Method for operating a steering system for a vehicle and steering system

Abstract

The invention relates to a method for operating a steering system (1) for a vehicle (50), wherein feedback (10) at a steering handle (2) of the steering system (1) is determined based on a first feedback component (10-1) and a second feedback component (10-2), wherein the first feedback component (10-1) represents a forward path (30) of an action chain originating from the steering handle (2) in the direction of the at least one steerable wheel (52) of the steering system (1), and wherein the second feedback component (10-2) represents a return path (31) of an action chain originating from the at least one steerable wheel (52) in the direction of the steering handle (2), wherein the second feedback component (10-2) is determined at least partially based on a detected and / or determined lateral acceleration (a y ) and / or a measured and / or determined shear force (F y ) is determined. Furthermore, the invention relates to a steering system (1).

Description

[0001] The invention relates to a method for operating a steering system for a vehicle and a steering system.

[0002] In conventional steering systems, a rack position is directly coupled to a steering wheel position via a steering column. Such a mechanical connection is no longer present in steer-by-wire systems. Feedback to the driver is typically determined from internal steering parameters using a rack force estimator. Traditionally, a torque from a motor at the steering gear is used for this purpose. Due to the mechanical coupling with the rack, this force qualitatively corresponds to the actual rack force. However, the motor must overcome inertial and frictional forces of the steering gear and axle to achieve rack movement, meaning these inertial and frictional forces of the steering gear and axle are included in the torque signal. The same applies to external excitations (e.g.,(due to road surface irregularities), which first pass through a low-pass filter formed by steering inertia and friction before a measurable motor movement is generated. These inherent inertial and friction components, as well as the mechanical coupling, have a partially negative impact on the feel of the steering wheel and fundamentally limit feedback.

[0003] WO 2018 / 167005 A1 describes a method for determining a rack force for a steer-by-wire steering system for a motor vehicle, wherein the rack force is determined from two components, wherein a first component of the rack force is generated in a module for vehicle model-based estimation of the rack force using a vehicle model and a second component of the rack force is generated in a module for steering system model-based estimation of the rack force using a steering system model.

[0004] DE 102 48 343 A1 describes a method for controlling an actuation force simulator of a vehicle steering system, which is associated with a steering actuation device, in particular a steering wheel, that can be operated by a driver. In the method, depending on at least one first input variable describing a driving dynamic state of the vehicle (driving dynamic variable), at least one second input variable describing a torque acting on the steerable wheels of the vehicle or on an actuating means connected or connectable to the steerable wheels of the vehicle, in particular the rack of a rack and pinion steering system (actuating torque), and at least one third input variable describing the angle of a pivoting of the steerable wheels of the vehicle (actuating angle), at least one output variable is determined which describes a torque acting on the steering actuation device (actuating torque).The actuation force simulator can be controlled according to the determined actuation torque, in order to apply a specific actuation torque or force to the steering actuation device.

[0005] German patent DE 10 2004 005 348 A1 describes a system and method for controlling a steer-by-wire assembly to generate an adjustable steering feel for a driver by controlling the steering wheel's response torque. The method includes a quantitative description of the steering feel, obtained by establishing a relationship between steering wheel response torque and steering wheel angle, wheel torque, and vehicle speed. The system and method incorporate steer-by-wire assembly feedback loops with an inner torque loop, a steering wheel speed feedback loop, and a steering wheel angle position feedback loop to implement the provision of steering feel, active steering wheel return at various rotational speeds, steering wheel stop according to wheel angle position when parking, and the generation of the directional reference angle to the wheels.

[0006] DE 10 2018 109 084 A1 describes a method for controlling a steer-by-wire steering system for motor vehicles, comprising a steering actuator acting on the steered wheels and electronically controlled depending on a driver steering input, a feedback actuator transmitting road feedback to a steering wheel, and a control unit that controls the feedback actuator, wherein the following method steps are provided for calculating an engine torque: determining a base engine torque; providing at least one steering function that is part of a first subgroup of steering functions; limiting the output value of the at least one steering function to achieve a predetermined safety level in a first limiter; adapting the base engine torque by means of the limited output value of the at least one steering function in a summing unit; controlling the feedback actuator with the resulting engine torque output by the summing unit.

[0007] DE 10 2012 102 629 A1 describes a method for controlling the steering of a motor vehicle by means of an electronic circuit, in which a steering force is controlled via a forward path and feedback of the steering force is controlled via a return path, wherein the forward path and the return path are decoupled from each other and a first amplification curve is integrated into the forward path and a second amplification curve into the return path.

[0008] The invention is based on the objective of improving a method for operating a steering system for a vehicle and a steering system, in particular with regard to feedback to a driver.

