Catalyst diagnosis apparatus for internal combustion engine

Abstract

A catalyst diagnosis apparatus comprises a reaction rate calculation unit for calculating a reaction rate of chemical reaction in a three-way catalyst based on an output of an oxygen sensor, and an OSC indicator calculation unit for calculating an OSC indicator indicating an oxygen storage capacity (OSC) of the three-way catalyst based on outputs of a linear air-fuel ratio sensor and the oxygen sensor, and a catalyst degradation determination unit for determining degradation of the three-way catalyst based on the reaction rate and the OSC indicator. The determination of the catalyst degradation can be performed with high accuracy in a manner adapted for influences of external environments, etc.

1 . A catalyst diagnosis apparatus for an internal combustion engine including a three-way catalyst disposed in an exhaust passage, an air-fuel ratio sensor for detecting an air-fuel ratio in exhaust gas upstream of said three-way catalyst, and an oxygen sensor for detecting oxygen density in exhaust gas downstream of said three-way catalyst, said catalyst diagnosis apparatus determining degradation of said three-way catalyst, wherein said catalyst diagnosis apparatus comprises: 
 reaction rate calculation means for calculating a reaction rate of chemical reaction in said three-way catalyst based on an output of said oxygen sensor;    OSC indicator calculation means for calculating an OSC indicator indicating an oxygen storage capacity of said three-way catalyst based on outputs of said air-fuel ratio sensor and said oxygen sensor; and    catalyst degradation determination means for determining degradation of said three-way catalyst based on the reaction rate calculated by said reaction rate calculation means and the OSC indicator calculated by said OSC indicator calculation means.    
   
   
       2 . The catalyst diagnosis apparatus for the internal combustion engine according to  claim 1 , wherein said OSC indicator calculation means calculates the OSC indicator based on a time of delay response from the time at which the output of said air-fuel ratio sensor is reversed from a rich state to a lean state, until the time at which the output of said oxygen sensor reaches a predetermined lean-determination threshold.  
   
   
       3 . A catalyst diagnosis apparatus for an internal combustion engine including, in an intake passage, intake air mass detection means for detecting intake air mass and, in an exhaust passage, a three-way catalyst, a linear air-fuel ratio sensor for detecting an air-fuel ratio in exhaust gas upstream of said three-way catalyst, and an oxygen sensor for detecting oxygen density in exhaust gas downstream of said three-way catalyst, wherein said catalyst diagnosis apparatus comprises: 
 center air-fuel ratio calculation means for calculating a center air-fuel ratio based on outputs of said intake air mass detection means, said linear air-fuel ratio sensor, and said oxygen sensor;    air-fuel ratio control means for controlling the air-fuel ratio based on the outputs of said intake air mass detection means, said linear air-fuel ratio sensor, said oxygen sensor, and said center air-fuel ratio calculation means;    center air-fuel ratio determination means for determining based on the output of said center air-fuel ratio calculation means whether the center air-fuel ratio is correctly calculated;    reaction rate calculation means for calculating a reaction rate of chemical reaction in said three-way catalyst based on the output of said oxygen sensor when said center air-fuel ratio determination means determines that the center air-fuel ratio is correctly calculated;    OSC indicator calculation means for calculating an OSC indicator indicating an oxygen storage capacity of said three-way catalyst based on the outputs of said linear air-fuel ratio sensor, said oxygen sensor, and said center air-fuel ratio calculation means when said center air-fuel ratio determination means determines that the center air-fuel ratio is correctly calculated; and    catalyst degradation determination means for determining degradation of said three-way catalyst based on the reaction rate calculated by said reaction rate calculation means and the OSC indicator calculated by said OSC indicator calculation means.    
   
   
       4 . The catalyst diagnosis apparatus for the internal combustion engine according to  claim 1 , wherein said reaction rate calculation means calculates the reaction rate before said OSC indicator calculation means calculates the OSC indicator.  
   
