Electronic control unit for controlling air fuel ratio to reduce NOx occluded in NOx catalyst

The invention provides an electronic control unit for controlling an air/fuel ratio of an engine having a lean NOx catalyst in its exhaust system in order to improve the cleaning of exhaust gas during rich process to reduce lean NOx catalyst. The electronic control unit comprises: an estimator for e...

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Bibliographic Details
Main Authors Wakui, Masayuki, Shimaoka, Minoru, Inagawa, Wataru
Format Patent
LanguageEnglish
Published 16.05.2002
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Summary:The invention provides an electronic control unit for controlling an air/fuel ratio of an engine having a lean NOx catalyst in its exhaust system in order to improve the cleaning of exhaust gas during rich process to reduce lean NOx catalyst. The electronic control unit comprises: an estimator for estimating NOx amount occluded in the lean NOx catalyst; means for performing shift-to-rich process responsive to the NOx amount estimated by said estimator exceeding a predetermined value; a calculator for calculating an accumulated value of an exhaust flow amount; and means for completing the shift-to-rich process responsive to the accumulated value of the exhaust flow amount exceeding a threshold value. Completing the shift-to-rich process using the accumulated value of the exhaust flow amount, which is correlated with the amount of the reducing agent (HC, CO), enables the NOx occluded in the lean NOx catalyst to be precisely reduced, and the exhaust gas is cleaned at higher level.