Limiting a steering rate of a motor vehicle

Abstract

To limit a steering rate of a motor vehicle (1), a traveled path (8) which has been traveled by the motor vehicle (1) up to a current point in time is determined. An expected position (Pex) which the motor vehicle (1) is expected to reach at a target point in time which lies a predefined time interval after the current point in time is determined as a function of the traveled path (8) and as a function of a current speed of the motor vehicle (1) and / or as a function of a target speed for the motor vehicle (1). A lateral position range which contains the expected position (Pex) is determined as a function of a predefined lateral position offset (D, D'). At least one limit value for the steering rate is determined as a function of the lateral position range.

Description

The present invention is directed to a method for limiting a steering rate of a motor vehicle and to a method for at least partially automatically guiding a motor vehicle, wherein such a method for limiting a steering rate of the motor vehicle is carried out. The invention is furthermore directed to a data processing device for carrying out such a method for limiting a steering rate of the motor vehicle, to an electronic vehicle guidance system having such a data processing device, and to a corresponding computer program product.When at least partially automatically guiding a motor vehicle, for example, at least the steering of the motor vehicle can be carried out automatically, in particular by an electronic vehicle guidance system of the motor vehicle. This may include cases of fully autonomous trucks, but also cases where automatic steering is performed as assistance to a driver or only temporarily. Other operations of the motor vehicle, such as deceleration and acceleration, may be performed manually, automatically, or partially automatically.For various reasons, there may be a requirement to change a lateral position of the motor vehicle. This may occur due to errors in the decision or control process or due to inconsistencies in sensor data, for example, positioning jumps in data from a global navigation satellite system receiver (GNSS) et cetera. When such a requirement is met by an electronic vehicle guidance system, this may result in an abrupt or sharp steering maneuver, which may be problematic in terms of occupant safety and / or comfort.It is possible to restrict the steering parameters, in particular a maximum steering angle and / or a maximum steering rate, that is to say the change over time in the steering angle, based on look-up tables or the like. However, this involves the disadvantage of a low flexibility level of the restriction and, for example, too pessimistic restriction or too high a security risk on the other hand.An object of the present invention is to provide an improved concept for limiting a steering rate of a motor vehicle which at least partially overcomes the mentioned disadvantages.This object is achieved by the subject matter of the independent claim. Further embodiments and preferred embodiments are subject matter of the dependent claims.The invention is based on the idea of providing a predefined time interval and a predefined transverse position offset. An expected position of the motor vehicle after the time interval has elapsed is estimated and a limit value for the steering rate is determined as a function of a transverse position range which is given by the transverse position offset at the expected position.According to one aspect of the invention, a method for limiting a steering rate of a motor vehicle is provided. In this case, a driven path which has been driven by the motor vehicle up to a present point in time is determined. An expected position that the motor vehicle is expected to reach at a target time that is a predefined time interval after the current time is determined depending on the path traveled and depending on a current speed of the motor vehicle at the current time and / or depending on a predefined target speed for the motor vehicle. A lateral position range including the expected position is determined depending on a predefined lateral position offset. At least one limit value for the steering rate is determined as a function of the transverse position range and is put into force in particular for at least partially automatic guidance of the motor vehicle.In some implementations, the method for limiting a steering rate of a motor vehicle is purely computer-implemented. Unless otherwise stated, all steps of a computer-implemented method can be carried out by a data processing device which contains at least one arithmetic unit, in particular a data processing device of the motor vehicle. In particular, the at least one computing unit is configured or adapted to carry out the steps of the computer-implemented method. For this purpose, the at least one arithmetic unit can store, for example, a computer program which contains instructions which, when executed by the at least one arithmetic unit, cause the at least one arithmetic unit to carry out the computer-implemented method.All computing units of the at least one computing unit can be included in the motor vehicle. However, it is possible for all computing units of the at least one computing unit to be part of an external computing system outside the motor vehicle, for example a backend server or a cloud computing system. It is also possible for the at least one computing unit to have at least one vehicle computing unit of the motor vehicle and at least one external computing unit which is contained by the external computing system. The at least one vehicle computing unit may be included, for example, by one or more electronic control units, ECUs (ECUs), and / or one or more zone control units, ZCUs (zone control units) and / or one or more domain control units, DCUs (DCUs) of the motor vehicle.For example, the motor vehicle can be automatically steered in such a way that the steering rate of the motor vehicle is limited by the determined at least one limit value. For example, the at least one limit value may include a maximum steering rate. The motor vehicle can then be automatically steered, so that the steering rate of the motor vehicle is less than or equal to the maximum steering rate. For example, the at least one threshold may include a minimum steering rate. The motor vehicle can then be automatically steered, so that the steering rate of the motor vehicle is greater than or equal to the minimum steering rate. Both cases may be combined in some implementations such that the motor vehicle is automatically steered such that the steering rate of the motor vehicle is greater than or equal to the minimum steering rate and less than or equal to the maximum steering rate.Unless stated otherwise, here and in the following a steering angle of the motor vehicle can be understood, for example, as a steering angle of a steerable wheel of the motor vehicle or as an effective steering angle of steerable wheels of the motor vehicle according to a predefined vehicle model, such as a two-wheel model. Generally, a steering wheel angle of a steering wheel within the driver's cab of the motor vehicle is different from the steering angle of the motor vehicle in this sense.Unless stated otherwise, a speed of the motor