Abstract: In a knocking discriminating system for an internal combustion engine, a knocking detecting signal obtained from a knocking sensor is passed through a band-pass filter for obtaining a sinusoidal waveform of approximately 8 KHz. The sinusoidal waveform signal is then applied to an A/D converter, the operational timing of which is controlled by a microcomputer, so that only a part of the knocking detecting signal nearby the peak portion is converted into digital values. A discrimination level is prepared from the average value of the digital values, and the knocking status is discriminated by comparing the maximum value of the digital values thus converted with the discriminating level.

Abstract: A spark timing control apparatus controls the spark timing to retard or advance in accordance with the output signal from a knock sensor. An accelerating condition of the engine is determined depending on a particular knock occurence patterns including; whether the interval of knock occurences is larger or small, the total amount of retard angles is larger or small, or the frequency of knock occurences. When the accelerating condition is determined, the advancing rate of the spark timing is increased until a steady state of the engine operation is determined based on the output signal of the knock sensor.