Method for determining and / or monitoring the mechanical condition of a tie rod device

Abstract

Method for determining and / or monitoring a mechanical condition of at least one tie rod assembly (10) of an electrically assisted steering system (12) of a vehicle (14), wherein the mechanical condition of the tie rod assembly (10) is linked to steering play, in particular caused by mechanical wear, wherein at least one operating characteristic (16) correlated with a steering movement of at least one steering actuator (18) and / or at least one steering control unit (20) of the steering system (12) is determined and evaluated for determining and / or monitoring the mechanical condition of the tie rod assembly (10), wherein the evaluation of the operating characteristic (16) takes place in a steering range in which forces (28, ) acting on the tie rod assembly (10)30) in the form of a steering force exerted on a steering actuating element (52) and a restoring force acting in the opposite direction to the steering force of at least one vehicle wheel (46) of the vehicle (14) at least substantially compensate.

Description

Prior ArtThe invention relates to a method for determining and / or monitoring a mechanical state of a track rod device of an electrically assisted steering system of a vehicle according to claim 1.The invention also relates to a computing unit for carrying out such a method and to a vehicle comprising an electrically assisted steering system having a track rod device, having a steering actuator and having a steering control unit which comprises a computing unit for carrying out such a method.DE 198 15 470 A1 discloses a method for determining a mechanical state of a steering system, wherein the compliance with or exceeding tolerances and / or defined limit values is determined and evaluated with the aid of sensors, such as a steering angle sensor, a lateral acceleration sensor, a yaw rate sensor or a sensor system of a driving stability controller. In this case, sensor characteristics or actual values of the sensor data are consequently matched to corresponding tolerance-affected setpoint values in order to draw conclusions about the state of the steering system. However, the acquisition, evaluation and linking of a plurality of different sensor characteristics requires a complex evaluation algorithm which requires a relatively large amount of computing power. In addition, the method mentioned can be used to determine only a mechanical state of the entire steering system, while conclusions about a state of a track rod or of a track rod device are not directly possible.In addition, DE 10 2006 043 069 A1 discloses a method for determining and / or monitoring a lane offset of a motor vehicle, in which forces occurring in a right-hand tie rod and / or in a left-hand tie rod are continuously detected and compared with one another or with a reference variable. However, a determination and / or monitoring of a mechanical state of a track rod device does not take place in this context.Furthermore, DE 10 2013 225 278 A1 discloses a method for determining and / or monitoring a mechanical state of at least one track rod device of an electrically assisted steering system of a vehicle, wherein at least one operating characteristic variable of the steering system correlated with a steering movement is determined and evaluated for determining and / or monitoring the mechanical state of the track rod device. In this context, in particular a sensor signal of at least one sensor assigned to the chassis, such as a steering angle sensor, a steering torque sensor or a wheel speed sensor, can be recorded and evaluated in the frequency space. The fault state can correspond, inter alia, to damage to hardware of an electromechanical power steering system, in particular to a track rod bearing.Furthermore, DE 102 44 070 A1 discloses a device and a method for driving situation-dependent steering assistance for vehicles with electromechanical steering, wherein a variable tendency of the vehicle to move obliquely can be corrected.Furthermore, DE 10 2013 008 830 B3 discloses a method for determining and / or for monitoring a mechanical state of a component of a steering train of a motor vehicle, such as a track rod, wherein at least one operating characteristic variable of the steering system correlated with a steering movement is determined and taken into account in the determination and / or monitoring of the mechanical state of the component. In particular, by means of the described method, a deformation of the component or the tie rod caused by an external force effect can be detected. For evaluating the operating characteristic variable, a first straight-ahead angle of the motor vehicle determined in advance is also matched to a second straight-ahead angle determined after the external force effect.DE 10 2011 008 337 A1 also discloses a method and a device for detecting at least one fault in a vehicle, wherein the device comprises at least one device for detecting and evaluating an assist torque, and wherein at least one temporal profile of an assist torque over a number of driving cycles can be detected and evaluated.The object of the invention is in particular to provide a method for determining and / or monitoring a mechanical state of a track rod device having improved properties with regard to an efficiency. The object is achieved by the features of claims 1, 12 and 13, while advantageous embodiments and developments of the invention can be gathered from the dependent claims.Disclosure of the InventionA method for, in particular automatically, ascertaining and / or for, in particular automatically, monitoring a mechanical state of at least one track rod device of an electrically assisted steering system of a vehicle, in particular of a motor vehicle, is proposed, wherein at least one operating characteristic variable of at least one steering actuator and / or of at least one steering control unit of the steering system correlated with a steering movement is ascertained and evaluated for ascertaining and / or for monitoring the mechanical state of the track rod device. If a behavior of the operating characteristic variable deviating from a normal state is detected during the evaluation of the operating characteristic variable, for example when defined threshold values are exceeded or undershot, a fault state, in particular in the form of a mechanical defect of the track rod device, is deduced. The mechanical state of the track rod device is linked to a steering play, which is effected in particular by mechanical wear. This configuration makes it possible, in particular, to provide a method with improved efficiency, in particular power efficiency, computing efficiency, component efficiency and / or cost efficiency. Moreover, operating safety can be advantageously increased, for example, by detecting deployed track rod heads in good time and by this means hazardous situations can be prevented.In particular, the steering system in the present case comprises the at least one track rod device, the at least one steering actuator, which acts in particular in an electrically supporting manner, and the at least one steering control unit. In addition, the steering system comprises in particular a computing unit which is provided to carry out the method for ascertaining and / or for monitoring the mechanical state of the track rod device. In addition, the steering system can also comprise further components and / or assemblies, such as at least one steering handle, for example designed as a steering wheel, a wheel steering angle actuator, in particular having at least one steering actuator, for example designed as a toothed rack, at least one sensor unit for detecting the