| 摘要 |
PURPOSE:To enhance exhaust emission control by improving each efficiency of rapid heating and catalyst combustion of an exhaust emission purifying catalyst at low temperature operation of an engine. CONSTITUTION:A catalyst unit 6 comprising a catalyst 7 with a heater and a normal catalyst 8 is disposed on an exhaust pipe 5 of an engine 3. Secondary air is introduced upstream of the catalyst unit through an air introducing-in pipe 10 with a control valve 12 in operation at a low temperature. A microcomputer 13 estimates unburnt quantity of the secondary air on the basis of a fuel behavior model and engine condition detecting data, to calculate or data-retrieve a quantity of secondary air suitable for catalyst combustion on the basis of the unburnt quantity. The quantity of secondary air is controlled through the control valve 12. Otherwise, the quantity of secondary air is controlled to be increased or decreased per fine unit in such a manner as to maximize a deviation between a real secondary air-fuel ratio and a target secondary air-fuel ratio, both of which are detected by an air-fuel ratio sensor 11, and a temperature of the catalyst unit 6. Alternatively, the quantity of secondary air is controlled to be increased or decreased according to the opening or closing of the exhaust valve.
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