Four-Wheel Steering Trajectory Tracking with Speed-Dependent Control
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Solution Overview
Problem
Conventional autonomous vehicle systems with four-wheel steering often operate similarly to two-wheel steering systems, limiting maneuverability and stability, especially at lower and higher speeds, due to fixed steering configurations.
Innovation Solution
Implementing a system that independently controls both leading and trailing wheels using a kinematic vehicle model for trajectory planning and a dynamic model for real-time control, allowing for adaptive steering angles based on speed and tracking errors, while also considering maximum steering constraints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional two-wheel steering is used, then the system is simpler and well-known, but maneuverability and stability are limited
Solution Approach 1:
The patent implements dynamic four-wheel steering where the rear wheels actively steer in coordination with the front wheels. The steering angle of the rear wheels is modulated based on vehicle speed and desired trajectory, transitioning between parallel steering (at low speeds for tight turns) and counter-steering (at high speeds for stability). This dynamic adaptation resolves the contradiction by providing enhanced maneuverability while maintaining system simplicity through a unified control framework.
Solution Approach 2:
The patent changes the steering parameter configuration by allowing independent control of front and rear wheel steering angles. The rear wheel steering angle is dynamically adjusted as a function of vehicle speed, trajectory curvature, and control gains, enabling the vehicle to achieve both tight turning radii at low speeds and stable high-speed operation, thereby improving maneuverability without complicating the manufacturing process.
2Adaptability or versatility
If four-wheel steering is used, then maneuverability and stability are improved, but the control system becomes more complex
Solution Approach 1:
The patent employs a universal control framework that handles both trajectory generation and tracking using the same four-wheel steering model. The kinematic vehicle model serves multiple functions: it generates feasible trajectories considering steering constraints and dynamically tracks them by computing required steering angles. This multi-functionality reduces control system complexity while maintaining enhanced maneuverability through coordinated four-wheel steering.
Solution Approach 2:
The patent implements feedback control where the actual vehicle state (position, orientation, velocity) is continuously compared with the desired trajectory, and steering commands are adjusted accordingly. The rear wheel steering angle is modulated based on tracking errors and vehicle speed feedback, enabling accurate trajectory following while simplifying the control architecture through a unified feedback loop that manages both front and rear steering independently yet cooperatively.
3Device complexity
If rear wheels are kept fixed, then the system operates like conventional vehicles, but maneuverability at lower speeds is reduced
Solution Approach 1:
The patent implements speed-dependent dynamic steering where the rear wheels remain fixed (zero steering angle) at high speeds for stability, but actively steer at low speeds to enable tight turning radii. The transition is smooth and continuous, with the rear wheel steering angle modulated based on vehicle speed threshold and trajectory requirements. This dynamic behavior resolves the contradiction by providing enhanced low-speed maneuverability while maintaining high-speed stability without requiring a fundamentally complex steering mechanism.
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.