| 摘要 |
<p>PROBLEM TO BE SOLVED: To prevent or suppress erroneous determination of deterioration of a purifying catalyst under an abnormal state fuel vapor is excessively supplied from a purging system. SOLUTION: A control valve 24 whose maximum opening is large is connected between a canistor 22 arranged on a purging passage 21 and a fuel tank 7. An atmospheric release valve 28 is connected to an atmospheric release passage of the canistor 22. Oxygen sensors 52, 54 are arranged on upstream and downstream sides of an exhaust gas purifying catalyst 53. Air-fuel ratio feedback control is performed based on an output of the oxygen sensor 52. Deterioration of the purifying catalyst 53 is determined based on output relation between the oxygen sensors 52 and 54. When the control valve 24 is fixed to be opened is detected or the atmospheric release valve 28 is fixed to be closed is detected, deterioration determination of the catalyst 53 is prohibited, or determination threshold value is varied so as to suppress deterioration determination.</p> |
