Control strategy for lean-to-rich transitions in an internal combustion engine

1. A control method for lean-to-rich modulation of an internal combustion engine comprising:

with the engine running lean at a particular speed, causing the engine to transition from running lean to running rich while striving to maintain a desired engine torque at that particular speed by

a) processing data values for engine speed and desired engine torque to develop a data value for desired mass airflow into the engine and a data value for desired air-fuel ratio for rich running,

b) processing the data value for desired air-fuel ratio for rich running, a data value for actual mass airflow into the engine, and a data value for actual air-fuel ratio to develop a data value for quantity of engine fueling,

c) processing the data value for quantity of engine fueling and other data relevant to a determination of the timing of introduction of that quantity of engine fueling into the engine during an engine cycle that will cause the engine to run rich while striving to maintain desired engine torque at the particular engine speed, to develop a data value for that timing,

d) forcing intake mass airflow toward that desired mass airflow, and

e) fueling the engine with that quantity of engine fueling at that timing.

2. A control method as set forth in claim 1 in which step c) comprises:

processing the data value for quantity of engine fueling, the data value for engine speed, the data value for actual air-fuel ratio, and the data value for desired engine torque to develop the data value for the timing of introduction of that quantity of engine fueling into the engine during an engine cycle that will cause the engine to run rich while striving to maintain desired engine torque at the particular engine speed.

3. A control method as set forth in claim 1 wherein step d) comprises:

forcing intake mass airflow toward that desired mass airflow by control of one or more components of an intake system of the engine through which the airflow enters the engine.

4. A control method as set forth in claim 3 wherein the step of forcing intake mass airflow toward that desired mass airflow by control of one or more components of an intake system of the engine through which the airflow enters the engine comprises control of exhaust gas recirculation (EGR).

5. A control method as set forth in claim 3 wherein the step of forcing intake mass airflow toward that desired mass airflow by control of one or more components of an intake system of the engine through which the airflow enters the engine comprises control of a throttle valve through which fresh intake air enters the intake system.

6. A control method as set forth in claim 3 wherein the step of forcing intake mass airflow toward that desired mass airflow by control of one or more components of an intake system of the engine through which the airflow enters the engine comprises controlling a signal that controls a turbocharger having a turbine in an exhaust system of the engine and a compressor in the intake system.

7. A control method as set forth in claim 3 wherein the step of forcing intake mass airflow toward that desired mass airflow by control of one or more components of an intake system of the engine through which the airflow enters the engine comprises controlling one or more components by closed-loop control for certain combinations of engine speed and torque, by open-loop control for certain other combinations of engine speed and torque, and by varying degrees of both open- and closed-loop control for still other combinations of engine speed and torque.

8. A method for regenerating a NOx adsorber in an exhaust system of an internal combustion engine by conditioning engine operation to generate excess CO for inducing regeneration, the strategy comprising:

with the engine running lean at a particular speed, generating excess CO by causing the engine to transition from running lean to running rich while striving to maintain a desired engine torque at that particular speed by

a) processing data values for engine speed and desired engine torque to develop a data value for desired mass airflow into the engine and a data value for desired air-fuel ratio for rich running,

b) processing the data value for desired air-fuel ratio for rich running, a data value for actual mass airflow into the engine, and a data value for actual air-fuel ratio to develop a data value for quantity of engine fueling,

c) processing the data value for quantity of engine fueling and other data relevant to a determination of the timing of introduction of that quantity of engine fueling into the engine during an engine cycle that will cause the engine to run rich while striving to maintain desired engine torque at the particular engine speed, to develop a data value for that timing,

d) forcing intake mass airflow toward that desired mass airflow, and

e) fueling the engine with that quantity of engine fueling at that timing.

9. A method as set forth in claim 8 in which step c) comprises:

processing the data value for quantity of engine fueling, the data value for engine speed, the data value for actual air-fuel ratio, and the data value for desired engine torque to develop the data value for the timing of introduction of that quantity of engine fueling into the engine during an engine cycle that will cause the engine to run rich while striving to maintain desired engine torque at the particular engine speed.

10. A method as set forth in claim 8 wherein step d) comprises:

forcing intake mass airflow toward that desired mass airflow by control of one or more components of an intake system of the engine through which the airflow enters the engine.

