Method and control circuit for controlling an active rear axle steering system during a turn from straight-line travel, and motor vehicle

Abstract

The present invention relates to a method for controlling an active rear axle steering device (16) of a motor vehicle (10) during a turn from straight-line travel (20) under a given actual dynamic condition guided by the wheels of the motor vehicle (10), wherein an actual steering signal (25) of the motor vehicle (10) is received from at least one sensor via a control circuit (23), and then a curve of a differential signal (26) changing over time is calculated from the actual steering signal (25) by means of a dynamic model guided by the wheels, the differential signal describing the deviation between the actual steering signal (25) and a virtual nominal steering signal, which is required, for example, to perform steering with a predetermined nominal dynamic, and a nominal steering signal (27) for the rear axle steering device (16) is generated from the differential signal (26) by a predetermined conversion rule, and the rear axle steering device (16) is driven with the nominal steering signal.

Description

Technical Field

[0001] This invention relates to a method and control circuit for controlling a rear axle steering system in a motor vehicle during a turn from straight-line travel. For this purpose, the rear axle steering system is designed to be active, that is, it has at least one actuator to adjust the rear wheel steering angle according to a control signal. The invention also includes a motor vehicle having an embodiment of such an active rear axle steering system and the control circuit. Background Technology

[0002] The “steering” process described herein refers to the time period during which the wheels on the front axle of a motor vehicle react to or track or turn according to a change in the steering wheel angle after such a change. The wheels do not react immediately to changes in the steering wheel angle, but the chassis possesses kinematics and / or elastokines, which, due to these kinematics and / or elastokines, create a dynamic process during which the wheels adjust their wheel deflection angle according to the newly set steering wheel angle, as the steering wheel angle changes or as the new steering wheel angle is adjusted to a new steering position. In other words, the lateral steering force required for the new steering wheel angle must first gradually increase. The steering thus ends when the wheel deflection angle reaches a predetermined angle value through the newly set steering wheel angle, i.e., until the final value of the lateral steering force is reached. The resulting delay in control, or the time misalignment between changing the steering wheel angle on one hand and reaching a fixed wheel deflection angle / final lateral steering force on the other, arises from elasticity and inertia within the chassis, which is known, for example, in itself.

[0003] Active rear axle steering systems are known, for example, from DE 10 2018 007 860 A1. This patent document describes an active rear axle steering system that can be used to stabilize the driving dynamics of a motor vehicle by reducing the required steering deflection angle on the front axle steering system, which is compensated for by the rear axle steering system.

[0004] Improved steering characteristics in motor vehicles are known from patent document DE 10 2015 005 023 A1. Accordingly, a superimposed steering is required on the front axle to generate an additional superimposed angle for adjusting the additional steering deflection angle. Additionally, the rear wheel steering angle can also be adjusted for the rear axle steering system. However, this is merely a proportional conversion; that is, given a current steering wheel angle, the rear wheel steering angle is set to a predetermined value according to a characteristic curve. However, this does not compensate for the dynamics of wheel guidance, which is given, for example, by elastic / limited inherent stiffness and / or by the natural frequency of the chassis. On the contrary, swaying may occur if the amplification is too high.

[0005] As is known from patent document DE 10 2016 210 256 A1, the driving dynamics of a motor vehicle can be stabilized by a rear axle steering system under conditions of severe steering movement on the steering wheel. However, for this to be achieved, severe steering sway on the steering wheel must be identified.

[0006] As is known from patent document DE 10 2019 213 969 A1, by adjusting the rear wheels relative to the front wheels, the chassis of a motor vehicle can be supported by an active rear axle steering system, thereby reducing its tendency to roll.