[0009] The problem is solved according to the invention by a method with the features of claim 1 and a steering system with the features of claim 9. Advantageous embodiments of the invention are set forth in the dependent claims.

[0010] In particular, a method for operating a steering system for a vehicle is provided, wherein feedback at a steering handle of the steering system is determined based on a first feedback component and a second feedback component, wherein the first feedback component represents a forward path of an action chain starting from the steering handle in the direction of the at least one steerable wheel of the steering system, and wherein the second feedback component represents a return path of an action chain starting from the at least one steerable wheel in the direction of the steering handle, wherein the second feedback component is determined at least partially based on a detected and / or determined lateral acceleration and / or a detected and / or determined lateral force.

[0011] Furthermore, a steering system is provided, in particular comprising a steering handle for detecting a steering input from a driver and for providing feedback to the driver, at least one steerable wheel, a steering mechanism for setting a steering angle of the at least one steerable wheel, and a control device, wherein the control device is configured to determine the feedback at the steering handle of the steering system based on a first feedback component and a second feedback component, wherein the first feedback component represents an outbound path of an action chain originating from the steering handle in the direction of the at least one steerable wheel of the steering system, and wherein the second feedback component represents a return path of an action chain originating from the at least one steerable wheel in the direction of the steering handle.and to determine the second feedback component at least partially based on a recorded and / or determined lateral acceleration and / or a recorded and / or determined lateral force.

[0012] The method and the steering system make it possible to consider both the forward path when the driver initiates steering and the return path when movement is triggered by an excitation from the rack, for example, due to uneven road surfaces. This allows the driver to receive feedback, even with a non-mechanical steering system, similar to that provided by a mechanical steering system.

[0013] The following explains a relationship underlying the idea of ​​the invention: In a mechanical or hydraulic steering system, moving parts in the steering gear have an inertial mass of approximately 2 kg. Electromechanical steering systems (due to an additional gear stage, ball screw drive, or worm gear, and the motor) exhibit a significantly greater apparent inertia, on the order of an inertial mass of approximately 650 to 1000 kg. Small road surface disturbances therefore only cause minimal rack movement, resulting in a small or even immeasurable reaction torque from the motor. Consequently, electromechanical steering systems are considered dull and offer little feedback, which is sometimes perceived as pleasantly quiet. Increasing the mass leads to a less jarring, smoother steering response, but also to reduced feedback from road surface disturbances (feedback for the return path; the second feedback component).However, when the driver steers (e.g., while driving straight ahead), a hand torque builds up, which is necessary to allow the rack to follow the steering wheel position. This requires accelerating the inertial masses in the steering gear and axle and overcoming friction (feedback for the steering path; first feedback component). In electromechanical steering systems, the inertia of the motor and steering gear is usually compensated for. When the driver initially steers, the tires have not yet generated any lateral forces. This only occurs gradually as the vehicle travels the so-called break-in distance, which is approximately between 70 and 120 cm. Initially, the driver therefore feels the first feedback component (steering path), which originates from the mechanics of the steering and axle. As the vehicle's response increases, the second feedback component, which arises from a lateral force in the road surface, is added to this.This also includes feedback from road surface irregularities, which are transmitted via the wheels and cause movement of the rack. These two feedback components originate from the contact in the contact shoe and are combined as a second feedback component.

[0014] The force acting on the rack (e.g., measured with track rods) and transmitted to the driver in a purely mechanical steering system consists primarily of two components: the driver's action and the vehicle's reaction, or, in the case of road surface excitation, the vehicle's action and the steering wheel's reaction. Both components underlie the method and steering system described in this disclosure. In other words, the method and steering system aim to replicate this behavior and feedback even in non-purely mechanical steering systems.

[0015] The forces acting on the steering system are determined, for example, by the movement of the steering wheel. In mechanical steering systems, a steering input is followed by a counterforce, as the masses of the mechanical system must be accelerated and frictional effects overcome. Therefore, a proportional-differential relationship arises between the steering wheel angular velocity and certain components of the resistance forces when steering. To account for these, a steering wheel angular velocity ̇φ̇ is used in particular. SW , a steering wheel angle φ SW and a steering wheel acceleration φ̈ SW These measurements are used to determine the resistance forces of the driver's steering inputs. Based on these recorded and / or determined measurements, the initial feedback component (forward path) can be determined.

[0016] The primary contact point or contact area through which vehicle forces are applied or introduced into the vehicle is the tire contact patch. Consequently, all this information is inherent in the tire's lateral forces. Lateral force can be determined via lateral acceleration, since, according to Newton's second law, the application of a force or the introduction of road surface information (e.g., road irregularities) directly results in lateral acceleration. The tire's lateral forces can thus be reconstructed from the lateral acceleration. The second feedback component (feedback path or road surface feedback) is at least partially determined from this lateral acceleration or force.

