Method and apparatus for estimating oxygen storage capacity and stored NOx in a lean NOx trap (LNT)

• US 6,826,902 B2
• Filed: 03/18/2003
• Issued: 12/07/2004
• Est. Priority Date: 03/18/2003
• Status: Active Grant

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Wang, Le Yi, Sun, Jing, Kim, Yong-Wha
• Primary Examiner(s): Tran, Binh Q.
• Application Number:
  US10/390,224
• Publication Number:
  US 20040182068A1
• Time in Patent Office: 630 Days
• Field of Search: 602/74, 602/76, 602/85, 602/86, 602/97
• US Class Current: 60/274
• 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 11/002 the diagnostic devices measuring or estimating temperature or pressure in, or downstream of the exhaust apparatus
• CPC Class Codes: F01N 11/007 the diagnostic devices measuring oxygen or air concentration downstream of the exhaust apparatus
• CPC Class Codes: F01N 13/009 having two or more separate purifying devices arranged in series
• CPC Class Codes: F01N 13/0097 the purifying devices are arranged in a single housing
• CPC Class Codes: F01N 2550/02 Catalytic activity of catalytic converters
• CPC Class Codes: F01N 2550/03 of sorbing activity of adsorbents or absorbents
• CPC Class Codes: F01N 2570/16 Oxygen
• CPC Class Codes: F01N 3/0814 combined with catalytic converters, e.g. NOx absorption/storage reduction catalysts
• CPC Class Codes: F01N 3/0842 Nitrogen oxides
• CPC Class Codes: F02D 2041/1433 using a model or simulation of the system
• CPC Class Codes: F02D 2200/0802 Temperature of the exhaust gas treatment apparatus
• CPC Class Codes: F02D 2200/0814 Oxygen storage amount
• CPC Class Codes: F02D 41/0275 the exhaust gas treating apparatus being a NOx trap or adsorbent
• CPC Class Codes: F02D 41/0295 Control according to the amount of oxygen that is stored on the exhaust gas treating apparatus
• CPC Class Codes: F02D 41/1441 Plural sensors
• CPC Class Codes: F02D 41/187 using a hot wire flow sensor
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

A method for predicting oxygen capacity of an LNT during storage phase of such LNT and the amount of NOx stored in the LNT during purge phase thereof as a function of the time history of an output signal produced by an exhaust gas sensor disposed downstream of the LNT. Oxygen storage capacity of the (LNT) is estimated by integrating output signal over time to determine the amount of oxygen stored in the LNT as function of time.

Claims

1. A method for estimating oxygen storage capacity of a lean NOx trap (LNT) used in an internal combustion engine, such engine having a sensor disposed downstream of the LNT, such sensor producing an output signal time history indicating an air-fuel ratio time history of such exhaust, such method comprising:

integrating the output signal over time to determine the amount of oxygen stored in the LNT as function of time;

evaluating the integrated output signal at a time the voltage indicates the exhaust has switched from a condition rich of stoichiometry to a condition lean of stoichiometry;

calculating a relative amount of oxygen stored in the LNT at the switch time, such calculation being a function of the air-fuel ratio of the exhaust and an air-fuel ratio of exhaust leaving the LNT; and

calculating the oxygen storage capacity as a function of the calculated relative amount of oxygen stored in the LNT at the switch time and the evaluated integrated output signal at the time the voltage indicates the exhaust has switched from rich of stoichiometry to lean of stoichiometry.

2. A method for estimating the amount of NOx in lean NOx trap (LNT) used in an internal combustion engine such engine having an sensor disposed downstream of the LNT, such sensor producing an output signal time history indicating an air-fuel ratio time history of such exhaust, such method comprising:

calculating an oxygen rate from the LNT over time as a function of the produced output signal and an estimated oxygen storage capacity of the LNT;

evaluating the calculated oxygen raze at a time the voltage indicates the exhaust has switched from a condition lean of stoichiometry to a condition rich of stoichiometry

calculating a NOx release rule at the switch time, such release rate being a function of the output voltage at the switch time;

calculating the amount of NOx in the LNT as a function of time using as an initial condition the calculated NOx release rate at the switch time.

