicle subsurface.By means of the first rack force signal 18 a, an operating parameter 20 acan then be determined, which can be used, for example, for controlling at least one steering function. In the present case, the operating parameter 20 ais used by way of example for controlling the feedback actuator 28 a. In this case, the steering function accordingly corresponds to a feedback torque provided by the feedback actuator 28 afor acting on the steering handle 26 aand serves for adapting a steering feel. The feedback actuator 28 ais activated with the operating parameter 20 ain this case in the manner of a control. Alternatively or additionally, however, the operating parameter 20 acan also be used in a vehicle system that differs from the steering system 10 aand can be used to control a corresponding vehicle function.Furthermore, in the present case, a second rack force signal 22 ais determined on the basis of the dynamics of the toothed rack 14 aby means of a second calculation block 50 a. The second calculation block 50 aincludes a second calculation algorithm, which is used for determining the second rack force signal 22 aand has a lower complexity compared to the first calculation algorithm. For example, the second calculation algorithm can use an equation of motion of the rack 14 ato calculate the second rack force signal 22 a, but dispense with at least one of the aforementioned further steering characteristics, for example a friction component and / or an inertia component, when calculating the second rack force signal 22 a.The second rack force signal 22 ais also used for monitoring and / or plausibility checking the first rack force signal 18 a. For this purpose, the first rack force signal 18 aand the second rack force signal 22 aare fed to a monitoring block 52 a, which determines a tolerance range for the first rack force signal 18 aby means of the second rack force signal 22 a. If the first rack force signal 18 ais within the limits of the tolerance range, the operating parameter 20 ais determined from the first rack force signal 18 ain a manner known per se. In principle, the first rack force signal 20 acan also be used as the operating parameter 20 a. If, on the other hand, the first rack force signal 18 ais outside the tolerance range, the first rack force signal 18 ais limited by means of the second rack force signal 22 a. In the present case, the first rack force signal 18 acan be limited, for example, to the tolerance range determined by the second rack force signal 22 a. The limitation ensures that no too great a torque is permitted in the direction of an end stop of the operating unit 24 a, which torque could lead to safety-critical situations, in particular when driving without hands on the steering handle 26 a. In particular in the case of cornering, with a corresponding configuration of a front axle of the vehicle 42 a, a steering force in the direction of a neutral or straight-ahead position can be achieved, wherein the steering force is correlated with the second rack force signal 22 aand this can therefore be used to limit the first rack force signal 18 a.Furthermore, by means of an additional monitoring algorithm, which can be implemented directly in the monitoring block 52 a, for example, a time duration of the first rack force signal 18 aout of the tolerance range and / or a distance of the first rack force signal 18 afrom the limit values of the tolerance range can be determined, and in the case that the time duration exceeds a time limit value and / or the distance exceeds a distance limit value, a system reaction can be initiated. As a system reaction, for example, the tolerance range determined by the second rack force signal 22 acan be reduced to such an extent that the first rack force signal 18 ais directly limited to the second rack force signal 22 a. Alternatively or additionally, however, the system reaction can also comprise generating an instruction message and / or degradation of the vehicle 42 aand / or of the steering system 10 a, in the present case for example in the form of switching off and / or reducing the feedback torque of the feedback actuator 28 a.FIG. 3 finally shows an exemplary flow diagram with main method steps of a method for operating the steering system 10 a.In a method step 70 a, the first rack force signal 18 ais ascertained on the basis of the dynamics of the rack 14 a, wherein the first calculation algorithm is used in the ascertainment of the first rack force signal 18 a. In addition, the operating parameter 20 acan be determined as a function of the first rack force signal 18 a, which operating parameter can be used, for example, for controlling at least one steering function, such as, for example, a steering feel.In a method step 72 a, the second rack force signal 22 ais determined on the basis of the dynamics of the rack 14 a, wherein the second calculation algorithm, which in particular has a lower complexity compared to the first calculation algorithm, is used in the determination of the second rack force signal 22 a.In a method step 74 a, the second rack force signal 22 ais used for monitoring and / or plausibility checking of the first rack force signal 18 a. For this purpose, for example, a tolerance range for the first rack force signal 18 acan be determined by means of the second rack force signal 22 a, and in the case that the first rack force signal 18 ais outside the tolerance range, the first rack force signal 18 acan be limited to the second rack force signal 22 aor by means of the second rack force signal 22 a. Alternatively, however, it is also conceivable to first convert or convert a first rack force signal and / or a second rack force signal