Method for operating a steering system - Patent application

Abstract

The present invention begins with a method for operating a steering system (10) of a vehicle (12), the steering system (10) including a steering mechanism (14) and at least one electric motor (16) cooperating with the steering mechanism (14), in which a stiffness of at least one steering assembly (18, 20, 22) of the steering mechanism (14) and / or a play within the steering mechanism (14) is determined. In the method, it is proposed that in order to determine the stiffness of the at least one steering assembly (18, 20, 22) and / or the play in the steering mechanism (14), the steering mechanism (14) is moved to a defined test position and / or stopped in the test position, the electric motor (16) is driven and controlled using an excitation signal, and the stiffness of the at least one steering assembly (18, 20, 22) and / or the play in the steering mechanism (14) are determined by monitoring a motor torque of the electric motor (16) and a rotor position angle of the electric motor (16) during the period of driving and controlling the electric motor (16) using the excitation signal, and evaluating the change in the motor torque depending on the rotor position angle.

Description

[Technical field]

[0001] Prior Art The invention starts from a method for operating a steering system according to the preamble of claim 1. Furthermore, the invention relates to a computing unit for implementing such a method, to a steering system comprising such a computing unit and to a vehicle comprising such a steering system. [Background technology]

[0002] Currently, only a small proportion of mechanical anomalies that may occur during the operation of a vehicle or steering system are detected automatically. The majority of such anomalies must therefore be found by the driver himself. However, with the trend towards an increasing number of automated and / or autonomous driving, this type of manual error identification is becoming impossible. Furthermore, vehicles with steer-by-wire steering systems are known, but these systems exist without a direct mechanical connection between the steering wheel and the wheels that are steered. Due to this mechanical separation, in this case, for example, mechanical anomalies that may occur in the steering gear are likewise difficult to detect manually, since they are not directly fed back at the steering wheel.

[0003] For this reason, in DE 10 2019 212 618 A1, a method is proposed for automated determination of the stiffness of at least one steering assembly and / or the play in the steering mechanism. For this purpose, the wheel positions are determined by means of a monitoring device using wheel position sensors and are related to input variables that are preset by an electric motor. In this case, the steering mechanism is not moved into a defined test position in any case and / or is not stopped in the test position. Furthermore, in a procedure of this kind, it is mandatory to determine the wheel state or wheel position, which may have undesirable consequences in certain situations.

[0004] Furthermore, DE 10 2018 112 812 A1 discloses a method for automated determination of play in a steering mechanism, in which excitation is performed via motor torques with different frequencies. However, even in this case, the steering mechanism is not moved into a defined test position and / or is not stopped in the test position. This has the consequence that excitation can only be performed for small torques, since otherwise the entire steering system would have to be moved. Accordingly, play can only be determined in this case in the low load range. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] DE 102019212618 [Patent Document 2] DE 102018112812 Summary of the Invention [Problem to be solved by the invention]

[0006] The object of the present invention is to provide a method for operating a steering system with improved properties, in particular with regard to efficiency. This object is achieved by the features of claims 1, 17, 18 and 19, whereas preferred embodiments and developments of the invention can be seen from the dependent claims. [Means for solving the problem]

[0007] Disclosure of the Invention The present invention begins with a method, in particular a computer-implemented method, for operating a steering system of a vehicle, the steering system comprising a steering mechanism and at least one electric motor cooperating with said steering mechanism, in which the stiffness of at least one steering assembly of the steering mechanism and / or the play within the steering mechanism are determined, in particular automatically and / or automated.

[0008] In the method, it is proposed that in order to determine the stiffness of the at least one steering assembly and / or the play in the steering mechanism, the steering mechanism is moved into a defined test position and / or stopped in the test position, the electric motor is controlled with an excitation signal, and the stiffness of the at least one steering assembly and / or the play in the steering mechanism is determined by monitoring the motor torque of the electric motor and the rotor position angle of the electric motor during the control of the electric motor with the excitation signal and evaluating the change in the motor torque as a function of the rotor position angle.Therefore, in this embodiment, in a first method step, the steering mechanism is positioned and / or stopped in the test position, in a second method step the steering system is excited, in particular by controlling the electric motor with an excitation signal while the steering mechanism is in the test position, and in a third method step the system response of the steering system to the excitation signal is determined and evaluated using the motor torque and the rotor position angle. Positioning of the steering mechanism in the test position can in this context be performed, for example, manually by the vehicle occupant and / or driver or automatically and / or automatically by drive control of a corresponding electric motor. Furthermore, the above three method steps for determining the stiffness and / or play-in-the-steering-mechanism-humidity characteristic variables of the at least one steering assembly can be repeated in a fourth method step for at least one further test position different from the test position. This repetition can apply here in particular to the same steering assembly or to a further steering assembly different from the steering assembly. This embodiment allows to improve efficiency, in particular test efficiency, performance efficiency, component efficiency, energy efficiency and / or cost efficiency. Furthermore, in particular the operational safety of the steering system can be increased. Furthermore, the stiffness of the at least one steering assembly and / or the play in the steering mechanism can be advantageously determined both in the low load range and in the high load range.

[0009] The steering system may in this embodiment be configured as a conventional steering system, in particular an electric power steering system, and may include mechanical interventions. Alternatively, however, the steering system may be configured as a steer-by-wire steering system, in which the steering presettings are preferably transmitted to the wheels purely electrically. The steering mechanism further comprises at least one steering assembly, preferably a plurality of, in particular steering assemblies of different types. The steering mechanism may for example comprise a first steering assembly configured as a servo train, a second steering assembly configured as a sensor train, and / or a third steering assembly configured as an axle and / or part of an axle. The servo train in this context corresponds in particular to the steering gear of the steering system, whereas the sensor train corresponds to the steering shaft and / or steering column of the steering system. Furthermore, the steering system preferably comprises an electrically and / or electronically configured steering actuator system, in particular having an electric motor. A "steering actuator system" is to be understood in this context to mean an actuator unit which is particularly preferably coupled to a servo train and arranged to transmit a steering torque to a steering mechanism, in particular to the servo train, by means of an electric motor in order to influence the driving direction of the vehicle. The steering actuator system is preferably arranged to provide, by means of an electric motor, a steering torque for assisting a manual torque applied to a steering wheel of the steering system and / or a steering torque for automatically and / or autonomously controlling the driving direction of the vehicle. Furthermore, the steering system may preferably include a mechanical locking mechanism, which is arranged to stop the steering mechanism in a test position, in particular to fix and / or lock it. For this purpose, the locking mechanism may in particular include at least one electrical and / or mechanical lock, for example a steering lock in the region of the steering wheel, a locking unit in the region of the steering shaft, in particular of the input shaft of the steering shaft, and / or a wheel lock in the region of the wheels of the vehicle.