vehicle here and below corresponds to a longitudinal speed of the motor vehicle. Unless otherwise stated, here and in the following, a position of the motor vehicle can be understood as a position in a predefined reference coordinate system, for example a map coordinate system of a digital map.The traveled path can be obtained, for example, from a storage device of the motor vehicle or at least one computing unit or from a data bus of the motor vehicle. The traveled path may also be calculated based on sensor data obtained from respective sensors of the motor vehicle, including, for example, inertial measurement units, IMUs (GNSS receivers, cameras, or other environmental sensor systems, et cetera. For example, odometry methods including classical odometry and / or visual odometry, simultaneous localization and mapping methods (SLAM) methods, and so forth, may be used. The expected position may be determined, for example, by extrapolating the traveled path over the time interval, assuming that the speed remains constant, or the like. Depending on the specific embodiment, the extrapolated path may assume a constant steering angle. Then, the extrapolated path is a straight line or a circular arc segment. However, the extrapolated path may also take into account a change in the steering angle. Then, the extrapolated path may be, for example, a polynomial or other planar curve.The transverse position range may correspond to a range of transverse positions in which the corresponding longitudinal position is given by the expected position. For example, a line perpendicular to a longitudinal direction may be constructed at the expected position and the transverse position range may be defined as a range along the perpendicular line, with the expected position being at the center of the range. The boundaries of the transverse position range may be given by the transverse position offset in each direction from the expected position along the perpendicular line. In general, however, different offsets may also be provided for the two different directions. For example, the longitudinal direction at the expected position may be given by a tangent to the extrapolated path at the expected position.The target speed may be given, for example, by a single predefined target value for the target time point. The target speed can be given, for example, by a system of the motor vehicle for longitudinal control of the motor vehicle, for example an adaptive cruise control system (adaptive cruise control system) or the like. Using the target speed may further increase the accuracy, particularly if the predefined time interval is relatively long. The target speed can also be given by a target speed profile.According to the invention, it is thus achieved that the steering rate is limited in a flexible manner, taking into account both predefined parameters such as the transverse position offset and the time interval, the historical movement of the motor vehicle with respect to the driven path and the current speed.According to some embodiments, the at least one limit value for the steering rate is determined depending on the lateral position range, such that a position of the motor vehicle according to the target time point is in the lateral position range if the speed of the motor vehicle is constant between the current time point and the target time point and the steering rate is equal to one of the at least one limit value.In other words, the position of the motor vehicle according to the target time point is in the lateral position range when the motor vehicle is driven, the speed is constantly the current speed, the steering angle starts at the current steering angle at the current time point, and the steering angle is changed at a steering rate given by any of the at least one limit values. For example, the at least one limit value may include a first limit value and a second limit value corresponding to the minimum steering rate and the maximum steering rate, respectively. When the steering rate is given by the first threshold value, the position of the motor vehicle according to the target timing corresponds to a first threshold position of the lateral position range. When the steering rate is given by the second threshold value, the position of the motor vehicle according to the target timing corresponds to a second threshold position of the lateral position range. In particular, the limits of the transverse position range, which are given by the first and the second limit positions of the transverse position range, are considered to be in the transverse position range.Consequently, the transverse deviation of the motor vehicle from the expected position is limited by the transverse position range, in particular by the transverse position offset.According to some embodiments, a request to change a lateral position of the motor vehicle is detected. The motor vehicle is automatically steered, such that the steering rate of the motor vehicle is limited by the determined at least one limit value in response to the request.In particular, the motor vehicle can be automatically steered according to a predefined trajectory for the motor vehicle, wherein the steering rate of the motor vehicle is limited by the determined at least one limit value. The predefined trajectory may be obtained, for example, from a path planning or a route planning or a navigation system of the motor vehicle and may be present, for example, in the form of a curve or a set of waypoints.The request can be generated, for example, by the at least one computing unit as a function of sensor data from one or more sensors of the motor vehicle and / or as a result of a path planning et cetera.It may be that some or all of the steps of determining the traveled path, the expected position, the lateral position range, and the at least one threshold are performed only when the request is detected. In other embodiments, said steps may be performed repeatedly and / or continuously independently of such a requirement in a preventive manner.According to some embodiments, a plurality of positions of the motor vehicle is determined between a predefined earlier time point that is earlier than the current time point and the current time point. At least one adjusted curve parameter is determined by adjusting a predefined curve to the plurality of positions. The driven path is determined as the curve with the at least one adjusted curve parameter between a position according to the earlier point in time and a current position of the motor vehicle according to the current point in time.The earlier time may be defined, for example, by defining another time interval before the current time. For example, odometry methods including classical odometry and / or visual odometry, simultaneous localization and mapping methods (SLAM) methods, and so forth may be used to determine the plurality of positions.The curve is predefined in the sense that the type of the curve is predefined depending on the at least one curve parameter. Different values of the at least one curve parameter lead to different shapes of the curve. The at least one adjusted curve parameter is obtained by a known adjustment method. For example, the curve may be defined as a straight line. Then, the at least one curve parameter includes, for example, a