Variable Time-Constant Filter for Steering Torque Pulsation
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Solution Overview
Problem
Conventional steering control devices struggle to accurately extract pulsating components due to cogging torque or torque ripple, leading to inadequate removal of steering and noise components, which affects the steering feel and stability of the electric power steering system.
Innovation Solution
A steering control device with a variable time-constant filter that adjusts its time constant based on the motor rotation angle to effectively filter out pulsating components from the steering torque, ensuring accurate extraction and reduction of pulsation, incorporating a torque detecting section, motor, electric power assist control, and current control sections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a filter with a fixed time constant is used to extract the pulsating component, then the filter can remove some noise, but it cannot sufficiently remove steering components and noise components in higher frequency bands because the pulsation frequency varies with motor rotation angular velocity
Solution Approach 1:
The patent applies the dynamics principle by making the filter time constant variable rather than fixed. The time-constant setting section dynamically adjusts the filter time constant based on the detected motor rotation angular velocity. When the motor rotates faster, the filter time constant is reduced to maintain appropriate filtering characteristics, allowing the system to adapt to varying operating conditions and accurately extract pulsating components across different speed ranges.
Solution Approach 2:
The patent implements parameter changes by modifying the filter time constant parameter according to the motor rotation angular velocity. The time-constant setting section changes the filter parameter (time constant) based on detected velocity conditions, enabling the filter to maintain optimal performance across varying operational states and accurately extract pulsating components regardless of speed variations.
2Adaptability or versatility
If the passband frequency range of the filter is set wide to accommodate varying pulsation frequencies, then the filter can track the pulsating component across different speeds, but components other than the pulsating component (steering components and noise) cannot be sufficiently removed
Solution Approach 1:
The patent applies dynamics by dynamically adjusting the filter time constant based on motor rotation angular velocity. This allows the filter to maintain appropriate bandwidth and selectivity characteristics for each operating speed, tracking the pulsating component accurately while rejecting unwanted steering components and noise across the full frequency range.
Solution Approach 2:
The patent changes the filter parameter (time constant) according to the detected motor rotation angular velocity. By adjusting this parameter dynamically, the filter maintains optimal selectivity and tracking performance across varying frequencies, achieving both adaptability to different speeds and precision in extracting only the pulsating component.
3Device complexity
If compensation control is performed with insufficiently extracted pulsating component, then the control system remains simple, but the steering feel of the driver changes due to inadequate pulsation reduction
Solution Approach 1:
The patent implements a dynamic filtering approach that adjusts the time constant based on motor rotation angular velocity, improving pulsating component extraction accuracy without requiring complex hardware modifications. This enhances steering feel quality while maintaining reasonable system complexity through software-based adaptive filtering.
Solution Approach 2:
The patent changes the filter time constant parameter dynamically based on operating conditions, enabling accurate pulsating component extraction that improves steering feel. This parameter adjustment approach achieves reliable compensation control without significantly increasing system complexity, as it utilizes existing sensors and computational resources.
Data Source
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AI summary
To accurately extract a pulsating component generated due to a cogging torque or a torque ripple to reduce a pulsation, the pulsating component is extracted using a bandpass filter having a variable time constant, and the time constant is set according to a frequency of cogging torque or torque ripple to be extracted. Further, a reference angle for a rotation angle of a motor is preset according to a generation harmonic order of the cogging torque or torque ripple, and the time constant of the bandpass filter is set from a time period required for the motor to rotate by the reference angle.