US 5,974,791 AGranted

Exhaust gas purification device for an internal combustion engine

AssigneeToyota Jidosha Kabushiki Kaisha

InventorsShinya Hirota, Toshiaki Tanaka

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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.

Claims6

Dependent claims

An exhaust gas purification device for an engine comprising:

a NO.sub.x absorbent disposed in an exhaust gas passage of an internal combustion engine, wherein said NO.sub.x absorbent absorbs NO.sub.x in the exhaust gas of the engine when the air-fuel ratio of the exhaust gas is at a lean air-fuel ratio and releases the absorbed NO.sub.x when the oxygen concentration in the exhaust gas is lowered, and wherein said NO.sub.x absorbent absorbs SO.sub.x in the exhaust gas when the air-fuel ratio of the exhaust gas is at a lean air-fuel ratio and releases the absorbed SO.sub.x when the oxygen concentration in the exhaust gas is lowered and when the temperature of the NO.sub.x absorbent is higher than a SO.sub.x releasing temperature;
SO.sub.x releasing means for raising the temperature of the NO.sub.x absorbent to a temperature higher than the SO.sub.x releasing temperature and for lowering the oxygen concentration of the exhaust gas flowing into the NO.sub.x absorbent to, thereby, release the absorbed SO.sub.x from the NO.sub.x absorbent;
and
SO.sub.x control means for controlling the amount of SO.sub.x absorbed in the NO.sub.x absorbent by controlling the SO.sub.x releasing means in such a manner that, when it is expected that the temperature of the NO.sub.x absorbent increases to a first predetermined temperature when the air-fuel ratio of the exhaust gas is lean, substantially all of the absorbed SO.sub.x is released from the NO.sub.x absorbent by the SO.sub.x releasing means before the temperature of the NO.sub.x absorbent reaches said first predetermined temp.

1 more element

Dependencies are inferred from the claim text.