Misfire determination device and misfire determination method for internal combustion engine

A misfire determination device for an internal combustion engine that is coupled to a transmission via a hydraulic power transmission equipped with a lock-up clutch, wherein the misfire determination device determines that there is a possibility that a misfire has occurred when a rotation fluctuation amount of the internal combustion engine exceeds a predetermined threshold, and makes a misfire determination by determining whether a rotation fluctuation pattern of the internal combustion engine is a pattern specific to occurrence of a misfire, the misfire determination device comprising:

• a first misfire determination unit that calculates a rotation fluctuation amount from a difference between an engine rotational speed in an expansion stroke of a misfire determination target cylinder for which it is determined that there is a possibility that the misfire has occurred and an engine rotational speed in an expansion stroke of another cylinder, and then makes a first misfire determination in which occurrence of a misfire is determined on the basis of whether a variation pattern of the rotation fluctuation amount substantially coincides with a predetermined misfire determination pattern;
• an engine rotational speed determination unit that, when it is not determined that a misfire has occurred in the first misfire determination made by the first misfire determination unit, makes an engine rotational speed determination in which it is determined whether an engine rotational speed in the expansion stroke of the misfire determination target cylinder when the lock-up clutch is in the lock-up state is lower than a predetermined threshold;
• and
• a second misfire determination unit that, when it is determined in the engine rotational speed determination made by the engine rotational speed determination unit that the engine rotational speed in the expansion stroke of the misfire determination target cylinder is lower than the predetermined threshold, makes a second misfire determination in which it is determined whether a misfire has occurred on the basis of the difference between the engine rotational speed in the expansion stroke of the misfire determination target cylinder and the engine rotational speed in the expansion stroke of the another cylinder.

A misfire determination method for an internal combustion engine that is coupled to a transmission via a hydraulic power transmission equipped with a lock-up clutch, wherein the misfire determination method determines that there is a possibility that a misfire has occurred when a rotation fluctuation amount of the internal combustion engine exceeds a predetermined threshold, and makes a misfire determination by determining whether a rotation fluctuation pattern of the internal combustion engine is a pattern specific to occurrence of a misfire, the misfire determination method comprising:

• calculating a rotation fluctuation amount from a difference between an engine rotational speed in an expansion stroke of a misfire determination target cylinder for which it is determined that there is a possibility that the misfire has occurred and an engine rotational speed in an expansion stroke of another cylinder, and then making a first misfire determination in which occurrence of a misfire is determined on the basis of whether a variation pattern of the rotation fluctuation amount substantially coincides with a predetermined misfire determination pattern;
• when it is not determined that a misfire has occurred in the first misfire determination, making an engine rotational speed determination in which it is determined whether an engine rotational speed in the expansion stroke of the misfire determination target cylinder when the lock-up clutch is in the lock-up state is lower than a predetermined threshold;
• and
• when it is determined in the engine rotational speed determination that the engine rotational speed in the expansion stroke of the misfire determination target cylinder is lower than the predetermined threshold, making a second misfire determination in which it is determined whether a misfire has occurred on the basis of the difference between the engine rotational speed in the expansion stroke of the misfire determination target cylinder and the engine rotational speed in the expansion stroke of the another cylinder.