Abnormality detecting system for oxygen sensor and abnormality detecting method

Abstract

An abnormality detecting system and method detect an abnormality in an oxygen sensor provided on a downstream side of a catalyst for purifying exhaust gas released from an internal combustion engine. An upstream side sensor is provided on an upstream side of the catalyst, and produces an output corresponding to an exhaust air-fuel ratio. A theoretical oxygen storage capacity of the catalyst is obtained, for example, by determining an amount of oxygen in the exhaust gas flowing into the catalyst during a period in which the oxygen sensor produces a rich output and the upstream side sensor produces a lean output. An abnormality in the oxygen sensor is detected to exist when the theoretical oxygen storage capacity has exceeded a maximum oxygen storage amount of the catalyst.

What is claimed is:  
     
         1 . An abnormality detecting system for detecting an abnormality in an oxygen sensor which is provided on a downstream side of a catalyst for purifying exhaust gas released from an internal combustion engine, comprising: 
 an upstream side sensor which is provided on an upstream side of the catalyst and which produces an output corresponding to an exhaust air-fuel ratio; and    a controller which obtains a theoretical oxygen storage capacity of the catalyst by determining an amount of oxygen in exhaust gas flowing into the catalyst during a period in which the oxygen sensor produces a rich output and the upstream side sensor produces a lean output, wherein the controller detects that there is an abnormality in the oxygen sensor when the theoretical oxygen storage capacity has exceeded a maximum oxygen storage amount of the catalyst.    
     
     
         2 . The abnormality detecting system according to  claim 1 , wherein the upstream side sensor is an air-fuel ratio sensor for detecting an exhaust air-fuel ratio, and the controller further obtains a difference ΔA/F between an air-fuel ratio detected by the upstream side sensor and a stoichiometric air-fuel ratio; detects a fuel supply amount to the internal combustion engine; and calculates an amount of oxygen in the exhaust gas based on the difference ΔA/F and the fuel supply amount.  
     
     
         3 . The abnormality detecting system according to  claim 2 , wherein the controller forcibly controls a target air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine to be lean while the oxygen sensor produces the rich output, so as to calculate the theoretical oxygen storage capacity.  
     
     
         4 . The abnormality detecting system according to  claim 1 , wherein the controller forcibly controls a target air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine to be lean while the oxygen sensor produces the rich output, so as to calculate the theoretical oxygen storage capacity.  
     
     
         5 . The abnormality detecting system according to  claim 3 , wherein the controller further forcibly controls the target air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine to be rich while the oxygen sensor produces the lean output, and inverts the target air-fuel ratio between rich and lean each time the output from the oxygen sensor is inverted by forcibly controlling the target air-fuel ratio to be rich and lean alternately.  
     
     
         6 . The abnormality detecting system according to  claim 3 , wherein the controller prohibits forcing setting of the target air-fuel ratio when an abnormality in the oxygen sensor is detected.  
     
     
         7 . An abnormality detecting system for detecting an abnormality in an oxygen sensor provided on a downstream side of a catalyst for purifying exhaust gas released from an internal combustion engine, comprising: 
 an upstream side sensor which is provided on an upstream side of the catalyst and which produces an output corresponding to an exhaust air-fuel ratio; and    a controller which obtains a theoretical oxygen storage capacity of the catalyst by determining an amount of oxygen deficiency in exhaust gas flowing into the catalyst during a period in which the oxygen sensor produces a lean output and the upstream side sensor produces a rich output, wherein the controller detects that there is an abnormality in the oxygen sensor when the theoretical oxygen storage capacity has exceeded a maximum oxygen storage amount of the catalyst.    
     
     
         8 . The abnormality detecting system according to  claim 7 , wherein the upstream side sensor is an air-fuel ratio sensor for detecting an exhaust air-fuel ratio, and the controller further obtains a difference ΔA/F between an air-fuel ratio detected by the upstream side sensor and a stoichiometric air-fuel ratio; detects a fuel supply amount to the internal combustion engine; and calculates an amount of oxygen deficiency in the exhaust gas based on the difference ΔA/F and the fuel supply amount.  
     
