Control apparatus for exhaust gas purification apparatus

Abstract

When the NSR temperature Tnsr is in a warming-up temperature range equal to or higher than the activation start temperature of the NSR catalyst and lower than the activation completion temperature of the NSR catalyst, a control apparatus according to the present invention controls the quantity of fuel supplied to the NSR catalyst by a fuel supply device such that the air-fuel ratio of the exhaust gas flowing into the NSR catalyst while the rich spike process is performed is lower when the NSR temperature Tnsr is lower than a specific temperature Tthr than when the NSR temperature Tnsr is equal to or higher than the specific temperature Tthr.

1 . A control apparatus applied to an exhaust gas purification apparatus which is equipped with an NOx storage reduction catalyst disposed in an exhaust passage of an internal combustion engine, and a fuel supply device that supplies fuel to exhaust gas flowing into the NOx storage reduction catalyst,
 the control apparatus comprising:   a controller comprising at least one processor configured to:   obtain an NSR temperature defined as the temperature of the NOx storage reduction catalyst;   obtain an NOx storage amount defined as the amount of NOx stored in the NOx storage reduction catalyst; and   perform a rich spike process, which is the process of reducing and removing NOx stored in the NOx storage reduction catalyst by supplying fuel through the fuel supply device so as to adjust the air-fuel ratio of exhaust gas flowing into the NOx storage reduction catalyst to a rich air-fuel ratio lower than the theoretical air-fuel ratio when the NOx storage amount is equal to or larger than a predetermined threshold in circumstances in which the NSR temperature is equal to or higher than the activation start temperature of the NOx storage reduction catalyst, wherein   when the NSR temperature is in a warming-up temperature range equal to or higher than the activation start temperature of the NOx storage reduction catalyst and lower than the activation completion temperature of the NOx storage reduction catalyst, the controller controls the quantity of fuel supplied through the fuel supply device such that the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst while the rich spike process is performed is lower when the NSR temperature is lower than a specific temperature than when the NSR temperature is equal to or higher than the specific temperature.   
     
     
         2 . A control apparatus for an exhaust gas purification apparatus according to  claim 1 , wherein
 the exhaust gas purification apparatus further comprises a selective catalytic reduction catalyst disposed in the exhaust passage downstream of the NOx storage reduction catalyst,   the controller is further configured to obtain an SCR temperature defined as the temperature of the selective catalytic reduction catalyst, wherein   when the SCR temperature is lower than the activation start temperature of the selective catalytic reduction catalyst, the controller does not perform the rich spike process even if the NSR temperature is in the warming-up temperature range and the NOx storage amount is equal to or larger than the threshold.   
     
     
         3 . A control apparatus for an exhaust gas purification apparatus according to  claim 2 , wherein
 when the NSR temperature is in the warming-up temperature range, if the SCR temperature at the time when the NOx storage amount becomes equal to or larger than the predetermined threshold is lower than the activation start temperature of the selective catalytic reduction catalyst, the controller performs the rich spike process after performing a heating-up process for raising the temperature of the selective catalytic reduction catalyst until the SCR temperature reaches or exceeds the activation start temperature of the selective catalytic reduction catalyst.   
     
     
         4 . A control apparatus for an exhaust gas purification apparatus according to  claim 1 , wherein
 the exhaust gas purification apparatus further comprises a selective catalytic reduction catalyst disposed in the exhaust passage downstream of the NOx storage reduction catalyst and an additive supply device that supplied an additive, which is ammonia or a precursor of ammonia, to the selective catalytic reduction catalyst,   the controller is further configured to:   obtain an SCR temperature defined as the temperature of the selective catalytic reduction catalyst, and   obtain an NH 3  adsorption amount defined as the amount of ammonia adsorbed in the selective catalytic reduction catalyst, wherein   when the NSR temperature is equal to or higher than the activation start temperature of the NOx storage reduction catalyst and the SCR temperature is equal to or higher than the activation start temperature of the selective catalytic reduction catalyst, if the NH 3  adsorption amount at the time when the NOx storage amount becomes equal to or larger than the predetermined threshold is smaller than a predetermined amount, the controller performs an NH 3  supply process to supply the additive by the additive supply device so as to make the NH 3  adsorption amount in the selective catalytic reduction catalyst equal to or larger than the predetermined amount and performs the rich spike process after completion of the NH 3  supply process.   
     
     
         5 . A control apparatus for an exhaust gas purification apparatus according to  claim 4 , wherein
 the controller is further configured to calculate a slipping NOx quantity defined as the quantity of NOx which flows into and slips through the NOx storage reduction catalyst per unit time, wherein   when the SCR temperature is equal to or higher than an adsorption limit temperature at which the amount of ammonia that the selective catalytic reduction catalyst can adsorb is smaller than the predetermined amount, the controller performs an equivalence ratio control to control the additive supply device such that a quantity of additive of which the equivalence ratio of the quantity of ammonia to the slipping NOx quantity is equal to a predetermined ratio is supplied to the selective catalytic reduction catalyst while the rich spike process is not performed and a quantity of additive of which the equivalence ratio of the quantity of ammonia to the slipping NOx quantity is larger than the predetermined ratio is supplied to the selective catalytic reduction catalyst while the rich spike process is performed.   
     
     
         6 . A control apparatus for an exhaust gas purification apparatus according to any one of  claim 2 , wherein
 when the NSR temperature is equal to or higher than the activation completion temperature of the NOx storage reduction catalyst, the controller controls the quantity of fuel supplied by the fuel supply device such that the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst while the rich spike process is performed is higher when the SCR temperature is equal to or higher than the activation start temperature of the selective catalytic reduction catalyst than when the SCR temperature is lower than the activation start temperature of the selective catalytic reduction catalyst.   
     
     
         7 . A control apparatus for an exhaust gas purification apparatus according to any one of  claim 3 , wherein
 when the NSR temperature is equal to or higher than the activation completion temperature of the NOx storage reduction catalyst, the controller controls the quantity of fuel supplied by the fuel supply device such that the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst while the rich spike process is performed is higher when the SCR temperature is equal to or higher than the activation start temperature of the selective catalytic reduction catalyst than when the SCR temperature is lower than the activation start temperature of the selective catalytic reduction catalyst.   
     
     
         8 . A control apparatus for an exhaust gas purification apparatus according to any one of  claim 4 , wherein
 when the NSR temperature is equal to or higher than the activation completion temperature of the NOx storage reduction catalyst, the controller controls the quantity of fuel supplied by the fuel supply device such that the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst while the rich spike process is performed is higher when the SCR temperature is equal to or higher than the activation start temperature of the selective catalytic reduction catalyst than when the SCR temperature is lower than the activation start temperature of the selective catalytic reduction catalyst.   
     
     
         9 . A control apparatus for an exhaust gas purification apparatus according to any one of  claim 5 , wherein
 when the NSR temperature is equal to or higher than the activation completion temperature of the NOx storage reduction catalyst, the controller controls the quantity of fuel supplied by the fuel supply device such that the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst while the rich spike process is performed is higher when the SCR temperature is equal to or higher than the activation start temperature of the selective catalytic reduction catalyst than when the SCR temperature is lower than the activation start temperature of the selective catalytic reduction catalyst.