Apparatus and method for recognizing misfire occurrence in multi-cylinder internal combustion engine

A misfire recognizing apparatus for a multi-cylinder internal combustion engine, comprising:

• a) a reference signal generating sensor for generating and outputting a reference signal (REF) for each predetermined crank angle rotation of an engine crankshaft, which angle rotation is expressed by 720.degree./n, where n denotes a number of engine cylinders within the engine, and said reference signal including a cylinder number identifying signal indicative of one of the engine cylinders;
• b) a second sensor for detecting an engine driving condition other than an engine revolution speed;
• and
• c) a control unit including:
• d) period measuring means for measuring a period of the reference signal for each predetermined crank angle rotation, the reference signal period corresponding to a combustion state of a corresponding one of the engine cylinders;
• e) misfire occurrence determining means for determining a presence or absence of misfire in each cylinder based on the measured period of the reference signal for the corresponding one of the engine cylinders;
• f) first determining means for determining whether a fuel supply to the engine is cut off or carried out based on the detected engine driving condition;
• g) first correction coefficient setting means for setting a first correction coefficient (KT.sub.i, where i=1to n in increments of 1) for each measured period of the reference signals so that stepwise variations (.DELTA.T) in the periods of the reference signals consecutively measured for all of the cylinders are mutually equal to one another when said first determining means determines that the fuel supply to the engine is cut off;
• h) second determining means for determining whether the misfire occurrence determining means has determined the absence of misfire in any the engine cylinders;
• and
• i) second correction coefficient determining means for setting a second correction coefficient (KKT.sub.i, where i=1 to n in increments of 1) for each measured period of the reference signals so that the respective periods of the reference signals for all of the engine cylinders, which are corrected according to the first correction coefficients set by the first correction coefficient setting means, are equal to an average value (T.sub.AVE) of the respective periods of the reference signals when the first determining means determines that the fuel supply to the engine is carried out and when said second determining means determines that the misfire occurrence determining means has determined the absence of misfire in any of the engine cylinders,
• wherein said misfire occurrence determining means comprises:
• j) correction means for correcting the periods of the respective reference signals continuously measured for all of the engine cylinders according to either or both of the first and second correction coefficients set by said first and second correction coefficient setting means and said misfire occurrence determining means determines the absence or presence of misfire in any engine cylinder based on the corrected periods of the reference signals by said correction means.