Control unit for exhaust gas purifying apparatus

Abstract

PM elimination or sulfur release are performed on both exhaust systems (exhaust passages 13 L, 13 R) using a common procedure regardless of the state of a catalyst arranged in each one of the exhaust systems. This reduces the number of recovery cycles of the catalysts and suppresses increase of fuel consumption caused by the PM elimination and the sulfur release compared to a case in which the PM elimination/sulfur release is carried out each time a request for catalyst control is generated by one of the exhaust systems. In the PM elimination control, the PM elimination is performed using a catalyst exhibiting a lowest catalyst bed temperature of the catalysts as a reference. In this manner, PM is prevented from remaining unburned. Further, in the sulfur release control, the sulfur release is performed using an average of catalyst bed temperatures of the catalysts as a reference. This maximally suppresses thermal deterioration of the catalysts and ensures sufficient release of sulfur.

1 . A control unit of an exhaust gas purifying apparatus used in an internal combustion engine having a plurality of sets of cylinders, wherein different exhaust systems are each connected to one of the sets of the cylinders, the exhaust gas purifying apparatus comprising catalysts each provided in one of the exhaust systems to purify exhaust gas,
 wherein the control unit performs a common PM elimination control or a common sulfur release control on the catalysts regardless of the states of the catalysts.   
   
   
       2 . The control unit according to  claim 1 , wherein the control unit carries out the PM elimination control using a catalyst of a lowest catalyst bed temperature among the catalysts as a reference, and wherein the control unit performs the sulfur release control using an average of catalyst bed temperatures of the catalysts. 
   
   
       3 . The control unit according to  claim 1 , wherein the control unit estimates a PM deposit amount of each of the catalysts based on an intake air amount, and wherein the control unit determines when the PM elimination control needs to be performed using a catalyst having a greatest value of the estimated PM deposit amounts as a reference. 
   
   
       4 . The control unit according to  claim 1 , wherein the control unit determines whether a lowest value of the catalyst bed temperatures of the catalysts has reached a temperature required for the PM elimination control, and wherein, if the lowest value is less than the temperature required for the PM elimination control, the control unit switches a combustion state of the engine to a state in which the catalyst bed temperatures of the catalysts are raised. 
   
   
       5 . The control unit according to  claim 1 , wherein the control unit performs the common PM elimination control or the common sulfur release control by controlling operations of fuel adding valves each provided in one of the exhaust systems. 
   
   
       6 . A method for controlling an exhaust gas purifying apparatus used in an internal combustion engine having a plurality of sets of cylinders, wherein different exhaust systems are each connected to one of the sets of the cylinders, the method comprising:
 purifying exhaust gas by means of catalysts each provided in one of the exhaust systems; and   performing a common PM elimination control or a common sulfur release control on the catalysts regardless of the states of the catalysts.