Combustion state detecting apparatus for internal combustion engine

Abstract

A combustion state detecting apparatus for an internal combustion engine is imparted with facility for determining discriminatively the causes for non-occurrence of combustion. The apparatus includes a spark plug (4) for generating a spark discharge upon application of a high voltage generated by an ignition coil (1) in response to an ignition signal (X1) to thereby fire an air-fuel mixture within a cylinder of the internal combustion engine, an ion current detecting means (6A) for detecting as ion current detection signals (X2a; X2) an ion current corresponding to an amount of ions produced within the cylinder immediately after combustion of the air-fuel mixture, a signal detecting means (7A; 7B; 9) for comparing the ion current detection signal (X2a) outputted from the ion current detecting means (6A) with a first reference voltage (Vth1) to thereby output a first decision signal (X3) while comparing the ion current detection signal (X2) with a second reference voltage (Vth2) to thereby output a second decision signal (X4) while invalidating output of the second decision signal (X4) during a predetermine time period from a time point at which the comparison of the ion current detection signal (X2) with the second reference voltage (Vth2) is started, and an estimating logic unit (9, 10; 112) for estimating a cause for nongeneration of a combustion signal on the basis of output statuses of the first decision signal (X3) and the second decision signal (X4).

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