[0007] Existing technologies do not provide a solution that can compensate for kinematics and elastokines in the wheel guidance of the front wheels, in order to delay the steering angle or lateral steering force of the front wheels when the vehicle is turning, and to utilize chassis-related dynamics to adapt to new angle values ​​predetermined by the newly set steering wheel angle. Summary of the Invention

[0008] The object of the present invention is to adjust the steering characteristics of a motor vehicle, starting from straight-line driving, at least with small changes in steering wheel angle, so as to obtain a time-varying curve of lateral force formation / lateral force construction toward a new fixed value, which is generated, for example, in an inherent stiffness greater than the available inherent stiffness of the wheel guide.

[0009] This objective is achieved through the subject matter of the independent claims. Advantageous extensions of the invention are obtained through the dependent claims, the following description, and the accompanying drawings.

[0010] As a solution, the present invention includes a method for controlling an active rear axle steering device for a motor vehicle during a turn from straight-line travel. The rear axle steering device thus has actuators for motor and / or hydraulic deflection of the rear wheels to adjust the rear wheel steering angle on the rear axle. "Steering" as used herein is the dynamic process described previously, from changing the steering wheel angle on the steering wheel until a corresponding fixed wheel deflection angle and / or lateral guiding force on the front wheels is reached. An alternative definition of steering is the dynamic process of changing the steering wheel angle from an initial value to a new value until a lateral guiding force on the road corresponding to that new steering wheel angle is reached. This method assumes that straight-line travel exists at the beginning. Therefore, it is assumed that the motor vehicle first travels in a straight line, and then the driver adjusts the steering wheel angle on the steering wheel to continue traveling diagonally forward, for example, to the right or left. The actual dynamics of wheel guidance describe how quickly and / or with what time-varying curve the wheel steering deflection angle or lateral guiding force follows the steering wheel position (i.e., with what kind of impulse response or step response). This is not an ideal step response (Dirac shock), but the actual dynamics of wheel guidance depend on the elasticity of chassis components, such as the elasticity of the steering rod and / or the inertia of the components. Natural frequencies, i.e., the inherent vibrational characteristics of the chassis, can also play a role. In short, it can be assumed that a mass-spring system is generated between the steering wheel on one side and the front wheel on the other side of the front axle, and the actual dynamics of wheel guidance are generated by the mass-spring system.

[0011] This method assumes (as a starting point) that the actual dynamics of the vehicle's wheel guidance are known. For example, the actual dynamics can be measured on a prototype of the vehicle and / or numerically calculated through simulation and / or vehicle models.

[0012] In this method, an actual steering signal (e.g., from the front axle steering system of a motor vehicle) is received from at least one sensor via a control circuit. A differential signal, describing the deviation of the actual steering signal from a virtual, rated steering signal, is calculated from the actual steering signal using a wheel-guided dynamic model. This differential signal describes the deviation of the actual steering signal from a virtual, rated steering signal, which is required, for example, to perform steering with a predetermined rated dynamic (in a given actual dynamic signal). Thus, for example, monitoring the current steering wheel angle, yaw rate, or lateral velocity generates the actual steering signal as a time signal. This actual steering signal can be converted or interpreted using the wheel-guided dynamic model to produce a described impulse or step response up to the chassis of the front axle. However, what is ultimately of interest here is what kind of differential signal is generated, i.e., what deviation it has from the ideal or at least one predetermined rated dynamic, such as an increase in lateral force or yaw rate (for the expected turn). Therefore, the differential signal describes what kind of rated steering signal is needed to achieve the desired or predetermined rated dynamics, i.e., the development of lateral force build-up or steering response characteristics or yaw rate over time (rotational speed around the vehicle's vertical axis), which, for example, mimics or simulates a stiffer-designed front axle. For example, in a very simple implementation, the differential signal can be predetermined from the actual steering signal via tables and / or characteristic curves, where, in the manner described, the differential signal is a dynamic signal, i.e., a predetermined curve that varies over time, which is not a simple constant (as is the case in the prior art), but rather describes a change over time (a continuously differentiable time signal that does not have a constant progression in time). The actual steering signal here can be a simple step function, describing a jump or change from the original or previous steering wheel angle to a new (fixed) steering wheel angle. For example, the differential signal describes what difference or what steering characteristics the driver or vehicle must exhibit if the driver wants to achieve the predetermined rated dynamics or lateral steering force of the front wheels (using only front-wheel steering). Differential signals can describe what additional value is still missing for lateral force increase or yaw rate in order to achieve rated dynamics.

