Device and method for controlling air-fuel ratio of internal combustion engine

Abstract

In a system for estimating an oxygen quantity stored in a catalytic converter of an internal combustion engine and feedback controlling a fuel injection quantity based on the estimated oxygen quantity, a detection value of the new intake air quantity is corrected according to an exhaust gas recirculation rate, and the oxygen quantity is estimated based on the corrected new intake air quantity.

What is claimed:  
     
         1 . An air-fuel ratio control device of an internal combustion engine comprising: 
 a fuel injection valve that injects fuel into said engine;    a catalytic converter disposed to an exhaust pipe of said engine;    an intake air quantity sensor that detects a new intake air quantity of said engine;    an oxygen sensor, disposed to said exhaust pipe on the upstream side of said catalytic converter, that detects an oxygen concentration of the exhaust;    an exhaust gas recirculation pipe that recirculates a portion of the exhaust gas of said engine into an intake pipe;    an exhaust gas recirculation rate detecting unit that detects a recirculation rate of the exhaust gas being recirculated via said exhaust gas recirculation pipe;    a new intake air quantity correcting unit that corrects the detection value of said new intake air quantity based on said exhaust gas recirculation rate;    an oxygen quantity estimating unit that estimates an oxygen quantity stored in said catalytic converter based on said oxygen concentration and said detection value of the new intake air quantity corrected based on the exhaust gas recirculation rate; and    a feedback control unit that feedback controls a fuel injection quantity of said fuel injection valve so that said oxygen quantity approximates a target quantity.    
     
     
         2 . An air-fuel ratio control device of an internal combustion engine according to  claim 1 , wherein 
 said new intake air quantity correcting unit corrects the detection value of said new intake air quantity to a higher value as the higher the exhaust gas recirculation rate is.    
     
     
         3 . An air-fuel ratio control device of an internal combustion engine according to  claim 1 , wherein 
 said new intake air quantity correcting unit comprises: 
 a correction coefficient setting unit that sets a correction coefficient according to said exhaust gas recirculation rate; and  
 a correction computing unit that multiplies said correction coefficient on the detection value of said new intake air quantity to output the multiplied result.  
   
     
     
         4 . An air-fuel ratio control device of an internal combustion engine according to  claim 1 , wherein 
 said oxygen quantity estimating unit comprises: 
 an air-fuel ratio deviation computing unit that computes a deviation between a stoichiometric air-fuel ratio and an air-fuel ratio corresponding to said oxygen concentration; and  
 an estimating unit that estimates the oxygen quantity stored in said catalytic converter based on said air-fuel ratio deviation and said corrected detection value of the new intake air quantity.  
   
     
     
         5 . An air-fuel ratio control device of an internal combustion engine according to  claim 1 , wherein 
 said oxygen quantity estimating unit comprises: 
 an air-fuel ratio deviation computing unit that computes a deviation between a stoichiometric air-fuel ratio and an air-fuel ratio corresponding to said oxygen concentration;  
 a first multiplying unit that multiplies said air-fuel ratio deviation and said corrected detection value of the new intake air quantity;  
 a second multiplying unit that multiplies the multiplied result of said first multiplying unit by a constant; and  
 an integrating unit that integrates the multiplied result of said second multiplying unit.  
   
     
     
         6 . An air-fuel ratio control device of an internal combustion engine according to  claim 1 , wherein 
 said feedback control unit comprises;    a target setting unit that sets half the oxygen quantity of the maximum oxygen quantity capable of being stored in said catalytic converter as said target value.    
     
     
         7 . An air-fuel ratio control device of an internal combustion engine according to  claim 1 , wherein 
 said feedback control unit comprises: 
 an oxygen quantity judging unit that judges whether said estimated oxygen quantity is greater than said target value or not;  
 a decremental correcting unit that decreasingly corrects said fuel injection quantity when the estimated oxygen quantity is smaller than said target value; and  
 an incremental correcting unit that increasingly corrects said fuel injection quantity when said estimated oxygen quantity is greater than said target value.  
   
     
     
         8 . An air-fuel ratio control device of an internal combustion engine comprising: 
 a fuel injection valve that injects fuel into said engine;    a catalytic converter disposed to an exhaust pipe of said engine;    an intake air quantity sensor that detects a new intake air quantity of said engine;    an oxygen sensor, disposed to said exhaust pipe on the upstream side of said catalytic converter, that detects an oxygen concentration of the exhaust;    an exhaust gas recirculation pipe that recirculates a portion of the exhaust gas of said engine into an intake pipe;    exhaust gas recirculation rate detecting means for detecting a recirculation rate of the exhaust gas being recirculated via said exhaust gas recirculation pipe;    new intake air quantity correcting means for correcting the detection value of said new intake air quantity based on said exhaust gas recirculation rate;    oxygen quantity estimating means for estimating an oxygen quantity stored in said catalytic converter based on said oxygen concentration and said detection value of the new intake air quantity corrected based on the exhaust gas recirculation rate; and    feedback control means for feedback controlling a fuel injection quantity of said fuel injection valve so that said oxygen quantity approximates a target quantity.    
     
     
         9 . An air-fuel ratio control method of an internal combustion engine comprising the steps of: 
 detecting a new intake air quantity of said engine;    detecting an oxygen concentration of the exhaust at the upstream side of a catalytic converter disposed to an exhaust pipe of said engine;    detecting a recirculation rate of the exhaust gas with respect to said engine;    correcting the detection value of said new intake air quantity based on said exhaust gas recirculation rate;    estimating an oxygen quantity stored in said catalytic converter based on said oxygen concentration and said detection value of the new intake air quantity corrected based on the exhaust gas recirculation rate; and    feedback controlling a fuel injection quantity of said fuel injection valve so that said oxygen quantity approximates a target quantity.    
     
     
         10 . An air-fuel ratio control method of an internal combustion engine according to  claim 9 , wherein 
 said step of correcting a new intake air quantity comprises the step of;    correcting the detection value of said new intake air quantity to a higher value as the higher the exhaust gas recirculation rate is.    
     
     
         11 . An air-fuel ratio control method of an internal combustion engine according to  claim 9 , wherein 
 said step of correcting a new intake air quantity comprises the steps of: 
 setting a correction coefficient according to said exhaust gas recirculation rate; and  
 multiplying said correction coefficient on the detection value of said new intake air quantity to output the multiplied result.  
   
     
     
         12 . An air-fuel ratio control method of an internal combustion engine according to  claim 9 , wherein 
 said step of estimating an oxygen quantity comprises the steps of: 
 computing a deviation between a stoichiometric air-fuel ratio and an air-fuel ratio corresponding to said oxygen concentration; and  
 estimating the oxygen quantity stored in said catalytic converter based on said air-fuel ratio deviation and said corrected detection value of the new intake air quantity.  
   
     
     
         13 . An air-fuel ratio control method of an internal combustion engine according to  claim 9 , wherein 
 said step of estimating an oxygen quantity comprises the steps of: 
 computing a deviation between a stoichiometric air-fuel ratio and an air-fuel ratio corresponding to said oxygen concentration;  
 multiplying said air-fuel ratio deviation and said corrected detection value of the new intake air quantity;  
 multiplying the multiplied result of said first multiplying unit by a constant; and  
 integrating the multiplied result of said second multiplying unit.  
   
     
     
         14 . An air-fuel ratio control method of an internal combustion engine according to  claim 9 , wherein 
 said step of feedback controlling a fuel injection quantity comprises the step of;    setting half the oxygen quantity of the maximum oxygen quantity capable of being stored in said catalytic converter as said target value.