Method for determining a control steering torque to be specified to a steering actuator of a motor vehicle

Abstract

The invention relates to a method used to determine a steering torque (SteerTrq) to be specified for a steering actuator (21). SAC According to the method, the steering torque (SteerTrq) is determined by means of a dual controller (1). SAC ) is determined using a dual controller (1). According to the procedure, the controller steering torque (SteerTrq) is determined. SAC ) is determined by means of a dual controller (1) comprising an outer controller (2a) and an inner controller (2i) downstream of the outer controller (2a). The outer controller receives as its controlled variable a steering angle (δ(t)) set by the steering actuator (21) in the vehicle. The outer controller (2a) outputs as its manipulated variable a setpoint d / dt δ Target the time derivative of the steering angle (d / dt δ). Additionally, according to the invention, a feedforward model steering torque (SteerTrq) is provided to the inner controller (2i) for calculating the manipulated variable. FF) supplied, which is determined in real time depending on the physical behavior of the steering actuator (21). The physical state of the steering actuator (21) is determined by a rotary single-mass spring damper with external excitation (Tmot(t) SAC+DRIVER The system is modeled using a time-dependent spring damper model parameter (J(t), D(t), C(t), Offs(t)). At least one further time-dependent spring damper model parameter (J(t), D(t), C(t), Offs(t)) is used to describe the spring damper. According to the invention, the at least one time-dependent spring damper model parameter (J(t), D(t), C(t), Offs(t)) is estimated using recursive least squares calculations. From this estimate, the feedforward model steering torque (SteerTrqFF) to be provided to the internal controller is determined.

Description

[0001] The invention relates to a method for determining a steering torque to be applied to a steering actuator of a motor vehicle. The invention further relates to a control unit configured / programmed to carry out this method. Finally, the invention relates to a motor vehicle with such a control unit.

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

[0003] Methods for determining the steering torque to be set in a steering actuator are known. Such conventional methods generally operate with a single- or two-stage controller and are for example, described in EP 3 321 149 B1, US2019 / 0308664 A1 and DE10 2014 208 786 A1.

[0004] A problem with such conventional methods is that the physical properties of the steering actuator significantly influence the control and thus the actual steering behavior of the steering actuator, which can have a detrimental effect on the control behavior of the controller.

[0005] Corresponding models of the physical properties of the steering actuator, which are implemented in the controller in the form of a so-called forward model to improve control performance, have proven to be comparatively inaccurate in practice and do not take into account changes in the physical properties of the steering actuator over the lifetime of the steering system.

[0006] It is therefore an object of the present invention to provide an improved method for determining a control steering torque to be specified to a steering actuator of a motor vehicle, in which the aforementioned disadvantage is at least partially, ideally even completely, eliminated.

[0007] This problem is solved by the subject matter of the independent patent claims. Preferred embodiments are the subject matter of the dependent patent claims.

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

[0009] According to the invention, it is proposed to provide the inner controller with a feedforward model steering torque as an additional input variable, by means of which the instantaneous physical properties of the steering actuator are taken into account in real time. It is further proposed to model the physical properties of the steering system as a function of time using a rotary single-mass spring damper with external excitation and with various spring damper model parameters. For the calculation of the feedforward model steering torque to be supplied to the inner controller, the selected time-dependent spring damper model parameters are estimated using recursive least squares. By taking the physical properties of the steering actuator into account, as presented here and essential to the invention, the control behavior of the two-stage controller can be significantly improved.This has a beneficial effect on the steering control of the motor vehicle, assisted or even autonomous driving of motor vehicles.

[0010] The method according to the invention serves to determine a steering torque to be applied to a steering actuator of a motor vehicle. According to the method, the desired steering torque is determined using a dual controller comprising an outer controller and an inner controller connected downstream of the outer controller. The outer controller receives a steering angle set by the steering actuator in the motor vehicle as its controlled variable. The outer controller outputs a setpoint of the time derivative of the steering angle as its manipulated variable, which is used as the controlled variable for the inner controller. Additionally, a feedforward model steering torque, determined in real time as a function of the physical behavior of the steering actuator, is supplied to the inner controller for calculating the manipulated variable.

[0011] The physical state of the steering system is modeled by a rotary single-mass spring damper with external excitation. The time-dependent steering angle is a free parameter of the model. Furthermore, at least one other time-dependent spring damper model parameter is used for the physical description of the spring damper. According to the invention, the at least one time-dependent spring damper model parameter is estimated using recursive least squares. From this estimate, the feedforward steering torque to be provided to the internal controller is determined.

[0012] At least one time-dependent spring damper model parameter is estimated using recursive least squares. From this estimate, the feedforward steering torque to be provided to the internal controller is calculated.

