Method for operating a steer-by-wire steering system and steer-by-wire steering system

Abstract

The invention relates to a method for operating a steer-by-wire steering system (1), wherein the steer-by-wire steering system (1) is coupled to a driver assistance system (54) which can perform steering interventions (10) superimposed on a steering input from the driver, wherein during a steering intervention (10) of the driver assistance system (54), a control variable (21) of the steering system (1) is estimated based on at least one steering wheel state variable (23) detected at a steering handle (51) by means of a sensor (5) and detected and / or obtained vehicle dynamics variables, wherein a feedback torque (20) generated at the steering handle (51) by means of an actuator (6) is determined based on the estimated control variable (21). The invention further relates to a steer-by-wire steering system (1).

Description

[0001] The invention relates to a method for operating a steer-by-wire steering system and a steer-by-wire steering system. In particular, the invention relates to a method for operating a steer-by-wire steering system and a steer-by-wire steering system in which the steer-by-wire steering system is coupled with a driver assistance system that can perform steering interventions superimposed on a steering input from the driver.

[0002] The transition from mechanically coupled to mechanically decoupled (steer-by-wire, SbW) steering systems will likely become state-of-the-art in the automotive industry within this decade. With this technology, the driver no longer has the ability to steer the wheels without an electronic connection. The driver's steering inputs are electronically recorded and implemented by a control algorithm at the steering gear using an electric motor. The elimination of the mechanical connection opens up numerous new possibilities for supporting the driver in various driving situations. For example, a superimposed (wheel) steering angle can be applied to stabilize the vehicle in critical driving situations. Furthermore, with steer-by-wire systems, the input for feedback to the driver is no longer inherently felt at the steering wheel but must be defined and transmitted as a target value to an actuator at a steering handle.

[0003] This combination allows for an additional steering input at the steering gear without the driver feeling this input at the steering wheel. Particularly when larger steering inputs are necessary for stabilization, decoupling the steering input from the steering wheel is in the driver's interest. However, this also raises the challenge of determining the proportions of the steering input (especially torque) that are derived from the driver's input and the superimposed steering input, in order to differentiate between the two and disregard the latter.

[0004] The invention is based on the objective of creating a method for operating a steer-by-wire steering system and a steer-by-wire steering system with which improved feedback is possible during decoupling.

[0005] The problem is solved according to the invention by a method with the features of claim 1 and a steer-by-wire steering system with the features of claim 9. Advantageous embodiments of the invention are set forth in the dependent claims.

[0006] In particular, a method for operating a steer-by-wire steering system is provided, wherein the steer-by-wire steering system is coupled with a driver assistance system which can perform steering interventions superimposed on a steering input from the driver, wherein during a steering intervention of the driver assistance system an actuating variable of the steering system is estimated based on at least one steering wheel state variable detected by a sensor at a steering handle and detected and / or obtained vehicle dynamics variables, wherein a feedback torque generated at the steering handle by an actuator is determined based on the estimated actuating variable.

[0007] Furthermore, a steer-by-wire steering system is created, comprising a steering wheel module with a sensor configured to detect at least one steering wheel state parameter as a steering input at a steering handle, and with an actuator configured to generate a feedback torque at the steering handle, a steering module configured to set a steering angle at at least one steerable wheel based on the detected steering input, a communication link between the steering wheel module and the steering module, and a control device, wherein the control device is configured to superimpose a steering intervention requested by a driver assistance system coupled with the steer-by-wire steering system with the detected steering input.and, during a steering intervention by the driver assistance system, to estimate a control variable of the steering system based on at least one steering wheel state parameter detected at the steering handle and detected and / or received vehicle dynamics parameters, and to determine a feedback torque generated at the steering handle based on the estimated control variable.

