Diagnosis of a urea SCR catalytic system

• US 6,925,796 B2
• Filed: 11/19/2003
• Issued: 08/09/2005
• Est. Priority Date: 11/19/2003
• Status: Active Grant

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Nieuwstadt, Michiel van, Upadhyay, Devesh
• Primary Examiner(s): Denion, Thomas
• Assistant Examiner(s): TRAN, DIEM T
• Application Number:
  US10/716,137
• Publication Number:
  US 20050103000A1
• Time in Patent Office: 629 Days
• Field of Search: 602/74, 602/76, 602/77
• US Class Current: 60/277
• CPC Class Codes: F01N 11/00 Monitoring or diagnostic devices for exhaust-gas treatment apparatus , e.g. for catalytic activity safety, indicating or supervising devices for internal combustion engines F02B77/08; testing of machines G01M13/00
• CPC Class Codes: F01N 13/009 having two or more separate purifying devices arranged in series
• CPC Class Codes: F01N 2550/00 Monitoring or diagnosing the deterioration of exhaust systems
• CPC Class Codes: F01N 2550/05 Systems for adding substances into exhaust
• CPC Class Codes: F01N 2610/02 the substance being ammonia or urea
• CPC Class Codes: F01N 2610/03 the substance being hydrocarbons, e.g. engine fuel
• CPC Class Codes: F01N 2900/14 said parameters being related to the exhaust gas
• CPC Class Codes: F01N 2900/1402 Exhaust gas composition
• CPC Class Codes: F01N 3/035 with catalytic reactors , e.g. catalysed diesel particulate filters
• CPC Class Codes: F01N 3/0871 Regulation of absorbents or adsorbents, e.g. purging by electrically controlling the supply of combustible mixture or its constituents only F02D41/0235
• CPC Class Codes: F01N 3/103 Oxidation catalysts for HC and CO only
• CPC Class Codes: F01N 3/208 Control of selective catalytic reduction [SCR], e.g. dosing of reducing agent
• CPC Class Codes: F02D 41/1441 Plural sensors
• CPC Class Codes: F02D 41/146 the characteristics being an NOx content or concentration
• CPC Class Codes: F02D 41/1495 Detection of abnormalities in the air/fuel ratio feedback system
• CPC Class Codes: F02D 41/222 relating to the failure of sensors or parameter detection devices
• CPC Class Codes: G01N 27/4175 Calibrating or checking the analyser
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

A method for diagnosing degradation in a pair of NOx sensors coupled upstream and downstream of a NOx catalyst is presented. The method is performed when catalyst temperature is such that its NOx conversion efficiency is substantially zero, such as when the catalyst temperature is very low (at cold start) or very high (e.g., following regeneration). Under those conditions, sensor degradation can be diagnosed if the upstream and downstream NOx sensor readings are not substantially the same.

Claims

1. A method for diagnosing degradation of an emission control system coupled downstream of an internal combustion engine, the system including a NOx catalyst having a first NOx sensor coupled upstream of the catalyst and a second NOx sensor coupled downstream of the catalyst, the method comprising:

providing an indication of an operating condition;

in response to said indication diagnosing the first NOx sensor degradation if a difference between a first NOx sensor signal and an estimated amount of NOx in an exhaust gas mixture upstream of the catalyst is greater than a first predetermined value; and

diagnosing the second NOx sensor degradation if a difference between a first NOx sensor signal and an estimated amount of NOx in an exhaust gas mixture upstream of the catalyst is less than said first predetermined value and a difference between said first NOx sensor signal and a second NOx sensor signal is greater than a second predetermined value.

2. The method as set forth in claim 1 wherein the NOx catalyst is an SCR catalyst.

3. The method as set forth in claim 1 wherein the NOx catalyst is an ALNC catalyst.

4. The method as set forth in claim 1 wherein said NOx catalyst is an LNT.

5. The method as set forth in claim 4 wherein said operating condition is a temperature of said LNT wherein there is substantially no NOx conversion or adsorption in said LNT.

6. The method as set forth in claim 1 wherein said operating condition is a catalyst temperature below 150°

C.

7. The method as set forth in claim 1 wherein said operating condition is a catalyst temperature greater than 450°

C.

8. A method for diagnosing degradation of a lean exhaust gas aftertreatment system, the system including a NOx catalyst having a first NOx sensor coupled upstream of the catalyst and a second NOx sensor coupled downstream of the catalyst, the method comprising:

comparing a first NOx sensor measurement and a second NOx sensor measurement when the catalyst is within a temperature range wherein a NOx conversion efficiency of the catalyst is substantially zero; and

providing an indication of system degradation when a difference between said first NOx sensor measurement and said second sensor measurement is greater than a predetermined value.

9. A method for diagnosing degradation of a lean exhaust gas aftertreatment system, the system including a Lean NOx Trap (LNT) having a first NOx sensor coupled upstream of the LNT and a second NOx sensor coupled downstream of the LNT, the method comprising:

comparing a first NOx sensor measurement and a second NOx sensor measurement when the catalyst is within a temperature range wherein there is substantially no NOx conversion or adsorption in the LNT; and

providing an indication of system degradation when a difference between said first NOx sensor measurement and said second sensor measurement is greater than a second predetermined value.