[0013] In a preferred embodiment of the method according to the invention, the feedforward model steering torque is calculated as part of the control loop of the inner controller. This increases the control accuracy of the inner controller.

[0014] The preferred approach is to calculate the steering torque using a feedforward model, taking into account the setpoint of the steering angle, the steering torque calculated by the internal controller, and the steering torque applied by the driver. This results in a particularly precise control outcome. The driver's steering torque can depend on the steering angle and other system states.

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

[0016] In a preferred embodiment, the inner controller uses the steering angle change as a reference input and calculates the desired controller steering torque not only based on a determined setpoint-actual deviation of the reference input, but also based on the determined feedforward model steering torque as the manipulated variable. Considering the feedforward model steering torque leads to a significantly improved control behavior of both controllers.

[0017] In another preferred embodiment, the external controller can use the steering angle set in the steering actuator as a reference variable. In this embodiment, the external controller also outputs the change in the steering angle as a manipulated variable.

[0018] In the method according to the invention, the estimation of the preceding spring damper model parameters is preferably carried out in real time. This allows for a response to real-time changes in the physical properties of the steering actuator, thereby improving the control behavior of both controllers.

[0019] Particularly preferably, the pre-control model steering torque can be determined from the estimated stiffness and the estimated offset depending on an externally specified target steering angle.

[0020] According to an advantageous embodiment of the method according to the invention, the at least one spring damper model parameter J(t), D(t), C(t), Offs(t) is determined using a Kalman filter. Using a Kalman filter, said spring damper model parameter can be estimated with particular accuracy, especially in real time.

[0021] According to an advantageous further development of the method according to the invention, the externally excited single-mass spring damper is described by the following differential equation: Jδ¨+Dδ˙+Cδ+Offs=Tmot(t)SAC+Driver

[0022] In a particularly preferred embodiment of the method according to the invention, the external excitation of the spring damper can be determined by the sum of a steering torque set by the driver and the steering torque specified by the controller to the steering actuator. In this embodiment, the steering torque set by the driver is also taken into account.

[0023] The invention further relates to a control unit for a motor vehicle, which is configured / programmed to carry out the method according to the invention described above. The advantages of the method according to the invention, as explained above, are therefore transferred to the control unit according to the invention.

[0024] The invention further relates to a motor vehicle with two front wheels and two rear wheels, as well as a steering actuator for setting a steering angle in the front wheels that determines the direction of travel of the motor vehicle. The motor vehicle also includes sensors for determining the currently set steering angle. For this purpose, the sensors may include a steering angle sensor. According to the invention, the motor vehicle also includes a control unit, described above, which interacts with the steering actuator and the sensors. The advantages of the method according to the invention, as explained above, are therefore transferred to the motor vehicle according to the invention.

[0025] Further important features and advantages of the invention will become apparent from the dependent claims, the drawings and the associated description of the figures based on the drawings.

[0026] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0027] Preferred embodiments of the invention are shown in the drawings and are explained in more detail in the following description.

[0028] They show, schematically: Fig. 1. By way of example, the structure of a control unit according to the invention in the form of a circuit diagram-like flowchart for the method according to the invention, Fig. 2 The following is a diagram illustrating the calculation of the feedforward model steering torque.

[0029] The Fig. Figure 1 shows, in the form of a circuit diagram-like flowchart, an exemplary structure of a control unit 10 according to the invention for a motor vehicle 20, which is only schematically indicated. The control unit 10 is configured to control a steering actuator 21 of the motor vehicle 20, by means of which a steering angle δ, determining the direction of travel of the motor vehicle, can be set. Furthermore, the control unit 10 is connected to a sensor 22 of the steering actuator 21 for data transmission to determine the currently set steering angle δ. For this purpose, the sensor 22 can comprise a suitable steering angle sensor (not shown).

[0030] As explained above, the method according to the invention serves to determine a steering torque SteerTrqSAC to be specified to the steering actuator 21 of the motor vehicle 20. The steering actuator 21 can then convert the determined steering torque SteerTrqSAC into an associated steering angle δ.

[0031] According to the procedure, the desired controller steering torque SteerTrqSAC is determined by means of a dual controller 1, which includes an outer controller 2a and an inner controller 2i connected downstream of the outer controller 2a. The steering angle δ(t) set by the steering actuator 21 in the motor vehicle 20 is supplied to the external controller 2a as the controlled variable. The actual value of the steering angle δ is thereby compared to a setpoint δ in the usual manner. Target compared and the rule deviation (δ - δ) was calculated by taking the difference. Target ) calculated. The external controller 2a outputs according to Fig. 1 as a control variable, a setpoint for the time derivative of the steering angle d / dt δ Target (t), which in turn is provided to the inner controller 2i as the controlled variable. The actual time derivative of the steering angle d / dt δ(t) is thereby compared with the setpoint d / dt δ provided by the outer controller 2a. Target(t) compared and, analogous to the external controller 2a, the control deviation (d / dt δ(t) - d / dt δ) was calculated by difference. Target (t)) is calculated. The internal controller 2i calculates as in Fig. 1 shows the desired control steering torque SteerTrq as the manipulated variable. SAC , which, as in Fig. 1 is identifiable by the steering actuator 21.

