Method for a steering operation in a steering system as well as steering system and vehicle

Abstract

The invention relates to a method for a steering operation (L) in a steering system (100), comprising: - Specifying (S1) at least one target value (Z) for the steering process (L), - Determine (S2) at least one guide value (F1, F2, F3) for the steering process (L), wherein the at least one guide value (F1, F2, F3) is determined according to at least one characteristic curve (K1, K2), wherein the at least one characteristic curve (K1, K2) characterizes a transmission behavior of the steering system (100), - Approaching (S3) at least one actual value (Y) to the specified at least one target value (Z) depending on the determined at least one guide value (F1, F2, F3), as well as a steering system (100) and a vehicle (200).

Description

[0001] The invention relates to a method for a steering operation in a steering system, as well as a steering system and a vehicle.

[0002] Modern vehicles are equipped with steering systems that function, for example, according to the so-called steer-by-wire principle, which translate steering instructions from a driver or a (partially) autonomous assistance system into a steering operation.

[0003] One goal is to implement steering commands as quickly as possible, so that, for example, no noticeable delays occur between a steering command and the corresponding steering action. However, if steering commands are implemented too quickly, this can lead to control instabilities in steering systems, such as excessive gain, phase shifts, or unwanted feedback. These instabilities, in turn, impair the precision of the steering behavior, resulting in a trade-off between speed and precision when implementing steering commands.

[0004] German patent DE 102 53 468 A1 discloses a power steering system for a non-track-bound vehicle whose steered wheels are controlled by means of a steering handle operated by the driver. The power steering system includes a servo motor for applying steering forces to the steered wheels, and in shunting mode, control commands for activating the servo motor can be triggered by the driver. Upon a first control command, the servo motor automatically moves the steered wheels to one steering end position, and upon a second control command, it automatically moves them to the other steering end position. The power steering system can also be designed as a steer-by-wire system.

[0005] From DE 10 2008 031 729 A1, a method for the electrical control of power steering for a vehicle is known, wherein an instantaneous target steering torque is determined for a steering torque applied to the vehicle's steering wheel as a function of a vehicle speed and a steering wheel angle and is used as a reference input for the control system. Preferably, the determination of the desired instantaneous target steering torque applied to the steering wheel is carried out as a function of a steering speed and / or predefinable vehicle-specific parameters using stored characteristic maps. Preferably, the instantaneous target steering torque is formed additively from a basic steering torque and an additional steering torque or determined as a function of the sum.

[0006] From DE 10 2020 201 286 A1 a method for operating a superimposed steering system of a motor vehicle is known.

[0007] From DE 10 2024 106 585 A1, an autonomous driving control device is known, comprising: a steering unit configured so that it can be operated by a driver; steered wheels configured so that they are steered in response to an actuation of the steering unit; an actuator configured to generate a steering force for steering the steered wheels; and a detection unit configured to detect an actuation amount of the steering unit, wherein the autonomous driving control device is configured to be able to switch between a first control mode and a second control mode, wherein the first control mode is a mode in which the actuator is controlled for driving without the driver having to actuate the steering unit, and the second control mode is a mode in which the actuator is controlled for driving such that a steering force required to actuate the steering unit is less than in the first control mode, wherein: The autonomous driving control device includes a controller that controls the actuator, the controller comprising: a steering determination unit configured to determine that the driver has actuated the steering unit while driving with the actuator controlled in the first control mode; an actuation speed calculation unit configured to calculate a speed that is at least one of a deviation speed and a steering speed, wherein the deviation speed is a rate of change of a deviation between a target steering angle during autonomous driving and an actual steering angle based on an actuation amount detected by the sensing unit, and the steering speed is a rate of change of the actual steering angle; and A control mode switching unit configured to change, when the steering determination unit detects that the driver has actuated the steering unit, a command value to be output to the actuator from a command value corresponding to a first target control amount of the actuator, determined according to the first control mode, to a command value corresponding to a second target control amount of the actuator, determined according to the second control mode, at a rate of change corresponding to a speed that is at least one of the deviation speed and the steering speed calculated by the actuation speed calculation unit.