at least one operating parameter and / or an output unit for outputting an, in particular acoustic, haptic and / or optical, notification message and / or warning message if a fault state and / or a behavior deviating from the normal state is detected during the monitoring of the mechanical state of the tie rod device. Furthermore, the steering system can be designed in particular as a conventional steering system or as a steer-by-wire steering system. A conventional steering system has, in particular, a direct mechanical connection between the steering handle and the wheel steering angle actuator, which is designed, in particular, as a steering gear, while a steer-by-wire steering system is free of a direct mechanical connection between the steering handle and the wheel steering angle actuator, which is also referred to, in particular, as a "steering rack actuator" in this case, in particular in at least one operating state. "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.Furthermore, a "track rod device" is to be understood to mean, in particular, a part and / or a subassembly of a track rod of the steering system and / or of a component of the steering system, such as a track rod bearing, which is connected, advantageously directly, to a track rod of the steering system. Furthermore, the track rod device has in particular at least one operative connection to the wheel steering angle actuator, in particular the steering actuator, and / or at least one vehicle wheel of the vehicle. Furthermore, a "steering actuator" is to be understood to mean, in particular, an actuator unit, in particular an electrically designed actuator unit, which advantageously has a direct operative connection with the steering actuator element and is provided, in particular, to transmit a steering torque to the steering actuator element and thereby advantageously influence a direction of travel of the vehicle. Preferably, the steering actuator is provided to provide a steering torque for assisting a hand torque applied to the steering handle and / or a steering torque for, in particular direct, adjusting the steering actuator element and thereby in particular for automatic and / or autonomous control of a direction of travel of the vehicle. For this purpose, the steering actuator can comprise at least one electric motor. The electric motor is advantageously designed as a brushless motor and preferably as an asynchronous motor or as a permanently excited synchronous motor. The steering actuator is preferably also designed as part of the wheel steering angle actuator. In addition, a "computing unit" is to be understood to mean, in particular, 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 operating memory, at least one input and / or output means, at least one operating program, at least one control routine, at least one control routine, at least one calculation routine and / or at least one evaluation routine. In particular, the computing unit is provided to ascertain and / or receive at least one operating parameter of the steering actuator and / or of the steering control unit of the steering system correlated with a steering movement and to evaluate it for ascertaining and / or for monitoring the mechanical state of the track rod device. In particular, the computing unit can be part of an, in particular central, external computer system, for example a server network and / or cloud network. However, the arithmetic unit is advantageously integrated into the steering control unit. Moreover, an "operating parameter" of the steering actuator and / or of the steering control device is to be understood in particular as a parameter which is correlated with an operation of the steering actuator and / or of the steering control device, in particular in the case of a steering movement. The operating characteristic variable can correspond, for example, to an energy consumption, a current consumption, an actual motor torque, a rotor position, a rotor angular acceleration, a rotor angular velocity and / or a torque of the steering actuator, in particular in the case of a steering movement, and / or an energy consumption, a current consumption, a control signal, a setpoint motor torque and / or a setpoint torque of the steering control device, in particular in the case of a steering movement. In the present case, the operating parameter is evaluated in a steering range in which forces acting on the track rod device in the form of a steering force exerted on the steering actuator element, advantageously a rack force, and a restoring force of at least one vehicle wheel of the vehicle opposed to the steering force, at least substantially balance out. The expression that a first force and a second force "at least substantially balance out" is to be understood in particular to mean that an absolute value of a force resulting from the first force and the second force is at most 15%, preferably at most 10% and particularly preferably at most 5%, of an absolute value of the first force and / or of an absolute value of the second force. Preferably, the first force and the second force are in this case opposed to one another and deviate from one another at least in terms of amount by at most 15%, advantageously by at most 10% and particularly preferably by at most 5%. Preferably, the steering range, in which the first force and the second force at least substantially balance, can also be determined on the basis of a change in sign of the resulting force.It is further proposed that, in particular additionally, at least one further operating characteristic variable correlated with the steering movement and / or a plurality of further operating characteristics of the vehicle, preferably of the steering system and particularly advantageously of the steering actuator and / or of the steering control unit, be determined and taken into account in the determination and / or monitoring of the mechanical state of the track rod device. In particular, the further operating parameter in this context could also correspond to an operating parameter of a vehicle sensor system, such as a steering angle sensor, a lateral acceleration sensor, a yaw rate sensor, a vehicle speed sensor, a wheel speed sensor and / or a gyro sensor, and / or an operating parameter of a driving dynamics control system. The further operating parameter and / or the further operating parameters are preferably provided here for verifying and / or plausibility checking the state of the track rod device, in particular determined by means of the operating parameter. In this way, in particular, an advantageous verification and / or plausibility check of the operating parameter can be achieved.It is furthermore proposed that the operating characteristic variable and / or the operating characteristics be / are detected and / or evaluated during a driving operation of the vehicle. In this way, in particular, an advantageous monitoring of the mechanical state of the tie rod device can be achieved, which is not immediately perceptible by a driver and / or an occupant of the vehicle.Alternatively or additionally, it is proposed that the operating parameter and / or the operating parameters be / are detected and / or evaluated when the vehicle is at a standstill, as a result of which in particular a particularly high level of operating reliability can be achieved, since the mechanical state of the track rod device can advantageously already be checked before a driving operation.Furthermore, it is proposed that the operating parameter is linked to a controller behavior, in particular a controller intervention, of a steering controller of the steering system, in particular for advantageously field-oriented control of the steering actuator. The