3. An article of manufacture comprising:

a computer storage medium having a program encoded therein for estimating oxygen storage capacity of a lean NOx trap (LNT) used in an internal combustion engine such engine having a sensor disposed downstream of the LNT, such sensor producing an output signal time history indicating an air-fuel ratio time history of such exhaust, such computer storage medium comprising;

code for integrating the output signal over time to determine the amount of oxygen stored in the LNT as function of time;

code for evaluating the integrated output signal at a time the voltage indicates the exhaust has switched from a condition rich of stoichiometry to a condition lean of stoichiometry;

code for calculating a relative amount of oxygen stored in the LNT at the switch time, such calculation being a function of the air-fuel ratio of the exhaust and an air-fuel ratio of exhaust leaving the LNT; and

code for calculating the oxygen storage capacity as a function of the calculated relative amount of oxygen stored in the LNT at the switch time and the evaluated integrated output signal at the time the voltage indicates the exhaust has switched from rich of stoichiometry to lean of stoichiometry.

4. The article of manufacture recited in claim 3 wherein the medium comprises is a semiconductor chip.

5. An article of manufacture comprising:

a computer storage medium having a program encoded therein for estimating the amount of NOx in lean NOx trap (LNT) used in an internal combustion engine such engine having an sensor disposed downstream of the LNT, such sensor producing an output signal time history indicating an air-fuel ratio time history of such exhaust, such computer storage medium comprising;

code for calculating an oxygen rate from the LNT over time as a function of the produced output signal and an estimated oxygen storage capacity of the LNT;

code for evaluating the calculated oxygen rate at a time the voltage indicates the exhaust has switched from a condition lean of stoichiometry to a condition rich of stoichiometry;

code for calculating a NOx release rate at the switch time, such release rate being a function of the output voltage at the switch time;

code for calculating the amount of NOx in the LNT as a function of time using as an initial condition the calculated NOx release rate at the switch time.

6. The article of manufacture recited in claim 5 wherein the medium comprises is a semiconductor chip.

7. A system for estimating oxygen storage capacity of a lean NOx trap (LNT) used in an internal combustion engine, comprising:

a sensor disposed downstream of the LNT, such sensor producing an output signal time history indicating an air-fuel ratio time history of such exhaust;

a processor for;

integrating the output signal over time to determine the amount of oxygen stored in the LNT as function of time;

evaluating the integrated output signal at a time the voltage indicates the exhaust has switched from a condition rich of stoichiometry to a condition lean of stoichiometry;

calculating a relative amount of oxygen stored in the LNT at the switch time, such calculation being a function of the air-fuel ratio of the exhaust and an air-fuel ratio of exhaust leaving the LNT; and

calculating the oxygen storage capacity as a function of the calculated relative amount of oxygen stored in the LNT at the switch time and the evaluated integrated output signal at the time the voltage indicates the exhaust has switched from rich of stoichiometry to lean of stoichiometry.

8. A system for estimating oxygen storage capacity of a lean NOx trap (LNT) used in an internal combustion engine, comprising:

a sensor disposed downstream of the LNT, such sensor producing an output signal time history indicating an air-fuel ratio time history of such exhaust;

a processor for

estimating the amount of NOx in lean NOx trap (LNT) used in an internal combustion engine such engine having an sensor disposed downstream of the LNT, such sensor producing an output signal time history indicating an air-fuel ratio time history of such exhaust

calculating an oxygen rate from the LNT a over time as a function of the produced output signal and an estimated oxygen storage capacity of the LNT;

evaluating the calculated oxygen rare at a time the voltage indicates the exhaust has switched from a condition lean of stoichiometry to a condition rich of stoichiometry;

calculating a NOx release rate at the switch time, such release rate being a function of the output voltage at the switch time;

calculating the amount of NOx in the LNT as a function of time using as an initial condition the calculated-NOx release rate at the switch time.