Attenuation of engine harshness during lean-to rich transitions

1. A method for regenerating a NOx adsorber in an exhaust system of an internal combustion engine that is fueled in accordance with a data value for desired engine fueling, the method comprising:

a) processing data values of certain parameters to develop a data value for desired engine fueling for causing the engine to develop a corresponding desired output torque without conditioning engine exhaust passing into the exhaust system for NOx adsorber regeneration;

b) processing data values of various parameters indicative of conditions relevant to initiation of NOx adsorber regeneration; and

c) after the processing of step b) has disclosed that NOx adsorber regeneration can be initiated, initiating NOx adsorber regeneration by changing engine fueling so as to condition engine exhaust passing into the exhaust system for regenerating the NOx adsorber, including developing a data value for desired engine fueling that is effective to condition the exhaust gas for NOx adsorber regeneration at a given engine speed while striving to maintain the output torque at the corresponding output torque that desired engine fueling would develop at the given engine speed without conditioning engine exhaust passing into the exhaust system for NOx adsorber regeneration, by processing data values for i) the desired engine fueling that would develop that corresponding output torque without conditioning engine exhaust passing into the exhaust system for NOx adsorber regeneration, ii) engine speed, and iii) actual air-fuel ratio at which the engine is operating according to a control algorithm that, for a given data value for i) provides a data value for desired engine fueling that is correlated with both a data value for ii) and a data value for iii) and that conditions the exhaust gas for NOx adsorber regeneration while striving to maintain the output torque at the corresponding output torque that would be developed without conditioning the exhaust gas for NOx adsorber regeneration.

2. A method as set forth in claim 1 wherein step a) comprises:

processing data values of engine speed and accelerator pedal position to develop the data value for desired engine fueling for causing the engine to develop a corresponding desired output torque without conditioning engine exhaust passing into the exhaust system for NOx adsorber regeneration.

3. A method as set forth in claim 1 wherein step b) further comprises:

conditioning initiation and continuation of NOx adsorber regeneration on an estimate of engine torque being greater than a lower torque limit and less than an upper torque limit.

4. A method as set forth in claim 1 in which the step of developing a data value for desired engine fueling that is effective to condition the exhaust gas for NOx adsorber regeneration at the given engine speed while striving to maintain the output torque at the corresponding output torque that desired engine fueling would develop at the given engine speed without conditioning engine exhaust passing into the exhaust system for NOx adsorber regeneration, comprises:

for each of multiple data values of desired engine fueling that do not condition engine exhaust passing into the exhaust system for NOx adsorber regeneration at the given engine speed, developing data values defining a range of relatively smaller air-fuel ratios below relatively larger air-fuel ratios, and within that range, a functional relationship between data values of air-fuel ratio and data values of desired engine fueling effective to condition the exhaust gas for NOx adsorber regeneration while striving to maintain the output torque at the corresponding output torque that desired engine fueling would develop at the given speed without conditioning engine exhaust passing into the exhaust system for NOx adsorber regeneration.

5. A method as set forth in claim 4 in which the step of developing data values defining a range of relatively smaller air-fuel ratios below relatively larger air-fuel ratios, and within the range of relatively smaller air-fuel ratios, a functional relationship between data values of the air-fuel ratio and data values of desired engine fueling effective to condition the exhaust gas for NOx adsorber regeneration comprises:

i) developing a boundary data value of air-fuel ratio that defines an upper limit of the relatively smaller range, and for that boundary data value of air-fuel ratio, a corresponding data value of desired engine fueling, and ii) within the range of relatively smaller air-fuel ratios, developing a data value of air-fuel ratio less than the boundary data value of air-fuel ratio, and for that data value of air-fuel ratio less, than the boundary data value of air-fuel ratio, a corresponding data value of desired engine fueling.

6. A method as set forth in claim 4 in which the step of developing a data value for desired engine fueling that is effective to condition the exhaust gas for NOx adsorber regeneration while striving to maintain the output torque at the corresponding output torque that desired engine fueling would develop at the given speed without conditioning engine exhaust passing into the exhaust system for NOx adsorber regeneration by processing data values for i) the desired engine fueling that does not condition engine exhaust passing into the exhaust system for NOx adsorber regeneration, ii) engine speed, and iii) actual air-fuel ratio at which the engine is operating comprises:

processing the data value for desired engine fueling resulting from step a) to select a corresponding functional relationship between data values of the air-fuel ratio and data values of desired engine fueling effective to condition the exhaust gas for NOx adsorber regeneration, and processing the data value for actual air-fuel ratio at which the engine is operating according to the selected corresponding functional relationship between data values of the air-fuel ratio and data values of desired engine fueling effective to condition the exhaust gas for NOx adsorber regeneration, to thereby provide a data value for desired engine fueling.

