Automotive catalyst state control method

Abstract

A control system and method for controlling an engine ( 10 ) of an automotive vehicle having a catalyst ( 34 ) is set forth herein. The control system maintains the efficiency of the catalyst by monitoring the catalyst state and driving the catalyst state to a target point. A first oxygen sensor ( 50 ) generates a first oxygen signal. A second oxygen sensor ( 52 ) downstream of the catalyst generates a second oxygen signal. A controller ( 12 ) is programmed to perform the steps of determining a catalyst state having a maximum value, a minimum value, and a target point therebetween; determining a commanded air-fuel ratio to drive the catalyst state to the target point; and operating the engine with the commanded air-fuel ratio.

What is claimed is:  
     
         1 . A method for controlling an engine coupled to a catalyst comprising: 
 determining a catalyst state having maximum value, a minimum value and a target point therebetween;    determining a commanded air fuel ratio to drive said catalyst state to the target point; and    operating the engine with the commanded air fuel ratio.    
     
     
         2 . A method as recited in  claim 1  wherein when the catalyst state is between said maximum value and said minimum value, determining a commanded air fuel ratio to drive said catalyst state to the target point.  
     
     
         3 . A method as recited in  claim 2  when the catalyst state is not between said maximum value and said minimum value, determining a lambda error.  
     
     
         4 . A method as recited in  claim 3  further comprising adjusting the commanded air-fuel ratio in response to said lambda error.  
     
     
         5 . A method as recited in  claim 1  wherein generating said catalyst state is a function of measured lambda and a reference lambda, airmass and a current catalyst capacity.  
     
     
         6 . A method as recited in  claim 1  further comprising the step of generating a current catalyst capacity as a function of airmass and catalyst temperature.  
     
     
         7 . A method as recited in  claim 1  further comprising the step of generating a reference lambda corresponding to a stoichiometry value.  
     
     
         8 . A method as recited in  claim 1  further comprising the step of when a downstream exhaust gas oxygen sensor value reaches a predetermined exhaust gas limit value, generating a reference lambda as a function of a lambda error.  
     
     
         9 . A method as recited in  claim 1  wherein generating a reference lambda comprises determining a lambda error in response to airmass, catalyst state, and a previous catalyst state.  
     
     
         10 . A method as recited in  claim 1  wherein said minimum value is about 1, said maximum value is about −1 and said set point is about zero.  
     
     
         11 . A method as recited in  claim 1  wherein said target point is a function of load.  
     
     
         12 . A method as recited in  claim 1  wherein said step of determining a commanded air fuel ratio comprises determining the commanded air-fuel ration as a function of airmass, current catalyst capacity and said target point.  
     
     
         13 . A method for controlling an engine coupled to a catalyst comprising: 
 determining a rate of change of a catalyst state;    estimating a current catalyst state by integrating the rate of change of the catalyst state;    determining a commanded air fuel ratio to drive said catalyst state to a target point; and    operating the engine with the commanded air fuel ratio.    
     
     
         14 . A method as recited in  claim 13  wherein generating said catalyst state is a function of measured lambda and a reference lambda, airmass and a current catalyst capacity.  
     
     
         15 . A method as recited in  claim 13  further comprising the step of generating a current catalyst capacity as a function of airmass and catalyst temperature.  
     
     
         16 . A method as recited in  claim 13  further comprising the step of generating a reference lambda corresponding to a stoichiometry value.  
     
     
         17 . A method as recited in  claim 13  further comprising the step of when a downstream exhaust gas oxygen sensor value reaches a predetermined exhaust gas limit value, generating a reference lambda as a function of a lambda error.  
     
     
         18 . A method as recited in  claim 13  wherein generating a reference lambda comprises determining a lambda error in response to airmass, catalyst state, and a previous catalyst state.  
     
     
         19 . A method as recited in  claim 13  wherein said target point is a function of load.  
     
     
         20 . A control system for an engine coupled to an emission catalyst having: 
 a controller configured to determinr a catalyst state having maximum value, a minimum value and a target point therebetween;    said controller further configured to determine a commanded air fuel ratio to drive said catalyst state to the target point; and    said controller further configured to operate the engine with the commanded air fuel ratio.    
     
     
         21 . An article of manufacture comprising a computer storage medium having a computer program therein for controlling an engine coupled to a catalyst, said computer storage medium comprising: 
 code for determining a rate of change of a catalyst state;    code for estimating a current catalyst state by integrating the rate of change of the catalyst state;    code for determining a commanded air fuel ratio to drive said catalyst state to a target point; and    code for operating the engine with the commanded air fuel ratio.