   
       5 . The catalyst diagnosis apparatus for the internal combustion engine according to  claim 4 , wherein the calculation of the OSC indicator by said OSC indicator calculation means is inhibited when the reaction rate calculated by said reaction rate calculation means is not larger than a predetermined value.  
   
   
       6 . The catalyst diagnosis apparatus for the internal combustion engine according to  claim 1 , wherein said reaction rate calculation means calculates the reaction rate based on a variation in the output of said oxygen sensor.  
   
   
       7 . The catalyst diagnosis apparatus for the internal combustion engine according to  claim 6 , wherein said reaction rate calculation means calculates the reaction rate based on at least one of parameters for the output of the oxygen sensor, including an amplitude, a standard deviation, a comparison result between a max-value and a minimum-value, and the number of times at which a peak value exceeds a predetermined range.  
   
   
       8 . The catalyst diagnosis apparatus for the internal combustion engine according to  claim 3 , wherein said center air-fuel ratio determination means determines whether the center air-fuel ratio is correctly calculated, depending on whether the air-fuel ratio exceeds a predetermined control range with respect to the center air-fuel ratio calculated by said center air-fuel ratio calculation means, and the calculation of the reaction rate by said reaction rate calculation means is stopped when the air-fuel ratio exceeds the predetermined control range with respect to the center air-fuel ratio.  
   
   
       9 . The catalyst diagnosis apparatus for the internal combustion engine according to  claim 8 , wherein even after the air-fuel ratio has returned to the predetermined control range with respect to the center air-fuel ratio, the calculation of the reaction rate by said reaction rate calculation means is continuously stopped until a predetermined time is lapsed from a time of returning to the predetermined control range.  
   
   
       10 . The catalyst diagnosis apparatus for the internal combustion engine according to  claim 1 , further comprising reaction rate revision means for revising the reaction rate calculated by said reaction rate calculation means.  
   
   
       11 . The catalyst diagnosis apparatus for the internal combustion engine according to  claim 10 , wherein said reaction rate revision means revises the reaction rate based on at least one of the difference between an average of the intake air mass during the calculation of the OSC indicator and an average of the intake air mass during the calculation of the reaction rate, and the difference between an average of fuel mass during the calculation of the OSC indicator and an average of fuel mass during the calculation of the reaction rate.  
   
   
       12 . An automobile mounting an internal combustion engine including, in an intake passage, intake air mass detection means for detecting intake air mass and, in an exhaust passage, a three-way catalyst, a linear air-fuel ratio sensor for detecting an air-fuel ratio in exhaust gas upstream of said three-way catalyst, and an oxygen sensor for detecting oxygen density in exhaust gas downstream of said three-way catalyst, said internal combustion engine including a catalyst diagnosis unit, wherein said catalyst diagnosis unit comprises: 
 center air-fuel ratio calculation means for calculating a center air-fuel ratio based on outputs of said intake air mass detection means, said linear air-fuel ratio sensor, and said oxygen sensor;    air-fuel ratio control means for controlling the air-fuel ratio based on the outputs of said intake air mass detection means, said linear air-fuel ratio sensor, said oxygen sensor, and said center air-fuel ratio calculation means;    center air-fuel ratio determination means for determining based on the output of said center air-fuel ratio calculation means whether the center air-fuel ratio is correctly calculated;    reaction rate calculation means for calculating a reaction rate of chemical reaction in said three-way catalyst based on the output of said oxygen sensor when said center air-fuel ratio determination means determines that the center air-fuel ratio is correctly calculated;    OSC indicator calculation means for calculating an OSC indicator indicating an oxygen storage capacity of said three-way catalyst based on the outputs of said linear air-fuel ratio sensor, said oxygen sensor, and said center air-fuel ratio calculation means when said center air-fuel ratio determination means determines that the center air-fuel ratio is correctly calculated; and    catalyst degradation determination means for determining degradation of said three-way catalyst based on the reaction rate calculated by said reaction rate calculation means and the OSC indicator calculated by said OSC indicator calculation means.