[0008] The technical problem is to create a procedure for a steering operation in a steering system, as well as a steering system and a vehicle that implement steering instructions precisely and quickly.

[0009] The solution to the technical problem is provided by the articles with the features of the independent claims. Further advantageous embodiments of the invention are described in the dependent claims.

[0010] A procedure for a steering operation in a steering system is proposed, comprising: - Specifying at least one target value for the steering process, - Determining at least one guide value for the steering process, wherein the at least one guide value is determined according to at least one characteristic curve, wherein the at least one characteristic curve characterizes a transmission behavior of the steering system, - Approximating at least one actual value to the specified at least one target value depending on the determined at least one guide value.

[0011] The method has the advantage of resolving the conflict of objectives explained at the outset. The inventor recognized that the control instabilities mentioned earlier could be attributed to a lack of consideration for the steering system's transfer characteristics. By determining the reference value while taking the steering system's transfer characteristics into account, these instabilities are largely minimized. This allows the actual value to be approximated to the target value quickly and precisely.

[0012] A steering system for a vehicle is further proposed, wherein the steering system is configured to execute a method according to an embodiment described in this disclosure. The steering system is, for example, a steer-by-wire steering system. The steering system can, in particular, be configured to execute one, several, or all steps of a method according to an embodiment described in this disclosure.

[0013] A steering maneuver in the steering system can be implemented by control or regulation. For this purpose, the steering system can include at least one evaluation unit, at least one actuator, at least one steering rod, and / or at least one sensor. The evaluation unit can be, for example, a microcontroller. The actuator can be, for example, an electric motor. The steering rod can be, for example, a rack and pinion. A wheel of the vehicle can be connected to the steering system at a free end of the steering rod. The sensor can be, for example, a position sensor of the steering rod. Furthermore, the steering system can include a steering handle, such as a steering wheel. The steering handle can be operated, for example, by the driver. The steering handle can be connected to the evaluation unit, the actuator, and / or the sensor, for example, via a cable.

[0014] Furthermore, a vehicle is proposed comprising at least one steering system according to an embodiment described in this disclosure. The vehicle can be, for example, a passenger car or a truck. The vehicle can be a vehicle that is at least partially or fully autonomous.

[0015] The technical effects and advantages explained in this disclosure for the process naturally also apply to the steering system and the vehicle, and vice versa.

[0016] The steering process can include, for example, cornering, changing lanes, turning, or maneuvering the vehicle while parking.

[0017] The actual value can be the current value of at least one controlled variable. The controlled variable could be, for example, the position of the steering rod. Alternatively, the controlled variable could be the steering rod velocity and / or acceleration. The actual value can be acquired by a sensor, for example, using the sensor mentioned earlier. The actual value at the beginning of the steering process can be the starting value of the steering process.

[0018] The target value can be a desired endpoint of at least one controlled variable, or it can be that endpoint itself. Alternatively or cumulatively, the target value can be a minimum or maximum duration of the steering maneuver, e.g., three seconds. This allows the duration of the steering maneuver to be limited.

[0019] The target value can be set using the evaluation unit described earlier. The evaluation unit can, for example, specify the target value as a steering command for a (semi-)autonomous steering maneuver of the vehicle. Alternatively, the target value can be set by a driver, for example, via the steering controls described earlier. In this case, the steering angle, steering angle velocity, and / or steering angle acceleration can be used to specify the target value.

[0020] The setpoint can be a target value of the controlled variable. It can also be an intermediate value of the controlled variable to be achieved between the initial value of the steering process and the target value. In particular, a multitude of setpoints are determined according to at least one characteristic curve to replicate the curve as accurately as possible. With respect to the setpoint, the controlled variable can also be referred to as the reference variable or target controlled variable. The setpoint can be determined, for example, using the evaluation unit.

[0021] The transfer function describes how the steering system, and in particular the actual value of the controlled variable, reacts to a change in the input value. The transfer function of the steering system may be known beforehand, for example, from a frequency response analysis, step response, simulation, or similar methods. The transfer function may be dependent on the vehicle's speed. Therefore, the characteristic curve can be adapted to the current vehicle speed.

