Deterioration determination device and method for exhaust emission reduction device, and engine control unit

Abstract

A deterioration determination device for an exhaust emission reduction device which is capable of accurately and rapidly determining deterioration of a NOx purifying catalyst. The deterioration determination device for the exhaust emission reduction device for determining deterioration of the NOx purifying catalyst includes an ECU. The ECU executes high NOx concentration control in deterioration determination, calculates a NOx supply amount based on upstream NOx concentration detected during execution of the high NOx concentration control, calculates a NOx slip amount based on downstream NOx concentration detected during execution of the high NOx concentration control, and determines the NOx purifying catalyst to be deteriorated when the condition of the NOx slip amount >a reference value is satisfied, in a case where the NOx supply amount> a reference value holds.

1 . A deterioration determination device for an exhaust emission reduction device including a NOx purifying catalyst that is provided in an exhaust passage of an internal combustion engine, for trapping, when exhaust gases forming an oxidation atmosphere flow therein, NOx in the exhaust gases, the deterioration determination device determining deterioration of the NOx purifying catalyst, comprising:
 upstream NOx concentration parameter-detecting means for detecting a parameter indicative of a NOx concentration in exhaust gases upstream of the NOx purifying catalyst, as an upstream NOx concentration parameter;   downstream NOx concentration parameter-detecting means for detecting a parameter indicative of a NOx concentration in exhaust gases downstream of the NOx purifying catalyst, as a downstream NOx concentration parameter;   control means for performing oxidation atmosphere control for controlling the exhaust gases flowing into the NOx purifying catalyst to an oxidation atmosphere;   NOx supply amount-calculating means for calculating an integrated value of an amount of NOx having flowed into the NOx purifying catalyst, as a NOx supply amount, using the upstream NOx concentration parameter detected during execution of the oxidation atmosphere control;   NOx slip amount-calculating means for calculating an integrated value of an amount of NOx having flowed through the NOx purifying catalyst, as a NOx slip amount, using the downstream NOx concentration parameter detected during execution of the oxidation atmosphere control; and   deterioration determination means for determining deterioration of the NOx purifying catalyst by comparing the calculated NOx slip amount with a predetermined reference value when the calculated NOx supply amount exceeds a predetermined threshold.   
   
   
       2 . A deterioration determination device as claimed in  claim 1 , further comprising:
 execution condition-determining means for determining whether or not conditions for executing the deterioration determination of the NOx purifying catalyst are satisfied during execution of the oxidation atmosphere control; and   zero point-correcting means for correcting a zero point of the downstream NOx concentration parameter detected after satisfaction of the conditions for executing the deterioration determination, and wherein said NOx slip amount-calculating means calculates the NOx slip amount, using the downstream NOx concentration parameter of which the zero point has been corrected.   
   
   
       3 . A deterioration determination device as claimed in  claim 2 , wherein said zero point-correcting means corrects the zero point of the downstream NOx concentration parameter based on an average value of a plurality of values of the downstream NOx concentration parameter detected during a predetermined time period after satisfaction of the conditions for executing the deterioration determination. 
   
   
       4 . A deterioration determination device as claimed in  claim 1 , further comprising:
 execution condition-determining means for determining whether or not the conditions for executing the deterioration determination for the NOx purifying catalyst are satisfied during execution of the oxidation atmosphere control; and   reference value-calculating means for calculating the predetermined reference value based on the downstream NOx concentration parameter detected after satisfaction of the conditions for executing the deterioration determination.   
   
   
       5 . A deterioration determination device as claimed in  claim 4 , wherein said reference value-calculating means calculates the predetermined reference value based on an average value of a plurality of values of the downstream NOx concentration parameter detected during a predetermined time period after satisfaction of the conditions for executing the deterioration determination. 
   
   
       6 . A deterioration determination device as claimed in  claim 1 , further comprising execution condition-determining means for determining whether or not the conditions for executing the deterioration determination for the NOx purifying catalyst are satisfied during execution of the oxidation atmosphere control, and
 wherein said control means controls, during execution of the oxidation atmosphere control, the NOx concentration in the exhaust gases to a higher value when the conditions for executing the deterioration determination are satisfied than when the conditions for executing the deterioration determination are not satisfied.   
   
   
       7 . A deterioration determination device as claimed in  claim 6 , wherein the NOx purifying catalyst has characteristics of reducing the trapped NOx when the exhaust gases flow therein form a reduction atmosphere,
 the deterioration determination device further comprising NOx trapping amount-calculating means for calculating an amount of NOx trapped by the NOx purifying catalyst during execution of the oxidation atmosphere control, as a NOx trapping amount,   wherein said control means terminates the oxidation atmosphere control when the NOx trapping amount calculated during execution of the oxidation atmosphere control exceeds a predetermined trapping reference value, and controls the exhaust gases flowing into the NOx purifying catalyst to the reduction atmosphere,   the deterioration determination device further comprising trapping reference value-setting means for setting the predetermined trapping reference value to a larger value when the conditions for executing the deterioration determination are satisfied during execution of the oxidation atmosphere control than when the conditions for executing the deterioration determination are not satisfied.   
   