[0010] The vehicle further comprises at least one computing unit arranged to implement the method for operating the steering system. A "computing unit" is understood to mean in particular an electrical and / or electronic unit having an information input, an information processing and an information output. Preferably, the computing unit further comprises at least one processor, at least one operating memory, at least one input means and / or output means, at least one operating program, at least one control routine, at least one adjustment routine, at least one calculation routine and / or at least one evaluation routine. In particular, the computing unit is arranged to determine at least one steering assembly stiffness and / or play in the steering mechanism. Furthermore, the computing unit is arranged to drive and control the electric motor. Furthermore, the computing unit may also be arranged to drive and control the locking mechanism. In this embodiment, the computing unit is arranged at least to drive and control the electric motor with the excitation signal, to monitor the motor torque of the electric motor and the rotor position angle of the electric motor during the period of driving and controlling the electric motor with the excitation signal, and to evaluate the change in the motor torque depending on the rotor position angle. Furthermore, the calculation unit may in particular be arranged to drive the steering mechanism into a defined test position by controlling the electric motor and / or to stop it in the test position by controlling the locking mechanism. Preferably, the calculation unit is integrated here in the control device of the vehicle and / or in the control device of the steering system, in particular in the form of a steering control device. "Provided" is in particular to be understood as meaning specially programmed, designed and / or equipped. Where an object is provided for a certain function, it is in particular to be understood as meaning that the object fulfills and / or executes this certain function in at least one application and / or operating state.

[0011] It is further preferably proposed that the stiffness of at least one steering assembly and / or the play in the steering mechanism is determined using the rotor position angle or the derivative of the motor torque according to the difference quotient from the motor torque and the rotor position angle, i.e. based on the rate of change of the motor torque as a function of the rotor position angle, which makes it particularly easy to monitor the change in the motor torque as a function of the rotor position angle.

[0012] In a further embodiment, it is proposed that the change in the motor torque is compared with a reference value in dependence on the rotor position angle in order to determine the stiffness of at least one steering assembly and / or the play in the steering mechanism, which provides a particularly favorable and simple evaluation algorithm.

[0013] It is further proposed that when determining the stiffness of at least one steering assembly and / or the play in the steering mechanism, a linearization is preferably used for different load levels. In this connection, it must be taken into account that the stiffness to be determined and / or the play to be determined usually have a non-linear relationship. However, in the present embodiment, it has been realized that even when using the corresponding linearization, a relatively accurate and precise prediction of the stiffness and / or play is possible, while at the same time the calculation effort can be significantly reduced.

[0014] The evaluation result can be made even more accurate if the current temperature is taken into account when determining the stiffness of at least one steering assembly and / or the play in the steering mechanism. The temperature is preferably captured in the area of ​​the steering mechanism, for example via an additional temperature sensor, or preferably directly in the area of ​​the electric motor. In the latter case, a temperature sensor system integrated in the steering actuator system can preferably be used to determine the current temperature, whereby additional costs can preferably be minimized.

[0015] According to a particularly preferred embodiment, it is proposed that the electric motor is controlled with an excitation signal in such a way that a quasi-static excitation is achieved, whereby the motor torque is continuously increased, in particular up to a specified and / or specifiable maximum motor torque, for example +5 Nm. This makes it possible, in particular, to achieve an excitation of the steering system that is particularly simple in terms of control technology. The electric motor is preferably controlled in this case with a ramp-like signal, whereby the excitation signal is increased continuously and / or ramp-like. In this embodiment, the increase in the motor torque can here be effected directly by controlling the motor torque. However, preferably the increase in the motor torque is effected by controlling the rotor position angle, whereby undesired acceleration and / or load peaks in the measurement can preferably be prevented. Furthermore, in this connection it is preferably proposed that the motor torque is increased continuously to the maximum motor torque in both steering directions if the steering mechanism is completely stopped in the test position, i.e. fixed and / or locked, for example using a locking mechanism, and that the motor torque is increased continuously to the maximum motor torque only in one steering direction if the steering mechanism is not completely stopped in the test position.

[0016] Alternatively or additionally, the electric motor is controlled with an excitation signal such that dynamic excitation is achieved, whereby it is proposed that the electric motor is controlled with a number of different frequencies at a number of constant amplitudes. This allows a particularly accurate evaluation. Preferably, a frequency sweep is used in this case for controlling the electric motor, which frequency sweep is performed for at least two different amplitudes of the motor torque. Particularly preferably, the frequency sweep is performed starting from a high frequency in the direction of low frequencies. Furthermore preferably, the maximum amplitude of the motor torque during the frequency sweep is also below the maximum possible motor torque, i.e. for example at most 75% or at most 50% of the maximum possible motor torque.

[0017] A particularly high operational safety can be achieved if, in particular, based on the determined stiffness of the at least one steering assembly and / or the determined play in the steering mechanism, at least one control parameter of the steering control of the steering system is adjusted, in particular for the drive control of the electric motor. In particular, a stiffness-sensitive and / or play-sensitive control parameter can thereby be adaptively adjusted based on the determined stiffness and / or the determined play. The steering control, in this case preferably has an electrical connection with the calculation unit and is particularly preferably integrated in the control of the vehicle and / or in the control of the steering system.