[0008] The method and the steer-by-wire steering system enable the driver to receive feedback at the steering wheel. This feedback does not include the steering input of the driver assistance system, but rather only the driver's steering input as detected at the steering wheel. This is achieved by determining the feedback torque during a steering input from a control variable estimated from at least one steering wheel state parameter detected at the steering wheel and from detected and / or received vehicle dynamics parameters. These vehicle dynamics parameters are, in particular, current vehicle dynamics parameters that are detected by sensors and / or determined in other ways and / or queried and / or received by a vehicle control unit. The feedback torque is therefore determined without considering the steering input of the driver assistance system.

[0009] A vehicle dynamics parameter is, for example, vehicle speed, lateral acceleration, yaw rate, or sideslip angle.

[0010] A steering wheel state parameter is, in particular, a steering wheel position or a change in the steering wheel position, for example a steering wheel angle or a steering wheel angle speed.

[0011] A steering condition parameter is, for example, a rack position, a rack speed, a motor angle of the electric steering machine, or a motor angle speed of the electric machine.

[0012] The manipulated variable is, in particular, a torque (motor torque), especially of an electric machine, which directly or indirectly moves a rack or pushrod of the steering system. In principle, however, the manipulated variable can also be another quantity, for example, a force or a voltage. A controlled variable is, in particular, a steering angle of the at least one steerable wheel or a rack or pushrod position.

[0013] The driver assistance system can also be integrated as part of the steer-by-wire steering system.

[0014] It is specifically intended that the defined feedback torque will be output via the actuator on the steering handle.

[0015] Parts of the steer-by-wire 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 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, include at least one computing unit and at least one memory.

[0016] In one embodiment, the manipulated variable is estimated using an Unknown Input Observer (UIO). This allows for particularly good results. Specifically, it is assumed that an estimated state vector used in the Unknown Input Observer converges to a real state vector. The state vector is estimated using the UIO; the manipulated variable (of the control in the steering module) is then calculated based on this estimated state vector. In this case, the manipulated variable (especially a torque) is calculated that would have been required for the steering state (especially a target rack position corresponding to the steering input) determined from the driver's steering input (actual steering wheel state, e.g., steering wheel angle) to match the actual steering state (especially a rack position).This control variable is assumed to be the control variable that would have been present without the superimposed steering intervention.

[0017] In one embodiment, the respective values ​​of the feedback torque are blended during the transition between states with and without steering intervention by the driver assistance system. This prevents a jerky change in the feedback at the steering handle. The blending can occur, in particular, within a predefined time period, e.g., within 0.3 s to 1 s.

[0018] In one embodiment, the crossfading is performed depending on the strength of the steering intervention by the driver assistance system. This allows the strength of the steering intervention to be taken into account during the crossfading, making it barely perceptible or even imperceptible to the driver depending on the situation. The strength of the steering intervention can be expressed, for example, as an additional steering angle and / or an additional steering angle speed, and / or another parameter of the steering system suitable as a measure of the strength of the steering intervention, such as an additional rack position and / or an additional rack speed. It can also be provided, for example, that the crossfading period is determined based on the strength of the steering intervention.In particular, the longer the time period is chosen, the greater the steering intervention of the driver assistance system. This period can range from fractions of a second to 1 to 2 seconds.

[0019] In one embodiment, the crossfading is performed according to a predefined characteristic curve with embedded crossfading factors. This allows for even finer tuning of the crossfading to, for example, steering input and / or vehicle dynamics parameters. The crossfading factors can, for example, encompass a predefined time period during which the crossfading occurs.

[0020] In one embodiment, a further manipulated variable is estimated by means of another unknown input observer, starting from at least one steering state variable. The difference between the estimated manipulated variable and the estimated further manipulated variable is determined, and this determined difference is subtracted from the further manipulated variable. The feedback torque generated at the steering handle by the actuator is then determined based on the result of this subtraction. This allows feedback of the road surface characteristics acting on the steering system via the at least one steerable wheel, despite the decoupling of the steering intervention by the driver assistance system. In particular, both the manipulated variable and the further manipulated variable are estimated by means of separate unknown input observers, with both unknown input observers using the same model.This has the advantage that any modeling errors that may exist cancel each other out, because only the difference and not the absolute accuracy of the Unknown Input Observer is relevant here.

