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A method of controlling an internal combustion engine for warm-up of catalyst of an exhaust gas treatment device is disclosed. The method comprises generating a warm-up demand for heating the catalyst subject to constraint on stable combustion. Based on the warm-up demand, a reduction in excess air

A method of controlling an internal combustion engine for warm-up of catalyst of an exhaust gas treatment device is disclosed. The method comprises generating a warm-up demand for heating the catalyst subject to constraint on stable combustion. Based on the warm-up demand, a reduction in excess air ratio is determined. A desired value in excess air ratio is modified by the reduction to provide a modified desired value in excess air ratio. Based on the reduction, a desired value in EGR rate is modified to provide a modified desired value in EGR rate. Based on the modified desired value in EGR rate, an EGR command signal is determined.

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1. A method of controlling an internal combustion engine for warm-up of a catalyst of an exhaust gas treatment device located in the engine exhaust path, the engine including an exhaust gas recirculation (EGR) system driven in response to an EGR command signal to recirculate exhaust to an engine int

1. A method of controlling an internal combustion engine for warm-up of a catalyst of an exhaust gas treatment device located in the engine exhaust path, the engine including an exhaust gas recirculation (EGR) system driven in response to an EGR command signal to recirculate exhaust to an engine intake, the method comprising:generating a warm-up demand for heating the catalyst subject to constraint on stable combustion; determining a reduction in excess air ratio of the engine intake based on the warm-up demand; modifying a desired value in excess air ratio by the reduction to provide a modified desired value in excess air ratio; modifying a desired value in EGR rate based on the reduction to provide a modified desired value in EGR rate; and determining the EGR command signal based on the modified desired value in EGR rate. 2. The method as claimed in claim 1, wherein the warm-up demand is generated upon and after cold start of the engine.3. The method as claimed in claim 1, wherein the warm-up demand is generated after a cylinder wall temperature has exceeded a cylinder wall temperature threshold when the catalyst has a temperature lower than a catalyst temperature threshold.4. The method as claimed in claim 1, wherein the warm-up demand is generated after a time from the beginning of cold start has reached a time threshold when the catalyst has a temperature lower than a catalyst temperature threshold.5. The method as claimed in claim 1, wherein the warm-up demand is generated after an idle fuel quantity has reached an idle fuel quantity threshold during cold start of the engine when the catalyst has a temperature lower than a catalyst temperature threshold.6. The method as claimed in claim 1, wherein, after the engine has achieved self-sustaining operation during cold start of the engine, the warm-up demand is increased at a controlled rate of one of a difference between and a ratio between an idle fuel quantity and an idle fuel quantity threshold, and wherein the determining a reduction in excess air ratio includes increasing the reduction in amount as a function of the warm-up demand.7. The method as claimed in claim 1, wherein, when a catalyst temperature threshold is exceeded, the warm-up demand is zero.8. The method as claimed in claim 1, wherein, when a catalyst-out temperature threshold is exceeded, the warm-up demand is zero.9. The method as claimed in claim 1, wherein, when a coolant temperature threshold is exceeded, the warm-up demand is zero.10. The method as claimed in claim 1, wherein, when the integral of fuel quantity from the beginning of cold start of the engine exceeds a threshold, the warm-up demand is zero.11. The method as claimed in claim 1, further comprising:adjusting an EGR valve of the EGR system in response to the EGR command signal. 12. The method as claimed in claim 1, wherein the warm-up demand is generated accounting for in-cylinder combustion environment when the catalyst has a temperature lower than a catalyst temperature threshold.13. The method as claimed in claim 12, wherein, when a second catalyst temperature threshold that is higher than the first mentioned catalyst temperature threshold is exceeded, the warm-up demand is zero.14. The method as claimed in claim 1, wherein, after the engine has achieved self-sustaining operation during cold start of the engine, the warm-up demand is increased at a controlled rate of one of a difference between and a ratio between time and a time threshold, and wherein the determining a reduction in excess air ratio includes increasing the reduction in amount as a function of the warm-up demand.15. The method as claimed in claim 14, wherein the time threshold is determined as a function of coolant temperature of the engine.16. The method as claimed in claim 1, further comprising:determining a throttle valve opening (TVO) command signal based on the modified desired value in excess air ratio; and adjusting a throttle valve located in the intake path in response to the TVO command signal. 