controller behavior serves in particular as an indicator for the mechanical state of the track rod device. In this context, advantage is taken of the fact that a controller behavior of the steering controller in the normal state deviates from a controller behavior of the steering controller in the fault state, in particular in the steering range in which, in particular, the forces acting on the track rod device at least substantially balance one another. Consequently, in the determination and / or monitoring of the mechanical state of the track rod device, in particular the controller behavior of the steering controller is taken into account. In this way, in particular a particularly simple monitoring of the mechanical state of the track rod device can be achieved.The operating characteristic variable could be detected, determined and / or evaluated, for example, over an entire steering cycle and / or over a plurality of steering cycles. In addition, the operating characteristic variable could also be detected, determined and / or evaluated, in particular, only temporarily, in particular in a defined time window, and / or only for specific steering angles. Furthermore, the operating parameter could be integrated for determining and / or for monitoring the mechanical state of the track rod device, in particular also over a plurality of steering cycles, wherein in particular changes in the integration result could serve as an indicator for the mechanical state of the track rod device. A particularly simple evaluation can be achieved, however, if the operating characteristic variable is determined and / or detected at least during an entire steering cycle and an evaluation signal correlated with the operating characteristic variable is generated for determining and / or for monitoring the mechanical state of the track rod device by limiting the operating characteristic variable to a defined time window. The time window is advantageously located in the steering range in which the forces acting on the track rod device at least substantially balance out. Furthermore, a time duration of the time window is in particular at least 50 ms, preferably at least 75 ms and particularly preferably at least 100 ms, and / or at most 500 ms, preferably at most 300 ms and particularly preferably at most 150 ms. This embodiment allows, in particular, an evaluation algorithm to be simplified in that the evaluation is advantageously restricted to a region in the steering cycle which is relevant to the mechanical state of the track rod device.The evaluation signal could then be evaluated in the time domain, for example on the basis of a comparison of the evaluation signal with a setpoint and / or reference signal or on the basis of a characteristic profile of the evaluation signal in a fault state. However, it is preferably proposed that a frequency spectrum is generated from the evaluation signal and, for the purpose of ascertaining and / or monitoring the mechanical state of the track rod device, at least one spectral characteristic variable of the frequency spectrum is matched to a reference characteristic variable. The frequency spectrum can be generated in particular by means of a suitable frequency transformation, such as a Fourier transformation, advantageously a discrete Fourier transformation (DFT), for example realized by a fast Fourier transformation (FFT), and / or a Welch method, and / or a periodogram. A "spectral characteristic variable" is to be understood in particular as a characteristic variable which is correlated in particular with the frequency spectrum and advantageously at least one, in particular defined, frequency value and / or amplitude value of the frequency spectrum. In particular, the spectral characteristic variable can also be at least one, preferably exactly one, in particular defined, frequency value and / or amplitude value of the frequency spectrum. Advantageously, the computing unit can infer a current state and / or a possible fault and / or defect of the track rod device at least on the basis of the spectral characteristic variable and in particular by means of a comparison of the spectral characteristic variable with the reference characteristic variable and / or determine a current state and / or a possible fault and / or defect of the track rod device. In this context, it is also conceivable, in particular, for the computing unit to be able to ascertain a near-reaching and / or soon-occurring fault and / or defect of the track rod device at least on the basis of the spectral characteristic variable and, in particular, by means of a comparison of the spectral characteristic variable with the reference characteristic variable and / or to estimate a probability of failure of the track rod device, for example, by means of a "close to failure" detection. Particularly preferably, the computing unit can be further provided to infer a specific type of error and / or a specific type of error on the basis of the spectral characteristic variable and in particular on the basis of a comparison of the spectral characteristic variable with the reference characteristic variable and / or to determine a specific type of error and / or a specific type of error, for example on the basis of a specific deviation of the spectral characteristic variable from the reference characteristic variable. In this context, a "reference characteristic variable" is to be understood to mean, in particular, a characteristic variable assigned to the spectral characteristic variable, preferably a reference frequency spectrum corresponding to the frequency spectrum, which maps and / or identifies an intact and / or fully functional track rod device. The reference characteristic variable and / or the reference frequency spectrum can be determined in this case in particular by means of test measurements and / or by means of special algorithms and in particular originate from the track rod device itself and / or from further track rod devices of other steering systems of identical construction. In this way, in particular a particularly simple evaluation of the operating parameter can be achieved with a high accuracy.It is furthermore proposed that at least one further operating characteristic variable is detected and a further evaluation signal correlated with the further operating characteristic variable and limited to the time window is generated, which evaluation signal is taken into account in the determination and / or monitoring of the mechanical state of the track rod device. The further operating parameter is preferably the already aforementioned further operating parameter, in particular for verifying and / or plausibility checking the state of the track rod device, in particular determined by means of the operating parameter. Preferably, the further operating characteristic variable is and / or is therefore not derived from the operating characteristic variable. The further operating characteristic variable is preferably also determined and / or recorded at least during an entire steering cycle, advantageously the same steering cycle as the operating characteristic variable. In particular, it can also be provided that a plurality of further operating parameters are detected and a further evaluation signal limited to the time window is generated from each of the further operating parameters, wherein each of the further evaluation signals is advantageously taken into account in the determination and / or monitoring of the mechanical state of the track rod device. In this way, in particular a particularly reliable and / or accurate determination of the mechanical state of the track rod device can be achieved.According to a further embodiment, it is proposed that a plurality of