Steer-By-Wire Power Limit Handling to Prevent Post-Steering
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Solution Overview
Problem
Steer-by-wire steering systems experience a post-steering effect during high dynamic maneuvers due to transient response limitations of the road wheel actuator, causing discomfort to the driver.
Innovation Solution
A method to control the steer-by-wire system by detecting power limits of the road wheel actuator and modifying the position request to ensure it remains within these limits, using rate limiting and predefined power characteristics to calculate motor torque requests, thereby preventing post-steering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the position controller acts with maximum motor torque to follow the reference position signal, then the steering response speed is improved, but the post steering effect occurs due to transient response limitations
Solution Approach 1:
The control method performs preliminary detection of power limit situations before the post-steering effect occurs. By monitoring motor torque and power characteristics in advance, the system identifies when the actuator is approaching its power limits and takes preventive action to avoid the transient response that causes post-steering.
Solution Approach 2:
The system continuously monitors the actual power state of the motor and compares it against predefined power characteristics. This feedback mechanism allows the controller to adjust the motor torque request in real-time, reducing torque when power limits are approached to prevent post-steering while maintaining responsive steering when within limits.
2Manufacturing precision
If the motor torque request is increased to improve steering performance, then the steering precision is improved, but the power limit of the electric motor is exceeded
Solution Approach 1:
The control method dynamically adjusts the motor torque request based on real-time power conditions. The system modifies the torque request according to the actual power state and predefined power characteristics, allowing maximum torque when power is available and reducing torque when approaching power limits, thus maintaining steering precision within physical constraints.
Solution Approach 2:
The system changes the motor torque parameter adaptively based on power limit detection. By comparing actual power state against predefined power characteristics and adjusting the torque request accordingly, the system optimizes steering precision while respecting the electric motor's power capabilities.
3Manufacturing precision
If a feedback actuator applies counter torque to the steering wheel, then the steering control accuracy is improved, but the driver feels increased steering resistance
Solution Approach 1:
The control method applies preliminary anti-action by detecting power limit situations before they occur and preemptively adjusting the motor torque request. This prevents the need for aggressive feedback correction that would require high counter-torque on the steering wheel, thereby maintaining control accuracy while minimizing perceived steering resistance.
Data Source
Figure 1~2
AI summary
The invention relates to a method to control a steer- by- wire steering system (1) for a road vehicle, the steer- by- wire steering system (1) comprising steering means (3), an road wheel actuator (5) to actuate road wheels (4) and a control unit (10) that calculates a motor torque request for the road wheel actuator (5) based on an actual or an estimated position and a position request, which is based on the position of the steering means (3), wherein the following steps are provided: • Detection of a road wheel actuator power limit situation; • Modifying the position request, so that it can be followed by the road wheel actuator (3) within power limits; and • Using the modified position request for calculating the motor torque request for the road wheel actuator (5).