Turbocharged internal combustion engine with EGR flow

1. An internal combustion engine with a plurality of cylinders, the engine including an intake manifold and an exhaust manifold, the engine being operated such that the intake manifold pressure generally exceeds the exhaust manifold pressure, the engine further comprising:

a low pressure turbocharger including a turbine driven by the exhaust gases and a compressor having an inlet receiving fresh intake air and an outlet providing low pressure charge air;

a high pressure turbocharger including a turbine driven by the exhaust gases and a compressor having an inlet receiving the low pressure charge air and an outlet providing high pressure charge air to the intake manifold;

an exhaust gas recirculation (EGR) system passively routing a portion of the exhaust gases to the high pressure turbocharger compressor inlet; and

wherein a compression ratio of the low pressure turbocharger is greater than a compression ratio of the high pressure turbocharger.

2. The internal combustion engine of claim 1 further comprising:

a charge air cooler between the low pressure turbocharger compressor outlet and the high pressure turbocharger compressor inlet.

3. The internal combustion engine of claim 1 further comprising:

a particulate filter located in the EGR system to filter particulate matter from the exhaust gases prior to introduction to the high pressure turbocharger compressor inlet.

4. The internal combustion engine of claim 1 further comprising:

an EGR cooler located in the EGR system to cool the exhaust gases prior to introduction to the high pressure turbocharger compressor inlet.

5. The internal combustion engine of claim 1 further comprising:

a particulate filter located in the EGR system to filter particulate matter from the exhaust gases prior to introduction to the high pressure turbocharger compressor inlet; and

an EGR cooler located in the EGR system downstream of the particulate filter to cool the exhaust gases prior to introduction to the high pressure turbocharger compressor inlet.

6. The internal combustion engine of claim 1 further comprising:

a charge air cooler between the low pressure turbocharger compressor outlet and the high pressure turbocharger compressor inlet;

a particulate filter located in the EGR system to filter particulate matter from the exhaust gases prior to introduction to the high pressure turbocharger compressor inlet; and

an EGR cooler located in the EGR system downstream of the particulate filter to cool the exhaust gases prior to introduction to the high pressure turbocharger compressor inlet, wherein the exhaust gases are introduced at a location downstream of the charge air cooler.

7. The internal combustion engine of claim 1 wherein the compression ratio of the low pressure turbocharger is greater than 1.5 times the compression ratio of the high pressure turbocharger.

8. A method of controlling an internal combustion engine with a plurality of cylinders, the engine including an intake manifold and an exhaust manifold, the engine being operated such that the intake manifold pressure generally exceeds the exhaust manifold pressure, the engine including a low pressure turbocharger including a turbine driven by the exhaust gases and a compressor having an inlet receiving fresh intake air and an outlet providing low pressure charge air, and the engine further including a high pressure turbocharger including a turbine driven by the exhaust gases and a compressor having an inlet receiving the low pressure charge air and an outlet providing high pressure charge air to the intake manifold, the method further comprising:

passively routing a portion of the exhaust gases to the high pressure turbocharger compressor inlet to provide exhaust gas recirculation, wherein a compression ratio of the low pressure turbocharger is greater than a compression ratio of the high pressure turbocharger.

9. The method of claim 8 further comprising:

cooling the low pressure charge air from the low pressure turbocharger compressor outlet prior to the high pressure turbocharger compressor inlet.

10. The method of claim 8 further comprising:

filtering particulate matter from the exhaust gases prior to introduction to the high pressure turbocharger compressor inlet.

11. The method of claim 8 further comprising:

cooling the exhaust gases prior to introduction to the high pressure turbocharger compressor inlet.

12. The method of claim 8 further comprising:

filtering particulate matter from the exhaust gases prior to introduction to the high pressure turbocharger compressor inlet; and

after filtering, cooling the exhaust gases prior to introduction to the high pressure turbocharger compressor inlet.

13. The method of claim 8 further comprising:

cooling the low pressure charge air from the low pressure turbocharger compressor outlet prior to the high pressure turbocharger compressor inlet;

filtering particulate matter from the exhaust gases prior to introduction to the high pressure turbocharger compressor inlet; and

after filtering, cooling the exhaust gases prior to introduction to the high pressure turbocharger compressor inlet, wherein the exhaust gases are introduced to cooled low pressure charge air.

14. The method of claim 8 wherein the compression ratio of the low pressure turbocharger is greater than 1.5 times the compression ratio of the high pressure turbocharger.