Method and apparatus for maintaining catalyst efficiency of a NO.sub.x trap

• US 5,832,722 A
• Filed: 03/31/1997
• Issued: 11/10/1998
• Est. Priority Date: 03/31/1997
• Status: Expired due to Term

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Farmer, David George, Hepburn, Jeffrey Scott, Cullen, Michael John, Brandt, Arnold William
• Primary Examiner(s): Ryznic, John E.
• Application Number:
  US08/829,291
• Time in Patent Office: 589 Days
• Field of Search: 60/274, 60/285, 60/297, 60/301
• US Class Current: 60/274
• CPC Class Codes: B01D 53/8696 Controlling the catalytic process
• CPC Class Codes: B01D 53/9431 Processes characterised by a specific device
• CPC Class Codes: B01D 53/9495 Controlling the catalytic process
• CPC Class Codes: F01N 2570/04 Sulfur or sulfur oxides
• CPC Class Codes: F01N 3/0842 Nitrogen oxides
• CPC Class Codes: F01N 3/0885 Regeneration of deteriorated absorbents or adsorbents, e.g. desulfurization of NOx traps
• CPC Class Codes: F01N 3/22 Control of additional air supply only, e.g. using by-passes or variable air pump drives
• CPC Class Codes: F01N 3/32 using air pump using jet air pumps F01N3/34; pumps in general F04
• CPC Class Codes: F02D 2200/0818 SOx storage amount, e.g. for SOx trap or NOx trap
• CPC Class Codes: F02D 41/028 Desulfurisation of NOx traps or adsorbent
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies

Abstract

An engine control computer estimates the cumulative SO_x stored in a NO_x trap and enters a SO_x purge mode of operation when a maximum storage capacity limit is exceeded. SO_x accumulation is estimated based on fuel flow to the engine, A/F and trap temperature. The purge mode is terminated when the estimated SO_x storage level drops below a minimum threshold level during the purging operation.

Claims

1. A method of estimating the amount of SO_x accumulated in a NO_x trap located in an exhaust passage of an engine comprising a sequence of the steps of:

determining an amount of SO_x accumulated per unit fuel flow, based on present A/F and present temperature of said trap;

calculating the rate of SO_x accumulation based on said determined amount of SO_x and the flow rate of fuel supplied to said engine; and

calculating the amount of S0_x accumulation based on said calculated rate of SO_x accumulation and the elapsed time since a previous calculation.

2. The method defined in claim 1 further comprising the step of:

adding the amount of SO_x stored since said previous calculation to the calculated amount previously stored to obtain a cumulative amount.

3. The method defined in claim 2 further comprising the steps of:

comparing the cumulative amount of SO_x stored with a maximum capacity level; and

initiating a SO_x purge operation when said maximum capacity level is exceeded in order to reduce the amount of SO_x stored in said trap.

4. The method defined in claim 3 wherein said purge operation comprises the steps of:

controlling the temperature of said trap above a predetermined minimum purging temperature; and

operating said engine at a rich A/F.

5. The method defined in claim 4 comprising the further steps of:

terminating said purge operation when the amount of SO_x stored in said trap is less than a minimum capacity level.

6. The method defined in claim 2 wherein said determined amount is positive when said engine is operating lean and negative when said engine is operating rich.

7. Apparatus for estimating the amount of SO_x accumulated in a NO_x trap located in an exhaust passage of an engine comprising:

a read only memory containing experimentally determined data representing the expected amount of SO_x that would be accumulated in said trap per quantity of fuel supplied to said engine at a specified A/F and trap temperature;

an engine controller for estimating the temperature of said trap, and for calculating the desired fuel quantity to achieve a desired A/F;

said controller calculating the incremental amount of SO_x accumulated in said trap since the previous calculation based on the product of the read only memory data, corresponding to the present A/F and trap temperature, and the amount of fuel supplied to said engine since the previous calculation.

8. The apparatus of claim 7 wherein said controller adds said incremental amount to a previously calculated total amount of accumulated SO_x to obtain a cumulative amount of stored SO_x.

9. The apparatus of claim 8 wherein said controller compares said cumulative amount of stored SO_x with a maximum capacity level and initiating a SO_x purge operation when said maximum capacity level is exceeded.

10. The apparatus defined in claim 9 wherein said controller operates said engine at a rich A/F and controls the amount of secondary air added to said exhaust, upstream of said trap, to maintain the temperature of said trap above a predetermined minimum purging temperature during said purge operation.

11. The apparatus defined in claim 10 wherein said controller terminates said purge operation when the amount of SO_x stored in said trap is less than a minimum capacity level.

12. The apparatus defined in claim 8 wherein said read only memory contains data that is positive when said engine is operating lean and negative when said engine is operating rich.

13. An article of manufacture comprising:

a computer storage medium having a computer program encoded therein for controlling the amount of fuel supplied to an engine having an exhaust passage with a NO_x trap located therein, said computer storage medium comprising;

code for determining the temperature of said trap;

code for calculating the amount of fuel to be delivered to said engine to achieve a desired A/F; and

code for calculating the incremental amount of SO_x accumulated in said trap at said A/F and trap temperature.

14. The article defined in claim 13 wherein said medium further comprises:

code for adding said incremental amount to a previously calculated total amount of accumulated SO_x.

15. The article defined in claim 14 wherein said medium further comprises:

code for comparing said total amount of accumulated SO_x with a maximum capacity level and initiating a SO_x purge operation when said maximum capacity level is exceeded.

16. The article defined in claim 15 wherein the incremental amount of SO_x accumulated in said trap is a function of the amount of fuel supplied to said engine since the previous calculation.