into another operating signal and to use these operating signals for monitoring and / or plausibility checking or for determining a tolerance range (cf. also the description relating to the following exemplary embodiment).The exemplary flowchart in FIG. 3 is intended to describe, merely by way of example, a method for operating the steering system 10 a. In particular, individual method steps can also vary or add additional method steps. For example, it is conceivable to determine a time duration of the monitored signal, in particular the first rack force signal 18 ain the present case, outside the tolerance range and / or a distance of the monitored signal, in particular the first rack force signal 18 ain the present case, from the limit values of the tolerance range by means of an additional monitoring algorithm, and to initiate a system reaction in the event that the time duration exceeds a time limit value and / or the distance exceeds a distance limit value.FIGS. 4 and 5 show further exemplary embodiments of the invention. The following descriptions and the drawings are limited substantially to the differences between the exemplary embodiments, wherein with regard to identically denoted components, in particular with regard to components with the same reference numerals, reference can in principle also be made to the drawings and / or the description of the other exemplary embodiments, in particular of FIGS. 1, 2 to 3. To distinguish between the exemplary embodiments, the letter a is appended to the reference numerals of the exemplary embodiment in FIGS. 1, 2 to 3. In the exemplary embodiments of FIGS. 4 and 5, the letter a is replaced by the letters b and c.FIG. 4 shows a first further exemplary embodiment of the invention. The letter b is appended to the exemplary embodiment of FIG. 4. The further exemplary embodiment of FIG. 4 differs from the previous exemplary embodiment at least substantially in terms of the operating signals used for monitoring and / or plausibility checking or for determining a tolerance range.Analogously to the previous exemplary embodiment, a first rack force signal 18 bis determined by means of a first calculation block 48 band a second rack force signal 22 ais determined by means of a second calculation block 50 b.In this case, however, the first rack force signal 18 bis supplied to a first conversion block 54 b, which determines a first torque signal 30 bfrom the first rack force signal 18 b. For this purpose, the first conversion block 54 bmay include, for example, a characteristic curve and / or a characteristic diagram which maps a rack force against a torque. In principle, however, a corresponding calculation algorithm could also be used. By means of the first torque signal 30 b, an operating parameter 20 bcan then be determined, which can be used in particular for controlling at least one steering function, such as a steering feel.Analogously, the second rack force signal 22 bis supplied to a second conversion block 56 b, which determines a second torque signal 32 bfrom the second rack force signal 22 b. For this purpose, the second conversion block 56 bmay include, for example, a characteristic curve and / or a characteristic diagram which maps a rack force against a torque. In principle, however, a corresponding calculation algorithm could also be used.The second rack force signal 22 bor, more precisely, the second torque signal 32 bdetermined from the second rack force signal 22 bis also used for monitoring and / or plausibility checking the first rack force signal 18 bor, more precisely, the first torque signal 30 bdetermined from the first rack force signal 18 b. For this purpose, the first torque signal 30 band the second torque signal 32 bare fed to a monitoring block 52 b, which determines a tolerance range for the first torque signal 30 bby means of the second torque signal 32 b. If the first torque signal 30 bis within the limits of the tolerance range, the operating parameter 20 bis determined from the first torque signal 30 bin a manner known per se. In principle, the first torque signal 30 bmay also be used as the operating parameter 20 b. If, on the other hand, the first torque signal 30 bis outside the tolerance range, the first torque signal 30 bis limited to the second torque signal 32 band / or by means of the second torque signal 32 b.Furthermore, a time duration of the first torque signal 30 bout of the tolerance range and / or a distance of the first torque signal 30 bfrom the limit values of the tolerance range can be determined again by means of an additional monitoring algorithm, which can be implemented directly in the monitoring block 52 b, for example, and a system reaction can be initiated in the event that the time duration exceeds a time limit value and / or the distance exceeds a distance limit value.FIG. 5 shows a further exemplary embodiment of the invention. The letter c is reproduced from the exemplary embodiment of FIG. 5. The further exemplary embodiment of FIG. 5 differs from the previous exemplary embodiments at least substantially in the composition of a first rack force signal 18 cand the operating signals used for monitoring and / or plausibility checking or for determining a tolerance range.In the present case, a first partial signal 34 c, in particular a first rack force partial signal, is determined by means of a first calculation block 48 c. The first calculation block 48 cis identical to a first calculation block 48 a, 48 bof the previous exemplary embodiments and accordingly comprises a first calculation algorithm. For example, the first calculation algorithm can use a motion equation of a rack to calculate the first partial signal 34 cand take