Electric Power Steering Handle Vibration Suppression
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Solution Overview
Problem
Conventional electric power steering apparatuses face challenges in suppressing handle vibrations due to inertia and spring characteristics, which affect steering feel and are difficult to address without altering the PI-control gain, leading to compromised frequency characteristics and steering responsiveness.
Innovation Solution
The electric power steering apparatus employs phase compensating sections with reverse characteristics at the front and rear stages of the assist map, or uses band pass and notch filters with reverse transfer functions, or lead-system and delay-system compensations to calculate the current command value, thereby suppressing handle vibrations without changing the PI-control gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If phase compensating sections with reverse characteristics are added at front and rear stages of the assist map, then handle vibrations are suppressed and steering feel is improved, but device complexity increases
Solution Approach 1:
The control system is segmented into multiple functional sections: a front-stage phase compensating section that applies phase lead compensation to the steering torque signal, an assist map calculation section, and a rear-stage phase compensating section that applies phase delay compensation to the current command value. This segmentation allows vibration suppression at specific frequencies while maintaining overall system functionality and enabling independent optimization of each section.
Solution Approach 2:
Phase compensating sections act as intermediary elements between the steering torque input and the current command value output. These intermediary sections introduce phase shift characteristics that counteract the resonant vibrations caused by handle inertia and torsion bar spring characteristics, thereby suppressing handle vibrations without directly modifying the PI-control gain.
2Speed
If PI-control gain is increased to improve steering responsiveness, then frequency characteristics improve, but handle vibrations due to resonance are exacerbated
Solution Approach 1:
Instead of changing the PI-control gain parameters, the invention introduces phase compensating sections with specific phase shift characteristics. The front-stage compensating section uses phase lead compensation with a zero point frequency lower than the handle frequency (≥3 Hz), while the rear-stage uses phase delay compensation. This parameter change approach suppresses resonant vibrations at the handle frequency while preserving the high-frequency responsiveness provided by the original PI-control settings.
3Ease of operation
If compensating sections are added to suppress vibrations, then steering feel is improved, but calculation time and processing load increase
Solution Approach 1:
The front-stage phase compensating section performs preliminary phase lead compensation on the steering torque signal before it enters the assist map calculation. This preliminary action pre-adjusts the signal characteristics to prevent resonance amplification, reducing the need for complex post-processing and minimizing overall calculation time while achieving vibration suppression.
Data Source
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AI summary
[Problem] An object of the present invention is to provide an electric power steering apparatus that suppresses the vibration of the operating member such as the handle and improves the steering feeling due to the characteristic compensation of the assist map, without of the change of the PI-control gain in the current control section. [Means for solving the problem] The present invention is an electric power steering apparatus that calculates a current command value with reference to an assist map inputting a steering torque and assist-controls a steering system of a vehicle by driving a motor based on the current command value, comprising: a first compensating section provided at a front stage of the assist map; and a second compensating section provided at a rear stage of the assist map; wherein the current command value is calculated with a characteristic of which sloping increases for an absolute value of the steering torque being inputted into the first compensating section and is outputted from the second compensating section, and vibrations of operating members are suppressed.