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摘要

An apparatus for detecting undesirable combustion characteristics in spark-ignited internal combustion engines. A sensor and band-pass filter tuned to the frequency of the knock vibration are provided with an output of the band-pass filter being compared with a reference value. The result of the comparison is correlated with undesirable combustion characteristics to be recognized. A rectifier is provided for solid borne sound signals received by the sensor with the signals passing through the band-pass filter. The signal is rectified in the rectifier to a knock signal and a series circuit composed of a band-stop filter tuned to the frequency of the knock vibration, an r.m.s. rectifier, and an amplifier is provided by means of which the sound signal received by the sensor is converted into a reference signal. A comparator is provided when the reference signal and the knock signals are compared and an output signal is generated if the knock signal exceeds the reference signal. A time comparison member receives the output signal from the comparator, with the time comparison member transmitting a signal of a predetermined time duration if the time duration of the signal of the comparator is longer than the specific time duration set in the time comparison member.