[0022] The characteristic curve can be a function of time. For example, the characteristic curve can define the temporal progression of the reference input during a steering process. The characteristic curve can end with a value corresponding to the target value. In particular, the steering process can be limited to a duration specified by the target value, e.g., three seconds. Each specific reference input, and especially each reference input within a plurality of reference inputs, can be assigned a temporal value according to the characteristic curve. This temporal value can represent the duration during which the respective reference input is used to approximate the actual value to the target value before the approximation transitions to, for example, the next reference input or the target value itself.

[0023] Approaching the predetermined target value can be achieved, for example, using the previously described actuator. This actuator can act on the steering rod depending on at least one defined setpoint, thus changing the actual value – for example, the steering rod position. To facilitate this approach, the defined setpoint can be specified as an intermediate value, so that the actual value is not immediately approached the target value. For example, the actual value is first approached to the at least one setpoint as an intermediate value before approaching the target value. This approach can be iterative, so that, for example, at least one iteration of the approach occurs for each setpoint in a set of multiple setpoints. The duration of each iteration can be limited to the previously described time value, which can be assigned to each setpoint, before the next setpoint is used for the approach.This allows the transfer behavior characterized by the characteristic curve to be represented even more accurately during the approach process. Alternatively, the approach can transition to the next setpoint when the actual value exceeds the currently specified setpoint. The approach can continue until at least one specified target value is reached. The target value can be considered reached when the actual value deviates from the specified target value by no more than a pre-known value, or when a new target value is specified. A new target value can be specified, for example, when the new target value differs from the specified target value by a pre-known threshold. This prevents excessively rapid changes in the target value.

[0024] To approach the target, the actuator can be triggered by a control-based setpoint and / or a model-based setpoint. The setpoint and / or the model-based setpoint can be determined based on the respective reference value. This is explained in more detail below.

[0025] In one embodiment, the method further comprises the step: - Determining at least one control-element-based actuating value by evaluating at least one control element of the steering system as a function of the determined at least one guide value.

[0026] In this way, when determining the controller-based control value, the transfer behavior of the steering system is indirectly taken into account via the reference value, thus further minimizing control instabilities. The controller-based control value can be a value of a manipulated variable of the previously described actuator. The manipulated variable can be, for example, a current or an electrical voltage for operating the actuator. The actuator can be, for example, an electric motor that generates a torque to move the steering system, in particular the steering column, using current and electrical voltage. Of course, the manipulated variable can also be the torque to be generated itself. The controller can be, for example, a PID controller. The controller can be computer-implemented and evaluated, for example, using the evaluation unit. Naturally, the controller can also be designed differently.For example, the control-based setpoint can be determined by providing the respective setpoint or an error or difference between the respective setpoint and the actual value as an input value for evaluation of the control element.

[0027] In one embodiment, the method further comprises the step: - Determine at least one model-based control value by evaluating a model of the steering system as a function of the determined at least one control value.

[0028] In this way, the required positional input can be determined using a model. The model-based positional input can be a positional input of the previously explained manipulated variable that is not determined by the control element itself, but rather, for example, by solving a system of linear equations. Determining the model-based positional input can be done, for example, using the evaluation unit described earlier. The model can also be referred to as a feed-forward model. The model can, for example, be a rigid body model of the steering system, which is represented by a system of equations. The model or the system of equations can be inverted. This is because the model-based positional input to be determined can—mathematically speaking—represent an input value for the system of equations, while the reference value can represent an output value.Inventorying allows the model to be evaluated with as few steps as possible, quickly determining the corresponding model-based setpoint for the reference value. Alternatively, the model can be represented by an assignment rule. Modeling the setpoint eliminates the need for the previously described control element. Alternatively or cumulatively, the model-based setpoint can be used to verify the control element-based setpoint, for example, to check whether the control element-based setpoint deviates from the model-based setpoint by no more than a pre-known value, or vice versa.

[0029] In one embodiment, the steering system is activated depending on at least one model-based control value. In this way, the model-based control value can be used to proactively approximate the actual value to the defined target value. This is because the model-based control value essentially acts as a control value, thus completely avoiding the previously described control instabilities.