slope of the straight line. For example, the curve may be defined as a circle. Then, the at least one curve parameter includes, for example, a radius and a center position of the circle. For example, the curve may be defined as a polynomial of the dthgrade. Then, the at least one curve parameter includes, for example, the d+1 polynomial coefficients. Other types of curves may also be used.According to some embodiments, the extrapolated path that ends at the expected position and in particular starts at the current time at the current position of the motor vehicle is determined by extrapolating the driven path depending on the current speed of the motor vehicle, wherein in particular it is assumed that the speed is constant.The time interval may be relatively short, for example its duration may be in the range [0.2 s, 5 s] or in the range [0.8 s, 2 s]. Consequently, the resulting lateral position range can be accurately constructed by means of the extrapolated path.According to some embodiments, an extrapolated path is determined as the curve with the at least one adjusted curve parameter between the position according to the current position of the motor vehicle and the position of the motor vehicle according to the target time point. The expected position is given by the position according to the target time point.In other words, for determining the expected position, it is assumed that the motor vehicle follows the same curve that also approaches the traveled path. The length of the extrapolated path is given by the current speed and time interval. For example, if the curve is a straight line, the extrapolated path is also a straight line having a length given by the current speed multiplied by the time interval. For example, if the curve is a circle or a circular arc segment, the extrapolated path is also a circular arc segment having an arc length given by the current speed multiplied by the time interval. Other curves can also be parameterized accordingly with time and speed. In this way, a realistic estimate of the expected position is achieved.According to some embodiments, the predefined curve is a circle or a circular arc portion or a straight line.In this way, a simple construction of the extrapolated path and the traveled path is possible, while the achievable accuracy is nevertheless high, in particular when observing the aforementioned ranges for the duration of the time interval.According to some embodiments, the predefined curve is a polynomial curve, in particular a polynomial of the dthgrade with d≥3.The accuracy and flexibility of the method can be further increased in this way.According to some implementations, as described above, the traveled path is determined as the curve with the at least one adjusted curve parameter and the predefined curve is a circle or a portion of a circular arc. If the radius of the circle or circular arc section is smaller than a predefined minimum radius, an extrapolated path is determined as a curve with the at least one adjusted curve parameter between the current position of the motor vehicle and the position according to the target time point, wherein the expected position is given by the position according to the target time point. When the radius of the circle or circular arc portion is larger than the minimum radius, the extrapolated path is determined as a straight line between the current position of the motor vehicle and the position according to the target time point, wherein a direction of the straight line is given by a tangent to the circle or circular arc portion at the current position of the motor vehicle and the expected position is given by the position according to the target time point.In particular, in the first case, the extrapolated path is a circular arc segment having an arc length given by the current speed multiplied by the time interval. In the second case, the extrapolated path is a straight line having a length given by the current speed multiplied by the time interval.If the radius of the circle or circular arc portion is equal to or greater than the minimum radius, the extrapolated path is determined as the said straight line in some embodiments and as the curve with the at least one adjusted curve parameter in other embodiments.The minimum radius may be, for example, on the order of thousands of meters, for example in the range [5000 m, 15000 m] or in the range [8000 m, 12000 m].In such embodiments, the design of the expected position is further simplified for very small curvatures of the driven path, while the accuracy is still high, particularly for larger curvatures of the driven path.According to some embodiments, a lateral offset of a lane boundary from the expected position is determined, and if the lateral offset of the lane boundary is determined to be greater than the lateral position offset, the motor vehicle is automatically decelerated.In other words, the speed of the motor vehicle is reduced from the current speed to a reduced speed in order to slow the motor vehicle. For example, the reduced speed may be given by subtracting a predefined decrement from the current speed or by multiplying the current speed by a predefined reduction factor that is greater than zero and less than one. The decrement or the reduction factor may have fixed values or may be determined depending on the current speed and / or the current steering angle according to a predefined rule.In particular, the motor vehicle is automatically decelerated when the lane boundary is outside the lateral position range. Consequently, it can be achieved that the limitation of the steering according to the at least one threshold value is not only sufficient to avoid abrupt changes in the lateral position of the motor vehicle, but also to safely guide the motor vehicle in the current lane.For example, the description may be repeated iteratively after the automatic deceleration of the motor vehicle until the lateral offset of the lane boundary is less than or equal to the lateral position offset.According to some embodiments, a further extrapolated path is determined by extrapolating the driven path depending on the current speed of the motor vehicle, wherein an end point of the further extrapolated path has a longitudinal position corresponding to a longitudinal position of a predefined path point for the motor vehicle, in particular a future path point for the motor vehicle. Another lateral position range including the end point is determined depending on the end point of the other extrapolated path and the lateral position offset. When a lateral position of the end point of the further extrapolated path is outside the further lateral position range, the motor vehicle is automatically decelerated.The explanations concerning the extrapolated path and the transverse position range can be correspondingly transferred to the further extrapolated path and the further transverse position range.In other words, the speed of the motor vehicle is reduced from the current speed to a reduced speed in order to slow the motor vehicle. For example, the reduced speed may be given by subtracting a predefined decrement from the current speed or by multiplying the current speed by a predefined reduction factor that is greater than zero and less than one. The decrement or the reduction factor may have fixed values