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 (,) for generating a spark discharge upon application of a high voltage generated by an ignition coil (,) in response to an ignition signal (X,) to thereby fire an air-fuel mixture within a cylinder of the internal combustion engine, an ion current detecting means (,A) for detecting as ion current detection signals (X,; X,) 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 (,A;,B;,) for comparing the ion current detection signal (X,) outputted from the ion current detecting means (,A) with a first reference voltage (Vth,) to thereby output a first decision signal (X,) while comparing the ion current detection signal (X,) with a second reference voltage (Vth,) to thereby output a second decision signal (X,) while invalidating output of the second decision signal (X,) during a predetermine time period from a time point at which the comparison of the ion current detection signal (X,) with the second reference voltage (Vth,) is started, and an estimating logic unit (,) for estimating a cause for nongeneration of a combustion signal on the basis of output statuses of the first decision signal (X,) and the second decision signal (X,).