Power Steering Gear Ratio Control for Stable Steering Limits
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Solution Overview
Problem
Existing power steering systems experience disturbances in driver experience due to varying upper limit steering wheel angles with vehicle speed, leading to torque-steer and return effects, and difficulty in finding suitable counter-steering angles during loss of grip.
Innovation Solution
A method for determining a gear ratio in power steering systems that adjusts based on vehicle speed and steering wheel angle, ensuring a consistent upper limit steering wheel angle across speeds, using formulas to define gear ratio as a function of these variables.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the gear ratio is adjusted via software as a function of vehicle speed, then vehicle maneuverability at low speed and controllability at high speed are improved, but the upper limit steering wheel angle varies with speed causing torque-steer and return effects
Solution Approach 1:
The patent applies parameter changes by modifying the gear ratio as a function of both vehicle speed and steering wheel angle, rather than solely based on speed. This dual-parameter approach allows the system to maintain adaptive steering characteristics while compensating for speed-induced variations in the upper limit steering wheel angle, thereby eliminating torque-steer and return effects.
2Ease of operation
If the gear ratio is low at low speed to facilitate maneuvering, then ease of operation is improved, but the upper limit rack position is reached at different steering wheel angles causing driver experience disturbance
Solution Approach 1:
The patent implements dynamics by making the gear ratio dynamically adjustable based on both vehicle speed and steering wheel angle. This dynamic adjustment ensures that the upper limit rack position corresponds to a consistent upper limit steering wheel angle across different speeds, while still maintaining low gear ratios at low speeds for ease of maneuvering.
3Reliability
If the gear ratio is high at high speed to improve controllability, then vehicle controllability is improved, but the upper limit steering wheel angle decreases causing return effect
Solution Approach 1:
The patent applies parameter changes by adjusting the gear ratio based on both vehicle speed and steering wheel angle. At high speeds, the system maintains high gear ratios for improved controllability while simultaneously adjusting the relationship between steering wheel angle and rack position to prevent the upper limit steering wheel angle from decreasing, thereby eliminating the return effect.
4Strength
If the upper limit rack position is fixed, then mechanical constraint is maintained, but the corresponding steering wheel angle varies with speed making counter-steering difficult during loss of grip
Solution Approach 1:
The patent implements dynamics by making the gear ratio dynamically adjustable based on both vehicle speed and steering wheel angle. This ensures that the fixed upper limit rack position corresponds to a consistent upper limit steering wheel angle across all speeds, providing predictable and responsive counter-steering capability during loss of grip situations.
Data Source
AI summary
A method for determining a gear ratio (VGR) for a power steering system of a vehicle, said power steering system comprising a steering wheel determining a steering wheel angle (Av) and a rack determining a rack position (Xc), said rack position (Xc) varying between a lower limit rack position and an upper limit rack position (Xcsup), the gear ratio (VGR) defining a ratio between the rack position (Xc) and the steering wheel angle (Av), or conversely, characterized in that the method comprises a definition step in which the gear ratio (VGR) is defined as a function of a vehicle speed (V1, V2, V3) and of the steering wheel angle (Av) so that the upper limit rack position (Xcsup) corresponds to a single upper limit steering wheel angle (Avsup).