Exhaust system for an internal combustion engine

An exhaust system for an internal combustion engine comprising:

• two or more main exhaust paths connected to respective two or more cylinders;
• an exhaust recirculation path for recirculating part of exhaust gas to an inlet system, the exhaust recirculation path has two or more separate exhaust recirculation paths being connected to the respective two or more main exhaust paths and a merged exhaust recirculation path into which the two or more separate recirculation paths are merged, the merged exhaust recirculation path is connected to the inlet system;
• a bypass branching out from the exhaust recirculation path and rejoining the main exhaust path to release the exhaust gas to outside, the bypass having a cross sectional path area that is smaller than that of the exhaust recirculation path;
• and
• a bypass catalytic converter provided in the bypass.

An exhaust system for an internal combustion engine, comprising:

• a first means for introducing exhaust gas into a main exhaust path that is connected to a cylinder of an internal combustion engine at an upstream end thereof and that has a main catalytic converter therein;
• a second means for introducing the exhaust gas into an exhaust recirculation path that branches out from the main exhaust path at a branching point that is located upstream of the main catalytic converter and that has a cross sectional path area smaller than that of the main exhaust path,
• a third means for introducing the exhaust gas to a bypass, that branches out from the exhaust recirculation path at the bypass branching point, that has a cross-sectional path area smaller than that of the exhaust recirculation path, and that has a bypass catalytic converter therein, wherein the bypass joins the main exhaust path at a bypass joining point between the branching point of the exhaust recirculation path and the main catalytic converter;
• a fourth means for blocking the main exhaust path between the branching point of the exhaust recirculation path and the bypass joining point;
• a fifth means for blocking the exhaust recirculation path that is downstream of the bypass branching point;
• and
• a sixth means for releasing the blocking of the main exhaust path between the branching point and the bypass joining point after the engine is warmed up.

A method for purifying exhaust gas, comprising the following steps of:

• introducing the exhaust gas into a main exhaust path that is connected to the cylinder of an internal combustion engine at an upstream end thereof and that has a main catalytic converter therein;
• introducing the exhaust gas into an exhaust recirculation path that branches out from the main exhaust path at a branching point that is located upstream of the main catalytic converter and that has a cross sectional path area smaller than that of the main exhaust path;
• introducing the exhaust gas to a bypass, that branches out from the exhaust recirculation path at the bypass branching point, that has a cross-sectional path area smaller than that of the exhaust recirculation path, and that has a bypass catalytic converter therein, wherein the bypass joins the main exhaust path at a bypass joining point between the branching point 6 of the exhaust recirculation path and the main catalytic converter;
• blocking the main exhaust path between the branching point of the exhaust recirculation path and the bypass joining point;
• blocking the exhaust recirculation path that is downstream of the bypass branching point;
• and
• releasing the blocking of the main exhaust path between branching point and the bypass joining point after the engine is warmed up.