[0018] It is further proposed that the stiffness of the at least one steering assembly and / or the play in the steering mechanism are compared with a threshold value, whereby if the stiffness of the at least one steering assembly and / or the play in the steering mechanism falls below or exceeds the threshold value, safety measures are initiated, which may in particular include at least the generation of an instruction message in the vehicle and / or on an external electronic device, for example in the form of a smartphone, and / or a downgrading of the driving mode, for example in the form of a reduction in the maximum vehicle speed, which in particular can achieve a warning effect and further increase the operating safety.

[0019] According to a further embodiment, it is proposed that the stiffness of at least one steering assembly and / or the play in the steering mechanism are used to determine a humidity characteristic variable. "Humidity characteristic variable" is understood to mean in particular a characteristic variable on the basis of which the humidity in the steering system can be inferred or from which the humidity in the steering system can be determined. In this context, in particular the change in the stiffness of at least one steering assembly and / or the play in the steering mechanism as a function of the humidity in the steering system is exploited. This in particular makes it possible to obtain additional information on the humidity in the steering system and / or to determine a correlated change in the determined stiffness and / or the determined play accordingly.

[0020] The stiffness of the at least one steering assembly and / or the play in the steering mechanism can be determined, for example, during a driving mode of the vehicle. However, it is preferably proposed that the stiffness of the at least one steering assembly and / or the play in the steering mechanism is determined in a stationary state of the vehicle and / or in a state in which the engine of the vehicle is switched off, for example when the vehicle is stopped, for example at a traffic light or when the vehicle is parked. This can advantageously reduce irritation of the driver and / or passengers while driving.

[0021] It is further proposed that the stiffness of the at least one steering assembly and / or the play in the steering mechanism is determined at regular time intervals, for example at each system start-up, at each system shutdown or annually or every other year, for example especially at regular vehicle inspections and / or after-sales servicing, in order to monitor changes in the stiffness of the at least one steering assembly and / or in the play in the steering mechanism, whereby changes in particular in the stiffness of the at least one steering assembly and / or in the play in the steering mechanism can be preferably quickly identified and the operational safety of the vehicle can be further increased.

[0022] According to an embodiment, the steering mechanism comprises at least one steering assembly in the form of a servo train, where in order to determine the stiffness of the servo train and / or the play in the steering mechanism, it is proposed that a steering adjustment element of the servo train, for example in the form of a rack, is positioned in the region of a mechanical end stop of the steering system and the electric motor is controlled by means of an excitation signal such that the motor torque increases continuously in the direction of the mechanical end stop up to a maximum motor torque. In this case, the position of the steering adjustment element in the region of the mechanical end stop corresponds to a test position. However, alternatively, the control of the electric motor can also be performed at a number of constant amplitudes with a number of different frequencies. Furthermore, the method steps can be repeated in further method steps for at least one further test position different from the test position. In this connection, it is for example conceivable that in a further method step, in particular for determining the stiffness of the servo train, the steering adjustment element is positioned in the region of a further mechanical end stop of the steering system, in particular in the region opposite the mechanical end stop, and the electric motor is driven with a further excitation signal, in particular a further excitation signal equivalent to said excitation signal, such that the motor torque increases continuously in the direction of the further mechanical end stop up to a maximum motor torque. However, as an alternative, the repetition in the further method step can also apply to a further steering assembly different from the steering assembly, in particular for determining the play in the steering mechanism. This makes it possible in a particularly preferred manner to determine the stiffness of the servo train and / or the play in the steering mechanism, in particular in the region of the servo train.

[0023] According to a further embodiment, the steering mechanism comprises at least one steering assembly in the form of a sensor train, where it is proposed that in order to determine the stiffness of the sensor train and / or the play in the steering mechanism, the sensor train is stopped in a straight-ahead position, in particular mechanically, for example by controlling a locking mechanism, and the electric motor is controlled by an excitation signal such that the motor torque increases continuously in both steering directions up to a maximum motor torque. In this case, the position of the sensor train in the straight-ahead position corresponds to the test position. Alternatively, however, the control of the electric motor can also be performed at a number of constant amplitudes with a number of different frequencies. Furthermore, the method steps can essentially be repeated in further method steps for at least one further test position different from the test position. However, preferably in this case, the repetition of the method can be omitted in order to determine the stiffness of the sensor train. In contrast, in order to determine the play in the steering mechanism, the repetition in the further method steps can also apply to a further steering assembly different from the steering assembly. This makes it possible in a particularly advantageous manner to determine the stiffness of the sensor train and / or the play in the steering mechanism, in particular in the region of the sensor train.

[0024] Furthermore, according to a further embodiment, the steering mechanism comprises at least one steering assembly in the form of an axle or part of an axle, where in order to determine the stiffness of the axle or part of the axle and / or the play in the steering mechanism, it is proposed that at least one wheel is stopped, in particular mechanically, for example by controlling a locking mechanism, and the electric motor is controlled by means of an excitation signal such that the motor torque increases continuously in both steering directions up to a maximum motor torque. In this case, the position of the wheel in the stopped state corresponds to the test position. However, alternatively, the control of the electric motor can also be performed at several constant amplitudes with several different frequencies. Furthermore, the method steps can also be repeated in this case in a further method step for at least one further test position different from the test position. In this connection, it is for example envisaged that in a further method step, in particular for determining the stiffness of an axle or part of an axle, at least one further wheel, in particular a further wheel opposite the axle, is stopped, in particular mechanically, for example by controlling a locking mechanism, and the electric motor is controlled with a further excitation signal, in particular a further excitation signal equivalent to the axle, such that the motor torque increases continuously in both steering directions up to a maximum motor torque. However, as an alternative, the repetition in the further method step can also apply to a further steering assembly different from the steering assembly, in particular for determining the play in the steering mechanism. This makes it possible in a particularly preferred manner to determine the stiffness of the axle or part of an axle and / or the play in the steering mechanism, in particular in the region of the axle or part of an axle.

[0025] The method for operating a steering system should not be limited to the applications and embodiments described herein, in particular, the method for operating a steering system may have a different number of individual elements, parts and units than those listed herein in order to fulfill the functional form described herein.

