Method for calculating controller steering torque to be predetermined for steering actuator of automobile

Abstract

To provide a method for determining a controller steering torque to be predetermined for a steering actuator of an automobile.SOLUTION: A controller steering torque is calculated by using a double controller (1) including an external controller (2a) and an internal controller (2i), and a steering angle set by a steering actuator (21) in an automobile is supplied to the external controller. A desired value of a time derivative of the steering angle is output as a manipulated variable. The internal controller (2i) is supplied with a feedforward model steering torque, which is determined in real time according to a physical behavior of the steering actuators (21). A physical state of the steering actuator (21) is modeled by a rotating single mass spring damper using external excitation. At least one time-dependent spring damper model parameter is estimated by a recursive compensation calculation. From this estimate, the feedforward model steering torque is determined.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for calculating a controller steering torque to be predetermined for a steering actuator of a motor vehicle. Furthermore, the present invention relates to a control device designed / programmed to carry out this method. Finally, the present invention relates to a motor vehicle equipped with such a control device. [Background technology]

[0002] In connection with the so-called steering angle or lane keeping assist function of a motor vehicle, it is known to determine, taking into account various factors, the steering angle that can be set on the steering actuator of the steering mechanism so that the motor vehicle follows a predetermined trajectory path when traveling on a roadway.

[0003] For this purpose, methods are known for calculating a steering torque that can be set for the steering actuator. Such conventional methods are usually implemented by one- or two-stage controllers and are described, for example, in EP 3321149 B1, US 2019 / 0308664 A1 and DE 102014208786 A1.

[0004] A problem with such conventional methods is that the physical characteristics of the steering actuator have been found to have a significant effect on the control, and therefore the actual steering behavior, of the steering actuator, which can adversely affect the control behavior of the controller.

[0005] The corresponding modelling of the physical characteristics of the steering actuator, which is implemented in the controller in the form of a so-called forward model for improved control performance, has proven to be relatively inaccurate in practice and does not take into account changes in the physical characteristics of the steering actuator over the life of the steering mechanism. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] European Patent No. 3321149B1 [Patent Document 2] US Patent Application Publication No. 2019 / 0308664A1 [Patent Document 3] German Patent Application Publication No. 102014208786A1 Summary of the Invention [Problem to be solved by the invention]

[0007] It is therefore an object of the present invention to create an improved method for determining a controller steering torque to be predetermined for a steering actuator of a motor vehicle, which at least partially, and ideally completely, overcomes the above-mentioned disadvantages. [Means for solving the problem]

[0008] This problem is solved by the subject matter of the independent claims. Preferred embodiments are the subject matter of the dependent claims.

[0009] The basic idea of ​​the present invention is therefore to determine a controller steering torque for the steering actuator using a double controller, an outer controller using the steering angle set by the steering actuator of the vehicle as control variable and an inner controller using the time derivative of this steering angle as control variable.

[0010] Here, according to the invention, it is proposed to provide the internal controller with a feedforward model steering torque as an additional input variable, whereby the current physical characteristics of the steering actuator are taken into account in real time. Furthermore, it is proposed to model the physical characteristics of the steering mechanism in a time-dependent manner by a rotating single mass spring-damper with an external excitation and various spring-damper model parameters. To calculate the feedforward model steering torque that is fed to the internal controller, selected time-dependent spring-damper model parameters are estimated using a recursive compensation calculation. The proposed inventive consideration of the physical characteristics of the steering actuator can significantly improve the control behavior of the two-stage controller. This advantageously has an effect on the steering control of the vehicle and on the assisted or even autonomous driving of the vehicle.

[0011] The method according to the invention is used to calculate a controller steering torque to be predefined for a steering actuator of a motor vehicle. According to the invention, the desired controller steering torque is calculated using a dual controller, which comprises an external controller and an internal controller connected downstream of the external controller. The external controller is supplied with a steering angle set by a steering actuator in the motor vehicle as a controlled variable. The external controller outputs a setpoint value of the time derivative of the steering angle as a manipulated variable, which is used as a controlled variable for the internal controller. Furthermore, the internal controller is supplied with a feedforward model steering torque for calculating the manipulated variable, which is determined in real time depending on the physical behavior of the steering actuator.

[0012] Here, the physical state of the steering mechanism is modeled by a rotating single mass spring-damper with external excitation. Here, the time-dependent steering angle is a free parameter of the model. Furthermore, at least one further time-dependent spring-damper model parameter is utilized for the physical description of the spring-damper. According to the invention, the at least one time-dependent spring-damper model parameter is estimated by a recursive compensation calculation. From this estimation, a feedforward model steering torque to be provided to the internal controller is determined.

