Internal combustion engine control apparatus and method for controlling the same

Abstract

A forced stoichiometric combustion is executed every time a cumulative travel distance of a vehicle increases by a distance, thereby creating an opportunity to determine an air-fuel ratio value in a region in which a rich spike control is performed. Therefore, the determination of an air-fuel ratio value can be precisely calculated so that the air-fuel ratio value corresponds to a value that reflects a deviation of the actual air-fuel ratio and a proper value. Accordingly, it becomes possible to control, with high precision, correlation between the air-fuel ratio and a proper value based on the determined air-fuel ratio value during a fuel-rich combustion that is caused by the rich spike control.

What is claimed is:  
     
         1 . A control apparatus of an internal combustion engine, comprising: 
 a NOx storage-reduction catalyst provided in an exhaust system; and    a controller that executes a rich spike control that temporarily shifts an air-fuel ratio to a fuel-rich air-fuel ratio when a condition for reducing NOx stored in the NOx storage-reduction catalyst is met, and that, during the rich spike control, controls the air-fuel ratio based on an air-fuel ratio value that is determined through an air-fuel ratio feedback control during execution of a stoichiometric combustion, wherein the controller forcibly executes the stoichiometric combustion regardless of a state of operation of the engine, every time the internal combustion engine is operated for a predetermined period.    
     
     
         2 . A control apparatus according to  claim 1 , wherein the controller forcibly executes the stoichiometric combustion regardless of the state of operation of the engine, every time a cumulative travel distance of a vehicle in which the internal combustion engine is installed increases by a predetermined distance.  
     
     
         3 . A control apparatus according to  claim 1 , wherein the controller forcibly executes the stoichiometric combustion regardless of the state of operation of the engine, every time a cumulative operation time of the internal combustion engine increases by a predetermined time.  
     
     
         4 . A control apparatus according to  claim 1 , wherein the controller discontinues a forced stoichiometric combustion on a condition that the air-fuel ratio value converges with a predetermined value due to the determination performed through the feedback control.  
     
     
         5 . A control apparatus according to  claim 4 , wherein: 
 the air-fuel ratio value is determined separately for each one of a plurality of air-fuel ratio determination regions that are set in an operation region in which a lean combustion is executed; and    the controller discontinues the forced stoichiometric combustion on a condition that all the air-fuel ratio values corresponding to the plurality of air-fuel ratio determination regions converge.    
     
     
         6 . A control apparatus according to  claim 4 , wherein the controller discontinues the forced stoichiometric combustion regardless of convergence of the air-fuel ratio value, if an execution time of the forced stoichiometric combustion is at least a predetermined time.  
     
     
         7 . A control apparatus in according to  claim 6 , wherein if the forced stoichiometric combustion is started with the air-fuel ratio value being an initial value, the controller continues the stoichiometric combustion regardless of the execution time of the stoichiometric combustion until the air-fuel ratio value converges.  
     
     
         8 . A method of controlling an internal combustion engine having a NOx storage-reduction catalyst in an exhaust system, comprising the steps of: 
 executing a rich spike control that temporarily shifts an air-fuel ratio to a fuel-rich air-fuel ratio when a condition for reducing NOx stored in the NOx storage-reduction catalyst is met; and    controlling the air-fuel ratio, during the rich spike control, based on an air-fuel ratio value that is determined through an air-fuel ratio feedback control during execution of a stoichiometric combustion, wherein the stoichiometric combustion is forcibly executed regardless of a state of operation of the engine, every time the internal combustion engine is operated for a predetermined period.    
     
     
         9 . The method according to  claim 8 , wherein the stoichiometric combustion is forcibly executed regardless of the state of operation of the engine, every time a cumulative travel distance of a vehicle in which the internal combustion engine is installed increases by a predetermined distance.  
     
     
         10 . The method according to  claim 8 , wherein the stoichiometric combustion is forcibly executed regardless of the state of operation of the engine, every time a cumulative operation time of the internal combustion engine increases by a predetermined time.  
     
     
         11 . The method according to  claim 8 , wherein the forced stoichiometric combustion is discontinued on a condition that the air-fuel ratio value converges with a predetermined value due to the determination performed through the feedback control.  
     
     
         12 . The method according to  claim 11 , wherein: 
 the air-fuel ratio value is determined separately for each one of a plurality of air-fuel ratio determination regions that are set in an operation region in which a lean combustion is executed; and    the forced stoichiometric combustion is discontinued on a condition that all the air-fuel ratio values corresponding to the plurality of air-fuel ratio determination regions converge.    
     
     
         13 . The method according to  claim 11 , wherein the forced stoichiometric combustion is discontinued regardless of convergence of the air-fuel ratio values, if an execution time of the forced stoichiometric combustion is at least a predetermined time.  
     
     
         14 . The method according to  claim 13 , wherein if the forced stoichiometric combustion is started with the air-fuel ratio values being an initial value, the stoichiometric combustion is continued regardless of the execution time of the stoichiometric combustion until the air-fuel ratio values converge.