Steering Reaction Force Control via Axial Force Deviation
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Solution Overview
Problem
In steer-by-wire type steering systems, the mechanical separation between the steering wheel and steered wheels results in a lack of tactile feedback, making it difficult for drivers to grasp road conditions, and existing solutions do not adequately enhance driver operability and comfort.
Innovation Solution
A vehicle control apparatus that calculates a command value for a motor based on steering conditions, using a first component derived from steering torque and a second component from feedback control to adjust the target rotation angle, reflecting road conditions through axial force deviation, thereby improving the steering reaction force and feel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If mechanical separation between steering wheel and steered wheels is implemented in steer-by-wire system, then steering operation comfort is improved, but tactile feedback and road condition graspability deteriorate
Solution Approach 1:
The control apparatus calculates axial force based on vehicle state variables (lateral acceleration, steering operation current, yaw rate) and feeds this information back to the driver through the steering wheel. The reaction force control unit generates steering reaction force that reflects road conditions, allowing the driver to grasp road information tactilely despite mechanical separation.
Solution Approach 2:
The control apparatus acts as an intermediary between the steered wheels and steering wheel. It receives steering operation input, calculates appropriate axial force based on vehicle state, and generates corresponding reaction force through the reaction motor, mediating the connection between driver input and road feedback.
2Loss of information
If reaction force control based on vehicle state variables is implemented, then road condition reflection in steering reaction force is improved, but device complexity increases
Solution Approach 1:
The control apparatus performs multiple functions using the same computational resources: it controls steering operation force, calculates vehicle state variables, determines axial force based on multiple parameters (lateral acceleration, steering current, yaw rate), and generates reaction force. This multi-functionality avoids additional dedicated hardware for each function.
Solution Approach 2:
The system changes the parameter of axial force dynamically based on vehicle state variables. By adjusting the calculated axial force according to lateral acceleration, steering operation current, and yaw rate, the system reflects varying road conditions without requiring physical hardware changes.
3Ease of operation
If blending ratio is adjusted based on steering condition, then steering feel appropriateness is improved, but calculation complexity increases
Solution Approach 1:
The blending ratio is not fixed but dynamically adjusted based on steering condition (steering angle). When steering angle is large, different blending ratios are applied compared to when steering angle is small. This dynamic adjustment optimizes steering feel for different operating conditions using straightforward conditional logic.
Data Source
AI summary
A control apparatus calculates an axial force deviation, which is a difference between an estimated axial force and an ideal axial force based on a target pinion angle of a pinion shaft in association with a turning operation of steered wheels. The estimated axial force is based on a state variable that reflects vehicle behavior or a road condition. The control apparatus includes a steering angle ratio change control circuit configured to calculate a target pinion angle serving as a basis for calculation of the command value. The steering angle ratio change control circuit calculates a speed increasing ratio from a steering angle ratio set based on a vehicle speed and a base gear ratio of a steering mechanism, and calculates a correction angle for a target steering angle by multiplying the speed increasing ratio and the target steering angle together.