[0021] In one embodiment, a yaw rate is detected as a vehicle dynamics parameter using a yaw rate sensor. This allows the detected yaw rate to be taken into account when determining the manipulated variable. Based on the detected yaw rate, a force acting on the steering gear due to the vehicle dynamics (tire lateral force Fyv) can be determined. This can be done using a vehicle model or with the aid of a detected lateral acceleration and the detected yaw rate. Furthermore, a force at the front axle resulting from the vehicle's motion can also be calculated using these measurement data.

[0022] In one embodiment, a yaw rate is estimated as a vehicle dynamics parameter using a single-track model. This allows the yaw rate to be taken into account when determining the manipulated variable even without an additional sensor.

[0023] Further characteristics of the steer-by-wire steering system are described in the various implementations of the method. The advantages of the steer-by-wire steering system are the same in each of these implementations.

[0024] Furthermore, a vehicle is created, comprising a steer-by-wire steering system according to one of the described embodiments. The vehicle is, in particular, a motor vehicle.

[0025] 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 steer-by-wire steering system; Fig. 2a, Fig. 2b Schematic representations to illustrate the estimation of the manipulated variable; Fig. 3 a schematic flowchart of an embodiment of the method; Fig. 4 a schematic flowchart of another embodiment of the method.

[0026] The Fig. Figure 1 shows a schematic representation of an embodiment of the steer-by-wire steering system 1. The steer-by-wire steering system 1 comprises a steering wheel module 2, a steering module 3, and a communication link 4 between the steering wheel module 2 and the steering module 3. The steer-by-wire steering system 1 is, in particular, arranged in a vehicle 50. The steer-by-wire steering system 1 operates in a manner known per se. The steer-by-wire steering system 1 is configured to perform the method described in this disclosure. The method is described in more detail below with reference to the steer-by-wire steering system 1.

[0027] The steering wheel module 2 is configured to detect a steering input from a driver at a steering handle 51 (e.g., steering wheel) and to generate a feedback torque 20 at the steering handle 51. The steering input is detected as a steering wheel state variable 23 by means of a sensor 5 of the steering wheel module 2. The feedback torque 20 is generated by means of an actuator 6 of the steering wheel module 2 and applied to the steering handle 51.

[0028] The steering module 3 is configured to set a steering angle at at least one steerable wheel 52 based on the detected steering input and to determine the feedback torque 20. The required rack position of a rack 53 (or alternatively a connecting rod) is detected directly or indirectly as the steering state variable 25 by means of a sensor 7 of the steering module 3. The steering input is applied to the rack 53 and thereby to the wheels 52 by means of an electric motor 8 of the steering module 3. This is accomplished via a steering gear 11.

[0029] The steering input (steering wheel state size 23) and the feedback torque 20 are each transmitted via the communication link 4.

[0030] Furthermore, the steer-by-wire steering system 1 comprises a control unit 9, which in particular performs a respective control of the feedback torque 20 and the steering angle in a manner known per se. In particular, the control unit 9 is configured to control the steering angle and for this purpose to determine a manipulated variable 21, in particular a (target) torque for the electric machine 8.

[0031] The one in Fig. The embodiment shown in Figure 1 provides that the control unit 9 is arranged in the steering module 3. However, the control unit 9 can also be arranged in the steering wheel module 2 or outside of the steering wheel module 2 and the steering module 3.

[0032] The control unit 9 is further configured to superimpose a steering intervention 10 requested by a driver assistance system 54 of the vehicle 50 coupled with the steer-by-wire steering system 1 with the detected steering input, and during a steering intervention 10 of the driver assistance system 54 to estimate a control variable 21 of the steering system 1 based on the at least one steering wheel state parameter 23 detected at the steering handle 51 and detected and / or received vehicle dynamic parameters 30, and to determine a feedback torque 20 generated at the steering handle 51 based on the estimated control variable 21. In other words, during the steering intervention 10, the manipulated variable 21, which serves as the basis for determining the feedback torque 20, is not determined according to the procedure based on a manipulated variable 21 resulting from the superposition, but in particular only based on the steering input (steering wheel state actual variable 23) of the driver.At the wheels, however, a control variable 21 is implemented, which takes the superposition into account. The feedback to the driver is thus decoupled from the steering intervention 10 of the driver assistance system 54.

