ENGINE SPEED MEASURING METHOD AND DEVICE FOR THE SAME

PROBLEM TO BE SOLVED: To provide an engine speed measuring device capable of accurately measuring engine speed from exhaust sound of an engine, even if an S/N ratio is not good.SOLUTION: An engine speed measuring device comprises two bandpass filters 6, 7 extracting primary frequency components and secondary harmonic components; signal RMS portions 14, 15 calculating effective values of output of the bandpass filters 6, 7; rotation speed PMS portions 12, 13 making the output of the bandpass filters 6, 7 pass through a lowpass filter to calculate the effective values; a selecting portion 17 selecting the output of either one of the rotation speed RMS portions 12, 13, and correcting the effective values calculated by the other of the rotation speed RMS portions 12, 13; a sampling frequency converting portion 5 thinning out an engine sound signal according to the magnitude of the effective value; and an engine speed calculating portion 19 calculating the engine speed from a thinning-out interval calculated by the sampling frequency converting portion 5.