Exhaust gas purification apparatus for internal combustion engine

Abstract

An exhaust gas purification apparatus for an internal combustion engine includes an exhaust passage through which exhaust gas flows, a selective catalytic reduction (SCR) catalyst provided in the exhaust passage, a urea water supply device and a control unit for controlling amount of urea water to be supplied into the exhaust passage upstream of the SCR catalyst at predetermined intervals. The control unit further estimates amount of ammonia converted from adsorbed deposit which is converted from the urea water and adsorbed on the SCR catalyst during the predetermined interval based on a physical quantity of the internal combustion engine or the exhaust gas purification apparatus, and determines amount of urea water to be supplied into the exhaust passage based on the estimated amount of ammonia converted from the adsorbed deposit on the SCR catalyst.

1 . An exhaust gas purification apparatus for an internal combustion engine, comprising:
 an exhaust passage through which exhaust gas discharged from the internal combustion engine is allowed to flow;   a selective catalytic reduction catalyst provided in the exhaust passage;   a urea water supply device provided upstream of the selective catalytic reduction catalyst in the exhaust passage with respect to the flowing direction of exhaust gas for supplying urea water into the exhaust passage; and   a control unit for controlling amount of urea water to be supplied into the exhaust passage at predetermined intervals, estimating amount of ammonia converted from adsorbed deposit based on a physical quantity of the internal combustion engine or the exhaust gas purification apparatus, wherein the adsorbed deposit is converted from the urea water and adsorbed on the selective catalytic reduction catalyst, and determining amount of urea water to be supplied into the exhaust passage based on at least the estimated amount of ammonia converted from the adsorbed deposit on the selective catalytic reduction catalyst.   
     
     
         2 . The exhaust gas purification apparatus according to  claim 1 , further comprising a temperature sensor for sensing the temperature of the selective catalytic reduction catalyst, wherein the physical quantity is temperature of the selective catalytic reduction catalyst. 
     
     
         3 . The exhaust gas purification apparatus according to  claim 2 , wherein the control unit stores therein a first data representing a relation between temperature of the selective catalytic reduction catalyst and the amount of ammonia converted from the supplied urea water during the predetermined interval, wherein the control unit determines the amount of urea water to be supplied based on the first data. 
     
     
         4 . The exhaust gas purification apparatus according to  claim 3 , wherein the control unit stores therein a second data representing a relation between temperature of the selective catalytic reduction catalyst and the amount of ammonia converted from the adsorbed deposit during the predetermined interval, wherein the control unit estimates the amount of ammonia converted from the adsorbed deposit based on the second data. 
     
     
         5 . The exhaust gas purification apparatus according to  claim 4 , wherein the selective catalytic reduction catalyst is provided with a heater connected to the control unit for raising temperature of the selective catalytic reduction catalyst, wherein the control unit controls heating temperature of the heater based on the second data. 
     
     
         6 . The exhaust gas purification apparatus according to  claim 4 , wherein the first data further comprises a relation between the temperature of the selective catalytic reduction catalyst and amount of adsorbed deposit which is to be converted from the supplied urea water during the predetermined interval and has a property of being converted to ammonia, wherein the control unit adds the first data to the second data and stores the second data for utilizing to determine next amount of urea water supply. 
     
     
         7 . The exhaust gas purification apparatus according to  claim 4 , wherein the second data further comprises a relation between the temperature of the selective catalytic reduction catalyst and amount of adsorbed deposit which has not been converted to the ammonia during the predetermined interval after the urea water supply and has a property of being converted to ammonia, wherein the control unit updates and stores the amount of adsorbed deposit of the second data for utilizing to determine next amount of urea water supply. 
     
     
         8 . The exhaust gas purification apparatus according to  claim 1 , further comprising a nitrogen oxide sensor for sensing amount of nitrogen oxide in the exhaust gas flowing through the exhaust passage, wherein the control unit determines the amount of ammonia needed to purify the sensed amount of nitrogen oxide and determines the amount of urea water to be supplied into the exhaust passage based on the amount of ammonia needed to purify the sensed amount of nitrogen oxide. 
     
     
         9 . The exhaust gas purification apparatus according to  claim 8 , wherein the control unit determines the amount of urea water to be supplied into the exhaust passage based on amount of ammonia which is subtracted the estimated amount of ammonia converted from the adsorbed deposit during the predetermined interval from the amount of ammonia needed to purify the sensed amount of nitrogen oxide.