[0013] A predetermined conversion rule is used to generate a rated steering signal for the rear axle steering system from the differential signal, and the rear axle steering system is driven by this rated steering signal. The differential signal, i.e., the missing part of the steering characteristics on the front axle, is therefore not realized through the superimposed angle for front wheel steering, but rather the rated steering signal is predetermined on the rear axle steering system, thereby achieving rated dynamics through the rear axle steering system in the motor vehicle.

[0014] The present invention offers the advantage that the inherent stiffness and / or natural frequency, i.e., the kinematics and elastic kinematics of the front axle in general, need not be designed so strictly or rigidly that a predetermined rated dynamic is achieved during a turn from straight-line driving, which would otherwise require a very “stiff” front axle design (at the expense of ride comfort). Instead, for the sake of ride comfort, the front axle can, for example, be designed to be “softer,” i.e., with lower inherent stiffness, and the rated dynamics desired for a turn from straight-line driving can be achieved or mimicked by a rear axle steering mechanism. Thus, in other driving conditions, the “softer” design of the front axle, which is advantageous for ride comfort, i.e., an inherent stiffness that is actually too low for rated dynamics, can also be retained.

[0015] The invention also includes extensions that generate additional advantages.

[0016] One extended scheme includes a dynamic model of wheel guidance for the inherent stiffness D and natural frequency ω0 of the front axle steering system, respectively considering the actual values ​​of D. ist ω 0ist and rated value D soll and ω 0soll The resulting advantage is that it takes into account both the stiffness of the front axle steering system and the spring characteristics, thus avoiding swaying motion of the vehicle. For example, the corresponding actual values ​​can be determined by measurement on a prototype vehicle and / or by simulation and / or a vehicle model, and these actual values ​​can be stored as parameters in the control circuit. The corresponding ratings can be predetermined according to the desired rated dynamics.

[0017] One extended approach involves the actual steering signal being a time signal with a continuous or sampled process, and the model including a transfer function describing the relationship V between the actual dynamics and the rated dynamics, wherein the rated dynamics, in particular, give a larger axle lateral stiffness compared to the actual dynamics, and the rated steering signal or differential signal is calculated using the transfer function. Therefore, the actual steering signal can be processed continuously or gradually as a continuous time signal or as a sampled time signal using the transfer function to continuously or gradually obtain the current value for the rated steering signal. For example, mathematical convolution can be used for this. Thus, the rated steering signal can be tracked even when the actual steering signal changes continuously. For example, the actual dynamics can describe the transfer of the curve from the actual steering signal to the actual steering deflection angle or actual lateral steering force over time. Correspondingly, the rated dynamics can describe the curve of the rated steering deflection angle or rated lateral steering force over time associated with the time signal of the actual steering deflection angle. To calculate the time signal of the actual steering signal using the transfer function, the aforementioned convolution can be used in the so-called time domain. However, preferably or with less computational cost, multiplication can be used instead of convolution in the frequency range, for example based on the Laplace transform, which is known itself, for example, from the prior art.

[0018] The following describes the preferred relationship V for describing actual dynamics and rated dynamics (natural stiffness D and natural frequency ω0). This extended scheme includes designing the transfer function as PD²T² terms and giving the relationship V as:

[0019]

[0020] Rated turn signal L dyn (s) is calculated from the actual steering signal L(s).

