Steering Assist Apparatus for Autonomous Path Following
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Solution Overview
Problem
Existing steering systems for autonomous vehicles face challenges in accurately following a target travel line, particularly on curved paths, due to differences in tread loads and cornering forces between inner and outer wheels, leading to excessive vehicle motion and reduced path-following ability.
Innovation Solution
A steering assist apparatus that includes an information acquirer, base target steered angle setters, correction amount calculators, and motor controllers to adjust steering angles dynamically based on lateral deviation, curvature, and turning states, ensuring precise control of both steering motors to maintain the vehicle on the target path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a steer-by-wire system with independent right and left steering actuators is used to increase layout flexibility, then the layout flexibility of the engine room is improved, but the vehicle's ability to follow the target travel line during turning is worsened due to unequal tread loads on inner and outer wheels
Solution Approach 1:
The patent applies local quality by setting different target steered angles for the right and left steered wheels based on their respective positions. The ECU calculates a right target steered angle and a left target steered angle separately, considering that the outer wheel requires a larger steered angle change than the inner wheel during turning to compensate for centrifugal force and unequal tread loads. This localized adjustment ensures each wheel contributes appropriately to path following.
Solution Approach 2:
The patent changes the steering control parameters by introducing different steered angle correction amounts for right and left wheels. The ECU calculates a right steered angle correction amount and a left steered angle correction amount based on vehicle speed, steering angle, and detected turning direction. These corrected parameters are then used to control the right and left steering actuators differently, optimizing path-following accuracy during turning maneuvers.
2Speed
If the steered angle of the outer wheel is increased during turning to compensate for centrifugal force, then the vehicle motion responsiveness is improved, but the vehicle motion becomes larger than intended by the driver, worsening the path-following accuracy
Solution Approach 1:
The patent implements feedback control by continuously monitoring the actual steered angles of both wheels and comparing them with the target steered angles calculated by the ECU. The system detects the turning direction and adjusts the steered angle correction amounts based on feedback from sensors monitoring vehicle speed, steering angle, and wheel positions. This closed-loop control ensures the vehicle responds appropriately to driver input while maintaining accurate path following.
Solution Approach 2:
The patent applies dynamics by making the target steered angles and correction amounts variable based on vehicle operating conditions. The ECU dynamically adjusts the right and left target steered angles according to vehicle speed, steering angle, and detected turning direction. This dynamic adjustment allows the system to optimize the balance between responsiveness and accuracy for each specific driving condition.
3Extent of automation
If autonomous steering control is used during autonomous driving mode, then the automation level is improved, but the ability to follow the target travel line on curved paths is worsened due to excessive vehicle motion during turns
Solution Approach 1:
The patent segments the steering control into independent right and left wheel control channels. The ECU separately calculates target steered angles and correction amounts for each wheel, allowing independent optimization of each side's performance. This segmentation enables the autonomous steering system to handle the complex dynamics of curved path following by treating each wheel's control as a separate but coordinated task.
Solution Approach 2:
The patent introduces asymmetry in the control system by applying different steered angle correction amounts to the right and left wheels. During right turns, the left (outer) wheel receives a larger correction amount than the right (inner) wheel, and vice versa for left turns. This asymmetric control strategy compensates for the unequal tread loads and centrifugal forces experienced by inner and outer wheels, improving curved path-following accuracy in autonomous mode.
Data Source
AI summary
A second target steered angle setter includes: a first multiplier configured to, when the vehicle is making a right turn, reduce a base target steered angle correction amount so as to set the reduced base target steered angle correction amount to be a left target steered angle correction amount, and configured to, in other states, set the base target steered angle correction amount to be the left target steered angle correction amount on an as-is basis; and a second multiplier configured to, when the vehicle is making a left turn, reduce the base target steered angle correction amount so as to set the reduced base target steered angle correction amount to be a right target steered angle correction amount, and configured to, in other states, set the base target steered angle correction amount to be the right target steered angle correction amount on an as-is basis.