Steer-by-Wire Torque Limiting via Adaptive Reference Controller
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Solution Overview
Problem
Existing steer-by-wire steering systems inadequately account for the driving situation, leading to late recognition of incorrect control commands and reduced safety and reliability due to a universally applied range signal applicable across various driving conditions.
Innovation Solution
A control method incorporating a signal limiting device with a reference controller that adjusts the permissible torque range based on the actual and desired steering angles, momentary angular velocity, and driving speed, ensuring safe and adaptive torque control to improve error detection and controllability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a universally applicable range signal is used for all driving situations, then the system can be simplified and easier to operate, but error detection is delayed and safety is reduced
Solution Approach 1:
The patent applies dynamics by making the torque range adaptive rather than static. The signal limiting device dynamically adjusts the permissible torque range based on actual driving conditions (vehicle speed, steering angle, angular velocity) instead of using a fixed universal range. This resolves the contradiction by enabling the system to be both simple to operate (automatic adaptation) and safe (context-appropriate limits).
Solution Approach 2:
The patent changes the parameter of torque range from a constant value to a variable that depends on driving conditions. By modifying the torque range parameter based on vehicle speed, steering angle, and angular velocity, the system achieves both ease of operation (automatic parameter adjustment) and improved reliability (situation-appropriate safety margins).
2Adaptability or versatility
If a large generalizable torque range is selected to cover all driving situations, then the system is more versatile, but incorrect control commands are recognized later reducing safety
Solution Approach 1:
The system transitions from a static torque range to a dynamic one that adapts to current driving conditions. The signal limiting device continuously adjusts the torque range based on real-time inputs (vehicle speed, steering angle, angular velocity), enabling the system to be versatile across situations while maintaining tight, safety-critical limits for each specific condition.
Solution Approach 2:
The patent applies local quality by tailoring the torque range to specific local driving conditions rather than using a single global range. Each driving situation (cornering, straight-ahead, high-speed, low-speed) receives a customized torque range appropriate to its requirements, achieving both versatility and timely error detection.
3Reliability
If the torque range is tightly limited for safety, then error detection is improved, but the system becomes less adaptable to different driving situations
Solution Approach 1:
The dynamic adaptation of torque range based on driving conditions resolves this contradiction. The system maintains tight safety-critical limits for each specific situation while automatically adapting to different driving contexts, achieving both error detection improvement and versatility without compromise.
Data Source
AI summary
A method for controlling a steer-by-wire steering system for a motor vehicle may involve determining a torque request signal with a position controller of an activation unit based at least on a desired steering angle and an actual steering angle, limiting the torque request signal in a signal limiting device of the activation unit such that the torque requested by the limited torque request signal is limited to a permissible torque range, and transmitting the limited torque request signal to an electronically controllable steering actuator. The signal limiting device may determine a reference torque signal by way of a reference controller based at least on the desired steering angle and the actual steering angle. The signal limiting device may define the permissible torque range by way of a selectable maximum deviation from the reference torque signal.