[0021] L dyn (s)=L(s·V

[0022] The differential signal is calculated as D(s) = L dyn (s)-L(s). The transfer function as the PD2T2 term can be realized, taking into account the first and second time derivatives, and therefore also the vibration characteristics of the front axle steering system. The differential signal is given here in the Laplace range D(s) and can be converted into a time signal in a manner known to itself via the inverse Laplace transform. This differential signal then indicates what contribution is needed by the rear axle steering system to achieve the rated dynamics given the actual steering signal from the front axle steering system. The rated dynamics specifically describe the time characteristics of the vehicle as a response to changes in the actual steering signal when the lateral steering force is adjusted or “fluctuated,” and here “acts” as or simulates the predetermined rated natural stiffness and rated natural frequency.

[0023] One extended approach involves calculating the rated steering signal for controlling the rear axle steering system from a differential signal using a scaling factor or a dynamic model of the vehicle. The rated steering signal for the rear axle steering system can be calculated from a time signal that can be derived from the differential signal D(s) using a scaling factor; this is particularly easy to implement in terms of computational techniques, as only one multiplication is required. However, a dynamic model of the vehicle can also be used to adjust the rear wheel steering angle for the rear axle steering system. Examples of such dynamic models are the so-called single-track model and models for tire forces. The steering angle signal for controlling the rear axle steering system is referred to herein as the "rated signal" to indicate that the rear axle steering system can also have an adjuster that can predetermine the rated steering signal as a rated value signal.

[0024] One extended approach involves parameterizing the dynamic model of the wheel-guided system as a function of the vehicle's current speed. In other words, different speed values ​​*v* can be specified, and correspondingly different or adapted values ​​for the inherent stiffness and / or natural frequency are also predetermined. These values ​​can be predetermined using tables and / or computational functions. In other words, the inherent stiffness *D* and / or natural frequency *ω0* are predetermined as a function of the vehicle's speed *v*. The speed *v* can be detected in a manner known per se. For example, the speed *v* can be a signal intercepted on the vehicle's data bus, such as in a CAN bus (CAN-Controller Area Network).

[0025] One extended approach includes generating a rated steering signal only upon recognition of prior straight-line driving, wherein, in order to recognize straight-line driving, at least one of the following signals is monitored:

[0026] Steering wheel angle

[0027] Front axle steering angle

[0028] · Lateral acceleration

[0029] ·Yaw rate

[0030] Furthermore, straight-line driving is identified if at least one or all of the monitored signals operate within their respective predetermined value ranges for a predetermined minimum duration. In other words, the rear axle steering is controlled only if straight-line driving is actually present as an initial condition. This initial condition can be identified in at least one of the described variables. Multiple of these signals can also be monitored in combination. By prescribing a minimum duration, such as at least one second, at least five seconds, or at least 30 seconds, it is possible to prevent the rear axle steering from being activated, for example, in S-curves. The minimum duration is preferably in the range of one second to one minute. The described signals are themselves available in the vehicle and can be read from the data bus, for example, in the manner described.

[0031] One extension includes generating a rated steering signal for the rear axle steering system only under predetermined driving conditions, including at least one of the following:

[0032] • The steering rate is less than the predetermined maximum value.

[0033] • Driving on highways and rural roads

[0034] Driving in construction site areas,

[0035] The actual steering signal indicates a fixed steering angle that is less than the predetermined maximum value.

[0036] Steering rate is the speed at which the steering wheel turns. If there is a response only at low steering rates, oversteer due to rear-wheel steering can be avoided in strong or abrupt steering situations. For example, highway and rural road driving can be detected based on map data by identifying the vehicle's current geographical location (determined, for example, by a receiver of a GNSS global navigation satellite system, such as GPS). Construction sites can be detected by monitoring the surrounding environment in a manner known per se, for example, by analyzing camera images from environmental cameras based on predetermined image patterns, such as the signal colors or patterns (red and white stripes) of a construction site. This method can also be limited to driving situations where the actual steering signal indicates only a small, fixed final steering angle, i.e., the actual steering signal is less than, for example, the maximum value in the range of 5 to 20 degrees, especially 5 to 15 degrees. If the change in steering wheel angle from the start of straight-line driving is greater than the maximum value, then the rated steering signal for the rear-axle steering system can also be suppressed or avoided.

