The present disclosure relates to systems and methods for constraining a commanded steering angle sent to a steering system that is part of a vehicle. More particularly, the present disclosure relates to systems and methods for limiting a rate of change of the commanded steering angle sent to the steering system based on a current trajectory of the vehicle.
Semi-autonomous and autonomous vehicles are becoming more ubiquitous on the road. During semi-autonomous or hands-free driving, model predictive control may be employed to determine the vehicle's acceleration, braking, and steering. A model predictive controller attempts to track a target trajectory of the vehicle by controlling a commanded steering angle that is provided to the vehicle's steering system. The model predictive controller determines the commanded steering angle based on time-based trajectory information, localization inputs, and planner inputs. However, it is to be appreciated that sometimes the localization inputs may be noisy and generate discontinuous signals. Noisy and discontinuous localization input signals may adversely affect the calculation of the commanded steering angle. In particular, if there are sudden jumps in the value of the commanded steering angle this may create nosiness or jerking in the steering wheel that some drivers may find objectionable.
Thus, while current systems achieve their intended purpose, there is a need in the art for an improved system for determining the commanded steering angle. In particular, there is a need in the art for a system that mitigates the impact of noisy or discontinuous localization inputs when determining the commanded steering angle.
According to several aspects a limiting system constraining a commanded steering angle for a vehicle including an electric power steering (EPS) system is disclosed. The limiting system includes a controller in electronic communication with at least one other system of the vehicle. The controller executes instructions to receive a plurality of trajectory planning inputs that are each expressed as an array including a plurality of values, where the plurality of trajectory planning inputs includes a trajectory velocity array, a trajectory acceleration array, and a trajectory curvature array. The controller also executes instructions to determine a corresponding ideal rate of change of the commanded steering angle for each curvature value that is part of the trajectory curvature array based on the trajectory planning inputs. The controller also executes instructions to determine a maximum rate of change allowed by the EPS system for each trajectory velocity value that is part of the trajectory velocity array. Finally, the controller executes instructions to determine a maximum rate of steering angle change based on the corresponding ideal rate of change of the commanded steering angle and the maximum rate change allowed by the EPS system, where the maximum rate of steering angle change limits the commanded steering angle.
In an aspect, the controller determines the corresponding ideal rate of change of the commanded steering angle for each curvature value that is part of the trajectory curvature array by executing instructions to determine a rate of change of a trajectory curvature based on a current value of the trajectory curvature, a subsequent value of the trajectory curvature, and a change in time between a current value of the trajectory curvature and the subsequent value of the trajectory curvature.
In another aspect, the rate of change of the trajectory curvature is determined by
where {dot over (ρ)} represents the rate of change of the trajectory curvature, ρn represents a current value of the trajectory curvature, ρn+1 represents the subsequent value of the trajectory curvature, and Δt represents the change in time between the current value of the trajectory curvature ρn and the subsequent value of the trajectory curvature.
In yet another aspect, the controller determines the corresponding ideal rate of change of the commanded steering angle for each curvature value that is part of the trajectory curvature array by executing instructions to determine the corresponding ideal rate of change of the commanded steering angle based on the rate of change of the trajectory curvature, a wheelbase of the vehicle, a steering gradient of the vehicle, and a longitudinal velocity component of the vehicle.
In still another aspect, the corresponding ideal rate of change of the commanded steering angle is determined by:
{dot over (δ)}ideal={dot over (ρ)}(L+EGvx2)
where {dot over (δ)}ideal is corresponding ideal rate of change of the commanded steering angle, {dot over (ρ)} is the rate of change of the trajectory curvature, L is a wheelbase of the vehicle, EG is a steering gradient of the vehicle, and vx is a longitudinal velocity component of a trajectory of the vehicle.
In one aspect, the controller includes one or more look-up tables saved in memory, and the one or more look-up tables provide the maximum rate of change allowed for a specific trajectory velocity value.
In another aspect, the controller determines the maximum rate of change allowed by the EPS system by executing instructions to locate a corresponding maximum rate of change value in the one or more look-up tables based on a specific trajectory velocity value.
In yet another aspect, the controller determines the maximum rate of steering angle change based on a calibration factor.
In still another aspect, the calibration factor ranges in value from 0 to 1.
In one aspect, the controller determines the maximum rate of change of the commanded steering angle by executing instructions to add the corresponding ideal rate of change of the commanded steering angle with a product to determine a first value, wherein the product is determined by multiplying the maximum rate of change with the calibration factor.
In another aspect, the controller determines the maximum rate of change of the commanded steering angle by executing instructions to compare the first value with the maximum rate of change, and in response to determining the first value is less than or equal to the maximum rate of change, set the maximum rate of change of the commanded steering angle to the first value.