     
         9 . The abnormality detecting system according to  claim 8 , wherein the controller forcibly controls a target air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine to be rich while the oxygen sensor produces the lean output, so as to calculate the theoretical oxygen storage capacity.  
     
     
         10 . The abnormality detecting system according to  claim 7 , wherein the controller forcibly controls a target air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine to be rich while the oxygen sensor produces the lean output, so as to calculate the theoretical oxygen storage capacity.  
     
     
         11 . A method for detecting an abnormality in an oxygen sensor provided on a downstream side of a catalyst for purifying exhaust gas released from an internal combustion engine, comprising the steps of: 
 detecting an exhaust air-fuel ratio upstream of the catalyst;    obtaining a theoretical oxygen storage capacity of the catalyst by determining an amount of oxygen in the exhaust gas flowing into the catalyst during a period in which the oxygen sensor produces a rich output and the exhaust air-fuel ratio upstream of the catalyst is detected to be lean; and    detecting that there is an abnormality in the oxygen sensor when the theoretical oxygen storage capacity has exceeded a maximum oxygen storage amount of the catalyst.    
     
     
         12 . The abnormality detecting method according to  claim 11 , further comprising the steps of: 
 obtaining a difference ΔA/F between an air-fuel ratio detected upstream of the catalyst and a stoichiometric air-fuel ratio;    detecting a fuel supply amount to the internal combustion engine; and    calculating an amount of oxygen in the exhaust gas based on the difference ΔA/F and the fuel supply amount.    
     
     
         13 . The abnormality detecting method according to  claim 12 , further comprising the step of: 
 forcibly controlling a target air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine to be lean while the oxygen sensor produces the rich output.    
     
     
         14 . The abnormality detecting method according to  claim 11 , further comprising the step of: 
 forcibly controlling a target air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine to be lean while the oxygen sensor produces the rich output.    
     
     
         15 . The abnormality detecting method according to  claim 14 , further comprising the steps of: 
 forcibly controlling the target air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine to be rich while the oxygen sensor produces the lean output; and    inverting the target air-fuel ratio between rich and lean by alternately switching the target air-fuel ratio between lean and rich each time the output from the oxygen sensor is inverted.    
     
     
         16 . The abnormality detecting method according to  claim 15 , further comprising the step of: 
 prohibiting forcing setting of the target air-fuel ratio when an abnormality in the oxygen sensor is detected.    
     
     
         17 . A method for detecting an abnormality in an oxygen sensor provided on a downstream side of a catalyst for purifying exhaust gas released from an internal combustion engine, comprising the steps of: 
 detecting an exhaust air-fuel ratio upstream of the catalyst;    obtaining a theoretical oxygen storage capacity of the catalyst by determining an amount of oxygen deficiency in the exhaust gas flowing into the catalyst during a period in which the oxygen sensor produces a lean output and the exhaust air-fuel ratio upstream of the catalyst is detected to be rich output; and    detecting that there is an abnormality in the oxygen sensor when the theoretical oxygen storage capacity has exceeded a maximum oxygen storage amount of the catalyst.    
     
     
         18 . The abnormality detecting method according to  claim 17 , further comprising the steps of: 
 obtaining a difference ΔA/F between an air-fuel ratio detected upstream of the catalyst and a stoichiometric air-fuel ratio;    detecting a fuel supply amount to the internal combustion engine; and    calculating an amount of oxygen deficiency in the exhaust gas based on the difference A A/F and the fuel supply amount.    
     
     
         19 . The abnormality detecting method according to  claim 18 , further comprising the step of: 
 forcibly controlling a target air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine to be rich while the oxygen sensor produces the lean output.    
     
     
         20 . The abnormality detecting method according to  claim 17 , further comprising the step of: 
 forcibly controlling a target air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine to be rich while the oxygen sensor produces the lean output.