[0017] These two approaches allow both feedback components of a steering system to be determined for the driver. Both feedback components (forward path and return path, or road feedback) are essential for comprehensive feedback. In particular, this can improve vehicle control and driving stability.

[0018] In particular, the steering system is a steer-by-wire steering system. The steer-by-wire steering system is designed in a manner known per se. The steering system can also, in particular, be an electromechanical steering system. The electromechanical steering system is designed in a manner known per se. The steering handle is, in particular, a steering wheel.

[0019] Parts of the steering system, in particular the control unit, can be designed individually or collectively as a combination of hardware and software, for example, as program code executed on a computing unit, in particular a microcontroller or microprocessor. However, it is also possible for parts to be designed individually or collectively as an application-specific integrated circuit (ASIC) and / or a field-programmable gate array (FPGA) and / or a graphics processing unit (GPU) and / or a digital signal processor (DSP). The control unit can, in particular, comprise at least one computing unit and at least one memory.

[0020] In one embodiment, the influence of the first feedback component and / or the second feedback component on the feedback is adjustable. This allows the driver to control how strongly each feedback component can or should be perceived. In particular, this enables the targeted simulation of the steering system's behavior in relation to the feedback provided to the driver.

[0021] In one embodiment, the first feedback component is taken into account by means of a spring-damper term, whereby a term proportional to the steering wheel angle and a term proportional to the steering wheel angular velocity are added to a rack force determined from the lateral acceleration or lateral force. This allows a forward path or the first feedback component that arises during steering input to be easily considered. Based on the determined rack force, a torque or steering wheel angular velocity is applied (or controlled) at the steering handle. The rack force F Zst This results in particular from: FZst=FZstaq+φ˙L⋅dL+φL⋅cL where F Zstaq a component of the rack force determined from a measured and / or determined lateral acceleration (or lateral force), φ L is a measured steering wheel angle and φ̇ LA steering wheel angular velocity, either measured or derived from the measured steering wheel angle. The coefficients c L and d L These coefficients serve as a weighting factor. In particular, they can be used to modify and / or adjust the characteristics of the steering system with regard to the initial feedback component.

[0022] The feedback components are intended to be determined using a modeled virtual steering system. This allows the first and second feedback components to be adjusted separately, particularly in an improved manner, enabling independent adjustment of the forward and return paths to achieve the desired steering behavior or feel.

[0023] To achieve freely adjustable steering behavior, a "virtual" steering gear is first simulated. Mass, friction, and other parameters are selected for the simulation to represent a "desired" steering gear—that is, a steering gear with a target or desired behavior for a vehicle. Based on the simulation, the "target feedback" transmitted to the driver is then determined. This feedback is used to control the real steering system so that the driver actually receives and feels the "target feedback" determined from the simulation at the steering wheel.

[0024] To achieve this, a simplified steering model is created, onto which the measured forces act and which represents a desired mechanics. In particular, it is possible to parameterize the mechanics of the virtual steering gear in ways that are impossible in reality, e.g., with very low masses, minimal friction, etc. It is also possible to adjust the depicted physical / mechanical properties during operation (e.g., situationally or via a steering mode selector switch).

[0025] To adjust the feedback level and frequency content, the steering gear will be modeled as a two-mass oscillator. A first mass m RWA The system represents an inertia of an axle and the steering gear, consisting of rack mass m Zst and in particular an inertia of corner modules θ Corner and an inertia of a support unit. A second mass m FFAforms an inertia of the FFA (driver feedback actuator), comprising its motor inertia θ mot off. On the mass m RWA The effect of the measured and / or determined lateral acceleration a y Vehicle reaction force F calculated at the front of the vehicle Y_ext The total mass m RWA is via a spring-damper system with mass m FFA connected to the FFA. On the mass m FFA A counterforce continues to act from the steering angle information. This affects the mass m. FFA This force is generated both by feedback from the road surface (e.g., unevenness in the road) and by steering wheel movement. The resulting kinetic force of the mass m FFA This information is passed on to the driver as feedback, particularly in the form of a set or regulated torque.

[0026] This implementation allows the respective influence of the first feedback component (resistance force during steering wheel movement) and the second feedback component (road surface) to be adjusted. Furthermore, the feedback components can be filtered by appropriately selecting the spring stiffnesses and damping constants.

