Deterioration detecting apparatus for catalyst

Abstract

A deterioration detecting method for a catalyst in an exhaust system of an internal combustion engine for purifying exhaust gases. The system includes a first oxygen concentration sensor and a second oxygen concentration sensor disposed, respectively, upstream and downstream of the catalyst. Intake air flow rate of the engine is detected. An amount of oxygen flowing into the catalyst is calculated according to an oxygen concentration detected by the first sensor and the detected intake air flow rate. An air-fuel ratio of an air-fuel mixture supplied to the engine is controlled by alternately switching between lean and rich with respect to the stoichiometric ratio according to a result of comparison between the calculated and target values of the inflowing oxygen amount. A deterioration degree of the catalyst is detected based on an output of the second sensor when performing the switching control of the air-fuel ratio.

1 . A deterioration detecting apparatus for a catalyst provided in an exhaust system of an internal combustion engine for purifying exhaust gases, said deterioration detecting apparatus detecting deterioration of said catalyst and comprising:
 intake air flow rate detecting means for detecting an intake air flow rate of said engine;   a first oxygen concentration sensor disposed upstream of said catalyst;   a second oxygen concentration sensor disposed downstream of said catalyst;   inflowing oxygen amount calculating means for calculating an amount of oxygen flowing into said catalyst according to an oxygen concentration detected by said first oxygen concentration sensor and the intake air flow rate detected by said intake air flow rate detecting means;   air-fuel ratio switching control means for controlling an air-fuel ratio of an air-fuel mixture to be supplied to said engine by alternately switching the air-fuel ratio to lean and rich with respect to the stoichiometric ratio according to a result of a comparison between the inflowing oxygen amount calculated by said inflowing oxygen amount calculating means and target values of the inflowing oxygen amount; and   deterioration detecting means for detecting a deterioration degree of said catalyst based on an output of said second oxygen concentration sensor during an operation of said air-fuel ratio switching control means.   
   
   
       2 . A deterioration detecting apparatus according to  claim 1 , wherein said air-fuel ratio switching control means performs the switching control of the air-fuel ratio according to a result of a comparison between an output of said second oxygen concentration sensor and predetermined values. 
   
   
       3 . A deterioration detecting apparatus according to  claim 1 , wherein said air-fuel ratio switching control means calculates the target values according to the intake air flow rate. 
   
   
       4 . A deterioration detecting apparatus according to  claim 1 , further including catalyst temperature detecting means for detecting a temperature of said catalyst, wherein said air-fuel ratio switching control means calculates the target values according to the detected temperature of said catalyst. 
   
   
       5 . A deterioration detecting apparatus according to  claim 1 , further including inhibiting means for inhibiting the detection of the deterioration degree by said deterioration detecting means according to the inflowing oxygen amount. 
   
   
       6 . A deterioration detecting apparatus according to  claim 1 , wherein said exhaust system is further provided with a catalyst for purifying exhaust gases downstream of said second oxygen concentration sensor. 
   
   
       7 . A deterioration detecting apparatus according to  claim 1 , wherein said air-fuel ratio switching control means sets at least one updating rate of the air-fuel ratio at the time of switching the air-fuel ratio according to the intake air flow rate of said engine and the target values. 
   
   
       8 . A deterioration detecting apparatus according to  claim 1  further including:
 characteristic change detecting means for detecting a characteristic change parameter indicative of a change in an output characteristic of said first oxygen concentration sensor; and   correcting means for correcting an output of said first oxygen concentration sensor according to the characteristic change parameter,   wherein said inflowing oxygen amount calculating means calculates the inflowing oxygen amount using the output corrected by said correcting means.   
   
   
       9 . A deterioration detecting method for a catalyst provided in an exhaust system of an internal combustion engine for purifying exhaust gases, said exhaust system having a first oxygen concentration sensor disposed upstream of said catalyst and a second oxygen concentration sensor disposed downstream of said catalyst, said deterioration detecting method comprising the steps of:
 a) detecting an intake air flow rate of said engine;   b) calculating an amount of oxygen flowing into said catalyst according to an oxygen concentration detected by said first oxygen concentration sensor and the detected intake air flow rate;   c) controlling an air-fuel ratio of an air-fuel mixture to be supplied to said engine by alternately switching the air-fuel ratio to lean and rich with respect to the stoichiometric ratio according to a result of comparison between the calculated inflowing oxygen amount and target values of the inflowing oxygen amount; and   d) detecting a deterioration degree of said catalyst based on an output of said second oxygen concentration sensor when performing the switching control of the air-fuel ratio in step c).   
   