In yet another aspect, the controller determines the maximum rate of change of the commanded steering angle by executing instructions to compare the first value with the maximum rate of change and in response to determining the first value is greater than the maximum rate of change, set the maximum rate of change of the commanded steering angle to the maximum rate of change allowed by the EPS system.
In one aspect, an autonomous driving and active safety (ADAS) system for a vehicle including an EPS system. The ADAS system includes a trajectory tracking controller that determines a commanded steering angle, where the trajectory tracking controller is in electronic communication with the EPS system and a limiting system including a controller in electronic communication with the trajectory tracking controller. The controller executes instructions to receive a plurality of trajectory planning inputs that are each expressed as an array including a plurality of values, where the plurality of trajectory planning inputs includes a trajectory velocity array, a trajectory acceleration array, and a trajectory curvature array. The controller also executes instructions to determine a corresponding ideal rate of change of the commanded steering angle for each curvature value that is part of the trajectory curvature array based on the trajectory planning inputs. The controller executes instructions to determine a maximum rate of change allowed by the EPS system for each trajectory velocity value that is part of the trajectory velocity array. Finally, the controller executes instructions to determine a maximum rate of steering angle change based on the corresponding ideal rate of change of the commanded steering angle and the maximum rate change allowed by the EPS system, where the maximum rate of steering angle change limits the commanded steering angle.
In one aspect, the trajectory tracking controller determines the commanded steering angle based on the maximum rate of steering angle change.
In another aspect, the controller determines the corresponding ideal rate of change of the commanded steering angle for each curvature value that is part of the trajectory curvature array by executing instructions to determine a rate of change of a trajectory curvature based on a current value of the trajectory curvature, a subsequent value of the trajectory curvature, and a change in time between a current value of the trajectory curvature and the subsequent value of the trajectory curvature.
In yet another aspect, the rate of change of the trajectory curvature is determined by
where {dot over (ρ)} represents the rate of change of the trajectory curvature, ρn represents a current value of the trajectory curvature, ρn+1 represents the subsequent value of the trajectory curvature, and Δt represents the change in time between the current value of the trajectory curvature ρn and the subsequent value of the trajectory curvature.
In still another aspect, the controller determines the corresponding ideal rate of change of the commanded steering angle for each curvature value that is part of the trajectory curvature array by executing instructions to determine the corresponding ideal rate of change of the commanded steering angle based on the rate of change of the trajectory curvature, a wheelbase of the vehicle, a steering gradient of the vehicle, and a longitudinal velocity component of the vehicle.
In one aspect, the corresponding ideal rate of change of the commanded steering angle is determined by:
{dot over (δ)}ideal={dot over (ρ)}(L+EGvx2)
where {dot over (δ)}ideal is corresponding ideal rate of change of the commanded steering angle, {dot over (ρ)} is the rate of change of the trajectory curvature, L is a wheelbase of the vehicle, EG is a steering gradient of the vehicle, and vx is a longitudinal velocity component of a trajectory of the vehicle.
In another aspect, the controller determines the maximum rate of steering angle change based on a calibration factor.
In one aspect, a method for constraining a commanded steering angle for a vehicle including an electric power steering (EPS) system is disclosed. The method includes receiving, by a controller, a plurality of trajectory planning inputs that are each expressed as an array including a plurality of values. The plurality of trajectory planning inputs includes a trajectory velocity array, a trajectory acceleration array, and a trajectory curvature array. The method also includes determining a corresponding ideal rate of change of the commanded steering angle for each curvature value that is part of the trajectory curvature array based on the trajectory planning inputs. The method further includes determining a maximum rate of change allowed by the EPS system for each trajectory velocity value that is part of the trajectory velocity array. Finally, the method includes determining a maximum rate of steering angle change based on the corresponding ideal rate of change of the commanded steering angle and the maximum rate change allowed by the EPS system, where the maximum rate of steering angle change limits the commanded steering angle.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.
The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.
Referring to
The disclosed limiting system 20 includes a controller 28 configured to determine a maximum rate of change of a commanded steering angle {dot over (δ)}cmndmax, which is sent to the trajectory tracking controller 22. The trajectory tracking controller 22 determines a commanded steering angle δcmnd, which is sent to the EPS controller 24 of the EPS system 14. The EPS controller 24 determines a motor command 34 based on the commanded steering angle δcmnd, which is sent to the electric motor 26. The electric motor 26 then generates the assist torque T provided to the steering system 16 based on the value of the motor command 34.
As explained below, the disclosed limiting system 20 constrains the commanded steering angle δcmnd sent to the EPS system 14 based on real-time data representing the current trajectory and velocity of the vehicle 10. Specifically, the limiting system 20 may reduce or prevent large variations or jumps in the value of the commanded steering angle δcmnd. In particular, the limiting system 20 mitigates the impact of noisy or discontinuous localization inputs 36 that are provided to the trajectory tracking controller 22 to determine the commanded steering angle δcmnd. It is to be appreciated that noisy or discontinuous localization data may create noisiness or jerking in the hand wheel 30 when the vehicle 10 operates in a semi-autonomous or hands-free driving mode, which some drivers may find objectionable.
