Exhaust purification device of internal combustion engine

Abstract

In an internal combustion engine, an NO x selective reduction catalyst ( 15 ) is arranged in the engine exhaust passage, and the amount of deposition of the HC deposited at the NO x selective reduction catalyst ( 15 ) is estimated. When the estimated HC deposition amount exceeds a predetermined allowable deposition amount, the NO x selective reduction catalyst ( 15 ) is raised in temperature to make the deposited HC desorb from the NO x selective reduction catalyst ( 15 ), and thereby the NO x selective reduction catalyst ( 15 ) from HC poisoning is restored.

1 . An exhaust purification device of an internal combustion engine arranging an NO x  selective reduction catalyst in an engine exhaust passage, feeding urea to said NO x  selective reduction catalyst, and using ammonia generated from the urea to selectively reduce NO x  contained in exhaust gas, wherein HC deposition estimating means for estimating an amount of HC deposited at said NO x  selective reduction catalyst is provided, and a temperature of the NO x  selective reduction catalyst is raised to make deposited HC desorb from the NO x  selective reduction catalyst when an amount of deposition of HC estimated by the HC deposition estimating means exceeds a predetermined allowable deposition amount, and thereby restores the NO x  selective reduction catalyst from HC poisoning. 
   
   
       2 . An exhaust purification device of an internal combustion engine as claimed in  claim 1 , wherein an amount of HC flowing into said NO x  selective reduction catalyst is calculated and said HC deposition estimating means estimates said HC deposition amount using an HC deposition rate at the NO x  selective reduction catalyst preset for a calculated inflowing HC amount and an HC desorption rate from the NO x  selective reduction catalyst. 
   
   
       3 . An exhaust purification device of an internal combustion engine as claimed in  claim 1 , where HC concentration sensor for detecting an HC concentration in an exhaust gas flowing into the NO x  selective reduction catalyst is provided, an amount of HC inflowing into the NO x  selective reduction catalyst is found by said HC concentration sensor, and said HC deposition estimating means estimates said HC deposition amount using an HC deposition rate at the NO x  selective reduction catalyst preset for a found inflowing HC amount and an HC desorption rate from the NO x  selective reduction catalyst. 
   
   
       4 . An exhaust purification device of an internal combustion engine as claimed in  claim 1 , where an oxidation catalyst is arranged in the engine exhaust passage upstream of the selective reduction catalyst, HC is fed into the oxidation catalyst when the NO x  selective reduction catalyst should be raised in temperature, and a temperature of the NO x  selective reduction catalyst is raised by a heat of oxidation reaction of the HC. 
   
   
       5 . An exhaust purification device of an internal combustion engine as claimed in  claim 1 , wherein when the HC deposition amount falls to a predetermined lower limit value after starting to raise a temperature of the NO x  selective reduction catalyst, a temperature raising action of the NO x  selective reduction catalyst is stopped.