Steering angle planning system for a vehicle and vehicle
Patent Information
- Application Number
- EP2024708995
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-03-01
- Filing Date
- 2024-02-29
- Publication Date
- 2026-01-07
AI Technical Summary
The existing steering angle planning systems for vehicles face challenges in achieving accurate and stable trajectory control due to variable influences like road contact and vehicle load, leading to inaccuracies and delays in steering angle control, which limit overall system performance.
A steering angle planning system that determines the first and second derivatives of actual and target steering angles, identifies suitable steering angle sections by exceeding threshold values, and uses a correlator to calculate a current time delay, which is then recursively estimated by a parameter estimator, such as a recursive least squares estimator or artificial neural network, to improve delay calculation accuracy.
This approach allows for online calculation of current time delay values, reducing inaccuracies and delays in steering angle control, enhancing tracking accuracy, stability, and robustness for automated or assisted driving systems.
Smart Images
Figure EP2024055171_06092024_PF_FP
Abstract
Description
[0001] Steering angle planning system for a vehicle and vehicle
[0002] The invention relates to a steering angle planning system for a vehicle, comprising a sensor device for measuring a respective current actual steering angle value and a storage unit with corresponding target steering angle values. Furthermore, the invention relates to a vehicle and a method for operating such a steering angle planning system.
[0003] Trajectory control for a vehicle in the context of automated or assisted driving is subject to high demands on tracking accuracy, stability, and robustness. These properties must be ensured across the entire operating range of the trajectory control. The steering system, as the primary interface between trajectory control and the vehicle's lateral dynamics, plays a key role. The specified guide path (target trajectory) is followed by electronically controlled steering axles, by retrieving and implementing the necessary steering angle settings (target steering angle values) from a memory based on the current vehicle position.
[0004] However, this is not readily possible, as the transmission chain from the target curvature to the actual curvature is subject to many variable or unknown influences, such as road contact, vehicle load, tires, etc. Due to the influences described above, it is a major challenge to select the steering angle input such that the desired actual curvature is achieved. Inaccuracies and, in particular, delays in the subsequent control of the target steering angle, which is calculated by the trajectory control, represent a significant limitation of the overall system performance.
[0005] EP 2977297 B1 discloses a method for determining a current steering angle of a motor vehicle, in which a steering wheel angle specified by means of a steering device of the motor vehicle is detected by means of a sensor device of the motor vehicle, and the steering angle set as a result of the specification by means of the steering device is determined by means of a control device of the motor vehicle on the basis of a predetermined steering angle characteristic curve, which describes a dependence of the steering angle on the steering wheel angle, wherein a delay function, which describes a time delay between the specification of the steering wheel angle and the setting of the steering angle, is determined and the steering angle is additionally determined by means of the control device as a function of the delay function.
[0006] It is an object of the invention to provide an improved steering angle planning system for a vehicle and a vehicle itself as well as a method for operating such a steering angle planning system.
[0007] This object is achieved by a steering angle planning system having the features of claim 1 as well as a vehicle having the features of claim 13 and a method having the features of claim 15.
[0008] The subclaims list further advantageous measures which can be suitably combined with one another to achieve further advantages.
[0009] The object is achieved by a steering angle planning system for a vehicle comprising a sensor device for measuring a respective current actual steering angle value, and a storage unit with corresponding target steering angle values, wherein the steering angle planning system is designed to determine the respective first actual derivative of the measured respective current actual steering angle value and the respective first target derivative of the respective current target steering angle value over time and further to determine a second actual derivative of the measured respective current actual steering angle value over time and a second target derivative of the respective current target steering angle value over time and to determine a respective current steering angle section in which the second actual derivative and the second target derivative each exceed a predetermined positive and negative threshold value at least once,wherein the current steering angle section has a maximum predetermined length, and wherein a correlator is further provided for determining a respective current time delay based on the respective first actual derivatives and the respective first desired derivatives in the respective current steering angle section, and wherein a parameter estimator is provided which is designed to recursively estimate a current time delay value based on a respective current time delay as input.
[0010] The derivatives are to be understood as time derivatives.
[0011] The angular velocity can preferably be equal to the first time derivative of the steering angle.
[0012] The second time derivative of the steering angle or the time derivative of the angular velocity can preferably be the angular acceleration.