evaluation signals correlated with the operating parameter are generated for the determination and / or for the monitoring of the mechanical state of the track rod device during an, in particular entire, monitoring time interval, wherein the evaluation signals are generated under at least substantially identical conditions, in particular driving conditions and / or steering conditions. In particular, in this case all evaluation signals are correlated with the same operating parameter, in particular of the steering actuator and / or of the steering control unit, and / or are obtained from the same operating parameter, in particular of the steering actuator and / or of the steering control unit. In addition, the monitoring time interval advantageously comprises a plurality of steering cycles and can have a time period of a plurality of hours or days, for example. Furthermore, the evaluation signals are assigned to different time windows, in particular. The time slots that differ over time can be assigned in particular to the same steering cycle and / or different steering cycles. Particularly advantageously, the time windows are each located in a steering range in which forces acting on the track rod device, in particular a steering force exerted on the steering control element, advantageously a rack force, and a restoring force of at least one vehicle wheel of the vehicle, in particular directed counter to the steering force, at least substantially balance out. The fact that the evaluation signals are generated "under at least substantially identical conditions" is to be understood in particular to mean that each of the evaluation signals is generated in a similar or identical vehicle speed range and / or steering range and / or at a similar or identical steering speed and / or rotor speed. In this way, in particular, operational reliability can be further increased and temporary fluctuations in the operational parameter and / or the evaluation signal, which are in particular not correlated with the state of the track rod device, can be safely excluded. In addition, statistically independent and unimportant changes in the operating characteristic can be reduced.The evaluation signals could then be evaluated, in particular in the time domain. Furthermore, the evaluation signals could in particular also be synchronized and averaged in the time domain, so that a frequency spectrum can be generated from the averaged evaluation signal and at least one spectral characteristic variable of the frequency spectrum from the averaged evaluation signal can be matched to a reference characteristic variable for the determination and / or for monitoring the mechanical state of the track rod device. According to a particularly preferred embodiment, however, it is proposed that a frequency spectrum, in particular its own frequency spectrum, is generated from each of the evaluation signals, the frequency spectra are combined to form an averaged, common frequency spectrum, and at least one spectral characteristic variable of the common frequency spectrum is matched to a reference characteristic variable for the purpose of ascertaining and / or monitoring the mechanical state of the track rod device. In this way, in particular, an advantageously robust evaluation of the operating parameter can be achieved.In addition, it is proposed that a learning routine, advantageously a machine, such as a random forest classifier and / or an artificial neural network, be used, which learning routine is provided, at least on the basis of the operating parameter and / or at least one operating reference parameter, for optimizing the determination and / or monitoring of the mechanical state of the tie rod device, for example by optimizing specific decision thresholds. Alternatively or additionally, the learning algorithm could, however, in particular also be provided for the direct determination and / or monitoring of the mechanical state of the track rod device on the basis of the operating characteristic variable and / or at least one operating reference characteristic variable. Advantageously, a typical behavior of the track rod device, in particular in the normal state and / or in the fault state, is learned by means of the learning routine. The learning routine preferably corresponds to a data-driven learning algorithm, wherein advantageously a plurality of determined and / or determinable data and / or parameters of the track rod device, of the steering system and / or of the vehicle are used and / or linked to one another. The learning routine is also advantageously stored in the operating memory of the arithmetic unit. In this context, an "operating reference characteristic variable" is to be understood to mean, in particular, an operating characteristic variable, in particular of the vehicle, preferably of the steering system and particularly advantageously of the steering actuator and / or of the steering control unit, which represents and / or identifies an intact and / or fully functional track rod device. The operating reference characteristic variable can be determined and / or learned in particular by means of test measurements and / or by means of special algorithms and can originate in particular from the vehicle with the track rod device itself and / or from other vehicles of identical construction. In this way, in particular an advantageously simple and / or automatic optimization of the determination and / or monitoring of the mechanical state of the track rod device can be achieved. In addition, an evaluation can advantageously be simplified by the learning routine in that the specification of specific reference parameters, decision thresholds and / or reference points, in particular in a frequency spectrum, can be dispensed with and the computing unit can automatically identify erroneous and / or error-free spectral parameters in the frequency spectrum.A further improvement of the learning routine can be achieved in particular if, in order to optimize the ascertainment and / or monitoring of the mechanical state of the track rod device, the learning routine is / are further supplied with an, in particular current, vehicle speed and / or an, in particular current, steering speed.The method, the computing unit and the vehicle are not intended to be limited to the application and embodiment described above. In particular, the method, the computing unit and the vehicle can have a number that differs from a number of individual elements, components and units mentioned herein in order to fulfil a mode of operation described herein.DRAWINGSFurther advantages are evident from the following description of the drawings. The drawings illustrate an embodiment of the invention. The drawings, specification and claims contain numerous aspects of the invention. The skilled person will expediently also consider these aspects individually and summarize them to form further meaningful combinations.The following are shown: FIGS. 1 a- b show an exemplary vehicle with a steering system comprising a track rod device in a simplified illustration, FIG. 2 shows the track rod device in a schematic illustration, with indicated forces acting on the track rod device, FIGS. 3 a- b show exemplary diagrams of various signals for determining and / or monitoring a mechanical state of the track rod device, FIG. 4 shows an exemplary further diagram with various signals for ascertaining and / or monitoring the mechanical state of the track rod device, and FIG. 5 shows an exemplary flow chart with main method steps of a method for ascertaining and / or monitoring a mechanical state of the track rod device.DESCRIPTION OF THE EMBODIMENTFIGS. 