| 摘要 |
PROBLEM TO BE SOLVED: To accurately calculate the quasi-average value and the false standard deviation in a short period of time, when a filtering frequency band of a filter is changed. SOLUTION: An oscillatory wave form signal detected by a sensor is filtered with a filter. On the basis of the oscillating intensity after filtering and the calculated value, the average value (average level AVE) and the standard deviation (effective deviation) in frequency distribution of the oscillation intensity are calculated, and the filtering frequency band of the filter is changed, according to rotational speed Ne of the engine. Based on the average level AVE calculated in a predetermined filtering frequency band, quasi-average values (learned values AVE(L), AVE(H)) immediately before the filtering frequency is changed, are calculated and maintained, until the oscillatory wave form signal is filtered again in the same filtering frequency band. When the frequency is changed to the same filtering frequency band, the maintained values AVE(L), AVE(H) are set as initial values of the calculated values, immediately after the change. The effective deviation is calculated in similar manner.
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