Method for monitoring the performance of a no.sub.x trap

• US 5,743,084 A
• Filed: 10/16/1996
• Issued: 04/28/1998
• Est. Priority Date: 10/16/1996
• Status: Expired due to Term

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Hepburn, Jeffrey Scott
• Primary Examiner(s): ARGENBRIGHT, TONY MICHAEL
• Application Number:
  US08/732,626
• Time in Patent Office: 559 Days
• Field of Search: 60/274, 60/276, 60/277, 60/297, 60/301, 60/311
• US Class Current: 60/274
• 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 2250/12 absorption or adsorption, and catalytic conversion
• CPC Class Codes: F01N 2260/04 for regeneration or reactivation, e.g. of catalyst
• CPC Class Codes: F01N 2550/03 of sorbing activity of adsorbents or absorbents
• CPC Class Codes: F01N 2570/04 Sulfur or sulfur oxides
• CPC Class Codes: F01N 2900/0422 measuring the elapsed time
• CPC Class Codes: F01N 3/0842 Nitrogen oxides
• CPC Class Codes: F01N 3/32 using air pump using jet air pumps F01N3/34; pumps in general F04
• CPC Class Codes: F01N 9/00 Electrical control of exhaust gas treating apparatus monitoring or diagnostic devices for exhaust-gas treatment apparatus F01N11/00; conjoint electrical control of two or more combustion engine functions F02D43/00
• CPC Class Codes: F02D 2200/0806 NOx storage amount, i.e. amount of NOx stored on NOx trap
• CPC Class Codes: F02D 2200/0811 NOx storage efficiency
• CPC Class Codes: F02D 41/0275 the exhaust gas treating apparatus being a NOx trap or adsorbent
• CPC Class Codes: F02D 41/028 Desulfurisation of NOx traps or adsorbent
• CPC Class Codes: F02D 41/1441 Plural sensors
• CPC Class Codes: F02D 41/1456 with sensor output signal being linear or quasi-linear with the concentration of oxygen
• CPC Class Codes: F02D 41/1462 with determination means using an estimation
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

A method and apparatus for on-board monitoring of NO_x trap performance is proposed that uses two HEGO sensors, one positioned upstream of the NO_x trap, and the other positioned downstream of the NO_x trap. When the engine A/F is reduced from lean to stoichiometric or rich operation to regenerate or purge the NO_x trap the difference in the time it takes for the upstream and downstream HEGO sensors to switch from a lean to a rich indication provides a quantitative measure of the amount of NO_x that was stored on the NO_x trap during the previous lean period of operation. This measure is related to an estimated amount of NO_x produced by the engine to infer the operating performance or efficiency of the NO_x trap. The difference in the output voltage of the two sensors is compared with a predetermined value to determined when to terminate the NO_x purge. When the efficiency drops below a predetermined value the time that the engine is run in a lean cruise mode is reduced. If the time is reduced below a minimum time interval, a sulfur purge is performed. If sulfur purges are required more often than a predetermined repetition time, the lean cruise mode is terminated and an indicator lamp is energized.

Claims

1. A vehicle on-board computer method of diagnosing the status of a NO_x trap disposed in an exhaust passage of an internal combustion engine, comprising a sequence of the following steps:

performing a purge of said trap after meeting predetermined lean mode engine operating criteria; and

providing an indication of trap deterioration if the time interval between successive purges is less than a predetermined time interval.

2. The invention defined in claim 1 wherein said purge is a SO_x purge.

3. The invention defined in claim 2 including the further step of performing a NO_x purge prior to said SO_x purge.

4. The invention defined in claim 3 wherein said NO_x purge is initiated periodically during a lean cruise mode of engine operation and the time interval of lean operation is adjusted to improve trap sorption efficiency whenever trap sorption efficiency drops below a predetermined trap sorption efficiency.

5. The invention defined in claim 3 wherein said SO_x purge is initiated whenever said time interval of lean operation drops below a predetermined time interval.

6. The invention defined in claim 5 wherein said indicator is energized whenever the time interval between SO_x purges drops below a predetermined time interval.

7. A method of diagnosing the status of a NO_x trap disposed in an exhaust passage of an internal combustion engine, comprising a sequence of the following steps:

performing a NO_x purge on said trap after operating said engine in a lean mode of operation;

determining the sorption efficiency of said trap;

reducing the time duration of said lean mode of operation if said efficiency drops below a predetermined level;

performing a SO_x purge on said trap if said time duration falls below a predetermined minimum time interval; and

providing an indication of trap deterioration if the time interval between SO_x purges is less than a predetermined time interval.

8. The method defined in claim 7 wherein the NO_x purge is initiated after operating the engine in said lean mode for a predetermined time interval and wherein the NO_x purge is terminated based on the oxygen content of the exhaust downstream from said trap.

9. The method defined in claim 8 wherein the sorption efficiency is computed by:

determining the amount of NO_x stored on the trap;

estimating the amount of NO_x produced by the engine during the last lean mode of operation; and

dividing the amount of NO_x stored on the trap by the estimated amount of NO_x produced by the engine.

10. The method defined in claim 9 wherein the determination of the amount of NO_x stored on the trap is based on the time interval between initiation of said NO_x purge and detection of a stoichiometric exhaust gas condition downstream of the trap.

11. A vehicle on-board computer diagnostic system for monitoring the status of a NO_x trap disposed in an exhaust passage of an internal combustion engine comprising:

a computer for generating a command to purge said NO_x trap;

a sensor disposed downstream from said trap;

an indicator;

said computer generating a command to energize said indicator based on the sorption efficiency of said trap.

12. The system of claim 11 wherein said sensor is an exhaust gas oxygen sensor.

13. The system of claim 12 wherein said computer generates a NO_x purge command causing a change in the mixture supplied to said engine from a relatively lean A/F to a relatively rich A/F.

14. The system of claim 13 wherein said sorption efficiency is the ratio of the amount of NO_x stored on the trap divided by the amount of NO_x generated by the engine.

15. The system of claim 14 wherein the amount of NO_x stored on the trap is a function of the trap temperature and the lean to rich response time of said sensor.

16. The system of claim 15 wherein the amount of NO_x generated by the engine is a function of engine speed and air mass inducted into said engine.

17. The system of claim 16 wherein said computer increases the frequency of NO_x purges if the sorption efficiency drops below a predetermined efficiency.

18. The system of claim 17 wherein said computer initiates a SO_x purge if the time between NO_x purges drops below a predetermined time interval.

19. The system of claim 18 wherein said indicator is energized if the time interval between SO_x purges drop below a predetermined time interval.

20. The system of claim 19 comprising a second exhaust gas oxygen sensor located upstream of said NO_x trap and said NO_x purge is terminated when the difference in the output of the downstream sensor and the upstream sensor is less than a predetermined threshold.