[0030] In one embodiment, at least one control value is used to readjust an initial excitation of the steering system. In this way, for example, any remaining error between the actual value and the specified target value after the initial excitation of the steering system can be minimized or even eliminated. The error may, for example, be due to model inaccuracies in the previously described model. The control value used for readjustment is, for example, the controller-based control value. In particular, the model-based control value and the controller-based control value can be added to form a total control value. This ensures that the actuator is also stimulated by the model-based control variable during readjustment, for example, if the actuator is to be stimulated with absolute control values.

[0031] In one embodiment, the at least one setpoint is determined according to a first characteristic curve when the at least one target value is specified in a critical range of the steering system, while the at least one setpoint is determined according to a further characteristic curve when the at least one target value is specified in a non-critical range of the steering system. In this way, a range-dependent transmission behavior of the steering system can be taken into account when determining the setpoint. The steering system, in particular the steering rod, may have a critical range in which changes to the setpoint must be made very carefully, since damage to the steering system is likely in this range, e.g., due to the actual value exceeding the target value.The steering system, particularly the steering rod, may also have a non-critical range in which changes to the input value can be executed very quickly, since in this range there is no risk of damage to the steering system, e.g., from the actual value exceeding the target value. The first characteristic curve can therefore characterize the transmission behavior of the steering system in the critical range, and the subsequent characteristic curve can characterize the transmission behavior in the non-critical range.

[0032] In one embodiment, the critical area is an outer section of a steering rod in the steering system, while the non-critical area is an inner section of the steering rod. This allows, for example, the outer end stops of the steering rod to be protected from damage caused by control system instabilities. The outer section can be multi-part, particularly two-part, with each part located at a free end of the steering rod. The inner section, on the other hand, can be located between the parts of the outer section. Tests have shown that the potential damage to the steering system is particularly well prevented when the outer section has a relative length of 1% to 50%, particularly 1% to 25%, of the total length of the steering rod, and the inner section comprises the remaining length of the total length of the steering rod.

[0033] In one embodiment, the slope of the at least one first characteristic curve is smaller than the slope of the at least one further characteristic curve. In this way, the actual value in the critical range of the steering system is more cautiously approximated to the target value. The slope of the respective characteristic curve is, in particular, an average slope in the first half of the steering process. The inventor has recognized, in particular, that the at least one further characteristic curve can intersect a maximum value curve of the at least one target value, since in the non-critical range, an overshoot of the actual value above the target value can be unproblematic. The maximum value curve can indicate a value of the further characteristic curve that corresponds to the predetermined at least one target value. This allows an overshoot of the actual value above the target value in the non-critical range.

[0034] The invention is explained in more detail using an exemplary embodiment. The figure shows: Fig. 1 A schematic representation of an embodiment of a vehicle with a steering system.

[0035] In the following, identical reference symbols denote elements with the same technical characteristics.

[0036] Fig. Figure 1 shows a schematic representation of an embodiment of a vehicle 200 designed as a passenger car with a steering system 100, which functions, for example, according to the steer-by-wire principle. Fig. Figure 1 shows in particular the execution of a procedure for a steering operation L in the steering system 100. The steering operation L can, for example, be a curve maneuver of the vehicle 200. The steps of the procedure are explained below.

[0037] In step S1, a target value Z is specified for the steering operation L. The target value Z can be a desired value of a controlled variable. The controlled variable can, for example, be the steering rod position of a steering rod 30 of the steering system 100. To specify the target value Z, the steering system 100 includes a steering handle 10 designed as a steering wheel or yoke. The steering handle 10 can be operated by a driver of the vehicle 200 and communicates, for example, a set steering angle W via a cable to an evaluation unit (not shown) of the steering system 100. The steering angle W can thus specify the target value Z. Alternatively, the target value Z – for example, in an autonomous driving mode of the vehicle 200 – can also be specified without the steering handle 10, for example, by the evaluation unit (not shown).

[0038] The evaluation unit is, for example, a microcontroller and is designed to process the specified target value Z and to steer the steering system 100 from a starting value A - e.g., the neutral position of the steering rod 30 - to the specified target value Z.

