| 摘要 |
PROBLEM TO BE SOLVED: To prevent deterioration of the exhaust emission characteristics and the fuel economy by accurately judging the time for starting the NOx discharging control. SOLUTION: A #1O2 sensor 26 for detecting the oxygen concentration in an exhaust emission flowing into the upstream side with respect to an occlusion type NOx catalyst 24 is provided, while a #2O2 sensor 27 for detecting the oxygen concentration in an exhaust emission discharged to the downstream side is provided. An output valueΔD is calculated by subtracting an output value D2 of the #2O2 sensor 27 from the output value D1 of the #1O2 sensor 26. Based on the output differenceΔD, the time for starting discharge of the occluded NOx is judged.
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