1 aand 1 b show a simplified illustration of a vehicle 14 which is designed as an example as a motor vehicle and has a plurality of vehicle wheels 46 and a steering system 12 which is designed as a conventional steering system in the present case by way of example. The vehicle 14 can be, for example, a vehicle having a partially automated, highly automated and / or fully automated driving mode. The steering system 12 has an operative connection to the vehicle wheels 46 and is provided for influencing a direction of travel of the vehicle 14. Furthermore, the steering system 12 is designed as an electrically assisted steering system and in the present case has, in particular, an electric power steering system in the form of a power steering system. In principle, however, it is also conceivable to design a steering system as a steer-by-wire steering system.The steering system 12 comprises a steering handle 48, which is designed in the present case as a steering wheel by way of example, for applying a hand torque, a wheel steering angle actuator 50, which is designed as a rack and pinion steering gear by way of example, and comprises a steering actuator element 52 and is provided for converting a steering specification on the steering handle 48 into a steering movement of the vehicle wheels 46, and a steering shaft 54 for, in particular, mechanically connecting the steering handle 48 to the wheel steering angle actuator 50. In principle, a steering system could also be free of a steering handle, for example in the case of a purely autonomously driving vehicle. In addition, a steering shaft could also only temporarily connect a steering handle to a wheel steering angle actuator, such as, for example, in a vehicle with autonomous driving operation and / or a steer-by-wire steering system with a mechanical fallback level. In this connection, it is of course also conceivable to completely dispense with a steering shaft.In addition, the steering system 12 comprises at least one track rod device 10. The track rod devices 10 each mechanically connect the wheel steering angle actuator 50, in particular the steering actuator 52, to one of the vehicle wheels 46.The steering system 12 furthermore comprises a steering actuator 18. The steering actuator 18 is assigned to the wheel steering angle actuator 50. The steering actuator 18 has an operative connection to the steering actuator 52. The steering actuator 18 is provided to provide a steering torque and to transmit it to the steering actuator 52. In the present case, the steering actuator 18 is provided at least for the purpose of transmitting a steering torque in the form of an assistance torque to the steering actuator element 52 and of assisting the manual torque which is applied in particular by the driver.For this purpose, the steering actuator 18 comprises at least one electric motor 56. the electric motor 56 is designed as a servomotor, in the present case in particular as a permanently excited synchronous motor. The electric motor 56 is coupled to the steering actuator 52 and is provided for generating the steering torque. Alternatively, however, a steering actuator could also have a plurality of electric motors. In addition, a steering actuator could additionally or alternatively also be provided to provide a steering torque for, in particular direct, adjustment of a steering actuator element and thereby in particular for automatic and / or autonomous control of a direction of travel of a vehicle.Furthermore, the steering system 12 comprises at least one sensor unit 58, 60, in the present case in particular a first sensor unit 58 and a second sensor unit 60. The first sensor unit 58 is provided for detecting at least one operating parameter 16 correlated with the steering actuator 18, for example a rotor angular acceleration, a rotor angular velocity and / or a rotor position of the electric motor 56. The second sensor unit 60 is assigned to the steering shaft 54. The second sensor unit 60 is designed as a steering angle sensor in the present case and is provided for detecting a further operating parameter 38, in particular a steering angle signal and / or a torque signal. The further operating parameter 38 supplies a setpoint specification, in particular in the form of a setpoint torque and / or a setpoint motor current, for the steering actuator 18 and is a measure of the manual torque applied in particular by the driver. In principle, however, a first sensor unit could also be provided for detecting an actual motor current or the like. In addition, a second sensor unit could also be designed as an angle difference sensor or the like. Furthermore, a second sensor unit could also be provided for detecting a setpoint torque and / or a setpoint motor current.In addition, the steering system 12 has a steering control unit 20. The steering control device 20 has an operative connection to the sensor units 58, 60 and to the steering actuator 18. The steering control unit 20 is provided to receive the operating characteristics 16, 38 and to actuate the electric motor 56 as a function of the operating characteristics 16, 38.For this purpose, the steering control device 20 comprises a computing unit 44. the computing unit 44 comprises 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 44 comprises at least one operating program stored in the operating memory, having at least one computation routine, at least one control routine, at least one control routine and at least one evaluation routine.Furthermore, in the present case, the steering control device 20 comprises a steering controller 22, The steering controller 22 has an operative connection to the arithmetic unit 44. In addition, the steering controller 22 has an operative connection to the steering actuator 18. The steering controller 22 is provided in the present case for field-oriented control of the steering actuator 18 and in particular of the electric motor 56.In addition, the vehicle 14 and / or the steering system 12 can comprise further components and / or assemblies, such as, for example, at least one further sensor unit (not shown), for example in the form of a lateral acceleration sensor, a yaw rate sensor, a vehicle speed sensor, a wheel speed sensor and / or a gyro sensor, a driving dynamics control system (not shown) and / or an output unit (not shown) for outputting an indication message.To increase the operational safety of vehicles, there is now a need to ascertain and / or monitor a mechanical state of a track rod device and in particular a steering play caused by mechanical wear in steering systems, such as in particular the steering system 12 mentioned at the beginning. In conventional steering systems, there is the risk, for example, that a driver become accustomed to the steering game after a certain time and the steering game is therefore no longer perceived over the course of time. In steer-by-wire steering systems, on the other hand, due to the absence of mechanical reach-through, a state of the tie rod device and / or a steering play is haptically transmitted only very indirectly or not at all to a restoring torque of a steering handle, so that haptic detection of the steering play by the driver is virtually ruled out. The same also applies to partially automated, highly automated and / or fully automated driving processes in which the driver does not receive haptic feedback from the steering system, as a result of which, for example, errors and / or defects in a track rod device or a steering cycle are no longer detected in good time and dangerous situations can occur, for example, as a result of a deployed track rod head and / or a suspension or breaking out of the track rod head.For this reason, a method for automatically ascertaining and / or automatically monitoring a mechanical state of the track rod