[0039] The steering rod 30 may have a critical area B1 in which the steering operation L must be carried out particularly carefully and precisely – i.e., without an actual value Y of the controlled variable exceeding the target value Z – in order to avoid damage to the steering rod 30. This is because the critical area B1 is located in Fig. The steering rod 30 is located at its outer ends, where sensitive end stops (not shown) can be found. Furthermore, the steering rod 30 has an inner, and therefore non-critical, area B2. In this non-critical area B2, the steering operation L can also be performed with an overshoot of the actual value Y above the target value Z, since the end stops of the steering rod 30 are sufficiently far away. For a better understanding of the procedure, step S1 is shown for two different steering operations L, whereby in the first steering operation L the target value Z occupies a steering rod position within the critical area B1, and in the second steering operation L the target value Z occupies a steering rod position within the non-critical area B2.

[0040] In step S2, a variety of reference values ​​F1, F2, F3 are determined for the steering process L. These reference values ​​F1, F2, F3 can, for example, be values ​​of a reference variable, which in turn is a setpoint for the controlled variable explained earlier.

[0041] The determination of the control values ​​F1, F2, F3 is carried out according to one of two characteristic curves K1, K2, as shown in sub-steps S21, S22. The characteristic curves K1, K2 indicate the time course of the control variable from a start T1 of the steering process L to an end T2 of the steering process L. Which of the characteristic curves K1, K2 is used to determine the control values ​​F1, F2, F3 depends on whether the specified target value Z lies within the critical range B1 or within the non-critical range B2. This is because the first characteristic curve K1 characterizes the transmission behavior of the steering system 100 in the critical range B1 of the steering rod 30. The second characteristic curve K2, on the other hand, characterizes the transmission behavior of the steering system 100 in the non-critical range B2 of the steering rod 30.

[0042] In Fig. Figure 1 shows that determining the control values ​​F1, F2, F3 is linked to the slope of the respective characteristic curves K1, K2, whereby the time interval between the control values ​​F1, F2, F3 is smaller the greater the slope of the respective characteristic curve K1, K2. This prevents the steering process L from being segmented too coarsely or too finely into the multitude of control values ​​F1, F2, F3.

[0043] The characteristic curves K1 and K2 differ in their shape. The second characteristic curve, K2, has a steeper slope than the first characteristic curve, K1. Furthermore, the second characteristic curve, K2, crosses a maximum value line X at least twice. The maximum value line X could, for example, be a line along which a value of the reference variable corresponds to the target value Z. The first characteristic curve, K1, does not cross the maximum value line X in order to prevent the actual value Y from overshooting the target value Z in the critical area B1 of the steering rod 30.

[0044] In step S3, the actual value Y is approached the specified target value Z. A sensor 40 of the steering system 100, designed as a position sensor, can be used to detect the actual value Y. This approach can be achieved by stimulating an actuator 20, designed as an electric motor, with a total control value U.

[0045] The total control value U can, for example, be a motor current with which the actuator 20 is energized. Based on the motor current, the actuator 20 generates a torque, which in turn acts on the steering rod 30 to change its position. For the sake of completeness, it should be mentioned that a transmission element (not shown), e.g., a ball screw drive, can be arranged between the actuator 20 and the steering rod 30 to convert a rotational movement of the actuator 20 into a linear movement of the steering rod 30.

[0046] The total setpoint U is determined in substep S33 by adding, for example, a controller-based setpoint U1 and a model-based setpoint U2. The controller-based setpoint U1 is determined, for example, in substep S31, starting from the first setpoint F1. Simultaneously, in substep S32, the model-based setpoint U2 is determined for the first setpoint F1. For each setpoint F1, F2, F3, at least one controller-based setpoint U1 and at least one model-based setpoint U2 are determined sequentially. For clarity, the connections between the setpoints F2, F3 and substeps S31, S32 are indicated only by dotted lines.

[0047] Determining the control element-based setpoint U1 (S31) is done by evaluating a control element R designed as a PID controller, e.g. by means of the evaluation unit (not shown).

