Four-Wheel Steering System with Dynamic Rear Wheel Control
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Solution Overview
Problem
Conventional four-wheel steering systems do not adequately enhance maneuverability with a small turning radius, especially at low speeds, limiting the driver's ability to make sharp turns in confined spaces.
Innovation Solution
A four-wheel steering system that steers rear wheels in the opposite direction of front wheels at low speeds, with a sharply increased rate of steered angle relative to the steering angle when the absolute value of the steering angle exceeds a threshold, allowing for a significantly smaller turning radius.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the rear wheels are steered in the opposite direction to the front wheels at low speeds with a proportional relationship, then the vehicle can turn with a smaller turning radius, but the driver cannot always turn the vehicle as desired in confined spaces or narrow roads
Solution Approach 1:
The patent applies dynamics by making the steering system adaptable and changeable based on operating conditions. The rear-wheel steering system switches between two different steering characteristics: at low steering angles, it provides proportional steering for stability, while at high steering angles, it provides sharply increased steered angle for enhanced maneuverability in confined spaces. This dynamic switching allows the system to adapt to different driving situations and achieve both stable normal operation and superior confined-space performance.
Solution Approach 2:
The patent applies parameter changes by modifying the steering angle relationship between front and rear wheels based on the magnitude of the steering angle. When the absolute value of the steering angle is below the threshold, the steered angle increases proportionally. When the absolute value exceeds the threshold, the rate of increase in steered angle is sharply increased. This parameter-based control strategy enables the system to provide different steering characteristics appropriate for different maneuvering requirements.
2Productivity
If the steering angle of rear wheels increases proportionally with steering angle, then the vehicle can turn with a smaller radius, but the driver may not be able to turn the vehicle as desired depending on driving situations
Solution Approach 1:
The system dynamically adjusts the steering characteristics based on the steering angle magnitude. At low steering angles, proportional steering provides efficient turning. At high steering angles, the sharply increased rate of steered angle provides enhanced control capability for confined spaces. This dynamic adaptation resolves the contradiction between turning efficiency and driver control capability.
Solution Approach 2:
The system changes the steering parameter relationship based on the steering angle threshold. Below the threshold, linear proportionality maintains efficient turning. Above the threshold, the sharply increased rate of change enables precise control in confined spaces. This parameter-based approach optimizes both turning efficiency and driver control.
Data Source
AI summary
The four-wheel steering system includes a rear-wheel steering system that steers rear wheels of the vehicle in accordance with a steering angle of a steering wheel. When the vehicle speed is lower than a vehicle speed threshold, the rear-wheel steering system steers the rear wheels in an opposite direction to that in which the front wheels are steered. When the vehicle speed is lower than the vehicle speed threshold, the rear-wheel steering system sharply increases the rate of increase in target steered angle of the rear wheels with respect to an increase in steering angle when an absolute value of the steering angle is equal to or larger than an absolute value of an angle threshold. The front-wheel steering system has a motor that is a source of a steering assist force and a first ECU that controls the motor in accordance with the steering state.