Exhaust Aftertreatment Control System And Method For Maximizing Fuel Efficiency While Reducing Emissions

Abstract

An engine exhaust treatment and fuel efficiency improvement system includes a NOx module that determines a quantity of NOx emitted from an engine. A selective catalytic reduction (SCR) efficiency module determines a SCR efficiency to reduce the determined NOx quantity below a predetermined threshold. A reagent dosing module determines a quantity of reagent required to reduce the NOx quantity below the predetermined threshold. An injection optimization module determines whether an increase in system operating efficiency may be obtained by changing an injected reagent quantity and an engine operating parameter in cooperation with each other while maintaining the NOx quantity below the threshold, the system being operable to change the reagent injection quantity and engine operating parameter to increase system efficiency.

What is claimed is: 
     
         1 . An engine exhaust treatment and fuel efficiency improvement system, comprising:
 a NO x  module that determines a quantity of NO x  emitted from an engine;   a selective catalytic reduction (SCR) efficiency module that determines a SCR efficiency to reduce the determined NO x  quantity below a predetermined threshold;   a reagent dosing module that determines a quantity of reagent required to reduce the NO x  quantity below the predetermined threshold; and   an injection optimization module that determines whether an increase in system operating efficiency may be obtained by changing both an injected reagent quantity and an engine operating parameter in cooperation with each other while maintaining the NO x  quantity below the threshold, wherein the system injection optimization module outputs a signal to change the reagent injection quantity and the engine operating parameter to increase system efficiency.   
     
     
         2 . The system of  claim 1 , wherein the engine operating parameter includes fuel injection rate. 
     
     
         3 . The system of  claim 2 , wherein the engine operating parameter includes exhaust gas recirculation flow rate. 
     
     
         4 . The system of  claim 1 , wherein the reagent includes urea. 
     
     
         5 . The system of  claim 1 , wherein the injection optimization module signals an increase in reagent injection quantity and a decrease in fuel injection rate. 
     
     
         6 . The system of  claim 1 , wherein the injection optimization module determines whether the engine NO x  output at the changed engine operating parameter may be reduced to the predetermined threshold by the exhaust treatment system and outputs a signal to change the engine parameter only when so determined. 
     
     
         7 . The system of  claim 1 , wherein the NO x  module, the SCR efficiency module and the injection optimization module, are operable on a common control unit that controls the engine operating parameter. 
     
     
         8 . A method of operating an engine exhaust treatment and fuel efficiency improvements system, the method comprising:
 determining an engine operating parameter;   calculating engine exhaust NO x ;   calculating a selective catalytic reduction (SCR) conversion efficiency required to reduce the engine exhaust NO below a predetermined threshold;   determining a quantity of reagent to inject into the exhaust to reduce the engine exhaust NO below the threshold;   determining whether an operating efficiency of the system may be increased by changing both the reagent quantity and the engine operating parameter while maintaining exhaust NO below the threshold; and   changing the reagent quantity and the operating parameter to reduce engine fuel consumption.   
     
     
         9 . The method of  claim 8 , wherein calculating engine exhaust NO is accomplished without receiving a NO sensor signal. 
     
     
         10 . The method of  claim 8 , wherein the engine operating parameter includes fuel injection rate. 
     
     
         11 . The method of  claim 10 , wherein changing the reagent quantity and the operating parameter includes increasing the reagent quantity and decreasing the fuel injection rate. 
     
     
         12 . The method of  claim 8 , wherein the engine operating parameter includes exhaust gas recirculation flow rate. 
     
     
         13 . The method of  claim 8 , wherein the reagent includes urea. 
     
     
         14 . The method of  claim 8 , wherein determining whether an operating efficiency may be increased includes determining whether the system includes a capacity to reduce NO x  below the threshold.