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Systems and methods for turbocharging an internal combustion engine include operating two turbochargers in a series configuration for a first operating region and a parallel configuration for a second operating region. Systems and methods for controlling exhaust gas recirculation (EGR) in a turbocha

Systems and methods for turbocharging an internal combustion engine include operating two turbochargers in a series configuration for a first operating region and a parallel configuration for a second operating region. Systems and methods for controlling exhaust gas recirculation (EGR) in a turbocharged internal combustion engine provide low pressure EGR upstream of a compressor inlet for a first operating region and high pressure EGR downstream of a compressor outlet for a second operating range to further improve turbocharger operating margin and overall efficiency.

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The invention claimed is: 1. A method for controlling a turbocharged internal combustion engine having at least two turbochargers with at least a first compressor and first turbine and a second compressor and a second turbine, respectively, the method comprising: operating the turbochargers in a se

The invention claimed is: 1. A method for controlling a turbocharged internal combustion engine having at least two turbochargers with at least a first compressor and first turbine and a second compressor and a second turbine, respectively, the method comprising: operating the turbochargers in a series configuration for a first operating region by selectively connecting an outlet of the first turbine to an inlet of the second turbine; and operating the turbochargers in a parallel configuration for a second operating region by decoupling an outlet of the second compressor from an inlet of the first compressor and coupling the outlet of the second compressor to an intake manifold of the internal combustion engine. 2. The method of claim 1 wherein the first and second operating regions correspond to demanded airflow. 3. The method of claim 1 wherein the step of operating the turbochargers in a series configuration comprises selectively connecting an outlet of the second compressor to an inlet of the first compressor. 4. The method of claim 1 further comprising selectively supplying a portion of exhaust gas from downstream of the first turbine to the inlet of the first compressor. 5. The method of claim 1 wherein the step of operating the turbochargers in a parallel configuration further comprises: decoupling an outlet of the first turbine from an inlet of the second turbine; and coupling the outlet of the first turbine to atmosphere. 6. The method of claim 5 wherein the internal combustion engine includes first and second after-treatment devices disposed downstream of outlets of the first and second turbines, respectively, the method further comprising: selectively directing at least a portion of exhaust gas from the outlet of the second turbine to the first after-treatment device based on current operating conditions. 7. A method for controlling a turbocharged internal combustion engine having at least two turbochargers including first and second turbochargers having corresponding first and second turbines and compressors, the method comprising: operating the turbochargers in a series configuration for a first operating region; operating the turbochargers in a parallel configuration for a second operating region; supplying a portion of exhaust gas to an inlet of the first compressor and outlet of the second compressor when operating in the series configuration; and supplying a portion of the exhaust gas to the outlet of the second compressor only when operating in the parallel configuration. 8. The method of claim 7 further comprising: supplying a portion of exhaust gas from downstream of the first turbine to an inlet of the first compressor when operating in the series configuration; and supplying a portion of the exhaust gas from upstream of the second turbine to the outlet of the second compressor only when operating in the parallel configuration. 9. A system for turbocharging an internal combustion engine, the system comprising: first and second turbochargers each having an associated compressor and turbine; a plurality of flow control devices for selectively routing intake and exhaust flow to and from the first and second turbochargers; and a controller in communication with the plurality of flow control devices, the controller selectively actuating the plurality of flow control devices to operate the first and second turbochargers in one of a series configuration and a parallel configuration based on current operating conditions to supply a portion of exhaust gas to an inlet of the first compressor and outlet of the second compressor when operating in the series configuration and to supply a portion of the exhaust gas only to the outlet of the second compressor when operating in the parallel configuration. 10. The system of claim 9 further comprising at least one EGR valve in communication with the controller for selectively providing exhaust gas recirculation, the controller selectively actuating the EGR valve in combination with at least one of the plurality of flow control devices to supply a portion of exhaust gas from downstream of the first turbine when operating the turbochargers in the series configuration and upstream of at least one of the first and second turbines when operating the turbochargers in the parallel configuration. 