Exhaust purification system and catalyst regeneration method

An exhaust purification system comprising:

• an NOx occlusion reduction catalyst that is disposed in an exhaust passage of an internal combustion engine to occlude and reduce a nitrogen compound contained in an exhaust gas discharged from the internal combustion engine;
• an aft flow sensor that detects an actual intake air amount of the internal combustion engine;
• and
• a controller that controls an air-fuel ratio of the exhaust gas discharged from the internal combustion engine, wherein the controller operates to execute a series of processes comprising:
• a catalyst regeneration process which performs an SOx purge control for recovering the NOx occlusion reduction catalyst from SOx-poisoning, using in combination both of:
• an air system control in which a target intake air amount, necessary for lowering the exhaust gas to a predetermined first target excess air ratio is set based on an operating state of the internal combustion engine and an intake aft amount of the internal combustion engine is feedback-controlled based on the target intake air amount;
• and an injection system control in which a target injection increase amount, necessary for lowering the exhaust gas to a predetermined second target excess air ratio is set based on the target intake aft amount and a fuel injection amount is feedback-controlled based on the target injection increase amount;
• a prohibition process that prohibits execution of the SOx purge control according to the operating state of the internal combustion engine;
• and
• a catalyst warming process that executes, during a period in which the SOx purge control is prohibited by the prohibition process, a catalyst warming control in which an air system of the internal combustion engine is open-loop controlled, the fuel injection amount is controlled, and thus the exhaust gas is maintained at a predetermined temperature, and
• wherein, when the catalyst regeneration process is executed after execution of the catalyst warming process has ended, the controller executes the injection system control by switching the target intake air amount, used for setting the target injection increase amount, to the actual intake air amount detected by the air flow sensor.

A catalyst regeneration method in an exhaust purification system including an NOx occlusion reduction catalyst that is disposed in an exhaust passage of an internal combustion engine to occlude and reduce a nitrogen compound contained in an exhaust gas discharged from the internal combustion engine, the method comprising:

• a catalyst regeneration process which performs an SOx purge control for recovering the NOx occlusion reduction catalyst from SOx-poisoning, using in combination both of:
• an air system control in which a target intake aft amount, necessary for lowering the exhaust gas to a predetermined first target excess aft ratio is set based on an operating state of the internal combustion engine and an intake air amount of the internal combustion engine is feedback-controlled based on the target intake aft amount;
• and an injection system control in which a target injection increase amount, necessary for lowering the exhaust gas to a predetermined second target excess air ratio is set based on the target intake air amount and a fuel injection amount is feedback-controlled based on the target injection increase amount;
• a prohibition process that prohibits execution of the SOx purge control according to the operating state of the internal combustion engine;
• and
• a catalyst warming process that executes, during a period in which the SOx purge control is prohibited by the prohibition process, a catalyst warming control in which an aft system of the internal combustion engine is open-loop controlled, the fuel injection amount is controlled, and thus the exhaust gas is maintained at a predetermined temperature,
• wherein, when the catalyst regeneration process is executed after execution of the catalyst warming process has ended, the injection system control is executed by switching the target intake aft amount, used for setting the target injection increase amount, to the actual intake air amount detected by an air flow sensor.