In one non-limiting embodiment, the trajectory tracking controller 22 is a model predictive controller, however, other types of controllers may be used as well. The trajectory tracking controller 22 determines the commanded steering angle δcmnd based on the maximum rate of change of the commanded steering angle {dot over (δ)}cmndmax and a plurality of trajectory variables 40, which are received from a trajectory generation system 32 of the vehicle 10 and are described below. As seen in
Continuing to refer to
The controller 28 of the limiting system 20 is in electronic communication with at least one other system in the vehicle 10 (i.e., the trajectory generation system 32 and the trajectory tracking controller 22). As explained below, the controller 28 determines the maximum rate of change of the commanded steering angle {dot over (δ)}cmndmax based on the trajectory planning inputs 42 and a change in time Δt (seen in
Referring to
The steering angle rate module 52 then determines the corresponding ideal rate of change of the commanded steering angle {dot over (δ)}ideal based on the rate of change of the trajectory curvature {dot over (ρ)}, a wheelbase L of the vehicle 10, a steering gradient LG of the vehicle 10, and a longitudinal velocity component vx of the vehicle 10. The wheelbase L and the steering gradient EG may be fixed values saved in a memory of the controller 28, and the longitudinal velocity vx is a longitudinal velocity component of a trajectory of the vehicle 10. Specifically, the corresponding ideal rate of change of the commanded steering angle {dot over (δ)}ideal is determined based on Equation 2, which is expressed as:
{dot over (δ)}ideal={dot over (ρ)}(L+EGvx2)
Referring back to
Continuing to refer to
In block 204, the steering angle rate module 52 determines the corresponding ideal rate of change of the commanded steering angle {dot over (δ)}ideal for each for each curvature value ρn of the trajectory curvature array 64 based on the trajectory planning inputs 42. As explained above, Equation 1 is used to determine the rate of change of the trajectory curvature {dot over (ρ)}, and Equation 2 is used to determine the corresponding ideal rate of change of the commanded steering angle {dot over (δ)}ideal. The method 200 may then proceed to block 206.
In block 206, the maximum steering angle rate module 54 determines the maximum rate of change {dot over (δ)}max allowed by the EPS system 14 for each trajectory velocity value that is part of the trajectory velocity array. Specifically, the maximum steering angle rate module 54 locates the corresponding maximum rate of change {dot over (δ)}max allowed by the EPS system 14 in the one or more look-up tables based on a specific trajectory velocity value. The method 200 may then proceed to block 208.
In block 208, the upper bound module 56 determines the maximum rate of steering angle change {dot over (δ)}cmndmax based on the corresponding ideal rate of change of the commanded steering angle {dot over (δ)}ideal, the maximum rate of change {dot over (δ)}max, and a calibration factory . Specifically, the upper bound module 56 determines the maximum rate of change of the commanded steering angle {dot over (δ)}cmndmax by first adding the corresponding ideal rate of change of the commanded steering angle {dot over (δ)}ideal with the product to determine a first value, wherein the product is determined by multiplying the maximum rate of change {dot over (δ)}max allowed by the EPS system 14 with the calibration factor . The upper bound module 56 then compares the first value with the maximum rate of change {dot over (δ)}max allowed by the steering system 16. In response to determining the first value is less than or equal to the maximum rate of change {dot over (δ)}max allowed by the EPS system 16, the upper bound module 56 sets the maximum rate of change of the commanded steering angle {dot over (δ)}cmndmax to the first value. However, if the upper bound module 56 determines that the first value is greater than the maximum rate of change {dot over (δ)}max, the upper bound module 56 sets the maximum rate of change of the commanded steering angle {dot over (δ)}cmndmax to the maximum rate of change {dot over (δ)}max allowed by the EPS system 14. As seen in
Referring generally to the figures, the disclosed limiting system provides various technical effects and benefits to a vehicle. Specifically, current vehicle systems may employ a calibratable look-up table to determine a single value limit that is placed on the maximum rate of change of the commanded steering angle. However, if the localization inputs are noisy or discontinuous, this may cause noisy or jerking movements in the hand wheel. The present disclosure provides an approach for replacing the current calibratable look-up tables with a system and method to analytically determine, in real time, the input constraints for the commanded steering angle based on the current trajectory of the vehicle. Determining the commanded steering angle based on the current trajectory of the vehicle may reduce or substantially eliminate the unwanted movement in the hand wheel.
The description of the present disclosure is merely exemplary in nature and variations that do not depart from the gist of the present disclosure are intended to be within the scope of the present disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the present disclosure.