Patent ID: 7596993
Filing Date: 2009-10-06
Classification: F02D,G01N

Abstract:
1. A gas sensor diagnostic method for diagnosing whether a gas sensor is in an abnormal state or not on the basis of a detection signal outputted by the gas sensor exposed in an exhaust gas exhausted from an internal combustion engine, the detection signal representing a concentration of a specific gas component in the exhaust gas, the gas sensor diagnostic method comprising: a target air-fuel-ratio reversal number counting step of counting the reversal number of times that a target air-fuel ratio for an air-fuel mixture to be supplied to the internal combustion engine reverses from a rich side to a lean side or from the lean side to the rich side through a specific air-fuel ratio defined as a boundary of the rich and lean sides; a detection signal obtaining step of obtaining the detection signal of the gas sensor at constant time intervals during a diagnosis period which is a period between a timing when the reversal number of times starts to be counted and a timing when the reversal number of times reaches a predetermined number of times; a moderated signal calculating step of calculating a deviation calculating step of calculating a deviation between the calculated first moderated signal and second moderated signal; and an abnormality diagnosing step of determining whether the gas sensor is in the abnormal state or not on the basis of the deviation obtained during the diagnosis period.