[0013] A current time delay is the delay at the current time and the current time delay value, for example, corresponds to a delay calculated over a period of time.
[0014] The steering angle section can, for example, have a starting point, for example when the positive or negative threshold value of the second actual / target derivative is exceeded, and a length with which an online calculation is still possible.
[0015] The parameter estimator can be a model to be optimized, for example an artificial neural network or a recursive least squares estimator, which has internal parameters to be optimized, for example the nodes in the artificial neural network.
[0016] According to the invention, it was recognized that a one-time offline determination of the temporal deceleration value of a steering system does not provide sufficiently good knowledge of the deceleration.
[0017] However, these time delays, particularly in the follow-up control of the target steering angle, which is calculated by the trajectory control, represent a significant limitation of the overall system performance. According to the invention, by determining the second derivatives of the target and actual steering angle values and determining a current steering angle segment, it is ensured that the time horizon is suitable for calculating such a current time delay value. The second derivative is used to determine suitable steering angle segments by checking whether the second actual-Ztarget derivative of the target and actual steering angle values in the current steering angle segment exceeds both a positive threshold value and a negative threshold value, i.e.a determination of suitable steering angle sections for the calculation of the current temporal deceleration value is carried out by checking the second actual / target derivative against a positive and a negative threshold value.
[0018] By checking against a positive and negative threshold value, it is ensured that a current time delay can be determined using a correlator, for example, through cross-correlation, i.e., that the first actual derivative / target derivative form half a sine wave in the current steering angle segment. Thus, the values of the first actual derivative / target derivative in the current steering angle segment can be used to calculate a current time delay.
[0019] This ensures that even a short time period, which can be calculated online, for example, in the vehicle, is suitable for applying a correlation. The current time delay is then passed to the parameter estimator as input for determining the current time delay value.
[0020] Thus, the current time delay value can be used for trajectory control.
[0021] The steering angle planning system according to the invention enables a temporal calculation of the current time delay value online. The use of the current time delay value in a steering angle planning system, for example, for a trajectory control system, is possible regardless of the speed of the calculation of the current time delay.
[0022] In addition, the current deceleration value reflects an improved, real-world deceleration, as several current decelerations are included in the calculations. Outliers, such as when the vehicle drives over a pothole and the derivatives of the actual steering angle value differ significantly due to a different friction coefficient, are thus averaged out.
[0023] The steering angle planning system according to the invention allows the current time delay value of the steering angle follow-up control to be determined online with reasonable computing and storage effort, which is a great advantage for trajectory control systems, especially for autonomously / semi-autonomously operated vehicles.
[0024] In a further embodiment, the parameter estimator can be designed to recursively estimate the current time delay value based on the current time delay and current vehicle parameters as input, wherein the vehicle parameters include at least the vehicle speed.
[0025] Additional vehicle parameters, such as the type of vehicle and the parameters related to the tires, can be entered.
[0026] These can be recorded using a suitable sensor system, for example a tachometer, or can be pre-set, for example, like the vehicle type.
[0027] In a further embodiment, the parameter estimator can be configured to recursively estimate the current time delay value based on the current time delay and current vehicle parameters as well as current environmental data as input, i.e., based on at least previous results of the parameter estimator, wherein the vehicle parameters include at least the vehicle speed. The environmental data can include at least the road condition or roadway condition and / or a detected coefficient of friction on the road surface.
[0028] This incorporates relevant influencing factors such as vehicle speed, tire specifications, road surface conditions, and other environmental / vehicle data. The parameter estimator then determines the current time delay based on the current / previous time delays as well as the environmental / vehicle data. This dependence on the current conditions allows the current time delay to be determined more precisely.
[0029] This means that the parameter estimator determines the current temporal deceleration value depending on the vehicle data such as vehicle speed and environmental data such as the road surface and the target steering angle.
[0030] In further development, the parameter estimator can be implemented as a least-squares estimator. In particular, the least-squares estimator is implemented as a recursive least-squares estimator. This allows for a stable and fast determination of the current time delay value. The recursive nature allows online use with currently accumulating data while maintaining the same complexity in each recursion step. In particular, a forgetting factor can be introduced, which forgets the results that are too old during the calculation. This allows historical data to become less important for optimization, and more weight to be given to current data.
