Electric Power Steering Stability Compensation for Noise and Phase-Lag
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Solution Overview
Problem
Conventional electric power steering apparatuses experience micro-vibration and uncomfortable steering feelings at low-speed steering due to high-frequency noise, and phase-lag at high-speed steering, which are not effectively addressed by existing filtering solutions.
Innovation Solution
An electric power steering apparatus with a stability compensating section that varies the cut-off frequency of filtering sections based on motor angular velocity and vehicle speed to reduce noise-induced micro-vibration and prevent phase-lag, using multiple cut-off frequency varying sections and filtering processes to optimize steering torque and current command values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a fixed cut-off frequency filtering section is used to reduce high-frequency noise, then micro-vibration is suppressed at low-speed steering, but phase-lag occurs at high-speed steering
Solution Approach 1:
The cut-off frequency of the filtering section is made variable rather than fixed. The control unit dynamically adjusts the cut-off frequency based on detected steering angular velocity, using a higher cut-off frequency at high-speed steering to prevent phase-lag and a lower cut-off frequency at low-speed steering to suppress micro-vibration effectively.
Solution Approach 2:
The filtering characteristics are changed by varying the cut-off frequency parameter according to operating conditions. The control unit changes the cut-off frequency parameter based on steering angular velocity detection, optimizing the filtering effect for different steering speeds while maintaining steering accuracy.
2Ease of operation
If a low cut-off frequency is used to suppress noise at low-speed steering, then steering feeling is improved, but steering response becomes slow at high-speed steering
Solution Approach 1:
The system dynamically adapts the cut-off frequency to match the steering speed. At low-speed steering, a lower cut-off frequency provides smooth steering feeling and noise suppression. At high-speed steering, the cut-off frequency increases to maintain fast steering response, eliminating the trade-off between comfort and speed.
Solution Approach 2:
The control unit changes the cut-off frequency parameter based on detected steering angular velocity. This parameter adaptation allows the system to optimize both steering feeling and response speed for different operating conditions, providing comfort when needed and speed when required.
3Object-affected harmful factors
If high-frequency noise is filtered out aggressively, then micro-vibration is reduced, but steering torque accuracy deteriorates
Solution Approach 1:
The cut-off frequency parameter is adjusted according to steering angular velocity to optimize the balance between noise suppression and torque detection accuracy. At low-speed steering, a lower cut-off frequency effectively suppresses micro-vibration while preserving torque signal accuracy. At high-speed steering, the higher cut-off frequency maintains signal fidelity for accurate torque detection.
Solution Approach 2:
The filtering characteristics are dynamically adapted to the operating conditions. The control unit detects steering angular velocity and adjusts the cut-off frequency in real-time, ensuring that the filtering section suppresses noise when appropriate while maintaining steering torque detection accuracy across different steering scenarios.
Data Source
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AI summary
[Problem] An object of the present invention is to provide an electric power steering apparatus that reduces an uncomfortable feeling due to a noise at a steering holding and a low-speed steering time, and can smoothly steers so as to prevent a phase-lag at a high-speed steering time. [Means for solving the problem] An electric power steering apparatus that has a torque control section to calculate a current command value based on at least a steering torque, and assist-controls a steering system by driving a motor by means of a current control system based on the current command value, comprising: a motor angular velocity calculating section to calculate a motor angular velocity from a motor rotational angle, a motor angular acceleration calculating section to calculate a motor angular acceleration from the motor angular velocity, and a stability compensating section to calculate a steering torque for compensation and a current command value for compensation based on the motor angular velocity and the motor angular acceleration (adding a vehicle speed as needed), wherein the steering torque for compensation compensates the steering torque, and the current command value for compensation compensates the current command value.