[0048] Determining the model-based control value U2 (S32) is performed by evaluating a model M of the steering system 100, e.g., using the evaluation unit (not shown). The model M can, for example, be called a feed-forward model and can be a rigid body model of the steering system 100, which is represented by an inverted system of equations. This is shown in Fig. 1 is indicated by a superscript "-1". This allows the model-based setpoint U2 to be determined particularly quickly and computationally efficiently.

[0049] The model-based control signal U2 can be used to initially excite the actuator 20. The control element-based control signal U1 can then be used to fine-tune the initial excitation. This may be necessary because, after the initial excitation, for example due to model inaccuracies of model M, an error may exist between the actual value Y and the respective setpoints F1, F2, F3. Determining the error is in Fig. 1 is marked by a minus sign.

[0050] Before the actual value Y is approximated to the target value F2, for example, the actual value Y can be iteratively approximated to the target value F1 such that the error between the actual value Y and the target value F1 is smaller than a pre-known value. However, this iterative approximation of the actual value Y to the first target value F1 can be limited to a duration corresponding to the time interval between the start T1 of the steering operation L and a corresponding point in time for the target value F1. This point in time is indicated in sub-step S21, for example, by a vertical dashed line. The approximation S3 can, in particular, continue until the actual value Y deviates from the target value Z by no more than the pre-known value or a new target value is specified (not shown). Reference symbol list 10 Steering handle 20 Actuator 30 handlebar 40 Sensor 100 steering system 200 vehicles A starting value B1 critical area B2 non-critical area F1, F2, F3 Guide value K1 first characteristic curve K2 further characteristic curve L Steering process M Model R Control element S1 step S2 step S21 partial step S22 Substep S3 step S31 Substep S32 Substep S33 Substep T1 Beginning T2 End Total setpoint U1 control element-based position value U2 model-based setpoint W steering angle X Maximum value line Y Actual value Z Target value

Claims

[1] Method for a steering operation (L) in a steering system (100), comprising: - Specifying (S1) at least one target value (Z) for the steering process (L), - Determine (S2) at least one guide value (F1, F2, F3) for the steering process (L), wherein the at least one guide value (F1, F2, F3) is determined according to at least one characteristic curve (K1, K2), wherein the at least one characteristic curve (K1, K2) characterizes a transmission behavior of the steering system (100), - Approaching (S3) at least one actual value (Y) to the specified at least one target value (Z) depending on the determined at least one guide value (F1, F2, F3). [2] Method according to claim 1, characterized by , that the procedure further includes the step: - Determine (S31) at least one control-element-based actuating value (U1) by evaluating at least one control element (R) of the steering system (100) as a function of the determined at least one guide value (F1, F2, F3). [3] Method according to claim 1 or 2, characterized by , that the procedure further includes the step: - Determine (S32) at least one model-based control value (U2) by evaluating a model (M) of the steering system (100) depending on the respective at least one guide value (F1, F2, F3). [4] Method according to claim 3, characterized by , that the steering system (100) is stimulated depending on at least one model-based control value (U2). [5] Method according to any of the preceding claims, characterized by , that at least one control value (U1, U2) is used to readjust an initial excitation of the steering system (100). [6] Method according to any of the preceding claims, characterized by, that the determination (S2) of the at least one guide value (F1, F2, F3) according to a first characteristic curve (K1) is carried out when the at least one target value (Z) is specified in a critical area (B1) of the steering system (100), wherein the determination (S2) of the at least one guide value (F1, F2, F3) according to a further characteristic curve (K2) is carried out when the at least one target value (Z) is specified in a non-critical area (B2) of the steering system (100). [7] Method according to claim 6, characterized by , that the critical area (B1) is an outer area of ​​a steering rod (30) of the steering system (100), wherein the non-critical area (B2) is an inner area of ​​the steering rod (30). [8] Method according to claim 6 or 7, characterized by , that a slope of at least one first characteristic curve (K1) is smaller than a slope of at least one further characteristic curve (K2). [9] Steering system (100) for a vehicle (200), wherein the steering system (100) is configured to perform a method according to any one of claims 1 to 8. [10] Vehicle (200) comprising at least one steering system (100) according to claim 9.

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