Steer-by-Wire Reaction Torque Control During Speed Signal Abnormality
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Solution Overview
Problem
Steer-by-wire systems may output unintended steering reaction torque when the vehicle speed signal becomes abnormal, leading to driver discomfort.
Innovation Solution
A steering device and method that includes a reaction force actuator and an electronic control unit to calculate a target reaction torque, using abnormal-time distribution ratios when the vehicle speed signal is abnormal, and employing signal holding and gradual change processes to stabilize the torque calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the vehicle speed signal is used for calculating steering reaction torque, then the steering responsiveness is improved, but when the vehicle speed signal becomes abnormal, unintended steering reaction torque is output causing driver discomfort
Solution Approach 1:
The system performs preliminary detection of vehicle speed signal abnormalities and switches to a safe mode calculation method before unintended torque can be output. The ECU continuously monitors the vehicle speed signal and prepares alternative calculation approaches (using only current axial force or proportional distribution) in advance, so when abnormality is detected, the system can immediately prevent harmful torque fluctuations without waiting for the abnormality to manifest.
Solution Approach 2:
The patent introduces an intermediary mechanism in the form of multiple calculation methods with different distribution ratios. Instead of directly using the potentially abnormal vehicle speed signal, the system employs intermediate calculation approaches: normal-time distribution ratio (when signal is normal), abnormal-time distribution ratio (when signal is abnormal), or current axial force only method. This intermediary layer filters out the harmful effects of abnormal signals while preserving the beneficial responsiveness.
2Stability of the object's composition
If the vehicle speed signal is held during abnormality to maintain calculation continuity, then the steering stability is improved, but the responsiveness to actual vehicle speed changes is reduced
Solution Approach 1:
The system dynamically adjusts the calculation method based on the operational state. During normal operation, the full vehicle speed signal is used for maximum responsiveness. When abnormality is detected, the system transitions to holding the last normal value or using alternative calculation methods. This dynamic switching allows the system to optimize between responsiveness and stability according to real-time conditions.
Data Source
AI summary
In a reaction torque calculation process, an electronic control unit included in a steer-by-wire steering device is configured to calculate a distributed axial force obtained by distributing an angle axial force and an electric current axial force based on a final distribution ratio. The reaction torque calculation process includes at least one of a first abnormal-time process and a second abnormal-time process. The first abnormal-time process is executed to hold, for calculation of the angle axial force, a vehicle speed signal value immediately before the vehicle speed signal becomes abnormal. The second abnormal-time process is executed to hold, for calculation of a normal-time distribution ratio, a vehicle speed signal value immediately before the vehicle speed signal becomes abnormal or hold a value of the normal-time distribution ratio immediately before the vehicle speed signal becomes abnormal, and then gradually change the final distribution ratio to an abnormal-time distribution ratio.