Patent ID: 7208029

Claim:
An exhaust gas cleaning system comprising: a particulate filter installed in an exhaust passage of an engine to capture particulate matter contained in an exhaust gas discharged from the engine; an NOx trapping catalytic converter disposed upstream of the particulate filter in the exhaust passage to absorb NOx contained in the exhaust gas; a particulate matter discharge amount determining section configured and arranged to determine a discharge amount of the particulate matter from the engine based on an operating condition of the engine; a particulate matter combustion amount determining section configured and arranged to determine a combustion amount of the particulate matter accumulated in the particulate filter that are combusted by the NOx in the exhaust gas; a combustion amount adjusting section configured and arranged to adjust the combustion amount of the particulate matter estimated in the particulate matter combustion amount determining section based on an NOx adsorption condition of the NOx trapping catalytic converter; and a particulate matter accumulation amount estimating section configured and arranged to estimate a particulate matter accumulation amount in the particulate filter by subtracting the combustion amount of the particulate matter adjusted in the combustion amount adjusting section from the discharge amount of the particulate matter.