[0033] The steering wheel state parameter 23 is in particular a steering wheel position (especially a steering wheel angle position).

[0034] The manipulated variable 21 is in particular a torque (motor torque) of the electric machine 8. In principle, starting from the steering wheel state variable 23, a controlled variable of the steering, in particular a corresponding rack or pushrod position, can be determined by means of a model in a manner known per se, from which the manipulated variable 21 is then determined.

[0035] It may be provided that the manipulated variable 21 is estimated using an Unknown Input Observer (UIO). This embodiment is shown schematically by reference to the Fig. 2a and Fig. 2b illustrates this and describes it in more detail below.

[0036] The steer-by-wire steering system 1 is modeled (especially on the side of the steering module 3) using a model that is schematically shown in the Fig. Figure 2a shows the model. It comprises the vehicle 50, the steering gear 11, and the electric motor 8. Two quantities act on the steering gear 11 in the model: the tire lateral force F. yv and the torque M Mot of the electric machine 8. Since the torque M Mot If a model input is unknown and must be estimated (the estimated torque M), then the torque M is unknown. Mot (can then be set as control variable 21 in the control path). Furthermore, the following influencing factors affect vehicle 50: the rack position x Zst and the vehicle speed v.

[0037] Starting from the driver's steering input in the form of at least one steering wheel state parameter (in particular in the form of a steering wheel angle), which is converted into a rack position x in a manner known per se Zst can be converted, and the recorded and / or obtained vehicle dynamics parameters (that is, in the example, in particular the vehicle speed v) should be used to generate the control variable 21 required according to the procedure ( Fig. 1), in the example the required torque M Mot , can be estimated. Non-measurable parameters of the steering gear 11 are estimated, in particular, using models. The tire lateral force F yv is calculated in particular from recorded and / or obtained vehicle dynamics parameters and a linear single-track model.

[0038] The basis for the estimation is a state-space representation of the controlled system: x˙=A⋅x+B⋅u y=C⋅x+D⋅u where x is the state vector (e.g., rotor position of electric machine 8, rotor speed, rack position, rack speed), A is the system matrix, B is the input matrix, and u is the input variable. C is the output matrix and D is the pass-through matrix. The state-space representation, as a dynamic model, represents the entire system (see...). Fig. 2a) In this example, the overall system consists of the vehicle 50 and the steering gear 11. The vehicle 50 is modeled specifically as a linear single-track model, while the steering gear 11 is modeled, for example, as a two-mass oscillator. The state-space representation allows for the simulation of the dynamic behavior of the overall system.

[0039] The Fig. Figure 2b illustrates how the estimation of the manipulated variable (especially the torque / motor torque) is performed. The controlled system 40 and the Unknown Input Observer 41 are shown. The state space is calculated as follows: x˙=A⋅x+B⋅u+D⋅w where w is the unmeasurable or unknown input, in this case the manipulated variable (in particular the torque M). Mot ), which is to be estimated. Furthermore, the following results for the state space: y=C⋅x→y˙=C⋅x˙=C⋅A⋅x+C⋅B⋅u+C⋅D⋅w

[0040] For the Unknown Input Observer (UIO), the following also applies: z˙^=A^⋅z^+B^⋅u+L⋅y

[0041] In this context, Â and B̂ no longer correspond to clearly interpretable physical quantities, but are specified or chosen within the framework of the UIO's design.

[0042] With ẑ = x̂ + E · y, we get: x˙^=A^⋅x^+B⋅u+L⋅y−E⋅y˙ L and E can be referred to as feedback matrices (analogous to a Luenberger observer). x̂ is the estimated state vector.