[0027] This creates a virtual steering gear, enabling a steering system with more degrees of freedom. Resonance frequencies, damping, and other parameters that cannot be freely selected in real mechanical steering systems due to various constraints and cannot be influenced during driving can be modified in this way, allowing for a wide range of steering feel. This makes it possible to represent different steering modes, such as Sport or Comfort.

[0028] Furthermore, the actual mechanical properties of the steering gear have no influence on the steering feedback as long as the position of the actual rack can be precisely set. Very high system friction in the steering gear does not affect the road feedback, which in particular results in potential savings and degrees of freedom in the design of the mechanical system.

[0029] In particular, a virtual steering wheel or motor mass acceleration of the FFA motor is determined by a detected steering wheel movement. This acceleration is torsionally elastically coupled to the virtual rack mass via a spring-damper system. As a result, the driver experiences a counterforce as soon as the steering input is applied, even before any lateral acceleration caused by the steering movement occurs. The virtual rack and corner module mass is excited by the rack force determined from the lateral acceleration. This measure divides the steering process into an action and a reaction.

[0030] The first feedback component (the forward path, i.e., feedback from the steering input) results from the movement of the virtual steering wheel or motor mass. Simultaneously, the resulting steering wheel movement is transmitted to the virtual steering system and acts on the rack mass, which in turn is excited by the estimated rack force derived from the lateral acceleration. In this way, the two feedback components (steering input and road feedback) can be represented separately, yet linked to each other via interactions through the coupling.

[0031] In one embodiment, parameters of the spring-damper assembly or the virtual steering system are adjustable. The coefficients c listed above can be used, in particular, to adjust the spring-damper assembly. L and d Lcan be used. In virtual steering, for example, the values ​​for masses or inertias and coefficients can be changed as parameters.

[0032] In one embodiment, friction acting on virtual masses of the virtual steering system is taken into account using friction models. The respective friction model of the virtual motor or steering wheel, which opposes the respective virtual movement, can influence the first feedback component (steering path, feedback during steering input): High friction results in a high torque level during steering movements, since a real movement of the steering wheel does indeed move the virtual mass, but this movement is hindered by the modeled friction.

[0033] The first feedback component results from a torque proportional to the difference in movement. "Holding" the virtual mass thus generates a larger counter-torque.

[0034] The friction opposing the virtual rack movement allows, in particular, the adjustment of the feedback level of the second feedback component. With high friction, a large proportion of the feedback from the lateral acceleration is reduced by the friction, resulting in smoother road feedback where much information is no longer present. Conversely, if the friction is low, a larger proportion of the road excitation is transmitted in the second feedback component.

[0035] Neglecting the nonlinear friction model, the virtual mass can be represented in particular by the following relationships: The acceleration force F B,Zst The rack and pinion in a purely mechanical steering system with a single-pinion steering gear, without mechanical intervention from the driver or a motor, results in FB,Zst=x¨ZstmZst=FRitzel−Fy,Zst−FReib with the force F acting on the pinion Ritzel , the transverse force F acting on the rack y,Zst and the friction F Reib In mechanically linked systems, the force transmitted to the rider would therefore correspond to the force at the sprocket. FRitzel=x¨ZstmZst+Fy,Zst+FReib

[0036] In the case of a stationary circular motion, the rack acceleration x¨Zst=0ms2 and consequently also the counterforce resulting from friction. The force acting on the pinion in this case results solely from the excitation of the rack by the lateral forces of the tire.

[0037] However, if the rack is to be set in motion, the inertia and the forces resulting from friction must be overcome. If it is further assumed that the steering wheel is torsionally elastically connected to the rack, spring-damper terms result in this equation. Accordingly, the resulting force depends on the excitation of the rack movement (driver's action) and on the vehicle's reaction (system reaction). When the system is excited by the road surface, this chain of effects is reversed. However, it remains constant that the vehicle's reaction and the overcoming of inertia, the torsionally elastic connection, and the frictional effects together result in the applied force. By assuming a steering wheel inertia θ L and a torsionally elastic connection of the steering wheel to the rack via the intermediate steering shaft with stiffness c L and damping constants d LThe equation is modified by adding a resulting force F. cd,L to FRitzel=x¨ZstmZst=Fy,Zst+FReib+Fcd,L extended. The tire lateral force included in this equation is calculated from the measured lateral acceleration using the concept described above. Furthermore, the force due to friction is neglected for haptic reasons and is given by F. Reib = 0. The force resulting from the torsionally elastic connection is in turn determined by the relationship Fcd,L=cL⋅(φL⋅iRitzel−xZst⋅iRitzel2)+dL⋅(φL⋅iRitzel−xZst⋅iRitzel2)

[0038] Described, where φ L a steering wheel angle and i Ritzel , a transmission ratio. This force also acts against the steering wheel movement when the driver initiates the movement, via the angle difference between the steering wheel and the pinion. This results in the following equation of motion for the steering wheel: MB,L=φ¨L⋅ΘL=Mhand−Mcd,L−MRib

[0039] Here too, considering friction is optional. Implementing static friction significantly improves phase stability, but can also have negative effects on haptics. In the implementation described here as an example, the following applies to the feedback concept in particular: M Reib = 0.