or may be determined depending on the current speed and / or the current steering angle according to a predefined rule.In particular, the motor vehicle is automatically decelerated when the path point is outside the further transverse position range. Consequently, it can be achieved that the limitation of the steering according to the at least one limit value is not only sufficient to avoid abrupt changes in the transverse position of the motor vehicle, but also to safely guide the motor vehicle to the path point.The description can be repeated iteratively, for example after the automatic deceleration of the motor vehicle, until the transverse offset of the end point of the further extrapolated path is less than or equal to the further transverse position offset.According to some embodiments, a first limit curve between the current position of the motor vehicle and a first limit position of the lateral position range is determined depending on the current speed of the motor vehicle and a current steering angle of the motor vehicle at the current time. A first limit value of the at least one limit value for the steering rate is determined depending on a curvature of the first limit curve at the first limit position and depending on the current steering angle, for example.For example, the first boundary position has a lateral distance from the expected position given by the lateral position offset. The first limit position is in particular in a first direction with respect to the expected position.In particular, the curvature of the first limit curve is proportional to a tangent of the steering angle. Consequently, the difference between the steering angle at the first limit position and the current steering angle may be used to define the first limit value for the steering rate, in particular by dividing the difference by the time interval.For determining the first limit curve, a curve of a predefined type, for example a straight line, a circular arc or a polynomial, can be provided and respective curve parameters, for example a slope of the straight line, a radius and center point of the circular arc or polynomial coefficient, can be determined depending on the current speed, the current steering angle, the current position and the first limit position.In this way, a particularly suitable and realistic limit value is obtained.According to some embodiments, a second limit curve between the current position of the motor vehicle and a second limit position of the lateral position range is determined depending on the current speed of the motor vehicle and the current steering angle of the motor vehicle at the current time. A second limit value of the at least one limit value for the steering rate is determined depending on a curvature of the second limit curve at the second limit position.For example, the second boundary position has a lateral distance from the expected position, which is given by the lateral position offset. The second limit position is in particular in a second direction of the expected position, which is opposite to the first direction.The difference between the steering angle at the second limit position and the current steering angle may be used to define the second limit value for the steering rate, in particular by dividing the difference by the time interval.For determining the second limit curve, a curve of a predefined type, for example a straight line, a circular arc or a polynomial, can be provided and respective curve parameters, for example an inclination of the straight line, a radius and center point of the circular arc or polynomial coefficient, can be determined depending on the current speed, the current steering angle and the second limit position.In this way, a particularly suitable and realistic second limit value is obtained. In particular, the second limit value may be the maximum steering rate and the first limit value may be the minimum steering rate or vice versa.According to some embodiments, the first boundary curve is determined as an nthgrade polynomial, where n is at least two, and / or the second boundary curve is determined as an mthgrade polynomial, where m is at least two.Consequently, a particularly accurate first limit curve and / or second limit curve is obtained.According to some embodiments, the first boundary curve is determined as a curve with constant curvature or with monotonically increasing curvature or with monotonically decreasing curvature between the current position of the motor vehicle and the first boundary position.According to some embodiments, the second boundary curve is determined as a curve with constant curvature or with monotonically increasing curvature or with monotonically decreasing curvature between the current position of the motor vehicle and the second boundary position.According to some embodiments, the first boundary curve is determined as a third degree polynomial, i.e., n=3, and / or the second boundary curve is determined as a third degree polynomial, i.e., m=3.An advantage of third order polynomials compared to higher order polynomials is that the third derivative of a third order polynomial is a constant. Thus, the curvature of a third order polynomial is monotone, i.e., monotone increasing or decreasing. Thus, the curvature of the first limit curve at the first limit position and the second limit curve at the second limit is a maximum curvature or a minimum curvature between the current position and the first limit position and the second limit position, respectively. Thus, the steering angle at the first limit position or the second limit position is also a maximum steering angle or a minimum steering angle. The same applies correspondingly to other curves with monotone curvature. The third order polynomial is a particularly simple curve with this property, which nevertheless provides a high degree of flexibility due to the number of its polynomial coefficients.According to some embodiments, a steering angle at the first limit position is calculated depending on the curvature of the first limit curve at the first limit position using a predefined vehicle model, for example a two-wheel model. A first angle difference between the steering angle at the first limit position and the current steering angle is calculated. The first limit value for the steering rate is determined as the first angle difference divided by the predefined time interval.In this way, a reliable first limit value is obtained.According to some embodiments, a steering angle at the second boundary position is calculated depending on the curvature of the second boundary curve at the second boundary position using the predefined vehicle model. A second angle difference between the steering angle at the second boundary position and the current steering angle is calculated. The second limit value for the steering rate is determined as the second angle difference divided by the predefined time interval.In this way, a reliable second limit value is obtained.According to some embodiments, the steering angle at the first limit position is calculated according to the vehicle model, in particular the two-wheel model, wherein V denotes the current speed, W denotes a wheel base of the motor vehicle, c L1 denotes the curvature of the first limit curve at the first limit position, and K is a