7. An internal combustion engine comprising:

an exhaust system comprising a NOx adsorber for adsorbing NOx from exhaust resulting from combustion of fuel in the engine;

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

a control system for processing various data to develop data for control of various engine functions including data values for desired engine fueling, wherein the control system comprises a control strategy

a) for processing data values of certain parameters to develop a data value for desired engine fueling for causing the engine to develop a corresponding desired output torque without conditioning engine exhaust passing into the exhaust system for NOx adsorber regeneration,

b) for processing data values of various parameters indicative of conditions relevant to initiation of NOx adsorber regeneration; and

c) after the processing of b) has disclosed that NOx adsorber regeneration can be initiated, for initiating NOx adsorber regeneration by changing engine fueling so as to condition engine exhaust passing into the exhaust system for regenerating the NOx adsorber, including developing a data value for desired engine fueling that is effective to condition the exhaust gas for NOx adsorber regeneration at a given engine speed while striving to maintain the output torque at the corresponding output torque that desired engine fueling would develop at the given engine speed without conditioning engine exhaust passing into the exhaust system for NOx adsorber regeneration, by processing data values for i) the desired engine fueling that would develop that corresponding output torque without conditioning engine exhaust passing into the exhaust system for NOx adsorber regeneration, ii) engine speed, and iii) actual air-fuel ratio at which the engine is operating according to a control algorithm that, for a given data value for i), provides a data value for desired engine fueling that is correlated with both a data value for ii) and a data value for iii) and that conditions the exhaust gas for NOx adsorber regeneration while striving to maintain the output torque at the corresponding output torque that would be developed without conditioning the exhaust gas for NOx absorber regeneration.

8. An engine as set forth in claim 7 in which the portion of the control strategy for processing data values of certain parameters to develop a data value for desired engine fueling for causing the engine to develop a corresponding desired output torque without conditioning engine exhaust passing into the exhaust system for NOx adsorber regeneration comprises strategy for:

processing data values of engine speed and accelerator pedal position to develop the data value for desired engine fueling for causing the engine to develop a corresponding desired output torque without conditioning engine exhaust passing into the exhaust system for NOx adsorber regeneration.

9. An engine as set forth in claim 7 in which the portion of the control strategy for processing data values of various parameters indicative of conditions relevant to initiation of NOx adsorber regeneration comprises strategy for conditioning initiation and continuation of NOx adsorber regeneration on an estimate of engine torque being greater than a lower torque limit and less than an upper torque limit.

10. An engine as set forth in claim 7 in which the portion of the control strategy for developing a data value for desired engine fueling that is effective to condition the exhaust gas for NOx adsorber regeneration at the given engine speed while striving to maintain the output torque at the corresponding output torque that desired engine fueling would develop at the given engine speed without conditioning engine exhaust passing into the exhaust system for NOx adsorber regeneration, comprises strategy that:

for each of multiple data values of desired engine fueling that do not condition engine exhaust passing into the exhaust system for NOx adsorber regeneration at the given engine speed, develops data values defining a range of relatively smaller air-fuel ratios below relatively larger air-fuel ratios, and within that range, a functional relationship between data values of air-fuel ratio and data values of desired engine fueling effective to condition the exhaust gas for NOx adsorber regeneration while striving to maintain the output torque at the corresponding output torque that desired engine fueling would develop at the given speed without conditioning engine exhaust passing into the exhaust system for NOx adsorber regeneration.

11. An engine as set forth in claim 10 in which the portion of the control strategy for developing data values defining a range of relatively smaller air-fuel ratios below relatively larger air-fuel ratios, and within the range of relatively smaller air-fuel ratios, a functional relationship between data values of the air-fuel ratio and data values of desired engine fueling effective to condition the exhaust gas for NOx adsorber regeneration comprises strategy for:

i) developing a boundary data value of air-fuel ratio that defines an upper limit of the relatively smaller range, and for that boundary data value of air-fuel ratio, a corresponding data value of desired engine fueling, and ii) within the range of relatively smaller air-fuel ratios, developing a data value of air-fuel ratio less than the boundary data value of air-fuel ratio, and for that data value of air-fuel ratio less than the boundary data value of air-fuel ratio, .a corresponding data value of desired engine fueling.

12. An engine as set forth in claim 10 in which the portion of the control strategy for developing a data value for desired engine fueling that is effective to condition the exhaust gas for NOx adsorber regeneration at the given engine speed while striving to maintain the output torque at the corresponding output torque that desired engine fueling would develop at the given engine speed without conditioning engine exhaust passing into the exhaust system for NOx adsorber regeneration by processing data values for i) the desired engine fueling that does not condition engine exhaust passing into the exhaust system for NOx adsorber regeneration, ii) engine speed, and iii) actual air-fuel ratio at which the engine is operating comprises strategy for:

processing the data value for desired engine fueling resulting from a) to select a corresponding functional relationship between data values of the air-fuel ratio and data values of desired engine fueling effective to condition the exhaust gas for NOx adsorber regeneration, and processing the data value for actual air-fuel ratio at which the engine is operating according to the selected corresponding functional relationship between data values of the air-fuel ratio and data values of desired engine fueling effective to condition the exhaust gas for NOx adsorber regeneration, to thereby provide a data value for desired engine fueling.