Abstract: 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 NH3CONS of an ammonia sensor 26. A reference injection amount calculating portion 31 calculates a reference injection amount GUREA—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 GUREA by setting a switching injection amount GUREA—SW to a negative value in response to having determined that ammonia slip has occurred, and increases in amount the injection amount GUREA by setting the switching injection amount GUREA—SW to a positive value in response to a storage amount estimated value STUREA having fallen below a predetermined switch storage amount STUREA—SW.

Abstract: A gas sensor controller 190 stops an operation of pumping in or out oxygen that is being performed by a first pump cell 111 in a state that the oxygen concentration (oxygen partial pressure) of a gas to be measured is equal to a status judgment reference value (20%). The gas sensor controller 190 calculates an oxygen pressure in a second measurement chamber 161 on the basis of a second pump current Ip2. If the oxygen pressure in the second measurement chamber 161 is equal to a deterioration judgment reference value, the gas sensor controller 190 judges that the second pump cell 113 is in a normal state. If the oxygen pressure in the second measurement chamber 161 is different from the deterioration judgment reference value, the gas sensor controller 190 judges that the second pump cell 113 is in a deteriorated state.

Abstract: In a sensor diagnosis process, a controller for controlling an NOx gas sensor performs processing of changing the oxygen partial pressure in a second measurement chamber by changing the oxygen partial pressure in a first measurement chamber (S190), processing of detecting a current flowing through a second pump cell before the change of the oxygen partial pressure (S180), and processing of detecting a current flowing through the second pump cell after the change of the oxygen partial pressure (S230). Furthermore, the controller performs processing of judging whether or not the ratio between the current values detected by the respective current detecting unit falls within an allowable range, judging that the second pump cell 113 is in a normal state if the ratio between the current values falls within the allowable range, and judging that the second pump cell 113 is in a deteriorated state if the ratio between the current values is out of the allowable range (S240 and S250).

Abstract: 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 NH3CONS of an ammonia sensor 26. A reference injection amount calculating portion 31 calculates a reference injection amount GUREA—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 GUREA by setting a switching injection amount GUREA—SW to a negative value in response to having determined that ammonia slip has occurred, and increases in amount the injection amount GUREA by setting the switching injection amount GUREA—SW to a positive value in response to a storage amount estimated value STUREA having fallen below a predetermined switch storage amount STUREA—SW.

Abstract: A gas sensor controller 190 stops an operation of pumping in or out oxygen that is being performed by a first pump cell 111 in a state that the oxygen concentration (oxygen partial pressure) of a gas to be measured is equal to a status judgment reference value (20%). The gas sensor controller 190 calculates an oxygen pressure in a second measurement chamber 161 on the basis of a second pump current Ip2. If the oxygen pressure in the second measurement chamber 161 is equal to a deterioration judgment reference value, the gas sensor controller 190 judges that the second pump cell 113 is in a normal state. If the oxygen pressure in the second measurement chamber 161 is different from the deterioration judgment reference value, the gas sensor controller 190 judges that the second pump cell 113 is in a deteriorated state.

Abstract: In a sensor diagnosis process, a controller for controlling an NOx gas sensor performs processing of changing the oxygen partial pressure in a second measurement chamber by changing the oxygen partial pressure in a first measurement chamber (S190), processing of detecting a current flowing through a second pump cell before the change of the oxygen partial pressure (S180), and processing of detecting a current flowing through the second pump cell after the change of the oxygen partial pressure (S230). Furthermore, the controller performs processing of judging whether or not the ratio between the current values detected by the respective current detecting unit falls within an allowable range, judging that the second pump cell 113 is in a normal state if the ratio between the current values falls within the allowable range, and judging that the second pump cell 113 is in a deteriorated state if the ratio between the current values is out of the allowable range (S240 and S250).