predefined constant depending on mechanical properties of the motor vehicle, in particular only mechanical properties of the motor vehicle.According to some embodiments, the steering angle at the second limit position is calculated according to the vehicle model, in particular the two-wheel model, where c L2 denotes the curvature of the second limit curve at the second limit position.For example, according to the two-wheel model, it is assumed that the front wheels of the motor vehicle are steerable and are represented by a single effective front wheel and that the rear wheels of the motor vehicle are not steerable and are represented by a single effective rear wheel.The mechanical properties of the motor vehicle can include or consist of, for example, the wheel base, a mass of the motor vehicle, a distance between the center of gravity of the motor vehicle and a front wheel axle of the motor vehicle, a distance between the center of gravity of the motor vehicle and a rear wheel axle of the motor vehicle, a cornering stiffness of the front tires of the motor vehicle and a cornering stiffness of the rear tires of the motor vehicle.More specifically, K may denote the mass, L R and L F the distances between the center of gravity and the rear wheel axle and the front wheel axle, respectively, and C R and C F the cornering stiffness of the rear tires and the front tires, respectively.In this way, a particularly accurate estimation of the steering angles is achieved.In alternative embodiments, the above equation with K=0 may be used. This can reduce the computational effort, especially in application cases where W is much greater than K*V 2.For use cases or application situations which can arise in the method according to the invention and which are not explicitly described here, provision can be made for an error message and / or a request for user feedback to be output according to the method and / or for a default setting and / or a predetermined initial state to be set.According to a further aspect of the invention, a method for at least partially automatically guiding a motor vehicle is provided. In this case, a method according to the invention for limiting a steering rate of the motor vehicle is carried out. At least one control signal for at least partially automatically guiding the motor vehicle is automatically generated depending on the at least one limit value for the steering angle, wherein the at least one control signal includes at least one steering control signal for automatically steering the motor vehicle according to the limit value for the steering angle. In particular, the at least one steering control signal for automatically steering the motor vehicle is generated as a function of the at least one limit value for the steering angle.The at least one control signal may be provided, for example, to one or more actuators of the motor vehicle, including, for example, one or more brake actuators and / or one or more steering actuators and / or one or more drive motors of the motor vehicle. The one or more actuators may influence a longitudinal and / or lateral control of the motor vehicle in order to at least partially automatically guide the motor vehicle.In particular, the at least one steering control signal can be provided to one or more steering actuators. The one or more steering actuators may affect lateral control of the motor vehicle to at least partially automatically steer the motor vehicle.According to a further aspect of the invention, a data processing device is provided, which has at least one arithmetic unit. The at least one arithmetic unit is adapted to carry out a method according to the invention for limiting a steering rate of the motor vehicle.In the present disclosure, a computing unit may be understood as, for example, a data processing apparatus including processing circuits. A computing unit can thus perform computing operations for processing data. The computational operations may also include indexed accesses to a data structure, such as a look-up table, LUT.In particular, the computing unit may include one or more computers, one or more microcontrollers and / or one or more integrated circuits, for example one or more application-specific integrated circuits, ASICs (application-specific integrated circuit), one or more field programmable gate arrays, FPGAs, and / or one or more single-chip systems, SoCs (system on a chip). The computing unit may also include one or more processors, for example one or more microprocessors, one or more central processing units, CPUs (CPUs), one or more graphics processing units, GPUs (GPUs) and / or one or more signal processors, in particular one or more digital signal processors, DSPs. The computing unit may also include a physical or virtual group of computers or other of the aforementioned units.A computing unit may also include one or more hardware and / or software interfaces and / or one or more memory units. A memory unit can be used as a volatile data memory, for example as a dynamic random access memory, DRAM (dynamic random access memory) or static random access memory, SRAM (static random access memory), or as a nonvolatile data memory, for example as read-only memory, ROM (read-only memory), as programmable read-only memory, PROM (programmable read-only memory), as erasable read-only memory, EPROM (erasable read-only memory), as electrically erasable read-only memory, EEPROM (electrically erasable read-only memory), as flash memory or flash EEPROM, as ferroelectric random access memory, FRAM (ferroelectric random access memory), as magnetoresistive random access memory, MRAM (magnetoresistive random access memory) or as phase-change random access memory, PCRAM (phase-change random access memory).According to another aspect of the invention, an electronic vehicle guidance system for a motor vehicle is provided. The electronic vehicle guidance system has a data processing device according to the invention. The at least one computing unit is configured to carry out a method according to the invention for at least partially automatically guiding a motor vehicle.An electronic vehicle guidance system can be understood as an electronic system which is configured to guide a vehicle fully automatically or fully autonomously and in particular without manual intervention or control by a driver or user of the vehicle being necessary. The vehicle automatically performs all necessary functions, such as steering maneuvers, deceleration maneuvers and / or acceleration maneuvers, and monitoring and recording of the road traffic, and corresponding reactions. In particular, the electronic vehicle guidance system may implement a fully automatic or fully autonomous driving mode according to level 5 of the SAE J3016 classification. An electronic vehicle guidance system may also be implemented as an Driver Assistance System, ADAS, that assists a driver in semi-automatic or semi-autonomous driving. In particular, the electronic vehicle guidance system may implement a semi-automatic or semi-autonomous driving mode according to levels 1 to 4 of the SAE J3016 classification. Here and below, SAE J3016 refers to the appropriate standard dated April 2021.The at least partially automatic driving of the vehicle may thus include driving the vehicle according to a fully automatic or fully