device 10 is proposed. In the present case, the computing unit 44 is provided to carry out the method for automatically ascertaining and / or for automatically monitoring the mechanical state of the track rod device 10 and, for this purpose, has, in particular, a computer program having corresponding program code means. The mechanical state of the track rod device 10 is linked in the present case to a steering play caused by mechanical wear.According to the invention, for the determination and / or for the monitoring of the mechanical state of the track rod device 10, at least one operating characteristic variable of the steering actuator 18 and / or of the steering control unit 20, correlated with a steering movement, in the present case, for example, the operating characteristic variable 16 of the steering actuator 18, for example in the form of a rotor position, a rotor angular acceleration and / or a rotor angular velocity of the electric motor 56, is detected and evaluated. A detection and / or evaluation of the operating parameter 16 can take place here depending on the vehicle model and / or safety requirement both during a driving operation of the vehicle 14 and also when the vehicle 14 is at a standstill. In the present case, the operating parameter 16 is further evaluated in a steering range in which forces 28, 30 acting on the track rod device 10, in particular a steering force 28 exerted on the steering control element 52 and a restoring force 30 of at least one of the vehicle wheels 46 directed opposite the steering force 28, are at least substantially compensated (in this regard, cf. in particular also FIG. 2 ). If a behavior of the operating characteristic 16 deviating from a normal state is detected during the evaluation of the operating characteristic 16, a fault state, in particular in the form of a mechanical defect of the track rod device 10, is deduced. In such a fault state, an alert message and / or warning message is advantageously generated and output by means of the output unit. In principle, any other operating parameter of a steering actuator and / or of a steering control device, such as, for example, an energy consumption, a current consumption, an actual motor torque and / or a torque of the steering actuator and / or an energy consumption, a current consumption, a control signal, a setpoint motor torque and / or a setpoint torque of the steering control device, could also be used as an operating parameter. In addition, an operating characteristic variable could also be evaluated in a steering range in which forces acting on a track rod device do not balance out, but rather have a specific relationship to one another, for example. In addition, it is also conceivable to ascertain a plurality of further operating parameters, in particular a vehicle sensor system, a driving dynamics control system and / or advantageously a steering actuator and / or a steering control unit, and to take them into account when ascertaining and / or monitoring the mechanical state of the track rod device.In said steering range, the mechanical state of the track rod device 10 can be monitored particularly easily. In this case, use is made in particular of the fact that a force equilibrium is produced on the track rod device 10 in the steering region and, in the fault state, in particular in the event of a mechanical defect of the track rod device 10 and an increased steering play caused thereby, a dead path 62 is traversed virtually free of forces (cf. in particular FIG. 2 ). In the fault state, a briefly reduced moment of inertia is established in the transition between the electric motor 56 and the steering control element 52 in the steering range and / or in the dead path 62, and in particular in the case of a setpoint torque and / or setpoint motor current predefined by the steering control unit 20, which moment of inertia results in a brief change in the rotor angular acceleration of the electric motor 56. In this case, α Rotor describes the rotor angular acceleration of the electric motor 56, M soll the setpoint torque and / or the setpoint motor current, and I Stell the moment of inertia. This brief change in the rotor angular acceleration is transferred to other operating characteristics of the steering actuator 18 and / or of the steering control unit 20, such as, for example, an actual motor torque, a rotor position, a rotor angular speed and / or a torque of the steering actuator 18 and / or a setpoint motor torque and / or a setpoint torque of the steering control unit 20, so that the steering clearance can in principle be detected by evaluating each of these operating characteristics.In addition, the operating parameter 16 is linked to a controller behavior, in particular a controller intervention, of the steering controller 22. The same applies in particular also to the aforementioned other operating characteristics of the steering actuator 18 and / or of the steering control unit 20. In the present case, the virtually force-free passing through the dead path 62 leads to a successive readjustment of the steering regulator 22, which is reflected in particular in the operating characteristic variable 16 and the other operating characteristics and can consequently be detected. In particular, during the almost force-free passing through the dead path 62, the steering regulator 22 detects an actual rotor speed and an actual motor current, which do not match one another and consequently successively re-regulates a setpoint motor current, which leads to the deviating regulator behavior of the steering regulator 22 in the fault state.In order to determine and / or evaluate the state of the track rod device 10, the operating characteristic variable 16 is also determined in the present case during an entire steering cycle and an evaluation signal 24 correlated with the operating characteristic variable 16 is generated in that the operating characteristic variable 16 is limited to a defined time window 26 (cf. in particular also FIGS. 3 aand 3 b). The time window 26 lies in the steering range in which, in particular, the forces acting on the track rod device 10 are at least substantially compensated. Furthermore, a time duration of the time window 26 in the present case is between 75 ms and 300 ms. In this context, use is made of the fact that fault-related controller interventions of the steering controller 22 occur only in the steering range and / or during the passage of the dead path 62, so that the previously mentioned time window 26 is particularly relevant for the state of the track rod device 10. Alternatively, however, it is also conceivable to dispense with such windowing of the operating characteristic variable 16, for example by the operating characteristic variable 16 being detected only in a relevant time range or being integrated over a plurality of steering cycles, wherein in particular changes in the integration result can serve as an indicator for the mechanical state of the track rod device 10.An evaluation of the evaluation signal 24 takes place advantageously in the frequency range. For this purpose, a frequency spectrum 32 is generated from the evaluation signal 24 (cf. in particular FIG. 4 ). To determine and / or to monitor the mechanical state of the track rod device 10, at least one spectral characteristic variable 34, such as a frequency value and / or an amplitude value of an extreme value, of the frequency spectrum 32 is then matched to a reference characteristic variable 36 of a reference frequency spectrum 64, wherein the reference frequency spectrum 64 in particular maps and / or identifies an intact and / or fully functional track rod device 10. In the present case, the computing unit 44 is thus provided to analyze