INTER-CYLINDER AIR-FUEL RATIO VARIATION ABNORMALITY DETECTION APPARATUS

摘要

An apparatus according to the present invention includes a control apparatus to detect an inter-cylinder air-fuel ratio variation abnormality based on an output fluctuation parameter correlated with a degree of variation in output from an air-fuel ratio sensor. The control apparatus is configured to calculate a positive slope value and a negative slope value when the output from the air-fuel ratio sensor changes to lean side and to a rich side; calculate a determination index value by dividing a difference or a ratio between the positive slope value and the negative slope value by an amplitude index value correlated with a magnitude of a maximum amplitude of the output waveform from the air-fuel ratio sensor; and determine whether a deviation of the air-fuel ratio in one cylinder is a lean-side deviation or a rich-side deviation, based on the determination index value.

主权项

1. An inter-cylinder air-fuel ratio variation abnormality detection apparatus comprising:
an air-fuel ratio sensor installed in an exhaust passage common to a plurality of cylinders in a multicylinder internal combustion engine; and a control apparatus configured to calculate an output fluctuation parameter correlated with a degree of variation in output from the air-fuel ratio sensor and to detect an inter-cylinder air-fuel ratio variation abnormality based on the calculated output fluctuation parameter, wherein the control apparatus is configured to execute: (a) a step of calculating, for an output waveform from the air-fuel ratio sensor during at least one cycle of the internal combustion engine, a positive slope value indicative of a magnitude of a slope of the output from the air-fuel ratio sensor obtained when the output from the air-fuel ratio sensor changes to a lean side and a negative slope value indicative of the magnitude of the slope obtained when the output from the air-fuel ratio sensor changes to a rich side; (b) a step of calculating a determination index value by dividing a difference or a ratio between the positive slope value and the negative slope value by an amplitude index value correlated with a magnitude of a maximum amplitude of the output waveform from the air-fuel ratio sensor; and (c) a step of determining whether a deviation of the air-fuel ratio in one cylinder with a most significant deviation of the air-fuel ratio is a lean-side deviation or a rich-side deviation, based on the determination index value.