[0043] With ẏ = C · ẋ = C · A · x + C · B · u + C ·D · w, we get: x˙^=A^⋅x^+B^⋅u+L⋅y−E⋅C⋅A⋅x−E⋅C⋅B⋅u−E⋅C⋅D⋅w

[0044] The deviation (estimation error) e˙=x˙−x˙^ corresponds: e˙=A⋅x+B⋅u+D⋅w−A^⋅x^−B^⋅u−L⋅y+E⋅C⋅A⋅x+E⋅C⋅B⋅u+E⋅C⋅D⋅w e˙=A⋅x+B⋅u+D⋅w−A^⋅x^−B^⋅u−L⋅y+E⋅C⋅A⋅x+E⋅C⋅B⋅u+E⋅C⋅D⋅w e˙=x⋅(A+E⋅C⋅A−L⋅C)−A^⋅x^+w⋅(D+E⋅C⋅D)+u⋅(B−B^+E⋅C⋅B)

[0045] The estimation error should be independent of the unknown input w (that is, in particular of the torque M to be estimated). Mot ) be such that: D+E⋅C⋅D=0 and thus E=−D⋅(C⋅D)−1

[0046] The estimation error should remain independent of the measured quantity or input quantity u (that is, in particular of the tire lateral force F). yv ) be such that: B−B^+E⋅C⋅B=0 and thus B^=B+E⋅C⋅B

[0047] What remains is a term that is independent of the known measured quantity u and the unknown measured quantity w: e˙=x⋅(A+E⋅C⋅A−L⋅C)−A^⋅x^

[0048] The matrix  is chosen such that the estimation error depends only on this matrix: A^=A+E⋅C⋅A−L⋅C

[0049] The estimation error ultimately amounts to: e˙=A^⋅e

[0050] Therefore, if the eigenvalues ​​of  have negative real parts, the estimation error converges to 0. The eigenvalues ​​can be chosen freely if Kalman's criterion for complete observability is met.

[0051] The unknown input w of the UIO, that is, the manipulated variable (in particular the torque M) Mot), is calculated in such a way that the estimation error ė is minimized. The estimation error here exists between the measured state variables (expressed in the state vector y, which includes, for example, a rack position, a rack velocity, a rotor position, and / or a rotor velocity) and the modeled state variables of the steering gear 11. In particular, it is assumed that an actual value of the measured state variables corresponds to a steering input (e.g., an actual position of the rack is equated with a target position, as resulting from a steering input by the driver at the steering handle). That is, it is assumed that the steering input as a target variable is immediately and without delay converted into the actual value. In other words: If the estimation error e = x - x̂ vanishes, then the unknown input w, and thus the manipulated variable (especially the torque M), can be determined. Mot) can be calculated (estimated) using the preceding equations.

[0052] In particular, it is provided that a steering input detected at a steering handle 51 of the steer-by-wire steering system 1 in the form of the steering wheel state variable 23 (especially a steering wheel angle) is fed as input to the Unknown Input Observer (UIO) (here in the form of the state vector y). The steering wheel state variable 23 is converted into the state vector in a manner known per se. For example, if a steering wheel angle is detected as the steering wheel state variable 23, it can be converted into a rack position x in a manner known per se. Zst The values ​​can be converted. A rack speed can be calculated from the time derivative of the values.

[0053] It may be provided that the respective values ​​of the feedback torque 20 are blended during the transition between states with and without steering intervention of the driver assistance system 54. The blending takes place over a predetermined period of time.

[0054] It may be provided that the crossfading occurs depending on the strength of the steering intervention 10 of the driver assistance system 54. In particular, it may be provided that the duration of the crossfading is selected depending on the strength of the steering intervention 10.

[0055] In particular, it may be provided that the blending takes place according to a predefined characteristic curve 12 with blending factors stored therein.

