Method for operating a steering system - Patent application

Abstract

A method is proposed 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 humidity characteristic variable is determined that correlates to humidity within the steering system (10), in which the steering mechanism (14) is moved to and / or stopped at a defined test position and the electric motor (16) is driven and controlled with an excitation signal to determine the humidity characteristic variable, and the humidity characteristic variable 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 in which the electric motor (16) is driven and controlled with the excitation signal, and evaluating a change in the motor torque depending on the rotor position angle.

Description

[Technical field]

[0001] Prior Art The present invention relates to a method for operating a steering system, and further to a computing unit for implementing such a method, a steering system comprising such a computing unit and a vehicle comprising such a steering system. [Background 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, a method is proposed in DE 10 2019 212 618 A1, in which the stiffness of at least one steering assembly and / or the play in the steering mechanism are determined in an automated manner. 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 the electric motor. However, in this case, no determination of the humidity characteristic variable is made. Furthermore, the steering mechanism is not moved into a defined test position 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 unfavorable consequences in certain circumstances.

[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, no determination of the humidity characteristic variable is performed. Furthermore, 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 in this case can only be determined 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 determining the humidity in the steering system. This object is achieved by the features of claims 1, 16, 17 and 18, 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 Here, a method, in particular a computer-implemented method, for operating a steering system of a vehicle, the steering system including a steering mechanism and at least one electric motor cooperating with said steering mechanism, in which a humidity characteristic variable correlating to the humidity in the steering system is determined, in particular automatically and / or automated, in which, in order to determine the humidity characteristic variable, the steering mechanism is moved to a defined test position and / or stopped in said test position, the electric motor is driven and controlled using an excitation signal, and the humidity characteristic variable is determined by monitoring 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 using the excitation signal, and evaluating the change in the motor torque depending on the rotor position angle. Thereby, in this embodiment, the steering mechanism is positioned and / or stopped in a test position in a first method step, in a second method step the steering system is excited by controlling the electric motor with an excitation signal, in particular 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. The positioning of the steering mechanism in the test position can in this context be performed, for example, manually by a vehicle occupant and / or driver or automatically and / or automatically by controlling the corresponding electric motor. Furthermore, the above three method steps for determining the humidity characteristic variable can be repeated in a fourth method step for at least one further test position different from the test position. This repetition can here in particular also apply to the same steering assembly or to a further steering assembly different from the steering assembly. This embodiment allows advantageously to improve the determination of the humidity in the steering system. In particular, this allows additional information on the humidity in the steering system to be obtained without additional sensors, such as humidity sensors. Furthermore, the efficiency, in particular the inspection efficiency, performance efficiency, component efficiency, energy efficiency and / or cost efficiency, can be improved, and further, in particular the operational safety of the steering system can be increased.Furthermore, the humidity characteristic variable can be advantageously determined both in the low load range and in the high load range.

[0008] 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.

[0009] The vehicle further comprises at least one computing unit arranged to carry out 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 the humidity characteristic variable. Furthermore, the computing unit is arranged to drive the electric motor. Furthermore, the computing unit may also be arranged to drive the locking mechanism. In this embodiment, the computing unit is arranged at least to drive 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 the electric motor with the excitation signal, and to evaluate the change in the motor torque as a function of the rotor position angle. Furthermore, the calculation unit may be arranged to move the steering mechanism into a defined test position, in particular by controlling the electric motor and / or to stop it in the test position, in particular by controlling the locking mechanism. Preferably, the calculation unit is integrated here in a control device of the vehicle and / or in a control device of the steering system, in particular in the form of a steering control device. "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 the humidity in the steering system can be determined. In this embodiment, the humidity characteristic variable can be determined directly here by evaluating the change in the motor torque as a function of the rotor position angle. However, preferably, exploitation is made of the fact that the stiffness of at least one steering assembly of the steering mechanism and / or the play in the steering mechanism change or can change as a function of the humidity in the steering system.Thus, in a first step, the stiffness of at least one steering assembly and / or the play in the steering mechanism can be determined by evaluating the change in the motor torque depending on the rotor position angle, and subsequently, in a second step, the stiffness of at least one steering assembly and / or the play in the steering mechanism can be used to determine the humidity characteristic variable. "Provided" is understood to mean, in particular, specially programmed, designed and / or equipped. Where an object is provided for a particular function, it is understood to mean, in particular, that the object fulfills and / or performs this particular function in at least one application and / or operating state.

