| 摘要 |
PURPOSE: To increase exhaust performance by providing a specified limit to the switching of air fuel ratio due to relationship with NOx adsorption capacity, etc., of an NOx adsorptive three way catalyst. CONSTITUTION: During lean operation (S16), a cumulative NOx adsorption amountΣCNO is calculated based on a sucked air flow Q (S13). During stoic operation (S22), a cumulative NOx treatment amountΣPNO is calculated based on a sucked air flow Q (S20). When stoic is switched over to lean, the cumulative NOx treatment amountΣPNO is compared with a slice level SL=C0×ΣCNO (S14) corresponding to the cumulative NOx adsorption amountΣCNO in the previous lean operation and, whenΣPNO<SL, switching to lean is prohibited (S10).
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