[0026] Further advantages will become apparent from the following description of the drawings, in which an embodiment of the invention is shown. [Brief description of the drawings]

[0027] [Figure 1a] FIG. 1 is a schematic diagram illustrating an exemplary vehicle with a steering system. [Figure 1b] FIG. 1 is a schematic diagram illustrating an exemplary vehicle with a steering system. [Figure 2a] 1 is an exemplary pictorial diagram showing various signals for determining the stiffness of at least one steering assembly of a steering mechanism of a steering system and / or play within the steering mechanism. [Figure 2b] 1 is an exemplary pictorial diagram showing various signals for determining the stiffness of at least one steering assembly of a steering mechanism of a steering system and / or play within the steering mechanism. [Diagram 3] 4 is an exemplary flow chart illustrating major method steps of a method for operating a steering system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Description of the embodiment 1a and 1b show a schematic representation of a vehicle 12, exemplarily configured as a passenger car, with a number of wheels 34, 36 and a steering system 10. The vehicle 12 is suitable for automated and / or autonomous driving. The steering system 10 has an active connection with the wheels 34, 36 and is provided for influencing the direction of travel of the vehicle 12. Furthermore, the steering system 10 is configured purely exemplarily as an electrically assisted steering system, with an electric power assist in the form of power steering. However, alternatively, the steering system may also be configured as a steer-by-wire steering system, known per se.

[0029] The steering system 10 includes a steering mechanism 14, which is known per se, and a steering actuator system 40, which interacts with the steering mechanism 14, which is known per se.

[0030] The steering mechanism 14 includes a steering wheel 42, exemplarily configured as a steering wheel in this embodiment for applying a manual torque, and a number of steering assemblies 18, 20, 22 operatively connected to the steering wheel 42. In this embodiment, the steering mechanism 14 includes a first steering assembly 18 configured as a servo train, a second steering assembly 20 configured as a sensor train, and a third steering assembly 22 configured as an axle and / or part of an axle. The first steering assembly 18 corresponds to a steering gear exemplarily configured as a rack-and-pinion steering gear, and includes at least one steering adjustment element 28, in this embodiment, in particular configured as a rack. The first steering assembly 18 is provided to convert a steering preset at the steering wheel 42 into a steering movement of the wheels 34, 36, in particular configured as front wheels. The second steering assembly 20 corresponds to a steering shaft in this embodiment, and is used to in particular mechanically connect the steering wheel 42 to the first steering assembly 18. The third steering assembly 22 may include at least a portion of the tie rods assigned to the wheels 34, 36 and / or a portion of the rims of the wheels 34, 36. Alternatively, the steering wheel may be configured as a steering lever and / or a steering ball, etc. Furthermore, it is also envisaged to omit the steering shaft and / or the steering wheel, as in the case of a steer-by-wire steering system.

[0031] The steering actuator system 40 includes the electric motor 16 and has an operative connection with the first steering assembly 18, and in particular the steering adjustment element 28. The steering actuator system 40 is arranged to provide a steering torque using the electric motor 16. In this embodiment, the steering actuator system 40 is arranged to provide and transmit at least a steering torque in the form of an assist torque to the steering adjustment element 28.

[0032] Furthermore, the steering system 10 comprises a rotor position sensor system 44 arranged in the region of the steering actuator system 40. This rotor position sensor system 44 is arranged to contactlessly capture at least one operating signal of the electric motor 16, in this embodiment in particular a rotor position signal or a rotor position angle.

[0033] Furthermore, the steering system 10 comprises a locking mechanism 46, which is provided for stopping, in particular for fixing and / or locking, the steering mechanism 14. For this purpose, the locking mechanism 46 in the present embodiment comprises a number of electrically and / or mechanically configured locks, in particular a steering lock 48 in the area of ​​the steering wheel 42, a first wheel lock 50 in the area of ​​a first one of the wheels 34, 36 and a second wheel lock 52 in the area of ​​a second one of the wheels 34, 36. In principle, however, it is also conceivable to omit such a locking mechanism.

[0034] Furthermore, the vehicle 12 comprises a control device 54. The control device 54 is configured as a steering control device and is therefore part of the steering system 10. The control device 54 has an electrical connection with the steering actuator system 40, in particular with the electric motor 16. Furthermore, the control device 54 has an electrical connection with the rotor position sensor system 44. Furthermore, the control device 54 has an electrical connection with the locking mechanism 46. The control device 54 is arranged to control the operation of the steering system 10. In this embodiment, the control device 54 is arranged to drive and control at least the electric motor 16. Alternatively, the control device may be different from the steering control device and may, for example, be directly configured as a centralized vehicle control device.

[0035] The controller 54 includes a computing unit 38. The computing unit 38 includes at least one processor (not shown), for example in the form of a microprocessor, and at least one operating memory (not shown). Furthermore, the computing unit 38 includes at least one operating program stored in the operating memory.

[0036] Furthermore, the control device 54 includes a steering control device 26, known per se, for controlling the drive of the electric motor 16. This steering control device 26 has an electrical connection with the computing unit 38. Furthermore, the steering control device 26 is electrically connected to the electric motor 16. In the present case, the steering control device 26 is provided for controlling the position of the steering adjustment element 28, and thus in particular the direction of travel of the vehicle 12, at least in the driving mode of the vehicle 12.

[0037] Usually, only a small part of mechanical anomalies that may occur during the operation of the vehicle 12 or steering system 10 are detected automatically, whereas the majority of such anomalies must be found by the driver himself. However, this fact may become more and more problematic in the future, especially for automated and / or autonomously driven vehicles and / or steering systems in the form of steer-by-wire steering systems. In this case, determining the stiffness of the steering assemblies 18, 20, 22 of the steering mechanism 14 and / or the play within the steering mechanism 14 plays a particularly important role, since signs of wear and / or ageing effects may have a particularly critical effect here.

[0038] Therefore, in order to increase the efficiency and / or operational safety, a corresponding method is proposed below for operating the steering system 10. In the present embodiment, here, in particular, a calculation unit 38 is provided for carrying out the method and for this purpose comprises a computer program with corresponding program code means.

