Exhaust purification device for internal combustion engine

Abstract

An exhaust purification device for an internal combustion engine can achieve high NOx purifying performance independent of operating conditions of the engine. The exhaust purification device has a NOx purification catalyst ( 33 ) mounted in an exhaust pipe ( 4 ) of the internal combustion engine, adsorbing or occluding NOx in exhaust gas when the exhaust gas air/fuel ratio is made lean, and reducing the adsorbed or occluded NOx when the exhaust gas air/fuel ratio is made rich; a fuel reformer ( 50 ) mounted separately from the exhaust pipe ( 4 ), reforming fuel to produce a reducing gas containing hydrogen and carbon monoxide, and supplying the reducing gas into that part of the exhaust pipe ( 4 ) which is located upstream of the NOx purification catalyst ( 33 ); and enriching means for enriching the exhaust gas air/fuel ratio. When one or more of operating conditions are satisfied, the enriching means enriches the air/fuel ratio of mixed gas to be combusted in the engine and causes the fuel reformer ( 50 ) to supply the reducing gas into the exhaust pipe ( 4 ) to enrich the exhaust gas air/fuel ratio.

1 . An exhaust purification device of an internal combustion engine including a NOx purification catalyst that is provided in an exhaust channel of the internal combustion engine and that, with an air/fuel ratio of exhaust flowing in the exhaust channel as an exhaust air/fuel ratio, adsorbs or occludes NOx in exhaust when the exhaust air/fuel ratio is made lean, and reduces the NOx adsorbed or occluded when the exhaust air/fuel ratio is made rich, the exhaust purification device comprising:
 a fuel reformer that is provided separately from the exhaust channel, produces a reducing gas containing hydrogen and carbon monoxide by reforming fuel, and supplies the reducing gas from an upstream side in the exhaust channel of the NOx purification catalyst into the exhaust channel; and   an enrichment means for enriching the exhaust air/fuel ratio,   wherein the enrichment means enriches the exhaust air/fuel ratio by supplying reducing gas of a pressure higher than atmospheric pressure by way of the fuel reformer into the exhaust channel, in a case of one or a plurality of conditions among a plurality of operating conditions being satisfied.   
     
     
         2 . An exhaust purification device of an internal combustion engine according to  claim 1 , wherein the plurality of operating conditions includes the internal combustion engine being in an idle operating state. 
     
     
         3 . An exhaust purification device of an internal combustion engine according to  claim 1 , wherein the plurality of operating conditions includes the internal combustion engine being in a deceleration operating state. 
     
     
         4 . An exhaust purification device of an internal combustion engine according to  claim 1 , wherein the plurality of operating conditions includes a fuel injection amount of the internal combustion engine being less than a predetermined judgment amount. 
     
     
         5 . An exhaust purification device of an internal combustion engine according to  claim 1 , wherein the plurality of operating conditions includes a generated torque of the internal combustion engine being less than a predetermined judgment value. 
     
     
         6 . An exhaust purification device of an internal combustion engine according to  claim 1 , wherein the plurality of operating conditions includes a temperature of exhaust flowing in the exhaust channel being lower than a predetermined judgment temperature. 
     
     
         7 . An exhaust purification device of an internal combustion engine according to  claim 1 , wherein the plurality of operating conditions includes a temperature of the NOx purification catalyst being lower than a predetermined judgment temperature. 
     
     
         8 . An exhaust purification device of an internal combustion engine according to  claim 1 , comprising a supply interruption means for stopping a supply of reducing gas from the fuel reformer, in a case where a temperature of the NOx purification catalyst has become at least a predetermined judgment temperature while reducing gas is being supplied from the fuel reformer. 
     
     
         9 . An exhaust purification device of an internal combustion engine according to  claim 1 , further comprising a timing means for measuring an elapsed time from starting a supply of reducing gas by the fuel reformer,
 wherein the enrichment means stops the supply of reducing gas by the fuel reformer in a case where the elapsed time thus measured by the timing means has become a predetermined judgment time.   
     
     
         10 . An exhaust purification device of an internal combustion engine according to  claim 1 , further comprising an enrichment determination means for determining whether to enrich the exhaust air/fuel ratio based on at least one among a temperature of the NOx purification catalyst, an estimated amount of NOx adsorbed or occluded to the NOx purification catalyst, a revolution speed of the internal combustion engine, and a generated torque of the internal combustion engine. 
     
     
         11 . An exhaust purification device of an internal combustion engine according to  claim 1 , further comprising an intake amount reduction means for reducing an intake air amount of the internal combustion engine when the exhaust air/fuel ratio is made rich. 
     
     
         12 . An exhaust purification device of an internal combustion engine according to  claim 1 , further comprising an exhaust air/fuel ratio target value determination means for determining a target value of the exhaust air/fuel ratio when enriching the exhaust air/fuel, based on at least one among a temperature of the NOx purification catalyst, an estimated amount of NOx adsorbed or occluded to the NOx purification catalyst, a rich control duration, a revolution speed of the internal combustion engine, and a generated torque of the internal combustion engine,
 wherein the enrichment means enriches the exhaust air/fuel ratio so that the exhaust air/fuel ratio matches a target value determined by the exhaust air/fuel ratio target value determination means.   
     
     
         13 . An exhaust purification device of an internal combustion engine according to  claim 12 , wherein the enrichment means adjusts at least one among a main injection amount of the internal combustion engine, a post injection amount of the internal combustion engine, an intake air amount of the internal combustion engine, and a supply amount of reducing gas supplied from the fuel reformer to the exhaust channel, so that the exhaust air/fuel ratio matches the target value determined by the exhaust air/fuel ratio target value determination means. 
     
     
         14 . An exhaust purification device of an internal combustion engine according to  claim 1 , wherein the fuel reformer produces reducing gas with carbon monoxide as a main component by way of a partial oxidation reaction of hydrocarbon fuel and air.