Steering Angle Limiting System for Autonomous Vehicles
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Solution Overview
Problem
Current semi-autonomous and autonomous vehicle systems experience jerking or noisiness in the steering wheel due to noisy and discontinuous localization inputs, which affect the calculation of the commanded steering angle.
Innovation Solution
A limiting system that constrains the commanded steering angle by determining an ideal rate of change based on trajectory planning inputs, including velocity, acceleration, and curvature arrays, and adjusts this rate using a calibration factor and look-up tables to match the capabilities of the electric power steering system, thereby mitigating the impact of noisy localization inputs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the model predictive controller uses noisy localization inputs to calculate the commanded steering angle, then the steering angle can be determined, but jerking and noisiness occur in the steering wheel
Solution Approach 1:
The limiting system performs preliminary action by calculating the maximum rate of change of steering angle before the steering command is executed. This pre-calculation uses trajectory planning inputs (curvature, velocity, acceleration) to determine a safe rate limit that prevents jerking while maintaining responsiveness to localization changes.
Solution Approach 2:
The maximum rate of change calculation acts as an intermediary between the noisy localization inputs and the steering system. Instead of directly applying raw localization data to steering commands, the system introduces this intermediate layer that filters and smooths the control signal while still achieving trajectory tracking.
2Productivity
If the commanded steering angle changes rapidly to track trajectory, then the trajectory tracking performance improves, but the EPS system cannot handle the rate of change
Solution Approach 1:
The system dynamically adjusts the rate of change parameter based on trajectory planning inputs. By calculating the maximum allowable rate of change from curvature, velocity, and acceleration data, the system adapts the steering command parameters to match both trajectory requirements and EPS system capabilities.
Solution Approach 2:
The limiting system implements dynamics by making the steering angle rate limit adaptive rather than fixed. The maximum rate of change varies based on current trajectory conditions, allowing faster response when appropriate and smoother transitions when trajectory curvature or velocity requires it.
Data Source
AI summary
A limiting system for constraining a commanded steering angle for a vehicle including an electric power steering (EPS) 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 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.