[0031] Alternatively, the parameter estimator can be implemented as an artificial neural network, such as a recurrent neural network. Such a network can also continuously improve.
[0032] Furthermore, in a further embodiment, the parameter estimator has internal parameters to be optimized for determining the current temporal delay value as output. These can be, for example, the nodes if the parameter estimator is designed as an artificial neural network. Preferably, the parameter estimator is designed to use the parameters to be optimized internally, for example, the nodes, as output for the future estimation of the current temporal delay value, starting from an achieved accuracy value.
[0033] This means that from a certain quality onwards, the parameter estimator is only used as a known function in space, in which the input data is entered and on the basis of which, for example, with the already optimized nodes, if the parameter estimator is an artificial neural network, the current time delay value is determined as output.
[0034] In a further embodiment, the correlator is designed to determine the current time delay by cross-correlating the respective first actual derivatives and the respective first desired derivatives in the current steering angle segment. This is suitable for the stable determination of a current time delay for relatively short time periods of approximately 5 seconds or approximately 500 data points, since the second desired / actual derivative exceeds a predetermined positive and negative threshold value, thus ensuring that the first actual / desired derivatives in the steering angle segment under consideration are essentially wave-shaped.
[0035] Furthermore, in a further embodiment, the steering angle planning system can be configured to determine a new current time delay value based on the parameter estimator only when a newly determined current time delay is present. The parameter estimator is thus only executed when a new current time delay, and thus a newly existing current steering angle segment, is available. This avoids excessive strain on the vehicle's computing capacity. This is particularly advantageous for autonomous / semi-autonomous vehicles.
[0036] In a further embodiment, a control unit can be provided for correcting the target steering angle value to be set based on the current temporal deceleration value and / or for adapting a target trajectory taking into account the target steering angle value in conjunction with the current temporal deceleration value. This allows the target trajectory to be better adhered to overall.
[0037] Furthermore, the problem is solved by a vehicle with a steering angle planning system as described above. This can, in particular, be a semi-autonomous or autonomously operated vehicle.
[0038] In a further embodiment, the vehicle can have a receiving unit for receiving target steering angle values to be set at predetermined positions by one or more preceding vehicles and / or a trajectory generation system for generating a target trajectory based on at least navigation data and environmental data.
[0039] This can be a tracking vehicle that follows a leading vehicle or, for example, an autonomously operated vehicle that creates the target trajectories based on navigation data and environmental data recorded by a sensor system.
[0040] The steering angle planning system according to the invention, which places only a minimal demand on the computing capacities, does not place any additional load on these capacities, particularly in the case of an autonomously driving vehicle which requires a high computing capacity.
[0041] Furthermore, the object is achieved by a method for operating a steering angle planning system for a vehicle comprising the steps:
[0042] - Measuring a current actual steering angle value,
[0043] - Providing corresponding target steering angle values,
[0044] - Determining the respective first actual derivative of the measured respective current actual steering angle value and the respective first target derivative of the respective current target steering angle value over time, - Determining a second actual derivative of the measured respective current actual steering angle value over time and a second target derivative of the respective current target steering angle value over time,
[0045] - Determining a respective current steering angle section in which the second actual derivative and the second desired derivative each exceed a predetermined positive and negative threshold value at least once, wherein the current steering angle section has a maximum predetermined length,
[0046] - Determining a current time delay based on the respective first actual derivatives and the respective first desired derivatives in the current steering angle section using a correlator,
[0047] - Inputting a respective current time delay into a parameter estimator to recursively estimate a current time delay value.
[0048] This can, in particular, involve the steering angle planning system described above. Furthermore, the advantages of the steering angle planning system can be transferred to the method.
[0049] Further features and advantages of the present invention will become apparent from the following description with reference to the accompanying figures. Variations may be devised by those skilled in the art without departing from the scope of the invention as defined by the following claims.
[0050] The figures show schematically:
[0051] FIG 1: a vehicle with a steering angle planning system according to the invention schematically in a first embodiment,
[0052] FIG 2: exemplary actual steering angle values and target steering angle values, as well as their derivatives, FIG 3: a cross-correlation applied offline to a first actual derivative and a first target derivative,
[0053] FIG 4: in comparison a cross-correlation applied according to the invention,
[0054] FIG 5: a current time delay,
[0055] FIG 6: the process schematically,
[0056] FIG 7: an example of the operation of the steering angle planning system.
