Four-Wheel Steering Control With Variable Wheel-Angle Ratio
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Solution Overview
Problem
Current four-wheel independent steering systems struggle to allow drivers to feel dynamic steering by instantaneously adjusting the turning radius while following a target yaw rate, as existing methods restrict performance by setting fixed gear ratios that fail to converge yaw rate and side slip angle to zero, limiting the ability to reduce the turning radius effectively.
Innovation Solution
A four-wheel independent steering system and method that includes a front/rear-wheel-angle-ratio calculation unit to calculate and adjust the ratio Kss between front and rear wheel angles, allowing the body slip angle to converge to zero while maintaining target yaw values, using a control unit to perform four-wheel steering control based on this ratio, and adjusting the target understeer gradient by applying a gain G stored in a lookup table to vary the yaw rate and transverse acceleration within vehicle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If fixed gear ratios are set for front and rear wheels to implement four-wheel independent steering control, then the system can provide original dynamic steering performance, but the turning radius cannot be reduced effectively because the yaw rate converges to zero
Solution Approach 1:
The patent applies dynamics by making the gear ratios of front and rear wheels variable rather than fixed. The control unit dynamically adjusts the gear ratios based on real-time vehicle state (steering angle, steering angular velocity, steering angular acceleration) to optimize the turning radius while maintaining dynamic steering performance. This resolves the contradiction by allowing the system to adapt its characteristics during operation.
Solution Approach 2:
The patent changes the parameters of gear ratios from fixed values to variable values that are continuously adjusted based on vehicle operating conditions. By modifying the gear ratio parameters dynamically, the system can reduce the turning radius effectively while maintaining stability, overcoming the limitation of fixed ratio systems where yaw rate converges to zero.
2Stability of the object's composition
If the yaw rate is set to converge to zero to determine gear ratios, then the system achieves stable control, but the turning radius inevitably increases reducing the advantage of four-wheel independent steering
Solution Approach 1:
The system transitions from static stability (fixed gear ratios with yaw rate converging to zero) to dynamic stability (variable gear ratios that maintain optimal performance during transient maneuvers). The control unit continuously adjusts gear ratios based on steering angular velocity and acceleration, allowing the system to maintain stability while achieving reduced turning radius during actual steering operations.
Solution Approach 2:
The control unit performs preliminary adjustment of gear ratios based on predicted vehicle state (using steering angle, angular velocity, and angular acceleration) before the actual maneuver completes. This anticipatory adjustment allows the system to prepare optimal gear ratios in advance, reducing turning radius while maintaining control stability throughout the maneuver.
3Device complexity
If fixed target values are used for gear ratios to implement dynamic steering performance, then the system structure is simple, but the performance of four-wheel independent steering control is restricted
Solution Approach 1:
The patent implements dynamics by making the gear ratios variable and adaptive rather than fixed. The control unit adjusts gear ratios in real-time based on vehicle state parameters, significantly improving the adaptability and versatility of the steering control system while maintaining a relatively simple overall structure through algorithmic control rather than complex mechanical adjustments.
Data Source
AI summary
A four-wheel independent steering system and a method of controlling the four-wheel independent steering system. The four-wheel independent steering system includes a front/rear-wheel-angle-ratio calculation unit to calculate a ratio Kss between front and rear wheel angles that allows a body slip angle to converge to ‘0’ and allows a yaw angle and a yaw rate to maintain target values, and a control unit to perform four-wheel steering control based on the ratio Kss between the front and rear wheel angles.