Steer-by-Wire Controller Corrects Operation Amount During Gear Ratio Shifts
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Solution Overview
Problem
In steer-by-wire steering systems, it is challenging to maintain an appropriate operation reaction force when the steering gear ratio abruptly changes, making it difficult to accurately convert the steering amount of the wheel to the operation amount of the operation member, especially when the actual steering does not follow the operation of the member or when the steering amount is prevented from abrupt changes.
Innovation Solution
A controller is implemented to execute a steering control process that determines the steering gear ratio and controls the steering device to maintain a set steering gear ratio, and a reaction force control process that adjusts the operation reaction force based on the difference between the actual and converted operation amounts, including a correction process to gradually decrease the converted steering amount offset value when the gear ratio changes abruptly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the steering gear ratio is changed to optimize steering performance, then the steering responsiveness is improved, but the operation reaction force becomes inappropriate due to abrupt changes in the converted operation amount
Solution Approach 1:
The system performs preliminary detection of gear ratio changes and proactively manages the converted operation amount before the abrupt change affects the operation reaction force. By detecting the gear ratio change event and pre-adjusting the converted operation amount, the system prevents the harmful effect of abrupt force changes while maintaining steering responsiveness.
Solution Approach 2:
The converted operation amount acts as an intermediary variable between the actual steering amount and the operation reaction force. By introducing this intermediate conversion process with explicit handling of gear ratio changes, the system decouples the direct relationship between steering input and reaction force, allowing independent optimization of responsiveness and force stability.
2Ease of operation
If the converted operation amount is calculated using the inverse of the steering gear ratio, then the operation reaction force can be controlled, but measurement precision deteriorates when the steering gear ratio changes abruptly
Solution Approach 1:
The system replaces direct mechanical coupling between steering input and reaction force control with an electronic calculation-based conversion process. By using electronic computation of the converted operation amount with explicit gear ratio change detection, the system achieves precise control while avoiding the measurement errors that would occur with direct mechanical linkage during abrupt gear ratio changes.
Solution Approach 2:
The system implements feedback by continuously monitoring the gear ratio and using this information to adjust the converted operation amount calculation. When a gear ratio change is detected, the feedback mechanism triggers a correction process that maintains measurement precision while preserving the ability to control the operation reaction force.
3Stability of the object's composition
If the steering amount is prevented from abrupt changes to ensure stability, then the steering smoothness is improved, but the converted operation amount cannot be accurately grasped during gear ratio transitions
Solution Approach 1:
The system performs preliminary detection of gear ratio changes and proactively manages the converted operation amount before information loss occurs. By detecting the gear ratio transition event in advance and pre-calculating the appropriate converted operation amount, the system maintains both steering smoothness and accurate information about the operation amount during transitions.
Solution Approach 2:
The system dynamically adjusts the converted operation amount based on the detected gear ratio and its rate of change. This dynamic adjustment allows the system to maintain accurate operation amount information during transitions while preventing abrupt changes in steering amount, achieving both smoothness and information accuracy through adaptive control.
Data Source
AI summary
A steer-by-wire steering system includes a controller configured to execute a steering control process and a determining process of determining a converted operation amount by converting an actual wheel steering amount to an operation amount of an operation member based on an inverse of a steering gear ratio. In the determining process, when the steering gear ratio abruptly changes, the controller converts a gap of the converted operation amount generated at a time point of occurrence of the abrupt change to a gap of the wheel steering amount to grasp a converted steering amount offset value. While gradually decreasing the converted steering amount offset value, the controller thereafter re-converts the converted steering amount offset value to the gap of the converted operation amount based on the inverse of the steering gear ratio to determine a converted operation amount correction value and corrects the converted operation amount based on the value.