Method and control device for determining a controller output variable with a controller for a controlled system, in particular for a rack and pinion actuator of a steer-by-wire steering system, a steering system comprising the control device and a vehicle comprising the steering system

Abstract

Method and control device (100) for determining a controller output variable (104) with a controller (102) for a controlled system (200), in particular for a rack and pinion actuator of a steer-by-wire steering system, comprising: acquiring a first parameter (106) that characterizes a force (4) acting on the controlled system (200), which in particular influences a dynamic behavior of the controlled system (200); acquiring a second parameter (108) that characterizes a manipulated variable of an actuator (202) of the controlled system (200); determining the controller output variable (104) as a function of the first parameter (106), the second parameter (108) and a setpoint (2) by means of the controller (100). Steering system comprising the control device (100) and a vehicle comprising the steering system.

Description

State of the art

[0001] The present invention relates to a method and a control device for determining a controller output variable with a controller for a controlled system, in particular for a rack and pinion actuator of a steer-by-wire steering system, a steering system comprising the control device and a vehicle comprising the steering system.

[0002] In a steer-by-wire steering system, the vehicle's wheels and, for example, a steering mechanism are connected by electrical signals. A torque applied to the steering mechanism, for instance by the driver, therefore has no direct mechanical effect on the wheels. The steer-by-wire steering system comprises two main subcomponents: a first subcomponent that receives the driver's input from the steering mechanism, and a second subcomponent that translates this input into a steering movement. The second subcomponent is mechanically connected to the wheels, with an electrical connection between the first and second subcomponents. This electrical connection transmits a directional command from the driver to the second subcomponent. The second subcomponent is responsible for lateral movements, such as those of the vehicle's front axle. The second subcomponent can, for example, be a rack and pinion actuator.

[0003] To achieve a good driving experience, the vehicle's response should accurately reflect the driver's directional or steering input. Therefore, for example, the time lag between a movement of the steering mechanism and the movement of the wheels should exhibit a defined behavior, or steering response. The movement of the wheels is caused by a lateral movement of the rack and pinion. In all possible driving situations, the steering system should maintain a certain degree of accuracy in the rack position.

[0004] To control the position of the rack, a controller generates motor torque for an actuator that drives the rack. The actuator's rotor movement is influenced by factors such as internal gearing phenomena and inertia. In known steering system designs, the rack position is estimated from the rotor position and the gear ratio. Due to variations in the steering system's properties, such as those caused by aging and wear, this estimation method cannot guarantee reliable steering behavior. For example, rotor movements may occur that, due to internal steering system friction, do not result in any rack movement. Nevertheless, this movement information is transmitted to the controller via the rack position estimation, which can lead to undesirable actuator oscillations.

[0005] Therefore, it is desirable to provide a control procedure for a steering system that is robust against disturbances and variable system properties of the steering system. Disclosure of the invention

[0006] This is achieved by a method, a control device, a steering system and a vehicle according to the independent claims.

[0007] The method for determining a controller output variable with a controller for a controlled system, in particular for a rack and pinion actuator of a steer-by-wire steering system, comprises: acquiring a first parameter that characterizes a force acting on the controlled system, which in particular influences the dynamic behavior of the controlled system; acquiring a second parameter that characterizes a manipulated variable of an actuator of the controlled system; and determining the controller output variable as a function of the first parameter, the second parameter, and a setpoint using the controller. By determining the controller output variable as a function of the first parameter, friction phenomena of the controlled system, for example, of the steering system, can be implicitly represented without requiring specific modeling or estimation of the friction phenomena.The first and second parameters allow the extraction of friction phenomena, such as those occurring during force transmission between the actuator and a rack in the steering system, and their consideration when determining the controller output. This enables a robust determination of the controller output, resistant to disturbances and varying system properties of the controlled system.

[0008] The procedure may include the acquisition of a third parameter that is influenced by the second and / or first parameter, for example, a controlled output variable of the controlled system, where the controller output variable is determined depending on the first, second, and third parameters. In this context, the third parameter is one that has an interaction with the first and / or second parameter. This interaction causes the dynamics of the third parameter and / or the third parameter itself to vary depending on the first and / or second parameter. This interaction could, for example, be a vehicle axle or the gearing of a rack and pinion actuator.By determining the controller output variable depending on the third parameter, the procedure becomes more dynamic, as relationships between the output variable of the controlled system to be controlled and the first parameter and / or second parameter can be taken into account.