[0057] FIG 1 shows a vehicle 1 according to the invention with a steering angle planning system 2 according to the invention.
[0058] This has a sensor device 3. The sensor device 3 is designed to detect the current actual steering angle values. For this purpose, the sensor device 3 can have rotation angle sensors and other sensors for detecting the actual steering angle values.
[0059] Furthermore, the steering angle planning system 2 comprises a storage unit 7 with stored target steering angle values.
[0060] If vehicle 1 is configured as an autonomously operated vehicle, a trajectory generation system (not shown) may be present for generating a target trajectory based on navigation data and environmental data, in this case, for example, environmental data such as other road users and static objects. Based on the target trajectory, the target steering angle values for the target trajectory to be traveled are generated and stored in the memory unit 7.
[0061] Vehicle 1 can also be designed as a tracking vehicle. Such a vehicle receives the desired steering angle values to be set from a preceding vehicle that has the same desired trajectory. For this purpose, vehicle 1 can have a corresponding receiving unit (not shown), for example, for receiving the desired steering angle values via radio (V2V connection). Furthermore, the steering angle planning system 2 is designed, for example, by means of a processor / processing unit, etc., to determine the first temporal actual derivatives and the second temporal desired derivatives over time.
[0062] Furthermore, the second temporal actual derivative of the measured respective current actual steering angle value over time and the second temporal target derivative of the respective current target steering angle value over time are determined.
[0063] The angular velocity can preferably be equal to the first time derivative of the steering angle.
[0064] The second time derivative of the steering angle or the time derivative of the angular velocity can preferably be the angular acceleration.
[0065] Subsequently, the steering angle planning system 2 determines a current steering angle section 4 (FIG 2) in which the second actual derivative and the second desired derivative each exceed a predetermined positive and negative threshold value at least once, wherein the current steering angle section 4 (FIG 2) has a maximum length.
[0066] The length of the considered steering angle section 4 (FIG 2) is selected such that a calculation of the current time delay is possible by, for example, a cross-correlation, ie a positive and negative threshold value of the second actual derivative and the second desired derivative are exceeded.
[0067] The steering angle section 4 (FIG. 2) can thus, for example, have a starting point, for example, when the positive or negative threshold value of the second actual / target derivative is exceeded, and a length in which an online calculation is still possible, ie in which the computing and memory requirements for an online application are still met. Preferably, a length of approximately 5 s or approximately 500 data points is selected, as these fulfill both conditions. FIG. 2 shows recorded actual steering angle values (actual) and values to be set.
[0068] Target steering angle values in an upper diagram over time
[0069] The first temporal actual derivative (actual) of the actual steering angle values over time and the first temporal target derivative (target) of the target steering angle values to be set are shown in the middle diagram.
[0070] The second temporal actual derivative (actual) of the actual steering angle values over time and the second target derivative (target) of the target steering angle values to be set are shown in the lower diagram.
[0071] Furthermore, the respective current steering angle section 4 in which the second actual derivative and the second desired derivative each exceed a predetermined positive and negative threshold value at least once, wherein the current steering angle section 4 may have a maximum length, is specified.
[0072] This ensures that the first actual derivative and first target derivative assume a wave-like, in particular sinusoidal, course over the steering angle section 4, so that a cross-correlation is subsequently possible
[0073] Furthermore, the steering angle planning system 2 (FIG. 1) has a correlator 5 which is designed to apply a cross-correlation to the first actual derivatives and the first desired derivatives in the steering angle section 4, i.e. in the section in which the first actual derivative and the first desired derivative have a wave-like course.
[0074] By applying the cross-correlation, a current time delay for the steering angle section 4 is determined.
[0075] FIG 3 shows a cross-correlation function applied offline to a first actual derivative function and a first target derivative function of actual steering angle values and target steering angle values over time. The actual steering angle values (act wheel angle front) and target steering angle values (tgt wheel angle front) are shown in the upper diagram, and the first cross-correlation of the first actual derivative and the first target derivative is shown in the lower diagram.
[0076] In comparison, FIG 4 shows a cross-correlation applied according to the invention, applied online only to the respective steering angle sections 4.