[0037] As an alternative solution, the present invention includes a control circuit for a motor vehicle, wherein the control circuit is configured to receive an actual steering signal from the front axle steering system of the motor vehicle, generate a rated steering signal for an active rear axle steering system by means of an embodiment of the method according to any one of the preceding claims, and drive the rear axle steering system with the rated steering signal. The control circuit may be formed, for example, based on a control device or a composite device consisting of multiple control devices of the motor vehicle. The control circuit may have at least one microprocessor for executing the method. The control circuit may have program code configured to cause the control circuit to execute the method when executed by the control circuit. The program code may be stored in a data memory of the control circuit, and at least one microprocessor may be coupled to the data memory. Alternatively or additionally relative to the at least one microprocessor, at least one microcontroller and / or at least one FPGA (Field Programmable Gate Array) and / or at least one DSP (Digital Signal Processor) may be provided as a processor circuit.

[0038] As an alternative solution, the present invention includes a motor vehicle having an active rear axle steering system and at least one sensor for detecting actual steering signals from the front axle steering system of the motor vehicle, wherein at least one sensor and the rear axle steering system are coupled through an embodiment of the described control circuit. For example, at least one sensor may include a steering wheel angle sensor. The motor vehicle according to the invention is preferably designed as a motor vehicle, particularly as a passenger car or van, or as a bus or motorcycle.

[0039] The present invention also includes combinations of features from the described embodiments. The present invention also includes implementations having combinations of features from multiple of the described embodiments, provided that these embodiments are not described as mutually exclusive. Attached Figure Description

[0040] Embodiments of the present invention are described below. Therefore:

[0041] Figure 1 A schematic diagram of an embodiment of a motor vehicle according to the present invention is shown;

[0042] Figure 2 The graphs shown illustrate the time-varying curves of the actual steering signal and the time-varying curves of the differential signal, which are generated from the actual steering signal based on the transfer function.

[0043] Figure 3 A graph showing the time-varying curves of the actual steering signal and the differential signal is presented. Detailed Implementation

[0044] The embodiments described below are preferred embodiments of the present invention. In the embodiments, the components described in the embodiments represent various features of the invention that can be considered independent of each other, and these features also independently extend the invention. Therefore, this disclosure should also include combinations different from the combinations of features shown in the embodiments. Furthermore, the described embodiments can be supplemented by other features of the invention already described.

[0045] In the accompanying drawings, the same reference numerals denote elements that have the same function.

[0046] Figure 1 A motor vehicle 10 is shown, which may be an automobile, especially a passenger car or a truck. It shows how, when the steering deflection angle 14 is different from 0 degrees, the steering deflection angle 14 of the front wheels can be adjusted or predetermined by adjusting the steering wheel angle 13 on the front axle steering device 11 with the aid of the steering wheel 12, thereby generating a lateral guiding force 22 for turning.

[0047] In addition, a rear axle steering device 16 may be provided in the motor vehicle 10, which, as an active rear axle steering device, can adjust the rear wheel steering angle or the rear axle steering angle 19 by at least one actuator 17 on the rear wheel 18.

[0048] Here, in the motor vehicle 10, for a driving situation where the driver (not shown) changes the steering wheel angle 13 from the neutral position 21 for straight-line driving 20 on the steering wheel 12, the rear axle steering device 16 can be controlled by the control circuit 23 to support or predetermine the change in steering deflection angle 14 and / or the change or formation / increase of the lateral guiding force 22 toward a fixed value (which corresponds to the newly set steering wheel angle 13), thereby generating rated dynamics when the wheels are guided or when the lateral guiding force 22 is formed.

