Dynamic Saturation Function for Power Steering Return Control
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Solution Overview
Problem
Existing power steering systems often cause artificial driving sensations and discomfort during sharp maneuvers due to viscous behavior and damping effects when returning the steering wheel to its central position, especially during quick counter-steering or sharp turns.
Innovation Solution
A power steering system with a dynamic saturation function that adjusts saturation thresholds based on the steering wheel speed setpoint, distinguishing between pure return components and undesirable viscous components, ensuring only the necessary return assist is applied to the assist motor, thus refining the return function and enhancing driving comfort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a return function uses servo-control to adjust steering wheel speed setpoint based on position deviation, then the steering wheel returns effectively to central position, but artificial viscous effects and damping behavior occur during quick counter-steering maneuvers
Solution Approach 1:
The patent applies dynamics by making the saturation threshold dynamic rather than fixed. The threshold adapts in real-time based on the steering wheel speed setpoint calculated from position deviation, allowing the system to automatically adjust between aggressive return (high threshold) and comfortable operation (low threshold) modes depending on the current steering state
Solution Approach 2:
The patent changes the parameter of saturation threshold dynamically based on the steering wheel speed setpoint. By linking the threshold to the calculated speed setpoint rather than using a constant value, the system adjusts its behavior according to the current maneuvering situation, eliminating viscous effects during quick counter-steering while maintaining effective return during normal operation
2Speed
If the return function applies high return assist setpoint to ensure fast return to central position, then return speed increases, but viscous disturbance and artificial driving sensations become more perceptible
Solution Approach 1:
The patent changes the saturation threshold parameter dynamically based on the steering wheel speed setpoint. During quick counter-steering maneuvers, when the speed setpoint is high, the threshold increases accordingly, allowing higher return assist setpoints without creating perceptible viscous disturbances. This dynamic adjustment maintains the benefit of fast return while eliminating the harmful viscous effect
3Device complexity
If the return function uses fixed saturation threshold, then implementation is simple, but it cannot adapt to different maneuvering situations and creates unwanted damping during sharp turns
Solution Approach 1:
The patent transforms the static saturation threshold into a dynamic parameter that automatically adapts to different maneuvering situations. The threshold is calculated based on the steering wheel speed setpoint, enabling the system to automatically adjust its characteristics according to whether the driver is performing normal steering, quick counter-steering, or sharp turns, thereby improving adaptability without requiring complex manual configuration
Data Source
AI summary
A power steering system including a steering wheel, a return function to automatically return the steering wheel to a given reference position, and includes a function for calculating a return-speed setpoint which calculates a steering wheel speed setpoint from the steering wheel position error differentiating between the effective instantaneous position of the steering wheel and the reference position, then a function for calculating the return assistance, defining from the steering wheel speed error which is the difference between the effective speed of the steering wheel and the steering wheel speed setpoint, a return assistance setpoint, the system including a dynamic saturation function defining at least one saturation threshold, that the dynamic saturation function sets according to the value of the steering wheel speed setpoint, and the dynamic saturation function applies to clip the peaks of the return assistance setpoint calculation to confine the return assistance setpoint to an authorized domain.