11. An internal combustion engine comprising:

a) a fueling system for fueling the engine in accordance with a data value for desired engine fueling,

b) an intake system through which airflow enters the engine, and

c) a control system for processing various data to develop data for control of various engine functions including data values for desired engine fueling, for desired mass airflow into the engine, and for desired air-fuel ratio, wherein the control system comprises a control strategy,

i) for causing the engine to transition from running lean to running rich while striving to maintain engine torque at a particular engine speed by,

ii) processing data values for engine speed and desired engine torque to develop a data value for desired mass airflow into the engine and a data value for desired air-fuel ratio for rich running,

iii) processing the data value for desired air-fuel — ratio for rich running, a data value for actual mass airflow into the engine, and a data value for actual air-fuel ratio to develop a data value for quantity of engine fueling,

iv) processing the data value for quantity of engine fueling and other data relevant to a determination of the timing of introduction of that quantity of engine fueling into the engine during an engine cycle that will cause the engine to run rich while striving to maintain desired engine torque at the particular engine speed, to develop a data value for that timing,

v) forcing intake mass airflow toward that desired mass airflow, and

vi) fueling the engine with that quantity of engine fueling at that timing.

12. An engine as set forth in claim 11 in which the pardon of the control strategy for processing the data value for quantity of engine fueling and other data relevant to a determination of the timing of introduction of that quantity of engine fueling into the engine during an engine cycle that will cause the engine to run rich while striving to maintain desired engine torque at the particular engine speed to develop a data value for that timing comprises strategy for processing the data value for quantity of engine fueling, the data value for engine speed, the data value for actual air-fuel ratio, and the data value for desired engine torque to develop the data value for the timing of introduction of that quantity of engine fueling into the engine during an engine cycle that will cause the engine to run rich while striving to maintain desired engine torque at the particular engine speed.

13. An engine as set forth in claim 11 in which the portion of the control strategy for forcing intake mass airflow toward that desired mass airflow comprises strategy for forcing intake mass airflow toward that desired mass airflow by closed-loop control of one or more components of an intake system of the engine through which mass airflow enters the engine.

14. An engine as set forth in claim 13 wherein the one or more components of the intake system comprise one or more of an exhaust gas recirculation (EGR) valve that controls recirculation of exhaust gas from an exhaust system of the engine to the intake system, a throttle valve through which fresh intake air enters the intake system, and a turbocharger having a turbine in an exhaust system and a compressor in the intake system.

15. An engine as set forth in claim 13 wherein the one or more components is controlled by closed-loop control for certain combinations of engine speed and torque, by open-loop control for certain other combinations of engine speed and torque, and by varying degrees of both open- and closed-loop control for still other combinations of engine speed and torque.

16. An internal combustion engine comprising:

a) a fueling system for fueling the engine in accordance with a data value for desired engine fueling;

b) an intake system through which airflow enters the engine;

c) a NOx adsorber in an exhaust system of the engine; and

d) an engine control system that at times conditions engine operation to generate excess CO for inducing regeneration of the NOx absorber and that comprises a strategy for generating excess CO by causing the engine to transition from running lean at a particular speed to running rich while striving to maintain a desired engine torque at that particular speed by

i) processing data values for engine speed and desired engine torque to develop a data value for desired mass airflow into the engine and a data value for desired air-fuel ratio for rich running,

ii) processing the data value for desired air-fuel — ratio for rich running, a data value for actual mass airflow into the engine, and a data value for actual air-fuel ratio to develop a data value for quantity of engine fueling,

iii) processing the data value for quantity of engine fueling and other data relevant to a determination of the timing of introduction of that quantity of engine fueling into the engine during an engine cycle that will cause the engine to run rich while striving to maintain desired engine torque at the particular engine speed, to develop a data value for that timing,

iv) forcing intake mass airflow toward that desired mass airflow, and

v) fueling the engine with that quantity of engine fueling at that timing.

17. An engine as set forth in claim 16 in which step iii) comprises:

processing the data value for quantity of engine fueling, the data value for engine speed, the data value for actual air-fuel ratio, and the data value for desired engine torque to develop the data value for the timing of introduction of that quantity of engine fueling into the engine during an engine cycle that will cause the engine to run rich while striving to maintain desired engine torque at the particular engine speed.

18. An engine as set forth in claim 16 wherein step iv) comprises:

forcing intake mass airflow toward that desired mass airflow by control of one or more components associated with the intake system.