Electric Power Steering Viscoelastic Control for Rack End Impact
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Solution Overview
Problem
Conventional electric power steering apparatuses face challenges in smoothly steering near the rack end due to strong impacts and uncomfortable noises, as they do not effectively control assist torque and are sensitive to steering angle and velocity variations, leading to uncomfortable vibrations for the driver.
Innovation Solution
An electric power steering apparatus that employs a viscoelastic model following control system, converting current command values into rack axial forces and using feedback control to adjust motor output, thereby reducing noise and shock at the rack end while maintaining a comfortable steering experience by limiting torque changes and adapting to vehicle speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional electric power steering apparatus performs feed-back control of motor current to accurately generate assist torque, then the steering assist accuracy is improved, but strong impact and hitting noise occur near the rack end position
Solution Approach 1:
The control device detects when the steering angle is within a predetermined range of the rack end position and proactively reduces the current command value before the rack actually reaches the end position. This preliminary action prevents the strong impact and hitting noise that would occur if normal assist torque were maintained until the very end of the steering range.
Solution Approach 2:
The system performs preliminary reduction of the current command value when detecting that the steering angle is within the predetermined range of the rack end position. This advance action ensures that the assist torque is already reduced before the rack approaches the end position, thereby preventing harmful impacts and noises.
2Object-affected harmful factors
If the current command value is reduced near the rack end to suppress hitting noise, then the hitting sound is decreased, but steering comfort may be compromised
Solution Approach 1:
The control device dynamically adjusts the current command value based on the steering angle's proximity to the rack end position. By continuously monitoring the steering angle and smoothly reducing the current command value within the predetermined range, the system maintains steering comfort while suppressing hitting sounds, avoiding abrupt changes that would discomfort the driver.
3Power
If the electric power steering apparatus applies full assist torque to the steering system, then the steering assistance is maximized, but uncomfortable vibrations occur due to sensitivity to steering angle and velocity variations
Solution Approach 1:
The control device applies different control strategies depending on the local steering condition. When the steering angle is within the predetermined range of the rack end position, the system locally reduces the current command value, while maintaining normal assist torque elsewhere. This localized quality adjustment suppresses uncomfortable vibrations near the rack end without compromising overall steering assistance.
Data Source
AI summary
[Problem] An object of the present invention is to provide an electric power steering apparatus that constitutes a control system based on a physical model, constitutes a model following control that an output (a distance to a rack end) of a controlled object follows-up to a reference model, suppresses the occurrences of a noisy sound and a shock force at an end hitting without giving any uncomfortable steering feeling to a driver, and is capable of smoothly steering.[Means for solving the problem]In the electric power steering apparatus that calculates a first current command value based on at least a steering torque and performs an assist-control of a steering system by driving a motor based on the first current command value, the apparatus comprises a configuration of a model following control comprising a feed-back control section including a viscoelastic model as a reference model within a predetermined angle at front of a rack end, wherein the configuration of the model following control comprises a feed-back control section, and the model following control has a noise-reducing function to reduce a noise so as to suppress a rack end hitting.