[0013] Here, at least one time-dependent spring-damper model parameter is estimated by a recursive compensation calculation, from which a feedforward model steering torque is calculated that is provided to an internal controller.

[0014] 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, which improves the control accuracy of the inner controller.

[0015] Particularly preferably, the feedforward model steering torque is calculated as a function of the setpoint value of the steering angle, the controller steering torque calculated by the internal controller and the driver steering torque applied by the driver of the vehicle, which results in particularly accurate control results, the driver steering torque being variable depending on the steering angle and other system conditions.

[0016] According to a further preferred embodiment, the following constants used in the rotational 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”.

[0017] In a preferred embodiment, the internal controller uses the change in steering angle as a reference variable and calculates the determined controller steering torque as a manipulated variable not only depending on the deviation between the calculated setpoint and actual values ​​of the reference variable but also depending on the calculated feedforward model steering torque, whereby the consideration of the feedforward model steering torque leads to a significant improvement of the control behavior of the two controllers.

[0018] In another preferred embodiment, the external controller can use the steering angle set in the steering actuator as the reference variable, and in this embodiment, the external controller further outputs the change in the steering angle as the manipulated variable.

[0019] In the method according to the invention, the estimation of said spring-damper model parameters is preferably performed in real time, thus being able to react to changes in the physical properties of the steering actuator occurring in real time, thereby improving the control behavior of the two controllers.

[0020] Here, it is particularly preferable that a feedforward model steering torque be calculated from the estimated stiffness and the estimated offset in accordance with a target steering angle that is preset from the outside.

[0021] 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 calculated using a Kalman filter, which allows the spring-damper model parameters to be estimated particularly accurately, in particular in real time.

[0022] According to an advantageous development of the method according to the invention, an externally excited single mass-spring damper is described by the following differential equation:

[0023]

number

[0024] 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 a driver steering torque set by the driver and a controller steering torque to be predefined in the steering actuator, in which variant the driver steering torque set by the driver is also taken into account.

[0025] The invention further relates to a control device for a motor vehicle, which is designed / programmed to carry out the method according to the invention proposed above, so that the above-mentioned advantages of the method according to the invention also apply to the control device according to the invention.

[0026] The invention further relates to a motor vehicle with two front and two rear wheels and a steering actuator at the front wheels for setting a steering angle that determines the direction of travel of the motor vehicle. The motor vehicle further comprises a sensor system for determining the currently set steering angle. For this purpose, the sensor system may comprise a steering angle sensor. According to the invention, the motor vehicle according to the invention further comprises a control device proposed above and therefore according to the invention, which cooperates with the steering actuator and the sensor system. The above-mentioned advantages of the method according to the invention therefore also apply to the motor vehicle according to the invention.

[0027] Further important features and advantages of the invention emerge from the dependent claims, the drawings and the associated drawing description based on the drawings.

[0028] It is to be understood that the features mentioned above, and those further described below, can be used not only in the combinations presented in each case, but also in other combinations or alone, without departing from the scope of the invention.

[0029] Preferred exemplary embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description. [Brief description of the drawings]

[0030] [Figure 1]2 shows an example of the structure of a control device according to the invention in the form of a flow chart, such as a circuit diagram, for the method according to the invention; [Diagram 2] Next, it is a diagram for explaining the calculation of the feedforward model steering torque. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] 1 shows by way of example the structure of a control device 10 according to the invention for a motor vehicle 20 (shown only diagrammatically) in the form of a flow chart, such as a circuit diagram. The control device 10 is designed to control a steering actuator 21 of the motor vehicle 20, by means of which a steering angle δ can be set, which determines the direction of travel of the motor vehicle. Furthermore, the control device 10 is data-transmittingly connected to a sensor system 22 of the steering actuator 21 in order to determine the currently set steering angle δ. For this purpose, the sensor system 22 can include a suitable steering angle sensor (not shown).

[0032] As described above, the method according to the invention is carried out by determining the controller steering torque SteerTrq to be predefined for the steering actuator 21 of the motor vehicle 20. SAC Then, the steering actuator 21 uses the calculated steering torque SteerTrq SAC can be converted to an assigned steering angle δ.

[0033] According to the present invention, a dual controller 1 including an external controller 2a and an internal controller 2i connected downstream of the external controller 2a is used to determine the controller steering torque SteerTrq SAC is calculated.