autonomous driving mode according to level 5 of the SAE J3016 classification. The at least partially automatic driving of the vehicle may also include driving the vehicle according to a semi-automatic or semi-autonomous driving mode according to levels 1 to 4 of the SAE J3016 classification.Further embodiments of the electronic vehicle guidance system according to the invention result directly from the various embodiments of the methods according to the invention and vice versa. In particular, individual features and corresponding explanations and advantages relating to the various embodiments of the method according to the invention can be correspondingly transferred to corresponding embodiments of the electronic vehicle guidance system according to the invention. In particular, the electronic vehicle guidance system according to the invention is configured or programmed to carry out a method according to the invention. In particular, the electronic vehicle guidance system according to the invention executes a method according to the invention.According to a further aspect of the invention, a computer program containing instructions is provided. When the commands are executed by the at least one arithmetic unit, the commands cause the at least one arithmetic unit to carry out a method according to the invention for limiting a steering rate of the motor vehicle and / or a method according to the invention for at least partially automatically guiding a motor vehicle.The instructions may be provided as program code, for example. The program code can be provided, for example, as binary code or assembler and / or as source code of a programming language, for example C, and / or as a program script, for example Python.According to a further aspect of the invention, a computer-readable storage medium is provided which stores a computer program according to the invention.The computer program and the computer readable storage medium are respective computer program products including the instructions.Further features of the invention are evident from the claims, the figures and the description of the figures. The features and combinations of features mentioned above in the description and the features and combinations of features mentioned below in the description of the figures and / or shown in the figures can be encompassed by the invention not only in the respectively specified combination but also in other combinations. In particular, embodiments and combinations of features may also be included in the invention that do not have all of the features of an originally formulated claim. Moreover, embodiments and combinations of features may be encompassed by the invention that go beyond or depart from the combinations of features set forth in the appended claims.The invention is explained in detail below with reference to specific exemplary embodiments and respective schematic drawings. In the drawings, identical or functionally identical elements can be denoted by the same reference numerals. The description of identical or functionally identical elements is not necessarily repeated with reference to different figures.The figures show: FIG. 1 schematically shows a motor vehicle having an exemplary embodiment of an electronic vehicle guidance system according to the invention; FIG. 2 schematically shows aspects for determining a travel path of a motor vehicle according to an exemplary embodiment of a method according to the invention for limiting a steering rate of a motor vehicle; FIG. 3 schematically shows aspects for determining an expected position according to a further exemplary embodiment of a method according to the invention for limiting a steering rate of a motor vehicle; FIG. 4 schematically shows aspects for determining a transverse position range according to a further exemplary embodiment of a method according to the invention for limiting a steering rate of a motor vehicle; FIG. 5 schematically shows aspects for determining a transverse position range according to a further exemplary embodiment of a method according to the invention for limiting a steering rate of a motor vehicle; FIG. 6 schematically shows aspects for determining a transverse position range according to a further exemplary embodiment of a method according to the invention for limiting a steering rate of a motor vehicle; FIG. 7 schematically shows aspects for determining a limit curve according to a further exemplary embodiment of a method according to the invention for limiting a steering rate of a motor vehicle; FIG. 8 is a schematic illustration of a vehicle model for use in another exemplary embodiment of a method according to the invention for limiting a steering rate of a motor vehicle; FIG. 9 shows a schematic illustration of a use case for a further exemplary embodiment of a method according to the invention for limiting a steering rate of a motor vehicle; and FIG. 10 shows a schematic illustration of a use case for a further exemplary embodiment of a method according to the invention for limiting a steering rate of a motor vehicle.FIG. 1 schematically shows a motor vehicle 1 with an exemplary embodiment of an electronic vehicle guidance system including steering angle sensors 4, one or more environment sensor systems 6, such as a camera, a lidar system, a radar system and / or an ultrasonic system et cetera, one or more inertial sensors 5, such as one or more inertial measurement units, IMUs (inertial measurement unit), one or more acceleration sensors and / or one or more yaw rate sensors. The electronic vehicle guidance system 2 may also include other sensors, such as a wheel rotation speed sensor, a GNNS receiver, and so forth. W denotes a wheel base of the motor vehicle 1, which is a distance between a front wheel axle and a rear wheel axle of the motor vehicle 1.The at least one computing unit 3 is configured to carry out a method according to the invention for limiting a steering rate of the motor vehicle 1. As a result, the at least one computing unit generates at least one limit value for the steering rate of the motor vehicle 1. the at least one computing unit 3 generates at least one control signal for at least partially automatically guiding the motor vehicle depending on the limit value for the steering rate, wherein the at least one control signal includes at least one steering control signal for automatically steering the motor vehicle 1 according to the at least one limit value for the steering rate.Some aspects of the method for limiting the steering rate of the motor vehicle 1 are explained below for exemplary embodiments of the method and in particular with reference to FIGS. 2 to 8.In order to carry out the method for limiting a steering rate of the motor vehicle 1, the at least one arithmetic unit 3 determines a driven path 8 which was driven by the motor vehicle 1 up to a present point in time.For example, a plurality of positions 7, P 1, P 2, P 3 of the motor vehicle 1 is determined between a predefined earlier time and the current time. At least one adjusted curve parameter is determined by adjusting a predefined curve to the plurality of positions 7, P 1, P 2, P 3, also referred to as historical positions. The traveled path 8 is determined as the curve with the at least one adjusted curve parameter between a position according to the