| 摘要 |
PROBLEM TO BE SOLVED: To prevent NOX from being emitted to the atmosphere and make unnecessary that air-fuel mixture is made rich forcibly in emitting the absorbed NOX. SOLUTION: An air-fuel ratio is detected by a lean sensor 30. When the continuation time of lean condition is less than a specified time α only a first valve 21 is opened to make exhaust gas flow into an NOX absorption and decomposition agent 18 only by which it is absorbed, while the continuation time of lean condition is more than the specified time α second valve 22 and a third valve 23 are opened to make exhaust gas flow into an NOX absorbing agent 27 too. When the continuation time of stoichiometric or lean condition is less than a specified time β only the first valve 21 is opened to make exhaust gas flow into the agent 18 only, while the continuation time thereof is more than the specified time β the first and second valves 21, 22 and fourth and fifth valves 24, 25 are opened and a pump 32 is driven to make exhaust gas flow into toward the agent 18 from the agent 27. |