[0010] It is further preferably proposed that the humidity characteristic variable is determined using the derivative of the motor torque according to the rotor position angle or a 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.

[0011] In a further embodiment, it is proposed that the change in the motor torque is compared with a reference value as a function of the rotor position angle in order to determine the humidity characteristic variable, which makes it possible to provide a particularly favorable and simple evaluation algorithm.

[0012] It is further proposed that when determining the humidity characteristic variable, 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, which can be used to determine the humidity characteristic variable, usually have a non-linear relationship. However, in the present embodiment, it has been realized that even when using a corresponding linearization, a relatively accurate and precise prediction of the stiffness and / or play and thus of the humidity in the steering system is possible, while at the same time the calculation effort can be significantly reduced.

[0013] If the current temperature is taken into account when determining the humidity characteristic variable, the evaluation result can be made even more accurate. 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 that is preferably integrated into the steering actuator system can be used to determine the current temperature, which can preferably minimize additional costs.

[0014] It is further proposed that the determination of the humidity characteristic variable is carried out in the high load range, where the electric motor is driven with an excitation signal such that the motor torque is in the upper half of the nominal range of the electric motor, which makes it possible to achieve a particularly accurate evaluation by carrying out the evaluation in a range that is particularly relevant for humidity in the steering system.

[0015] According to a particularly preferred embodiment, it is proposed that the electric motor is controlled by means of the excitation signal in such a way that the motor torque increases continuously, in particular up to a defined and / or definable maximum motor torque, for example +5 Nm, thus achieving a particularly quasi-static excitation. This makes it possible, in particular, to achieve an excitation of the steering system that is particularly simple in terms of control technology. Preferably, the electric motor is controlled in this case by means of a ramp-like signal, whereby the excitation signal increases 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 takes place 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 by means of 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] A particularly high operational safety can be achieved, in particular, if at least one control parameter of a steering control device of the steering system, in particular for the drive control of the electric motor, is adjusted on the basis of the determined humidity characteristic variable, in particular so that a humidity-sensitive control parameter can be adaptively adjusted on the basis of the determined humidity characteristic variable. The steering control device, in this case preferably has an electrical connection to the computing unit, and is particularly preferably integrated in the control device of the vehicle and / or in the control device of the steering system.

[0017] It is further proposed that the humidity characteristic variable is compared with a threshold value, whereby safety measures are initiated if the humidity characteristic variable falls below or exceeds the threshold value, 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 reduction in the driving mode, for example in the form of a reduction in the maximum vehicle speed, thereby in particular achieving a warning effect and further increasing operational safety.

[0018] The humidity characteristic variable can be determined, for example, during a driving mode of the vehicle. However, it is preferably proposed that the humidity characteristic variable is determined when the vehicle is stationary and / or when 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 prevent irritation of the driver and / or passengers during driving.

[0019] It is further proposed that the humidity characteristic variable 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 said humidity characteristic variable, whereby changes in particular in the humidity characteristic variable can be preferably quickly identified and the operational safety of the vehicle can be further increased.

[0020] According to an embodiment, it is proposed that the steering mechanism comprises at least one steering assembly in the form of a servo train, whereby, for determining the humidity characteristic variable, 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. Furthermore, the above method steps can be repeated in a further method step 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 humidity characteristic variable, 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 controlled by means of a further excitation signal, in particular a further excitation signal equivalent to the 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. Alternatively, however, the repetition in further method steps can also apply to a further steering assembly different from the steering assembly, whereby in a particularly advantageous manner the humidity characteristic variable can be determined in particular in the region of the servo train.

