Signal processing method for an engine knock signal
View Patent ↗The duration of a knock detection window over which a filtered knock signal is single-point DFT-processed for engine knock detection is user adjustable. The knock detection window is defined by at least two overlapping identical duration sub-windows, and the extent of the sub-window overlap is changed to adjust the duration of the knock detection window. The DFT processing is performed over each sub-window and the processing results are combined for knock detection.
1. A method of processing a knock signal produced by an engine knock sensor to determine a magnitude of the knock signal at a specified knock frequency for knock detection, comprising the steps of:
anti-alias filtering the knock signal to pass a range of knock signal frequencies including the specified knock frequency;
sampling and digitizing the filtered knock signal to form a series digital samples for DFT-processing;
characterizing a specified knock detection interval as a combination of at least first and second processing windows of fixed and identical duration with a variable amount of overlap;
DFT-processing said digital samples over said first processing window to form a first knock signal magnitude, and DFT-processing said digital samples over said second processing window to form a second knock signal magnitude; and
combining said first and second knock signal magnitudes to form the knock signal magnitude for knock detection.
2. The method of claim 1 , including the step of:
determining an overlap of said first and second processing windows so that their combined duration corresponds to the specified knock detection interval.
3. The method of claim 1 , including the steps of:
storing an array of pre-calculated terms for use in DFT-processing said digital samples; and
retrieving the stored pre-calculated terms for DFT-processing the digital samples over both first and second processing windows.
4. The method of claim 1 , including the step of:
averaging said first and second knock signal magnitudes to form the knock signal magnitude for knock detection.