[0034] The external controller 2a is supplied with a steering angle δ(t) set by a steering actuator 21 in the vehicle 20 as a control variable. Here, the actual value of the steering angle δ is converted in the usual way into a setpoint value δ(t). Target The control deviation (δ-δ Target) is calculated. According to FIG. 1, the external controller 2a calculates a target value d / dtδ Target The external controller 2a outputs the steering angle d / dtδ(t) as a manipulated variable, which is further provided to the internal controller 2i as a controlled variable. Here, the actual time derivative of the steering angle d / dtδ(t) is calculated based on the target value d / dtδ provided by the external controller 2a. Target (t), and similar to the external controller 2a, the control deviation (d / dtδ(t)-d / dtδ Target The internal controller 2i calculates the required controller steering torque SteerTrq (t) as shown in FIG. SAC is calculated as the manipulated variable, which is output to the steering actuator 21 as can be seen in FIG.

[0035] Controller steering torque SteerTrq SAC For the calculation of the steering torque SteerTrq, the internal controller 2i has a feedforward model according to the figure. FF is provided, which is determined time-dependently, in particular in real time, as an output variable depending on the physical behavior of the steering actuator 21, by a calculation unit 3 connected to the control loop of the internal controller 2i.

[0036] Here, the physical state of the steering actuator 21 is determined by the external excitation "Tmot(t) SAC+DRIVER The system is modeled by a rotating single mass spring-damper with an external excitation Tmot(t) SAC+DRIVER " is the driver steering torque "SteerTrq " applied by the driver of the vehicle 20 Driver " and a controller steering torque "SteerTrq SAC " is determined by the sum of the two parameters "SteerTrq Driver " and "SteerTrq SAC " is supplied to the calculation unit 3 as an input variable.

[0037] 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 used to model the physical properties of the spring-damper. That is, as spring-damper model parameters, the time-dependent variables used are the known variables for describing a rotational single-mass spring-damper, namely 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 the time-dependent offset=Offs(t). Here, the externally excited single-mass spring-damper is described by the following differential equation:

[0038]

number

[0039] The two spring-damper model parameters J and D shape the non-stationary, i.e. dynamic, behavior of the steering actuator, while the parameter C generates a quasi-stationary relationship between the steering angle δ and the steering torque acting on the steering actuator 21.

[0040] The values ​​of the spring-damper model parameters J(t), D(t), C(t), and Offs(t) are estimated by a recursive compensation calculation, where the estimation of the spring-damper model parameters J(t), D(t), C(t), and Offs(t) is performed in real time. From this estimation, the feedforward model steering torque SteerTrq is finally provided to the internal controller 2i. FF is calculated.

[0041] Target value of steering angle change amount d / dtδ Target The internal controller 2i uses the calculated feedforward model steering torque SteerTrq as a control variable. FF Taking into account the above, the desired controller steering torque SteerTrq to be supplied to the steering actuator 21 as the manipulated variable SACThat is, in addition to the steering angle change amount d / dtδ, the internal controller 2i calculates the feedforward model steering torque SteerTrq FF is provided as a reference variable, which depends on the dynamic physical behavior of the steering actuator 21, as explained above.

[0042] Here, an externally excited single mass-spring damper is expressed by the differential equation

[0043]

number

[0044] It is described by:

[0045] The calculation of the feedforward model steering torque will now be described by way of example on the basis of the diagram of FIG. 2, which shows the calculation unit 3 diagrammatically.

[0046] For the recursive compensation calculation, the four spring-damper model parameters J, D, C, Offs are considered as a vector variable Z=Z(t).

[0047] Z(t)=[J(t)D(t)C(t)Offs(t)] The steering angle δ(t) and its first and second derivatives as input variables for the calculation unit

[0048]

number

[0049] can be similarly formulated as a vector variable θ.

[0050]

number

[0051] The recursive calculation Z(t) can be performed according to the following equation:

[0052] Z(t) i =Z(t) i-1 +K gain (t) i (Tmot(t) SAC+Driver -θ(t) T i Z(t) i-1 ) A 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, K in the above equations Gain is the Kalman gain defined recursively as follows:

[0053] K gain (t) i =P(t) i ×θ(t) i =P(t) i-1 θ(t) i (λ+θ(t) T i P(t) i-1 θ(t) i ) -1 In the above equation, P(t) i is a finite positive covariance matrix defined as follows:

[0054]

number

[0055] where λ is a weighting factor, also known to those skilled in the art as the “forgetting factor”, with 0<λ≦1.

