A method and a device for purifying exhaust gas of an internal combustion engine

摘要

A device for purifying exhaust gas includes an HC adsorbent (5) and an exhaust gas purifying catalyst (7) disposed in an exhaust gas passage (3) in this order from the upstream side. The exhaust gas purifying catalyst (7) is provided with an O2 storage capability, i.e., the exhaust gas purifying catalyst is capable of absorbing oxygen in the exhaust gas when the air-fuel ratio of the exhaust gas is lean, and is capable of releasing the absorbed oxygen when the air-fuel ratio of the exhaust gas becomes rich. When the engine starts, the HC adsorbent (5) adsorbs HC in the exhaust gas. When the temperature of the exhaust gas becomes high, the HC adsorbent (5) releases the adsorbed HC. The device also includes an engine control unit (30) which operates the engine at a lean air-fuel ratio during a predetermined period before the releasing of the HC from the HC adsorbent (5) occurs. Therefore, oxygen is absorbed and stored in the exhaust gas purifying catalyst (7) before the releasing of HC occurs. When the releasing of HC from the HC adsorbent (5) occurs, the air-fuel ratio of the exhaust gas flowing into the exhaust gas purifying catalyst (7) becomes rich due to the HC released from the HC adsorbent (5). This causes the exhaust gas purifying catalyst (7) to release the absorbed oxygen, and the HC in the exhaust gas is purified by the exhaust gas purifying catalyst (7) using the released oxygen.