Active Steering Overlay Rate Limiting for Driver Disturbance
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Solution Overview
Problem
Limited by-wire active front steering systems face stability issues during non-linear maneuvers, particularly on low friction surfaces, due to inadequate control over steering angle and feedback to the driver.
Innovation Solution
A method and apparatus that measure input braking force and steering angle rate to calculate a maximum steering angle overlay rate limit, communicated to the steering actuator, which minimizes undesirable feedback to the driver by limiting the steering angle overlay rate during stability maneuvers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the steering actuator applies a corrective steering angle overlay during non-linear maneuvers, then vehicle stability is improved, but excessive torque feedback is transmitted to the driver through the steering column
Solution Approach 1:
The system dynamically adjusts the steering angle overlay rate limit based on real-time driving conditions, including vehicle speed, steering angle rate, and braking force. This dynamic adaptation allows the system to apply corrective steering inputs effectively while minimizing driver disturbance across varying operational scenarios
Solution Approach 2:
The system implements a feedback mechanism that monitors steering angle rate and braking force to calculate an appropriate maximum overlay rate limit. This feedback loop ensures that corrective steering actions are applied in a controlled manner that maintains stability without creating excessive feedback to the driver
2Speed
If the steering system allows high steering rates during stability maneuvers, then vehicle responsiveness is improved, but excessive torque feedback disturbs the driver
Solution Approach 1:
The system changes the parameter of maximum overlay rate limit based on input steering angle rate and braking force. By adjusting this parameter dynamically, the system permits high steering rates when necessary for stability while preventing excessive torque feedback that would disturb the driver
3Stability of the object's composition
If the steering actuator applies corrective overlay during non-linear maneuvers, then vehicle stability is enhanced, but driver impedance increases causing excessive feedback
Solution Approach 1:
The system performs preliminary calculation of the maximum overlay rate limit based on anticipated driving conditions, including expected driver impedance levels. This preliminary action allows the system to prepare appropriate corrective steering inputs that will be effective without causing excessive feedback when driver impedance is high
Data Source
AI summary
A method is provided for limiting a steering angle overlay applied by a steering actuator in a limited by-wire active front steering (AFS) system. The method includes determining a maximum rate limit for the steering angle overlay in order to minimize an undesired disturbance to the driver in the form of a torque and/or angle feedback while maximizing the rate of steering overlay allowed for a given set of vehicle operating conditions. The maximum rate limit is determined by a function of the input steering rate and braking level. A limited AFS system includes both steering and braking input devices, a steering actuator, and a controller having an algorithm. The controller uses the algorithm to calculate the maximum overlay rate limit and limits the steering actuator to the maximum overlay rate limit.