Method for determining controller steering torque predefined for steering actuator of motor vehicle

Abstract

The invention relates to a method for determining a controller steering torque specified for a steering actuator. The controller steering torque is determined by means of a double controller, which comprises an outer controller and an inner controller connected downstream of the outer controller. A steering angle adjusted by a steering actuator in the motor vehicle is supplied to the outer controller as a control variable. The outer regulator outputs a target value of a time derivative of the steering angle as an execution variable. A pre-control model steering torque is provided to an inner regulator for calculating an execution variable, the regulator steering torque being determined in real time as a function of the physical behavior of the steering actuator. The physical state of the steering device is modeled by having an external stimulus. The time-dependent steering angle is a free parameter. At least one further spring damper model parameter is taken into account for describing the spring damper. At least one time-dependent spring damper model parameter is estimated by means of a recursive fitting calculation, from which the pre-control model steering torque is calculated.

Description

Technical Field

[0001] The invention relates to a method for determining a controller steering torque predefined for a steering actuator of a motor vehicle. The invention also relates to a control unit which is configured / programmed to carry out the method. Finally, the invention also relates to a motor vehicle having such a control unit. Background Art

[0002] In connection with so-called steering angle or lane keeping assist of motor vehicles, it is known to determine the steering angle to be set in the steering actuator of the steering device taking into account various factors so that the motor vehicle follows a predefined trajectory when traveling over the roadway.

[0003] For this purpose, methods for determining the steering torque to be adjusted in the steering actuator are known. Such conventional methods usually work with a regulation having a one-stage or two-stage regulator and are described, for example, in EP 3 321 149 B1, US 2019 / 0308664 A1 and DE 10 2014 208 786 A1.

[0004] The problem with this conventional approach is that the physical behavior of the steering actuator influences the control and thus the actual steering behavior of the steering actuator to a considerable extent, which can have a negative impact on the control behavior of the controller.

[0005] The corresponding modeling of the physical behavior of the steering actuator, which is performed in the controller in the form of a so-called forward model in order to improve the control performance, has proven to be relatively inaccurate in practice and does not take into account changes in the physical behavior of the steering actuator during the service life of the steering device. Summary of the invention

[0006] It is therefore an object of the present invention to provide an improved method for determining a controller steering torque predefined for a steering actuator of a motor vehicle, in which method the above-mentioned disadvantages are at least partially, ideally or even completely eliminated.

[0007] This object is achieved by the method according to the invention. Preferred embodiments are given below.

[0008] The basic idea of ​​the invention is therefore to determine a controller steering torque for a steering actuator by means of a dual controller, wherein an outer controller uses a steering angle set by a steering actuator in the motor vehicle as a controlled variable and an inner controller uses a time derivative of the steering angle as a controlled variable.

[0009] According to the invention, it is proposed that a pre-control model steering torque is provided as an additional input variable for the inner regulator, with the aid of which the instantaneous physical behavior of the steering actuator is taken into account in real time. It is also proposed that the physical behavior of the steering device is modeled in a time-dependent manner by means of a rotary single-mass spring damper with external excitation and different spring-damper model parameters. In order to calculate the steering torque to be supplied to the pre-control model of the inner regulator, the selected time-dependent spring-damper model parameters are estimated by means of a recursive fitting calculation (recursive Ausgleichsrechnung). The control characteristics of the two-stage regulator can be significantly improved by taking into account the physical behavior of the steering actuator, which is proposed here and is important for the invention. This has a favorable effect on the steering control of auxiliary motor vehicles or even the automatic driving of motor vehicles.

[0010] The method according to the invention is used to determine a controller steering torque predefined for a steering actuator of a motor vehicle. According to the method, the controller steering torque sought is determined by means of a dual controller, which includes an outer controller and an inner controller connected after the outer controller. The steering angle adjusted by the steering actuator in the vehicle is supplied to the outer controller as a control variable. The outer controller outputs a target value of the time derivative of the steering angle as a control variable, which is used as a control variable for the inner controller. In addition, a pre-control model steering torque is supplied to the inner controller for calculating an actuating variable, which is determined in real time according to the physical behavior of the steering actuator.

[0011] The physical state of the steering system is modeled here by a rotating single mass spring-damper with external excitation. The time-dependent steering angle is a free parameter of the model. In addition, at least one time-dependent spring-damper model parameter is taken into account for the physical description of the spring-damper. According to the invention, at least one time-dependent spring-damper model parameter is estimated by means of a recursive fitting calculation. From this estimate, the pilot control model steering torque to be provided to the internal controller is determined.

[0012] At least one time-dependent spring-damper model parameter is estimated by means of a recursive fitting calculation. From this estimation, a pilot control model steering torque is calculated which is provided to the internal controller.

