Active Noise Reduction Device Harmonic Step Size Control
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Solution Overview
Problem
Existing active noise reduction devices face challenges in adapting to sudden changes in engine rotation rate, leading to inadequate noise reduction during acceleration or deceleration, as the step size parameter for filter coefficients may diverge, resulting in unusual noise generation.
Innovation Solution
The active noise reduction device includes adaptive filters for each harmonic component of the engine noise, with a step size determiner that adjusts the step size parameter based on frequency variations, ensuring adaptability and stability in reducing all harmonic components, especially high-order frequency components, by setting suitable step size parameters for each harmonic.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a common filter coefficient is used for all harmonic components, then the device complexity is reduced, but the adaptability to sudden changes in engine rotation rate deteriorates
Solution Approach 1:
The patent segments the filter coefficient management by creating separate adaptive filters for each harmonic component (2nd order, 4th order, 6th order, etc.). Each harmonic component has its own filter coefficient that can be independently updated, allowing the system to adapt to sudden changes in engine rotation rate for each frequency component separately, thereby resolving the contradiction between device complexity and adaptability.
2Manufacturing precision
If a small step size parameter is used, then the manufacturing precision of noise reduction is improved, but the convergence rate deteriorates
Solution Approach 1:
The patent implements dynamic adjustment of the step size parameter based on the convergence state of each adaptive filter. When the filter coefficient has not yet converged, a larger step size parameter is used to accelerate convergence. When the filter coefficient has converged, a smaller step size parameter is used to maintain high noise reduction accuracy. This dynamic adjustment resolves the contradiction between convergence rate and noise reduction precision.
3Productivity
If filter coefficient updating is continued during sudden rotation rate changes, then the productivity of noise reduction is maintained, but the reliability deteriorates due to coefficient divergence
Solution Approach 1:
The patent incorporates a convergence determination mechanism that continuously monitors whether each adaptive filter has converged. When sudden rotation rate changes are detected, the system uses feedback from the convergence status to decide whether to continue or pause filter coefficient updating. This feedback control prevents coefficient divergence while maintaining noise reduction productivity, resolving the contradiction between reliability and productivity.
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
This configuration ensures effective reduction of control target sounds arising from engine vibration, even during sudden changes in engine rotation rate, by stabilizing the adaptation of filter coefficients and minimizing residual noise.
Implementation Method 1
the control signal generator generates corresponding one of the harmonic components of the control signal by multiplying the corresponding one of the harmonic components of the standard signal by a filter coefficient
Implementation Method 2
the filter coefficient updating part updates the filter coefficient based on the reference signal and the error signal so as to minimize the error signal
Implementation Method 3
An optimization algorithm such as a least mean square (LMS) algorithm is applied to the filter coefficient updating part
Implementation Method 4
These devices reduce engine booming noise generated in a cabin of a traveling vehicle by letting the noise and a control sound with opposite phases and the same amplitude interfere with each other
Implementation Method 5
The step size determiner sets the step size parameter for the corresponding one of the harmonics based on a frequency variation in the corresponding one of the harmonic components of the standard signal
Data Source
AI summary
An active noise reduction device includes a standard signal generator, adaptive filters, a control sound emitter, and an error signal detector. The standard signal generator generates a standard signal including harmonics of a fundamental frequency correlated with the control target sound. The adaptive filters each generates corresponding one of harmonic components of a control signal based on the standard signal. The adaptive filters each is for corresponding one of the harmonics. The control sound emitter emits a control sound based on the control signal. The error signal detector collects residual noise left over after interference between the control target sound and the control sound, and detects an error signal based on the residual noise. Each of the adaptive filters includes a step size determiner. The step size determiner sets the step size parameter based on a frequency variation in the corresponding one of the harmonic components of the standard signal.