Steer-by-Wire Mode Switching with Coordinated SFA and RWA Control
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Solution Overview
Problem
In steer-by-wire systems, the difference in movement between the steer wheel feedback actuator (SFA) and the road wheel actuator (RWA) during mode switching from autonomous driving to normal driving mode leads to rapid vehicle behavior.
Innovation Solution
An electronic steering device with a first ECU controlling the SFA to change the steering wheel angle based on a steering control command and obtaining a target rack position, and a second ECU controlling the RWA to change the rack position based on the target rack position, ensuring consistent steering control across modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the SFA inverts the current position and moves when autonomous driving mode is stopped, then the steering angle can be adjusted, but there is a difference in the movement of the SFA and the RWA, resulting in rapid vehicle behavior
Solution Approach 1:
The patent applies preliminary action by maintaining the SFA at its inverted position during autonomous driving mode and preventing it from moving back to the original position until mode switching is complete. This preliminary positioning prevents the harmful movement difference between SFA and RWA that would cause rapid vehicle behavior, while still allowing steering angle adjustment through controlled movement of both actuators together.
2Measurement precision
If the RWA moves following the steering angle of the SFA in normal mode, then the steering response is accurate, but the SFA and RWA movement directions are opposite in autonomous mode, causing movement difference during mode switching
Solution Approach 1:
The patent applies dynamics by implementing different control strategies for different operating modes. In normal mode, the SFA and RWA move in opposite directions for accurate steering response. In autonomous driving mode, both actuators move in the same direction to maintain coordination stability. The system dynamically adjusts the control approach based on the operating mode, resolving the contradiction between steering accuracy and actuator coordination.
Data Source
AI summary
The electronic steering device and the operating method thereof according to the present disclosure change the traveling direction of a vehicle using the same steering control method as that is a case where the vehicle is not operated in the autonomous driving mode even when the vehicle is operated in the autonomous driving mode, and thus vehicle safety can be improved since there is no movement difference between the steer wheel feedback actuator (SFA) and the road wheel actuator (RWA) during the mode switching process.