previous time and a current position of the motor vehicle 1 according to the current time.This is illustrated for an exemplary case of a circle as the predefined curve in FIGS. 2 and 3. Referring to FIG. 2, the circle may be defined based on only three historical positions P1=(XP1, YP1), P2=(XP2, YP2), P3=(XP3, YP3). To this end, the slope m 12 of the line connecting P 1 to P 2 may be calculated and the slope m 23 of the line connecting P 2 to P 3 may be calculated.The X coordinate of the center position C=(XC, YC) of the circle may be calculated as.The Y coordinate of the center position C=(XC, YC) can also be calculated because m12 and m23 are not both equal to zero. For example, m23 is different from zero: or m23 = 0 and m12 is different from zeroThe radius of the circle is then given, for example, byThe at least one computing unit 3 determines an expected position P ex, which is expected to be reached by the motor vehicle 1 at a target time which is a predefined time interval after the current time, depending on the driven path 8 and depending on a current speed of the motor vehicle 1 at the current time.Following the example of FIG. 2, the expected position P ex can be determined, for example, by expanding the circle through an extrapolated path 9 which is a circular arc having an arc length d=V*T, where V is the current speed and T is the time interval as shown in FIG. 3. The end point of the extrapolated path 9 is the expected position P ex.The at least one arithmetic unit 3 determines a transverse position range which contains the expected position P ex as a function of a predefined transverse position offset D, D'.Specifically, a straight line is constructed which is ex to the tangent to the extrapolated path 9 at the expected position P. In the case of a circle, this line passes through the center position C. A first boundary point A lies on said line at a distance D from the expected position P ex and a second boundary point B lies on said line at a distance D' from the expected position P ex in an opposite direction compared to A. For example, D=D'.The transverse position range is then given by the straight line which connects the boundary points A and B to one another.It is also possible that extrapolated path 9 does not lie on the same circle as traveled path 8. For example, if the radius R is greater than a predefined minimum radius, for example 10,000 m, then the extrapolated path 9 may be given by a straight line of length d=V*T, as shown in FIGS. 5 and 6. In the example of FIG. 5, the extrapolated path 9 is parallel to a tangent to the traveled path 8 at the current position, while this is not the case in FIG. 6. The situation of Fig. 6 is not possible when the only steerable wheels of the motor vehicle 1 are front wheels. If the rear wheels are also steerable, the situation of FIG. 6 is possible.The at least one arithmetic unit 3 determines at least one limit value for the steering rate depending on the transverse position range.For this purpose, the at least one arithmetic unit 3 can determine, for example, a first limit curve 10 between the current position of the motor vehicle 1 and the first limit position A of the transverse position range and a second limit curve 11 between the current position of the motor vehicle 1 and the second limit position B of the transverse position range as a function of the current speed and a current steering angle of the motor vehicle 1 at the current point in time. A first limit value of the at least one limit value for the steering rate is determined as a function of a curvature of the first limit curve 10 at the first limit position A and a second limit value of the at least one limit value for the steering rate is determined as a function of a curvature of the second first limit curve 11 at the second limit position B.The limit curves 10, 11 can be constructed, for example, as polynomials of third degree. Using Ackermann's law based on the two-wheel model illustrated in FIG. 8, the curvature c refers to the steering angle θ over the speed V and a constant K given by m denotes the mass of the motor vehicle 1, L R and L F denote the distances between the center of gravity G and the rear wheel axle and the front wheel axle of the motor vehicle 1, respectively, and C R and C F denote the cornering rigidity of the rear tires 17 and the front tires 16, respectively.The first limit curve 10 can be written, with the current steering angle ω and the coordinates of the first limit position A, the coordinates of the first limit position A (XA, YA) are:The steering angle at the first limit position A is then given by where c L1 denotes the curvature of the first limit curve 10 at the first limit position A. The first limit value for the steering rate can then be calculated, for example.The second boundary curve 11 can be written, with the coordinates of the second boundary position B (XB, YB):The steering angle at the first second limit position B is then given by where c L2 denotes the curvature of the second limit curve 11 at the second limit position B. The second limit value for the steering rate can then be calculated, for example.As illustrated in FIG. 9, upon an abrupt request to change the lateral position of the motor vehicle 1, for example, from one lane 12 to an adjacent lane 13, the steering rate may be limited according to the first and second thresholds.As schematically illustrated in FIG. 10, in some embodiments, a lateral offset of a lane boundary 14, 15 from the expected position P ex is determined, and when the lateral offset of the lane boundary 14, 15 is greater than the lateral position offset D, D', the motor vehicle 1 is automatically decelerated.As described, particularly with reference to the figures, the invention overcomes disadvantages of conventional approaches for limiting steering parameters when a motor vehicle is at least partially automatically steered.According to some embodiments, an acceptable vehicle path distance deviation is predefined within a fixed time delay.For example, it may be defined that the motor vehicle does not deviate more than 1 m from the current motor vehicle path during the next one second. The limit value for the steering rate may be determined to achieve said limit position deviation after the time delay. The boundary deviations mentioned can also be used to define the acceptable speed in a scenario with varying lane curvature.According to some embodiments, the steering rate is limited in the case of a jump in lane detection. For example, if a security driver is present, e may be informed of the limitation so that the driver may respond accordingly. For example, in the case of a fully autonomous vehicle, the time interval may be used to analyze the problem causing the jump in lane detection and determine, for example, a minimal risk maneuver.According to some embodiments, a speed limit for traversing a variation in lane curvature may be determined. If the future path is known, for example in the form of waypoints, the permissible speed for compliance with the steering rate limit can be estimated for each waypoints. For each waypoints, it is possible to track an estimate of the path deviation ahead based on the earlier waypoints. If the next path point is not between the maximum left and right lateral deviation, the speed may be reduced.

