ABNORMALITY DETECTION APPARATUS FOR EXHAUST GAS PURIFICATION APPARATUS

摘要

An object of the present invention is to detect an abnormality in an exhaust gas purification apparatus having an NSR catalyst and an SCR catalyst disposed on a downstream side of the NSR catalyst more favorably. Air-fuel ratio reduction control is executed to reduce NOx occluded to the NSR catalyst when an integrated value of an amount of NOx flowing into the NSR catalyst reaches an upper limit value of an amount of NOx that can be occluded to the NSR catalyst in a normal condition. It is determined whether or not the exhaust gas purification apparatus is in an abnormal state on the basis of a NOx purification ratio of the exhaust gas purification apparatus calculated at this time.

主权项

1. An abnormality detection apparatus for an exhaust gas purification apparatus provided in an exhaust passage of an internal combustion engine,
the exhaust gas purification apparatus including an NOx storage reduction catalyst and an NOx selective reduction catalyst, the NOx selective reduction catalyst reducing NOx using NH3 as a reducing agent, and being disposed on a downstream side of the NOx storage reduction catalyst, the abnormality detection apparatus comprising: an air-fuel ratio control unit that executes air-fuel ratio reduction control to reduce an air-fuel ratio of exhaust gas flowing into the NOx storage reduction catalyst temporarily to an extent at which a peripheral atmosphere of the NOx storage reduction catalyst becomes a reducing atmosphere; a NOx inflow amount acquisition unit that acquires a NOx inflow amount, which is an amount of NOx flowing into the NOx storage reduction catalyst; and a NOx outflow amount acquisition unit that acquires a NOx outflow amount, which is an amount of NOx flowing out of the NOx selective reduction catalyst; and a determination unit that determines, when the air-fuel ratio reduction control is executed again by the air-fuel ratio control unit when the integrated value of the NOx inflow amount following completion of a latest air-fuel ratio reduction control reaches a predetermined threshold, whether or not the exhaust gas purification apparatus is in an abnormal condition on the basis of a NOx purification ratio of the exhaust gas purification apparatus, which is calculated from an integrated value of the NOx inflow amount and an integrated value of the NOx outflow amount over a period extending from a completion point of the latest air-fuel ratio reduction control executed by the air-fuel ratio control unit to completion of the air-fuel ratio reduction control that is executed again by the air-fuel ratio control unit, wherein the threshold is set at an upper limit value of an amount of NOx that can be occluded to the NOx storage reduction catalyst in a normal condition.