   
       10 . A deterioration detecting method according to  claim 9 , wherein the switching control of the air-fuel ratio is performed according to a result of comparison between an output of said second oxygen concentration sensor and predetermined values. 
   
   
       11 . A deterioration detecting method according to  claim 9 , wherein the target values are calculated according to the intake air flow rate. 
   
   
       12 . A deterioration detecting method according to  claim 9 , further including the step of detecting a temperature of said catalyst, wherein the target values are calculated according to the detected temperature of said catalyst. 
   
   
       13 . A deterioration detecting method according to  claim 9 , further including the step of inhibiting the detection of the deterioration degree according to the inflowing oxygen amount. 
   
   
       14 . A deterioration detecting method according to  claim 9 , wherein said exhaust system is further provided with a catalyst for purifying exhaust gases downstream of said second oxygen concentration sensor. 
   
   
       15 . A deterioration detecting method according to  claim 9 , wherein at least one updating rate of the air-fuel ratio at the time of switching the air-fuel ratio is set according to the intake air flow rate of said engine and the target values. 
   
   
       16 . A deterioration detecting method according to  claim 9 , further including the steps of:
 i) detecting a characteristic change parameter indicative of a change in an output characteristic of said first oxygen concentration sensor; and   ii) correcting an output of said first oxygen concentration sensor according to the characteristic change parameter,   wherein the inflowing oxygen amount is calculated using the corrected output of said first oxygen concentration sensor.   
   
   
       17 . A computer program embodied on a computer-readable medium, for causing a computer to implement a deterioration detecting method for a catalyst provided in an exhaust system of an internal combustion engine for purifying exhaust gases, said exhaust system having a first oxygen concentration sensor disposed upstream of said catalyst and a second oxygen concentration sensor disposed downstream of said catalyst, said deterioration detecting method comprising the steps of:
 a) detecting an intake air flow rate of said engine;   b) calculating an amount of oxygen flowing into said catalyst according to an oxygen concentration detected by said first oxygen concentration sensor and the detected intake air flow rate;   c) controlling an air-fuel ratio of an air-fuel mixture to be supplied to said engine by alternately switching the air-fuel ratio to lean and rich with respect to the stoichiometric ratio according to a result of comparison between the calculated inflowing oxygen amount and target values of the inflowing oxygen amount; and   d) detecting a deterioration degree of said catalyst based on an output of said second oxygen concentration sensor when performing the switching control of the air-fuel ratio in step c).   
   
   
       18 . A computer program according to  claim 17 , wherein the switching control of the air-fuel ratio is performed according to a result of comparison between an output of said second oxygen concentration sensor and predetermined values. 
   
   
       19 . A computer program according to  claim 17 , wherein the target values are calculated according to the intake air flow rate. 
   
   
       20 . A computer program according to  claim 17 , wherein said deterioration detecting method further includes the step of detecting a temperature of said catalyst, and the target values are calculated according to the detected temperature of said catalyst. 
   
   
       21 . A computer program according to  claim 17 , wherein said deterioration detecting method further includes the step of inhibiting the detection of the deterioration degree according to the inflowing oxygen amount. 
   
   
       22 . A computer program according to  claim 17 , wherein said exhaust system is further provided with a catalyst for purifying exhaust gases downstream of said second oxygen concentration sensor. 
   
   
       23 . A computer program according to  claim 17 , wherein at least one updating rate of the air-fuel ratio at the time of switching the air-fuel ratio is set according to the intake air flow rate of said engine and the target values. 
   
   
       24 . A computer program according to  claim 17 , wherein said deterioration detecting method further includes the steps of:
 i) detecting a characteristic change parameter indicative of a change in an output characteristic of said first oxygen concentration sensor; and   ii), correcting an output of said first oxygen concentration sensor according to the characteristic change parameter,   wherein the inflowing oxygen amount is calculated using the corrected output of said first oxygen concentration sensor.