[0013] In a preferred embodiment of the method according to the invention, the pilot control model steering torque is calculated as part of a control loop of the internal controller. This makes it possible to increase the control accuracy of the internal controller.

[0014] Particularly preferably, the pilot control model steering torque is calculated as a function of the target value of the steering angle, the controller steering torque calculated by the internal controller and the driver steering torque applied by the vehicle driver. This results in a particularly precise control result. The driver steering torque can be dependent on the steering angle and other system states.

[0015] According to a further preferred embodiment, the following constants used in a rotary single mass spring damper are estimated as time-dependent variables as spring-damper model parameters: time-dependent rotational moment of inertia J(t), time-dependent damping D(t), time-dependent stiffness(t) and time-dependent offset “Offs”.

[0016] In a preferred embodiment, the inner controller uses the steering angle change as the control variable and calculates the desired controller steering torque not only based on the determined target-actual deviation of the control variable but also based on the determined pilot control model steering torque as the control variable. Taking into account the pilot control model steering torque leads to a significantly improved control behavior of both controllers.

[0017] In another preferred embodiment, the external regulator can use the steering angle adjusted in the steering actuator as the master variable. In this embodiment, the external regulator also outputs the steering angle change as the execution variable.

[0018] In the method according to the invention, the front spring-damper model parameters are preferably estimated in real time. It is thus possible to react to changes in the physical behavior of the steering actuator that occur in real time, thereby improving the control characteristics of both controllers.

[0019] Particularly advantageously, the pilot control model steering torque can be ascertained here from the estimated stiffness and the estimated offset as a function of an externally predefined target steering angle.

[0020] According to an advantageous development of the method according to the invention, at least one spring-damper model parameter J(t), D(t), C(t), Offs(t) is determined with the aid of a Kalman filter. The spring-damper model parameter can be estimated particularly accurately, in particular in real time, with the aid of a Kalman filter.

[0021] According to an advantageous development of the method according to the invention, the externally excited single-mass-spring damper is described by the following differential equation:

[0022]

[0023] In a particularly preferred variant of the method according to the invention, the external excitation of the spring damper can be determined by the sum of the driver's steering torque adjusted by the driver and the regulator steering torque pre-set to the steering actuator. In this variant, the driver's steering torque adjusted by the driver is also considered.

[0024] The invention also relates to a control unit for a motor vehicle, which is configured / programmed to carry out the method proposed above. The advantages of the method according to the invention explained above are therefore transferred to the controller according to the invention.

[0025] The invention also relates to a motor vehicle having two front wheels and two rear wheels and a steering actuator for adjusting a steering angle in the front wheels which determines the direction of travel of the motor vehicle. The motor vehicle also comprises a sensor device for determining the instantaneously adjusted steering angle. For this purpose, the sensor device can comprise a steering angle sensor. According to the invention, the motor vehicle according to the invention also comprises the aforementioned control device and therefore according to the invention, which interacts with the steering actuator and the sensor device. The advantages of the method according to the invention explained above are thus transferred to the motor vehicle according to the invention.

[0026] Further important features and advantages of the invention emerge from the dependent claims, the drawings and the associated description of the figures with reference to the drawings.

[0027] Of course, the features mentioned above and those yet to be explained below can be used not only in the respectively stated combination but also in other combinations or alone without departing from the scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Preferred exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description.

[0029] Here they are schematically shown:

[0030] Figure 1 : An exemplary structure of a controller according to the invention in the form of a flow chart in the form of a circuit diagram for the method according to the invention;

[0031] Figure 2 : A schematic diagram of the calculation of the steering torque of the pre-control model is explained below. DETAILED DESCRIPTION

[0032] Figure 1 An exemplary structure of a control unit 10 according to the invention for a motor vehicle 20, which is only schematically shown, is shown in the form of a flow chart in the form of a circuit diagram. The control unit 10 is provided for controlling a steering actuator 21 of the motor vehicle 20, by means of which a steering angle δ which determines the driving direction of the motor vehicle can be adjusted. In addition, the control unit 10 is connected to a sensor device 22 of the steering actuator 21 in the form of data transmission for determining the instantaneously adjusted steering angle δ. For this purpose, the sensor device 22 can include a suitable steering angle sensor (not shown).

[0033] As explained above, the method according to the invention is used to determine a controller steering torque SteerTrq predefined for a steering actuator 21 of a motor vehicle 20 SAC Then, the steering actuator 21 can generate the steering torque SteerTrq SAC is converted into the associated steering angle δ.

[0034] According to the method, the controller steering torque SteerTrq is sought SAC The ascertainment is carried out using a dual regulator 1 which comprises an outer regulator 2 a and an inner regulator 2 i connected downstream of the outer regulator 2 a .

