Exhaust gas control apparatus and exhaust gas control method for internal combustion engine

1. An exhaust gas control system for an internal combustion engine including an exhaust gas control apparatus, the exhaust gas control apparatus including an injector and a catalyst, the injector being configured to add urea water to exhaust gas, and the catalyst being configured to adsorb ammonia resulting from the urea water and remove NOx in the exhaust gas by using the adsorbed ammonia, the exhaust gas control system comprising:

an electronic control unit configured to:

(i) set a target adsorption amount for the ammonia adsorbed onto the catalyst;

(ii) control a urea water addition amount by the injector based on the target adsorption amount;

(iii) acquire a temperature of the catalyst;

(iv) when the acquired temperature of the catalyst is equal to or higher than a threshold temperature determined in advance, execute an integration processing that calculates an integrated value of the temperature of the catalyst by summing plural acquisitions of the acquired temperature of the catalyst acquired at a predetermined cycle; and

(v) execute an initialization processing that decreases the amount of the ammonia adsorbed on the catalyst on a condition that the integrated value of the temperature of the catalyst calculated in the integration processing has become equal to or higher than a predetermined value.

2. The exhaust gas control system according to claim 1 , wherein the electronic control unit is configured to

(1) acquire a temperature of the exhaust gas flowing into the catalyst,

(2) acquire a flow rate of the exhaust gas flowing into the catalyst, and

(3) correct the acquired temperature of the exhaust gas to decrease as the acquired flow rate of the exhaust gas decreases, and use the corrected temperature of the exhaust gas to calculate the integrated value of the temperature of the catalyst in the integration processing.

3. The exhaust gas control system according to claim 1 ,

wherein the electronic control unit is configured to execute, as the initialization processing, a temperature-raising processing that raises the exhaust gas temperature of the exhaust gas flowing into the catalyst to a temperature at which the ammonia is desorbed from the catalyst.

4. The exhaust gas control system according to claim 1 ,

wherein the electronic control unit is configured to execute, as the initialization processing, a processing that stops the urea water addition by the injector.

5. The exhaust gas control system according to claim 1 ,

wherein the electronic control unit is configured to measure an execution time of the initialization processing and execute the initialization processing until the measured execution time reaches a threshold determined in advance.

6. An exhaust gas control method for an internal combustion engine including an exhaust gas control apparatus, the exhaust gas control apparatus including an injector and a catalyst, the injector being configured to add urea water to exhaust gas, and the catalyst being configured to adsorb ammonia resulting from the urea water and remove NOx in the exhaust gas by using the adsorbed ammonia, the exhaust gas control method comprising:

(i) setting, by an electronic control unit, a target adsorption amount for the ammonia adsorbed onto the catalyst;

(ii) controlling, by the electronic control unit, a urea water addition amount by the injector based on the target adsorption amount;

(iii) acquiring, by the electronic control unit, a temperature of the catalyst;

(iv) when the acquired temperature of the catalyst is equal to or higher than a threshold temperature determined in advance, executing, by the electronic control unit, an integration processing that calculates an integrated value of the temperature of the catalyst by summing plural acquisitions of the acquired temperature of the catalyst acquired at a predetermined cycle; and

(v) executing, by the electronic control unit, an initialization processing that decreases the amount of the ammonia adsorbed on the catalyst on a condition that the integrated value of the temperature of the catalyst calculated in the integration processing has become equal to or higher than a predetermined value.

7. The exhaust gas control method according to claim 6 , further comprising:

(1) acquiring, by the electronic control unit, a temperature of the exhaust gas flowing into the catalyst,

(2) acquiring, by the electronic control unit, a flow rate of the exhaust gas flowing into the catalyst, and

(3) correcting, by the electronic control unit, the acquired temperature of the exhaust gas to decrease as the acquired flow rate of the exhaust gas decreases, and using the corrected temperature of the exhaust gas to calculate the integrated value of the temperature of the catalyst in the integration processing.

8. The exhaust gas control method according to claim 6 ,

wherein executing the initialization processing includes raising the exhaust gas temperature of the exhaust gas flowing into the catalyst to a temperature at which the ammonia is desorbed from the catalyst.

9. The exhaust gas control method according to claim 6 ,

wherein executing the initialization processing includes stopping the urea water addition by the injector.

10. The exhaust gas control method according to claim 6 , further comprising

measuring, by the electronic control unit, an execution time of the initialization processing and executing the initialization processing until the measured execution time reaches a threshold determined in advance.