Claims

Method for limiting a steering rate of a motor vehicle (1), wherein - a driven path (8) which has been driven by the motor vehicle (1) up to a present time is determined; - an expected position (P ex), which the motor vehicle (1) is expected to reach at a target time which lies a predefined time interval after the present time, is determined depending on the driven path (8) and depending on a present speed of the motor vehicle (1) and / or is determined depending on the driven path (8) and depending on a predefined target speed for the motor vehicle (1); - a transverse position range which contains the expected position (P ex) is determined depending on a predefined transverse position offset (D, D'); at least one limit value for the steering rate is determined depending on the transverse position range.Method according to claim 1, wherein the at least one limit value for the steering rate is determined depending on the lateral position range, such that a position of the motor vehicle (1) according to the target time point lies in the lateral position range, if the speed of the motor vehicle (1) is constant between the current time point and the target time point and the steering rate is equal to one of the at least one limit value.Method according to one of the preceding claims, wherein - a request to change a transverse position of the motor vehicle (1) is detected; and - the motor vehicle (1) is automatically steered in response to the request, such that the steering rate of the motor vehicle (1) is limited by the determined at least one limit value.Method according to one of the preceding claims, wherein - a plurality of positions (7, P1, P2, P3) of the motor vehicle (1) is determined between a predefined earlier time and the current time; - at least one adjusted curve parameter is determined by adjusting a predefined curve to the plurality of positions (7, P1, P2, P3); and - the driven path (8) is determined as the curve with the at least one adjusted curve parameter between a position according to the earlier time and a current position of the motor vehicle (1) according to the current time.Method according to claim 4, wherein an extrapolated path (9) is determined as the curve with the at least one adjusted curve parameter between the current position of the motor vehicle (1) and the position of the motor vehicle (1) according to the target time, wherein the expected position (P ex) is given by the position according to the target time.The method according to any one of claims 4 or 5, wherein the predefined curve is a circle or a section of a circular arc or a straight line or a polynomial curve.Method according to claim 4, wherein the predefined curve is a circle or a section of a circular arc, and - if a radius (R) of the circle or section of a circular arc is smaller than a predefined minimum radius (R), an extrapolated path (9) is determined as the curve with the at least one adjusted curve parameter between the current position of the motor vehicle (1) and a position according to the target time, wherein the expected position (P ex) is given by the position according to the target time; and if the radius (R) of the circle or circular arc section is larger than the minimum radius (R), the extrapolated path (9) is determined as a straight line between the current position of the motor vehicle (1) and the position according to the target time, wherein a direction of the straight line is given by a tangent to the circle or circular arc section at the current position of the motor vehicle (1) and the expected position (P ex) is given by the position according to the target time.Method according to one of Claims 1 to 3, wherein an extrapolated path (9) which ends at the expected position (P ex) is determined by extrapolating the driven path (8) as a function of the current speed of the motor vehicle (1) and / or as a function of the target speed.Method according to one of the preceding claims, wherein a transverse offset of a lane boundary (14, 15) from the expected position (P ex) is determined and, if the transverse offset of the lane boundary (14, 15) is greater than the transverse position offset (D, D'), the motor vehicle (1) is automatically decelerated.Method according to one of the preceding claims, wherein - a further extrapolated path (9) is determined by extrapolating the driven path (8) depending on the current speed of the motor vehicle (1) and / or depending on the target speed, wherein an end point of the further extrapolated path (9) has a longitudinal position corresponding to a longitudinal position of a predefined path point for the motor vehicle (1); - a further transverse position range including the end point is determined depending on the transverse position offset (D, D'); and - if a transverse position of the end point of the further extrapolated path (9) is outside the further transverse position range, the motor vehicle (1) is automatically decelerated.Method according to one of the preceding claims, wherein - a first limit curve (10, 11) between the current position of the motor vehicle (1) and a first limit position (A, B) of the transverse position range is determined as a function of the current speed of the motor vehicle (1) and / or the target speed and as a function of a current steering angle of the motor vehicle (1) at the current point in time; and - a first limit value of the at least one limit value for the steering rate is determined as a function of a curvature of the first limit curve (10, 11) at the first limit position (A, B).Method according to claim 11, wherein - the first limit curve (10, 11) is determined as an n-th degree polynomial, wherein n is at least two; or - the first limit curve (10, 11) is determined as a third degree polynomial.Method according to one of Claims 11 or 12, wherein the first limit curve (10, 11) is determined as a curve with constant curvature or with monotonically increasing curvature or with monotonically decreasing curvature between the current position of the motor vehicle (1) and the first limit position (A, B).Method according to any of claims 11 to 13, wherein - a steering angle at the first limit position (A, B) is calculated depending on the curvature of the first limit curve (10, 11) at the first limit position (A, B) using a predefined vehicle model; and - an angle difference between the steering angle at the first limit position (A, B) and the current steering angle is calculated; and - the first limit value is determined as the angle difference divided by the time interval.The method according to claim 14, wherein the steering angle at the first limit position (A, B) is calculated according to the vehicle model as θ L 1 = atan ( c L 1 ( W + K ≥ V 2 )) where V denotes the current speed, W denotes a wheel base of the motor vehicle (1), c L1, denotes the curvature of the first limit curve (10, 11) at the first limit position (A, B), and K is a predefined constant depending on mechanical properties of the motor vehicle (1).Method according to one of the preceding claims, wherein - a second limit curve (10, 11) between the current position of the motor vehicle (1) and a second limit position (A, B) of the transverse position range is determined as a function of the current speed of the motor vehicle (1) and the current steering angle of the motor vehicle (1) at the current point in time; and - a second limit value of the at least one limit value for the steering rate is determined as a function of a curvature of the second limit curve (10, 11) at the second limit position (A, B).Method for at least partially automatically guiding a motor vehicle (1), wherein - a method for limiting a steering rate of the motor vehicle (1) according to one of the preceding claims is carried out; and - at least one control signal for at least partially automatically guiding the motor vehicle (1) is generated as a function of the limit value for the steering rate, wherein the at least one control signal comprises at least one steering control signal for automatically steering the motor vehicle (1) according to the at least one limit value for the steering rate.Data processing device, having at least one arithmetic unit (3) which is adapted to carry out a method according to one of Claims 1 to 16.Electronic vehicle guidance system (2) for a motor vehicle (1) which has a data processing device according to Claim 18, wherein the at least one arithmetic unit (3) is configured to carry out a method according to Claim 17.A computer program product comprising instructions which, when executed by a data processing device, cause the data processing device to perform a method according to any one of claims 1 to 17.

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