System and method for controlling an engine

Abstract

A system and method for controlling an engine coupled to an emission system is provided. The system includes an emission catalyst and a HEGO sensor disposed downstream of the catalyst. The method includes adjusting an air-fuel ratio of the engine to substantially maintain an output signal from the downstream HEGO sensor within a predetermined linear operating range.

We claim:  
     
         1 . A method for controlling an engine coupled to an emission system, the system having an emission catalyst and a HEGO sensor disposed downstream of at least a portion of the catalyst, the method comprising: 
 adjusting an air-fuel ratio of said engine to substantially maintain an output signal from said downstream HEGO sensor within a predetermined linear operating range.    
     
     
         2 . The method of  claim 1  wherein said system includes an UEGO sensor disposed upstream of said catalyst, said adjusting step including: 
 determining a catalyst state indicative of an amount of oxygen stored in said emission catalyst based on an output signal from said UEGO sensor;  
 determining a catalyst oxygen capacity range based on said HEGO sensor; and,  
 generating a commanded air-fuel signal based on said catalyst state and said catalyst oxygen capacity range.  
 
     
     
         3 . A system for controlling an engine coupled to a downstream emission catalyst, comprising: 
 a HEGO sensor disposed downstream of at least a portion of the catalyst generating a first output signal; and,    a controller receiving said output signal, said controller configured to adjust an air-fuel ratio of the engine to substantially maintain said output signal from said HEGO sensor within a predetermined linear operating range.    
     
     
         4 . The system of  claim 3  further including an UEGO sensor disposed upstream of said catalyst generating a second output signal, said controller being further configured to determine a catalyst state indicative of an amount of oxygen stored in said emission catalyst based on said second output signal, said controller being further configured to determine a catalyst oxygen capacity range based on said first output signal, said controller configured to further generate a commanded air-fuel signal based on said catalyst state and said catalyst oxygen capacity range.  
     
     
         5 . An article of manufacture, comprising: 
 a computer storage medium having a computer program encoded therein for controlling an engine coupled to an emission system, the system having an emission catalyst an a HEGO sensor disposed downstream of at least a portion of the catalyst generating an output signal, the computer storage medium comprising: 
 code for adjusting an air-fuel ratio of said engine to substantially maintain an output signal from said downstream HEGO sensor within a predetermined linear operating range.