[0021] 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 humidity characteristic variable, the sensor train is stopped in the 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. Furthermore, the above method steps can essentially be repeated in further method steps for at least one further test position different from the test position. This allows the humidity characteristic variable to be determined in a particularly preferred manner, in particular in the region of the sensor train.

[0022] Furthermore, according to a further embodiment, it is proposed that the steering mechanism comprises at least one steering assembly in the form of an axle or part of an axle, where, for determining the humidity characteristic variable, at least one wheel is stopped, in particular mechanically, for example by controlling a locking mechanism, and the electric motor is controlled with 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. Furthermore, the above method steps can also be repeated in this case for at least one further test position different from the test position in a further method step. In this connection, it is for example envisaged that, in particular in a further method step for determining the humidity characteristic variable, at least one further wheel, in particular a further wheel opposite the first wheel, is stopped, in particular mechanically, for example by controlling a locking mechanism, and the electric motor is controlled with an excitation signal such that the motor torque increases continuously in both steering directions up to a maximum motor torque in both steering directions. However, 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 humidity characteristic variable, in particular in the axle or in a part of the axle region.

[0023] 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.

[0024] 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]

[0025] [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] FIG. 1 is an exemplary pictorial diagram showing various signals for determining a humidity characteristic variable that correlates with humidity within a steering system. [Figure 2b] FIG. 1 is an exemplary pictorial diagram showing various signals for determining a humidity characteristic variable that correlates with humidity within a steering system. [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

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] Usually, only a small part of mechanical anomalies that may occur during the operation of the vehicle 12 or steering system 10 are detected in an automated manner, whereas the majority of such anomalies must be found out by the driver himself. However, this fact may become more and more problematic in the future, in particular for automated and / or autonomously driven vehicles and / or steering systems in the form of steer-by-wire steering systems. Determining the humidity in the steering system 10 here plays a particularly important role, since humidity of this kind may have particularly critical effects here.

[0036] Therefore, in order to improve the humidity determination and / or to increase the operating safety, a corresponding method is proposed in the following for operating the steering system 10. In the present embodiment, here in particular the calculation unit 38 is arranged to carry out the method and for this purpose comprises a computer program with corresponding program code means.

[0037] In the present embodiment, in order to determine a humidity characteristic variable that correlates with the humidity in the steering system 10, the steering mechanism 14 is first moved into a defined test position and / or stopped in the test position. Preferably, the humidity characteristic variable is determined here with the vehicle 12 at a standstill and / or with the engine of the vehicle 12 switched 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.

[0038] The electric motor 16 is then controlled with the excitation signal. In this embodiment, the electric motor 16 is controlled with the 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. Furthermore, the electric motor 16 is driven and controlled using an excitation signal such that the motor torque is in the upper half of the nominal range of the electric motor 16, so that the determination of the humidity characteristic variable is performed in the high load range.

[0039] The humidity characteristic variable 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 case, in the present embodiment, 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 humidity characteristic variable (see also FIG. 2b).

[0040] Advantageously, exploitation is made here of the fact that the stiffness of at least one steering assembly 18, 20, 22 of the steering mechanism 14 and / or the play in the steering mechanism 14 changes or can change depending on the humidity in the steering system 10, in particular due to changes in the properties of plastic parts such as the belt and / or the screw wheel. Thus, in a first step, the stiffness of at least one steering assembly 18, 20, 22 and / or the play in the steering mechanism 14 can be determined by evaluating the change in the motor torque depending on the rotor position angle, followed by using the stiffness of at least one steering assembly 18, 20, 22 and / or the play in the steering mechanism 14 in a second step to determine a humidity characteristic variable. However, alternatively, the humidity characteristic variable can also be determined directly by evaluating the change in the motor torque depending on the rotor position angle. In this case, the determination of the stiffness and / or the play can therefore be omitted.

