Importance

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Abstract

In an exhaust gas purification device, an exhaust gas passage of a diesel engine diverges into two branch pipes and a particulate filter (DPF) is disposed in each of the branch pipes. The DPF uses a metallic substrate and NO.sub.x absorbent is attached to the wall of the paths in the DPF. Therefore, the DPF act as both a normal particulate filter and a NO.sub.x absorbent. During the operation of the engine, SO.sub.x, as well as NO.sub.x, in the exhaust gas is absorbed in the NO.sub.x absorbent in the DPF. An electronic control unit (ECU) monitors the amount of SO.sub.x absorbed in the DPF during the operation and, when the amount of SO.sub.x absorbed in one DPF increases, switches the exhaust gas flow to the other DPF. The ECU further performs the SO.sub.x recovery operation to release the absorbed SO.sub.x from the DPF. After completing the SO.sub.x recovery operation, the ECU performs the regenerating operation of the DPF in which the particulate matter trapped in the DPF is burned. Since SO.sub.x in DPF is already released by the previous SO.sub.x recovery operation when the regenerating operation of the DPF is performed, the growth of sulfate particle in the DPF does not occur even if the DPF is exposed to a high temperature lean air-fuel ratio atmosphere of the regenerating operation.

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First Claim