Electric Power Steering Torsional Angle Control
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Solution Overview
Problem
Conventional electric power steering apparatuses face challenges in maintaining consistent steering torque due to variations in road surface states and aging mechanism characteristics, requiring complex operations to set target steering torques based on steering angles and using PI-control for feedback adjustments.
Innovation Solution
An electric power steering apparatus that generates a target steering torque based on vehicle driving information, converts it into a target torsional angle using the torsion bar's spring constant, and controls the motor current to maintain the desired torsional angle, incorporating a stabilization compensating section to suppress oscillations and improve followability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional PI-control feedback adjustment is used to maintain steering torque, then the steering torque can be adjusted based on detected current, but the steering torque becomes affected by road surface state variations and aging mechanism characteristics
Solution Approach 1:
The patent implements feedback control by detecting the torsional angle of the torsion bar and comparing it with the target torsional angle, then adjusting motor current based on the deviation. This closed-loop feedback mechanism ensures the actual steering torque follows the target value despite external disturbances like road surface variations and aging effects.
Solution Approach 2:
The patent replaces direct mechanical torque sensing with torsional angle detection. By measuring the torsional angle of the torsion bar and using the known spring constant to calculate torque, the system avoids direct mechanical torque sensors that are sensitive to road surface states and aging, while achieving the same control objective.
2Adaptability or versatility
If complex operations are used to set target steering torques based on steering angles, then the steering torque can be adjusted for different conditions, but the control system complexity increases
Solution Approach 1:
The patent changes the control parameter from direct torque control to torsional angle control. By setting the target torsional angle based on steering angle and vehicle speed, and then controlling motor current to achieve this target angle, the system maintains adaptability to different driving conditions while simplifying the control logic through a single primary control loop.
3Speed
If the torsional angle control responds quickly to steering inputs, then the followability to target torsional angle improves, but oscillations and vibrations may occur
Solution Approach 1:
The patent implements dynamic control by adjusting the motor current based on the real-time deviation between target and actual torsional angles. The control system dynamically responds to steering inputs while the motor's inertial properties and the torsion bar's elastic characteristics naturally dampen rapid changes, achieving both fast followability and stability without requiring complex damping controls.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system effectively generates a consistent steering torque following vehicle driving information, enhancing steering feel and stability by suppressing vibrations and improving followability to the target torsional angle, even under abrupt steering conditions.
Implementation Method 1
a torsion bar which is provided in a column shaft (a steering shaft, or a handle shaft)
Data Source
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AI summary
[Problem] An object of the present invention is to provide an electric power steering apparatus that easily obtains equivalent steering torques to vehicle driving information such as a steering angle without being affected by a road surface state and aging-changes of mechanism characteristics of a steering system. [Means for solving the problem] The electric power steering apparatus that assist-controls a steering system, comprises: a target steering torque generating section to generate a target steering torque based on vehicle driving information, a converting section to convert the target steering torque into a target torsional angle, and a torsional angle control section to calculate the current command value based on the target torsional angle, a torsional angle of the torsion bar and a motor angular velocity; and the torsional angle control section comprises a torsional angle feedback compensating section to output a target torsional angular velocity corresponding to a deviation between the target torsional angle and the torsional angle, a velocity control section to output the current command value based on the target torsional angular velocity, and a stabilization compensating section to perform feedback to the current command value by setting a transfer function to at least one of angle relation information.