Steer-by-Wire Angle Limiter for Vehicle Stability
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Solution Overview
Problem
A steer-by-wire system with independent right and left steering mechanisms is vulnerable to instability if the higher-level control device malfunctions, supplying inappropriate target steered angles to the lower-level control device, leading to potential vehicle instability during steering.
Innovation Solution
The vehicle steering system incorporates a lower-level control device with an allowable upper limit setter and a target steered angle limiter to restrict the absolute difference between target steered angles for the right and left wheels, ensuring stability by limiting the target angles within a predetermined allowable upper limit, even if the higher-level control device fails to provide accurate inputs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If a higher-level control device is used to calculate target steered angles for automatic driving, then advanced drive assisting functions are enabled, but vehicle instability may occur if the control device malfunctions and supplies inappropriate target steered angles
Solution Approach 1:
The lower-level control device preliminarily checks the appropriateness of target steered angles before executing steering control by comparing the absolute difference between right and left target steered angles against a predetermined threshold. This preliminary validation prevents malfunction-induced instability while preserving automatic driving capabilities.
Solution Approach 2:
The system implements feedback control by continuously monitoring the difference between right and left target steered angles and comparing it against a threshold value. When the difference exceeds the threshold, the system identifies the input as inappropriate and prevents execution, thereby maintaining vehicle stability through closed-loop validation.
2Adaptability or versatility
If right and left steered wheels are controlled by individual steering actuators without a steering gear device, then layout flexibility of the engine room is increased, but the system becomes vulnerable to instability from inappropriate target angle inputs
Solution Approach 1:
Before the independent steering actuators execute target steered angles, the lower-level control device performs preliminary validation by checking whether the absolute difference between right and left target angles exceeds a predetermined threshold. This prevents instability caused by inappropriate inputs while maintaining the layout flexibility benefits of the steer-by-wire architecture.
Solution Approach 2:
The lower-level control device acts as an intermediary between the higher-level control device and the independent steering actuators. It validates target steered angles by comparing the absolute difference against a threshold, serving as a protective mediator that prevents malfunction propagation to the steering actuators while preserving system flexibility.
Data Source
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AI summary
A vehicle steering system includes a higher-level ECU and a lower-level ECU. The lower-level ECU includes a steered angle limit setter (43), and steered angle limiters. The steered angle limit setter (43) sets an allowable upper limit to a target inner and outer wheel steered angle difference responsive to the absolute value of a target outer steered angle. The steered angle limit setter (43) calculates a limit to the absolute value of a target inner steered angle. The steered angle limit setter (43) subsequently sets this limit for one of the steered angle limiters that is fed the target inner steered angle in the present calculation cycle. The limiter, which is fed the target inner steered angle, limits the absolute value of the target inner steered angle so that the absolute value of the target inner steered angle is equal to or below the limit, and outputs the resulting value.