Four-Wheel Steering Trajectory Control for Maneuverability and Stability
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Solution Overview
Problem
Existing autonomous vehicle systems that provide independent steering for front and rear wheels often operate similarly to conventional two-wheel steering vehicles, limiting their maneuverability and stability, especially in bidirectional driving scenarios.
Innovation Solution
The system employs a four-wheel steering approach where both leading and trailing wheels are independently steerable, using a kinematic vehicle model to determine trajectories and a dynamic model for real-time control, allowing for mirrored steering and adaptive steering angle ratios based on speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If four-wheel steering is implemented with independent steering control for all wheels, then maneuverability and stability are improved, but device complexity increases
Solution Approach 1:
The system changes the steering angle parameter relationship between front and rear wheels based on driving conditions. At low speeds, the rear wheels are steered at a larger angle than the front wheels (counter-phased) to achieve tight turning radii. At high speeds, the rear wheels are steered at a smaller angle and in-phase with front wheels to maintain stability. This dynamic parameter adjustment enables both high maneuverability at low speeds and high stability at speeds without requiring complex mechanical steering linkages.
Solution Approach 2:
The steering system transitions from a static configuration to a dynamic one where the steering angle ratio and phase relationship between front and rear wheels are continuously adjusted based on vehicle speed and driving conditions. The control system dynamically modifies the steering commands sent to each wheel, enabling the vehicle to adapt its steering characteristics in real-time. This dynamic control approach achieves multiple steering modes (low-speed maneuvering, high-speed stability, neutral steering) through software control rather than complex mechanical mechanisms.
2Stability of the object's composition
If four-wheel steering is implemented with independent steering control for all wheels, then stability at high speeds is improved, but ease of operation deteriorates
Solution Approach 1:
The steering system operates autonomously based on vehicle speed and driving conditions without requiring manual intervention from the driver. The control system automatically determines the appropriate steering mode (low-speed counter-phased, high-speed in-phase, or neutral steering) and adjusts the rear wheel steering angles accordingly. This self-service capability maintains simplicity for the operator while achieving improved stability through automated four-wheel steering control.
Solution Approach 2:
The system continuously monitors vehicle speed and steering angle as feedback parameters to automatically adjust the rear wheel steering commands. Based on the feedback from speed sensors and steering angle sensors, the control system dynamically modifies the steering angle ratio between front and rear wheels to maintain optimal stability characteristics across different operating conditions. This closed-loop feedback control achieves automatic adaptation without complex mechanical feedback mechanisms.
3Adaptability or versatility
If four-wheel steering is implemented with independent steering control for all wheels, then maneuverability at low speeds is improved, but device complexity increases
Solution Approach 1:
The system achieves enhanced low-speed maneuverability by dynamically changing the steering angle parameter relationship between front and rear wheels. When vehicle speed falls below a threshold, the control system switches to counter-phased steering mode where rear wheels are steered at a larger angle than front wheels, creating a smaller effective turning radius. This parameter change enables tight maneuvering in confined spaces without requiring complex mechanical steering linkages or additional steering components.
Solution Approach 2:
The steering system transitions from a static two-wheel steering configuration to a dynamic four-wheel steering configuration based on vehicle speed. The control system dynamically activates rear wheel steering only when needed for low-speed maneuvering, while maintaining simple two-wheel steering at high speeds. This dynamic switching approach achieves enhanced maneuverability when required while minimizing the operational complexity of the control system during normal high-speed driving.
Data Source
AI summary
Four-wheel steering of a vehicle, e.g., in which leading wheels and trailing wheels are steered independently of each other, can provide improved maneuverability and stability. A first vehicle model may be used to determine trajectories for execution by a vehicle equipped with four-wheel steering. A second vehicle model may be used to control the vehicle relative to the determined trajectories. For instance, the second vehicle model can determine leading wheels steering angles for steering leading wheels of the vehicle and trailing wheels steering angles for steering trailing wheels of the vehicle, independently of the leading wheels.