the frequency spectrum 32 for ascertaining and / or for monitoring the mechanical state of the track rod device 10, to ascertain and / or select the at least one spectral characteristic variable 34 of the frequency spectrum 32 and to compare it with the corresponding reference characteristic variable 36 of the reference frequency spectrum 64. On the basis of a comparison of the spectral characteristic variable 34 with the reference characteristic variable 36, the computing unit 44 can then infer a current state and / or a possible fault and / or defect of the track rod device 10 and / or determine a current state and / or a possible fault and / or defect of the track rod device 10. If, for example, an exceeding or falling short of defined threshold values is determined during the comparison of the spectral characteristic variable 34 with the reference characteristic variable 36, a fault state, in particular in the form of a mechanical defect of the track rod device 10, is deduced. Alternatively, an evaluation signal could also be evaluated in the time domain, for example on the basis of a comparison of the evaluation signal with a setpoint and / or reference signal or on the basis of a characteristic profile of the evaluation signal in a fault state. It is also conceivable to dispense with a reference frequency spectrum. In this case, it is conceivable, for example, for the reference characteristic variable to correspond to a defined decision threshold, in particular for a defined frequency value and / or amplitude value, or to a plurality of defined decision thresholds, in particular for a plurality of defined frequency values and / or amplitude values.To further improve the determination and / or monitoring of the track rod device 10, it can additionally be provided to generate a plurality of, for example at least three or at least ten, evaluation signals 24 correlated with the operating characteristic variable 16 during a total monitoring time interval, which can comprise a plurality of steering cycles, for example, and can have a time period of a plurality of hours or days, as a result of which, in particular, temporary fluctuations in the operating characteristic variable 16 and / or the evaluation signal 24, which are not correlated with the state of the track rod device 10, can be reliably excluded. The evaluation signals 24 are generated under at least substantially identical conditions, in particular at least substantially identical driving conditions and / or steering conditions. Furthermore, all evaluation signals 24 are thus correlated with the same operating parameter 16 and are obtained from the same operating parameter 16. In addition, the evaluation signals 24 are assigned to different time windows 26 in this case, which advantageously each lie in a steering range in which the forces 28, 30 acting on the track rod device 10 at least substantially balance out. The mentioned evaluation signals 24 can then in turn be advantageously evaluated in the frequency range. In this case, a frequency spectrum 32 can be generated from each of the evaluation signals 24, the frequency spectra 32 can be combined to form an averaged, common frequency spectrum and, for the determination and / or for the monitoring of the mechanical state of the track rod device 10, at least one spectral characteristic variable of the common frequency spectrum can be matched to a reference characteristic variable 36. Alternatively, however, the evaluation signals 24 can also be evaluated or synchronized and averaged in the time domain, wherein in the latter case a frequency spectrum can advantageously be generated from the averaged evaluation signal and, for the determination and / or for the monitoring of the mechanical state of the track rod device, at least one spectral characteristic variable of the frequency spectrum from the averaged evaluation signal can be matched to a reference characteristic variable.In addition, in the present case, at least one further operating characteristic variable 38, in particular during the same steering cycle as the operating characteristic variable 16, can be detected and a further evaluation signal 40 correlated with the further operating characteristic variable 38 and limited to the time window 26 can be generated, which evaluation signal is taken into account in the determination and / or monitoring of the mechanical state of the track rod device 10, as a result of which in particular a particularly reliable and / or accurate determination of the mechanical state of the track rod device 10 can be achieved. The further operating parameter 38 can be, for example, the steering angle signal and / or the torque signal of the second sensor unit 60 and / or an actual torque, a setpoint torque, an actual motor current and / or a setpoint motor current. The further operating parameter 38 and in particular the further evaluation signal 40 serve in this case for verifying and / or plausibility checking the state of the track rod device 10 determined by means of the operating parameter 16 and in particular the evaluation signal 24. In addition, a plurality of further operating parameters could be detected and a further evaluation signal limited to a time window could be generated from each of the further operating parameters for verifying and / or plausibility checking a state of a track rod device. In principle, however, it is also conceivable to dispense with a detection and / or evaluation of a further operating parameter.Furthermore, the computing unit 44 in the present case comprises a machine learning routine 42. The learning routine 42 is stored in the operating memory of the computing unit 44. The learning routine 42 is provided, at least on the basis of the operating parameter 16, for optimizing the determination and / or monitoring of the mechanical state of the track rod device 10. To this end, a plurality of determined and / or determinable data and / or parameters of the track rod device 10, the steering system 12 and / or the vehicle 14 can be supplied to the learning routine 42. In the present case, at least a current vehicle speed of the vehicle 14 and a current steering speed of the vehicle 14 can be fed to the learning routine 42 for optimizing the ascertainment and / or monitoring of the mechanical state of the track rod device 10. In principle, however, such a learning routine could also be dispensed with.FIGS. 3 aand 3 b show again exemplary diagrams of a temporal profile of the operating parameter 16 and / or of the evaluation signal 24, a temporal profile of the further operating parameter 38 and / or of the further evaluation signal 40, which is embodied in this case as a steering angle signal and / or torque signal, for example, and a window function 66 correlated with the time window 26. On an abscissa axis 70, time is shown in [s]. A first curve 72 shows the operating parameter 16 and / or the evaluation signal 24. a second curve 74 shows the further operating parameter 38 and / or the further evaluation signal 40 A third curve 76 shows the window function 66 correlated with the time window 26.FIG. 4 shows exemplary diagrams of the frequency spectrum 32 and of the reference frequency spectrum 64. An axis of ordinates 78 is again formed as a size axis. A frequency in [Hz] is shown on an abscissa axis 80. A first curve 82 shows the frequency spectrum 32 with the spectral characteristic variable 34 generated from the evaluation signal 24, and a second curve 84 shows the reference frequency spectrum 64 with the reference characteristic variable 36, wherein it can be seen, for example, that a frequency value and an amplitude value of extreme values, in particular the spectral characteristic variable 34 and the reference