Misfire determination apparatus for internal combustion engine

A misfire determination method for an internal combustion engine including a plurality of cylinders and an output shaft, the misfire determination method comprising:

• detecting a rotational speed of the output shaft;
• calculating a misfire parameter having a correlation with a change amount of the rotational speed in a combustion stroke of each of the plurality of cylinders based on the rotational speed, the misfire parameter increasing as an increase amount of the rotational speed is large;
• and
• determining whether a misfire of the internal combustion engine has occurred and a manner of the misfire, based on the misfire parameter, wherein the manner of the misfire includes a single-cylinder misfire where the misfire has occurred in a single cylinder among the plurality of cylinders and a multi-cylinder misfire where the misfire has occurred in two or more cylinders among the plurality of cylinders,
• the calculating includes calculating the misfire parameter based on a relative rotational speed with respect to a rotational speed detected at a compression top dead center of the each of the plurality of cylinders, and
• the determining includes identifying a cylinder during the combustion stroke among the plurality of cylinders defined as a subject cylinder, and determining that the single-cylinder misfire has occurred in the subject cylinder when the misfire parameter is less than a first predetermined value, while determining that the multi-cylinder misfire has occurred in two or more cylinders including the subject cylinder when the misfire parameter is equal to or greater than the first predetermined value and less than a second predetermined value greater than the first predetermined value.

A misfire determination apparatus for an internal combustion engine including a plurality of cylinders and an output shaft, the misfire determination apparatus comprising:

• a rotational speed detector configured to detect a rotational speed of the output shaft;
• and
• an electronic control unit having a microprocessor and a memory connected to the microprocessor, wherein
• the microprocessor is configured to perform:
• calculating a misfire parameter having a correlation with a change amount of the rotational speed in a combustion stroke of each of the plurality of cylinders based on the rotational speed detected by the rotational speed detector, the misfire parameter increasing as an increase amount of the rotational speed is large;
• and
• determining whether a misfire of the internal combustion engine has occurred and a manner of the misfire, based on the misfire parameter, the manner of the misfire includes a single-cylinder misfire where the misfire has occurred in a single cylinder among the plurality of cylinders and a multi-cylinder misfire where the misfire has occurred in two or more cylinders among the plurality of cylinders, and
• the microprocessor is configured to perform
• the determining including identifying a cylinder during the combustion stroke among the plurality of cylinders defined as a subject cylinder, and determining that the single-cylinder misfire has occurred in the subject cylinder when the misfire parameter is less than a first predetermined value, while determining that the multi-cylinder misfire has occurred in two or more cylinders including the subject cylinder when the misfire parameter is equal to or greater than the first predetermined value and less than a second predetermined value greater than the first predetermined value,
• the plurality of cylinders include the subject cylinder and a reference cylinder different from the subject cylinder, and
• the microprocessor is configured to further perform
• the calculating including calculating a first misfire parameter and a second misfire parameter based on the rotational speed detected by the rotational speed detector, and a sum of the first misfire parameter and the second misfire parameter defined as a sum misfire parameter, the first misfire parameter having a correlation with a change amount of the rotational speed in the combustion stroke of the subject cylinder, the second misfire parameter having a correlation with a change amount of the rotational speed in the combustion stroke of the reference cylinder in a range going back from the combustion stroke of the subject cylinder by one cycle of the internal combustion engine, and
• the determining further including determining that the misfire has occurred in the subject cylinder when the first misfire parameter is less than the first predetermined value or when the sum misfire parameter is less than a third predetermined value and the first misfire parameter is less than the second predetermined value, while determining that the misfire has not occurred in the subject cylinder when the first misfire parameter is equal to or greater than the first predetermined value and the sum misfire parameter is equal to or greater than the third predetermined value, even if the first misfire parameter is less than the second predetermined value.