11. The system of claim 9 further comprising at least one EGR valve in communication with the controller for selectively providing exhaust gas recirculation, the controller selectively actuating the EGR valve in combination with at least one of the flow control devices to supply a portion of exhaust gas from upstream of the first and second turbines to an inlet of one of the compressors when operating in the series configuration, and an outlet of at least one of the compressors when operating in the parallel configuration. 12. The system of claim 9 wherein the controller operates the turbochargers based on current operating conditions including at least demanded airflow. 13. The system of claim 9 wherein the controller actuates the plurality of flow control devices to couple an outlet of the second compressor to an inlet of the first compressor when operating the turbochargers in the series configuration. 14. The system of claim 9 wherein the controller actuates the plurality of flow control devices to couple an outlet of the first turbine to an inlet of the second turbine when operating the turbochargers in the series configuration. 15. The system of claim 9 wherein the plurality of flow control devices comprises: a first intake valve for selectively coupling an inlet of the first compressor to ambient or an outlet of the second compressor; and a second intake valve for selectively coupling an outlet of the second compressor to an intake manifold or the inlet of the first compressor. 16. The system of claim 9 wherein the plurality of flow control devices comprises: a first exhaust valve for selectively coupling and decoupling an inlet of the second turbine to an exhaust manifold; and at least one additional exhaust valve for selectively coupling an outlet of the first turbine to ambient or an inlet of the second turbine. 17. The system of claim 9 further comprising: first and second after-treatment devices disposed downstream of the first and second turbines, respectively; wherein the plurality of flow control devices comprises an exhaust valve for selectively coupling an outlet of the first turbine to at least one of the first and second after-treatment device. 18. A system for turbocharging an internal combustion engine, the system comprising: first and second turbochargers each having an associated compressor and turbine; a plurality of flow control devices for selectively routing intake end exhaust flow to and from the first and second turbochargers; at least one EGR valve for selectively providing exhaust gas recirculation; and a controller in communication with the plurality of flow control devices and the at least one EGR valve, the controller selectively actuating the plurality of flow control devices to operate the first and second turbochargers in one of a series configuration and a parallel configuration based on current operating conditions and selectively actuating the EGR valve in combination with at least one of the plurality of flow control devices to supply a portion of exhaust gas to an inlet of the first compressor when operating the turbochargers in the series configuration and to an outlet of the second compressor when operating the turbochargers in the parallel configuration. 19. A system for turbocharging en internal combustion engine, the system comprising: first and second turbochargers each having an associated compressor and turbine; a plurality of flow control devices for selectively routing intake and exhaust flow to and from the first and second turbochargers; and a controller in communication with the plurality of flow control devices, the controller selectively actuating the plurality of flow control devices to operate the first and second turbochargers in one of a series configuration, where the outlet of one turbine is coupled to the inlet of another turbine and/or the outlet of one compressor is coupled to the inlet of another compressor and a parallel configuration, where both compressors have inlets coupled to atmosphere and/or both turbines are connected to a common exhaust, based on current operating conditions, wherein the controller actuates the plurality of flow control devices to selectively couple an outlet of the second compressor to an inlet of the first compressor and to selectively couple an outlet of the first turbine to an inlet of the second turbine when operating the turbochargers in the series configuration. 20. A computer readable storage medium having stored data representing instructions executable by a computer for controlling a turbocharged internal combustion engine having at least two turbochargers, the computer readable storage medium comprising: instructions for operating the turbochargers in a series configuration for a first operating region by actuating a plurality of valves to couple an outlet of a second compressor to an inlet of a first compressor and to couple an outlet of a first turbine to an inlet of a second turbine; and instructions for operating the turbochargers in a parallel configuration for a second operating region. 21. The computer readable storage medium of claim 20 wherein the instructions for operating the turbochargers in a parallel configuration include instructions for actuating a plurality of valves to connect the turbocharger compressor inlets to ambient and outlets to an intake manifold.