[0009] It can be stipulated that the controller output for a rack and pinion actuator is determined, where the first parameter is a force acting on a rack of the rack and pinion actuator and / or the second parameter is a position signal from an actuator driving the rack and pinion actuator, for example, an electric motor. The rack and pinion actuator is used, for example, to control the direction of travel of a vehicle, with the rack and pinion actuator moving the vehicle's wheels via an axle. By determining the controller output as a function of the force acting on the rack and pinion, friction phenomena and varying system properties of the rack and pinion actuator can be taken into account without having to model them explicitly. Internal friction phenomena and system stiffnesses of the rack and pinion actuator therefore do not need to be explicitly observed, but are implicitly considered in the control algorithm.The method becomes more robust against variations in driving conditions and axle stiffness because the force is directly considered in the control algorithm. This means the method's performance is independent of, for example, the properties of the axle that interacts with the rack and pinion actuator. Integrating the force, as the first parameter, into the method allows the controller to better represent the existing conditions and system properties of the rack and pinion actuator and to react more quickly to changes. This results in more precise and reliable control, especially in demanding driving situations.

[0010] It can be stipulated that the third parameter is a position signal of the rack of the rack actuator. The rack position signal characterizes the position of the rack. This position has a direct influence on the axle and the wheels of the vehicle. Conversely, forces acting on the wheels influence the position, or rather the dynamics, of the rack's position. By using the position signal in the process, it is possible to react more quickly to changes, thus making the process more dynamic.

[0011] It may be provided that the controller output variable characterizes a drive signal of the rack actuator, in particular a drive torque of the actuator of the rack actuator.

[0012] The setpoint may be defined as a predetermined position of the rack of the rack actuator. This setpoint is determined, for example, based on a direction input from the vehicle's driver. The driver can input this direction using a control device. Alternatively, the direction input may be provided by a driver assistance system, such as in autonomous driving mode.

[0013] The controller can be designed to include a model of the controlled system, with the controller output variable determined based on this model. This allows for efficient controller implementation and accounts for the dynamics of the controlled system with a predefined level of accuracy. This makes the method more robust and reliable.

[0014] The control device, which is configured to determine a controller output variable for a controlled system, in particular for a rack and pinion position control of a steer-by-wire steering system, by means of a method according to the above descriptions, wherein the control device comprises a first sensor device 105, which is configured to detect the first characteristic variable and optionally a second sensor device, which is configured to detect the third characteristic variable.

[0015] The steering system, in particular a steer-by-wire steering system, includes a control device according to the above design.

[0016] The vehicle includes a steering system as described above.

[0017] Further embodiments are shown in the drawing and the following description. The drawing shows: Fig. 1 a block diagram of a control device for determining a controller output variable; Fig. 2 a block diagram of an embodiment of the control device; Fig. 3a a flowchart of a procedure for determining a controller output variable; Fig. 3b a flowchart of an embodiment of the method; Fig. 4 a schematic representation of a section of a vehicle comprising a steering system comprising the control device.

[0018] The Fig. Figure 1 shows a block diagram of a control device 100. The control device 100 is configured to determine a controller output variable 104 with a controller 102 for a controlled system 200, in particular for a rack and pinion actuator of a steer-by-wire steering system. The control device 100 is configured to detect a first characteristic variable 106 by means of a first sensor device 105, which characterizes a force 4 acting on the controlled system 200. The force 4 particularly influences a dynamic behavior of the controlled system 200. The control device 100 is configured to detect a second characteristic variable 108, which characterizes a manipulated variable of an actuator 202 of the controlled system 200. The actuator 202 serves, for example, to influence or set a controlled variable of the controlled system 200.The control device 100 is configured to determine the controller output variable 104 based on the first characteristic variable 106, the second characteristic variable 108, and a setpoint 2 using the controller 100. The setpoint 2 is, for example, a predetermined value of the variable to be controlled in the controlled system 200.

[0019] The Fig. Figure 2 shows a block diagram of an embodiment of the control device 100. The control device 100 may be configured to detect a third parameter 110 by means of a second sensor device 109, which is influenced by the second parameter 108 and / or the first parameter 106, for example, an output variable of the controlled system 200 to be controlled. The control device 100 is configured to determine the controller output variable 104 depending on the first parameter 106, the second parameter 108, and the third parameter 110. The third parameter 110 may characterize or be the output variable of the controlled system 200 to be controlled.

[0020] It may be provided that the controller output size 104 is for a rack and pinion actuator 200 of a steering system 500 ( Fig. 4) is determined, wherein the first parameter 106 is a force 4 acting on a rack 204 of the rack actuator 200 and / or the second parameter 108 is a position signal from an actuator 202 driving the rack actuator, for example, an electric motor. The rack actuator 200 is an exemplary embodiment of the control system 200. The dynamics of the rack actuator 200 can be described, for example, by the following equations. ω¨rot=f(ωrot,ω˙rot,xrack,x˙rack,Tmo) x¨ra=g(ωrot,ω˙rot,xra,x˙ra,Fra)

[0021] Here, ω describes rot a rotor position of actuator 202, which can, for example, represent the second characteristic value. ω̇ rot describes a rotor speed of the actuator and ω̈ rot a rotor acceleration. The variable x ra describes a position, ẋ ra a speed and ẍ raan acceleration of the rack 204. By T mo A drive torque of the actuator 202 is described, the variable F ra describes the force 4 acting on the rack actuator 200, in particular on the rack 204. The force 4 F ra For example, an external steering signal caused by the axle influences the dynamics of the rack actuator 200.