into account at least one further steering characteristic variable, such as a transmission and / or motor behavior of a steering actuator and / or friction effects in the wheel steering angle actuator and / or inertia effects in the wheel steering angle actuator. Furthermore, a second partial signal 36 c, in particular a second rack force partial signal, is determined by means of a third calculation block 58 c. The third calculation block 58 ccomprises a third calculation algorithm which is used to determine the second partial signal 36 c. The second partial signal 36 cmay be calculated, for example, on the basis of a toe-in model and as a function of a deflection of a steering handle and a vehicle speed. The first partial signal 34 cand the second partial signal 36 care then fed to a superposition block 60 c, which ascertains the first rack force signal 18 cfrom the first partial signal 34 cand the second partial signal 36 c. Consequently, in this case as well, in the determination of the first rack force signal 18 c, the first calculation algorithm is used. By means of the first rack force signal 18 c, an operating parameter 20 cmay then be determined, which may be used in particular for controlling at least one steering function, such as a steering feel. Alternatively, however, in this case a base signal could also be determined by means of a first calculation algorithm and the base signal could be modified by means of at least one modification characteristic variable, wherein a first rack force signal is determined from the modified base signal. It is also conceivable to ascertain a base signal from the aforementioned first partial signal 34 cand the aforementioned second partial signal 36 c, which base signal is subsequently modified with a modification characteristic variable and used for ascertaining the first rack force signal.Furthermore, analogously to the preceding exemplary embodiments, a second rack force signal 22 cis determined by means of a second calculation block 50 c.Moreover, in this case, a third rack force signal 38 cis obtained. In the present case, the third rack force signal 38 cis determined by means of a fourth calculation block 62 c. The fourth calculation block 62 ccomprises a fourth calculation algorithm which is used for determining the third rack force signal 38 c. The third rack force signal 38 cmay be calculated, for example, on the basis of a toe-in model and as a function of a deflection of the steering handle and a vehicle speed. Accordingly, the fourth calculation algorithm may correspond to the third calculation algorithm.The second rack force signal 22 cand the third rack force signal 38 care used in this case for monitoring and / or plausibility checking of the first rack force signal 18 c. For this purpose, the first rack force signal 18 c, the second rack force signal 22 cand the third rack force signal 38 care fed to a monitoring block 52 c, which determines a, in particular common, tolerance range for the first rack force signal 18 cby means of the second rack force signal 22 cand by means of the third rack force signal 38 c. If the first rack force signal 18 cis within the limits of the tolerance range, the operating parameter 20 cis determined from the first rack force signal 18 cin a manner known per se. In principle, the first rack force signal 20 cmay also be used as the operating parameter 20 c. If, on the other hand, the first rack force signal 18 cis outside the tolerance range, the first rack force signal 18 cis limited to the second rack force signal 22 c. Alternatively, however, a limitation to the third rack force signal 38c could also take place. By means of the limitation, it can also be ensured in this case that, in the case that the operating parameter 20 cis used for controlling a feedback actuator, no excessively large torque is permitted in the direction of an end stop of an operating unit, which torque could lead to safety-critical situations, in particular when driving without hands on a steering handle. In particular in the case of cornering, with a corresponding configuration of a front axle of the vehicle, a steering force in the direction of a neutral or straight-ahead position can be achieved, wherein the steering force is correlated with the second rack force signal 22 cand is therefore ideally used for limiting the first rack force signal 18 c. Alternatively, however, the first rack force signal 18 cmay also be monitored by means of two consecutive tolerance ranges, wherein, for example, in a first step a check is made as to whether the first rack force signal 18 cis within the limits of a tolerance range for the first rack force signal 18 cdetermined by means of the second rack force signal 22 cand in a second step a check is made as to whether the first rack force signal 18 cis within the limits of a further tolerance range for the first rack force signal 18 cdetermined by means of the third rack force signal 38 c.In addition, in this case too, a time duration of the first rack force signal 18 cout of the tolerance range and / or a distance of the first rack force signal 18 cfrom the limit values of the tolerance range can be determined by means of an additional monitoring algorithm, which can be implemented directly in the monitoring block 52 c, for example, and a system reaction can be initiated in the event that the time duration exceeds a time limit value and / or the distance exceeds a distance limit value.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2017 217 470 A1

[0003] DE 10 2011 052 881 A1

[0004] DE 10 2018 219 560 A1

[0005]

Claims

