Misfire detecting apparatus for internal combustion engine

A misfire detecting apparatus for an internal combustion engine, having engine rotational speed parameter detecting means for detecting an engine rotational speed parameter indicative of a rotational speed of said engine of which an output shaft is connected via a torsion element to an input shaft of a transmission mechanism, and detecting a misfire of said engine based on the detected engine rotational speed parameter, said misfire detecting apparatus comprising:

• transmission rotational speed parameter detecting means for detecting a transmission rotational speed parameter indicative of a rotational speed of said input shaft of said transmission mechanism;
• modifying means for calculating a modified engine rotational speed parameter by modifying the detected engine rotational speed parameter based on the transmission rotational speed parameter, an engine rotation moment on the input side of said torsion element, and a transmission rotation moment on the output side of said torsion element;
• correcting means for calculating, at predetermined crank angles, an average change amount of the modified rotational speed parameter in a predetermined period, and an inertia speed changing component which is generated with rotation of said engine, and further calculating a corrected rotational speed parameter by correcting the modified rotational speed parameter according to the average change amount and the inertia speed changing component;
• relative speed parameter calculating means for calculating a relative speed parameter according to a difference between a reference value and the corrected rotational speed parameter, the reference value being the corrected rotational speed parameter corresponding to the rotational speed parameter which is detected at a reference timing at which a piston of a cylinder, which is subjected to the misfire determination, is positioned in the vicinity of the compression top dead center;
• determination parameter calculating means for calculating a determination parameter by integrating the relative speed parameter for an integration period corresponding to 720/N degrees of the crank angle (“N” is a number of cylinders of said engine);
• determining means for performing a misfire determination based on the determination parameter;
• and
• providing means for providing an indication of normal or abnormal combustion of the internal combustion engine based on the misfire determination,
• wherein the reference timing and a start timing of the integration period are set according to the ignition timing of said engine, and
• wherein said modifying means calculates the modified engine rotational speed parameter using the following equation (C):
• OMG=OMGCRK+(IMAIN/ICRK)×OMGMAINAC (C)
• where “OMG” is the modified engine rotational speed parameter, “OMGCRK” is the detected engine rotational speed parameter, “OMGMAINAC” is a changing component parameter indicative of a changing component contained in the detected transmission rotational speed parameter, “ICRK” is the engine rotation moment, and “IMAIN” is the transmission rotation moment.

A misfire detecting method for detecting a misfire of an internal combustion engine, of which the output shaft is connected via a torsion element to an input shaft of a transmission mechanism, said misfire detecting method comprising the steps of:

• a) detecting an engine rotational speed parameter indicative of a rotational speed of said engine;
• b) detecting a transmission rotational speed parameter indicative of a rotational speed of said input shaft of said transmission mechanism;
• c) calculating a modified engine rotational speed parameter by modifying the detected engine rotational speed parameter based on the transmission rotational speed parameter, an engine rotation moment on the input side of said torsion element, and a transmission rotation moment on the output side of said torsion element;
• d) calculating, at predetermined crank angles, an average change amount of the modified rotational speed parameter in a predetermined period, and an inertia speed changing component which is generated with rotation of said engine;
• e) calculating a corrected rotational speed parameter by correcting the modified rotational speed parameter according to the average change amount and the inertia speed changing component;
• f) calculating a relative speed parameter according to a difference between a reference value and the corrected rotational speed parameter, the reference value being the corrected rotational speed parameter corresponding to the rotational speed parameter which is detected at a reference timing at which a piston of a cylinder, which is subjected to the misfire determination, is positioned in the vicinity of the compression top dead center;
• g) calculating a determination parameter by integrating the relative speed parameter for an integration period corresponding to 720/N degrees of the crank angle (“N” is a number of cylinders of said engine);
• h) performing a misfire determination based on the determination parameter;
• and
• i) providing an indication of normal or abnormal combustion of the internal combustion engine based on the misfire determination,
• wherein the reference timing and a start timing of the integration period are set according to the ignition timing of said engine, and
• wherein the modified engine rotational speed parameter is calculated using the following equations (A) and (B):
• OMG=KRI×OMGCRK+(1−KRI)×OMGMAIN (A)
• KRI=ICRK/(ICRK+IMAIN) (B)
• where “OMG” is the modified engine rotational speed parameter, “OMGCRK” is the detected engine rotational speed parameter, “OMGMAIN” is the detected transmission rotational speed parameter, “KRI” is an inertia moment ratio given by the equation (B), “ICRK” is the engine rotation moment, and “IMAIN” is the transmission rotation moment.