| 摘要 |
<p>PROBLEM TO BE SOLVED: To permit efficient elimination of SOx absorbed by NOx purification means, by controlling so as to vary the air-fuel ratio of the mixture between a lean side and a rich side in detecting degradation of the NOx purification means, and keeping the air-fuel ratio on the rich side when the temperature of the NOx purification means becomes higher than a regeneration temperature. SOLUTION: A NOx purification device 16 is interposed in an exhaust pipe 12 of an engine 1. The device occludes NOx in an exhaust gas lean state where the air-fuel ratio of the mixture is set on a leaner side than the stoichiometric air-fuel ratio and the concentration of oxygen in exhaust gas is relatively high (high NOx ratio), and emits occluded NOx in an exhaust gas rich state where the air-fuel ratio of mixture is set at a rich side and the concentration of oxygen in exhaust gas is relatively low. When degradation of a NOx absorbing agent is detected, the air-fuel ratio of the mixture is varied between the lean side and the rich side at a predetermined period. When the temperature of the NOx purification device 16 becomes higher than a regeneration temperature, the air-fuel ratio is kept on the rich side.</p> |
