Exhaust Purification System of Internal Combustion Engine

Abstract

An NOx adsorbent is arranged in an exhaust passage of an internal combustion engine, a fuel addition valve ( 28 ) is arranged in the exhaust passage upstream of the NOx adsorbent, and, when the NOx adsorbent should be made to release the NOx, the fuel addition valve ( 28 ) adds fuel to the NOx adsorbent in the required fuel addition amount to make the air-fuel ratio of the exhaust gas flowing into the NOx adsorbent temporarily rich. In this case, the required fuel addition amount is added divided into a plurality of operations. The fuel addition rate of the fuel addition valve ( 28 ) is detected and the overall addition time from the start of the initial divided addition to the end of the final divided addition is corrected in accordance with the fuel addition rate. Further, the divided addition time, interval, or number of divided additions is corrected so that the amount of fuel actually added from the fuel addition valve ( 28 ) is maintained at the required fuel addition amount.

1 . An exhaust purification system of an internal combustion engine provided with:
 an NOx adsorbent arranged in an engine exhaust passage, said NOx adsorbent absorbing NOx in exhaust gas when the inflowing exhaust gas has a lean air-fuel ratio and releasing the absorbed NOx when the inflowing exhaust gas has a rich air-fuel ratio,   a fuel addition valve arranged in the engine exhaust passage upstream of said NOx adsorbent,   an addition controlling means for adding fuel from the fuel addition valve to the NOx adsorbent in the required fuel addition amount when the NOx adsorbent should be made to release the NOx so that the air-fuel ratio of the exhaust gas flowing into the NOx adsorbent becomes temporarily rich, said addition controlling means performing divided addition adding said required fuel addition amount of fuel divided into a plurality of operations,   a detecting means for detecting a fuel addition rate of the fuel addition valve or the amount of fluctuation of the fuel addition rate with respect to a regular value, and   a correcting means for correcting the overall addition time from a start of an initial divided addition to an end of a final divided addition to shorten it and correcting control parameters of divided addition in accordance with said detected fuel addition rate or amount of fluctuation of the fuel addition rate so that the amount of fuel actually added from the fuel addition valve is maintained at the required fuel addition amount.   
     
     
         2 . An exhaust purification system of an internal combustion engine as set forth in  claim 1 , wherein said control parameters of divided addition are a divided addition time and an interval from a previous divided addition to a next divided addition or number of divided additions. 
     
     
         3 . An exhaust purification system of an internal combustion engine as set forth in  claim 1 , wherein said correcting means corrects the overall addition time so as to become shorter the smaller said fuel addition rate or the larger the drop of said fuel addition rate. 
     
     
         4 . An exhaust purification system of an internal combustion engine as set forth in  claim 1 , wherein the system is further provided with an NOx purification rate detecting means for detecting an NOx purification rate of the NOx adsorbent and said correcting means corrects the overall addition time to shorten it or corrects it to extend it so that said detected NOx purification rate matches a target value. 
     
     
         5 . An exhaust purification system of an internal combustion engine as set forth in  claim 1 , wherein the system is further provided with an HC amount detecting means for detecting an amount of HC in the exhaust gas flowing out from the NOx adsorbent when fuel is added and said correcting means corrects the overall addition time to shorten it or corrects it to extend it so that said detected HC amount matches a target amount. 
     
     
         6 . An exhaust purification system of an internal combustion engine as set forth in  claim 1 , wherein the system is further provided with an NOx purification rate detecting means for detecting an NOx purification rate of the NOx adsorbent and a determining means for determining that the fuel addition valve is broken when the drop in the detected NOx purification rate is larger than an allowable value or said detected NOx purification rate is lower than an allowable limit even if correcting the overall addition time to shorten it and correct the control parameters of the divided addition.