[0035] The steering angle δ(t) set by the steering actuator 21 in the motor vehicle 20 is supplied as a control variable to the external controller 2a. The actual value of the steering angle δ is compared with the target value δ in the conventional manner. Target The comparison is made and the control deviation (δ-δ) is calculated by forming the difference Target ).according to Figure 1 , the external regulator 2a outputs the time derivative d / dtδ for the steering angle Target The actual time derivative of the steering angle d / dtδ(t) is compared with the target value d / dtδ provided by the external controller 2a. Target (t) is compared and the control deviation (d / dtδ(t)-d / dtδ) is calculated by forming a difference similar to the external controller 2a. Target (t)). Figure 1 As shown in FIG. 1 , the internal controller 2i calculates the desired controller steering torque SteerTrq SAC As the execution variable, the controller steering torque is Figure 1 As can be seen in FIG. 2 , it is output to the steering actuator 21 .

[0036] In order to calculate the regulator steering torque SteerTrq SAC According to the figure, the pre-control model steering torque SteerTrq is supplied to the inner regulator 2i FF The pilot control model steering torque is determined as an output variable by a computing unit 3 connected to the control loop of the inner controller 2 i as a function of the physical behavior of the steering actuator 21 in a time-dependent manner and in particular in real time.

[0037] Here, the physical state of the steering actuator 21 is controlled by an external excitation “T mot (t) SAC+DRIVER " is a rotating single mass-spring damper model. The external excitation of the spring damper is "T mot (t) SAC+DRIVERHere, the driver steering torque “SteerTrq” applied by the driver of the motor vehicle 20 Driver " and the controller steering torque "SteerTrq" pre-set to the steering actuator 21 SAC "The sum of the two parameters "SteerTrq Driver ” and “SteerTrq SAC ” is supplied to the computing unit 3 as an input variable.

[0038] When modeling the spring damper, the time-dependent steering angle δ(t) is a free parameter. In addition, four time-dependent spring damper model parameters J(t), D(t), C(t), Offs(t) are considered for the modeling of the physical behavior of the spring damper. Thus, the known variables used to describe the rotary single-mass spring damper, namely the time-dependent moment of inertia J=J(t), the time-dependent damping D=D(t), the time-dependent stiffness C=C(t) and the time-dependent deflection Offs(t) are used as time-dependent variables as spring damper model parameters. The single-mass spring damper with external excitation is described here by the following differential equation:

[0039]

[0040] The two spring-damper model parameters J and D form the transient, ie, dynamic, behavior of the steering actuator, and the parameter C forms the quasi-static relationship between the steering angle δ and the steering torque acting on the steering actuator 21 .

[0041] The values ​​of the spring-damper model parameters J(t), D(t), C(t), Offs(t) are estimated by means of a recursive fitting calculation. The estimation of the spring-damper model parameters J(t), D(t), C(t), Offs(t) is done in real time. Finally, the pre-control model steering torque SteerTrq provided to the internal regulator 2i is calculated from the estimation. FF .

[0042] Using the steering angle change d / dt Target The internal controller 2i takes the target value of the steering torque SteerTrq as the control variable into consideration when considering the determined pre-control model FF The desired controller steering torque SteerTrq supplied to the steering actuator 21 is calculated as the actuating variable. SAC Therefore, in addition to the steering angle change d / dtδ, the pre-control model steering torque SteerTrq is supplied to the inner regulator 2i FF As a control variable, the pilot control model steering torque is dependent on the dynamic physical behavior of steering actuator 21 , as explained above.

[0043] The externally excited single mass-spring damper is described here by the following differential equation:

[0044]

[0045] In the following Figure 2 The schematic diagram of the calculation unit 3 schematically illustrates, for example, the calculation of the pilot control model steering torque.

[0046] For the recursive fitting calculation, the four spring-damper model parameters J, D, C, Offs are considered as vector variables Z = Z(t):

[0047] Z(t)=[J(t) D(t) C(t) Offs(t)]

[0048] Steering angle δ(t) and its first and second time derivatives The input variable for the calculation unit can also be expressed as a vector variable θ:

[0049]

[0050] The recursive calculation of Z(t) can be performed according to the following equation:

[0051]

[0052] The Kalman filter can be used to estimate the values ​​of the four spring damper model parameters J(t), D(t), C(t), and Offs(t). Then, in the above equation, K Gain is the Kalman gain defined recursively as follows:

[0053]

[0054] In the above equation, P(t) i is a positive definite covariance matrix defined as follows

[0055] Kovarianz-Matrix):

[0056]

[0057] Here, λ is a weighting factor, which is also called “forgetting factor” by technicians, ie, 0<λ<=1 applies.