[0022] It can be provided that the controller output variable 104 characterizes a drive signal of the rack actuator 200, in particular the drive torque T. mo of actuator 202 of rack and pinion actuator 200. The drive torque T mo is used to determine position x ra to control the rack 204.

[0023] It can be provided that the third parameter 110 is a position signal of the rack 204 of the rack actuator 200. The third parameter 110 can, for example, be the position x racharacterize or be these.

[0024] It can be provided that the controller 102 includes a model 112 of the controlled system 200, whereby the controller output variable 104 is determined depending on the model 112. The model 112 can, for example, be expressed in the form of the following dynamic equations. Jmo⋅ω¨rot=−Kx(ωrot−ixra)−(dmo+dx)ω˙rot+dxix˙ra+Tmo mra⋅x¨ra=Kxi(ωrot−ixra)+dxi(ω˙rot−ix˙ra)−Fra

[0025] The parameter K x describes the stiffness of the system, for example of the rack and pinion actuator 200, d x This includes, for example, all damping phenomena that occur between the actuator 202 and the rack 204 and d modescribes internal friction phenomena of the actuator 202. These parameters can vary, for example, depending on the driving situation and the ambient temperature. The parameter i denotes a gear ratio that can be provided between the actuator 202 and the rack 204. The parameter J mo characterizes the inertia of the rotor of actuator 202. The parameter m ra describes a mass of the rack 204.

[0026] Using the first parameter 106 in the form of the force F ra , the second parameter 108 in the form of the rotor position ω rot and the third parameter 110 in the form of position x ra The dynamic equation (3) can be simplified as shown below for the rack 204, which are recorded and therefore are known in particular. Kx(ωrot−ixra)+dx(ω˙rot−ix˙ra)=Tmo−dmoω˙rot−Jmoω¨rot

[0027] Equation (5) can be substituted into the dynamic equation (4), as shown below. mra⋅x¨ra=i(Tmo−dmoω˙rot−Jmoω¨rot)−Fr

[0028] It may be intended that the setpoint 2 characterizes a predetermined position of the rack 204 of the rack actuator 200. It is conceivable that the setpoint represents the predetermined position x. req the rack 204. This can be determined, for example, based on a desired direction input from the driver of a vehicle that includes the rack actuator 200. Accordingly, it can be provided that the control device 100 is designed by means of the controller 102 to minimize the following relationship within the framework of a control system. x˜=xreq−xra

[0029] Starting from equation (6), for example a sliding mode controller can be determined which might have the following sliding surface S defined: S=x˜¨+(λ1+λ2)x˜˙+(λ1λ2+1)x˜

[0030] The following can be defined within the framework of the well-known sliding-mode method. h=((λ1+λ2)x˜˙+(λ1λ2+1)x˜)

[0031] Using equations (9) and (8), the following relationship can be formulated starting from equation (6). mra⋅S=i(Tmo−dmoω˙rot−Jmoω¨rot)−Fra−mra⋅x¨ra+mrah(λ1,λ2,xra,xreq)

[0032] Starting from equation (10) and the sliding-mode method, for example the following control algorithm can be formulated for the controller 102, where T mo The controller output size is 104. Tmo=dmoω˙rot+Jmoω¨rot+1i(Fra+mrax¨req−mrah(λ1,λ2,xra,xreq))−μ¯1(xra,xreq)

[0033] Here, µ1 describes a parameter of the sliding-mode method. The first recorded characteristic value 106, in the form of the force 4 F acting on the rack 204, is ra, and the recorded third parameter 110, in the form of position x ra The rack 204, flow directly into the described control algorithm. The stiffness of the rack actuator 200 does not need to be monitored, nor do internal transmission losses of the rack actuator 200 need to be monitored. External steering signals, such as road feedback information, are incorporated by the detected force 4 F. ra taken into account in the control algorithm (11).

[0034] Alternatively, the control algorithm can be reformulated based on the dynamic equations (3) and (4) and the sliding-mode method, if, for example, only the first parameter 106, in the form of the force 4 F, is used. ra , and the second parameter 108, in the form of the rotor position ω rot is captured. This control algorithm can be defined, for example, as follows, where T mo The controller output size is 104. Tmo=(mra(ω¨roti)+Fra)i+dmoω˙rot+Jmoω¨rot−Jmoh(λ1,λ2,ωrot,ωreq)−μ¯2(ωrot,ωreq)

[0035] The target value 2 represents a desired rotor position ω. req of actuator 202 of rack and pinion actuator 200 is used. This is because the position x ra Since the movement of the rack 204 is not directly incorporated into the control algorithm (12), fast or high-frequency movements of the rack 204 are not immediately detected, making the control algorithm (12) more robust and less susceptible to interference.