[0041] Advantageously, linearization can also be used when determining the humidity characteristic variable. In this connection, it must be taken into account that the stiffness to be determined and / or the play to be determined, which can be used to determine the humidity characteristic variable, usually have a non-linear relationship. However, in this 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, and thus the humidity in the steering system 10, is possible while the calculation effort can be significantly reduced.

[0042] To improve the accuracy of the measurement, the current temperature can also be taken into account when determining the humidity characteristic variable. In this connection, in particular, the fact that the stiffness of 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. This therefore also applies to the humidity characteristic variable. 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.

[0043] Then, once the humidity characteristic variable has been determined, various actions may be performed and / or initiated depending on the determined value.

[0044] For example, at least one control parameter of the steering control device 26 can be adjusted based on the determined humidity characteristic variable, whereby preferably a humidity-sensitive control parameter can be adaptively adjusted based on the determined humidity characteristic variable.

[0045] Furthermore, the humidity characteristic variable can be compared with a threshold value, whereby if the humidity characteristic variable falls below or exceeds the threshold value, safety measures are initiated, which may include at least the generation of an instruction message in the vehicle and / or the generation of an instruction message on an external electronic device, for example in the form of a workshop visit reminder, and / or a reduction in the driving mode, for example in the form of a reduction in the maximum vehicle speed.

[0046] Furthermore, in this embodiment, the humidity characteristic variable is determined at regular time intervals, for example at the start-up or shutdown of each system, in order to monitor changes in the humidity characteristic variable, which allows preferably rapid recognition of changes in the humidity characteristic variable and further increases 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.

[0047] 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.

[0048] According to a first embodiment, for determining the humidity characteristic variables, in particular in the region of the first steering assembly 18 or the servo train, the steering adjustment element 28 is positioned in the region of the 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 increases continuously in the direction of the mechanical end stop 30 up to a maximum motor torque. The position of the steering adjustment element 28 in the region of the mechanical end stop 30 therefore corresponds in this case to the test position. To position the steering adjustment element 28 in the test position, the steering 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 at a constant movement speed (approximately 10 mm / s to 40 mm / s) in the direction of the mechanical end stop 30 until the test position is reached or until 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 / c 1 =(1 / c Servo )+(1 / c A ) (1) applies.

[0049] 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. The stiffness of the first steering assembly 18 or the servo train can then be used to determine the humidity characteristic variable, in particular in the region of the first steering assembly 18 or the servo train.

[0050] 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 humidity characteristic variable can now be carried out using the above-mentioned methodology.

[0051] According to a second embodiment, in order to determine the humidity characteristic variable, in particular in the region 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 locking mechanism 46 or, more precisely, by controlling the steering lock 48, 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 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 locking mechanism 46. 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 then be determined. Here, the following formula is used: 1 / c 2 =(1 / c Sensor )+(1 / c Servo ) (2) applies.

[0052] Here, c 2 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). This stiffness of the second steering assembly 20 or sensor train can then be used to determine the humidity characteristic variable, in particular in the region of the second steering assembly 20 or sensor train. Repetition of the method steps can be omitted in this case, since excitation is performed in both steering directions as described above.

[0053] According to a third embodiment, in order to determine the humidity characteristic variable, in particular in the third steering assembly 22 or in the axle or in a part of the axle region, 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 in which it can rotate freely, for example on a lift platform. The position of the wheels 34, 36 in the stopped state therefore corresponds in this case 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 / c 3 =(1 / c FZ )+(1 / c Servo ) (3) applies.

[0054] Here, c 3 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 the servo train. When the stiffness of the first steering assembly 18 or the servo train has been 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). This stiffness of the third steering assembly 22 or the axle or part of the axle can then be used to determine the humidity characteristic variable, in particular in the area of ​​the third steering assembly 22 or the axle or part of the axle.

[0055] 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 evaluation of the humidity characteristic variable can again be carried out using the methodology described above.

