| 摘要 |
PROBLEM TO BE SOLVED: To promptly converge the air fuel-ratio in the downstream of the catalyst on the target air fuel-ratio with almost no influence of disturbance when carrying out air fuel-ratio feedback control on the basis of air fuel-ratio information detected by an air fuel-ratio sensor arranged in the front and rear of the catalyst. SOLUTION: On the basis of air flow rate G, a catalyst boundary point setting part 22 sets a boundary point by which the inside of a catalyst 8 is virtually separated into two areas of the upper reaches where purification efficacy can be fully utilized and of the lower reaches where unpurified components unable to be cleaned at the upper reaches are cleaned. An air fuel-ratio distribution estimation part 23 estimates the air flow-ratio distribution within the catalyst 8 by the linear interpolation computing on the basis of the air fuel-ratios FA/F and RA/F detected by air fuel-ratio sensors 10 and 11 arranged in the front and rear of the catalyst 8. A boundary point actual air flow-ratio setting part 24 calculates the boundary point actual air floe-ratioαat the boundary point Pb on the basis of the air flow-ration distribution in the estimated catalyst 8. A fuel injection setting part 25 sets the fuel correction quantityλfor correcting the fuel injection quantity on the basis of the boundary point actual air flow-ratio deviationΔαacquired from a difference between the target air flow-ratioαo set on the basis of an engine operating state and the boundary point actual air flow-ratioα.
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