Four-Wheel Steering Control for Rear-Wheel Resonance Suppression
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Solution Overview
Problem
Four-wheel steering vehicles experience resonance and excessive lateral acceleration during quick steering, particularly at low speeds, due to the use of variable gear ratio steering devices or steer-by-wire systems, which impair ride comfort and steering stability.
Innovation Solution
A control device that restricts the turning of rear wheels when the absolute values of steered angle velocities exceed predetermined thresholds, fixing the steered angle or reducing the steered amount of rear wheels, and adjusts these thresholds based on vehicle speed to prevent resonance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If variable gear ratio steering devices or steer-by-wire systems are used to enable quick steering, then steering responsiveness is improved, but resonance and excessive lateral acceleration occur during quick steering at low speeds
Solution Approach 1:
The control device determines in advance whether quick steering is occurring by monitoring steered angle velocity thresholds before resonance can occur. When quick steering is detected, the system proactively restricts rear wheel steering to prevent resonance, rather than reacting after resonance has begun.
Solution Approach 2:
The control device continuously monitors the steered angle velocity of both front and rear wheels, comparing it against predetermined thresholds. This feedback mechanism allows the system to detect quick steering conditions and adjust rear wheel steering restrictions accordingly, maintaining stability while preserving responsiveness.
2Length of moving object
If rear wheels are turned in opposite phase to front wheels during low-speed travel, then turning radius is reduced, but resonance occurs during quick steering
Solution Approach 1:
The control device dynamically adjusts rear wheel steering based on detected steering conditions. During normal low-speed turning, rear wheels turn in opposite phase to reduce turning radius. During quick steering detection, the system dynamically restricts rear wheel steering to prevent resonance, adapting the steering behavior to current operating conditions.
Solution Approach 2:
The control device changes the steering control parameters based on detected conditions. When quick steering is detected through threshold comparison of steered angle velocity, the system modifies the rear wheel steering parameter from normal opposite-phase turning to restricted or zero steering, preventing resonance while maintaining the ability to turn when needed.
3Reliability
If steering control is restricted to prevent resonance, then steering stability is improved, but steering responsiveness may be degraded
Solution Approach 1:
The control device applies partial restriction on rear wheel steering rather than complete restriction. By using threshold-based detection and applying restrictions only when necessary (when both front and rear wheel steered angle velocities exceed thresholds), the system maintains steering responsiveness in normal conditions while providing stability control during quick steering scenarios.
Data Source
AI summary
A control device for a four-wheel steering vehicle including a steering wheel, a front wheel steering device, and a rear wheel steering device, and operating the front wheel steering device and the rear wheel steering device, wherein first steering and second steering are continuously performed, and when the rear wheels are steered in the direction opposite to the steering direction of the front wheels, the absolute value of the steered angle velocity of the front wheels to be steered is higher than the first threshold, and the absolute value of the steered angle velocity of the front wheels to be steered in response to the second steering is higher than the second threshold, the steering of the rear wheels corresponding to the second steering is restricted.