Steer-by-Wire Transmission Ratio Adjustment for Position Error Minimization
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Solution Overview
Problem
Steer-by-wire steering systems face challenges in responding appropriately when the driver steers beyond the software full deflection, leading to position errors between the steering control and the final control element, which can result in unresponsive steering behavior during reversals.
Innovation Solution
The system introduces positive and negative delta values for the transmission ratio, allowing it to adjust and minimize position errors when the steering control is over-rotated, ensuring the driver experiences a customary steering feel by accepting or compensating remaining errors, with delta values determined to be imperceptible or symmetrically corrected.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a software end stop is implemented on the steering control, then the steering system can prevent over-rotation and maintain position accuracy, but the driver may experience unresponsive steering behavior when steering beyond the software end stop
Solution Approach 1:
The transmission ratio is made dynamically adjustable based on the steering state. When over-rotation is detected, the control unit changes the transmission ratio from a first value to a second value, allowing the system to adapt its response characteristics to different operational conditions and resolve the conflict between position accuracy and steering responsiveness.
Solution Approach 2:
The control unit changes the transmission ratio parameter from a first value to a second value when over-rotation is detected. This parameter change allows the system to maintain position accuracy while improving steering responsiveness by adjusting the relationship between steering control rotation and final control element position.
2Ease of operation
If the transmission ratio is reduced to allow steering wheel revolutions, then the driver can steer beyond the software end stop, but the neutral position of the steering wheel no longer corresponds to the neutral position of the steering system
Solution Approach 1:
The transmission ratio is dynamically adjusted based on the detected steering state. When over-rotation is detected, the system switches to a different transmission ratio that allows the steering wheel to complete revolutions while maintaining an acceptable correspondence between the neutral position of the steering wheel and the neutral position of the steering system.
Solution Approach 2:
The control unit detects over-rotation in advance and proactively changes the transmission ratio before the steering system reaches a state of poor position correspondence. This preliminary action prevents the mismatch between steering wheel neutral position and steering system neutral position from occurring in the first place.
3Reliability
If the actuator produces sufficient counter-torque to prevent over-rotation, then the steering control remains within the software end stop, but the system becomes less adaptable when the actuator fails to produce adequate counter-torque
Solution Approach 1:
The control unit continuously monitors the rotation angle of the steering control and detects when over-rotation occurs. Based on this feedback, the system automatically adjusts the transmission ratio to maintain stable and predictable steering behavior, ensuring the steering response remains acceptable even when the actuator cannot produce sufficient counter-torque.
Solution Approach 2:
The transmission ratio is made dynamically adjustable based on the steering state and actuator performance. When over-rotation is detected, the system switches to a different transmission ratio that maintains stability and adaptability, allowing the steering system to respond appropriately regardless of actuator counter-torque capabilities.
Data Source
AI summary
A steer-by-wire steering system having a steering control, a rotation angle sensor for detecting a position of the steering control, an actuator for producing a counter-torque on the steering control, a steering actuator for adjusting a steering angle depending on the data of the rotation angle sensor on a final control element, wherein the final control element has a mechanical end stop and the actuator implements a software end stop on the steering control, wherein a transmission ratio is set between the rotation angle on the steering control and the steering angle, wherein a positive delta value and a negative delta value are defined for the set transmission ratio, wherein the steer-by-wire steering system is embodied so the adjusted transmission ratio is selected so that a remaining position error of the steering control is minimized.