[0058] The recursive estimated parameter Z(t) described above can be expressed as Figure 2 As can be seen in FIG. 1 , the steering torque SteerTrq of the pilot control model is calculated or estimated by the calculation unit 3 as follows: FF :

[0059] SteerTrqFF (t)=C(t)*δ Target (t)+Offs(t)

[0060] Particularly advantageously, the estimated stiffness C EST and the estimated offset Offs_ EST According to the externally specified target steering angle δ Target Obtain the steering torque SteerTrq of the pre-control model FF .

Claims

1. A method for determining a controller steering torque (SteerTrq) predefined for a steering actuator (21) of a motor vehicle (20) SAC (t)) method, According to the method, the controller steering torque (SteerTrq SAC (t)), the dual regulator comprises an outer regulator (2a) and an inner regulator (2i) connected after the outer regulator (2a), According to the method, the outer controller (2a) is supplied with a steering angle (δ(t)) set by a steering actuator (21) in the motor vehicle as a control variable, According to the method, the external regulator (2a) outputs a target value (d / dtδ) of the time derivative of the steering angle Target ) as an execution variable, the target value is supplied to the internal regulator (2i) as a control variable, According to the method, the inner controller (2i) outputs the desired controller steering torque (SteerTrq SAC (t)) as the execution parameter, - According to the method, a pre-control model steering torque (SteerTrq FF (t)) as the execution parameter for calculating the regulator steering torque (SteerTrq SAC (t)), the pre-control model steering torque is determined in real time according to the physical behavior of the steering actuator (21), According to the method, the physical state of the steering device (21) is modeled by a rotary single mass-spring damper with an external excitation (T mot (t) SAC+DRIVER (t)) and the steering angle (δ) and at least one further spring-damper model parameter (J(t), D(t), C(t), Offs(t)) characterizing the instantaneous physical state of the steering actuator (21), -in, At least one time-dependent spring-damper model parameter (J(t), D(t), C(t), Offs(t)) is estimated by means of a recursive fitting calculation, and -in, The pre-control model steering torque (SteerTrq FF (t)).

2. The method according to claim 1, It is characterized in that The pre-control model steering torque (SteerTrq FF (t)) is calculated as part of the control loop of the inner controller (2i).

3. The method according to claim 1 or 2, It is characterized in that The pre-control model steering torque (SteerTrq FF (t)) according to the target value of the steering angle (δ Target ), the regulator steering torque (SteerTrq calculated by the inner regulator (2i) SAC (t)) and a driver steering torque (SteerTrq) applied by a driver of the motor vehicle (20) SAC +SteerTrq DRIVER )calculate.

4. The method according to any one of claims 1 to 3, It is characterized in that As spring-damper model parameters, the following constants used in a rotary single-mass-spring damper are estimated as time-dependent variables: - moment of inertia (J(t)); and - damping D(D(t)); and - stiffness C(C(t)); and -Offset Offs(t).

5. The method according to any one of the preceding claims, It is characterized in that The estimation is performed in real time.

6. The method according to claim 4 or 5, It is characterized in that The pre-control model steering torque (SteerTrq FF ) is calculated from the estimated stiffness (C_EST) and the estimated offset (Offs_EST) according to the externally predetermined target steering angle (δ Target ) to obtain.

7. The method according to any one of the preceding claims, It is characterized in that At least one spring-damper model parameter (J(t), D(t), C(t), Offs(t)), in particular the spring-damper model parameter (J(t), D(t), C(t), Offs(t)) according to claim 4, is estimated by means of a Kalman filter.

8. The method according to any one of the preceding claims, Features A single mass-spring damper with external excitation is described by the following differential equation:

9. The method according to any one of the preceding claims, It is characterized in that For the recursive fitting calculation, the four spring-damper model parameters J(t), D(t), C(t), and Offs(t) are regarded as vector parameters Z=Z(t).

10. The method according to any one of the preceding claims, It is characterized in that External excitation of the spring-damper (SteerTrq SAC +SteerTrq DRIVER ) by a driver steering torque (SteerTrq) applied by the driver of the motor vehicle (20) SAC +SteerTrq DRIVER ) and a controller steering torque (SteerTrq) predefined for the steering actuator (21) SAC ) and is determined.

11. A controller for a motor vehicle (20), It is characterized in that The controller is configured / programmed to perform a method according to any one of the preceding claims.

12. A motor vehicle having: - Two front wheels and two rear wheels, a steering actuator (21) for adjusting a steering angle (δ) in the front wheels which determines the direction of travel, - a sensor device (22) for determining the instantaneously set steering angle (δ), - A control unit (10) according to claim 11, which cooperates with the steering actuator (21) and the sensor system.

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