[0032] For the calculation of the controller steering torque SteerTrqSAC, a feedforward model steering torque SteerTrq is applied to the inner controller 2i as shown in the figure. FF supplied, which is determined as an output variable by a calculation unit 3 integrated into the control loop of the inner controller 2i, depending on the physical behavior of the steering actuator 21, in a time-dependent manner and in particular in real time.

[0033] The physical state of the steering actuator 21 is here determined by a rotary single-mass spring damper with external excitation “T mot (t) SAC+DRIVER “modeled. The external stimulus “Tmot(t)SAC+DRIVER" The spring damper is defined by the sum of the driver steering torque “SteerTrqDriver” exerted by the driver of the motor vehicle 20 and the control steering torque “SteerTrq” to be specified by the steering actuator 21. SAC “ set. The two parameters “SteerTrq” Driver “ and “SteerTrq” SAC “ are fed to calculation unit 3 as input variables.

[0034] In the modeling of the spring damper, the time-dependent steering angle δ(t) is a free parameter. Furthermore, four time-dependent spring damper model parameters J(t), D(t), C(t), and Offs(t) are used to model the physical properties of the spring damper. These spring damper model parameters are the quantities known for describing the rotational single-mass spring damper: the time-dependent rotational moment of inertia J = J(t), the time-dependent damping D = D(t), the time-dependent stiffness C = C(t), and a time-dependent offset = Offs(t). The externally excited single-mass spring damper is described by the following differential equation: Jδ¨+Dδ˙+Cδ+Offs=Tmot(t)SAC+Driver

[0035] The two spring damper model parameters J and D represent the non-stationary, i.e. dynamic, behavior of the steering actuator, and the parameter C represents the quasi-stationary relationship between the steering angle δ and the steering torque acting on the steering actuator 21.

[0036] The values ​​of the spring damper model parameters J(t), D(t), C(t), and Offs(t) are estimated using recursive least squares. This estimation of the spring damper model parameters J(t), D(t), C(t), and Offs(t) is performed in real time. From this estimate, the feedforward model steering torque SteerTrq, which is provided to the internal controller 2i, is then calculated. FF calculated.

[0037] The target value of the steering angle change d / dt δ Target The internal controller 2i, which uses the controlled variable, is calculated taking into account the determined feedforward model steering torque SteerTrq. FFThe control variable is the desired steering torque SteerTrqSAC, which is to be supplied to the steering actuator 21. In addition to the steering angle change d / dt δ, the inner controller 2i is therefore supplied with the feedforward control model steering torque SteerTrqFF as a reference variable, which, as explained above, depends on the dynamic physical behavior of the steering actuator 21.

[0038] The externally excited single-mass spring damper is described by the following differential equation: Jδ¨+Dδ˙+Cδ+Offs=Tmot(t)SAC+Driver The following section uses the diagram to illustrate the Fig. 2, which schematically shows the calculation unit 3, explains the calculation of the feedforward model steering torque by way of example.

[0039] For the recursive adjustment calculation, the four spring damper model parameters J, D, C, Offs are considered as a vector quantity Z = Z(t): Z(t)=[J(t)D(t)C(t)Offs(t)]

[0040] The steering angle δ(t) and its first and second time derivatives δ̇̇̇̇, δ̈̈ as input variables for the computation unit can also be formulated as a vector quantity θ: θ(t)=[δ¨ δ˙ δ]

[0041] The recursive calculation Z(t) can be performed according to the following equation: Z(t)i=Z(t)i−1+Kgain(t)i(Tmot(t)SAC+Driver−θ(t)TiZ(t)i−1)

[0042] A Kalman filter can be used to estimate the values ​​of the four spring damper model parameters J(t), D(t), C(t), Offs(t). Then, in the preceding equation, K Gain the Kalman gain, defined recursively as follows: Kgain(t)i=P(t)i∗θ(t)i=p(t)i−1θ(t)i(λ+θ(t)Tip(t)i−1θ(t)i)−1

[0043] In the preceding equation, P(t) i the positive definite covariance matrix defined as follows: P(t)i=(I−Kgain(t)iθ(t)Ti)P(t)i−11λ

[0044] Here, λ is a weighting factor, also known to those skilled in the art as the "forgetfulness factor", for which 0 < λ <= 1 applies.

