Steer-by-Wire Offset Ramping for Accurate Pinion Alignment
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Solution Overview
Problem
In steer-by-wire (SBW) systems, the steering angle and pinion angle differ due to software variable gear ratio (VGR), leading to inaccuracies in autonomous driving commands, making it difficult to perform accurate cooperative control.
Innovation Solution
An electronic steering system that calculates steering and command angle offsets and adjusts a ramp-down gain to match the cooperative control command angle with the pinion angle, switching to steering angle position control mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If software variable gear ratio (VGR) is used to adjust steering characteristics, then steering performance and adaptability are improved, but position control accuracy between steering angle and pinion angle deteriorates
Solution Approach 1:
The system pre-calculates and stores the relationship between steering angles and pinion angles across different VGR settings in a lookup table before operation. When VGR changes, the controller retrieves the corresponding offset values from the pre-stored table, eliminating the need for real-time calculation and ensuring accurate position control despite VGR variations.
Solution Approach 2:
The system continuously monitors the actual steering angle and pinion angle positions, calculates the deviation from the expected relationship based on current VGR settings, and applies real-time compensation through offset values. This closed-loop feedback mechanism maintains position control accuracy even as VGR dynamically adjusts steering characteristics.
2Adaptability or versatility
If VGR dynamically adjusts pinion angle command based on vehicle speed and mode, then cooperative control flexibility is improved, but control stability and consistency deteriorate
Solution Approach 1:
Offset values for different VGR settings are pre-calculated and stored in a lookup table, allowing the system to quickly switch between different control characteristics without real-time computation. This pre-preparation ensures consistent and stable transitions between different driving modes and speed conditions.
Solution Approach 2:
The system dynamically selects appropriate offset values from the lookup table based on current vehicle speed and driving mode, allowing the control characteristics to adapt to changing operating conditions. This dynamic selection maintains control consistency within each mode while providing flexibility across different modes.
Data Source
AI summary
An electronic steering system for a vehicle includes an input module configured to receive a steering command angle from a cooperative control unit, a steering angle sensor configured to detect a steering angle of a steering wheel of the vehicle, a memory, and a processor operatively coupled to the input module, the steering angle sensor, and the memory. The processor is configured to, when a cooperative control command angle is input from the input module, calculate a steering angle offset and a command angle offset, and then perform steering angle position control with respect to the cooperative control command angle by sequentially ramping down the steering angle offset and the command angle offset to output a pinion angle of a wheel of the vehicle.