Exhaust gas purification system of internal combustion engine

Abstract

An exhaust gas purification system of an internal combustion engine supplies hydrocarbon by performing a post injection and the like in order to combust particulate matters accumulated in a diesel particulate filter (a DPF) having an oxidation catalyst. An electronic control unit (an ECU) senses temperature of exhaust gas upstream of the DPF with an exhaust gas temperature sensor and determines an upper limit value of permissible quantity of the hydrocarbon supplied to the DPF based on the sensed temperature. The ECU controls post injection quantity so that the quantity of the actually supplied hydrocarbon does not exceed the upper limit value. Thus, hydrocarbon poisoning can be precluded, since the quantity of the actually supplied hydrocarbon does not exceed the upper limit value.

What is claimed is:  
     
         1 . An exhaust gas purification system of an internal combustion engine, the exhaust gas purification system comprising: 
 an exhaust gas after-treatment device, which is disposed in an exhaust passage of the engine and supports a catalyst;    temperature sensing means for estimating temperature of the exhaust gas after-treatment device;    hydrocarbon supplying means for supplying hydrocarbon to the exhaust gas after-treatment device; and    hydrocarbon supply quantity controlling means for determining an upper limit value of the permissible quantity of the hydrocarbon supplied to the exhaust gas after-treatment device in accordance with the temperature of the exhaust gas after-treatment device estimated by the temperature sensing means, and for controlling the hydrocarbon supplying means so that the quantity of the hydrocarbon supplied to the exhaust gas after-treatment device becomes equal to or less than the upper limit value.    
     
     
         2 . The exhaust gas purification system as in  claim 1 , wherein 
 the hydrocarbon supplying means supplies the hydrocarbon to the exhaust gas after-treatment device by performing a post injection of fuel after a main injection of the fuel, by retarding injection timing of the fuel, or by increasing a quantity of the exhaust gas recirculated into intake air.    
     
     
         3 . The exhaust gas purification system as in  claim 1 , further comprising: 
 hydrocarbon quantity sensing means for sensing the quantity of the hydrocarbon supplied to the exhaust gas after-treatment device, wherein    the hydrocarbon supply quantity controlling means controls the hydrocarbon supplying means so that the quantity of the hydrocarbon sensed by the hydrocarbon quantity sensing means becomes equal to or less than the upper limit value.    
     
     
         4 . The exhaust gas purification system as in  claim 3 , wherein 
 the hydrocarbon quantity sensing means calculates the quantity of the hydrocarbon supplied to the exhaust gas after-treatment device by adding a quantity of unburned hydrocarbon generated through combustion in the engine to the quantity of the hydrocarbon supplied by the hydrocarbon supplying means.    
     
     
         5 . The exhaust gas purification system as in  claim 1 , wherein 
 the temperature sensing means senses temperature of the exhaust gas upstream of the exhaust gas after-treatment device as the temperature of the exhaust gas after-treatment device.    
     
     
         6 . The exhaust gas purification system as in  claim 1 , wherein 
 the exhaust gas after-treatment device includes at least one selected from the group of a diesel particulate filter having an oxidation catalyst, a nitrogen oxide removal catalyst, an oxidation catalyst and a three-way catalyst.