| 摘要 |
PROBLEM TO BE SOLVED: To remove a positioning substance of a catalyst accumulated in the lapse of time from the catalyst by making exhaust gas exhausted from an internal combus tion engine in a logical air-fuel ratio or rich fuel state and holding exhaust gas tempera ture at higher than specified for longer than a specified period of time. SOLUTION: An ECU 25 decides an operating air fuel ratio by evaluating an operating state and a state of a NOx adsorptive catalyst 18 and sets fuel concentration at a specified value by controlling injection time of an injector 5, etc. Air-fuel mixture is ignited and burnt by an ignition plug 6, and combustion exhaust gas is led to an exhaust gas purifying system provided with the NOx adsorptive catalyst 18. At the time of stoichiometrical driving, NOx, NH, CO in exhaust gas is purified by its catalytic converter rhodium function, and at the time of lean driving, NOx is purified by a NOx adsorptive function and HC, CO is purified by a combustion function. Additionally, NOx purifying capacity of the NOx adsorptive catalyst 18 is constantly judged at the time of lean driving by judgement and a control signal of the ECU 25, and the NOx adsorptive capacity is recovered by shifting an air-fuel ratio of combustion, etc., to the rich side and holding exhaust gas temperature higher than specified and for longer than specified time. |