[0036] The Fig. Figure 3a shows a flowchart of a method 300 for determining the controller output variable 104 with the controller 102 for the controlled system 200, in particular for the rack and pinion actuator 200 of a steer-by-wire steering system. The method 300 comprises acquiring 302 the first parameter 106, which characterizes the force 4 acting on the controlled system 200, which in particular influences the dynamic behavior of the controlled system 200. Furthermore, the method 300 comprises acquiring 304 the second parameter 108, which characterizes a manipulated variable of an actuator 202 of the controlled system 200, and determining 306 the controller output variable 104 as a function of the first parameter 106, the second parameter 108, and the setpoint 2 using the controller 102. This can be done, for example, using a control algorithm according to equation (12).

[0037] The Fig. Figure 3b shows an embodiment of the method 300 in a flowchart. The method 300 may include acquiring 308 the third parameter 110, which is influenced by the second parameter 108 and / or the first parameter 106, for example, a controlled output parameter of the controlled system 200, wherein the controller output parameter 104 is determined depending on the first parameter 106, the second parameter 108, and the third parameter 110. This can be done, for example, by means of a control algorithm according to equation (11).

[0038] It may be provided that the control device 100 is trained to execute the procedure 300 to determine the controller output variable 204.

[0039] The Fig.Figure 4 shows a schematic representation of a section of a vehicle 400. This section depicts a wheel 402 of the vehicle, which is controlled by a steering system 500. The steering system 500 includes the control unit 100. The wheel is coupled to the rack and pinion actuator 200 of the steering system 500 by means of an axle 404. The force 4 acting on the rack 204, for example, is transmitted via the axle 404.

[0040] The vehicle may include 400 additional wheels 402 which are controlled by means of the steering system 500 or further steering systems 500. In the example shown, the vehicle includes a control device 406 by means of which the driver of the vehicle 400 can specify a direction of travel. Based on this direction of travel or direction specification, the setpoint 2 for the control device 100 can be determined.

Claims

[1] Method (300) for determining a controller output variable (104) with a controller (102) for a controlled system (200), in particular for a rack and pinion actuator of a steer-by-wire steering system, comprising: - Acquiring (302) a first parameter (106) that characterizes a force (4) acting on the controlled system (200), which in particular influences a dynamic behavior of the controlled system (200); - Acquisition (304) of a second parameter (108) that characterizes a manipulated parameter of an actuator (202) of the controlled system (200); - Determining (306) the controller output variable (104) depending on the first parameter (106), the second parameter (108) and a setpoint (2) using the controller (100). [2] The method (300) according to claim 1, comprising acquiring (308) a third parameter (110) which is influenced by the second parameter (108) and / or the first parameter (106), for example an output parameter of the controlled system (200) to be controlled, wherein the controller output parameter (104) is determined depending on the first parameter (106), the second parameter (108) and the third parameter (110). [3] The method (300) according to one of the preceding claims, wherein the controller output variable (104) is determined for a rack actuator (200) of a steering system (500), wherein the first parameter (106) is a force (4) acting on a rack (204) of the rack actuator and / or the second parameter (108) is a position signal of an actuator (202), for example an electric motor, driving the rack actuator. [4] The method (300) according to claims 2 and 3, wherein the third parameter (110) is a position signal of the rack (204) of the rack actuator (200). [5] The method (300) according to claim 3 or 4, wherein the controller output variable (104) characterizes a drive signal of the rack actuator (200), in particular a drive torque of the actuator (202) of the rack actuator (200). [6] The method (300) according to any one of claims 3 to 5, wherein the setpoint (2) characterizes a predetermined position of the rack (204) of the rack actuator. [7] The method (300) according to one of the preceding claims, wherein the controller (102) comprises a model (112) of the controlled system (200), wherein the controller output variable (104) is determined (306) depending on the model (112). [8] Control device (100) configured to determine a controller output variable (102) for a controlled system (200), in particular for a rack and pinion actuator (200) of a steer-by-wire steering system, by means of a method (200) according to claims 1 to 7, wherein the control device (100) comprises a first sensor device 105 configured to detect the first characteristic variable (106) (302) and optionally a second sensor device (109) configured to detect the third characteristic variable (110) (308). [9] Steering system (500), in particular a steer-by-wire steering system, comprising a control device (100) according to claim 8. [10] Vehicle (400) comprising a steering system (500) according to claim 9.

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