[0040] By inserting the coupling torque, the equation becomes MB,L=φ¨LRθL=MHand−cL(φLiRitzel−xZstiRitzel2)+dL(φL⋅iRitzel−xZst⋅iRitzel2)−MRib extended. The virtual steering torque is calculated via a spring-damper term from the relative motion of the measured steering wheel movement and the virtual steering wheel movement: MHand=cCL(φL−φMeas)+dL(φ˙LR−φ˙Measure)

[0041] By substituting the equations into each other and rearranging for the virtual steering wheel acceleration φ̈ LThe following algebraic relationship results: φ¨L=φ˙L(−dL,1+dL,2θL)+φL(−cL,1+cL,2θL) +x˙Zst(dL,2θL iRitzel)+xZst(cL,2θL iRitzel) +φ˙Meas(dL,1θL)+φMeas(cL,1θL)

[0042] The acceleration of the virtual rack mass is achieved using the same procedure: x¨Zst=x˙Zst(−dL,2mZst iRitzel2)+xZst(−cL,2mZst iRitzel2)+φ˙L(dL,2mZst iRitzel)+φLR(cL,2mZstiRitzel)−FZstmZst

[0043] This system is transformed into state space for further analysis. The three input variables of the system are the rack force F. Zst , the detected and / or determined steering wheel angular velocity φ̇ Mess and the detected and / or determined steering wheel angle φ MessThe state vector is composed of the four internal motion variables. These include the virtual motion of the rack and the steering wheel. The state equation can be determined from the differential equations and corresponds to: [ φ¨L φ˙Lx¨Zstx˙Zst]=[−dL,1+dL,2θLR−cL,1+cL,2θLRdL,2θL iRitzelcL,2θL iRitzel1000dL,2mZst iRitzelcL,2mZst iRitzel−dL,2mZst iRitzel2−cL,2mZst iRitzel20010][ φ˙L φLx˙ZstxZst]+[dL,1θLcL,1θL000000−1mzst000][φ˙L φL FZst]

[0044] The output of the modeled system, and thus the feedback for the driver, corresponds in particular to the coupling moment between the measured motion variables and the virtual steering wheel movement. The dependence of the output variable on the measured and / or motion variables results in a feedback effect of the input variables. The output equation is therefore: Fyf=[−dL,1 −cL,1 0 0][φ˙LφLx˙ZstxZst]+[dL,1cL,1 0][φ˙L φL FZst]

[0045] This structure generates a counterforce at the steering wheel due to the measured steering wheel movement and the inertia of the virtual system. This results in particular advantages in phase control, which improve stability. In this way, the driver's action already generates a counterforce before the vehicle's lateral acceleration builds up. The structure of the concept is particularly evident in Fig. 2 clarifies.

[0046] In one embodiment, various selectable steering modes are provided via the parameters. This allows for easy adjustment of the steering behavior. Such steering modes can, for example, provide stronger feedback from the road (e.g., for sporty driving) or less strong feedback from the road (e.g., for a comfort mode) through appropriate parameter selection. It can be provided that the driver can select the desired steering mode using a control device.

[0047] In one embodiment, the parameters are selected, or already selected, taking into account a situation, scenario, and / or user preference. This allows the steering behavior to be adjusted situationally (e.g., city traffic, highway, country road, off-road, etc.) and / or scenario-dependently (e.g., turning at an intersection, parallel parking, etc.) in relation to the provided feedback. The parameters can, for example, be stored in a memory of the control unit for each situation, scenario, or user profile and retrieved automatically or manually from memory as needed for parameterization.

[0048] In one embodiment, it is provided that friction and / or inertia occurring in the steering system are compensated. This allows for the generation of a steering feel that is independent of the physical properties of the steering system. In other words, the feedback, and thus the steering feel, can be arbitrarily selected when friction and / or inertia are compensated. The feedback or steering feel is then adjusted, in particular, via the parameters (especially friction and inertia) of the virtual steering system. For this purpose, the friction is estimated, in particular, using a friction model of the steering system in a manner known per se. The estimated friction is then subtracted (see Eq. 3).

