Air-fuel ratio control system for engine with in-catalyst state compensation

Abstract

An air-fuel ratio control system has a catalyst and controls the air-fuel ratio properly in accordance with the in-catalyst state. The in-catalyst state amount variation is calculated based on the deviation between the actual excess fuel factor detected by means of an air-fuel ratio sensor on the upstream side of the catalyst and the target excess fuel factor, and then accumulated to obtain the current in-catalyst state amount. At that time, the previous air flow derived earlier by a lag time corresponding to the time period from the time of fuel injection to the time of detection of the excess fuel factor of exhaust gas is used as the air flow. The calculated in-catalyst state amount value is subjected to guard processing, and thereafter the target excess fuel factor on the upstream side of the catalyst is calculated by use of various gains and control parameters.

What is claimed is:  
     
         1 . An air-fuel ratio control system for an internal combustion engine having a catalyst for purifying exhaust gas comprising: 
 gas concentration detection means for detecting gas concentration of exhaust gas on an upstream or downstream of the catalyst;    air flow detection means for detecting air flow taken into the internal combustion engine;    in-catalyst state amount calculation means for calculating in-catalyst state amount based on the detected gas concentration of exhaust gas and the detected air flow; and    injection control means for correcting a fuel injection amount so that a deviation between the calculated in-catalyst state amount and a target in-catalyst state amount is reduced.    
     
     
         2 . The air-fuel ratio control system according to  claim 1 , wherein: 
 the injection control means sets the target air-fuel ratio on the upstream of the catalyst so that the deviation between the in-catalyst state amount and the target in-catalyst state amount is decreased, and corrects the fuel injection amount so that the air-fuel ratio on the upstream of the catalyst is controlled to the target air-fuel ratio.    
     
     
         3 . The air-fuel ratio control system according to  claim 1 , wherein: 
 the in-catalyst state amount calculation means at least uses a previous air flow derived earlier by a lag time corresponding to a time period from time of fuel injection to time of detection of the gas concentration of exhaust gas as the air flow used when the in-catalyst state amount is calculated.    
     
     
         4 . The air-fuel ratio control system according to  claim 1 , further comprising: 
 guard processing means for restricting the calculated in-catalyst state amount value by use of a guard value corresponding to the saturated adsorption amount of the catalyst.    
     
     
         5 . The air-fuel ratio control system according to  claim 4 , wherein: 
 the guard processing means varies the guard value corresponding to the air flow.    
     
     
         6 . The air-fuel ratio control system according to  claim 1 , wherein, 
 the gas concentration detection means is an air-fuel ratio sensor provided on the upstream of the catalyst for detecting air-fuel ratio of exhaust gas, and    the in-catalyst state amount calculation means calculates the variation of the in-catalyst state amount based on the deviation between the target air-fuel ratio and the air-fuel ratio of exhaust gas every predetermined operation cycle, and calculates the current in-catalyst state amount by accumulating the variation.    
     
     
         7 . The air-fuel ratio control system according to  claim 1 , wherein: 
 the in-catalyst state amount calculation means is has correction means for correcting the calculated value corresponding to the actual in-catalyst state amount when the in-catalyst state amount is calculated.    
     
     
         8 . The air-fuel ratio control system according to  claim 7 , wherein: 
 the correction means detects the actual in-catalyst state amount based on the output of an oxygen sensor provided on the downstream of the catalyst and corrects the calculated in-catalyst state amount based on the oxygen sensor output.    
     
     
         9 . The air-fuel ratio control system according to  claim 7 , wherein: 
 the correction means has parameter varying means for varying the parameter for controlling the target value of the in-catalyst state amount corresponding to the deviation between the calculated in-catalyst state amount and the actual in-catalyst state amount.    
     
     
         10 . The air-fuel ratio control system according to  claim 9 , wherein: 
 the parameter varying means regards the deviation as 0 if the deviation between the calculated in-catalyst state amount and the actual in-catalyst state amount is equal to or smaller than a predetermined value.    
     
     
         11 . The air-fuel ratio control system according to  claim 9 , wherein: 
 the parameter varying means varies the parameter of an equation for calculating the in-catalyst state amount as the parameter for controlling the target value of the in-catalyst state amount.    
     
     
         12 . The air-fuel ratio control system according to  claim 1 , further comprising: 
 an oxygen sensor for detecting whether exhaust gas on the downstream of the catalyst is lean or rich,    wherein the injection control means sets the target air-fuel ratio on the upstream of the catalyst based on the in-catalyst state amount and the output of the oxygen sensor so that the deviation between the calculated in-catalyst state amount and the target in-catalyst state amount is reduced to a small value, and corrects the fuel injection amount so that the air-fuel ratio on the upstream of the catalyst is equalized to the target air-fuel ratio.    
     
     
         13 . The air-fuel ratio control system according to  claim 9 , wherein: 
 the correction means detects the actual in-catalyst state amount based on the output of an oxygen sensor provided on the downstream of the catalyst and corrects the calculated in-catalyst state amount based on the oxygen sensor output.    
     
     
         14 . An air-fuel ratio control system for an internal combustion engine having a catalyst for purifying exhaust gas comprising: 
 in-catalyst state amount calculation means for calculating in-catalyst state amount based on an air-fuel ratio on an upstream side of the catalyst and intake air flow taken into the internal combustion engine;    injection control means for controlling a fuel injection amount so that the air-fuel ratio on the upstream of the catalyst is equalized to the target air-fuel ratio;    target air-fuel ratio correction means for correcting the target air-fuel ratio based on air-fuel ratio on the downstream of the catalyst; and    second correction means for correcting correction value used for correcting the target air-fuel ratio based on the catalyst in-catalyst state amount.