[0039] In the present embodiment, in order to determine the stiffness of at least one steering assembly 18, 20, 22 and / or the play in the steering mechanism 14, the steering mechanism 14 is first moved into a defined test position and / or stopped in the test position. Preferably, the stiffness of at least one steering assembly 18, 20, 22 and / or the play in the steering mechanism 14 is determined here with the vehicle 12 at a standstill and / or with the engine of the vehicle 12 turned off. Furthermore, the positioning of the steering mechanism 14 in the test position can be performed manually, for example by a passenger and / or a driver of the vehicle 12, or, preferably, automatically and / or automatically by a corresponding drive control of the electric motor 16. Furthermore, the stopping of the steering mechanism 14 in the test position can be performed by an automated drive control of the locking mechanism 46.

[0040] The electric motor 16 is then driven and controlled using the excitation signal. The electric motor 16 can be driven and controlled using the excitation signal in two different ways.

[0041] On the one hand, the electric motor 16 can be controlled with an excitation signal such that a quasi-static excitation is achieved, in which the motor torque of the electric motor 16 is continuously increased to a maximum motor torque, for example +5 Nm. In this case, the electric motor 16 is controlled with a ramp-like signal, whereby the excitation signal is increased continuously and / or ramp-like. Furthermore, the increase in the motor torque is preferably performed by controlling the rotor position angle of the electric motor 16, whereby undesired acceleration and / or load peaks in the measurement can be prevented. Furthermore, the motor torque is continuously increased to the maximum motor torque in both steering directions if the steering mechanism 14 is completely stopped in the test position, and is continuously increased to the maximum motor torque only in one steering direction if the steering mechanism 14 is not completely stopped in the test position.

[0042] Alternatively or additionally, for example in further applications, the electric motor is controlled with an excitation signal such that dynamic excitation is achieved, where the electric motor is controlled at a number of constant amplitudes with a number of different frequencies. In this case, a frequency sweep is used for controlling the electric motor 16, which is carried out for at least two different amplitudes of the motor torque. Preferably, the frequency sweep is carried out here starting from a high frequency in the direction of a low frequency, for example starting from a frequency of 100 Hz in the direction of 0 Hz or starting from a frequency of 40 Hz in the direction of 0 Hz. Furthermore, the maximum amplitude of the motor torque during the frequency sweep is preferably also below the maximum possible motor torque, i.e. for example at most 75% or at most 50% of the maximum possible motor torque. In this context, for example amplitudes of 0.2 Nm to 0.5 Nm have proven suitable. By positioning and / or stopping at least one steering assembly 18, 20, 22 in a test position, it is then possible to determine the stiffness of the at least one steering assembly 18, 20, 22 and / or the play in the steering mechanism 14 both in the low load range and in the high load range.

[0043] The stiffness of the at least one steering assembly 18, 20, 22 and / or the play in the steering mechanism 14 is then determined by monitoring the motor torque of the electric motor 16 and the rotor position angle of the electric motor 16 during the drive control of the electric motor 16 with the excitation signal and evaluating the change in the motor torque as a function of the rotor position angle. The motor torque of the electric motor 16 can here, for example, be read out directly from the control device 54 or can be captured using an additional capture sensor system, whereas the rotor position angle of the electric motor 16 can preferably be determined from the rotor position signal of the rotor position sensor system 44. In this embodiment, in this case, the derivative of the motor torque according to the rotor position angle or the difference quotient from the motor torque and the rotor position angle is formed and compared with the reference value 24 in order to determine the stiffness of the at least one steering assembly 18, 20, 22 and / or the play in the steering mechanism 14 (see also FIG. 2b).

[0044] Advantageously, linearization can also be used when determining the stiffness of at least one steering assembly 18, 20, 22 and / or the play in the steering mechanism 14. In this connection, it must be taken into account that the stiffness to be determined and / or the play to be determined usually have a non-linear relationship. However, in the present embodiment, it has been recognized that even when using the corresponding linearization, a relatively accurate and precise prediction of the stiffness of at least one steering assembly 18, 20, 22 and / or the play of the steering mechanism 14 is possible, while at the same time the calculation effort can be significantly reduced.

[0045] To improve the accuracy of the measurement, the current temperature can also be taken into account when determining the stiffness of the at least one steering assembly 18, 20, 22 and / or the play in the steering mechanism 14. In this connection, in particular, the fact that the stiffness of the at least one steering assembly 18, 20, 22 and / or the play in the steering mechanism 14 varies depending on the current temperature is utilized. Preferably, the temperature is captured here directly in the area of ​​the electric motor 16, in particular by means of a temperature sensor system integrated in the steering actuator system 40. However, as an alternative, an additional temperature sensor can also be used in the area of ​​the electric motor 16 or in the area of ​​the steering mechanism 14. Furthermore, existing temperature sensors in the vehicle 12, for example a temperature sensor for indicating the outside air temperature, can also be used to determine the temperature. Furthermore, it is also conceivable to completely omit the additional determination of the temperature.

[0046] Then, once the stiffness of at least one steering assembly 18, 20, 22 and / or the play in the steering mechanism 14 has been determined, various actions can be performed and / or initiated depending on the determined values.

[0047] For example, at least one control parameter of the steering control device 26 can be adjusted based on the determined stiffness of at least one steering assembly 18, 20, 22 and / or play in the steering mechanism 14, whereby, preferably, stiffness-sensitive and / or play-sensitive control parameters can be adaptively adjusted based on the determined stiffness and / or determined play.

[0048] Furthermore, the stiffness of at least one steering assembly 18, 20, 22 and / or play in the steering mechanism 14 can be compared to a threshold value, whereby safety measures are initiated if the stiffness and / or play is below or above the threshold value, which may include at least the generation of an instruction message in the vehicle and / or on an external electronic device, for example in the form of an instruction to visit a workshop, and / or a downgrading of the driving mode, for example in the form of a reduction in the maximum vehicle speed.