[0049] For this purpose, the steering wheel angle 13 can be measured, detected, or indicated as an actual steering signal 25 by at least one sensor 24. The control circuit 23 can receive the actual steering signal 25 and convert or map it into a differential signal 26 via a transfer function H. This differential signal indicates how many degrees or values ​​the steering wheel angle 13 must change to achieve a predetermined rated dynamic. The rated steering signal 27 can be determined, for example, from the differential signal 26 by multiplying it by a predetermined scaling factor. The rated steering signal 27 is provided to the rear axle steering unit 16 as a specification or rating for adjusting the rear axle steering deflection angle or rear axle steering angle 19; that is, the rear axle steering unit 16 can be controlled by the rated steering signal 27 via the control circuit 23.

[0050] Therefore, when adjusting the steering wheel angle 13, the driver generates a rated dynamic when the steering deflection angle 14 and / or the lateral guiding force 22 changes or tends to be stable or fluctuates. Although the front axle steering device 11 is not designed for this rated dynamic, for example, it may have a smaller inherent stiffness and / or other inherent frequency, which corresponds to the actual dynamic, for example.

[0051] Figure 2 This illustrates how, at time t, in relation to the actual steering signal 25, which can here correspond to the steering wheel angle 13 or yaw rate and is also denoted here as L(t), a dynamic or modified steering angle signal 30, also referred to here as L, is generated from the wheel-guided dynamic model according to the transfer function H. dyn (t) and describes the steering angle signal, which is needed, for example, to achieve rated dynamics in the curve of the increase or change of lateral steering force 22 or yaw rate over time. It is shown how, starting from straight-line driving 20 (the actual steering signal at 0 degrees), a new fixed angle value 31 can be generated by turning the steering wheel 12, which here can be, exemplarily, approximately 8 degrees. A turn 32 is thus generated. For this purpose, the front axle steering system generates a lateral steering force 22, which, however, cannot be provided immediately at the start of the steering maneuver. To accelerate or, according to rated dynamics, to increase or adjust the lateral steering force 22 to track the newly set actual steering signal 25 (with a new angle value 31), a virtual steering angle signal L... dyn (t) That is, the steering angle signal 30 is required, which can be calculated through a dynamic model, for which a larger inherent stiffness and / or other natural frequencies are assumed compared to the given actual dynamics. Based on steering signals 25 and 30, a virtual steering angle signal 30L can be derived. dyn The differential signal 26 is calculated by the difference between (t) and the actual steering signal 25.

[0052] At the end of the steering maneuver for turn 32, the driver can turn the steering wheel 12 in the opposite direction, generating another steering maneuver 34 at the new steering wheel angle 31'. In the manner shown, the driver can therefore also perform straight-line driving 20 by alternately performing the steering maneuvers for turns 32 and 34.

[0053] Figure 3 As shown, during steering maneuvers, the rear axle steering system steers in the opposite direction to the front axle (opposite oscillation). It can then be identified that there is no significant difference between the two steering angles shown, so that dynamic adjustment from the center (on-center) does not produce additional rated angles for the rear axle after the predetermined lateral guiding force is reached.

[0054] To optimally design the vehicle's steering response from straight-line driving (on-center) even with the presence of a soft and comfortable elastic motion characteristic of the front axle, a rear-axle steering system can be used. Because the rear axle of a vehicle typically has higher axle lateral stiffness than the front axle, even a small tilt angle on the rear axle results in significant lateral forces.

[0055] Optimizing steering response and ride comfort when driving in a straight line (on-center) is no longer a conflicting objective, but can be achieved simultaneously.

[0056] Specifically, the driver's steering wheel angle is measured using a steering wheel angle sensor (optionally, the steering angle of the front wheels). Based on this signal, a counter-steering motion of the rear wheels is calculated for small steering wheel angles (straight-line driving). This calculated additional angle of the rear wheels may only be effective for a very short period after the initial steering wheel movement so as not to negatively impact steering action and further progress of the turn.

[0057] For example, possible mathematical calculations can be performed using the described PD2T2 transfer function H. The parameterization of the PD2T2 transfer function preferably depends on the driving speed.

