Engine Harmonic Cancellation Leakage Factor Dynamics
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Solution Overview
Problem
Engine harmonic cancellation systems often produce audible noise artifacts, known as 'afterglow,' due to their output levels remaining high when engine noise suddenly decreases, such as during transmission shifts, leading to temporary noise gains as the system readjusts.
Innovation Solution
The adaptive filter's leakage factor is dynamically reduced when sudden changes in engine RPM occur, allowing the EHC system to quickly lower its output tone to match the reduced engine noise level, thereby minimizing afterglow. This is achieved through a processor-controlled system that monitors engine speed and adjusts the filter's leakage factor and adaptation rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the adaptive filter uses a fixed leakage factor for noise cancellation, then the system maintains stable noise cancellation performance under normal conditions, but the system produces audible noise artifacts (afterglow) when engine noise suddenly decreases
Solution Approach 1:
The patent applies dynamics by making the leakage factor variable rather than fixed. The system dynamically adjusts the leakage factor based on the rate of change of engine RPM: using a first leakage factor under normal conditions and a second, lower leakage factor when RPM changes exceed a threshold. This dynamic adaptation eliminates afterglow artifacts while maintaining stable noise cancellation during normal operation.
Solution Approach 2:
The patent changes the parameter of the leakage factor based on operating conditions. When the absolute value of RPM change exceeds a predetermined threshold, the system switches to a different leakage factor value. This parameter change allows the system to respond appropriately to sudden engine noise decreases, preventing the loudspeaker output from remaining elevated and causing audible artifacts.
2Measurement precision
If the EHC system readapts to sudden engine noise decreases using normal adaptation rate, then the system maintains accurate noise cancellation, but the readaptation process is slower than necessary causing temporary noise gain
Solution Approach 1:
The system dynamically adjusts the adaptation rate based on the magnitude of RPM change. When sudden engine noise decrease is detected (|RPM change| > threshold), the system uses a higher adaptation rate to quickly reduce the loudspeaker output and eliminate afterglow. Once the system stabilizes, it returns to the normal adaptation rate to maintain accurate noise cancellation. This dynamic rate adjustment reduces readaptation time while preserving cancellation accuracy.
3Speed
If the adaptive filter uses a high leakage factor to respond quickly to RPM changes, then the system reduces afterglow rapidly, but the system becomes less stable and may produce oscillations
Solution Approach 1:
The patent applies local quality by using different leakage factor values for different operating conditions. A lower leakage factor is used specifically when RPM changes exceed the threshold to rapidly reduce afterglow, while a higher leakage factor is used during normal operation to maintain filter stability. This localized parameter adjustment allows the system to achieve rapid response when needed without compromising overall stability.
Data Source
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AI summary
A device and method that is configured to operate an active noise reduction system for a motor vehicle, where there is an active noise reduction system input signal that is related to the vehicle engine speed, and where the active noise reduction system comprises one or more adaptive filters that use a filter coefficient to modify the amplitude and/or phase of a noise cancellation reference signal and output noise reduction signals that are used to drive one or more transducers with their outputs directed to reduce engine noise, where the value of the coefficient is related to an adaptive filter leakage factor. Changes in the engine speed, based on the input signal that is related to the vehicle engine operation, are monitored. In response to changes in the engine speed, the adaptive filter leakage factor is temporarily modified.