Deterioration diagnosis apparatus for selective catalytic reduction catalyst

Patent metadata

Field	Value
Publication number	US-2017167352-A1
Application number	US-201615375800-A
Country	US
Kind code	A1
Filing date	Dec 12, 2016
Priority date	Dec 14, 2015
Publication date	Jun 15, 2017
Grant date	—

Abstract

In a deterioration diagnosis apparatus for a selective catalytic reduction (SCR) catalyst in which when an air fuel ratio of a mixture to be combusted in an internal combustion engine is a lean air fuel ratio, inducement processing is executed which is to induce a water gas shift reaction in a pre-stage catalyst, by changing the air fuel ratio of the mixture from the lean air fuel ratio to a predetermined rich air fuel ratio, and diagnosis processing is executed which is to diagnose deterioration of the SCR catalyst based on an output difference between two air fuel ratio sensors at the time of the execution of the inducement processing, when the SCR catalyst is in a state of being subjected to sulfur poisoning resulting from the execution of the S purge processing of the pre-stage catalyst, diagnosis processing is not executed.

First claim

What is claimed is:

1 . A deterioration diagnosis apparatus for a selective catalytic reduction catalyst, which is applied to an exhaust gas purification system including:
a pre-stage catalyst that is arranged in an exhaust passage of an internal combustion engine which is able to be operated in a lean burn state, and that is configured to generate a water gas shift reaction by making use of a reducing agent produced at the time of a mixture being combusted, when an air fuel ratio of the mixture is a predetermined rich air fuel ratio which is lower than a stoichiometric air fuel ratio; a selective catalytic reduction catalyst that is arranged in the exhaust passage at a location downstream of the pre-stage catalyst, and configured to have a function to store oxygen in exhaust gas when an air fuel ratio of the exhaust gas is a lean air fuel ratio higher than the stoichiometric air fuel ratio, but to desorb the oxygen thus stored when the air fuel ratio of the exhaust gas is equal to or lower than the stoichiometric air fuel ratio; a first air fuel ratio sensor that is arranged in the exhaust passage at a location between the pre-stage catalyst and the selective catalytic reduction catalyst, and that is configured to measure a physical quantity correlated with an air fuel ratio of exhaust gas flowing into the selective catalytic reduction catalyst; and a second air fuel ratio sensor that is arranged in the exhaust passage at a location downstream of the selective catalytic reduction catalyst, and that is configured to measure a physical quantity correlated with an air fuel ratio of exhaust gas flowing out from the selective catalytic reduction catalyst; the deterioration diagnosis apparatus comprising: a controller that is configured to execute an inducement processing, which is to induce a water gas shift reaction in the pre-stage catalyst, by controlling an operating state of the internal combustion engine so that the air fuel ratio of the mixture is changed to the predetermined rich air fuel ratio, when the air fuel ratio of the mixture is the lean air fuel ratio, and to execute a diagnosis processing, which is to diagnose deterioration of the selective catalytic reduction catalyst based on a total sensor output difference which is an integrated value of a difference between a measured value of the first air fuel ratio sensor and a measured value of the second air fuel ratio sensor in a period of time in which the water gas shift reaction occurs in the pre-stage catalyst by the execution of the inducement processing; wherein the controller inhibits the execution of the diagnosis processing in a period of time from when S purge processing, which is to eliminate sulfur poisoning of the pre-stage catalyst, is terminated, until a desorption period of time, which is a period of time in which oxygen is estimated to be supplied to the selective catalytic reduction catalyst in a state where the temperature of the selective catalytic reduction catalyst becomes equal to or higher than a desorption temperature which is a temperature at which sulfur components desorb from the selective catalytic reduction catalyst, exceeds a predetermined period of time.