[0049] Furthermore, the stiffness of at least one steering assembly 18, 20, 22 and / or the play in the steering mechanism 14 can be used to determine a humidity characteristic variable based on which the humidity in the steering system 10 can be inferred or determined, thereby providing additional information regarding the humidity in the steering system 10 and / or allowing correlated changes in the determined stiffness and / or the determined play to be determined.

[0050] Furthermore, in this embodiment, the stiffness of the at least one steering assembly 18, 20, 22 and / or the play in the steering mechanism 14 is determined at regular time intervals, for example at start-up or shutdown of each system, in order to monitor changes in the stiffness of the at least one steering assembly 18, 20, 22 and / or changes in the play in the steering mechanism 14. This allows changes in the stiffness of the at least one steering assembly 18, 20, 22 and / or changes in the play in the steering mechanism 14 to be recognized, preferably quickly, further increasing the operational safety of the vehicle 12. However, it is also conceivable to provide a relatively long monitoring interval, for example daily, monthly or yearly, as an alternative.

[0051] Hereinafter, some specific applications of the above general facts will be described for a first steering assembly 18 configured as a servo train, a second steering assembly 20 configured as a sensor train, and a third steering assembly 22 configured as an axle and / or part of an axle.

[0052] According to a first embodiment, in order to determine the stiffness of the first steering assembly 18 or the servo train, the turning adjustment element 28 is positioned in the region of a mechanical end stop 30 of the steering system 10, and the electric motor 16 is driven by an excitation signal such that the motor torque is continuously increased in the direction of the mechanical end stop 30 up to a maximum motor torque. The position of the turning adjustment element 28 in the region of the mechanical end stop 30 therefore corresponds in this case to the test position. To position the turning adjustment element 28 in the test position, the turning adjustment element 28 can be positioned directly in the region of the mechanical end stop 30, for example by driving the electric motor 16 and by means of a correspondingly learned software function, or can be moved in the direction of the mechanical end stop 30 at a constant movement speed (approximately 10 mm / s to 40 mm / s) until the test position is reached or the test position is recognized on the basis of a decreasing movement speed. Then, based on the motor torque of the electric motor 16 and the rotor position angle of the electric motor 16, the total stiffness from the servo train and the mechanical end stopper 30 can be calculated for the corresponding load direction, i.e., in the direction of the mechanical end stopper 30. Here, the following formula is used: 1 / c1=(1 / c Servo )+(1 / c A ) (1) applies.

[0053] Here, c1 describes the total stiffness from the servo train and the mechanical end stop 30 for the corresponding load direction, and c Servo describes the stiffness of the first steering assembly 18 or servo train, and c Adescribes the stiffness of the mechanical end stop 30. After the stiffness of the mechanical end stop 30 is known, the stiffness of the first steering assembly 18 or the servo train can be deduced accordingly based on equation (1). In particular, here, if an end stop damper is used, the stiffness of the mechanical end stop 30 is governed by the proportion of this end stop damper. Alternatively, however, the drive control of the electric motor can be performed at several constant amplitudes, again with several different frequencies.

[0054] The above-mentioned method steps can then be repeated on the opposite side, where the steering adjustment element 28 is positioned in the region of a further mechanical end stop 32 of the steering system, in particular in the region opposite the mechanical end stop 30, and the electric motor 16 is driven with a further excitation signal, in particular an equivalent further excitation signal, such that the motor torque increases continuously in the direction of the further mechanical end stop 32 up to the maximum motor torque. The position of the steering adjustment element 28 in the region of the further mechanical end stop 32 thus corresponds in this case to a further test position. The positioning of the steering adjustment element 28 in the further test position and the evaluation of the stiffness can now be carried out using the above-mentioned methodology.

[0055] According to a second embodiment, in order to determine the stiffness of the second steering assembly 20 or the sensor train, the sensor train is stopped in the straight-ahead position, in particular by controlling the lock mechanism 46 or, more precisely, by controlling the steering lock 48, and the electric motor 16 is controlled by means of an excitation signal such that the motor torque increases continuously in both steering directions up to the maximum motor torque. The position of the sensor train in the straight-ahead position therefore corresponds in this case to the test position. The positioning of the sensor train in the straight-ahead position can be performed manually or, preferably, by corresponding control of the electric motor 16 and the lock mechanism 46. Then, based on the motor torque of the electric motor 16 and the rotor position angle of the electric motor 16, the total stiffness from the sensor train and the servo train can be determined. Here, the following formula is used: 1 / c2=(1 / c Sensor )+(1 / c Servo ) (2) applies.

[0056] Here, c2 describes the total stiffness from the sensor train and servo train, and c Sensor describes the stiffness of the second steering assembly 20 or sensor train, and c Servo describes the stiffness of the first steering assembly 18 or servo train. If the stiffness of the first steering assembly 18 or servo train is determined as described above and is therefore known, the stiffness of the second steering assembly 20 or sensor train can be deduced accordingly on the basis of equation (2). Alternatively, however, the drive control of the electric motor can also be performed at several constant amplitudes, again with several different frequencies. The repetition of the method steps can be omitted in this case, since the excitation is performed in both steering directions as described above.

[0057] According to a third embodiment, in order to determine the stiffness of the third steering assembly 22 or the axle or part of the axle, one of the wheels 34, 36 is stopped, in particular by controlling the locking mechanism 46, or more precisely by controlling the wheel lock 50 or the wheel lock 52, and the electric motor 16 is controlled by an excitation signal such that the motor torque increases continuously in both steering directions up to the maximum motor torque. The other of the wheels 34, 36 is in this case in a state where it can rotate freely, for example on a lift platform. Therefore, in this case, the position of the wheels 34, 36 in the stopped state corresponds to the test position. Then, based on the motor torque of the electric motor 16 and the rotor position angle of the electric motor 16, the total stiffness from the axle and the servo train can be determined. Here, the following formula is used: 1 / c3=(1 / c FZ )+(1 / c Servo ) (3) applies.