Method for operating a steering system (10a), wherein the steering system (10a) comprises at least one wheel steering angle actuator (12a) having a toothed rack (14a) for changing a wheel steering angle of at least one vehicle wheel (16a), wherein a first toothed rack force signal (18a-c) is determined on the basis of a dynamic of the toothed rack (14a) and a first calculation algorithm is used in the determination of the first toothed rack force signal (18a-c), and wherein an operating characteristic variable (20a-c) is determined as a function of the first toothed rack force signal (18a-c), which operating characteristic variable is used in particular for controlling at least one steering function, characterized in that, wherein at least one second rack force signal (22a-c) is determined for monitoring and / or plausibility checking the first rack force signal (18a-c) on the basis of the dynamics of the rack (14a), and a second calculation algorithm having a lower complexity compared to the first calculation algorithm is used in the determination of the second rack force signal (22a-c).Method according to Claim 1, characterized in that the steering system (10a) comprises an operating unit (24a), which is mechanically separate from the at least one wheel steering angle actuator (12a), has a steering handle (26a) and has a feedback actuator (28a) which interacts with the steering handle (26a), and the operating parameter (20a-c) is used at least for actuating the feedback actuator (28a).Method according to Claim 1 or 2, characterized in that the first rack force signal (18a-c) and the second rack force signal (22a-c) are calculated on the basis of an equation of movement of the rack (14a).Method according to one of the preceding claims, characterized in that a tolerance range for the first rack force signal (18a) is determined by means of the second rack force signal (22a), and in the case that the first rack force signal (18a) lies outside the tolerance range, the first rack force signal (18a) is limited by means of the second rack force signal (22a).Method according to Claim 4, characterized in that a time duration of the first rack force signal (18a) outside the tolerance range and / or a distance of the first rack force signal (18a) from the limit values of the tolerance range is determined, and in the event that the time duration exceeds a time limit value and / or the distance exceeds a distance limit value, a system reaction is initiated.Method according to one of Claims 1 to 3, characterized in that a first torque signal (30b) is determined on the basis of the first rack force signal (18b) and a second torque signal (32b) is determined on the basis of the second rack force signal (22b), wherein the first torque signal (30b) is used to determine the operating characteristic variable (20b), and wherein a tolerance range for the first torque signal (30b) is determined by means of the second torque signal (32b), and in the case that the first torque signal (30b) is outside the tolerance range, the first torque signal (30b) is limited by means of the second torque signal (32b).Method according to Claim 6, characterized in that a time duration of the first torque signal (30b) outside the tolerance range and / or a distance of the first torque signal (30b) from the limit values of the tolerance range is determined, and in the event that the time duration exceeds a time limit value and / or the distance exceeds a distance limit value, a system reaction is initiated.Method according to one of Claims 1 to 3, characterized in that - a first partial signal (34c) is determined by means of the first calculation algorithm and, in particular, a second partial signal (36c) is determined by means of a third calculation algorithm, the first rack force signal (18c) being determined from the first partial signal (34c) and the second partial signal (36c), or - a base signal is determined by means of the first calculation algorithm and the base signal is modified by means of at least one modification characteristic variable, in particular correlated with the steering function, the first rack force signal being determined from the modified base signal.Method according to one of the preceding claims, characterized in that at least one third rack force signal (38c) is determined for monitoring and / or plausibility checking of the first rack force signal (18c).Method according to Claim 9, characterized in that the third rack force signal (38c) is calculated as a function of a deflection of the steering handle and a vehicle speed.Method according to Claim 9 or 10, characterized in that a further tolerance range for the first rack force signal (18c) is determined by means of the third rack force signal (38c), and in the event that the first rack force signal (18c) lies outside the further tolerance range, the first rack force signal (18c) is limited by means of the second rack force signal (22c).Method according to Claim 11, characterized in that a time duration of the first rack force signal (18c) outside the further tolerance range and / or a distance of the first rack force signal (18c) from the limit values of the further tolerance range is determined, and in the event that the time duration exceeds a further time limit value and / or the distance exceeds a further distance limit value, a system reaction is initiated.Arithmetic unit (40a) for carrying out a method according to one of the preceding claims.Vehicle (42a), in particular motor vehicle, having a steering system (10a) which comprises at least one wheel steering angle actuator (12a) having a toothed rack (14a) for changing a wheel steering angle of at least one vehicle wheel (16a), and having a computing unit (40a) according to Claim 13.

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