Electric Power Steering Phase Control for Return Stability
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Solution Overview
Problem
In electric power steering systems, abrupt reduction in steering torque during return steering leads to abrupt steering assist power decrease, causing unstable wheel convergence.
Innovation Solution
The system incorporates a phase control element that alters the gain in the higher frequency band of the torque sensor's frequency response characteristic based on steering state, reducing the abrupt decrease in assist torque and improving convergence by adjusting the phase control characteristic in response to steering state judgments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the cut-off frequency of the low-pass filter is set to a larger value during return steering to reflect high-frequency components of counter electromotive force, then the motor driving current converges stably on the target value, but the steering assist power decreases abruptly when steering torque decreases, causing abrupt return of the steering wheel and deteriorated convergence
Solution Approach 1:
The patent applies dynamics by making the phase control characteristic adjustable based on steering state. The system dynamically switches between different phase control characteristics (first and second) depending on whether the steering wheel is in positive steering or return steering state, allowing the control parameters to adapt to different operational conditions and prevent abrupt motion
Solution Approach 2:
The patent changes the phase control parameter (phase advance amount) based on the steering state. By detecting whether the steering angle is increasing or decreasing, the system adjusts the phase advance amount to different values, thereby changing the frequency response characteristics to suppress abrupt variations in assist power during return steering
2Stability of the object's composition
If the gain in the higher frequency band is reduced in the return steering state, then the abrupt decrease in basic assist torque is suppressed and steering wheel convergence is improved, but the control characteristics must be more complex to accommodate different steering states
Solution Approach 1:
The system uses the steering state detection capability that already exists in the electric power steering apparatus to automatically determine when to apply which phase control characteristic. The steering state judgment element self-services by using the same steering angle information already being processed by the control system, avoiding the need for additional sensors or complex external control mechanisms
Data Source
AI summary
In an electric power steering apparatus, a steering torque is detected by a torque sensor, and a motor which generates steering assist power is controlled so that steering assist power is generated in accordance with basic assist torque which corresponds to the detected steering torque. The phase of the output signal of the torque sensor is caused to vary by a phase control element. The phase control characteristic of the phase control element is altered in accordance with the judgment results of a steering state judgment element as to whether the steering state is a return steering state or positive steering state, so that, in the frequency response characteristic of the output to input of the torque sensor, the gain at the higher frequency band where the frequency is greater than a set value is reduced in the return steering state in comparison to the positive steering state.