[0045] From the quantity Z(t), which was estimated recursively as explained above, the computational unit 3 can be calculated as in Fig. 2. The pre-control model steering torque SteerTrq is recognizable. FF as follows: SteerTrqFF(t)=C(t)*δTarget(t)+Offs(t)

[0046] Particularly preferably, the estimated stiffness C_EST and the estimated offset OFFS_EST can be used as a function of an externally specified target steering angle δ. target The pre-control model steering torque SteerTrqFF is determined. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] EP 3 321 149 B1

[0003] US 2019 / 0308664 A1

[0003] DE 10 2014 208 786 A1

[0003]

Claims

[1] Method for determining a controller steering torque (SteerTrq SAC (t)), - according to which the controller steering torque (SteerTrq SAC (t)) is determined by means of a dual controller (1) comprising an outer controller (2a) and an inner controller (2i) connected downstream of the outer controller (2a), - according to which the external controller (2a) is supplied with a steering angle (δ(t)) set by the steering actuator (21) in the motor vehicle as a controlled variable, - according to which the external controller (2a) uses as a control variable a setpoint value of the time derivative of the steering angle (d / dt δ Target ), which is fed to the inner controller (2i) as a controlled variable, - according to which the inner controller (2i) provides the desired controller steering torque (SteerTrq SAC (t)) - according to which the inner controller (2i) for calculating the controller steering torque (SteerTrqSAC (t)) as a control variable a feedforward model steering torque (SteerTrq FF (t)) is provided, which is determined in real time as a function of the physical behavior of the steering actuator (21), - according to which the physical state of the steering device (21) is determined by a rotational single-mass spring damper with external excitation (Tmot(t) SAC+DRIVER (t)) and with the steering angle (δ) and with at least one further spring damper model parameter (J(t), D(t), C(t), Offs(t)) characterizing the current physical state of the steering actuator (21), - wherein the at least one time-dependent spring damper model parameter (J(t), D(t), C(t), Offs(t)) is estimated by means of recursive compensation calculation, and - where the pre-control model steering torque (SteerTrq FF (t)) is calculated. [2] Method according to claim 1, characterized bythat the feedforward model steering torque (SteerTrq FF (t)) is calculated as part of the control loop of the inner controller (2i). [3] Method according to claim 1 or 2, characterized by that the feedforward model steering torque (SteerTrqFF(t)) depends on the setpoint of the steering angle (δ Target ), the controller steering torque (SteerTrqSAC(t)) calculated by the inner controller (2i) and the driver steering torque (SteerTrq SAC +SteerTrq DRIVER ) is calculated. [4] Method according to one of claims 1 to 3, characterized by that the following constants used in the rotational single-mass spring damper are estimated as time-dependent quantities as spring damper model parameters: - the rotational moment of inertia (J(t)); and - the damping D (D(t)); and - the stiffness C (C(t); and - an offset OFFS(t). [5] Method according to one of the preceding claims, characterized by that the estimation is carried out in real time. [6] Method according to claim 4 or 5, characterized by that the estimated stiffness (C_EST) and the estimated offset (OFFS_EST) depending on an externally specified target steering angle (δ target ) the feedforward model steering torque (SteerTrq FF ) is determined. [7] Method according to one of the preceding claims, characterized by that the at least one spring damper model parameter (J(t), D(t), C(t), OFFS(t)), in particular the spring damper model parameters (J(t), D(t), C(t), OFFS(t)) according to claim 4, are estimated by means of a Kalman filter. [8] Method according to one of the preceding claims, characterized by that the externally excited single-mass spring damper is described by the following differential equation: Jδ¨+Dδ˙+Cδ+Offs=Tmot(t)SAC+Driver [9] Method according to one of the preceding claims, characterized by that for the recursive compensation calculation the four spring damper model parameters J(t), D(t), C(t), Offs(t) are considered as vector quantity Z = Z(t). [10] Method according to one of the preceding claims, characterized by that the external excitation (SteerTrq SAC +SteerTrq DRIVER ) of the spring damper by the sum of a driver steering torque (SteerTrq SAC +SteerTrq DRIVER ) and the controller steering torque (SteerTrq SAC ) is specified. [11] Control unit for a motor vehicle (20), characterized by that the control device is set up / programmed to carry out the method according to one of the preceding claims. [12] Motor vehicle, - with two front wheels and two rear wheels, - with a steering actuator (21) for setting a steering angle (δ) in the front wheels which determines the direction of travel, - with a sensor (22) for determining the currently set steering angle (δ), - with a control unit (10) according to claim 11, which interacts with the steering actuator (21) and with the sensor system.

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