[0049] Further features for the design of the steering system result from the description of the various embodiments of the method. The advantages of the steering system are the same in each case as in the embodiments of the method.

[0050] The invention is explained in more detail below with reference to preferred embodiments and the figures. These show: Fig. 1 a schematic representation of an embodiment of the steering system; Fig. 2 a schematic representation to illustrate a model of the steering system; Fig. 3. A further schematic representation to illustrate a model of the steering system; Fig. 4 a schematic flowchart of embodiments of the method for operating a steering system for a vehicle.

[0051] The Fig. Figure 1 shows a schematic representation of an embodiment of the steering system 1. The steering system 1 comprises a steering handle 2, at least one steerable wheel 52, a steering mechanism 3, and a control unit 4. The steering system 1 is, in particular, arranged in a vehicle 50. The method is described below by way of example using the steering system 1. The steering system 1 can be an electromechanical steering system or a steer-by-wire steering system.

[0052] The steering handle 2 is designed to detect a steering input from the driver and to provide feedback 10 to the driver. For this purpose, the steering system 1 includes, in particular, a steering wheel angle sensor 2-1 and an actuator 2-2. The steering wheel angle sensor 2-1 can detect and / or determine the steering wheel angle and steering wheel angular velocity. The actuator 2-2 can apply torque and / or steering wheel angular velocity to the steering handle 2.

[0053] The steering system 3 is configured to set the steering angle of the at least one steerable wheel 52. For this purpose, the steering system 3 comprises, in particular, an electric motor 3-1, a steering gear 3-2, and a rack 3-3. By means of the electric motor 3-1, a rack position of the rack 3-3 can be set via the steering gear 3-2, thereby setting the steering angle of the at least one steerable wheel 52. Furthermore, the steering system 3 comprises, in particular, steering sensors 3-4 for directly or indirectly detecting a rack position.

[0054] The control unit 4 comprises, for example, a computing unit 4-1 and a memory 4-2. The control unit 4 is configured to determine the feedback 10 at the steering handle 2 of the steering system 1 based on a first feedback component 10-1 and a second feedback component 10-2. The first feedback component 10-1 represents an outbound path 30 of an action chain originating from the steering handle 2 in the direction of the at least one steerable wheel 52 of the steering system 1. The second feedback component 10-2 represents a return path 31 of an action chain originating from the at least one steerable wheel 52 in the direction of the steering handle 2.

[0055] The control unit 4 is further configured to calculate the second feedback component 10-2 at least partially based on a detected and / or determined lateral acceleration a y and / or a recorded and / or determined shear force F y to determine.

[0056] The lateral acceleration a y or the shear force F y These can be detected, for example, by means of a lateral acceleration sensor 5 or a lateral force sensor 6. The lateral acceleration sensor 5 or lateral force sensor 6 can be part of the steering system 1 or provided by the vehicle 50. These provide, in particular, a lateral acceleration signal or a lateral force signal.

[0057] It may be possible to configure the influence of the first feedback component 10-1 and / or the second feedback component 10-2 on the feedback 10. For this purpose, parameters of the respective feedback components 10-1 and 10-2 can be individually defined or set.

[0058] It may be provided that the first feedback component 10-1 is taken into account by means of a spring-damper term, whereby a steering wheel angle-proportional term and a steering wheel angle-velocity-proportional term are derived from the lateral acceleration a y or shear force F y The specific rack force is added. The procedure has already been described in the general description.

[0059] It is planned that the feedback components 10⁻¹ and 10⁻² will be determined using a modeled virtual steering system. The procedure has already been described as an example in the general description.

[0060] It may be provided that parameters of the spring-damper term or the virtual steering are adjustable.

[0061] It may be possible to take into account friction acting on virtual masses of the virtual steering system using friction models.

[0062] It may be possible to provide different selectable steering modes using the parameters.

[0063] It may be intended that the parameters are selected, or have already been selected, taking into account a situation, a scenario, and / or user preference. For this purpose, combinations of parameters are stored in memory 4-2, for example, and can be retrieved from there taking into account the situation, the scenario, and / or user preference.

[0064] It may be provided that friction and / or inertia occurring in steering 2 are compensated.

