| 摘要 |
<p>PURPOSE:To prevent erroneous decision of deterioration owing to blowby phenomenon of a catalyst and to improve precision on discrimination of deterioration by providing a means which is operated to determine a ratio through comparison of the computed degree of oscillation of air-fuel ratio with the reference value of the degree of oscillation of an air-fuel ratio set according to a parameter indicating a running state and change the comparison reference value in an increase direction according to the ratio. CONSTITUTION:A degree of oscillation of air-fuel ratio computing means 107 is provided to compute the degree of oscillation of an air-fuel ratio to rich/lean of the fluctuation of an air-fuel ratio on the upper stream side of a catalyst 100. Further, the degree of oscillation of an air-fuel ratio computed by a degree of oscillation of air-fuel ratio reference value setting means 108 and a degree of oscillation of air-fuel ratio computing means 107 is compared with a reference value set by the degree of oscillation of air-fuel ratio reference value setting means 108 according to a parameter indicating the running sate of an engine to determine a ratio. A computing means 109 is provided to change a comparison reference value for discrimination in an increase direction according to the ratio. This constitution prevents deterioration of a catalyst based on blowby phenomenon of a catalyst.</p> |