2 . The deterioration diagnosis apparatus for a selective catalytic reduction catalyst according to claim 1 ,
wherein the controller calculates an integrated time calculation value correlated with an integrated value of a period of time in which a condition is satisfied under which after the end of the S purge processing, oxygen is estimated to be supplied to the selective catalytic reduction catalyst in the state where the temperature of the selective catalytic reduction catalyst becomes equal to or higher than the desorption temperature which is the temperature at which sulfur components desorb from the selective catalytic reduction catalyst, and makes a determination that the desorption period of time has exceeded the predetermined period of time, when the integrated time calculation value thus obtained has exceeded a required desorption period of time.

3 . The deterioration diagnosis apparatus for a selective catalytic reduction catalyst according to claim 2 ,
wherein a first temperature range, a second temperature range higher than the first temperature range, and a third temperature range higher than the second temperature range are included in a temperature region which is equal to or higher than the desorption temperature, wherein, in the desorption period of time, when the temperature of the selective catalytic reduction catalyst falls within the first temperature range or the third temperature range, the controller makes larger an amount of update per time of the integrated time calculation value in comparison with the time when the temperature of the selective catalytic reduction catalyst falls within the second temperature range.

4 . The deterioration diagnosis apparatus for a selective catalytic reduction catalyst according to claim 2 ,
wherein the controller makes larger an amount of update per time of the integrated time calculation value in the case where the temperature of the selective catalytic reduction catalyst at the time of the execution of the S purge processing is low, in comparison with the case where it is high.

5 . The deterioration diagnosis apparatus for a selective catalytic reduction catalyst according to claim 3 ,
wherein the controller makes larger an amount of update per time of the integrated time calculation value in the case where the temperature of the selective catalytic reduction catalyst at the time of the execution of the S purge processing is low, in comparison with the case where it is high.

6 . The deterioration diagnosis apparatus for a selective catalytic reduction catalyst according to claim 1 ,
wherein the controller calculates an instantaneous desorption amount correlation value which is a physical quantity correlated with an amount of sulfur components desorbing per unit time from the selective catalytic reduction catalyst, by using, as a parameter, an amount of oxygen supplied to the selective catalytic reduction catalyst in the desorption period of time, and makes a determination that the desorption period of time has exceeded the predetermined period of time, when an integrated value of the instantaneous desorption amount correlation value has exceeded a predetermined amount of desorption.

7 . The deterioration diagnosis apparatus for a selective catalytic reduction catalyst according to claim 6 ,
wherein a first temperature range, a second temperature range higher than the first temperature range, and a third temperature range higher than the second temperature range are included in a temperature region which is equal to or higher than the desorption temperature; and wherein, in the desorption period of time, when the temperature of the selective catalytic reduction catalyst falls within the first temperature range or the third temperature range, the controller makes larger the instantaneous desorption amount correlation value in comparison with the time when the temperature of the selective catalytic reduction catalyst falls within the second temperature range.

8 . The deterioration diagnosis apparatus for a selective catalytic reduction catalyst according to claim 6 ,
wherein the controller makes larger the instantaneous desorption amount correlation value in the case where the temperature of the selective catalytic reduction catalyst at the time of the execution of the S purge processing is low, in comparison with the case where it is high.

9 . The deterioration diagnosis apparatus for a selective catalytic reduction catalyst according to claim 7 ,
wherein the controller makes larger the instantaneous desorption am

Assignees

• Toyota Motor Co Ltd

Inventors

• Hagiwara Koji
• Kidokoro Toru
• Iwazaki Yasushi
• Fujiwara Takahiko

Classifications

• F01N2900/1404

  Exhaust gas temperature · CPC title

• B01D53/9495

  Controlling the catalytic process · CPC title

• B01D53/9431

  Processes characterised by a specific device · CPC title

• B01D53/9418

  for removing nitrogen oxides by selective catalytic reduction [SCR] using a reducing agent in a lean exhaust gas · CPC title

• F01N11/002

  the diagnostic devices measuring or estimating temperature or pressure in, or downstream of the exhaust apparatus · CPC title