[0065] The Fig. Figure 2 shows a schematic representation to illustrate a model of the steering system 1. Here, the steering system 1 is simplified and described as a two-mass oscillator. A first mass m RWAThe system represents an inertia of an axle and the steering gear 3-2, consisting of a rack mass m Zst (plus in particular an inertia of corner modules θ) Corner and an inertia of a support unit). A second mass m FFA forms an inertia of actuator 2-2 (driver feedback actuator, FFA), comprising its motor inertia θ mot off. On the mass m RWA The effect of the measured and / or determined lateral acceleration a y Vehicle reaction force F calculated at the front of the vehicle Y The total mass m RWA is connected via a spring-damper system 40-2 with mass m FFA connected to the FFA. On the mass m FFA A counterforce continues to act from the steering angle information (detected steering wheel angle φ). LMess ), wherein the steering handle has an inertia J L also via a spring-damper system 40-1 with mass m FFAof the FFA is connected. This results in the mass m FFA both through road feedback (e.g., through uneven road surfaces) and through steering wheel movement (M Hand ) excited. The resulting kinetic force of the mass m FFA is used as feedback information (M Feedback ) forwarded to the driver (or set at the FFA actuator). The parameters d L , c L , d Zst , c Zst In the virtual steering system, this determines the strength of the first feedback (m FFA to steering handle) and the second feedback (m Zst (to FFA). Thus, the steering system's feedback characteristics can be adjusted.

[0066] The Fig. Figure 3 shows a further schematic representation to illustrate the modeling of the steering system 1 as a virtual steering system in the form of a control loop with several mutual couplings. The modeling shown is fundamentally similar to that in the Fig. Model 2 shown. A steering wheel angular velocity ̇φ̇ is applied to the steering handle. LMess the steering handle is captured. This acts via a spring-damper term 40-1 on an FFA with inertia J mot The spring-damper term provides, in particular, a torque M proportional to the steering wheel angle. cL and a steering wheel angle speed proportional torque M dL In total, these form the feedback (torque M). Feedback ) to the driver, which is provided in particular by an engine of the FFA.

[0067] On inertia J motThese torques act on the motor of the FFA via a further spring-damper term 40-2 and the resulting torques M cZst and M dZst (in the translation ratio i SP of the steering gear and the resulting torque M cd ) onto the rack with mass m Zst As an intermediate step, starting from the sum of the torques M cL , M dL (via a resultant torque M) BMot specific engine angle acceleration φ̈ Mot ) a (target) motor angular velocity φ̇ Mot a motor (the steering or RWA) is determined, which is simultaneously used to determine a control deviation Δ φ , Δ φ ̇ with the corresponding steering wheel angular velocity φ LMess serves.

[0068] The external shear force F continues to act on the rack Zst, which is determined at least partially from a detected or determined lateral acceleration signal or lateral force signal. The resulting torque M BZst is (via a rack and pinion acceleration ẍ Zst the rack mass m Zst ) a rack speed ẋ Zst set. The rack speed ẋ Zst is regulated accordingly, whereby a control deviation of a corresponding motor angular velocity φ̇ is used. Mot with the help of a translation ratio i SP is determined by the steering gear.

[0069] Furthermore, friction can be taken into account in both the FFA and the steering gear using a friction model 41-1, 41-2. This is based on the motor angular velocity φ̇. Mot or the rack speed ẋ Zst a torque M caused by friction ReibMot or a force F ReibZstdetermined. Known friction models can be used for this purpose.

[0070] A further control deviation is calculated based on the specified (target) torque M. cdZst an electric machine on the steering gear and the result of the spring-damper term 40-1, whereby in particular the torque M caused by friction ReibMot is taken into account.

[0071] Through the parameters d CL , c CL In particular, the first feedback component can be adjusted using the parameters d. Zst , c Zst The second feedback component, in particular, can be adjusted. Furthermore, parameters of the friction models can also be used to adjust the feedback components. Additionally, the inertia J can also be adjusted. mot and the rack mass m Zst as parameters.

[0072] By setting (or regulating) the motor angular velocity φ̇Mot The driver experiences the torque M of the FFA's engine at the steering handle. Feedback . Due to the respective couplings in the control loop, both the first feedback component (incoming path) and the second feedback component (return path) are included.

[0073] The Fig. Figure 4 shows a schematic flowchart of embodiments of the method for operating a steering system for a vehicle. The method can be implemented, in particular, by means of a steering system such as the one described in the Fig. 1 is shown.

[0074] In process step 100, feedback at a steering handle of the steering system is determined based on a first feedback component and a second feedback component, wherein the first feedback component represents a forward path of an effect chain starting from the steering handle in the direction of the at least one steerable wheel of the steering system and wherein the second feedback component represents a return path of an effect chain starting from the at least one steerable wheel in the direction of the steering handle.

[0075] In process step 101, the second feedback component is determined at least partially based on a recorded and / or determined lateral acceleration and / or a recorded and / or determined lateral force.

[0076] Procedure steps 100 and 101 can also be performed simultaneously. Procedure steps 100 and 101 are, in particular, performed repeatedly.