[0077] The steering angle sections 4 with the actual steering angle values (act weel angle front) and the target steering angle values (tgt weel angle front) are shown in the upper diagram. The steering angle sections 4 describe the areas in which the second actual derivative and the second target derivative exceed a positive and a negative threshold value. This ensures that the cross-correlation can be easily applied to the first actual derivative and the first target derivative (wave-like curve of the first actual derivative and target derivative). The cross-correlation is shown in the lower diagram.
[0078] FIG 5 shows the current time delay in the respective steering angle sections 4 above.
[0079] Furthermore, the steering angle planning system 2 has a parameter estimator, which is designed in particular as a recursive least squares estimator 6. This estimator delivers results quickly and reliably. The recursive nature allows online use with currently accumulating data while maintaining the same complexity in each recursion step. Alternatively, the parameter estimator can be designed, for example, as an artificial neural network.
[0080] The Recursive Least Squares Estimator 6 receives the current time delay as input data.
[0081] Furthermore, the recursive least squares estimator 6 receives the current vehicle data, in particular the vehicle speed and environmental data such as road conditions and the friction coefficient of the tires in the steering angle section 4. Based on the vehicle data and the environmental data and the current time delay, a current time delay value is now determined recursively, ie, based on at least some of the previous results of the recursive least squares estimator 6. Such a current time delay value can be determined online with reasonable computing and storage effort.
[0082] Furthermore, a forgetting factor can be introduced, by which the old results of the recursive least squares estimator 6 are forgotten.
[0083] The steering angle planning system 2 determines a new current time delay value only when a newly determined current time delay and a new current steering angle segment 4 are present. Since the previous current time delay value is used until then, no real-time calculation requiring excessive computing capacity is absolutely necessary. This prevents excessive strain on the vehicle's computing capacity. This is particularly advantageous for autonomous / semi-autonomous vehicles.
[0084] The steering angle planning system 2 according to the invention can prevent inaccuracies and, in particular, delays in the follow-up control of the target steering angle. The steering angle planning system 2 takes into account that the delays resulting from the steering angle follow-up control are variable within the operating range and depend, for example, on the vehicle speed and the environmental parameters. This results in improved overall system performance.
[0085] Furthermore, a control unit (not shown) may be provided for correcting the target steering angle value to be set based on the current time delay value.
[0086] The steering angle planning system 2 according to the invention thus ensures the high requirements for tracking accuracy, stability and robustness for a trajectory control for a vehicle in the context of automated or assisted driving with respect to the steering system in the entire working range of the trajectory control.
[0087] FIG 6 shows an overview of the steering angle planning system 2 and its method,
[0088] In a first step, the actual steering angle values are recorded and the target steering angle values to be set are provided.
[0089] In a second step, the first temporal actual derivative and the first temporal target derivative of the actual steering angle values and target steering angle values, as well as the second temporal actual derivative and the second temporal target derivative of the actual steering angle values and target steering angle values, are determined over a period of time. If the second actual derivative and the second target derivative exceed a positive and negative threshold value, a current steering angle section 4 of a predefined length is created. The current steering angle section 4 has a length within which an online calculation is still possible.
[0090] In a third step, a cross-correlation of the first actual derivatives and first target derivatives, which lie in the current steering angle section 4, is carried out in order to determine a current time delay.
[0091] Subsequently, the current time delay together with at least the vehicle speed and the friction coefficient / road condition are entered as parameters into the Recursive Least Squares Estimator 6, which recursively, ie based on at least some previous results, estimates the current time delay value.
[0092] FIG 7 shows an example of an online estimation of the current time delay value.
[0093] The first upper diagram shows the target steering angle values (tgt weel angle front) and the actual steering angle values (act weel angle front). The second diagram below shows the determined current steering angle segments 4.
[0094] The third diagram below shows the current time delays and the average current time delay value.
[0095] The fourth diagram shows the vehicle speed.