[0058] Here, c3 describes the total stiffness from the axle and servo train, and c FZ describes the stiffness of the third steering assembly 22 or the axle or part of the axle, and c Servo describes the stiffness of the first steering assembly 18 or servo train. If the stiffness of the first steering assembly 18 or servo train is determined as described above and is therefore known, the stiffness of the third steering assembly 22 or the axle or part of the axle can be deduced accordingly based on equation (3). However, alternatively, the drive control of the electric motor can again be performed at several constant amplitudes with several different frequencies.

[0059] The above method steps can then be repeated on the opposite side, where the other of the wheels 34, 36 is stopped and the electric motor 16 is driven with a further excitation signal, in particular an equivalent further excitation signal, such that the motor torque increases continuously in both steering directions up to the maximum motor torque. The stiffness evaluation can again be carried out using the methodology described above.

[0060] To determine the play in the steering mechanism 14, according to a fourth aspect, at least two of the above-mentioned methodologies for determining stiffness can be combined with each other.

[0061] According to one variant, here, in order to determine the play in the steering mechanism 14, in particular the play between the first steering assembly 18 and the second steering assembly 20, the stiffness of the first steering assembly 18 or the servo train is determined using the first methodology described above, and the stiffness of the second steering assembly 20 or the sensor train is determined using the second methodology described above. Then, based on the motor torque of the electric motor 16 and the rotor position angle of the electric motor 16, the total play from the servo train and the sensor train can be determined, here using the following formula: Δφ1=Δφ Servo +Δφ Sensor (4) applies.

[0062] Here, Δφ1 describes the total play from the servo train and the sensor train, and Δφ Servo describes the play in the area of ​​the first steering assembly 18 or servo train, and Δφ Sensor describes the play in the area of ​​the second steering assembly 20 or the sensor train. In this case, Δφ Servo and Δφ Sensor There is no need to distinguish between 0 and 1, since if the corresponding threshold value is exceeded, then it should be brought to the factory anyway. A repetition of the method steps is likewise unnecessary in this case.

[0063] According to a further variant, in order to determine the play in the steering mechanism 14, in particular between the first steering assembly 18 and the third steering assembly 22, the stiffness of the first steering assembly 18 or the servo train is determined using the first methodology described above, and the stiffness of the third steering assembly 22 or the axle or part of the axle is determined using the third methodology described above. Then, based on the motor torque of the electric motor 16 and the rotor position angle of the electric motor 16, the total play from the servo train and the axle can be determined, where the following formula is used: Δφ2=Δφ Servo +Δφ FZ (5) applies.

[0064] Here, Δφ2 describes the total play from the servo train and the axle, and Δφ Servo describes the play in the area of ​​the first steering assembly 18 or servo train, and Δφ FZ describes the play in the third steering assembly 22 or in the area of ​​the axle or part of the axle. In this case, Δφ Servo and Δφ FZ No distinction is necessary between the above threshold and the above threshold, since if the corresponding threshold is exceeded, it should be brought to the factory anyway, where the cause can then be finally narrowed down. A repetition of the method steps is likewise unnecessary in this case.

[0065] Furthermore, the total play from the servo train, axle and sensor train can also be determined in principle by a combination of all the above methodologies.

[0066] 2a and 2b show exemplary diagrams of various signals for determining the stiffness of at least one steering assembly 18, 20, 22 and / or the play in the steering mechanism 14. The example shown in Figs. 2a and 2b is here limited to the first steering assembly 18 and the third steering assembly 22.

[0067] 2a, the motor torque of the electric motor 16 is plotted on the vertical axis 56. The rotor position angle of the electric motor 16 is plotted on the horizontal axis 58. A curve 60 shows the course of the motor torque as a function of the rotor position angle, in particular the linearized course.

[0068] A first region 62 shows diagrammatically an exemplary course of the motor torque as a function of the rotor position angle for determining the stiffness in the region of the first steering assembly 18 or servo train.

[0069] A second area 64 shows diagrammatically an exemplary course of the motor torque as a function of the rotor position angle for determining the stiffness of the third steering assembly 22 or an axle or a part of an axle area.

[0070] In Fig. 2b, the stiffness is plotted on a further ordinate 66. On a further abscissa 68, the rotor position angle of the electric motor 16 is again plotted. A curve 70 shows the course of the stiffness as a function of the rotor position angle. To determine the curve 70, the derivative of the motor torque as a function of the rotor position angle or the difference quotient from the motor torque and the rotor position angle is formed.

[0071] The first region 72 in this case shows, diagrammatically, an exemplary course of the total stiffness from the servo train and the mechanical end stop 30 for the corresponding load direction, i.e. in the direction of the mechanical end stop 30 .

[0072] A second region 74 illustrates generally an exemplary progression of the total stiffness from the axle, servo train, and Bohr friction between the tire contact patch and the road surface.

[0073] The third region 76 further characterizes the play within the steering mechanism 14 , and in particular the play between the first steering assembly 18 and the third steering assembly 22 .

[0074] Finally, FIG. 3 shows an exemplary flow chart with the main method steps of a method for operating the steering system 10.

[0075] In method step 80, the steering mechanism 14 is positioned and / or stopped in a corresponding test position. Positioning of the steering mechanism 14 in the test position can in this connection be performed manually, for example by a passenger and / or a driver of the vehicle 12, or preferably automatically and / or automated by corresponding drive control of the electric motor 16.

[0076] In the subsequent method step 82, the steering system 10 is excited by controlling the electric motor 16 with the excitation signal, in particular while the steering mechanism 14 is in the test position. The electric motor 16 can then be controlled with the excitation signal in such a way that quasi-static and / or dynamic excitation is achieved.

[0077] In a subsequent method step 84, a system response of the steering system 10 to the excitation signal is determined and evaluated using the motor torque of the electric motor 16 and the rotor position angle of the electric motor 16, in particular using the derivative of the motor torque according to the rotor position angle or using a difference quotient from the motor torque and the rotor position angle. This system response can then be used to determine the stiffness of at least one steering assembly 18, 20, 22 of the steering mechanism 14 and / or the play within the steering mechanism 14.

[0078] Then, in the subsequent method step 86, depending on the determined stiffness and / or play values, various actions can be performed and / or initiated, such as adjusting at least one control parameter of the steering control device 26 and / or initiating safety measures if a threshold value is exceeded or fallen below.