[0056] From the variables Z(t) estimated recursively as described above, the calculation unit 3 calculates the feedforward model steering torque SteerTrq FF can be calculated or estimated as follows:

[0057] SteerTrq FF (t)=C(t)*δ Target(t)+Offs(t) Here, it is particularly preferable to use the feedforward model steering torque SteerTrq FF is a target steering angle δ that is preset from the outside target is calculated from the estimated stiffness C_EST and the estimated offset OFFS_EST depending on [Explanation of symbols]

[0058] 1 Dual Controller 2a External Controller 2i Internal Controller 3. Computational Unit 10 Control device 20. Automobiles 21 Steering actuator 22 Sensor System d / dtδ Steering angle change amount SteerTrq Driver Driver Steering Torque SteerTrq FF Feedforward model steering torque SteerTrq SAC Controller steering torque Tmot(t) SAC+DRIVER External Excitation δ steering angle δ Target Target value

Claims

1. A controller steering torque (SteerTrq) to be predetermined for a steering actuator (21) of a vehicle (20) ＳＡＣ (t) comprising the steps of: The controller steering torque (SteerTrq ＳＡＣ (t)) is calculated by a dual controller (1) including an external controller (2a) and an internal controller (2i) connected downstream of the external controller (2a); the external controller (2a) is supplied with the steering angle (δ(t)) set by the steering actuator (21) in the vehicle as a control variable, The external controller (2a) sets a target value of the time derivative of the steering angle (d / dtδ Ｔａｒｇｅｔ ) as manipulated variables, which are supplied to the internal controller (2i) as control variables; The internal controller (2i) determines the desired controller steering torque (SteerTrq ＳＡＣ (t)) is output as an operational variable, The controller steering torque (SteerTrq ＳＡＣ In order to calculate the steering torque (SteerTrq ＦＦ (t)) is provided, and the feedforward model steering torque (SteerTrq ＦＦ (t) is determined in real time in response to the physical behavior of the steering actuator (21); The physical state of the steering mechanism (21) is determined by the external excitation (Tmot(t) ＳＡＣ＋ＤＲＩＶＥＲ (t)), a steering angle (δ) and 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); the at least one time-dependent spring-damper model parameter (J(t), D(t), C(t), Offs(t)) is estimated by a recursive compensation calculation; From the estimation, the feedforward model steering torque (SteerTrq ＦＦ (t) is calculated, method.

2. The feedforward model steering torque (SteerTrq ＦＦ (t) is calculated as part of the control loop of said inner controller (2i) 2. The method of claim 1 .

3. The feedforward model steering torque (SteerTrq ＦＦ (t)) is the target value (δ Ｔａｒｇｅｔ ), the controller steering torque (SteerTrq ＳＡＣ (t)), and a driver steering torque (SteerTrq) applied by a driver of the vehicle (20). ＳＡＣ (t)+SteerTrq ＤＲＩＶＥＲ ) is calculated according to 3. The method according to claim 1 or 2.

4. The following constants are used in the rotating single mass spring damper as spring damper model parameters: Rotational moment of inertia (J(t)), Attenuation D (D(t)), stiffness C(C(t)), and Offset OFFS(t) are estimated as time-dependent variables 4. The method according to claim 1, wherein the first and second electrodes are arranged in a first direction.

5. The estimation is performed in real time.

5. The method according to claim 1, wherein the first and second electrodes are arranged in a first direction.

6. From the estimated stiffness (C_EST) and the estimated offset (OFFS_EST), a target steering angle (δ ｔａｒｇｅｔ ) according to the feedforward model steering torque (SteerTrq ＦＦ ) is calculated 6. The method according to claim 4 or 5.

7. 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, is estimated using a Kalman filter.

7. The method according to any one of claims 1 to 6.

8. The externally excited single mass-spring damper is configured to satisfy the following differential equation: [0010] Described by 8. The method according to claim 1, wherein the first and second electrodes are arranged in a first direction.

9. For the recursive compensation calculation, the four spring-damper model parameters J(t), D(t), C(t), and Offs(t) are considered as a vector variable Z=Z(t).

9. The method according to any one of claims 1 to 8.

10. The external excitation of the spring damper (SteerTrq ＳＡＣ +SteerTrq ＤＲＩＶＥＲ ) is the driver steering torque (SteerTrq) applied by the driver of the vehicle (20); ＳＡＣ +SteerTrq ＤＲＩＶＥＲ ), and the controller steering torque (SteerTrq ＳＡＣ ) is determined by the sum of 10. The method according to any one of claims 1 to 9.

11. A control device for a motor vehicle (20), characterized in that it is designed / programmed to implement the method according to any one of claims 1 to 10.

12. two front wheels and two rear wheels; A steering actuator (21) for setting a steering angle (δ) on the front wheels that determines the direction of travel; a sensor system (22) for determining said currently set steering angle (δ); A control device (10) according to claim 11, cooperating with said steering actuator (21) and said sensor system; A vehicle equipped with:

Images