| 摘要 |
An exhaust purification system is provided that can continuously maintain a NOx purification rate to be high while suppressing the occurrence of ammonia slip. The exhaust purification system includes a slip determination portion 34 that determines the occurrence of ammonia slip based on an output value NH3 CONS of an ammonia sensor 26. A reference injection amount calculating portion 31 calculates a reference injection amount G UREA BS based on a parameter correlating to an operating state of an engine. A switching injection amount calculating portion 32 decreases in amount a urea injection amount G UREA by setting a switching injection amount G UREA SW to a negative value in response to having determined that ammonia slip has occurred, and increases in amount the injection amount G UREA by setting the switching injection amount G UREA SW to a positive value in response to a storage amount estimated value ST UREA having fallen below a predetermined switch storage amount ST UREA SW . |