17. The method as claimed in claim 16, further comprising:determining a post-ignition fuel quantity based on the modified desired value in excess air ratio; and performing injection of the post-ignition fuel quantity after ignition of in-cylinder charge to heat the catalyst. 18. The method as claimed in claim 1, further comprising:determining a variable geometry turbocharger (VGT) command signal based on the modified desired value in excess air ratio; and adjusting a variable geometry turbocharger (VGT) of the engine in response to the VGT command signal. 19. The method as claimed in claim 18, further comprising:determining a post-ignition fuel quantity based on the modified desired value in excess air ratio; and performing injection of the post-ignition fuel quantity after ignition of in-cylinder charge to heat the catalyst. 20. An engine system comprising:an engine block having a plurality of combustion chambers; an intake manifold for supplying intake to the combustion chambers; an exhaust manifold for discharging exhaust from the combustion chambers; an exhaust gas treatment device including a catalyst located in the engine exhaust path communicating with the exhaust manifold; an exhaust gas recirculation (EGR) system driven in response to an EGR command signal to recirculate exhaust to the engine intake path communicating with the intake manifold; an engine controller; and a computer readable storage medium having instructions stored thereon that are executable by the engine controller to perform a method of controlling the internal combustion engine for warm-up of the catalyst, wherein the medium includes instructions for operating the engine controller to: generate a warm-up demand for heating the catalyst subject to constraint on stable combustion; determine a reduction in excess air ratio of the engine intake based on the warm-up demand; modify a desired value in excess air ratio by the reduction to provide a modified desired value in excess air ratio; modify a desired value in EGR rate based on the reduction to provide a modified desired value in EGR rate; and determine the EGR command signal based on the modified desired value in EGR rate. 21. The engine system as claimed in claim 20, further comprising a throttle valve, located in the engine intake path, which opens in response to a throttle valve opening (TVO) command signal, and wherein the computer readable storage medium further includes instructions for the engine controller to:determine the TVO command signal based on the modified desired value in excess air ratio. 22. The engine system as claimed in claim 21, further comprising a variable geometry turbocharger (VGT) driven in response to a VGT command signal, and wherein the computer readable storage medium further includes instructions for the engine controller to:determine the VGT command signal based on the modified desired value in excess air ratio. 23. The engine system as claimed in claim 22, further comprising a device to perform post-ignition injection of a post-ignition fuel quantity for heating the catalyst, and wherein the computer readable storage medium further includes instructions for the engine controller to:determine the post-ignition fuel quantity based on modified desired values in excess air ratio. 24. The engine system as claimed in claim 23, wherein the computer readable storage medium further includes instructions for the engine controller to:calculate a desired air quantity using the modified desired value in excess air ratio; and calculate a desired EGR gas quantity using the desired air quantity and the modified desired value in excess air ratio. 25. An apparatus for controlling an internal combustion engine for warm-up of a catalyst of an exhaust gas treatment device located in the engine exhaust path, the engine including an exhaust gas recirculation (EGR) system driven in response to an EGR command signal to recirculate exhaust to an engine intake, the apparatus comprising:a logic block that generates a warm-up demand for heating the catalyst subject to constraint on stable combustion; a reduction block that determines a reduction in excess air ratio of the engine intake based on the warm-up demand; an excess air ratio modifier block that modifies a desired value in excess air ratio by the reduction to provide a modified desired value in excess air ratio; an EGR rate modifier block that modifies a desired value in EGR rate based on the reduction to provide a modified desired value in EGR rate; and an EGR controller that determines the EGR command signal based on the modified desired value in EGR rate. 26. The apparatus as claimed in claim 25, whereinthe logic block determines whether a need remains for warm-up of the catalyst; the logic block determines whether in-cylinder combustion environment allows for engine operation with reduced excess air ratio to increase the temperature of the catalyst; and the logic block generates the warm-up demand when the in-cylinder combustion environment allows for the engine operation under the presence of the need. 27. The apparatus as claimed in claim 25, wherethe logic block determines whether a need remains for warm-up of the catalyst; the logic block determines whether the engine has achieved self-sustained operation; the logic block increases warm-up demand at a controlled rate after the engine has achieved self-sustained operation; and the logic block generates the warm-up demand under the presence of the need. 28. The apparatus as claimed in claim 25, further comprising:an air quantity calculation block that calculates a desired air quantity based on the modified desired value in excess air ratio; and an EGR gas quantity calculation block that calculates a desired EGR gas quantity based on the desired air quantity and the modified desired value in EGR rate. 29. The apparatus as claimed in claim 28, wherein the EGR controller receives the desired EGR gas quantity and engine speed.30. The apparatus as claimed in claim 29, further comprising:a throttle valve (TV) controller that receives the desired air quantity and engine speed to determine a TV command signal; and a variable geometry turbocharger (VGT) controller that receives the desired air quantity and engine speed to determine a VGT command signal. 