| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To wholly restrain the deterioration in emission and drivability, by determining abnormality of an oxygen gas sensor having a catalyst downstream side Z output characteristic, in air-fuel ratio forced setting control for determining the deterioration in a three way catalyst. <P>SOLUTION: The control target air-fuel ratio on the catalyst upstream side is set to the preset lean air-fuel ratio abyfLean or the preset rich air-fuel ratio abyfRich for determining the deterioration in the three way catalyst provided in an exhaust passage. The O2 sensor detects that the air-fuel ratio on the catalyst downstream side is switched to lean or rich by straddling a threshold value from the initial rich or lean air-fuel ratio, and determines the existence of the deterioration in the three way catalyst on the basis of this fact. At this time, a rate of changeΔv/Δt of a detecting value of the oxygen gas sensor is investigated, and when the detecting value of the oxygen gas sensor indicates a stable value without straddling the threshold value, its value is detected, and the air-fuel ratio forced setting control is immediately stopped as failure of the oxygen gas sensor. <P>COPYRIGHT: (C)2006,JPO&NCIPI</p> |
