Steering Torque Control via Variable Gain Scheduling
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Solution Overview
Problem
Lane keeping systems in autonomous mode often provide excessive handwheel torque assist, leading to objectionable variations in lateral acceleration and increased handwheel movement, which can disengage drivers and cause discomfort for vehicle occupants.
Innovation Solution
A steering system that determines a proportional gain value based on lateral position error, near field and far field heading angles, lane curvature, and vehicle lateral position to calculate a torque assist command, reducing handwheel activity through a combination of proportional and derivative gains, and closed loop gains for improved stability and handling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the lane keeping system provides high torque assist in autonomous mode to maintain lane position, then the lane keeping capability is improved, but the handwheel movement becomes excessive causing driver disengagement and passenger discomfort
Solution Approach 1:
The patent applies dynamics by making the proportional gain value variable rather than fixed. The gain is dynamically adjusted based on multiple lane characteristics including lateral position error, near field heading angle, far field heading angle, curvature of the lane, and lateral position of the vehicle. This dynamic adjustment allows the torque assist to adapt to different driving conditions, providing sufficient correction when needed while reducing excessive handwheel movement in stable conditions, thereby resolving the contradiction between lane keeping reliability and ease of operation
Solution Approach 2:
The patent changes the parameter of proportional gain from a constant value to a scheduled value that varies based on lane characteristics. By modifying this key control parameter according to the vehicle's position relative to the lane center, heading angles, and lane curvature, the system optimizes torque assist levels to maintain effective lane keeping while minimizing unnecessary handwheel movements that cause driver disengagement
2Measurement precision
If the proportional gain value is increased to reduce lateral position error, then the lane keeping precision is improved, but the handwheel activity increases causing driver disengagement
Solution Approach 1:
The patent schedules the proportional gain value based on lateral position error and other lane characteristics, changing the gain parameter dynamically rather than using a fixed high value. This allows the system to achieve precise lateral position control when the vehicle is near the lane center while reducing gain and corresponding handwheel activity when corrections are smaller, thus maintaining both control accuracy and driver engagement
3Reliability
If the torque assist is increased to compensate for lane curvature, then the lane following accuracy is improved, but the lateral acceleration variations become objectionable to passengers
Solution Approach 1:
The patent incorporates lane curvature as one of the factors for scheduling the proportional gain value. By adjusting the gain based on curvature information along with lateral position error and heading angles, the system provides appropriate torque assist to maintain lane following accuracy while avoiding excessive corrections that would create objectionable lateral acceleration variations for passengers
Data Source
AI summary
A steering system providing an assist torque to a handwheel is provided, and includes a proportional gain module and a torque command module. The proportional gain module determines a proportional gain value. The proportional gain value is scheduled as a function of a lateral position error and at least one of the following: a near field heading angle, a far field heading angle, a curvature of the lane, and a lateral position of the vehicle. The torque command module determines the torque assist based on the proportional gain value.