   
       8 . A deterioration determination device as claimed in  claim 1 , wherein said deterioration determination means executes determining the deterioration of the NOx purifying catalyst when the NOx slip amount exceeds a predetermined value in a case where the NOx supply amount is not more than the predetermined threshold. 
   
   
       9 . A deterioration determination device as claimed in  claim 1 , wherein a downstream NOx purifying catalyst is provided downstream of the NOx purifying catalyst in the exhaust passage of the engine, for trapping, when exhaust gases forming the oxidation atmosphere flow therein, NOx in the exhaust gases. 
   
   
       10 . A deterioration determination method for an exhaust emission reduction device including a NOx purifying catalyst that is provided in an exhaust passage of an internal combustion engine, for trapping, when exhaust gases forming an oxidation atmosphere flow therein, NOx in the exhaust gases, the deterioration determination method determining deterioration of the NOx purifying catalyst, comprising:
 detecting a parameter indicative of a NOx concentration in exhaust gases upstream of the NOx purifying catalyst, as an upstream NOx concentration parameter;   detecting a parameter indicative of a NOx concentration in exhaust gases downstream of the NOx purifying catalyst, as a downstream NOx concentration parameter;   performing oxidation atmosphere control for controlling the exhaust gases flowing into the NOx purifying catalyst to an oxidation atmosphere;   calculating an integrated value of an amount of NOx having flowed into the NOx purifying catalyst, as a NOx supply amount, using the upstream NOx concentration parameter detected during execution of the oxidation atmosphere control;   calculating an integrated value of an amount of NOx having flowed through the NOx purifying catalyst, as a NOx slip amount, using the downstream NOx concentration parameter detected during execution of the oxidation atmosphere control; and   determining deterioration of the NOx purifying catalyst by comparing the calculated NOx slip amount with a predetermined reference value when the calculated NOx supply amount exceeds a predetermined threshold.   
   
   
       11 . A deterioration determination method as claimed in  claim 10 , further comprising:
 determining whether or not conditions for executing the deterioration determination of the NOx purifying catalyst are satisfied during execution of the oxidation atmosphere control; and   correcting a zero point of the downstream NOx concentration parameter detected after satisfaction of the conditions for executing the deterioration determination,   wherein said calculating the NOx slip amount includes calculating the NOx slip amount, using the downstream NOx concentration parameter of which the zero point has been corrected.   
   
   
       12 . A deterioration determination method as claimed in  claim 11 , wherein said correcting a zero point includes correcting the zero point of the downstream NOx concentration parameter based on an average value of a plurality of values of the downstream NOx concentration parameter detected during a predetermined time period after satisfaction of the conditions for executing the deterioration determination. 
   
   
       13 . A deterioration determination method as claimed in  claim 10 , further comprising:
 determining whether or not the conditions for executing the deterioration determination for the NOx purifying catalyst are satisfied during execution of the oxidation atmosphere control; and   calculating the predetermined reference value based on the downstream NOx concentration parameter detected after satisfaction of the conditions for executing the deterioration determination.   
   
   
       14 . A deterioration determination method as claimed in  claim 13 , wherein said calculating the predetermined reference value includes calculating the predetermined reference value based on an average value of a plurality of values of the downstream NOx concentration parameter detected during a predetermined time period after satisfaction of the conditions for executing the deterioration determination. 
   
   
       15 . A deterioration determination method as claimed in  claim 10 , further comprising determining whether or not the conditions for executing the deterioration determination for the NOx purifying catalyst are satisfied during execution of the oxidation atmosphere control, and
 wherein said performing oxidation atmosphere control includes controlling, during execution of the oxidation atmosphere control, the NOx concentration in the exhaust gases to a higher value when the conditions for executing the deterioration determination are satisfied than when the conditions for executing the deterioration determination are not satisfied.   
   
   
       16 . A deterioration determination method as claimed in  claim 15 , wherein the NOx purifying catalyst has characteristics of reducing the trapped NOx when the exhaust gases flow therein form a reduction atmosphere,
 the deterioration determination method further comprising calculating an amount of NOx trapped by the NOx purifying catalyst during execution of the oxidation atmosphere control, as a NOx trapping amount,   wherein said performing oxidation atmosphere control includes terminating the oxidation atmosphere control when the NOx trapping amount calculated during execution of the oxidation atmosphere control exceeds a predetermined trapping reference value, and controls the exhaust gases flowing into the NOx purifying catalyst to the reduction atmosphere,   the deterioration determination method further comprising trapping reference value-setting means for setting the predetermined trapping reference value to a larger value when the conditions for executing the deterioration determination are satisfied during execution of the oxidation atmosphere control than when the conditions for executing the deterioration determination are not satisfied.   
   
   
       17 . A deterioration determination method as claimed in  claim 10 , wherein said determining deterioration includes executing determining the deterioration of the NOx purifying catalyst when the NOx slip amount exceeds a predetermined value in a case where the NOx supply amount is not more than the predetermined threshold. 
   
