| 摘要 |
<P>PROBLEM TO BE SOLVED: To accurately acquire degree of deterioration of a catalyst even if sensor response varies in a device changing over air fuel ratio of gas in an upstream of the catalyst to lean or rich, and acquiring degree of deterioration of the catalyst based on timing of changeover of output of an air fuel ratio sensor in the downstream of the catalyst to a value indicating lean or rich. <P>SOLUTION: This device calculates a reduction gradient of the maximum oxygen storage quantity Cmax with respect to increase of air flow rate Ga based on two maximum oxygen storage quantities Cmax and two air flow rates Ga estimated respectively when air flow rates Ga are two different values. The reduction gradient is larger as degree of deterioration of a catalyst 53 is larger. When degrees of deterioration of the catalyst 53 are same, the reduction gradients tend to be same even if degree of responses of change in output of downstream side air fuel ratio sensors 67 vary. Consequently, the calculated reduction gradient can be a value accurately indicating degree of deterioration of the catalyst 53. <P>COPYRIGHT: (C)2009,JPO&INPIT |