[0096] List of reference symbols
[0097] 1 vehicle
[0098] 2 Steering angle planning system
[0099] 3 Sensor device
[0100] 4 Steering angle section
[0101] 5 Correlator
[0102] 6 Recursive Least Squares Estimator Storage Unit
Claims
Patent claims 1. Steering angle planning system (2) for a vehicle (1) comprising a sensor device (3) for measuring a respective current actual steering angle value, and a storage unit (7) with corresponding target steering angle values, characterized in that the steering angle planning system (2) is designed to determine the respective first actual derivative of the measured respective current actual steering angle value and the respective first target derivative of the respective current target steering angle value over time, and further to determine a second actual derivative of the measured respective current actual steering angle value over time and a second target derivative of the respective current target steering angle value over time, and to determine a respective current steering angle section (4) in which the second actual derivative and the second target derivative each exceed a predetermined positive and negative threshold value at least once,wherein the current steering angle section (4) has a maximum predetermined length, and wherein a correlator (5) is further provided for determining a respective current time delay based on the respective first actual derivatives and the respective first desired derivatives in the respective current steering angle section (4), and wherein a parameter estimator is provided which is designed to recursively estimate a current time delay value based on a respective current time delay as input.
2. Steering angle planning system (2) according to claim 1, characterized in that the parameter estimator is designed to recursively estimate the current time delay value based on the current time delay and current vehicle parameters as input, wherein the vehicle parameters include at least the vehicle speed.
3. Steering angle planning system (2) according to claim 1 or 2, characterized in that the parameter estimator is designed to use the current time delay and current vehicle parameters as well as current environmental data as Input recursively to estimate the current time delay value, where the vehicle parameters include at least the vehicle speed.
4. Steering angle planning system (2) according to claim 3, characterized in that the environmental data include at least the road condition and / or a detected friction coefficient.
5. Steering angle planning system (2) according to one of the preceding claims, characterized in that the parameter estimator is designed as a recursive least squares estimator (6).
6. Steering angle planning system (2) according to claim 5, characterized in that the recursive least squares estimator (6) has a forgetting factor for forgetting results of the recursive least squares estimator (6) from a predetermined age.
7. Steering angle planning system (2) according to one of the preceding Claims 1 to 4, characterized in that the parameter estimator is designed as an artificial neural network.
8. Steering angle planning system (2) according to one of the preceding claims, characterized in that the parameter estimator has internal parameters to be determined for determining the current temporal delay value as an output, wherein the parameter estimator is designed to use the parameters to be determined internally as an output for the future estimation of the current temporal delay value, starting from an achieved accuracy value of the parameters to be determined internally.
9. Steering angle planning system (2) according to one of the preceding claims, characterized in that the correlator (5) is designed to determine the current time delay by means of a cross-correlation of the respective first actual derivatives and the respective first desired derivatives in the current steering angle section (4).
10. Steering angle planning system (2) according to one of the preceding claims, characterized in that the steering angle planning system (2) is designed to determine a new current time delay value based on the parameter estimator only when a newly determined current time delay is present.
11. Steering angle planning system (2) according to one of the preceding claims, characterized in that a control unit is provided for correcting the desired steering angle value to be set on the basis of the current temporal delay value and / or for adapting a desired trajectory taking into account the desired steering angle value in conjunction with the current temporal delay value.
12. Steering angle planning system (2) according to one of the preceding claims, characterized in that the steering angle planning system (2) is designed to determine the current time delay value online.
13. Vehicle (1) with a steering angle planning system (2) according to one of the preceding claims.
14. Vehicle (1) according to claim 13, characterized in that the vehicle (1) has a receiving unit for receiving desired steering angle values to be set at predetermined positions by one or more preceding vehicles and / or a trajectory generation system for generating a desired trajectory based on at least navigation data and environmental data.
15. Method for operating a steering angle planning system (2) for a vehicle (1) comprising the steps: - Measuring the current actual steering angle value, - Providing corresponding target steering angle values, - Determining the respective first actual derivative of the measured respective current actual steering angle value and the respective first target derivative of the respective current target steering angle value over time, - Determining a second actual derivative of the measured respective current actual steering angle value over time and a second target derivative of the respective current target steering angle value over time, - Determining a respective current steering angle section (4) in which the second actual derivative and the second desired derivative each exceed a predetermined positive and negative threshold value at least once, wherein the current steering angle section (4) has a maximum predetermined length, - Determining a respective current time delay based on the respective first actual derivatives and the respective first desired derivatives in the current steering angle section (4) using a correlator (5), - Inputting a respective current time delay into a parameter estimator to recursively estimate a current time delay value.