Power Steering Rack Servo-Control via Speed Setpoint Limiting
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Solution Overview
Problem
Existing power steering systems experience sudden and rapid rack movements due to environmental variations, degrading driver comfort and safety, as they cannot manage changes in vehicle weight and traffic surface conditions without modifying system parameters.
Innovation Solution
A method for servo-controlling the rack position using nested closed-loop regulations, where the steering computer sets a speed setpoint and limits it to a maximum threshold, ensuring the rack moves at a continuous and predictable pace, adapting to kinematic constraints and maintaining vehicle stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the rack position is servo-controlled to a position setpoint using motor torque, then the vehicle trajectory can be kept close to the reference trajectory, but the rack movement becomes sudden and rapid when environmental conditions change
Solution Approach 1:
The patent applies dynamics by making the rack movement adaptive to environmental conditions. The control system adjusts the rack movement characteristics based on detected changes in vehicle weight or traffic surface conditions, transitioning from fixed-speed control to variable-speed control that responds to real-time environmental variations.
Solution Approach 2:
The patent changes the control parameter from direct motor torque control to speed-based control with position feedback. By controlling the rack speed rather than applying direct torque, the system can maintain smooth, predictable rack movement while still achieving accurate trajectory following, preventing sudden and rapid movements.
2Productivity
If the rack moves rapidly to respond to position errors, then the position control responsiveness is improved, but the driver comfort and safety are degraded
Solution Approach 1:
The patent implements feedback control by continuously monitoring the actual rack position and comparing it with the desired position setpoint. This feedback mechanism allows the system to make incremental adjustments to correct position errors without causing sudden or excessive movements, thereby maintaining both responsiveness and comfort.
Solution Approach 2:
The control system operates with periodic adjustments, making gradual corrections to the rack position rather than applying large, sudden corrections. This periodic action approach maintains smooth rack movement while still achieving the desired position control, preventing driver discomfort and safety issues.
3Adaptability or versatility
If the system parameters are modified to manage environmental variations, then the adaptability to changing conditions is improved, but the system complexity increases
Solution Approach 1:
The control system performs self-adjustment by automatically detecting environmental changes (vehicle weight, traffic surface conditions) and adapting its control parameters accordingly. This self-service capability allows the system to handle environmental variations without requiring manual parameter modification or complex external intervention, maintaining simplicity while improving adaptability.
Data Source
AI summary
A method for controlling an assist motor of a power steering system, power steering system including the assist motor configured to apply a motor torque on a rack, and at least one steering computer, method being designed to servo-control a position of the rack to a position setpoint, method including: a maneuvering step in which the assist motor exerts a motor torque on the rack according to a motor torque setpoint; wherein the method also includes: servo-control step in which the steering computer determines a speed setpoint of the rack according to the position setpoint and to the position of the rack; limitation step in which the steering computer issues a limited speed setpoint which is lower than or equal to a maximum speed threshold; control step in which the steering computer determines the motor torque setpoint according to the limited speed setpoint and to a speed of the rack.