[0056] 2a and 2b show exemplary diagrams of various signals for determining the humidity characteristic variable. The example shown in Fig. 2a and 2b is here exemplarily limited to the first steering assembly 18 and the stiffness of the first steering assembly 18.

[0057] In Fig. 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. Curve 60 shows the course, in particular the linearized course, of the motor torque as a function of the rotor position angle in the dry state of the steering system 10. Curve 62 shows the course, in particular the linearized course, of the motor torque as a function of the rotor position angle in the wet state of the steering system 10.

[0058] Area 64 shows diagrammatically an exemplary course of the motor torque as a function of the rotor position angle for determining a humidity characteristic variable in the region of the first steering assembly 18 or the servo train.

[0059] 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 shown. Curve 70 shows the course of the stiffness as a function of the rotor position angle in the dry state of the steering system 10. Curve 72 shows the course of the stiffness as a function of the rotor position angle in the wet state of the steering system 10. To determine curves 70 and 72, 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.

[0060] The area 74 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, ie, in the direction of the mechanical end stop 30 .

[0061] 2a and 2b, it can be seen that the course of the curves 60, 62 or 70, 72 varies depending on the humidity in the steering system 10. This fact can be used to determine a humidity characteristic variable.

[0062] Finally, FIG. 3 shows an exemplary flow chart with the main method steps of a method for operating the steering system 10.

[0063] 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.

[0064] 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 a quasi-static excitation is achieved.

[0065] In a subsequent method step 84, the 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 the difference quotient from the motor torque and the rotor position angle. This system response can then be used to determine the humidity characteristic variable.

[0066] Then, in the subsequent method step 86, depending on the determined humidity characteristic variable, 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.

[0067] 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 humidity characteristic variable correlating to humidity within the steering system (10) is determined, comprising: In order to determine the humidity characteristic variable, 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; The method includes: determining the humidity characteristic variable by monitoring a motor torque and a rotor position angle of the electric motor during a period in which the electric motor is driven and controlled 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 humidity characteristic variable 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 the motor torque is compared with a reference value (24) in dependence on the rotor position angle in order to determine the humidity characteristic variable.

4. 4. The method according to claim 1, wherein linearization is used in determining the humidity characteristic variable.

5. 5. The method according to claim 1, wherein the current temperature is taken into account when determining the humidity characteristic variable.

6. 6. The method according to claim 1, wherein the determination of the humidity characteristic variable is performed in a high load range and the electric motor (16) is driven and controlled using an excitation signal such that the motor torque is in the upper half of the nominal range of the electric motor (16).

7. 7. The method according to any one of claims 1 to 6, wherein the electric motor (16) is driven and controlled by means of an excitation signal such that the motor torque increases continuously up to a maximum motor torque.

8. 8. The method according to claim 7, 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.

9. 9. The method according to claim 1, wherein at least one control parameter of a steering control device (26) of the steering system (10), in particular for controlling the drive of the electric motor (16), is adjusted based on the determined humidity characteristic variable.

10. 10. The method according to any one of the preceding claims, wherein the humidity characteristic variable is compared to a threshold value and a safety measure is initiated if the humidity characteristic variable falls below or exceeds the threshold value.

11. 11. The method according to any one of the preceding claims, wherein the humidity characteristic variable is determined in a stationary state of the vehicle (12) and / or in an engine-off state of the vehicle (12).

12. 12. The method according to any one of the preceding claims, wherein the humidity characteristic variable is determined at regular time intervals to monitor changes in the humidity characteristic variable.

13. 13. 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, 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) to determine the humidity characteristic variable, 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.

14. 14. The method according to claim 1, 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 humidity characteristic variable, 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.

15. 15. The method according to any one of claims 1 to 14, wherein the steering mechanism (14) includes at least one steering assembly (22) in the form of an axle or part of an axle, and wherein, to determine the humidity characteristic variable, 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.

16. A computing unit (38) for carrying out the method according to any one of claims 1 to 15.

17. 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 16.

18. A vehicle (12), in particular a motor vehicle, comprising a steering system (10) according to claim 17.

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