| 摘要 |
PROBLEM TO BE SOLVED: To efficiently remove hydro carbon when an engine is started by disposing a hydro carbon absorbing catalyst which liberates absorbed hydro carbon when it reaches a desorption temperature, and introducing secondary air for a definite period of time when exhaust temperature at the inlet port of the catalyst is equal to or more than a definite temperature. SOLUTION: A hydro carbon absorbing catalyst 16 is disposed in the exhaust system of an engine 14, exhaust temperature at its inlet port and the water temperature of an engine are measured, and let a control unit 10 execute secondary air control and lean control 12 on an air-fuel ratio for the engine. The absorbed quantity of hydro carbon is estimated based on the period of time consumed by the catalyst until its temperature is raised up to a temperature equal to or more than a temperature where the hydro carbon absorbing catalyst 16 starts absorbing hydro carbon, and furthermore, the period of time for introducing secondary air or the period of time for placing an air-fuel ratio under lean control, is thereby obtained. By this constitution, the greater quantity of absorbed hydro carbon by the hydro carbon absorbing catalyst 16 is much more subject to the longer period of time for introducing secondary air or the longer period of time for placing an air-fuel ration under lean control, and thereby hydro carbon liberated out of the hydro carbon absorbing catalyst 16 is positively purified. |