[0077] In process steps 100 and 101, it may be provided in particular that the feedback components are determined by means of a modeled virtual steering system.

[0078] Further embodiments of the method have already been described above with reference to the steering system. Reference symbol list 1 Steering system 2 Steering handle 2-1 Steering wheel angle sensor 2-2 Actuator 3 Steering 3-1 electric machine 3-2 Steering gear 3-3 rack 3-4 Steering sensors 4 Control unit 4-1 Computing Equipment 4-2 storage 5 Lateral acceleration sensor 6 Lateral force sensor 10 Feedback 10-1 first feedback component (outbound path) 10-2 second feedback component (return path) 30 Outbound path 31 Return path 40-x Spring-damper term / -system 41-x friction model 50 vehicles 52 steerable wheel 100-101 procedural steps a y Lateral acceleration c L Parameters of the spring-damper system c Zst Parameters of the spring-damper system d L Parameters of the spring-damper system d Zst Parameters of the spring-damper system F ReibZst Force caused by friction F y Lateral force (vehicle reaction force) F Zst Rack and pinion force i SP Translation ratio J L Inertia of the steering handle J mot Inertia of the FFA engine m FFA second mass (FFA) m RWA first mass (RWA) m Zst mass of the rack M BZst Resultant torque M cdZst (Target) torque M cLSteering wheel angle-proportional torque M cZst Resultant torque M dL Steering wheel angle speed proportional to torque M Feedback Feedback to the driver M ReibMot torque caused by friction ẋ Zst Rack speed φ LMess detected steering wheel angle φ̇ Mot Motor angle speed

Claims

[1] Method for operating a steering system (1) for a vehicle (50), wherein feedback (10) at a steering handle (2) of the steering system (1) is determined starting from a first feedback component (10-1) and a second feedback component (10-2), wherein the first feedback component (10-1) represents a forward path (30) of an effect chain starting from the steering handle (2) in the direction of the at least one steerable wheel (52) of the steering system (1), and wherein the second feedback component (10-2) represents a return path (31) of an effect chain starting from the at least one steerable wheel (52) in the direction of the steering handle (2), where the second feedback component (10-2) is at least partially based on a detected and / or determined lateral acceleration (a y ) and / or a recorded and / or determined shear force (F y ) is determined; where the feedback components (10-x) are determined by means of a modeled virtual steering system, and where the steering system (1) is modeled as a two-mass oscillator. [2] Method according to claim 1, characterized by , that the influence of the first feedback component (10-1) and / or the second feedback component (10-2) on the feedback (10) is adjustable. [3] Method according to claim 1 or 2, characterized by , that the first feedback component (10-1) is taken into account by means of a spring-damper term (40-1), wherein a steering wheel angle-proportional term and a steering wheel angle-velocity-proportional term are derived from the lateral acceleration (a y ) or shear force (F y ) specific rack force (F Zst ) are added. [4] Method according to any of the preceding claims, characterized by , that parameter (c L , d L , c Zst , d Zst) of the spring-damper term (40-x) or the virtual steering are adjustable. [5] Method according to any of the preceding claims, characterized by , that friction acting on virtual masses of the virtual steering is taken into account by means of friction models (40-x). [6] Method according to one of claims 4 or 5, characterized by , that by means of the parameters (c L , d L , c Zst , d Zst ) various selectable steering modes are provided. [7] Method according to any one of claims 4 to 6, characterized by , that the parameters (c L , d L , c Zst , d Zst ) are chosen or have been chosen taking into account a situation and / or a scenario and / or a user preference. [8] Method according to any of the preceding claims, characterized by , that any friction and / or inertia occurring in the steering system is compensated for. [9] Steering system (1), comprising: a steering handle (2) for detecting a steering input from a driver and for providing feedback (10) to the driver, at least one steerable wheel (52), a steering mechanism (3) for setting a steering angle of the at least one steerable wheel (52), and a control device (4) wherein the control device (4) is configured to determine the feedback (10) at the steering handle (2) of the steering system (1) starting from a first feedback component (10-1) and a second feedback component (10-2), wherein the first feedback component (10-1) represents a forward path (30) of an effect chain starting from the steering handle (2) in the direction of the at least one steerable wheel (52) of the steering system (1), and wherein the second feedback component (10-2) represents a return path (30) of an effect chain starting from the at least one steerable wheel (52) in the direction of the steering handle (2), and the second feedback component (10-2) at least partially based on a recorded and / or determined lateral acceleration (a y ) and / or a recorded and / or determined shear force (F y ) to determine; where the feedback components (10-x) are determined by means of a modeled virtual steering system, and where the steering system (1) is modeled as a two-mass oscillator.

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