Steering Actuator Control Circuit for Lane Keeping
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Solution Overview
Problem
Existing vehicle steering systems face issues with large changes in steered wheel angles due to insufficient user steering torque, leading to unstable lane departure prevention assist systems, as the integral term in PID control accumulates steady-state deviations.
Innovation Solution
An actuator control device that calculates two assist components, one based on user operation and the other on environmental factors, with a limitation process to prevent the integral term from increasing excessively, thereby reducing the likelihood of large changes in steered wheel angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PID control with integral term is used to eliminate steady-state deviation, then lane keeping accuracy is improved, but large changes in steered wheel angle occur when user steering torque is insufficient
Solution Approach 1:
The control circuit changes the parameter of the control term based on the detected steering torque. When steering torque is below the threshold, the control term is limited to prevent excessive accumulation of the integral term, thereby preventing large changes in steered wheel angle while still maintaining lane keeping accuracy through feedback control.
Solution Approach 2:
The control system dynamically adjusts the control term based on real-time steering torque detection. The control term is made variable rather than fixed, allowing the system to adapt its integral term accumulation behavior according to the driver's steering input, thus preventing instability when torque is low while maintaining accuracy when torque is sufficient.
2Measurement precision
If feedback control continuously accumulates integral term to eliminate deviation, then lane keeping precision is improved, but control stability deteriorates when steering torque is low
Solution Approach 1:
The control circuit dynamically changes the parameter of the control term based on steering torque levels. When torque drops below the threshold, the control term is constrained to prevent excessive integral term accumulation, thereby maintaining control stability while preserving lane keeping precision through continuous feedback control.
Solution Approach 2:
The system takes preliminary action by detecting steering torque before excessive accumulation occurs. When low torque is detected, the control term is proactively limited to prevent the integral term from accumulating to levels that would cause large steered wheel angle changes, thus preventing control instability before it occurs.
3Ease of operation
If assist component is calculated based on operational state to provide steering assistance, then ease of operation is improved, but large changes in steered angle occur when user torque decreases
Solution Approach 1:
The control circuit adjusts the control term parameter based on steering torque detection. When user torque decreases below the threshold, the control term is limited to prevent the assist component from causing large steered angle changes, thereby maintaining steering assistance functionality while ensuring steered angle stability.
Data Source
AI summary
The actuator control device includes an assist control circuit for calculating a first assist component and an automatic steering control circuit for calculating a second assist component. The automatic steering control circuit is allowed to calculate the second assist component while a steering torque is less than a first threshold value. The automatic steering control circuit calculates the second assist component by performing PID control that uses an integral term obtained on the basis of an angle deviation. When the steering torque is less than the first threshold value but not less than a second threshold value, the automatic steering control circuit limits the integral term in such a manner that it is harder for the integral term to increase while the steering torque is not less than the second threshold value than while the steering torque is less than the second threshold value.