[0058] Straight-line driving can be defined based on the following signals:

[0059] - Steering wheel angle or front axle steering angle

[0060] - Lateral acceleration

[0061] - Yaw rate.

[0062] To achieve the rated dynamic design of the vehicle's steering response from straight-line driving (on-center) despite the soft and comfortable elasticity of the front axle, a rear-axle steering system can be used. Because the rear axle of a vehicle typically has higher axle lateral stiffness than the front axle, even a small tilt angle on the rear axle results in significant lateral forces.

[0063] In summary, these examples demonstrate how center-of-care (straight-line) steering response can be optimized using a "rear-axle steering" system.

Claims

1. A method for controlling an active rear axle steering device (16) of a motor vehicle (10) during a turn from straight-line travel (20) under given actual dynamic conditions of wheel guidance of the motor vehicle (10), the steering describing a dynamic process from changing the steering wheel angle on the steering wheel until reaching a corresponding fixed wheel deflection angle and / or lateral guiding force on the front wheels, wherein, Through the control circuit (23), Receive actual steering signals (25) from the vehicle (10) from at least one sensor. The curve of the differential signal (26) as a function of time is calculated from the actual steering signal (25) using a wheel-guided dynamic model. The differential signal describes the deviation between the actual steering signal (25) and the virtual rated steering signal required to perform steering with a predetermined rated dynamic. The wheel-guided dynamic model for the inherent stiffness D and natural frequency of the front axle steering device (11) takes into account the actual value D. ist ω 0ist and rated value D soll and ω 0soll ; A rated steering signal (27) for the rear axle steering device (16) is generated from the differential signal (26) according to a predetermined conversion rule, and the rear axle steering device (16) is driven by the rated steering signal. The actual steering signal (25) is a time signal. The model includes a transfer function (H) describing the relationship V between the actual dynamics and the rated dynamics. Compared to the actual dynamics, the rated dynamics provide a larger axle lateral stiffness. The rated steering signal or the differential signal (26) is calculated using the transfer function (H), and the relationship V is: The rated steering signal L is calculated from the actual steering signal L(s) using the formula Ldyn(s)=L(s)·V. dyn (s); The formula D(s) = L dyn The differential signal is calculated using (s)-L(s).

2. The method according to claim 1, wherein, The rated steering signal (27) for the rear axle steering device (16) is calculated from the differential signal (26) by means of the scaling factor or by means of the dynamic model of the motor vehicle (10).

3. The method according to claim 1 or 2, wherein, The parameterization (D) of the dynamic model of wheel guidance soll ω 0soll ) is set as a function of the current driving speed of the motor vehicle (10).

4. The method according to claim 1 or 2, wherein, The generation of the rated turn signal (27) is activated only when previous straight driving (20) is recognized, wherein, for recognition, at least one of the following signals is monitored: Steering wheel angle (13), Front axle steering angle Lateral acceleration, yaw rate, If at least one monitored signal operates within a predetermined value range for a predetermined minimum duration, then straight-line driving is identified (20).

5. The method according to claim 1 or 2, wherein, The generation of the rated steering signal (27) is limited to a predetermined driving condition, which includes at least one of the following: The steering rate is less than the predetermined maximum value. Driving on highways and rural roads. Driving in the construction site area The actual steering signal (25) indicates a fixed steering angle that is less than the predetermined maximum value.

6. A control circuit (23) for a motor vehicle (10), wherein, The control circuit (23) is configured to receive the actual steering signal (25) of the front axle steering device (11) of the motor vehicle (10), and to generate a rated steering signal (27) for the active rear axle steering device (16) by means of any one of the preceding claims, and to drive the rear axle steering device (16) with the rated steering signal.

7. A motor vehicle (10) having an active rear axle steering system (16) and at least one sensor, said at least one sensor being used to detect an actual steering signal (25) of the front axle steering system (11) of the motor vehicle (10), wherein, At least one sensor and the rear axle steering device (16) are coupled via the control circuit (23) according to claim 6.

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