Exhaust Purification System of Internal Combustion Engine

Abstract

HC feed control for feeding HC into exhaust gas upstream of an SOx trap 11 when a predetermined condition stands is executed. When an SOx trap amount is smaller than a predetermined amount, as HC feed control, first HC feed control feeding HC into the exhaust gas upstream of the SOx trap by a predetermined pattern is executed. When the SOx trap amount is larger than a predetermined amount, as HC feed control, second HC feed control feeding HC into the exhaust gas upstream of the SOx trap by a pattern different from the predetermined pattern, which pattern keeping the temperature of the SOx trap from locally becoming higher than the predetermined temperature or suppressing the formation of a region in the exhaust gas flowing into the SOx trap where the air-fuel ratio becomes locally rich, is executed.

1 . An exhaust purification system of an internal combustion engine providing an SOx trap for trapping the SOx in the exhaust gas inside an exhaust passage, said SOx trap trapping the SOx in the exhaust gas when an air-fuel ratio of the exhaust gas flowing into said SOx trap is an air-fuel ratio leaner than a stoichiometric air-fuel ratio and a temperature of said SOx trap is lower than a predetermined temperature and releasing the trapped SOx when the air-fuel ratio of the exhaust gas flowing into said SOx trap is the stoichiometric air-fuel ratio or an air-fuel ratio richer than that and the temperature of said SOx trap is higher than said predetermined temperature and executing HC feed control feeding HC into the exhaust gas upstream of the SOx trap when a predetermined condition stands, said exhaust purification system of an internal combustion engine executes, as said HC feed control, first HC feed control feeding HC into the exhaust gas upstream of the SOx trap by a predetermined pattern when the amount of SOx which the SOx trap traps is smaller than a predetermined amount and executes, as said HC feed control, second HC feed control feeding HC into the exhaust gas upstream of the SOx trap by a pattern different from said predetermined pattern, which pattern keeping the temperature of the SOx trap from locally becoming higher than said predetermined temperature or suppressing the formation of a region in the exhaust gas flowing into the SOx trap where the air-fuel ratio becomes locally rich, when the amount of SOx which the SOx trap traps is larger than said predetermined amount. 
   
   
       2 . An exhaust purification system of an internal combustion engine as set forth in  claim 1 , wherein, in said first HC feed control, a predetermined amount of HC is fed into the exhaust gas upstream of the SOx trap per unit time, while in said second HC feed control, an amount of HC smaller than said predetermined amount is fed into the exhaust gas upstream of the SOx trap per unit time. 
   
   
       3 . An exhaust purification system of an internal combustion engine as set forth in  claim 1 , wherein, in said second HC feed control, HC with a higher diffusion ability into the exhaust gas than the HC fed into the exhaust gas upstream of the SOx trap in said first HC feed control is fed into the exhaust gas upstream of the SOx trap. 
   
   
       4 . An exhaust purification system of an internal combustion engine as set forth in  claim 2 , wherein, in said second HC feed control, HC is fed into the exhaust gas upstream of the SOx trap so that a lean degree of the air-fuel ratio of the exhaust gas flowing into the SOx trap is kept larger than a predetermined lean degree. 
   
   
       5 . An exhaust purification system of an internal combustion engine as set forth in  claim 3 , wherein, in said second HC feed control, HC is fed into the exhaust gas upstream of the SOx trap so that a lean degree of the air-fuel ratio of the exhaust gas flowing into the SOx trap is kept larger than a predetermined lean degree. 
   
   
       6 . An exhaust purification system of an internal combustion engine as set forth in  claim 4 , wherein said predetermined lean degree is set larger the lower the temperature of the SOx trap. 
   
   
       7 . An exhaust purification system of an internal combustion engine as set forth in  claim 5 , wherein said predetermined lean degree is set larger the lower the temperature of the SOx trap. 
   
   
       8 . An exhaust purification system of an internal combustion engine as set forth in  claim 1 , wherein, in said second HC feed control, HC is fed into the exhaust gas upstream of the SOx trap so that the amount of local temperature rise of the SOx trap per unit time is kept smaller than the amount of local temperature rise of the SOx trap per unit time allowed in said first HC feed control. 
   
   
       9 . An exhaust purification system of an internal combustion engine as set forth in  claim 8 , wherein, in said second HC feed control, HC is fed into the exhaust gas upstream of the SOx trap so that an amount of temperature rise of the SOx trap as a whole per unit time is kept smaller than an amount of temperature rise of the SOx trap as a whole per unit time allowed in said first HC feed control. 
   
   
       10 . An exhaust purification system of an internal combustion engine as set forth in  claim 8 , wherein a particulate filter trapping particulate matter in the exhaust gas is arranged in the exhaust passage downstream of said SOx trap, one said predetermined condition is a burnaway condition where it is judged if the temperature of said particulate filter should be raised to a predetermined target temperature to burn away particulate matter trapped by the particulate filter, and, when said second HC feed control is executed when said burnaway condition stands, in said second HC feed control, HC is fed into the exhaust gas upstream of the SOx trap using as a target temperature a temperature lower than said target temperature in said first HC feed control in the case where said first HC feed control is executed when said burnaway condition stands. 
   
   
       11 . An exhaust purification system of an internal combustion engine as set forth in  claim 9 , wherein, in said second HC feed control, HC is fed into the exhaust gas upstream of the SOx trap so that a temperature amplitude of the SOx is kept smaller than a temperature amplitude of the SOx trap allowed in said first HC feed control. 
   
   
       12 . An exhaust purification system of an internal combustion engine as set forth in  claim 10 , wherein, in said second HC feed control, HC is fed into the exhaust gas upstream of the SOx trap so that a temperature amplitude of the SOx is kept smaller than a temperature amplitude of the SOx trap allowed in said first HC feed control. 
   
   
       13 . An exhaust purification system of an internal combustion engine as set forth in  claim 8 , wherein, an NOx absorbent absorbing the NOx in the exhaust gas is arranged in the exhaust passage downstream of said SOx trap, one said predetermined condition is an NOx release condition where it is judged that said NOx absorbent should release NOx, and, when said second HC feed control is executed when said NOx release condition stands, in said second HC feed control, HC is fed into the exhaust gas upstream of the SOx trap so that a temperature amplitude of the SOx trap is kept smaller than a temperature amplitude of the SOx trap allowed in said first HC feed control in the case where said first HC feed control is executed when said NOx release condition stands. 
   
   
       14 . An exhaust purification system of an internal combustion engine as set forth in  claim 1 , wherein an oxidation catalyst provided with an oxidizing ability higher than even the oxidizing ability of said SOx trap is arranged in the exhaust passage upstream of said SOx trap.