| 摘要 |
An electronic control unit 6 estimates the amount of sulfur accumulated in a filter 35 for purifying PM and NOx based on the operating state of an engine. On condition that an estimated value Sx is equal to or greater than a determination value Smax, a first regeneration procedure is executed, in which sulfur is released from the filter 35 by raising the temperature of the filter 35 up to a temperature ± and lowering the exhaust air-fuel ratio is executed. When the number of times N of the execution of the first regeneration procedure after the execution of a second regeneration procedure is a determination number of times A or more, the second regeneration procedure is executed separately from the first regeneration procedure. In the second regeneration procedure, sulfur is completely released from the filter 35 by raising the temperature of the filter 35 up to a temperature ²(> ±) and lowering the exhaust air-fuel ratio. The estimated value Sx is reset upon completion of the second regeneration procedure. Even if deviation between the actual amount of accumulated sulfur and its estimated value increases, the deviation can be corrected and the emission is prevented from deteriorating. |
