Apparatus for diagnosing deterioration of nox absorption-reduction catalyst

Abstract

An apparatus for diagnosing deterioration of a NOx absorption-reduction catalyst provided at an exhaust path of an engine includes a sensor disposed upstream of the catalyst to sense a NOx concentration in emission gas, a calculating unit calculating a first ratio of emission of NOx to inflow of NOx or a second ratio of absorption of NOx to inflow of NOx, and a diagnosing unit which diagnoses deterioration of the catalyst using the first or second ratio as an indicator. The calculating unit calculates inflow of NOx based on an output of the sensor and either the flow volume of the emission gas or a correlation value of the flow volume of the emission gas, calculates the absorption of NOx based on the amount of rich components required for reducing the NOx, and calculates the emission of NOx based on the difference between the inflow and absorption of NOx.

1 . An apparatus for diagnosing deterioration of a NOx absorption-reduction catalyst provided at an exhaust path of an internal combustion engine, comprising:
 a NOx sensor disposed upstream of the catalyst to sense a NOx concentration in emission gas that flows into the catalyst;   a deterioration diagnostic indicator calculating unit which calculates a first ratio of the amount of emission of NOx from the catalyst, to the amount of inflow of NOx into the catalyst, or a second ratio of the amount of absorption of NOx in the catalyst, to the amount of inflow of NOx into the catalyst; and   a deterioration diagnosing unit which diagnoses deterioration of the catalyst by using the first ratio or the second ratio as a deterioration diagnostic indicator,   wherein the deterioration diagnostic indicator calculating unit calculates the amount of inflow of NOx into the catalyst based on an output of the NOx sensor and either the flow volume of the emission gas into the catalyst or a correlation value of the flow volume of the emission gas, calculates the amount of absorption of NOx in the catalyst based on the amount of rich components required for reducing the NOx absorbed by the NOx catalyst, and calculates the amount of emission of NOx from the catalyst based on the difference between the amount of inflow of NOx into the catalyst and the amount of absorption of NOx in the catalyst.   
   
   
       2 . The apparatus according to  claim 1 , wherein
 the deterioration diagnostic indicator calculating unit inhibits the calculation of the amount of inflow of NOx into the catalyst during a rich period when the emission gas flowing around the NOx sensor is richer than a theoretical air-fuel ratio.   
   
   
       3 . The apparatus according to  claim 2 , wherein
 the NOx sensor senses an O 2  concentration or an air-fuel ratio in the emission gas, and   the deterioration diagnostic indicator calculating unit determines whether or not the emission gas flowing around the NOx sensor is richer than the theoretical air-fuel ratio, based on the O 2  concentration or the air-fuel ratio sensed by the NOx sensor.   
   
   
       4 . An apparatus for diagnosing deterioration of a NOx absorption-reduction catalyst provided at an exhaust path of an internal combustion engine, comprising:
 a NOx sensor disposed downstream of the catalyst to sense a NOx concentration in emission gas that is emitted from the catalyst;   a deterioration diagnostic indicator calculating unit which calculates a first ratio of the amount of emission of NOx from the catalyst, to the amount of inflow of NOx into the catalyst, or a second ratio of the amount of absorption of NOx in the catalyst, to the amount of inflow of NOx into the catalyst; and   a deterioration diagnosing unit which diagnoses deterioration of the catalyst by using the first ratio or the second ratio as a deterioration diagnostic indicator,   wherein the deterioration diagnostic indicator calculating unit calculates the amount of emission of NOx from the catalyst based on an output of the NOx sensor and either the flow volume of the emission gas from the catalyst or a correlation value of the flow volume of the emission gas, calculates the amount of absorption of NOx in the catalyst based on the amount of rich components required for reducing the NOx absorbed in the NOx catalyst, and calculates the amount of inflow of NOx into the catalyst by adding the amount of absorption of NOx in the catalyst to the amount of emission of NOx from the catalyst.   
   
   
       5 . The apparatus according to  claim 4 , wherein
 the deterioration diagnostic indicator calculating unit inhibits the calculation of the amount of emission of NOx from the catalyst during a rich period when the emission gas flowing into the catalyst is richer than a theoretical air-fuel ratio.   
   
   
       6 . The apparatus according to  claim 4 , wherein
 the deterioration diagnostic indicator calculating unit calculates, during a rich period when the emission gas flowing into the catalyst is richer than a theoretical air-fuel ratio, the amount of emission of NOx from the catalyst by using a value resulting from an upper limit guard process to which an output of the NOx sensor during the rich period is subjected with an output of the NOx sensor immediately before the rich period.   
   
   
       7 . The apparatus according to  claim 5 , further comprising an O 2  sensor disposed upstream of the catalyst to sense an O 2  concentration in the emission gas, wherein
 the deterioration diagnostic indicator calculating unit determines whether or not the emission gas flowing into the catalyst is richer than the theoretical air-fuel ratio, based on the O 2  concentration sensed by the O 2  sensor.   
   
   
       8 . The apparatus according to  claim 5 , further comprising an air-fuel ratio sensor disposed upstream of the catalyst to sense an air-fuel ratio in the emission gas, wherein
 the deterioration diagnostic indicator calculating unit determines whether or not the emission gas flowing into the catalyst is richer than the theoretical air-fuel ratio, based on the air-fuel ratio sensed by the air-fuel ratio sensor.   
   
   
       9 . The apparatus according to  claim 1 , wherein
 the deterioration diagnostic indicator calculating unit calculates the amount of absorption of NOx in the catalyst based on the difference between the amount of rich components flowing into the catalyst and the amount of rich components emitted from the catalyst, when reducing the NOx absorbed in the catalyst.