Degradation detection method for an engine having a NOx sensor

• US 6,860,100 B1
• Filed: 03/14/2001
• Issued: 03/01/2005
• Est. Priority Date: 03/17/2000
• Status: Active Grant

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Surnilla, Gopichandra, Bidner, David Karl
• Primary Examiner(s): Denion, Thomas
• Assistant Examiner(s): NGUYEN, TU MINH
• Application Number:
  US09/805,028
• Time in Patent Office: 1,448 Days
• Field of Search: 602/74, 602/76, 602/77, 602/85, 123/688, 204/424, 204/425, 204/426, 204/427, 204/428, 204/429, 205/781, 205/784, 205/784.5, 205/785
• US Class Current: 60/277
• CPC Class Codes: F01N 11/007 the diagnostic devices measuring oxygen or air concentration downstream of the exhaust apparatus
• CPC Class Codes: F01N 3/0807 by using absorbents or adsorbents
• CPC Class Codes: F01N 3/0885 Regeneration of deteriorated absorbents or adsorbents, e.g. desulfurization of NOx traps
• CPC Class Codes: F02D 2041/389 for injecting directly into the cylinder
• CPC Class Codes: F02D 2200/023 Temperature of lubricating oil or working fluid
• CPC Class Codes: F02D 2200/0802 Temperature of the exhaust gas treatment apparatus
• CPC Class Codes: F02D 2200/0806 NOx storage amount, i.e. amount of NOx stored on NOx trap
• CPC Class Codes: F02D 2200/0808 NOx storage capacity, i.e. maximum amount of NOx that can be stored on NOx trap
• CPC Class Codes: F02D 2200/0811 NOx storage efficiency
• CPC Class Codes: F02D 2200/703 Atmospheric pressure
• CPC Class Codes: F02D 41/028 Desulfurisation of NOx traps or adsorbent
• CPC Class Codes: F02D 41/1446 the characteristics being exhaust temperatures
• CPC Class Codes: F02D 41/1454 the characteristics being an oxygen content or concentration or the air-fuel ratio
• CPC Class Codes: F02D 41/1465 with determination means using an estimation
• CPC Class Codes: F02D 41/187 using a hot wire flow sensor
• CPC Class Codes: F02D 41/22 Safety or indicating devices for abnormal conditions in air/fuel ratio feedback systems F02D41/1495, in electric control linkage F02D11/107, in purge control systems F02M25/0809
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

An engine diagnostic system for use with an internal combustion engine coupled to a lean NOx trap with a NOx sensor coupled downstream of the trap is disclosed. Degradation of the NOx sensor is determined by estimating NOx exiting the trap based on engine out NOx and various other operating conditions. When the difference between the measured NOx and estimated NOx is greater than a predetermined value for a predetermined duration, degradation is indicated.

Claims

1. A method for determining degradation in an emission control system coupled to an internal combustion engine comprising:

providing first and second signals from a sensor coupled downstream of the engine, said first output signal and said second output signal respectively indicative of a first exhaust gas constituent flowing through the emission control system and a second exhaust gas constituent flowing through the emission control system;

generating an estimate of said second exhaust gas constituent based at least on said first exhaust gas constituent and an engine operating condition; and

indicating when said estimate of said second exhaust gas constituent and said second exhaust gas constituent differ by a predetermined value at least during stoichiometric conditions.

2. The method recited in claim 1 wherein said indicating further comprises indicating when said estimate of said exhaust gas constituent and said second exhaust gas constituent differ by said predetermined value for a preselected time.

3. The method recited in claim 2 wherein said second exhaust gas constituent is a NOx concentration.

4. The method recited in claim 3 wherein said generating further comprises generating said estimate based at least on an engine out NOx concentration.

5. The method recited in claim 4 wherein said generating further comprises generating said estimate based at least on an exhaust air-fuel ratio.

6. The method recited in claim 5 where said generating further comprises taking into consideration efficiency of the emission control system.

7. The method recited in claim 6 wherein said emission control system is a NOx trap.

8. The method recited in claim 7 further comprising taking into account temperature of the emission control system.

9. An article of manufacture, comprising:

a computer storage medium having a computer program encoded therein method for determining degradation in an emission control system coupled to an internal combustion engine, said computer storage medium comprising;

code for providing first and second signals from a sensor coupled downstream of the engine, said first output signal and said second output signal respectively indicative of a NOx concentration and an air-fuel ratio flowing through the emission control system;

code for generating an estimate of said NOx concentration based at least on said air-fuel ratio and an engine operating condition; and

code for indicating when said estimate and said NOx concentration differ by a predetermined value for a preselected duration at least during stoichiometric conditions.

10. An emission control system for an internal combustion engine, comprising:

a NOx absorbent disposed in an exhaust passage downstream of the internal combustion engine that stores and reacts NOx under certain operating conditions;

a NOx sensor disposed in the exhaust passage downstream of the NOx absorbent, a first output of the NOx sensor corresponding to a NOx concentration of exhaust gas flowing out of the NOx absorbent, and a second output of the NOx sensor corresponding to an oxygen concentration;

a controller controlling a lean operating condition of the internal combustion engine based on the first output value of the NOx sensor;

determining a deviation of the first output value of the NOx sensor from a predetermined value, said predetermined value based on said second output value of the NOx sensor, said deviation determined when preselected engine operating conditions, including stoichiometric operation conditions, are met; and

determining degradation of the NOx sensor based on said deviation; and

an electronically controlled throttle plate disposed in an intake passage of the internal combustion engine receiving a command from said controller.