   
       18 . A deterioration determination method as claimed in  claim 10 , wherein a downstream NOx purifying catalyst is provided downstream of the NOx purifying catalyst in the exhaust passage of the engine, for trapping, when exhaust gases forming the oxidation atmosphere flow therein, NOx in the exhaust gases. 
   
   
       19 . An engine control unit including a control program for causing a computer to execute a deterioration determination method for an exhaust emission reduction device including a NOx purifying catalyst that is provided in an exhaust passage of an internal combustion engine, for trapping, when exhaust gases forming an oxidation atmosphere flow therein, NOx in the exhaust gases, the deterioration determination method determining deterioration of the NOx purifying catalyst,
 wherein the deterioration determination method comprises:   detecting a parameter indicative of a NOx concentration in exhaust gases upstream of the NOx purifying catalyst, as an upstream NOx concentration parameter;   detecting a parameter indicative of a NOx concentration in exhaust gases downstream of the NOx purifying catalyst, as a downstream NOx concentration parameter;   performing oxidation atmosphere control for controlling the exhaust gases flowing into the NOx purifying catalyst to an oxidation atmosphere;   calculating an integrated value of an amount of NOx having flowed into the NOx purifying catalyst, as a NOx supply amount, using the upstream NOx concentration parameter detected during execution of the oxidation atmosphere control;   calculating an integrated value of an amount of NOx having flowed through the NOx purifying catalyst, as a NOx slip amount, using the downstream NOx concentration parameter detected during execution of the oxidation atmosphere control; and   determining deterioration of the NOx purifying catalyst by comparing the calculated NOx slip amount with a predetermined reference value when the calculated NOx supply amount exceeds a predetermined threshold.   
   
   
       20 . An engine control unit as claimed in  claim 19 , wherein the deterioration determination method further comprises:
 determining whether or not conditions for executing the deterioration determination of the NOx purifying catalyst are satisfied during execution of the oxidation atmosphere control; and   correcting a zero point of the downstream NOx concentration parameter detected after satisfaction of the conditions for executing the deterioration determination,   wherein said calculating the NOx slip amount includes calculating the NOx slip amount, using the downstream NOx concentration parameter of which the zero point has been corrected.   
   
   
       21 . An engine control unit as claimed in  claim 20 , wherein said correcting a zero point includes correcting the zero point of the downstream NOx concentration parameter based on an average value of a plurality of values of the downstream NOx concentration parameter detected during a predetermined time period after satisfaction of the conditions for executing the deterioration determination. 
   
   
       22 . An engine control unit as claimed in  claim 19 , wherein the deterioration determination method further comprises:
 determining whether or not the conditions for executing the deterioration determination for the NOx purifying catalyst are satisfied during execution of the oxidation atmosphere control; and   calculating the predetermined reference value based on the downstream NOx concentration parameter detected after satisfaction of the conditions for executing the deterioration determination.   
   
   
       23 . An engine control unit as claimed in  claim 22 , wherein said calculating the predetermined reference value includes calculating the predetermined reference value based on an average value of a plurality of values of the downstream NOx concentration parameter detected during a predetermined time period after satisfaction of the conditions for executing the deterioration determination. 
   
   
       24 . An engine control unit as claimed in  claim 19 , wherein the deterioration determination method further comprises determining whether or not the conditions for executing the deterioration determination for the NOx purifying catalyst are satisfied during execution of the oxidation atmosphere control, and
 wherein said performing oxidation atmosphere control includes controlling, during execution of the oxidation atmosphere control, the NOx concentration in the exhaust gases to a higher value when the conditions for executing the deterioration determination are satisfied than when the conditions for executing the deterioration determination are not satisfied.   
   
   
       25 . An engine control unit as claimed in  claim 24 , wherein the NOx purifying catalyst has characteristics of reducing the trapped NOx when the exhaust gases flow therein form a reduction atmosphere, wherein the deterioration determination method further comprises calculating an amount of NOx trapped by the NOx purifying catalyst during execution of the oxidation atmosphere control, as a NOx trapping amount,
 wherein said performing oxidation atmosphere control includes terminating the oxidation atmosphere control when the NOx trapping amount calculated during execution of the oxidation atmosphere control exceeds a predetermined trapping reference value, and controls the exhaust gases flowing into the NOx purifying catalyst to the reduction atmosphere,   wherein the deterioration determination method further comprises trapping reference value-setting means for setting the predetermined trapping reference value to a larger value when the conditions for executing the deterioration determination are satisfied during execution of the oxidation atmosphere control than when the conditions for executing the deterioration determination are not satisfied.   
   
   
       26 . An engine control unit as claimed in  claim 19 , wherein said determining deterioration includes executing determining the deterioration of the NOx purifying catalyst when the NOx slip amount exceeds a predetermined value in a case where the NOx supply amount is not more than the predetermined threshold. 
   
   
       27 . An engine control unit as claimed in  claim 19 , wherein a downstream NOx purifying catalyst is provided downstream of the NOx purifying catalyst in the exhaust passage of the engine, for trapping, when exhaust gases forming the oxidation atmosphere flow therein, NOx in the exhaust gases.