| 摘要 |
PURPOSE:To enable the constantly stable operation of the titled tachometer system irrespective of the kinds of vehicles by a constitution wherein an attenuator making variable the level of an injection signal is provided on the input side of the signal to make adjustable the difference in signal level based on the kinds of vehicles. CONSTITUTION:The level of the signal (a) of a sound of fuel injection in an injection pipe 1, which is detected by a microphone 2, is adjusted by an attenuator 9, and thereby the difference in the level of an injection signal among the kinds of vehicles is compensated. A signal (h) obtained through the level adjustment is sent to a high-frequency amplifying circuit 10 having a tuning frequency of 1-4MHz. Then, an amplified high-frequency signal (b) is detected 4, and a detection signal (c) thus obtained is subjected to AC subharmonic amplification 5 so that it has a crest value not lower than a comparison voltage Vref. A signal (d) obtained from this amplification is compared with the comparison voltage Vref. While the comparison voltage Vref is controlled to be an optimum value constantly by a pulse output signal (e) of a voltage comparison circuit 6, a monostable multivibrator 7 is also controlled thereby, and a tachometer 8 is driven by the vibrator. |
