Electric Power Steering Dynamic Assist Control
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Solution Overview
Problem
Existing electric power steering systems face delays in returning the steering wheel and steered road wheels to the neutral position when the driver releases their hands, leading to an uncomfortable steering experience.
Innovation Solution
An electric power steering apparatus with a control device that computes and applies both a rotating assist force and a returning assist force, using sensors for steering torque, vehicle speed, steering angle, and angular velocity to adjust the assist forces dynamically, ensuring quicker return to neutral position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If steering assist force is generated in the rotating direction to assist steering wheel rotation, then ease of steering operation is improved, but the return of steered road wheels to neutral position is delayed when driver releases hands
Solution Approach 1:
The patent applies dynamics by making the steering assist force dynamic rather than static. The control device continuously adjusts the magnitude and direction of the steering assist force based on real-time detection of steering wheel angle, angular velocity, and angular acceleration. When the steering wheel is rotated, assist force is provided in the rotation direction; when the steering wheel returns to neutral (detected by angular velocity and acceleration patterns), the assist force automatically switches to support the return motion, thus resolving the contradiction between aiding rotation and enabling quick return.
Solution Approach 2:
The patent implements feedback control by using sensors to detect steering wheel state (angle, angular velocity, angular acceleration) and using this information to continuously adjust the steering assist force. The control device receives feedback from the steering wheel state and modifies the motor output accordingly - providing rotating assist force during steering input and switching to returning assist force during return-to-neutral motion, thereby solving the time delay problem while maintaining ease of operation.
2Speed
If steering assist command value is restricted in return state to enable wheel return, then return speed is improved, but steering assist force in rotating direction continues to occur causing delayed return
Solution Approach 1:
The patent makes the steering assist force dynamic by continuously monitoring steering wheel angular velocity and angular acceleration. When the system detects that the steering wheel is in a return-to-neutral state ( characterized by specific angular velocity and acceleration patterns), it dynamically switches the assist force direction to support the return motion. This dynamic adjustment eliminates the harmful continuous rotating assist force during return while maintaining high return speed.
Solution Approach 2:
The patent changes the parameters of the steering assist force based on the detected steering state. By monitoring steering wheel angle, angular velocity, and angular acceleration, the control device adjusts the magnitude and direction parameters of the assist force. During rotation, the assist force parameter is set to support rotation; during return-to-neutral motion, the parameters are changed to support return, thereby eliminating the harmful effect of continuous rotating assist force while maximizing return speed.
Data Source
AI summary
An electric power steering apparatus includes a rotating assist force computing unit for computing an assist force in the rotating direction of a steering wheel, a returning assist force computing unit for computing a returning assist force, which is a steering assist force in a direction opposite to the rotating direction, and a summing unit for adding up the computed assist force in the rotating direction and the computed returning assist force. The electric power steering apparatus returns the steering wheel and steered road wheels to the neutral position at an earlier time if a driver releases his or her hands from the steering wheel when rotating the steering wheel.