Electric Power Steering Velocity I-P Control Vibration Suppression
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Solution Overview
Problem
Conventional electric power steering systems face challenges in accurately following a target steering angle during automatic steering control, especially due to varying road surface conditions and friction, leading to potential vibrations and discomfort for the driver, as they do not effectively account for the spring-inertial system of the steering wheel and often introduce delays in assist torque adjustments.
Innovation Solution
The electric power steering apparatus employs a velocity I-P control (proportional-lead type PI-control) to suppress vibrations and improve control accuracy by calculating a compensation value from steering torque and torque differential, which is added to the motor current command to drive the motor, and incorporates a rate limiter and low-pass filter to smooth target steering angle changes and reduce high-frequency vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional feedback control with PWM adjustment is used to generate steering assist torque, then the motor current can be controlled, but steering wheel vibrations occur during automatic steering control and the actual steering angle cannot follow the target steering angle with high accuracy
Solution Approach 1:
The patent changes the control parameters by introducing velocity I-P control (proportional-lead type PI control) instead of conventional feedback control. This control method calculates compensation values based on steering torque and torque differential, and adjusts motor current command dynamically. The rate limiter and low-pass filter further modify the control parameters by smoothing target steering angle changes and filtering high-frequency vibrations, thereby improving tracking accuracy while suppressing vibrations.
Solution Approach 2:
The patent implements a feedback mechanism where the actual steering angle is continuously detected and compared with the target steering angle. The deviation is used to calculate compensation values through velocity I-P control. Additionally, the steering torque and torque differential are fed back to calculate real-time compensation, creating a closed-loop control system that improves tracking accuracy and suppresses vibrations through continuous adjustment.
2Speed
If the motor assist torque is adjusted rapidly to make the actual steering angle follow the target steering angle, then the tracking accuracy improves, but the spring-inertial system of the steering wheel causes vibrations and driver discomfort
Solution Approach 1:
The patent applies dynamics by making the control system adaptive to the spring-inertial characteristics of the steering wheel. The velocity I-P control dynamically adjusts the compensation value based on the current state (steering torque and torque differential), allowing the system to respond quickly while accounting for the physical dynamics of the steering wheel system. This prevents rigid, vibration-inducing corrections.
Solution Approach 2:
The patent uses rate limiter and low-pass filter to smooth the target steering angle changes before they are executed. This beforehand cushioning prevents abrupt torque adjustments that would excite the spring-inertial system. By pre-processing the control signal to remove high-frequency components and limit rate of change, the system maintains fast response while avoiding vibrations.
3Adaptability or versatility
If conventional assist control is used without considering road surface conditions and friction variations, then the control system is simple, but the actual steering angle cannot accurately follow the target steering angle under varying conditions
Solution Approach 1:
The patent adapts to varying road surface conditions and friction by dynamically changing the control parameters through velocity I-P control. The compensation value is calculated based on real-time steering torque and torque differential, allowing the system to adjust its behavior according to current conditions. The rate limiter and low-pass filter parameters are also adjusted to maintain optimal performance across different operating conditions.
Data Source
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AI summary
[Problem] An object of the present invention is to provide an electric power steering apparatus that realizes vibration suppression of response characteristics and has a control performance having resistance properties against disturbances such as a road surface change by using a velocity I-P control (a proportional-lead type PI control) in a vehicle having functions of an automatic steering control and a manual steering control. [Means for solving the problem] An electric power steering apparatus comprising: a steering angle control section that calculates a second motor current command value in automatic steering control so as to bring an actual steering angle close to a target steering angle; and a switching section that inputs a first motor current command value and the second motor current command value and switches between the first and second motor current command values depending on a switching signal, wherein the steering angle control section comprises a rate limiter that performs smoothing with respect to the target steering angle, and outputs as the second motor current command value on the basis of a first deviation between an output of the rate limiter and the actual steering angle and a motor angular velocity.