[0079] The exemplary flow chart of Fig. 3 merely exemplarily illustrates a method for operating the steering system 10. In particular, the individual method steps can be modified or additional method steps can be added, so that, for example, these method steps 80, 82 and 84 can be repeated for at least one further test position different from the test position in question, in a method step that directly follows the method step 84. This repetition can in particular apply to the same steering assembly 18, 20, 22 or to one of the other steering assemblies 18, 20, 22.

Claims

1. A method for operating a steering system (10) of a vehicle (12), comprising: The steering system (10) includes a steering mechanism (14) and at least one electric motor (16) cooperating with the steering mechanism (14); A method in which a stiffness of at least one steering assembly (18, 20, 22) of the steering mechanism (14) and / or a play within the steering mechanism (14) is determined, comprising: the steering mechanism (14) is moved to a defined test position and / or stopped at the test position and the electric motor (16) is driven and controlled with an excitation signal to determine the stiffness of the at least one steering assembly (18, 20, 22) and / or the play in the steering mechanism (14); The method, wherein the stiffness of the at least one steering assembly (18, 20, 22) and / or the play in the steering mechanism (14) is determined by monitoring a motor torque of the electric motor (16) and a rotor position angle of the electric motor (16) during a period of drive control of the electric motor (16) using the excitation signal, and evaluating a change in the motor torque depending on the rotor position angle.

2. 2. The method of claim 1, wherein the stiffness of the at least one steering assembly (18, 20, 22) and / or the play in the steering mechanism (14) is determined using the rotor position angle or a derivative of the motor torque according to a difference quotient from the motor torque and the rotor position angle.

3. 3. The method according to claim 1 or 2, wherein the change in motor torque is compared with a reference value (24) in dependence on the rotor position angle to determine a stiffness of the at least one steering assembly (18, 20, 22) and / or a play in the steering mechanism (14).

4. 4. The method according to claim 1, wherein linearization is used in determining the stiffness of the at least one steering assembly (18, 20, 22) and / or the play in the steering mechanism (14).

5. 5. The method according to any one of claims 1 to 4, wherein the current temperature is taken into account when determining the stiffness of the at least one steering assembly (18, 20, 22) and / or the play in the steering mechanism (14).

6. 6. The method according to claim 1, wherein the electric motor (16) is driven and controlled by means of the excitation signal in such a way that a quasi-static excitation is achieved, in particular in a first application case, and wherein the motor torque is continuously increased up to a maximum motor torque.

7. 7. The method of claim 6, wherein the motor torque is increased to a maximum motor torque continuously in both steering directions if the steering mechanism (14) is stopped in the test position, and is increased to a maximum motor torque continuously in one steering direction if the steering mechanism (14) is not stopped in the test position.

8. 8. The method according to claim 1, wherein the electric motor (16) is controlled by means of the excitation signal in such a way that dynamic excitation is achieved, in particular in the second application case, and wherein the electric motor (16) is controlled by means of a plurality of constant amplitudes using a plurality of different frequencies.

9. 9. The method according to claim 1, wherein based on the determined stiffness of the at least one steering assembly (18, 20, 22) and / or on the determined play in the steering mechanism (14), at least one control parameter of a steering control device (26) of the steering system (10), in particular for drive control of the electric motor (16), is adjusted.

10. 10. The method according to claim 1, wherein the stiffness of the at least one steering assembly (18, 20, 22) and / or the play in the steering mechanism (14) is compared to a threshold value and a safety measure is initiated if the stiffness of the at least one steering assembly (18, 20, 22) and / or the play in the steering mechanism (14) falls below or exceeds the threshold value.

11. 11. The method according to any one of the preceding claims, wherein the stiffness of the at least one steering assembly (18, 20, 22) and / or the play in the steering mechanism (14) are used to determine a humidity characteristic variable.

12. 12. The method according to any one of claims 1 to 11, wherein the stiffness of the at least one steering assembly (18, 20, 22) and / or the play in the steering mechanism (14) is determined in a stationary state of the vehicle (12) and / or in an engine-off state of the vehicle (12).

13. 13. The method according to any one of claims 1 to 12, wherein the stiffness of the at least one steering assembly (18, 20, 22) and / or the play in the steering mechanism (14) is determined at regular time intervals in order to monitor changes in the stiffness of the at least one steering assembly (18, 20, 22) and / or changes in the play in the steering mechanism (14).

14. 14. The method according to claim 1, wherein the steering mechanism (14) comprises at least one steering assembly (18) in the form of a servo train, and in order to determine the stiffness of the servo train and / or the play in the steering mechanism (14), a steering adjustment element (28) of the servo train is positioned in the area of ​​a mechanical end stop (30, 32) of the steering system (10), and the electric motor (16) is driven and controlled using the excitation signal such that the motor torque increases continuously in the direction of the mechanical end stop (30, 32) up to a maximum motor torque.

15. 15. The method according to any one of claims 1 to 14, wherein the steering mechanism (14) includes at least one steering assembly (20) in the form of a sensor train, and in order to determine the stiffness of the sensor train and / or the play in the steering mechanism (14), the sensor train is stopped in a straight ahead position and the electric motor (16) is driven and controlled using the excitation signal such that the motor torque increases continuously in both steering directions up to a maximum motor torque.

16. 16. The method according to any one of claims 1 to 15, wherein the steering mechanism (14) comprises at least one steering assembly (22) in the form of an axle or part of an axle, and in order to determine the stiffness of the axle or part of the axle and / or the play in the steering mechanism (14), at least one wheel (34, 36) is stopped and the electric motor (16) is driven and controlled using the excitation signal such that the motor torque increases continuously in both steering directions up to a maximum motor torque.

17. A computing unit (38) for carrying out the method according to any one of the preceding claims.

18. A steering system (10) comprising a steering mechanism (14), at least one electric motor (16) cooperating with said steering mechanism (14), and a calculation unit (38) according to claim 17.

19. A vehicle (12), in particular a motor vehicle, comprising a steering system (10) according to claim 18.

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