characteristic variable 36, deviate from one another, so that a current state and / or a possible error and / or defect of the track rod device 10 can be concluded on the basis of a comparison of the spectral characteristic variable 34 with the reference characteristic variable 36. Alternatively or additionally, a spectral characteristic variable could of course also be matched to a reference characteristic variable on the basis of a number of extreme values, a position of saddle points, an integral value formation in a defined frequency range or in any other manner.FIG. 5 finally shows an exemplary flow chart with main method steps of the method for ascertaining and / or monitoring the mechanical state of the track rod device 10.In a method step 90, the operating parameter 16, in particular by means of the first sensor unit 58, is detected and made available to the computing unit 44 for further processing. A detection and / or evaluation of the operating parameter 16 can take place here depending on the vehicle model and / or safety requirement both during a driving operation of the vehicle 14 and also when the vehicle 14 is at a standstill.In a method step 92, an evaluation signal 24 correlated with the operating characteristic variable 16 is generated for ascertaining and / or for monitoring the mechanical state of the track rod device 10, in that the operating characteristic variable 16 is limited to the time window 26.In a method step 94, a frequency spectrum 32 is advantageously generated from the evaluation signal 24, for example by means of a discrete Fourier transform (DFT), in particular by a fast Fourier transform (FFT) and / or a Welch method, and / or by a periodogram or the like.In a method step 96, the frequency spectrum 32 is analyzed and the at least one spectral characteristic variable 34 of the frequency spectrum 32 is determined and / or selected. Subsequently, the spectral characteristic variable 34 can be matched to the corresponding reference characteristic variable 36 of the reference frequency spectrum 64 in order to determine the mechanical state of the track rod device 10.Optional method steps can then follow, such as, for example, a determination and / or consideration of the further operating parameter 38 and / or the generation of an alert message and / or warning message.The exemplary flow diagram in FIG. 5 is intended here to describe, in particular merely by way of example, a method for ascertaining and / or monitoring the mechanical state of the track rod device 10. In particular, individual method steps and / or a sequence of the method steps can vary. In principle, a limitation of an operating parameter and / or an evaluation in the frequency range could also be dispensed with here and, for example, an evaluation in the time range could take place.

Claims

Method for determining and / or for monitoring a mechanical state of at least one track rod device (10) of an electrically assisted steering system (12) of a vehicle (14), wherein the mechanical state of the track rod device (10) is linked to a steering play, in particular one caused by mechanical wear, wherein at least one operating characteristic variable (16) of at least one steering actuator (18) and / or at least one steering control unit (20) of the steering system (12) correlated with a steering movement is determined and evaluated for determining and / or for monitoring the mechanical state of the track rod device (10), wherein the evaluation of the operating characteristic variable (16) takes place in a steering range in which forces (28, 28 acting on the track rod device (10) are detected, 30) in the form of a steering force exerted on a steering actuator (52) and a restoring force of at least one vehicle wheel (46) of the vehicle (14) directed counter to the steering force, at least substantially balance out.Method according to Claim 1, characterized in that the operating characteristic variable (16) is detected and / or evaluated during a driving mode of the vehicle (14).Method according to Claim 1, characterized in that the operating characteristic variable (16) is detected and / or evaluated when the vehicle (14) is at a standstill.Method according to one of the preceding claims, characterized in that the operating parameter (16) is linked to a controller behavior of a steering controller (22) of the steering system (12).Method according to one of the preceding claims, characterized in that the operating characteristic variable (16) is determined at least during an entire steering cycle and an evaluation signal (24) correlated with the operating characteristic variable (16) is generated for determining and / or for monitoring the mechanical state of the track rod device (10), in that the operating characteristic variable (16) is limited to a defined time window (26).Method according to Claim 5, characterized in that the time window (26) lies in the steering range in which the forces (28, 30) acting on the track rod device (10) at least substantially balance out.Method according to Claim 5 or 6, characterized in that a frequency spectrum (32) is generated from the evaluation signal (24), and at least one spectral characteristic variable (34) of the frequency spectrum (32) is matched to a reference characteristic variable (36) in order to determine and / or to monitor the mechanical state of the track rod device (10).Method according to one of Claims 5 to 7, characterized in that at least one further operating characteristic variable (38) is detected and a further evaluation signal (40), which is correlated with the further operating characteristic variable (38) and is limited to the time window (26), is generated, which evaluation signal is taken into account in the determination and / or monitoring of the mechanical state of the track rod device (10).Method according to one of the preceding claims, characterized in that, in order to determine and / or to monitor the mechanical state of the track rod device during a monitoring time interval, a plurality of evaluation signals (24) correlated with the operating characteristic variable (16) are generated, wherein the evaluation signals (24) are generated under at least substantially identical conditions, and wherein a frequency spectrum (32) is generated from each of the evaluation signals (24), the frequency spectra (32) are combined to form an averaged, common frequency spectrum, and, in order to determine and / or to monitor the mechanical state of the track rod device (10), at least one spectral characteristic variable of the common frequency spectrum is matched to a reference characteristic variable (36).Method according to one of the preceding claims, characterized in that a learning routine (42) is used which is provided for optimizing the determination and / or monitoring of the mechanical state of the track rod device (10) at least on the basis of the operating characteristic variable (16) and / or at least one operating reference characteristic variable.Method according to Claim 10, characterized in that a vehicle speed and / or a steering speed is / are also supplied to the learning routine (42) for optimizing the ascertainment and / or monitoring of the mechanical state of the track rod device (10).Arithmetic unit (44) which is provided for carrying out a method according to one of Claims 1 to 11.Vehicle (14) comprising an electrically assisted steering system (12) having a wheel steering angle actuator (50) which comprises at least one steering actuator (52), having at least one track rod device (10), having at least one steering actuator (18) and having at least one steering control unit (20) which comprises a computing unit (44) for carrying out a method according to one of Claims 1 to 11.

Images