[0056] It can be provided that a further manipulated variable 24 is estimated by means of another unknown input observer based on at least one steering state actual variable 25, whereby a difference between the estimated manipulated variable 21 and the estimated further manipulated variable 24 is determined, wherein the determined difference is subtracted from the further manipulated variable 24, and wherein the feedback torque 20 generated at the steering handle 51 by means of the actuator 6 is determined based on the subtraction result. The steering state actual variable 25 is in particular a rack (actual) position (or pushrod (actual) position) which takes the superposition into account, i.e., is actually present at the steering 1. The manipulated variable 21 and the further manipulated variable 24 are in particular torques of the electric machine 8. The two unknown input observers are structurally identical and are executed independently of each other.In other words, the procedure for estimating the further control variable 24 using the further Unknown Input Observer corresponds to that with reference to the . Fig. 2a and Fig. Procedure described in 2b.

[0057] It may be provided that a yaw rate 26 is recorded as a vehicle dynamics parameter by means of a yaw rate sensor 13.

[0058] It may be intended that a yaw rate of 26 is estimated as a driving dynamics parameter using a single-track model.

[0059] The Fig. Figure 3 shows a schematic flowchart of an embodiment of the method for operating a steer-by-wire steering system. The method is carried out, for example, using the steer-by-wire steering system as described above with reference to the Fig. 1 was described.

[0060] In step 100, it is checked whether a steering intervention by a driver assistance system is currently taking place. If this is not the case, step 100 is repeated.

[0061] If, however, this is the case, then in measure 101 at least one steering wheel state parameter, in particular a steering wheel angle, is recorded by means of a sensor on a steering handle.

[0062] In measure 102, vehicle dynamics parameters are recorded and / or maintained. These parameters include, in particular, vehicle speed.

[0063] In measure 103, a control variable of the steering system, in particular a torque of an electric machine, is estimated based on at least one steering wheel state variable detected at the steering handle by means of the sensor, in particular based on the detected steering wheel angle or a corresponding target value for a rack position, and the detected and / or obtained vehicle dynamics variables. The estimation can be carried out in particular using an Unknown Input Observer, as described above.

[0064] In measure 104, a feedback torque generated at the steering handle by means of an actuator is determined in a manner known per se, starting from the estimated manipulated variable, in particular from the estimated torque of the electric machine.

[0065] In particular, in measure 105, the specific feedback torque is output via the actuator on the steering handle.

[0066] The Fig. Figure 4 shows a schematic flowchart of another embodiment of the method for operating a steer-by-wire steering system. The embodiment is fundamentally the same as that shown in Figure 4. Fig. 3. The embodiment shown is designed as follows; identical measures are marked with the same reference numerals.

[0067] In this further embodiment, it is provided that a further manipulated variable, in particular a further torque of the electric machine, is estimated by means of a further unknown input observer starting from at least one steering state variable, in particular starting from a rack position, wherein a difference between the estimated manipulated variable and the estimated further manipulated variable is determined, wherein the determined difference is subtracted from the further manipulated variable, and wherein the feedback torque generated at the steering handle by means of the actuator is determined starting from the subtraction result. Measures 201 to 206 are implemented for this purpose.

[0068] In measure 201, at least one steering condition parameter, in particular the rack position, is detected by means of a sensor or determined in another way.

[0069] Measure 202 involves recording and / or maintaining vehicle dynamics parameters. These parameters include, in particular, vehicle speed. Measures 102 and 202 can also be implemented as a single, combined measure.

[0070] In measure 203, the additional control variable of the steering system, in particular a torque of an electric machine, is estimated based on at least one steering state parameter, specifically the rack position, and the recorded and / or obtained vehicle dynamics parameters. The estimation is performed using the additional Unknown Input Observer, as described above.

[0071] In measure 204, a difference is determined between the estimated manipulated variable and the estimated additional manipulated variable.

[0072] In measure 205, the determined difference is subtracted from the other control variable.

