Calibration optimization method

• US 6,304,812 B1
• Filed: 04/28/2000
• Issued: 10/16/2001
• Est. Priority Date: 04/28/2000
• Status: Expired due to Fees

• Current Assignee: Ford Motor Company
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Sun, Jing, Kolmanovsky, Ilya Vladimir, van Nieuwstadt, Michiel Jacques
• Primary Examiner(s): Dolinar, Andrew M.
• Assistant Examiner(s): Vo, Hieu T.
• Application Number:
  US09/560,735
• Time in Patent Office: 536 Days
• Field of Search: 701/103, 701/108, 701/109, 701/107, 701/101, 602/74, 602/76, 602/85, 606/02, 123/480, 123/672, 123/674, 123/679
• US Class Current: 701/103
• 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 2570/14 Nitrogen oxides
• CPC Class Codes: F01N 3/0842 Nitrogen oxides
• CPC Class Codes: F02D 2041/1418 Several control loops, either as alternatives or simultaneous
• CPC Class Codes: F02D 2041/1433 using a model or simulation of the system
• CPC Class Codes: F02D 2041/389 for injecting directly into the cylinder
• 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 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 41/1406 with use of a optimisation method, e.g. iteration
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies

Abstract

An calibration optimization method for a direct injection spark ignition (DISI) engine with a lean NO_x trap is disclosed. The method relies on a fixed structure optimization whereby reasonable powertrain operating policies are assumed and parametrized with a small number of variables with some of the variables playing the role of parameters for an inner loop optimization of an outer loop/inner loop two-stage optimization formulation. The values of the parameters are determined via a numerical solution of the resulting (outer loop) optimization to minimize the fuel consumption over the drive cycle subject to emission constraints.

Claims

1. A method of optimizing the desired set-points for engine operating variables for an engine with a trap located in the engine exhaust path, said method comprising a sequence of the following steps:

generating set-points for engine operating variables as functions of engine speed and engine torque based on a finite number of parameters that affect engine and aftertreatment operation;

utilizing the values of said set-points to determine fuel consumption and exhaust emissions over a predetermined drive cycle using engine and aftertreatment models;

adjusting the values of said parameters to obtain optimized parameters corresponding to minimum fuel consumptions within predetermined emission constraints and outputting the desired set-point values in tables corresponding to said optimized parameters.

3. The method of claim 1 wherein said trap is a NO_x trap, said exhaust emissions are emissions of NO_x and said constraints are NO_x emission constraints.

4. The method of claim 3 wherein said trap is located downstream of said catalyst.

2. The method of 1 wherein said trap is located downstream of said catalyst.

5. A method of optimizing the desired set-points for engine operating variables for an engine with a trap located in the engine exhaust path downstream from a catalyst, said method comprising a sequence of the following steps:

generating set-points for engine operating variables as functions of engine speed and engine torque based on parameters that include a post-TWC NO_x emission index bound (EI_NOx,lim) and a purge activation threshold(PAT) for a plurality of normal mode calibrations including stoichiometric, lean homogeneous and lean stratified modes of engine operation and a single purge mode calibration;

utilizing the values of said set-points to determine fuel consumption and NO_x exhaust emissions over a predetermined drive cycle using engine and aftertreatment models;

adjusting the values of said parameters to obtain optimized parameters corresponding to minimum fuel consumptions within predetermined emission constraints and outputting the desired set-point values in tables corresponding to said optimized parameters and outputting said purge activation threshold.

6. A method of optimizing calibration tables of engine operating variables for an engine with a NO_x trap located in the engine exhaust path downstream of a catalyst, said method comprising a sequence of the following steps:

generating calibration tables based on a finite number of parameters that affect engine and aftertreatment operation;

utilizing the values in said generated tables in a model of said engine to determined fuel consumption and NO_x emission over a predetermined drive cycle;

adjusting the values of said parameters to obtain optimized parameters corresponding to minimum fuel consumption within predetermined NO_x emission constraints over said drive cycle; and

outputting calibration table data obtained from said optimized parameters.

7. The method of claim 6 wherein tables for a plurality of normal mode calibrations and a single purge mode calibration are generated.

8. The method of claim 7 wherein the normal mode calibrations include stoichiometric, lean homogeneous and lean stratified modes of engine operation.

9. The method of claim 7 where the optimization is performed by searching through values of air-to-fuel ratio, spark timing, and EGR rate over a specified grid to determine those values that minimize fuel consumption while satisfying a constraint on NO_x emission index for the normal mode operation;

and those values that minimize the purge time for the purge mode calibrations.

10. The method of claim 9 where the minimization of the purge time is achieved by maximizing CO emissions.

11. The method of claim 6 wherein one of said parameters is a post-TWC NO_x emission index bound (EI_NOx,lim).

12. The method of claim 11 wherein another one of said parameters is a purge activation threshold (PAT).

13. The method of claim 12 wherein said adjusting step includes the steps of:

adjusting the value of the purge activation threshold while maintaining the value of the emission index constant until said determined amount of NO_x emission is equal to a predetermined NO_x emission bound; and

thereafter

adjusting the value of the emission index bound and repeating the step of adjusting the value of the purge activation threshold.

14. The method of claim 13 wherein the normal mode calibrations are generated in an inner loop optimization process and the emission index bound and purge activation threshold are adjusted in an outer loop optimization process.

15. The method of claim 6 wherein the step of adjusting the values of said parameters includes using a predetermined optimization algorithm.

16. The method of claim 6 wherein the step of adjusting the values of said parameters comprises searching over a grid of possible parameter values.

17. The method of claim 16 wherein said searching is performed by an optimization algorithm.

18. The method of claim 6 wherein said adjusting step includes the steps of:

optimizing the tables for best fuel economy; and

generating a plurality of normal mode calibration tables using a constraint

19. The method of claim 6 wherein the step of evaluating fuel economy and emissions over a drive cycle is achieved by simulating LNT NO_x storage and TWC oxygen storage models over a drive cycle.

20. The method of claim 6 wherein the step of determining fuel economy and emissions over a drive cycle is achieved by selecting at each time instant of the drive cycle either a stoichiometric, homogeneous lean or stratified lean calibration values for air-to-fuel ratio, EGR rate and spark timing based on the best fuel economy.