31. The apparatus as claimed in claim 25, further comprising:a set-point generating block that establishes set-point values of engine operating variables, which include excess air ratio and EGR rate, for engine speed and fuel quantity conditions; and wherein the excess air ratio modifier block receives a set-point value of excess air ratio established by the set-point generating block to determine the desired value in excess air ratio; and wherein the EGR rate modifier block receives a set-point value of EGR rate established by the set-point generating block to determine the desired value in EGR rate. 32. The apparatus as claimed in claim 31, wherein the EGR rate modifier block receives the modified desired value in excess air ratio and the reduction in excess air ratio and determines a correction coefficient, and multiplies the correction coefficient with the desired value in EGR rate to determine the modified desired value in EGR rate.33. A computer readable storage medium having instructions stored thereon that are executable by a controller to perform a method of controlling an internal combustion engine for warm-up of a catalyst of an exhaust gas treatment device located in the engine exhaust path, the engine including an exhaust gas recirculation (EGR) system driven in response to an EGR command signal to recirculate exhaust to an engine intake, the computer readable storage medium comprising:instructions for generating a warm-up demand for heating the catalyst subject to constraint on stable combustion; instructions for determining a reduction in excess air ratio of the engine intake based on the warm-up demand; instructions for modifying a desired value in excess air ratio by the reduction to provide a modified desired value in excess air ratio; instructions for modifying a desired value in EGR rate based on the reduction to provide a modified desired value in EGR rate; and instructions for determining the EGR command signal based on the modified desired value in EGR rate. 34. The computer readable storage medium as claimed in claim 33, wherein the instructions for generating a warm-up demand include:instructions for determining whether a need remains for warm-up of the catalyst; instructions for determining whether in-cylinder combustion environment allows for engine operation with reduced excess air ratio to increase the temperature of the catalyst; and instructions for generating the warm-up demand when the in-cylinder combustion environment allows for the engine operation under the presence of the need. 35. The computer readable storage medium as claimed in claim 33, wherein the instructions for generating a warm-up demand include:instructions for determining whether a need remains for warm-up of the catalyst; instructions for determining whether the engine has achieved self-sustained operation; instructions for increasing warm-up demand at a controlled rate after the engine has achieved self-sustained operation; and instructions for generating the warm-up demand under the presence of the need. 36. A computer readable storage medium having instructions stored thereon that are executable by a controller to perform a method of controlling an internal combustion engine for warm-up of a catalyst of an exhaust gas treatment device located in the engine exhaust path, the engine including an exhaust gas recirculation (EGR) system driven in response to an EGR command signal to recirculate exhaust to an engine intake, the computer readable storage medium comprising:instructions for determining whether a need remains for warm-up of the catalyst; instructions for determining whether an in-cylinder combustion environment allows for engine operation with reduced excess air ratio to increase the temperature of the catalyst; and instructions for generating a warm-up demand when the in-cylinder combustion environment allows for the engine operation under the presence of the need. 37. A computer readable storage medium having instructions stored thereon that are executable by a controller to perform a method of controlling an internal combustion engine for warm-up of a catalyst of an exhaust gas treatment device located in the engine exhaust path, the engine including an exhaust gas recirculation (EGR) system driven in response to an EGR command signal to recirculate exhaust to an engine intake, the computer readable storage medium comprising:instructions for determining whether a need remains for warm-up of the catalyst; instructions for determining whether the engine has achieved self-sustained operation; instructions for increasing warm-up demand at a controlled rate after the engine has achieved self-sustained operation; and instructions for generating a warm-up demand under the presence of the need.