[0073] In measure 206, the feedback torque generated at the steering handle by means of the actuator is determined based on the subtraction result. Reference symbol list 1 Steer-by-wire steering system 2 Steering wheel module 3 Steering module 4 Communication link 5 Sensor 6 Actuator 7 Sensor 8 Electric motor 9 Control unit 10 Steering intervention (driver assistance system) 11 Steering gear 12 characteristic curve 13 Yaw rate sensor 20 Feedback moment 21 Control variable 23 Steering wheel condition is size 24 additional control variables 25 Steering condition is size 26 Yaw rate 30 Driving dynamics parameter(s) 40 Control section 41 Unknown Input Observer (UIO) 50 vehicles 51 Steering handle 52 steerable wheel 53 Rack and pinion 54 Driver assistance systems 100-105 measures of the procedure 200-206 Measures of the procedure A system matrix B Input matrix C Output matrix D through matrix F yv Tire lateral force M Mot Torque (engine torque) u Input size v Vehicle speed w non-measurable / unknown input (estimated) x state vector (target) x Zst Rack position y state vector (actual state)

Claims

[1] Method for operating a steer-by-wire steering system (1) wherein the steer-by-wire steering system (1) is coupled with a driver assistance system (54) which can perform steering interventions (10) superimposed on a steering input from the driver, wherein during a steering intervention (10) of the driver assistance system (54) a control variable (21) of the steering system (1) is estimated based on at least one steering wheel state variable (23) detected at a steering handle (51) by means of a sensor (5) and detected and / or received driving dynamics variables, wherein a feedback torque (20) generated at the steering handle (51) by means of an actuator (6) is determined starting from the estimated manipulated variable (21). [2] Method according to claim 1, characterized by , that the manipulated variable (21) is estimated using an Unknown Input Observer (41). [3] Method according to claim 1 or 2, characterized by, that the respective values ​​of the feedback torque (20) are blended during the transition between states with steering intervention (10) and without steering intervention (10) of the driver assistance system (54). [4] Method according to claim 3, characterized by , that the crossfading occurs depending on the strength of the steering intervention (10) of the driver assistance system (54). [5] Method according to claim 3 or 4, characterized by , that the blending takes place according to a predefined characteristic curve (12) with blending factors stored therein. [6] Method according to any of the preceding claims, characterized by, that a further manipulated variable (24) is estimated by means of a further Unknown Input Observer starting from at least one steering state actual variable (25), wherein a difference between the estimated manipulated variable (21) and the estimated further manipulated variable (24) is determined, wherein the determined difference is subtracted from the further manipulated variable (24), and wherein the feedback torque (20) generated at the steering handle (51) by means of the actuator (6) is determined starting from the subtraction result. [7] Method according to any of the preceding claims, characterized by , that a yaw rate is recorded as a vehicle dynamics parameter by means of a yaw rate sensor (13). [8] Method according to any of the preceding claims, characterized by , that a yaw rate is estimated as a vehicle dynamics parameter using a single-track model. [9] Steer-by-wire steering system (1), comprising: a steering wheel module (2) with a sensor (5) configured to detect at least one steering wheel state parameter (23) as a steering input at a steering handle (51), and with an actuator (6) which is configured to generate a feedback torque (20) at the steering handle (51), a steering module (3) configured to set a steering angle at at least one steerable wheel (52) based on the detected steering input, a communication link (4) between the steering wheel module (2) and the steering module (3), and a control device (9), wherein the control device (9) is configured to to overlay a steering intervention (10) requested by a driver assistance system (54) coupled with the steer-by-wire steering system (1) with the detected steering input, and during a steering intervention (10) of the driver assistance system (54) to estimate a control variable (21) of the steering system (1) based on the at least one steering wheel state parameter (23) detected at the steering handle (51) and detected and / or received vehicle dynamics parameters, and to determine a feedback torque (20) generated at the steering handle (51) starting from the estimated manipulated variable (21). [10] Vehicle (50) comprising a steer-by-wire steering system (1) according to claim 9.

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